1 cellular telephony Wireless Communication 2 2G cellular telephony Wireless Communication Zero Generation System (1975 – 1990)

3 kHz voice bandwidth (like POTS) Frequency Division Multiple Access (FDMA) Analog FM modulation Total bandwidth divided into hundreds of channels 2G Cellular Full duplex transmission 2 frequencies per telephone during call Dedicated Base Station (BS) transmission frequency (uplink) Telephony Dedicated Mobile Station (MS) transmission frequency (downlink) Various non-compatible national and commercial systems 2G systems evolved from US AT&T AMPS Downlink Forward Channel British Telecom TACS Uplink Reverse Channel MS BS

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

3 2G cellular telephony Wireless Communication 4 2G cellular telephony Wireless Communication — Advance Systems (AMPS) Commercial Diversity (Competition)

North American first generation analog system — IS-553 Split 25 MHz band for 2 service providers 25 MHz transmission band per direction B band for the established Telco 20 MHz frequency band per direction (1976) A band for a second cellular operator Mobile Station (uplink): 825 - 845 MHz 832 channels / 2 bands = 416 channels per service provider Base Station (downlink): 870 - 890 MHz 118 channels per cell / 2 bands < 59 channels per cell per provider Additional 5 MHz band per direction (1986) Mobile Station (uplink): 845 - 849 MHz Band Frequency Range (MHz) Use Base Station (downlink): 890 - 895 MHz B B G C 824 to 835 and 845 to 846.5 MS: Transmit from mobile A Frequency Division Multiple Access (FDMA) G C A 869 to 880 and 890 to 891.5 BS: Receive at mobile Divide band into 30 kHz RF voice channels A F D 835 to 845 and 846.5 to 849 MS: Transmit from mobile F D E B 25 MHz per cluster E B 880 to 890 and 891.5 to 894 BS: Receive at mobile = 832 channels per cluster 30 kHz per channel G C A 7 cell frequency reuse pattern (A, B, …, G) F D E 832 channels / 7 cells < 118 channels per cell Typically 90 useful channels per cell

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 5 2G cellular telephony Wireless Communication 6 2G cellular telephony Wireless Communication AMPS Digital Call Control Total Access Communications System (TACS)

AMPS similar to POTS British first generation analog standard Most channel capacity allocated to voice 25 MHz transmission band Limited call control MS (uplink): 890 - 915 MHz Call control channel BS (downlink): 935 - 960 MHz 10 kbps FSK (digital FM) Not compatible with AMPS Registration 25 kHz per channel Authentication 25 MHz per cluster / 25 kHz per channel = 1000 channels per cluster Operations, Administration, Maintenance (OAM) 7 cell reuse pattern Control information 1000 channels / 7 cells = 140 channels per cell From phone Mobile Identification Number (10 digit phone number) Electronic Serial Number (32-bit ID of telephone) Home System Identification (15-bit provider code) From network Frequencies available to phone

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

7 2G cellular telephony Wireless Communication 8 2G cellular telephony Wireless Communication Second Generation Systems Narrowband AMPS (N-AMPS)

2G Analog systems Based on AMPS standard Triple number of channels per cell Developed by Motorola proprietary products Allocate 10 kHz per channel — instead of 30 kHz in AMPS Narrowband Advance Mobile Phone Systems (N-AMPS) Triples number of channels Motorola Integrated Radio System (MIRS) Combines data compression and lower voice quality Time Division Multiple Access (TDMA) First standard Short Message Service (SMS) Divide FDMA radio channel into time slots Alphanumeric characters in control channel MS transmits digitized voice in one time slot on one frequency Standards North American d-AMPS N-AMPS is IS-88, 89, 90 European GSM Combined with AMPS as IS-91 Code Division Multiplex Access (CDMA) Create orthogonal binary digital transmission codes MS transmits in one code on one frequency

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 9 2G cellular telephony Wireless Communication 10 2G cellular telephony Wireless Communication Review of E1 Time Division Multiplexing (TDM) Digital AMPS (d-AMPS)

