SRA-MSDU: Enhanced A-MSDU frame aggregation with selective retransmission in 802.11n wireless networks

The main goal of the IEEE 802.11n standard is to achieve more than 100 Mbps of throughput at the MAC service access point. This high throughput has been achieved via many enhancements in both the physical and MAC layers. One of the MAC enhancements is the frame aggregation in which multiple frames are concatenated into a single large frame before being transmitted. The 802.11n MAC layer defines two types of aggregation, aggregate MAC service data unit (A-MSDU) and aggregate MAC protocol data unit (A-MPDU). The A-MPDU outperforms A-MSDU due to its large aggregation size and the subframes retransmission in erroneous channels. However, in error free channels and under the same aggregation size the A-MSDU performs better than the A-MPDU due to its smaller headers. Thus, adding a selective retransmission capability to the A-MSDU would improve the system performance. In this paper, we have proposed an MSDU frame aggregation scheme that enables selective retransmission at the MSDU level without altering the original MAC header. In this proposed scheme an implicit sequence control mechanism has been introduced in order to keep the frames in sequence and preserve their correct order at the receiver side. The results show that the proposed scheme improves the system performance in terms of throughput and delay even under highly erroneous channels.     

DFA：基于802.11的无线网络动态帧分片与聚集方案

提出了一种适用于基于IEEE 802.11的无线网络的动态帧分片与聚集方案。该方案依据实时的信噪比信息来判断链路误码率,利用分片和聚集操作动态调整发送帧的长度,从而减少误码重传的发生。模拟实验证明,该方案能够有效提高WLAN以及无线Mesh网络为代表的基于802.11的无线单跳以及多跳网络的传输性能。     

Leveraging data aggregation algorithm in LoRa networks

The Journal of Supercomputing - Long Range (LoRa) is an interference-free, single-hop, low-power wide area network (LPWAN) technology. LoRa offers customization of its physical layer parameters...     

Application of neural networks for achieving 802.11 QoS in heterogeneous channels

In error-prone IEEE 802.11 WLAN (Wireless Local Area Network) environments, heterogeneous link qualities can significantly affect channel utilizations of mobile stations and consequently the user-perceived QoS (Quality of Services) of multimedia applications. In this paper we propose a novel optimization framework which provides QoS by adjusting IWSs (Initial Window Size) according to current channel states and QoS requirements. It is a table-driven approach which off-line pre-establishes the table of the best IWSs based on a cost-reward function. Neural networks are utilized to learn the mapping correlation and then to generalize that to other situations of interest. At runtime, the IWS of each user can thus be determined optimally with a simple table lookup rapidly without much time spent on learning about the nonlinear and complicated correlation. A video streaming transmission scenario is used to evaluate the performance of our scheme. The simulation results demonstrate that the proposed mechanism can effectively provide QoS for each user when the capacity of the network is sufficient for the requirements of all users.     

Dynamic and distributed packet aggregation to solve the performance anomaly in 802.11 wireless networks

In the widely used IEEE 802.11 standard, the so-called performance anomaly is a well-known issue. Several works have tried to solve this problem by introducing mechanisms such as packet fragmentation, backoff adaptation, or packet aggregation during a fixed time interval. In this article, we present and thoroughly analyze PAS, a dynamic and distributed approach solving the performance anomaly problem. PAS is based on packets’ aggregation using a dynamic time interval, which depends on the wireless channel occupation time perceived by each node. Since each station senses the medium independently, this makes PAS a totally distributed solution. Even more, PAS may coexist with standard IEEE 802.11 nodes without any particular adaptation, yet being able to improve performance. Our solution differs from other propositions in the literature because of its dynamic and distributed nature, which makes it suitable in the context of multi-hop networks. Furthermore, it allows increasing fairness, reactivity, and in some cases efficiency. In this article, we thoroughly analyze and emphasize the performance evaluation of our proposal.     

Analyzing the effective throughput in multi-hop IEEE 802.11n networks

In this paper we characterize the effective throughput for multi-hop paths in IEEE 802.11n based wireless mesh networks. We derive an analytical model capturing the effects of frame aggregation and block acknowledgements, features found in the new IEEE 802.11n standard. We describe the throughput at MAC layer as a function of physical data rate, error rate, aggregation level and path length. While being mathematically tractable, the proposed model is flexible enough to account for complex and realistic error characteristics of the wireless channel, such as long-term fluctuations and burstiness. We further show how to integrate the well-known Gilbert-Elliot channel model into our model and evaluate both models in our indoor wireless testbed.     

