Clear Channel Assessment Threshold Research Articles

A Hierarchical Deep Learning Approach for Optimizing CCA Threshold and Transmit Power in Wi-Fi Networks

The nodes, e.g., access points and clients, in current WiFi networks rely on carrier sense multiple access (CSMA) for channel access. This means they rely on a clear channel assessment (CCA) threshold to determine when it is safe to transmit a packet. In practice, this threshold is fixed, and nodes do not adapt their CCA threshold given varying channel conditions. To this end, this paper proposes and studies the use of deep reinforcement learning (DRL) to optimize the CCA threshold and transmit power of an AP. It allows an AP to learn the optimal policy for setting its CCA threshold and transmit power given its queue length and interference level. We outline a semi-Markov decision process (Semi-MDP) for the problem at hand and solve it using a decentralized deep hierarchical reinforcement learning (HRL) approach. We then evaluate its performance using traffic generated via a Poisson distribution and also from a trace file. The results show that when compared to two competing solutions, an AP with HRL reduces its average queue length by 24.4% and 52.4%, respectively.

Mitigating Cross-Technology Interference Through Fast Signal Identification

With the prosperity of Internet of Things, a large number of heterogeneous wireless devices share the same unlicensed spectrum, leading to severe cross-technology interference (CTI). Especially, the transmission power asymmetry of heterogeneous devices will further deteriorate this problem, as the high-power devices (like WiFi) always corrupt the ongoing transmissions of low-power devices (like ZigBee), because the energy of the ZigBee signal perceived by WiFi is too weak to achieve the CCA (Clear Channel Assessment) threshold and the channel is considered to be idle. This paper proposes an enhanced CCA (E-CCA) mechanism to mitigate CTI in WiFi and ZigBee coexistence networks. E-CCA contains ZShark which can identify signals within a tolerable time duration. It also contains a MAC layer design, with which a WiFi device can still determine the channel to be busy when the detected energy is below the CCA threshold while a ZigBee signal is identified, thus to avoid CTI to ZigBee transmissions. We set up a testbed based on USRP B200 and TelosB to collect data and evaluate the performance of ZShark. We further evaluate the performance of E-CCA through both theoretical analysis and simulations on NS-3. The results show significant performance improvement of ZigBee.

A Deep Q-Network Approach to Optimize Spatial Reuse in WiFi Networks

The proliferation of IEEE 802.11 or WiFi networks, and the explosive growth in traffic demands call for solutions to maximize the capacity of WiFi networks. Hence, maximizing the spatial reuse of WiFi networks is critical as doing so allows multiple concurrent transmissions. In this respect, a critical network parameter, Clear Channel Assessment (CCA) threshold, plays a vital role as it dictates whether a node is allowed to transmit after sensing the channel. In this paper, we propose to use Deep Q-network (DQN) under two learning patterns to select the CCA threshold of devices. We further consider Transmit Power Control (TPC) in conjunction with CCA threshold selection to improve the capacity of a WiFi network. The simulation results show that our approach is capable of selecting the optimal CCA threshold for each device. As a result, the average throughput is 62.4% higher than that of a legacy Dynamic Sensitivity Control (DSC) algorithm.

Vulnerability of WiFi’s Noise Floor Calibration

Most wireless technologies, including WiFi, rely heavily on clear channel assessment (CCA) to avoid collisions, not only among the devices within the same technology but also against cross-technology interference. If the CCA threshold is not configured properly, both the transmission and reception performance will be seriously affected with behaviors unexpected from the protocol's perspective. On the other hand, WiFi uses an adaptive CCA threshold based on a noise floor (NF) calibration algorithm to account for ambient NF changes and slight differences in hardware. However, this turns out to be a serious vulnerability of WiFi. In this work, we show that one can easily generate a wireless signal that can take advantage of the NF calibration algorithm of WiFi to inflate the CCA threshold and degrade performance significantly. The signal can be generated from a commercial off-the-shelf ZigBee device, and if well designed, need not be too long nor strong. We show that WiFi is vulnerable to such attack, and more surprisingly, the network performance does not recover long after the signal disappears. We exemplify and verify our findings through extensive real-world experiments using five types of commercial WiFi NICs and three different WiFi access points to show that this is a critical problem that exists in reality and must be addressed.

A Pragmatic Approach to Clear Channel Assessment Threshold Adaptation and Transmission Power Control for Performance Gain in CSMA/CA WLANs

We propose practical sets of rules for adapting Clear Channel Assessment (CCA) and Transmit Power (TP) parameters by simulating ensembles of randomly generated wireless networks and collecting throughput statistics. The rules’ performances depend strongly on network topology, with increases in throughput in many cases. However, networks with a high clustering coefficient are often adversely effected by the adaptations. But simulations of small-scale networks show that apparently adverse adaptations may still yield benefits for uneven demand combinations. Finally, we have found that throughput is not usually correlated with the number of hidden or exposed nodes in any non-trivial network set-up.

