We consider a wireless cognitive radio network in which a set of secondary users (SUs) opportunistically utilize the wireless spectrum licensed to the primary users (PUs) to transmit packets to the secondary base station (SBS). It is challenging to maximize the spectrum utilization while limiting the interference imposed to PUs due to SUs. To achieve the optimal tradeoff between the spectrum utilization and the interference caused by SUs, we propose the adaptive spectrum sharing schemes for code division multiple access (CDMA) based cognitive medium access control (MAC) in the uplink communications over the cognitive radio networks. Our proposed schemes address the joint problems of channel sensing, data transmission, and power and rate allocations. Under our proposed schemes, the SUs can adaptively select between the intrusive spectrum sharing and the non-intrusive spectrum sharing operations to transmit data to SBS based on the channel utilization, traffic load, and interference constraints. Our proposed schemes enable the SUs to efficiently utilize the available frequency spectrum which is licensed to the PUs while stringently limiting the interference to the PUs. Also conducted are extensive simulations to validate and evaluate our proposed schemes, which show the superiority of our proposed schemes as compared with the other schemes.

Spectrum sensing, which finds spectrum opportunities for the secondary users (SUs), plays a pivotal role in the cognitive radio-based dynamic spectrum access networks. In this paper, we develop the optimal spectrum sensing scheduling for the energy-constraint cognitive radio networks where the SUs are not synchronized with the primary users (PUs). First, we develop the analytical models to investigate the tradeoff between the sensing energy consumption and the missed spectrum opportunity for the SUs. Second, building on top of the analytical models, we derive the optimal spectrum sensing scheduling which minimizes the sensing energy consumption while confining missed spectrum opportunity to a predefined threshold. Third, we take into account the sensing errors, namely, missed detection and false alarm, in the analytical models. In particular, we analyze the impact of the sensing errors on the energy consumption and missed spectrum opportunity when adopting the two-threshold based sequential sensing policy. Finally, we conduct simulations to validate and evaluate our proposed scheme.

We propose the network-coding-based relay MAC protocols that aim at providing drive-thru Internet services to the moving vehicles by utilizing the dedicated short range communication (DSRC) over vehicular networks. Our proposed MAC protocols can adaptively switch between two communications modes according to the highway traffic-load conditions. When the highway traffic load is heavy, our system works under the one-hop communications mode. When the density of vehicles on the road is low, the service base station turns on the network-coding-based two-hop relay mode that can extend the coverage of the non-safety data services to the two-hop area. We propose the wireless-network-coding schemes in the relay communications mode to improve the network performance. We also develop the analytical models to analyze the performance of our protocols. Also conducted are simulation experiments to validate and evaluate our proposed MAC protocols. Compared with the traditional IEEE 802.11 MAC protocol for Internet drive-thru services, our proposed relay MAC protocol can significantly increase the network efficiency.

This paper focuses on the spectrum sensing issues in the unslotted cognitive radio networks with wireless fading channels. To overcome the energy-inefficiency problem of the existing continuous/fixed-schedule spectrum sensing schemes in the cognitive radio networks, we propose an efficient spectrum sensing scheme for secondary users (SUs). The design goal of our proposed scheme is to save the sensing energy consumption while guaranteeing the priority of the PUs and the spectrum opportunity for SUs in terms of available spectrum usage time. In particular, our proposed energy-efficient spectrum sensing scheme adaptively adjusts the spectrum sensing periods and determines between the presence and vacancy of the PU by taking advantage of PU's activity patterns. We also develop a novel two-threshold based sequential sensing policy to reduce the false alarm probability while limiting the missed detection probability. We conduct simulations to validate and evaluate our proposed scheme.

This paper focuses on the unslotted cognitive radio networks in which the secondary users (SUs) are not synchronized with the primary users (PUs). The SUs can opportunistically utilize the wireless channel as long as the channel is not occupied by the PUs. Due to the half-duplex nature of the wireless medium, the SUs may inevitably impose interference to the PUs because the SUs cannot precisely predict when the PUs becomes active again, and stop transmitting in time. To overcome this challenge, we propose an interference-confined adaptive transmission scheme, which can dynamically adjust the transmission duration of the SUs based on the statistical information of PUs' activity such as to confine the interference with PUs to the acceptable level. Also conducted are extensive simulations to validate and evaluate our proposed scheme. The simulation results show that our proposed scheme can significantly outperform the existing transmission schemes.

