1. A FAST SELECTIVE-DIRECTION MMSE TIMING RECOVERY ALGORITHM FOR SPATIAL-TEMPORAL EQUALIZATION IN EDGE
Hanks H. Zeng
Ye Li
Jack H. Winters
AT&T Labs - Research
Red Bank, NJ
September 27, 2000

2. OUTLINE EDGE Spatial-Temporal equalization
Selective-direction timing recovery
Results
Conclusions

3. THIRD GENERATION TDMA SYSTEM: EDGE
EDGE: Enhanced Data Rates for Global Evolution
High data rate (384 kbps) service based on GSM, evolution of IS-136 and GSM
8PSK at ksps
26 symbol training sequence
1/3, 3/9 or 4/12 reuse
Both ISI and CCI 58 3
8.25 3 26 58 s

4. SMART ANTENNAS IN TDMA SYSTEMS
Currently, 2 receive antennas at base stations with IS-136
Combining changed from maximal ratio to MMSE combining in 1999 => 3-4 dB SINR gain
Planned upgrade to 4 antennas for further improvement
Spatial processing (track channel across time slot)
Want to use smart antenna techniques in EDGE
Spatial-Temporal processing (constant weights across time slot)

5. SMART ANTENNAS IN EDGE
Spatial-Temporal processing using DDFSE for interference suppression
5 feedforward taps, 5 feedback taps, 8-state Viterbi Equalizer
Degradation due to shortened equalizer => timing critical

6. WEIGHT ESTIMATION AND TIMING RECOVERY
Previous technique:
Weight estimation: Train as MMSE-DFE
Timing: MPE - Minimize ratio of precursor to cursor energy
Issue:
Much poorer performance with strong precursor versus postcursor ISI

7. WEIGHT ESTIMATION AND TIMING RECOVERY
Solution: Selective-direction equalization
Since time slot is processed as a block, select either the forward or reverse direction for processing, with timing that minimizes the MMSE (trained as MMSE- DFE).

8. WEIGHT ESTIMATION AND TIMING RECOVERY
Issue: Computational complexity of training is doubled (with two directions) - important since inverse of large matrix is required, which is computationally intensive
Solution: As shown in paper, the training algorithm can be modified so that the same matrix inverse is used for both directions => minimal computational-complexity increase with our technique

9. BER with 2 antennas, HT profile, and single interferer

10. BLER with single interferer (MCS-5)

11. CONCLUSIONS
Proposed a selective-direction MMSE timing recovery algorithm for ST processing:
Improves performance with minimal increase in computational complexity
Applied algorithm to EDGE:
3 dB lower SIR for 1% raw BER with 2 antennas as compared to previous technique
Up to 25 dB interference suppression at 10% BLER with two antenna versus single antenna receiver