Excellent Knowledge Notes [Ashwani]

7/22/2019 Excellent Knowledge Notes [Ashwani]

1/53

[Ashwani Kumar] [Ericsson]

Centralized Radio Access Network (C-RAN)

Current architecture of Radio Access Network (RAN) is soon reaching the limit of sustaining theamount of data traffic on the network. Especially in population concentrated areas, such as majorstations and giant commercial complexes, it is no longer acceptable to simply increase thenumber of base stations (BTS) in order to provide smooth network accesses to users, for variousreasons.

One reason is the cost effectiveness of building BTS. Each BTS needs a complete system, frompower sources, backup battery, cooling, and monitoring system. However, when there are manyBTS in concentrated areas, average utilization of each BTS goes down significantly although thecost of each BTS remains the same. Interference among BTS is another reason. More BTS beingbuilt in close range, there are more chances that the same frequency range will be used by

multiple BTS.

To overcome such problems, Centralized Radio Access Network (C-RAN) was invented, with thefollowing concepts in mind:

1. Centralized Deployment2. Collaborative Radio3. Real-time Cloud Computing4. Clean system

A single master base station of C-RAN can connect multiple Remote Radio Heads (RRH), so that

BTS controls are centralized. This scheme can greatly improve the utilization of processingresources, and at the same time, provide versatile coverage to large areas with a combination ofmacro cells and small cells (Figure 1).

Figure 1: C-RAN Architecture

To enhance the capabilities of C-RAN further, Advanced C-RAN architecture is already indevelopment. The advanced architecture incorporates "Add-on Cell" which uses different

frequency ranges to avoid interferences and even supports higher throughput (Figure 2). The newtechnology uses Carrier Aggregation, one of the key features of LTE-Advanced, and is extensible


2/53

-2-

to the maximum downlink throughput of 3Gbps. With the capability to support up to 48 cells, C-RAN paves way for new possibility in mobile broadband.

Figure 2: Advanced C-RAN Architecture

Figure 3: Carrier Aggregation

Sharp Rise in Heavy C-plane Traffic

A Lesson Learned from NTT docomo's Network Collapse

Subscribers in Japan have recently encountered a series of large scale network outages. NTTdocomo had total of 5 outages in 7 months from June 2011 to January 2012, and KDDI has 5


3/53

-3-

outages in 10 months from April 2011 to February 2012. The impact of the incidents was sosevere that it has led the Internal Affairs and Communications Ministry in Japan order the serviceoperators to a total investigation of the whole network capacity and detail reporting.

It was clear that the explosion in the number of smartphones has been the reason for these

outages. The smartphone's control plane (C-plane) traffic surges 2 to 5 times of feature phones,and user plane (U-plane) traffic as much as 10 times. Service providers are eager to promotesmartphones to generate data traffic revenues, but as a result, the sharp rise in data traffic hasexceeded network capacity and it is causing frequent service disruptions.

Smartphones have two distinguishable characteristics from feature phones, i.e., the larger amountof data traffic and the higher network access frequency. Obviously, large data traffic can ultimatelylead to service disruptions, but the same can be said of the network access frequency.

Radio resources are shared among all subscribers, and large data traffic can easily create a

bottleneck by heavily utilizing the resources. When they are fully occupied, the data throughputand accessibility for all subscribers is seriously affected. Likewise, frequent network access canalso affect the network, but in a different way. The high network access frequency causesunexpectedly high amount of C-plane traffic, and it creates a very high stress on core networkprocessing. When it exceeds the networks processing capability, it can take down all the mobileservices in the area (Figure 1).

Figure 1: Two Major Challenges for Cellular Network

Starting from some of the population-concentrated spots, this type of outages has spread acrossmajor cities in Japan and affected millions of subscribers in Japan since 2010. The root cause ofthe outages is found to be the sharp rise in C-plane traffic (Figure 2). (Refer to this article)NTTdocomo's Executive Vice President Fumio Iwasaki told, "Our estimate (of the communication
http://www.artizanetworks.com/file/JapanTimes_docomo.pdfhttp://www.artizanetworks.com/file/JapanTimes_docomo.pdfhttp://www.artizanetworks.com/file/JapanTimes_docomo.pdfhttp://www.artizanetworks.com/file/JapanTimes_docomo.pdf


4/53

-4-

volume) was insufficient . . . We apologize to our subscribers for causing the trouble," at a newsconference.

Figure 2: C-plane Traffic

Boosting a Network Capacity for C-plane Traffic

Service operators have reacted by boosting a network capacity and reducing the number of C-

plane messages per network access. NTT docomo and other operators have already reinforcedtheir networks with a number of powerful packet switches and revised their C-plane processingsoftware.

Not only to avoid rising CAPEX, but new technologies are introduced for more efficient C-planeprocessing. One of such examples is Fast Dormancy. If terminal and network support thisspecification, the number of C-plane messages can become one third of the current volume.Some of the popular smartphones, such as iPhones, have already implemented Fast Dormancy,and the service operators in Japan are preparing to support this feature from 2011 to 2013.

Reducing the Number of Messages in C-plane TrafficC-plane messages are generated by terminals to set up and release the radio links. Thesemessages represent only a very limited amount of bandwidth, yet C-plane fault can trigger fataldisruptions of the radio link. In case of NTT docomo, sharp rise in C-plane traffic of smartphoneshas overloaded the packet switches and brought down the network. Frequent network accesscauses terminals to transmit C-plane messages to set up, but then soon release the radio linkupon idle timeout from no data activity. Multiple background applications can add up to create ahigh load of C-plane traffic, resulting in high load processing in core network, so reducing C-planemessages is one of the main challenges to be resolved.

Underestimating C-plane Traffic

NTT docomo has admitted they have underestimated the amount of C-plane traffic generated bysmartphones. NTT docomo's spokesperson Mr. Hiramatsu told that C-plane traffic can create the


5/53

-5-

high stress environment not only for radio access but for the core network. The reason behind thehigh stress comes from the mechanism where C-plane messages re-write data on radio networkcontrollers (RNC) and packet switches (PS).

CEO of NTT docomo Mr. Yamada also told that NTT docomo was focusing solely on handling the

bursting user traffic. NTT docomo introduced new packet switches on January 25, 2012 inresponse to the network incidents.

Core network nodes keep logical connections for certain periods, told Ericsson Japan CTO Mr.Fujisawa. However, physical radio links are set up and released frequently to increase radiousage efficiency. While NTT docomo had increased simultaneous connection capacity from 880Kto 1.8M by introducing new packet switches to accommodate smartphone traffic, C-planeperformance was reduced from 27.5M to 14.1M packets per hour. However, before the packetswitches were reinforced, sharp rise in C-plane traffic attacked the NTT docomo's network (Figure3).

Figure 3: Underestimating PS Performance

Introducing Fast DormancyAt the current rate, just reinforcing packet switches can lead to limitless CAPEX. To avoid theincreased cost, a new technology called Fast Dormancy is introduced in 3GPP Release 8 to

reduce C-plane messages to one third (Figure 4). Fast Dormancy specifies intermediate state(PCH) to avoid frequent return to idle state. Newer iPhone has already integrated this technologyand so have some of the Android phones, depending on the chipset. In addition, Android 4.0implements a new mechanism to reduce C-plane messages.

