The Evolution of TDMA to 3G & 4G Wireless Systems Nelson Sollenberger AT&T Labs-Research Wireless Systems Research Division
AT&T Wireless Services AT&T serves over 14 million subscribers with digital TDMA technology and some remaining analog technology, and provides packet data service with CDPD technology TDMA European GSM over 250 million North American TDMA ~ 50 million Japanese PDC ~ 50 million CDMA North American CDMA ~ 60 million (including S. Korea) Other TDMA operators - Rogers AT&T - Cingular (SBC & BellSouth) - throughout Mexico, Central & South America
Cellular Telephony Handsets Nokia 5160 Nokia 8860 Ericsson PD 328 Motorola StarTAC ST7790 Phone Various TDMA phones available today
TDMA parameters 30 KHz channels (like analog & CDPD) 20 msec speech frames 24.3 kbaud symbol rate 3 time-slots/users 7.4 kbps ACELP speech coding 1/2-rate channel coding on important bits interleaved over 2 bursts in 40 msec Differential pi/4-qpsk modulation
TDMA Capacity Roadmap 2000 2001 2002 Reuse N = 7 N = 5 N = 4 Dual band base Operation at 800 or 1900 MHz. Calls can be set up on either frequency band and handed between them to manage traffic Additional spectrum at 1900 MHz adds directly to capacity of cell Smart Antennas Base station antennas systems that use digital signal processing to cancel interference Dynamic Channel Assignment Network automatically assigns radio frequencies to cell sites for more efficient utilization of frequencies Base Station Power Control Base stations only transmit power required to reach mobile with adequate signal quality resulting in lower interference Discontinuous Transmission Mobiles transmit only during when user is speaking. Lowers interference in the system and increases talk time
IS-136 Smart Antenna Test Bed Reuse of 3/9 to 4/12, instead of 7/21, approximately 2x capacity Two dual polarization uplink antennas, downlink multibeam antenna with 4-30 beams Shared linear power amplifier unit with Butler matrices Real-time downlink power control with beam tracking
Wireless Data Terminals Sierra PCMCIA CDPD Modem Nokia 9110 The new Ericsson R380 phone, which features wireless data 3COM Palm VII functions Nokia 3G vision
WIRELESS COMPUTING WIRELESS GROWTH INTERNET GROWTH - web access - e-mail - file transfer - location services - streaming audio & video RF & DIGITAL TECHNOLOGY MOBILE SOFTWARE
Macrocellular Wireless Data Evolution & AT&T s Roadmap 5 M Wideband OFDM data rate 1 M HDR 384 k EDGE WCDMA GPRS 64 k IS-136+ IS-95+ PDC 9.6 k GSM IS-136 CDPD IS-95 1995 2000 2005
EDGE Technology Enhanced Data-rates for Global Evolution Evolutionary path to 3G services for GSM and TDMA operators Builds on General Packet Radio Service (GPRS) air interface and networks Phase 1 (Release 99 & 2002 deployment) supports best effort packet data at speeds up to about 384 kbps Phase 2 (Release 2000 & 2003 deployment) will add Voice over IP capability
GPRS Airlink General Packet Radio Service (GPRS) Same GMSK modulation as GSM 4 channel coding modes Packet-mode supporting up to about 144 kbps Flexible time slot allocation (1-8) Radio resources shared dynamically between speech and data services Independent uplink and downlink resource allocation
EDGE Airlink Extends GPRS packet data with adaptive modulation/coding 2x spectral efficiency of GPRS for best effort data 8-PSK/GMSK at 271 ksps in 200 KHz RF channels supports 8.8 to 59.2 kbps per time slot Supports peak rates over 384 kbps Requires linear amplifiers with < 3 db peak to average power ratio using linearized GMSK pulses Initial deployment with less than 2x 1 MHz using 1/3 reuse with EDGE Compact as a complementary data service
GPRS Networks consists of packet wireless access network and IP-based backbone shares mobility databases with circuit voice services and adds new packet switching nodes (SGSN & GGSN) will support GPRS, EDGE & WCDMA airlinks provides an access to packet data networks Internet X.25 provides services to different mobile classes ranging from 1-slot to 8-slot capable radio resources shared dynamically between speech and data services