We consider the time-unslotted cognitive radio based dynamic spectrum access (DSA) networks, where the secondary users (SUs) are unsynchronized with the primary users (PUs). We analytically derive the tradeoff between the energy consumption for spectrum sensing and the spectrum opportunity for SUs in terms of available spectrum usage time. We also consider the impact of the sensing errors, including missed detection and false alarm, on the energy consumption. Taking into consideration the sensing energy consumption, spectrum opportunities, and sensing errors, we propose a power-efficient periodic spectrum sensing scheme, which can save the sensing energy consumption while guaranteeing the priority of the PUs and the spectrum opportunity for the SUs. Also conducted are simulations to validate and evaluate our proposed sensing scheme.

Since the unlicensed 60 GHz band has the extensively wide continuous spectrum and its corresponding millimeter-wave signal has high directivity gain, the 60 GHz band is a good option for the broadband wireless mesh networks. This paper focuses on link scheduling and routing over the 60 GHz multi-channel wireless mesh networks, where each mesh router has multiple radios and multiple directional antennas. We formulate a linear programming based framework, which incorporates multi-channel and multi-radio, directional antenna, and 60 GHz millimeter-wave communications, to model the network throughput of the directional antenna based 60 GHz mesh networks. Under this framework, we derive the solution to the problem of maximizing the network throughput subject to the fairness constraint and the directional-antenna based wireless channel interference constraint. Then, we design a heuristic joint link scheduling and routing scheme which aims at approximately attaining the optimal solution to the joint optimization problem under our proposed framework. We conduct extensive simulations to validate and evaluate our proposed scheme.

Cognitive radio technology is widely accepted as an efficient approach to solve the problem that the wireless spectrum has been getting scarcer and scarcer due to the rapid growth in the ubiquitous wireless applications. Several cognitive medium access control (MAC) protocols have been proposed for the secondary users (non-licensed users) to take advantage of the vacant channels whenever they are not occupied by the primary users (licensed users) in the wireless time division multiple access (TDMA)-based networks. In this paper, by exploiting the unique property of the wireless fading channel and cross-layer design technique, we develop a packet scheduling scheme for the primary users in the context of wireless TDMA networks, which is set up to operate friendly towards the secondary users in terms of vacant-channel probability. Our proposed scheme can be implemented with just slight modification on the traditional TDMA scheduling algorithm. We develop a rigorous queuing model and then quantitatively analyze the tradeoff among multiple performance metrics to identify when and where the cost for favoring the secondary users is worthy. The analytical results show that our proposed scheme can generate more vacant-channel opportunities for secondary users, at the expense of little increasing packet delay, as compared with the traditional wireless TDMA scheduling algorithm. In addition, since the implementation of our proposed scheme only needs little modification on the existing TDMA scheduling algorithm, our proposed scheme is a practical and cost-effective approach to increase the wireless spectrum utilization.

Wireless network coding (NC) has emerged as a promising technology that improves network throughput and spectrum efficiency. How large can the coding gain be? In this paper, we study the network throughput gains of two types of wireless NC schemes, the conventional wireless NC and the analog NC, respectively, over the traditional non-NC scheme in multi-hop, multi-channel, and multi-radio wireless networks. In particular, we propose an analytical framework, which can exploit the best coding opportunities among all the possible realistic ones, for deriving the network throughput gains of the wireless NC schemes. By solving the problem of maximizing the network throughput subject to the fairness requirements under our proposed framework, we quantitatively analyze the network throughput gains of these two types of wireless NC schemes under various wireless network topologies.

We propose the cross-layer based battery-aware time division multiple access (TDMA) medium access control (MAC) protocols for wireless body-area monitoring networks in wireless healthcare applications. By taking into account the joint effect of electrochemical properties of the battery, time-varying wireless fading channels, and packet queuing characteristics, our proposed schemes are designed to prolong the battery lifespan of the wireless sensor nodes while guaranteeing the reliable and timely message delivery, which is critically important for the patient monitoring networks. In addition, we develop a Markov chain model to analyze the performance of our proposed schemes. Both the obtained analytical and simulation results show that our proposed schemes can significantly increase the battery lifespan of sensor nodes while satisfying the reliability and delay-bound quality of service (QoS) requirements for wireless body-area monitoring networks. Furthermore, the case study of the electrocardiogram (ECG) monitoring application shows that besides meeting the delay requirements, our proposed schemes outperform the IEEE 802.15.4 and Bluetooth protocols in terms of battery lifespan.

