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High propagation delay, high error probability, floating node mobility, and low data rates are the key challenges for Underwater Wireless Multimedia Sensor Networks (UMWSNs). In this article, we propose RL-MAC, a Reinforcement Learning (RL)–based Medium Access Control (MAC) protocol for multimedia sensing in an Underwater Acoustic Network (UAN) environment. The proposed scheme uses Transmission Opportunity (TXOP) for relay nodes in a multi-hop network for improved efficiency concerning the mobility of the relays and sensor nodes. The access point (AP) and relay nodes calculate traffic demands from the initial contention of the sensor nodes. Our solution uses Q-learning to enhance the contention mechanism at the initial phase of multimedia transmission. Based on the traffic demands, RL-MAC allocates TXOP duration for the uplink multimedia reception. Further, the Structural Similarity Index Measure (SSIM) and compression techniques are used for calculating the image quality at the receiver end and reducing the image at the destination, respectively. We implement a prototype of the proposed scheme over an off-the-shelf, low-cost hardware setup. Moreover, extensive simulation over NS-3 shows a significant packet delivery ratio and throughput compared with the existing state-of-the-art. [ABSTRACT FROM AUTHOR]

Designing an efficient spectrum assignment (SA) mechanism is a key issue for realizing dynamic spectrum access in cognitive radio network. In multi-channel selection based SA schemes, secondary users (SUs) are able to utilize multiple channels simultaneously to enhance the network throughput. However, a fairness problem may happen if few SUs utilize too many idle data channels that other SUs are left with no idle channels, thus increasing the blocking probability and reducing the fairness. Aiming at improving the network throughput with multi-channel selection capability while maintaining fairness among the SUs, in this paper, we propose a fair multi-channel assignment scheme (FMCA) for distributed cognitive radio networks. For the FMCA scheme, we design a new MAC framework for sensing and access contention resolution, which is integrated into the FMCA scheme. Channel-aggregation (CA) technique is used in each SU to enable the multi-channel selection ability. Considering both of the idle data channel utilization efficiency and the transmit power budget constrained CA ability of each SU, we analytically formulate a channel assignment problem according to the well-known Jain's fairness criterion. Our objective is to find a channel assignment with maximal fairness index for all SUs. The optimization problem is turned out to be a quadratic integer programming (QIP). According to the definition of Jain's fairness criterion, we design an algorithm to get the optimal solution of the QIP. With the optimal channel assignment solution, the FMCA scheme is realized in the channel assignment phase of the proposed MAC protocol. Extensive simulation results show that the proposed FMCA scheme gets a good tradeoff between throughput and fairness compared with the existing SA schemes.

Medium Access Control (MAC) protocol plays an important role in full-duplex wireless networks. Theoretically, full-duplex communications have this ability to increase the capacity of traditional half-duplex wireless systems by up to twice. However, designing and implementing an efficient MAC protocol is a central issue in this way. Increasing throughput, collision avoidance, and fairness are common challenges in designing an efficient full-duplex MAC protocol. After giving a short introduction to the general classification of traditional MAC protocols, IEEE 802.11 MAC protocol, and the identified challenges of full-duplex communications in wireless networks, this review paper provides a comprehensive survey of current major MAC protocols for full-duplex wireless communications and classifies them in to three categories i.e. distributed wireless local area networks, centralized wireless local area networks, and other types of networks. This paper also explores and gives a comparative analysis of current full-duplex MAC protocols with stating their advantages and disadvantages as well as comparing them one with another. [ABSTRACT FROM AUTHOR]

The major challenge encountered by battery-driven wireless local area networking devices is to conserve their energy for prolonged operation. This paper presents an energy-efficient medium access mechanism called group control slot allocation (GCSA) protocol for cognitive radio (CR) networks. GCSA utilizes the group priority allocation algorithm to allocate stations (STAs) into groups; subsequently STAs that have traffic buffered in an access point are assigned to a higher priority group. A management frame, namely group monitoring pointer, optimizes the sleep-awake cycle of the STAs by allocating transmission opportunities to groups based on their priority. GCSA employs publisher-subscriber and point-to-point messaging models for communication between the base station and STAs, respectively. Performance analysis of GCSA demonstrates that increasing the number of STAs which enter into sleep mode augments the percentage of energy saved. The overall system-level results show that energy saved is around 20% higher for GCSA than the IEEE 802.11e standard hybrid coordination function power-saving mode. Since GCSA benefits from history-assisted-led spectrum sensing, the paper also presents the relationship of the local storage of CRs with respect to history and suggests a hybrid approach as best option to keep a balance between the sensed data and its sharing with analytical engine database for history enrichment leading toward improved energy efficiency. [ABSTRACT FROM AUTHOR]

