Dongyao Wang

Optimized time-domain resource partitioning for enhanced inter-cell interference coordination in heterogeneous networks

Heterogeneous networks (HetNets) are expected to be one of the major performance enhancement enablers of LTE-Advanced. Due to significantly challenging interference scenarios, enhanced inter-cell interference coordination (eICIC) based on almost blank subframes (ABS) is the key technology enabler that makes HetNets a reality. The key factor determining the gain of ABS-based eICIC is the configured number of ABS which depends closely on the number of UEs requesting protection from ABS. In this paper, we study the optimal amount of ABS for synchronous ABS configuration by formulating this optimization as a network-wide utility maximization problem. We firstly propose a distributed method to determine victim UEs protected by ABS for any given amount of ABS via dynamic programming, and then find the optimal amount of ABS by evaluating the overall system utility. A remarkable feature of the proposed solution is that only limited information exchange via backhaul is required and the optimal amount of ABS could be individually derived at each eNB. Extensive simulations demonstrate that our solution can not only improve the overall system throughput significantly but also provide better network-wide fairness.

Optimized Fairness Cell Selection for 3GPP LTE-A Macro-Pico HetNets

Pico cell has been brought to cellular networks as a new technology to deliver cost-effective coverage and capacity to hard-to-reach places, and also increase capacity by cell splitting in hotspots with very dense phone usage. However, according to existing strongest receiving signal association method, pico cells with the extremely low transmitting power are significantly limited in the presence of macro coverage. Thus, the new introduced pico frequency resource will not be fully exploited in this unbalanced user distributions among macro and pico cells. In this paper, by jointly considering the long term channel condition and load balance in this macro-pico coexisted heterogeneous network, we formulate the cell selection problem into a network-wide proportional fairness optimization. Both optimal solution (by dynamic programming) and cost efficient algorithm (greedy heuristics) are proposed. In 3GPP LTE-A heterogeneous network scenario, the system-level performance evaluation shows that, compared with the conventional strongest signal cell selection scheme, the proposed optimized fairness cell selection methods could achieve significant performance gains especially for the cell edge users.

Channel Estimation and Optimal Training Design for Amplify and Forward MIMO Relay Channel under Spatial Fading Correlation

In this paper, we study the channel estimation problem for time division multiplex amplify-and-forward (AF) relay channels. Both the source and the destination and also the in-between relay node comprise multiple antennas, and there are spatial fading correlations in each hop. We first derive a linear minimum mean square error (LMMSE) channel estimator from a simple scenario where there are no correlations among the relay antennas to a more general scenario where the multiple relay antennas are also spatially correlated. And then we design the optimal training sequences by minimizing the mean square error (MSE). Also the impacts of spatial correlations, relay power gain and the number of relay antennas on the MSE are studied to some extent. It is proved that the channel estimation and optimal training sequences have nothing to do with the spatial correlation at the destination and the derived estimator and designed sequences can be directly extended to multi-hop relay channels. Simulations are conducted to corroborate the proposed studies.

Uplink power control and interference coordination for heterogeneous network

Heterogeneous deployment is a promising solution to enhance both system capacity and coverage, where the planned macro cell is overlaid with pico cells. However, higher transmit power of macro eNB (MeNB) results in small coverage for pico cell, which causes insufficient offloading from macro cell to pico cell and inefficient cell splitting gain exploration. Cell range expansion (CRE) is one of alternative cell associations to enhance offloading, but would bring severe interference on the uplink reception of macro cell. Hence, the use of enhanced inter-cell interference coordination (eICIC) techniques is required to realize the promised performance of macro user equipments (MUEs). In this paper, an adaptive uplink power control scheme is proposed for heterogeneous network (HetNet) with CRE, wherein the uplink power control parameters of pico cells could be dynamically optimized based on admissible interference level of macro cell. In addition, the proposed scheme manages to improve the performance of pico UEs (PUEs) on condition that the Quality of Service (QoS) of MUEs can be well guaranteed. Numerical simulation results verify the validity of the proposed scheme.