支持QoS的无线传感器网络数据聚合技术研究

结合数据聚合技术的特点,通过分析现有无线传感器网络的QoS研究,提出了数据聚合的三个QoS度量指标,即网络生命周期、数据时延、数据质量,讨论并分析了保证这些数据聚合QoS指标的关键技术,对于进一步深入研究无线传感器网络的数据聚合技术具有比较重要的参考价值.     

QoS provisioning in IEEE 802.11-compliant networks: Past,present, and future

Proliferation of portable, wireless-enabled laptop computers and PDAs, cost-effective deployment of access points, and availability of the license-exempt bands and appropriate networking standards contribute to the conspicuous success of IEEE 802.11 WLANs. In the article, we provide a comprehensive overview of techniques for capacity improvement and QoS provisioning in the IEEE 802.11 protocol family. These techniques represent the R&D efforts both in the research community and the IEEE 802.11 Working Groups. Specifically, we summarize the operations of IEEE 802.11 legacy as well as its extension, introduce several protocol modeling techniques, and categorize the various approaches to improve protocol capacity, to provide QoS (by either devising new MAC protocol components or fine-tuning protocol parameters in IEEE 802.11), and to judiciously arbitrate radio resources (e.g., transmission rate and power). To demonstrate how to adapt QoS provisioning in newly emerging areas, we use the wireless mesh network as an example, discuss the role IEEE 802.11 plays in such a network, and outline research issues that arise.     

Analyzing Hadoop power consumption and impact on application QoS

Energy efficiency is often identified as one of the key reasons for migrating to Cloud environments. It is stated that a data center hosting the Cloud environment is likely to achieve greater energy efficiency (at a reduced cost) compared to a local deployment. With increasing energy prices, it is also estimated that a large percentage of operational costs within a Cloud environment can be attributed to energy. In this work, we investigate and measure energy consumption of a number of virtual machines running the Hadoop system, over an OpenNebula Cloud. Our workload is based on sentiment analysis undertaken over Twitter messages. Our objective is to understand the tradeoff between energy efficiency and performance for such a workload. From our results we generalize and speculate on how such an analysis could be used as a basis to establish a Service Level Agreement (SLA) with a Cloud provider—especially where there is likely to be a high level of variability (both in performance and energy use) over multiple runs of the same application (at different times). Among the service level objectives that might be included in a SLA, Quality of Service (QoS) related metrics (i.e., latency) are one of the most challenging to support. This work provides some insight on the relationship between power consumption and QoS related metrics, describing how a combined consideration of these two metrics could be supported for a particular workload.     

IEEE 802.11n系统中自适应混合优化功率分配算法*

为解决IEEE 802.11n系统中的功率浪费现象,提出了一种先注水后调和平均值（first-water filling-last-harmonic, FWLH）的自适应混合优化功率分配算法。首先利用注水算法（water-filling algorithm）计算判别信道质量的阈值,对阈值以下的信道关闭不分配功率,对阈值以上的信道采用调和平均值算法(harmonic algorithm, HARM)进行功率分配。仿真表明,在误码率方面,FWLH算法比注水算法和HARM算法分别降低了大约100倍和20倍,使     

Efficient resource-aware control on SIP servers in 802.11n wireless edge networks

World Wide Web - Voice transmission over wireless edge networks is a conventional, cost-effective technology to transmit voice calls over 802.11 edge networks. In this type of service, Session...     

Providing MAC QoS for multimedia traffic in 802.11e based multi-hop ad hoc wireless networks