Figure 4: Fast Dormancy


6/53

-6-

ConclusionToday's rapidly changing cellular network environments create a challenge for service operators,especially by the wide spread of smartphones. No longer are the service disruptions unusualincidents, highly congested networks became the major issues in most major cities in the world.Fast increasing smartphones are responsible for high congestion in terms of network capacity, butmore importantly, the associated C-plane traffic is causing fatal damage to take down mobileservices. The need for comprehensive testing including C-plane performance testing is increasingfor both vendors and operators to know the true limit of their network capacities. To better preparefor the worst case scenarios, it is highly recommended to evaluate communication nodes of radioaccess and core networks with total testing solution, such as Artiza LTE Tester DuoSIM.

LTE-Advanced Tutorial

LTE Breakthrough to Real 4G

In the spring of 2009, 3GPP LTE Release 8 (LTE Rel.8) specification was completed, and it hastriggered LTE service deployment by leading mobile network operators. LTE Rel.8 has set varioustarget requirements for LTE, designed to achieve higher system performance than HSPA in 3GPPRelease 6. It has improved system capacity, cell edge user throughput and lower C/U-planelatency, supported by introduction of new radio interface technologies, such as OFDM, frequency

domain scheduling and MIMO. In the following year, spring of 2010, 3GPP LTE Release 9 (LTERel.9) has also been completed to extend various functionalities in LTE Rel.8. The area ofenhancement includes closed subscriber group (CSG), self-organizing network (SON), and newfunctionalities such as location information service and MBMS (Multimedia Broadcast andMulticast Service).

The next important milestone is the standardization of LTE-Advanced (LTE Rel.10 and beyond).To keep up with the today's rapidly growing traffic, especially by the wide spread of smart phonedevices, it became necessary to further enhance LTE Rel.9 and achieve much higher level ofsystem performance, while keeping the backward compatibility. Accordingly, the radio accessinterface specifications for LTE-Advanced has been developed in the beginning of 2011. ITU-T

has announced new requirements including spectral efficiency, higher bandwidth, and lowerlatency. To meet these competitive requirements, a series of new technologies have been


7/53

-7-

discussed to introduce into LTE-Advanced, such as Carrier Aggregation, Enhanced Uplink Multi-antenna Transmission, and CoMP Transmission/Reception. LTE-Advanced will enable 1Gbpsdownlink bandwidth in addition to the existing LTE service and open a new era of true wirelessbroadband services in the near future.

Figure 1: Standardization Schedule

LTE-Advanced services will become available from leading mobile network operators around2014. Additional features include higher downlink bandwidth and non-contiguous spectra usage tofurther enhance the current LTE services.

Evaluation Results against ITU-R Technical CriteriaITU-R has specified minimum requirements and evaluation criteria for IMT-Advanced in the eighttechnical areas as listed below.

Peak spectral efficiency Cell spectral efficiency Cell edge user spectral efficiency Bandwidth Latency Mobility Handover interruption time VoIP capacity

3GPP TR 36.912 V9.0.0 (2009-09) describes the detailed evaluation results for the ITU-Rtechnical criteria. The 3GPP self-evaluation concluded that LTE Rel.10 & beyond (LTE-Advanced), SRIT (Set of Radio Interface Technology), individual FDD RIT (FDD Radio InterfaceTechnology) and TDD RIT (TDD Radio Interface Technology) components completely satisfied

the criteria of the decision step and should move forward to Step 7 of the process. It concluded


8/53

-8-

that, "consequently, the 3GPP LTE Release 10 & beyond (LTE-Advanced) technology should beincluded in the ITU-R IMT-Advanced terrestrial component radio interface Recommendation(s)."

DL/UL Acceleration Technologies

There are series of technologies in LTE-Advanced as shown in Figure 2. But new MIMO andCarrier Aggregation (CA) are the two key technologies for DL/UL acceleration. Thesetechnologies will improve communication performance and expand the effective bandwidth,enabling the maximum downlink speed of even up to 3 Gbps as shown Figure 3.

Figure 2: New Technology Adaptation into LTE-Advanced

Figure 3: DL Acceleration with CA and MIMO


9/53

-9-

Carrier Aggregation

Carrier Aggregation (CA) is an innovative approach to create wider bandwidth by using multipleaggregated Carrier Components (CCs). LTE Rel.10 adopts the CA technique to increase spectralbandwidth up to 100 MHz using multiple CCs. The aggregated CCs must be on compatible

spectral bandwidth supported by LTE Rel.8 (i.e., 1.4 MHz/3 MHz/5 MHz/10 MHz/15 MHz/20MHz). It allows seamless migration into LTE Rel.10 by re-utilizing LTE Rel.8 eNB along with radiofrequency (Figure 4), adjacent channel leakage ratio (ACLR), spectrum emission mask (SEM),adjacent channel selectivity (ACS) and blocking.As the LTE Rel.10 UEs are backward-compatible to LTE Rel.8 standards, it has great advantageon reducing redundant implementation with this approach. Thus, CA-enabled LTE Rel.10 UEwould achieve higher user throughput than LTE Rel.8.There are three types of CA, depending on CC combination as shown in Figure 5.

Figure 4: Carrier Aggregation

Figure 5: Three Types of Carrier Aggregation


10/53

-10-

1. Intra-band Contiguous CAContiguous bandwidth wider than 20 MHz is used in this scenario. For example, wideband suchas 3.5 GHz band would fit this model.

2. Inter-band Non-contiguous CANon-contiguous band over multiple bands is used in this scenario. Network with two spectrumbands (i.e., 2 GHz and 800 MHz) would fit this model. This scenario would have advantage onhaving higher throughput simply by two carriers as well as the improvement on stabletransmission by two different spatial paths on different spectrum bands.

3. Intra-band Non-contiguous CANon-contiguous band in same band is used in this scenario. This model would fit operators inNorth America or Europe, who have fragmental spectrum in one band or share same cellularnetwork.

CA ScenariosThere are four possible CA Scenarios in real LTE-Advanced deployment.

(a) Multiple CCs over contiguous bandwidth (Figure 6).

Figure 6: Overlapped Coverage


11/53

-11-

(b) CCs over different bands with different coverage in cells (Figure 7).

Figure 7: Different Coverage

(c) CCs cover cell edges of different CC cells (Figure 8).

Figure 8: Cell Edge Beamforming

(d) Macro-coverage with lower CC and Hotspot with RRH (Remote Radio Head) (Figure 9).

Figure 9: RRH Integration


12/53

-12-

New MIMO Techniques

LTE Rel.8 supported up to four layers of MIMO multiplexing for downlink and no MIMO for uplink.LTE-Advanced supports single user MIMO (SU-MIMO) scheme up to eight layers (8x8 MIMO) fordownlink and four layers (4x4 MIMO) for uplink. With this technology, it achieves peak spectralefficiency of 30 bit/s/Hz for downlink and 15 bit/sec/Hz for uplink. In other words, single 20MHzbandwidth to achieve up to 600Mbps downlink speed.

