On the Capacity of Slotted Aloha Based Multi-Hop Virtual MIMO Systems

The performance of multi-hop Virtual Multiple-Input-Multiple-Output (V-MIMO) systems, when Slotted Aloha is used to select the radio resource at each hop, is investigated. Source, destination and relaying nodes, cooperate with neighboring devices (distributed according to a Poisson Point Process) to exploit spatial diversity by means of the concept of Virtual Antenna Array (VAA). Performance is evaluated in terms of outage probability, defined as the probability that the capacity between source and destination is smaller than a given threshold. It is computed as a function of the density of cooperating nodes, and the number of relaying VAAs. It is shown that depending on the level of required capacity, the optimum number of slots per frame in the slotted structure may differ. The performance degradation with Slotted Aloha with respect to a deterministic centralised re-use of radio resources, is assessed.