3G LTE Long Term Evolution Tutorial & Basics- developed by 3GPP, LTE, Long Term Evolution is the successor to 3G UMTS and HSPA providing much higher data download speeds and setting the foundations for 4G LTE Advanced. Discover more about LTE basics in this tutorial.IN THIS SECTION LTE Introduction OFDM, OFDMA, SC-FDMA LTE MIMO TDD & FDD Frame & subframe Physical logical & transport channels Bands and spectrum UE categories SAE architecture LTE SON VoLTE SRVCC LTE-M LTE-U / LAA SecuritySee also 4G LTE AdvancedLTE, Long Term Evolution, the successor to UMTS and HSPA is now being deployed and is the way forwards for high speed cellular services.In its first forms it is a 3G or as some would call it a 3.99G technology, but with further additions the technology can be migrated to a full 4G standard and here it is known as LTE Advanced.There has been a rapid increase in the use of data carried by cellular services, and this increase will only become larger in what has been termed the "data explosion". To cater for this and the increased demands for increased data transmission speeds and lower latency, further development of cellular technology have been required.

The UMTS cellular technology upgrade has been dubbed LTE - Long Term Evolution. The idea is that 3G LTE will enable much higher speeds to be achieved along with much lower packet latency (a growing requirement for many services these days), and that 3GPP LTE will enable cellular communications services to move forward to meet the needs for cellular technology to 2017 and well beyond.Many operators have not yet upgraded their basic 3G networks, and 3GPP LTE is seen as the next logical step for many operators, who will leapfrog straight from basic 3G straight to LTE as this will avoid providing several stages of upgrade. The use of LTE will also provide the data capabilities that will be required for many years and until the full launch of the full 4G standards known as LTE Advanced.3G LTE evolutionAlthough there are major step changes between LTE and its 3G predecessors, it is nevertheless looked upon as an evolution of the UMTS / 3GPP 3G standards. Although it uses a different form of radio interface, using OFDMA / SC-FDMA instead of CDMA, there are many similarities with the earlier forms of 3G architecture and there is scope for much re-use.In determining what is LTE and how does it differ from other cellular systems, a quick look at the specifications for the system can provide many answers. LTE can be seen for provide a further evolution of functionality, increased speeds and general improved performance.WCDMA(UMTS)HSPAHSDPA / HSUPAHSPA+LTE

Max downlink speedbps384 k14 M28 M100M

Max uplink speedbps128 k5.7 M11 M50 M

Latencyround trip timeapprox150 ms100 ms50ms (max)~10 ms

3GPP releasesRel 99/4Rel 5 / 6Rel 7Rel 8

Approx years of initial roll out2003 / 42005 / 6 HSDPA2007 / 8 HSUPA2008 / 92009 / 10

Access methodologyCDMACDMACDMAOFDMA / SC-FDMA

In addition to this, LTE is an all IP based network, supporting both IPv4 and IPv6. Originally there was also no basic provision for voice, although Voice over LTE, VoLTE was added was chosen by GSMA as the standard for this. In the interim, techniques including circuit switched fallback, CSFB are expected to be usedLTE basics:- specification overviewIt is worth summarizing the key parameters of the 3G LTE specification. In view of the fact that there are a number of differences between the operation of the uplink and downlink, these naturally differ in the performance they can offer.LTE BASIC SPECIFICATIONS

PARAMETERDETAILS

Peak downlink speed64QAM(Mbps)100 (SISO), 172 (2x2 MIMO), 326 (4x4 MIMO)

Peak uplink speeds(Mbps)50 (QPSK), 57 (16QAM), 86 (64QAM)

Data typeAll packet switched data (voice and data). No circuit switched.

Channel bandwidths(MHz)1.4, 3, 5, 10, 15, 20

Duplex schemesFDD and TDD

Mobility0 - 15 km/h (optimised),15 - 120 km/h (high performance)

LatencyIdle to active less than 100msSmall packets ~10 ms

Spectral efficiencyDownlink: 3 - 4 times Rel 6 HSDPAUplink: 2 -3 x Rel 6 HSUPA

Access schemesOFDMA (Downlink)SC-FDMA (Uplink)

Modulation types supportedQPSK, 16QAM, 64QAM (Uplink and downlink)

These highlight specifications give an overall view of the performance that LTE will offer. It meets the requirements of industry for high data download speeds as well as reduced latency - a factor important for many applications from VoIP to gaming and interactive use of data. It also provides significant improvements in the use of the available spectrum.Main LTE technologiesLTE has introduced a number of new technologies when compared to the previous cellular systems. They enable LTE to be able to operate more efficiently with respect to the use of spectrum, and also to provide the much higher data rates that are being required. OFDM (Orthogonal Frequency Division Multiplex): OFDM technology has been incorporated into LTE because it enables high data bandwidths to be transmitted efficiently while still providing a high degree of resilience to reflections and interference. The access schemes differ between the uplink and downlink: OFDMA (Orthogonal Frequency Division Multiple Access is used in the downlink; while SC-FDMA(Single Carrier - Frequency Division Multiple Access) is used in the uplink. SC-FDMA is used in view of the fact that its peak to average power ratio is small and the more constant power enables high RF power amplifier efficiency in the mobile handsets - an important factor for battery power equipment.Read more aboutLTE OFDM / OFDMA / SCFMDA MIMO (Multiple Input Multiple Output): One of the main problems that previous telecommunications systems has encountered is that of multiple signals arising from the many reflections that are encountered. By using MIMO, these additional signal paths can be used to advantage and are able to be used to increase the throughput.

When using MIMO, it is necessary to use multiple antennas to enable the different paths to be distinguished. Accordingly schemes using 2 x 2, 4 x 2, or 4 x 4 antenna matrices can be used. While it is relatively easy to add further antennas to a base station, the same is not true of mobile handsets, where the dimensions of the user equipment limit the number of antennas which should be place at least a half wavelength apart.Read more aboutLTE MIMO SAE (System Architecture Evolution): With the very high data rate and low latency requirements for 3G LTE, it is necessary to evolve the system architecture to enable the improved performance to be achieved. One change is that a number of the functions previously handled by the core network have been transferred out to the periphery. Essentially this provides a much "flatter" form of network architecture. In this way latency times can be reduced and data can be routed more directly to its destination.Read more aboutLTE SAEA fuller description of what LTE is and the how the associated technologies work is all addressed in much greater detail in the following pages of this tutorial.LTE OFDM, OFDMA SC-FDMA & Modulation- LTE, Long term Evolution uses the modulation format, OFDM - orthogonal frequency division multiplex, adapted to provide a mulple access scheme using OFDMA and SC-FDMA.LTE TUTORIAL INCLUDES LTE Introduction OFDM, OFDMA, SC-FDMA LTE MIMO TDD & FDD Frame & subframe Physical logical & transport channels Bands and spectrum UE categories SAE architecture LTE SON VoLTE SRVCC LTE-M LTE-U / LAA SecuritySee also 4G LTE AdvancedOne of the key elements of LTE is the use of OFDM, Orthogonal Frequency Division Multiplex, as the signal bearer and the associated access schemes, OFDMA (Orthogonal Frequency Division Multiplex) and SC-FDMA (Single Frequency Division Multiple Access).OFDM is used in a number of other of systems from WLAN, WiMAX to broadcast technologies including DVB and DAB. OFDM has many advantages including its robustness to multipath fading and interference. In addition to this, even though, it may appear to be a particularly complicated form of modulation, it lends itself to digital signal processing techniques.In view of its advantages, the use of ODFM and the associated access technologies, OFDMA and SC-FDMA are natural choices for the new LTE cellular standard.LTE modulation & OFDM basicsThe use of OFDM is a natural choice for LTE. While the basic concepts of OFDM are used, it has naturally been tailored to meet the exact requirements for LTE. However its use of multiple carrier each carrying a low data rate remains the same.

Note on OFDM:Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted is split across all the carriers to give resilience against selective fading from multi-path effects..Click on the link for anOFDM tutorial

