TPC (transmission power control) can compensate the near-far problem and so is a key technology of DS (direct sequence) -CDMA (code divison multiple access) systems. There are two kinds of TPC. One is closed loop and the other is open loop. In practical systems, both methods are used to compensate the variation in reception signal level. However, adoption of one simple TPC scheme is preferable from the viewpoint of transceiver configuration at the BS (base station) and MSs (mobile stations). Reception signal variation in wide-band DS-CDMA systems is shallower and we have the possibility of using only open loop as the TPC method. To evaluate the TPC accuracy of open loop, it becomes important to estimate the lower bound of TPC error because TPC error directly influences user capacity. This paper evaluates the lower bound of open loop TPC error by a theoretical analysis and laboratory tests; both results agree well. It is found that as the average power difference between paths increases, the lower bound of open loop TPC error increases. Ir is also found if the number of paths increases, the lower bound of open loop TPC error decreases. If the number of paths is 10 and the power difference between the nearest paths is less than 0.2 dB, the lower bound of open loop TPC error is larger than 1 dB. When the TPC error is larger than 1 dB, the reduction in user capacity is above 30%.

In this paper, we propose a spread spectrum pulse position modulation (SS-PPM) system, and describe its basic performances. In direct sequence spread spectrum (DS/SS) systems, pseudo-noise (PN) matched filters are often used as information demodulation devices. In the PN matched filter demodulation systems, for simple structure and low cost of each receiver, it is desired that each demodulator uses only one PN matched filter, and that signals transmitted from each transmitter are binary. In such systems, on-off keying (SS-OOK), binary-phase-shift keying (SS-BPSK) and differential phase-shift keying (SS-DPSK) have been conventionally used. As one of such systems, we propose the SS-PPM system; the SS-PPM system is divided into the following two systems: 1) the SS-PPM system without sequence inversion keying (SIK) of the spreading code (Without SIK for short); 2) the SS-PPM system with SIK of the spreading code (With SIK for short). As a result, we show that under the same bandwidth and the same code length, the data transmission rate of the SS-PPM system is superior to that of the other conventional SS systems, and that under the same band-width, the same code length and the same data transmission rate, the SS-PPM system is superior to the other conventional SS systems on the following points: 1) Single channel bit error rate (BER) (BER characteristics of the SS-PPM system improve with increasing the number of chip slots of the SS-PPM system, and as the number of chip slots increases, it approaches Shannon's limit); 2) Asynchronous CDMA BER; 3) Frequency utilization efficiency. In addition, we also show that With SIK is superior to Without SIK on these points.