Qingyang Song

Network selection in an integrated wireless LAN and UMTS environment using mathematical modeling and computing techniques

The increasing demand for broadband service, at least in hot spot areas, in todays wireless communications is causing cellular network providers to consider the integration of 3G cellular systems and wireless LAN. This has the particular advantage of high data rates and unlicensed spectrum. Consequently, network selection techniques play a vital role in ensuring quality of service in heterogeneous networks. In this article we develop a network selection scheme for an integrated cellular/wireless LAN system. The design goal is to provide the user the best available QoS at any time. The proposed scheme comprises two parts, with the first applying an analytic hierarchy process (AHP) to decide the relative weights of evaluative criteria set according to user preferences and service applications, while the second adopts grey relational analysis (GRA) to rank the network alternatives with faster and simpler implementation than AHP. Simulations conducted in a heterogeneous system with UMTS and wireless LAN reveal that the proposed network selection technique can effectively decide the optimum network through making trade-offs among network condition, user preference, and service application, while avoiding frequent handoffs.

A network selection mechanism for next generation networks

The predominant objective of next-generation networks (i.e. 4G) is to support high bandwidth with high mobility. 3G technologies provide low bandwidth at a cellular level, and wireless local area network (WLAN) supports much higher bandwidth at a local level. The two types of technologies are seamlessly integrated in 4G networks. In this paper, we present an efficient network selection mechanism for next-generation networks to guarantee mobile users being always best connected (ABC). Two mathematical techniques are combined in the mechanism to decide the optimum network for mobile users through finding the tradeoff among users preference, service application, and network condition.

A quality of service negotiation-based vertical handoff decision scheme in heterogeneous wireless systems

This paper introduces a novel vertical handoff decision scheme. The objective is to provide users with enhanced quality of service (QoS) and maximize the network revenue. This scheme balances both-side interests via a suitably defined network merit function and a user-operator negotiation model. The merit function evaluates network performance based on user preferences and decides the most appropriate network for users. The negotiation model is defined as a semi-Markov decision process (SMDP). An optimal policy that maximizes the network revenue without violating QoS constraints is found by resolving the SMDP problem using Q-learning. Furthermore, a time-adaptive QoS monitoring mechanism is combined with the merit function in order to decrease the power consumption on terminal interface activation. The simulation results demonstrate that the proposed vertical handoff decision scheme enhances the performance in terms of power consumption, handoff call-dropping probability (HCDP) and network revenue.

Rate and Power Adaptation for Analog Network Coding

Network coding is an emerging technique of packet forwarding that encodes the packets at the relay node to increase the throughput of a relaying network. Analog network coding (ANC) encodes the packets by superposing the signals at the physical layer, which can further bring throughput improvements. In this paper, we first analyze the coding procedure of ANC and elaborate the fact that the maximum possible number of coding nodes in ANC is two for common wireless transceivers. Then, we propose a rate adaptation scheme for ANC. We show that the transmission powers of nodes affect the data rate and that transmitting at the maximum power is not always optimal. Based on this observation, we propose a method of finding the optimal transmission power that maximizes the data rate. We also discuss some issues that need to be considered when implementing the proposed scheme in practical wireless systems. Then, the performance of the proposed scheme is evaluated through extensive simulations. The simulation results show that the proposed joint rate and power adaptation scheme outperforms ANC without power adaptation and that it is beneficial over other relaying schemes in a broad range of scenarios of mobile and vehicular applications.

An adaptive quality-of-service network selection mechanism for heterogeneous mobile networks

The success of broadband service has attracted more people to surf internet with the demand of high mobility and high bandwidth. The ongoing wireless local area network (WLAN) standardization and development activities allow WLAN to provide high data rate in unlicensed spectrum. It motivates cellular network operators to adopt WLAN as a complement to cellular 3G systems in hot spot areas. Consequently, it is imperative to develop a network selection technique to assure quality-of-service (QoS) for the integrated cellular/WLAN system. In this paper, an optimization scheme for mobile users to select a network in an integrated WLAN and universal mobile telecommunication system (UMTS) system is proposed. In order to provide users a prospect of being always best connected, analytic hierarchy process (AHP) and grey relational analysis (GRA) techniques are integrated to make decision. The former defines selection criteria and the latter evaluates network alternatives. The network selection module is built at the link layer, and collects the time-varying QoS information through cross-layer message signaling. Simulations conducted in a heterogeneous system with UMTS and WLAN show that the proposed network selection technique can successfully satisfy QoS requirements for a variety of applications through a fair decision on the optimum network for mobile users at any time. Copyright

