TXOP Limit Research Articles

Effectiveness of a Hybrid Method of Block Ack and Unsolicited Retry on Binary Data Lossless Groupcast over Wireless LANs

In this paper, we propose a combined method of GCR Block Ack and Unsolicited Retry for binary data lossless groupcast over wireless LANs. The two mechanisms are standardized as IEEE 802.11aa GCR for audiovisual transmission. In the proposed method, the sender transmits each frame twice without acknowledgment as Unsolicited Retry under lossy wireless link conditions. After transmitting twice, the sender enters the Block Ack sequence. In addition, we apply TXOP-Bursting, which allows a terminal to send frames sequentially with high priority during the TXOP limit, to the combined method. To show the proposal's effectiveness, we carry out a computer simulation. We assume binary data transmission of about 40MB and assess the time of complete reception at all the receivers. From the result, we find that the proposed method can shorten the received time against the conventional Block Ack method.

Power-Optimized NOMA With TXOP Tuning-Based Channel Access Scheme for IEEE 802.11ah Dense IoT Networks

In this letter, we propose a power-optimized NOMA with TXOP tuning based novel channel access scheme for IEEE 802.11ah dense IoT networks. Using the proposed method, we form the NOMA-clusters to mitigate the number of contending nodes in a group. Further, the proposed scheme enables nodes in a NOMA-cluster to transmit simultaneously using power-domain NOMA, as well as multiple frames based on the TXOP limit in single resource block. With an analytical model, we evaluate the throughput and connectivity performance. From the analytical and simulation results, it is evident that the proposed scheme significantly improve the performance of NOMA-IoT networks.

An enhanced dynamic transmission opportunity scheme to support varying traffic load over wireless campus networks.

Transmission opportunity (TXOP) is a key factor to enable efficient channel bandwidth utilization over wireless campus networks (WCN) for interactive multimedia (IMM) applications. It facilitates in resource allocation for the similar categories of multiple packets transmission until the allocated time is expired. The static TXOP limits are defined for various categories of IMM traffics in the IEEE802.11e standard. Due to the variation of traffic load in WCN, the static TXOP limits are not sufficient enough to guarantee the quality of service (QoS) for IMM traffic flows. In order to address this issue, several existing works allocate the TXOP limits dynamically to ensure QoS for IMM traffics based on the current associated queue size and pre-setting threshold values. However, existing works do not take into account all the medium access control (MAC) overheads while estimating the current queue size which in turn is required for dynamic TXOP limits allocation. Hence, not considering MAC overhead appropriately results in inaccurate queue size estimation, thereby leading to inappropriate allocation of dynamic TXOP limits. In this article, an enhanced dynamic TXOP (EDTXOP) scheme is proposed that takes into account all the MAC overheads while estimating current queue size, thereby allocating appropriate dynamic TXOP limits within the pre-setting threshold values. In addition, the article presents an analytical estimation of the EDTXOP scheme to compute the dynamic TXOP limits for the current high priority traffic queues. Simulation results were carried out by varying traffic load in terms of packet size and packet arrival rate. The results show that the proposed EDTXOP scheme achieves the overall performance gains in the range of 4.41%—8.16%, 8.72%—11.15%, 14.43%—32% and 26.21%—50.85% for throughput, PDR, average ETE delay and average jitter, respectively when compared to the existing work. Hence, offering a better TXOP limit allocation solution than the rest.

Tuning Wi-Fi Traffic Differentiation by Combining Frame Aggregation with TXOP Limits

There are two IEEE 802.11 mechanisms which enhance Wi-Fi network efficiency by lowering communication overhead: the legacy transmission opportunity (TXOP) limit and frame aggregation. According to the IEEE 802.11 standard, frame aggregation has priority over TXOP duration settings, in some cases completely overriding legacy behavior. Therefore, Wi-Fi vendors and administrators may resign from enabling TXOP limit which, as we show in this letter, is not always a good choice. We base our findings on the presented analytical throughput model of 802.11ac (validated by ns-3 simulations), which allows measuring interactions between the two considered mechanisms and their impact on traffic differentiation in 802.11 networks.

Enhancements of the Dynamic TXOP Limit in EDCA Through a High-Speed Wireless Campus Network

IEEE802.11e is a concrete challenge to providing quality of service (QoS) aimed at interactive multimedia (IMM) applications due to the resource allocation parameter for heterogeneous traffic flows. This parameter is fixed for different specific IMM traffic flows in the IEEE802.11e standard. However, due to the variation in traffic load on wireless campus networks (WCNs), the fixed allocation of the channel resource parameter is not sufficient to guarantee QoS for IMM traffic flows. Thus, many researchers have investigated dynamic regulation of this resource allocation parameter to ensure QoS. However, there are still some unresolved problems with this parameter. This paper introduces an enhanced EDCA resource allocation parameter named dynamic transmission opportunity (TXOP) limit that regulates according to the variation in traffic load over WCN. This work also employs a mathematical modelling approach for the proposed parameter and numerical analysis of the existing and proposed parameters. The evaluation of the proposed model is simulated using Qualnet 5.1. The simulation results show that the proposed scheme allows improving the QoS performance of IMM traffic by reducing end-to-end delay. Additionally, the results show that the proposed scheme significantly improves global throughput.