Constrained-energy underwater acoustic nodes are typically connected via a multi-hop underwater acoustic network (MHUAN) to cover a broad marine region. Recently, protocols for efficiently connecting such nodes have received considerable attention. In this paper, we show that the time reversal (TR) process plays an important role in the medium access control (MAC) because of its physical capability to exploit the multi-path energy from the richly scattering underwater environment, as well as to focus the signal energy in both spatial and temporal domains. In MHUANs, with severe multi-path propagation at the physical layer, the active TR process spatially focuses the signals to the location of the intended receiver; this significantly diminishes the interference among parallel links. We propose an active TR-based MAC (TRMAC) protocol for MHUANs, with the aim of minimizing collision and maximizing channel utilization simultaneously. Furthermore, by considering the impact of the cross correlation between different links on the TR-based medium access, we derive the threshold of the link cross correlation to resolve collision caused by the high cross correlation between realistic links. We perform simulations using the OPNET and BELLHOP environments, and show that the proposed TRMAC results in significantly improved throughput, decreased delay, and reduced data drop ratio in MHUANs. [ABSTRACT FROM AUTHOR]

In PRI-MAC (Pipelined-forwarding, routing-Integrated and effectively-Identifying MAC) protocol, a node gets only one chance to succeed in data transmission scheduling per cycle and on success, a node can transmit only one data packet. On the other hand, in JRAM (joint routing and MAC) protocol, a node gets multiple $\left ({k}\right)$ chances to succeed in data transmission scheduling per cycle and on success, a node can transmit multiple $\left ({N^{\prime}}\right)$ data packets. Therefore, the analytical model proposed for performance analysis of PRI-MAC in a multi-hop linear wireless sensor network (LWSN) is not useful for the performance analysis of JRAM. In this paper, we develop an analytical model for the performance analysis of JRAM in a multi-hop LWSN. Using the model, we evaluate the network performance in terms of packet delivery ratio (PDR), average energy consumption of a sensor node per second and end-to-end transmission delay (E2ETD). Through extensive ns-2.35-based simulations, we validate our proposed model and show the dependence of performance on various system parameters. Since most of the existing pipelined-forwarding MAC protocols can be modeled as a special case of JRAM, our proposed approach can be extended to analyze the performance of those protocols as well. [ABSTRACT FROM AUTHOR]

In wake-up radio (WuR) enabled wireless sensor networks (WSNs), a node triggers a data communication at any time instant by sending a wake-up call (WuC) in an on-demand manner. Such wake-up operations eliminate idle listening and overhearing burden for energy consumption in duty-cycled WSNs. Although WuR exhibits its superiority for light traffic, it is inefficient to handle high traffic load in a network. This paper makes an effort towards improving the performance of WuR under diverse load conditions with a twofold contribution. We first propose three protocols that support variable traffic loads by enabling respectively clear channel assessment (CCA), backoff plus CCA, and adaptive WuC transmissions. These protocols provide various options for achieving reliable data transmission, low latency, and energy efficiency for ultralow power consumption applications. Then, we develop an analytical framework based on an M/G/1/2 queue to evaluate the performance of these WuR protocols. Discrete-event simulations validate the accuracy of the analytical models. [ABSTRACT FROM PUBLISHER]

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We present a dynamic capacity allocation mechanism based on the Quality of Service (QoS) for different mobile users (MU) in 60 GHz radio-over-fiber (RoF) local access networks. The proposed mechanism is capable for collecting the request information of MUs to build a full list of MU capacity demands and service types at the Central Office (CO). A hybrid algorithm is introduced to implement the capacity allocation which can satisfy the requirements of different MUs at different network traffic loads. Compared with the weight dynamic frames assignment (WDFA) scheme, the Hybrid scheme can keep high priority MUs in low delay and maintain the packet loss rate less than 1% simultaneously. At the same time, low priority MUs have a relatively better performance. [ABSTRACT FROM AUTHOR]

