Yongyu Chang’s research while affiliated with Beijing University of Posts and Telecommunications and other places

The heterogeneous network (HetNet) has been discussed in detail in the Long-Term Evolution (LTE) and LTE Advanced standards. However, the standardization of High-Speed Packet Access HetNet (HSPA HetNet) launched by 3GPP is pushing at full steam. Interference coordination (IC), which is responsible for dealing with the interference in the system, remains a subject worthy of investigation in regard to HSPA HetNet. In this paper, considering the network framework of HSPA HetNet, we propose a quasi-distributed IC (QDIC) scheme to lower the interference level in the co-channel HSPA HetNet. Our QDIC scheme is constructed as slightly different energy-efficient non-cooperative games in the downlink (DL) and uplink (UL) scenarios, respectively. The existence and uniqueness of the equilibrium for these games are first revealed. Then, we derive the closed-form best responses of these games. A feasible implementation is finally developed to achieve our QDIC scheme in the practical DL and UL. Simulation results show the notable benefits of our scheme, which can indeed control the interference level and enhance the system performance.

Heterogeneous network (HetNet) has been discussed earlier in LTE system. But recently, there also exist some studies concerning the standardization of HSPA HetNet. Interference coordination is still a critical topic in HSPA HetNet. Considering the network architecture of HSPA HetNet, in this paper, we develop a distributed interference coordination (DIC) scheme which involves power allocation and scheduling to reduce the negative effect of interference in the downlink co-channel HSPA HetNet. Our DIC scheme is modeled as an energy-efficient non-cooperative game with QoS constraint (EENGQ). We first reveal the existence and uniqueness of the equilibrium for this game. Then, a closed-form best response of this game is derived. Finally, a feasible implementation is proposed to achieve our DIC scheme in practice. Simulation results show the notable advantages of our proposed scheme which can remarkably mitigate the interference and enhance the energy efficiency.

Multi-point transmission has not received adequate attention in the evolution of UMTS networks until multi-flow transmission is proposed in the HSPA+ network recently. In the multi-flow transmission, the cross-point coordination is regarded as an important technique to enhance the system performance. In the existing research, most studies have only involved the multi-flow transmission in a non-coordinated pattern and considered it in the single-carrier HSPA+ system. The major contribution of this paper is to propose a cross-point coordination scheme in the multi-carrier Multi-flow HSDPA (MF-HSDPA) network. Our scheme is able to achieve the coordination of both the aggregated scheduling and power allocation to improve the system performance in the multi-point and multi- carrier layout. Simulation results will show the advantages of the proposed scheme.

Co-channel heterogeneous network (HetNet) where the conventional macro cells are underlaid with some co-channel low power node (LPN) cells has been recently introduced into HSPA+ to satisfy the rapidly growing demands for improving system coverage and capacity. However, the severe cross-tier uplink interference caused by applying the heterogeneous deployment will inevitably limit the uplink performance in HSPA+. Thus, the uplink interference issues have become a critical topic in this area. In this paper, we propose a quasi-distributed uplink interference coordination (QDUIC) scheme based on non-cooperative game with local restriction to reduce the uplink interference in HSPA+ HetNet. The existence and uniqueness of Nash equilibrium for our proposed game are justified in detail. Furthermore, to achieve our scheme in practice, we develop a feasible implementation for practical HSPA+ HetNet system. System-level simulation results show that our scheme can not only mitigate the uplink interference level, but also save the uplink power consumption and enhance the throughput performance of HSPA+ HetNet.

Heterogeneous network (HetNet) which can provide the remarkable cell-splitting gain has already received adequate attention in the LTE-A system. Since the standardization of HetNet in HSPA+ is currently in progress, it is necessary to focus on the application of HetNet in the HSPA+ system. Cross- tier interference coordination is one of the crucial issues to be discussed in this area. Considering the HetNet deployment in the multi-flow HSDPA (MF- HSDPA), the main contribution of this paper is to propose a novel cross-tier interference coordination scheme in the MF-HSDPA HetNet. Our method combines the cross-tier multi-flow transmission with the adaptive time domain muting and cross-tier scheduling to deal with the interference problem. System-level simulation results will show the advantages of our proposed scheme.

