Experimenting with commodity 802.11 hardware: overview and future directions

The huge adoption of 802.11 technologies has triggered a vast amount of experimentally-driven research works. These works range from performance analysis to protocol enhancements, including the proposal of novel applications and services. Due to the affordability of the technology, this experimental research is typically based on commercial off-the-shelf (COTS) devices, and, given the rate at which 802.11 releases new standards (which are adopted into new, affordable devices), the field is likely to continue to produce results. In this paper, we review and categorise the most prevalent works carried out with 802.11 COTS devices over the past 15 years, to present a timely snapshot of the areas that have attracted the most attention so far, through a taxonomy that distinguishes between performance studies, enhancements, services, and methodology. In this way, we provide a quick overview of the results achieved by the research community that enables prospective authors to identify potential areas of new research, some of which are discussed after the presentation of the survey.This work has been partly supported by the European Community through the CROWD project (FP7-ICT-318115) and by the Madrid Regional Government through the TIGRE5-CM program (S2013/ICE-2919).Publicad

Performance modelling of fairness in IEEE 802.11 wireless LAN protocols

PhD ThesisWireless communication has become a key technology in the modern world, allowing network services to be delivered in almost any environment, without the need for potentially expensive and invasive fixed cable solutions. However, the level of performance experienced by wireless devices varies tremendously on location and time. Understanding the factors which can cause variability of service is therefore of clear practical and theoretical interest. In this thesis we explore the performance of the IEEE 802.11 family of wireless protocols, which have become the de facto standard for Wireless Local Area Networks (WLANs). The specific performance issue which is investigated is the unfairness which can arise due to the spatial position of nodes in the network. In this work we characterise unfairness in terms of the difference in performance (e.g. throughput) experienced by different pairs of communicating nodes within a network. Models are presented using the Markovian process algebra PEPA which depict different scenarios with three of the main protocols, IEEE 802.11b, IEEE 802.11g and IEEE 802.11n. The analysis shows that performance is affected by the presence of other nodes (including in the well-known hidden node case), by the speed of data and the size of the frames being transmitted. The collection of models and analysis in this thesis collectively provides not only an insight into fairness in IEEE 802.11 networks, but it also represents a significant use case in modelling network protocols using PEPA. PEPA and other stochastic process algebra are extremely powerful tools for efficiently specifying models which might be very complex to study using conventional simulation approaches. Furthermore the tool support for PEPA facilitates the rapid solution of models to derive key metrics which enable the modeller to gain an understanding of the network behaviour across a wide range of operating conditions. From the results we can see that short frames promote a greater fairness due to the more frequent spaces between frames allowing other senders to transmit. An interesting consequence of these findings is the observation that varying frame length can play a role in addressing topological unfairness, which leads to the analysis of a novel model of IEEE 802.11g with variable frame lengths. While varying frame lengths might not always be practically possible, as frames need to be long enough for collisions to be detected, IEEE 802.11n supports a number of mechanisms for frame aggregation, where successive frames may be sent in series with little or no delay between them. We therefore present a novel model of IEEE 802.11n with frame aggregation to explore how this approach affects fairness and, potentially, can be used to address unfairness by allowing affected nodes to transmit longer frame bursts.Kurdistan Region Government of Iraq (KRG) sponso

An efficient multichannel wireless sensor networks MAC protocol based on IEEE 802.11 distributed co-ordinated function.

