An admission control scheme for IEEE 802.11e wireless local area networks

Includes bibliographical references (leaves 80-84).Recent times has seen a tremendous increase in the deployment and use of 802.11 Wireless Local Area Networks (WLANs). These networks are easy to deploy and maintain, while providing reasonably high data rates at a low cost. In the paradigm of Next-Generation-Networks (NGNs), WLANs can be seen as an important access network technology to support IP multimedia services. However a traditional WLAN does not provide Quality of Service (QoS) support since it was originally designed for best effort operation. The IEEE 802. 11e standard was introduced to overcome the lack of QoS support for the legacy IEEE 802 .11 WLANs. It enhances the Media Access Control (MAC) layer operations to incorporate service differentiation. However, there is a need to prevent overloading of wireless channels, since the QoS experienced by traffic flows is degraded with heavily loaded channels. An admission control scheme for IEEE 802.11e WLANs would be the best solution to limit the amount of multimedia traffic so that channel overloading can be prevented. Some of the work in the literature proposes admission control solutions to protect the QoS of real-time traffic for IEEE 802.11e Enhanced Distributed Channel Access (EDCA). However, these solutions often under-utilize the resources of the wireless channels. A measurement-aided model-based admission control scheme for IEEE 802.11e EDCA WLANs is proposed to provide reasonable bandwidth guarantees to all existing flows. The admission control scheme makes use of bandwidth estimations that allows the bandwidth guarantees of all the flows that are admitted into the network to be protected. The bandwidth estimations are obtained using a developed analytical model of IEEE 802.11e EDCA channels. The admission control scheme also aims to accept the maximum amount of flows that can be accommodated by the network's resources. Through simulations, the performance of the proposed admission control scheme is evaluated using NS-2. Results show that accurate bandwidth estimations can be obtained when comparing the estimated achievable bandwidth to actual simulated bandwidth. The results also validate that the bandwidth needs of all admitted traffic are always satisfied when the admission control scheme is applied. It was also found that the admission control scheme allows the maximum amount of flows to be admitted into the network, according the network's capacity

Channel quality estimation and impairment mitigation in 802.11 networks

Wireless communication has been boosted by the adoption of 802.11 as standard de facto for WLAN transmission. Born as a niche technology for providing wireless connectivity in small office/enterprise environments, 802.11 has in fact become a common and cheap access solution to the Internet, thanks to the large availability of wireless gateways (home modems, public hot-spots, community networks, and so on). Nowdays, the trend towards increasingly dense 802.11 wireless deployments is creating a real need for effective approaches for channel allocation/hopping, power control, etc. for interference mitigation while new applications such mesh networks in outdoor contexts and media distribution within the home are creating new quality of service demands that require more sophisticated approaches to radio resource allocation. The new framework of WLAN deployments require a complete understanding of channel quality at PHY and MAC layer. Goal of this thesis is to assess the MAC/PHY channel quality and mitigate the different channel impairments in 802.11 networks, both in dense/controlled indoor scenarios and emerging outdoor contexts. More specifically, chapter 1 deals with the necessary background material and gives insight into the different channel impairments/quality it can be encountered in WLAN networks. Then the thesis pursues a down/top approach: chapter 2, 3 and 4 aim at affording impairments/quality at PHY level, while chapter 5 and 6 analyse channel impairments/quality from a MAC level perspective. An important contribution of this thesis is to undisclose that some PHY layer parameters, such as the transmission power, the antenna selection, and interference mitigation scheme, have a deep impact on network performance. Since the criteria for selecting these parameters is left to the vendor specific implementations, the performance spread of most experimental results about 802.11 WLAN could be affected by vendor proprietary schemes. Particularly, in chapter 2 we find that switching transmit diversity mechanisms implemented in off-the-shelf devices with two antenna connectors can dramatically affect both performance and link quality probing mechanisms in outdoor medium-range WLAN deployments, whenever one antenna deterministically works worse than the other one. A second physical algorithm with side-effects is shown in chapter 3. Particulary the chapter shows that interference mitigation algorithms may play havoc with the link-level testbeds, since they may erroneously lower the sensitivity threshold, and thus not detect the 802.11 transmit sources. Finally, once disabled the interference mitigation algorithm — as well as any switching diversity scheme described in the previous chapter — link-level experimental assessment concludes that, unlike 802.11b, which appears a robust technology in most of the operational conditions, 802.11g may lead to inefficiencies when employed in an outdoor scenario, due to the lower multi-path tolerance of 802.11g. Since multipath is hard to predict, a novel mechanism to improve the link-distance estimation accuracy — based on CPU clock information — is outlined in chapter 4. The proposed methodology can not only be applied in localization context, but also for estimating the multi-path profile. The second part of the thesis moves the perspective to the MAC point of view and its impairments. Particularly, chapter 5 provides the design of a MAC channel quality estimator to distinguish the different types of MAC impairments and gives separate quantitative measures of the severity of each one. Since the estimator takes advantage of the native characteristics of the 802.11 protocol, the approach is suited to implementation on commodity hardware and makes available new measures that can be of direct use for rate adaptation, channel allocation, etc. Then, chapter 6 introduces a previous unknown phenomenon, the Hidden ACK, that may cause frame losses into multiple WLAN networks when a node replies with an ACK frame. Again, a solution is provided without requiring any modification to the 802.11 protocol. Whenever possible, the quantitative analysis has been led through experimental assessments with implementation on commodity hardware. This was the adopted methodology in chapter 2, 3, 4 and 5. Particularly, this has required an accurate investigation of two brands of WLAN cards, particularly the Atheros and Intel cards, and their driver/firmware, respectively MADWiFi and IPW2200, which are currently the most adopted, respectively, by researchers and layman users

