Innovative coding schemes for cooperative multihop radio systems

• Main Author: James, Ashish
• Other Authors: A S Madhukumar
• Format: Theses and Dissertations
• Language: English
• Published: 2012
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Wireless communication systems
• Online Access: http://hdl.handle.net/10356/50935
• Institution: Nanyang Technological University

Cooperative communication with its distributed structure is considered as a promising energy efficient paradigm for future green radio communications. In such systems, multiple wirelessly communicating devices cooperate with each other to create a network of wireless nodes with virtual antenna arrays. Such wireless networks with an omnidirectional antenna exhibit some distinct and interesting properties. The most pivotal one is that the transmissions are broadcast by nature which enables the nodes within its vicinity to overhear the transmissions. This enables the intermediate nodes to process the overheard information and cooperate in transmissions. However, the realization of such schemes for wireless multihop networks is challenging, owing to the lack of bandwidth efficiency and the coordination overheads required for reliably transmitting the information to the receiver. In this thesis, such challenges are tackled by analysing the wireless transmission properties from a different perspective. These properties are exploited to develop novel and unconventional solutions to enhance the spectral efficiency and reliability of such networks. The key aspect of exploiting the broadcast nature of transmissions to obtain information and co-ordinate actions implicitly i.e., without dedicated information exchange, is proposed in this context. The proposed scheme processes the implicit information to select the best transmitter, i.e., either source or relay, for the additional coded bits based on the quality of relaying. Such a scheme enhances the reliability as it ensures the availability of the correct information at the receiver for decoding. Two powerful rate-compatible codes namely, rate-compatible punctured convolutional (RCPC) codes and punctured low-density parity-check (LDPC) codes with inherent incremental redundancy features are analysed. The analysis is protracted to multihop networks which are emerging as a key concept with extended coverage and enhanced capacity. However, in practical heterogeneous networks relaying is not always beneficial due to the node locations. A location aware incremental relaying scheme with power allocation that dynamically makes the routing decisions to maximize the network capacity is proposed in this context. Using appropriate power allocation strategies, the proposed algorithm allocates entire power to the direct link when the propagation conditions are hostile at the relay. For all other cases, it allocates power equally and adapts the code-rate to make relaying beneficial.