Iterative Waterfilling for Frequency Selective Gaussian Interference Channels

Mr. Seong-Taek Chung

Stanford University, Palo Alto, CA, USA

Thursday, March 27th, 2:00 PM, ENS 637

Abstract

Recently, frequency selective Gaussian interference channels have excited enormous interest in both wireless and wireline communication systems. In order to satisfy a high-speed data-rate demand, more bandwidth is allocated per user; hence, the channels are frequency selective. Furthermore, coordinating among physically separated users can be quite expensive. Sometimes coordination is impossible if users are supported by different service providers or the channels are changing very fast.

For a single-user frequency-selective channel, the data rate maximization scheme has been found under a given total power budget. Several previous results are also known for a multi-user frequency-selective channel. However, most previous work assumes signal coordination at either the transmitter or the receiver. Hence, these results are not viable in interference channels where no coordination is allowed. The capacity-achieving scheme is not yet known for the general Gaussian interference channel. When the interference is strong, the capacity-achieving scheme is known, but impractical to implement. Hence, We consider a pragmatic transmission scheme, Iterative Waterfilling (IW) technique.

The power allocation in IW is observed to converge for all channel scenarios; however, a proof for the convergence has not yet been provided. A sufficient condition is provided under which the power allocation process in IW is guaranteed to converge. Furthermore, when the power allocation process in IW is modeled as a game, IW can be analyzed from a game theoretic viewpoint. In particular, it is shown that a Nash equilibrium always exists in the game. A condition for the uniqueness of the Nash equilibrium is also found. Lastly, an enumeration algorithm is provided so that all Nash equilibrium points can be derived numerically.

Next we compare the performance of IW to that of the optimal scheme for general channel scenarios. IW is composed of a suboptimal multi-user coding scheme and a suboptimal multi-user power allocation scheme. Therefore, the performance is compared in two different aspects. First, IW is compared to the capacity-achieving scheme, which is composed of the optimal coding scheme and power allocation scheme. Secondly, we compare IW to the scheme in which the suboptimal coding in IW is used and the optimal power allocation with respect to the suboptimal coding is adopted.

Biography

Seong Taek Chung received the B.S. degree with honors in electrical engineering from Seoul National University, Korea, in 1998, and the M.S. degree in electrical engineering from Stanford University, Stanford, CA, in 2000. He is expecting the Ph.D. degree in electrical engineering from Stanford University in June, 2003.

During the summer of 2000, he was an intern with Bell Laboratories, Lucent Technologies, where he worked on multiple antenna systems. His general research interests lie in the areas of communication theory and information theory. His recent work has focused on the multi-user communication theory when no coordination among users is allowed.

A list of Wireless Networking and Communications Seminars is available at from the ECE department Web pages under "Seminars". The Web address for the Wireless Networking and Communications Seminars is http://signal.ece.utexas.edu/seminars