Cooperative Communication Networks
an abstract by Mohammad Amir Khojastepour


The primary challenge in wireless networks, unlike wireline networks, is the existence of interference and channel variations (fading). Having more users at higher data rates means that current point-to-po9int networks will not scale. To engineer a scalable network, a new paradigm is needed to exploit different network characteristics. We show that cooperation between users in the network can effectively exchange possible interferences from other users for useful information.

In this thesis, we explore the problem of source and channel coding over wireless networks, ranging from theoretical information analysis to code design and practical implementation issues. We show that significant gains in throughput can be achieved through network coding. Despite the importance of the problem and the work already done in this area, little is known about network coding and the optimal choice of relaying function in the intermediate nodes. A clear example is the problem of optimal communication over the relay channel, the simplest form of a network, which has been an outstanding question for the last three decades.

In this thesis, we propose a new approach to network coding that improves upon the best-known coding schemes of many dB. Specifically, we develop two main coding techniques: the estimate-forward and the scale-forward coding schemes. We show that by using the new coding techniques, higher rates than those previously achieved are possible for the relay channel. In particular, the scale-forward scheme provides a fresh look at the current use of linear relaying functions. While the previous use of linear relaying functions has never achieved significant gain over existing techniques, the scale-forward coding scheme presents an extremely simple and implementable choice of linear relaying function whose achievable rate surpasses all previously known coding techniques for many cases of interest.

Furthermore, the new coding technique has proved its strength in the presence of channel variation, i.e., in the Rayleigh fading environment, which is the most commonly used model for the wireless channel. To this end, we derive the exact capacity of the ergodic fading relay channel for many channel conditions of interest, and also present a coding scheme which nearly achieves the universal minimum bound on outage probability for the block fading relay channel. This is the first capacity result for the wireless fading relay channel.