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Department of Computer Science and Engineering ETE-508: Mobile and Wireless Communication System

Summer 2008 Instructor: Miftahur Rahman, Ph.D.

During 1950s and 1960s AT&T Bell Labs and other telecom companies throughout the world developed the theory and techniques of cellular radiotelephony the concept of breaking a coverage zone (market) into small cells. In 1983, the Federal Communications Commission, Inc., allocated 666 duplex channels (40 MHz of spectrum in the 800 MHz band, each channel having a one-way bandwidth of 30 kHz for a total spectrum occupancy of 60 kHz for each duplex channel for the US AMPS.

Reverse Channel

991

992

……

.

1023

1 2

……

799

824-849 MHz

1 ≤ N ≤ 799, 0.030N + 825.0 991 ≤ N ≤ 1023, 0.030(N-1023) + 825.0

N = 991, 0.030(991 -1023) + 825 = 824.04 MHz

2

N = 992, 0.030(992 -1023) + 825 = 824.07 MHz N = 993, 0.030(993 -1023) + 825 = 824.10 MHz . . . N = 1023, 0.030(1023 -1023) + 825 = 825 MHz N = 1, 0.030(1) + 825 = 825.03 MHz N = 2, 0.030(2) + 825 = 825.06 MHz . . . N = 799, 0.030(799) + 825 = 848.97 MHz

Forward Channel

991

992

……

.

1023

1 2

……

799

869-894 MHz

1 ≤ N ≤ 799, 0.030N + 870.0 991 ≤ N ≤ 1023, 0.030(N-1023) + 870.0

N = 991, 0.030(991 -1023) + 870 = 869.04 MHz N = 992, 0.030(992 -1023) + 870 = 869.07 MHz N = 993, 0.030(993 -1023) + 870 = 869.10 MHz

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.

.

. N = 1023, 0.030(1023 -1023) + 870 = 870.0 MHz N = 1, 0.030(1) + 870 = 870.03 MHz N = 2, 0.030(2) + 870 = 870.06 MHz . . . N = 799, 0.030(799) + 870 = 893.97 MHz (Please make a note that channels 800-990 are unused.)

Reverse Channel

991

992

……

.

1023

1 2

……

799

824.

04

MH

z 82

4.07

M

Hz

……

..

825

MH

z 82

5.03

M

Hz

825.

06

MH

z

……

.

848.

97

MH

z

4

Forward Channel

991

992

……

.

1023

1 2

……

799

869.

04

MH

z 86

9.07

M

Hz

……

..

870

MH

z 87

0.03

M

Hz

870.

06

MH

z

……

.

893.

97

MH

z

In late 1991, the first US Digital Cellular (USDC) system hardware was installed. Capacity of USDC is three times that of AMPS. USDC employs digital modulation, speech coding, and time division multiple access (TDMA). CDMA by Qualcomm, Inc., standardized by Telecommunications Industry Association (TIA) as an Interim Standard (IS-95). CDMA supports a variable number of users in 1.25 MHz wide channel using direct sequence spread spectrum. AMPS requires signal by at least 18 dB above co-channel interference.

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CDMA can operate at much higher interference level or much lower SNR. Nextel and Motorola formed an extended specialized Mobile Radio Service (E-SMR) network in the 800 MHz band. 1995, Motorola replaced Motorola’s Integrated Radio System (MIRS) with the Integrated Digital Enhanced Network (iDen). Table 1.1 Major Mobile Radio Standards in North America Standard Type Year Multiple

Access Frequency Band

Modulation Channel Bandwidth

AMPS Cellular 1983 FDMA 824-894 MHz

FM 30 kHz

NAMPS Cellular 1992 FDMA 824-894 MHz

FM 10 kHz

USDC Cellular 1991 TDMA 824-894 MHz

Π/4-DQPSK 30 kHz

CDPD Cellular 1993 FH/Packet 824-894 MHz

GMSK 30 kHz

IS-95 Cellular/PCS 1993 CDMA 824-894 MHz 1.8-2.0 GHz

QPSK/BPSK 1.25 MHz

Table 1.2 Major Mobile Radio Standards in Europe Standard Type Year Multiple

Access Frequency Band

Modulation Channel Bandwidth

ETACS Cellular 1985 FDMA 900 MHz FM 25 kHz NMT-450 Cellular 1981 FDMA 450-470

MHz FM 25 kHz

NMT-900 Cellular 1986 FDMA 890-960 MHz

FM 12.5 kHz

GSM Cellular/PCS 1990 TDMA 890-960 MHz

GMSK 200 kHz

C-450 Cellular 1985 FDMA 450-465 MHz

FM 20 kHz/10 kHz

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Table 1.3 Major Mobile Radio Standards in Japan Standard Type Year Multiple

