Channel Access Delay Research Articles

Dependability of Decentralized Congestion Control for Varying VANET Density

IEEE 802.11p is an amendment to the IEEE 802.11 standard for Wireless Access in Vehicular Environments (WAVE). Lower layer wireless transmission formats and protocols are defined for both vehicle-to-infrastructure and vehicle-to-vehicle communication links to support cooperative intelligent transport systems. The medium access control (MAC) layer uses carrier sensing as a means for detecting the busy state of the radio channel before transmitting. In heavily loaded vehicular ad hoc networks (VANETs), the channel access delay, when attempting to access the channel, unpredictably increases when it is sensed as busy. The European Telecommunications Standards Institute (ETSI) defines safety-related messages. These messages require a dependable behavior of the communication link. In this context, dependable behavior translates to the reliable delivery of data packets within a specified deadline regardless of changes in traffic density. Unfortunately, the WAVE amendment does not fulfill the requirements for such dependable behavior. This contribution reports on performance evaluations by simulation studies of the WAVE MAC and the decentralized congestion control (DCC) mechanism specified by the ETSI in addition to the existing enhanced distributed channel access. The simulation scenario under study is a two-VANET-merging highway situation. The MAC protocol has to adapt to variable traffic densities in this scenario. The performance is evaluated in terms of coverage range and MAC-to-MAC delay reliability and DCC state stability. Furthermore, a novel performance indicator is defined, evaluated, and discussed, which the authors of this work have named data novelty. Finally, a multistate-active DCC mechanism is proposed, which achieves a dependable behavior.

A Cross-Layer MAC Protocol for Underwater Acoustic Sensor Networks

One of the major challenges for the deployment of underwater acoustic sensor networks is the development of a medium access control (MAC) protocol catering for the harsh underwater environment. In particular, an underwater MAC protocol should provide high end-to-end throughput, low channel access delay, and fair share of the scarce network bandwidth. In this paper, a cross-layer MAC protocol is proposed. It interacts with a price-based rate allocation scheme at the network layer. To accurately reflect the clique constraint of the wireless medium, the clique-based price is generalized to act as the congestion signal, which controls the end-to-end rates of multihop flows. The MAC protocol then schedules contention-free packet transmissions of single-hop subflows in each maximum clique. Both the MAC protocol and rate allocation algorithm are simple and direct, thus owning low computational complexity. Through analysis and simulation, we show that the proposed MAC protocol enables multihop flows to acquire the max-min fair share of the network bandwidth from the end-to-end perspective.

HARQ in Relay-Assisted Transmission for Machine Type Communications

This letter describes the impact of unknown channel access delay on the timeline of the hybrid automatic repeat request (HARQ) process in the 3rd generation partnership project long term evolution (3GPP LTE) system when a relay node (RN) is used for coverage extension of machine type communication (MTC) devices. A solution is also proposed for the determination of unknown channel access delay when the RN operates in the unlicensed spectrum band. The proposed mechanism is expected to help MTC operation in typical coverage holes areas such as smart meters located in the basement of buildings.

An Efficient Mac Protocol for Reducing Channel Interference and Access Delay in Cognitive Radio Wireless Mesh Networks

With the increase of wireless mesh networks, channel access, bandwidth usage and channel interferences are the major key issues of multi-channel WMNs and MAC specifications. The multi-radio, multi-channel wireless mesh networks (MR-MC-WMNs) are a kind of networks that provide high reliable communication for a large number of mesh nodes. These networks have mesh routers and channels that are stationary and each router or node has multiple channels. Although IEEE 802.11 versions support up to 3 and 12 multiple non-overlapping channels, it is the major challenge of the multichannel environment which exploits all channels to communicate a large volume of network data in WMNs. Cognitive radio users has the capability to access unused portion of the multichannel spectrum. The major interference can be created by CR as well as licensed user. Traditional MAC based operations are implemented using common-control-channel to handle cognitive radio end users. We proposed a new Multi-objective based CMR-MC-WMNs framework using TDMA based MAC protocol to optimize the network performance, channel interference and access delay issues in the network. Experimental results prove that, proposed work has less delay and inference rates compared to traditional models.