Analysis and enhancement of wireless LANs in noisy channels

Without a doubt, Wireless Local Area Networks (WLANs) technology has been encountering an explosive growth lately. IEEE 802.11 is the standard associated with this promising technology, which enures shared access to the wireless medium through the distributed coordination function (DCF). Recently, the IEEE 802.11e task group has made extensions to WLANs medium access control (MAC) in order to support quality of service (QoS) traffic. An inherited problem for WLANs, is the volatility of the propagation medium, which is a challenging issue that affects the system performance significantly. Consequently, enhancing the operation of the DCF in noisy environments is of great interest, and has attracted the attention of many researchers. Our first major contribution in the presented thesis, is an analytical and simulation analysis for the binary exponential backoff (BEB) scheme of the DCF, in the presence of channel noise. We show that following the BEB procedure when a host encounters erroneous transmission is needed only if the channel was highly loaded. However, incrementing the contention window (CW) upon each packet failure, whether caused by instantaneous transmission (i.e. collision) or channel noise, will result in the waste of air time if the channel was lightly loaded. Accordingly, we present a hybrid access method that adapts the CW according to the channel load along with the frame error rate (FER). Other means to overcome the channel noise is the adjustment of the transmission rate. Many rate adaptation (RA) algorithms were introduced in the past few years, including the Automatic Rate Fallback (ARF) which is currently implemented in the wireless cards. Yet, many drawbacks are associated with these RA algorithms; specifically, in regard to the techniques and events that should trigger the rate change. Moreover, the IEEE 802.11e QoS flows requirements were not considered with the latter schemes. Accordingly, our next major contribution in this work is the presentation of a novel rate adaptation scheme. The simplicity of the introduced rate adaptation scheme is that it relies on the MAC layer parameters rather than those of the PHY layer when adjusting the rate. Furthermore, our algorithm supports the IEEE 802.11e MAC extensions where QoS traffic requirements were integrated in the procedure of adjusting the bit rate. Hence, strict real-time flow parameters such as delay and maximum drop rate are respected. Finally, we enhance the dynamic assignment of transmission opportunities (TXOPs) in order to offer fair air-time for nodes facing high packet loss rat

Improving Performance for CSMA/CA Based Wireless Networks

Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) based wireless networks are becoming increasingly ubiquitous. With the aim of supporting rich multimedia applications such as high-definition television (HDTV, 20Mbps) and DVD (9.8Mbps), one of the technology trends is towards increasingly higher bandwidth. Some recent IEEE 802.11n proposals seek to provide PHY rates of up to 600 Mbps. In addition to increasing bandwidth, there is also strong interest in extending the coverage of CSMA/CA based wireless networks. One solution is to relay traffic via multiple intermediate stations if the sender and the receiver are far apart. The so called “mesh” networks based on this relay-based approach, if properly designed, may feature both “high speed” and “large coverage” at the same time. This thesis focusses on MAC layer performance enhancements in CSMA/CA based networks in this context. Firstly, we observe that higher PHY rates do not necessarily translate into corresponding increases in MAC layer throughput due to the overhead of the CSMA/CA based MAC/PHY layers. To mitigate the overhead, we propose a novel MAC scheme whereby transported information is partially acknowledged and retransmitted. Theoretical analysis and extensive simulations show that the proposed MAC approach can achieve high efficiency (low MAC overhead) for a wide range of channel variations and realistic traffic types. Secondly, we investigate the close interaction between the MAC layer and the buffer above it to improve performance for real world traffic such as TCP. Surprisingly, the issue of buffer sizing in 802.11 wireless networks has received little attention in the literature yet it poses fundamentally new challenges compared to buffer sizing in wired networks. We propose a new adaptive buffer sizing approach for 802.11e WLANs that maintains a high level of link utilisation, while minimising queueing delay. Thirdly, we highlight that gross unfairness can exist between competing flows in multihop mesh networks even if we assume that orthogonal channels are used in neighbouring hops. That is, even without inter-channel interference and hidden terminals, multi-hop mesh networks which aim to offer a both “high speed” and “large coverage” are not achieved. We propose the use of 802.11e’s TXOP mechanism to restore/enfore fairness. The proposed approach is implementable using off-the-shelf devices and fully decentralised (requires no message passing)