Access Frequency Band

Modulation Channel Bandwidth

JTACS Cellular 1988 FDMA 860-925 MHz

FM 25 kHz

PDC Cellular 1993 TDMA 810-1501 MHz

Π/4-DQPSK 25 kHz

NTT Cellular 1979 FDMA 400/800 MHz

FM 25 kHz

NTACS Cellular 1993 FDMA 843-925 MHz

FM 12.5 kHz

PHS Cordless 1993 TDMA 1895-1907 MHz

Π/4-DQPSK 300 kHz

First Generation (1G) Cellular Networks: NMT-450: Nordic Mobile Telephone AMPS: Advanced Mobile Phone System NTACS, TACS: Narrowband Total Access Communication System 1G networks (NMT, AMPS, TACS) are considered to be the first analog cellular systems, which started early 1980s. The world’s first cellular system was implemented by the Nippon Telephone and Telegraph company (NTT) in Japan. The system, deployed in 1979, uses 600 FM duplex channels (25 kHz for each one-way link) in the 800 MHz band.

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In Europe, the Nordic Mobile Telephone System (NMT-450) was developed in 1981 for the 450 MHz band and uses 25 kHz channels. In 1985 European Total Access Cellular System (ETACS) was developed which is identical to US AMPS system. In Germany, a Cellular standard GSM (Global System for Mobile) was introduced in 1990 in a new 900 MHz band to bring uniformity across the world. In Japan, the Pacific Digital Cellular (PDC) standard provides digital cellular coverage similar to USDC. 1G analog technologies are: Second Generation (2G) Cellular Networks: The most popular second generation standards include three TDMA standards and one CDMA standard:

1. Global System Mobile (GSM): supports eight time slotted users for each 200 kHz radio channel and has been deployed by service providers in Europe, Asia, Australia,

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South America, and some parts of the US (in the PCS spectrum band only).

2. Interim Standard 136 (IS-136): also known

as North American Digital Cellular (NADC) which supports three time slotted users for each 30 kHz radio channel and is popular and is popular in North America, South America, and Australia (in both the cellular and PCS bands).

3. Pacific Digital Cellular (PDC): A Japanese

TDMA standard that is similar to IS-136 with more than 50 million users.

4. 2G CDMA standard Interim Standard 95

Code Division Multiple Access (IS-95), also known as cdmaOne, which supports up to 64 users that are orthogonally coded and simultaneously transmitted on each 1.25 MHz channel. CDMA is widely deployed by carriers in North America (in both cellular and PCS bands), as well as Korea, Japan, China, South America, and Australia.

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Key Specifications of 2G Technologies CDMAOne, IS-

95, ANSI J-STD-008

GSM, DCS-1900, ANSI J-STD-007

NADC, IS-54/IS-136, ANSI J-STD-011, PDC

Uplink Frequencies

824-849 MHz (US Cellular) 1850-1910 MHz (US PCS)

890-915 MHz (Europe) 1850-1910 MHz (US PCS)

800 MHz, 1500 MHz (Japan) 1850-1910 MHs (US PCS)

Downlink Frequencies

869-894 MHz (US Cellular) 1930-1990 MHz (US PCS)

935-960 MHz (Europe) 1930-1990 MHz (US PCS)

869-894 MHz (US Cellular) 1930-1990 MHz (US PCS) 800 MHz, 1500 MHz (Japan)

Duplexing FDD FDD FDD Multiple Access Technology

CDMA TDMA TDMA

Modulation BPSK with quadrature spreading

GMSK with BT = 0.3

π/4 DQPSK

Carrier separation 1.25 MHz 200 kHz 30 kHz (IS-136) (25 kHz for PDC)

Channel Data Rate

1.2288 Mchips/sec

270.833 kbps 48.6 kbps (IS-136) (42 kbps for PDC)

Voice channels per carrier

64 8 3

GMSK: Gaussian Minimum Shift Keying BT: 3-dB bandwidth-bit duration product for GMSK DQPSK: Differential Quadrature PSK 2.5G Mobile Radio Networks 2.5G standards with increased capability to support increased data rates that are required to support Internet applications, new data-centric standards. The three TDMA upgrade options include:

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1. High Speed Circuit Switched Data (HSCSD) for 2.5 GSM: HSCSD is a circuit switched technique that allows a single mobile subscriber to use consecutive user time slots in the GSM standard.

2. General Packet Radio Service (GPRS) for 2.5

GSM and IS-136: GPRS is a packet-based data network, which is well suited for non-real time Internet usage, including the retrieval or email, faxes, and asymmetric web browsing, where the user downloads much more data than it uploads on the Internet.

