即時無線感測網路之IEEE 802.15.4時槽型CSMA/CA分析與改善

The importance of Wireless Sensor Network (WSN) increases due to deployment for geographical, environmental and surveillance purpose in war fields. WSN facing several challenges due to its complex nature including key problems, such as routing and medium access control protocols. Several approaches were proposed for the performance evaluation of WSN on the basis of these issues due to the fact that MAC layer access protocols have a great impact on the performance of WSN. In this paper, we investigated the performance evaluation of three well known MAC Access protocols, i.e. sensor medium access control protocol (SMAC), carrier sense multiple access with collision avoidance (CSMA/CA), and time division multiple access (TDMA) over adhoc on demand distance vector (AODV) routing protocol. The number of simulation scenarios were carried out by using NS- 2, the simulation metrics used are throughput, end-to-end delay and energy consumed. Simulation results showed that SMAC out perform CSMA/CA and TDMA by consuming less energy, less end to end delay and high throughput due to contention based approach to access the medium for transmission.

Wireless networks have become a very attractive solution for soft real-time data transport in the industry. For such technologies to carry real-time traffic, reliable bounds on end-to-end communication delays have to be ascertained to warrant a proper system behavior. As for legacy wired embedded and real-time networks, two main wireless multiple access methods can be leveraged: one is time division multiple access (TDMA), which follows a time-triggered paradigm, and the other is carrier sense multiple access with collision avoidance (CSMA/CA), which follows an event-triggered paradigm. This paper proposes an analytical comparison of the time behavior of two representative TDMA and CSMA/CA protocols in terms of the worst-case end-to-end delay. This worst-case delay is expressed in a probabilistic manner because our analytical framework captures the versatility of the wireless medium. Analytical delay bounds are obtained from delay distributions, which are compared to fine-grained simulation results. Exhibited study cases show that TDMA can offer smaller or larger worst-case bounds than CSMA/CA depending on its settings.

An airdropped meteorological parameters measurement network (AMPMN) is introduced in this paper. AMPMN with star topology is composed of two kinds of nodes, sensor nodes and one relay node, all equipped with nRF905 radio frequency (RF) modules. A three-layer protocol is built on nRF905 in terms of its configuration. The RF configuration parameters and the payloads formats are set to enable the implementation of carrier sense multiple access with collision avoidance (CSMA/CA) or time division multiple access (TDMA) schemes through programming. The performances of two presented CSMA/CA schemes and one designed TDMA scheme are evaluated by simulation. Based on the simulation results and the difficulty of practical implementation, the CSMA/CA scheme without RTS/CTS is selected for AMPMN. AMPMN will be used in unmanned meteorological parameters measuring over hazard area.

IEEE 802.15.4g is a recent standard for Smart Utility Networks (SUN). SUN is a house-to-house level subordinate network in the Smart Grid network. IEEE 802.15.4g uses a Carrier Sense Multiple Access/Collision Avoidance (CSMA/CA) algorithm for channel access whose performance is limited by collision probability. In this paper, we propose a multi-channel CSMA/CA operation in IEEE 802.15.4g system to mitigate the collision problem, by modifying modulator structures for two physical (PHY) layer techniques of IEEE 802.15.4g, orthogonal frequency division multiplexing (OFDM) PHY, and multi-rate and multi-regional offset quadrature phase-shift keying (MR-O-QPSK) PHY and also propose proper channel selection schemes for multi-channel CSMA/CA based on those PHYs. Moreover, we evaluate the performance of both cases with single channel CSMA/CA and multi-channel CSMA/CA through link-level simulations and system-level simulations. The simulation results demonstrate that the proposed frequency division two-channel based OFDM PHY system yields a 16 percent increase in the maximum throughput, compared with that of the conventional single-channel OFDM PHY system.

