Research On Joint Transmission In Heterogeneous Network

With the introduction of MIMO and OFDM technology in LTE, the capacity of the single radio link has met its Shannon limit. In the future wireless network, the most promising way to further enhance the system capacity is to deploy Heterogeneous Network (HetNet). By placing the low power node to cover the hot-zone areas within the coverage of MeNB, the system performance can be improved. On basis of the modern wireless technologies and the research projects in the research group, this paper explores joint transmission in HetNet in the dimensions of power and frequency. The main contributions of this paper include:First, this paper sets up the basic system model for single-carrier joint transmission in HetNet. This paper puts forward the optimal user selection criteria and the optimal power allocation of Macro eNodeB (MeNB) through the analysis of the monotonicity and convexity of capacity function. The simulation results verify the optimality of the proposed scheme.In addition, this paper further investigates the multiple sub-carrier joint transmission based on the optimal power allocation scheme in single carrier joint transmission. By strict mathematical derivation, this paper proves that the original optimal power allocation could be achieved by decomposing it into several sub quais-convex problems. The simulation results show that the performance of the proposed scheme is much better than other schemes.Third, considering that the computational complexity of the optimal power allocation scheme in multiple sub-carrier joint transmission is quite large, this paper proposes two sub-optimal low-complexity power allocation schemes. The first one is based on the preset power threshold. In the threshold based power allocation scheme, based on the threshold, MeNB selects certain low power nodes to conduct joint transmission. Thus, the original complex non-convex problem can be turned into one quasi-convex problem whose computational complexity is greatly reduced. The second one is constant-power allocation scheme. MeNB selects the certain subcarrier groups to allocated equal power. Also, this paper presents the closed-form solution for the bound between the optimal power allocation scheme and constant power allocation scheme based on duality theory. The simulation results justify the significant performance gain and the low computational complexity of the two sub-optimal power allocation schemes.Finally, the paper proposes a CoMP-based joint transmission scheme by frequency resource orthogonal-division. MeNB divides the whole frequency band into several sub-bands. In each band, MeNB chooses one low power node to jointly transmit to reduce the cross-tier interference and improve the joint transmission gain. The simulation results demonstrate that the proposed scheme could improve the system throughput significantly.