In this paper, we model the network throughput gains of two types of wireless network coding (NC) schemes, including the conventional NC and the analog NC schemes, over the traditional non-NC transmission scheduling schemes in multihop, multi-channel, and multi-radio wireless ad hoc networks. In particular, we first show that the network throughput gains of the conventional NC and analog NC are (2n)/(2n-1) and n/(n-1), respectively, for the n-way relay networks where n ges 2. Second, we propose an analytical framework for deriving the network throughput gain of the wireless NC schemes over general wireless network topologies. By solving the problem of maximizing the network throughput subject to the fairness requirements under our proposed framework, we quantitatively analyze the network throughput gains of these two types of wireless NC schemes for a variety of wireless ad hoc network topologies with different routing strategies. Finally, we develop a heuristic joint link scheduling, channel assignment, and routing algorithm that aims at approaching the optimal solution to the optimization problem under our proposed framework.

One of the critical problems for the wireless sensor networks is how to prolong the battery lifespan of the wireless sensor nodes. We proposed the cross-layer based battery-aware time division multiple access (TDMA) scheduling schemes for wireless sensor networks, which aim at maximizing the battery capacity utilization of wireless sensor nodes while satisfying the delay quality of service (QoS) requirements. Our proposed schemes take into account the joint effect of electrochemical properties of the battery, time-varying wireless fading channels, and packet queuing management. We develop a Markov chain model to analyze the performance of our proposed schemes. Based on the analytical model, we identify the tradeoff between the battery lifespan and the packet transmission delay. The analytical and simulation results show that our proposed schemes can significantly increase the battery lifespan of sensor nodes at the expense of acceptable increase of packet transmission delay.

Cognitive radio technology has emerged as the novel and effective approach to improve the utilization of precious radio spectrum. Employing the cognitive radio technology, secondary (unlicensed) users can opportunistically utilize the unused licensed spectrum in a way that constrains the level of interference to the primary (licensed) users. However, there are many new challenges associated with cognitive radio based wireless networks, such as the multi-channel hidden terminal problem and the fact that the time-varying channel availability is different for different secondary users, in the medium access control (MAC) layer. To overcome these challenges, we propose an efficient Cognitive Radio-EnAbled Multi-channel MAC (CREAM-MAC) protocol, which integrates the spectrum sensing at physical layer and packet scheduling at MAC layer, over the wireless networks. Under the proposed CREAM-MAC protocol, each secondary user is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. The proposed CREAM-MAC enables the secondary users to best utilize the unused frequency spectrum while avoiding the collisions among secondary users and between secondary users and primary users. In addition, we develop the analytical models to quantitatively analyze our proposed CREAM-MAC protocol in the saturated network case. We also conduct simulation experiments to validate our developed analytical models.

We propose the cross-layer based opportunistic multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing at physical (PHY) layer with the packet scheduling at MAC layer, for the wireless ad hoc networks. Specifically, the MAC protocols enable the secondary users to identify and utilize the leftover frequency spectrum in a way that constrains the level of interference to the primary users. In our proposed protocols, each secondary user is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is designed specifically as a cognitive radio that can periodically sense and dynamically use the identified un-used channels. To obtain the channel state accurately, we propose two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the availability of leftover channels. Under the random sensing policy, each secondary user just randomly selects one of the channels for sensing. On the other hand, under the negotiation-based sensing policy, different secondary users attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We develop the Markov chain model and the M/GY/1-based queueing model to characterize the performance of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respectively. In the non-saturation network case, we quantitatively identify the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.

We propose the cognitive-radio-based multi-channel medium access control (MAC) protocols, which integrate the spectrum sensing and packet scheduling, for the wireless ad hoc networks. Specifically, the cognitive MAC protocols allow secondary users to identify and use the unused frequency spectrum in a way that constrains the level of interference to the primary users. Under our proposed protocols, each secondary user is equipped with two transceivers. One of the transceivers operates on a dedicated control channel, while the other is used as a cognitive radio that can periodically sense and dynamically utilize the identified unused channels. To obtain the channel status accurately, we propose two types of collaboratively channel- sensing policies, namely random sensing policy and negotiation- based sensing policy, to help the MAC protocols detect the unused channels. We also develop the analytical models to study the proposed MAC protocols with the two types of channel-sensing policies.

We propose a spreading code medium access control (MAC) protocol with each node equipped with single transceiver for wireless ad hoc networks, based on the code division multiple access (CDMA) techniques. Our proposed scheme adopts the time division method to solve the near-far problem inherently associated with the CDMA-based networks. Specifically, by employing the ad-hoc traffic indication messages (ATIM) phase to properly determine the required transmission power for data packets, our scheme enables the interference-limited simultaneous transmissions to achieve the high utilization of the limited/precious bandwidth in wireless ad hoc networks. In addition, our scheme requires only one transceiver per node, which reduces the hardware costs for large scale wireless ad hoc networks. We use the Markov chain model to characterize the throughput of the proposed scheme. Based on the numerical and simulation evaluations, we thoroughly investigate the impact of various parameters on the performance of our proposed scheme.

