The next generation wireless communication systems bring along new challenges, since the degrading factors such as fading and multi-user interference become harder to deal with as the number of users and the bandwidth requirements increase. However, the propogative and time varying nature of the wireless channels also gives rise to the concept of diversity, which can be carefully exploited to the network’s advantage.
In this talk, we provide a basic treatment of some recent and some not so recent results on two main approaches that are used to overcome fading and interference, by exploiting the inherent diversity of the wireless channel: power control, and user cooperation.
We present some preliminaries on the capacity of fading multiple access channels, and the optimal power control for these channels. We review the concept of bidirectional user cooperation, based on block Markov encoding and backward decoding. We demonstrate that cooperation and optimal power control, when used jointly, lead to significantly improved rates, and yield some guidelines for cross layer design: the optimal policy also dictates when and how the users should transmit/relay signals.
We then extend the results from the scalar MAC to an OFDMA channel, by propos- ing the so called inter-subchannel cooperative encoding which allows the users to share the same subchannels. Combined with the additional diversity created by the orthogo- nal subchannels in OFDMA, the free side information supplied by the wireless channel leads to even larger rate improvements, if we also allocate the power optimally across subchannels, cooperative codewords, and fading states.
Nov 16 Wednesday at 14.40, FENS L058