Radio-frequency (RF) recharging can extend maintenance-free operation of wireless sensor networks. However, the period between recharging is limited by the distance between the most distant sensor node and the master, which sends out recharging pulses. To increase this period, we propose a zoning scheme in which nodes are logically grouped into circular zones centered at the master so that nodes in a given zone send their data to their neighbors in the next closer zone, which act as relays. We describe and analyze a polling Medium Access Control (MAC) protocol that supports zoning and relaying through a probabilistic model of the energy depletion process and a queueing model of the packet transmission process. Our results indicate that zoning extends the time interval between recharge pulses and leads to equalization of node lifetimes, but limits the available data transmission bandwidth as well. [ABSTRACT FROM PUBLISHER]

This work focused on the problem of finding a suitable medium access control protocol so that the nodes of a given cluster could communicate efficiently within their respective activity window. The nodes thus saved energy by turning off their transceivers during the time that they did not have to exchange information. This work’s main objective was to ensure that the nodes were mainly focused on energy efficiency and delivering packages, taking quality of service (QoS) requirements into account and comparing their performance to an existing protocol called sensor medium access control (S-MAC). The parameters being compared were the time that the nodes were asleep, energy consumption and average delay. This work was completed by using the OPNET simulator tool (OPNET Modeler, version 11.5.A PL3, OPNET Technologies Company Inc). This approach greatly improved the “PCF + Sleep” performance proposed in this work over the earlier S-MAC.

In this paper, we propose a novel framework to improve the end-to-end transmission delay (E2ETD) and packet delivery ratio (PDR) of existing contention-based synchronous MAC protocols designed for wireless sensor networks, without increasing the duty cycle. This is achieved by partitioning the $n$ deployed sensor nodes into $k$ disjoint sets, which are of almost equal size. It then suitably modifies the cycle structure followed by the existing contention-based synchronous MAC protocols by mapping the data transmission process of $k$ existing cycles into one restructured cycle. To evaluate the performance of this approach, we implement RMAC, PRMAC, and CLMAC protocols in the proposed framework using ns2.35 simulator. Results indicate that our scalable framework reduces the E2ETD and increases the PDR significantly at the cost of a very small increase in average energy consumption. [ABSTRACT FROM PUBLISHER]

Vehicular ad hoc networks (VANETs) provide information and entertainment to drivers for safe and enjoyable driving. Wireless Access in Vehicular Environments (WAVE) is designed for VANETs to provide services efficiently. Since the control messages transmitted in WAVE are broadcast, the probability of collision increases by increasing the number of vehicle nodes. In this paper, we propose a coordinated multichannel medium access control (C-MAC) protocol for VANETs. The proposed C-MAC protocol provides contention-free broadcasting for safety messages by the coordination of roadside units (RSUs). An RSU schedules the broadcasting order of transmissions for safety messages. Contention-free broadcasting lowers the probability of collision and reduces the required time for transmissions of safety messages. An RSU may play the role of harvesting energy wirelessly to coordinated VANET terminals, which are gateways for Internet-of-things devices in the car. The contention interval for service channels is optimized to provide maximum throughput. The proposed C-MAC protocol is shown to enhance throughput and delay via analysis and simulation. [ABSTRACT FROM AUTHOR]

Cognitive radio (CR) is introduced to improve spectrum efficiency by unlicensed usage when a licensed band is idle. These devices monitor licensed users to find spectral opportunities for transmission. A cognitive radio network (CRN) is defined as a structure, which is constructed by both licensed users and unlicensed CR users. In an effort to improve spectrum efficiency, CR users' spectrum issues have been widely studied over the last few years. However, the existing solutions are not capable of dealing with the following scenario: multiple CRNs operating simultaneously without a centralized coordinator. This issue is often referred to as a coexistence problem of heterogeneous CRNs. This problem is caused in a distributed framework of CRNs without a centralized component to negotiate spectrum usages with one another. The system characteristics of these heterogeneous networks are different; thus, the fairness issue between CR users must be considered. In this paper, a decentralized solution that does not limit the hardware capacity of a CR device is proposed as an added fairness feature. Several Markov chain models are proposed to study these unfairness conditions, and a medium access control layer approach is introduced. Numerical and simulation results are presented to verify the proposed solution. [ABSTRACT FROM PUBLISHER]

