Diversity and Multiplexing: A Fundamental Tradeoff in Multiple-Antenna CHannels

Authors:

• Lizhong Zheng; Tse, D.N.C.;

Complete Citation

Lizhong Zheng; Tse, D.N.C., "Diversity and multiplexing: a fundamental tradeoff in multiple-antenna channels," Information Theory, IEEE Transactions on , vol.49, no.5, pp. 1073-1096, May 2003 doi={10.1109/TIT.2003.810646}

Abstract

Multiple antennas can be used for increasing the amount of diversity or the number of degrees of freedom in wireless communication systems. We propose the point of view that both types of gains can be simultaneously obtained for a given multiple-antenna channel, but there is a fundamental tradeoff between how much of each any coding scheme can get. For the richly scattered Rayleigh-fading channel, we give a simple characterization of the optimal tradeoff curve and use it to evaluate the performance of existing multiple antenna schemes.

Annotations

This paper investigates the theory behind two different potentail benefits from MIMO in a wireless channel.

The first potential benefit is spacial diversity, this is the diversity you get from having multiple antenna (and hence paths) from the sender and receiver. Ideally the antennas are placed a some multple of wavelength of the transmission frequency apart (1 wavelength ~= 4.5in). Otherwise the distance between the nodes is not considered to be significant enough to make much difference. Spacial diversity will give reliability.

The next is multiplexing streams across the various send/receive antenna's. This will allow for greater transmission rates as more bits per hertz is transmitted over the same channel. This paper was interesting to me because it is one of the first to consider the tradeoff between the two models, where as previous research just looked at the maximum benefit in terms of reliability or in terms of multiplexing.

They find that there is not a linear relationship, but that the relationship is shaped somewhat like the curve of f(x) = 1/x. Which means that if you optimize for both diversity and multiplexing you will get substantially less benefit then you optimize for one or the other.

-- DavidSalyers - 14 Nov 2007