This research aimed to create new knowledge and pioneer a path in the area relating to future trends in the WSN, by resolving some of the issues at the MAC layer in Wireless Sensor Networks. This work introduced a Multi-channel Distributed Coordinated Function (MC-DCF) which takes advantage of multi-channel assignment. The backoff algorithm of the IEEE 802.11 distributed coordination function (DCF) was modified to invoke channel switching, based on threshold criteria in order to improve the overall throughput for wireless sensor networks. This work commenced by surveying different protocols: contention-based MAC protocols, transport layer protocols, cross-layered design and multichannel multi-radio assignments. A number of existing protocols were analysed, each attempting to resolve one or more problems faced by the current layers. The 802.15.4 performed very poorly at high data rate and at long range. Therefore 802.15.4 is not suitable for sensor multimedia or surveillance system with streaming data for future multichannel multi-radio systems. A survey on 802.11 DCF - which was designed mainly for wireless networks –supports and confirm that it has a power saving mechanism which is used to synchronise nodes. However it uses a random back-off mechanism that cannot provide deterministic upper bounds on channel access delay and as such cannot support real-time traffic. The weaknesses identified by surveying this protocol form the backbone of this thesis The overall aim for this thesis was to introduce multichannel with single radio as a new paradigm for IEEE 802.11 Distributed Coordinated Function (DCF) in wireless sensor networks (WSNs) that is used in a wide range of applications, from military application, environmental monitoring, medical care, smart buildings and other industry and to extend WSNs with multimedia capability which sense for instance sounds or motion, video sensor which capture video events of interest. Traditionally WSNs do not need high data rate and throughput, since events are normally captured periodically. With the paradigm shift in technology, multimedia streaming has become more demanding than data sensing applications as such the need for high data rate protocol for WSN which is an emerging technology in this area. The IEEE 802.11 can support data rates up to 54Mbps and 802.11 DCF was designed specifically for use in wireless networks. This thesis focused on designing an algorithm that applied multichannel to IEEE 802.11 DCF back-off algorithm to reduce the waiting time of a node and increase throughput when attempting to access the medium. Data collection in WSN tends to suffer from heavy congestion especially nodes nearer to the sink node. Therefore, this thesis proposes a contention based MAC protocol to address this problem from the inspiration of the 802.11 DCF backoff algorithm resulting from a comparison of IEEE 802.11 and IEEE 802.15.4 for Future Green Multichannel Multi-radio Wireless Sensor Networks

Belaidžio ryšio tinklų terpės prieigos valdymo tyrimas

Over the years, consumer requirements for Quality of Service (QoS) has been growing exponentially. Recently, the ratification process of newly IEEE 802.11ad amendment to IEEE 802.11 was finished. The IEEE 802.11ad is the newly con-sumer wireless communication approach, which will gain high spot on the 5G evolution. Major players in wireless market, such as Qualcomm already are inte-grating solutions from unlicensed band, like IEEE 802.11ac, IEEE 802.11ad into their architecture of LTE PRO (the next evolutionary step for 5G networking) (Qualcomm 2013; Parker et al. 2015). As the demand is growing both in enter-prise wireless networking and home consumer markets. Consumers started to no-tice the performance degradation due to overcrowded unlicensed bands. The un-licensed bands such as 2.4 GHz, 5 GHz are widely used for up-to-date IEEE 802.11n/ac technologies with upcoming IEEE 802.11ax. However, overusage of the available frequency leads to severe interference issue and consequences in to-tal system performance degradation, currently existing wireless medium access method can not sustain the increasing intereference and thus wireless needs a new methods of wireless medium access. The main focal point of this dissertation is to improve wireless performance in dense wireless networks. In dissertation both the conceptual and multi-band wireless medium access methods are considered both from theoretical point of view and experimental usage. The introduction chapter presents the investigated problem and it’s objects of research as well as importance of dissertation and it’s scientific novelty in the unlicensed wireless field. Chapter 1 revises used literature. Existing and up-to-date state-of-the-art so-lution are reviewed, evaluated and key point advantages and disadvantages are analyzed. Conclusions are drawn at the end of the chapter. Chapter 2 describes theoretical analysis of wireless medium access protocols and the new wireless medium access method. During analysis theoretical simula-tions are performed. Conclusions are drawn at the end of the chapter. Chapter 3 is focused on the experimental components evaluation for multi-band system, which would be in line with theoretical concept investigations. The experimental results, showed that components of multi-band system can gain sig-nificant performance increase when compared to the existing IEEE 802.11n/ac wireless systems. General conclusions are drawn after analysis of measurement results