Figure 10: Closed-Loop MIMO (4x4 MIMO rank-2)

Figure 11: Rank Adaptation


13/53

-13-

Multi-user MIMO (MU-MIMO) is also the important technology to increase peak data rate as wellas the system capacity and cell edge user throughput. MU-MIMO and CoMP transmission, whichwill be described later, are applying various advanced signal processing techniques, e.g.dedicated downlink beamforming, adaptive transmission power control, and multi cellsimultaneous transmission.

CoMP Techniques

Coordinated multi-point transmission/reception (CoMP) is a DL/UL orthogonalization technique toimprove system capacity and cell edge user throughput. Currently, there are two differentapproaches for CoMP techniques (Figure 12). One approach is a decentralized autonomouscontrol based on independent eNB architecture, and the other is a centralized control based onremote radio equipment (RRE) architecture.

In the approach with independent eNB architecture, CoMP is performed by signaling betweeneNBs. This technique can utilize legacy cells, but the disadvantage is signaling delay and otheroverheads. In the second approach with RRE technique, the eNB can centralize and control allthe radio resource by transmitting baseband data directly between eNB and RREs on optical fiberconnections. There is little signaling delay or other overheads in this technique, and Intra-cellradio resource control is relatively easy. However, CAPEX on optical fibers is not negligible, andcentralized eNB must be able to accept higher load according to the number of RREs. Therefore,both approaches are under consideration for LTE-Advanced.

Figure 12: Centralized/Autonomous Decentralized Control


14/53

-14-

1. Downlink CoMPDownlink CoMP also has two approaches under consideration for LTE-Advanced, i.e.,Coordinated Scheduling/Beamforming (CS/CB) (Figure 13) and Joint Processing (Figure 14).In CS/CB, the transmission to a single UE is performed from the serving cell, exactly as in thecase of non-CoMP transmission. However, the scheduling is dynamically coordinated betweenthe cells, including any beamforming functionality. In that way, the interference between differenttransmissions can be controlled and reduced. In principle, schedule optimization will be performedbased on the serving set of users, so that the transmitter beams are constructed to reduceinterference to other neighboring user, while increasing the served users signal strength. In Joint Transmission feature of Joint Processing, the transmission to a single UE issimultaneously performed from multiple transmission points in practice cell sites. The multi-pointtransmissions will be coordinated as a single transmitter with multiple antennas that aregeographically separated. This scheme has the potential for higher performance, compared toCS/CB, but comes at the expense of more stringent requirement on backhaul communication.



2. Uplink CoMPUplink CoMP utilizes geographically separated antennas for signal reception from UE, andscheduling decisions are coordinated by multiple cells to control interference from each other. UEis not aware of multi-cell reception of its signal, so that impact on radio interface specification is atminimal. Implementation of Uplink CoMP largely depends on scheduler and receiver in the cells.

Deployment Possibilities


15/53

-15-

Deployment of the first LTE-Advanced service is expected to be around 2013 to 2014, with limitedset of features. Not all the advanced technologies will be implemented in the beginning, but therest will be "added-on" as the various conditions are cleared. Such conditions may include radioregulations, frequency allocations, and some technical barriers. Many of the new features areexpected to be software upgrades on LTE nodes.

Unlike the general expectations of 4G, LTE-Advanced will not initially reach 1 Gbps or even 600Mbps. One of the biggest reasons is the spectrum, which is strictly controlled by the governments.Currently, only the 3.5 GHz spectrum is going to be assigned for wireless broadband (in Japan),but it will not become available until 2014 to 2015. NTT docomo has announced its plan to startLTE-Advanced service with 40 MHz bandwidth on the 3.5GHz spectrum, which is enough toachieve 1.2 Gbps speed theoretically. However, 8x8 MIMO required for such link speed will not betechnically possible by 2015.

On the other hand, LTE services on 2 GHz spectrum will be able to provide around 100 Mbpsbandwidth in 2015. LTE-Advanced will only achieve the same speed as the existing LTE services

at this point, or in the best case, it may be able to reach up to 300 Mbps with 2x2 MIMO andCarrier Aggregation on 40 MHz bandwidth. Thus, LTE-Advanced will not initially achieve full specservices, but it only indicates the roadmap for the future enhancements.

LTE-Advanced is the real 4G specification that greatly enhances the performance of existing LTEservices. Although the maximum link speed may not greatly exceed the current LTE in the initialstage, deployment of LTE-Advanced will be an important milestone to set clear path for thebeginning of true wireless broadband.

Essential Performance Testing

Performance Testing Not Optional

Most vendors recognize functional testing as mandatory and as an important part of productdevelopment in the early phases. A significant amount of engineering effort is made on functionaltesting, but unfortunately, few vendors make similar effort on performance testing. In some cases,it is even seen as completely optional. In reality, neglecting performance testing can be verydangerous. It is the last defense to detect performance issues and even functional issues thatoccur only when a large number of UEs are involved. Products without performance testing arefar from perfect and cannot be ready to ship out to customers. It is important to realize how muchOPEX must be spent for fixing endless service problems, and also that tremendous amount ofthose problems can be avoided by spending upfront CAPEX on performance testing. It can endup with 100 times more expensive without performance testing. Thus, LTE eNB/EPC performancetesting is vital for vendors as well as for service operators.

Figure 1: Positioning of Functional and Performance Testing


16/53

-16-

Performance Testing Needed at Every Release

Performance Testing is the type of testing that needs continuous usage, whereas FunctionalTesting is most used in the early phase of product development and at the first release ofproducts (i.e., Ver1 in Figure 2). For the second and later releases (i.e., Ver2, Ver3 and so on),Functional Testing is limited and usually performed on newly added enhanced functionality only.On the other hand, Performance Testing takes a more important role to ensure that newenhancement does not make any degradation in terms of product performance. In the long run,Performance Testing is the only tool to promise final quality upon release after release.

Figure 2: Performance Testing at Every Release

Performance Testing Finds More Critical Issues

Functional Testing can find functional issues that are easy-to-reproduce and easy-to-fix. It may beenough in the first stage of product development, but in later stages, it is necessary to usePerformance Testing to find more critical issues and performance related problems which are

found only under high load conditions. Usually, when problems are found under higher load, it ismore difficult and takes longer time to resolve. Performance Testing can find a number of suchcritical issues, and they are usually identified as one of the five major groups.


17/53

-17-

Functional Issues on Massive UE connections Performance Requirement Not Reached Function Block Stability Issues at Max Performance Critical Timing Issues in Inter-Function Block Communications Sustainability Issues

Figure 3: LTE eNB Function Block

Problems Found by Performance Testing

Artiza LTE Testers have been used worldwide to find a number of critical issues, and savedvendors and operators from major service problems. Table 1 lists some of the typical issues thatare found from performance testing with Artiza LTE Testers.