3. Enhanced Data Rates for GSM Evolution

(EDGE) for 2.5 GSM and IS-136: EDGE is a more advanced upgrade to the GSM standard, and requires the addition of new hardware and software at existing base stations. EDGE uses 8-PSK (octal phase shift keying), which is used additional to GSM’s standard GMSK modulation.

3G Wireless Networks 3G standard support multi-megabit Internet access, Voice over Internet Protocol (VoIP), voice activated calls, unparalleled network capacity.

1. 3G W-CDMA (UMTS): Universal Mobile Telecommunications System (UMTS): UMTS air interface standard that has evolved since late 1996 under the European Telecommunications

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Standards Institute (ETSI). UMTS was submitted by ETSI to ITU’s IMT-2000 body in 1998 for consideration as a world standard.

2. 3G CDMA2000: Based on the original IS-95 and

IS-95A (CDMAOne) CDMA standards, as well as the 2.5G IS-95B air interface, the CDMA2000 3G standard allows wireless carriers to introduce a family of new high new data rate Internet access.

3. 3G TD-SCDMA: Time Division Synchronous

CDMA: The China Academy of Telecommunications Technology (CATT) and Siemens Corporation jointly submitted an IMT-2000 3G standard proposal in 1998, based on Time Division Synchronous Code Division Multiple Access (TD-SCDMA). This proposal was adopted by ITU as one of the 3G options in late 1999.

4G Wireless Networks: is mainly a marketing buzzword at the moment. Some basic 4G research is being done, but no frequencies have been allocated. The Forth Generation could be ready for implementation around 2012.

Multiple Access Techniques In cellular systems a geographic region is divided into many small areas called cells. A mobile set in a given cell communicate with another mobile set in the same cell or in a different cell through the use of a base station. The

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cellular systems are able to accommodate as many calls as possible and termed as capacity. The following are several techniques of accessing the channels.

Frequency division multiple-access (FDMA) Time division multiple access (TDMA) Wavelength division multiple access (WDMA) Code division multiple access (CDMA) o Frequency-hop CDMA o Direct-sequence CDMA o Multi-carrier CDMA (FH or DH) Time/frequency multiple-access Random access

5.15 Cellular Telephone Systems

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5.16 Frequency Reuse As the Fig. 5-15-1 shows, the same sets of frequencies are used in all three clusters, which essentially increases the number of usable cellular channels available threefold. The letters A, B, C, D, E, F, and G denote the seven sets of frequencies. Thus, the total number of cellular channels available in a cluster can be expressed mathematically as F = GN where F = number of full-duplex cellular channels available in a cluster G = number of channels in a cell N = number of cells in a cluster When the cluster is duplicated m times within a given service area, the total number of full-duplex channels can be expressed mathematically as C = mGN = mF where C = total channel capacity in a given area m = number of clusters in a given area G = number of channels in a cell N = number of cells in a cluster

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Example-5-15-1: Determine the number of channels per cluster and the total channel capacity for a cellular telephone area comprised of 10 clusters with seven cells in each cluster and 10 channels in each cell. Solution: F = (10) (7) = 70 channels per cluster C = (10) (7) (10) = 700 channels total The number of users is called the frequency reuse factor (FRF). The frequency reuse factor is defined mathematically as FRF = N/C where FRF = frequency reuse factor (unitless) N = total number of full-duplex channels in an area C = total number of full-duplex channels in a cell

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5.18 Interference The two major kinds of interferences produced within a cellular telephone system are co-channel interference and adjacent-channel interference. 5.19 Co-channel Interference

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5.20 Adjacent Channel Interference

5.21 Handoffs The transfer of a mobile unit from one base station’s control to another base station’s control is called a handoff (or handover).

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AMPS and ETACS Air Interface: Table 11.1 ETACS: European Total Access Cellular System was developed in 1985 and is identical to the US AMPS system. Parameter AMPS ETACS Multiple Access FDMA FDMA Duplexing FDD FDD Channel Bandwidth 30 kHz 25 kHz Traffic channel per RF channel

1 1

Reverse channel frequency

824-849 MHz 890-915 MHz

Forward channel frequency

869-894 MHz 935-960 MHz

Voice modulation FM FM Peak deviation: voice channels control

± 12 kHz ± 8 kHz

± 10 kHz ± 6.4 kHz

Channel coding for data BCH (40,28) on FC BCH (40,36) on FC Transmission BCH (48,36) on RC BCH (48,36) on RC Data rate on control 10 kbps 8 kbps Spectral efficiency 0.33 bps/Hz 0.33 bps/Hz Number of channels 832 1000

