Abstract This paper introduces an algebraic approach to generate the super‐set of perfect complementary (PC) codes suitable for new generation CDMA applications, characterized by isotropic multiple access interference (MAI) free and multipath interference (MI) free properties. The code design methodology proposed in this paper takes into account major impairing factors existing in real applications, such as MAI, MI, asynchronous transmissions, and random signs in consecutive symbols, such that a CDMA system using the generated codes can insure a truly interference‐free operation. Two important facts will be revealed by the analysis given in this paper. First, implementation of an interference‐free CDMA will never be possible unless using complementary code sets, such as the PC code sets generated in this paper. In other words, all traditional spreading codes working on an one‐code‐per‐user basis are not useful for implementation of an MAI‐free and MI‐free CDMA system. Second, to enable the interference‐free CDMA operation, the flock size of the PC codes should be made equal to the set size of the codes, implying that a PC code set can support as many users as the flock size of the code set. A systematic search has been carried out to generate the super‐set of various PC codes with the help of carefully selected seed codes belonging to distinct sub‐sets. This paper will also propose an implementation scheme based on multi‐carrier CDMA architecture and its performance is compared by simulations with the ones using traditional spreading codes. Copyright © 2006 John Wiley & Sons, Ltd.

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.

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.

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.

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.

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.

To improve demodulated signal to noise ratios for colored noise environments, a new direct-sequence spread-spectrum receiver system which has the function of shaping demodulated chip waveforms has been proposed. This function modifies the frequency characteristics of the damp-integrated output to be applied to the decision circuit. This principle is applied here to construct a whitening filter with which an optimum receiver can be implemented. A theory which provides the maximum SNR by designing the best despreading code sequence for a given spreading code sequence is derived for conditions where an additive colored noise spectrum is given. The performance is analyzed and the results of computer simulation are shown. It is consequently verified that a large SNR improvement can be achieved over conventional systems.

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.

Construction methods for digital video networks which transmit various kinds of information signals are studied. It is pointed out that, in order to construct the actual video networks, such problems appear as the introductory process or changing process of the networks. Network flexibility, transparency, and cost performance are major requirements to consider, especially for video networks. To resolve these problems, three important items, i.e., codec arrangements, selective control of analog-digital circuits, and multiplexing with group switching, are taken up and examined. Several systems comprising new proposals are analyzed and compared with one another.

Space-division digital-switching networks are proposed as switching systems of a future communication network suitable for introduction of new services. Network construction methods for video signals are considered. Hybrid-switching networks using two kinds of coding systems will be available for both simplification of equipment and high-quality transmission. Consideration is also given to future network formats, which will be gradually digitalized. Introduction of a pulse-stuffing synchronization system into switching networks is proposed here. For video signals, this system is presumed to be more economical than the mutual synchronization system. New techniques, such as junctor-stuffing synchronization and destuffing with qnantized clock rates, are discussed.

Construction of a highly accurate segment companding voice codec is described in this paper. It is shown that an ideal precompressor placed in front of the segment coder enables moderating the accuracy required by 4 times in the 13-segment coder and by 8 times in the 15-segment coder. Two precompressor circuits with a negligible accuracy degradation are proposed and their performances are thoroughly discussed. It is shown that highly accurate sequential feedback segment companding coders, such as the 8-bit 13- or 15-segment coder, can be realized easily with these precompressors.