Harnessing Interaction in Bursty Interference Networks

Transcription

1 215 IEEE Hong Kong-Taiwan Joint Workshop on Information Theory and Communications Harnessing Interaction in Bursty Interference Networks I-Hsiang Wang NIC Lab, NTU GICE 1/19, 215

2 Modern Wireless: Grand Challenges Global mobile data traffic is expected to increase nearly 11-fold from (source: Cisco VNI mobile forecast) What drives this increase? - Growing # of users - Data-hungrier (smarter) mobile devices Grand challenges: Support higher data rate Accommodate more users Increase spectral efficiency 2

3 More Users + Growing Demand more interference along with abed ㄅㄆ ø kklkle #$# πø $@#ßå µ orzz Toy example: people talking in a crowded room 3

4 Also, more chances for interaction 4

5 Interference vs. Intermittence Interference: - Born-nature of wireless medium - Limits the throughput of modern wireless networks Intermittence: - Lack of coordination across distributed terminals - Born-nature of data traffic - Not a critical issue if users do not interfere with one another Major bottleneck: interference 5

6 Modern View on Interference Traditional techniques: orthogonalization (2G), treating interference as noise (3G, 4G) Recent advances in network information theory shed light on how to break the interference barrier: Two-user IC: approximate capacity to within 1 bit/s/hz - Partial interference cancellation [Etkin et al IT8] K-user IC: total # of degrees of freedom = K/2 - Interference alignment [Maddah-Ali et al IT8] [Cadambe & Jafar IT8] Caveat: (in most information theoretic literature) Assume that interference is always present 6

7 Interaction Helps Manage Interference Cooperation among Tx/Rx terminals - Cloud RAN, cooperative MIMO, etc. - Capacity increase is bounded by the cooperation capacity [W & Tse IT11] Feedback from Rx to Tx - With perfect output feedback, capacity increase is multiplicative [Suh & Tse IT11] However, interaction cannot increase the total multiplexing gain (degrees of freedom) [Cadambe & Jafar IT9] Caveat: (in most information theoretic literature) Assume that interference is always present 7

8 Interference can be Intermittent At PHY, interference may not be always present Medium access control mechanism - Decentralized resource allocation Time 1 Time 2 Time 3 User 1 f1 f1 f1 User 2 f1 f2 f1 Network layer protocol/demand - Bursty network traffic Time 1 Time 2 Time 3 User 1 On Off On User 2 Off On On 8

9 Exploit Intermittence of Interference Naive idea: send more when there is no interference but may not know if there is interference beforehand Not completely hopeless: we may have delayed information about the presence of interference, thanks to interaction (feedback/cooperation) If interferer s activity can be predicted from the past, then obviously such delayed information can help If not (in the extreme case when coherence time = 1 symbol time), it seems such delayed information will not help 9

10 Question 1: Two Major Questions In bursty/intermittent environment, does delayed state information help mitigate interference? Question 2: In bursty/intermittent environment, does interaction play a more important role in interference management, compared with the static one? Both answers are YES. 1

11 Two Case Studies in this Talk Bursty Interference Channel with Feedback Bursty Interference Channel with a Relay Intermittent Interference Bursty Traffic With delayed state information, in both cases interaction increases the multiplexing gain degrees of freedom (DoF) 11

12 Major Findings and Contributions Bursty IC with feedback: - One-bit feedback increases DoF - Characterize the approximate capacity - An adaptive coding scheme - Novel outer bounds Intermittent Interference Bursty (MIMO) IC with a relay: - In-band cooperation increases DoF - DoF increase linearly with the # of relay antennas - Derive conditions for interference-free DoF performances Bursty Traffic 12

13 Gaussian Interference Channel X 1 [t] Y 1 [t] W 1 Tx1 h 11 h 12 Rx1 cw 1 X 2 [t] h 21 Y 2 [t] W 2 Tx2 h 22 Rx2 cw 2 Unit power constraint CN(, 1) Y 1 [t] =h 11 X 1 [t]+h 12 X 2 [t]+z 1 [t] Y 2 [t] =h 22 X 2 [t]+h 21 X 1 [t]+z 2 [t] 13

14 Modeling Burstiness/Intermittence X 1 [t] Y 1 [t] W 1 Tx1 h 11 h 12 Rx1 cw 1 X 2 [t] Interference Channel h 21 Y 2 [t] W 2 Tx2 h 22 Rx2 cw 2 Random Activity State Controls the presence of interference 14

15 Bursty Interference Channel: Two Models Intermittent Interference: motivated by the MAC layer Bursty Traffic: motivated by the Network layer 15

16 Part I: Bursty Interference Channel with Feedback Joint work with S. Diggavi, C. Suh, P. Viswanath Intermittent Interference 16

17 Model Y 1 [1 : t 1],S[1 : t 1] X 1 [t] Y 1 [t] h 11 W 1 Tx1 h 12 Rx1 cw 1 S[t] S[t] X 2 [t] h 21 Y 2 [t] W 2 Tx2 h 22 Rx2 cw 2 Y 2 [1 : t 1],S[1 : t 1] {S [t ]}: i.i.d. Bernoulli Ber(p) process Y 1 [t] =h 11 X 1 [t]+h 12 (S[t]X 2 [t]) + Z 1 [t] Y 2 [t] =h 22 X 2 [t]+h 21 (S[t]X 1 [t]) + Z 2 [t] Encoding: X i [t] =(W f i, Y i [1 : t 1],S[1 : t 1]) 17

