The provision of location-based services with high positional accuracy requires the use of Time of Arrival (TOA)-based techniques. However, existing TOA-based WLAN location service schemes are inefficient due to the individual query and response ranging method employed. We present a highly efficient WLAN location service architecture which includes a modification to the Transmit Opportunity (TXOP) technique in the IEEE 802.11e standard. Our Location Service with TXOP (LSOP) scheme achieves high efficiency by minimizing the number of TOA transmissions and eliminating the contention overhead for TOA messages. The adaptation of TXOP technique also improves location accuracy by protecting TOA messages from collision and by grouping the TOA messages into one compact burst. Our analysis shows that the LSOP scheme achieves the highest location update rate compared to previous schemes. Our simulation results show that the LSOP scheme has minimum impact on data traffic and achieves higher accuracy than the previous schemes. Experimental results demonstrate the degradation in localization performance caused by packet collisions. These results validate that our LSOP scheme, which implements contention-free broadcast of TOA messages with a modified TXOP, provides the best combination of high location update rate, low network load, and high location accuracy compared to other schemes.

802.11e enhanced distributed channel access (EDCA) introduces different parameters to provide differentiated QoS support for various traffic classes. This brings additional difficulties and complexities to the traditional per-slot based Markov chain modeling techniques, where the transmission probability relies on generic time slots. Channel access cycle based modeling, which does not depend on per-slot states, breaks new ground in 802.11e EDCA study. However, the current cycle based model only considers saturated traffic load conditions, while typical network conditions are unsaturated with significant idle periods. We define a new unsaturated channel access cycle that includes a potential idle period and post-backoff procedure, in addition to the backoff procedure and a transmission attempt of the saturated cycle. A new EDCA model for unsaturated traffic conditions is proposed based on this channel access cycle. Our model achieves high accuracy in describing channel access operations over a wide range of traffic conditions. The model solutions, validated by ns-2 simulations, accurately characterize the unique features of 802.11e EDCA in unsaturated traffic conditions.

We consider the impacts of channel fading on the quality of service (QoS) performance of the IEEE 802.11 system. Traditional 2-D Markov chain models, while suitable for throughput analysis, are unable to capture the QoS performance due to the lack of a proper queueing model. We present a 3-D Markov chain queueing model that incorporates channel fading effects and solve the Markov chain efficiently with our Collapsed Transition onto Basis approach. In doing so, we are able to investigate important QoS measures, packet delay and loss, as well as throughput, for a 802.11 system under practical channel fading conditions. The analytical results are validated by extensive simulations. Our 3-D model offers new insights in channel fading effects on system capacity and QoS performance. We demonstrate that our 3-D model can also be used to provides guidelines for traffic control.

Wireless tracking is being increasingly used in elite and professional sports for training and performance monitoring. Accurate and high update rate tracking in indoor venues is the challenge that we are addressing. In this paper we propose a new algorithm for network round-trip ranging based on the measurement of time of arrival that supports high update rates and tracks and removes errors caused by changes in propagation delay in the analog electronics. The localization performance of our proposed algorithm is validated by results acquired in a sporting venue using our localization system, which is based on a custom TDMA protocol. We then discuss the issues with implementing the scheme in an 802.11 wireless network, propose an extension to the standard to support our scheme, and present analysis and simulation results to demonstrate the benefit over other schemes.

In multi-hop cognitive radio networks (CRNs), there can be dramatic increase in end-to-end delay when a traffic flow switches between a number of channels along its path. We propose a new Maximum Flow-Segment (MFS) based scheme to channel assignment in CRN by minimizing the number of times the channel is switched along a flow. Our MFS based scheme has been efficiently integrated into the AODV on-demand routing protocol. We demonstrate that our MFS based scheme reduces the number of channel switches for the traffic flows and reduces the end-to-end delay by 50%. Our scheme also minimizes the routing overhead, and achieves a higher and more stable throughput than the link based approach.

The capture effect can occur in IEEE 802.11 distributed coordination function (DCF) wireless systems when packets arrive with different powers. Packets with high power can effectively swamp low power packets, such that they are received successfully, when otherwise a collision would have occurred. We present a network performance prediction model that accurately incorporates the capture effect into a 3-D Markov Chain. The model is solved efficiently with the Collapsed Transition onto Basis (CTB) approach. The performance of the model is significantly better than existing models in terms of estimating important QoS measures, including packet delay and loss, as well as collision probability and throughput.

The major objective of an admission control in wireless mesh networks is to prevent excessive real-time traffic from over-utilizing the bandwidth resources. A key component of an admission control is an accurate estimator of the bandwidth available at each node and of the actual bandwidth (including the MAC overhead) required by a new flow. This estimation problem is particularly difficult when node localization information is not available. We propose a novel admission control based on active neighbor bandwidth reservation (AC-ANBR), by which active neighbors periodically broadcast bandwidth reservation information and flow setup requests carry their bandwidth reservation states. Our proposed AC-ANBR accurately estimates the available bandwidth at each node, as well as the bandwidth required by each new flow. The effectiveness of AC-ANBR in multi-hop wireless networks is demonstrated by NS-2 simulations.

