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 onN-shift cross-orthogonal sequence families (N-CO-SFs) . We show theoretical bounds on the size ofN-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.

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.

Although the single antenna vector OFDM (V-OFDM) proposed by Xia is robust to channel spectral nulls, it does not necessarily attain full diversity for multi-path fading channels. In this paper, we propose a novel constellation-rotated V-OFDM (CRV-OFDM) system based on modified V-OFDM, and analyze its performance over Rayleigh fading channels. In CRV-OFDM, we design rotation angles for each symbol to minimize upper bounds on bit error rate (BER) with full diversity order. Our simulation results show that, compared with V-OFDM, proposed CRV-OFDM always attains the maximum diversity order determined by the vector length M. As a result, for BER 10-4, CRV-OFDM improves the performance of V-OFDM by 2 dB for both BPSK and QPSK modulation for M = 2, and, for M = 4, the improvement is about 1.3 dB. To verify optimality of the derived angles, we also test, in therms of BER, some other angles including the angles derived from minimum product distance (MPD) criterion and compare with the theoretical union bounds and show that the BERs take the smallest values at our derived optimal angles.

In an approximately synchronous CDMA (ASCDMA) system, zero correlation zone (ZCZ) sequences are known as the sequences to eliminate co-channel and multi-path interferences. Therefore, numerous constructions of zero correlation zone (ZCZ) sequences have been introduced e.g. based on perfect sequences, m-sequences and complete complementary codes etc.. However, the previous construction method which based on complete complementary code is lacking for merit figure. In this paper, a new construction method of ZCZ sequences based on complete complementary codes is proposed. By proposed method, the ZCZ sequences with greater than 1/2 merit figure are constructable.

N-shift cross-orthogonal sequences are powerful materials for constructing complete complementary codes. In this paper, we present six theorems concerning general construction and expansion methods with the least upper bounds for N-shift cross-orthogonal sequences and complete complementary codes. Applying the theorems that about construction and expansion method of N-shift cross-orthogonal sequences, many types of N-shift cross orthogonal sequences are constructed systematically. Those include the sequence sets consisting of different lengths and include previous classes as special cases. Based on the generated N-shift cross orthogonal sequences, a complete complementary code are constructed by the theorem of construction method of complete complementary code. The last theorem which is about expansion method of complete complementary code are given for increase the number of sequence sets.

For mobile systems higher than 3G, multi-rate data service is becoming an important issue. This paper proposes a multi-rate block-spreading CDMA system as an efficient scheme which is capable of intra-cell-interference free operation and inter-cell-interference reduction by a factor of reciprocal of the spreading factor. With a use of an accurate pilot transmission scheme, it is shown that a high frequency utilization efficiency can be achieved for various mixed data rate services.

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.

Abstract In recent years, a new quasi‐synchronous CDMA (QS‐CDMA) system based on complete complementary codes with zero correlation zones (ZCZ), named ZCZ‐CDMA system, has been proposed. In a ZCZ‐CDMA system, data transmission efficiency can be greatly improved by accurately detecting the multi‐path properties of the communication channel utilizing the unique correlation features of the ZCZ sequence. As for the despreading operation and the code acquisition, the ZCZ‐CDMA system however is more complicated and difficult than the conventional DS‐CDMA systems. In this paper, we discuss the issues of the code acquisition in ZCZ‐CDMA systems, and propose an efficient code acquisition scheme, called two‐stage search (TSS) scheme. In the first stage of the TSS code acquisition scheme, a predictive code phase is coarsely searched, and then a fine search utilizing the unique features of the ZCZ‐sequences is carried out in the second stage. Simulation results show that the proposed scheme achieves better performance in terms of search time and hardware complexity than conventional code acquisition schemes. Copyright © 2003 John Wiley & Sons, Ltd.

For future information technology, the efficiency of the wireless frequency usage is very important. In the current technology, the most serious problem for wireless communication is the multipath problem. We have proposed a very efficient frequency usage system based on multipath estimation and spread time signals based on the signal design of zero correlation zone (ZCZ) signals using complete complementary codes. In this paper, the new zero cross-correlation zone (ZCCZ) signal method proposed by us is applied on the method. The system uses the pilot signal for measuring the multipath properties such as the complex time delay, and the data transmission signals. The pilot signal and the data transmission signals can be used independently in the same time and the same frequency band without crosscorrelation or interference. The system can obtain the current multipath properties and use them to detect the transmitted data by adding the multipath signal coherently.

A pilot assisted CDMA system which uses extended spreading sequences with guard sequences under a quasi-synchronous condition is capable of separating the interference components included in the input of a decorrelating receiver by solving a system of linear equations. The performance of such a system, however, depends on the property of the de-correlating matrix made of the pilots responses. The regularity of the matrix often tends to degrade due to primarily the multipaths, resulting in the solutions vulnerable to AWGN. This paper proposes an effective technique to solve this problem by introducing a dummy pilot associated with a virtual user into a group of the real users to be served. The simulation indicates a remarkable improvement in the bit-error-rate performance. In addition, it proves a RAKE like function with power-sum-characteristics.

