A measurement-based approach to service modeling and bandwidth estimation in IEEE 802.11 wireless networks

[no abstract

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

A Survey of Medium Access Mechanisms for Providing QoS in Ad-Hoc Networks

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Medium access control and network planning in wireless networks

Wireless Local Area Networks (WLANs) and Wireless Metropolitan Area Networks (WMANs) are two of the main technologies in wireless data networks. WLANs have a short range and aim at providing connectivity to end users. On the other hand, WMANs have a long range and aim at serving as a backbone network and also at serving end users. In this dissertation, we consider the problem of Medium Access Control (MAC) in WLANs and the placement of Relay Stations (RSs) in WMANs. We propose a MAC scheme for WLANs in which stations contend by using jams on the channel. We present analytic and simulation results to find the optimal parameters of the scheme and measure its performance. Our scheme has a low collision rate and delay and a high throughput and fairness performance. Secondly, we present a MAC scheme for the latest generation of WLANs which have very high data rates. In this scheme, we divide the stations into groups and only one station from each group contends to the channel. We also use frame aggregation to reduce the overhead. We present analytic and simulation results which show that our scheme provides a small collision rate and, hence, achieves a high throughput. The results also show that our scheme provides a delay performance that is suitable for real-time applications and also has a high level of fairness. Finally, we consider the problem of placing Relay Stations (RSs) in WMANs. We consider the Worldwide Interoperability for Microwave Access (WIMAX) technology. The RSs are used to increase the capacity of the network and to extend its range. We present an optimization formulation that places RSs in the WiMAX network to serve a number of customers with a pre-defined bit rate. Our solution also provides fault-tolerance by allowing one RS to fail at a given time so that the performance to the users remains at a predictable level. The goal of our solution is to meet the demands of the users, provide fault-tolerance and minimize the number of RSs used

Achieving Soft Real-time Guarantees for Interactive Applications in Wireless Mesh Networks

The use of 802.11-based multi-hop wireless mesh networks for Internet access is extensive and growing. The primary advantages of this approach are ease of deployment and lower cost. However, these networks are designed for web and e-mail applications. Highly interactive applications, such as multiplayer online games and VoIP, with their requirements for low delay, present significant challenges to these networks. In particular, the interaction between real-time traffic and TCP traffic tends to result in either a failure of the real-time traffic getting its needed QoS or the TCP traffic unnecessarily experiencing very poor throughput. To solve this problem we place real-time and TCP traffic into separate queues. We then rate-limit TCP traffic based on the average queue size of the local or remote real-time queues. Thus, TCP traffic is permitted to use excess bandwidth as long as it does not interfere with real-time traffic guarantees. We therefore call our scheme Real-time Queue-based Rate and Admission Control, RtQ-RAC. Extensive simulations using the network simulator, ns-2, demonstrate that our approach is effective in providing soft real-time support, while allowing efficient use of the remaining bandwidth for TCP traffic

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

Capacity and performance study of IEEE 802.11e in WLANs and ad hoc networks

This master thesis focuses on the IEEE 802.11e Enhanced Distribution Channel Access (EDCA). The IEEE 802.11e protocol became an IEEE standard in November 2005 and is a very popular research topic. Even though the protocol has been tested for faults and errors a long time there are still research topics to explore. This thesis will try to answer some of those topics. The main topic in this thesis is how the IEEE 802.11e MAC operates in a multihop ad hoc network. We discuss and evaluated the findings along with simulation results, and compare our work with earlier work on the same topic that used the legacy IEEE 802.11 standard. The results we present are interesting throughput results that seem to tell us that the new IEEE 802.11e is better then the original WLAN standard when it comes to multihop ad hoc network forwarding