This paper proposes a hardware configuration using only single pole dual throw (SPDT) switches to realize the previously proposed automatic calibration method using transmitting signals (ACT) for the adaptive array in TDD communication systems. The proposed configuration obtains the same calibration values as the conventional ACT does while reducing the number of switch branches. The transmission pattern using the proposed calibration method is also presented based on an experimental adaptive array testbed in an actual microcell environment. The experimental results show that the ideal radiation pattern formation is achieved by employing the proposed calibration method in an environment with a moving terminal station and where arriving co-channel interference exists.

This paper proposes a novel adaptive array configuration that reduces high-power co-channel interference (CCI) by utilizing the difference in arrival times between CCI and the desired signal in asynchronous TDD systems. The proposed adaptive array extracts only the CCI and employs pre-null steering for only the CCI by utilizing the fact that only the CCI arrives during the guard time in asynchronous TDD systems. Since the proposed adaptive array enables us to apply the Minimum Mean Square Error (MMSE) algorithm through synchronization with the desired signal using the output signal obtained by pre-null steering, high quality transmission can be achieved even in the presence of high-power CCI. Moreover, based on measurements using a fading simulator and field data, an adaptive array testbed exemplifying the proposed configuration is presented to show the reduction in the high-power CCI.

We propose a new bit timing recovery (BTR) scheme, what we call Step Sampled BTR (SSBTR), that can lower the sampling clock frequency and shorten the clock phase convergence time, for burst signals in high bit rate wireless access systems. The SSBTR scheme has the following characteristics. A sine wave resulting from the BTR code passing through a Nyquist Transmission System is always used, the sampling clock has a lower frequency than the system clock, and the clock phase of Intermediate Frequency (IF) signal input can be estimated from as few as 3 sampled data. The SSBTR scheme corrects the clock phase only once in a burst signal. Therefore, in some wireless access systems, some kind of operation must be performed after the SSBTR, in order to deal with long burst signals, instability of the system clock, and so on. In other wireless access systems that do not have these problems, clock phase can be fixed by the SSBTR scheme alone. The preformance of the SSBTR scheme with respect to additive white Gaussian noise (AWGN) was examined by computer simulation. In addition, when SSBTR is implemented in hardware, there are imperfections in the circuitry that lead to phase estimation error and thus deterioration, so we studied the effects of several such imperfections by computer simulation. The results of these simulations clarify the performance of the SSBTR scheme.

Hybrid direct sequence/slow frequency hopping-time division duplex (DS/SFH-TDD) multiple access system has some good features of each system. However it has a problem of hit between multiple users. If the designed frequency hopping patterns are inadequate, the quality of the multiple access system is degraded due to the frequent hit. In this paper, we propose an adaptive hopping pattern control system which is able to avoid the multiple access interference of hit. The proposed system decreases the influence of hit and increases the user capacity in the cell. And this adaptive hopping pattern control is applied to both single-cell and multi-cell systems. By computer simulation to evaluate the performance of this system, we found that this system is effective in increasing the multiple access capability.

An antenna and multi-carrier combined diversity system using Time Division Duplex (TDD) is proposed to combat with multi-path channel problem which produces frequency-selective fading and degrades the quality of signal transimission. So far multi-carrier modulation technique has been studied to solve this problem. On the other hand, TDD method has been studied to use a transmitter antenna diversity as pre-diversity against flat fading (non-selective fading). Our proposed system merges these two methods in a micro-cellular system as follows. On the reverse link, the base station can select the best combination between the carriers and antennas after receiving the multi-carrier signal from the mobile station. On the forward link, the same combination selected on the reverse link can be used to send the signal from the base station with multi-antenna to the mobile station with a single antenna and produces pre-diversity (transmitter diversity) effect which can reduce the complexity at the mobile station. The pre-diversity must be based on TDD function because the channel has to be observed before the signal transimission. By computer simulations we find that our proposed system can achieve far better performance than conventional systems.