Recently, Dynamic Time Division Duplex (TDD) has been proposed to handle the asymmetry of traffic demand between DownLink (DL) and UpLink (UL) in Heterogeneous Networks (HetNets). However, for mixed traffic consisting of best effort traffic and soft Quality of Service (QoS) traffic, the resource allocation problem has not been adequately studied in Dynamic TDD HetNets. In this paper, we focus on such problem in a two-tier HetNet with co-channel deployment of one Macro cell Base Station (MBS) and multiple Small cell Base Stations (SBSs) in hotspots. Different from existing work, we introduce low power almost blank subframes to alleviate MBS-to-SBS interference which is inherent in TDD operation. To tackle the resource allocation problem, we propose a two-step strategy. First, from the view point of base stations, we propose a transmission protocol and perform time resource allocation by formulating and solving a network capacity maximization problem under DL UL traffic demands. Second, from the view point of User Equipments (UEs), we formulate their resource allocation as a Network Utility Maximization (NUM) problem. An efficient iterative algorithm is proposed to solve the NUM problem. Simulations show the advantage of the proposed algorithm in terms of network throughput and UE QoS satisfaction level.
Future wireless communication systems feature heterogeneous networks (HetNets), with small cells underlying existing macrocells. In order to maximize the off-loading benefits of small cells and mitigate the interference from the macrocell tier to the small cell tier, cell range expansion (CRE) and almost blank subframes (ABSs) have been designed for small cells and macrocells, respectively. Besides, enhanced 4th generation (4G) networks are also envisaged to adopt dynamic time division duplexing (TDD) transmissions for small cells to adapt their communication service to the fast variation of downlink (DL) and uplink (UL) traffic demands. However, up to now, it is still unclear whether it is technically feasible to introduce dynamic TDD into HetNets. In this paper, we investigate this fundamental problem and propose a feasible scheme to enable small cell dynamic TDD transmissions in HetNets. Simulation results show that compared with the static TDD scheme with CRE and ABS operations, the proposed scheme can achieve superior performance gains in terms of DL and UL packet throughputs when the traffic load is low to medium, at the expense of introducing the DL-to-UL interference cancellation (IC) functionality in macrocell base stations (BSs) and or small cell BSs. Dynamic downlink and uplink resource adaptation in TDD (Time Domain Duplex) systems by flexibly changing the ratio of time slots for downlink and uplink transmissions is studied under Heterogonous Network (HetNet) scenarios. The time-scale of the resource adaptation and the interference management between downlink and uplink transmissions from different cells are important factors in determining the achievable level of resource efficiency, user experience and energy saving in TDD systems. In this paper, we apply the dynamic downlink and uplink resource adaptation in multi-cell macro-pico scenarios with co-channel interference. The performance is evaluated in system level for LTE-Advanced TDD configurations. Reconfiguration rates of 10 msec and 640 msec are considered as the time-scale of the dynamic resource adaptation. In addition, the time domain inter-cell interference coordination between the macro cells and the pico cells is applied for handling the high level of interference from macro cells to pico cells in the downlink multi-cell dynamic simulations. Almost-blank subframe (ABSF) is a time-domain technique, proposed by the 3GPP to handle Inter-Cell Interference (ICI) in heterogeneous network environments (HetNet). We consider a HetNet environment comprised of a macro-cell and femto-cells distributed across the macro-cell area. We propose a novel approach, called ABSF offsetting, to reduce the blanking rate at the femto-cells while preserving the required optimal blanking rate at the macro-cell. We also study the problem of optimal resource partitioning and offset assignment in the ABSF mode. The proposed solution for the problem is based on multistage Nash bargaining. The performance of the optimal resource partitioning, and ABSF offsetting is evaluated through simulations. The results show that the throughput of the macro-cell is improved, while the degradation in the aggregate femto-cell throughput is reduced due to the reduction in the blanking rate due to offsetting. The simulation results also demonstrate the fairness of the ABSF offsetting with the fairness index approaching 1 among the macro-cell UEs at low loads. 