Carrier Sense Threshold Research Articles

Performance analysis of spatially distributed LTE-U/NR-U and Wi-Fi networks: An analytical model for coexistence study

To access an unlicensed channel, Wi-Fi follows the Listen Before Talk (LBT) mechanism, whereas LTE-U (and future New Radio in Unlicensed (NR-U) Patriciello et al., 2020; Lagen et al., 2019) adopts the ON–OFF duty-cycled mechanism to fairly share the channel with Wi-Fi. These different mechanisms result in quite different performance for Wi-Fi and LTE-U/NR-U based on their relative deployment and density in the environment. In this work, we present an analytical model for the characterization of achievable throughputs of Wi-Fi and LTE-U networks in spatially distributed scenarios with downlink-prevalent traffic. The proposed model is used to study how LTE-U and Wi-Fi coexist with each other in spatially distributed scenarios. Our extensive simulation results show that it is a reliable model for estimating the throughput of both Wi-Fi and LTE-U in a spatially distributed deployment. The impact of various network parameters such as energy detection and carrier sense threshold on Wi-Fi and LTE-U coexistence is explored as a byproduct and corroborated via a National Instrument experimental test bed. Our model gives very high accuracy in throughput estimation and the mean normalized error is less than 3% for a 80-node scenario in which 50% of nodes belong to each of Wi-Fi and LTE-U network. The analytical model is also used to conduct coexistence studies of LTE-U and Wi-Fi.

Stochastic Geometry Analysis of Inversely Proportional Carrier Sense Threshold and Transmission Power for WLAN Spatial Reuse

Stochastic Geometry Analysis of Inversely Proportional Carrier Sense Threshold and Transmission Power for WLAN Spatial Reuse

Throughput Enhancement of Full-Duplex CSMA Networks Using Multiplayer Bandits

This article studies the network-level throughput of a full-duplex (FD)-enabled CSMA network, considering the link's transmit power (TP) control, carrier-sensing threshold (CST) adjustment, and logarithm access intensity (LAI) adaptation. With the FD technique, a transmitter-receiver pair can transmit and receive simultaneously in the same frequency band. We aim to find the best combination of TP, CST, and LAI for each link to maximize the FD-CSMA network throughput. However, adjusting each link's TP and CST will change the network's carrier-sensing relation or contention graph, consequently leading to a computationally intractable network optimization problem. On the other hand, it is difficult to jointly optimize these three parameters in a fully distributed network. To overcome these, we first decompose this network optimization problem into two subproblems: 1) a joint control and scheduling problem in the transport- and media access control (MAC)-layer and 2) a parameter selection problem in the PHY-layer. Then, the multiplayer multiarmed bandit (MPMAB) framework has been introduced to address this problem by solving the two subproblems alternately. We put forth a fully distributed algorithm, named the stochastic and adversarial optimal FD-CSMA (SAO-FD-CSMA) algorithm, to solve the MPMAB problem by taking advantage of the optimization tool and the bandit theory. The numerical results show that the proposed algorithm outperforms the state-of-the-art bandit algorithms and can improve the network throughput by 43% compared with the random selection method.

Group-Wise Listen-Before-Talk Protocol for Dynamic Spectrum Sharing: A New Framework for Full Frequency Reuse

In existing dynamic spectrum sharing (DSS) systems, each node arbitrates channel access independently based on carrier-sensing mechanisms such as the listen-before-talk (LBT) protocol. Owing to the uncoordinated channel access between all nodes, the channel is occupied in a random pattern. This makes it difficult to reduce the mismatch in channel quality indicator (CQI) while increasing the spatial reuse gain between the different nodes; therefore, the areal capacity gain obtained by adding nodes is much lower in existing DSS systems than in the cellular system. In this paper, we propose a different means of improving the areal capacity for downlink DSS systems. It is a group-wise DSS approach that ensures full frequency reuse in each group of base stations (BSs) by performing LBT only between the representative BSs, each of them selected by each group. Once a channel is secured by each group, all its member BSs share a channel simultaneously. This approach makes closed-loop feedback-based link adaptation practical while boosting spatial reuse gain even in the DSS environment. To implement the group-wise DSS, we propose a single unified framework that employs elementary algorithms for BS grouping and carrier-sensing threshold adjustment. Our system-level simulation results demonstrate that the proposed framework boosts the areal capacity gain by approximately 4.42 times as much as the conventional approach.

