This paper investigates joint design and optimization of both low density parity check （LDPC） codes and M-algorithm based detectors including iterative tree search （ITS） and soft-output M-algorithm （SOMA） in multiple-input multiple-output （MIMO） systems via the tool of extrinsic information transfer （EXIT） charts. First, we present EXIT analysis for ITS and SOMA. We indicate that the extrinsic information transfer curves of ITS obtained by Monte Carlo simulations based on output log-likelihood rations are not true EXIT curves, and the explanation for such a phenomenon is given, while for SOMA, the true EXIT curves can be computed, enabling the code design. Then, we propose a new design rule and method for LDPC code degree profile optimization in MIMO systems. The algorithm can make the EXIT curves of the inner decoder and outer decoder match each other properly, and can easily attain the desired code with the target rate. Also, it can transform the optimization problem into a linear one, which is computationally simple. The significance of the proposed optimization approach is validated by the simulation results that the optimized codes perform much better than standard non-optimized ones when used together with SOMA detector.
YOU MingHou1,2, TAO XiaoFeng1,2, CUI QiMei1,2 & ZHANG Ping1,2 1 Wireless Technology Innovation Institute, Beijing University of Posts and Telecommunications, Beijing 100876, China
To mitigate inter-cell interference in 3G evolution systems, a novel inter-cell interference coordination scheme called soft fractional frequency reuse is proposed in this article, which enables to improve the data rate in cell-edge. On this basis, an inter-cell power control is presented for the inter-cell interference coordination, and the inter-cell balanced signal to interference plus noise ratio （SINR） among users is established for power allocation, which enables mitigation of inter-cell interference. Especially, the power control is based on a novel exponential kernel arithmetic kernel equations. Numerical results show that the proposed rate compared to the existing power control algorithms. equation at higher convergence speed than the traditional scheme improves the throughput and reduces the blocking
With the advances of the 4th generation （4G） mobile communications targeting multi-user QoS-guaranteed multimedia services, multiple input multiple output （MIMO） combined with multi-level quadrature amplitude modulation （M-QAM） technique gains great popularity for its capability of supporting high data rate. In this article, the statistical distribution of signal to noise plus interference ratio （SINR） in each recursive step of optimal ordered zero-forcing perfect successive interference cancellation （ZF-OOPSIC） detection is deduced based on order statistics theory. The symbol error rate （SER） of M-QAM MIMO system with ZF-OOPSIC detector is analyzed under fiat Rayleigh fading channel. This precise analytical SER result could be taken as the lower bound of various zero-forcing ordered successive interference cancellation （ZF-OSIC） receivers. Combining the analytical SER expression for linear zero-forcing （ZF） receiver as upper bound, the rough range of SER for various ZF-OSIC detectors could be obtained. Monte Carlo （MC） simulations validate the analytical results and prove the conclusions.
Utility based resource allocation strategy in multi-cell orthogonal frequency-division multiplexing （OFDM） system plays a critical role in next generation mobile communication systems. Based on the analysis of risk aversion utility functions, this article proposed the system utility based utility, which is named the customer satisfaction （CS） utility. Compared with the proportional fairness （PF） utility, the CS utility reflects the user demands better, and enables the system to adjust its resource allocation according to both the traffic requirements and the resource situation.
HAO Zhi-jie XU Xiao-dong ZHAO Ying-hong TAO Xiao-feng LI Lin-jun ZHANG Zhong-qi
As a new technology, coordinated multipoint （CoMP） transmission is included in LTE-Advanced study item. Moreover, the network architecture in LTE-Advanced system is modified to take into account coordinated transmission. Under this background, a novel power allocation game model is established to mitigate inter-cell interference with cellular coordination. In the light of cellular cooperation relationship and centralized control in eNodeB, the power allocation in each served antenna unit aims to make signal to interference plus noise ratio （SINR） balanced among inter-cells. Through the proposed power allocation game algorithm, the users＇ SINR can reach the Nash equilibrium, making it feasible to reduce the co-frequency interference by decreasing the transmitted power. Numerical results show that the proposed power allocation algorithm improves the throughput both in cell-center and cell-edge. Moreover, the blocking rate in cell-edge is reduced too.
ZHANG HuiXU XiaoDongLI JingYaTAO XiaoFengZHANG PingSVENSSON TommyBOTELLA Carmen
In the two-tier femtocell network, a central macroceU is underlaid with a large number of shorter range femtocell hotspots, which is preferably in the universal frequency reuse mode. This kind of new network architecture brings about urgent challenges to the schemes of interference management and the radio resource allocation. Motivated by these challenges, three contributions are made in this paper： 1） A novel joint subchannel and power allocation problem for orthogonal frequency division multiple access （OFDMA） downlink based femtocells is formulated on the premise of minimizing radiated interference of every Femto base station. 2） The pseudo-handover based scheduling information exchange method is proposed to exchange the co-tier and cross-tier information, and thus avoid the collision interference. 3） An iterative scheme of power control and subchannel is proposed to solve the formulated problem in contribution 1）, which is an NP-complete problem. Through simulations and comparisons with four other schemes, better performance in reducing interference and improving the spectrum efficiency is achieved by the proposed scheme.
LI Hong-jia HU Dan XU Xiao-dong TAO Xiao-feng ZHANG Ping
