Yuxia Lin

An MDP-Based Vertical Handoff Decision Algorithm for Heterogeneous Wireless Networks

The architecture for the Beyond 3rd Generation (B3G) or 4th Generation (4G) wireless networks aims at integrating various heterogeneous wireless access networks. One of the major design issues is the support of vertical handoff. Vertical handoff occurs when a mobile terminal switches from one network to another (e.g., from wireless local area network to code-division multiple-access 1x radio transmission technology). The objective of this paper is to determine the conditions under which vertical handoff should be performed. The problem is formulated as a Markov decision process with the objective of maximizing the total expected reward per connection. The network resources that are utilized by the connection are captured by a link reward function. A signaling cost is used to model the signaling and processing load incurred on the network when vertical handoff is performed. The value iteration algorithm is used to compute a stationary deterministic policy. For performance evaluation, voice and data applications are considered. The numerical results show that our proposed scheme performs better than other vertical handoff decision algorithms, namely, simple additive weighting, the technique for order preference by similarity to ideal solution, and Grey relational analysis.

WSN01-1: Frame Aggregation and Optimal Frame Size Adaptation for IEEE 802.11n WLANs

The IEEE 802.11a/b/g have been widely accepted as the de facto standards for wireless local area networks (WLANs). The recent IEEE 802.11n proposals aim at providing a physical layer transmission rate of up to 600 Mbps. However, to fully utilize this high data rate, the current IEEE 802.11 medium access control (MAC) needs to be enhanced. In this paper, we investigate the performance improvement of the MAC protocol by using the two frame aggregation techniques, namely A-MPDU (MAC Protocol Data Unit Aggregation) and A-MSDU (MAC Service Data Unit Aggregation). We first propose an analytical model to study the performance under uni-directional and bi-directional data transfer. Our proposed model incorporates packet loss either from collisions or channel errors. Comparison with simulation results show that the model is accurate in predicting the network throughput. We also propose an optimal frame size adaptation algorithm with A-MSDU under error-prone channels. Simulation results show that the network throughput performance is significant improved when compared with both randomized and fixed frame aggregation algorithms.

Saturation throughput of IEEE 802.11e EDCA based on mean value analysis

The IEEE 802.11-based wireless LANs have been widely deployed for local area high-speed data access. The IEEE 802.11e amendment aims at providing QoS provisioning to support real-time multimedia traffic in WLANs. The enhanced distributed channel access (EDCA) is a QoS extension of the distributed coordination function (DCF) in IEEE 802.11a/b/g. In this paper, we propose an analytical model to evaluate the saturation throughput of the IEEE 802.11e EDCA. Our analytical model is based on the use of mean value analysis. We carry out extensive simulation study to validate the accuracy of the proposed model. Our scheme models accurately the effects of the change of contention window size and AIFS (arbitration inter-frame space). Our analytical model is applicable to real-time system tuning and on-line admission control algorithms which require a low computation complexity

A Vertical Handoff Decision Algorithm for Heterogeneous Wireless Networks

One of the major design issues in heterogeneous wireless networks is the support of vertical handoff. Vertical handoff occurs when a mobile terminal switches from one network to another (e.g., from WLAN to CDMA 1timesRTT). The objective of this paper is to determine the conditions under which vertical handoff should be performed. The problem is formulated as a Markov decision process. A link reward function and a signaling cost function are introduced to capture the tradeoff between the network resources utilized by the connection and the signaling and processing load incurred on the network. A stationary deterministic policy is obtained when the connection termination time is geometrically distributed. Numerical results show good performance of our proposed scheme over two other vertical handoff decision algorithms, namely: SAW (simple additive weighting) and GRA (grey relational analysis).

Cooperative protocols design for wireless ad-hoc networks with multi-hop routing

Wireless ad-hoc networks can experience significant performance degradation under fading channels. Spatial diversity has been shown to be an effective way of combating wireless fading with the multiple-input multiple-output (MIMO) technique by transmitting correlated information through multiple antennas. The virtual MIMO technique, which allows multiple wireless stations with single antenna to form a virtual transmission array, is shown to be a viable solution from several recent studies. In this paper, we propose a complete system framework for wireless ad-hoc networks utilizing two different cooperative relaying techniques at the physical layer: the repetition coding and the space-time coding. In the data link layer, two medium access control protocols are proposed to accommodate the corresponding physical layer cooperative diversity schemes. In the network layer, diversity-aware routing protocols are proposed to determine the routing path and the relaying topology. Simulations with both constant bit rate and TCP (transmission control protocol) traffic show significant performance gains of the proposed cooperative relaying schemes.