높은 효율의 무선랜을 위한 MAC/PHY 기법

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2016. 8. 최성현.Along with the steady increase in mobile data traffic, wireless local area network (WLAN) technology has been developed to support heavy traffic for various mobile devices. The-state-of-art IEEE 802.11 specifications such as 802.11n and 802.11ac have focused on improving physical layer (PHY) rate by enabling multiple stream transmission via multiple-input multiple-output (MIMO) technology, wide bandwidth transmission via channel bonding, and high order modulation via 256-QAM and short guard interval. While the emerging technologies greatly increase PHY rate over 1~Gb/s, the achievable throughput is much limited due to the low reliability with high PHY rates and medium sharing among the nodes operating on the same channel. In this dissertation, we tackle three different strategies to enhance the achievable throughput in IEEE 802.11 WLANs. Firstly, we study a cost-effective approach, namely antenna subset selection, to enhance reliability even for the high PHY rates. There are practical challenges to employ antenna subset selection in WLANs such as the lack of channel state information at the transmitter and multiple retry chain utilization. Only few researches have addressed those practical challenges, which result in a limited employment of antenna subset selection in WLANs. We propose a practical antenna subset selection system considering those practical challenges, and evaluate the performance of the proposed system via prototype implementation and extensive experiments. Secondly, we focus on the clear channel assessment (CCA) of IEEE 802.11 WLAN which is too conservative to exploit spatial reuse. The problem is arise due to a limitation of the current CCA mechanism. Only the received signal strength (RSS) of an ongoing transmission is used to determine the status of the medium, i.e., busy or idle. We propose a novel CCA mechanism which utilizes the information delivered in PHY header of the ongoing transmission so that it can stimulate concurrent transmissions for better spatial reuse. Through simulations, we evaluate our proposed approach and demonstrate throughput gain in various scenarios. Lastly, we investigate transmit power and data rate control method to further exploit spatial reuse. Along with our proposed CCA mechanism, more concurrent transmissions become feasible by adapting transmit power and data rate depending on the ongoing transmission. Accordingly, we propose a joint transmit power and data rate control algorithm which operates dynamically depending on the existence of ongoing transmission. We evaluate our proposed algorithm under various scenarios through extensive simulations. In summary, we propose three different methodologies for high efficiency WLANs, one for reliability enhancement and the other two for better spatial reuse. The operation and performance gain of each methodology are verified by testbed experiments or network level simulations.Chapter 1 Introduction 1 1.1 Motivation 1 1.2 Overview of Existing Approaches 4 1.2.1 Practical Antenna Selection for WLAN AP 4 1.2.2 Protective Clear Channel Assessment 5 1.2.3 Dynamic Transmit Power and Data Rate Control 5 1.3 Main Contributions 7 1.3.1 Reliability Enhancement 7 1.3.2 Spatial Reuse Exploitation 9 1.4 Organization of the Dissertation 9 Chapter 2 Practical Antenna Selection for WLAN AP 11 2.1 Introduction 11 2.2 System Description 14 2.2.1 Characteristics of O-the-Shelf Devices 14 2.2.2 Antenna Selection for WLAN AP 18 2.3 Measurement Studies 22 2.3.1 Throughput with Dierent Antenna Combinations 22 2.3.2 DL/UL Link Analysis 26 2.4 Proposed Antenna Selection Algorithm 28 2.4.1 Transmit Antenna Selection 28 2.4.2 Default Antenna Selection 36 2.5 Performance Evaluation 38 2.5.1 Performance of Proposed Transmit Antenna Selection 38 2.5.2 Performance of Proposed Default Antenna Selection 45 2.6 Summary 47 Chapter 3 Protective Clear Channel Assessment 48 3.1 Introduction 48 3.2 Background and Motivation 50 3.2.1 Ideal Operation of CCA 50 3.2.2 IEEE 802.11 Frame Format and CCA Method 52 3.2.3 Physical Layer Header Utilization for CCA 54 3.3 Protective Clear Channel Assessment 55 3.3.1 Signal Quality Table 56 3.3.2 Feasibility Check of Spatial Reuse 57 3.3.3 Consideration of Link Asymmetry 58 3.4 Performance Evaluation 60 3.5 Summary 64 Chapter 4 Dynamic Transmit Power and Data Rate Control 66 4.1 Introduction 66 4.2 Transmit Power and Rate Control for Spatial Reuse 68 4.2.1 RTS-CTS Based 69 4.2.2 Feedback Based 70 4.2.3 Limitations of existing approach 71 4.3 Dynamic Transmit Power and Rate Control 72 4.3.1 Information Gathering 73 4.3.2 Dynamic TPC & RA 76 4.3.3 Normal TPC & RA 77 4.3.4 DCF Throughput Analysis 78 4.3.5 Multi-cell Consideration 85 4.4 Performance Evaluation 86 4.5 Summary 91 Chapter 5 Conclusion 93 5.1 Research Contributions 93 5.2 Future Research Directions 95 Bibliography 97 초록 102Docto