Analog voice channel (300 Hz to 3300 Hz) North American 2G digital cellular on AMPS infrastructure Sampled at 8000 samples/second byte from line 1 AMPS-based FDMA 125 μsec/frame 3.9 μsec Round-off to 1-byte sample = 32 bytes/frame byte 25 MHz per cluster = 832 voice channels per cluster Digital voice bit stream (DS-0) byte from line 2 30 kHz per voice channel 8000 samples 8 bits byte from line 3 Digital transmission ×=64 kbps second sample Transmit 48,600 bps in each 30 kHz voice channel E1 frame contains 32 bytes Voice channel modulation — DQPSK (encoded PSK) control byte 1 byte each from 30 DS-0 streams Control channel modulation — AMPS compatible FSK 125μ s 2 control bytes 1 2 3 ... 32 Time Division Multiple Access (TDMA) 125μ s Isochronous real time Divide each voice channel into 6 time slots 1 = 125 μs/frame 1 byte sample every 125 μsec 8000 frames/second Allocate 2 time slots per user 32 bytes per frame 3 users per voice channel E1 = 32 × 64 kbps = 2.048 Mbps 48,600 bps per channel / 3 users per channel = 16,200 bps per user Squeeze 125 μsec sample into 125 μsec / 32 = 3.9 μsec transmission time Standards IS-54 replaced by IS-136

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

11 2G cellular telephony Wireless Communication 12 2G cellular telephony Wireless Communication d-AMPS Digital Frames d-AMPS Data Rates

40 ms Slot width Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Slot 6 260 data bits + 64 control bits = 324 bits per slot User 1 User 2 User 3 User 1 User 2 User 3 Frame size 6.67 ms 324 bit per slot × 6 slots per frame = 1,944 bits per frame Frame and slot rates MS to BS (uplink) Slot Fields 40 ms per frame / 6 time slots per frame = 6.67 ms per time slot Control Traffic Control Traffic Control Traffic 40 ms per frame ⇒ 25 frames per second 12 16 28 122 24 122 Total transmission rate BS to MS (downlink) Slot Fields 25 frames per second × 1,944 bits per frame = 48,600 bps Control Traffic Control Traffic Control User rates 25 frames 2 user slots 260 traffic bits 40 130 12 130 12 ×× =13,000 bps (user traffic rate) second frame user slot Time slot contains 25 frames 2 user slots 64 control bits ×× =3,200 bps (user control rate) 260 traffic bits (digitized voice) second frame user slot 64 control bits (call control, synchronization, OAM) total user rate= 16,200 bps

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 13 2G cellular telephony Wireless Communication 14 2G cellular telephony Wireless Communication d-AMPS Channels Voice Encoding

832 radio channels 3 users 2496 users Analog to frequency channels ×= cluster channel cluster Vector Sum Excited Linear Prediction

Channel 1 Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Slot 6 Generates 159-bit sample every 20 ms Data rate = 159 bits / 20 ms = 7,950 bps Channel 2 Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Slot 6 Forward error correction (protection) Channel 3 Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Slot 6 Encoding permits error correction at receiver 77 most significant speech bits encoded to 178 bits 159 – 77 = 82 less significant bits not encoded Encoded data = 178 + 82 bits = 260 bits

260 bits / 20 ms = 13,000 bps 40 ms User time slots Slot 1 Slot 2 Slot 3 Slot 4 Slot 5 Slot 6 Transmit frame every 40 ms 20 ms Frame contains two time slots per user Channel 832 Time slot contains 260-bit digitized 20 ms voice sample Time slots

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

15 2G cellular telephony Wireless Communication 16 2G cellular telephony Wireless Communication GSM GSM Digital Frames 120 ms Global System for Mobile Communications 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 European Union 2G digital cellular on TACS frequencies Non-TACS channelization 26-frame multiframe Divide band into 200 kHz RF channels (8 TACS voice channels) 26 × 1,250 bits = 32,500 bits 25 MHz per cluster / 200 kHz per channel = 125 channels per cluster Frames 12 and 25 carry no traffic Digital transmission 0 1 2 3 4 5 6 7 8-user frame Transmit 270.883 kbps in each 200 kHz radio channel 8 × 156.25 bits = 1,250 bits Voice and control modulation Gaussian minimum-shift keying (GMSK) — optimized FSK Time Division Multiple Access (TDMA) Traffic Traffic Divide each channel into 8 time slots 3 57 1 26 1 57 3 8.25 Allocate 1 time slot per user User time slot Time slot contains 270.883 kbps per channel / 8 users per channel = 33,086 bps per user 156.25 bits 57 + 57 = 114 traffic bits (digitized voice or data) Standards 42.25 control bits for call control, synchronization, OAM European Telecommunications Standards Institute (ETSI) 8.25-bit field — variable no-transmission interval between frames Total bits in time slot = 114 + 42.25 = 156.25