D2D: Delay-Aware Distributed Dynamic Adaptation of Contention Window in Wireless Networks

The IEEE 802.11e enhanced distributed channel access (EDCA) protocol follows class-based service differentiation for providing differentiated quality-of-service (QoS). However, its collision avoidance mechanism using backoff algorithm can be inefficient for providing improved performance with respect to throughput and channel access delay, especially in a high network configuration (i.e. number of stations) with imperfect wireless channel. The existing and emerging works have devoted considerable attention on tuning the backoff parameters for achieving optimal throughput only. The prior works do not consider the channel access delay and throughput metrics altogether for performance improvement. Additionally, in most of the cases, the optimal configuration of backoff parameters are performed by a centralized controller. In this paper, we propose a delay-aware distributed dynamic adaptation of contention window scheme, namely D2D , for the cumulative improvement of both the throughput and the channel access delay at runtime. The D2D scheme requires two ad-hoc, distributed, and easy-to-obtain estimates— delay deviation ratio and channel busyness ratio —of the present delay level and channel congestion status of the network, respectively. A key advantage of the D2D scheme is that it is compliant with the IEEE 802.11 standard, and, thus, can be seamlessly integrable with the existing wireless card. We show the integrated model of the medium access control protocol, namely D2D Channel Access ( D2DCA ), for the IEEE 802.11e networks. We further propose a two-dimensional Markov chain model of the D2DCA protocol for analyzing its theoretical performance in saturated networks with imperfect wireless channel. Theoretical comparison with the benchmark protocols establishes the effectiveness of the D2DCA protocol.

Beamforming‐based feature extraction and RVM‐based method for attacker node classification in CRN

SummaryCognitive radio is a promising technology for the future wireless spectrum allocation to improve the utilization rate of the licensed bands. However, the cognitive radio network is susceptible to various attacks. Hence, there arises a need to develop a highly efficient security measure against the attacks. This paper presents a beamforming‐based feature extraction and relevance vector machine (RVM)‐based method for the classification of the attacker nodes in the cognitive radio network. Initially, the allocation of the Rayleigh channel is performed for the communication. The quaternary phase shift keying method is used for modulating the signals. After obtaining the modulated signal, the extraction of the beamforming‐based features is performed. The RVM classifier is used for predicting the normal nodes and attacker nodes. If the node is detected as an attacker node, then communication with that node is neglected. Particle swarm optimization is applied for predicting the optimal channel, based on the beamforming feature values. Then, signal communication with the normal nodes is started. Finally, the signal is demodulated. The signal‐to‐noise ratio and bit‐error rate values are computed to evaluate the performance of the proposed approach. The accuracy, sensitivity, and specificity of the RVM classifier method are higher than the support vector machine classifier. The proposed method achieves better performance in terms of throughput, channel sensing/probing rate, and channel access delay. Copyright © 2016 John Wiley & Sons, Ltd.

CH-CSMA-CA: a MAC protocol for asynchronous channel hopping rendezvous in 802.11 DCF-based cognitive radio networks

Blind rendezvous paradigm recently expedites the approach to the control channel establishment problem in cognitive radio networks. As a result, many novel asynchronous channel hopping CH rendezvous schemes are proposed for realising blind rendezvous in these years. However, how to integrate these asynchronous CH rendezvous schemes with CSMA/CA MAC has not been researched so far. In this paper, we propose a CH rendezvous-based CSMA/CA MAC named CH-CSMA/CA to work with existing asynchronous CH rendezvous schemes by tailoring mechanisms of 802.11 DCF to the slotted operation manner of these rendezvous schemes. Moreover, we identify that the channel busy-time inconsistency problem unique to CH-CSMA/CAMAC design is caused by virtual carrier sensing VCS mechanism of 802.11 DCF, and an enhanced virtual carrier sensing EVCS mechanism is proposed to alleviate its impact on networking performance i.e., channel access delay and throughput. Extensive simulation results verify the effectiveness of our MAC design.

Access Delay of Cognitive Radio Networks Based on Asynchronous Channel-Hopping Rendezvous and CSMA/CA MAC

As a promising approach to the rendezvous problem in cognitive radio networks (CRNs), a blind rendezvous paradigm has recently spawned various asynchronous channel-hopping (CH) rendezvous schemes that enable any two neighboring secondary users to meet among multiple channels within a finite time, even with no synchronization. However, the rendezvous delay that was derived in existing work is unable to reflect the actual channel access delay performance in multiuser CRNs, as it only relies on hopping patterns of the elaborately designed CH sequences (CHSs) and ignores the impact of network factors (e.g., channel availability and multiuser contention). In this paper, channel access delay is investigated by jointly considering asynchronous CH rendezvous schemes, channel availability, and a medium-access control (MAC) protocol in a single-hop multiuser CRN. To coordinate multiuser contention, a carrier sense multiple access with collision avoidance (CSMA/CA) MAC is adopted by tailoring the IEEE 802.11 distributed coordination function (DCF) properly to the operation features of existing asynchronous CH rendezvous schemes. The channel access delay is analyzed based on a modified Bianchi model and an absorbing Markov chain model, which captures the aggregate effect of hopping patterns of CHSs, the dynamic nature of channel availability, and the behavior of the MAC protocol. The analytical results are verified through extensive simulations. Both simulation and analytical results reveal that the rendezvous delay in existing asynchronous CH rendezvous schemes is insufficient to ensure satisfactory channel access delay in multiuser CRNs.