The performance of Transmission Control Protocol (TCP) degrades over wireless links which are characterized by varying channel condition and high error rate. TCP misinterprets these as network congestion. In this paper, we analyze the TCP send rate of parallel multi-radio transmission diversity (MRTD) schemes with and without redundancy in heterogeneous wireless networks (HWNs). Through developing a cross-layer model, MAC layer packet error rate and link rate are taken into consideration. By comparing the performance of these schemes, we propose a hybrid MRTD scheme which aims at obtaining good tradeoff between robustness and efficiency to improve TCP performance. The feasibility of the proposed scheme is validated by user-level simulation. Moreover, system-level simulation results show that hybrid MRTD scheme improves the wireless TCP performance comparing with parallel MRTD schemes.

Multi-point transmission has been paid attention in the evolution of multi-carrier HSPA+ networks because of its capability to deal with the negative channel conditions. Multipoint coordination is a key issue to be investigated in this area. In the existing deployment, the multi-point transmission is only applied in a non-coordinated way in the current multi-carrier Multi-flow HSDPA (MF-HSDPA) network. Besides, the metric measuring the quality of multi-point transmission is limited. In this paper, we propose a cross-cell coordination scheme which considers both the maximization of sum-rate and the minimization of packet sum-delay in multi-carrier MF-HSDPA network. The proposed scheme involves the cooperation of the cross-cell scheduling and power optimization. The cross-cell scheduling can be further divided into the intra-cell and inter-cell processes. Then, we propose a heuristic method based on the theory of flow network to solve the whole scheduling issue with a reasonable tradeoff between the performance and complexity. Simulation results will show the advantages of our proposed scheme.

Heterogeneous network (HetNet) has been studied earlier in the context of LTE. But lately, there are also some discussions about HetNet in HSPA. Cross-tier interference (CTI) is an annoying issue to be investigated in the co-channel HSPA HetNet (CHH) scenario. In this paper, we will focus on the downlink CTI problem in CHH and propose a solution to mitigate it. Our scheme involves the macro muting (MM) in which macro NodeB will mute itself at some certain sub-frames to reduce the CTI level in the system. We also enhance the MM scheme by introducing the adaptive CQI hysteresis (ACH) mechanism to avoid the issue that the low power node (LPN) in HetNet may use the improper CQI for transmitting when MM is implemented. Simulation results will show the benefits of our proposed scheme.

Coordinated multi-point transmission with limited rate feedback has been paid much attention recently due to its ability to overcome the detrimental propagation conditions. In the limited feedback multi-point transmission, how to allocate the appropriate feedback bits among the users has become a critical issue to be investigated. The existing schemes have not considered the impact of the flexible power allocation on the feedback bit allocation among the users. The main contribution of this paper is to propose a user-specific coordination scheme to dynamically coordinate the feedback bit number for each user according to the overall result of power allocation in the limited feedback multi-point transmission. We also develop an iteration algorithm to efficiently achieve the satisfactory solution of our proposed issue. Simulation results will show the advantages of our proposed scheme.

The future wireless communication networks will integrate different radio access technologies (RATs), which are referred to as heterogeneous wireless networks (HWNs). In this paper, we deal with two data oriented access networks, the Long Term Evolution (LTE) and the high speed downlink packet access (HSDPA). Assuming that the networks can support multi-homing access and the user can be served by both networks simultaneously, we propose a traffic split scheme with the aim of maximizing the throughput based on common radio resource management (CRRM). The split ratio in the scheme is dynamically adjusted under the consideration of the user's channel quality and the network load. The simulation results show that the proposed scheme can improve the throughput, also reduce the delay of the networks compared with the scheme using the fixed split ratio.