The actual implementation of the technology will be different between the downlink (i.e. from base station to mobile) and the uplink (i.e. mobile to the base station) as a result of the different requirements between the two directions and the equipment at either end. However OFDM was chosen as the signal bearer format because it is very resilient to interference. Also in recent years a considerable level of experience has been gained in its use from the various forms of broadcasting that use it along with Wi-Fi and WiMAX. OFDM is also a modulation format that is very suitable for carrying high data rates - one of the key requirements for LTE.In addition to this, OFDM can be used in both FDD and TDD formats. This becomes an additional advantage.sLTE channel bandwidths and characteristicsOne of the key parameters associated with the use of OFDM within LTE is the choice of bandwidth. The available bandwidth influences a variety of decisions including the number of carriers that can be accommodated in the OFDM signal and in turn this influences elements including the symbol length and so forth.LTE defines a number of channel bandwidths. Obviously the greater the bandwidth, the greater the channel capacity.The channel bandwidths that have been chosen for LTE are:1. 1.4 MHz2. 3 MHz3. 5 MHz4. 10 MHz5. 15 MHz6. 20 MHzIn addition to this the subcarriers spacing is 15 kHz, i.e. the LTE subcarriers are spaced 15 kHz apart from each other. To maintain orthogonality, this gives a symbol rate of 1 / 15 kHz = of 66.7 s.Each subcarrier is able to carry data at a maximum rate of 15 ksps (kilosymbols per second). This gives a 20 MHz bandwidth system a raw symbol rate of 18 Msps. In turn this is able to provide a raw data rate of 108 Mbps as each symbol using 64QAM is able to represent six bits.It may appear that these rates do not align with the headline figures given in the LTE specifications. The reason for this is that actual peak data rates are derived by first subtracting the coding and control overheads. Then there are gains arising from elements such as the spatial multiplexing, etc.LTE OFDM cyclic prefix, CPOne of the primary reasons for using OFDM as a modulation format within LTE (and many other wireless systems for that matter) is its resilience to multipath delays and spread. However it is still necessary to implement methods of adding resilience to the system. This helps overcome the inter-symbol interference (ISI) that results from this.In areas where inter-symbol interference is expected, it can be avoided by inserting a guard period into the timing at the beginning of each data symbol. It is then possible to copy a section from the end of the symbol to the beginning. This is known as the cyclic prefix, CP. The receiver can then sample the waveform at the optimum time and avoid any inter-symbol interference caused by reflections that are delayed by times up to the length of the cyclic prefix, CP.The length of the cyclic prefix, CP is important. If it is not long enough then it will not counteract the multipath reflection delay spread. If it is too long, then it will reduce the data throughput capacity. For LTE, the standard length of the cyclic prefix has been chosen to be 4.69 s. This enables the system to accommodate path variations of up to 1.4 km. With the symbol length in LTE set to 66.7 s.The symbol length is defined by the fact that for OFDM systems the symbol length is equal to the reciprocal of the carrier spacing so that orthogonality is achieved. With a carrier spacing of 15 kHz, this gives the symbol length of 66.7 s.LTE OFDMA in the downlinkThe OFDM signal used in LTE comprises a maximum of 2048 different sub-carriers having a spacing of 15 kHz. Although it is mandatory for the mobiles to have capability to be able to receive all 2048 sub-carriers, not all need to be transmitted by the base station which only needs to be able to support the transmission of 72 sub-carriers. In this way all mobiles will be able to talk to any base station.Within the OFDM signal it is possible to choose between three types of modulation for the LTE signal:1. QPSK (= 4QAM) 2 bits per symbol2. 16QAM 4 bits per symbol3. 64QAM 6 bits per symbol

Note on QAM, Quadrature Amplitude Modualtion:Quadrature amplitude modulation, QAM is widely sued for data transmission as it enables better elvels of spectral efficiency than other forms of modulation. QAM uses two carriers on the same frequency shifted by 90 which are modulated by two data streams - I or Inphase and Q - Quadrature elements.

The exact LTE modulation format is chosen depending upon the prevailing conditions. The lower forms of modulation, (QPSK) do not require such a large signal to noise ratio but are not able to send the data as fast. Only when there is a sufficient signal to noise ratio can the higher order modulation format be used.Downlink carriers and resource blocksIn the downlink, the subcarriers are split into resource blocks. This enables the system to be able to compartmentalize the data across standard numbers of subcarriers.Resource blocks comprise 12 subcarriers, regardless of the overall LTE signal bandwidth. They also cover one slot in the time frame. This means that different LTE signal bandwidths will have different numbers of resource blocks.

Channel bandwidth(MHz)1.435101520

Number of resource blocks615255075100

LTE SC-FDMA in the uplinkFor the LTE uplink, a different concept is used for the access technique. Although still using a form of OFDMA technology, the implementation is called Single Carrier Frequency Division Multiple Access (SC-FDMA).One of the key parameters that affects all mobiles is that of battery life. Even though battery performance is improving all the time, it is still necessary to ensure that the mobiles use as little battery power as possible. With the RF power amplifier that transmits the radio frequency signal via the antenna to the base station being the highest power item within the mobile, it is necessary that it operates in as efficient mode as possible. This can be significantly affected by the form of radio frequency modulation and signal format. Signals that have a high peak to average ratio and require linear amplification do not lend themselves to the use of efficient RF power amplifiers. As a result it is necessary to employ a mode of transmission that has as near a constant power level when operating. Unfortunately OFDM has a high peak to average ratio. While this is not a problem for the base station where power is not a particular problem, it is unacceptable for the mobile. As a result, LTE uses a modulation scheme known as SC-FDMA - Single Carrier Frequency Division Multiplex which is a hybrid format. This combines the low peak to average ratio offered by single-carrier systems with the multipath interference resilience and flexible subcarrier frequency allocation that OFDM provides.ByIan PooleLTE MIMO: Multiple Input Multiple Output Tutorial- MIMO is used within LTE to provide better signal performance and / or higher data rates by the use of the radio path reflections that exist.IN THIS SECTION LTE Introduction OFDM, OFDMA, SC-FDMA LTE MIMO TDD & FDD Frame & subframe Physical logical & transport channels Bands and spectrum UE categories SAE architecture LTE SON VoLTE SRVCC LTE-M LTE-U / LAA SecuritySee also 4G LTE AdvancedMIMO, Multiple Input Multiple Output is another of the LTE major technology innovations used to improve the performance of the system. This technology provides LTE with the ability to further improve its data throughput and spectral efficiency above that obtained by the use of OFDM.Although MIMO adds complexity to the system in terms of processing and the number of antennas required, it enables far high data rates to be achieved along with much improved spectral efficiency. As a result, MIMO has been included as an integral part of LTE.

LTE MIMO basicsThe basic concept of MIMO utilizes the multipath signal propagation that is present in all terrestrial communications. Rather than providing interference, these paths can be used to advantage.

General Outline of MIMO systemThe transmitter and receiver have more than one antenna and using the processing power available at either end of the link, they are able to utilize the different paths that exist between the two entities to provide improvements in data rate of signal to noise.

Note on MIMO:Two major limitations in communications channels can be multipath interference, and the data throughput limitations as a result of Shannon's Law. MIMO provides a way of utilising the multiple signal paths that exist between a transmitter and receiver to significantly improve the data throughput available on a given channel with its defined bandwidth. By using multiple antennas at the transmitter and receiver along with some complex digital signal processing, MIMO technology enables the system to set up multiple data streams on the same channel, thereby increasing the data capacity of a channel.Click on the link for aMIMO tutorial

MIMO is being used increasingly in many high data rate technologies including Wi-Fi and other wireless and cellular technologies to provide improved levels of efficiency. Essentially MIMO employs multiple antennas on the receiver and transmitter to utilise the multi-path effects that always exist to transmit additional data, rather than causing interference.

LTE MIMOThe use of MIMO technology has been introduced successively over the different releases of the LTE standards.MIMO has been a cornerstone of the LTE standard, but initially, in releases 8 and 9 multiple transmit antennas on the UE was not supported because in the interested of power reduction, only a single RF power amplifier was assumed to be available.It was in Rel. 10 that a number of new schemes were introduced. Closed loop spatial multiplexing for SU-MIMO as well as multiple antennas on the UE.LTE MIMO modesThere are several ways in which MIMO is implemented in LTE. These vary according to the equipment used, the channel function and the equipment involved in the link. Single antenna: This is the form of wireless transmission used on most basic wireless links. A single data stream is transmitted on one antenna and received by one or more antennas. It may also be referred to as SISO: Single In Single Out or SIMO Single In Multiple Out dependent upon the antennas used. SIMO is also called receive diversity. Transmit diversity: This form of LTE MIMO scheme utilizes the transmission of the same information stream from multiple antennas. LTE supports two or four for this technique.. The information is coded differently using Space Frequency Block Codes. This mode provides an improvement in signal quality at reception and does not improve the data rate. Accordingly this form of LTE MIMO is used on the Common Channels as well as the Control and Broadcast channels. Open loop spatial multiplexing: This form of MIMO used within the LTE system involves sending two information streams which can be transmitted over two or more antennas. However there is no feedback from the UE although a TRI, Transmit Rank Indicator transmitted from the UE can be used by the base station to determine the number of spatial layers. Close loop spatial multiplexing : This form of LTE MIMO is similar to the open loop version, but as the name indicates it has feedback incorporated to close the loop. A PMI, Pre-coding Matrix Indicator is fed back from the UE to the base station. This enables the transmitter to pre-code the data to optimize the transmission and enable the receiver to more easily separate the different data streams. Closed loop with pre-coding: This is another form of LTE MIMO, but where a single code word is transmitted over a single spatial layer. This can be sued as a fall-back mode for closed loop spatial multiplexing and it may also be associated with beam forming as well. Multi-User MIMO, MU-MIMO: This form of LTE MIMO enables the system to target different spatial streams to different users. Beam-forming: This is the most complex of the MIMO modes and it is likely to use linear arrays that will enable the antenna to focus on a particular area. This will reduce interference, and increase capacity as the particular UE will have a beam formed in their particular direction. In this a single code word is transmitted over a single spatial layer. A dedicated reference signal is used for an additional port. The terminal estimates the channel quality from the common reference signals on the antennas.

