Power allocation, rate, and coverage for relay-assisted downlink data transmission

The coverage of a base station terminal (BST) in a cellular network can generally be increased through the use of a relay node within the cell boundary. We consider the downlink for a single, one-dimensional cell with a relay node, or access point (AP), which serves a separate set of (non-cellular) users (e.g., corresponding to a WiFi system). The BST and AP jointly allocate available power across users and the BST-AP link to maximize the sum data rate across all cellular and AP users. Two relay schemes are considered: (i) the information flows to the cellular users served by the relay are jointly encoded and transmitted from the BST to the AP; and (ii) the preceding information flows are transmitted in parallel from the BST to the AP. We give an upper bound on the increase in rate provided by the AP, which depends on the relative powers and bandwidths available to the BST and AP. Although the increase in total rate provided by sharing AP resources is typically modest, it can provide a more equitable rate distribution across cellular users, and extend the coverage of the BST.