A general construction for orthogonal sets of quadriphase sequences based on the sequence family A discovered by Sole (1989), Boztas, Hammons, and Kumar (1992) is presented. The sequence family A is equivalent to the S(0) family that belongs to a chain of sequence families S(i),i=0,1,2,..., m with each family in the chain containing the preceding family. Therefore, a number of orthogonal subsets can be generated for an arbitrary family S(m). The algorithm for an efficient implementation of the bank of correlators corresponding to any orthogonal subset of family S(m) is derived as well.

In this paper, we propose a construction of periodic complete complementary codes composed of the expanded modulatable orthogonal sequences. Because the number of the expanded modulatable orthogonal sequences of period N/sup 2/ is infinite, the number of the periodic complete complementary codes of period N/sup 2/ is also infinite. It is already proved that the proposed sequences are periodic complete complementary codes. In the meantime Suehiro (1998) has proposed a signal design method for approximately synchronized CDMA systems without co-channel interference. In this signal design method, we can assign the proposed periodic complete complementary codes as code words to each user so that the information transmission rate is increased.

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 signal demodulation system for CDMA receivers is proposed. This system has an effective function of canceling the interference noise components in the received symbol frames. For a target symbol frame to be detected, the differential frames are produced, each of which is made by subtracting one of the neighboring symbol frames from the target frame. The interference noise being left in some of the differential frames is much less than that in the target frame. By demodulating only such noise cancelled differential frames that have been estimated with effective analyzing sequences, the information conveyed on the target frame with a heavy interference can be detected. The simulation indicates powerful canceling performance for all the possible interference disturbance is achieved.

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 signal design method for the uplink in cellular mobile CDMA systems is simulated. The simulated method uses binary complete complementary code as comb-spectrum pseudo-periodic sequences. The designed signals are without co-channel interference nor influence of multipath fading, when the system is synchronized approximately. Any approximation of synchronization is acceptable by arranging the signal design. The results of simulation shows us the usefulness of this signal design without co-channel interference for an approximately synchronized uplink in cellular CDMA systems.

A new sequence generation method and a method for reconstructing information symbols for a modulated orthogonal sequence are suggested: the sequence is generated by only integer sums and modular techniques. The autocorrelation and cross-correlation characteristics of the sequence are investigated via a new procedure. A modified sequence also having the orthogonality and satisfying the mathematical lower bound of the cross-correlation is proposed, and the symbol error probability of the sequence is investigated.

Suehiro (1985) has proposed a quadriphase signal design method for the uplink of the cellular CDMA mobile communication systems. The designed signals work without co-channel interference when the systems are synchronized approximately. The designed signals are free from the influence of multipath signals within some delay. The filters for the designed signals can be realized as SAW devices. We assign plural quadriphase signals as M-ary signals for each user so that the information-transmission rate is increased. The property of without co-channel interference remains the same, but the multipath property becomes a little bit worse. The filters for M-ary signals can also be realized as SAW devices.

Hadamard matrices are often used for some applications, such as error-correcting codes and spread sequences. This article gives the construction of complex Hadamard matrices of order p/sup n/, where p is prime and n is even. The complex Hadamard matrices include bi-phase Hadamard matrices whose elements take {-1, +1}, and four-phase Hadamard matrices whose elements take {/spl plusmn/1, /spl plusmn/j} with j=/spl radic/(-1).

In contrast with direct sequence-spread spectrum, an M-ary system characterized by frequency shift keying-spread spectrum (FSK-SS) is proposed. FSK-SS is comprised of two modulation stages; one selecting a frequency to represent the multiple levels, and the other multiplying a code sequence with the frequency. The shift frequencies are selected in a range less than the chip frequency, while satisfying an orthogonal relationship. Practical design examples show that FSK/BPSK-SS is able to achieve 1.4/spl sim/2.7 times larger capacity than that of conventional DS-SS. The interference tolerant capability is also discussed.

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 set of N-1 orthogonal sequences of period N/sup 2/ is proposed, where N is a natural number. Each orthogonal sequence proposed can be modulated by N complex numbers of absolute value 1, so the modulated sequence is also orthogonal. When N is an odd prime number, the absolute value of the cross-correlation function between any two of the N-1 orthogonal sequences is constant and satisfies the mathematical lower bound. This property of the cross-correlation function is not changed when each of the two orthogonal sequences is modulated by N complex numbers of absolute value 1. Two spread-spectrum multiple-access (SSMA) systems using these sequences are proposed. One system is an asynchronous SSMA system, using the proposed sequences unmodulated. The cochannel interference peak between any two channels in this system realizes the mathematical lower bound for an asynchronous SSMA system using a set of orthogonal sequences. The other system is a synchronous SSMA system without cochannel interference which uses the modulated form of the proposed sequences.>

N-shift cross-orthogonal sequences and a complete complementary code derived from them are defined and discussed. A general method for generating this code is also discussed. A synchronous multiple-user spread-spectrum multiple system is proposed that uses N-shift cross-orthogonal sequences.>

A new matrix factorization is proposed for DCT-IV, which is the basis of fast algorithms for many sinusoidal transforms. A new fast algorithm for complex-data DFT based on the new factorization requires the same number of multiplications and far fewer additions than the Preuss algorithm. A new fast algorithm for real-data DFT based on a new algorithm for the discrete Hartley transform is also proposed.