Symbol timing synchronization for IEEE 802.11n WLAN systems

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.

In this paper, we propose efficient symbol timing synchronization algorithms for IEEE 802.11a/g wireless LAN systems in multipath channels. The algorithms utilize an elongated training symbol together with soft-limiting of the correlator output and estimate the position of the first arriving path.

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.

In this paper, we present a new symbol timing and frequency synchronization method for OFDM WLAN system. A new method for synchronization using preamble structure of the IEEE 802.11a is proposed. The consecutive preamble structure is exploited to find the symbol starting-point and frequency offset accurately even under low SNR. The proposed timing synchronizer performs the fine timing synchronization first, and recognizes the end of short training symbol by coarse timing synchronization. The new frequency synchronization which means the estimation of frequency offset is more accurate than conventional method by considering the amplitude of preamble samples. Simulations show that it has distinct advantage over the conventional methods under multipath wireless channel condition even though it uses the fixed threshold for decision.

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.

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.

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

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.

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.

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.

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.

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.

Recently, the use of wireless LANs (WLAN) as a complementary technology to 3G systems has been identified. WLANs can be used to supplement the available bandwidth and capacity of a 3G network in hotspot areas, such as railway stations and airports, without sacrificing the capacity provided to cellular users. It provides support for data intensive applications and enables smooth on-line access to corporate data services, while still allowing users to roam from the private picocell network to wide area 3G networks. The paper addresses some of the current thinking within the ETSI BRAN (broadband radio access network) project regarding the interworking of the HIPERLAN/2 wireless LAN system into a 3G cellular system. Of the two initial solutions investigated (tight and loose coupling), current work has concentrated on the loose variant, producing viable solutions for security, mobility and QoS. The standardisation activity thus hopes to ensure that HIPERLAN/2 can provide a value added service within hotspot environments for both customers and operators of 3G systems.

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 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.