Compact vs Classic Classic 4/12 reuse continuous downlinks on first 12 carriers 2.4 MHz x2 minimum spectrum Compact 1/3 reuse in space frame synchronized base stations reuse of 4 in time for control channels partial loading for traffic channels discontinuous downlinks 600 KHz x2 minimum spectrum
EDGE Channel Coding and Frame Structure Burst N 464 bits 1 data block Convolutional Coding Rate = 1/3 Length = 7 Puncture 1392 bits 1392 bits Interleave Burst N+1 Burst N+2 348 bits/ burst 156.25 symbols/slot 8PSK Modulate 468.75 bits Burst Format 348 bits Burst N+3 20 msec frame with 4 time-slots for each of 8 bearers 8 Time Slots 0 1 2 3 4 5 6 7 1 Time Slot = 576.92 µs Tail symbols 3 Data symbols 58 Training symbols 26 Data symbols 58 Tail symbols 3 Guard symbols 8.25 Modulation: 8PSK, 3 bits/symbol Symbol rate: 270.833 ksps Payload/burst: 348 bits Gross bit rate/time slot: 69.6 kbps - overhead = 59.2 kbps user data
EDGE Modulation, Channel Coding & Bit Rates Scheme Modulation Maximum rate [kb/s] Code Rate Family MCS-9 8PSK 59.2 1.0 A MCS-8 54.4 0.92 A MCS-7 44.8 0.76 B MCS-6 29.6 0.49 A MCS-5 22.4 0.37 B MCS-4 GMSK 17.6 1.0 C MCS-3 14.8 0.80 A MCS-2 11.2 0.66 B MCS-1 8.8 0.53 C
EDGE Link Throughput 9
EDGE Compact System Performance Probability throughput < = X per timeslot 100 90 80 70 60 50 40 30 20 10 0 % % 0 10 20 30 40 50 60 70 X (kb/s) 100 90 80 70 60 50 40 30 20 10 0 Probability packet delay < = X 0 1000 2000 3000 4000 5000 X (msec) 26 users/sector at 3.5 kbps average load per user
EDGE Classic Multi-slot Gain Average User Throughput (kb/s) 300 250 200 150 100 50 0 single-slot Multi-slot 9 18 27 36 45 Ave. # of users per sector
EDGE Evolution Best effort IP packet data on EDGE Voice over IP on EDGE circuit bearers Network based intelligent resource assignment Smart antennas & adaptive antennas Downlink speeds at several Mbps based on wideband OFDM and/or multiple virtual channels
Normalized voice capacity (Erlang/Site/MHz) VoIP over EDGE Bearer Performance Focused on GMSK full-rate & 8PSK half-rate EDGE channels with dedicated MAC & random frequency hopping for 7.4 kbps voice coding 55 50 45 7.2 MHz Spectrum 50 40 35 30 30 29 35 25 20 20 15 10 5 7 11 10 0 Baseline Enhanced GSM IS-136 EGPRS/GMSK/F EGPRS/8PSK/H * 1/3 reuse * no shadow fading change due to mobility *Signal-based power control is assumed for baseline EGRPS *SINR-based power control & LI-DCA assumed for enhanced *This assumes 30 mph vehicle speed for micro fading * SINR-based power control with adaptive target
Smart Antennas for EDGE Key enhancement technique to improve system capacity and user experience Leverage Smart Antennas currently in development/deployment for IS-136 & GSM BEAMFORMER SIGNAL Uplink Adaptive Antenna INTERFERENCE SIGNAL OUTPUT BEAMFORMER WEIGHTS Downlink Switched Beam Antenna SIGNAL BEAM SELECT SIGNAL OUTPUT Aggressive frequency re-use High spectrum efficiency Increased co-channel interference INTERFERENCE Smart antennas provide substantial interference suppression for enhanced performance
EDGE Smart Antenna Processing Dual Diversity Receiver Using DDFSE for Joint ISI and CCI Suppression Output Data Viterbi Decoder Receiver Deinterleaver Rx Rx Rx Filter Rx Filter Symbol Timing and Recovery Feed-forward Filter Feed-forward Filter Soft Output DDFSE Equalizer Equalizer Training Jack Winters Hanks Zeng Ashutosh Dixit Simulation results show a 15 to 30 dbimprovement in S/I with 2 receive antennas Real-time EDGE Test Bed supports laboratory and field tests to demonstrate improved performance
EDGE 2-Branch Smart Antenna Performance Laboratory Tests Block Error Rate EDGE MCS-5 with Interference Suppression in a Typical Urban Environment 20 db SNR Signal-to-Interference Ratio (db) Laboratory results show a 15 to 30 db improvement in S/I with 2 receive antennas
