Medium Access Control Delay Research Articles

Delay-Guaranteed Admission Control for LAA Coexisting With WiFi

Licensed-assisted-access (LAA) is used to extend the LTE link into the unlicensed band. How to guarantee the quality-of-service (QoS) for LTE devices in the unlicensed band is a challenging problem due to the listen-before-talk contention access in 5-GHz unlicensed bands. In this letter, we quantitatively analyze the medium access control delay for tagged LAA eNBs and propose a delay-guaranteed admission control scheme. We consider the freezing time of busy slots caused by collision or successful transmission, and introduce the exponential backoff mechanism for delay analysis. Validated by simulation results, our method provides important insights into the system admission performance and fairness of access.

Impact of MAC Delay on AUV Localization: Underwater Localization Based on Hyperbolic Frequency Modulation Signal.

Medium Access Control (MAC) delay which occurs between the anchor node’s transmissions is one of the error sources in underwater localization. In particular, in AUV localization, the MAC delay significantly degrades the ranging accuracy. The Cramer-Rao Low Bound (CRLB) definition theoretically proves that the MAC delay significantly degrades the localization performance. This paper proposes underwater localization combined with multiple access technology to decouple the localization performance from the MAC delay. Towards this goal, we adopt hyperbolic frequency modulation (HFM) signal that provides multiplexing based on its good property, high-temporal correlation. Owing to the multiplexing ability of the HFM signal, the anchor nodes can transmit packets without MAC delay, i.e., simultaneous transmission is possible. In addition, the simulation results show that the simultaneous transmission is not an optional communication scheme, but essential for the localization of mobile object in underwater.

Performance Analysis of IEEE 802.11ad MAC Protocol

IEEE 802.11ad specifies a hybrid medium access control (MAC) protocol consisting of contention as well as noncontention-based channel access mechanisms. Further, it also employs directional antennas to compensate for the high freespace path loss observed in 60GHz frequency band. Therefore, it significantly differs from other IEEE 802.11(b/g/n/ac) MAC protocols and thus requires new methods to analyze its performance. In this paper, we propose a new analytical model for performance analysis of IEEE 802.11ad employing a threedimensional Markov chain considering all the features of IEEE 802.11ad medium access mechanisms including the presence of non-contention access and the different number of sectors due to the use of directional antennas. We show that the number of sectors has a high impact on the network throughput. We also show that the MAC packet delay is significantly affected by the duration of the contention period. Our results indicate that a suitable choice of the number of sectors and contention period can illustriously improve the channel utilization and MAC delay performance.

Enhanced Clear Channel Assessment for Slotted CSMA/CA in IEEE 802.15.4

IEEE 802.15.4 Standard is defined for ultra-low complexity and ultra-low power consumption as well as for low cost implementation. Realization of Wireless Sensor Networks (WSNs) is possible by configuring IEEE 802.15.4 in peer-to-peer topology as it fits the requirements of WSNs. Underlying protocols should take care of energy consumption as most of the nodes are battery operated and inaccessible after deployment. Focus should also be given to delay introduced due to channel sensing. Carrier Sense Multiple Access with Collision Avoidance in IEEE 802.15.4 ensures reduced probability of collision with the use of sporadic backoff delay before channel assessment. Channel assessment is performed by either one Clear Channel Assessments (CCA) or two consecutive CCAs. In this paper efforts have been made to reduce energy consumption and to reduce average delay by reducing the number of backoff periods taken before channel sensing. Method mentioned in this paper also reduces the number of backoffs as well as channel access failures. Proposed method also reduces the number of collisions. To achieve these goals, proposed method takes two, three or four consecutive CCAs to decide upon current channel status. An analytical Markov Chain Model is developed for the derivation of various probabilities associated with proposed method and then it has been analyzed with the help of illustrations. The proposed algorithm is implemented and validated using Network Simulator-2. Simulation results show that proposed method reduces energy consumption as well as average Medium Access Control delay by reducing number of backoffs.

