Infrastructure Mode Research Articles

Network-Load Aware Adaptive Channel Access Control for WLAN

Wireless local area network (WLAN) brings us a low cost and high bandwidth experience and thus plays a critically important role in current/future networks to support high-rate transmissions. To better provide quality-of-service (QoS) for WLAN users, we in this paper propose an improved scheme called “A-EDCA”(adaptive EDCA), based on enhanced distributed channel access (EDCA) of IEEE 802.11e under the infrastructure mode. Our proposed scheme aims at efficiently adapting the transmission over WLAN to the time-varying network conditions and mitigating the competition ability unfairness between access point (AP) and non-AP stations (STAs). Specifically, all non-AP STAs adaptive-ly modify the contention window based on the network condition. Moreover, AP skips the backoff phase by setting its backoff counter as zero when non-AP STA completes transmission successfully to relieve the unfairness. At last, simulation results demonstrate the effectiveness of the proposed approach.

Design of Wi-Fi Based Mobile Electrocardiogram Monitoring System on Concerto Platform

A wireless electrocardiogram (ECG) monitoring system is developed which integrates Wi-Fi technology. This Wi-Fi based system is comprised of a single-chip ECG signal acquisition module on Concerto MCU, a SimpleLink CC3000 Wi-Fi module and a smart-phone. The Concerto is a multi-core system-on-chip microcontroller (MCU) with independent communication and real-time control subsystems. The data rate of the system is 11Mbps at least and 54Mbps at most. The Wi-Fi module uses infrastructure mode network of IEEE802.11g. Apple's iPhone 4S is selected as the mobile device platform, which embedded with Wi-Fi and iOS. In this paper, the monitoring system is able to acquire ECG signals through 2-lead electrocardiogram (ECG) sensor, transmit the ECG data via the wireless link, process and display the ECG waveform in a smart-phone. The results show that implementation of Wi-Fi technology in the existing ECG monitoring system not only eliminates the physical constraints imposed by hard-wired link but also highly reduces the power consumption of the long-term monitoring system.

Multicast Capacity for VANETs with Directional Antenna and Delay Constraint

Vehicular Ad Hoc Networks (VANETs) with base stations are called hybrid VANET, where base stations are deployed to improve the throughput capacity. In this paper, we study the multicast throughput capacity for hybrid wireless VANET with a directional antenna on each vehicle and the end-to-end delay is constrained. In the hybrid VANET, there are n mobile vehicles (or nodes) distributed in a unit area with m strategically deployed base stations connected using high-bandwidth wire links. There are n_s multicast sessions and each multicast session has one source which transmits identical data to its associated p destinations. We investigate the multicast throughput capacity for two mobility models with two mobility scales, respectively, while each vehicular node is equipped with a directional antenna and with a tolerant delay D. That is, a source node transmits to its p destinations only with the help of normal nodes within D consecutive time slots. Otherwise, the transmission will be performed with in the infrastructure mode, i.e., with the help of base stations. We demonstrate that the one dimensional i.i.d. slow mobility pattern catch the main feature of VANETs. And we find that the multicast throughput capacity of the hybrid wireless VANET greatly depends on the delay constraint D, the number of base stations m, and the beamwidth of directional antenna θ. In the order of magnitude, we obtain the closed form of the multicast throughput capacity of the hybrid directional VANET, where the impact of D, m and θ on the multicast throughput capacity is analyzed. Moreover, we derive the lower bound of the muticast throughput using a similar raptor coding approach.

