We propose a new resource management scheme, Distributed Channel Allocation Protocol (DCAP), for multimedia Ad hoc Wireless LANs (AWLANs). This scheme implements a Quality-of-Service (QoS) providing distributed resource management on the Orthogonal Frequency Division Multiplexing-Code Division Multiple Access (OFDM-CDMA) channel architecture. According to the performance evaluation results for MPEG traffic sources, DCAP can be a good choice of resource management scheme for AWLANs supporting multimedia services on the Broadband Wireless Access (BWA)-type physical layer.

Wireless LAN (WLAN) systems transmit and receive via a common frequency band. In this band, signals of other wireless applications operate on a WLAN beamformer as interferences, and so the problem in adaptive antenna is increasing the canceling performance in the presence of moving interference sources. The performance of conventional adaptive beamformer is severely degraded and the robust adaptive beamformer must be equipped with additional sensors to obtain desired performances. Therefore, in order to avoid having to install additional sensors, an efficient algorithm is necessary. In this paper, we introduce a fast adaptive algorithm with variable forgetting factor, which does not require any further additional modifications. Through computer simulations, we can obtain better performances than those of other techniques under a variety of operating conditions.

The paper presents a dual-band switchable low noise amplifier implemented in 0.25-µm CMOS technology for 5-GHz wireless multimedia applications. The high-speed wireless multimedia applications call for broadband design techniques for RF circuits. Instead of using conventional broadband techniques not well suitable for CMOS implementation, a dual-band switchable load is proposed for broadband LNA design. The dual-band switchable load enables the LNA operate at the lower or the upper band at 5-GHz band by a 1-bit control signal. The LNA exhibits over 17 dB power gain, 3.5 dB noise figure and input 1-dB compression point -23 dBm in both frequency bands. It draws 9.5 mA from 2.5 V supply. The power gain remains larger than 16 dB as temperature varies from -5 to 65.

In this paper the development of the prototyping platform of a partly reconfigurable System-on-Chip (SoC) for wireless LANs, is described. It is designed to realize both HIPERLAN/2 and IEEE 802.11a wireless LAN systems. The current version of the system includes Mobile Terminal and AP functionality only for indoor use. Future firmware versions (configurations for its reconfigurable part) will upgrade system's functionality to allow its operation in outdoor environments and in wireless point-to-point links. The target System-on-Chip implementation platform will include instruction set processor cores, ASIC blocks and embedded reconfigurable blocks to achieve an optimal balance between implementation efficiency (area, power, performance) and flexibility. The system's prototype is developed on the ARM integrator platform and all firmware versions will be verified before ASIC prototyping.

We propose a new scheme of indoor optical wireless LAN based on a special CMOS image sensor (CIS), which realizes a low-power compact communication module with large uplink capacity due to space division multiple access. In our scheme, all nodes and a hub utilize the CIS as a photoreceiver as well as a position-sensing device for finding the positions of the communication modules, while a single large photodiode is used in the conventional systems. Although conventional image sensors cannot detect modulated signals because they integrate photocurrents, our CIS has a high-speed readout function for receiving optical data from the specific pixels receiving optical signals. The advantages of the proposed scheme are 1) compact embodiment of the communication module due to no need of the bulky mechanical components for searching the other modules, 2) space division multiple access, which leads to 3) large capacity of uplink, and 4) applicability of simple modulation and coding schemes for optical signals. In our scheme, diffusive and narrow beam lights are complementally used for position detection and communication, respectively, which leads to the advantage 5) low power consumption of both light emitter and receiver circuits. To demonstrate two basic functional modes of our CIS: an IS (image sensor) mode and a COM (communication) mode, we fabricate an 88-pixel CIS by use of a 0.8µm BiCMOS technology. In the experiments, the image of a light source is successfully captured in the IS mode for integration time of 29.6msec and optical power of 1.1nW. After the functional mode of the pixel receiving the light is changed to the COM mode, the eye pattern of the modulated light is obtained from the pixel at frequency of 1MHz. We also fabricate a test pixel circuit with in-pixel amplifier, with which operation speed is improved to 100MHz.

This paper proposes a novel synchronization method of jointly estimating symbol frame timing and carrier frequency-offset for Orthogonal Frequency Division Multiplexing (OFDM) signal operating in the burst mode which is usually employed in the wireless LAN communications systems. The proposed method enables a fast and accurate synchronization for the burst mode OFDM signal even under the presence of large frequency-offset, very low C/N and frequency selective fading environments by using only two preamble symbols inserted at the start of every burst frame. This paper presents the various computer simulation results to verify the performance of proposed synchronization methods both for symbol timing and carrier frequency.