수중 네트워크의 전파 비대칭성을 고려한 BTB-TDMA 성능 분석

ABSTRACT A Block-Time-Bounded Time Division Multiple Access (BTB-TDMA) medium access control protocol, which estimates the propagation delay of nodes according to their location and moving velocity information, has been proposed for underwater acoustic networks. BTB-TDMA provides nodes with their transmission schedules by a time block that is a time unit, newly designed for BTB-TDMA. In this paper, we investigate how the receiver collision, that is induced by the asymmetry between node’s uplink and downlink propagation delay due to its mobility, affects the performance of BTB-TDMA. To do this, we analytically obtain the collision rate, the channel access delay, and the channel utilization by considering the asymmetry of propagation delay. Then, simulations are extensively performed with respect to the length of a time block by varying the number of nodes, the network range, and the node's velocity. Thus, the simulation results can suggest performance criteria to determine the optimal length of a time block which minimizes the collision rate and concurrently maximizes the channel access delay and the channel utilization.

A Distributed Medium Access Control Protocol for Cognitive Radio Ad Hoc Networks

We propose a distributed medium access control protocol for cognitive radio networks to opportunistically utilize multiple channels. Under the proposed protocol, cognitive radio nodes forecast and rank channel availability observing primary users’ activities on the channels for a period of time by time series analyzing using smoothing models for seasonal data by Winters’ method. The proposed approach protects primary users, mitigates channel access delay, and increases network performance. We analyze the optimal time to sense channels to avoid conflict with the primary users. We simulate and compare the proposed protocol with the existing protocol. The results show that the proposed approach utilizes channels more efficiently.

Performance Evaluation of a New Cooperative MAC Protocol with a Helper Node Selection Scheme in Ad Hoc Networks

A new cooperative MAC protocol called the busy tone cooperative medium access control (BT-COMAC) protocol is proposed to overcome the drawbacks and maximize the advantages of existing schemes. This scheme uses a new metric called decibel power to decide an appropriate helper node. Using received power strength is more efficient in selecting an appropriate helper node, especially in a densely populated network, than the effective transmission rates used in conventional schemes. All communication nodes in a communication service area are assumed to move independently. Two performance metrics are used: System throughput and channel access delay. A performance evaluation of the BT-COMAC protocol is conducted using a computer simulation over a slow fading wireless channel, and its performance results are compared with those of four existing schemes. The numerical results show that the BT-COMAC protocol improves the system throughput by approximately 15% as compared to the best existing scheme.

Analysis of Channel Access Delay in CR-MAC Protocol for Ad Hoc Cognitive Radio Wireless Sensor Networks without a Common Control Channel

Ad hoc cognitive radio wireless sensor networks allow secondary wireless sensor nodes to recognize spectrum opportunities and transmit data. Most existing protocols proposed for ad hoc cognitive radio wireless sensor networks require a dedicated common control channel. Allocating one channel just for control packet exchange is a waste of resources for channel-constrained networks. There are very few protocols that do not rely on a common control channel and that exchange channel-negotiation control packets during a pre-allocated time on the data channels. This, however, can require a substantial amount of time to access the channel when an incumbent is present on the channel, where the nodes are intended to negotiate for the data channel. This study examined channel access delay on cognitive radio wireless sensor networks that have no dedicated common control channel.

Effect of relay nodes and transmit power on end-to-end delay in multi-hop wireless ad hoc networks

Channel access delay in a wireless multi-hop ad hoc network is the major source of delay while considering end-to-end delay. In this work, end-to-end delay is analysed considering silent relay nodes and effect of network parameters like node density and throughput. Given network parameter requirements and bound on end-to-end delay, optimal ranges of transmission radius and channel access probability can be obtained from the proposed analysis. Effect of silent relay nodes must be considered to maintain quality of service (QoS) metrics. Transmission power adaptability to reduce end-to-end delay is analysed considering the interference model. Increase in transmission power is not reducing end-to-end delay linearly. Simulation results show that increase in end-to-end delay due to channel access probability and throughput is considerably higher than node density. Also given the network parameters, end-to-end delay can be minimised only up to certain value irrespective of increase in transmit power.

