David Tung Chong Wong

Opportunistic spectrum access for energy-constrained cognitive radios

This paper considers a scenario in which a secondary user (SU) opportunistically accesses a channel allocated to some primary network (PN) that switches between idle and active states in a time-slotted manner. At the beginning of each time slot, SU can choose to stay idle or to carry out spectrum sensing to detect the state of PN. If PN is detected to be idle, SU can carry out data transmission. Spectrum sensing consumes time and energy and introduces false alarms and mis-detections. The objective is to dynamically decide, for each time slot, whether SU should stay idle or carry out sensing, and if so, for how long, to maximize the expected reward. We formulate this as a partially observable Markov decision process and prove important properties of the optimal control policies. Heuristic control policies with low complexity and good performance are also proposed. Numerical results show the significant performance gain of our dynamic control approach for opportunistic spectrum access.

Directional Cooperative MAC Protocol Design and Performance Analysis for IEEE 802.11ad WLANs

In this paper, we consider the directional multigigabit (DMG) transmission problem in IEEE 802.11ad wireless local area networks (WLANs) and design a random-access-based medium access control (MAC) layer protocol incorporated with a directional antenna and cooperative communication techniques. A directional cooperative MAC protocol, namely, D-CoopMAC, is proposed to coordinate the uplink channel access among DMG stations (STAs) that operate in an IEEE 802.11ad WLAN. Using a 3-D Markov chain model with consideration of the directional hidden terminal problem, we develop a framework to analyze the performance of the D-CoopMAC protocol and derive a closed-form expression of saturated system throughput. Performance evaluations validate the accuracy of the theoretical analysis and show that the performance of D-CoopMAC varies with the number of DMG STAs or beam sectors. In addition, the D-CoopMAC protocol can significantly improve system performance, as compared with the traditional IEEE 802.11ad MAC protocol.

Design and Analysis for an 802.11-Based Cognitive Radio Network

This paper considers a distributed opportunistic spectrum access (D-OSA) scenario in which multiple cognitive radio (CR) users attempt to access a channel licensed to some primary network. CR users operate on a frame-by-frame basis and need to carry out spectrum sensing at the beginning of each frame to determine if the primary network is active or idle. Upon detecting the primary network being idle, each CR user employs a modified 802.11 DCF protocol for contention-based channel access. Spectrum sensing is imperfect and introduces false alarms and mis-detections. To protect primary users, it is required that the combined probability of mis-detection of all CR users must be below a specified threshold. We provide concrete protocol design, performance analysis, and extensive simulation results for our D-OSA design. Our results highlight the importance of taking a cross-layer view and jointly designing PHY-layer spectrum sensing and MAC-layer channel access.

Performance Analysis of Saturated Throughput of PCA in the Presence of Soft DRPs in WiMedia MAC

An analytical formulation of the saturated throughput of prioritized contention access (PCA) in the presence of soft distributed reservation protocols (DRPs) and beacon period (BP) in WiMedia MAC (formerly multi-band OFDM alliance (MBOA) MAC) is presented. The analytical framework is formulated for one soft DRP class and N PCA classes. The state transition diagram for the ith priority PCA class is modeled by a tri-dimensional discrete-time Markov chain. One dimension of the Markov chain is for the backoff stage, the second dimension is for the value of the backoff counter, while the third dimension is mainly for the delay due to DRP transmissions or BP. Numerical results of the saturated throughput corresponding to typical parameter values are presented.

Wireless Broadband Networks

This book combines theory with advanced practical applications in wireless broadband networks, presenting the reader with a standard reference that covers all aspects of the technology. It discusses the key theories underlying wireless broadband networks and shows readers how these theories are applied to real-world systems. It is an ideal resource for researchers in electrical engineering and computer science, as well as for students in advanced undergraduate and graduate courses in these fields.

Performance Analysis of Saturated Throughput of PCA in the Presence of Hard DRPs in WiMedia MAC

An analytical formulation of the saturated throughput of prioritized contention access (PCA) in the presence of hard distributed reservation protocols (DRPs) and beacon period (BP) in WiMedia MAC (formerly multi-band OFDM alliance (MBOA) MAC) is presented. The analytical framework is formulated for one hard DRP class and N PCA classes. The state transition diagram for the ith priority PCA class is modeled by a tri-dimensional discrete-time Markov chain. One dimension of the Markov chain is for the backoff stage, the second dimension is for the value of the backoff counter, while the third dimension is mainly for the delay due to DRP transmissions or BP. Numerical results of the saturated throughput corresponding to typical parameter values are presented.