Applying the code division multiple access (CDMA) techniques, we propose an efficient medium access control (MAC) protocol with single-transceiver for wireless ad hoc networks. Our protocol adopts the time-division method to solve the near-far power control problem inherently associated with the CDMA-based networks. In particular, employing the variable ad-hoc traffic indication messages (ATIM) window to properly determine the required transmission power for data packets, our scheme enables the interference-limited simultaneous transmissions to achieve the high utilization of the limited/precious bandwidth in wireless networks. In addition, our scheme requires only one transceiver per node, which reduces the hardware costs for large scale wireless networks. Using the Markov-chain techniques, we develop an analytical model to evaluate the aggregate throughput under our protocol. Both the analytical and simulation results show that our protocol can improve the network throughput significantly as compared with other existing schemes.

Because of the inherent constraints imposed by sensor nodes themselves, prolonging the span of network lifetime for the wireless sensor networks (WSNs) introduces many new challenges. In this paper, we consider the cluster-based heterogeneous WSNs, which consist of two types of nodes, namely, the powerful cluster-heads and the inexpensive sensor nodes. In particular, in the WSN, the sensor nodes are deployed along the grid points. To better balance the energy consumption, the sensor nodes exchange data with the cluster-heads through mixed communication modes, i.e., they can communicate with cluster-heads by either single-hop or multi-hop mode. Given the initial energy of the sensor nodes, we develop the analytical models to derive the optimal communication range and identify the optimal mixed communication modes to maximize the span of WSN's lifetime. Also presented are the simulation results which verify our developed analytical models.

Under the DSRC architecture, we propose a cluster-based multi-channel communication scheme to provision the quality of service (QoS), especially the real-time delivery of safety traffics, over the vehicle ad hoc networks (VANET). Our scheme integrates the clustering algorithm, contention-free, and contention-based MAC to support the real-time transmission of safety-messages. We develop the analytical model to conduct the safety message delay analyses. Our analyses show that our scheme can guarantee the real-time transmission of safety messages. The analytical results are also verified by our simulation experiments.

One of the most crucial requirements of a wireless ad-hoc network is to work efficiently and reliably over a long period of time. It is important to design a control technique that minimizes the transmission power of each mobile node without losing much of the performance while retaining the fairness of the network. The contribution of this paper is twofold. First, we show that the transmission energy consumption and the media access delay can be expressed as a function of the conditional collision probability in the IEEE 802.11 MAC protocol. Based on the analyses, a fundamental tradeoff between the system energy consumption and its performance can be found by tuning up the system control parameter CWmin. Second, we propose an enhanced energy-aware scheme based on the IEEE 802.11 protocol. The simulation results show that this technique is more energy efficient than the original IEEE 802.11 protocol while keeping a similar media access delay and a better fairness.

We develop energy-efficiency data gathering schemes for wireless sensor networks (WSN), where the channel is characterized by the slow Rayleigh fading. We consider the homogeneous WSN which consists of a large number of sensor nodes equipped with the identical hardware. In the WSN, the sensor nodes are distributed randomly in a specific area. A mobile base station periodically stops by the area to collect the data from the senor nodes. Energy efficiency, which is the performance metric we adopt for our scheme design, is defined as the energy consumption by transmitting a bit sensing information. We develop analytical models to study the proposed data gathering schemes. First, we demonstrate that clustering and data-fusion technology can help improve the energy efficiency compared to the naive data gathering scheme where the sensor nodes send sensing data directly to the mobile base station. Second, we show that making full use of the channel state information (CSI) can further reduce the energy consumption for data gathering. Finally, we found that there is a tradeoff between the energy consumption and the data gathering delay.

Prolonging the network lifetime is one of the most important designing objectives in wireless sensor networks (WSN). We consider a heterogeneous cluster-based WSN, which consists of two types of nodes: powerful cluster-heads and basic sensor nodes. All the nodes are randomly deployed in a specific area. To better balance the energy dissipation, we use a simple mixed communication modes where the sensor nodes can communicate with cluster-heads in either single-hop or multi-hop mode. Given the initial energy of the basic sensor nodes, we derive the optimal communication range and identify the optimal mixed communication mode to maximize the WSN's lifetime through optimizations. Moreover, we also extend our model from 2-D space to 3-D space.