1 Downlink Single-user MIMO Comparison for IEEE m Document Number: C80216m-08/407 Date Submitted: May 05, 2008 Source: Senjie Zhang Guangjie Li Intel Yanchun Li Intel Hongming Zheng Intel Yang-Seok Choi Intel Shanshan Zheng Feng Zhou Intel May Wu Minnie Ho Intel Sassan Ahmadi Venue: Macau, China Purpose: Discussion and Approval Notice: This document does not represent the agreed views of the IEEE Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: and. Further information located at and. C80216m-08/407

2 Outline Overview Open-loop Schemes Closed-loop Schemes Comparison between SCW and MCW Summary and Recommendations

3 Overview Single-user MIMO is to improve per link performance in terms of high data rate and good coverage Design criteria and requirements –Evaluate and select schemes in e spec [1] to make m solution concise and effective –Improve e existing schemes if possible –Low system complexity –Support Single Codeword (SCW) –Evaluate if there is obvious gain from MCW over SCW especially with MLD receiver e Scheme Overview –Open-loop For 2-TX, STBC (matrix A) for rate 1 and Spatial Multiplexing (matrix B) for rate 2 For 4-TX, STBC (matrix A) for rate 1 and hybrid STBC/SM (matrix B) for rate 2. They are with antenna hopping Cyclic delay diversity (CDD) [2] –Closed-loop Antenna grouping/ selection Codebook-based precoding Sounding-based precoding

4 Open-loop Schemes 2-TX schemes –In IEEE STD e specification, STBC such as Alamouti code is supported to provide spatial diversity and reduce fade margin. Spatial multiplexing is also supported to take advantage of higher peak rates and increased throughput –The 2-antenna rate 1 scheme is a basic STC scheme, enabled by matrix A –The 2-antenna rate 2 scheme is enabled by matrix B –2-TX STBC/SM is legacy MIMO mode in e reference system, and should be supported in m.

5 Open-loop Schemes (Cont.) 4-TX Matrix A/B with antenna hopping –applying A1~A3 or B1~B6 periodically CDD [3] –Same process to pilot and data –Same power on Physical antenna –Combined with STBC or SM

6 Open-loop Scheme Performance CDD has <1dB performance loss with non-ideal CE

7 Open-loop Scheme Summary CDD vs. AH –Pros Low transmitter complexity: Only ‘copy and shift’ operation Low receiver complexity: For MMSE receiver, AH requires 4x4 matrix inversion, CDD requires 2x2 only Small pilot overhead Simple channel estimation: CDD uses same pilot pattern with 2-TX systems –Cons <1dB performance loss with non-ideal CE Channel estimator’s coefficients need be adaptive to cyclic delay value Open-loop summary –Support STBC/SM –CDD+STBC/SM is good candidate for asymmetric antenna configuration e.g. 4x2 –Antenna hopping is more complicated in receiver side than CDD, and need twice of the pilot though about 1dB better

8 Closed-loop Schemes e’s Antenna Grouping for 4-TX antenna is –To choose the best matrix from A1~A3 or B1~B6 as described in page 5 –equivalent to precoding with the simplest W matrix (elements is 0 or 1) Antenna Selection for 4-TX antenna is –To choose best antenna(s) from 4-TX antenna and apply power boosting –equivalent to precoding with the simplest W matrix (elements is 0 or 1)

9 Closed-loop Schemes e provides a set of codebooks based on Grassmann subspace packing –For example, the 3-bit codebook for 4-TX rate 1 is: –Newly-designed codebooks can be evaluated for improvement Sounding-based solution requires careful study [4] –CQI is still needed because DL interference is unknown –RF calibration issue –Uplink interference’s impact –Other pending issues

10 Closed-loop Scheme Performance For rate-1 schemes, codebook-based precoding provides best performance –Best approaching to perfect feedback –5dB better than open-loop –1~2.5dB better than AG/AS with comparable feedback

11 Closed-loop Scheme Performance (Cont.) For rate-2 schemes, codebook-based precoding provides best performance –Best approaching to perfect feedback –5dB better than open-loop –1~2.5dB better than AG/AS with comparable feedback

12 Closed-loop/ Open-loop Performance Comparison Codebook closed- loop is better than open-loop: With non-ideal CE and MLD receiver, it still has 3~4dB’s performance gain

13 Closed-loop Scheme Summary Codebook vs. AG/AS –Codebook provides better approaching to perfect feedback –With comparable feedback (Codebook: 3bits, AG/AS:2bits), codebook has 1~2dB gain –Antenna selection is not good in terms of TX power balance Codebook vs. Sounding [4] –RF Calibration is required –Difficult for wideband sounding –CQI still needed to be fed back Closed-loop Summary –Recommend to support codebook-based precoding

14 Comparing Single Codeword (SCW) & Multiple Codeword (MCW) SCW is simple and with less feedback overhead MCW provides better adaptation to channel condition, but requires more CQI feedback and is more complicated than SCW –MCW can utilize SIC receiver to improve its performance. MCW+SIC receiver can outperform SCW+MMSE receiver, but it has little gain over SCW+MLD receiver. As the following figure shows. Summary: Support Single Codeword (SCW)

15 Single-user MIMO Comparison and Summary Example Antenna Configuration Open-loopClosed-Loop 2x2STBC/SMCodebook precoding 4x2Antenna Hopping CDD+STBC/SM Antenna selection Antenna Grouping Codebook precoding Open-loop –Support STBC/SM to backward compatible to e reference system –Recommend to support CDD+STBC/SM for asymmetric antenna configuration e.g. 4x2 Low complexity in both Tx and Rx side Good performance Small pilot overhead for asymmetric antenna configuration –Antenna Hopping is more complicated in receiver side than CDD, and need twice of the pilot Closed-loop –Recommend to support codebook based solution –Antenna selection is not good in terms of power utilization issue Use Open-loop (OL) and Closed-loop (CL) for different scenarios - OL: high speed - CL: medium/low speed

16 Appendix Reference documents [1] IEEE P802.16Rev2/D1, “IEEE Standard for Local and metropolitan area networks Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems,” 2007 [2] WiMAX Forum Technical Working Group, “RPD recommandations for CDD usage ”, 2007 [3] C80216maint-08_006, “Definitions for transparent transmit diversity”, 2008 [4] Intel, ““DL_MIMO_Proposal_08xx”, 2008 Simulation settings –16x6 RB size –eITU-PedB –3Km/h –CTC ½ coding rate –QPSK, 16QAM, 64QAM –MMSE, MLD and SIC receiver –Ideal CE or non-ideal CE using LMMSE estimator