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 17 2G cellular telephony Wireless Communication 18 2G cellular telephony Wireless Communication GSM Data Rates GSM Voice Encoding

Time slot width A/D conversion 114 traffic bits + 42.25 control bits = 156.25 bits Analog voice signal filtering at 3.3 kHz Frame width Sampling at 8000 samples / second 8 time slots per frame × 156.25 bits per slot = 1,250 bits per frame Rounded off to 13-bit quantization (213 level encoding) Multiframe width 8000 samples/second × 13-bits/sample = 104 kbps 26 frames × 1,250 bits per frame = 32,500 bits per multiframe Total transmission rate Voice Encoding 32,500 bits per multiframe / 120 ms = 270.833 kbps Regular Pulse Excited Long Term Prediction (RPE-LTP) User traffic rate 8-times voice compression Traffic in 24 frames — frames 12 and 25 carry no traffic 104 kbps / 8 = 13 kbps compressed data rate ⎛⎞2× 57 bits 24 time slots 120 ms ⎜⎟× = 22.8 kbps ⎝⎠time slot multiframe multiframe

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

19 2G cellular telephony Wireless Communication 20 2G cellular telephony Wireless Communication GSM Voice Error Protection GSM Voice Transmission Summary

Compressed 20 ms sample 3300 Hz 104 kbps Voice 8000 13-bit 8:1 Uncompressed sample size = 104 kbps × 20 ms = 2080 bits Filter Samples/sec Quantization Compression Compressed sample size = 13 kbps × 20 ms = 260 bits CRC Error protection on most significant bits 13 kbps 260-bit 13 kbps 456 bits = 8 blocks× 57 bits/block Generator buffer 260-bit sample → 456-bit protected sample 260:456 Protected sample transmitted in 8 time sequential slots 104 kbps× 20 msec = 2080 bits 20 ms sample / 8 slots = 2.5 ms sample per slot 13 kbps× 20 msec = 260 bits 57 57 456 bits / 8 time slots = 57 bits per time slot Sample Sample 2 × 57-bit traffic fields per time slot n n+1 57 57 1 2 3 4 5 6 7 8 1 user time slot / frame Each time slot holds 1/8 of 2 sequential samples 2.5 ms 2.5 ms 24 frames / multiframe 2 fields per time slot × 2.5 ms per field = 5 ms traffic per time slot 0 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16 17 18 19 20 21 22 23 24 On large (uncorrectable) error at receiver Sample replaced with previous sample 57 user bits per field× 2 fields per frame× 24 frames per multiframe = 2736 user bits per multiframe 2736 bits per multiframe / 120 ms per multiframe = 22.8 kbps Large error in 1 sample worse than small errors in 2 samples 22.8 kbps / (456/260) = 13 kbps

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 21 2G cellular telephony Wireless Communication 22 2G cellular telephony Wireless Communication GSM Transmission Rate vs Service Rate Comparing d-AMPS and GSM