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Block code is referred to an an (n,k) code BCH: Bose-Chaudhuri-Hocquenghem (BCH) codes BCH (n,k), (n,k) = (2m-1, 2m-1-m) In a block encoder k information bits are encoded into n code bits. Examples of block codes: Hamming codes, Hadamard codes, Golay codes, Cyclic codes, BCH codes, Reed-Solomon Codes etc. Voice modulation and demodulation of AMPS The Manchester code is applied to both control channel and voice channel blank-and-burst transmission in AMPS and ETACS. The Manchester coded wideband data stream is filtered and channel coded using BCH block codes. The (40,28) BCH codes for forward voice channel blank-and-burst transmissions and are able to correct 5 errors whereas (48,36) BCH codes are used on the reverse voice channel blank-and-burst transmission. The encoded data are used to modulate the transmitter carrier using direct frequency-shift keying. Binary ones correspond to a frequency deviation of +8 kHz and binary zeros correspond to a deviation of -8 kHz (± 6.4 kHz for ETACS). USDC (IS-54 and IS-136)

Table 11.2 USDC Radio Interface Specifications Parameter USDC IS-54 Multiple Access TDMA/FDD Modulation л/4 DQPSK: Differential quadrature

PSK Channel bandwidth 30 kHz Reverse channel 824-849 MHz Forward channel 869-894 MHz Data rate 48.6 kbps Spectrum efficiency 1.62 bps/Hz Channel coding 7 bit CRC and rate ½ convolutional

coding

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TDMA Frame Structure for USDC Slot-1 Slot-2 Slot-3 Slot-4 Slot-5 Slot-6 One frame = 1944 bits (972 symbols) = 40 ms; 25 frames/sec G R data sync data SACCH CDVCC Data 6 6 16 28 122 12 12 122 Mobile to BS sync SACCH data CDVCC data Reserved 28 12 130 12 130 12 BS to Mobile CDVCC: Coded Digital Verification Color Code SACCH: Slow Associated Control Channel Speech Coding in USDC- The USDC speech coder is called the Vector Sum Excited Linear Predictive Coder (VSELP). The VSELP algorithm uses a code book that has a predefined structure. Global System for Mobile (GSM) GSM uses FDD and a combination of TDMA and FHMA schemes to provide multiple access to mobile users. The available forward and reverse frequency bands are divided into 200 kHz wide channels called ARFCNs (Absolute Radio Frequency Channel Numbers). The channel data rate of 270.833 kbps (1625.0/6.0 kbps) using binary BT = 0.3 Gaussian Minimum Shift Keying (GMSK) modulation. The signaling bit = 1/270.833 = 3.692 µs Effective channel transmission rate per user = 270.833 kbps/(8 users) = 33.854 kbps

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Taking the overhead into consideration, GSM data rate = 24.7 kbps 576.92 µs (156.256 bits)

TS0 TS1 TS2 TS3 TS4 TS5 TS6 TS7 4.615 ms

26 TDMA frames make one speech Multiframe

Table 11.3 GSM Air Interface Parameter Specifications

Reverse Channel 890-915 MHz Forward Channel 935-960 MHz ARFCN Number 0 to 124 & 975 to 1023

Tx/Rx Frequency Spacing 45 MHz Data Rates 270.833333 kbps

Frame Period 4.615 ms User per frame 8

Time slot period 576.9 µs Bit period 3.692 µs

Modulation 0.3 GMSK ARFCN Channel Spacing 200 kHz Interleaving (max. delay) 40 ms

Voice Coder Bit Rate 13.4 kbps GSM Frame Structure Superframe has 51 multiframes

6.12 s

Multiframe has 26 frames

120 ms

Frame has 8 time slots

4.615 ms 0 1 2 3 4 5 6 7

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One time slot has 156.25 bits 576.92 µs

3 57 1 26 1 57 3 8.25 Tail bit

Coded data

Stealing flag

Midamble Stealing flag

Coded data

Tail bit Guard period

Signal Processing in GSM Speech Coding – GSM Speech Coder is based on the Residually Excited Linear Predictive Coder (RELP), which is enhanced by including a Long-Term Predictor (LTP). Channel Coding for Control Channels – GSM control channel messages are defined to be 184 bits long, and are coded using a shortened binary cyclic fire code, followed by a half rate convolution codes. The fire code uses the generator polynomial G5(x) = (x23 + 1) (x17 + x3 + 1) = x40 + x26 + x23 + x17 + x3 + 1 which produces 184 message bits, followed by 40 parity bits. Four tail bits are added to clear the convolutional coder which follows, yielding a 228 bit data block. This block is applied to a half-rate K = 5 convolutional code (CC(2,1,5)) using the generator polynomials G0(x) = 1 + x3 + x4 and G1(x) = 1 + x + x3 + x4. The resulting 456 encoded bits are interleaved onto eight consecutive frames in the same manner as TCH speech data.