Clear Channel Assessment Research Articles

A distributed transmission rate adjustment algorithm in heterogeneous CSMA/CA networks.

Distributed transmission rate tuning is important for a wide variety of IEEE 802.15.4 network applications such as industrial network control systems. Such systems often require each node to sustain certain throughput demand in order to guarantee the system performance. It is thus essential to determine a proper transmission rate that can meet the application requirement and compensate for network imperfections (e.g., packet loss). Such a tuning in a heterogeneous network is difficult due to the lack of modeling techniques that can deal with the heterogeneity of the network as well as the network traffic changes. In this paper, a distributed transmission rate tuning algorithm in a heterogeneous IEEE 802.15.4 CSMA/CA network is proposed. Each node uses the results of clear channel assessment (CCA) to estimate the busy channel probability. Then a mathematical framework is developed to estimate the on-going heterogeneous traffics using the busy channel probability at runtime. Finally a distributed algorithm is derived to tune the transmission rate of each node to accurately meet the throughput requirement. The algorithm does not require modifications on IEEE 802.15.4 MAC layer and it has been experimentally implemented and extensively tested using TelosB nodes with the TinyOS protocol stack. The results reveal that the algorithm is accurate and can satisfy the throughput demand. Compared with existing techniques, the algorithm is fully distributed and thus does not require any central coordination. With this property, it is able to adapt to traffic changes and re-adjust the transmission rate to the desired level, which cannot be achieved using the traditional modeling techniques.

Analytical and comparative investigation of 60 GHz wireless channels

This work analytically studies the channel characteristics of 60 GHz wireless communication, particularly from five aspects: path loss, multi-path fading, spatial diversity, peak-to-average power ratio of OFDM and clear channel assessment. This investigation is performed in comparison to the 2.4 GHz wireless system. The observed merits of the 60 GHz wireless channels include: 1) the support of packing a large number of antennas at a transceiver to exploit spatial diversity, 2) light effect from multi-path fading due to its small average fade duration and 3) a fast detection of signals in carrier sense to achieve clear channel assessment. Its weaknesses consists of: 1) large path losses that lead to short communication ranges and 2) high peak-to-average power ratio that increases the cost and complexity in implementing OFDM in transceivers.

Modeling of variable Clear Channel Assessment MAC protocol for Wireless Sensor Networks

Toward devising a new efficient Medium Access Control (MAC) protocol that overcomes the shortcomings of the IEEE 802.15.4 standard MAC, we work on exploiting the Clear Channel Assessment (CCA) feature in a more efficient fashion. This paper proposes the Variable CCA MAC protocol; a new MAC protocol that increases the number of CCAs performed by a node beyond the standard value of two. We develop a Markov-based mathematical model that describes the functionality of this new protocol. We also validate our mathematical model through conducting extensive simulations that focus on a rich set of performance parameters, including the probability of collision, throughput, channel idle time, channel collision time, energy consumption, delay, and reliability.

A Ladder CCA Threshold Selection Mechanism for Multi-Hop Vehicle EWM Transmission

Emergency warning message (EWM) transmission insurance is one of the most interesting topics for Vehicular Cyber-physical System (V-CPS) application. A relatively low transmission requirement should improve EWM's real-time delivery, and however, decrease reliability of packet delivery by its corresponding burst converge-cast, especially under multi- hop condition. In this paper, based on a series experiments, a clear channel assessment (CCA) threshold ladder selection method is proposed to ensure both real-time and reliability for EWM transmission. The experimental results show that the threshold adjusting method has a positive effect on the delivery rate. With an appropriately diminishing clear channel assessment threshold related to the packet hops, the global dissemination successful rate can be up to 73.5%, and more than 90% of the 1-hop nodes can receive the correct packet. The experiment results provide a practicable method to improve EWM dissemination performance.

