4G Wireless Access based on Wideband OFDM


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  • Enhanced IS-136 includes smart antennas & DCA to reach 4/12 Enhanced GSM includes 3/9 reuse with RFH & signal-based power control
  • 4G Wireless Access based on Wideband OFDM

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