Power allocation for two-cell two-user joint transmission

In this paper, we develop a power allocation scheme for the downlink of a two-cell two-user joint transmission system. The objective is to maximize the sum rate under per-cell power constraints. We study a worst case scenario where the carrier phases between the two base stations are un-synchronized, so that joint transmission must be performed without precoding. The derived power allocation scheme is remarkably simple, i.e., each cell transmits with full power to only one user. Note that joint transmission is still possible, when two cells select the same user for data transmission. Moreover, we prove that, in this scenario, the joint transmission case happens with higher probability when the maximum transmit power is high, or the two users are in the overlapped cell-edge area

Power Allocation for Multi-Point Joint Transmission with Different Node Activeness

We study the power allocation problem for the downlink of a cooperative system with different node activeness, i.e., each receiving node requests for data transmission according to a certain probability. Data symbols of the active nodes are jointly transmitted from cooperative transmission points using zero-forcing precoding. The problem is cast in form of maximizing the ergodic achievable rate subject to per-transmit-point average total power constraints. The derived power allocation indicates that depending on the channel conditions and receiving nodes' activation probability, the optimal solution takes the form of either greedy power allocation or power sharing allocation

On the Impact of Control Channel Reliability on Coordinated Multi-Point Transmission

In the heterogeneous networks (HetNets), co-channel interference is a serious problem. Coordinated multi-point (CoMP) transmission has emerged as a powerful technique to mitigate co-channel interference. However, all CoMP techniques rely on information exchange through reliable control channels, which are unlikely to be available in HetNets. In this paper, we study the effect of unreliable control channels, consisting of the access links and backhaul links, on the performance of CoMP. A control channel model is introduced by assigning link failure probability (LFP) to backhaul and access links for the cooperative clusters. Three CoMP architectures, namely the centralized, semi-distributed and fully distributed are analyzed. We investigate the probability of deficient control channels reducing quality of service, and impeding transmission. General closed-form expressions are derived for the probability of a cooperative transmission node staying silent in a resource slot due to unreliable control links. By evaluating the average sum rate of users within a CoMP cluster, we show that the performance gains offered by CoMP quickly diminish, as the unreliability of the control links grows