A Mac Protocol Implementation for Wireless Sensor Network

IEEE 802.15.4 is an important standard for Low Rate Wireless Personal Area Network (LRWPAN). The IEEE 802.15.4 presents a flexible MAC protocol that provides good efficiency for data transmission by adapting its parameters according to characteristics of different applications. In this research work, some restrictions of this standard are explained and an improvement of traffic efficiency by optimizing MAC layer is proposed. Implementation details for several blocks of communication system are carefully modeled. The protocol implementation is done using VHDL language. The analysis gives a full understanding of the behavior of the MAC protocol with regard to backoff delay, data loss probability, congestion probability, slot effectiveness, and traffic distribution for terminals. Two ideas are proposed and tested to improve efficiency of CSMA/CA mechanism for IEEE 802.15.4 MAC Layer. Primarily, we dynamically adjust the backoff exponent (BE) according to queue level of each node. Secondly, we vary the number of consecutive clear channel assessment (CCA) for packet transmission. We demonstrate also that slot compensation provided by the enhanced MAC protocol can greatly avoid unused slots. The results show the significant improvements expected by our approach among the IEEE 802.15.4 MAC standards. Synthesis results show also hardware performances of our proposed architecture.

A priority-based CCA threshold adjusting method for EWM dissemination in vehicular ad-hoc networks

Emergency warning message (EWM) transmission insurance is one of the most interesting topics for vehicular ad-hoc network application. Clear channel assessment (CCA) threshold is deemed to be a key factor influencing EWM dissemination performance. Considering vehicle abnormal event hazard level and EWM's important level, a new parameter, EWM priority rank, is defined. Based on EWM priority rank, a new CCA threshold self-adjusting method is proposed in this paper. Moreover, according to the proposed CCA threshold selection method, an EWM dissemination algorithm is designed. A series of experiments on the sensor network testbed are conducted to evaluate the impact of proposed method on EWM dissemination. The experimental results show that an appropriate CCA threshold is beneficial to increase global dissemination success rate and to shorten packet delivery delay.

A novel method for mitigating the effects of dynamic coexistence on the operation of IEEE 802.15.4‐based mobile WSNs

AbstractWireless networks dynamically coexist when their transmission ranges overlap as a result of mobility. Mobile wireless sensor networks (WSNs) may suffer from significant degradation of performance due to the interference caused by dynamic coexistence, which is particularly critical for health monitoring WSNs. In this paper, we propose a novel method to detect and mitigate the harmful effects of dynamic coexistence on the operation of IEEE 802.15.4‐based mobile health monitoring WSNs. IEEE 802.15.4 uses the guaranteed time slots (GTS) mechanism to eliminate contention; however, successful transmissions cannot be guaranteed for coexisting WSNs. We show that using limited clear channel assessments at the beginning of the GTS enables the mobile WSNs to avoid collisions with minimum overhead. This method can also be used in combination with the previously proposed mechanisms for coexistence management. We analytically investigate the effects of using this method on the performance of the dynamically coexisting WSNs. We use OPNET simulation to investigate the coexistence of health monitoring WSNs and also to validate the proposed method. Our results indicate that using the proposed mechanism, 2–10 coexisting mobile WSNs with relatively high transmission rates (20–30% of maximum throughput) can achieve 20–90% higher rates of successful transmissions, with less than 10% increase in power consumption. Copyright © 2014 John Wiley & Sons, Ltd.

Dynamic 20/40/60/80 MHz Channel Access for 80 MHz 802.11ac

This paper is to contribute a new dynamic channel access method for wireless local area networks. It allows a station accessing the 80 or 160 MHz channel to capture every idle non-primary 20 MHz channel along with the primary 20 MHz channel, whereas the number of channel configurations in which the station can transmit according to the 802.11ac standard is strictly limited. Simulation results shown in the paper prove the proposed access method to be superior to the method provided by the 802.11ac standard in terms of average network throughput. What is important for legacy reasons, the proposed method employs the conventional clear channel assessment function to determine which of the 20 MHz channels are idle and which are busy. The paper proposes a new receiver design that is able to reject the adjacent channel interference, arising as a result of the presence of the legacy 802.11a/n station signals inside the 80 or 160 MHz accessed channel.