Ad hoc wireless networks with their widespread deployment, now need to support applications that generate multimedia and real-time traffic. Video, audio, real-time voice over IP, and other multimedia applications require the network to provide guarantees on the Quality of Service (QoS) of the connection. The 802.11e Medium Access Control (MAC) protocol was proposed with the aim of providing QoS support at the MAC layer. The 802.11e performs well in wireless LANs due to the presence of Access Points (APs), but in ad hoc networks, especially multi-hop ones, it is still incapable of supporting multimedia traffic.One of the most important QoS parameters for multimedia and real-time traffic is delay. Our primary goal is to reduce the end-to-end delay, thereby improving the Packet Delivery Ratio of multimedia traffic, that is, the proportion of packets that reach the destination within the deadline, in 802.11e based multi-hop ad hoc wireless networks.Our contribution is threefold: first we propose dynamic ReAllocative Priority (ReAP) scheme, wherein the priorities of packets in the MAC queues are not fixed, but keep changing dynamically. We use the laxity and the hop length information to decide the priority of the packet. ReAP improves the PDR by over 28% in comparison with 802.11e, especially under heavy loads. Second, we introduce Adaptive-TXOP (A-TXOP), where transmission opportunity (TXOP) is the time interval during which a node has the right to initiate transmissions. This scheme reduces the delay of video traffic by reducing the number of channel accesses required to transmit large video frames. It involves modifying the TXOP interval dynamically based on the packets in the queue, so that fragments of the same packet are sent in the same TXOP interval. A-TXOP is implemented over ReAP to further improve the performance of video traffic. ReAP with A-TXOP helps in reducing the delay of video traffic by over 27% and further improves the quality of video in comparison with ReAP without A-TXOP. Finally, we have TXOP-sharing, which is aimed at reducing the delay of voice traffic. It involves using the TXOP to transmit to multiple receivers, in order to utilize the TXOP interval fully. It reduces the number of contentions to the channel and thereby reduces the delay of voice traffic by over 14%. A-TXOP is implemented over ReAP to further improve the performance of voice traffic. The three schemes (ReAP, A-TXOP, and TXOP-sharing) work together to improve the performance of multimedia traffic in 802.11e based multi-hop ad hoc wireless networks.     

A new adaptive MAC protocol with QoS support based on IEEE 802.11 in ad hoc networks

With the expanding of applications, the demand of quality of service (QoS) has become strongly increased in ad hoc networks. Since the efficient and reasonable MAC protocol is a key factor for providing QoS in ad hoc networks, in this paper we propose an adaptive QoS MAC protocol (AMP) based on IEEE 802.11. In AMP, we introduce the concept of transmission license, where only the node which holds transmission license can participate in the channel contention for changing the number of licenses according to the load of the network adaptively, controlling the number of the nodes that participate in the channel contention, and ensuring the nodes with licenses share the channels through contention. In addition, AMP assigns different priority classes for different traffic according to the special characteristics and performance types of the different networks, and it sets the different contention parameters for the different priorities services for guaranteeing these services performances to have advantages in the channel contention. Simulation shows that compared to IEEE 802.11 protocol, AMP not only can meet the QoS requirement with high priority in the networks but also can well solve the hidden terminal problems and the fairness issues between different network nodes; that is, it can satisfy the high efficiency, pertinence, spatial-reuse, etc. to the largest extent at the same time in limited channels.     

Modelling and optimization of power consumption in wireless access networks

The power consumption of wireless access networks will become an important issue in the coming years. In this paper, the power consumption of base stations for mobile WiMAX, fixed WiMAX, UMTS, HSPA, and LTE is modelled and related to the coverage. A new metric, the power consumption per covered area PC_area, is introduced, to compare the energy efficiency of the considered technologies for a range of bit rates. Assuming the model parameters are correct, the conclusions are then as follows. For a 5 MHz channel, UMTS is the most energy-efficient technology until a bit rate of 2.8 Mbps, LTE between 2.8 Mbps and 8.2 Mbps, fixed WiMAX between 8.2 Mbps and 13.8 Mbps and finally mobile WiMAX for bit rates higher than 13.8 Mbps. Furthermore, the influence of MIMO is investigated.For a 2 × 2 MIMO system, PC_area decreases by 36% for mobile WiMAX and by 23% for HSPA and LTE compared to the SISO system, resulting in a higher energy efficiency.The power consumption model for base stations is used in the deployment tool GRAND (Green Radio Access Network Design) for green wireless access networks. GRAND uses a genetic based algorithm and is applied on an actual case for the Brussels Capital Region, showing the possibilities of energy-efficient planning.     

An efficient joint channel assignment and QoS routing protocol for IEEE 802.11 multi-radio multi-channel wireless mesh networks

