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Pipelining and number theory for multiuser detection

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. Motivation. Several multiuser detection schemes Hardware implementation infeasible Optimize algorithm + hardware

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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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