WiCop: Engineering WiFi Temporal White-Spaces for Safe Operations of Wireless Personal Area Networks in Medical Applications

ZigBee and other wireless technologies operating in the (2.4GHz) ISM band are being applied in Wireless Personal Area Networks (WPAN) for many medical applications. However, these low duty cycle, low power, and low data rate medical WPANs suffer from WiFi co-channel interferences. WiFi interference can lead to longer latency and higher packet losses in WPANs, which can be particularly harmful to safety-critical applications with stringent temporal requirements, such as ElectroCardioGraphy (ECG). This paper exploits the Clear Channel Assessment (CCA) mechanism in WiFi devices and proposes a novel policing framework, WiCop, that can effectively control the temporal white-spaces between WiFi transmissions. Such temporal white-spaces can be utilized for delivering low duty cycle WPAN traffic. We have implemented and validated WiCop on SORA, a software-defined radio platform. Experimental results show that with the assistance of the proposed WiCop policing schemes, the packet reception rate of a ZigBee-based WPAN can increase by up to 116% in the presence of a heavy WiFi interferer. A case study on the medical application of WPAN ECG monitoring demonstrates that WiCop can bound ECG signal distortion within 2% even under heavy WiFi interference. An analytical framework is devised to model the CCA behavior of WiFi interferers and the performance of WPANs under WiFi interference with or without WiCop protection. The analytical results are corroborated by experiments.

An adaptive collision resolution scheme for energy efficient communication in IEEE 802.15.4 networks

IEEE 802.15.4 provides a widely accepted solution for low-cost and low-power wireless communications, and it is known to be applicable to many types of WSN application scenarios. To enhance energy efficiency and throughput of sensor nodes, many CSMA/CA schemes based on IEEE 802.15.4 have been proposed. However, they still suffer from unnecessary waste of energy and bandwidth due to inefficient backoff management. In order to overcome these problems, we propose an enhancement to existing schemes, called adaptive collision resolution (ACR). ACR appropriately adapts backoff exponent (BE) to the current network contention level based on physical and link-layer measurements. In addition, it adjusts backoff periods (BP) to avoid meaningless backoffs and additional clear channel assessments (CCAs) by using the estimated time remaining until the channel becomes idle. To verify the feasibility and applicability of our scheme, we studied mathematical analysis and tested it on the Matlab and USRP/GNU Radio testbed. We also performed simulation study using OPNET, and our simulation results indicate that ACR shows improved energy efficiency and throughput performance over existing schemes.

Capacity and interference modeling of CSMA/CA networks using SSI point processes

The relative location of simultaneous transmitters, i.e. the set of nodes transmitting a frame at a given time, has a crucial impact on the performance of multi hop wireless networks. Two fundamental aspects of wireless network performances are related to these locations: capacity and interference. Indeed, as interference results from the summation of signals stemmed by concurrent transmitters, it directly depends on the transmitters' location. On the other hand, the network capacity is proportional to the number of simultaneous transmitters. In this paper, we investigate original point processes that can be used to model the location of transmitters that comply with the CSMA/CA policies, i.e. the Medium Access Control protocol used in 802.15.4 and 802.11 families of wireless technologies. We first propose the use of the Simple Sequential Inhibition point process to model CSMA/CA networks where clear channel assessment depends on the strongest emitter only. We then extend this point process to model a busy medium detection based on the strength of all concurrent signals. We finally compare the network capacity obtained through realistic simulations to a theoretical capacity estimated using the intensity of the SSI point process. It turns out that the proposed model is validated by the simulations.

