Uplink Achievable Rate and Power Allocation in Cooperative LTE-Advanced Networks

Abstract

This paper studies the achievable rate and power allocation to improve the uplink (UL) spectrum efficiency in a Long-Term Evolution Advanced (LTE-A) cooperative cellular network with the deployment of Type-II in-band decode-and-forward (DF) relay stations (RSs). The physical-layer UL transmission technology is based on single-carrier frequency-division multiple access (SC-FDMA) with frequency-domain equalization (FDE). Different from the downlink (DL) orthogonal FDMA system, signals on all subcarriers in the SC-FDMA system are transmitted sequentially rather than in parallel; thus, the user's achievable rate is not simply the summation of the rates on all allocated subcarriers. Moreover, each user equipment (UE) device has its own transmission power constraint instead of a total power constraint at the base station in the DL case. Therefore, the UL resource allocation problem in the LTE-A system is more challenging. To this end, we first derive the achievable rates of the SC-FDMA system with two commonly used FDE techniques, namely, zero-forcing (ZF) equalization and minimum-mean-square-error (MMSE) equalization, based on the joint superposition coding for cooperative relaying. We then propose optimal power allocation schemes among subcarriers at both the UE and RS to maximize the overall throughput of the system. Both theoretical analysis and numerical results demonstrate that our proposed power allocation schemes can drastically improve system throughput.