Joint optimization of cooperative diversity and spatial reuse in multihop hybrid cellular/ad hoc networks

Abstract

Advanced cellular networks are expected to use multihop transmission (relaying) in the cells for the connection between the users and the base station BS as well as for peer to peer connection between two users within the same cell. Therefore they become a mixture of cellular and ad hoc networks that will be referred to as cellular/ ad hoc or CAH network. We apply a conventional resource reuse scheme used for cellular networks for inner partitioning of each cell in order to increase the number of concurrent transmissions in the system. This partitioning can be considered as a special form of surface tessellation technique used in conventional network information theory so that a number of results from that area can be adapted for the analysis of peer to peer communications (Ad Hoc segment of the network). For the communication between the users and BS the cell partitioning enables the use of a specific Round Robin MAC protocol within the cluster of inner cells making the system feasible for implementation. For multihop cellular segment of the system in this paper we present a joint optimization of cooperative diversity and spatial reuse which maximizes the throughput in the network. The increased number of concurrent transmissions, enabled by spatial cell partitioning, increases the system throughput but also increases the level of interferences that reduces the capacity of simultaneously used links in the network. The diameter of inner cells determines the relaying hop range and the amount of interlink interference. All transmissions are recorded by the neighboring receivers and combined in a cooperative diversity transmission. The increased number of hops increases the diversity order but at the same time reduces the throughput per user since the network capacity has to be shared between the increased number of users. By introducing a proper utility function we can simultaneously optimize the system throughput, power consumption and packet delivery delay, as a function of relaying range. The optimum relaying range defines the optimum inner cell partitioning and the spatial reuse in the network. By controlling the transmission power in the optimization process, we directly control the probability of intercept in the system.