Situation-Aware Rate and Power Adaptation Techniques for IEEE 802.11

The current generation of IEEE 802.11 Wireless Local Area Networks (WLANs) provide multiple data rates from which the different physical (PHY) layers may choose. The rate adaptation algorithm (RAA) is an essential component of 802.11 WLANs which completely determines the data rate a device may use. Some of the key challenges facing data rate selection are the constantly varying wireless channel, selecting the data rate that will result in the maximum throughput, assessing the conditions based on limited feedback and estimating the link conditions at the receiver. Current RAAs lack the ability to sense their environment and adapt accordingly. 802.11 WLANs are deployed in many locations and use the same technique to choose the data rate in all locations and situations. Therefore, these RAAs suffer from the inability to adapt the method they use to choose the data transmission rate. In this thesis, a new RAA for 802.11 WLANs is proposed which provides an answer to the many challenges faced by RAAs. The proposed RAA is termed SARA which stands for Situation-Aware Rate Adaptation, and combines the use of the received signal strength and packet error rate to enable situational awareness. SARA adapts to the current environmental situation experienced at the moment to rapidly take advantage of changing channel conditions. In addition to SARA, a method to optimize the transmission power for, but not limited to, IEEE 802.11 WLANs is proposed which can determine the minimum transmission power required by a station (STA) or base station (BS) for successful transmission of a data packet. The technique reduces the transmission power to the minimum level based on the current situation while maintaining QoS constraints. The method employs a Binary Search to quickly determine the minimum transmission power with low complexity and delay. Such a technique is useful to conserve battery life in mobile devices for 802.11 WLANs. Both algorithms are implemented on an Atheros device driver for the FreeBSD operating system. SARA is compared to the benchmark algorithm SampleRate while an estimate of the energy consumed as well as the energy saved is provided for the minimum transmission power determination

Design of rate-adaptive MAC and medium aware routing protocols for multi-rate, multi-hop wireless networks

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The IEEE 802.11 standard conformant wireless communication stations have multi-rate transmission capability. To achieve greater communication efficiency, multi-rate capable stations use rateadaptation to select appropriate transmission rate according to variations in the channel quality. The thesis presents two rate-adaptation schemes, each belonging to one of the two classes of rateadaptation schemes i.e.(1) the frame-transmission statistics based schemes, and (2) Signal-to-Noise Ratio (SNR) based, closed loop schemes. The SNR-based rate-adaptation scheme, proposed in this thesis uses a novel mechanism of delivering a receiver’s feedback to a transmitter; without requiring any modification in the standard frames as suggested by existing research. The frame-transmissionstatistics based rate adaptation solution uses an on-demand incremental strategy for selecting a rate-selection threshold. This solution is based on a cross-layer communication framework, where the rate-adaptation module uses information to/from the Application layer along with relevant information from the Medium Access Control (MAC) sub-layer. The proposed solutions are highly responsive when compared with existing rate-adaptation schemes; responsiveness is one of the key factors in the design of such protocols. The novel feedback mechanism makes it possible to achieve frame-loss differentiation with just three frames, avoiding the use of Request To Send/ Clear To Send (RTS/CTS) frames and further delays in this process. Performance tests have affirmed that the proposed rate-adaptation schemes are energy efficient; with efficiency up to 19% in specific test scenarios. In terms of throughput and frame loss-differentiation mechanisms, the proposed schemes have shown significantly better performance.Routing protocols for Mobile Ad-Hoc Networks (MANETs) use broadcast frames during the route discovery process. The 802.11 mandates the use of different transmission rates for broadcast and unicast (data-) frames. In many cases it causes creation of communication gray zones, where stations which are marked as ‘reachable neighbours’ using the broadcast frames (using lower transmission rate) are not accessible during normal, unicast communication (mainly at a higher rate). Similarly, higher device density, interference and mobility cause variable medium access delays. The IEEE 802.11e introduces four different MAC level queues for four access categories, maintaining service priority within the queues; which implies that frames from a higher priority queue are serviced more frequently than those belonging to lower priority queues. Such an enhancement at the MAC sub-layer introduces uneven queuing delays. Conventional routing protocols are unaware of such MAC specific constraints and as a result these factors are not considered which result in severe performance deterioration. To meet such challenges, the thesis presents a medium aware distance vector (MADV) routing protocol for MANETs. MADV uses MAC and physical layer (PHY) specific information in the route metric and maintains a separate route per-AC-per-destination in its routing tables. The MADV-metric can be incorporated into various routing rotocols and its applicability is determined by the possibility of provision of MAC dependent arameters that are used to determine the hop-by-hop MADV-metric values. Simulation tests and omparison with existing MANET protocols demonstrate the effectiveness of incorporating the medium dependent parameters and show that MADV is significantly better in terms of end-to-end delay and throughput

