Search

In this paper, M-ary/spread spectrum multiple access communication systems (SSMA) are studied to improve spectral efficiency. A novel method of calculation of the spectral efficiency for several tip waveforms and bit error rate is shown. For M-ary/ SSMA using orthogonal codes, the spectral efficiency can be improved considerably, however, the code length is becoming too long to achieve satisfactory spectral efficiency. To shorten the code length for the same spectral efficiency, M-ary/SSMA is adopted using concatenated Reed-Solomon codes, and the effectiveness is shown. [ABSTRACT FROM AUTHOR]

This paper proposes a novel direct sequence/spread spectrum communication system for use in power line data transmission where the transmission characteristic varies largely and rapidly. In the proposed system, two similar PN sequences are used, one of which is loaded with data and the other is used as a reference PN. Waveform distortion during transmission can be cancelled out by an appropriate process utilizing two PN sequences. Data can be recovered as the sign of correlations between two PN sequences at the receiver. Results of computer simulation show considerable improvement in the data error rote over the conventional DS/SS system. [ABSTRACT FROM AUTHOR]

This paper reviews recent worldwide activities concerning research and development for spread spectrum communication technologies. Included are various novel proposals, remits of analysis, and experimental results concerning spreading code, synchronization, device, system construction, and applications to consumer and mobile communications. For the spreading code, however, two invited papers are presented in this special issue and hence only a brief explanation is made hole. Instead, considerable space is devoted to the recent progress toward development of CDMA public land mobile telecommunication systems in the United States. [ABSTRACT FROM AUTHOR]

Rapid acquisition is an important problem in the direct sequence spread spectrum communication system, especially when code length is long. This paper proposes a novel code construction method of making rapid acquisition, in which majority logic combination sequences constructed from M-sequences mutually of prime length (hereafter M-MAJ sequences) are used. By lacking cross-correlation of incoming M-MAJ sequence with component M-sequences at the receiver, acquisition time can be reduced considerably. Calculated results of the average acquisitions time and comparisons with conventional code construction methods (JPL sequence, concatenated sequence) are shown. [ABSTRACT FROM AUTHOR]

This paper proposes differential parallel combinatory spread spectrum (DPC/SS) communication systems; one of the parallel combinatory spread spectrum (SS) communication systems the authors have been studying so far. The parallel combinatory SS system is a spectral efficient SS system in which the system transforms several bits of data into a combination of pseudonoise (PN) sequence with modulation of positive and negative signs and transmits them. The proposed DPC/SS system applies differential encoding to the positive or negative sign modulation of the PN sequences, and then they are transmitted. In the receiver, the combination of a transmitted sequence set is estimated by noncoherent detection and the coded sign is demodulated by differential detection. Thus, the receiver does not need to regenerate the phase of the carrier frequency. The proposed systems will be applicable to a mobile cellular system in which a large phase variation interferes with the communications. This paper evaluates the error performances of the DPC/SS systems in additive white Gaussian noise (AWGN) channels and frequency-nonselective, slowly Rayleigh fading channels. It also evaluates the effect of diversity in the Rayleigh fading channels. In the AWGN channel, the DPC/SS system is superior by 1 dB to the differential phase-shift keying (DPSK) system and to the BPSK system in terms of required signal-to-noise ratio at 10 bit error rate (BER) at the same spectral efficiency. In the Rayleigh fading channel, diversity reception in the DPC/SS system gains more improvement in the BER performance, as the number of branches increases, than that obtained in a direct-sequence spread spectrum system with DPSK. [ABSTRACT FROM AUTHOR]

This paper presents direct sequence/spread spectrum (DS/SS) systems using chip interleaving and its burst noise suppression effect for data transmissions on power lines. First, to protect from the impulsive or periodic burst noise, a convolutional chip interleaving method for randomizing the time intervals of interleaved chips and synchronizing with PN sequence is applied. Second, to obtain the randomness of chip intervals, multielement M-sequences and Tausworthe-Lewis-Payne (TLP) sequences are adopted, and several properties (generation frequency of each element, autocorrelation function, etc.) are shown. Finally, as an application, experimental results for high-speed (8.2 kbit/s) data transmissions on power lines are shown. [ABSTRACT FROM AUTHOR]

This paper introduces a method for suppression of multiple access interference in the direct sequence/spread spectrum multiple access system (DS/SSMA). It is especially effective for the near-far problem. When an integration period of cross correlation is divided into subintervals in the DS/SSMA system, the partial cross correlation values in the presence of noise and interference vary considerably from subinterval to subinterval. In the proposed system, allocating small weight coefficients to subintervals with large cross-correlation values and large weight coefficients to subintervals with small cross-correlation values results in considerable, improvement in signal-to-noise ratio. Using this method, multiple access interference can be suppressed without knowing the PN sequences of other users. The principle of this system, a novel algorithm using partial correlation weight coefficient control techniques, will be illustrated with the help of computer simulations. [ABSTRACT FROM AUTHOR]

This paper discusses the application of the error control techniques for parallel combinatory spread spectrum (PC-SS) communication system proposed previously by the authors. This paper considers the case where k-bit information is transmitted in the spreading sequences and considers the following two coding methods as suited to PC-SS systems: 1) to use 2k-ary Reed-Solomon code; and 2) to use the constant-weight code by Chung et al. in the transmitter, converting the data into the combinatory spreading sequences, and to suppress the error in the receiver by taking the double correlation. The bit-error rate performance is examined for the two methods and the effectiveness is discussed. It is shown as a result that both methods are useful in improving the bit-error rate of the PC-SS system. In the latter method, the number of spreading sequences needed per user is reduced to approximately one-fourth compared to the conventional PC-SS system with nearly the same bit-error rate. [ABSTRACT FROM AUTHOR]