A wireless ATM LAN system for multimedia communications

Many wireless LAN (WLAN) systems are densely used in conference rooms and cafes owing to the widespread use of mobile access points (APs) and smart phones with tethering functions. Under this situation, duplicate (the same) channels are often used in the 2.4-Ghz band owing to a limited bandwidth. In addition, adjacent channels interfering with other channels are also used. Then, if the WLAN uses a channel easily affected by adjacent channels, the throughput of the WLAN can decrease. As a result, it is possible that the fairness of the WLAN will decrease. Therefore, this study proposes a switching method for media access control (MAC) to improve the throughput fairness in an adjacent channel interference environment. The proposed method attempts to apply a modified MAC method to a WLAN under a dense environment in which the throughput is appropriately decreased. From the simulation results, it was found that the proposed method can improve the throughput fairness. Therefore, we confirmed the effectiveness of our method in an adjacent channel interference environment.

The effect of terminal movement on the performance of the IEEE 802.11 g wireless LAN (WLAN) system is evaluated using a measurement set-up including a radio channel simulator. The evaluation is based on laboratory measurements of WLAN PC cards in different simulated radio environments. In the measurements, two different radio channel models are used; the exponential channel model and the UMTS vehicular channel model. The measurement results indicate promising operation of IEEE 802.11 g WLAN systems as such. However, the use of different packet sizes has a significant effect on the system behaviour. With large packets the terminal is more likely to experience channel estimation errors than with small packets. This is due to the fact that the IEEE 802.11 g receiver estimates the channel only once per frame, and uses this estimation over the entire frame. Based on the measurement results we suggest a modification to the medium access control (MAC) layer operation that overcomes this problem: the use of optimized fragmentation.

The study of the impact of a self-similar traffic, with respect to that of a Poisson classical one, on ad-hoc Wireless LAN (WLAN) systems is performed. The self-similar traffic generation is obtained by using a chaotic system, with structural parameters varied in order to have different self-similarity degrees and activity factors, and to permit a correct comparison with the Poisson traffic. The WLAN systems considered are based on polling MAC protocols and on different packet delivery strategies. In the performance analysis, obtained by means of simulations, some simple models for channel impact, retransmission strategy and terminal mobility are taken into account.

Based on the requirements of the offshore wind farm construction, an intelligent remote control system has been proposed for jacking-up offshore platform. The system consists of a wireless LAN, a master control system, an intelligent node control system, and front sensors. The master control system is composed of a master control decision-making expert system, a malfunction diagnosis and disposal decision-making expert system, and database system, a virtual reality display system, and a wireless LAN system. The intelligent node control system consists of a control decision-making expert system, a jacking control system, a locking control system, a malfunction diagnosis system, executing controllers, status sensors, a database system, a pier-side control interface, and wireless LAN system. This remote control system enables a real-time analysis of the status of the platform, self adjusting of the platform, and memorizing previous decision for a better efficient control. This system supports independent execution with fault diagnosis & recovery ability. So it is recommended because it meets the requirements of offshore platform of wind farm construction.

In this paper, we propose a robust symbol timing synchronization method for IEEE 802.11n wireless LAN (WLAN) systems. Symbol timing synchronization using a preamble is affected by the timing of the packet detection and automatic gain control (AGC) completion. However, conventional methods assumed that symbol timing synchronization starts at the beginning of the preamble, which is typically invalid in 802.11n systems. Also, the cyclic shift diversity (CSD) scheme is adopted for achieving spatial diversity and avoiding undesired beamforming in 802.11n standard. However, it induces a pseudo multipath problem which generates multiple-peaks of the cross-correlation. In order to solve these problems, a novel symbol timing synchronization method which is not affected by the pseudo multipath problem is devised. This method estimates a coarse time-offset of short training symbols (STSs) using the cross-correlation and detects a coarse boundary between the last STS and GI which is prior to long training symbols (LTSs) using maximum normalized correlation (MNC)-based algorithm and dividing the preamble into units of STS length. At last, to improve precision of boundary detection, the fine timing of GI start is refined by a verification stage using periodicity of STS. Simulation results show that the proposed method has the SNR gain of 2.4 dB and 3.2 dB compared to the conventional method at the rate of 1% synchronization failure probability in 2TX-2RX and 4TX-4RX WLAN systems, respectively.

Wireless local area network (WLAN) systems are typically designed to provide fixed or nomadic access. Using WLAN systems for military purposes raises the question of how WLAN terminals can be utilized in a fully mobile outdoor environment. In these environments, there typically exists multipath propagation with a large delay spread in the radio channel. This paper investigates the effect of terminal movement on the physical layer performance and capacity of IEEE 802.11b WLAN systems in a realistic outdoor mobile environment. Several wireless network interface cards are measured in laboratory conditions using a simulated radio channel. The measurement results indicate that WLAN systems can operate in mobile outdoor environment up to a certain mobile speed, and there are significant differences between equipment from product vendors

For a wireless communication system to work effectively without electromagnetic interference, the electromagnetic environment needs to be controlled. We experimentally investigated methods for controlling the electrical field strength and the delay spread so as to achieve communications without electromagnetic interference in selected regions for a 2.4-GHz-ISM-band wireless LAN system. Several indoor environments in which partitions with electromagnetic absorbing board were placed around desks were used. The transmission loss and delay spread were investigated experimentally, and the BER and throughput characteristics were measured. We found that the coverage of a wireless LAN could be controlled by using partitions with absorbing boards. We identified several requirements for controlling the coverage that should be useful in designing indoor wireless communication systems.