There is a growing number of LTE frequency bands that are being designated as possibilities for use with LTE. Many of the LTE frequency bands are already in use for other cellular systems, whereas other LTE bands are new and being introduced as other users are re-allocated spectrum elsewhere.FDD and TDD LTE frequency bandsFDD spectrum requires pair bands, one of the uplink and one for the downlink, and TDD requires a single band as uplink and downlink are on the same frequency but time separated. As a result, there are different LTE band allocations for TDD and FDD. In some cases these bands may overlap, and it is therefore feasible, although unlikely that both TDD and FDD transmissions could be present on a particular LTE frequency band.The greater likelihood is that a single UE or mobile will need to detect whether a TDD or FDD transmission should be made on a given band. UEs that roam may encounter both types on the same band. They will therefore need to detect what type of transmission is being made on that particular LTE band in its current location.The different LTE frequency allocations or LTE frequency bands are allocated numbers. Currently the LTE bands between 1 & 22 are for paired spectrum, i.e. FDD, and LTE bands between 33 & 41 are for unpaired spectrum, i.e. TDD.

LTE frequency band definitions

FDD LTE frequency band allocationsThere are a large number of allocations or radio spectrum that has been reserved for FDD, frequency division duplex, LTE use.The FDD LTE frequency bands are paired to allow simultaneous transmission on two frequencies. The bands also have a sufficient separation to enable the transmitted signals not to unduly impair the receiver performance. If the signals are too close then the receiver may be "blocked" and the sensitivity impaired. The separation must be sufficient to enable the roll-off of the antenna filtering to give sufficient attenuation of the transmitted signal within the receive band.

FDD LTE BANDS & FREQUENCIES

LTE BANDNUMBERUPLINK(MHZ)DOWNLINK(MHZ)WIDTH OF BAND (MHZ)DUPLEX SPACING (MHZ)BAND GAP (MHZ)

11920 - 19802110 - 217060190130

21850 - 19101930 - 1990608020

31710 - 17851805 -1880759520

41710 - 17552110 - 215545400355

5824 - 849869 - 894254520

6830 - 840875 - 885103525

72500 - 25702620 - 26907012050

8880 - 915925 - 960354510

91749.9 - 1784.91844.9 - 1879.9359560

101710 - 17702110 - 217060400340

111427.9 - 1452.91475.9 - 1500.9204828

12698 - 716728 - 746183012

13777 - 787746 - 75610-3141

14788 - 798758 - 76810-3040

151900 - 19202600 - 262020700680

162010 - 20252585 - 260015575560

17704 - 716734 - 746123018

18815 - 830860 - 875154530

19830 - 845875 - 890154530

20832 - 862791 - 82130-4171

211447.9 - 1462.91495.5 - 1510.9154833

223410 - 35003510 - 36009010010

232000 - 20202180 - 220020180160

241625.5 - 1660.51525 - 155934-101.5135.5

251850 - 19151930 - 1995658015

26814 - 849859 - 89430 / 4010

27807 - 824852 - 869174528

28703 - 748758 - 803455510

29n/a717 - 72811

302305 - 23152350 - 2360104535

31452.5 - 457.5462.5 - 467.55105

TDD LTE frequency band allocationsWith the interest in TDD LTE, there are several unpaired frequency allocations that are being prepared for LTR TDD use. The TDD LTE bands are unpaired because the uplink and downlink share the same frequency, being time multiplexed.

TDD LTE BANDS & FREQUENCIES

LTE BANDNUMBERALLOCATION (MHZ)WIDTH OF BAND (MHZ)

331900 - 192020

342010 - 202515

351850 - 191060

361930 - 199060

371910 - 193020

382570 - 262050

391880 - 192040

402300 - 2400100

412496 - 2690194

423400 - 3600200

433600 - 3800200

44703 - 803100

There are regular additions to the LTE frequency bands / LTE spectrum allocations as a result of negotiations at the ITU regulatory meetings. These LTE allocations are resulting in part from the digital dividend, and also from the pressure caused by the ever growing need for mobile communications. Many of the new LTE spectrum allocations are relatively small, often 10 - 20MHz in bandwidth, and this is a cause for concern. With LTE-Advanced needing bandwidths of 100 MHz, channel aggregation over a wide set of frequencies many be needed, and this has been recognised as a significant technological problem. . . . . . . . .In the same way that a variety of other systems adopted different categories for the handsets or user equipment, so too there are 3G LTE UE categories. These LTE categories define the standards to which a particular handset, dongle or other equipment will operate.LTE UE category rationaleThe LTE UE categories or UE classes are needed to ensure that the base station, or eNodeB, eNB can communicate correctly with the user equipment. By relaying the LTE UE category information to the base station, it is able to determine the performance of the UE and communicate with it accordingly.As the LTE category defines the overall performance and the capabilities of the UE, it is possible for the eNB to communicate using capabilities that it knows the UE possesses. Accordingly the eNB will not communicate beyond the performance of the UE.

LTE UE category definitionsthere are five different LTE UE categories that are defined. As can be seen in the table below, the different LTE UE categories have a wide range in the supported parameters and performance. LTE category 1, for example does not support MIMO, but LTE UE category five supports 4x4 MIMO.It is also worth noting that UE class 1 does not offer the performance offered by that of the highest performance HSPA category. Additionally all LTE UE categories are capable of receiving transmissions from up to four antenna ports.A summary of the different LTE UE category parameters is given in the tables below.

HEADLINE DATA RATES FOR LTE UE CATEGORIES

CATEGORY

LINK12345

Downlink1050100150300

Uplink525505075

While the headline rates for the different LTE UE categories or UE classes show the maximum data rates achievable, it is worth looking in further detail at the underlying performance characteristics.

UL AND DL PARAMETERS FOR LTE UE CATEGORIES

CATEGORY

PARAMETERCAT 1CAT 2CAT 3CAT 4CAT 5

Max number of DL-SCH transport block bits received in a TTI10 29651 024102 048150 752302 752

Max number of bits of a DL-SCH block received in a TTI10 29651 02475 37675 376151 376

Total number of soft channel bits250 3681 237 2481 237 2481 827 0723 667 200

Maximum number of supported layers for spatial multiplexing in DL12224

Max number of bits of an UL-SCH transport block received in a TTI5 16025 45651 02451 02475 376

Support for 64-QAM in ULNoNoNoNoYes

From this it can be seen that the peak downlink data rate for a Category 5 UE using 4x4 MIMO is approximately 300 Mbps, and 150 Mbps for a Category 4 UE using 2x2 MIMO. Also in the Uplink, LTE UE category 5 provides a peak data rate of 75 Mbps using 64-QAM.

Note: DL-SCH = Downlink shared channel UL-SCH = Uplink shared channel TTI = Transmission Time IntervalLTE Category 0With the considerable level of development being undertaken into the Internet of Things, IoT and general machine to machine, M2M communications, there has been a growing need to develop an LTE category focussed on these applications. Here, much lower data rates are needed, often only in short bursts and an accompanying requirement is for the remote device or machine to be able to draw only low levels of current.To enable the requirements of these devices to be met using LTE, and new LTE category was developed. Referred to as LTE Category 0, or simply Cat 0, this new category has a reduced performance requirement that meets the needs of many machines while significantly reducing complexity and current consumption. Whilst Category 0 offered a reduced specification, it still complied with the LTE system requirements.

LTE CATEGORY 0 PERFORMANCE SUMMARY

PARAMETERCATEGORY 0 PERFORMANCE

Peak downlink rate1 Mbps

Peak uplink rate1 Mbps

Max number of downlink spatial layers1

Number of UE RF chains1

Duplex modeHalf duplex

UE receive bandwidth20 MHz

Maximum UE transmit power23 dBm

The new LTE Category 0 was introduced in Rel 12 of the 3GPP standards. And it is being advanced in further releases.One major advantage of LTE Category 0 is that the modem complexity is considerably reduced when compared to other LTE Categories. It is expected that the modem complexity for a Cat 0 modem will be around 50% that of a Category 1 modem.LTE UE category summaryIn the same way that category information is used for virtually all cellular systems from GPRS onwards, so the LTE UE category information is of great importance. While users may not be particularly aware of the category of their UE, it will match the performance an allow the eNB to communicate effectively with all the UEs that are connected to it.

Along with 3G LTE - Long Term Evolution that applies more to the radio access technology of the cellular telecommunications system, there is also an evolution of the core network. Known as SAE - System Architecture Evolution. This new architecture has been developed to provide a considerably higher level of performance that is in line with the requirements of LTE.As a result it is anticipated that operators will commence introducing hardware conforming to the new System Architecture Evolution standards so that the anticipated data levels can be handled when 3G LTE is introduced.The new SAE, System Architecture Evolution has also been developed so that it is fully compatible with LTE Advanced, the new 4G technology. Therefore when LTE Advanced is introduced, the network will be able to handle the further data increases with little change.

Reason for SAE System Architecture EvolutionThe SAE System Architecture Evolution offers many advantages over previous topologies and systems used for cellular core networks. As a result it is anticipated that it will be wide adopted by the cellular operators.SAE System Architecture Evolution will offer a number of key advantages:1. Improved data capacity: With 3G LTE offering data download rates of 100 Mbps, and the focus of the system being on mobile broadband, it will be necessary for the network to be able to handle much greater levels of data. To achieve this it is necessary to adopt a system architecture that lends itself to much greater levels of data transfer.2. All IP architecture: When 3G was first developed, voice was still carried as circuit switched data. Since then there has been a relentless move to IP data. Accordingly the new SAE, System Architecture Evolution schemes have adopted an all IP network configuration.3. Reduced latency: With increased levels of interaction being required and much faster responses, the new SAE concepts have been evolved to ensure that the levels of latency have been reduced to around 10 ms. This will ensure that applications using 3G LTE will be sufficiently responsive.4. Reduced OPEX and CAPEX: A key element for any operator is to reduce costs. It is therefore essential that any new design reduces both the capital expenditure (CAPEX)and the operational expenditure (OPEX). The new flat architecture used for SAE System Architecture Evolution means that only two node types are used. In addition to this a high level of automatic configuration is introduced and this reduces the set-up and commissioning time.