Quality of service differentiation for multimedia delivery in wireless LANs

Delivering multimedia content to heterogeneous devices over a variable networking environment while maintaining high quality levels involves many technical challenges. The research reported in this thesis presents a solution for Quality of Service (QoS)-based service differentiation when delivering multimedia content over the wireless LANs. This thesis has three major contributions outlined below: 1. A Model-based Bandwidth Estimation algorithm (MBE), which estimates the available bandwidth based on novel TCP and UDP throughput models over IEEE 802.11 WLANs. MBE has been modelled, implemented, and tested through simulations and real life testing. In comparison with other bandwidth estimation techniques, MBE shows better performance in terms of error rate, overhead, and loss. 2. An intelligent Prioritized Adaptive Scheme (iPAS), which provides QoS service differentiation for multimedia delivery in wireless networks. iPAS assigns dynamic priorities to various streams and determines their bandwidth share by employing a probabilistic approach-which makes use of stereotypes. The total bandwidth to be allocated is estimated using MBE. The priority level of individual stream is variable and dependent on stream-related characteristics and delivery QoS parameters. iPAS can be deployed seamlessly over the original IEEE 802.11 protocols and can be included in the IEEE 802.21 framework in order to optimize the control signal communication. iPAS has been modelled, implemented, and evaluated via simulations. The results demonstrate that iPAS achieves better performance than the equal channel access mechanism over IEEE 802.11 DCF and a service differentiation scheme on top of IEEE 802.11e EDCA, in terms of fairness, throughput, delay, loss, and estimated PSNR. Additionally, both objective and subjective video quality assessment have been performed using a prototype system. 3. A QoS-based Downlink/Uplink Fairness Scheme, which uses the stereotypes-based structure to balance the QoS parameters (i.e. throughput, delay, and loss) between downlink and uplink VoIP traffic. The proposed scheme has been modelled and tested through simulations. The results show that, in comparison with other downlink/uplink fairness-oriented solutions, the proposed scheme performs better in terms of VoIP capacity and fairness level between downlink and uplink traffic

Contributions to QoS and energy efficiency in wi-fi networks

The Wi-Fi technology has been in the recent years fostering the proliferation of attractive mobile computing devices with broadband capabilities. Current Wi-Fi radios though severely impact the battery duration of these devices thus limiting their potential applications. In this thesis we present a set of contributions that address the challenge of increasing energy efficiency in Wi-Fi networks. In particular, we consider the problem of how to optimize the trade-off between performance and energy effciency in a wide variety of use cases and applications. In this context, we introduce novel energy effcient algorithms for real-time and data applications, for distributed and centralized Wi-Fi QoS and power saving protocols and for Wi-Fi stations and Access Points. In addition, the di¿erent algorithms presented in this thesis adhere to the following design guidelines: i) they are implemented entirely at layer two, and can hence be easily re-used in any device with a Wi-Fi interface, ii) they do not require modi¿cations to current 802.11 standards, and can hence be readily deployed in existing Wi-Fi devices, and iii) whenever possible they favor client side solutions, and hence mobile computing devices implementing them can benefit from an increased energy efficiency regardless of the Access Point they connect to. Each of our proposed algorithms is thoroughly evaluated by means of both theoretical analysis and packet level simulations. Thus, the contributions presented in this thesis provide a realistic set of tools to improve energy efficiency in current Wi-Fi networks

