Presentation on theme: "Comparison of N1 and N2 Cycling Document Number: IEEE C80216m-09_0716 Date Submitted: 2009-03-09 Source: Kiran Kuchi, J. Klutto Milleth, Vinod R, Dileep."— Presentation transcript:
Comparison of N1 and N2 Cycling Document Number: IEEE C80216m-09_0716 Date Submitted: 2009-03-09 Source: Kiran Kuchi, J. Klutto Milleth, Vinod R, Dileep M K, Divagar, Padmanabhan M S, Bhaskar R, Giridhar KVoice: CEWiT, IndiaE-mail: email@example.com, firstname.lastname@example.org Venue: Call for Comments on IEEE 802.16m-09/0010 IEEE 802.16m Amendment text Base Contribution: None Purpose: To discuss and adopt the proposed text in amendment text To discuss in TGm for appropriate action. Notice: This document does not represent the agreed views of the IEEE 802.16 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 802.16. Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: and.http://standards.ieee.org/guides/bylaws/sect6-7.html#6http://standards.ieee.org/guides/opman/sect6.html#6.3 Further information is located at and.http://standards.ieee.org/board/pat/pat-material.htmlhttp://standards.ieee.org/board/pat
Presentation Outline CDF of CQI CQI mismatch analysis for 2D-POD (N2-cycling in frequency+precoder cycling over sub-frames) 1D-POD (N2 cycling in frequency) N1 Cycling+best-M Performance of POD (DFT) and 16e code books with correlated antennas Discussion
N1 Vs N2 Precoder cycling Pre-coding Vector Table Let pre-coding vector used in the i th PRU in the m th sub frame be P i. N1 Cycling : C i = C(:, k) where k = floor( i / N1)% 4, N1 = 4, i =0 to 47, m=0 to1 N2 Cycling (1D-POD) : C i = C(:, k) where k = i % 4, N2 = 1,i =0 to 47, m=0 to 1 N2 Cycling (2D POD) : C i,m = C(:, k) where k = ( i % 4) + ((i%2)*2 +1)*m, N2 = 1,i =0 to 47, m=0 to 1
N1 Vs N2 precoder cycling Examples of precoder cyling in two subframes Ci C0C1 C2 C3 C0 N1 cycling N2 Cycling (2D-POD) C0 C1 C2 C3 N2 Cycling (1D-POD) PRU(i,0)PRU(i,1) PRU(i+1,0)PRU(i+1,1) PRU(i+2,0)PRU(i+2,1) PRU(i+3,0)PRU(i+3,1)
System Model and CQI Definition System Model :Y = HCx + n Y (N r x 1) ==> Received Signal vector at an OFDMA sub carrier H (N r x N t ) ==> Channel matrix at an OFDMA sub carrier C (N t x 1) ==> Pre-coding vector X ==> Transmitted symbol vector n==> zero mean unity variance Gaussian noise vector CQI at a sub-carrier = ∑ (HC) H HC CQI i,m => the CQI in the i th PRU in the m th sub frame = CQI averaged over all the sub-carriers in the PRU CQI subband => the CQI averaged over all PRUs in a pair of sub bands spanning in time
CQI Calculation CQI subband = ( CQI i,0 + CQI i,0 + CQI i+1,0 + CQI i+1,1 + CQI i+2,0 +CQI i+2,1 +CQI i+3,0 + CQI i+3,1 )/8 CQI(i,0)CQI(i,1) CQI(i+1,0)CQI(i+1,1) CQI(i+2,0)CQI(i+2,1) CQI(i+3,0)CQI(i+3,1) The channel frequency selectivity within sub-band is quite high in mPED-B channel In mPED-B, 2-Tx, 2Tx system the channel hardening effect is similar for N1 and N2 cycling
CQI CDF in 2Tx, 2Rx System (mPED-B Channel, 3 Kmph) In mPED-B, 2-Tx, 2Tx system the channel hardening effect is similar for N1 and N2 cycling (i.e., not much difference in the upper part of the CDF) Lower outages for N2 cycling (Diversity gain) Pr(CQI<0 dB) = 8% for N2 cycling Pr(CQI< 0 dB) = 16 % for N1 cycling At the higher end of CDF Pr(CQI> 5 dB)= 15% for N1 cycling Pr(CQI> 5 dB)= 10% for N2 cycling
CDF of CQI with N1 Cycling with Best-M CDF of best-2 sub bands in selected from 12 sub bands Best-band scheduling gain diminishes at high mobile speeds
CQI Mismatch Caused by Channel Frequency Selectivity Within the Subband
CQI mismatch due to frequency selective channel CQI is reported for each sub-band but scheduler may assign only a portion of the sub-band for a given user Data may be scheduled in a single sub-frame or in multiple sub-frames Over the sub-band, channel varies due to frequency selectivity Some amount of CQI mismatch unavoidable in real system At low speeds, little CQI mismatch when full sub-band is scheduled Let CQI i,m be the CQI in the i th PRU in the m th subframe Case-1: CQI Mismatch when a single PRU pair (two contiguous PRUs in time) is allocated (worst case scenario) Case-2: CQI Mismatch when a two PRU pairs (two contiguous PRUs in frequency and two contiguous PRUs in time) are allocated
CQI mismatch due to frequency selective channel (low speed) Channel model: mPED-B 3 kmph At low speeds, feedback delay does not cause significant CQI mismatch Frequency selective channel causes some CQI mismatch when only a portion of the sub-band is not allocated to the user In this scenario N2-cycling (2D-POD) has least CQI mismatch CQI mismatch for Case-1CQI mismatch for Case-2
Conclusions 2D-POD (N2 cycling in frequency + precoder cycling over subframes) Enables a “pure” OL transmit diversity scheme for time only, frequency only and joint time and frequency resource allocations Least CQI mismatch over all other techniques including N1 cycling N1 cycling + best-M Semi-closed loop technique Gain is prone to mobile speed, feedback delay etc. At 30 Kmph, best-M gains start to vanish For 5 and 10 MHz BW with 4-frequency partitions, best-M not feasible Only one or two sub-bands available per frequency partition At low mobile speeds: No significant performance difference between 2D-POD+best-M and N1 cycling+best-M For medium to high mobile speeds 2D-POD outperforms N1 cycling+best-M 2D-POD recommended for OL rank-1 precoding
Proposed Text For Non-Adaptive Precoder Cycling Duration The OL non-adaptive precoder W changes every PRU and every sub-frame.
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