Youzheng Wang

QoS aware relay selection and subcarrier allocation in cooperative OFDMA systems

Most existing works on resource allocation in cooperative OFDMA systems have focused on homogeneous users with same service and demand. In this letter, we investigate relay selection and subcarrier allocation in a cooperative OFDMA system with considerations of QoS guarantees and service support. By introducing QoS price, this combinatorial problem with exponential complexity is converted into a convex one, and a dual based QoS-aware schedule (QAS) algorithm is proposed to tackle the problem. Simulation results reveal that our proposed algorithm significantly outperforms previous works in terms of both services support and QoS satisfaction.

Stable enhancement for AODV routing protocol

Routing algorithm has been the challenge in the wireless ad-hoc network for a long time because of the quick mutability of the network topology introduced by the mobility of nodes. AODV is appealing for ad hoc networks as an efficient on-demand routing protocol because of the low routing overhead and high performance. As an optimization for the current AODV, a novel stable adaptive enhancement for AODV routing protocol was proposed in this paper, which considers joint route hop count, node stability and route traffic load balance as the route selection criteria. Comparing with AODV protocol, the new algorithm has better performance as shown with the simulations results.

Joint ML channel estimation and data detection for STBC via novel sphere decoding algorithms

Space-time block codes (STBC) are very effective and simple schemes to utilize the diversity gain in multiple-input multiple-output (MIMO) wireless systems. In previous research on STBC data detection, channel state information is usually assumed to be known at the receiver side, which enables simple maximum-likelihood (ML) decoding at the receiver. We consider the problem of joint ML channel estimation and data detection for STBC systems when the channel state information is not available at the receiver. It is shown that the joint ML channel estimation and data detection for complex STBC system is an integer least-square optimization problem for constant-modulus modulation. We propose novel sphere decoders which provide a low-complexity exact optimal solution to this optimization problem. The proposed sphere decoder visits the minimum number of tree nodes in finding the ML solution. In addition, by modifying the novel sphere decoder, we provide efficient exact ML joint channel estimation and data detection for STBC wireless systems employing non-constant modulus modulation schemes. Considerable performance gain and complexity reduction are achieved with these methods.

On QoS-Guaranteed Downlink Cooperative OFDMA Systems with Amplify-and-Forward Relays: Optimal Schedule and Resource Allocation

This paper considers joint schedule and resource allocation in downlink cooperative OFDMA systems with multiple sources, multiple relays and a single destination. Each user has individual QoS requirements and the relays operate in amplify-and-forward and half-duplex mode. We try to find optimal power allocation, relay selection and subcarrier assignment to maximize overall system rates. The problem is formulated as a Mixed Binary Integer Programming (MBIP). Although the original problem is comprehensive in nature, a novel two-level dual-primal decomposition based algorithm is proposed to tackle the problem. Optimal solutions are given in closed-form and the algorithm has a polynomial complexity in general. The efficiency of the algorithm is finally illustrated by numerical results.

Performance evaluation of MIMO systems in a mixture of Gaussian noise and impulsive noise

Most of the analyses of multiple-input multiple-output (MIMO) systems so far have been based on the ideal Gaussian noise model. In this paper, performance analysis of MIMO systems is performed in a mixture of Gaussian noise and impulsive noise modeled as a symmetric alpha stable process. Three typical MIMO systems are considered: 1) zero-forcing (ZF) system, 2) maximum likelihood (ML) system and 3) space time block coding (STBC) system. The symbol-error-rates (SER) or the upper bound of SER of each system is derived. Simulations are performed in the mixed noise with different impulsive intensity and impulsive level and the results show that the performances of all the systems are degraded greatly in the mixed noise and STBC has no performance gain over ZF and ML when high impulsive noise appears.

DCC-MAC: a new MAC protocol for ad-hoc networks based on dual control channel

In this paper, we propose a new MAC protocol for ad-hoc networks that uses multiple channels and a dynamic channel selection scheme. The proposed protocol, DCC-MAC (dual control channel based MAC), deploys two control channels (CH/sub R/C/ and CH/sub ACK/ and N data channels, where N is independent of the number of nodes in the network. Through RTS/CTS dialogues on CH/sub R/C/ senders and receivers negotiate the most robust channel for data transmission with maximum-CIR selection criterion. ACK transmission on CH/sub ACK/ contributes to the unidirectional transmission on data channels and therefore the decrease of the co-channel reuse distance. Performance evaluation has been carried out and the simulation results demonstrate the effectiveness of the proposed protocol.

QoS Aware Resource Allocation in Cooperative OFDMA Systems with Service Differentiation

Most existing works on resource allocation in cooperative OFDMA systems have focused on homogeneous users with same service and demand. In this paper, we focus on resource allocation in a service differentiated cooperative OFDMA system where each user has individual QoS requirement. We investigate joint power allocation, relay selection and subcarrier assignment to maximize overall system rates with considerations of QoS guarantees and service support. By introducing \emph{QoS price}, this combinatorial problem with exponential complexity is converted into a convex one, and a two-level dual-primal decomposition based QoS-aware resource allocation (QARA) algorithm is proposed to tackle the problem. Simulation results reveal that our proposed algorithm significant outperforms previous works in terms of both services support and QoS satisfaction.

A faster ML sphere decoder with competing branches

A novel fast recursive sphere decoder with parallel competing branches (P-SD) is proposed for exact maximum-likelihood (ML) detection in multiple-input multiple-output (MIMO) systems. P-SD introduces a novel competition mechanism which makes P-SD dynamically choose the targeted branch to perform a bounded search among the competing parallel branches. In P-SD, the search radius shrinks to the minimum Euclidean distance as early as possible. Numerical results show that P-SD achieves considerable computational complexity reduction even compared with the Schnorr-Euchner enumeration (SEE) based sphere decoder (SE-SD).

Delay-Aware Power and Bandwidth Allocation for Multiuser Satellite Downlinks

This paper addresses the problem of joint power and bandwidth allocation for a general multiuser satellite downlink system. In contrast to existing studies, this work focuses on the heterogeneous services, including both real-time and non-real-time ones. Subject to the delay constraints of real-time services, the system throughput is maximized over multiple time slots, while a Weibull-based channel model is exploited for the rain attenuation prediction. Based on the dual decomposition method, the power and bandwidth allocation is derived with the relaxation of delay constraints. Then by introducing a delay-violation parameter, we propose an algorithm to approach the optimal resource allocation solution, while satisfying the delay constraints before relaxation. Simulation results show our algorithm effectively achieves a well-performed trade-off between throughput and delay performance.

Synchronization in TDMA ad hoc network

The ad hoc network may play an important part in future wireless communication systems. However, system synchronization of the ad hoc network is a big challenge due to the lack of a fixed infrastructure and the dynamically changing topology. A novel self synchronization algorithm is proposed for the ad hoc network based on TDMA; the network topology structure information is gathered in some assigned time slots to build a connected domain set and broadcast the system synchronization messages over the whole network. The system time slot cost of synchronization is about 16.7%, and the probability of a node being successfully synchronized is higher than 95% in typical network environments, as shown by simulation.