In industrial applications of wireless sensor networks (WSNs), synchronized sampling of data on each sensor node is often required. Thus, the wireless communication protocol needs to support accurate timing synchronization. If due to a high sampling rate also high data throughput is required, WSNs based on the IEEE 802.15.4 physical layer often do not provide sufficient data rate. Wireless communications based on the well-established IEEE 802.11 wireless local area network (WLAN) standard provides high data throughput but not an accurate timing synchronization unless the protocol stack is severely changed. We propose two low-complexity consensus-based synchronization algorithms for the hybrid WSN introduced, which are executable at limited embedded computing capacity, e.g., on an 8-b microcontroller. A time division multiple access-based synchronization packet broadcasting with three-step-controlled or proportional-integral (PI)-controlled clock adjustment enables 1-kHz sensor sampling rate with a sampling jitter <15 $\mu $ s for the three-step-controlled synchronization algorithm and < 1\;\mathrm {\mu s} for the PI-controlled algorithm. [ABSTRACT FROM PUBLISHER]

Wireless sensor networks based on the IEEE 802.15.4 standard is able to carry out short-distance transmissions in low-rate and low-power wireless personal area networks. To access the channel, it uses the slotted carrier sense multiple access with collision avoidance (CSMA/CA) in the contention access period (CAP) under superframe structure with beacon frame broadcast to bound the duration of superframe. However, the beacon frame is transmitted periodically without CSMA/CA so that it could be collided continuously. This type of collision causes node lost synchronization and unable to join a network because the beacon frame cannot be normally received. This paper proposes a simple time shift scheme based on IEEE 802.15.4 to keep original superframe structure and distribute transmission of beacon frame over active period to avoid beacon frame collisions. We use a simple function to allocate beacon frame transmission in the active period. The simulation results show that the proposed scheme significantly reduces the beacon collision and lost synchronization rate, and it also improves the throughput. [ABSTRACT FROM AUTHOR]

Recent advances in wireless sensor networking (WSN) techniques have encouraged interest in the development of vehicle health monitoring (VHM) systems. These have the potential for use in the monitoring of railway signaling systems and rail tracks. Energy efficiency is one of the most important design factors for the WSNs as the typical sensor nodes are equipped with limited power batteries. In earlier research, an energy-efficient cluster-based adaptive time-division multiple-access (TDMA) medium-access-control (MAC) protocol, named EA-TDMA, has been developed by the authors for the purpose of communication between the sensors placed in a railway wagon. This paper proposes another new protocol, named E-BMA, which achieves even better energy efficiency for low and medium traffic by minimizing the idle time during the contention period. In addition to railway applications, the EA-TDMA and E-BMA protocols are suitable for generic wireless data communication purposes. Both analytical and simulation results for the energy consumption of TDMA, EA-TDMA, BMA, and E-BMA have been presented in this paper to demonstrate the superiority of the EA-TDMA and E-BMA protocols. [ABSTRACT FROM PUBLISHER]

In this paper, we consider the channel assignment problem for cognitive radio networks with hardware-constrained secondary users (SUs). In particular, we assume that SUs exploit spectrum holes on a set of channels where each SU can use at most one available channel for communication. We present the optimal brute-force search algorithm to solve the corresponding nonlinear integer optimization problem and analyze its complexity. Because the optimal solution has exponential complexity with the numbers of channels and SUs, we develop two low-complexity channel assignment algorithms that can efficiently utilize the spectrum holes. In the first algorithm, SUs are assigned distinct sets of channels. We show that this algorithm achieves the maximum throughput limit if the number of channels is sufficiently large. In addition, we propose an overlapping channel assignment algorithm that can improve the throughput performance compared with its nonoverlapping channel assignment counterpart. Moreover, we design a distributed medium access control (MAC) protocol for access contention resolution and integrate it into the overlapping channel assignment algorithm. We then analyze the saturation throughput and the complexity of the proposed channel assignment algorithms. We also present several potential extensions, including the development of greedy channel assignment algorithms under the max–min fairness criterion and throughput analysis, considering sensing errors. Finally, numerical results are presented to validate the developed theoretical results and illustrate the performance gains due to the proposed channel assignment algorithms. [ABSTRACT FROM PUBLISHER]