SCRRM: a stability‐aware cooperative routing scheme for reliable high‐speed data transmission in multi‐rate mobile ad hoc wireless networks

SummaryIn this paper, we propose a Stability‐aware Cooperative Routing scheme for Reliable high‐speed data transmission in Multi‐rate mobile ad hoc wireless networks, called SCRRM, to provide high data transmission with stable and reliable routes. The main features and contributions of our proposed routing scheme are as follows: First, we use the cross‐layer concept with network layer, media access control (MAC) layer, and physical (PHY) layer. Second, a stable routing path based on link lifetime calculated from node mobility information is selected as the main routing path. Third, we use the received signal strength indicator (RSSI), PHY delay, and MAC delay for adaptively choosing relay and appropriate data rate. Fourth, we derive mathematical models to investigate the tradeoff between point‐to‐point transmission rates and the corresponding effective transmission ranges. The performance evaluation through analysis and simulation demonstrates that our proposed routing scheme can adaptively select optimal data rate and outperforms single‐rate routing protocol in terms of packet delivery ratio, network throughput, and average end‐to‐end delay in all settings of node density and node mobility. Copyright © 2014 John Wiley & Sons, Ltd.

Relay-volunteered multi-rate cooperative MAC protocol for IEEE 802.11 WLANs

In IEEE 802.11, the rate of a station (STA) is dynamically determined by link adaptation. Low-rate STAs tend to hog more channel time than high-rate STAs due to fair characteristics of carrier sense multiple access/collision avoidance, leading to overall throughput degradation. It can be improved by limiting the transmission opportunities of low-rate STAs by backoff parameters. This, however, may cause unfair transmission opportunities to low-rate STAs. In an attempt to increase overall throughput by volunteer high-rate relay STAs while maintaining fairness, we propose a new cooperative medium access control (MAC) protocol, relay-volunteered multi-rate cooperative MAC (RM-CMAC) based on ready to send/clear to send in multi-rate IEEE 802.11. In the RM-CMAC protocol, we show that the effect of hogging channel time by low-rate STAs can be remedied by controlling the initial backoff window size of low-rate STAs and the reduced transmission opportunity of low-rate STAs can be compensated by the help of volunteer high-rate relay STAs. We analyze the performance of RM-CMAC, i.e., throughput and MAC delay, by a multi-rate embedded Markov chain model. We demonstrate that our analysis is accurate and the RM-CMAC protocol enhances the network throughput and MAC delay while maintaining the fairness of low-rate STAs.

On the Trade-off Between Accuracy and Delay in UWB Navigation

We investigate the relation between medium access control (MAC) delay and ultra-wide bandwidth (UWB) tracking accuracy. We quantify this relation by deriving fundamental lower bounds on tracking accuracy and MAC delay for arbitrary finite networks. Our main finding is that the traditional ways to increase accuracy (e.g., increasing the number of anchors or the transmission power) may lead to large MAC delays. We evaluate two methods to mitigate these delays.

Research and Optimization on Media Access Control Delay of CAN

With data quantity increasing dramatically and signal transmission period becoming more and more fast, the media access control delay has proved to be one of the main influence factors of CAN network real-time. Firstly, an equivalent numerical simulation model of CAN bus network is built to derivate the mathematical expression of media access control delay. Secondly, optimization measures are further proposed to improve the data communication real-time. At last, the optimization measures tested by experiments are proved to be correct and effective.

An Improvement of Slotted CSMA/CA Algorithm in IEEE 802.15.4 Medium Access Layer

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.

An Adaptive Contention Control Strategy for IEEE 802.15.4-Based Wireless Sensor Networks

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.

Performance behaviour of IEEE 802.11 distributed coordination function

The authors present an extensive investigation of the performance of the IEEE 802.11 medium access control (MAC) protocol, with respect to throughput and delay. For the protocol analysis, a new model, which describes the protocol's behaviour to a great extent by incorporating and extending the existing models, is proposed. The authors also present a detailed analysis of the end-to-end delay through the study of the MAC delay and the queueing delay. The authors use the Z-transform of backoff duration to obtain the mean value, the variance and the probability distribution of the MAC delay. For the queueing analysis, first the authors consider an M/G/l queue in order to provide a first look at the queueing delay. Second, the authors modify the input process of the queue so that the packet arrival process is described by an ON- OFF model, which expresses the bursty nature of traffic. In the investigations, data rates of 1, 5.5 and 11 Mbps are assumed to highlight the effect of the bit rate on network performance for both Basic and request-to-send/ clear-to-send access mechanisms. The throughput and delay analyses are validated by simulating the distributed coordination function, whereas the models are compared with the existing models based on their results. The accuracy of the analyses was found to be quite satisfactory.