With the emerging of video, voice over IP (VoIP) and other real-time multimedia services, more and more people pay attention to quality of service (QoS) issues in terms of the bandwidth, delay and jitter, etc. As one effective way of broadband wireless access, it has become imperative for wireless mesh networks (WMNs) to provide QoS guarantee. Existing works mostly modify QoS architecture dedicated for ad hoc or sensor networks, and focus on single radio and single channel case. Meanwhile, they study the QoS routing or MAC protocol from view of isolated layer. In this paper, we propose a novel cross-layer QoS-aware routing protocol on OLSR (CLQ-OLSR) to support real-time multimedia communication by efficiently exploiting multi-radio and multi-channel method. By constructing multi-layer virtual logical mapping over physical topology, we implement two sets of routing mechanisms, physical modified OLSR protocol (M-OLSR) and logical routing, to accommodate network traffic. The proposed CLQ-OLSR is based on a distributed bandwidth estimation scheme, implemented at each node for estimating the available bandwidth on each associated channel. By piggybacking the bandwidth information in HELLO and topology control (TC) messages, each node disseminates information of topology and available bandwidth to other nodes in the whole network in an efficient way. From topology and bandwidth information, the optimized path can be identified. Finally, we conduct extensive simulation to verify the performance of CLQ-OLSR in different scenarios on QualNet platform. The results demonstrate that our proposed CLQ-OLSR outperforms single radio OLSR, multi-radio OLSR and OLSR with differentiated services (DiffServ) in terms of network aggregate throughput, end-to-end packet delivery ratio, delay and delay jitter with reasonable message overheads and hardware costs. In particular, the network aggregate throughput for CLQ-OLSR can almost be improved by 300% compared with the single radio case.     

一种增强Web Services的服务质量和性能的方法

为了更好地把握股票价格的波动,应用了在处理序列数据输入输出具有优越性的Elman 递归神经网络建立股市预测模型,并用两支股票进行了检测,检测结果说明人工神经网络应用于中国股票市场的预测是可行和有效的,有着良好的前景。     

DFA:基于 802. 11的无线网络动态帧分片与聚集方案 *

提出了一种适用于基于 IEEE 802. 11的无线网络的动态帧分片与聚集方案。该方案依据实时的信噪比信息来判断链路误码率 ,利用分片和聚集操作动态调整发送帧的长度 ,从而减少误码重传的发生。模拟实验证明 ,该方案能够有效提高 WLAN以及无线 Mesh网络为代表的基于 802. 11的无线单跳以及多跳网络的传输性能。     

Denial-of-Service attacks and countermeasures in IEEE 802.11 wireless networks

IEEE 802.11 access points deployed in shopping malls, university campuses, crowded streets, airports, and many other locations provide ubiquitous Internet access to millions of stations. However, these hot spots are vulnerable to Denial-of-Service (DoS) attacks due to the broadcast nature of wireless communication. It does not require specialized hardware or particularly high level of experience to render 802.11 networks inoperable through DoS attacks. Standard off-the-shelf equipment is sufficient for a malicious station to disrupt the service between access points and stations. In this paper we present a systematic survey of DoS attacks, which exploits MAC and physical layer vulnerabilities of 802.11 networks. Available countermeasures against DoS attacks are discussed and compared. Future research directions and open issues are also discussed.     

A game theoretic approach for power allocation with QoS constraints in wireless multimedia sensor networks

The distinctive features of wireless multimedia sensor networks (WMSNs) include application-specific quality-of-service (QoS) requirements and limited energy supply, with which each node makes its own decisions selfishly. Therefore this paper presents a power control game theoretic approach for WMSNs by studying the effect of transmission power on QoS and energy efficiency. The game approach determines the transmission strategy using utility optimization according to the fluctuation of channel states. Here, the utility function is defined by effective throughput per unit power while satisfying the user’s delay QoS constraints. The existence and uniqueness of Nash equilibrium for the proposed game are proved. Finally, the simulation results show that each user chooses the optimal transmission power to maximize its utility based on other constant parameters and the effects of delay constraints on the user’s utility are quantified as well.     

Scheduling to minimize gaps and power consumption

This paper considers scheduling tasks while minimizing the power consumption of one or more processors, each of which can go to sleep at a fixed cost  $\alpha $ . There are two natural versions of this problem, both considered extensively in recent work: minimize the total power consumption (including computation time), or minimize the number of “gaps” in execution. For both versions in a multiprocessor system, we develop a polynomial-time algorithm based on sophisticated dynamic programming. In a generalization of the power-saving problem, where each task can execute in any of a specified set of time intervals, we develop a $(1+{2 \over 3} \alpha )$ -approximation, and show that dependence on $\alpha $ is necessary. In contrast, the analogous multi-interval gap scheduling problem is set-cover hard (and thus not $o(\lg n)$ -approximable), even in the special cases of just two intervals per job or just three unit intervals per job. We also prove several other hardness-of-approximation results. Finally, we give an $O(\sqrt{n})$ -approximation for maximizing throughput given a hard upper bound on the number of gaps.