This paper reviews in Spread Spectrum Communications in Japan from its birth to the present. The period is divided into three; Birth, Race and Stable Progress Period. A technical overview traces development up to the entrance to the stable progress period, and available references are also given.

Spread spectrum theory and techniques have been studied and developed for commercial applications in Japan, rather than for military use as in USA. Main purpose of the study and development is not to prevent jamming or intentional interference, but to carry out more efficient utilization of available frequency spectra. This paper introduces some spread spectrum theory and techniques which have been studied for the past several years in Japan for improving capacity of transmission. Co-channel interference in code-division multiple access (CDMA) based on spread spectrum technique is the most dominant factor in the limitation of capacity. Various classes of pseudo-noise (PN) sequences or spreading sequences have been proposed in order to reduce co-channel interference or achieve fast acquisition and high security. On the other hand, co-channel interference can be eliminated by digital signal processing approaches, such as adaptive digital filtering and beam-forming. This paper gives an overview of these PN sequences and interference cancellation techniques which appear to be most promising for use in commercial spread spectrum systems.

The recent progress in communication devices has reduced the cost of spread spectrum systems that have been mainly used in the military field, enabling the possibility of using spread spectrum systems for nonmilitary use. Nonmilitary communication networks are classified into two categories: public communication networks and consumer communication networks. At the present, the public communication network share is much larger than that of the consumer communication networks. Both of them will increase; however, the consumer communication network share will be comparable to the public one. The progress of consumer communications is due to inexpensiveness (without charge), user privacy, free design from regulations and advantages of local and small zone communications. To overcome fading, power restrictions, interference and interception is very important for its progress, One of the key technologies of consumer communications is the spread spectrum. Consumer communication networks are characterized by user possession of the network itself in addition to the possession of personal terminals. From the viewpoint of analogy between communication networks and transportation networks, "from public to individual" seems to be today's trend. Several spread spectrum applications for consumer communications in Japan have been introduced as follows: a home security system using power line communication as a wire spread spectrum communication system; a data carrier, a radio remote control, low-power radio systems and a clock rate modulation system as radio spread spectrum communication systems. In addition SAW device applications and digital signal processing applications are introduced.

This paper shows a heterodyne-typed autocorrelator for direct-sequence spread-spectrum (SS-DS) communications, without using local despreading PN-code and active synchronization circuit. In our proposed autocorrelator, the transmitting SS-DS signal is frequency-converted on every second data by the unique frequency assigned to each user in advance, which is separated not so as to interfere with each other. The received signal is autocorrelated with the delay version and becomes the narrowband signal with the unique centerfrequency. Therefore, our proposed autocorrelator can provide the anti-narrowband interference and random access capability, unlike the conventional autocorrelators.

This paper shows a Direct-Sequence Spread-Spectrum (SS-DS) demodulator using block signal processing. One of the difficulties in applying SS-DS techniques to the packet radio network is that each packet needs a long initial-acquisition time for despreading. The acquisition time causes the large degradation of the data transmission efficiency. Our proposed SS-DS demodulator uses the block signal processing, unlike the conventional SS-DS demodulators using real time signal processing. Received signal demodulated quasi-coherently is once stored in memory, and after extracting matched-pulse timing and estimating carrier offset, the signal is demodulated. Incoming data, therefore, are all demodulated without being lost by the initial-acquisition time, and our proposed SS-DS demodulator can provide the higher data transmission efficiency.

This paper considers the problem of realizing excellent performance of rapid acquisition in direct-sequence spread-spectrum communication systems. In this paper, we consider a scheme of digital matched filter (DMF) combined with soft decision function, which has potential capability of improving the characteristics of hard decision function by about 2dB in the environment of additive white Gaussian noise (AWGN) channel and is capable of handling long PN codes by means of simple LSIs. Analysis is made on the performance in the environment of AWGN channel and results of experiments are provided. It is confirmed that the scheme provides attractive means for acquisition of direct-sequence spread-spectrum signals. Namely, soft decision DMF achieves rapid acquisition; the dwell time for soft decision DMF in the process of acquisition is half of that for hard decision DMF. In addition, it is shown that the correlator output signal produced by the acquisition circuit can also be used for the purpose of demodulation; excellent performance of bit error probability is experimentally observed.