Vehicular ad hoc network technologies can improve traffic safety for drivers and provide comfort services for passengers. Because the hardware of a roadside unit (RSU) is costly, in most previous research, vehicles might exchange data with an RSU through multihop transmissions. However, the vehicle with a larger number of hops to the RSU has fewer opportunities and longer time to exchange its data with the RSU because the contentions and collisions increase with the number of hops. This paper proposes the bandwidth utilization and fairness enhancements medium access control (BUFE MAC) protocol, which considers a vehicular ad hoc network that accesses the Internet through fixed Internet Gateways along the road. BUFE-MAC aims at increasing bandwidth utilization, maintaining fairness, and avoiding collision. The performance study reveals that the proposed MAC protocol not only avoids the collision problem but improves the performance in terms of end-to-end throughput and fairness as well. [ABSTRACT FROM PUBLISHER]

The standard of IEEE 802.15.4 is able to achieve low-power transmissions in low-rate and short-distance wireless personal area networks. It employs the slotted carrier sense multiple access with collision avoidance (CSMA/CA) for the contention mechanism. The blind backoff process in the slotted CSMA/CA will cause lower channel utilization. Sensor node performs backoff process immediately when the clear channel assessment (CCA) detecting busy channel. It may neglect the implicit information of CCA failed detection and further cause the redundant senses. This paper proposes an additional carrier sensing (ACS) algorithm based on IEEE 802.15.4 to enhance the carrier sensing mechanisms in original slotted CSMA/CA. An analytic model is developed to evaluate the performance of ACS algorithm. The analytical and simulation results demonstrate that the proposed scheme significantly improves the throughput, average medium access control delay and power consumption of CCA detecting. [ABSTRACT FROM AUTHOR]

We demonstrate an analytical model for calculating the saturation throughput performance of a medium transparent medium access control (MAC) protocol in 60 GHz radio-over-fiber (RoF) networks. The proposed model incorporates effectively the medium transparent MAC mechanism, assuming a finite number of terminals and ideal channel conditions. It takes into account contention both at the optical and wireless layer, ensuring seamless and dynamic capacity allocation over both transmission media. This model enables extensive saturation throughput performance analysis for the medium transparent MAC and has been applied to 60 GHz RoF network scenarios considering variable numbers of available optical wavelengths, wireless nodes and serving antenna elements and for two different data rate values, namely 155 Mbps and 1 Gbps. Comparison between the model-based throughput results and respective simulation-based outcomes reveals that our model is extremely accurate in predicting the system throughput. Moreover, it confirms that the proposed medium transparent MAC protocol can effectively operate in high-speed 60 GHz RoF LAN environments. [ABSTRACT FROM PUBLISHER]

In this paper, we investigate the joint optimal sensing and distributed Medium Access Control (MAC) protocol design problem for cognitive radio (CR) networks. We consider both scenarios with single and multiple channels. For each scenario, we design a synchronized MAC protocol for dynamic spectrum sharing among multiple secondary users (SUs), which incorporates spectrum sensing for protecting active primary users (PUs). We perform saturation throughput analysis for the corresponding proposed MAC protocols that explicitly capture the spectrum-sensing performance. Then, we find their optimal configuration by formulating throughput maximization problems subject to detection probability constraints for PUs. In particular, the optimal solution of the optimization problem returns the required sensing time for PUs' protection and optimal contention window to maximize the total throughput of the secondary network. Finally, numerical results are presented to illustrate developed theoretical findings in this paper and significant performance gains of the optimal sensing and protocol configuration. [ABSTRACT FROM PUBLISHER]

