Cross-layer power allocation scheme for two-way amplify-and-forward relaying system

Two-way relaying can considerably improve spectral efficiency in relay-assisted bidirectional communication. However, most existing works focus on physical layer to exploit its resource optimizes. The benefits and flexible structures of two-way relaying on datalink layer are much less investigated. So in this paper, the cross-layer optimization for amplify-and-forward (AF) two-way relaying system is studied and an optimal power allocation scheme is proposed. Our goal is to find the optimal power allocation factors to maximize the weighted sum effective capacity of two sources in the physical layer while guaranteeing the statistical delay quality-of-service (QoS) requirement for each source in the datalink layer. This statistical delay QoS requirement is characterized by the QoS exponent θ, which is the only requested information exchanged between the physical layer and the datalink layer in our cross-layer design based scheme. By integrating the concept of effective capacity, the cross-layer optimization problem is equivalent to a weighted sum effective capacity maximization problem. This problem is formulated into a convex optimization problem, and an algorithm is presented to solve this problem. Simulation results show that proposed optimal power allocation scheme can achieve better weighted sum effective capacity than equal power allocation scheme and direct transmission scheme, and the relay transmission combined with direct links can get the max weighted sum effective capacity.