24 user frames serviced in 120 ms multiframe Feature d-AMPS GSM 120 ms Total bandwidth 25 MHz per direction per cluster 25 MHz per direction per cluster = 5 ms user traffic per frame MS (uplink): 825 - 849 MHz MS (uplink): 890 - 915 MHz 24 user frames Frequency bands BS (downlink): 870 - 895 MHz BS (downlink): 935 - 960 MHz Squeeze 8 user slots into frame transmission time Voice encoding 13 kbps (compressed protected) 22.8 kbps (compressed protected) 5 ms 5 ms user traffic serviced in = 0.625 ms 25 MHz 25 MHz FDM (radio) 832 channels 8 channels per cluster = cluster 125 channels 30 kHz cluster = cluster 200 kHz cluster 26 physical frames per multiframe transmission channel channel 120 ms 60 Digital capacity = ms per frame = 4.62 ms per frame 48.6 kbps per 30 kHz channel 270.833 kbps per 200 kHz channel 26 frames 13 per FDM channel TDMA (digital) 3 digital voice streams/channel 8 digital voice streams/channel Squeeze 8 user slots into physical frame transmission time slots per channel 60 1 15 832 channels 3 slots 2,496 slots 124 channels 8 slots 992 slots TDMA channels ×= ×= ms×== ms 0.58 ms per slot transmission per cluster 13 8 26 cluster channel cluster cluster channel cluster Protocol Simple ⎯ comparable to POTS Complex ⎯ comparable to ISDN Structure

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

23 2G cellular telephony Wireless Communication 24 2G cellular telephony Wireless Communication Comparison of User Slots Basic GSM Architecture Public Land Mobile Network (PLMN) d-AMPS to GSM d-AMPS GSM Ratio User slots 2496 992 2.5 Bits / Hz 48.6 / 30 = 1.62 270.8 / 200 = 1.35 1.2 Used slots 100% 24 / 26 = 92% 1.08 Traffic / total 260 / 324 = 0.80 114 / 156 = 0.73 1.09 Bits per 20 ms voice 20 ms × 13 kbps 20 ms × 22.8 kbps sample = 260 bits = 456 bits MS Mobile Station HLR Home Location Register 20 ms voice BSS Base Station Subsystem VLR Visitor Location Register samples per 1000 / 260 = 3.85 1000 / 456 = 2.19 1.75 1000 bits BTS Base Transceiver Station AUC Authentication Center Radio system for one cell User authentication / encryption keys BSC Base Station Controller EIR Equipment Identity Register Breakdown of d-AMPS to GSM user slot advantage Controller for one or more BTS Hardware ID database (theft control) 1.2 × 1.08 × 1.09 × 1.75 = 2.5 MSC Mobile Switching Center OMC Operations and Maintenance Center

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 25 2G cellular telephony Wireless Communication 26 2G cellular telephony Wireless Communication GSM Registration Procedure

Registration MS activated Performed when mobile station (MS) activated in Service Area Scans all possible frequencies Authentication Synchronizes to BS beacon message Verify authenticity of Mobile Station Beacon — control frame within larger data frame Call Establishment MS learns frame timings Performed when the user initiates or receives call MS initiates registration procedure Handoff () Requests registration on control channel Performed when MS changes connection point to network Base station system (BSS) authenticates MS Security Checks ID number on SIM (subscriber identity module) card Protects from fraud and eavesdropping BSS assigns TMSI (Temporary Mobile Subscriber Identity) BSS updates VLR against HLR BSS closes control channel

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

27 2G cellular telephony Wireless Communication 28 2G cellular telephony Wireless Communication GSM Registration GSM Call Establishment

MS Initiated MS BTS BSC MSC VLR HLR MS BTS BSC MSC Channel request Request control channel Activation response Assign control channel Activation ACK Call establishment request Channel assignment Authentication request Location update request Authentication response Authentication request Encryption key Authentication response Encryption response Authentication check Destination address TMSI assignment Routing response TMSI ACK Traffic channel request Update VLR / HLR entries Assign traffic channel Channel release Available or busy Call accepted Connection established Data exchange

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 29 2G cellular telephony Wireless Communication 30 2G cellular telephony Wireless Communication GSM Call Establishment Handoff

Mobile Terminated MS MS MS MS MS BTS BSC MSC VLR HLR GMSC PSTN Caller Standard call set-up Request to Gateway MSC HLR user request BTS BTS BTS BTS Assign roaming number Request to MSC (user location) BSC BSC BSC Update user status Page MS Intra-cell MSC MSC Authentication Change frequencies to avoid interference Call connection Inter-cell — Intra-BSC MS moves between cells within control of one BSC Inter-BSC — Intra-MSC MS moves between cells controlled by different BSCs MSC controls handover Inter MSC MS moves between cells controlled by different MSCs

