Creating and exploiting diversity in wireless systems: a signal processing perspective

Diversity techniques have a critical role to play in counteracting the effects of signal-to-noise ratio variation due to multipath-propagation in wireless communication systems. We give an overview of some key ways in which computationally efficient signal processing algorithms can be used at the transmitters and receivers of multiuser communication systems to realize effective forms of diversity. Such diversity is achieved by, in effect, spreading the transmission of symbols spectrally, temporally, and/or spatially to within the limits imposed by bandwidth, delay, and other physical system constraints. We discuss how both recently introduced spread-signature CDMA protocols and suitably designed multiple-element transmitter antenna arrays can be used to realize spreading of this type. All such techniques have the characteristic that they improve both average and worst-case performance, and can be used in conjunction with-or as an alternative to-coding in such systems