Evaluation of beamforming algorithm effectiveness for the smart wireless LAN system

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 Smart Wireless LAN (SWL) system integrates the Space- Division-Multiple-Access technique (also called smart antennas) with spread spectrum wireless LAN systems, such as IEEE 802.11 systems, to enable multiple wireless LAN users to transmit simultaneously in a frequency band. This advantage creates a potential problem because the 802.11 standard requires that all terminals use the same spreading code, so a straightforward application of the 802.11 standard could result in the loss of the 10 dB of spreading gain achieved by each terminal. This isn't a problem in a conventional system where only one user may transmit at a time in a frequency band, so the solution to this problem was created specifically for the SWL system. The Timing Synchronization Algorithms studied in this paper enable multiple (up to 11) users to use the same spreading code without a loss of the spreading gain. Two complimentary algorithms, in their sorted and unsorted formats, are studied in this paper and their simulation results are analyzed.

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.

We propose a wireless ATM LAN system, which operates in the 5 GHz band at a channel rate of 25 Mb/s, to provide customer premises network (CPN) users with multimedia services. For the development of the wireless ATM LAN system, the system level requirements are described, and an architecture of the wireless ATM LAN system to support multimedia communications is proposed. In addition, we consider the technical issues to realize the wireless ATM LAN system.

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.

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

Wireless LANs (WLANs) still offer low capacity compared to conventional wired LANs. To increase the capacity of a bandwidth-limited wireless system, its spatial efficiency can be improved. Pico-cellular WLAN architectures have been proposed to this aim. However, we showed in a previous study that pico-cellularisation has serious disadvantages. Instead, space division multiple access (SDMA) enables spatial selectivity within one cell. We present a blind SDMA algorithm suitable for a 100 Mbps WLAN. Its design is based on rigorous indoor channel modeling and is targeted towards implementation. The performance of the proposed algorithm in typical office environments is assessed using a semi-analytic simulation approach. Furthermore, the complexity required for a hardware realization is determined. We conclude that a frequency re-use factor of four is achieved by a four antenna receiver using 2000 snapshots for channel estimation.

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.

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.

This paper proposes an orthogonally positioned inverted triangular monopole antenna over a compact plane reflector with stable radiation pattern for octave band of frequencies. Two triangles are placed crossed and orthogonal to each other to obtain nearly uniform omni-direction radiation pattern. The antenna is placed over a square reflector exhibits 73% bandwidth at (4.5 GHz). The measured impedance bandwidth and radiation pattern of the antenna match well with Finite Element Method (FEM) and Method of Moments (MOM) analysis of the structure. The antenna is novel in its orthogonal design and the triangles fed differently with compact reflector. The designed octave band planar antenna (3.0–6.5 GHz) has applications in Wireless LAN and intelligent transportation systems (ITS). The compact antenna design with uniform radiation pattern is used as radiator inside a room and cabinets for RF isolation measurements.

The estimation of carrier and sampling frequency offsets is considered, for IEEE 802.11a-based OFDM wireless LAN (WLAN) systems, based on the guard interval and two long symbols (GI2L) in the preamble of an OFDM WLAN packet. The model of the measurement of the GI2L is developed, in the presence of both carrier and sampling frequency offsets. Based on this model, a method is proposed, based on the GI2L. Improved performance, measured by estimation error and bit error rate, is achieved by the proposed method, as compared with some relevant existing methods.

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.

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.

Low proflle, light weight, easily mounted and broad bandwidth are the key charac- teristics for antennae designed for wireless applications. The microstrip antenna (MSA) suits the features mentioned except for its narrow bandwidth. The bandwidth of the microstrip antenna usually ranges from less than 1% to several percent. This paper experimentally investigates an alternative approach in enhancing the bandwidth of the microstrip antenna for the Wireless Lo- cal Area Network (WLAN) application operating at a frequency of 2.45GHz. The bandwidth enhancement technique which is studied is the Identical Dual Patch Microstrip Antenna with Air-Gap (IDMA). A bandwidth enhancement of more than 11% was achieved. Wireless applications have undergone rapid development in recent years. One particular wireless application that has experienced this trend is the Wireless Local Area Network (WLAN). The wireless application that is selected to be studied is the 2.4GHz to 2.5GHz frequency band which is based on the 802.11b WLAN standard. This frequency band is very popular due to its low cost. WLAN antenna requires being low proflle, light weight and broad bandwidth. The microstrip antenna suits the features very well except for its narrow bandwidth. The WLAN antenna should have a minimum bandwidth of 100MHz to fully utilize the WLAN band based on the 802.11b standard. The conventional microstrip antenna could not fulflll this requirement as its bandwidth usually ranges from less than 1% to several percent (1). Although the required operating frequency range is from 2.4GHz to 2.5GHz, at least double the bandwidth is required to avoid expensive tuning operations and to cause uncritical manufacturing. Therefore, there is a need to enhance the bandwidth of the microstrip antenna for WLAN applications. This paper investigates a technique which can enhance the bandwidth of the microstrip antenna without increasing the lateral size and the complexity of the microstrip antenna too much. The Identical Dual Patch Microstrip Antenna with Air-Gap (IDMA) bandwidth enhancement technique takes the advantage of using the air gap to lower the efiective permittivity and increase the total thickness of the microstrip antenna which is essential for bandwidth enhancement. This bandwidth enhanced microstrip antenna can be deployed for the WLAN application operating at a frequency of 2.45GHz. 2. SIMULATED AND MEASURED RESULTS OF THE SINGLE-LAYER MICROSTRIP ANTENNA