Compared with the SAW convolver and the digital correlator, the SAW matched filter (tapped delay line) has many advantages in commercial wireless LAN applications, because of its high efficiency and simple configuration. A new type of SAW device for the spread spectrum (SS) transceiver and a low-loss SAW matched filter for the wireless LAN system is described. Two matched filters which correspond to bi-phase data modulation and bandpass filters for the intermediate frequency (IF) section are combined into one device. This SAW matched filter fabricated on ST cut quartz has been practically used in commercial wireless LAN systems and has good temperature stability. To reduce the conversion loss further we have developed an extremely low loss SAW matched filter. The output correlation peak of the matched filter is 3 dB larger than the input level at a 50 /spl Omega/ input and output impedance. This low loss SAW matched filter is fabricated on 128/spl deg/ Y-X LiNbO/sub 3/ substrate and consists of unidirectional transducers. The phase error caused by the temperature coefficient of delay is compensated by using a temperature dependent change of local frequency in the spread spectrum receiver. Under the critical conditions of a 2.4 GHz wireless LAN (data rate is 1.4 Mbps, C/N>2 dB, that is E/sub b//N/sub 0/>13.6 dB, and operation temperature is from -20/spl deg/C to +60/spl deg/C), good performance is achieved with less than a 10/sup -5/ bit error rate.

The smart wireless LAN (SWL) system integrates the space-division-multiple-access (SDMA) technique with the IEEE 802.11 wireless LAN standard to enable multiple users to transmit on a wireless LAN at the same time in the same frequency band. Four beamforming algorithms are studied which the SWL system can use to minimize the interference that each user experiences from the other users. Computer simulations of the signal-to-interference (SIR) performance of the four beamforming algorithms are presented, and their SIR results are compared with results from previous experiments. Simulation results for the complete SWL physical layer are presented and analyzed.

The popularity of agents in artificial intelligence (AI) can be seen almost everywhere in the form of effective decision making, predictive analysis, expert systems, and so on. In parallel, wireless communication systems in the form of wireless local area networks (WLANs) and wireless personal area networks (WPANs) are also providing tremendous support for data communication. Exploring and utilizing the benefits of artificial intelligence and wireless communication systems together in an environment are still in the nascent stage due to the divergent characteristics of the respective domain. One of the major drawbacks in the existing wireless communication system is interference in 2.4 GHz band. This work proposes a multi-agent-based interference mitigation technique to mitigate the interference issues in wireless communication system and aims to enhance the communication process in terms of packet delivery ratio. This work is implemented as a pilot project in an educational institution for teaching students in wireless communication environment, the result shows that technology has added new dimensions to teaching–learning process, and performance of the wireless communication system is also increased in terms of packet delivery ratio.

In recent years, wireless LAN systems that utilize a wideband channel have been used in many cases, so that the problem of wireless LAN interference often occurs. In order to solve the wireless LAN interference problem, various interference management methods have been proposed. Among them, interference alignment algorithm is the most popular. In order to overcome the limitations of existing interference alignment algorithms in wideband WLAN interfering environment, in this paper, we propose a new SA-OIA (Sub-band Allocated Opportunistic Interference Alignment) method and analyze the performance.

The present generation of the wireless LAN (WLAN) products are implemented on Personal Computer Memory Card International Association (PCMCIA) cards (also called PC card) that are used in laptops, computers and portable devices. The technical issues for WLAN systems are size, power consumption, bit rate, aggregate throughput, coverage range and interference robustness. Scarcity of spectrum is the biggest issue in wireless communication. The challenge is to serve the largest number of users with a specified system quality. For this purpose, network architecture and the study thereof play a very important role. This paper first discusses the considered WLAN, after which explanations of WLAN system design are given, taking into consideration critical issues such as coverage, cell planning, interference, power management and security, especially for IEEE 802.11 WLAN based on direct sequence spread spectrum (DS-SS) in the 2.4 GHz ISM band.

Software radio, whose functions can be changed simply by replacing only software, is the key to next generation wireless communication systems. We have constructed a software radio prototype based on a multiprocessor architecture. This prototype supports the Japanese personal handy-phone system (PHS) and IEEE 802.11 wireless LAN systems. The paper reports the performance of the prototype. The system re-configuration function and the over-the-air (OTA) download protocol of the prototype are described in detail. The system re-configuration function changes the wireless communication mode of the software radio by replacing the software. To enter the PHS mode takes about ten seconds. The proposed general-purpose OTA download protocol works over TCP/IP. It is very secure because it uses secure socket layer (SSL). It is confirmed that the software can be downloaded from the download server normally.

Auto rate fallback (ARF) is a link adaptation algorithm that uses layer-2 acknowledgement messages to make decisions to increase or decrease the transmission rate. The algorithm is configured by choosing thresholds to define its behavior. The ARF algorithm is applied to voice-over-IP users in an IEEE 802.11a wireless LAN system, and system simulation is used to determine the optimal ARF configuration. Configuration performance is judged using a unique voice quality metric, which is used to establish a measure of system capacity for a single access point with several voice users. Results indicate that the ARF configuration can significantly impact capacity, and one configuration of ARF provides a capacity within 13% of the available capacity.

In this paper, we basically researched an environmental monitoring system method using digital cameras on airship. We used two types of normal digital camera and infrared camera with wireless LAN system. We also proposed some applied environmental monitoring system for residents using wireless LAN system.