This paper investigates the cell search time performance of our previously proposed three-step cell search method in a two-cell site environment by laboratory and field experiments supporting asynchronous cell site operation, which is one of the most notable features of wideband direct sequence code division multiple access (W-CDMA) mobile communications. The cell search methods used in the paper are based on the ongoing third generation partnership project (3GPP), in which our original scheme was refined with respect to several points in order to reduce the complexity of the receiver. The experimental results demonstrate that the method achieves the fast cell search time of less than one second in real multipath-fading channels. The cell search is accomplished in less than approximately 700 msec at 90% of the detection probability when 4.7% and 0.5% of the total transmit power of a cell site is assigned to the common pilot channel (CPICH) and synchronization channels (SCHs), respectively, in a two-cell site environment. We also elucidate that the cell search time at the detection probability of 90% using time switched transmit diversity (TSTD) is decreased by approximately 100 msec compared to that without TSTD in low-mobility environments such as the average vehicular speed of 5 km/h with a transmit power assignment of the CPICH of 4.7%.

This paper presents the design, implementation and test results of a complete wideband CDMA modem with a modulator and a demodulator for use in next-generation cell sites. The modem is based on Japanese proposal for the next generation W-CDMA air interface. The modulator has a flexible architecture, which can transmit the data of different physical channels such as common control physical channels, and dedicated physical channels by setting the channel selection registers of the modulator. The modulator performs the transmission power control digitally according to the physical channel setting. The receiver consists of a searcher, four fingers and a combiner. The searcher supports path selected search operation considering antenna diversity which is employed to reduce the effect of excessively deep fades, and early dump operation to speed up the searching process. Since the simulation results to determine the number of finger showed that the system with more than four fingers had no essential performance improvement, demodulation performed with four-finger rake receiver. The proposed cell site modem was implemented with FPGAs and verified by the board-level experiment. Experiments have verified that the modem fully complied with the specifications.

This paper proposes a novel mobile communications system of integrating microcell and macrocell for future land mobile communications which allows the user to enjoy mobile communications services by using one terminal regardless of his terminal speed. Current and developing digital land mobile communications systems are classified into two categories according to their differences in cell size, operating environments, service requirements and terminal speeds. One is a microcell system offering cordless telephone services for the user moving at low speeds and the other is a macrocell system offering vehicle telephone services for the user moving at high speeds. In order to access these two systems, the user needs to have two different terminals and to use an appropriate one according to the operating environments, service requirements and terminal speeds. In this paper, we propose a land mobile communications system in which the user can place a call without any of the inconvenienced described above. The proposed system consists of multi layered composite microcell system with no handover areas, each layer being composed of a number of microcells. This paper presents the detailed structure of this system and evaluates the performances of the channel capacity and the frequency of handovers during a call based on computer simulation results.