Wireless Network Cocast: Location-Aware Cooperative Communications with Linear Network Coding

In wireless networks, reducing aggregate transmit power and having even power distribution increase the network lifetime. The conventional direct transmission (DTX) scheme results in high aggregate transmit power and uneven power distribution. In conventional DTX, where mobile units directly transmit their information to a common destination, the distant mobile units require more transmit power to provide a comparable quality of service (QoS) to that of the closer ones. Consequently, high aggregate transmit power (the sum of all transmit power of individual mobile units) and uneven power distribution among the units exist in the network. These two issues result in low network lifetime, which is defined as the time until the first mobile unit dies. It is wellknown that diversity techniques such as time diversity, frequency diversity, and spatial diversity result in reduction of transmit power and thus can be used to improve network lifetime. Three location- aware cooperation-based schemes considered in this work are immediateneighbor cooperation (INC), maximal cooperation (MAX), and wireless network cocast (WNC) that achieve spatial diversity to reduce aggregate transmit power and even power distribution. Cooperative communication makes use of the broadcast nature of wireless transmission. Nodes in a network acting as relays can retransmit overheard information to a destination, where the intended information from the source signal and the relay signals is jointly detected. The distributed antennas among the relays are used to provide spatial diversity without the need to use multiple antennas at the source. Various cooperative diversity protocols have been proposed and analyzed. In decodeand- forward (DAF) protocol, each relay decodes the overheard information from the source, re-encodes it, and then forwards it to the destination. In amplify- and-forward (AAF) protocol, each relay simply amplifies the overheard signal and forwards it to the destination.