Power Allocation and Coverage for a Relay-Assisted Downlink with Voice Users

We study the downlink coverage of a base station terminal (BST), which has access to a relay node. Continuing a previous study in which the BST is assumed to provide a variable-rate data service, here we assume that each active user requires a target data rate, corresponding to a voice type of service. The relay is assumed to serve a separate set of (non-cellular) users, corresponding to a WiFi Access Point (AP). A one-dimensional model is considered in which cellular and non-cellular users are uniformly distributed along a line. The BST and AP jointly allocate available power across users and the BST-AP link to maximize the total number of users served. We characterize the optimized set of active cellular users served by the BST directly and the AP relay, and the non-cellular users served by the AP. We also give a closed-form upper bound on the increase in the total number of users provided by the relay as a function of user densities and path loss exponents. Our results show that depending on the distance between the BST and the AP, the addition of a relay gives a modest increase in the total number of active users.