In this letter, we propose PQ-MAC: a priority-based medium access control (MAC) protocol for providing quality of service (QoS) in wireless sensor networks (WSNs) which minimizes the energy consumption with traffic-based sleep-wakeup scheduling and supports QoS using differentiating channel access policy, packet scheduling, and queue management. The PQ-MAC utilizes the advantages of time division multiple access (TDMA) and slotted carrier-sense multiple access (CSMA). The proposed protocol is an energy-efficient, priority-based, and QoS compatible MAC protocol. It consists of multi-level queue management, sleep-wakeup scheduling, and an ordered contention period (CP) scheme. It also guarantees time-bounded delivery of QoS packets. Performance evaluation is conducted between PQ-MAC and S-MAC with respect to three performance metrics: energy consumption, throughput, and average latency. The simulation results show that the performance of PQ-MAC is better than that of S-MAC.

To analyze the saturation performance of IEEE 802.11 DCF, several discrete-time Markov chain models for a station and sets of channel equations have been introduced. We take into account a frame retry limit, freezing of backoff counter, and the dependence of backoff procedure on the previous channel status all together. Our method is simple even though it is accurate under the assumption of no consecutive transmissions over the shared channel.

We develop an enrichment protocol, called a 2-hop Path Selection Protocol (2PSP) for a set of nodes, in which data can be sent faster using adaptive rate control capability of IEEE 802.11a/b/g MAC protocol via a relaying concept than via a direct connection. The main objective of this protocol is to build upon opportunistic rate adaptation in order to assist a sender, a relay node, and a receiver to reach a higher rate data transmission through Medium Access Control (MAC) layer relaying. We propose a relay mechanism to further improve the performance of 2PSP protocol. In the relay mechanism, new contention window, called a Short Backoff Internal (SBI) is applied for a set of relay nodes. A potential node that succeeds as a relay is allowed to send a Ready-To-Relay (RTR) message. In this paper, two collision resolution algorithms are proposed to deal with the case when the potential relay node is more than one. Simulation results indicate that the proposed 2PSP protocol can achieve high reduction of delay and power consumption and also an improvement in the throughput compared to both Receiving-based Auto Rate (RBAR) and Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocols.

Nowadays, numerous Medium Access Control (MAC) contention protocols for ad hoc networks typically use a fixed transmit power level without using any transmit power control. In this paper, we present an enhancement scheme, called Power Adapted Medium Access Control (PAMAC) scheme for achieving energy conservation, which allows a node to vary its own transmit power on a packet basis. The primary objective of this scheme is to use suitable transmit power level for Clear-To-Send (CTS), DATA, and Acknowledgement (ACK) that still allows to achieve a correct reception of a packet despite intervening path loss, noise and interference. The evaluation of the throughput efficiency per node, energy consumption per node and energy per successfully transmitted bit is performed by a computer simulation. Simulation results indicate that the proposed PAMAC scheme can achieve a high reduction of the energy consumption and energy per successfully transmitted bit and also an improvement in the throughput efficiency per node compared to the conventional Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol.

This paper proposes a new effective data transfer method for IEEE 802.11 wireless LANs by integrating priority control and multirate mechanism. The IEEE 802.11 PHY layer supports a multirate mechanism with dynamic rate switching and an appropriate data rate is selected in transmitting a frame. However, the multirate mechanism is used with the CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) protocol, low rate transmissions need much longer time than high rate transmissions to finish sending a frame. As a result, the system capacity is decreased. The proposed method assumes the same number of priority levels as the data rates, and a data rate is associated to a priority level. Priority of a transmission goes up with the used data rate. For this purpose, we have modified the CSMA/CA protocol to support prioritized transmission. By selecting the appropriate priority depending on the data rate and giving more transmission opportunities for high rate transmission, the system capacity is increased. The effect of the proposed mechanism is confirmed by computer simulations.

In this paper, a novel carrier-sense multiple-access (CSMA) scheme for UWB ad-hoc network is proposed and evaluated. UWB is a kind of spread spectrum communication and it is possible to detect the distance between the nodes. With this positioning capability of the UWB systems, DS-CDMA (DS-UWB) scheme with variable spreading factor is used. In this paper, a novel CSMA scheme that employs the correlation of the spreading code is proposed.