Improvement with Terminal Diversity and Interference Suppression: User Experience Prototype Dual Antenna Handset External Whip Internal Patch 100 90 80 70 60 50 40 30 20 10 0 Prob. (throughput <=X) (%) No Diversity Simple Diversity Interference Suppression 0 10 20 30 40 50 60 70 Multi-cell EDGE Compact Simulation X (kb/s) - 1/3 reuse - 18 users per sector - 3.5 kbps average load per user Typical user throughput increased from 30 to 45 kbps per time-slot
4G Wireless: One View 4G WOFDM high speed downlink a wireless cable modem Complement to EDGE/UMTS High peak data rates (up to 10 Mb/s) in a 5 MHz channel spectrum - 500 MHz to 3 GHz 3G EDGE/WCDMA network for uplink, downlink, control and signalling
Path Loss and Fading Challenge Delay Spread Reflected signals arrive spread out over 5 to 20 microsecond Path Loss path loss up to ~ 150 db (that is a 1 followed by 15 zeroes) Rayleigh Fading rapid fading of 20 to 30 db (power varies by 100 to 1000 times in level at rates of about 100 times per second)
Cumulative Probability Cellular Interference Challenge 1 Each base station is equipped with three 120 degree directional antennas to reduce interference & improve capacity 0.1 0.01 1 3 reuse 2 6 reuse 3 9 reuse 4 12 reuse 7/21 reuse 0.001-5 0 5 10 15 20 25 Signal to Interference ratio in db
AT&T Labs-Research Work on 4G Smart antennas Multiple-Input-Multiple-Output Systems Space-Time Coding Dynamic Packet Assignment Wideband OFDM
MIMO Radio Channel Measurements Multiple antennas at both the base station and terminal can significantly increase data rates with sufficient multipath Ability to separate signals from closely spaced antennas has been demonstrated indoors and in AT&T-Lucent IS-136 field trial Lucent has demonstrated 26 bps/hz in 30 khz channel with 8 Tx and 12 Rx antennas indoors AT&T has performed measurements on 4 Tx by 4 Rx antenna configurations in full mobile & outdoor to indoor environments
MIMO Channel Measurement System Transmitter 4 antennas mounted on a laptop 4 coherent 1 Watt 1900 MHz transmitters with synchronous waveform generator Receive System Dual-polarized slant 45 PCS antennas separated by 10 feet and fixed multibeam antenna with 4-30 beams 4 coherent 1900 MHz receivers with real-time baseband processing using 4 TI TMS320C40 DSPs
MIMO Measured Channel Capacity Potential Capacity Relative to a Single Antenna System Capacity increase close to 4 times that of a single antenna is possible with 4 transmit and 4 receive antennas Capacity for pedestrians is similar to mobile users
Performance Measure Complex channel measurement: H = [ H ij ] for the i th transmit and j th receive antenna Capacity (instantaneous and averaged over 1 second) for 4 TX by 4 RX: C = log 2 (det[i + ( /4)H H]) = log 2 (1 + ( /4) i ) where is the total signal-to-noise ratio per antenna and i is the i th eigenvalue of H H To eliminate the effect of shadow fading, the capacity is normalized to the average capacity with a single antenna: C n = log 2 (1 + ( /4) i ) / (1/16) log 2 (1 + H ij )
Multiple Input Multiple Output Wireless RX diversity - HF, terrestrial microwave, cellular. TX frequency offset diversity & simulcasting for paging - 70 s Adaptive array processing in military systems TX diversity - 80 s frequency offset (channel decoding combining) delay (equalizer combining) Optimum combining for cellular (multipath channels) - 80 s Space-division multiple access - 80 s & 90 s angle-of-arrival based multi-path based (supports co-location & multi-channels per user) MIMO - 80 s & 90 s Multiple spatial channels using adaptive antenna arrays BLAST - successive interference cancellation combined with coding Space-Time coding
Space-Time Coding How do you enhance TX delay diversity ( a repetition code)?