This paper presents a theoretical analysis of the maximum throughput of a wireless mesh backhaul network that is achievable over a practical carrier sense multiple access with collision avoidance (CSMA/CA) medium access control (MAC) protocol. We resort to the multicommodity flow (MCF) formulation augmented with the conflict-graph constraints, whereas we use a novel approach to take into account the collision overhead in the distributed CSMA/CA MAC. Such overhead due to random access has been ignored by existing MCF-based capacity studies, which assume impractical centralized scheduling and result in aggressive capacity planning, which is unachievable over the CSMA/CA MAC. This paper makes the following three main contributions: 1) we develop a generic method of integrating the CSMA/CA MAC analysis with the MCF formulation for optimal network capacity analysis, which readily generates an upper bound of the network throughput; 2) we define a new concept of CSMA/CA clique and theoretically study its relationship to a CSMA/CA area in terms of throughput; and 3) using the CSMA/CA clique as a tool, we derive a lower bound of the network throughput achievable over the CSMA/CA MAC by clique-based MCF formulation. NS-2 simulation results are presented to demonstrate the tightness of the upper and lower bounds that are newly developed, compared to those based on the MCF formulation assuming a slotted system and centralized scheduling.

Recently, the Wi-Fi alliance announced a new Wi-Fi standard known as IEEE 802.11ah (or Wi-Fi HaLow) to efficiently support Internet of Things (IoT) applications. However, the existing registration method under IEEE 802.11ah, based on carrier-sense multiple access with collision avoidance (CSMA/CA), was analyzed as not efficient enough for registration of large-scale machine-to-machine (M2M) communications where a massive number of devices try to access a single, centralized access point (AP). In this paper, we propose a hybrid slotted-CSMA/CA–time-division multiple access (TDMA) (HSCT) medium access control (MAC) protocol for efficient massive registration of IoT devices (up to 8000) in M2M networks. We focus on situations, where a large number of M2M devices simultaneously try to register at a single, centralized AP. In the proposed HSCT, contention-based slotted-CSMA/CA allows devices to send an authentication request via randomly selected backoff slots, whereas contention-free TDMA permits those devices to send/receive the subsequent association request/association response via an individually allocated TDMA slot. In addition, a centralized authentication control (CAC)-based mechanism with modified algorithms for optimal selection of CAC parameters and the slotted fixed-window CSMA protocol with Sift geometric probability distribution are used to mitigate severe contention between massive registrations upon network (re-)initialization from an AP reboot. This paper also analyzes the performance of the proposed scheme and determines the optimal configuration to enhance registration performance. Simulation results demonstrate that the proposed HSCT MAC protocol achieves substantial improvement, compared with the contention-free transmission, a combined authentication/association scheme, and the conventional IEEE 802.11ah with CSMA/CA.

The strength of carrier-sense multiple access with collision avoidance (CSMA/CA) can be combined with that of time-division multiple access (TDMA) to enhance the channel access performance in wireless networks such as the IEEE 802.15.4-based wireless personal area networks. In particular, the performance of legacy CSMA/CA-based medium access control scheme in congested networks can be enhanced through a hybrid CSMA/CA-TDMA scheme while preserving the scalability property. In this paper, we present distributed and centralized channel access models that follow the transmission strategies based on Markov decision process (MDP) to access both contention period and contention-free period in an intelligent way. The models consider the buffer status as an indication of congestion provided that the offered traffic does not exceed the channel capacity. We extend the models to consider the hidden node collision problem encountered due to the signal attenuation caused by channel fading. The simulation results show that the MDP-based distributed channel access scheme outperforms the legacy slotted CSMA/CA scheme. The centralized model outperforms the distributed model but requires the global information of the network.

