Capacity scaling laws in MIMO wireless networks

Authors

Rohit U. Nabar, Özgür Oyman, Helmut Bölcskei, and Arogyaswami J. Paulraj

Reference

Allerton Conference on Communication, Control, and Computing, Monticello, IL, pp. 378-389, Oct. 2003, (invited paper).

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Abstract

The use of multiple antennas at both ends of a wireless link, popularly known as multiple-input multiple-output (MIMO) wireless, has been shown to o ffer significant improvements in spectral efficiency and link reliability through spatial multiplexing and space-time coding, respectively. This paper demonstrates that similar performance gains can be obtained in wireless relay and adhoc networks employing terminals with MIMO capability. In the relay case a source terminal communicates with a destination terminal assisted by multiple relay terminals. For this scenario, assuming that transmitter and receiver employ M antennas and operate in spatial multiplexing mode, we show that the network capacity scales as C = (M/2)log(KN)+O(1) for a large number of relay terminals K and large number of antennas N>=M at each of the relay terminals. For fi nite N>=M, we fi nd that capacity scales as C = (M/2)log(K) + O(1). Furthermore, we propose an asymptotically optimal architecture which requires that each of the relay terminals knows its backward and forward channels. Our results are extended to the adhoc case where L source-destination pairs communicate concurrently in spatial multiplexing mode through the same set of relay terminals and sum-capacity is shown to scale as C = (LM/2)log(KN) + O(1) for large K and N and C = (LM/2)log(K) + O(1) for fi nite N>=LM. Finally, we establish the importance of stream separation and coherent combining at the relay terminals, in the absence of which we show that for any N, asymptotically in K, C = (M/2)log(SNR) + O(1), demonstrating that the number of relays does not enter the scaling law.

Keywords

Wireless networks, MIMO, relay channels, capacity, protocols


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Copyright Notice: © 2003 R. U. Nabar, Ö. Oyman, H. Bölcskei, and A. J. Paulraj.

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