SAE System Architecture Evolution basicsThe new SAE network is based upon the GSM / WCDMA core networks to enable simplified operations and easy deployment. Despite this, the SAE network brings in some major changes, and allows far more efficient and effect transfer of data.There are several common principles used in the development of the LTE SAE network: a common gateway node and anchor point for all technologies. an optimized architecture for the user plane with only two node types. an all IP based system with IP based protocols used on all interfaces. a split in the control / user plane between the MME, mobility management entity and the gateway. a radio access network / core network functional split similar to that used on WCDMA / HSPA. integration of non-3GPP access technologies (e.g. cdma2000, WiMAX, etc) using client as well as network based mobile-IP.The main element of the LTE SAE network is what is termed the Evolved Packet Core or EPC. This connects to the eNodeBs as shown in the diagram below.

LTE SAE Evolved Packet CoreAs seen within the diagram, the LTE SAE Evolved Packet Core, EPC consists of four main elements as listed below: Mobility Management Entity, MME: The MME is the main control node for the LTE SAE access network, handling a number of features: Idle mode UE tracking Bearer activation / de-activation Choice of SGW for a UE Intra-LTE handover involving core network node location Interacting with HSS to authenticate user on attachment and implements roaming restrictions It acts as a termination for the Non-Access Stratum (NAS) Provides temporary identities for UEs The SAE MME acts the termination point for ciphering protection for NAS signaling. As part of this it also handles the security key management. Accordingly the MME is the point at which lawful interception of signalling may be made. Paging procedure The S3 interface terminates in the MME thereby providing the control plane function for mobility between LTE and 2G/3G access networks. The SAE MME also terminates the S6a interface for the home HSS for roaming UEs.It can therefore be seen that the SAE MME provides a considerable level of overall control functionality. Serving Gateway, SGW: The Serving Gateway, SGW, is a data plane element within the LTE SAE. Its main purpose is to manage the user plane mobility and it also acts as the main border between the Radio Access Network, RAN and the core network. The SGW also maintains the data paths between the eNodeBs and the PDN Gateways. In this way the SGW forms a interface for the data packet network at the E-UTRAN.

Also when UEs move across areas served by different eNodeBs, the SGW serves as a mobility anchor ensuring that the data path is maintained. PDN Gateway, PGW: The LTE SAE PDN gateway provides connectivity for the UE to external packet data networks, fulfilling the function of entry and exit point for UE data. The UE may have connectivity with more than one PGW for accessing multiple PDNs. Policy and Charging Rules Function, PCRF: This is the generic name for the entity within the LTE SAE EPC which detects the service flow, enforces charging policy. For applications that require dynamic policy or charging control, a network element entitled the Applications Function, AF is used.

LTE SAE PCRF Interfaces

LTE SAE Distributed intelligenceIn order that requirements for increased data capacity and reduced latency can be met, along with the move to an all-IP network, it is necessary to adopt a new approach to the network structure.For 3G UMTS / WCDMA the UTRAN (UMTS Terrestrial Radio Access Network, comprising the Node B's or basestations and Radio Network Controllers) employed low levels of autonomy. The Node Bs were connected in a star formation to the Radio Network Controllers (RNCs) which carried out the majority of the management of the radio resource. In turn the RNCs connected to the core network and connect in turn to the Core Network.To provide the required functionality within LTE SAE, the basic system architecture sees the removal of a layer of management. The RNC is removed and the radio resource management is devolved to the base-stations. The new style base-stations are called eNodeBs or eNBs.The eNBs are connected directly to the core network gateway via a newly defined "S1 interface". In addition to this the new eNBs also connect to adjacent eNBs in a mesh via an "X2 interface". This provides a much greater level of direct interconnectivity. It also enables many calls to be routed very directly as a large number of calls and connections are to other mobiles in the same or adjacent cells. The new structure allows many calls to be routed far more directly and with only minimum interaction with the core network.In addition to the new Layer 1 and Layer 2 functionality, eNBs handle several other functions. This includes the radio resource control including admission control, load balancing and radio mobility control including handover decisions for the mobile or user equipment (UE).The additional levels of flexibility and functionality given to the new eNBs mean that they are more complex than the UMTS and previous generations of base-station. However the new 3G LTE SAE network structure enables far higher levels of performance. In addition to this their flexibility enables them to be updated to handle new upgrades to the system including the transition from 3G LTE to 4G LTE Advanced.The new System Architecture Evolution, SAE for LTE provides a new approach for the core network, enabling far higher levels of data to be transported to enable it to support the much higher data rates that will be possible with LTE. In addition to this, other features that enable the CAPEX and OPEX to be reduced when compared to existing systems, thereby enabling higher levels of efficiency to be achieved.With LTE requiring smaller cell sizes to enable the much greater levels of data traffic to be handled, there networks have become considerably more complicated and trying to plan and manage the network centrally is not as viable. Coupled with the need to reduce costs by reducing manual input, there has been a growing impetus to implement self-organizing networks.Accordingly LTE can be seen as one of the major drivers behind the self-organizing network, SON philosophy.Accordingly 3GPP developed many of the requirements for LTE SON to sit alongside the basic functionality of LTE. As a result the standards for LTE SON are embedded within the 3GPP standards.

LTE SON developmentThe term SON came into frequent use after the term was adopted by the Next Generation Mobile Networks, NGMN alliance. The idea came about as result of the need within LTE to be able to deploy many more cells. Femtocells and other microcells are an integral part of the LTE deployment strategy. With revenue per bit falling, costs for deployment must be kept to a minimum as well as ensuring the network is operating to its greatest efficiency.3GPP, the Third Generation Partnership Programme has created the standards for SON and as they are generally first to be deployed with LTE, they are often referred to as LTE SON.While 3GPP has generated the standards, they have been based upon long term objectives for a 'SON-enabled broadband mobile network' set out by the NGMN.NGMN has defined the necessary use cases, measurements, procedures and open interfaces to ensure that multivendor offerings are available. 3GPP has incorporated these aspirations into useable standards.

Major elements of LTE SON ( SELF ORGANIZING NETWORK )Although LTE SON self-optimising networks is one of the major drivers for the generic SON technology, the basic requirements remain the same whatever the technology to which it will be applied.The main elements of SON include: Self configuration: The aim for the self configuration aspects of LTE SON is to enable new base stations to become essentially "Plug and Play" items. They should need as little manual intervention in the configuration process as possible. Not only will they be able to organize the RF aspects, but also configure the backhaul as well. Self optimisation: Once the system has been set up, LTE SON capabilities will enable the base station to optimise the operational characteristics to best meet the needs of the overall network. Self-healing: Another major feature of LTE SON is to enable the network to self-heal. It will do this by changing the characteristics of the network to mask the problem until it is fixed. For example, the boundaries of adjacent cells can be increased by changing antenna directions and increasing power levels, etc..Typically an LTE SON system is a software package with relevant options that is incorporated into an operator's network.

Note on SON, Self Organizing Networks:SON mainly came out of the requirements of LTE and the more complicated networks that will arise. However the concepts behind SON can be applied at any network enabling its efficiency to be increased while keeping costs low. Accordingly, it is being used increasingly to reduce operational and capital expenditure by adding software to the network to enable it to organise and run itself.Click on the link for further information aboutSelf Organising Networks, SON

LTE SON and 3GPP standardsLTE Son has been standardised in the various 3GPP standards. It was first incorporated into 3GPP release 8, and further functionality has been progressively added in the further releases of the standards.One of the major aims of the 3GPP standardization is the support of SON features is to ensure that multi-vendor network environments operate correctly with LTE SON. As a result, 3GPP has defined a set of LTE SON use cases and the associated SON functions.As the functionality of LTE advances, the LTE SON standardisation effectively track the LTE network evolution stages. In this way SON will be applicable to the LTE networks.

The Voice over LTE, VoLTE scheme was devised as a result of operators seeking a standardized system for transferring traffic for voice over LTE.Originally LTE was seen as a completely IP cellular system just for carrying data, and operators would be able to carry voice either by reverting to 2G / 3G systems or by using VoIP in one form or another.

From around 2014 Phones like this iPhone6 incorporated VoLTE as standardHowever it was seen that this would lead to fragmentation and incompatibility not allowing all phones to communicate with each other and this would reduce voice traffic. Additionally SMS services are still widely used, often proving a means of set-up for other applications.Even though revenue from voice calls and SMS is falling, a format for voice over LTE and messaging, it was as necessary to have a viable and standardized scheme to provide the voice and SMS services to protect this revenue.Options for LTE VoiceWhen looking at the options for ways of carrying voice over the LTE system, a number of possible solutions were investigated. A number of alliances were set up to promote different ways of providing the service. A number of systems were prosed as outlined below: CSFB, Circuit Switched Fall Back: The circuit switched fall-back, CSFB option for providing voice over LTE has been standardized under 3GPP specification 23.272. Essentially LTE CSFB uses a variety of processes and network elements to enable the circuit to fall back to the 2G or 3G connection (GSM, UMTS, CDMA2000 1x) before a circuit switched call is initiated.

