Tensor-Based Multiuser Detection

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Since Release 8 Long-Term Evolution (LTE) by the 3rd Generation Partnership Project (3GPP), the uplink control channel called the physical uplink control channel (PUCCH) is specified. In this paper, we propose a new multi-user joint receiver processing for LTE PUCCH that counteracts the intra-cell interference (ICI). Using the fact that the received signal in PUCCH signaling follows a constrained tensor model, a multi-user receiver based on an iterative joint channel/code estimation and symbol detection is proposed. The interest in such a challenging setting relies on the overhead reduction synchronization errors defined by time offset and inaccuracies of timing align. Simulation results show remarkable performance gains of the proposed receiver compared to the conventional time-frequency decorrelator based receiver under the same conditions.

Text of Tensor-Based Multiuser Detection

  • 1. TELFOR-2013 November 26-28, 2013 Tensor-Based Multiuser Detection and Intra-Cell Interference Mitigation in LTE PUCCH www.huawei.com Vladimir Lyashev | Ivan Oseledets | Delai Zheng Huawei Technologies Russian Research Center, Moscow (vladimir.lyashev@huawei.com) Huawei Technologies Co., Ltd. All right reserved Slide 1
  • 2. Why does PUCCH important? 40% Of YouTube Traffic Now Mobile, Up From 25% In 2012, 6% In 2011. PUCCH occupies too much bandwidth and is used not in the most efficient way. Field-test scenario: eRAN7, 10 MHz 60 connected UEs 30 UEs constantly downloading large files (i.e. video streaming) eNodB allocates 10RB for PUCCH, 3 UE per RB in average VoLTE dramatically increases PUCCH usage. 8 million VoLTE users worldwide VoLTE will take off in 2015-2016 worldwide over 10-20 MHz spectrum - hundreds users 46% MBB providers required VoLTE during 1 year Huawei Technologies Co., Ltd. All right reserved AMR calls/1MHz GSM 8 UMTS 12 HSPA 24 VoLTE 50 Slide 2
  • 3. LTE Uplink: resources Huawei Technologies Co., Ltd. All right reserved Slide 3
  • 4. PUCCH Allocation and SRS Signal SRS bandwidth is multiplied by 4RB: 4, 8, 12, Huawei Technologies Co., Ltd. All right reserved Slide 4
  • 5. Intra-cell Interference in LTE PUCCH Up to: 36UE per 1RB in Format 1x 12UE per 1RB in Format 2x Separation by CAZAC sequence In practice, time-alignment of the signals at the eNodeB receiver is not perfect. Huawei Technologies Co., Ltd. All right reserved Slide 5
  • 6. Timing Error: Main Reasons limited resolution and measurement errors propagation time change due to UE movement oscillator drift abrupt change of the multipath channel misdetection of the Timing Advance (Initial or Update) command Huawei Technologies Co., Ltd. All right reserved Slide 6
  • 7. Abrupt changes in channel delay profile cant be compensated by TA commands alone! 200ms-1s 200ms-1s 200ms-1s TA command abs(timing error) Huawei Technologies Co., Ltd. Timing correction at UE Timing correction at UE Path birthdeath All right reserved Timing correction at UE Path birthdeath Slide 7
  • 8. Field-test measurements: scenario 20 km/h speed 600 m length difference 720kHz (6RB) SRS signal generation // blue line 1 14.4 MHz measurement signal // red line 2 2 1 Huawei Technologies Co., Ltd. All right reserved Slide 8
  • 9. Field test measurements: results Huawei Technologies Co., Ltd. All right reserved Slide 9
