Modulation-Level Coding for Wireless Network Coding

Abstract

When intermediate nodes encode messages in wireless network coding, a question arises: Which modulation scheme should be used to broadcast the encoded message? Should it be limited to a receiver with a low modulation-level requirement to maintain an acceptable BER or should it be broadcasted at the desired modulation-level of a receiver with a higher rate requirement? Such conflicting requirements typically arise when one receiver has a low channel capacity while the other has a higher one.

Recently, the deployment of network coding in wireless networks has attracted significant research attention, mainly due to the capability of network coding to improve throughput and save energy. However, a challenging problem in wireless network coding is to determine which modulation scheme to employ in the broadcast phase when receivers have diverse modulation scheme requirements, e.g., Node A may desire an 8-PSK modulation scheme on the broadcasted signal, while Node B may require a QPSK on the same broadcasted signal.

In this thesis, we introduce a new coding scheme aimed at solving the diverse modulation problem. The scheme is based on coding information such that a receiver with a high modulation-level requirement can decode more information from a broadcasted signal than a receiver with a low one. Several codes have been designed for various combinations of modulation schemes. Analytical studies have been carried out to quantify the performance of the proposed scheme. Extensive simulations have been conducted to demonstrate the performance of the proposed scheme and validate the accuracy of our analytic model.