Distributed MAC Protocol Supporting Physical-Layer Network Coding

Physical-layer network coding (PNC) is a promising approach for wireless networks. It allows nodes to transmit simultaneously. Due to the difficulties of scheduling simultaneous transmissions, existing works on PNC are based on simplified medium access control (MAC) protocols, which are not applicable to general multihop wireless networks, to the best of our knowledge. In this paper, we propose a distributed MAC protocol that supports PNC in multihop wireless networks. The proposed MAC protocol is based on the carrier sense multiple access (CSMA) strategy and can be regarded as an extension to the IEEE 802.11 MAC protocol. In the proposed protocol, each node collects information on the queue status of its neighboring nodes. When a node finds that there is an opportunity for some of its neighbors to perform PNC, it notifies its corresponding neighboring nodes and initiates the process of packet exchange using PNC, with the node itself as a relay. During the packet exchange process, the relay also works as a coordinator which coordinates the transmission of source nodes. Meanwhile, the proposed protocol is compatible with conventional network coding and conventional transmission schemes. Simulation results show that the proposed protocol is advantageous in various scenarios of wireless applications.

Fault-tolerant routing mechanism based on network coding in wireless mesh networks

As an essential part of next generation Internet, Wireless Mesh Networks (WMNs) have attracted much research attention due to their potential advantages, including low up-front cost, ease of deployment, enhanced capacity and service coverage. However, the inherit features of wireless channels (e.g., interference, noise, fading and limited bandwidth) have put forward a severe challenge for network reliability. Conventional fault-tolerant techniques either waste too many bandwidth resources or postpone the recovery speed. This paper proposes a random linear network coding based fault-tolerant routing mechanism to instantaneously recover the native packets omitted by the source. This mechanism couples the multi-path routing and random linear network coding technique by improving the conventional method of coding nodes selection. Simulation results demonstrate that our proposed fault-tolerant routing mechanism, which includes Random linear Network Coding in Multi-path with Source Coding (RNCM-SC) and Random linear Network Coding in Multi-path with Source Forwarding (RNCM-SF), perform better in terms of packet delivery ratio, resource redundancy degree, end-to-end delay and useful throughput ratio than the traditional method.

Link stability estimation based on link connectivity changes in mobile ad-hoc networks

Link stability issue is significant in many aspects, especially for the route selection process in mobile ad-hoc networks (MANETs). Most previous works focus on the link stability in static environments, with fixed sampling windows which are only suitable for certain network topologies. In this paper, we propose a scheme to estimate the link stability based on link connectivity changes, which can be performed on the network layer, without the need of peripheral devices or low layer data. We adopt a variable sized sampling window and propose a method to estimate the link transition rates. The estimation scheme is not restricted to specific network topologies or mobility models. After that, we propose a routing method which adjusts its operating mode based on the estimated link stability. Simulation results show that the proposed scheme can provide correct estimation in both stationary and non-stationary scenarios, and the presented routing protocol outperforms conventional routing schemes without link stability estimation.

Constellation mapping for physical-layer network coding with M-QAM modulation

The denoise-and-forward (DNF) method of physical-layer network coding (PNC) is a promising approach for wireless relaying networks. In this paper, we consider DNF-based PNC with M-ary quadrature amplitude modulation (M-QAM) and propose a mapping scheme that maps the superposed M-QAM signal to coded symbols. The mapping scheme supports both square and non-square M-QAM modulations, with various original constellation mappings (e.g. binary-coded or Gray-coded). Subsequently, we evaluate the symbol error rate and bit error rate (BER) of M-QAM modulated PNC that uses the proposed mapping scheme. Afterwards, as an application, a rate adaptation scheme for the DNF method of PNC is proposed. Simulation results show that the rate-adaptive PNC is advantageous in various scenarios.

A Time-Adaptive Vertical Handoff Decision Scheme in Wireless Overlay Networks

This paper presents a time-adaptive vertical handoff decision scheme for overlapping wireless networks. The proposed scheme discovers all the reachable networks and then selects the most suitable one as the handoff target through performance evaluation that relies on user preferences and service requirements. In order to guarantee the right decisions can be made timely with the minimum battery power consumption on interface activation, two algorithms of producing dynamic activating intervals are developed. The simulation results reveal that the proposed method can effectively balance the spent time and consumed power for making handoff decisions