During the past few years the wireless technology market has experienced a tremendous growth. Users today expect to be able to communicate and access data anytime, anywhere, using almost any portable device. Infrared Data Association (IrDA) addressed the requirement for indoor multipoint wireless connectivity with the development of the advanced infrared (AIr) protocol stack utilizing the infrared spectrum. AIr medium access control (MAC) protocol employs a carrier sensing multiple access with collision avoidance (CSMA/CA) protocol in addition to a request to send/clear to send (RTS/CTS) packet exchange reservation scheme and a linear adjustment of the contention window (CW). This paper develops a new modelling approach to evaluate saturation performance of the AIr protocol based on conditional probability arguments rather than bi‐dimensional Markov chains. Moreover, we extend performance studies in former literature papers by providing an intuitive AIr packet delay analysis assuming error‐free transmissions and a fixed number of stations. Using OPNET simulation results, we validate our mathematical analysis and we show that the proposed model predicts AIr packet delay performance very accurately. Utilizing the derived mathematical analysis, we determine the significance of both link layer and physical parameters, such as burst size, minimum CW size value and minimum turnaround time on AIr packet delay performance. Finally, we propose suitable values for both backoff and protocol parameters that reduce average packet delay and, thus, maximize performance. Copyright © 2005 John Wiley & Sons, Ltd.

Studies of the IEEE 802.15.4 Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) scheme have been received considerable attention recently, with most of these studies focusing on homogeneous or saturated traffic. Two novel transmission schemes—OSTS/BSTS (One Service a Time Scheme/Bulk Service a Time Scheme)—are proposed in this paper to improve the behaviors of time-critical buffered networks with heterogeneous unsaturated traffic. First, we propose a model which contains two modified semi-Markov chains and a macro-Markov chain combined with the theory of M/G/1/K queues to evaluate the characteristics of these two improved CSMA/CA schemes, in which traffic arrivals and accessing packets are bestowed with non-preemptive priority over each other, instead of prioritization. Then, throughput, packet delay and energy consumption of unsaturated, unacknowledged IEEE 802.15.4 beacon-enabled networks are predicted based on the overall point of view which takes the dependent interactions of different types of nodes into account. Moreover, performance comparisons of these two schemes with other non-priority schemes are also proposed. Analysis and simulation results show that delay and fairness of our schemes are superior to those of other schemes, while throughput and energy efficiency are superior to others in more heterogeneous situations. Comprehensive simulations demonstrate that the analysis results of these models match well with the simulation results.

The potential of multiantenna interference cancellation receiver algorithms for increasing the uplink throughput in WLAN systems such as 802.11 is investigated. The medium access control (MAC) in such systems is based on carrier sensing multiple-access with collision avoidance (CSMA/CA), which itself is a powerful tool for the mitigation of intrasystem interference. However, due to the spatial dependence of received signal strengths, it is possible for the collision avoidance mechanism to fail, resulting in packet collisions at the receiver and a reduction in system throughput. The CSMA/CA MAC protocol can be complemented in such scenarios by interference cancellation (IC) algorithms at the physical (PHY) layer. The corresponding gains in throughput are a result of the complex interplay between the PHY and MAC layers. It is shown that semiblind interference cancellation techniques are essential for mitigating the impact of interference bursts, in particular since these are typically asynchronous with respect to the desired signal burst. Semiblind IC algorithms based on second- and higher-order statistics are compared to the conventional no-IC and training-based IC techniques in an open access network (OAN) scenario involving home and visiting users. It is found that the semiblind IC algorithms significantly outperform the other techniques due to the bursty and asynchronous nature of the interference caused by the MAC interference avoidance scheme.

Hybrid communication of power line and wireless can improve the performance without dedicated communication lines and meet the requirements of in-vehicle communication. Aiming at the medium access control (MAC) design of dual-connection architecture, we propose a parallel access scheme for power line and wireless hybrid communication suitable for parallel diversity transmission, and establish transmission and collision probability equations on the basis that the two channel conditions are consistent. Further, the influences of the carrier sense multiple access with collision avoidance (CSMA/CA) and time division multiple access (TDMA) on the performance of the parallel access scheme are analyzed. Based on numerical results, it is shown that the proposed scheme can significantly improve the performance of throughput and delay when compared to power line and wireless network alone.