Integrating RFID and WLAN for indoor positioning and IP movement detection

Location awareness in an indoor environment and wireless access to Internet applications are major research areas towards the overwhelming success of wireless and mobile communications. However, the unpredictable indoor radio propagation and handover latency due to node mobility are the main challenging issues that need to be addressed. For tackling efficiently both problems of indoor localization and handover management, we propose combining key benefits of two outstanding wireless technologies, i.e. radio frequency identification (RFID) and a wireless local area network (WLAN) infrastructure. WLANs, such as IEEE 802.11 (WiFi), are now very common in many indoor environments for providing wireless communication among WiFi-enabled devices by accessing an Access Point (infrastructure mode) or through peer to peer connections (ad hoc mode). However, the small cell size of the Access Points (APs) in a WiFi-based network drives the need for frequent handovers leading to increased latency. RFID is an emerging technology consisting of two basic components, a tag and a reader, and its main purpose is the automatic identification of tagged objects by a reader. However, in the presence of multiple readers, RFID suffers from the so-called reader collision problem, mainly due to the inability for direct communication among them. In this paper, we propose a hybrid RFID and WLAN system; the RFID technology is employed for collecting information that is used for both localization and handover management within the WLAN, whereas the WLAN itself is utilized for controlling and coordinating the RFID reading process. In our system architecture, tag IDs of a RFID tag deployment are correlated with both location and topology information in order to determine the position and predict the next subnetwork of a Mobile Node (MN) with a reader attached to its mobile device. The role of the WLAN is to coordinate the readers when accessing the RFID channel for retrieving tags' IDs, hence compensating the persisting RFID collision problem among multiple readers. Numerical results based on extensive simulations validate the efficiency of the proposed hybrid system in providing accurate and time efficient localization and reducing the IP handover latency.

Performance of CSMA in multi-channel wireless networks

We analyze the performance of CSMA in multi-channel wireless networks, accounting for the random nature of traffic. Specifically, we assess the ability of CSMA to fully utilize the radio resources and in turn to stabilize the network in a dynamic setting with flow arrivals and departures. We prove that CSMA is optimal in the ad-hoc mode, when each flow goes through a unique dedicated wireless link from a transmitter to a receiver. It is generally suboptimal in infrastructure mode, when all data flows originate from or are destined to the same set of access points, due to the inherent bias of CSMA against downlink traffic. We propose a slight modification of CSMA that we refer to as flow-aware CSMA, which corrects this bias and makes the algorithm optimal in all cases. The analysis is based on some time-scale separation assumption which is proved valid in the limit of large flow sizes.

Discuss Charging-Discharging and Sale Technology of the Electric Vehicle

Development of EV is an important means which optimize chinese energy supply structure and break security strategy of energy.As the state increasing subsidy strength and constructing large-scale charging infrastructure for EV,EV is expected to become an important means of transport,and in the future EV is becoming to an important mobile storage unit in smart grid, playing the dual role of energy comsume and energy storage. Combination of domestic charging infrastructure and charge mode, discuss the charge and discharging and sale of electric technology for EV, which provide some reference for business model of the charging infrastructure,proposed to help the orderly charging and discharging for EV, realize win-win situation for power grid and the user.

A study on mobile ad-hock networks (manets)

As we know that wireless technology becomes very famous among all the aspects of different technologies of computer networking of present era, the Wireless networks really provide the convenient and easy approach to communications between different areas. Wi-Fi is commonly called as wireless LAN, it is one of those networks in which high frequency radio waves are required for transmission of data from one place to another. Wi-Fi operates on several hundred feet between two places of data transmission. This technology only works on high frequency radio signals. Nowadays this technology is used as office or home network and in many electronic devices. Wireless LAN or Wi-Fi is divided into three main parts on which its whole working depends and all of its applicationsdepend on these parts such as infrastructure mode and ad hoc mode of networking. However, the important type that plays a vital role almost in application is the Ad Hoc mode of networking.This type of networking is also commonly called as peer-to-peer networking or P2P networking. Mobile ad hoc network (MANET) is an autonomous system of mobile nodes connected by wireless links. There is still ongoing research on mobile ad hoc networks and the research may leadto even better protocols and will probably face new challenges. The current goal is to find an optimal balance between scalable routing and media access control, security, and service management.

Automatic management of forums via artificial immune systems

This paper presents a protocol to eliminate the necessity for human moderators in forums, thus automatising the moderation process. The protocol uses a bio-inspired approach: well- and ill-behaving posters are modelled as healthy and infected cells of a living organism. Moderators are modelled as leukocytes that remove infected cells. The identification of infected cells is supported by a feedback mechanism that allows posters to rate both other posters and the performance of the moderators. To achieve an adaptive moderation, an artificial lymphatic system, modifies the group of moderators with the aim of improving the immune response when needed. This paper focuses on ad hoc wireless networks, however the modifications needed to port the protocol to a wireless network using infrastructure mode are described. To evaluate the performance of the protocol, the outcome of a simulation of the forum is presented.