A Novel Method for Service Differentiation in IEEE 802.15.4 : Priority Jamming

IEEE 802.15.4 employs carrier sense multiple access with collision avoidance (CSMA/CA), which is known to have difficulty for supporting quality of service (QoS). In this paper, a new priority scheme called priority jamming (PJ) is proposed for service differentiation for IEEE 802.15.4. The main idea of the proposed scheme is deferring the low priority packet transmission for the high priority packet. Clear channel assessment of IEEE 802.15.4 is modified to support the proposed PJ. The efficiency of the proposed scheme is validated by comparing the delay, throughput, and energy-per-bit with those of standard CSMA/CA. Simulations results showed that PJ improves the delay and throughput simultaneously while maintaining marginal difference in energy efficiency.

Short Clear Channel Assessment in Slotted IEEE 802.15.4 Networks

One of the major concerns in wireless sensor networks is energy saving due to lack of power sources. IEEE 802.15.4 provides CSMA/CA to reduce the possibility of a collision by checking whether the medium is in use. This checking operation is CCA (Clear Channel Assessment). Currently, IEEE 802.15.4 defines CCA as two consecutive channel assessment for slotted CSMA/CA. Obviously, always performing the channel assessment twice is wasteful and inefficient, since it requires more delay and energy consumption than when the channel assessment is performed once. In this paper, we propose a SCCA (Short Clear Channel Assessment) scheme which performs the channel assessment once, not twice, with minimal effort. Simulation results show that the SCCA operation provides reduced CCA processing time and energy consumption than when IEEE 802.15.4 CCA is used.

Detection of Selfish Manipulation of Carrier Sensing in 802.11 Networks

Recently, tuning the clear channel assessment (CCA) threshold in conjunction with power control has been considered for improving the performance of WLANs. However, we show that, CCA tuning can be exploited by selfish nodes to obtain an unfair share of the available bandwidth. Specifically, a selfish entity can manipulate the CCA threshold to ignore ongoing transmissions; this increases the probability of accessing the medium and provides the entity a higher, unfair share of the bandwidth. We experiment on our 802.11 testbed to characterize the effects of CCA tuning on both isolated links and in 802.11 WLAN configurations. We focus on AP-client(s) configurations, proposing a novel approach to detect this misbehavior. A misbehaving client is unlikely to recognize low power receptions as legitimate packets; by intelligently sending low power probe messages, an AP can efficiently detect a misbehaving node. Our key contributions are: 1) We are the first to quantify the impact of selfish CCA tuning via extensive experimentation on various 802.11 configurations. 2) We propose a lightweight scheme for detecting selfish nodes that inappropriately increase their CCAs. 3) We extensively evaluate our system on our testbed; its accuracy is 95 percent while the false positive rate is less than 5 percent.

An Ultra-Low Power and Flexible Acoustic Modem Design to Develop Energy-Efficient Underwater Sensor Networks

This paper is focused on the description of the physical layer of a new acoustic modem called ITACA. The modem architecture includes as a major novelty an ultra-low power asynchronous wake-up system implementation for underwater acoustic transmission that is based on a low-cost off-the-shelf RFID peripheral integrated circuit. This feature enables a reduced power dissipation of 10 μW in stand-by mode and registers very low power values during reception and transmission. The modem also incorporates clear channel assessment (CCA) to support CSMA-based medium access control (MAC) layer protocols. The design is part of a compact platform for a long-life short/medium range underwater wireless sensor network.

Avoiding collisions between IEEE 802.11 and IEEE 802.15.4 through coexistence aware clear channel assessment

More and more devices are becoming wirelessly connected. Many of these devices are operating in crowded unlicensed bands, where different wireless technologies compete for the same spectrum. A typical example is the unlicensed ISM band at 2.4 GHz, which is used by IEEE 802.11bgn, IEEE 802.15.4, and IEEE 802.15.1, among others. Each of these technologies implements appropriate Media Access Control (MAC) mechanisms to avoid packet collisions and optimize Quality of Service. Although different technologies use similar MAC mechanisms, they are not always compatible. For example, all CSMA/CA-based technologies use Clear Channel Assessment (CCA) to detect when the channel is free; however, in each case it is specifically designed to improve detection reliability of the specific technology. Unfortunately, this approach decreases the detection probability of other technologies, increasing the amount of cross-technology collisions. In this article, we introduce the concept of coexistence aware CCA (CACCA), which enables a node operating in one technology to backoff for other coexisting technologies as well. As a proof of concept, we analyze the Packet Error Rate(PER) incurred by an IEEE 802.15.4 network in the presence of IEEE 802.11bg interference, and assess the PER reduction that is achieved by using CACCA.