ANALYSIS OF DATA TRANSMISSION IN WIRELESS-LAN FOR 802.11 E2ET

The aim of this paper is to investigate the transmi ssion of data between client and server through dif ferent IEEE 802.11 wireless LAN multi- HOP network. To improve this issue, the tran smission opportunity (TXOP) mechanism is defined in the IEEE 802.11e standard, with which a wireless node can transmit multiple fr ames consecutively for a maximum channel occupancy time, called TXOP limit. This paper considers the performance of the TXOP me chanism for multi-hop wireless networks. Focusing oa three-node chain topology, we model it as a tandem queuing network w ith two nodes. The E2ET is derived and the analysis is validated by simulation. Numerical results show that the TXOP mechanism work s well for multi-hop wireless networks. It is also shown that adjusting TXOP limit is significantly important in order to increa se the overall throughput. In terms of multi-hop wi reless networks, there is little analytical work with regard to the E2ET performance . One of the rationales for the analytical difficulty for multi-hop wireless networks is that IEEE 802.11 MAC protocol is too co mplex to model the behavior of multi-hop frame tran smissions.

Service Differentiation without Prioritization in IEEE 802.11 WLANs

Wireless LANs carry a mixture of traffic, with different delay and throughput requirements. The usual way to provide low-delay services is to give priority to such traffic. However, this creates an incentive for throughput sensitive traffic also to use this service, which degrades overall network performance. We show, analytically and by simulation, that the performance of both delay and throughput sensitive traffic can be improved by scaling IEEE 802.11's CWmin and TXOP limit parameters in equal proportion. This reduces, but does not eliminate, the incentive for bulk data users to use the low-delay service. We further show that this incentive can be removed, while still giving improved performance to both classes, by reducing the CWmin of the high throughput class by a constant that is independent of the traffic load.

무선랜 QoS의 성능향상을 위한 최적 파라미터에 관한 연구

IEEE 802.11과 같은 무선 LAN 환경에서 실시간 멀티미디어 통신이 전송 데이터의 많은 부분을 차지하면서 성능 문제와 함께 네트워크의 QoS(Quality of Service)가 중요한 문제로 대두되고 있다. 802.11e MAC(Medium Access Control)은 기존 802.11 MAC의 문제를 해결하기 위해 우선순위 기반의 차별화 서비스를 제공한다. 특히 각 스테이션의 TXOP(Transmission Opportunity)는 한 번에 여러 프레임을 전송할 수 있는 시간을 규정하며 Priority와 함께 네트워크 성능 및 QoS 향상에 중요한 요소가 된다. 따라서 본 논문에서는 스테이션 수의 변화에 따라 네트워크의 최대 성능을 위한 프레임 사이즈와 TXOP, 그리고 Priority 값을 분석하고 최적의 값을 도출한다. 802.11e 표준 파라미터를 사용하여 시뮬레이션을 수행한 결과 Throughput은 스테이션의 수가 5일 때, TXOP Limit의 값이 6.016ms 일 때 가장 좋은 결과를 보였고 공정성은 TXOP Limit의 값이 3.008ms이고 Priority는 우선순위가 가장 높은 CW(Contention Window) 값이 7-15일 때가 아니고 그보다 낮은 CW 15-31일 때 가장 좋은 결과를 나타내었다. Since multimedia data takes large part of realtime transmission in wireless communication environments such as IEEE 802.11, QoS issues became one of the important problems with network performance. 802.11e MAC provides differentiated services based on priority schemes to solve existing 802.11 MAC problems. The TXOP is an important factor with the priority to improve network performance and QoS because it defines the time duration in which multiple frames can be transferred at one time for each station. In this paper, therefore frame sizes, TXOP Limit, and Priority values in accordance with the number of stations are experimented and derived for best network performance and QoS. Using 802.11e standard parameters, simulation results show the best throughput when the number of stations is 5 and TXOP Limit value is 6.016ms. For fairness, the best result is achieved at 3.008ms of TXOP Limit value and 15-31 of CW(Contention Window) that is lower priority than CW 7-15.

GTXOP: A Game Theoretic Approach for QoS Provisioning Using Transmission Opportunity Tuning

In unsupervised contention-based networks such as EDCA mode of IEEE 802.11(e)(s), upon winning the channel, each node gets a transmission opportunity (TXOP) in which the node can transmit multiple frames consequently without releasing the channel. Adjusting TXOP can lead to better bandwidth utilization and QoS provisioning. To improve WLAN throughput performance, EDCA packet bursting can be used in 802.11e, meaning that once a station has gained an EDCA-TXOP, it can be allowed to transmit more than one frame without re-contending for the channel. Following the access to the channel, the station can send multiple frames as long as the total access time does not exceed the TXOP Limit. This mechanism can reduce the network overhead and increase the channel utilization instead. However, packet bursting may cause unfairness in addition to increasing jitter, delay and loss. To the best of the authors’ knowledge, although TXOP tuning has been investigated through different methods, it has not been considered within a game theory framework. In this study, based on the analytical models of EDCA, a game theoretic approach called GTXOP is proposed to determine TXOP dynamically (i.e. according to the dynamisms of WLAN networks and the number of nodes in the network). Using GTXOP, each node can choose its TXOP autonomously, such that in addition to QoS improvement, the overall network performance is also improved.

