Coordinated Multi-point (CoMP) transmission has long been known for its ability to improve cell edge throughput. However, in a CoMP cellular network, fixed CoMP clustering results in cluster edges where system performance degrades due to non-coordinated clusters. To solve this problem, conventional studies proposed dynamic clustering schemes. However, such schemes require a complex backhaul topology and are infeasible with current network technologies. In this paper, small power base stations (BSs) are introduced instead of dynamic clustering to solve the cluster edge problem in CoMP cellular networks. This new cell topology is called the diamond cellular network since the resultant cell structure looks like a diamond pattern. In our novel cell topology, we derive the optimal locations of small power base stations and the optimal resource allocation between the CoMP base station and small power base stations to maximize the proportional fair utility function. By using the proposed architecture, in the case of perfect user scheduling, a more than 150% improvement in 5% outage throughput is achieved, and in the case of successive proportional fair user scheduling, nearly 100% improvement of 5% outage throughput is achieved compared with conventional single cell networks.

A leakage-aware Coordinated Scheduling/Coordinated Beamforming (CS/CB) scheme for heterogeneous networks with layered limited feedback is proposed. In particular, all pico cells cooperatively select an optimal beamforming vector for the macro cell within a CoMP cluster so as to minimizing leakage power from the macro cell. Simulations show that the proposed scheme outperforms the conventional non-CoMP scheme with perfect channel state information at teansmitter (CSIT). Furthermore, the feedback amount and scheduler complexity is decreased greatly.

In this study, we investigate reference signal (RS) transmission schemes that aim to efficiently support coordinated multi-point (CoMP) transmission by providing improved channel estimation accuracy so that transmission parameters can be appropriately chosen on a cellular network. First, we investigate typical scenarios for transmission parameter selection with the widely used CoMP transmission and precoding schemes aligned with those considered for Long Term Evolution (LTE)-Advanced systems. Second, we investigate an RS transmission scheme that can provide accurate channel estimation even with severe inter-cell interference. Finally, we verify the performance benefit of the investigated scheme by a multi-cell link level evaluation. The results obtained indicate: 1) the investigated scheme improves block error rate performance compared to conventional schemes for fixed modulation and coding schemes (MCSs) allocation with a better precoding control accuracy on the LTE-Advanced system downlink and 2) the investigated scheme provides a throughput performance gain compared to conventional schemes for adaptive MCS allocation and coordinated beamforming.