Achieving Airtime Fairness and Maximum Throughput in IEEE 802.11 under Various Transmission Durations

IEEE 802.11 Wireless LANs (WLANs) support multiple transmission rates. When some stations transmit at low transmission rates, the performance of the high transmission rate stations degrades heavily, and this phenomenon is known as the performance anomaly. As a solution to the performance anomaly, airtime fairness was proposed. However, the distributed coordination function (DCF) of IEEE 802.11 cannot provide airtime fairness to all competing stations because the protocol is designed to ensure fair attempt probability. In this paper, we propose a new medium access control, successful transmission time fair MAC (STF-MAC), which is fair in terms of successful transmission time and also provides the maximum aggregate throughput of a basic service set (BSS) in distributed manner. STF-MAC can be easily applied to solve the uplink/downlink fairness problem in infrastructure mode. Through simulations, we demonstrate that STF-MAC not only remedies the performance anomaly but also maximizes the aggregate throughput under the fairness constraint.

On the Validity of IEEE 802.11 MAC Modeling Hypotheses

We identify common hypotheses on which a large number of distinct mathematical models of WLANs employing IEEE 802.11 are founded. Using data from an experimental test bed and packet-level ns-2 simulations, we investigate the veracity of these hypotheses. We demonstrate that several of these assumptions are inaccurate and/or inappropriate. We consider hypotheses used in the modeling of saturated and unsaturated 802.11 infrastructure mode networks, saturated 802.11e networks, and saturated and unsaturated 802.11s mesh networks. In infrastructure mode networks, we find that even for small numbers of stations, common hypotheses hold true for saturated stations and also for unsaturated stations with small buffers. However, despite their widespread adoption, common assumptions used to incorporate station buffers are erroneous. This raises questions about the predictive power of all models based on these hypotheses. For saturated 802.11e models that treat differences in arbitration interframe space (AIFS), we find that the two fundamental hypotheses are reasonable. For 802.11s mesh networks, we find that assumptions are appropriate only if stations are lightly loaded and are highly inappropriate if they are saturated. In identifying these flawed suppositions, this work identifies areas where mathematical models need to be revisited and revised if they are to be used with confidence by protocol designers and WLAN network planners.

A Cross-Layer Multi-Hop Simulator for IEEE 802.11e

In this work we simulate the ad hoc mode of IEEE 802.11e for routing optimisation. We simulate the behaviour of routing algorithms at the network layer by using a custom-made cross-layer network simulator developed by our team, which simultaneously considers the physical and Medium Access Control (MAC) layers. Although the simulator also supports the infrastructure mode, in this paper we focus on the ad hoc feature which was introduced by the authors. We opted for the simulator approach over the theoretical analysis, but we also present a mathematical model for IEEE 802.11 ad hoc networks. Some initial tests were performed by using a simple routing algorithm (to evaluate the behaviour of the system in terms of selection of the path between a source and a destination, and the correctness of the calculated metrics, which include end-to-end delay, packets lost, packets delivered), but more advanced cross-layer design solutions were also tested. When information from the physical and MAC layers is used as an input to the routing algorithm, improvements are achieved in the performance of the network. Several functions were compared and the algorithm that privileges shorter links accounting with the metric "collision rate" achieves the best results. When compared with a standard routing solution, this cross-layer approach allows to increase the number of packets delivered, while not significantly affecting the end-to-end delay of the packets.

Capacity of Hybrid Wireless Networks with Directional Antenna and Delay Constraint

We study the throughput capacity of hybrid wireless networks with a directional antenna. The hybrid wireless network consists of n randomly distributed nodes equipped with a directional antenna, and m regularly placed base stations connected by optical links. We investigate the ad hoc mode throughput capacity when each node is equipped with a directional antenna under an L-maximum-hop resource allocation. That is, a source node transmits to its destination only with the help of normal nodes within L hops. Otherwise, the transmission will be carried out in the infrastructure mode, i.e., with the help of base stations. We find that the throughput capacity of a hybrid wireless network greatly depends on the maximum hop L, the number of base stations m, and the beamwidth of directional antenna \theta. Assuming the total bandwidth W bits/sec of the network is split into three parts, i.e., W_1 for ad hoc mode, W_2 for uplink in the infrastructure mode, and W_3 for downlink in the infrastructure mode. We show that the throughput capacity of the hybrid directional wireless network is \Theta(\frac{nW_1}{\theta^2L\log n})+\Theta(mW_2), if L=\Omega(\frac{n^{1/3}}{\theta^{4/3}\log^{2/3} n}); and \Theta((\theta^2L^2\log n)W_1)+\Theta(m W_2), if L=o(\frac{n^{1/3}}{\theta^{4/3}\log^{2/3} n}), respectively. Finally, we analyze the impact of L, m and \theta on the throughput capacity of the hybrid networks.

