Impact of Delayed Limited Feedback on the Sum- Rate of Intercell Interference Nulling

Transcription

1 Impact of Delayed Limited Feedback on the Sum- Rate of Intercell Interference Nulling Ramya Bhagavatula * Robert W. Heath, Jr. # *ASSIA, Inc. Redwood City, CA # Wireless Networking and CommunicaJons Group Electrical and Computer Engineering Dept. The University of Texas at AusJn AusJn, TX

2 IntroducJon (1) Universal frequency reuse o High levels of co- channel interference (CCI) Frequency = f 0 Signal = s 1 User 2 Frequency = f 0 Signal = s 2 Base StaJon 1 Base StaJon 2 User 1 Transmissions on the same frequency CCI limits performance of cell systems o Especially nojceable with MIMO systems [Catreux2000,Blum2002] CCI management is important 2/18

3 SoluJon: Base stajon cooperajon IntroducJon (2) Broadcast channel Interference channel Base StaJon 1 Joint base stajon Base StaJon 2 Also called CoMP Network MIMO MulJcell MIMO Frequency = f 0 Signal = s 1 Frequency = f 0 Signal = s 12 Control and traffic data Creates a super MIMO channel, increased data rates, reduced outage o By exchanging data over backhaul link High cost of backhaul may impact prac8cal backhaul bandwidth [Simeone2009] 3/18

4 MulJcell Limited CSI Feedback (1) ParJal cooperajon [Ng2005,Ng2008,Zhang2009,Lee2008,Lee2009] o Only CSI exchanged between base stajons, not data o Good tradeoff between backhaul constraints and performance Performance gains depend on quality of CSI at base stajons Most exisjng muljcell work assumes full CSI SoluJon: Limited feedback o Finite- bandwidth feedback link o QuanJze CSI [Love2008] CSI exchange CSI of desired/ interfering channels 5/18

5 MulJcell Limited CSI Feedback (2) Single- cell non- coopera8ve systems Mul8cell coopera8ve systems CCI CCI Feedback of CSI of single channel Delay due to signal processing, protocol overhead etc. Single channel CSI Feedback of CSI of muljple channels AddiJonal source of delay backhaul Different signal strengths, delays of muljple channels Single- CSI feedback not directly extended to muljple CSI case 6/18

6 MulJcell Limited CSI Feedback (3) Feedback CSI of muljple channels o ParJJon available feedback resources Determines resolujon of CSI at base stajon Why not use equal parjjons for all channels? For example: 8 bits available for feedback No. of bits determines CSI resolujon Interfering signal strength SINR = Weak (/no) interferer Desired signal SINR Noise Desired signal Interfering signal + Noise Strong interferer Desired signal SINR Interfering signal Assign all bits to desired channel Assign most bits to interfering channel 6/18

7 MulJcell Limited CSI Feedback (4) Delay/ Temporal CorrelaJon Small delay Delay due to signal processing, protocol overhead etc. Large delay Channel Channel Delay Time Delay Time How outdated is the CSI fed back? Assign most bits to least outdated channel Equal- bit parjjon - Feedback resources should be parjjoned adapjvely 8/18

8 MISO systems o Single user/cell, error- free links System Model (1) Channel Unit- norm direcjon QuanJzed direcjon Rx signal strength Desired ( ) Interfering ( ) Desired signal path loss Interfering signal path loss 8/18

9 System Model (2) Rx signal Sum- rate Desired signal Interfering signals Each BTS has CSI knowledge of desired and interference caused Used to design beamforming vector, designed using intercell interference nulling [Zhang2009, Jorswieck2008, Lindblom2009] 9/18

10 Separate CSI QuanJzaJon QuanJze channel direcjons using separate codebooks CSI quanjzajon Base stajon nulls out delayed CSI [Zhang2009, Jorswieck2008, Lindblom2009] Delayed (quanjzed) CSI Loss in sum- rate unnecessary at base stajon when Clustering cells 10/18

11 Performance Loss Gauss- Markov channel model [Haykin1996,Tan2000] Temporal correlajon of interfering channel FuncJon of delay, mobility Mean loss in sum- rate with RVQ Result Increasing decreasing mean loss in sum- rate Define Represents temporal correlajon and signal strength 11/18

12 AdapJve Limited Feedback (1) Large large signal strength + small delays Assign feedback bits to an interferer in proporjon to its ParJJon bits adapjvely among interferers Result where is the dominant set of interferers. o Largest set of interferers, to sajsfy Interferers with large relajve strengths and small delays Feedback bits allocated only to dominant interferers o Efficient use of bandwidth 12/18