The specification also allows for SMS to be carried as this is essential for very many set-up procedures for cellular telecommunications. To achieve this the handset uses an interface known as SGs which allows messages to be sent over an LTE channel. SV-LTE - Simultaneous Voice LTE: SV-LTE allows packet switched LTE services to run simultaneously with a circuit switched voice service. SV-LTE facility provides the facilities of CSFB at the same time as running a packet switched data service. It has the disadvantage that it requires two radios to run at the same time within the handset which has a serious impact on battery life which is already a major issue.

VoLGA, Voice over LTE via GAN: The VoLGA standard was based on the existing 3GPP Generic Access Network (GAN) standard, and the aim was to enable LTE users to receive a consistent set of voice, SMS (and other circuit-switched) services as they transition between GSM, UMTS and LTE access networks. For mobile operators, the aim of VoLGA was to provide a low-cost and low-risk approach for bringing their primary revenue generating services (voice and SMS) onto the new LTE network deployments. One Voice / later called Voice over LTE, VoLTE: The Voice over LTE, VoLTE scheme for providing voice over an LTE system utilises IMS enabling it to become part of a rich media solution. It was the option chosen by the GSMA for use on LTE and is the standardised method for providing SMS and voice over LTE.Voice over LTE, VoLTE formationOriginally the concept for an SMS and voice system over LTE using IMS had been opposed by many operators because of the complexity of IMS. They had seen it as far too expensive and burdensome to introduce and maintain.However, the One Voice profile for Voice over LTE was developed by collaboration between over forty operators including: AT&T, Verizon Wireless, Nokia and Alcatel-Lucent.At the 2010 GSMA Mobile World Congress, GSMA announced that they were supporting the One Voice solution to provide Voice over LTE.To achieve a workable system, a cut down variant of IMS was used. It was felt that his would be acceptable to operators while still providing the functionality required.The VoLTE system is based on the IMS MMTel concepts that were previously in existence. It has been specified in the GSMA profile IR 92.Voice over LTE, VoLTE basicsVoLTE, Voice over LTE is an IMS-based specification. Adopting this approach, it enables the system to be integrated with the suite of applications that will become available on LTE.

Note on IMS:The IP Multimedia Subsystem or IP Multimedia Core Network Subsystem, IMS is an architectural framework for delivering Internet Protocol, IP multimedia services. It enables a variety of services to be run seemlessly rather than having several disparate applications operating concurrently.Click for anIMS tutorial

In order that IMS was implemented in fashion that would be acceptable to operators, a cut down version was defined. This not only reduced the number of entities required in the IMS network, but it also simplified the interconnectivity - focussing on the elements required for VoLTE.

Reduced IMS network for VoLTEAs can be seen there are several entities within the reduced IMS network used for VoLTE: IP-CAN IP, Connectivity Access Network: This consists of the EUTRAN and the MME. P-CSCF, Proxy Call State Control Function: The P-CSCF is the user to network proxy. In this respect all SIP signalling to and from the user runs via the P-CSCF whether in the home or a visited network. I-CSCF, Interrogating Call State Control Function: The I-CSCF is used for forwarding an initial SIP request to the S-CSCF. When the initiator does not know which S-CSCF should receive the request. S-CSCF, Serving Call State Control Function: The S-CSCF undertakes a variety of actions within the overall system, and it has a number of interfaces to enable it to communicate with other entities within the overall system. AS, Application Server: It is the application server that handles the voice as an application. HSS, Home Subscriber Server: The IMS HSS or home subscriber server is the main subscriber database used within IMS. The IMS HSS provides details of the subscribers to the other entities within the IMS network, enabling users to be granted access or not dependent upon their status.The IMS calls for VoLTE are processed by the subscriber's S-CSCF in the home network. The connection to the S-CSCF is via the P-CSCF. Dependent upon the network in use and overall location within a network, the P-CSCF will vary, and a key element in the enablement of voice calling capability is the discovery of the P-CSCF.An additional requirement for VoLTE enabled networks is to have a means to handing back to circuit switched legacy networks in a seamless manner, while only having one transmitting radio in the handset to preserve battery life. A system known as SRVCC - Single Radio Voice Call Continuity is required for this.Read more aboutSRVCC - Single Radio-Voice Call ContinuityVoLTE codecsAs with any digital voice system, a codec must be used. The VoLTE codec is that specified by 3GPP and is the adaptive multi-rate, AMR codec that is used in many other cellular systems from GSM through UMTS and now to LTE. The AMR-wideband codec may also be used.The used of the AMR codec for VoLTE also provides advantages in terms of interoperability with legacy systems. No transcoders are needed as most legacy systems now are moving towards the AMR codec.In addition to this, support for dual tone multi-frequency, DTMF signalling is also mandatory as this is widely used for many forms of signalling over analogue telephone lines.VoLTE IP versionsWith the update from IPv4 to IPv6, the version of IP used in any system is of importance.VoLTE devices are required to operate in dual stack mode catering for both IPv4 and IPv6.If the IMS application profile assigns and IPv6 address, then the device is required to prefer that address and also to specifically use it during the P-CSCF discovery phase.One of the issues with voice over IP type calls is the overhead resulting from the IP header. To overcome this issue VoLTE requires that IP header compression is used along with RoHC, Robust Header Compression, protocol for voice data packet headers.

SRVCC - Single Radio Voice call Continuity is a level of functionality that is required within VoLTE systems to enable the packet domain calls on LTE to be handed over to legacy circuit switched voice systems like GSM, UMTS and CDMA 1x in a seamless manner.As LTE systems deploy VoLTE coverage will be limited and it is anticipated that it will be many years before complete LTE coverage will be available.As a result it is necessary for operators to have a system whereby this complicated handover can be accommodated in a seamless fashion. This scheme needs to be in place as soon as they start to deploy VoLTE.What is SRVCC?SRVCC, Single radio Voice Call Continuity, is a scheme that enables Inter Radio Access Technology, Inter RAT handover as well as a handover from packet data to circuit switched data voice calls.By using SRVCC operators are able to make the handovers while maintaining existing quality of service, QoS and also ensuring that call continuity meets the critical requirements for emergency calls.Some ideas for handover require that the handset has two active radios to facilitate handover. This is not ideal because it requires additional circuitry to enable the two radios to be active simultaneously and it also adds considerably to battery drain.The SRVCC requires only a single active radio in the handset and requires some upgrades to the supporting network infrastructure.SRVCC network architectureThe concept for SRVCC was originally included in the 3GPP specification Release 8. Since then it has evolved to take account of the various issues and changing requirements. As a result GSMA recommends that 3GPP Rel 10 or later is implemented as this ensures a considerably lower level of voice interruption and dropped calls.The network upgrades required to the cellular network are needed in both the LTE network and that of the legacy network or networks. SRVCC requires that software upgrades are required to the MSS - Mobile SoftSwitch subsystem in the legacy MSC - Mobile Switching Centre, the IMS subsystem and the LTE/EPC subsystem. No upgrades are required for the radio access network of the legacy system, meaning that the majority of the legacy system remains unaffected.The upgrades required for the MSC are normally relatively easy to manage. The MSC is normally centrally located and not dispersed around the network, and this makes upgrades easier to manage. If they are not easily accessible then a new dedicated MSC can be used that has been upgraded to handles the SRVCC requirements.How SRVCC worksThe SRVCC implementation controls the transfer of calls in both directions.

LTE to legacy network handoverHandover from LTE to the legacy network is required when the user moves out of the LTE coverage area. Using SRVCC, the handover is undertaken in two stages. Radio Access Technology transfer: The handover for the radio access network and this is a well-established protocol that is in use for transfers from 3G to 2G for example. Session transfer: The session transfer is the new element that is required for SRVCC. It is required to move the access control and voice media anchoring from the Evolved Packet Core, EPC of the packet switched LTE network to the legacy circuit switched network.During the handover process the CSCF within the IMS architecture maintains the control of the whole operation.

Voice handover using SRVCC on LTEThe SRVCC handover process takes place in a number of steps:1. The handover process is initiated by a request for session transfer from the IMS CSCF.2. The IMS CSCF responds simultaneously with two commands, one to the LTE network, and the other to the legacy network.3. the LTE network receives a radio Access Network handover execution command through the MME and LTE RAN. This instructs the user device to prepare to move to a circuit switched network for the voice call.4. The destination legacy circuit switched network receives a session transfer response preparing it to accept the call from the LTE network.5. After all the commands have been executed and acknowledged the call is switched to the legacy network with the IMS CSCF still in control of the call.