Table 1: Typical Problems Found on Performance Testing by Artiza LTE Tester

No eNB Problem Description Detected TDD/FDD

1 No RACH response on a number ofsimultaneous RACH preamble

Detected by MAC statistics on UE-SIM TDD

2 RRCConnectionReject on a numberof simultaneous attach sequence

Detected by Message Monitor on UE-SIM TDD

3 Teardown on S1 and Uu by UL rateexceeding a threshold

Detected by Message Monitor on UE-SIM TDD

4 No radio transmission after 72-hour

sustainability test

Detected by UE-SIM SIR monitor TDD

5 Occasional no return of RAR with Detected by Message Monitor on UE-SIM. eNB FDD


18/53

-18-

multiple UE connections shows CPU usage reaches 70%

6 Out of sync on DL transmission at150 Mbps

Detected by Message Monitor on UE-SIM FDD

7 No retransmission on MAC/RLClayers with massive UE connections

Detected by MAC/RLC statistics on UE-SIM FDD

8 No UL grant assignment for anumber of simultaneous UEconnections

Detected by MAC statistics on UE-SIM FDD

9 No attach completion with BurstGeneration

Detected by Message Trace and MAC statisticson UE-SIM

TDD

10 eNB halt/reboot during 12-hoursustainability test

Detected by statistics on UE-SIM and S1/X2-SIM

FDD

What is LTE?

LTE (Long Term Evolution) is the project name of a new high performance air interface for cellular

mobile communication systems. It is the last step toward the 4th generation (4G) of radiotechnologies designed to increase the capacity and speed of mobile telephone networks. Wherethe current generation of mobile telecommunication networks are collectively known as 3G, LTE ismarketed as 4G.

According to 3GPP, a set of high level requirements was identified

Reduced cost per bit Increased service provisioningmore services at lower cost with better user experience Flexibility of use of existing and new frequency bands Simplified architecture, Open interfaces Allow for reasonable terminal power consumption

Figure 1: Roadmap to 4G


19/53

-19-

Although there are major step changes between LTE and its 3G predecessors, it is neverthelesslooked upon as an evolution of the UMTS / 3GPP 3G standards. Although it uses a different formof radio interface, using OFDMA / SC-FDMA instead of CDMA, there are many similarities withthe earlier forms of 3G architecture and there is scope for much re-use. LTE can be seen forproviding a further evolution of functionality, increased speeds and general improvedperformance.

Table 1: LTE and 3G/3.5G Specification (from NTT docomo Press Release)

3G WCDMA (R99) 3.5G HSPA LTE

Frequency Common frequency assigned for 3G

Bandwidth 5MHz 5/10/20MHz

Radio Access DS-CDMA DL: OFDMA

UL: SC-FDMA

Uplink Peak Rate 384kbps 5.7Mbps >50Mbps

Downlink Peak Rate 384kbps 14Mbps >100Mbps

LTE has introduced a number of new technologies when compared to the previous cellularsystems. They enable LTE to be able to operate more efficiently with respect to the use ofspectrum, 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 betransmitted efficiently while still providing a high degree of resilience to reflections andinterference.

MIMO (Multiple Input Multiple Output)One of the main problems that previous telecommunications systems have encountered is that of

multiple signals arising from the many reflections that are encountered. By using MIMO, theseadditional signal paths can be used to advantage and are able to be used to increase thethroughput.


20/53

-20-

SAE (System Architecture Evolution)With the very high data rate and low latency requirements for 3G LTE, it is necessary to evolvethe system architecture to enable the improved performance to be achieved. One change is that anumber of the functions previously handled by the core network have been transferred out to theperiphery. Essentially this provides a much "flatter" form of network architecture. In this waylatency times can be reduced and data can be routed more directly to its destination.

Requirement for LTE

The following target requirements were agreed among operators and vendors at the project todefine the evolution of 3G networks started.

Peak data rate Instantaneous downlink peak data rate of 100 Mbps within a 20 MHz downlink spectrum allocation

(5 bps/Hz) Instantaneous uplink peak data rate of 50 Mbps (2.5 bps/Hz) within a 20MHz uplink spectrum

allocationControl-plane latency

Transition time of less than 100 ms from a camped state, such as Release 6 Idle Mode, to anactive state such as Release 6 CELL_DCH

Transition time of less than 50 ms between a dormant state such as Release 6 CELL_PCH andan active state such as Release 6 CELL_DCHControl-plane capacity

At least 200 users per cell should be supported in the active state for spectrum allocations up to 5MHzUser-plane latency

Less than 5 ms in unload condition (i.e., single user with single data stream) for small IP packetUser throughput

Downlink: average user throughput per MHz, 3 to 4 times Release 6 HSDPA Uplink: average user throughput per MHz, 2 to 3 times Release 6 Enhanced Uplink

Spectrum efficiency Downlink: In a loaded network, target for spectrum efficiency (bits/sec/Hz/site), 3 to 4 times

Release 6 HSDPA Uplink: In a loaded network, target for spectrum efficiency (bits/sec/Hz/site), 2 to 3 times Release

6 Enhanced UplinkMobility

E-UTRAN should be optimized for low mobile speed from 0 to 15 km/h Higher mobile speed between 15 and 120 km/h should be supported with high performance Mobility across the cellular network shall be maintained at speeds from 120 km/h to 350 km/h (or

even up to 500 km/h depending on the frequency band)Coverage

Throughput, spectrum efficiency and mobility targets above should be met for 5 km cells, and witha slight degradation for 30 km cells. Cells range up to 100 km should not be precluded.Further Enhanced Multimedia Broadcast Multicast Service (MBMS)

While reducing terminal complexity: same modulation, coding, multiple access approaches andUE bandwidth than for unicast operation.

Provision of simultaneous dedicated voice and MBMS services to the user. Available for paired and unpaired spectrum arrangements.

Spectrum flexibility E-UTRA shall operate in spectrum allocations of different sizes, including 1.25 MHz, 1.6 MHz, 2.5

MHz, 5 MHz, 10 MHz, 15 MHz and 20 MHz in both the uplink and downlink. Operation in paired

and unpaired spectrum shall be supported


21/53

-21-

The system shall be able to support content delivery over an aggregation of resources includingRadio Band Resources (as well as power, adaptive scheduling, etc) in the same and differentbands, in both uplink and downlink and in both adjacent and non-adjacent channel arrangements.A "Radio Band Resource" is defined as all spectrum available to an operatorCo-existence and Inter-working with 3GPP Radio Access Technology (RAT)

Co-existence in the same geographical area and co-location with GERAN/UTRAN on adjacentchannels.

E-UTRAN terminals supporting also UTRAN and/or GERAN operation should be able to supportmeasurement of, and handover from and to, both 3GPP UTRAN and 3GPP GERAN.

The interruption time during a handover of real-time services between E-UTRAN and UTRAN (orGERAN) should be less than 300 msec.Architecture and migration

Single E-UTRAN architecture The E-UTRAN architecture shall be packet based, although provision should be made to support

systems supporting real-time and conversational class traffic E-UTRAN architecture shall minimize the presence of "single points of failure" E-UTRAN architecture shall support an end-to-end QoS

Backhaul communication protocols should be optimizedRadio Resource Management requirements Enhanced support for end to end QoS Efficient support for transmission of higher layers Support of load sharing and policy management across different Radio Access Technologies

Complexity Minimize the number of options No redundant mandatory features

We can find significantly higher data rate (50-100Mbps) and faster connection times as mostremarkable requirements relative to 3G/3.5G. In order to achieve the high data rate, 3GPPdecided to use OFDMA and MIMO together for radio access technology. LTE also introducescheduling for shared channel data, HARQ and AMC (Adaptive Modulation and Coding).