On the Performance of Interference-Aware Cognitive Ad-Hoc Networks

In this paper we analyze the effects of channel availability on channel access delay and service probability of cognitive networks using a modified IEEE 802.11 Media Access Control Protocol (MAC). For the designed cognitive network, cognitive communication is limited by the interference imposed on primary users. We determine the probability of accessing the channel under Rayleigh fading condition for this opportunistic network. We then use this probability to determine the embedded Markov model of the cognitive nodes. We use this Markov model to determine the average channel access delay, and service rate of cognitive nodes. Both simulation and analytical results are presented to access the system performance.

Fair and efficient Transmission Control Protocol access in the IEEE 802.11 infrastructure basic service set

AbstractWhen the stations in an IEEE 802.11 infrastructure basic service set employ Transmission Control Protocol (TCP), this exacerbates per‐flow unfair access problem. We propose a novel analytical model to approximately calculate the maximum per‐flow TCP congestion window limit that prevents packet losses at the access point buffer and therefore provides fair TCP access both in the downlink and uplink. The proposed analysis is unique in considering the effects of varying number of uplink and downlink TCP flows, differing round trip times among TCP connections and the use of delayed TCP acknowledgment (ACK) mechanism. Motivated by the findings of this theoretical analysis and simulations, we design a link layer access control block to be employed only at the access point in order to resolve the unfair access problem. The proposed link layer access control block uses congestion control and ACK filtering approach by prioritizing the access of TCP data packets of downlink flows over TCP ACK packets of uplink flows. Via simulations, we show that the proposed algorithm can provide both short‐term and long‐term fair accesses while improving channel utilization and access delay. Copyright © 2013 John Wiley & Sons, Ltd.

협력통신용 신규 도움노드 선정기법 설계 및 성능평가

In this paper, we carried out a study on how to find an appropriate helper node for cooperative communications, the role of which is very import to enhance system throughput of wireless communication system. The busy tone cooperative MAC (BT-COMAC) protocol proposed in this paper is a new cooperative MAC protocol with a reactive helper node scheme and maximizes the benefits of existing schemes while making up for their shortcomings. We conducted performance evaluation of this new protocol using computer simulation experiment. System throughput in bps and channel access delay are utilized as performance measures. We used a random way point mobility model where every communication node moves independently one another, and slow fading channel where every communication node decided its transmission rate with received power basis. Numerical results show that the new MAC protocol enhances system throughput as much as 15% of the existing scheme.

Decentralized Predictive MAC Protocol for Ad Hoc Cognitive Radio Networks

A new problem of spectrum scarcity has emerged due to the incredible technological advances in wireless communication. The spectrum scarcity issue is a bottleneck for the next generation of wireless communications. Therefore, efficient spectrum utilization has attracted considerable attention. This paper proposes a novel method of utilizing the white spaces in the licensed spectrum while ensuring the incumbent licensees' rights. The protocol predicts the incumbents' arrival using a historical prediction method and protects the incumbent users from the interference of opportunistic spectrum users. Distributed sensing is used to determine the network wide spectrum opportunity. The channel access delay in the proposed protocol is evaluated by simulation and mathematical analysis. The protocol has the advantages of a decentralized system, flexibility and low computing complexity. The simulations show that the protocol outperforms the existing opportunistic spectrum-sharing, media-access-control protocols in terms of the goodput and delay.

