Naoki Suehiro

A signal design without co-channel interference for approximately synchronized CDMA systems

A signal design is proposed for a CDMA system that is approximately synchronized. The signals are called pseudoperiodic sequences. The set of pseudoperiodic polyphase sequences are introduced from a set of periodic polyphase sequences with ideal autocorrelation for small shifts and zero cross correlation for all shifts. The system works without cochannel interference, even when the signals are modulated by data. >

A new class of zero-correlation zone sequences

In this correspondence, two new methods for constructing sets of zero-correlation zone (ZCZ) sequences are proposed. These methods are based on perfect sequences and unitary matrices. Compared with previous methods, the proposed methods can generate sets of nonbinary ZCZ sequences having a longer zero-correlation zone. The sequences obtained by these methods are suitable for approximately synchronized code-division multiple-access (AS-CDMA) systems.

Very efficient frequency usage system using convolutional spread time signals based on complete complementary code

We have proposed a method for increasing the information transmission rate and the frequency usage rate based on a new method for estimating multipath channels and spread time signals convolution. We used a pilot signal and data-transmission signals in the same frequency and in the same time. For this purpose, we used the complete complementary code on approximately synchronized systems. The information transmission rate came to (1.3/k) chip/bit, where k was the QAM factor. In this paper, a new usage method for a complementary code is proposed. The new method is far simpler than the old method. By applying the proposed usage method for a complete complementary code on the above high rate information transmission method, the high rate information transmission can be realized easier.

A New Class of Polyphase Sequence Sets with Optimal Zero-Correlation Zones

This paper proposes a new class of polyphase ZCZ (zero-correlation zone) sequence sets which satisfy a mathematical upper bound. The proposed ZCZ sequence sets are obtained from DFT matrices and unitary matrices. In addition, this paper discusses the cross-correlation property between different ZCZ sequence sets which belong to the proposed class.

Multiple-access interference reduction for QS-CDMA systems with a novel class of polyphase sequences

In this paper, a new class of polyphase sequences for CDMA systems and its generation method are suggested, and the correlation properties of the sequence are investigated. The performance of the sequence in quasi-synchronous CDMA (QS-CDMA) systems is investigated under a frequency-selective, time-nonselective, slow Nakagami fading channel with additive white Gaussian noise (AWGN). It is shown that the performance of the QS-CDMA systems using the suggested sequence is independent of the number of users and is much better than that using the PN sequence.

A Systematic Framework for the Construction of Optimal Complete Complementary Codes

The complete complementary code (CCC) that was proposed by Suehiro and Hatori is a sequence family, that is a set of sequence sets, with ideal correlation sums. Numerous studies in the literature show its applications to direct-spread code-division multiple access (DS-CDMA) systems for interchannel interference (ICI)-free communication with improved spectral efficiency. In this paper, we propose a systematic framework for the construction of CCCs based on N -shift cross-orthogonal sequence families (N-CO-SFs) . We show theoretical bounds on the size of N-CO-SFs and CCCs and give a set of four algorithms for their generation and extension. The algorithms are optimal in the sense that the size of the resultant sequence families achieves theoretical bounds and, with the algorithms, we can construct an optimal CCC consisting of sequences whose lengths are not only almost arbitrary but even variable between sequence sets. We also discuss the family size, alphabet size, and length of constructible CCCs based on the proposed algorithms.

Constellation-rotated vector OFDM and its performance analysis over rayleigh fading channels

Although the single antenna vector OFDM (VOFDM) proposed by Xia shows performance robust to channel spectral nulls, it does not necessarily attain full diversity for multi-path fading channels. It is known that the degradation in diversity order is sometimes rescued by the rotation of constellation. A simple application of constellation rotation to the V-OFDM system does not, however, improve its performance. In this paper, we discuss the sub-channel spectral structure of the V-OFDM signal and give upper bounds on its pair-wise error probability over multi-path Rayleigh fading channels and propose a novel constellation-rotated V-OFDM (CRV-OFDM) with improved diversity. To this end, we design rotation angles for sub-channel symbols to minimize upper bounds on BER. Simulation results show that the proposed CRV-OFDM attains diversity order min{M,P} for the vector length M and the number of paths P. As the results, for BER 10¿4, CRV-OFDM improves the performance of V-OFDM by 2 dB for both BPSK and QPSK modulation when M is 2, and, for M = 4, the improvement factor is about 1.3 dB. We also discuss the effects of M on the transmitter and receiver complexities and on the peak-to-averate power ratio. Finally, we compare several methods for rotational angle determination.

Very efficient wireless fyequency usage based on pseudo-coherent addition of multipath signals using kronecker product with rows of dft matrix

The authors have been proposed a method of very efficient wireless frequency usage. It is based on the measurement of multipath property for each timeslot, and the coherent addition of multipath signals. The method has been implemented an LSI chip. This paper applies a new signal design method on the coherent addition of multipath signals.

Binary signal design for approximately synchronized CDMA systems without detection sidelobe nor co-channel interference using auto- and cross-complementary codes

For mobile cellular CDMA systems, co-channel interference in the uplink is the most serious problem, because the power control or the interference cancellation required increase the systems cost. From this view point, Suehiro (1993, 1994) proposed a method for signal design by applying the pseudo-periodic sequences concept on the periodic sequence set without cross-correlation. Using this method, we can design CDMA signals without co-channel interference when the system is approximately synchronized. Approximate synchronization is not difficult for uplink in cellular mobile systems, so this signal design method is useful. Another problem of multipath fading is also solved by the proposed method, because the filter output has no sidelobe in the small shift terms. A signal design method is proposed by using a complete complementary code. Using the proposed method, we can design binary CDMA signals for far wider shifts of without sidelobe nor co-channel interference. In fact, the length of shifts without the influence of multipath is 2/sup n/ for any n.

Comparison of the Two Signal Design Methods in the CDMA Systems Using Complete Complementary Codes

Some signal design methods for the approximately synchronized CDMA systems based on complete complementary codes have been proposed. It has been shown that estimating the multipath channels and applying the convolution of the spread-time signals can increase both the information transmission rate and the frequency usage rate. It is also pointed out that the dynamic range of the signals needs to be constrained before transmission in these methods because the convoluted information signals often have a very large value at each chip. This is a very serious problem in the actual communication systems. In this paper we consider two of those signal design methods using complete complementary codes. The efficiency of the communication systems using these two methods are analyzed and compared through some numerical simulations. The influences of the signals with constrained dynamic range are also included.