This paper proposes an Orthogonal Frequency Division Multiplexing system with Grouping Adaptive Modulation method (GAM-OFDM). The salient feature of the proposed system is to enable the reduction of required transmission bits for adaptive modulation information (AMI) that is required in the demodulation process at the receiver. This paper also proposes an efficient AMI transmission method for the GAM-OFDM system to enable the efficient transmission of AMI bits by using only two preamble symbols, and the Multi-Carrier Spectrum Spreading (MC-SS) technique to achieve the excellent performance of AMI transmission even under severe multi-path fading environments. This paper presents the various computer simulation results to verify the performance of proposed GAM-OFDM system.

The adaptive phase tracking scheme for orthogonal frequency division multiplexing (OFDM) signals can provide superior PER performance in channels with varying phase noise power. It is an effective technique for achieving high-rate and high quality wireless transmission. This paper proposes a new simple adaptive phase tracking scheme for OFDM signals in order to realize high-rate wireless local area networks (LANs). The proposed scheme measures the integrated phase rotation in order to appropriately set the properties of the FIR filter in the phase tracking circuits. This scheme uses the fact that the integrated phase rotation is correlated to the phase noise power. Assuming an RMS delay spread of 100 ns, computer simulations show that the proposed scheme offers superior required Eb/N0 performance (with regard to the phase noise power) compared to the conventional fixed-tap scheme, where the phase noise to signal power ratios are below -18 dB. It also offers excellent PER performance at the packet length of 1000 bytes unlike the conventional schemes, which suffer degraded PER performance.

A software defined radio (SDR) prototype based on a multiprocessor architecture (MPA) is developed. Software for Japanese personal handy phone system (PHS) of a 2G mobile system, and IEEE 802.11 wireless LAN, which has much wider bandwidth than the 2G systems, is successfully implemented. Newly developed flexible-rate pre-/ post-processor (FR-PPP) achieves the flexibility and wideband performance that the platform needs. This paper shows the design of the SDR prototype and evaluates its performance by experiments that include PHS processor load and wireless LAN throughput characteristics and processor load.

In this paper, how the new service of non-authenticated multicasting can be implemented on the AWA system is described. The AP is forced to send IGMP packets periodically in order to keep transmitting IP multicast data grams. The program tables of the non-authenticated multicast are transmitted as IP multicast data to allow the all clients to receive the material. Furthermore, the list of program tables which shows the pairs of the ID of the AP and the IP address of the program table are used so that different APs can offer different program tables and programs. Experiments on non-authenticated multicasting were successfully conducted and we confirmed that the proposed service works well.

In this paper, the performance of HIPERLAN (HIgh PErformance Radio Local Area Networks) CAC (Channel Access Control) of ETSI (European Telecommunication Standards Institute) in Europe, as High speed wireless LAN, is analyzed mathematically. The CAC protocol of HIPERLAN is the EY-NPMA (Elimination Yield-Nonpreemptive Priority Multiple Access) in which data is transmitted after prioritization, elimination and yield phase. We analyzed channel contention phase composed of elimination and yield phase and then throughput is inspected by simulation. This result is useful to design and implement of Ad hoc wireless networks.

In the Mobile IP handoff procedure, mobile node movement is detected from advertisements of foreign agents that differ from previously received advertisement and the new "care-of" address is registered with the home agent. However, user packets are not forwarded to the new foreign agent until a registration is completed and this interruption may degrade the quality of service especially in real-time applications such as audio and video, or may lower the TCP throughput due to retransmission timeout. To tackle these issues, we propose a new low latency handoff method, where access points used in a wireless LAN environment and a dedicated MAC bridge are jointly used to alleviate packet loss without altering the Mobile IP specifications. In this paper, we present design architecture of the proposed method and evaluate its performance in an actual network environment to verify the effectiveness of our approach.

VoIP (Voice over IP) is one of the real time applications that demand wireless LAN systems meet severe quality requirements which commonly involve delay time, jitter, and packet loss. However, it is difficult for CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to achieve the service quality demanded by VoIP if voice and data traffic coexist, so some form of priority control is needed. This paper proposes a novel multiple access protocol based on autonomous distributed control that allows wireless LANs to satisfy the VoIP requirements. This new protocol suits both VoIP and data traffic and executes priority control dynamically according to whether the VoIP packet collides with a data packet or another VoIP packet. The results of a theoretical analysis and computer simulations indicate its excellent performance. This proposed protocol reduces the delay time of VoIP packets by 54 to 70% compared with conventional CSMA/CA even if the traffic load increases provided that the packet loss probability is less than 3%.

This paper investigates the problem of finding the optimal access point placement in simultaneous broadcast system using orthogonal frequency division multiplexing (OFDM) for public access wireless LAN with micrometer or millimeter frequency band. We define our design criteria such that the quality of service is provided uniformly throughout a given service area. The optimal access point placement with a uniform quality of service was obtained by setting the cost function as the combination of a standard deviation of BER and the average of BER in a very fast simulated annealing algorithm. We applied the algorithm to the cases of fixed and mobile terminals, and obtained optimal access point placement results for both cases.

