One of the problems in multi-carrier modulation is nonlinear distortion due to nonlinearity of channels, such as in HPA (High Power Amplifier). This problem is also true of multi-carrier SS (Spread Spectrum) systems. In this paper, an inter-modulation compensation scheme for multi-carrier M-ary/SS system is proposed. We propose two methods to control the sequences transmitted in parallel to avoid the occurrence of severe inter-modulation distortion. One is the "package sequence selection" method, which requires slight redundancy. The other method is based on error correction code, which requires no additional frequency or power except the redundancy for error correction. We confirm the validity of our proposed scheme by computer simulation, and the BER (Bit Error Rate) performance in an AWGN (Additive White Gaussian Noise) channel is presented.

Optical Code Division Multiple Access (OCD- MA) has been emerging as an attractive scheme in fiber optic communication systems as well as in space communication systems in past few years. In OCDMA systems, M-ary Pulse Position Modulation (PPM), has been regarded as an efficient signalling format which has the capability to reduce the channel interference caused by the other users and also to increase the number of simultaneous users. We apply error control coding to improve the system performance of pulse position modulated OCDMA (PPM/OCDMA) systems and this paper investigates the performance of M-ary PPM/OCDMA systems with M-ary convolutional coding. Dual-k code is used as the M-ary convolutional code and Optical Orthogonal Codes with the maximum cross correlation value of 1 and 2 are employed as the signature sequences. We derive an expression for the bit error probability of the new system and show that combining M-ary convolutional coding and M-ary PPM results in an improved error performance. Also it is shown that the number of simultaneous users can be significantly increased with the proposed system compared to the uncoded PPM/OCDMA system with the same bit error probability and with the same information bit rate. We also analyze the system with binary convolutional coding and a comparison with the proposed system is given.

In this letter, we propose the channel estimation technique in the uplink of a DS/CDMA system with M-ary orthogonal signaling over multipath fading channels. The channel estimation is carried out using the maximum correlator output of RAKE receiver. With the estimated channel parameters, the RAKE receiver can coherently combines the received multipath signals, resulting in a significant performace improvement. The hardware complexity of the proposed detection technique is slightly increased when compared to that of noncoherent detection.

Adaptive maximum likelihood differential detection implemented by a reduced state-transition Viterbi algorithm (called adaptive 3-state RSTVDD) is presented for adaptive reception of M-ary differential phase shift keying (DPSK) signals transmitted over additive white Gaussian noise (AWGN) and frequency-nonselective Rayleigh fading channels. The adaptive 3-state RSTVDD comprises 1DD, a differential encoder, and reverse modulator, followed by reduced-state (3-state) Viterbi DD (RSVDD) with adaptive phase reference estimation. The adaptive 3-state RSVDD detector estimates the sequence of phase errors of the 1DD output. The phase reference estimator is an adaptive least mean square (LMS) filter with a step-size that adapts to changing channel conditions. The final detected symbol sequence is the modulo-2π sum of the 1DD output phase sequence and the detected phase error sequence. The bit error rate (BER) performance of M-ary DPSK, M=4, 8, and 16, in the AWGN and Rayleigh fading channels is evaluated by computer simulation to show that adaptive 3-state RSTVDD can achieve almost the same BER performance as the previously developed adaptive M-state RSVDD. Since the number of trellis states is reduced to three irrespective of M, the adaptive 3-state RSTVDD has lower computation complexity and it is particularly useful for M-ary DPSK with M8.

A Pragmatic Trellis Coded MPSK on a Rayleigh fading channel is analyzed. This scheme allows bandwidth expansion ratio to be varied aiming at an optimization between complexity of the system design and improvement of coding gain. In order to vary the bandwidth expansion ratio, a punctured convolutional code is used. The performance of the proposed TC-2mPSK on a Rayleigh fading channel is theoretically analyzed. In the test examples, the BER performances of TC-QPSK and TC-8PSK are evaluated by theoretical analyses and computer simulations at the encoder parameters of K3 and r3/4. The results show that the proposed scheme can attain better performance not only over the uncoded scheme but over the conventional Pragmatic TCM.

A simple near-orthogonal code is used as frequency-hopping patterns for the frequency-hopped multiple access systems. Extended RS code is used as channel coding to deplete the effects of hits from simultaneous users. Packet error probability and channel throughput for the system utilizing the near-orthogonal code are evaluated and compared to the corresponding values obtained from the system utilizing random patterns. Results show that the former can provide substantial improvement over the latter. In our illustrated examples, we also show that under the constraint of packet error probability PE 10-2, the maximum achievable number of users with most (n,k) RS codes of interest is less than the number of distinct codewords in the near-orthogonal code. Thus, the number of codewords of the near-orthogonal code is large enough to support the practical application.

