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Wan H.,Shanghai JiaoTong University | Wan H.,Guangxi University | Chen W.,Shanghai JiaoTong University | Wang X.,DOCOMO Beijing Communications Laboratories Co.
IEEE Communications Letters

In this letter, we address the optimal source and relay matrices design for the multiple-input multiple-output (MIMO) relaying broadcast channels (BC) with direct links (DLs) based on weighted sum-rate criterion. This problem is nonlinear nonconvex and its optimal solution remains open. To develop an efficient way to solve this problem, we first set up an equivalent problem, and solve it by decoupling it into two tractable subproblems. Finally, we propose a general linear iterative design algorithm based on alternative optimization. This iterative design algorithm is convergent since the solution of each subproblem is optimal and unique. The advantage of the proposed iterative design scheme is demonstrated by numerical experiments. © 1997-2012 IEEE. Source

Bai Y.,Hainan University | Chen L.,DOCOMO Beijing Communications Laboratories Co.
Eurasip Journal on Wireless Communications and Networking

When deploying two-tier LTE cellular networks with coexistence of macrocells and underlaid femtocells, the strategies of spectrum arrangement need to be investigated to efficiently utilize the scarce spectrum resource. Co-channel spectrum usage and dedicated-channel spectrum usage are two traditional strategies of spectrum arrangement. Nevertheless, there are pros and cons of them from the perspective of achievable network capacity in two-tier LTE network as they result in different amounts of available spectrum at each tier and disparate cross-tier interferences. To improve overall spectrum utilization, we propose a novel approach of spectrum arrangement, which is called hybrid spectrum arrangement, to take advantage of their merits. In our proposal, an underlaid femtocell can select its spectrum usage mode according to a criterion aiming to benefit both macrocell and femtocell in terms of achieved capacities. Consequently, the femtocells embedded in macrocell are self-organized as inner and outer femtocells, which operate in dedicated-channel spectrum usage and co-channel spectrum usage, respectively. Then, we examine distinct characteristics of cross-tier interferences in the context of hybrid spectrum arrangement and present corresponding schemes to mitigate the residual significant interferences. Analysis and system level simulation are given to validate the effectiveness of our proposed methods for two-tier LTE cellular network. © 2013 Bai and Chen. Source

Kayama H.,DOCOMO Beijing Communications Laboratories Co. | Jiang H.,DOCOMO Beijing Communications Laboratories Co.
Conference Record - Asilomar Conference on Signals, Systems and Computers

The paradigm shift toward smartphones caused distinct traffic expansion in mobile networks. Indeed, the total amount of traffic in Japan is glowing nearly 1.8-fold in yearly basis during the past few years. To cope with this problem, many mobile operators are now speeding up their deployment of LTE/LTE-A. In this paper, current situation of LTE deployment in Japan, including area deployment and spectrum assignment are introduced. Then, the technical trend for further enhancement of LTE-A is presented based on the current standardization activities in 3GPP Rel.11 and Rel.12. Finally, the requirements and some expected technologies for the next generation mobile system, namely 5G or Future Radio Access (FRA), will be presented. Here, small cell deployment and its interwork with macro-cell is regarded as one of promising ways for increasing channel capacity while maintaining mobility support. As to radio access technologies, advanced interference mitigation and non-orthogonal multiple access (NOMA) are likely to be key issues for FRA. Initial evaluations of Massive-MIMO performance are also presented for clarifying the feasibility in the assumed scenario. © 2014 IEEE. Source

Bo H.,Beijing University of Posts and Telecommunications | Hui T.,Beijing University of Posts and Telecommunications | Lan C.,DOCOMO Beijing Communications Laboratories Co. | Jianchi Z.,DOCOMO Beijing Communications Laboratories Co.
IEEE Communications Letters

The Long Term Evolution (LTE) system adopts Discontinuous Reception (DRX) in the link level for power saving to extend the battery life of the User Equipment (UE). A novel real-time DRX-aware scheduling method is proposed for delay-sensitive services in wireless downlink systems. In the scheme, DRX parameters are introduced into the scheduling determinants, so as to reduce packet loss caused by the sleeping process during DRX. Simulation results show that, significant performance gain in terms of packet loss rate and power consumption, can be achieved by the proposed scheme compared with traditional schemes. © 2010 IEEE. Source

Song Y.,DOCOMO Beijing Communications Laboratories Co. | Yun X.,DOCOMO Beijing Communications Laboratories Co. | Nagata S.,NTT DoCoMo | Chen L.,DOCOMO Beijing Communications Laboratories Co.
2013 IEEE International Conference on Communications Workshops, ICC 2013

This paper investigates and analyzes three typical elevation beamforming scenarios which are most likely to be applied in future LTE-Advanced systems: vertical sectorization with same carrier frequency, vertical sectorization with different carrier frequency based on carrier aggregation, and user-specific elevation beamforming. Preliminary evaluation using WINNERII/WINNER+ based 3D MIMO channel modeling is carried out to compare these scenarios with the conventional system with single downtilting. It is shown that the latter two elevation beamforming scenarios can achieve good performance. © 2013 IEEE. Source

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