The hybrid fiber coax (HFC) technology enables the conventional cable-television (CATV) network to provide subscribers with Internet access services. In this paper, we propose a new preemptive priority scheme (PPS) for IEEE 802.14 hybrid fiber coax (HFC) networks with the intelligent nodes (INs). The INs are placed between the headend controller and stations. By using INs, that stand for downstream subscribers to contend for the demand resources, the collision probability, and the collision resolving period can be reduced. In this paper, we further extend such network architecture to support multi-priority access. In each IN or individual station, the proposed PPS will prevent a higher priority request from colliding with requests of lower priority. Moreover, in PPS, the granted bandwidth for lower priority requests can be preempted by the waiting request with higher priority. This will speedup the channel capture by priority data. The efficiency of PPS is investigated by simulations. Simulation results show that by adopting INs with PPS to be an agent for subscribers can not only shorten the collision resolving period but also minimize the average request delay of priority data.

We propose adaptive variable-rate constant-power scheme for ad hoc wireless networks, employing the modification of Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. Potential improvements in throughput and back-off probability are presented for different system parameters.

This paper proposes a new scheme that can evaluate the cell throughput performance of wireless local area network (LAN) systems, which use carrier sense multiple access/collision avoidance (CSMA/CA) and multiple transmission bit-rates (multi-rate). We extend the interference model of the conventional scheme in order to deal with interference more accurately in multi-cell environments. Unlike the conventional scheme, the proposed scheme is able to handle multi-rate systems. We use the proposed scheme to evaluate the IEEE 802.11a system and systems whose signal-bandwidth is expanded from that of the IEEE 802.11a system. We find that a system with 35(75) MHz signal-bandwidth achieves about 1.3(1.25) times higher cell throughput than the IEEE 802.11a system. Furthermore, the system with 35(75) MHz signal-bandwidth is also shown to have the potential to achieve up to 1.5(1.8) times higher cell throughput performance than the IEEE 802.11a system if the transmission efficiency on the media access control (MAC) layer is assumed to be ideal. It is concluded that the proposed scheme confirms that the approach to expand the signal bandwidth of the IEEE 802.11a system is effective to improve the cell throughput performance. This result is virtually impossible to derive with the conventional scheme.

In this paper, we propose a new IEEE 802.11 based multichannel MAC protocol, which satisfies a single transceiver constraint and which is still compatible with the IEEE 802.11 standard. Our proposed protocol does not need any additional transceivers, and we can make use of the current IEEE 802.11 hardware for the implementation of our multichannel protocol. We propose and investigate two kinds of channel selection algorithms, these are, the sender based channel selection scheme and the receiver based channel selection scheme. We evaluate the TCP performance over our proposed multichannel MAC protocol by the simulations taking account of the overhead, the time taken by changing the frequency channel and the time taken by the carrier sense in each channel. It is shown that our proposed scheme improves the performance significantly with a single transceiver. It is shown that the overhead costs are quite large in the multichannel MAC protocol, and the sender based channel selection scheme achieves better performance than that of the receiver based channel selection scheme in most cases. It is also shown that there exists a break-even value of the PLL synthesizer lockup time if we compare with the single channel IEEE 802.11 MAC protocol.

VoIP (Voice over IP) is one of the real time applications that demand wireless LAN systems meet severe quality requirements which commonly involve delay time, jitter, and packet loss. However, it is difficult for CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to achieve the service quality demanded by VoIP if voice and data traffic coexist, so some form of priority control is needed. This paper proposes a novel multiple access protocol based on autonomous distributed control that allows wireless LANs to satisfy the VoIP requirements. This new protocol suits both VoIP and data traffic and executes priority control dynamically according to whether the VoIP packet collides with a data packet or another VoIP packet. The results of a theoretical analysis and computer simulations indicate its excellent performance. This proposed protocol reduces the delay time of VoIP packets by 54 to 70% compared with conventional CSMA/CA even if the traffic load increases provided that the packet loss probability is less than 3%.