Beyond OFDM: Best-Effort Dynamic Spectrum Access Using Filterbank Multicarrier

Orthogonal frequency division multiplexing (OFDM), widely recommended for sharing the spectrum among different nodes in a dynamic spectrum access network, imposes tight timing and frequency synchronization requirements. We examine the use of filterbank multicarrier (FBMC), a somewhat lesser known and understood alternative, for dynamic spectrum access. FBMC promises very low out-of-band energy of each subcarrier signal when compared to OFDM. In order to fully understand and evaluate the promise of FBMC, we first examine the use of special pulse-shaping filters of the FBMC PHY layer in reliably transmitting data packets at a very high rate. Next, to understand the impact of FBMC beyond the PHY layer, we devise a distributed and adaptive medium access control (MAC) protocol that coordinates data packet traffic among the different nodes in the network in a best-effort manner. Using extensive simulations, we show that FBMC consistently achieves at least an order of magnitude performance improvement over OFDM in several aspects including packet transmission delays, channel access delays, and effective data transmission rate available to each node in static, indoor settings. Using measurements of power spectral density and high data rate transmissions from a transceiver that we build using our National Instruments hardware platform, we show that while FBMC can decode/distinguish all the received symbols without any errors, OFDM cannot. Finally, we also examine the use of FBMC in a vehicular network setup. We find that FBMC achieves an order of magnitude performance improvement over large distances in this setup as well. Furthermore, in the case of multihop vehicular networks, FBMC can achieve about 20 × smaller end-to-end data packet delivery delays and relatively low packet drop probabilities. In summary, FBMC offers a much higher performing alternative to OFDM for networks that dynamically share the spectrum among multiple nodes.

해수운동의 특성을 활용한 수중 무선 네트워크 시각 동기화

많은 기존 연구들에서 수중 환경에 적합한 시각 동기화를 제안하고 있으나 동기화의 정확도에 영향을 미치는 높은 채널접근지연이나 노드 간의 상대적 위치에 대한 고려가 없었다. 또한 양방향 메시지 교환 방식을 사용하는 기존 연구에서는 많은 수의 송수신 및 불필요한 오버히어링이 발생하여 네트워크 수명과 처리량이 감소하는 문제가 있다. 이에 본 연구에서는 수중환경의 특성을 반영한 향상된 시각 동기화 방법을 제안한다. 특히 제안 방법에서는 해수운동과 센서노드가 배치되는 환경의 특성을 활용한 메시지 전송 시점 조절 기법을 소개한다. 또한 채널접근지연이 제거된 타임스탬프를 사용하여 동기화의 정확도를 높인다. 더불어 전원공급 및 교체가 어려운 수중환경에 더욱 적합한 시각 동기화를 위해 제안 방법은 기존 방법보다 적은 수의 송수신으로 시각 동기화를 수행한다. 마지막으로 실험결과를 통해 제안 방법이 비교대상인 TSHL(Time Synchronization for High Latency)과 MU-Sync에 비해 각각 2.5ms, 0.56ms의 시각 동기화 오차를 줄이는 동시에 68.4%의 소비 에너지를 절감하였음을 보인다. Time synchronization in underwater environment is challenging due to high propagation delay and mobility of sensor nodes. Previous researches do not consider practical issues affecting on the accuracy of time synchronization such as high-channel access delay and relative position between sensor nodes. Also, those protocols using bidirectional message exchange shorten the network lifetime and decrease the network throughput because numerous transmission, reception and unnecessary overhearing can be occurred. Therefore, in our research, we suggest enhanced time synchronization based on features of underwater environment. It controls the instant of transmission by exploiting the feature of an oceanic movement and node deployment. Moreover, the protocol uses more accurate time information by removing channel access delay from the timestamp. The proposed scheme is also practical on the underwater sensor network requiring low-power consumption because the scheme conducts time-synchronization with smaller transmission and reception compared with previous works. Finally, simulation results show that the proposed protocol deceases time error by 2.5ms and 0.56ms compared with TSHL and MU-Sync respectively, reducing energy consumption by 68.4%.

A concurrent access MAC protocol for cognitive radio ad hoc networks without common control channel

Abstract Cognitive radio ad hoc networks (CRAHNs) consist of autonomous nodes that operate in ad hoc mode and aim at efficient utilization of spectrum resources. Usually, the cognitive nodes in a CRAHN exploit a number of available channels, but these channels are not necessarily common to all nodes. Such a network environment poses the problem of establishing a common control channel (CCC) as there might be no channel common to all the network members at all. In designing protocols, therefore, it is highly desirable to consider the network environment with no CCC. In this article, we propose a MAC protocol called concurrent access MAC (CA-MAC) that operates in the network environment with no CCC. The two devices in a communication pair can communicate with each other even if they have only one common channel available. Therefore, the problems with CCC (such as channel saturation and denial of service attacks) can also be resolved. In CA-MAC, channel accesses are distributed over communication pairs, resulting in increased network connectivity. In addition, CA-MAC allows different communication pairs to access multiple channels concurrently. According to our performance study, CA-MAC provides higher network connectivity with shorter channel access delay compared to SYN-MAC, which is the conventional key MAC protocol for the network environment with no CCC, resulting in better network throughput.