Legacy network to LTEWhen returning a call to the LTE network much of the same functionality is again used.To ensure the VoLTE device is able to return to the LTE RAN from the legacy RAN, there are two options the legacy RAN can implement to provide a swift and effective return: Allow LTE information to be broadcast on the legacy RAN so the LTE device is able to perform the cell reselection more easily. Simultaneously release the connection to the user device and redirect it to the LTE RAN.SRVCC interruption performanceOne of the key issues with VoLTE and SRVCC is the interruption time when handing over from an LTE RAN to a legacy RAN.The key methodology behind reducing the time is to simultaneous perform the redirections of RAN and session. In this way the user experience is maintained and the actual interruption time is not unduly noticeable.It has been found that the session redirection is the faster of the two handovers, and therefore it is necessary for the overall handover methodology to accommodate the fact that there are difference between the two.ByIan Poole

M2MThe Internet of Things, IoT and machine to machine, M2M communications are growing rapidly.LTE, the Long Term Evolution cellular system is well placed to carry a lot of the traffic for machine to machine communications.The issue is that LTE is a complex system capable of carrying high data rates.To overcome this issue a "variant" of LTE, often referred to as LTE-M has been developed for LTE M2M communications.LTE-M key issuesThere are several requirements for LTE M2M applications if the cellular system is to be viable in these scenarios: Wide spectrum of devices: Any LTE machine to machine system must be able to support a wide variety of different types of devices. These may range from smart meters to vending machines and automotive fleet management to security and medical devices. These different devices have many differing requirements, so any LTE-M system needs to be able to be flexible. Low cost of devices: Most M2M devices need to be small and fit into equipment that is very cost sensitive. With many low cost M2M systems already available, LTE-M needs to provide the benefits of a cellular system, but at low cost. Long battery life : Many M2M devices will need to be left unattended for long periods of time in areas where there may be no power supply. Maintaining batteries is a costly business and therefore any devices should be able to have a time between battery changes of up to ten years. This means that the LTE-M system must be capable of draining very little battery power. Enhanced coverage : LTE-M applications will need to operate within a variety of locations - not just where reception is good. They will need to operate within buildings, often in positions where there is little access and where reception may be poor. Accordingly LTE-M must be able to operate under all conditions. Large volumes - low data rates: As it is anticipated that volumes of remote devices will be enormous, the LTE-M must be structured so that the networks are be able to accommodate vast numbers of connected devices that may only require small amounts of data to be carried, often in short peaks but with low data rates.Rel 12 updates for LTE-MA number of updates were introduced in 3GPP Rel 12 to accommodate LTE-M requirements.These updates mean that the cost of a low cost M2M modem could be 40 to 50% that of a regular LTE devices, making them comparable with EGPRS ones.To accommodate these requirements a new a new UE category has been implemented LTE Category 0. These categories define the broad capabilities of the device so that the base station is able to communicate properly.Read more aboutLTE UE categories.These low cost LTE-M, M2M modems have limited capability and are: Antennas: There is the capability for only one receive antenna compared to two receive antennas for other device categories. Transport Block Size: There is a restriction on the transport block size These low cost LTE-M devices are allowed to send or receive up to 1000 bits of unicast data per sub-frame. This reduces the maximum data rate to 1 Mbps in both the uplink and the downlink. Duplex: Half duplex FDD devices are supported as an optional feature - this provides cost savings because it enables RF switches and duplexers that are needed for the full performance modems to be removed. It also means there is no need for a second phase locked loop for the frequency conversion, although having only one PLL means that switching times between receive and transmit are longer.LTE-M features planned for Rel 13There are several features that are being proposed and prepared for the next release of the 3GPP standards in terms of LTE M2M capabilities. These include some of the following capabilities: Reduce bandwidth to 1.4 MHz for uplink and downlink Reduce transmit power to 20dBm Reduce support for downlink transmission modes Relax the requirements that require high levels of processing, e.g. downlink modulation scheme, reduce downlink HARQ timelineIt should be stated that these last points for Rel 13 are currently only proposals and are not implemented.

With a number of cellular style M2M wireless communication systems like LoRa and SIGFOX being deployed, LTE needs its own M2M capability to ensure that it is able to compete with these growing standards. Otherwise LTE may not be suitable for carrying this form of low data rate date from devices that require long battery life, etc. LTE-M is the cellular operators' answer to this.ByIan PooleLTE-U Unlicensed, LTE-LAA- LTE-U (LTE-Unlicensed), or as it is also known LTE-LAA (LTE-License Assisted Access) utilises unlicensed spectrum, typically in the 5GHz band to provide additional radio spectrum.LTE TUTORIAL INCLUDES LTE Introduction OFDM, OFDMA, SC-FDMA LTE MIMO TDD & FDD Frame & subframe Physical logical & transport channels Bands and spectrum UE categories SAE architecture LTE SON VoLTE SRVCC LTE-M LTE-U / LAA SecuritySee also 4G LTE AdvancedLTE networks are carrying an increasing amount of data. Although cells can be made smaller to help accommodate this, it is not the complete solution and more spectrum is needed.One approach is to use unlicensed spectrum alongside the licensed bands. Known in 3GPP as LTE-LAA - LTE License Assisted Access or more generally as LTE U - LTE Unlicensed, it enables access to unlicensed spectrum especially in the 5GHz ISM band.LTE-U backgroundThere is a considerable amount of unlicensed spectrum available around the globe. These bands are used globally to provide unlicensed access for short range radio transmissions. These bands, called ISM - Industrial, Scientific and Medical bands are allocated in different parts of the spectrum and are used for a wide variety of applications including microwave ovens, Wi-Fi, Bluetooth, and much more.The frequency band of most interest for LTE-U, Unlicensed / LTE-LAA, License Assisted Access is the 5GHz band. Here there are several hundred MHz of spectrum bandwidth available, although the exact bands available depend upon the country in question.

5GHz bands for LTE-U / LTE-LAAIn addition to the basic frequency limits, the use of the 5GHz bands for applications such as LTE-U or LTE-LAA carries some regulatory requirements.One of the main requirements for access to these frequencies is that of being able to coexist with other users of the band - a method of Clear Channel Assessment, CCA, or Listen Before Talk, LBT is required. This often means that instantaneous access may not always be available when LTE-U is being implemented.Another requirements is that there are different power levels allowed dependent upon the country and the area of the band being used. Typically between 5150 and 5350 MHz there is a maximum power limit of 200 mW and operation is restricted to indoor use only, and the upper frequencies often allow power levels up to 1 W.LTE-U / LTE-LAA basicsThe use of LTE-U (Unlicensed) / LTE-LAA (License Assisted Access) was first introduced in Rel13 of the 3GPP standards. Essentially, LTE-U is built upon the carrier aggregation capability of LTE-Advanced that has been deployed since around 2013. Essentially Carrier aggregation seeks to increase the overall bandwidth available to a user equipment by enabling it to use more than one channel, either in the same band, or within another band.There are several ways in which LTE-U can be deployed: Downlink only: This is the most basic form of LTE-U and it is similar in approach to some of the first LTE carrier aggregation deployments. In this the primary cell link is always located in the licensed spectrum bands.

Also when operating in this mode, the LTE eNodeB performs most of the necessary operations to ensure reliable operation is maintained and interference is not caused to other users by ensuring the channel is free. Uplink and downlink: Full TDD LTE-U operation with the user equipment having an uplink and downlink connection in the unlicensed spectrum requires the inclusion of more features.

FDD / TDD aggregation: LTE-CA allows the use of carrier aggregation mixes between FDD and TDD. This provides for much greater levels of flexibility when selecting the band to be used with in unlicensed spectrum for LTE-LAA operation.LTE-U relies on the existing core network for the backhaul, and other capabilities like security and authentication. As such no changes are needed to the core network. Some changes are needed to the base station so that it can accommodate the new frequencies and also incorporate the capabilities required to ensure proper sharing of the unlicensed frequencies. In addition to this, the handsets or UEs will need to have the new LTE-U / LTE-LAA capability incorporated into them so they can access LTE on these additional frequencies.LTE-U / Wi-Fi coexistenceOne of the great fears that many have is that the use of LTE-U will swamp the 5GHz unlicensed band and that Wi-Fi using these frequencies will suffer along with other users.The LTE-U system is being designed to overcome this issue and using an listen before transmit, LBT solution, all users should be able to coexist without any undue levels of interference.There will be cases where LTE-U operation and Wi-Fi use different channels and under these circumstances there will be only minimal levels of interference.It is also possible to run LTE-U and Wi-Fi on the same channel. Under these circumstances both are able to operate, although with a lower data throughput. It is also possible to place a "fairness" algorithm into the eNodeB to ensure that the Wi-Fi signal is not unduly degraded and is still able to support a good data thro0ughput.

LTE Security- overview, about the basics of LTE security including the techniques used for LTE authentication, ciphering, encryption, and identity protection.IN THIS SECTION LTE Introduction OFDM, OFDMA, SC-FDMA LTE MIMO TDD & FDD Frame & subframe Physical logical & transport channels Bands and spectrum UE categories SAE architecture LTE SON VoLTE SRVCC LTE-M LTE-U / LAA SecuritySee also 4G LTE AdvancedLTE security is an issue that is of paramount importance. It is necessary to ensure that LTE security measures provide the level of security required without impacting the user as this could drive users away.Nevertheless with the level of sophistication of security attacks growing, it is necessary to ensure that LTE security allows users to operate freely and without fear of attack from hackers. Additionally the network must also be organised in such a way that it is secure against a variety of attacks.