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

31 2G cellular telephony Wireless Communication 32 2G cellular telephony Wireless Communication Handoff Procedure GSM Protocol Stack

MSC MS BTSold BSCold BSCnew BTSnew CM CM measurement MM MM report measurement report RRM RRM BSSAP BSSAP Handoff required Handoff RRM' RRM' BTSM BTSM SCCP SCCP request Channel LAPDm LAPDm LAPD LAPD MTP MTP activation Handoff Radio Radio 64 kbps 64 kbps 64 kbps Request Handoff Handoff Activation ACK MS BTS BSC MSC Handoff ACK command command command CM Connection Management MM Mobility Management Handoff link establishment Radio Resource Management RRM Handoff Separate protocol instances at MS/BTS layer and MS/BSC layer clear command clear command Handoff complete complete LAPD Link Access Protocol D — ISDN layer 2 protocol (Q.920/921) BTSM Base Transceiver Station Management clear complete clear complete BSSAP BSS Application Part SCCP Signaling Connection Control Part (SCCP) — MSC/BSS management MTP Message Transfer Part — standard PSTN signaling and management

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 33 2G cellular telephony Wireless Communication 34 2G cellular telephony Wireless Communication GSM Logical Channel Structure GSM Control Channels

BCH — Broadcast Channel TCH CCH CBCH Frequency Correction Channel (FCCH) Traffic Channel Control Channel Cell Broadcast Channel MSC to MS broadcasts Synchronization Channel (SCH) — frame numbers and cell ID Broadcast Control Channel (BCCH) — broadcast services and cell ID TCH/F TCH/H Common Control Channel (CCCH) Full rate Half rate Paging Channel (PCH) Access Grant Channel (AGCH) — BTS assigns control channel to MS BCH CCCH DCCH Random Access Channel (RACH) — MS requests to BTS Broadcast Channel Common Control Channel Dedicated Control Channel DCCH (Dedicated Control Channel) SDCCH (Stand-alone Dedicated Control Channel) Service requests, authentication, traffic channel assignment FCCH SCH BCCH PCH AGCH RACH ACCH SDCCH Call establishment and mobility management F/SACCH (Fast / Slow Associated Control Channel) SACCH FACCH Preemptive / background messages for maintenance and handoff

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

35 2G cellular telephony Wireless Communication 36 2G cellular telephony Wireless Communication Direct Sequence (DSSS) CDMA

Transmit data bit as chip sequence Code Division Multiple Access Chip Commercial system developed by Qualcomm Shortest binary pulse on transmission channel Operates on AMPS frequencies n-chip sequence is symbol for one data bit Non-AMPS channelization 25 MHz radio band per direction Multiplies transmission rate data 1 chip sequence User generates data at m bits per second Divide band into 1.25 MHz RF channels 25 MHz per cluster / 1.25 MHz per channel = 20 channels per cluster Transmit n-chip sequence for every user bit data 0 chip sequence DSSS digital transmission Example Transmit 1.2288 Mcps in 1.25 MHz radio channel 1-sequence for data 1 = 10110100 Voice and control modulation — QPSK 0-sequence for data 0 = 01001011 Code division Chip rate = n bps × m chips per bit = n × m chips per second (cps) Users transmit simultaneously using independent chip sequences Receiver easily distinguishes 1-sequence from 0-sequence Orthogonal (Walsh) Codes / Pseudorandom noise (PN) codes Bit error requires > n / 2 chip errors Receiver separates channels by decoding chip sequences Works well in noisy environment Standards IS-95 — now called CDMAone