In a spread spectrum multiple access system, a tracking system in the receiver causes a tracking error due to the other users. In this paper, we discuss the effect of the interference on a code tracking error in a synchronous SSMA, suggest a new tracking system which can eliminate the steady state error due to the interference and analyze the tracking performance of the newly proposed system.

The performance of a digital matched filter receiver with multi-bit quantized correlators for Direct Sequence Spread Spectrum (DSSS) mobile satellite applications is evaluated with experiments. A Coherent Matched Filter (CMF) technique is used to accomplish fast code acquisition, automatic frequency control and coherent detection of data with a single matched filter circuit to satisfy the requirements for the mobile satellite applications. Loop-back test and field test results in suburban areas with the ETS-V satellite are presented, in which the use of multi-bit quantized correlators improve the initial acquisition and the bit error rate performances. The dynamic performance of the CMF receiver is confirmed to be satisfactory for the mobile satellite fading channels.

In this paper, we discuss autocorrelation properties of a truncated m-sequence which is used in communication and ranging systems based on a Direct-Sequence Spread Spectrum technique such as Tracking and Data Relay Satellite System (TDRSS) of NASA. A truncated m-sequence is obtained by removing a short part or sequential chips from an original m-sequence. We derive methods to calculate periodic and partial autocorrelation functions of a truncated m-sequence with small complexity. Some constraints for truncated m-sequences which originates in system regulation of TDRSS and its related systems are described. In such systems, partial correlation of a truncated m-sequence is important to achieve fast and stable acquisition. We propose some criteria to select a proper set of truncated m-sequence, and derive the set by using the method to simply calculate correlation.

This paper shows the analysis of a multihop Fast Frequency Hopping/Spread Spectrum Multiple Access (FFH/SSMA) System in a selective fading channel, in which we consider the frequency correlation characteristics between the signals on the adjacent hopping frequencies of the desired and intersymbol interference and we also take into account of the effects of interference having close hopping frequencies. A multihop-FFH scheme in which several hopping frequencies are used in order to transmit one data symbol, can be classified into a serialhop-FFH and a parallelhop-FFH scheme. More precise bit error probabilities of the multihop-FFH/SSMA systems are theoretically derived with reducing approximation than the bit error probability corresponding to a conventional analysis using the hit probability. As a result, it is classified that the parallelhop-FFH/SSMA system can achieve the better performance of bit error probability than the singlehop and the serialhop-FFH/SSMA systems in a selective fading channel, while the serialhop-FFH/SSMA system can considerably improve the bit error probability over the singlehop and the parallelhop-FFH/SSMA system in an AWGN channel. The performances depend on the number of simultaneously accessing users. Moreover, the computer simulations confirm the theoretical results.

This paper proposes and analyzes experimentally an SSMA (Spread Spectrum Multiple Access) signal transmission over a high speed QPSK (Quadrature Phase Shift Keying) modulated signal to achieve higher transmission efficiency per transponder and to facilitate a lower power transmitter for SSMA signal transmission. The employment of high-coding-gain forward error correction for SSMA-QPSK signals makes it possible to transmit SSMA-QPSK signals over a non-linearly amplified QPSK signal transmission channel. Experimental results show that under the condition of a 20dB less transmission power assignment to SSMA-QPSK signals than QPSK signals, the QPSK signals achieve only 0.5dB E_b/N_o degradation (at P_e=110^-4) by employing coding-rate seven-eighth FEC, and the SSMA-QPSK signals achieve about 7dB E_b/N_o degradation (at P_e=110^-4) by employing coding-rate one-half FEC. The satellite link budget shows that even if the SSMA-QPSK signal transmission generates about 7dB E_b/N_o degradation, it requires 20 dB less transmission power and it still has an extra margin of 8.5dB compared with the high speed QPSK signals (total relative gain of 28.5dB). Thus, the proposed system makes it possible to realize one-way digital video signal transmission in QPSK mode and both-way digital voice signal transmission over one transponder for business video communication systems.