Multiple Antennas increase System Capacity MIMO (BLAST & space-time coding) techniques increase bit rate and/or quality on a link by creating multiple channels and/or enhancing diversity Switched/steered beam antennas for base stations and interference suppression/adaptive antennas for terminals reduce interference, increasing system capacity
OFDM for 4G Wireless ~ 800 tones ~ 5 MHz ~ 6 khz Mobile OFDM parameters: ex. OFDM is being increasingly used in high -speed information transmission systems: - European HDTV - Digital Audio Broadcast (DAB) - Digital Subscriber Loop (DSL) - IEEE 802.11 Wireless LAN 5 MHz channels ~ 6 KHz tones ~ 13/26 MHz sample rate 2048 FFT size (160 usec OFDM blocks) 256/512 sample OFDM block guard time QPSK & 16-QAM modulation adaptive modulation/coding 1 to 2 msec time-slots in 20 to 40 msec frames
OFDM Characteristics High peak-to-average power levels Preservation of orthogonality in severe multi-path Efficient FFT based receiver structures Enables efficient TX and RX diversity Adaptive antenna arrays without joint equalization Support for adaptive modulation by subcarrier Frequency diversity Robust against narrow-band interference Efficient for simulcasting Variable/dynamic bandwidth Used for highest speed applications Supports dynamic packet access
OFDM Robust Channel Estimation received signals FFT FFT data remove data 2-branch maximal-ratio combining IFFT...... synch word............ FFT Estimator 1 Estimator 2
Word Error Rate WOFDM 2-Branch Diversity Performance 1 0.1 0.01 CC, k=9 CC, k=3 RS 0.001-1 0 1 2 3 4 5 6 7 SNR (db)
Spectrum Efficiency Efficiency 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 5 7.5 10 12.5 15 SNR (db) Synch CDMA Dynamic Channel Allocation with Power Control Dynamic Channel Allocation Source: G. J. Pottie, IEEE Personal Communications, pp. 50-67, October 1995 Efficiency: IS-136 0.04; IS-95 0.07; GSM 0.04
Dynamic Packet Assignment 2. Mobile sends measurements of path losses for nearby bases to serving base 4. Bases assign channels to all packets/mobiles 1. Mobile locks to the STRONGEST base 3. Serving base forwards measurements to nearby bases 5. Bases forward channel assignment info to nearby bases ~ 50 % improvement in performance
Wideband OFDM Staggered Frame Superframe Superframe 80 ms 80 ms 1 2 3 4 1 2 3 4... Frame 20 ms Control Slots 16 resources in 1 msec time-slots Control Slots... 4 ms 20 OFDM Blocks 5 Blocks 5 Blocks 5 Blocks 5 Blocks group A group B group C group D 2 B data 1B Sync & data 2 B data
Ave. User Packet Delay (msec) WOFDM Performance with Dynamic Packet Assignment & 5 MHz of Spectrum 120 100 80 60 40 20 MR, No beam-forming IS, No beam-forming MR, Four beams per sector IS, Four beams per sector 0 0 500 1000 1500 2000 2500 3000 3500 Throughput per site (kb/s)
OFDM Experimental Program Baseband signal processing based on commercial off-the-shelf DSP hardware with some custom designed components Sony-provided 1900 MHz transceivers Real-time performance measured through RF channel fading simulator Phase 1 parameters: - >384 kb/s end user data rate - 800 khz downlink bandwidth - GSM-derived clocks (2.166 MHz sample rate with 512 FFT) - 3.467 kbaud - 189 OFDM tones with 4.232 khz tone spacing - differential detection - Reed-Solomon channel coding
Typical Urban channel 800 khz RF A/D FFT RF A/D FFT Demodulator OFDM receiver Erasure detection Decoder Data Intf
Summary: Key Features of 4G W-OFDM IP packet data centric Support for streaming, simulcasting & generic data Peak downlink rates of 5 to 10 Mbps Full macro-cellular/metropolitan coverage Asymmetric with 3G uplinks (EDGE) Variable bandwidth - 1 to 5 MHz Adaptive modulation/coding Smart/adaptive antennas supported MIMO/BLAST/space-time coding modes Frame synchronized base stations using GPS Network assisted dynamic packet assignment