Search

Wireless sensor networks based on the IEEE 802.15.4 standard are able to achieve low-power transmissions in the guise of low-rate and short-distance wireless personal area networks (WPANs). The slotted carrier sense multiple access with collision avoidance (CSMA/CA) is used for contention mechanism. Sensor nodes perform a backoff process as soon as the clear channel assessment (CCA) detects a busy channel. In doing so they may neglect the implicit information of the failed CCA detection and further cause the redundant sensing. The blind backoff process in the slotted CSMA/CA will cause lower channel utilization. This paper proposes an additional carrier sensing (ACS) algorithm based on IEEE 802.15.4 to enhance the carrier sensing mechanism for the original slotted CSMA/CA. An analytical Markov chain model is developed to evaluate the performance of the ACS algorithm. Both analytical and simulation results show that the proposed algorithm performs better than IEEE 802.15.4, which in turn significantly improves throughput, average medium access control (MAC) delay and power consumption of CCA detection.

The personal area network (PAN) coordinator can assign a guaranteed time slot (GTS) to allocate a particular duration for requested devices in IEEE 802.15.4 beacon-enabled mode. The main challenge in the GTS mechanism is how to let the PAN coordinator allocate time slot duration for the devices which request a GTS. If the allocated devices use the GTS partially or the traffic pattern is not suitable, wasted bandwidth will increase, which degrades the performance of the network. In order to overcome the abovementioned problem, this paper proposes the Partitioned GTS Allocation Scheme (PEGAS) for IEEE 802.15.4 networks. PEGAS aims to decide the precise moment for the starting time, the end, and the length of the GTS allocation for requested devices taking into account the values of the superframe order, superframe duration, data packet length, and arrival data packet rate. Our simulation results showed that the proposed mechanism outperforms the IEEE 802.15.4 standard in terms of the total number of transmitted packets, throughput, energy efficiency, latency, bandwidth utilization, and contention access period (CAP) length ratio.

The challenges of CSMA/CA as following: first, when the device nodes detect the channel in busy condition, the device nodes have to increase the value of backoff exponent which cause range of blind backoff process also increase. Second, the blind backoff process will cause lower channel utilization and more energy consumptions. This article proposes a scheme to improve IEEE 802.15.4 medium access control, called adjustment delay scheme (ADES). This article also presents a comprehensive Markov chain analysis to predict the probability of successful transmission, network goodput, bandwidth utilization and total network energy consumption. The validity of the analytical model is proven by closely matching the simulation experiments. ADES performs better than those of other algorithms in term of the probability of successful packet transmission, network goodput, bandwidth utilization as well as energy consumption in the networks. [ABSTRACT FROM AUTHOR]

The personal area network (PAN) coordinator can assign a guaranteed time slot (GTS) to allocate a particular duration for requested devices in IEEE 802.15.4 beacon-enabled mode. The main challenge in the GTS mechanism is how to let the PAN coordinator allocate time slot duration for the devices which request a GTS. If the allocated devices use the GTS partially or the traffic pattern is not suitable, wasted bandwidth will increase, which degrades the performance of the network. In order to overcome the abovementioned problem, this paper proposes the Partitioned GTS Allocation Scheme (PEGAS) for IEEE 802.15.4 networks. PEGAS aims to decide the precise moment for the starting time, the end, and the length of the GTS allocation for requested devices taking into account the values of the superframe order, superframe duration, data packet length, and arrival data packet rate. Our simulation results showed that the proposed mechanism outperforms the IEEE 802.15.4 standard in terms of the total number of transmitted packets, throughput, energy efficiency, latency, bandwidth utilization, and contention access period (CAP) length ratio. [ABSTRACT FROM AUTHOR]

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]

IEEE 802.11e supports the guaranteed quality of service (QoS) by providing different transmission priorities. IEEE 802.11e improves the media access control layer of IEEE 802.11 to satisfy the different QoS requirements by introducing two channel access functions: the enhanced distributed channel access (EDCA) and the hybrid coordination function (HCF) controlled channel access (HCCA). Signal quality may affect the available bandwidth and transmission rate, because the characteristic of communication channel in wireless environment is in random time-variation manner. Generally a station using a lower transmission rate will occupy communication channel for a longer time and degrade system performance, which causes unfairness and cannot provide the guaranteed QoS for the stations with higher transmission rates. We propose a bandwidth control scheme (BCS) by combining the IEEE 802.11e enhanced distributed channel access function (EDCAF) protocol to overcome the guaranteed bandwidth issue in multirate environments. A multirate discrete Markov chain model is analyzed for the multirate transmission system in this paper. According to the obtained results, BCS improves performance especially in throughput and makes the different QoS requirements be processed efficiently and flexibly. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

VoIP (voice over Internet protocol) technology has rapidly been growing up recently, which transmits voice packets by using the user datagram protocol (UDP). VoIP quality is difficult to expect because it is hard to predict the influence of packet delay, packet lose, packet error, etc. This paper proposes an embedded call admission control (CA C) mechanism by applying real-time transfer protocol (RTP) and the real-time con trol protocol (RTCP) for VoIP services over hybrid fiber/coaxial (HFC) networks. The proposed CAC mechanism is evaluated by the impact of the various traffic load in cable modem termination system (CMTS), which estimates how VoIP quality satisfies the user's requirements under different constrains on cable networks. We discuss VoIP CAC mechanism for the upstream channel according to the data over cable service interface specifications (DOCSIS) version 1.1 and particularly consider G. 723.1 voice packets at the transmission rate of 6.3 kbps. The performance measurement of the proposed embedded CAC mechanism is obtained by simulation experiments under various network constrains, which includes throughput, packet dropping ratio and call blocking ratio. Obviously this paper provides an efficiency and fast method for CMTS to decide how many calls can be accepted. [ABSTRACT FROM AUTHOR]

Focuses on multicast routing strategies for zoned virtual path (VP)-based asynchronous transfer mode (ATM) networks. Methods of constructing VP; Relationship between the number of VP connections and the size of a zone; Strategy of dynamic loading; Steps to establish multicast transfer calls; Comparison between the minimum spanning tree routing and the independent routing algorithms.