Hongcheng Zhuang

Slot allocation algorithms in centralized scheduling scheme for IEEE 802.16 based wireless mesh networks

In IEEE 802.16 based wireless mesh networks (WMNs), TDMA (Time Division Multiple Access) is employed as the channel access method and only TDD (Time Division Duplex) is supported and there are no clearly separate downlink and uplink subframes in the physical frame structure. As the uplink and downlink traffic has different characteristics in that the uplink traffic decentralizes in each MSS (Mesh Subscriber Station) and the downlink traffic centralizes in the MBS (Mesh Base Station), different scheduling methods should be taken in the uplink and downlink. This paper presents a uniform slot allocation algorithm which is suitable for both uplinks and downlinks. To achieve higher spatial reuse and greater throughput and to avoid switching frequently between receiving and transmitting within two adjacent time slots when a relay node forwards traffic, different link selection criteria are taken into account when allocating slots for uplinks and downlinks. A combined uplink and downlink slot allocation algorithm is proposed for further improving the spatial reuse and network throughput. The proposed algorithms are evaluated by extensive simulations and the results show that it has good performance in terms of spatial reuse and network throughput. To the best of the authors knowledge, this work is the first one that considers combined uplink and downlink slot allocation on the centralized scheduling scheme in IEEE 802.16 based WMNs.

Cross-Layer Fair Resources Allocation for Multi-Radio Multi-Channel Wireless Mesh Networks

A multi-radio multi-channel wireless mesh network (MRMC-WMN) consists of multiple wireless routers. Each router is equipped with multiple radios. There are multiple orthogonal frequency channels available in the network. Given the physical topology of the routers and the traffic flows, four important issues should be addressed in MRMC-WMN: logical topology formulation, channel allocation, routing and bandwidth assignment. In this paper, we mathematically formulate the cross-layer fair resources allocation problem as an integer linear programming problem (ILP) problem. The optimization object is max-min fairness of bandwidth allocation. A near optimal metaheuristic TSILS algorithm is proposed which is more feasible and has less optimization error. We compare it with the solutions obtained from the optimal branch-and-bound and ILS algorithm [3]. Performance impact of available network resources is assessed in terms of aggregate network throughput and fairness index.

Jointly optimal congestion control, channel allocation and power control in multi-channel wireless multihop networks

In this paper, to increase end-to-end throughput and energy efficiency of the multi-channel wireless multihop networks, a framework of jointly optimize congestion control in the transport layer, channel allocation in the data link layer and power control in the physical layer is proposed. It models the network by a generalized network utility maximization (NUM) problem with elastic link data rate constraints. Through binary linearization and log-transformation, and after relaxing the binary constraints on channel allocation matrix, the NUM problem becomes a convex optimization problem, which can be solved by the gateway centralized through branch and bound algorithm with exponential time complexity. Then, a partially distributed near-optimal jointly congestion control, channel allocation and power control (DCCCAPC) algorithm based on Lagrangian dual decomposition technique is proposed. Performance is assessed through simulations in terms of network utility, energy efficiency and fairness index. Convergence of both centralized and distributed algorithms is proved through theoretic analysis and simulations. As the available network resources increase, the performance gain on network utility increases.

A Novel Relay Selection Strategy for Multi-User Cooperative Relaying Networks

Relay selection is a challenging issue in cooperative communication networks. In particular, in a multi-user multi- concurrent-transmission network, effects of the resource sharing of a relay by its served users on the relay selection strategy need to be taken into account. There is little research on this investigation in literature. In this paper, we propose a novel efficient and fair relay selection strategy, in which individual users QoS requirement is inherently taken into account. In terms of efficiency, the proposed strategy is of low computational complexity. In terms of fairness, the system resource is utilized fairly among all relaying nodes so that the system has the best potential to accommodate as many users as possible. Simulation results indicate that the proposed selection strategy outperforms many existing ones, therefore justifying our arguments.