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 37 2G cellular telephony Wireless Communication 38 2G cellular telephony Wireless Communication Orthogonal CDMA Codes Example ⎯ 4-Chip CDMA m-dimensional vector space with inner product Code vectors for m = 4 stations 1 m UV⋅=UV × m ∑i=1 ii ⎡⎤−−−−1111 ⎡⎤ ⎡⎤ ⎡⎤ m orthonormal basis vectors ⎢⎥−+−+1111 ⎢⎥ ⎢⎥ ⎢⎥ ⎢⎥ ⎢⎥ ⎢⎥ ⎢⎥ SSSS1234==== Sii ,= 1, ... , m ⎢⎥−++−1111 ⎢⎥ ⎢⎥ ⎢⎥ m ⎢⎥ ⎢⎥ ⎢⎥ ⎢⎥ TT=×tS, with coefficient t for any vector −−++1111 ∑ i=1 ii i ⎣⎦ ⎣⎦ ⎣⎦ ⎣⎦ ⎧0, ij≠ 4-bit transmission levels (chips) SSij⋅=×= mδ ij⎨ ⎩mi, = j Binary 1 Binary 0 11mm 1 m Station 1 –1 –1 –1 –1 +1 +1 +1 +1 tS=⋅=⋅T S tS × = t ×() SS ⋅ = tm × = t ii imm∑∑jj==11 jj j ij m ∑ j = 1 j iji Station 2 –1 +1 +1 –1 +1 -1 -1 +1 Code scheme Station 3 –1 –1 +1 +1 +1 +1 -1 -1 Station 4 –1 +1 -1 +1 +1 -1 +1 -1 Basis vector Si is code assigned to station i ⎧−1,data 0 ⎪ Station i transmits t × S with coefficient t = 0,no transmission i i i ⎨ Radio signal amplitudes added together ⎪ Total transmission from all stations ⎩+1,data 1 m T = tS× ∑ i=1 ii δ

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

39 2G cellular telephony Wireless Communication 40 2G cellular telephony Wireless Communication Example ⎯ 2-bit Transmission Example ⎯ 2-bit Transmission

Data 0 1 Data Station 1 1 Signal +1 +1 +1 +1 -1 -1 -1 -1 Data 0 1 Chip Station 2 Signal +1 -1 -1 +1 -1 +1 +1 -1 2 Data no data 1 Station 3 0 0 0 0 -1 -1 +1 +1 Signal 3 Data 0 1 Station 4 Signal +1 -1 +1 -1 -1 +1 -1 +1 4 Total Transmission Signal +3 -1 +1 +1 -4 0 0 0

T

+3 -1 +1 +1 -4 0 0 0

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 41 2G cellular telephony Wireless Communication 42 2G cellular telephony Wireless Communication Example ⎯ Decoding Orthogonal Walsh Codes

1 4 Inner Product UV⋅= UV t j =⋅TSj Walsh 0 W0 = 1 W0' = -1 4 ∑ i=1 ii

W1 W1 1 1 Walsh 1 W1 = = 11 W1 W1' 1 -1 t1 =−++⋅−−−−=−+−−=−⇒44()()3,1,1,1 1,1,1,1[ 3111] 1 0 First bit t =11()()3,1,1,1 −++ ⋅−++− 1,1,1,1 =[] −−+− 3111 =−⇒ 1 0 W W 1 1 1 1 S 2 44 Walsh 2 W = 2 2 = = 1 11 2 T = (+3, -1,+1,+1) t3 =44()()3, −++ 1, 1, 1 ⋅−−++ 1, 1, 1, 1 =[] −+++ 3 1 1 1 = 0 ⇒no data W2 W2' 1 -1 1 -1 S4 11 S t4 =44()()3,1,1,1 −++ ⋅−+−+ 1,1,1,1 =[] −−−+ 3111 =−⇒ 1 0 1 1 -1 -1 3

1 -1 -1 1 S2

11 t1 =44()() −4,0,0,0 ⋅−−−−= 1, 1, 1, 1[] 4 =+⇒ 1 1 W4 W4 11 Walsh 3 W = Second bit t2 =−44()()4,0,0,0 ⋅−++−= 1,1,1,1[] 4 =+⇒ 1 1 3 W4 W4' 11 T = (-4,0,0,0) t3 =44()() −4,0,0,0 ⋅−−++= 1, 1, 1, 1[] 4 =+⇒ 1 1 11 t4 =−44()()4,0,0,0 ⋅−+−+= 1,1,1,1[] 4 =+⇒ 1 1 N N WN-1 WN-1 Walsh N is 2 × 2 matrix Walsh N WN = WN-1 WN-1'

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

43 2G cellular telephony Wireless Communication 44 2G cellular telephony Wireless Communication Pseudo-Noise (PN) Coding Channel Coding