Anti-Collision Adaptations of BLE Active Scanning for Dense IoT Tracking Applications

Bluetooth low energy (BLE) is one of most promising technologies to enable the Internet-of-Things (IoT) paradigm. The BLE neighbor discovery process (NDP) based on active scanning may be the core of multiple IoT applications in which a large and varying number of users/devices/tags must be detected in a short period of time. Minimizing the discovery latency and maximizing the number of devices that can be discovered in a limited time are challenging issues due to collisions between frames sent by advertisers and scanners. The mechanism for resolution of collisions between scanners has a great impact on the achieved performance, but backoff in NDP has been poorly studied so far. This paper includes a detailed analysis of backoff in NDP, identifies and studies the factors involved in the process, reveals the limitations and problems presented by the algorithm suggested by the specifications and proposes simple and practical adaptations on scanner functionality. They are easily compatible with the current definitions of the standard, which together with a new proposal for the backoff scheme, may significantly improve the discovery latencies and, thus, the probability of discovering a large number of devices in high density scenarios

Advanced Protocols for Peer-to-Peer Data Transmission in Wireless Gigabit Networks

This thesis tackles problems on IEEE 802.11 MAC layer, network layer and application layer, to further push the performance of wireless P2P applications in a holistic way. It contributes to the better understanding and utilization of two major IEEE 802.11 MAC features, frame aggregation and block acknowledgement, to the design and implementation of opportunistic networks on off-the-shelf hardware and proposes a document exchange protocol, including document recommendation. First, this thesis contributes a measurement study of the A-MPDU frame aggregation behavior of IEEE 802.11n in a real-world, multi-hop, indoor mesh testbed. Furthermore, this thesis presents MPDU payload adaptation (MPA) to utilize A-MPDU subframes to increase the overall throughput under bad channel conditions. MPA adapts the size of MAC protocol data units to channel conditions, to increase the throughput and lower the delay in error-prone channels. The results suggest that under erroneous conditions throughput can be maximized by limiting the MPDU size. As second major contribution, this thesis introduces Neighborhood-aware OPPortunistic networking on Smartphones (NOPPoS). NOPPoS creates an opportunistic, pocket-switched network using current generation, off-the-shelf mobile devices. As main novel feature, NOPPoS is highly responsive to node mobility due to periodic, low-energy scans of its environment, using Bluetooth Low Energy advertisements. The last major contribution is the Neighborhood Document Sharing (NDS) protocol. NDS enables users to discover and retrieve arbitrary documents shared by other users in their proximity, i.e. in the communication range of their IEEE 802.11 interface. However, IEEE 802.11 connections are only used on-demand during file transfers and indexing of files in the proximity of the user. Simulations show that NDS interconnects over 90 \% of all devices in communication range. Finally, NDS is extended by the content recommendation system User Preference-based Probability Spreading (UPPS), a graph-based approach. It integrates user-item scoring into a graph-based tag-aware item recommender system. UPPS utilizes novel formulas for affinity and similarity scoring, taking into account user-item preference in the mass diffusion of the recommender system. The presented results show that UPPS is a significant improvement to previous approaches

Final report on the evaluation of RRM/CRRM algorithms

Deliverable public del projecte EVERESTThis deliverable provides a definition and a complete evaluation of the RRM/CRRM algorithms selected in D11 and D15, and evolved and refined on an iterative process. The evaluation will be carried out by means of simulations using the simulators provided at D07, and D14.Preprin