A Typology of Strategic Behaviour in PPPs for Expressways: Lessons from China and Implications for Europe

In line with governance trends around the world, a growing number of expressways in the People’s Republic of China are managed as Public-Private Partnerships (PPPs). The tremendous growth in demand for mobility in newly emerging economies has led to a gap between investment needs and available public funding. Using private funds is potentially helpful in closing this gap and accommodating the social and economic needs of motorization. By some, it is also hoped that contracting-out and involvement of the private sector will lead to higher transparency and accountability. However, in line with what has been found in various transport infrastructure modes, during uncertain and hazy transition periods that arise after infrastructure reforms, many forms of potentially pernicious strategic behaviour can pop up. Strategic behaviour emerges from information a-symmetry between private and public players, where the former act as agents and the latter as principals. In this article, China’s evidence on various types of strategic behaviour in the management of expressways is found. Several PPP projects for expressways in China are investigated empirically. And conclusions are drawn as to what possible cures are effective countermeasures of strategic behaviour, and what are the implications for Europe.

Measuring the capacity of in-car to in-car vehicular networks

A particular class of vehicular networks is the one that includes off-the-shelf end-user equipment (e.g., laptops and PDAs) running from the interior of vehicles: in-car nodes. They are subject to limited communication conditions when compared with nodes specifically designed to this context. Existing works either consider antennas installed on top of the vehicle roof or nodes that operate in infrastructure mode. In this article, we investigate through real experiments the characteristics of links formed by in-car nodes running off-the-shelf wireless technologies such as IEEE 802.11(a/g) in ad hoc mode. We surprisingly observe that in-car nodes do show enough performance in terms of network capacity to be used in a number of applications, such as file transfer in peer-to-peer applications. Nonetheless, we identify some key performance issues and devise a number of configuration recommendations and future work directions.

Throughput and Delay in Cooperative Wireless Networks With Partial Infrastructure

Hybrid wireless networks have been shown to scale only when the number of base stations m is on the same order of the number of nodes n in the network. Pure wireless ad hoc networks with multiple-input-multiple-output (MIMO) distributed communications have also been shown to scale. A natural question arises: Do hybrid wireless networks always scale no matter how many base stations are placed if MIMO distributed communications are used? In this paper, we address this question and show that hybrid wireless networks cannot always scale with the proposed resource-allocation strategy. Specifically, they can only scale either when m = Theta(1) and all resources are exclusively allocated to ad hoc mode transmissions or when m = Theta(n), and all resources are exclusively allocated to infrastructure mode transmissions; moreover, the delay is significantly large in the first case, whereas it is Theta(1) in the second case, where Theta(f(n)) means on the order of f(n) when n is large.

IEEE 802.11b based ad hoc networking and its performance in mobile channels

It is widely believed that IEEE 802.11 standard is aimed mainly for fixed indoor wireless local area networks and is not suited for mobile applications, even though the IEEE 802.11b systems may work in either infrastructure mode or ad hoc mode. The impact of node mobility on ad hoc network performance has already been studied intensively, but these studies mostly do not consider temporal fluctuations of the mobile wireless channel due to the Doppler shift. An investigation of the mobility impact on the performance of IEEE 802.11b ad hoc systems with Rician/Rayleigh fading under different node velocities is presented. A comprehensive and in-depth analysis of the impacts of a multitude of different signal distortions on an IEEE 802.11b system performance is also presented. Specifically, the authors study the bit-error rate performances with respect to node velocities for different modulation schemes. The simulation results show that, owing to its extremely low implementation and deployment cost, the current IEEE 802.11b standard has its potential to be deployed in a mobile ad hoc environment if the line-of-sight path between transmitter and receiver exists.

