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Title Single Relay Selection for Two-Hop Cooperative Communications under Interference Environments
Degree MS
Author Binh Van Nguyen
Advisor Kiseon Kim
Graduation Date 2012.08.24 File
    Date 2013-09-03 22:18
  Cooperative communications (CC) utilizes the broadcast nature of wireless signals by observing that a source signal intended for a particular destination can be ”overheard” at neighboring nodes. These nodes, called relays, process the signals they overhear and transmit toward the destination. In other words, CC groups wireless terminal’s antennas to create virtual antenna arrays. Therefore, CC helps wireless systems to achieve some benefits related to multiple-input multiple-output (MIMO) technique, such as the improvement in coverage, capacity, cell edge throughput. There are two common relaying protocols, amplify-and-forward (AnF) and decode-and-forward (DnF). In the former protocol, each relay receives a noisy version of the signals transmitted by the source. The relays then amplify and and retransmit this noisy version toward the receiver. In the latter protocol, instead of amplifying the overheard signals the relays decode, re-encode, and then transmit a noiseless version toward the destination. The destination combines the signals coming from the source and the relays, enabling higher transmission rates and robustness against channel variation due to fading.
  In cooperative communications, relay selection (RS) is a promising technique which has been attracted intensively investigation from researchers. Instead of using all potential relays, RS chooses the most proper relay to cooperate in source-destination transmission. Hence, RS reduces the system requirement in the number of orthogonal channels, synchronization, and the complexity at the receiver side while maintains the system performance. Relay selection principles are maximizing the received signal-to-noise-ratio (SNR), the transmission rate, the end-to-end throughput, and so on. Based on these principles, several RS criteria have been proposed: nearest neighbor, best harmonic mean, best worse channel. However, most of the existing works have been proposed intendedly for ideal configuration with no interference at all. Moreover, it has been shown that the presence of interference during relaying process significantly degrades the system performance. Therefore, in the thesis we investigate RS issue in interference environments. Using some approximation relations and exploiting the undesired signal coming to the destination during the first phase, we propose novel RS techniques that can improve the system performance in interference environments.
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