Priority-Based CCA Periods for Efficient and Reliable Communications in Wireless Sensor Networks

The IEEE 802.15.4 standard utilizes the CSMA-CA mechanism to control nodes’ access to the shared wireless communication medium. CSMA-CA implements the Binary Exponential Backoff (BEB) algorithm by which a node refrains from sending any packet before the expiry of its backoff period. After that, the node is required to sense the medium for two successive time slots to assert that the medium is clear from any ongoing transmissions (this is referred to as Clear Channel Assessment (CCA)). Upon finding the medium busy, the node doubles its backoff period and repeats that process. While effective in reducing the likelihood of collisions, this approach takes no measures to preserve the priorities among the nodes contending to access the medium. In this paper we propose the Priority-Based BEB (PB-BEB) algorithm in which we enhance BEB such that nodes’ priority is preserved. We provide a simulation study to examine the performance of PB-BEB. Our simulations show that the latter not only outperforms BEB in terms of fairness, but also show promising results in terms other parameters like channel utilization, reliability, and power conservation.

Coexistence Performance of IEEE 802.15.4 Wireless Sensor Networks Under IEEE 802.11b/g Interference

IEEE 802.15.4 Wireless Sensor Networks (WSNs) and IEEE 802.11b/g Wireless Local Area Networks (WLANs) are often collocated, causing a coexistence issue since these networks share the same 2.4GHz Industrial, Scientific, and Medical band. In our previous work, we built a coexistence model of IEEE 802.15.4 WSNs and IEEE 802.11b/g WLANs. By identifying three distinct coexistence regions, the model explained the coexistence behavior of IEEE 802.15.4 WSNs and IEEE 802.11b/g WLANs, and the model was experimentally validated. In this paper, we improve the model by introducing two important implementation factors: the transceiver’s Rx-to-Tx turnaround time and the Clear Channel Assessment partial detection effect. The enhanced model significantly improves the accuracy on explaining and predicting the coexistence performance of IEEE 802.15.4 WSNs in the real-life environment. Furthermore, under the guidance of the model, the coexistence performance of IEEE 802.15.4 WSNs is extensively investigated in various coexistence scenarios by analysis, simulation and experiments, respectively. The simulation and experimental results agree with our analysis. The coexistence model is believed to be helpful in resolving the coexistence issue.

New Energy Efficient Clear Channel Assessment for Wireless Network

In this paper, a new clear channel assessment (CCA) method: cascaded-CCA, is proposed. The primary motivation for the proposed approach is to integrate the respective advantages of two standard CCA mechanisms, energy detect and preamble detect, to arrive at a new dual threshold CCA family that can provide greater flexibility towards tuning MAC performance. Cascaded-CCA integrates energy efficiency of the energy detector (ED) and the reliability of the preamble detector (PD). The probability of detection/false alarm and power consumption of cascaded-CCA in the CCA modules of IEEE 802.11b are analyzed and compared with ED and PD as an example. The performance of cascaded-CCA is explored via MATLAB simulations that implement the CCA modules and medium access control (MAC) protocol for IEEE 802.11 and IEEE 802.15.4. Simulation results showed that cascaded-CCA improves the energy efficiency significantly compared to ED-only or PD-only CCA. In addition, ED, PD, and cascaded CCA are applied to a cognitive network scenario to validate the effectiveness of the proposed cascaded-CCA.

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.