Capacity scaling laws in MIMO wireless networks


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


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

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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.


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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