SAE Technology

System Architecture Evolution (SAE) is the network architecture and designed to simplify thenetwork to other IP based communications network. SAE uses an eNB and Access Gateway(aGW) and removes the RNC and SGSN from the equivalent 3G network architecture, to make asimpler mobile network. This allows the network to be built as an All-IP based networkarchitecture. SAE also includes entities to allow full inter-working with other related wirelesstechnology (WCDMA, WiMAX, WLAN, etc.). These entities can specifically manage and permitthe non-3GPP technologies to interface directly into the network and be managed from within the

same network.

Figure 2: SAE (System Architecture Evolution) and LTE Network


22/53

-22-

Figure 3: LTE Network

Figure 4: Bearer Services in LTE/SAE Network


23/53

-23-

E-UTRAN Architecture

In order to achieve the requirements in previous section, the LTE radio access network E-UTRANarchitecture is improved dynamically from 3G/3.5G radio access network UTRAN. It has beenchanged to be flat from legacy hierarchy mobile network architecture. The functions of eNB in E-UTRAN include not only base station (NodeB) to terminate radio interface but also Radio NetworkController (RNC) to manage radio resource.

According to 3GPP TR 25.912, E-UTRAN is described as follows.The evolved UTRAN consists of eNB, providing the evolved UTRAN U-plane and C-planeprotocol terminations towards the UE. The eNBs are interconnected with each other by means ofthe X2 interfaces. It is assumed that there always exist an X2 interface between the eNBs that

need to communicate with each other, e.g., for support of handover of UEs in LTE_ACTIVE. TheeNBs are also connected by means of the S1 interface to the EPC (Evolved Packet Core). The S1interface supports a many-to-many relation between aGWs and eNBs.

Figure 5: E-UTRAN Architecture


24/53

-24-

Protocol Stack

C-plane protocol stack on Uu and S1-C interfaces is shown in Figure 6.

Figure 6: C-plane Protocol Stack on Uu (UE/eNB) and S1-C (eNB/MME)

C-plane protocol stack on Uu and X2-C interfaces is shown in Figure 7.

Figure 7: C-plane Protocol Stack on X2-C (eNB/eNB)


25/53

-25-

U-plane protocol stack on Uu and S1-U interfaces is shown in Figure 8.

Figure 8: U-plane Protocol Stack on Uu (UE/eNB) and S1-U (eNB/MME)

C-plane protocol stack on Uu and X2-U interfaces is shown in Figure 9.

Figure 9: U-plane Protocol Stack between eNB/eNB

Physical Interface

According to Overview of 3GPP, LTE radio access technology is described as follows:The multiple access scheme for the LTE physical layer is based on Orthogonal FrequencyDivision Multiple Access (OFDM) with a Cyclic Prefix (CP) in the downlink and a Single CarrierFrequency Division Multiple Access (SC-FDMA) with CP in the uplink.OFDMA technique is particularly suited for frequency selective channel and high data rate. It


26/53

-26-

transforms a wideband frequency selective channel into a set of parallel flat fading narrowbandchannels, thanks to CP. This ideally, allows the receiver to perform a low complex equalizationprocess in frequency domain, i.e., 1 tap scalar equalization.

The baseband signal representing a downlink physical channel is defined in terms of the following

steps:

scrambling of coded bits in each of the code words to be transmitted on a physical channel modulation of scrambled bits to generate complex-valued modulation symbols mapping of the complex-valued modulation symbols onto one or several transmission layers precoding of the complex-valued modulation symbols on each layer for transmission on the

antenna ports mapping of complex-valued modulation symbols for each antenna port to resource elements generation of complex-valued time-domain OFDM signal for each antenna port

The baseband signal representing the physical uplink shared channel is defined in terms of thefollowing steps, as shown in the below figure:

scrambling modulation of scrambled bits to generate complex-valued symbols transform precoding to generate complex-valued symbols mapping of complex-valued symbols to resource elements generation of complex-valued time-domain SC-FDMA signal for each antenna port

Figure 10: Overview of downlink physical channel processing.

Figure 11: Overview of uplink physical channel processing.

OFDMA (Orthogonal Frequency Division Multiple Access)

One of the key elements of LTE is the use of OFDM (Orthogonal Frequency Division Multiplex) asthe signal bearer and the associated access schemes, OFDMA (Orthogonal Frequency DivisionMultiple Access) and SC-FDMA (Single Carrier Frequency Division Multiple Access).OFDM is used in a number of other of systems from WLAN, WiMAX to broadcast technologiesincluding DVB and DAB. OFDM has many advantages including its robustness to multipath fadingand interference. In addition to this, even though, it may appear to be a particularly complicatedform 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 naturalchoices for the new LTE cellular standard. OFDM is a form of transmission that uses a largenumber of close spaced carriers that are modulated with low rate data. Normally these signalswould be expected to interfere with each other, but by making the signals orthogonal to each


27/53

-27-

another there is no mutual interference. This is achieved by having the carrier spacing equal tothe reciprocal of the symbol period. This means that when the signals are demodulated they willhave a whole number of cycles in the symbol period and their contribution will sum to zero - inother words there is no interference contribution. The data to be transmitted is split across all thecarriers and this means that by using error correction techniques, if some of the carriers are lostdue to multi-path effects, then the data can be reconstructed. Additionally having data carried at alow rate across all the carriers means that the effects of reflections and inter-symbol interferencecan be overcome. It also means that single frequency networks, where all transmitters cantransmit on the same channel, can be implemented.

Figure 12: OFDMA

MIMO (Multiple-Input Multiple-Output)

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 MIMOemploys multiple antennas on the receiver and transmitter to utilize the multi-path effects thatalways exist to transmit additional data, rather than causing interference.The schemes employed in LTE again vary slightly between the uplink and downlink. The reasonfor this is to keep the terminal cost low as there are far more terminals than base stations and asa result terminal works cost price is far more sensitive.For the downlink, a configuration of two transmit antennas at the base station and two receiveantennas on the mobile terminal is used as baseline, although configurations with four antennasare also being considered.For the uplink from the mobile terminal to the base station, a scheme called MU-MIMO (Multi-UserMIMO) is to be employed. Using this, even though the base station requires multiple antennas,the mobiles only have one transmit antenna and this considerably reduces the cost of the mobile.In operation, multiple mobile terminals may transmit simultaneously on the same channel or


28/53

-28-

channels, but they do not cause interference to each other because mutually orthogonal pilotpatterns are used. This techniques is also referred to as spatial domain multiple access (SDMA).

Figure 13: 2 x 2 MIMO Channel Matrix

Physical Channel Structure

Downlink physical channels and downlink physical signals are as follows. Downlink physicalchannels carry layer 2 information but downlink physical signals are only used by the physicallayer.

Downlink physical channels:

Physical downlink shared channel (PDSCH)Carries the DL-SCH and PCH. DL-SCH contains actual user data.

Physical downlink control channel(PDCCH)Informs the UE about the resource allocation of PCH and DL-SCH, and HARQ information relatedto DL-SCH. Carries the uplink scheduling grant.