18 Generalized Degrees of Freedom For better illustration, let us focus on the symmetric setting: h 11 2 = h 22 2 = SNR, h 21 2 = h 12 2 = INR INR INR SNR SNR Generalized degrees of freedom: d := Achievable Rate under Interference Interference Free Capacity R 2 (R sym,r sym ) d( ) = lim SNR!1 R sym log INR, with fixed := log SNR log SNR capacity region R 1 GDoF: a function of - strength of interference - probability of interference p Gain in GDoF multiplicative gain in capacity 18

19 Baseline d( ) Non-bursty, no-feedback Non-bursty, feedback Bursty, p=.5, no-feedback 1 No gain in the regime 2 2 for 3, 2 1 p 2 Can Feedback Really Help? DoF? [Suh & Tse IT11] [Etkin et al IT8] [Khude et al ISIT9]

20 In the regime 2 2, 2 3 (moderate to strong interference) Feedback in non-bursty case No gain in GDoF and DoF Exploiting intermittence without feedback No gain in GDoF and DoF 2

21 Baseline d( ) Non-bursty, no-feedback Non-bursty, feedback Bursty, p=.5, no-feedback 1 No gain in the regime 2 2 for 3, 2 1 p 2 Can Feedback Really Help? DoF? [Suh & Tse IT11] [Etkin et al IT8] [Khude et al ISIT9]

22 One- Bit Feedback Increases DoF Phase Fresh Transmit as if there is no interference X1 L1(X1,X2) State No interference Rx Operation Both Decode Tx Operation Stay in Phase F Interference Hold Phase Retransmit Retransmit the unresolved symbol State No interference Interference Rx Operation Both Decode Both Decode (exploit side info.) Jump to Phase R Tx Operation Back to Phase F Back to Phase F X2 DoF = 1 1 p F L2(X1,X2) DoF = p 1 DoF = 1 R Stationary Distribution: (F) = 1 1+p, (R) = p 1+p =) DoF = 1 1+p 22

23 Synergetic Bene_it of Feedback d( ) Non-bursty, no-feedback Non-bursty, feedback Bursty, p=.5, no-feedback Bursty, p=.5, feedback 1 No gain in the regime 2 2 for 3, 2 1 p 2 [Khude et al ISIT9] 1 1+p [Suh & Tse IT11] [Etkin et al IT8]

24 Harnessing Output Feedback Weak interference regime Analog interference refinement Strong interference regime Interference refinement with structured codes Very strong interference regime Opportunistic relaying with structured codes 24

25 Part II: Bursty Interference Channel with a Relay Joint work with S. Kim, C. Suh Bursty Traffic 25

26 Model M Tx antennas S t 1 Y R (t) Z R (t) S t L Relay antennas Enc Relay R X R (t) N Rx antennas W 1 Enc Tx11 X 1 (t) Y 1 (t) Dec Rx11 Ŵ 1 S t 1 S 1 (t) Z 1 (t) W 2 Enc Tx22 X 2 (t) Y 2 (t) Dec Rx22 Ŵ 2 S 2 (t) S := (S 1,S 2 ) Z 2 (t) Y 1 (t) =H 11 (S 1 (t)x 1 (t)) + H 12 (S 2 (t)x 2 (t)) + H 1R X R + Z 1, Y 2 (t) =H 21 (S 1 (t)x 1 (t)) + H 22 (S 2 (t)x 2 (t)) + H 2R X R + Z 2, Y R (t) =H R1 (S 1 (t)x 1 (t)) + H R2 (S 2 (t)x 2 (t)) + Z R. {S1 [t]} {S 2 [t]}: i.i.d. Bernoulli Ber(p) processes 26

27 In- Band Relay Increases DoF Bursty P2P M Ber(p) N Tx Rx d = p min (M,N) = pn for M sufficiently large Adding a relay L Relay Ber(p) M N Tx Rx d =min{p min (M,N + L),pmin (M + L, N)+(1 p)min(l, N)} = pn + min{pl, (1 p)min(l, N)} for M sufficiently large 27

28 d N pn N L DoF increase is linear in L, # of relay antennas DoF is boost by up to p 1 times 28

29 Interference- Free Communication For two-user bursty interference channel with a relay, main focus is on getting interference-free DoF p [,1) Sufficient condition$ $ $ $ Necessary condition 2M apple N or M 2N + L and L 2N 2M apple N or M 2N + L and L 2N or or M 2N + L and 3L apple N M 2N and 3L apple N 29

30 Cooperative Zero- Forcing 4 a 5 + b t sent received a 1 + b 1 a 1 + b 1 a 1 + b 1 b 5 a 5 Relay 4 L = a 9 a 5 a 5 a b 1 b 5 a a 1 + b 1 +a 1 + b a Tx 1 Rx1 a 3 b 1 a 7 +a 1 + b 1 +a 1 + b a 1 5 a 5 a 9 b 9 b 1 b 11 b 12 a 1 b 9 sent b 1 b 11 b 12 a 1 b 9 b 9 b 5 b 6 b 7 b 8 a a 1 b 5 b 1 b 1 b1 b 2 b 3 b 4 Tx 2 t (S 1,S 2 ) 1 (1, 1) 2 (, 1) 3 (1, ) 4 (, ) Rx 2 M =7 N =3 a 4 b 2 + a 1 b 3 b 4 a 1 + b 1 b 6 received +a 1 + b 1 b 7 +a 1 + b 1 b 8 +a 1 + b 1 a 8 +a 1 + b 1 a 5 +a 1 + b 1 a 1 +a 1 + b 1 a 1 + b 1 a 5 + b 5 a 5 + b 5 a 5 + b 5 a 5 + b 5 a 5 + b 5 a 5 + b 5 3

31 Takeaway 1 Interaction (feedback and cooperation) is more helpful in bursty communication 2 Harnessing delayed state information and interaction boost up capacity greatly 31

32 Since interaction is so useful, please give us feedback and let us collaborate! Website: 32

33 Thank You! 33