Downlink Interference Control of LAA-LTE for Coexistence With Asymmetric Hidden Wi-Fi APs

To confront the increasing mobile traffic demand and the scarcity of the licensed band, 3GPP has standardized a new type of LTE, called License Assisted Access (LAA) LTE (LAA-LTE), which aggregates licensed bands with unlicensed bands. Since the conventional Wi-Fi devices employ −62 dBm clear channel assessment threshold to LAA-LTE's signals, the appearance of LAA-LTE in the unlicensed band leads to a new phenomenon, asymmetric hidden terminal problem , which severely degrades the throughput and delay performance of LAA-LTE as well as Wi-Fi. We propose a downlink interference control scheme for an LAA-LTE eNB to prevent the asymmetric hidden Wi-Fi APs nearby from recklessly transmitting and thereby interfering the eNB's transmission. Specifically, we analyze the distortion of Wi-Fi's signals received at LAA-LTE and LAA-LTE's signals received at Wi-Fi due to the difference of physical-layer parameters between LAA-LTE and Wi-Fi. Based on this analysis, we develop an AP suppression and power control technique to control incoming and outgoing interference of the LAA-LTE eNB. Extensive simulations confirm that the proposed scheme improves the throughput and delay performance of LAA-LTE while maintaining or even improving the performance of Wi-Fi.

A QoS Enhancement Scheme through Joint Control of Clear Channel Assessment Threshold and Contending Window for IEEE 802.11e Broadcasting

In a WLAN, when a great many nodes coexist, the network may readily be congested, thus causing packets dropping and network performance degradation. To solve this issue, a lot of schemes have been proposed. However, most of the previous works attempt to avoid the possible channel congestion by controlling the packets generation rate and/or transmitting power of nodes, while the effects of Clear Channel Assessment (CCA) threshold are not well examined. In our paper, a Joint CCA threshold and contending window control algorithm (JCCA) is proposed to avoid channel congestion or reduce the congestion probability of broadcasting in an IEEE 802.11e network. Both the network conditions and the priorities of messages are taken into account to improve the broadcasting performance in our paper. According to the simulation results, it can be concluded that our scheme can significantly increase the network throughput as well as packets delivery ratio and reduce the packet transmission delay compared to the IEEE 802.11e and Adaptive Carrier Sensing-Based MAC Designs (ACSBM) protocol.

Modeling and Analyzing the Coexistence of Wi-Fi and LTE in Unlicensed Spectrum

We leverage stochastic geometry to characterize key performance metrics for neighboring Wi-Fi and LTE networks in unlicensed spectrum. Our analysis focuses on a single unlicensed frequency band, where the locations for the Wi-Fi access points and LTE eNodeBs are modeled as two independent homogeneous Poisson point processes. Three LTE coexistence mechanisms are investigated: 1) LTE with continuous transmission and no protocol modifications; 2) LTE with discontinuous transmission; and 3) LTE with listen-before-talk and random back-off. For each scenario, we derive the medium access probability, the signal-to-interference-plus-noise ratio coverage probability, the density of successful transmissions (DST), and the rate coverage probability for both Wi-Fi and LTE. Compared with the baseline scenario where one Wi-Fi network coexists with an additional Wi-Fi network, our results show that Wi-Fi performance is severely degraded when LTE transmits continuously. However, LTE is able to improve the DST and rate coverage probability of Wi-Fi while maintaining acceptable data rate performance when it adopts one or more of the following coexistence features: a shorter transmission duty cycle, lower channel access priority, or more sensitive clear channel assessment thresholds.

Performance Evaluation of Dynamic CCA-ED Threshold Control Scheme for WLAN

An effort has been made to achieve and maintain a high data rate, which is actually experienced by the users and less affected by the nearby devices even in a Wi-Fi dense area. An IEEE 802.11ax TG (task group) was formed to standardize these efforts, so called HEW (high efficiency WLAN). As a way of alleviating the effect of nearby devices, the IEEE 802.11ax TG is considering a scheme which changes the CCA (clear channel assessment) threshold dynamically. In this paper we explain how the scheme tries to resolve the hidden terminal problem and the exposed terminal problem at the same time. We also analyze the performance of the dynamic CCA threshold control scheme in various density of APs/STAs through simulation.

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 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.

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.

Clear Channel Assessment in Integrated Medical Environments

Complementary WLAN and WPAN technologies as well as other wireless technologies will play a fundamental role in the medical environments to support ubiquitous healthcare delivery. This paper investigates clear channel assessment (CCA) and its impact on the coexistence of WLAN (IEEE 802.11 high rate direct sequence spread spectrum (HR/DSSS) PHY) andWPAN (IEEE 802.15.4b) in the 2.4 GHz industrial, scientific, and medical (ISM) band.We derived closed-form expressions of both energy-based CCA and feature-based CCA. We qualified unequal sensing abilities between them and termed this inequality asymmetric CCA, which is different from the traditional hidden node or exposed node issues in the homogeneous network. The energy-based CCA was considered in the considered integratedmedical environment because the 2.4 GHz ISM band is too crowded to apply feature-based CCA. The WPAN is oversensitive to the 802.11 HR/DSSS signals and the WLAN is insensitive to the 802.15.4b signals. Choosing an optimal CCA threshold requires some prior knowledge of the underlying signals. In the integrated medical environment we considered here, energy-based CCA can effectively avoid possible packet collisions when they are close within the heterogeneous exclusive CCA range (HECR). However, when they are separated beyond the HECR, WPAN can still sense the 802.11 HR/DSSS signals, but WLAN loses its sense to the 802.15.4b signals. The asymmetric CCA leads to WPAN traffic in a position secondary to WLAN traffic.