Physical HARQ indicator channel (PHICH)Carries ACK/NACKs in response to uplink transmissions.

Physical control format indicator channel(PCFICH)

Informs the UE about the number of OFDM symbols used for the PDCCHs; Transmitted in everysubframe.

Physical broadcast channel (PBCH)The coded BCH transport block is mapped to four subframes within a 40 ms interval.Downlink physical signals:

Reference signal Synchronization signal (P-SS and S-SS)

Downlink physical channel and downlink physical signal structure is shown in Figure 14

Figure 14: Downlink Physical Channel Structure


29/53

-29-

Back to top | Next pageUplink physical channels and uplink physical signals are as follows. Uplink physical channelscarries layer 2 information but uplink physical signals are only used by the physical layer.

Uplink physical channels:

Physical uplink shared channel (PUSCH)Carries the UL-SCH, ACK/NACK and CQI. UL-SCH contains actual user data.

Physical uplink control channel (PUCCH)Carries ACK/NACKs in response to downlink transmission. Carries CQI (Channel QualityIndicator) report and SR (Scheduling Request).

Physical random access channel (PRACH)Carries random access preamble.Uplink physical signals:

Demodulation reference signal (UL-RS), associated with transmission of PUSCH andPUCCH.

Sounding reference signal (SRS), not associated with transmission of PUSCH and PUCCH.Uplink physical channel and uplink physical signal structure is shown in Figure 15.

Figure 15: Uplink Physical Channel Structure
http://www.artizanetworks.com/lte_tut_lay_2.htmlhttp://www.artizanetworks.com/lte_tut_lay_2.html


30/53

-30-

Layer 2

Transport channels, Layer2 structure, Logical channels, and the procedures are introduced in thissection.

Transport Channels

Downlink transport channel types are:

Broadcast Channel (BCH)characterized by:o fixed, pre-defined transport formato requirement to be broadcast in the entire coverage area of the cell. Downlink Shared Channel (DL-SCH)characterized by:o support for HARQo support for dynamic link adaptation by varying the modulation, coding and transmit powero possibility to be broadcast in the entire cello possibility to use beamforming

o support for both dynamic and semi-static resource allocationo support for UE discontinuous reception (DRX) to enable UE power saving. Paging Channel (PCH)characterized by:o support for UE discontinuous reception (DRX) to enable UE power saving (DRX cycle is indicated

by the network to the UE)o requirement to be broadcast in the entire coverage area of the cello mapped to physical resources which can be used dynamically also for traffic/other control

channels. Multicast Channel (MCH) (from Release 9)characterized by:o requirement to be broadcast in the entire coverage area of the cello support for MBSFN combining of MBMS transmission on multiple cellso support for semi-static resource allocation e.g., with a time frame of a long cyclic prefix.

Uplink transport channel types are:


31/53

-31-

Uplink Shared Channel (UL-SCH)characterized by:o possibility to use beamforming (likely no impact on specifications)o support for dynamic link adaptation by varying the transmit power and potentially modulation and

codingo support for HARQo support for both dynamic and semi-static resource allocation. Random Access Channel(s) (RACH)characterized by:o limited control informationo collision risk

Layer 2 Structure

According to 3GPP, Layer 2 structure consists of PDCP/RLC/MAC layers. Transport channels arelocated between physical layer and MAC layer. MAC multiplexes RLC links and scheduling andpriority handling serving via logical channels. Layer 2 downlink and uplink structures are shown inFigure 16 and Figure 17.

Figure 16: Layer 2 Downlink Structure

Figure 17: Layer 2 Uplink Structure


32/53

-32-

Logical Channels

According to 3GPP, several types of data transfer services are offered by MAC. Each logical

channel type is defined by the type of information to be transferred.A general classification of logical channels is into two groups:

Control Channels (for the transfer of control plane information) Traffic Channels (for the transfer of user plane information).

Control Channels:Control channels are used for transfer of control plane information only. The control channelsoffered by MAC are:

Broadcast Control Channel (BCCH)A downlink channel for broadcasting system control information.

Paging Control Channel (PCCH)

A downlink channel that transfers paging information and system information change notifications.This channel is used for paging when the network does not know the location cell of the UE.

Common Control Channel (CCCH)Channel for transmitting control information between UEs and network. This channel is used forUEs having no RRC connection with the network.

Dedicated Control Channel (DCCH)A point-to-point bi-directional channel that transmits dedicated control information between a UEand the network. Used by UEs having an RRC connection.Traffic Channels:Traffic channels are used for the transfer of user plane information only. The traffic channelsoffered by MAC are:


33/53

-33-

Dedicated Traffic Channel (DTCH)A Dedicated Traffic Channel (DTCH) is a point-to-point channel, dedicated to one UE, for thetransfer of user information. A DTCH can exist in both uplink and downlink.

Multicast Traffic Channel (MTCH) (from Release 9)A point-to-multipoint downlink channel for transmitting traffic data from the network to the UE. Thischannel is only used by UEs that receive MBMS.The figure below depicts the mapping between logical channels, transport channels and physicalchannels for downlink and uplink:

Figure 18: Downlink Channel Mapping

Figure 19: Uplink Channel Mapping

RRC Protocol

According to 3GPP TS 36.331, the RRC protocol includes the following main functions:


34/53

-34-

Broadcast of system information:o Including NAS common informationo Information applicable for UEs in RRC_IDLE, e.g., cell (re-)selection parameters, neighboring cell

information and information (also) applicable for UEs in RRC_CONNECTED, e.g., commonchannel configuration information.

o Including ETWS notification RRC connection control:o Pagingo Establishment/modification/release of RRC connection, including e.g., assignment/ modification of

UE identity (C-RNTI), establishment/ modification/ release of SRB1 and SRB2, access classbarring

o Initial security activation, i.e., initial configuration of AS integrity protection (SRBs) and ASciphering (SRBs, DRBs)

o RRC connection mobility including e.g., intra-frequency and inter-frequency handover, associatedsecurity handling, i.e., key/ algorithm change, specification of RRC context information transferredbetween network nodes

o Establishment/ modification/ release of RBs carrying user data (DRBs)

o Radio configuration control including e.g., assignment/ modification of ARQ configuration, HARQconfiguration, DRX configurationo QoS control including assignment/ modification of semi-persistent scheduling (SPS) configuration

information for DL and UL, assignment/ modification of parameters for UL rate control in the UE,i.e., allocation of a priority and a prioritized bit rate (PBR) for each RB

o Recovery from radio link failure Inter-RAT mobility including e.g., security activation, transfer of RRC context information Measurement configuration and reporting:o Establishment/ modification/ release of measurements (e.g., intra-frequency, inter-frequency and

inter- RAT measurements)o Setup and release of measurement gapso Measurement reporting

o Other functions including e.g., transfer of dedicated NAS information and non-3GPP dedicatedinformation, transfer of UE radio access capability information, support for E-UTRAN sharing(multiple PLMN identities)

o Generic protocol error handlingo Support of self-configuration and self-optimization

NOTE: Random access is specified entirely in the MAC including initial transmission powerestimation.

