Yuehua Ding

Hybrid Duplex Switching in Heterogeneous Networks

In this paper, a novel hybrid-duplex scheme based on received power is proposed for heterogeneous networks (HetNets). In the proposed scheme, the duplex mode (half or full duplex) of each user is switchable according to the received power from its serving base station. The signal-to-interference-plus-noise-ratio and spectral efficiency are analyzed for both downlink and uplink channels by using the tools of inhomogeneous Poisson point process. Furthermore, determining power threshold for duplex mode switching is investigated for sum rate maximization, which is formulated as a nonlinear integer programming problem and a greedy algorithm is proposed to solve this problem. The theoretical analysis and the proposed algorithm are evaluated by numerical simulations. Simulation results show that the proposed hybrid-duplex scheme outperforms the half-duplex or full-duplex HetNet schemes.

Distance-Based Hybrid Duplex in Heterogeneous Networks

In this paper, we propose a novel distance-based hybrid-duplex scheme for heterogeneous networks (HetNets). Assuming each user can select half- or full-duplex mode based on the transmit distance to its serving base station (BS), we derive the bidirectional full-duplex and downlink half-duplex signal-tointerference-ratio (SINR) and achievable rate using stochastic geometry. The numerical results show good a agreement with our analyze and verify that the proposed distance-based hybridduplex scheme significantly outperforms the conventional HetNet schemes.

Widely Linear Sphere Decoder in MIMO Systems by Exploiting the Conjugate Symmetry of Linearly Modulated Signals

This paper investigates the widely linear processing (WLP) for the detection of circular signals, such as M-ary phaseshift keying (MPSK) signals and M-ary quadrature amplitude modulation (MQAM) signals. First, a unified mathematical model is derived to describe the conjugate symmetry of general MPSK/MQAM signals. In the unified model, a phase-rotation matrix (PRM) is introduced to partition the constellation of multiple-input multiple-output (MIMO) signals into subsets. Signals in a subset share the same PRM. Second, a widely linear receiver is proposed in each subset for MIMO detection. To avoid repetitive WLP in each subset, a widely linear sphere decoder (WLSD) is further proposed for MIMO systems. WLSD transforms the traditional sphere decoder (SD) searching for a true transmitted vector into a shrunk one by searching for the corresponding phase-rotation vector. Finally, the diversity order of WLSD is proven to be more than NR - NT -1/2 and less than NR, where NT (or NR) denotes the number of transmitting (or receiving) antennas. Additional performance analysis is also conducted to quantify the signal-to-noise ratio improvement. The complexity analysis reveals that the candidate phase-rotation vectors of WLSD are no more than (1/2)NT of the SD candidates. Simulation results show that the proposed WLSD can achieve quasi-optimal bit error rate performance, while the computational complexity is reduced by more than a half compared with the Schnorr-Euchner sphere decoder.

Scalable cross-layer multipath routing under interference constraints in wireless mesh networks

This paper investigates the problem of flow routing under interference constraints for wireless mesh networks. A new routing metric called cross-layer weight function CLWF, which is proved to be isotonic using virtual network decomposition, is initially developed by considering the traffic load and interference. Based on CLWF, a new routing algorithm called weighted hybrid multipath routing algorithm WHMRA is proposed in which the joint design of CLWF-based multipoint relay selection algorithm and fuzzy-slighted routing algorithm is introduced to improve the routing scalability. In addition, a cross-layer design framework is also developed in WHMRA in order to exchange information and enable interaction between layers where is enforced strict boundaries in original OSI networking model. Finally, through the system simulation and performance comparison, the proposed algorithms are demonstrated to succeed in improving network performance in terms of delay, packet loss ratio, throughput and overhead.

SINR analysis of heterogeneous networks with hybrid duplex

In this paper, we propose a novel distance-based hybrid-duplex scheme for heterogeneous networks (HetNets). Assuming each user can select half- or full-duplex mode based on the transmit distance to its serving base station (BS), we derive uplink signal-to-interference-plus-noise-ratio (SINR) and spectral efficiency using stochastic geometry. Our results demonstrate that the proposed distance-based hybrid-duplex HetNet can achieve higher spectral efficiency over a wide range of self-interference cancellation (SIC) capability, while the full-duplex mode only outperforms than the half-duplex HetNet for high SIC capability.

Physical Layer Security in Heterogeneous Networks With Jammer Selection and Full-Duplex Users

In this paper, we enhance physical layer security for downlink heterogeneous networks by using friendly jammers and full-duplex users. The jammers are selected to transmit jamming signal if their interfering power on the scheduled users is below a threshold, meanwhile the scheduled users confound the eavesdroppers using artificial noise by full-duplexing. Using the tools of stochastic geometry, we derive the expressions of connection probability and secrecy probability. In particular, the locations of active jammers are modeled by a modified Poisson hole process. Determining the jammer selection threshold is further investigated for connection probability maximization subject to the security constraints. A greedy algorithm is proposed to efficiently solve this problem. The accuracy of the theoretical analysis and the efficiency of the proposed algorithm are evaluated by numerical simulations.

Cross-layer resource allocation in wireless multi-hop networks with outdated channel state information

The cross-layer resource allocation problem in wireless multi-hop networks (WMHNs) has been extensively studied in the past few years. Most of these studies assume that every node has the perfect channel state information (CSI) of other nodes. In practical settings, however, the networks are generally dynamic and CSI usually becomes outdated when it is used, due to the time-variant channel and feedback delay. To deal with this issue, we study the cross-layer resource allocation problem in dynamic WMHNs with outdated CSI under channel conditions where there is correlation between the outdated CSI and current CSI. Two major contributions are made in this work: (1) a closed-form expression of conditional average capacity is derived under the signal-to-interference-plus-noise ratio (SINR) model; (2) a joint optimization problem of congestion control, power control, and channel allocation in the context of outdated CSI is formulated and solved in both centralized and distributed manners. Simulation results show that the network utility can be improved significantly using our proposed algorithm.

Frequency Collision Elimination Method Based on Negotiation and Non-Cooperative Game in Femtocell Networks

In the user deployed femtocell networks, the frequency collision dramatically decreases the throughput of femtocell networks. In this paper, we propose a frequency collision elimination method based on negotiation and non- cooperative game to avoid frequency collisions between neighboring femtocells. The frequency collisions inside a cluster are figured out by using the negotiation mechanism. The game theoretical mechanism deals with the inter-cluster frequency collisions. The femtocell network gets an equilibrium point rapidly by using the proposed methods in the context of stable femtocell network topology. Furthermore, the method is achievable in realistic communication system. Simulation results show that the proposed scheme significantly reduces the interference and considerably increases the average capacity of femtocells. Index Terms—Femtocell network, fractional frequency reuse, frequency collision, game theory