Fairness Assurance through TXOP Tuning in IEEE 802.11p Vehicle-to-Infrastructure Networks for Drive-Thru Internet Applications

This paper addresses an unfairness problem that exists among vehicles of distinct velocities in IEEE 802.11p based vehicle-to-infrastructure (V2I) networks used for drive-thru Internet applications. The standard IEEE 802.11p does not take into account, the residence time of vehicles within the coverage of each road side unit (RSU), for granting channel access. Due to this, a vehicle moving with higher velocity has less chance to communicate with the RSU, as compared to vehicles with lower velocity, due to its shorter residence time in the coverage area of RSU. Accordingly, the data transfer performance of a higher velocity vehicle gets degraded significantly, as compared to that of the vehicle with lower velocity, resulting in unfairness among them. In this paper, our aim is to resolve this unfairness problem by assigning the transmission opportunity (TXOP) limits to vehicles according to their mean velocities. Using an analytical model, we prove that tuning TXOP limit proportional to mean velocity can ensure fairness among vehicles belonging to distinct classes of mean velocities, in the sense of equal chance of communicating with RSU. Analytical results are validated using extensive simulations.

Performance Improvement Using Residual Time of TXOP Limit

Performance Improvement Using Residual Time of TXOP Limit

Performance Analysis of IEEE 802.11 WLANs With Saturated and Unsaturated Sources

This paper proposes a comprehensive but tractable model of IEEE 802.11 carrying traffic from a mixture of saturated and unsaturated (Poisson) sources, with potentially different quality-of-service (QoS) parameters, i.e., TXOP limit, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CW</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> , and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CW</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> . The model is used to investigate the interaction between these two types of sources, which is particularly useful for systems seeking to achieve load-independent “fair” service differentiation. We show that, when the TXOP limit for unsaturated sources is greater than one packet, batches are distributed as a geometric random variable clipped to TXOP limit. Furthermore, we present asymptotic results for access delay distribution, which indicates that it is infeasible to obtain real-time service in the presence of eight or more saturated sources, regardless of the real-time traffic load, given that all stations use a <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CW</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> of 32.

Achieving Fairness Between Uplink and Downlink Flows in Error-Prone WLANs

This letter considers an unfairness problem between uplink and downlink in 802.11 WLANs. One of existing solutions for this problem is giving a larger transmission opportunity (TXOP) limit to an AP than stations. This TXOP differentiation scheme, however, does not work well in error-prone environments since a packet bursting during a TXOP duration is terminated when a data transmission fails due to channel errors. To overcome this, we propose a new scheme in which an AP controls its minimum contention window size and TXOP limit dynamically according to the packet error rate and the number of stations. Our simulation results show that the proposed scheme provides fair channel accesses between uplink and downlink in error-prone 802.11 WLANs.

IEEE 802.11e EDCA Under Bursty Traffic—How Much TXOP Can Improve Performance

In this paper, we analyze an IEEE 802.11e enhanced distributed channel access (EDCA) based single-hop ad hoc network under bursty traffic addressing all four differentiation parameters. We investigate the performance of the network considering both nonsaturation and saturation regimes under an error-prone channel. We develop an accurate analytical model for the network and validate it with a simulation model. Our results indicate that adjusting the transmission opportunity (TXOP) limit in accordance with the burst size distribution can considerably improve the performance of the network and the burst delay, which is an important parameter for the application. Although large TXOP allocations improve the medium utilization and extend the stability region of the network, serious unfairness and security concerns due to the possibility of denial of service attacks may arise. The results also show that under bursty traffic, the TXOP limit can play an important role in helping the lower priority classes avoid starvation.

An Access Delay Model for IEEE 802.11e EDCA

We analyze the MAC access delay of the IEEE 802.11e EDCA mechanism under saturation. We develop a detailed analytical model to evaluate the influence of all EDCA differentiation parameters, namely AIFS, CWmin, CWmax and TXOP limit, as well as the backoff multiplier $\beta$. Explicit expressions for the mean, standard deviation and generating function of the access delay distribution are derived. By applying numerical inversion on the generating function, we are able to efficiently compute values of the distribution. Comparison with simulation confirms the accuracy of our analytical model over a wide range of operating conditions. We derive simple asymptotics and approximations for the mean and standard deviation of the access delay, which reveal the salient model parameters for performance under different differentiation mechanisms. We also use the model to numerically study the differentiation performance and find that $\beta$ differentiation, though rejected during the standardization process, is an effective differentiation mechanism that has some advantages over the other mechanisms.