Capacity and delay of hybrid wireless broadband access networks

An optical network is too costly to act as a broadband access network. On the other hand, a pure wireless ad hoc network with n nodes and total bandwidth of W bits per second cannot provide satisfactory broadband services since the pernode throughput diminishes as the number of users goes large. In this paper, we propose a hybrid wireless network, which is an integrated wireless and optical network, as the broadband access network. Specifically, we assume a hybrid wireless network consisting of n randomly distributed normal nodes, and m regularly placed base stations connected via an optical network. A source node transmits to its destination only with the help of normal nodes, i.e., in the ad hoc mode, if the destination can be reached within L (L /spl geq/ 1) hops from the source. Otherwise, the transmission will be carried out in the infrastructure mode, i.e., with the help of base stations. Two transmission modes share the same bandwidth of W bits/sec. We first study the throughput capacity of such a hybrid wireless network, and observe that the throughput capacity greatly depends on the maximum hop count L and the number of base stations m. We show that the throughput capacity of a hybrid wireless network can scale linearly with n only if m = Omega(n), and when we assign all the bandwidth to the infrastructure mode traffics. We then investigate the delay in hybrid wireless networks. We find that the average packet delay can be maintained as low as Theta(1) even when the per-node throughput capacity is Theta(W).

Performance analysis of power save mode in IEEE 802.11 infrastructure wireless local area network

For the battery-powered wireless stations, power saving is one ofthe significant issues in IEEE 802.11 wireless local area network(WLAN). Recently, Lei and Nilsson investigated the power save modein IEEE 802.11 infrastructure mode by an M/G/1 queue with bulkservice. They obtained the average packet delay and lower and upperbounds of the average Percentage of Time a station stays in the Dozestate (PTD). In this paper, the further investigation of power savemode is done; simple derivation of the average and the variance ofpacket delay and the exact value of PTD are obtained. Numericalresults show that our analytic results for PTD match quite well withsimulation results. Using our performance analysis, we can find themaximal listen interval which minimizes the power consumption of astation while satisfying the required quality of service (QoS) onthe average and the variance of packet delay.

An Asymmetric Access Point for Solving the Unfairness Problem in WLANs

In atypical deployment of IEEE 802.11 wireless LANs in the infrastructure mode, an access point acts as abridge between the wireless and the wired parts of the network. Under the current IEEE 802.11 Distributed Coordination Function (DCF) access method, which provides equal channel access probability to all devices in a cell, the access point cannot relay all the frames that it receives on the downlink. This causes significant unfairness between upload and download connections, long delays, and frame losses. This unfairness problem comes from the not-so-complex interaction of transport-layer protocols with the MAC-layer access method. The main problem is that the access point requires more transmission attempt probability than wireless stations for correct operation at the transport layer. In this paper, we propose to solve the unfairness problem in a simple elegant way at the MAC layer. We define the operation of an Asymmetric Access Point that benefits from a sufficient transmission capacity with respect to wireless stations so that the overall performance improves. The proposed method of operation is intrinsically adaptive so that when the access point does not need the increased capacity, it is used by wireless stations. We validate the proposed access method by simulation to compare it with other solutions based on IEEE 802.11e. Unlike many papers in this domain, which only validate MAC-layer modifications through simulation or analytical modeling, we provide measurement data gathered on an experimental prototype that uses wireless cards implementing the proposed method.

Implementing and evaluating three routing protocols in dual-radio-dual-mode IEEE 802.11(b) wireless mesh networks

In a dual-radio-dual-mode IEEE 802.11(b) wireless mesh network (WMN), each mesh access point has two IEEE 802.11(b) interfaces. One interface operates in infrastructure mode to serve IEEE 802.11(b) client devices so that they can readily use the mesh network without any software modification or installation. The other interface operates in ad hoc mode to forward packets among mesh access points until they reach an Internet gateway or the access point with which the destination client device is associated. Compared with a single-radio WMN, such a WMN offers ease of use and higher network throughputs for client devices. In this paper, we implement and evaluate the performance of three routing protocols (OSPF, AODV, and STP) operating in dual-radio-dual-mode IEEE 802.11(b) WMNs. Our simulation results show that among the tested protocols, OSPF provides the highest system total througput and results in the largest number of stable connections in such a WMN.