13 AdapJve Limited Feedback (2) Bit- parjjoning among dominant interferers Example: 4 dominant interferers {1,2,3,4} are equally strong with same delays {1,4} are stronger/have smaller delays than {2,3} 13/18

14 SimulaJon Results (1) Symmetric three- cell three- user case for simulajons SimulaJon parameters o No. of interferers = 2 o Carrier freq. = 2 GHz o = K = 3 o = 5 ms o Received SNR = 10 db o o = [- 30, 0] db o o Temporal correlajon coefficients Clarke s model [Turin2001] 14/18

15 SimulaJon Results (2) Mean sum- rate vs. ISR for velocity = 3 mph Proposed technique yields higher data rates 15/18

16 SimulaJon Results (3) Mean sum- rate vs. 16/18

17 Conclusions Proposed a separate CSI quanjzajon technique o AdapJvely parjjon feedback bits among interfering channels o FuncJon of delay, temporal correlajon, and signal strength Proposed approach outperforms EBA o At almost all ISRs o Even at higher mobility Future work o AdapJve limited feedback with joint quanjzajon Developed efficient muljcell limited feedback techniques to realize performance gains from cooperajon 17/18

18 Thank you! QuesJons?

19 References (1) [Catreux2000] S. Catreux, P. F. Driessen, and L. J. Greenstein, SimulaJon results for an interference limited muljple- input muljple- output cellular system, IEEE Communica8ons LePers, vol. 4, no. 11, pp , [Blum2002] S. Ye and R. S. Blum, Some properjes of the capacity of MIMO systems with co- channel interference, in Proc. of the IEEE Interna8onal Conference on Acous8cs, Speech and Signal Processing, vol , [Ng2005] B. L. Ng, J. S. Evans, S. V. Hanly, and D. Aktas, Transmit beamforming with cooperajve base stajons, Proc. of the IEEE Interna8onal Symposium on Informa8on Theory, Sept. 2005, pp [Ng2008] B. L. Ng, J. S. Evans, S. V. Hanly, and D. Aktas, Distributed downlink beamforming with cooperajve base stajons, IEEE Transac8ons on Informa8on Theory, vol. 54, no. 12, pp , Dec [Zhang2009] J. Zhang and J. G. Andrews, AdapJve spajal intercell interference cancellajon in muljcell wireless networks, IEEE Journal on Selected Areas on Communica8on, to appear, [Lee2008] B. O. Lee, H. W. Je, I. Sohn, O.- S. Shin, and K. B. Lee, Interference- aware decentralized precoding for muljcell MIMO TDD systems, in Proc. of IEEE Global Telecommunica8ons Conference, Dec. 2008, pp [Lee2009] B. O. Lee, H. W. Je, O.- S. Shin, and K. B. Lee, A novel uplink MIMO transmission scheme in a muljcell environment, IEEE Transac8ons on Wireless Communica8ons, vol. 8, no. 10, pp , Opt [Love2008] D. J. Love, R. W. Heath, Jr., V. K. N. Lau, D. Gesbert, B. D. Rao, and M. Andrews, An overview of limited feedback in wireless communicajon systems, IEEE Journal on Selected Areas in Communica8ons, vol. 26, no. 8, pp , Oct [Jorswieck2008] E. Jorswieck, E. G. Larsson, and D. Danev, Complete characterizajon of the Pareto boundary for the MISO interference channel, IEEE Transac8ons on Signal Processing, vol. 56, no. 10, pp , Oct

20 References (2) [Lindblom2009] J. Lindblom, E. Karipidis, and E. G. Larsson, Selfishness and altruism on the MISO interference channel: The case of parjal transmizer CSI, IEEE Communica8ons LePers, 13(9):667{669, Sept [Haykin1996] S. Haykin, AdapJve Filter Theory, 3rd ed. Englewood Cliffs, NJ, USA: PrenJce- Hall, [Tan2000] C. C. Tan and N. C. Beaulieu, On first- order Markov modeling for the Rayleigh fading channel, IEEE Transac8ons on Communica8ons, vol. 48, no. 12, pp , Dec

21 IntroducJon o Base StaJon CooperaJon o MulJcell Limited CSI Feedback System Model Separate CSI QuanJzaJon AdapJve Limited Feedback SimulaJon Results Conclusions Outline 21/18