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Pipelining and number theory for multiuser detection

Explore pipelining and number theory for multiuser detection in 3GPP W-CDMA. Learn about reducing complexity, improving throughput, and optimizing algorithms and hardware implementation.

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Pipelining and number theory for multiuser detection

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  1. Pipelining and number theory for multiuser detection Sridhar Rajagopal and Joseph R. Cavallaro Rice University This work is supported by Nokia, TI, TATP and NSF

  2. Motivation • Several multiuser detection schemes • Hardware implementation infeasible • Optimize algorithm + hardware • Design a reduced complexity multiuser detection algorithm and its implementation for 3GPP W-CDMA

  3. Approaches • Algorithm • parallel interference cancellation • reduced complexity, parallel structure • Pipelining • bit-streaming, avoid block detection • Number theory • Most Significant Digit First (MSDF) computation • sign detection

  4. Contributions • decrease detection latency and storage requirements by window length (12X) • On-line arithmetic based on MSDF computation • further latency reduction by 1.9X • increase in throughput by 3X • possible savings in area

  5. Outline • Parallel interference cancellation • Pipelining • On-line arithmetic • Conclusions • Current research directions

  6. ri-2 ri-1 ri ri+1 User 1 time bi+1 bi Interference from future bits of other users ri Desired user Interference from previous bits of other users User j Multiuser detection

  7. Multiuser detection • Optimal - MLSE • Decorrelating • MMSE • Serial/Parallel interference cancellation • Top 3 require inversion of matrices • Block based detection

  8. Parallel interference cancellation Block based detection

  9. Block detection

  10. Outline • Parallel interference cancellation • Pipelining • On-line arithmetic • Conclusions • Current research directions

  11. Parallel interference cancellation Block Toeplitz structure - suitable for pipelining

  12. Pipelined detection

  13. Being designed as a class project in Elec 422/423 VLSI class

  14. Outline • Parallel interference cancellation • Pipelining • On-line arithmetic • Conclusions • Current research directions

  15. Redundant number systems • Conventional systems ( 0.34578, r=10) • radix r has r possible digits • Redundant (0.34578,0.35578,…. r=10) • >r possible digits. • Limit carry propagation • Totally parallel addition/subtractionONLY.

  16. On-line arithmetic • Uses a redundant number system • Pipelined bit-serial arithmetic • Most Significant Digit First computation • Successive computations as soon as  inputs available ( = 1-4, typically) • Can do operations such as addition, multiplication, division, square-root etc.

  17. On-line detection and decoding Entire chain can be done on-line Work with hard decisions (sign of MSD) simple way to use softer decisions (2 or more digits)

  18. On-line arithmetic for detection

  19. Conventional arithmetic - matched filter

  20. On-line matched filter

  21. Conventional multiuser detection

  22. On-line multiuser detection

  23. Comparisons N = K =32, d = 8, S = 3, r = 4, tol = 2, tconv = 1, tstop = 2

  24. Outline • Parallel interference cancellation • Pipelining • On-line arithmetic • Conclusions • Current research directions

  25. Conclusions • Techniques such as pipelining and on-line arithmetic can be used to implement multi-user detection for W-CDMA. • Lower latency • Higher throughput • Smaller area • Simple hardware - adders and multipliers

  26. Current research directions • Reconfigurable computing -RENE • Chameleon - hardware • mNIC card

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