In this paper, we propose a coordinated non-sensing medium access control (MAC) protocol in dynamic spectrum access networks namely distributed coordinated dynamic spectrum reservation (DCDSR) protocol, which is not based on the cognitive radio technology. All licensed users (LUs) and unlicensed users (UUs) have two transceivers operating in a common control channel and licensed data channels to access control and data packets in the corresponding control and data frames respectively. LUs will inform UUs which channels will be used in next data frame and then UU reserve one of remainder channels by contending with each other during contention interval (CI) in control frame. The available channels which can be reserved by UUs will depend on the channel utilization of LUs and further affect the throughput of UUs. Whenever UU successfully reserves channel in a CI, it will start access the channel in next data frame. This will cause the wasted idle time for UUs which have successfully reserved channel and wait to enter next data frame. UU which couldn't successfully reserve channel in current control frame should try to reserve again in next control frame. Thus, the duration of CI will affect the delay and wasted idle time of UUs. We analyze and simulate the performance of throughput, delay and wasted idle time in DCDSR. The analytical and simulation results show that the proposed DCDSR performs very well. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we discuss and evaluate two proposed metro wavelength division multiplexing (WDM) ring network architectures for variable-length packet traffic in storage area networks (SANs) settings. The paper begins with a brief review of the relevant architectures and protocols in the literature. Subsequently, the network architectures along with their medium access control (MAC) protocols are described. Performance of the two network architectures is studied by means of computer simulation in terms of their queuing delay, node throughput and proportion of packets dropped. The network performance is evaluated under symmetric and asymmetric traffic scenarios with Poisson and self-similar traffic. [Copyright &y& Elsevier]

The IEEE 802.15.4 standard is designed to achieve low-power transmissions in low-rate and short-distance wireless personal area networks (WPANs). For the sake of reducing the control overheads, the modified CSMA/CA protocol used by 802.15.4 does not have the hidden device protection mechanism, such as RTS/CTS mechanism. Previous studies indicated that the probability of any two devices in an infrastructure network unheard of each other is around 41%. Therefore, the hidden device problem (HDP) results in inefficient data transmission and serious power consumption issues in WPAN. In this paper, we propose a cross-layer detection and allocation (CL-DNA) scheme to solve the HDP in IEEE 802.15.4 without the cost of extra control overhead in data transmissions. The proposed scheme detects relationships of hidden devices based on the overlapped signals and then allocates the hidden devices into distinct subperiods for transmissions. Simulation results validated by mathematical analysis show that the proposed scheme significantly improves the goodput with the reduction in power consumption. [ABSTRACT FROM PUBLISHER]

Wireless Sensor Networks (WSNs) represent a very promising solution in the field of wireless technologies for industrial applications. However, for a credible deployment of WSNs in an industrial environment, four main properties need to be fulfilled, i.e., energy efficiency, scalability, reliability, and timeliness. In this paper, we focus on IEEE 802.15.4 WSNs and show that they can suffer from a serious unreliability problem. This problem arises whenever the power management mechanism is enabled for energy efficiency, and results in a very low packet delivery ratio, also when the number of sensor nodes in the network is very low (e.g., 5). We carried out an extensive analysis—based on both simulation and experiments on a real WSN—to investigate the fundamental reasons of this problem, and we found that it is caused by the contention-based Medium Access Control (MAC) protocol used for channel access and its default parameter values. We also found that, with a more appropriate MAC parameters setting, it is possible to mitigate the problem and achieve a delivery ratio up to 100%, at least in the scenarios considered in this paper. However, this improvement in communication reliability is achieved at the cost of an increased latency, which may not be acceptable for industrial applications with stringent timing requirements. In addition, in some cases this is possible only by choosing MAC parameter values formally not allowed by the standard. [ABSTRACT FROM PUBLISHER]