Pseudorandom Bernoulli sequence of 1 or –1 Forward channels Equivalent to sequence of m coin tosses 64 orthogonal Walsh codes to 64 users Nearly equal number of 1 and –1 in each code Theoretically perfect separation between users By central limit theorem All signals in same cell scrambled using PN sequence 111 Reduces interference between same Walsh code in neighboring cells PP−+11=() −=+11δδδ PP =() +=− < 22m Short PN sequence uses cell ID as seed Codes are "nearly orthogonal" Paging and traffic scrambled with long PN sequence before Walsh (A) (B) Reverse channels For codes A and B with chip patterns Ci and Ci Orthogonal codes not applicable in uplink 11mm2 AB=⇒ C()AB × C () = ±=11 Orthogonality requires time synchronization ∑∑ii==11ii [] mm MSs transmit asynchronously

1 m Long PN sequence AB≠⇒ C()AB × C () m ∑ i=1 ii Stream is scrambled using short PN sequence

14m 2 Carries cell ID =×−×−×+×=<[]P P P PPP PP 4δ mm∑ i=1 ++11 + 1-1-11-1-1 +

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 45 2G cellular telephony Wireless Communication 46 2G cellular telephony Wireless Communication Power Control North American IS-95 CDMA

Near/far problem 25 MHz AMPS frequency band Signal from MS close to BS stronger than same signal from far MS 1.25 MHz per FDM band ⇒ 20 FDM bands Solution — dynamic control of MS signal power In every 1.25 MHz FDM band Open loop power control at MS 64 users transmit in same 1.25 MHz band (on same carrier MS senses strength of pilot signal and adjusts power frequency) Strong signal Each station has unique 64-bit chip sequence MS close to BS Digital channel Power lowered Allocate 19.2 kbps / user for voice, data, control Closed loop power control at MS 19.2 kbps/channel × 64 channels = 1.2288 Mbps Power control information sent to MS from BS All cells use all frequencies and all codes (reuse = 1) Requests transition up or down in power Transmissions from neighboring cells are not time-synchronized Open loop power control at BS Unsynchronized codes are close to orthogonal BS decreases power gradually (to avoid interference in other cells) Users 64 users 20 channels 7 cells users Raises power when MS reports high frame error rate (FER) ××= 8,960 radio channel cell cluster cluster

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

47 2G cellular telephony Wireless Communication 48 2G cellular telephony Wireless Communication Reuse Pattern in GSM and CDMA GSM and CDMA Multiplexing

GSM GSM CDMA Transmit 8 time slots on 1 FDM channel Total Bandwidth 25 MHz 25 MHz Channels on different FDM channels do not interfere FDM Bandwidth 200 kHz 1.25 MHz Channels in different time slots do not interfere Radio channels 25 MHz / 200 kHz = 125 25 MHz / 1.25 MHz = 20 Each cell uses 1/7 to 1/3 of all FDM channels to avoid interference User bit rate 22.8 kbps 19.2 kbps Minimum distance between cells on same frequency = 2 Users per channel 8 64 Bit rate in CDMA 8 × 22.8 kbps = 182.4 kbps 64 × 19.2 kbps = 1.2288 Mbps channel Transmit 64 different codes on 1 FDM channel Total Bit Rate 182.4 kbps × 124 = 22.6 Mbps 1.2288 Mbps × 20 =24.6 Mbps Channels on different FDM channels do not interfere Reuse 2, 3, 7 1 Channels using different codes do not interfere Channels per cell 124 / 7 ≈ 17 20 All codes and FDM channels used in all cells Users per cell (124 / 7) × 8 ≈ 141 20 × 64 = 1280 Most codes do not interfere when not synchronized User at cell boundary assigned a non-interfering code Users per cluster (124 / 7) × 8 × 7 = 992 20 × 64 × 7 = 8960 Multipath signals are not synchronized CMDA principal advantage — reuse GSM with reuse = 1 ⇒ 992 users / cell × 7 cells / cluster = 6944 users per cluster

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 49 2G cellular telephony Wireless Communication 50 2G cellular telephony Wireless Communication CDMA Codes Compared to TDMA CDMA Codes and TDMA "Codes"