Wireless LANs have been used for realizing fully-distributed users in a multimedia environment that has the ability to provide real-time bursty traffic (such as voice or video) and data traffic. In this paper, we present a new realistic and detailed system model and a new effective analysis for the performance of wireless LANs which support multimedia communication with non-persistent carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In this CSMA/CA model, a user with a packet ready to transmit initially sends some pulse signals with random intervals within a collision avoidance period before transmitting the packet to verify a clear channel. The system model consists of a finite number of users to efficiently share a common channel. Each user can be a source of both voice traffic and data traffic. The time axis is slotted, and a frame has a large number of slots and includes two parts: the collision avoidance period and the packet transmission period. A discrete-time Markov process is used to model the system operation. The number of slots in a frame can be arbitrary, dependent on the chosen lengths of the collision avoidance period and packet transmission period. Numerical results are shown in terms of channel utilization and average packet delay for different packet generation rates. They indicate that the network performance can be improved by adequate choice of ratios between the collision avoidance period and transmission period, and the pulse transmission probability.

IEEE 802. 11 is a standard for wireless LANs. The basic access method in its MAC layer protocol is the distributed coordination function (DCF) for the ad hoc networks. It is based on the mechanism of carrier sense multiple access with collision avoidance (CSMA/CA). DCF is used to support asynchronous data transmission. However, frames in DCF do not have priorities, making it unsuitable for real-time applications. With a little bad luck, a station might have to wait arbitrarily long to send a frame. In this paper, we propose a method to modify the CSMA/CA protocol such that station priorities can be supported. The method is simple, efficient and easy to implement in comparison to point coordination function (PCF), another access method in IEEE 802. 11 based on access points (base stations). Simulations are conducted to analyze the proposed scheme. The results show that DCF is able to carry the prioritized traffic with the proposed scheme.

A random access micro-cellular system based on CSMA (RAMCS/CSMA) is proposed. On uplink in RAMCS/ CSMA, packets are transmitted by means of CSMA at the same carrier frequency in any cell. On downlink, packets are broadcast conforming to TDMA, also at the same carrier frequency in any cell. In RAMCS/CSMA, deployed microcells produce higher system capacity. Nevertheless, " handoff on a terminal " isn't required. In this paper, overview of the system, fundamental uplink performance, and two kinds of power control methods are presented. As for the control methods, one is control according to packet priority. The other is a way according to location of a mobile terminal. By means of CSMA, throughput performance on uplink becomes great and is saturated at 0. 39 per cell. And the performance strongly depends on the threshold level on carrier sense. Such a throughput performance is peculiar to RAMCS/CSMA and different from an ordinary CSMA system. The optimum threshold is also indicated here. Furthermore, it is clarified that both power control methods highly improve the throughput performance. As a result, it is found that RAMCS/CSMA is excellent for mobile communications.

The channel throughput and packet delay of wireless medium access control (MAC) protocols with Rayleigh fading, shadowing and capture effect are analyzed. We consider CSMA/CA protocols as the wireless MAC protocols, since CSMA/CA protocols are based on the standard for wireless Local Area Networks (LANs) IEEE 802. 11. We analyze the channel throughput and packet delay for three types of CSMA/CA protocols; Basic CSMA/CA, Stop-and-Wait CSMA/CA and 4-Way Handshake CSMA/CA. We calculate the capture probability of an Access Point (AP) in a channel with Rayleigh fading, shadowing, and near-far effects, and we derive the throughput and packet delay for the various protocols. We have found that the performance of CSMA/CA in a radio channel model is 50 percent less than in an error free channel model in low traffic load, while the throughput and packet delay of CSMA/CA in a radio channel model show better performance than in an error free channel model in high traffic load. We also found that the 4-Way Handshake CSMA/CA protocol is superior to the other CSMA/CA protocols in high traffic load.

The throughput performance of the non-persistent carrier sense spread spectrum with overload detection (NP-CSSS/OD) protocol is analysed and compared with that of the conventional non-persistent and one-persistent carrier sense multiple access with collision detection (NP-CSMA/CD and 1P-CSMA/CD) and the one-persistent carrier sense spread spectrum with overload detection (1P-CSSS/OD) protocols. We also introduced utilization measurements and did some performance comparisons between these protocols. At high offered loads, the NP-CSSS/OD protocol is found to offer the best throughput and utilization performances amongst them.