Cooperative diversity is a promising and practical technique for realizing spatial diversity through a virtual antenna array formed by multiple distributed antennas of different nodes. In this paper, we propose and evaluate a novel cooperative cross-layer medium access control (CC–MAC) protocol, which combines space–time coding and adaptive modulation at the physical layer and employs truncated automatic repeat request (ARQ) at the data-link layer. The transmitter's partner is selected in the previous hop, and the receiver invites a partner to participate in data reception in the current hop, and in this situation, a two-transmitter two-receiver model is constructed. Because distributed space–time coding is applied at the transmitting set (transmitter and its partner), cooperative diversity and coding gain can be obtained. Based on the instantaneous channel state measured at the receiver, an adaptive modulation scheme is adopted to improve the link throughput at the physical layer. In addition, the truncated ARQ scheme is employed to further enhance the throughput performance at the data-link layer. Furthermore, under different system models with or without the truncated ARQ scheme, performances of the average packet error rate (PER) and symbol error rate (SER) with multiple phase shift keying (M-PSK) modulation and multiple quadrature amplitude modulation (M-QAM) over Rayleigh fading channel are analyzed. Simulation results verify the correctness of the performance analysis and show that CC–MAC can significantly improve system throughput and energy efficiency compared with other transmission schemes. [ABSTRACT FROM PUBLISHER]

In this paper, we present a cross-layer framework for optimizing the performance of opportunistic network coding in wireless multihop networks. The target scenario considers a wireless ad hoc network (WANET) with backlogged nodes and with multiple unicast packet flows. Initially, we focus on modeling the expected network-coded throughput individually for each wireless station as a function of parameters at the lower layers, like the maximum number of link-layer retransmissions and the transmission mode at the physical layer (PHY). Based on this analysis, we develop a network-coding algorithm that opportunistically and locally optimizes the expected information content of individual packet transmissions. To address the problem in a multihop setting, we focus on controlling the air time that is consumed by the resulting transmissions of coded packets. More specifically, we devise a distributed-cooperation algorithm that allows nodes to select the optimal PHY transmission mode by also considering the PHY selection of their neighbors. Nodes use only a partial view of the link contention relationships up to their interference range. Compared with existing works on opportunistic network coding and scheduling in ad hoc networks, our approach can yield significant throughput gains without employing complex link-scheduling algorithms. [ABSTRACT FROM AUTHOR]

The IEEE 802.15.4 standard is able to achieve low-power transmissions in low-rate and short-distance wireless personal area networks (WPANs). Due to the constitutional design of the sensor node and the transmission architecture (client-server model), any data communication between two sensor nodes will involve the coordinator. One shortcoming of redundant channel-access steps will result in excessive contention overheads and, thus, the decrease of channel utilization. This paper proposes an adaptive contention control strategy (ACCS) to solve the problem of transmission efficiency in IEEE 802.15.4. ACCS can be implemented in the IEEE 802.15.4 medium access control (MAC) protocol standard adding no new message type. An analytic model and a simulation model are developed to evaluate the performance of IEEE 802.15.4 and ACCS. The simulation results demonstrate that the proposed scheme significantly improves the goodput, the average queuing delay, the average MAC delay, and the energy consumption. [ABSTRACT FROM AUTHOR]

This paper presents an energy-efficient medium access control protocol suitable for communication in a wireless body area network for remote monitoring of physiological signals such as EEG and ECG. The protocol takes advantage of the static nature of the body area network to implement the effective time-division multiple access (TDMA) strategy with very little amount of overhead and almost no idle listening (by static, we refer to the fixed topology of the network investigated). The main goal is to develop energy-efficient and reliable communication protocol to support streaming of large amount of data. TDMA synchronization problems are discussed and solutions are presented. Equations for duty cycle calculation are also derived for power consumption and battery life predictions. The power consumption model was also validated through measurements. Our results show that the protocol is energy efficient for streaming communication as well as sending short bursts of data, and thus can be used for different types of physiological signals with different sample rates. The protocol is implemented on the analog devices ADF7020 RF transceivers. [ABSTRACT FROM AUTHOR]

This paper proposes a novel multichannel medium access control (MAC) protocol based on CDMA that improves network performance and reduces collision probability in wireless ad hoc networks. In the scheme, the code channel is divided into common channel, broadcast channel and several data channels. Simulation results show that the proposed protocol can achieve significantly better performance than the IEEE 802.11 standard. [ABSTRACT FROM AUTHOR]

This paper proposes a new multi-channel Medium Access Control (MAC) protocol named as Dual Reservation Code Division Multiple Access (CDMA) based MAC protocol with Power Control (DRCPC). The code channel is divided into common channel, broadcast channel and several data channels. And dynamic power control mechanism is implemented to reduce near-far interference. Compared with IEEE 802.11 Distributed Coordination Function (DCF) protocol, the results show that the proposed mechanism improves the average throughput and limits the transmission delay efficiently. [ABSTRACT FROM AUTHOR]