CMDA 4 Chip Walsh Codes Each station transmits a 64-bit code Station 1 -1 -1 -1 -1 All stations transmit continuously at the same -1 +1 +1 -1 Station 2 Transmissions are separated by orthonormality of codes -1 -1 +1 +1 Station 3 -1 +1 -1 +1 CMDA codes Station 4 264 different 64-bit sequences 64 orthogonal 64-bit sequences t Orthogonal transformation on orthogonal code is an orthogonal code 4 Chip TDM "Codes" ()j Sii = 'th chip in code basis vector j Station 1 ()jj64 () +1 -1 -1 -1 STSi'== 'th chip in new code basis vector j -1 +1 -1 -1 iikk∑ k =1 Station 2 -1 -1 +1 -1 -1 Orthogonal matrix TTik= ki Station 3 -1 -1 -1 +1 ()j Pick S 'iij= δ System looks like TDMA Station 4 Station i only transmits on chip i t Station i transmits 1 bit per chip sequence

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

51 2G cellular telephony Wireless Communication 52 2G cellular telephony Wireless Communication Noise Immunity in GSM and CDMA Noise Averaging in CDMA

GSM transmits Total transmitted data from 64 users 64 8 user samples transmitted in time required to make 1 sample T = tS ∑ i=1 ii Each 5 ms sample transmitted in 5 × (24/26) × (1/8) = 0.58 ms 8 voice streams of 22.8 kbps = 182.4 kbps in 200 kHz Total received signal 182.4/200 Shannon: Required SNR = 2 –1 = 0.88 64 64 T =+tS noise = tS + N 1 CDMA transmits ∑∑i=1 iii=1 ii ii 1 user voice sample transmitted in time to make 1 voice sample Calculated coefficient for user i is

No time multiplexing 64 Calculated tStSNS=+T Noise ⋅ = +⋅ Every user transmits a different set of symbols ji()()jij()∑ i=1 () ()

64 symbols transmitted at one time with multilevel modulation 64 64 () kk kk =+⋅()tSi ij N S , N is noise amplitude on chip k 64 voice streams of 19.2 kbps = 1.2288 Mbps in 1.25 MHz ∑∑ki==11 () 64 64 64 Shannon: Required SNR = 21.2288/1.25 – 1 = 0.98 =⋅+×tSS ()kk () NS k k () ∑∑ik==11i ij ∑ k = 1 j Better noise immunity because of noise averaging 64 64 () () =+×=−×=−tNifSNifS δ kkkk1 ( 1) 1 ( 1) ∑∑ik==11iij jj =+t Noise − Noise j chip =+ 1-1 chip =

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 53 2G cellular telephony Wireless Communication 54 2G cellular telephony Wireless Communication Rake Receiver Logical Channels

Overcomes multipath interference Captures delayed signals in multipath reception Adds contributions from all paths

t+t2

t+t1 delay = 0

t delay = t1 Receiver

delay = t2

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land

55 2G cellular telephony Wireless Communication 56 2G cellular telephony Wireless Communication Forward Logical Channels Reverse Logical Channels

Pilot channel Access channel Transmitted in all frames Random access channel used by MS for messages to BS Phase and timing reference for MS Contention access Provides signal strength to MS for channel acquisition Choose access channel at random Reused in every cell with local short PN code offset Collision ⇒ lost data → no ACK → retry after random wait 1 pilot frame per 64 channel system Paired with up to 32 paging channels Sync channel MS responds to paging message on corresponding access channel Timing, system and, network IDs to MS Reverse traffic channel Can be received by MS after locking onto pilot signal User data (primary and secondary) and signaling 8 synch frames per 64 channel system Signaling information multiplexed with user data Forward traffic channels User data and signaling data Variable data rates Two modes Blank and burst — signaling data instead of voice Dim and burst — multiplexes signaling data with voice data 55 traffic frames per 64 channel system

Spring 2010 Hadassah College Dr. Martin Land Spring 2010 Hadassah College Dr. Martin Land 57 2G cellular telephony Wireless Communication Distribution of 2G Systems

Cellular telephones in use — July 2001

(TDMA cellular in )

Spring 2010 Hadassah College Dr. Martin Land