Transmit diversity schemes are an effective capacity improvement method for down link of wideband code division multiple access (W-CDMA) systems. In this paper, we propose to use transmit antenna subset selection scheme in conjunction with closed loop transmit adaptive array (TxAA). The proposed scheme selects NS optimum antennas among NT (>NS) transmit antennas in order to maximize diversity gain from the selected antennas, and also reduces the cost of RF chains by employing two different types of RF modules for the selected and the unselected antenna group, respectively. Computer simulation results show performance improvement by the proposed scheme over the conventional TxAA when considering up link control information feedback.

This paper proposes a power control algorithm with fast convergence suited for wideband code division multiple access (WCDMA). Conventional algorithms are developed with continuous mode power control not binary mode power control. The new power control algorithm is suggested to support the binary mode power control and to offer the optimal relaxation factor for fast convergence.

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.

A constant amplitude transmission scheme for multicode wideband CDMA systems is proposed. Multicode wideband CDMA systems result in large amplitude fluctuation because the multicode signal is the sum of constituent code channel signals. This large amplitude fluctuation brings out large non-linear distortion and then, if unaccounted, can significantly degrade the bit error rate (BER) performance. Constant amplitude transmission, achieved by using a Walsh code and parity generator, is proposed to combat the large amplitude fluctuation and reduce the peak-to-average power ratio (PAPR). Unlike other constant amplitude transmission scheme, the proposed scheme does not use a redundant code channel. Computer simulation results show that the proposed scheme improves BER performance significantly and that the proposed scheme is extremely effective to the non-linear distortion of high power amplifier (HPA).

Experimental results of 1. 92 Mbps data transmission over a 20 MHz wideband DS-CDMA (W-CDMA) mobile radio link under frequency selective multipath fading are presented. 1. 92 Mbps data were transmitted using an orthogonal multicode transmission scheme. The combined use of antenna diversity reception, RAKE combining, and concatenated channel coding is applied to improve transmission performance. Laboratory and field experimental results demonstrated the possibility of 2 Mbps data transmission in a real fading environment.