Dynamic Carrier-Sense Threshold Selection for Improving Spatial Reuse in Dense Wireless LANs

As density of a wireless LAN grows, per-user throughput degrades severely, deteriorating user experience. To improve service quality, it is important to increase system spectral efficiency. Controlling carrier-sense threshold is one of the key techniques to achieve the goal, because frequently transmissions are unnecessarily blocked by carrier sensing, even though these transmissions can take place without causing packet losses. Using high carrier-sense threshold and allowing nodes to transmit aggressively may increase the system throughput, but this approach can lead to unfair channel share and cause starvation for the edge nodes. In this paper, we propose a medium access control protocol where transmitters include the carrier-sense threshold required to protect its packet in the preamble. Nodes receiving the preamble only transmit concurrently, when they are confident that their own transmission as well as the on-going transmission will both be successfully received at the respective receivers. The simulation results show that this dual-threshold approach can achieve higher system throughput compared to using a single carrier-sense threshold, without penalizing edge nodes.

A Simple and Practical Scheme Using Multiple Channels for Improving System Spectral Efficiency of Highly Dense Wireless LANs

As the density of wireless LANs increases, performance degradation caused by hidden terminals and exposed terminals becomes significant. These problems come from carrier sensing based medium access control used in current wireless LANs. Hidden terminals are created if carrier sense threshold is too high, whereas exposed terminals are created if carrier sense threshold is too low. A good threshold depends on how far nodes are placed from their destinations, but that cannot be controlled by the system. In this paper, we propose a simple scheme that makes use of multiple channels. Multiple channels could be utilized by equipping multiple radios or using advanced hardware such as SDR to divide a single channel into multiple channels. Nodes are assigned channels based on their estimated distance from the AP. Once the assignment is done, carrier sense threshold for the channel is selected so that as many concurrent transmissions take place as possible, while preventing hidden terminals. Simulation results show that the proposed mechanism achieves significantly higher throughput without causing starvation at the edge nodes.

Stochastic Geometry Analysis of Individual Carrier Sense Threshold Adaptation in IEEE 802.11ax WLANs

This paper discusses the impact of spatial reuse and carrier sense threshold (CST) optimization on the performance of wireless local area networks using stochastic geometry analysis. The adjustment of the CST is a promising approach to improve spatial reuse, and has been proposed for the IEEE 802.11ax standard. Considering the situation where each access point (AP) individually adjusts its CST based on the individual received power, this paper derives the probability of transmission success and the density of successful transmissions (DST). The evaluation results of these metrics reveal that the optimal setting is to increase the CST linearly (in terms of dB) with respect to the average received signal power. Because the maximization of the DST causes unfairness from the viewpoint of success of transmission, the maximization of the product of the transmission success probabilities is proposed to improve the performance of the entire system and restrain unfairness. Using the trend of the optimal CST function, the impact of the density of APs on the optimal CST function is determined. Moreover, individual CST adjustment is found to improve spatial reuse compared with identical adjustment, i.e., setting the CST of all APs to an identical value.

Enhanced Dual Carrier Sensing With Transmission Time Control for Fair Spatial Reuse in Heterogeneous and Dense WLANs

In this paper, we focus on fairness and spatial reuse in heterogeneous and dense wireless local area networks (WLANs) where stations (STAs) have different capabilities of carrier sensing and basic service sets (BSSs) are densely deployed. First, we show a serious problem of unfairness arising when STAs with different carrier sensing threshold (CSTH) coexist and compete for channel access. To cope with this problem, a dual carrier sensing mechanism has been proposed in the on-going IEEE 802.11ax standardization. This mechanism uses two differentiated CSTHs: a conservative CSTH for fairness among intra-BSS STAs and an aggressive CSTH for spatial reuse by inter-BSS STAs. This dual carrier sensing mechanism may be effective in improving fairness. However, we show that its gain is marginal in terms of spatial reuse because an acknowledgment (ACK) frame is liable to be corrupted due to interference from a data frame transmitted by an inter-BSS STA. In order to avoid ACK corruption, we enhanced the dual carrier sensing mechanism by controlling the transmission time of the data frame. Depending on the receiving signal strength of data frame transmitted by an inter-BSS STA, the proposed mechanism selectively adjusts the concurrent transmission time of the data frame so that ACK frames can be successfully delivered. Results from simulation confirmed the outstanding performance of the proposed mechanism in heterogeneous and dense WLANs; compared with conventional mechanisms, the total throughput was considerably increased by more than two-fold while the fairness among the STAs was improved.

