On the tightness of signal to noise ratio gain bound of maximum ratio transmission

Antenna array diversity is one of the most effective techniques to improve the performance of a wireless communication system in a fading environment. Especially in a mobile system, it is more practical to employ an antenna array at the base station rather than at the mobile units. We discuss the tightness of the upper bound on signal-to-noise ratio (SNR) gain in maximum ratio transmission in Lo (1999). It is proved that when the receiver antenna number is not more than two, the upper bound of SNR gain can be achieved. Otherwise, the upper bound of SNR gain can almost surely not be achieved.

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