Abstract-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/G Y /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.Index Terms-Cognitive radio, multi-channel MAC, opportunistic spectrum access, cross-layer design, M/G Y /1 queueing theory, QoS provisionings.

Abstract-We propose a quality-of-service (QoS) driven power and rate adaptation scheme over wireless links in mobile wireless networks. Specifically, our proposed scheme aims at maximizing the system throughput subject to a given delay QoS constraint. First, we derive an optimal adaptation policy by integrating information theory with the concept of effective capacity for a block fading channel model. Our analyses reveal an important fact that there exists a fundamental tradeoff between throughput and QoS provisioning. In particular, when the QoS constraint becomes loose, the optimal power-control policy converges to the well-known water-filling scheme, where Shannon (ergodic) capacity can be achieved. On the other hand, when the QoS constraint gets stringent, the optimal policy converges to the total channel inversion scheme under which the system operates at a constant rate. Inspired by the above observations, we then consider a more practical scenario where variable-power adaptive modulation is employed over both block fading and Markov correlated fading channels. In both cases, we derive the associated power and rate adaptation policies. The obtained results suggest that the channel correlation has a significant impact on QoS-driven power and rate adaptations. The higher the correlation is, the faster the power-control policy converges to the total channel inversion when the QoS constraint becomes more stringent. Finally, we conduct simulations to verify that the adaptation policy proposed for Markov channel models can also be applied to the more general channel models.Index Terms-Mobile wireless networks, quality-of-service (QoS), effective capacity, power control, adaptive modulation, information theory, cross-layer design and optimization.

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Abstract-We propose a cross-layer-model based adaptive resource-allocation scheme for the diverse quality-of-service (QoS) guarantees over downlink mobile wireless networks. Our proposed scheme dynamically assigns power-levels and timeslots for heterogeneous real-time mobile users to satisfy the variation of statistical delay-bound QoS requirements. To achieve this goal, we apply Wu and Negi's effective capacity approach to derive the admission-control and power/time-slot allocation algorithms, guaranteeing the statistical delay-bound for heterogeneous mobile users. When designing such an algorithm, we study the impact of physical-layer issues such as adaptive power-control and channel-state information (CSI) feedback delay on the QoS provisioning performance. Through numerical and simulation results, we observe that the adaptive power adaptation has a significant impact on statistical QoS-guarantees. In addition, the analyses indicate that our proposed resourceallocation algorithms are shown to be able to efficiently support the diverse QoS requirements for various real-time mobile users over different wireless channels. Also, in an in-door mobile environment, e.g., the widely used wireless local-area networks (WLAN), our proposed algorithm is shown to be robust to the CSI feedback delay.

Swollenin is a novel plant expansin-like protein that has been proposed to have a cellulose disruption activity. In this study, the recombinant swollenin (SWO2) from Trichoderma pseudokoningii S38 was successfully produced and purified in Aspergillus niger with a final yield of up to 10 mg of purified protein from 1 l of fermentation supernatant. The recombinant protein was found to exhibit very low level of endoglucanase activity and caused a slight increase in the crystallinity when treating cellulose. Simultaneous incubation of SWO2 with lowdose cellulases resulted in a significant synergistic activity in cellulose hydrolysis. Specifically, an even greater increase in the synergistic activity was obtained when cellulose was pretreated with swollenin followed by cellulase hydrolysis. Our results, therefore, provide a novel approach for the potential application of swollenin in the efficient saccharification of cellulosic materials.

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Function classificationsCommunication domains MAC types usedOperating channels INTERVEHICULAR COMMUNICATIONS INTRODUCTIONIntelligent Transport System (ITS) architecture provides a framework for the much needed overhaul of the highway transportation infrastructure. The immediate impacts include alleviating the vehicle-traffic congestion and improving operations management in support of public safety goals, such as collision avoidance. Equipping vehicles with various kinds of on-board sensors and instrumenting the vehicle-to-vehicle (V2V) communication capability will allow large-scale sensing, decision, and control actions in support of these objectives. The allocation of 75 MHz in the 5.9 GHz band licensed for Dedicated Short Range Communication (DSRC) [1], which supports seven separate channels, may also enable the future delivery of rich multimedia contents to vehicles at short-to-medium range via either V2V or vehicle-to-roadside (V2R) links in Vehicle Ad Hoc Networks (VANETs). While there has been a large body in the literature studying both V2V [2, 3] and V2R [4,5] networks, there are several advantages of using V2V-based VANETs as compared with the V2R-based VANETs. First, the V2V-based VANET is more flexible and independent of the roadside conditions, which is particularly attractive for the most developing countries or remote rural areas where the roadside infrastructures are not necessarily available/furnished. Second, the V2V-based VANET is less expensive than V2R-based, since it does not need expensive roadside infrastructures. Third, V2V-based VANET can avoid the fast fading, short connectivity time, high frequent hand-offs, and so forth caused by the high relative-speed difference between the fast-moving vehicles and the stationary basestations. Finally, the V2V-based VANET much better fits vehicle-related applications, which only needs to exchange data/information among neighboring vehicles within their nearby areas. Motivated by the above observations, in this article we will focus on the V2V-based VANETs.The data transmitted over the VANETs can be classified into the real-time traffic (such as safety messages and video/audio signals) and the non-real-time traffic (such as e-maps and road/vehicle-traffic/weather information), which impose the diverse quality-of-service (QoS) requirements for VANETs designs. Supporting ABSTRACTThe Dedicated Short Range Communications (DSRC) standard equipped with seven channels is designated for Intelligent Transportation System (ITS) applications to improve the driving safety and support networking services among moving vehicles. Making best use of the DSRC multichannel architecture, we propose a clusterbased multichannel communications scheme, which integrates the clustering with contentionfree/contention-based MAC protocols. In our proposed scheme, the elected cluster-head (CH) vehicle functions as the coordinator (like WLAN's basestation) to collect/deliver the realtime safety messages within its own cluster and forward the consolidated safety messages to the ne...