It also depends on whether rate can be adaptive or constant, as well as whether or not service outage can be tolerated. Our recent results in this area include investigating capacity or capacity regions of fading broadcast channels, fading multiple access channels, broadcast channels with intersymbol interference and colored noise, and multiantenna channels with covariance feedback. We are also investigating capacity limits of ad-hoc networks with both a finite and asymptotically large number of nodes. We have investigated adaptive CDMA techniques for voice and data users. The data users adaptively vary their rate using multiple spreading gain, multiple codes, or variable signal constellations.
Results indicate that the variable spreading gain approach achieves the highest throughput.
We are currently investigating extensions of this work to incorporate power control and multiple classes of users. Turbo Codes and Iterative Decoding Turbo codes have created much excitement in the research community due to their exceptional performance in AWGN channels. Our work in this area is investigating adaptive turbo coded modulation, turbo codes for multiantenna systems, and turbo coded CPM modulation. Multiantenna systems Multiple antennas are known to significantly increase the capacity of wireless systems. We are investigating multiple facets of using multiple antennas in a wireless system design.