A game theoretic channel allocation scheme for multi-user OFDMA relay system

A game theoretic resource allocation approach is proposed in this paper to distribute the channels in multiuser orthogonal frequency division multiplexing access (OFDMA) relay system. The goal is to maximize the system throughput while considering the fairness of the users. The basic idea is to consider backhaul link and access link together as a bundle. Nash bargaining solution (NBS) is used to distribute subchannels among these bundles. The multi-bundle bargaining algorithm is derived based on the two-bundle bargaining algorithm by grouping the bundles into coalitions. Within each bundle, the backhaul link and access link compete for the resources via the two-band partition algorithm to achieve a maximum data rate with the available resource. Simulation results show that the NBS based resource allocation scheme achieves higher user throughput but comparable user fairness compared with two-hop proportional fairness scheduler and round robin scheduler.

Load Balance Based Dynamic Inter-Cell Interference Coordination for Relay Enhanced Cellular Network

The relaying technologies have been considered in cellular networks (such as LTE-A and WiMAX) as one of the advanced techniques to extend the network coverage and enhance the cell edge performance. However, the relays will bring extra interference to macro cell and the popular solution is to allocate different bandwidth for relays and base stations. In this paper, we use proportional fairness mode to formulate this frequency resource allocation optimization problem and presented a new adaptive method (both centralized and distributed algorithm) with interference coordination based on dynamic traffic load for cell-edge relay deployment. This resource allocation scheme with both intra and inter cell interference coordination (ICIC) can greatly improve the spectrum efficiency compared with conventional static ICIC schemes, in which the cell- edge bandwidth is equally allocated among the neighboring base stations or relays. Based on our performance evaluation, the proposed method can flexibly adapt the case when the traffic load distribution is non-uniformed or mobility occurs frequently, which accordingly exploit the cellular capacity with the experience enhancement of the cell-edge users.

Self-Optimization of Downlink Transmission Power in 3GPP LTE-A Heterogeneous Network

Co-channel full-reuse transmission is an important property in LTE downlink, which will generate strong inter-cell interference (ICI), especially in case of heterogeneous networks. The current LTE standardization supports the control of PDSCH transmission power to some extent via radio resource control signaling. In this paper, we propose a self- optimized downlink power allocation algorithm to efficiently use the transmission power while minimizing the interference to other users, which utilizes the concepts of game theory and fuzzy logic inference system. The proposed algorithm is suitable for the flat system architecture in 3GPP LTE-A system through a distributed operation manner, and minimizes the required information exchange among eNBs by the usage of fuzzy logic. And the simulation results illustrate the system performance benefits of the proposal compared to the conventional distributed waterfilling algorithm.

Approximate minimum SER precoding for spatial multiplexing over Ricean channels

The approximate minimum average symbol error rate (SER) precoder is designed for spatial multiplexing (SM) system in Ricean channels. Based on long-term channel state information (CSI), a closed-form solution that combines eigen-beamforming (E-BF) and power allocation is presented for correlated Ricean channel. Moreover, a simple precoder only based on K-factor and line-of-sight (LOS) departure angle is derived for independent Ricean channel, which needs less feedback overhead and lower computational complexity. The simulation results confirm the effectiveness of these precoders.

Path Diversity with a New Coded Cooperation Scheme over Multi-hop Wireless Channels

A new coded cooperation scheme is proposed to efficiently enhance the error correction capability for multi-hop path diversity. In this scheme, an intelligent coding scheme is used to generate correlated codewords delivered over multiple paths. The codeword over each path is self decodable to efficiently prevent error accumulation along the path. In the case of decoding failure in the intermediate nodes, different from conventional schemes, the intermediate nodes continue forward irrecoverable codeword to the destination instead of dropping it. This correlated codeword, when combined with other codewords from different paths at the destination, enables the receiver to recover large errors. The simulations are used to verify the effectiveness of the proposal scheme.

Multi-Antenna Uplink Transmission for LTE-A

Clustered DFT-S-OFDM has been accepted as the uplink multiple access scheme for LTE-Advanced. In this paper, a new transmit diversity with four transmit antennas is proposed for Clustered DFT-S-OFDM system. A modified Frequency Switched Transmit Diversity (FSTD) algorithm is proposed, where the multiple clusters can be divided into two groups by four antennas, thus the number of clusters on each antenna will be reduced. As a result, the PAPR performance of each antenna has been improved. Meanwhile, in order to obtain additional frequency diversity gain, the proposed scheme has introduced more channels by a symbol-based dynamic cluster allocation method, which makes one turbo coded stream transmitted multiple channels. Moreover, the Space-Time Block Coding (STBC) is employed for the two antennas in each group to achieve spatial diversity and coding gain. Simulation results show that the proposed scheme has good PAPR and Bit Block Error Rate (BLER) performance on frequency selective MIMO channels.