FACT: Fine-Grained Adaptation of Carrier Sense Threshold in IEEE 802.11 WLANs

A fine-grained carrier sense threshold (CST) adaptation method, which controls CST, depending on both the interferer and destination nodes, is proposed to improve spatial reuse in wireless local area networks (WLANs). The proposed method utilizes predefined functions in the WLAN standard, thus making itself easily implementable in commercial WLAN devices. A supplementary clear channel assessment (CCA) method is also proposed to further enhance network performance by reducing CCA overhead. The performance of the proposed methods is comparatively evaluated via ns-3 simulation. Simulation results show that the proposed methods significantly improve network throughput compared with the legacy method in a two-cell environment.

Throughput assurance of wireless body area networks coexistence based on stochastic geometry.

Wireless body area networks (WBANs) are expected to influence the traditional medical model by assisting caretakers with health telemonitoring. Within WBANs, the transmit power of the nodes should be as small as possible owing to their limited energy capacity but should be sufficiently large to guarantee the quality of the signal at the receiving nodes. When multiple WBANs coexist in a small area, the communication reliability and overall throughput can be seriously affected due to resource competition and interference. We show that the total network throughput largely depends on the WBANs distribution density (λp), transmit power of their nodes (Pt), and their carrier-sensing threshold (γ). Using stochastic geometry, a joint carrier-sensing threshold and power control strategy is proposed to meet the demand of coexisting WBANs based on the IEEE 802.15.4 standard. Given different network distributions and carrier-sensing thresholds, the proposed strategy derives a minimum transmit power according to varying surrounding environment. We obtain expressions for transmission success probability and throughput adopting this strategy. Using numerical examples, we show that joint carrier-sensing thresholds and transmit power strategy can effectively improve the overall system throughput and reduce interference. Additionally, this paper studies the effects of a guard zone on the throughput using a Matern hard-core point process (HCPP) type II model. Theoretical analysis and simulation results show that the HCPP model can increase the success probability and throughput of networks.

Research on an uplink carrier sense multiple access algorithm of large indoor visible light communication networks based on an optical hard core point process.

The IEEE 802.15.7 protocol suggests that it could coordinate the channel access process based on the competitive method of carrier sensing. However, the directionality of light and randomness of diffuse reflection would give rise to a serious imperfect carrier sense (ICS) problem [e.g., hidden node (HN) problem and exposed node (EN) problem], which brings great challenges in realizing the optical carrier sense multiple access (CSMA) mechanism. In this paper, the carrier sense process implemented by diffuse reflection light is modeled as the choice of independent sets. We establish an ICS model with the presence of ENs and HNs for the multi-point to multi-point visible light communication (VLC) uplink communications system. Considering the severe optical ICS problem, an optical hard core point process (OHCPP) is developed, which characterizes the optical CSMA for the indoor VLC uplink communications system. Due to the limited coverage of the transmitted optical signal, in our OHCPP, the ENs within the transmitters' carrier sense region could be retained provided that they could not corrupt the ongoing communications. Moreover, because of the directionality of both light emitting diode (LED) transmitters and receivers, theoretical analysis of the HN problem becomes difficult. In this paper, we derive the closed-form expression for approximating the outage probability and transmission capacity of VLC networks with the presence of HNs and ENs. Simulation results validate the analysis and also show the existence of an optimal physical carrier-sensing threshold that maximizes the transmission capacity for a given emission angle of LED.