Experiments show that IEEE 802.11 DCF system exhibits unstable behavior in the congestion onset load range where the system starts to become saturated. This phenomenon is not well investigated due to the lack of proper models. In this paper, we propose a two-dimensional (2-D) Markov chain model by combining the well-known saturated model with newly created idle states. Closed-form solution to the 2-D Markov chain is derived, and system performances are validated by simulations. With the proposed 2-D model, we are able to characterize the unstable system behavior, and provide insights into 802.11 DCF system dynamics.

This paper addresses when and how to adjust bandwidth allocation on uplink and downlink in a multi-service mobile wireless network under dynamic traffic load conditions. Our design objective is to improve system bandwidth utilization while satisfying call level QoS requirements of various call classes. We first develop a new threshold-based multi-service admission control scheme (DMS-AC) as the study base for bandwidth re-allocation. When the traffic load brought by some specific classes under dynamic traffic conditions in a system exceeds the control range of DMS-AC, the QoS of some call classes may not be guaranteed. In such a situation, bandwidth re-allocation process is activated and the admission control scheme will try to meet the QoS requirements under the adjusted bandwidth allocation. We explore the relationship between admission thresholds and bandwidth allocation by identifying certain constraints for verifying the feasibility of the adjusted bandwidth allocation. We conduct extensive simulation experiments to validate the effectiveness of the proposed bandwidth re-allocation scheme. Numerical results show that when traffic pattern with certain bandwidth asymmetry between uplink and downlink changes, the system can re-allocate the bandwidth on uplink and downlink adaptively and at the same time improve the system performance significantly.

This paper addresses when and how to adjust bandwidth allocations between uplink and downlink in a multi-service wireless network with bandwidth asymmetry under dynamic traffic load conditions. A new distributed multi-service admission control policy is developed first to guarantee the call level QoS requirements. When the traffic load brought by the calls of some specific classes in a cell exceeds the control range of the admission control, bandwidth re-allocation process could be activated and the admission control policy will try to meet the QoS requirements under the adjusted bandwidth allocation. The numerical results show that the QoS requirements of different call classes can be guaranteed under the dynamic traffic conditions while the system resources are utilized efficiently by using the proposed bandwidth re-allocation strategy.

For the design of call admission control (CAC) policy in wireless networks, how to decrease the average system cost is a key issue. In this paper, we study the optimal admission policy for minimizing the system cost. By modeling the admission control problem into a Markov decision process (MDP) and analyzing the corresponding value function, we obtain some monotonicity properties of the optimal policy. These properties suggest that the optimal admission control policy for the bandwidth asymmetry wireless networks should have a threshold structure and the threshold specified for a class of calls may change with the system state. Due to the prohibitively high complexity for computing the thresholds in a system with large state space, we propose a heuristic CAC policy called call-rate- based dynamic threshold (CRDT) policy to approximate the theoretical optimal policy based on the insights we obtain from the modeling and the analytical study on the properties of the optimal policy. The CRDT policy is efficient and can be easily implemented. The numerical results show that the performance of average system cost of the proposed CRDT policy is close to that of the optimal policy from the MDP model and is better than that of some known existing CAC schemes, including those performing well in bandwidth asymmetry wireless networks.

In reliable multicast, data packets can be cached at some nodes such as repair servers for future possible retransmission in loss recovery schemes. How to cache packets to optimize the performance of loss recovery is an important issue in reliable multicast protocol design. In this paper, we present a general solution which addresses the main design problems of caching policies. We first formulate the caching policy design as an optimization problem by employing caching utility as a uniform measure. Based on caching utility, we propose an algorithm called Optimal Caching Time (OCT) for configuring the caching time of packets and demonstrate that it solves the optimization problem. Furthermore, we analyze the performance improvement of OCT caching policy compared to the existing caching policies such as FIFO, Probabilistic FIFO (P-FIFO), and Timer-Based Caching Policy (TBCP). We use ns-2 simulations to demonstrate the performance gains brought by OCT caching policy. The numerical results show that OCT caching policy improves the performance significantly, especially for heterogeneous groups of receivers. With the inherent generality of the proposed model and the OCT algorithm, they can be easily applied to the general cache design in reliable unicast or multicast applications, and in both wired and wireless networks.

In multi-service mobile networks, asymmetric bandwidth allocation has been proposed to satisfy the requirements of the asymmetric traffic load introduced by some data applications. However, it is difficult to promptly adjust bandwidth allocation on the uplink and downlink according to the traffic load dynamics. Superfluous real-time (RT) calls or non-real-time (NRT) calls might be accepted. This may lead to a low bandwidth utilization. In this paper, we propose and evaluate a new call admission control (CAC) scheme to address the problems caused by the mismatch of bandwidth allocation and traffic changes. By determining the admissible bandwidth region for the NRT calls, the proposed scheme prevents the calls from overusing the bandwidth resources. Thus the bandwidth utilization is improved and the blocking probability of the high priority calls can be guaranteed at a low level. The simulation results demonstrate that the proposed CAC scheme can achieve better performance compared to the existing schemes, even those performing well in multi-service mobile networks with asymmetric bandwidth allocation.