M-ary/SS systems are compared with DS/SS systems applied the multicarrier systems and the RAKE receiver in the presence of AWGN, frequency selective Rayleigh fading and partial-band interference. In particular, the BER performance and SSMA capability are evaluated. Consequently, the M-ary/SSMA system using the multicarrier techniques is subject to the M-ary/SSMA system with the RAKE receiver in the presence of partial-band interference. The BER performance of the M-ary/SSMA system is better than that of the DS/SSMA system when the number of users is smaller than 20. And the spectral efficiency of the multicarrier M-ary/SSMA system is best in the four systems when JSR=20 [dB] and BER=10-3.

This paper presents a new approach to computing symbol error probability of fast frequency-hopped M-ary frequency shift keying (FFH/MFSK) systems with majority vote under multitone jamming. For illustrating the applications, we first consider the case in which the source data rate is fixed and the hopping rate is allowed to vary. In this case, the optimum orders of diversity for several values of M are examined. Results show that M=4 outperforms other values. Then, we treat another case in which the hopping rate is fixed and the data rate is adjusted so as to obtain maximum throughput under a given constraint of error probability. In addition to the case of diversity alone, we also evaluate the performances of the fixed hopping rate case with channel coding using convolutional code and BCH code.

In this paper, to obtain higher spectral efficiency than a conventional M-ary/Spread Spectrum (SS) communication system using an orthogonal code, we propose Double M-ary/SS communication systems in which transmitting sequences are produced by multiplying two sequences obtained from different M-ary/SS systems. First, we estimate the system performance of a Double M-ary/SS in which transmitting sequences are composed of two kinds of sequences which have the same chip duration and the same sequence length in AWGN environment by theoretical analysis and computer simulations using random sequences. And we show that the bit error rate (BER) of the system can be improved, compared to that of the conventional M-ary/SS. Next, we propose two concrete examples of the Double M-ary/SS systems. We investigate the performance of these systems in AWGN environment by computer simulations, and show that the BER and spectral efficiency can be improved by the two systems compared to those of the conventional M-ary/SS. Further, we consider a modified method of the demodulation for one of the examples of Double M-ary/SS systems, and show that we can reduce quantity of calculations by the method.

This paper presents the performance of FH/MFSK systems, which exploit silent gaps in speech to accommodate more users, over Rayleigh fading channels. Two kinds of receivers are considered: one uses a threshold on the received signal strength to declare whether the signals were present or not, and the other is assumed to have perfect transmitter-state information obtained from using additional bandwidth. Results show that, if the codeword dropping and codeword error are assumed to be equally costly, the former can achieve slightly better performance than the latter in the decoding error probability. This finding suggests that, for the system to exploit silent gaps in speech, it is advantageous for the receiver to use a threshold to declare whether signals were present or not instead of relying on the transmitter-state information.

It is well known that M-ary/spread spectrum (M-ary/SS) system is superior to direct-sequence spread spectrum system under AWGN, and can achieve high spectral efficiency. On the other hand, however, the main drawback of this system is that the synchronization acquisition is difficult. In this paper, we propose a new synchronization acquisition method of M-ary/SS system. This method acquires the code synchronization by introducing a symmetrical property in spreading sequences, and detecting this property with the differential decoding technique. As spreading sequences, a set of orthogonal sequences and a set of non-orthogonal sequences are considered. The strong features of proposed systems are that the systems can acquire the code synchronization in carrier band and can reduce the complexity of calculation greatly. Among the comparison results of the systems with newly proposed orthogonal and some specific non-orthogonal spreading sequences, it is especially noted that the latter can reduce the mean acquisition time and calculation complexity much greater than the former.

In this paper, a simple frame synchronization system for M-ary Spread Spectrum (M-ary/SS) communication system is analyzed. In particular, synchronization performance, bit error rate performance, and Spread Spectrum Multiple Access (SSMA) performance are analyzed. The frame synchronization system uses the racing counters. The transmitted signal contains framing chips that are added to spreading sequences. In the receiver, the framing chips are detected from several frames. The authors have proposed the simple frame synchronization system that detects framing chips from consecutive 2 frames. In this system, as the number of framing chips increases, synchronization performance improves and bit error rate performance degrades. In this paper a frame synchronization system that improves bit error rate performance is treated and analyzed. As the rusult, when the number of reference frames is 3, the bit error rate is much improved than the conventional system.