Identifying and coordinating joint impact of spatial reuse and multi-rate capability on wireless ad-hoc networks

In this paper, we derive an analytical model to evaluate the effect of jointly tuning the carrier sense threshold and employing multiple data rates on the network capacity in wireless ad-hoc networks. In order to capture the effect of the carrier sense threshold, the proposed model characterizes the channel states within the carrier sense range of an individual transmitter. Multi-rate capability for transmission is incorporated in identifying the channel states observed by a node. Towards maximizing the per-node throughput derived from the analytical model, a control reference and its optimal operating range is then identified. Based on the findings we propose a reference based channel access scheme, working in run-time and distributed fashion. Under the proposed scheme, each node measures the number of idle slots between two consecutive busy slots on-line and tunes the contention window size so as to ensure the measured control reference located within its optimal operation range. At the same time each node performs the selection of the data rate and the corresponding carrier sense threshold dealing with the current channel and network dynamics. Simulation results show that the proposed scheme achieves a performance improvement of up to 81 % in terms of per-node throughput over conventional 802.11 DCF algorithm.

Transport Capacity of Distributed Wireless CSMA Networks

In this paper, we study the transport capacity of large multi-hop wireless CSMA networks. Different from previous studies which rely on the use of centralized scheduling algorithm and/or centralized routing algorithm to achieve the optimal capacity scaling law, we show that the optimal capacity scaling law can be achieved using entirely distributed routing and scheduling algorithms. Specifically, we consider a network with nodes Poissonly distributed with unit intensity on a $\sqrt{n}\times\sqrt{n}$ square $B_{n}\subset\Re^{2}$. Furthermore, each node chooses its destination randomly and independently and transmits following a CSMA protocol. By resorting to the percolation theory and by carefully tuning the three controllable parameters in CSMA protocols, i.e. transmission power, carrier-sensing threshold and count-down timer, we show that a throughput of $\Theta\left(\frac{1}{\sqrt{n}}\right)$ is achievable in distributed CSMA networks. Furthermore, we derive the pre-constant preceding the order of the transport capacity by giving an upper and a lower bound of the transport capacity. The tightness of the bounds is validated using simulations.

A Modified Hard Core Point Process for Analysis of Random CSMA Wireless Networks in General Fading Environments

For spectrum sharing and avoidance of mutual interference, carrier-sense multiple access (CSMA) protocols are very popular in distributed wireless networks. CSMA protocols aim to maximize the spatial frequency reuse while limiting the mutual interference and outage. The hard core point process (HCPP) is a very popular tool for modeling and analysis of random CSMA networks. However, the traditional HCPP suffers from the node intensity (and hence the interference) underestimation flaw. Therefore, we propose a modified hard core point process to mitigate this flaw. The proposed modified HCPP is generalized for any fading environment. To this end, we derive a closed-form expression for the intensity of simultaneously active transmitters in a random wireless CSMA network. Then, we derive a closed-form expression for approximating the outage probability experienced by a generic receiver in the network, and subsequently, use it to obtain the transmission capacity of the network. Finally, we show the existence of an optimal carrier-sensing threshold for the CSMA protocol that maximizes the transmission capacity of the network. Simulation results validate the analysis and also provide interesting insights into the design of practical CSMA networks.

RFID reader collision problem: performance analysis and medium access

AbstractThe RFID reader collision problem, in which an RFID reader's interrogation is interfered by other concurrent readers' transmission, is considered an important issue to reliable operation and thus to the wide‐spread deployment of RFID networks. In this paper, we present modeling and analysis of the RFID reader collision problem. We observe asymmetry between an RFID reader's and a tag's communication capabilities and develop an RFID radio model based on the asymmetry. By the model, we characterize the spatial reuse of RFID reader networks, and derive concurrent interrogation distance beyond which readers can transmit simultaneously without causing collision and the carrier sense threshold corresponding to the distance. We also examine the dual‐channel mode where available bandwidth is divided into two channels by which reader‐to‐tag communication and tag‐to‐reader communication are separated. We analyze and evaluate the performance of the dual‐channel mode in terms of spatial reuse and interrogation completion time. Copyright © 2010 John Wiley & Sons, Ltd.

The case for SIMO random access in multi-antenna multi-hop wireless networks

In this paper, we demonstrate that multiple concurrent asynchronous and uncoordinated Single-Input Multiple-Output (SIMO) transmissions can successfully take place even though the respective receivers do not explicitly null out interfering signals. Hence, we propose simple modifications to the widely deployed IEEE 802.11 Medium Access Control (MAC) to enable multiple non-spatially-isolated SIMO sender-receiver pairs to share the medium. Namely, we propose to increase the physical carrier sense threshold, disable virtual carrier sensing, and enable message-in-message packet detection. We use experiments to show that while increasing the peak transmission rate, spatial multiplexing schemes such as those employed by the IEEE 802.11n are highly non-robust to asynchronous and uncoordinated interferers. In contrast, we show that the proposed multi-flow SIMO MAC scheme alleviates the severe unfairness resulting from uncoordinated transmissions in 802.11 multi-hop networks. We analytically compute the optimal carrier sense threshold based on different network performance objectives for a given node density and number of receive antennas.

