Manabu Mukai

Path-search algorithm introducing path-management tables for a DS-CDMA mobile terminal

Generally, in a DS-CDMA receiver, the received multipath fading signals are resolved into each path having different time-delay with a searcher and then combined to generate original signal with a Rake combiner. One of the most important design objectives of the Rake combiner is how to search the paths accurately. Particularly from the viewpoint of power dissipation, the searcher operates during a discontinuous path-search mode only, i.e., it can turn power on/off periodically according to the time slot, to save the battery. However, as this period for performing the path search becomes longer, accuracy of the path detection deteriorates. In this paper, a path-search algorithm that improves the path-detection accuracy without shortening the path-search period is proposed. Path detection was carried out by the proposed method utilizing the delay profile detected in the path searcher, the combined signal in the Rake combiner, and also three management tables for paths-data. Computer simulation results show that the proposed approach performance is superior to that of the conventional path-search method.

DS-SS code acquisition in a rapid fading environment

In CDMA mobile communication systems, a frequency-spread pilot signal often plays an important role, e.g., for synchronization and for channel impulse response measurement; therefore it usually is given a quite large process gain. However, in a fast fading environment, the received pilot signal level may decrease making synchronization performance deteriorate substantially. In the analysis, modeling the temporal fading function as a lowpass-filtered complex Gaussian process, it is shown that the probability density function (pdf) of the despread signal level follows a Rayleigh distribution whose variance is given by a summation of the discrete-time sampled values of the impulse response of the lowpass filter. The pdf then is used to obtain the mean acquisition time. It is shown that there is no advantage in using a long code when the Doppler frequency is high. The optimum code length is determined as a function of the maximum Doppler frequency. Furthermore, a rapid PN code acquisition scheme expected to be robust under fast fading conditions is proposed. The scheme is based on partial code correlation and a majority decision rule. Partial code correlation is less influenced than full code correlation by a rapid fading and the majority decision rule reduces the misdetection and false alarm probabilities. The optimum parameter values for the proposed scheme are also determined. For a large process gain signal, the partial code length should be optimized for the maximum Doppler frequency.

A software oriented modem architecture for 3G terminal

In this paper we discuss a software oriented modem LSI. At first, the target system is focused on 3GPP DS-FDD mode and signal processing complexity of the developed software simulator is measured. According to the signal processing requirement, modem functions are partitioned into hardware and software. At the same time, a layered modem architecture which is a kind of multiprocessor architecture is proposed. This architecture can perform parallel processing by plural CPU cores, and therefore, it can lower the CPU clock and make software simple. We consider the support service switching possibility for further discussion. Moreover we have developed an evaluation board system. Referring to the implementation results, we discuss hardware complexity and the amount of memory from the viewpoint of LSI development.