Figure 20 : RRC States (from 3GPP TS 36.331)


35/53

-35-

Signaling Radio Bearers (SRB) are defined as Radio bearers that are used only to transmit RRCand NAS messages. SRBs are classified into

Signaling Radio Bearer 0: SRB0: RRC message using CCCH logical channel.Signaling Radio Bearer 1: SRB1: is for transmitting NAS messages over DCCH logical channel.Signaling Radio Bearer 2: SRB2: is for high priority RRC messages. Transmitted over DCCHlogical channel.

What is LTE eNB?

One of the biggest differences between LTE network and legacy mobile communication system3G is a base station. There used to be intelligent and centralizing node like RNC (Radio NetworkController) in 3G for example, and it needed to control all the radio resources and mobility overmultiple NodeB (3G base stations) underneath in hieratical radio access network (Figure 21). AllNodeB need to do is behave exactly according to command from RNC through Iub interface. InLTE, on the other hand, eNB (evolved NodeB) as base station have to manage radio resourceand mobility in the cell and sector to optimize all the UEs communication in flat radio networkstructure (Figure 22). Therefore, the performance of LTE eNB depends on radio resourcemanagement algorithm and its implementation.

Figure 21: 3G Radio Access Network (UTRAN) Architecture


36/53

-36-

Figure 22: E-UTRAN Architecture

LTE eNB Functions

According to overview of 3GPP Release 8, the eNB hosts the following functions:

Radio Resource Managemento

Radio Bearer Controlo Radio Admission Controlo Connection Mobility Control


37/53

-37-

o Dynamic allocation of resources to UEs in both uplink and downlink (scheduling) IP header compression and encryption of user data stream Selection of an MME at UE attachment when no routing to an MME can be determined from the

information provided by the UE Routing of User Plane data towards Serving Gateway Scheduling and transmission of paging messages (originated from the MME) Scheduling and transmission of broadcast information (originated from the MME or O&M) Measurement and measurement reporting configuration for mobility and scheduling

Figure 23: Functional Split between E-UTRAN and EPC

LTE eNB Architecture

In order to reduce Capital Expenditure (CAPEX) for LTE operators, most of equipment vendorsare developing LTE eNB using generic off-the-shelf platforms, such as ATCA, Micro-TCA, andAMC in PICMG. On the other hand, legacy proprietary platforms have been used until 3G/3.5Gnetwork era. Micro-TCA platform (see Figure 24) is one of the powerful options dedicated to

applying telecom equipment especially for the use in LTE eNB. Many component vendors aredeveloping modules based on general purpose Micro-TCA modules with powerful CPU, DSP, andFPGA, with high speed memory with GbE I/F on front side. Each module in the platform cancommunicate with not only GbE interface as control interface from server module but also with the10Gbps Serial Rapid I/O (sRIO) interface. Micro-TCA Connection Handler (MCH) module enablesstar topology on backplane, switching the packets from all of modules in the platform. 10GbE isselectable for this start topology connection on Micro-TCA.

Figure 24: MicroTCA platform


38/53

-38-

The sRIO interface is used for connection between Uu side baseband module and S1/X2 sidenetwork I/F module. The baseband function and network interface function are usuallyimplemented on different modules, and connected with sRIO I/F over MCH. Most of equipmentdevelopers use FPGAs for PHY/Baseband, DSPs or Network processors for Lower layerprotocols (HARQ/MAC/RLC), and CPUs or Network processors with operation system for PDCPand upper layers, as shown in Table 2.

Table 2: LTE eNB Implementation Example

Function Implementation

PHY/ Baseband FPGAs/ASSPs

Low layer protocol DSPs/Network processor

PDCP and upper layerprotocol

CPUs/Network processor with operation system

eNB vendors can minimize their development effort using generic components, not only with

hardware module but with intellectual property like baseband logical circuit on FPGAs, protocolstack software. An example of LTE eNB implementation on Micro-TCA platform is shown inFigure 20, Figure 21 and Figure 22.

Figure 25: LTE eNB implementation example (C-plane)

Figure 26: LTE eNB implementation example (U-plane)


39/53

-39-

Figure 27: LTE eNB implementation on MicroTCA platform

Figure 22 shows an example of eNB implementation, which connects two eNB that covers sixsectors over two cells. The eNB is connected to S1/X2 with two GbE interfaces.

Concept

LTEs radio interface testing methodology has been developed along with the specifications forLTE network implementation, yet a de facto way of evaluating the whole LTE eNB system does

not exist as of today. There are testing standards in 3GPP that are focused on separatedelements (layers) of User Equipment (UE) and eNB, as listed below. However, specification of


40/53

-40-

integrated methodology for the system evaluation has not been established, so the NEMs andoperators are evaluating their equipment as a system with their own methodology from theexperiences in legacy mobile development.

TS 36.101 User Equipment (UE) radio transmission and reception TS 36.104 Base Station (BS) radio transmission and reception TS 36.133 E-UTRA Requirements for support of radio resource management TS 36.141 Base Station (BS) conformance testing TS 36.211 Physical channels and modulation TS 36.212 Multiplexing and channel coding TS 36.213 Physical layer procedures TS 36.214 Physical layer - Measurements TS 36.321 Medium Access Control (MAC) protocol specification

In todays advanced wireless technology, a single evaluation method for separate basicfunctionalities is inadequate. The industry needs a new approach to evaluate the comprehensiveperformances of the eNB, which carries out the most complicated functionality in E-UTRAN. Asmatter of fact, eNB comprises the largest number of network nodes in the LTE system, and thebiggest capital expenditure is invested to deploying the eNB. At Artiza Networks, we proposeLTE eNB Evaluation Methodology, setting the new standard of system evaluation for the LTEeNB. Artiza LTE eNB Tester is a complete test suite including C-plane test to evaluate radioresource management, U-plane QoS test, C-U combined test, NAS testing, and various types ofsystem evaluation. As the first trial in the industry, Artiza has developed a comprehensivemethodology for operators and manufacturers QA team to overcome a big challenge of effectiveevaluation of LTE eNB ever.

Requirement for Testers

An example for the maximum number of LTE eNB deployment in one cell with 6 sectors is shownin Figure 28: Example of LTE eNB deployment, and UE-SIM and S1/X2-SIM specification for theeNB is also shown in Table 3.

Figure 28

Table 3 : Example of LTE eNB Load Tester (UE-SIM and S1/X2-SIM) Requirement


41/53

-41-

Parameter Side Requirement Comment

No. of sectors UE-SIM 6 sector/system 6 sectors/cell

No. of UEs to simulate UE-SIM 840 UEs/sector 5,040 UEs/system

No. of MMEs to simulate S1X2-SIM 2 2 associations/MME

No. of S-GWs to simulate S1X2-SIM 2 2 IPs/S-GW

No. of eNB to simulate S1X2-SIM 2 2 associations/eNB

No. of external IP stations S1X2-SIM 10 Support IPv4

No. of UEs to simulate UE-SIM/S1X2-SIM 840 UEs/sector 5,040 UEs/system

No. of bearers to simulate UE-SIM/S1X2-SIM 3 bearers/UE 7200 bearers/system

No. of GbE I/Fs S1X2-SIM 2 Including external I/F

No. of RACH Mux UE-SIM 64 Mux/msec RACH performance

DL Throughput (SISO) UE-SIM 75 Mbps/system Max MAC RX Rate

DL Throughput (MIMO) UE-SIM 150 Mbps/system Max MAC RX Rate

DL Throughput S1X2-SIM 450 Mbps/System Max TX Rate

UL Throughput UE-SIM 50 Mbps/system Max TX MAC Rate

UL Throughput S1X2-SIM 300 Mbps/system Max RX Rate

No. of RRC msgs to generate UE-SIM 6000 msgs/sec

C-plane Protocol Procedures

C-plane protocol procedure test is mandatory, and it includes not only functional testing but alsothe testing under load condition. There are multiple protocol procedures in C-plane, and all theprocedures are covered in this section. Equipment vendors test RRC connectionestablishment/release procedure as functional test in early phase of eNB system testing.