On link-level starvation in dense 802.11 wireless community networks

With the growing number of spontaneously deployed WiFi hotspots and home networks, end-users often experience significant performance degradation or even starvation. However, we observe that tuning individual system parameters (channel, Tx power, carrier sense threshold, transmit rate, etc.) is insufficient and may lead to starvation in some cases. In this paper, we develop a comprehensive analytical model to characterize the throughput of individual links in dense IEEE 802.11 wireless community networks that accounts for heterogeneous transmission power levels and CS thresholds, as well as various sources of packet collisions. Based on the insight from the theoretical analysis, we propose a simple identification mechanism that can determine the sources of starvation using local measurements. Both the theoretical model and the identification algorithm are validated using testbed experiments and ns-2 simulations.

Power control of control frames in IEEE 802.11 networks

Power control design is important in IEEE 802.11 wireless networks, because the equipment sometimes is powered by the battery. There has been some research into the power control in IEEE 802.11 wireless networks. In most cases, the nodes use the same transmitted power to transmit the RTS (request to send) control frames and CTS (clear to send) control frames. We propose a protocol for power control of control frames (PCCF) in IEEE 802.11 networks. In this PCCF protocol, the RTS transmitted power is based on the carrier sense threshold, the receiving threshold and the maximum transmitted power, and then the data transmitted power is calculated based on the SINR (signal to interference and noise ratio) threshold. Based on the RTS transmitted power and the data transmitted power, the CTS transmitted power is calculated. Simulation results show that compared to the IEEE 802.11 DCF protocol, the PCCF protocol increases the system throughput, and decreases the delay and energy consumption.

Optimal physical carrier sense in wireless networks

We investigate the problem of maximizing Medium Access Control (MAC) throughput in Carrier Sense Multiple Access (CSMA) wireless networks. By explicitly incorporating the carrier sense threshold and the transmit power into our analysis, we derive an analytical relation between MAC throughput and system parameters. In homogeneous networks, we derive the optimal carrier sense range at a given node density as a function of the ratio between the transmit power and the carrier sense threshold. The obtained optimal carrier sense range is smaller than that for covering the entire interference range, which is in sharp contrast to what has been considered to be optimal in previous studies. Only when the node density goes to infinity, the optimal carrier sense range converges to that for exactly covering the interference range, thereby eliminating all the hidden nodes. For nonhomogeneous networks, any distributed algorithm for tuning the carrier sense threshold, in which each node tries to maximize its own throughput without coordination, may significantly degrade MAC throughput. In order to properly design a distributed algorithm, each node not only considers its own throughput, but also needs to take account of its adverse impact on others. Our analysis is verified by simulation studies under various network scenarios.

Adaptive Physical Carrier Sense in Topology-Controlled Wireless Networks

Transmit power and carrier sense threshold are key MAC/PHY parameters in carrier sense multiple access (CSMA) wireless networks. Transmit power control has been extensively studied in the context of topology control. However, the effect of carrier sense threshold on topology control has not been properly investigated in spite of its crucial role. Our key motivation is that the performance of a topology-controlled network may become worse than that of a network without any topology control unless carrier sense threshold is properly chosen. In order to remedy this deficiency of conventional topology control, we present a framework on how to incorporate physical carrier sense into topology control. We identify that joint control of transmit power and carrier sense threshold can be efficiently divided into topology control and carrier sense adaptation. We devise a distributed carrier sense update algorithm (DCUA), by which each node drives its carrier sense threshold toward a desirable operating point in a fully distributed manner. We derive a sufficient condition for the convergence of DCUA. To demonstrate the utility of integrating physical carrier sense into topology control, we equip a localized topology control algorithm, LMST, with the capability of DCUA. Simulation studies show that LMST-DCUA significantly outperforms LMST and the standard CSMA protocol.