This paper reports the field test performance of a base station (BS) equipped with a linear parallel multi-stage interference canceller for uplink of wideband CDMA in a suburban area. The field test was performed with one desired mobile station (MS) moving around the BS, and three fixed interfering MSs having a target SIR 11 dB higher than that of the desired MS. The field test clearly demonstrates that using interference cancellation with a proper suppression factor (or weighting factor), can reduce the transmission power of the desired MS by around 6 dB. This performance was also compared with calculated data and the interference canceller was verified to function as theoretically expected. The receive power capture ratio was estimated at around 96%. This paper therefore establishes that interference cancellation performance of CDMA systems in the field can be found by estimating the receive power capture ratio and the theoretical results of interference cancellation.

A novel carrier recovery method for preambleless demodulation is proposed. The salient feature of this demodulation method is the carrier recovery in the frequency domain for a low rate burst PSK signal by digital signal processing. Firstly, the received signal is transformed to a frequency domain signal by FFT technique. The power spectrum of the received signal is searched to find its center frequency by the 1st estimator, and the frequency offset of the received carrier and excessive noise are removed. Then, the signal is frequency-multiplied to extract the carrier component. The precise frequency and phase of the carrier component are estimated by the 2nd estimator in the frequency domaim. Filtering, clock timing recovery, and data decision are also realized by digital signal processing. The carrier recovery in the frequency domain enable to accomplish coherent demodulation at a very low received C/N irrespective of the amount of carrier frequency offset. For a 600 bit/s BPSK burst signal, less than 0.5 dB degradation of bit error rate performance is achieved at the received C/N of 2 dB with frequency offset of as large as 2 kHz. The performance of carrier recovery is also analyzed through the error probability of q-ary FSK. In the frequency domain, the power spectra can be considered as the output of narrow bandwidth filters for a q-FSK demodulator. Thus the detection performance of the carrier component can be estimated through that of q-FSK, where the q would be the number of spectrum within the modulated bandwidth. The error rate performance in carrier detection obtained by a computer simulation is congruent with that caculated for q-FSK demodulation.

An improvement is made on the previously proposed preambleless demodulation method based on FFT(Fast Fourier Transform) technique(1), in order to cope with a short-term frequency variation caused by an acceleration of a vehicle in mobile communications. The major modification to the previous method is an introduction of a novel phase synchronizer which can synchronize to a signal having a short-term frequency variation. In the mobile communications, the carrier frequency of the received carrier may vary in a short-term because of an acceleration of a vehicle, a rolling of a ship and the like. A carrier synchronization for a burst signal under such an environment would be quite involved and a countermeasure is imperative for the short-term frequency variation. In order to cope with the short-term frequency variation within a received burst, this paper proposes a novel phase synchronizer based on iterative use of a PLL. The phase synchronizer repeats a carrier pull-in process back and forth consecutively along the buffered burst signal. After a forward or backward pull-in process, a value of short-term frequency variation is calculated from a change in an internal state of the PLL. Then this value is used as a new initial state for the next pull-in process which proceeds to the reverse direction to correct the short-term frequency variation is in the burst. By executing this sequence several times, the PLL can complete carrier synchronization regardless of the amount of frequency variation in a burst. The parameter design of the improved preambleless demodulation method incorporating the newly proposed phase synchronizer is performed for the INMARSAT-C signalling channel as a good example of the burst mode channel which suffers a short-term frequency variation. The preambleless demodulation method with the designed parameters shows a good performance under an anticipated operating environment.

In this paper, we propose an interference canceller for asynchronous DS-CDMA. The principle is based on parallel cancellation using soft decision(PCSD), however, we propose to add an operation to suppress the strength of interfering signals replica on PCSD. We show here that this operation plays a very important theoretical role in PCSD, and that the performance of our proposed scheme approaches that of a perfect decorrelating detector under certain conditions. With this theoretical background in mind, we named this scheme the "Near-Decorrelating Multistage Detector"(NDMD). To demonstrate NDMD performance, we performed two kinds of computer simulations. In the first kind of simulation, simple conditions are assumed in order to evaluate basic cancelling performance. In the other kind of simulation, essential techniques for CDMA cellular systems such as FEC, transmission power control(TPC), and base band filtering were implemented while taking into account NDMD as applied to such systems. These simulations numerically demonstrate that NDMD is very efficient in cancelling out interference and that it improves asynchronous DS-CDMA performance.

Multiple wireless communication systems are often operated together in the same area in such manufacturing sites as factories where wideband noise may be emitted from industrial equipment over channels for wireless communication systems. To perform highly reliable wireless communication in such environments, radio wave environments must be monitored that are specific to each manufacturing site to find channels and timing that enable stable communication. The authors studied technologies using machine learning to efficiently analyze a large amount of monitoring data, including signals whose spectrum shape is undefined, such as electromagnetic noise over a wideband. In this paper, we generated common supervised data for multiple sensors by conjointly clustering features after normalizing those calculated in each sensor to recognize the signal reception timing from identical sources and eliminate the complexity of supervised data management. We confirmed our method's effectiveness through signal models and actual data sampled by sensors that we developed.

This paper shows accuracy of using azimuth-variable path-loss fitting in white-space (WS) boundary-estimation. We perform experiments to evaluate this method, and demonstrate that the required number of sensors can be significantly reduced. We have proposed a WS boundary-estimation framework that utilizes sensors to not only obtain spectrum sensing data, but also to estimate the boundaries of the incumbent radio system (IRS) coverage. The framework utilizes the transmitter position information and pathloss fitting. The pathloss fitting describes the IRS coverage by approximating the well-known pathloss prediction formula from the received signal power data, which is measured using sensors, and sensor-transmitter separation distances. To enhance its accuracy, we have further proposed a pathloss-fitting method that employs azimuth variables to reflect the azimuth dependency of the IRS coverage, including the antenna directivity of the transmitter and propagation characteristics.