Opportunistic Large Array Concentric Routing Algorithm (OLACRA) over Wireless Fading Channels

An opportunistic large array (OLA) is a group of simple, inexpensive relays or forwarding nodes that operate without any mutual coordination, but naturally fire together in response to energy received from a single source or another OLA. Therefore, OLAs do a simple form of cooperative transmission. The opportunistic large array concentric routing algorithm (OLACRA) is an energy efficient upstream routing algorithm that has been proposed for OLA-based networks and has been shown to save over 70 percent of the energy in comparison to whole network OLA flooding for the non-faded channel. This paper analyzes the performance of OLACRA over the Rayleigh flat-fading channel. Distributed delay diversity using direct sequence spread spectrum (DSSS) waveforms is proposed to obtain diversity in such channels. Each node in an OLA chooses its transmission time randomly from a limited set of choices, thereby creating a limited set of orthogonal channels, which are then combined with RAKE receivers. Performance comparison is made with orthogonal non-faded channels. Simulations results demonstrate that the performance of OLACRA over the flat-fading channel approaches the performance of the deterministic channel for a diversity order of 4.