IEEE 802.11n WLAN에서 프레임 전송 시간 조절을 통한 네트워크 성능 향상 MAC 프로토콜

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2013. 8. 최종호.최근 스마트폰, 태블릿 PC 등의 무선 네트워크를 사용하는 모바일 기기의 사용이 급증함에 따라 무선 랜 (wireless local area network (WLAN))에 대한 수요가 빠르게 증가하고 있다. 하지만, IEEE 802.11 표준에서 기본적으로 사용하는 MAC (medium access control) 프로토콜인 DCF (distributed coordination function) 는 single-cell 네트워크에서 MAC 효율 (MAC efficiency) 성능이 떨어지는 문제점과 ad-hoc 네트워크에서 노드간에 공평성 성능이 크게 저하 되는 문제점을 지니고 있다. 본 논문에서는 이러한 네트워크에서 DCF가 지니고 있는 문제점을 각각 해결할 수 있는 두 가지 다른 방식의 MAC 프로토콜들을 제안하였다. 기존의 MAC 프로토콜에서는 패킷 (packet) 이나 프레임 (frame) 의 크기가 정해지면, 각 노드 (node) 의 데이터 전송 속도에 따라 (data transmission rate) 프레임 전송 시간 (frame transmission duration) 이 정해졌다. 하지만, 본 논문에서는 IEEE 802.11n/ac/ad 표준에서 사용하는 프레임 결합 (frame aggregation) 과 block ACK 기법을 이용하여 프레임 전송 시간을 정확히 조절 할 수 있는 방법을 제안하였다. 만약 이와같이 프레임 전송 시간을 우리가 원하는 데로 정확하게 조절 할 수 있게된다면, 네트워크 상에 각 노드들은 추가적인 오버헤드 (overhead) 없이 자신이 알려주고자 하는 정보를 프레임 전송 시간을 이용하여 자신 주변의 노드들에게 간접적으로 알려줄 수 있게 된다. 즉, 프레임 전송 시간을 정확히 조절하는 것을 통해서 기존의 컨트롤 메시지 (control message) 가 수행했던 역할인 정보 전달의 역할을 수행 할 수 있게 된다. 이 아이디어는 간단하지만, 각 노드들이 네트워크 성능을 향상 시킬 수 있는 정보를 교환하는데 효과적이다. 본 논문에서 제안된 두 개의 MAC 프로토콜들은 이 아이디어를 활용하여 네트워크 성능을 향상시키고자 하였다. 우선, IEEE 802.11 single-cell 네트워크에서의 MAC 효율 성능을 향상시키기 위해 Transmission Order Deducing MAC (TOD-MAC) 프로토콜을 제안하였다. 최근 물리 계층 (physical layer) 에서의 전송 속도가 Gbps 범위까지 비약적으로 발전하고 있다. 하지만, 이러한 물리 계층 전송 속도의 증가가 MAC 계층 (MAC layer) 에서의 처리량 (throughput) 성능 향상에 효과적으로 기여하지 못하고 있는 실정이다. 왜냐하면, 물리 계층에서의 전송 속도가 올라 갈수록 PHY header와 컨텐션 시간 (contention time) 등의 MAC 계층에서 발생하는 오버헤드들이 처리량 성능 향상에 큰 걸림돌이 되기 때문이다. 이러한 문제점을 해결 하기 위해서 TOD-MAC에서 각 노드들은 자신의 전송 순서에 따라 앞서 제안된 방법을 이용하여 프레임 전송 시간을 정확히 조절하여 데이터를 전송한다. 이를 통해 네트워크 상의 각 노드들은 자신 주변 노드들의 전송 순서를 프레임 전송 시간을 통해 추정할 수 있게 되고, 자신에게 알려진 전송 순서 정보를 이용하여 순환 순서 방식 (round robin manner) 으로 데이터를 전송한다. 이를 통해 제안된 MAC 프로토콜은 전송 충돌 (transmission collision) 과 컨텐션 시간을 효율적으로 줄일 수 있게 되고, CSMA/CA (carrier sensing multiple access with collision avoidance) 기반의 single-cell 네트워크에서의 MAC 효율을 극대화 시킬 수 있게 된다. 또한, 실험을 통해 TOD-MAC이 다양한 환경에서 높은 처리량 성능과, 좋은 short/long-term 채널 점유 시간 공평성 (air-time fairness) 성능을 보여주는 것을 확인할 수 있었다. 또한, 본 논문에서는 IEEE 802.11 ad-hoc 네트워크에서의 최대-최소 채널 점유 시간 공평성 (max-min air-time fairness) 을 향상 시킬 수 있는 Max-min Air-time Fairness MAC (MAF-MAC) 프로토콜을 제안하였다. 최근 IEEE 802.11 ad-hoc 네트워크를 기반으로한 서비스에 대한 요구가 빠르게 증하하면서, ad-hoc 네트워크에서 노드들 간에 공평한 서비스를 제공하는 것이 중요한 문제가 되고 있다. 이를 위해 MAF-MAC에서는 각 노드들이 자신의 채널 점유 시간에 대한 정보를 프레임 전송 시간을 통해 주변 노드들에게 알려주고, 각 노드들은 이 정보를 이용하여 자신의 contention window (CW) 값을 적절하게 조절하여 ad-hoc 네트워크에서의 최대-최소 채널 점유 시간 공평성 성능을 향상시키고자 하였다. 이를 통해 제안된 MAC 프로토콜은 네트워크에 있는 노드들에게 보다 공평한 서비스를 제공함과 동시에 채널 점유율과 사용율을 효율적으로 향상 시킬 수 있었다. 또한, 다른 연구에서 제안된 히든 노드 감지 (hidden node detection) 방법과 히든 노드 해결 (hidden node resolving) 방법을 MAF-MAC에 적용함으로써 ad-hoc 네트워크에서 발생 할 수 있는 히든 노드 문제를 효과적으로 해결 할 수 있었다. 시뮬래이션을 통해 히든 노드의 존재 여부와 관계 없이 다양한 환경에서 MAF-MAC에 기반한 방법이 좋은 채널 점유 공평성 성능을 보여줌과 동시에 효율적으로 채널을 사용하고 있다는 것을 확인 할 수 있었다.The demand for wireless local area network (WLAN) has drastically increased due to the prevalence of the mobile devices such as smart phones and tablet PCs. However, the distributed coordination function (DCF), which is the basic MAC protocol used in IEEE 802.11 WLANs, needs to be improved on MAC efficiency in single-cell networks and fairness performance in ad-hoc networks. In this dissertation, we propose two MAC protocols that can enhance MAC