Hierarchical and Adaptive Spectrum Sensing in Cognitive Radio Based Multi-Hop Cellular Networks

In a spectrum overlay system, the secondary users (SUs) with cognitive radio capability need to detect the presence of primary users promptly and reliably in order to prevent excessive interference. Likewise, to make full use of the available spectra, such systems have to attain low false alarm probability. Having a high detection probability while maintaining a low false alarm probability is challenging as these are conflicting goals; therefore, an appropriate tradeoff needs to be determined. In this paper we propose a Hierarchical and Adaptive Spectrum Sensing (HASS) solution to multi-hop cellular networks, which is based on cooperative sensing and soften hard detection fusion mechanisms with one-bit overhead. SUs that are able to make local detection decisions either directly report their one-bit decisions to the cognitive radio base station or they relay their decisions to other favorable SUs based on the states of their reporting channels. If SUs can not make detection decisions, they relay the observed signals to other favorable SUs for further processing. Simulation results show HASS solution improves spectrum sensing performance in multi-hop cellular networks.

Correlative Coding Based Channel Estimation for Practical OFDM Systems over Time Varying Channels

OFDM systems encounter performance degradations in mobile environments due to inter-carrier interference (ICI) caused by Doppler spread. We find that previous studies using pilots to track the channel time variations always regard the ICI on pilots as additive white noise, which actually increases the estimation errors. As an enhancement of our previous studies on uneven pilot-assisted time-varying (TV) channel estimation (CE) for practical OFDM systems, to further improve the estimation precision, this paper employs the correlative coding to compress the ICI from data to pilots. Simulation results show that by using such a simple coding method, the ICI coefficient is reduced greatly and the estimation Mean Square Error (MSE) dropped by 3dB. It is proved that the correlative code based TV CE method is feasible for practical mobile OFDM systems with good performance and bandwidth efficiency.

Ant-Colony-Based Resource Allocation in OFDMA MESH Network

Although OFDMA is a candidate physical layer protocol for 802.16, there are few solutions for the wireless resource-allocating problem in OFDMA mesh network. In this paper, we study the current resource allocation methods in OFDM and OFDMA network, and introduce the architecture of OFDMA mesh network. We build a mathematic system model for the OFDMA mesh network, and propose a sophisticated ACO-based algorithm for wireless resource allocation. With our algorithm, we get acceptable solution, while fulfilling power and QoS constraints. Since our algorithm is easy to adapt to more realistic problems, it turns out to be a feasible method. The simulation result showed our algorithm is able to find a sub-optimal answer for resource allocation in OFDMA mesh network.

Cross-Layer Design: A Software Engineering Perspective

Cross-layer design is critical for efficient utilization of the scarce radio resources under time varying wireless channel. In this paper, a cross-layer design architecture named CLIME is proposed, which introduces the theory of modern software engineering to analyze the coupling in protocol stack brought by cross-layer designs. CLIME has the following distinct advantages. Firstly, DSA mechanism is used to build a loose coupling system by separating cross-layer interactions implementation from its management. Secondly, the modularity of protocol stack is considered to simplify the implementation of cross-layer interaction, while keeping good system architecture. Thirdly, CLIME supports query based local and global cross-layer interaction, and proposes a simple way to manage the consistency of multiple cross-layer designs. And simulation is done on time expense of different cross-layer interactions in CLIME.

Two-fold pricing for competitive spectrum sharing in cognitive wireless mesh networks

A market-based two-fold relay-spectrum pricing (TFRSP) scheme for competitive spectrum sharing in cognitive wireless mesh network is proposed. The TFRSP scheme can guarantee non-negative profit for each secondary user for a wide range of user utilities and pricing functions. We determine the relay and spectrum pricing functions according to traffic load and profit maximization. Simulation results show that, compared to two recently proposed single-fold pricing schemes, the proposed TFRSP scheme significantly increases the time average network profit and time average network throughput, and results in a more fair profit distribution among the mesh routers.

A novel successive relaying protocol based on superposition coding

Successive relaying is a prominent way to efficiently reduce the multiplexing loss in cooperation system. In this paper, we design a successive relaying protocol based on superposition coding. After solving the co-channel interference at the relays, they have capacity of forwarding the superposition code of the relaying signal and the source signal. An analysis model is established in terms of system achievable rate. The BER performance of our approach is also compared with that of some cooperation protocols. It is shown that the proposed protocol can reduce the system BER and offer some diversity gain, while achieves almost the same multiplexing performance compared with direct communication.