In this paper, a route control method for ad-hoc networks in a multipath fading environment is studied which is based on received power of repeater nodes and the history of established links. When repeater nodes received HELLO Message, these nodes obtain the received power information from Physical Layer in order to decide whether a link is stable or not. If the received power is lower than a threshold, repeater nodes start route discovery procedure while maintaining the link by referring the history of established link. From the results of computer simulations, it has been clarified that the route discovery time of the proposed method is shortened by about up to 1.8 s, the route effective time is lengthened by about up to 13 s and the average throughput is improved by about up to 50 kbps from the previous proposed method which is an improved method of AODV.

This paper describes both link budget analysis and field experimental results on a mobile WiMAX system deployed in Azumino city, the city scale of which is corresponding to suburban. Firstly, in this paper, the link budget analysis is performed in order to evaluate the system performance based on propagation distance, delay spread, average BER (Bit Error Rate) under a multipath fading environment, and throughput performance. Then, received power and throughput in UDP layer are measured on the system deployed in Azumino city. Received power is measured by driving within a 3km radius centering on a BS (Base Station). Throughput is measured by the fix-point observation at arbitrary 11-point within a 3km radius. From the result of the field experiment for received power, the received power is a sufficient level for wireless communications at some points even exceeding a 3km radius. On the other hand, in an area shadowed by trees, buildings and so on, the received power becomes an insufficient level for wireless communications even within a 1km radius. From the result of the field experiment for throughput performance, it has been clarified that the upper limit of throughput is about 16Mbps for DL (downlink) and about 6Mbps for UL (uplink).

In this paper, proposed is a symbol timing synchronization method for OFDM systems. Firstly, the proposed method temporarily detects a symbol timing based on a peak value of the correlation function of training signals at the head of a burst signal. Then, the proposed method modifies the symbol timing based on a time delay spread which is estimated both from upper and lower bounds of correlation function having high correlation around the temporarily detected symbol timing. From simulation results, BER (Bit Error Rate) of the proposed method can be improved by about 1.5~2.5 times than that of a conventional method under the 18-ray Rayleigh fading model with maximum Doppler frequency of 30Hz.

This paper deals with the problem of noise suppression for white and colored noises. Kalman filter based noise suppression is well known as effective approach, and usually performs the parameter estimation algorithm of AR (auto-regressive) system and then the Kalman filter algorithm. In this paper, we propose Kalman filter for robust noise suppression without the conception of AR system. The algorithm aims to achieve robust noise suppression using only Kalman filter theory from the canonical state space models with (i) a state equation composed of the speech signal and (ii) an observation equation composed of the speech signal and additive noise. We also show the effectiveness of the proposed method, which utilizes Kalman filter theory for the proposed canonical state space model with the colored driving source, using numerical results and subjective evaluation results.

The ATM wireless access (AWA) prototype was developed in order to realize a broadband wireless access service with connections to the wired ATM network. Radio channel control techniques are used to control the AWA prototype and perform radio resource management. The radio channel control is made up of two main functions. One is the function of radio resource control, which includes channel establishment, allocation, and connection control. The other involves quality control, which includes channel switching and quality observation. This paper proposes a radio channel control method in which channel capacity is allocated according to the transmission rate requested by the user and ATM connections are controlled independently of channel assignment. This paper also proposes a method to ensure appropriate communication quality. Results of testing the proposed radio channel control on the prototype are provided.

This paper proposes a newly developed, highly precise cross-polarization interference canceller (XPIC), utilizing digitalized transversal filters. Performance of the digitalized XPIC is solely determined by quantization and tap numbers and is not affected by any circuit imperfection. Moreover, it can be universally applied to different bit rates and various modulation schemes. Performance of the XPIC is analytically estimated for various modulation schemes and various interference conditions. Then, the digitalized XPIC is realized and applied to a 12.5 MB 256 QAM digital radio system. Experimental results have closely conformed with theoretical estimations and it is confirmed that the XPIC is a powerful countermeasure against multipath fading for a future digital radio.