A vehicular ad hoc network (VANET) is designed to enable efficient and authentic node/infrastructure communication. The primary role of VANETs is to distribute time-sensitive safety messages (sm) regularly, which causes packet congestion and broadcast failure due to the network’s limited spectrum. For efficient and reliable delivery, the proposed paper uses a spatial hybrid division multiple access (SDMA) and time division multiple access (TDMA) over the control channel interval and hence termed a spatially distributed multichannel MAC (SDM-MAC) protocol. The frequency reuse approach is used to transfer data while efficiently utilising bandwidth, and throughput is considerably enhanced with carrier sense multiple access with collision avoidance (CSMA/CA) and with the help of TDMA. Moreover, an adaptive algorithm is proposed for an intelligent channel frame structure using this protocol to manage the highly dynamic scenario. The Markov chain defines the protocol, and the network simulator (NS2) analyses several performance metrics. Comparing the response with two existing MAC protocols, the proposed protocol reduces average latency compared to current MAC methods and improves the packet delivery ratio and throughput by an average of 26% and 28%, respectively.

Power consumption, latency, and complexity are considered to be a benchmark for comparing Medium Access Control (MAC) protocols in Wireless Sensor Networks (WSN). However, the importance of these elements varies according to the application. In this paper, three MAC protocols are proposed for forest fire detection. Basically, two of these protocols are based on the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol with some modification to suit the forest fire detection application. These protocols are called Persistent CSMA (P-CSMA) and Per Hope Synchronization CSMA (PHS-CSMA). The third one is a Time Division Multiple Access (TDMA)-based protocol, called Sensor TDMA (S-TDMA). These three protocols are investigated and analyzed by simulation. Results show that there is no superior protocol which outperforms others in terms of power consumption, delay and complexity. However, a trade-off does exist. In terms of power consumption, S-TDMA outperforms other protocols but it has the worst performance in terms of delay. On the other hand, considering the design complexity, S-TDMA is the most complex as it needs time synchronization over the entire cluster while PCSMA and PHS-CSMA don't require time synchronization between nodes.

Reader to reader collision is a common problem in Radio Frequency Identification (RFID) networks where are large number of RFID readers are present close to each other. Motion of readers can further cause difficulty in reading of tags. Evaluation and comparison of anti-collision algorithms must be done using simulation tools specifically designed for the same rather than general purpose simulation platforms to improve ease of operation and get greater insight into the performance of the protocols. A comparison between protocols that use single and multiple channels was done to study the increase in performance with added channels. Performance of these protocols for different reader speed was analyzed. Two anti-collision protocols Listen Before Talk (LBT) and Neighbor Friendly Reader Anti-collision protocol (NFRA) based on Carrier Sense Multiple Access with Collision Avoidance (CSMA-CA) and Time Division Multiple Access (TDMA) respectively are simulated using a Java based tool R2RIS. Simulation results showed that the LBT protocol gave approximately 4 times lesser waiting time when using 4 channels than the single channel NFRA protocol. Both protocols deliver similar performance at different reader speeds.

With the advanced physical layer techniques such as multiple-input and multiple-output (MIMO) and orthogonal frequency-division multiplexing (OFDM), transmission real-time 2D/3D contents and applications becomes more and more necessary in wireless networks for the amazing growing in demand of customers. However, the low efficiency of medium access control (MAC) protocol degrades the performance of real-time traffic greatly in multihop, wireless and mobile environment. Focusing on supporting real-time multimedia traffic in cognitive wireless mesh networks (WMNs), an enhanced MAC protocol is proposed. And the contribution of this paper is twofold: (1) An efficient carrier sense multiple access with collision avoidance (CSMA/CA) compatible time division multiple access (TDMA)-like MAC protocol called T-MAC is proposed, which aims to improve the system performance by allocating more channel access time in centralized manner and decreasing overhead. (2) An optimal adaptive scheduling scheme is proposed to support real-time multimedia applications and guarantee QoS for different priority traffic, which aims to find the optimized schedule among all possible sequences of concurrent transmissions by minimizing the occupied resources. Detailed simulation results and comparison with IEEE 802.11e MAC scheme show that the proposed T-MAC can effectively improve quality of service (QoS) for multimedia traffic in terms of throughput, end-to-end delay and packet loss rate, which also manifests that T-MAC is an efficient multimedia applications transmission scheme for mobile terminals and MAPs in cognitive WMNs.