efficiency in single-cell network, and max-min air-time fairness in ad-hoc network by adjusting frame transmission duration, respectively. In the traditional MAC protocol, the length of a packet or a frame is usually fixed and the transmission duration is determined by the data rate. However, we show how each node can precisely adjust the transmission duration when the frame aggregation and block ACK features are used in very high-speed IEEE 802.11n/ac/ad WLANs. If the transmission duration can be precisely controlled, it plays the role usually carried out by a control message. Therefore, a node can indirectly announce necessary information to the other nodes, which can sense the transmission of the node, without incurring any overhead. This idea is simple, but very effective to enhance the network performance by exchanging the necessary information without overheads. First, we propose the Transmission Order Deducing MAC (TOD-MAC) protocol to improve MAC layer efficiency in IEEE 802.11 single-cell network. Recently, the physical (PHY) layer transmission rate increases to Gbps range in the IEEE 802.11 WLANs. However, the increase in the PHY layer transmission rates does not necessarily translate into corresponding increase in the MAC layer throughput of IEEE 802.11 WLANs because of MAC overheads such as PHY headers and contention time. TOD-MAC precisely controls the frame length and transmission duration to indirectly provide necessary information to a node to determine the transmission order among all the nodes in a network. Each node transmits frames of different duration, and thus the other nodes can determine the time when they can transmit, which has the same effect as announcing the transmission order, without using a control message. Each node transmits a frame in a round robin manner, which minimizes the idle time between two consecutive transmissions without collisions, and significantly enhances the MAC efficiency in very high speed CSMA/CA wireless networks. The results of extensive simulations indicate that TOD-MAC achieves high throughput performance, short/long-term air-time fairness in multi-rate networks and excellent transient behavior in dynamic environments. Secondly, we propose Max-min Air-time Fairness MAC (MAF-MAC) to improve max-min air-time fairness in IEEE 802.11 ad-hoc networks. As the demand for services based on ad-hoc networks rapidly increases, enhancing fairness among nodes becomes important issue in ad-hoc networks. The concept of max-min fairness is that a node may use more channel resource as long as it does take away the channel resource from the other nodes who uses less channel resource. In MAF-MAC, the transmission duration is adjusted so that it can indirectly perform the function of a control message in announcing the state of a node, called the busy time ratio. On the basis of this information, each node adjusts its $CW$ value to improve max-min air-time fairness. Moreover, we also adopt the hidden node detection and resolving mechanism to MAF-MAC to improve the max-min air-time fairness even when there are hidden nodes in ad-hoc networks. We show through simulation that MAF-MAC incorporating hidden node detection/resolution mechanisms can provide good air-time fairness with high channel occupation and utilization ratio whether or not there are hidden nodes in the network.Docto