Efficient and fast retransmission for wireless networks

This paper proposes efficient and fast retransmission (EFR) schemes for IEEE 802.11 multi-rate wireless networks. Without major modification of IEEE 802.11 standard, EFR provides immediate data transmission for both ad hoc wireless local area networks (WLAN) and infrastructure WLAN. Also, EFR can compensate for high frame error rates resulting from existing poor rate control algorithms. We develop an analytical model and a simulation model to investigate the performance of EFR. Our study indicates that in terms of average medium access control delay, average queuing delay, completion rate and average collision times per transmission. EFR outperforms standard IEEE 802.11 carrier sense multiple access/collision avoidance mechanism.

Synchronous wavelength reusing/sharing protocols for nonregenerative WDM dual buses

The dual-bus optical network with nonregenerative stations has become popular. In general, the nonregenerative station implementation is better than the regenerative station implementation in media access control delay, cost, and susceptibility of station failures, etc. In this paper, two novel cycle-based protocols, named as synchronous wavelength sharing protocol (SWSP) and synchronous wavelength reusing/sharing protocol (SWRP), are proposed for nonregenerative wavelength-division-multiplexing dual-bus networks. The simulation results show that the network throughput and delay of SWRP are better than those of SWSP, when the numbers of wavelengths and tunable receivers are both limited, and/or the network traffic load is heavy.

A Fast Optimal Non-Continuous Slot Reuse Scheme for CRMA High-Speed Networks

Cyclic-Reservation Multiple-Access (CRMA) is an effective access scheme for high-speed networks. In CRMA, the headend periodically generates reserve commands. If necessary, each station may reserve a number of empty slots in each reserve command. For each reserve command, the headend generates a cycle of length equal to the total number of empty slots which are reserved to serve the reservations. Generally speaking, a longer cycle length means a longer access delay and a lower throughput. Therefore, it is desirable to study how to reduce the cycle length. However, it has been shown that the problem is NP-complete if all the empty slots used by a station in a cycle are required to be consecutive [1]. In this paper, we remove the slot-contiguity constraint and propose a fast, optimal non-continuous slot reuse scheme with low time complexity O(M^2), where M denotes the number of stations. Experimental results demonstrate that our new scheme has much shorter cycle lengths, much higher throughput, and much shorter MAC (Medium Access Control) delay than the original CRMA scheme.

An optimal time slot assignment algorithm for CRMA high-speed networks

Cyclic-Reservation Multiple-Access (CRMA) is an access scheme for high-speed local and metropolitan area networks based on a folded-bus or dual-bus configuration. CRMA provides high throughput and fairness independent of the network speed or distance. In CRMA, the headend generates reserve commands periodically. Each station may reserve a number of empty slots in each reserve command if necessary. Corresponding to every reserve command, the headend generates a cycle of length equal to the total number of slots reserved. Every cycle is used to serve the reservations made on its corresponding reserve command. Generally, a longer cycle length means a longer access delay and a lower throughput. Therefore, it is desirable to have a scheme to make the cycle length as short as possible. In this paper, we will study the problem of reducing the total number of empty slots generated within every cycle as much as possible. However, it has been shown that the problem is NP-complete under the constraint that all the slots used by a station in a cycle are required to be consecutive [1][N.F. Huang, H.I. Liu, G.K. Ma, A cycle compression algorithm for CRMA high-speed networks, IEEE ICC'93, 1993, pp. 1363–1367]. In this paper, we discover that if this slot-contiguity constraint is released, then the problem can be optimally solved in polynomial time. Furthermore, we propose an optimal slot scheduling algorithm with time complexity O ∑ i≔1 M α i 2 where α i is the number of empty slots reserved by Station i in the cycle and M is the number of stations. To evaluate the effectiveness of our algorithm, a large number of computer simulations were performed. We compare our algorithm with the original CRMA in terms of the following three important performance measurements: average cycle length, average throughput, and average medium access control (MAC) delay. Experimental results demonstrate that our algorithm has much shorter cycle lengths, much higher throughput, and much shorter MAC delay. Therefore, our algorithm is very attractive.