Effective Carrier Sensing in CSMA Networks under Cumulative Interference

Transcription

1 INFOCOM 2010 Effective Carrier Sensing in MA Networks under Cumulative Interference Liqun Fu Soung Chang Liew Jianwei Huang Department of Information Engineering, The Chinese University of Hong Kong

2 Introduction Broadcast nature of wireless media interference Interference-safe (collision free) transmission MA protocol: coordinate with carrier sensing Sense before transmit Operate interference-safe transmissions in MA networks? Effective Carrier Sensing in MA Networks under Cumulative Interference 2

3 Overview Requirement of Interference Safe in MA Network Real Interference in Practice: Cumulative interference safe carrier-sensing range Implementation: IP Incremental-Power Carrier Sense Incremental Power range concept IP can improve spatial reuse and network throughput Effective Carrier Sensing in MA Networks under Cumulative Interference 3

4 Safe carrier-sensing range Under pair-wise interference model [1] The interferences are considered one by one No collision between any pair No collision overall Safe carrier sensing range requirement For example, if γ = 8 and α = 3, 1 α Safe R = ( γ + 2) d pairwise then Safe R = 4d pairwise [1] L.B. Jiang and S.C. Liew, Hidden-node Removal and Its Application in Cellular WiFi Networks IEEE Trans. Veh. Technol. Vol. 56. no. 5, Sep Effective Carrier Sensing in MA Networks under Cumulative Interference 4

5 Safe carrier-sensing range However, in practice Interference is cumulative 1 Safe R = ( γ α + 2) d is too optimistic pairwise γ = 8, α = 3 Safe R = 4d pairwise 3 Pt ( d ) ( 6 ) + ( 2 ) SIR( R1 ) = = < γ 3 3 P d P d t t Not sufficient to prevent collisions under cumulative interference Effective Carrier Sensing in MA Networks under Cumulative Interference 5

6 Under cumulative interference model Theorem: Setting the carrier sensing range as 1 α, where Safe Rcumulative = ( K + 2) d 2 1 K = 6γ 1+ 3 α 2 is sufficient to ensure interference-safe transmissions in MA networks under cumulative interference model. γ = 8 α = 3, Worst-case interference in an infinite large network The safe carrier sensing range need to be increased Safe R = 4d Not amendable with current carrier sensing in P P is an absolute power: consists of the sum total powers Detect a power compare with a power threshold pairwise Does not contain enough information for all the required distances α Safe R = 6.96d cumulative Pth Effective Carrier Sensing in MA Networks under Cumulative Interference 6

7 Implementation: IP IP (Incremental-Power Carrier Sense) The detected power is a function of time Key idea: incremental power required distance information Check every increment with a power threshold P () t Separate the interference one by one Interference safe : ( ) P = P Safe R th t cumulative α Effective Carrier Sensing in MA Networks under Cumulative Interference 7

8 Comparison current carrier sensing in v.s. IP Absolute power v.s. incremental power Current carrier sensing reduces spatial reuse The location of the third concurrent link Current IP α ( ) ( ) P ( T ) = Pd T, T + Pd T, T l 3 3 t 3 1 t 3 2 ( ) = 2 Pd TT, P t 3 1 α th α ' ( ) ' ( ) α Δ P3 ( t1) = Pt d T3, T1 Pth α Δ P3 ( t2) = Pt d T3, T2 Pth l 3 ' The separation between transmitters increases progressively ΔP ( t ) 3 1 ΔP ( t ) 3 2 Effective Carrier Sensing in MA Networks under Cumulative Interference 8

9 Throughput Improvement Ideal packing of transmitters: improve by 60% 3 2 unit area: ( ) 2 Safe R cumulative Effective Carrier Sensing in MA Networks under Cumulative Interference 9

10 Conclusion Propose the concept of the safe carrier sensing range under the cumulative interference model Propose a new carrier sensing mechanism, IP, to implement accurately IP is the bridge between theoretical analysis and the real protocol in practice IP can improve spatial reuse and network throughput. Effective Carrier Sensing in MA Networks under Cumulative Interference 10

11 Thanks!