LTE security basicsWhen developing the LTE security elements there were several main requirements that were borne in mind: LTE security had to provide at least the same level of security that was provided by 3G services. The LTE security measures should not affect user convenience. The LTE security measures taken should provide defence from attacks from the Internet. The security functions provided by LTE should not affect the transition from existing 3G services to LTE. The USIM currently used for 3G services should still be used.To ensure these requirements for LTE security are met, it has been necessary to add further measures into all areas of the system from the UE through to the core network.The main changes that have been required to implement the required level of LTE security are summarised below: A new hierarchical key system has been introduced in which keys can be changed for different purposes. The LTE security functions for the Non-Access Stratum, NAS, and Access Stratum, AS have been separated. The NAS functions are those functions for which the processing is accomplished between the core network and the mobile terminal or UE. The AS functions encompass the communications between the network edge, i.e. the Evolved Node B, eNB and the UE. The concept of forward security has been introduced for LTE security. LTE security functions have been introduced between the existing 3G network and the LTE network.

LTE USIMOne of the key elements within the security of GSM, UMTS and now LTE was the concept of the subscriber identity module, SIM. This card carried the identity of the subscriber in an encrypted fashion and this could allow the subscriber to keep their identity while transferring or upgrading phones.With the transition form 2G - GSM to 3G - UMTS, the idea of the SIM was upgraded and a USIM - UMTS Subscriber Identity Module, was used. This gave more functionality, had a larger memory, etc.For LTE, only the USIM may be used - the older SIM cards are not compatible and may not be used.ByIan Poole

4G LTE Advanced Tutorial- overview, information, tutorial about the basics of LTE Advanced, the 4G technology being called IMT Advanced being developed under 3GPP.IN THIS SECTION LTE Advanced Tutorial Carrier Aggregation Coordinated Multipoint - CoMP LTE Relay LTE D2D LTE HetNetSee also 3G LTEWith the standards definitions now available for LTE, the Long Term Evolution of the 3G services, eyes are now turning towards the next development, that of the truly 4G technology named IMT Advanced. The new technology being developed under the auspices of 3GPP to meet these requirements is often termed LTE Advanced.In order that the cellular telecommunications technology is able to keep pace with technologies that may compete, it is necessary to ensure that new cellular technologies are being formulated and developed. This is the reasoning behind starting the development of the new LTE Advanced systems, proving the technology and developing the LTE Advanced standards.

In order that the correct solution is adopted for the 4G system, the ITU-R (International Telecommunications Union - Radiocommunications sector) has started its evaluation process to develop the recommendations for the terrestrial components of the IMT Advanced radio interface. One of the main competitors for this is the LTE Advanced solution.One of the key milestones is October 2010 when the ITU-R decides the framework and key characteristics for the IMT Advanced standard. Before this, the ITU-R will undertake the evaluation of the various proposed radio interface technologies of which LTE Advanced is a major contender.Key milestones for ITU-R IMT Advanced evaluationThe ITU-R has set a number of milestones to ensure that the evaluation of IMT Advanced technologies occurs in a timely fashion. A summary of the main milestones is given below and this defines many of the overall timescales for the development of IMT Advanced and in this case LTE Advanced as one of the main technologies to be evaluated.

KEY MILESTONES ON THE DEVELOPMENT OF 4G LTE-ADVANCED

MILESTONEDATE

Issue invitation to propose Radio Interface Technologies.March 2008

ITU date for cut-off for submission of proposed Radio Interface Technologies.October 2009

Cutoff date for evaluation report to ITU.June 2010

Decision on framework of key characteristics of IMT Advanced Radio Interface Technologies.October 2010

Completion of development of radio interface specification recommendations.February 2011

LTE Advanced development historyWith 3G technology established, it was obvious that the rate of development of cellular technology should not slow. As a result initial ideas for the development of a new 4G system started to be investigated. In one early investigation which took place on 25 December 2006 with information released to the press on 9 February 2007, NTT DoCoMo detailed information about trials in which they were able to send data at speeds up to approximately 5 Gbit/s in the downlink within a 100MHz bandwidth to a mobile station moving at 10km/h. The scheme used several technologies to achieve this including variable spreading factor spread orthogonal frequency division multiplex, MIMO, multiple input multiple output, and maximum likelihood detection. Details of these new 4G trials were passed to 3GPP for their considerationIn 2008 3GPP held two workshops on IMT Advanced, where the "Requirements for Further Advancements for E-UTRA" were gathered. The resulting Technical Report 36.913 was then published in June 2008 and submitted to the ITU-R defining the LTE-Advanced system as their proposal for IMT-Advanced.The development of LTE Advanced / IMT Advanced can be seen to follow and evolution from the 3G services that were developed using UMTS / W-CDMA technology.

COMPARISON OF LTE-A WITH OTHER CELLULAR TECHNOLOGIES

WCDMA(UMTS)HSPAHSDPA / HSUPAHSPA+LTELTE ADVANCED(IMT ADVANCED)

Max downlink speedbps384 k14 M28 M100M1G

Max uplink speedbps128 k5.7 M11 M50 M500 M

Latencyround trip timeapprox150 ms100 ms50ms (max)~10 msless than 5 ms

3GPP releasesRel 99/4Rel 5 / 6Rel 7Rel 8Rel 10

Approx years of initial roll out2003 / 42005 / 6 HSDPA2007 / 8 HSUPA2008 / 92009 / 102014 / 15

Access methodologyCDMACDMACDMAOFDMA / SC-FDMAOFDMA / SC-FDMA

LTE Advanced is not the only candidate technology. WiMAX is also there, offering very high data rates and high levels of mobility. However it now seems less likely that WiMAX will be adopted as the 4G technology, with LTE Advanced appearing to be better positioned.LTE Advanced key featuresWith work starting on LTE Advanced, a number of key requirements and key features are coming to light. Although not fixed yet in the specifications, there are many high level aims for the new LTE Advanced specification. These will need to be verified and much work remains to be undertaken in the specifications before these are all fixed. Currently some of the main headline aims for LTE Advanced can be seen below:1. Peak data rates: downlink - 1 Gbps; uplink - 500 Mbps.2. Spectrum efficiency: 3 times greater than LTE.3. Peak spectrum efficiency: downlink - 30 bps/Hz; uplink - 15 bps/Hz.4. Spectrum use: the ability to support scalable bandwidth use and spectrum aggregation where non-contiguous spectrum needs to be used.5. Latency: from Idle to Connected in less than 50 ms and then shorter than 5 ms one way for individual packet transmission.6. Cell edge user throughput to be twice that of LTE.7. Average user throughput to be 3 times that of LTE.8. Mobility: Same as that in LTE9. Compatibility: LTE Advanced shall be capable of interworking with LTE and 3GPP legacy systems.These are many of the development aims for LTE Advanced. Their actual figures and the actual implementation of them will need to be worked out during the specification stage of the system.LTE Advanced technologiesThere are a number of key technologies that will enable LTE Advanced to achieve the high data throughput rates that are required. MIMO and OFDM are two of the base technologies that will be enablers. Along with these there are a number of other techniques and technologies that will be employed. Orthogonal Frequency Division Multiplex, OFDM OFDM forms the basis of the radio bearer. Along with it there is OFDMA (Orthogonal Frequency Division Multiple Access) along with SC-FDMA (Single Channel Orthogonal Frequency Division Multiple Access). These will be used in a hybrid format. However the basis for all of these access schemes is OFDM.

Note on OFDM:Orthogonal Frequency Division Multiplex (OFDM) is a form of transmission that uses a large number of close spaced carriers that are modulated with low rate data. Normally these signals would be expected to interfere with each other, but by making the signals orthogonal to each other there is no mutual interference. The data to be transmitted is split across all the carriers to give resilience against selective fading from multi-path effects..Click on the link for anOFDM tutorial

Multiple Input Multiple Output, MIMO: One of the other key enablers for LTE Advanced that is common to LTE is MIMO. This scheme is also used by many other technologies including WiMAX and Wi-Fi - 802.11n. MIMO - Multiple Input Multiple Output enables the data rates achieved to be increased beyond what the basic radio bearer would normally allow.

Note on MIMO:Two major limitations in communications channels can be multipath interference, and the data throughput limitations as a result of Shannon's Law. MIMO provides a way of utilising the multiple signal paths that exist between a transmitter and receiver to significantly improve the data throughput available on a given channel with its defined bandwidth. By using multiple antennas at the transmitter and receiver along with some complex digital signal processing, MIMO technology enables the system to set up multiple data streams on the same channel, thereby increasing the data capacity of a channel.Click on the link for aMIMO tutorial

For LTE Advanced, the use of MIMO is likely to involve further and more advanced techniques including the use of additional antennas in the matrix to enable additional paths to be used, although as the number of antennas increases, the overhead increases and the return per additional path is less.