RRC Connection Establishment/Release Procedure

The first step to evaluate the C-place protocol is to test the basic function, such as connectionestablishment/release procedure for LTE eNB. In RRC protocol in E-UTRAN, there are only two

states, RRC_IDLE and RRC_CONNECTED (shown in Figure 24), so that connection can be setup faster. Connection establishment and release procedure initiated by UE on Uu and S1interface is shown in Figure 25. Paging (Connection establishment and release procedure initiatedby E-UTRAN) on Uu and S1 interface is shown in Figure 26. RRC protocol procedure is describedin details in 3GPP TS36.331. In order to evaluate C-plane performance of LTE eNB, the reliabletransition between these two states is critical.

Figure 29: RRC Protocol State Transition


42/53

-42-

Figure 30 : Connection Establish and Release Procedure

Figure 31 : Paging and Release Procedure


43/53

-43-

Handover Procedures

Handover procedure is intended to reduce the interruption time, less than the circuit-switchedhandover in 2G networks, and it is an important function for LTE eNB. There are multipleHandover procedures to be tested shown Table 4. LTE eNB is required to implement handoverprocedure inside E-UTRAN (Inter eNB/Intra eNB) and also between legacy Radio AccessTechnologies (RAT) like UMTS.

Table 4: Handover Procedures

Handover Description

Inter eNB Handover (Source) Handover inside E-UTRAN. Procedure that side of UE leaving out fromthe cell.


44/53

-44-

Inter eNB Handover (Target) Handover inside E-UTRAN. Procedure that side of UE coming into thecell.

Inter RAT Handover (Source) Handover from E-UTRAN to different RAT. Procedure that side of UEleaving out from the cell.

Inter RAT Handover (Target) Handover from E-UTRAN to different RAT. Procedure that side of UEcoming into the cell.

Intra eNB Handover (Source) Handover inside the same E-UTRAN cell. Procedure that side of UEleaving out from the sector.

Intra eNB Handover (Target) Handover inside the same E-UTRAN cell. Procedure that side of UEcoming into the sector.

Test Configurations

Test configuration for Inter eNB Handover and Inter RAT Handover is shown in Figure 32. Thereare two types of procedures that can be tested in this configuration. The first type of the procedure

is the Source where UE leaves out of the cell, and the other is the Target where UE comes intothe cell. The eNB (DUT) is connected to S1/X2 Simulator with X2AP and S1AP interface, and it isalso connected to UE Simulator as UE in the Cell. Source and Target procedures can betested with same configuration. Inter RAT (Source) and Inter RAT (Target) can also be testedin this configuration.

Figure 32: Test Configuration for Inter eNB Handover

Test configuration for Intra eNB Handover is shown in Figure 33.

Figure 33: Test Configuration for Intra eNB Handover


45/53

-45-

Inter eNB Handover (Source) is shown in Figure 34.

Figure 34: Inter eNB Handover (Source)

Inter eNB Handover (Source) procedure is shown in Figure 35, Figure 36 and Figure 37.

Figure 35: Inter eNB Handover (Source) (UE side)


46/53

-46-

Figure 36: Inter eNB Handover (Source) (Core side X2HO)

Figure 37: Inter eNB Handover (Source) (Core side S1HO)


47/53

-47-

Inter eNB Handover (Target) is shown in Figure 38.

Figure 38: Inter eNB Handover (Target)

Inter eNB Handover (Target) procedure is shown in Figure 39, Figure 40 and Figure 41.

Figure 39: Inter eNB Handover (Target) (UE side)

Figure 40: Inter eNB Handover (Target) (Core side X2HO)


48/53

-48-

Figure 41: Inter eNB Handover (Target) (Core side S1HO)

Inter RAT (Radio Access Technology) Handover (Source) is handover between LTE and differentradio access technology, i.e., UMTS. The test configuration and procedures are exactly the sameas Inter eNB Handover (Source).

The test configuration and procedures for Inter RAT Handover (Target) is exactly the same asInter eNB Handover (Source).

Intra eNB Handover is shown in Figure 42.

Figure 42: Intra eNB Handover (to next sector)


49/53

-49-

Inter eNB Handover procedure is shown in Figure 43.

Figure 43: Intra eNB Handover

C-plane Test Configuration

Logical configuration of the C-plane performance testing is shown in Figure 44. The eNB (DUT:Device Under Test) and S1/X2-SIM is connected with four GbE interfaces. Two of the fourinterfaces are used as X2-C, simulated the connection of two eNBs in E-UTRAN, and the othertwo are used as S1-C, simulated the connection of two MMEs in Core Network.

Figure 44: Logical Configuration of the C-plane Performance Test


50/53

-50-

U-plane Test Configuration

Logical configuration of the U-place performance testing is shown in Figure 45. The eNB (DUT)and S1/X2-SIM are connected with four GbE interfaces. Two of the four interfaces are used asX2-U simulated a connection of two eNBs in E-UTRAN. The other two interfaces are used as S1-U simulated connection of two S-GWs in Core Network.

Figure 45: Logical Configuration of U-plane Performance Testing


51/53

-51-

C-U plane combined Test Configuration

Logical configuration of C-U-plane performance testing is shown in Figure 46. The eNB (DUT)and S1/X2-SIM are connected with six GbE interfaces. Two of the interfaces are used as X2-CUsimulated connections of two eNBs in E-UTRAN, next two interfaces are used as S1-C simulatedconnection of two MMSs in Core Network and last two interfaces are S1-U simulated connectionof two S-GWs.

Figure 46: Logical Configuration of C-U-plane Combined Performance Testing


52/53

-52-

C-U plane combined Test Configuration with External Device

Logical configuration of C-U-plane combined performance testing with external device is shown inFigure 47. The configuration is same as the previous C-U-plane combined performance testingexcluding external device connected to S-GW.

Figure 47: Logical Configuration of C/U-plane Combined Performance Testing with

External Device


53/53

-53-

An example of external devices is shown in Table 5.

Table 5: Example of External Devices

Device Comments

IP performance tester Generic equipment to test Benchmarking Methodology for NetworkInterconnect Devices RFC2544.

Video quality tester Generic equipment to test Video quality over IP reference MediaDelivery Index (MDI) RFC4445

V i lit t t G i i t t t t V i IP lit lik R F t /PESQ/

Excellent Knowledge Notes [Ashwani]

Documents

Transcript of Excellent Knowledge Notes [Ashwani]