Dynamic Spectrum Access with Imperfect Sensing in Open Spectrum Wireless Networks

Analytical formulations of dynamic spectrum access (DSA) with perfect sensing (PS) and imperfect sensing (IS) for two radio systems are presented. The DSA with PS model is solved explicitly using a two-dimensional Markov chain, respectively, while the DSA with IS model is solved numerically using a two-dimensional Markov chain. Grades of service (GoSs) like system airtime and blocking probabilities are considered. The performance of these GoS measures and the effect of the probability of false alarm and probability of misdetection for DSA with IS are evaluated. Numerical results illustrate that the effect of DSA with IS as compared with DSA with PS.

Capacity balancing between the reverse and forward links in multiservice CDMA cellular networks with cross-Layer design

Capacity unbalance is a practical problem for future cellular networks where the forward link traffic and the reverse link traffic are asymmetric. In this paper, an analytical framework for balancing the reverse and forward link capacities with an adaptive soft handoff probability (SHP) scheme in multiservice code-division multiple-access cellular networks is presented. With the proposed adaptive SHP scheme, system capacity can be balanced under various reverse and forward link traffic volumes, and system performance is optimized at the optimal SHP. A cross-layer model involving the physical layer, the link layer, and the network layer is presented. SHP in the physical layer, the outage probability in the link layer, and connection admission control (CAC) schemes, including complete sharing and virtual partitioning, in the network layer are jointly considered. The quality of service metrics in the link layer, including SIR and the outage probability, is derived with the information from the physical layer. The admission region is obtained by satisfying the outage probability requirements in both the forward and reverse links. Based on the admission region, the network layer grade of service, including the new connection blocking probability, the handoff connection dropping probability, and the throughput, is formulated as the performance metrics. The optimal SHP is selected by looking for the lowest penalty of connection blocking, which counts in both new connection blocking and handoff connection dropping probabilities. The cross-influences between the selection of the optimal SHP and the CAC schemes are also investigated. Numerical results show that the maximum achievable gain in throughput for the high-revenue services is about 80% by combining the benefits from the adaptive SHP and dynamic CAC schemes as compared to when none of these schemes is used

Resource allocation for end-to-end QoS provisioning in a hybrid wireless WCDMA and wireline IP-based DiffServ network

In the future UMTS network, the heterogeneous traffics of multimedia services demand various QoS provisioning. At the same time, the seamlessly conveying of information between mobile users and a hybrid network requires the networking from wireless to wireline domains. However, in both academia and industries, the end-to-end QoS provisioning in the integration of wireline and wireless networks remains a challenge. In this paper, a modeling of a hybrid wireless WCDMA and wireline IP-based DiffServ network is presented to investigate the resource allocation for end-to-end QoS provisioning for multimedia services. In the wireless domain, the mathematical modeling of the cross-layer model including the physical layer, the link layer and the network layer is built. The connection admission control scheme is implemented based on the cross-layer model to determine the amount of resource for different services. In the wireline domain, we define the mapping of QoS classes between UMTS and DiffServ networks according to different QoS requirements. We propose a bandwidth allocation scheme to provide satisfactory packet loss and delay guarantee in DiffServ networks. The final end-to-end admission control scheme combines the resource allocation and admission control in both wireless and wireline domains. The analytical and simulation results show that the proposed resource allocation and admission control schemes work cooperatively in the presented hybrid wireless and wireline networks to guarantee the end-to-end QoS requirements for multimedia services.

Performance Enhancement of IEEE 802.11e using DIPO/MOHD Backoff Mechanism

An analytical formulation of the saturated throughput enhancement of IEEE 802.11e using double increment plus one/ minus one half decrement (DIPO/MOHD) backoff mechanism for multiclass traffic is presented The analytical framework is formulated for N classes. The state transition diagram for the ith priority class is modeled by a two-dimensional discrete-time Markov chain One dimension of the Markov chain is for the backoff stage, and the second dimension is for the value of the backoff counter. The backoff stage moves to its previous backoff stage after a successful packet transmission and not back to the backoff stage 0 as in IEEE 802. lie. The advantages of this backoff mechanism are that it is easy to be implemented and can enhance the saturated throughputs. Numerical results of the saturated throughput corresponding to typical parameter values are presented The results show that the total saturated throughput using DIPO/MOHD can be better than that of IEEE 802. lie by up to 19%.