Experimental comparisons between SAODV and AODV routing protocols

There have been various secure routing protocols proposed for mobile ad hoc networks. Most of these protocols are analyzed by two standard techniques: simulation and security analysis. There has been a lack of work related to the performance of secure routing protocols in real network testbed. In this paper, we present quantitative results for the performance comparisons between AODV and SAODV routing protocols by using a small-scale experimental testbed, which consists of 10 laptops within a 250 m by 100 m rugby field. Apart from outdoor testing, we also compare the results with those obtained via simulation and indoor emulation. The workload includes both UDP and TCP traffic. Results show that SAODV is effective in preventing routing message tampering and data dropping attacks. For outdoor experiments, we also estimate the average distance within a communication gray zone under different bit rates.

Cross-Layer Design of MIMO-Enabled WLANs With Network Utility Maximization

Wireless local area networks (WLANs) have become a ubiquitous high-speed data-access technology. The recent IEEE 802.11e standard provides quality-of-service (QoS) support, and the pending 802.11n standard further increases the transmission rate by using the multiple-input-multiple-output (MIMO) technique. Multiple antennas can be used to improve the performance gain by either increasing the transmission reliability through spatial diversity or increasing the transmission rate through spatial multiplexing. This new characteristic at the wireless physical (PHY) layer requires the corresponding adaptation at the medium access control (MAC) layer to reach the best performance gain. In this paper, we propose cross-layer design schemes for WLANs under two different MAC protocols: the carrier sense multiple access with collision avoidance (CSMA/CA)-based 802.11e MAC and the slotted Aloha MAC. For the 802.11e MAC, two different contention window (CW) size adaptation schemes, namely, U-MAC and D-MAC, are proposed, which facilitate the MAC protocol to jointly adapt its CW size with the PHY layers MIMO operating parameters. For the slotted Aloha MAC, a cross-layer optimization framework NUM-O is proposed to jointly optimize the MIMO configuration at the PHY layer and the persistent probabilities for different classes of multimedia traffic at the MAC layer. A distributed algorithm NUM-D based on dual decomposition and a simplified version NUM-S are also proposed. Simulation results are presented to show the effectiveness of the proposed methods.

An admission control algorithm for multi-hop 802.11e-based WLANs

Recently, wireless local area network (WLAN) hotspots have been deployed in many areas. The new IEEE 802.11e standard further provides quality of service (QoS) provisioning by grouping the applications into four different access categories. The coverage area of WLANs can be extended by allowing the neighboring mobile devices to relay data to the access points. This concept is known as multi-hop WLANs or wireless mesh networks. Due to the limited network capacity and the contention-based channel access mechanism, admission control is required to regulate the number of simultaneous flows to maintain QoS. The multi-hop extension of WLANs present further challenges for admission control design due to the location-dependent contention in the network. In this paper, we propose an admission control algorithm for multi-hop 802.11e-based WLANs. In our proposed admission control algorithm, we first use a contention graph to model the contention situation in the multi-hop WLAN. It is followed by an estimation of the capacity for each maximal clique in the contention graph. A new flow is admitted if the aggregated traffic load is less than the estimated network capacity. The proposed algorithm supports both stationary and mobile nodes, as well as handoff and new connections. Simulation results show that the proposed algorithm is effective in providing QoS guarantee to the existing voice and video flows while maintaining a good performance for best effort traffic.

An admission control algorithm for multi-hop 802.11e based WLANs

Recently, wireless local area network (WLAN) hotspots have been deployed in many areas (e.g., cafes, airports, university campuses). The new IEEE 802.11e standard further provides quality of service (QoS) provisioning by grouping the applications (or traffic) into four different access categories. The coverage area of WLANs can be extended by allowing the neighboring mobile devices to relay data to the access points. This concept is known as multi-hop WLANs. Due to the limited network capacity and the contention-based channel access mechanism, admission control is required to regulate the number of simultaneous flows to maintain QoS. The multi-hop extension of WLANs present further challenges for admission control design due to the location-dependent contention in the network. In this paper, we propose an admission control algorithm for multi-hop 802.11e WLANs. The admission control algorithm first constructs the networks contention graph to break down the network contention situation into areas comprised of maximal cliques. Then, the admission decision is made by analyzing the available capacity of each maximal clique with 802.11e saturation throughput analysis. Simulation results show that our proposed algorithm is effective in providing QoS guarantee to the existing voice and video flows while maintaining a good performance for best effort traffic.

Analysis of Distributed Reservation Protocol for UWB-Based WPANs with ECMA-368 MAC

The recent ECMA-368 standard specifies the use of ultra wideband (UWB) technology for high rate communications in wireless personal area networks (WPANs). This paper proposes an analytical model for the performance analysis of the medium access control (MAC) protocol standardized in ECMA-368. The MAC protocol uses a superframe structure. Each superframe has a beacon period, a distributed reservation protocol (DRP) period, and a prioritized contention access (PCA) period. By using the Markovian arrival process (MAP) and phase type distribution (PH), we model this MAC layer as a MAP/PH/1 queueing system, and focus our study on the performance of the DRP period in this paper. The probability mass function of the number of DRP packets in the system, as well the cumulative distribution of the DRP packets waiting time are derived and compared with the simulation results in OPNET.