  • 10. Mathematical Model 1, = 0, CAZAC property for ideal sync.: = ; . Q Y j P H j T j P j X j P H q Tq Pq X q P I q 1 power loss q j H j H j Measurement # Measurement results NUE = 6, TAerror = 0 s Desired user Interference 23.7 0.11 12.52 0.67 13.37 0.95 9.83 0.65 7.5 0.26 10.6 0.51 Huawei Technologies Co., Ltd. 2 H j intra cell interference SIR 23 dB 22 dB 11 dB 12 dB 15 dB 13 dB NUE = 6, TAerror = 1.56 s Desired user Interference 14.41 4.12 11.23 2.63 16.91 1.01 2.42 3.15 7.97 2.71 5.11 4.21 All right reserved Slide 10 SIR 5.5 dB 6.5 dB 12 dB -1.2 dB 4.5 dB 0.8 dB
  • 11. Mathematical Model and Its Approximation Q Y (n, l , k ) P(q, k , l ) H (q, n, k , l ) X (q, l )T (q, k ) E (n, l , k ) q 1 B-rank channel approximation: B H ( q , n, k , l ) W ( , q , n ) S ( , k ) 1 Rank-2 model basically gives a very good fit to the experimental channel H(q, n, l, k), usually of a fit of order 95%. The rank-1 model also look promising, and can approximate 70% of the energy. Huawei Technologies Co., Ltd. All right reserved Slide 11
  • 12. Rank-1 (B=1) Model Approximation Mathematical Notation in Slice Form Yl (n, k ) Y (n, l , k ) l th slice for 3D tensor (received signal) Pl (q, k ) P(q, l , k ) T (k ) T (k ) S (k ) Huawei Technologies Co., Ltd. Yl WX l Pl T El All right reserved Slide 12 Joint Algorithm ALS-1 l th slice for 3D tensor (reference sequence)
  • 13. Joint Detection ^ Update T Update W WX l Pl T IT Yl Update X W X I Xl Pl Yl W X l W I Yl Iteration++ Receive Signal Y Simple Channel Estimation & MRC with equalizing H0 W0 QPSK-symbols demapping & decoding XMRC X0 Set as initial guess for ALS iterations X ALS-1 iterations ^ T0= I12x12 Huawei Technologies Co., Ltd. All right reserved Slide 13 Output CQI bits
  • 14. Quality decoding Joint Detection with Quality Control TErr = 3 TErr = 0 Pilots FER in MRC: FER in ALS-1: MRC & ALS-1 have the same error frames: ALS-1 males mistake (MRC not): FER in MRC: FER in ALS-1: MRC & ALS-1 have the same error frames: ALS-1 males mistake (MRC not): Huawei Technologies Co., Ltd. 128 / 12 000 225 / 12 000 114 / 12 000 111 / 12 000 407 / 12 000 180 / 12 000 107 / 12 000 73 / 12 000 All right reserved Slide 14
  • 15. Simulation Parameters Parameter LTE PUCCH format Bandwidth CQI Modulation type Number of Rx antennas Number of Tx antennas per user Number of users Cyclic shift (CS) interval for RS Value format 2 1.4 MHz 7 bits QPSK 4 1 6 /3 Power of desired user (CS=0) Power for UE with CS=1,3,5 Power for UE with CS=2,4 Timing error (uniform distribution) Propagation channel Number of simulated sub-frames Huawei Technologies Co., Ltd. All right reserved 0 dB 3 dB 0 dB -1.56 1.56 us ETU70 20 000 Slide 15
  • 16. Convergence without Quality Decoding Control Huawei Technologies Co., Ltd. All right reserved with Quality Decoding Control Slide 16
  • 17. Simulation Results without Quality Decoding Control Gap: 0.8 dB Huawei Technologies Co., Ltd. with Quality Decoding Control Gap: 0.4 dB All right reserved Slide 17
  • 18. Outlook Non-Orthogonal Access MU-MIMO and Massive-MIMO Algorithm Diversity for Cloud RAN (cRAN) Dimension Reduction in Non-Linear Signal Processing Huawei Technologies Co., Ltd. All right reserved Slide 18
  • 19. TELFOR-2013 November 26-28, 2013 www.huawei.com Dr. Vladimir Lyashev, IEEE Member [ lyashev@ieee.org ] [ linkedin.com/in/lyashev/ ] Huawei Technologies Co., Ltd. All right reserved Slide 19