User relay with channel coding

Abstract

User relaying system is a cooperative communication scheme between users in order to increase achievable rates of the destination user in downlink network. Using user relay system expands the achievable rate region of general broadcast channel (BC) by using zero-forcing dirty paper coding (ZF-DPC) which is known as an optimal transmission scheme for the downlink channel. In this thesis, we analyze the performance of the user relaying system with applying channel coding methods. First, we calculate outage probability and show that the user relaying system outperforms general BC in terms of reliability as well. However, the mobile users have to operate as a relay in user relaying system, processing complexity or overhead of data forwarding causes severe problem. Channel coding is a practical method to overcome fading effect. We analyze the necessity of the channel coding at the relaying user because the forwarding data at the relaying user is already encoded for source to destination channel once. We simulate with specific encoding scenario for user relaying system by using convolutional code and turbo code both and study the necessity of the channel coding at the relay. Since only the part of the data for user 2 is transmitted by relaying user, re-encoding at the relay will break the balancing of the encoded codeword. So single encoding at the source performs better than separate encoding at the source and relay. Therefore, in this thesis, we conclude that it is not necessary to re-encode at the relaying user in the user relaying system for improving BER or FER performance.