MIMO communication systems have been studied as a way to increase system capacity and to improve spectrum efficiency. This paper proposes a novel branch metric generation method for soft-decision Viterbi decoding in coded OFDM systems employing SDM (OFDM-SDM) systems, one form of MIMO communication, that employ the maximum likelihood decision (MLD) algorithm. In coded OFDM systems, the branch metric for forward error correction (FEC) is normally calculated based on received sub-carrier power level and the constellation point likelihood. This conventional approach fails in OFDM-SDM systems. In the proposed method, branch metric is derived based on the likelihood calculated by MLD algorithm, which improves FEC performance effectively. Then, availability of coded OFDM-SDM to realize wireless LANs with data rate above 100 Mbit/s in a bandwidth of 20 MHz is evaluated in office environments using required CNR calculated by computer simulation. The evaluation indicates that OFDM-SDM has the possibility of realizing 100 Mbit/s in office environments.

We propose a subchannel power control scheme in the OFDM system, which transmits data with a variable power level for each subchannel based on the received SNR. The OFDM system, employing the D-QPSK modulation and the proposed subchannel power control with a grouping coefficient equal to 3, gives about 2.3 dB gain in Eb/N0 comparing with the conventional OFDM system, under the two-ray multipath channel with the mean value of the second-ray's attenuation coefficient equal to 0.25, for the required BER equal to 10-5.

We investigated the use of the Wireless 1394 standard in an intra-vehicle environment. Wireless 1394 services are expected to be used both in homes and in vehicles, however the installation of twisted wire pairs in a car is difficult. In a vehicular environment, there is a problem of interference from nearby vehicles using the same frequency. In this paper, we examined the above problem of interference for vehicles using Wireless 1394 equipments, and measured the propagation characteristics between a transmitter in one vehicle and a receiver in another vehicle. We developed a mitigation method, based on the use of directional antennas as a solution to the problem of interference.

This paper presents the HiperSonic 1, a multi-standard, application-specific signal processor, designed to execute the baseband conversion algorithms in IEEE802.11a- and HIPERLAN/2-based 5 GHz wireless LAN applications. In contrast to widely existing, dedicated implementations, most of the computational effort here was mapped onto a configurable, data- and instruction-parallel DSP core. The core is supplemented by mixed signal A/D, D/A converters and hardware accelerators. Memory and register architecture, instruction set and peripheral interfaces of the chip were carefully optimized for the targeted applications, leading to a sound combination of flexibility, die area and power consumption. The 120 MHz, 7.6 million-transistor solution was implemented in 0.18 µm CMOS and performs IEEE802.11a or HiperLAN/2 compliant baseband processing at data rates up to 60 Mbit/s.

Wireless LANs have been used for realizing fully-distributed users in a multimedia environment that has the ability to provide real-time bursty traffic (such as voice or video) and data traffic. In this paper, we present a new realistic and detailed system model and a new effective analysis for the performance of wireless LANs which support multimedia communication with non-persistent carrier sense multiple access with collision avoidance (CSMA/CA) protocol. In this CSMA/CA model, a user with a packet ready to transmit initially sends some pulse signals with random intervals within a collision avoidance period before transmitting the packet to verify a clear channel. The system model consists of a finite number of users to efficiently share a common channel. Each user can be a source of both voice traffic and data traffic. The time axis is slotted, and a frame has a large number of slots and includes two parts: the collision avoidance period and the packet transmission period. A discrete-time Markov process is used to model the system operation. The number of slots in a frame can be arbitrary, dependent on the chosen lengths of the collision avoidance period and packet transmission period. Numerical results are shown in terms of channel utilization and average packet delay for different packet generation rates. They indicate that the network performance can be improved by adequate choice of ratios between the collision avoidance period and transmission period, and the pulse transmission probability.

The worldwide availability of the Industrial Scientific and Medical (ISM) bands has prompted the proposal of several communication systems for indoor application at the 2.4 and 5 GHz bands. Although adaptive array antennas have been thoroughly investigated for various outdoor scenarios, their application to indoor communications has been overlooked. Experimental results indicating that conventional array antenna techniques exhibit poor performance when implemented indoors have recently been published. An important peculiarity of the indoor channel is the coexistence of both near-field and far-field propagating waves. Therefore, algorithms that can indifferently cope with both near-field and far-field wavefronts for source location and beamforming are desirable. In this paper, the following are presented. First, a mathematical analysis of the performance of array antennas in the indoor environment is taken up. Second, a new, simple, cost-effective and statistically coherent scheme, the Adaptive Sampling algorithm, is proposed for location estimation of sources anywhere from near field to far field. It is shown that the proposed algorithm achieves ubiquitous source location, allowing for symmetric uplink/downlink beamforming with seamless performance. Finally, the performance of the proposed Adaptively Sampled Array Antenna is performance analyzed via computer simulations under the specifications of the IEEE802.11b DS Wireless Local Area Network (W-LAN).