In this paper, a simple frame synchronization method for the SS-CSC syytem is proposed, and the synchronization performance is analyzed. There have been growing interests in the M-ary/SS communication system and the bi-orthogonal modulation system because these systems can achieve the high frequency utilization efficiency. However, the frame synchronization is difficult. We proposed the SS-CSC system, and evaluated the bit error rate (BER) performance of the SS-CSC system under the completed synchronization. The BER performance of the SS-CSC system is much the same as that of the bi-orthogonal modulation system. In this paper, a frame synchronization method using the differential detector and racing counters is proposed. In particular, the lose lock time, the recovery time and the BER performance considering the synchronizing performance are analyzed. In consequence, the BER performance considering the synchronization performance can approach the lower bound of the SS-CSC system by tuning the number of the stages in racing counters.

In this paper, we examine a new initial symbol acquisition method for M-ary spread-spectrum (M-ary/SS) signals that are affected by large carrier frequency offset. By the effect of the carrier frequency offset, preamble signal energy is dispersed to the undersired outputs. The proposed method is based on the collection of such dispersed signal energies by using reference patterns. The reference patterns are constructed by using the characteristic of Hadamard code sequences. The effectiveness of the proposed method is evaluated in terms of mean acquisition time.

Approximate maximum likelihood (ML) detection implemented by a reduced state Viterbi algorithm (VA), called the reduced state Viterbi coherent detection (RSVCD) algorithm in this paper, is described for the reception of uncoded M-ary PSK (MPSK) signals transmitted over additive white Gaussian noise (AWGN) channels. An M-state trellis, each state representing one of M signal constellation points, is used. The RSVCD algorithm performs parallel channel estimation based on the per-survivor processing principle (PSPP). Simple decision feedback CD (DFCD) is deduced as a special case of RSVCD. Unified BER expressions are derived for RSVCD, DFCD, and approximate ML detection implemented as an ML-state Viterbi algorithm (referred to as VACD) [6] as well as ideal CD and differential detection (DD). Computer simulation results are also presented and compared with theoretical results.

We have investigated the BER performance of TC 8PSK with 2 branch SC and MRC diversities on spatially correlated Rayleigh fading channel. The upper bounds using the transfer function bounding technique are derived several numerical results are shown. Although the correlation between branches causes signal-to-noise (SNR) loss (relative to uncorrelated fading case) for SC and MRC diversities, the diversity can lead to achieve the diversity gain compared to the system without diversity. It is found that the diversity gain of 4-state TC 8PSK is larger than 8-state TC 8PSK. It is also shown that the BER performance of TC 8PSK is decreased as the antenna separation is decreased.

In this paper, the bit error rate (BER) performance of the Spread Spectrum communication system with Constrained Spreading Codes (SS-CSC) is analyzed. The BER of the SS-CSC system is the same as that of the Bi-orthogonal system. Moreover, the frequency utilization efficiency of the SS-CSC system is better than that of the Bi-orthogonal system when K 10 and N = 3.

In this paper, the bit error rate (BER) considering tracking performance is evaluated, by theoretical analysis and computer simulation, for a bi-orthogonal system using a synchronizing pseudo-noise (PN) sequence and co-channel interference cancellers. A system that improves on Tachikawa's system is proposed. It is found that the optimum ratio of the information signal energy to the synchronizing signal energy varies with Eb/No, and the canceller is better for small L than for large L (L = length of the sequence). Moreover, it is found that the BER considering synchronization performance improvse as the equivalent noise bandwidth Bn decreases.

In this paper, a simple frame synchronization system for M-ary/SS communication systems is proposed, and synchronization performance and the resulting bit error rate performance are analyzed. The frame synchronization system uses racing counters and framing chips which are added to spreading sequences. M-ary/SS communication systems can improve bit error rate performance under the condition in which there is an additive white gaussian noise. Synchronization of M-ary/SS communication systems is difficult, however, because M-ary/SS communication systems have several spreading sequences. The authors proposed the simple frame synchronization system which uses only one chip in the spreading sequence as a framing signal. This system needs a long time for initial acquisition as the frame length is longer. The proposed system in this paper can make initial acquisition time short by increasing the number of framing chips. The proposed system corresponds to the conventional system when the number of framing chips is l. As the result, it is shown that several framing chips contribute to decrease the initial acquisition time. Moreover, the frame synchronization system can be applied to asynchronous M-ary/SSMA system when different framing chip pattern is assigned to each user.

An algorithm for finding the unequal error protection (UEP) capability of a q-ary image of a low-rate qm-ary cyclic code is presented by combining its concatenated structure with the UEP capability of concatenated codes. The results are independent of a choice of a basis to be used for expanding an element over GF (qm) into GF (q). A table of the UEP capability of binary images of low-rate Reed-Solomon codes over GF (26) is given. It is shown that the encoding and decoding algorithms for superimposed concatenated codes can be applied to a q-ary image as a linear UEP code.