VIEWS: 1 PAGES: 22 POSTED ON: 6/21/2013
An Optimal Link Layer Model for Multi-hop MIMO Networks Yi Shi Virginia Tech, Dept. of ECE (with Jia Liu, Canming Jiang, Cunhao Gao, and Thomas Hou) IEEE INFOCOM 2011 – Shanghai, China MIMO l Multiple antennas at both transmitter and receiver l Benefits n Increase throughput, mitigate interference n Without additional bandwidth or transmit power IEEE INFOCOM 2011 2 Current Status l Two modeling approaches n Matrix-based model n Degree of freedom (DoF)-based model l Matrix-based model l DoF-based model n Accurate: Characterize MIMO n Simple: Use DoF to identify a channel by a matrix feasible rate region n High complexity: Due to n Not optimal: Existing DoF- matrix manipulations based models cannot achieve the maximum rate region An optimal DoF-based model for multi-hop MIMO networks IEEE INFOCOM 2011 3 ZFBF Scheme l DoF-based model is for the zero-force beam-forming (ZFBF) scheme n An effective MIMO technique l Two benefits associated with ZFBF n Spatial multiplexing (SM) uEnables multiple data streams on the same link n Interference cancellation (IC) uEnables more links to transmit at the same time IEEE INFOCOM 2011 4 Spatial Multiplexing – An Example 1 0 0 1 IEEE INFOCOM 2011 5 Interference Cancellation – An Example 0 IEEE INFOCOM 2011 6 Matrix-Based Model l IEEE INFOCOM 2011 7 Troubles with Matrix-Based Model l Networking research using matrix-based model has very limited success IEEE INFOCOM 2011 8 Understanding DoF l DoF is associated with each transmit/receive vector l Initially, each vector has no constraint n Each element in a vector can be adjusted to optimize network performance n Feasible region of this vector includes all possible values n # of DoFs of this feasible region is equal to # of elements in a vector (or # of antennas at the node) IEEE INFOCOM 2011 9 Understanding DoF Consumption - An Example - l IEEE INFOCOM 2011 10 Understanding DoF Consumption - A Second Example - l # of consumed DoFs due to a set of constraints is equal to # of independent constraints IEEE INFOCOM 2011 11 DoF Consumption by SM l IEEE INFOCOM 2011 12 DoF Consumption by IC l Interference can be cancelled by either transmit or receive vector l Which vector? n To answer this question, we need an order among vectors IEEE INFOCOM 2011 13 IC DoF Consumption Under An Order l IEEE INFOCOM 2011 14 Vector-Level to Node-Level - A Transformation - l IEEE INFOCOM 2011 15 Total DoFs Consumed by SM & IC l Is the total number of consumed DoFs a simple sum of those by SM and IC? n The answer is Yes! n Show that there is no dependency among SM and IC constraints IEEE INFOCOM 2011 16 DoF-Based Model l Half-duplex constraint l Constraints for node activity l Ordering constraints IEEE INFOCOM 2011 17 DoF-Based Model (Cont’d) l DoF consumption constraints IEEE INFOCOM 2011 18 Matrix-Based Model vs. New DoF-Based model l Consider a three -link network l Two models achieve the same rate region l Complexity comparison IEEE INFOCOM 2011 19 An Application Example l Objective: Maximize the sum of weighted session rates l A linear optimization problem n Similar complexity to that for single-antenna networks IEEE INFOCOM 2011 20 Node Ordering Results in Each Time Slot IEEE INFOCOM 2011 21 Summary l The matrix-based MIMO model is too complex for network performance analysis n Results based on the matrix-based model are very limited l Developed an optimal DoF-based model n Retains the similar simplicity as single-antenna networks n Offers the same achievable rate region as that by the matrix-based model l Showed how to use our optimal DoF-based model for a multi-hop MIMO network problem IEEE INFOCOM 2011 22
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