Optical burst switching is a core architecture designed to reconcile the available optical technology with the increasing burstiness of traffic. However, disappointing performance in terms of high packet loss and/or low system utilization discouraged broader experimental implementations. A method to avoid these losses by first sending over the control channel a short scout packet that simulates the events that the actual burst will experience is proposed in this paper. Once the scout message detects a drop at any intermediate node, it returns back to the source to avert the payload emission and repeat the process. The way the control works results in essential service quality features, i.e., no loss of bursts, no out-of-order emissions, increased efficiency, much reduced delay variation, and graceful throttling of the load respecting the contracted rates [ABSTRACT FROM PUBLISHER]

Packet-based optical access ring is becoming a promising solution in metropolitan networks. Its performance depends mainly on how optical resource sharing takes place among the different competing access nodes. This network architecture has mostly been explored with regard to synchronous transmission, i.e., slotted wavelength-division multiplexing (WDM) ring. However, in this paper, we focus on the performance of asynchronous transmission-based networks with variable packet sizes. Analytical models are presented in an attempt to provide explicit formulas that express the mean access delay of each node of the bus-based optical access network. We prove that in such a network, fairness problems are likely to arise between upstream and downstream nodes sharing a common data channel. Furthermore, we show that sharing the channel's available bandwidth fairly but arbitrarily between access nodes, as in slotted WDM rings, does not resolve the fairness problem in asynchronous system. In this regard, we exhibit the inherent limitations of the token bucket access rate-based algorithm once applied to asynchronous transmission bus-based networks. To alleviate the aforementioned problem, we device a new strategy called traffic control architecture using remote descriptors. The proposed solution is based on a preventive mechanism to grant access to the shared resource. As illustrated in this paper, the proposed solution alleviates the performance degradation and the resource underutilization, while achieving fairness among bus nodes. [ABSTRACT FROM AUTHOR]

A system of slotted interconnected wavelength-division-multiplexing (WDM) rings controlled by a medium access control (MAC) protocol is shown to offer very high utilization within a queuing delay less than a few round-trip times, by means of a very-fast-reacting explicit reservation mechanism. The system can be used to provide interconnectivity in a metropolitan area transferring optical payloads on-the-fly without buffering or converting from the optical domain. All necessary control information is transferred on a dedicated wavelength and is processed in the electrical domain to provide both collision-free packet access at the ring nodes and contention resolution at the hub interconnecting the rings. The end result is a flexible and efficient metropolitan network suitable for bursty data services. [ABSTRACT FROM PUBLISHER]

In this paper, we present a reservation-based medium access control (MAC) protocol with multicast support for wavelength-division multiplexing networks. Our system is based on the single-hop, passive optical star architecture. Of the available wavelengths (channels), one channel is designated as a control channel, and the remaining channels are used for data transmission. Each node is equipped with a pair of fixed transceiver to access the control channel, and a fixed transmitter and a tunable receiver to access data channels. For easy implementation of the protocol in hardware and for precisely computing the protocol's processing overhead, we give a register-transfer model of the protocol. We simulate the protocol to study its throughput behavior, and present its analytic model. For a node to be able to send data packets in successive data slots with no time gap between them, in spite of the situation that the protocol's execution time may be longer than data transmission time, we propose the idea of multiple MAC units at each node. Unicast throughput of our protocol reaches the theoretically possible maximum throughput for MAC protocols with distributed control, and the multicast throughput is at least as good as, and even better than, those delivered by existing MAC protocols with distributed control. [ABSTRACT FROM AUTHOR]

This article considers a WDM slotted-ring network architecture. A slotted MAC protocol was designed to be used in a metropolitan environment. The results of a discrete event simulation are presented. Assuming that a maximum load threshold is not exceeded, fairness between access nodes is achieved by introducing a very simple mechanism. Excellent queuing delay and packet dropping probability results are obtained. Future developments are presented as they are expected to improve the efficiency and introduce QoS capabilities and congestion avoidance mechanisms. Copyright © 2001 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]