In additional to the numbers of antennas increasing, it is likely that techniques such as beamforming may be used to enable the antenna coverage to be focused where it is needed. Carrier Aggregation, CA: As many operators do not have sufficient contiguous spectrum to provide the required bandwidths for the very high data rates, a scheme known as carrier aggregation has been developed. Using this technology operators are able to utilise multiple channels either in the same bands or different areas of the spectrum to provide the required bandwidth.Read more aboutCarrier Aggregation, CA Coordinated Multipoint : One of the key issues with many cellular systems is that of poor performance at the cell edges. Interference from adjacent cells along with poor signal quality lead to a reduction in data rates. For LTE-Advanced a scheme known as coordinated multipoint has been introduced.Read more aboutCoordinated Multipoint, CoMP LTE Relaying: LTE relaying is a scheme that enables signals to be forwarded by remote stations from a main base station to improve coverage.Read more aboutLTE Relaying Device to Device, D2D: LTE D2D is a facility that has been requested by a number of users, in particular the emergency services. It enables fast swift access via direct communication - a facility that is essential for the emergency services when they may be on the scene of an incident.Read more aboutDevice to Device communicationsWith data rates rising well above what was previously available, it will be necessary to ensure that the core network is updated to meet the increasing requirements. It is therefore necessary to further improve the system architecture.These and other technologies will be used with LTE Advanced to provide the very high data rates that are being sought along with the other performance characteristics that are needed. . . . . . . . . . .ByIan PooleLTE CA: Carrier Aggregation Tutorial- 4G LTE Advanced CA, carrier aggregation or channel aggregation enables multiple LTE carriers to be used together to provide the high data rates required for 4G LTE Advanced.4G LTE ADVANCED INCLUDES: LTE Advanced Tutorial Carrier Aggregation Coordinated Multipoint - CoMP LTE Relay LTE D2D LTE HetNetSee also 3G LTELTE Advanced offers considerably higher data rates than even the initial releases of LTE. While the spectrum usage efficiency has been improved, this alone cannot provide the required data rates that are being headlined for 4G LTE Advanced.To achieve these very high data rates it is necessary to increase the transmission bandwidths over those that can be supported by a single carrier or channel. The method being proposed is termed carrier aggregation, CA, or sometimes channel aggregation. Using LTE Advanced carrier aggregation, it is possible to utilise more than one carrier and in this way increase the overall transmission bandwidth.These channels or carriers may be in contiguous elements of the spectrum, or they may be in different bands.Spectrum availability is a key issue for 4G LTE. In many areas only small bands are available, often as small as 10 MHz. As a result carrier aggregation over more than one band is contained within the specification, although it does present some technical challenges.Carrier aggregation is supported by both formats of LTE, namely the FDD and TDD variants. This ensures that both FDD LTE and TDD LTE are able to meet the high data throughput requirements placed upon them.

LTE carrier aggregation basicsThe target figures for data throughput in the downlink is 1 Gbps for 4G LTE Advanced. Even with the improvements in spectral efficiency it is not possible to provide the required headline data throughput rates within the maximum 20 MHz channel. The only way to achieve the higher data rates is to increase the overall bandwidth used. IMT Advanced sets the upper limit at 100 MHz, but with an expectation of 40 MHz being used for minimum performance. For the future it is possible the top limit of 100 MHz could be extended.It is well understood that spectrum is a valuable commodity, and it takes time to re-assign it from one use to another in view - the cost of forcing users to move is huge as new equipment needs to be bought. Accordingly as sections of the spectrum fall out of use, they can be re-assigned. This leads to significant levels of fragmentation.To an LTE terminal, each component carrier appears as an LTE carrier, while an LTE-Advanced terminal can exploit the total aggregated bandwidth.

RF aspects of carrier aggregationThere are a number of ways in which LTE carriers can be aggregated:

Types of LTE carrier aggregation Intra-band: This form of carrier aggregation uses a single band. There are two main formats for this type of carrier aggregation:

Contiguous: The Intra-band contiguous carrier aggregation is the easiest form of LTE carrier aggregation to implement. Here the carriers are adjacent to each other.

Contiguous aggregation of two uplink component carriers

The aggregated channel can be considered by the terminal as a single enlarged channel from the RF viewpoint. In this instance, only one transceiver is required within the terminal or UE, whereas more are required where the channels are not adjacent. However as the RF bandwidth increases it is necessary to ensure that the UE in particular is able to operate over such a wide bandwidth without a reduction in performance. Although the performance requirements are the same for the base station, the space, power consumption, and cost requirements are considerably less stringent, allowing greater flexibility in the design. Additionally for the base station, multi-carrier operation, even if non-aggregated, is already a requirement in many instances, requiring little or no change to the RF elements of the design. Software upgrades would naturally be required to cater for the additional capability. Non-contiguous: Non-contiguous intra-band carrier aggregation is somewhat more complicated than the instance where adjacent carriers are used. No longer can the multi-carrier signal be treated as a single signal and therefore two transceivers are required. This adds significant complexity, particularly to the UE where space, power and cost are prime considerations. Inter-band non-contiguous: This form of carrier aggregation uses different bands. It will be of particular use because of the fragmentation of bands - some of which are only 10 MHz wide. For the UE it requires the use of multiple transceivers within the single item, with the usual impact on cost, performance and power. In addition to this there are also additional complexities resulting from the requirements to reduce intermodulation and cross modulation from the two transceiversThe current standards allow for up to five 20 MHz carriers to be aggregated, although in practice two or three is likely to be the practical limit. These aggregated carriers can be transmitted in parallel to or from the same terminal, thereby enabling a much higher throughput to be obtained.

Carrier aggregation bandwidthsWhen aggregating carriers for an LTE signal, there are several definitions required for the bandwidth of the combined channels. As there as several bandwidths that need to be described, it is necessary to define them to reduce confusion.

LTE Carrier Aggregation Bandwidth Definitions for Intra-Band Case

LTE carrier aggregation bandwidth classesThere is a total of six different carrier aggregation, CA bandwidth classes which are being defined.

CARRIER AGGREGATIONBANDWIDTH CLASSAGGREGATED TRANSMISSIONBW CONFIGURATIONNUMBER OF COMPONENT CARRIERS

A1001

B1002

C100 - 2002

NB:classes D, E, & F are in the study phase.

LTE aggregated carriersWhen carriers are aggregated, each carrier is referred to as a component carrier. There are two categories: Primary component carrier: This is the main carrier in any group. There will be a primary downlink carrier and an associated uplink primary component carrier. Secondary component carrier: There may be one or more secondary component carriers.There is no definition of which carrier should be used as a primary component carrier - different terminals may use different carriers. The configuration of the primary component carrier is terminal specific and will be determined according to the loading on the various carriers as well as other relevant parameters.In addition to this the association between the downlink primary carrier and the corresponding uplink primary component carrier is cell specific. Again there are no definitions of how this must be organised. The information is signalled to the terminal of user equipment as part of the overall signalling between the terminal and the base station.

Carrier aggregation cross carrier schedulingWhen LTE carrier aggregation is used, it is necessary to be able to schedule the data across the carriers and to inform the terminal of the DCI rates for the different component carriers. This information may be implicit, or it may be explicit dependent upon whether cross carrier scheduling is used.Enabling of the cross carrier scheduling is achieved individually via the RRC signalling on a per component carrier basis or a per terminal basis.When no cross carrier scheduling is arranged, the downlink scheduling assignments achieved on a per carrier basis, i.e. they are valid for the component carrier on which they were transmitted.For the uplink, an association is created between one downlink component carrier and an uplink component carrier. In this way when uplink grants are sent the terminal or UE will know to which uplink component carrier they apply.Where cross carrier scheduling is active, the PDSCH on the downlink or the PUSCH on the uplink is transmitted on an associate component carrier other than the PDCCH, the carrier indicator in the PDCCH provides the information about the component carrier used for the PDSCH or PUSCH.It is necessary to be able to indicate to which component carrier in any aggregation scheme a grant relates. To facilitate this, component carriers are numbered. The primary component carrier is numbered zero, for all instances, and the different secondary component carriers are assigned a unique number through the UE specific RRC signalling. This means that even if the terminal or user equipment and the base station, eNodeB may have different understandings of the component carrier numbering during reconfiguration, transmissions on the primary component carrier can be scheduled.4G LTE CoMP, Coordinated Multipoint Tutorial- 4G LTE Advanced CoMP, coordinated multipoint is used to send and receive data to and from a UE from several points to ensure the optimum performance is achieved even at cell edges.4G LTE ADVANCED INCLUDES: LTE Advanced Tutorial Carrier Aggregation Coordinated Multipoint - CoMP LTE Relay LTE D2D LTE HetNetSee also 3G LTELTE CoMP or Coordinated Multipoint is a facility that is being developed for LTE Advanced - many of the facilities are still under development and may change as the standards define the different elements of CoMP more specifically.LTE Coordinated Multipoint is essentially a range of different techniques that enable the dynamic coordination of transmission and reception over a variety of different base stations. The aim is to improve overall quality for the user as well as improving the utilisation of the network.Essentially, LTE Advanced CoMP turns the inter-cell interference, ICI, into useful signal, especially at the cell borders where performance may be degraded.Over the years the importance of inter-cell interference, ICI has been recognised, and various techniques used from the days of GSM to mitigate its effects. Here interference averaging techniques such as frequency hopping were utilised. However as technology has advanced, much tighter and more effective methods of combating and utilising the interference have gained support.

LTE CoMP and 3GPPThe concepts for Coordinated Multipoint, CoMP, have been the focus of many studies by 3GPP for LTE-Advanced as well as the IEEE for their WiMAX, 802.16 standards. For 3GPP there are studies that have focussed on the techniques involved, but no conclusion