In this paper, we discuss on the realization of reduced peak power transmission for the multicarrier systems. Since the signals have large amplitude fluctuations in conventional multicarrier systems, signals amplified by a nonlinear amplifier are greatly distorted, resulting in severe performance degradation. In order to avoid this large amplitude fluctuation, we propose a scheme for reducing the nonlinear distortion by using the set of the signal point series which show low peak to mean envelope power ratio (PMEPR) value. In this system, one symbol is transmitted with multicarriers and the received signal is detected with maximum likelihood sequence detection.

The performance of M-ary code shift keying (CSK) in multipath fading channels is analyzed in this letter. In conventional spread spectrum (SS) systems, which employ a single spreading code, the interference due to the delay signal depends on the auto-correlation property of the spreading code. In CSK, since one code is selected from a code set that contains multiple codes, the effect of the delay signal differs from that for conventional SS systems. Analytical results reveal that, in the multipath fading channel, the error rate of CSK depends on the cross-correlation property with the other codes in addition to the auto-correlation of transmitted code.

In this letter, we present bit error analysis (BER) of orthogonal multi-carrier direct sequence code division multiple access (DS-CDMA) system with multi-rate (multimedia) traffic. Analysis is carried out with random signature codes for an AWGN channel. Interference in such a system is severe because all users of all media transmit over the same assigned sub-carriers. This makes the analysis difficult. In our analysis, we divide this interference into different types and carry out our analysis to obtain the BER taking into account all these types. We show that the performance of the system is improved as the number of assigned sub-carriers M increases until a limit where the improvement does not continue even when M increases more. This is because of, as we show, the interference due to other sub-carriers becomes constant even in the case of M , and the interference in a multi-rate multi-carrier system is bigger than that in a single-carrier (M=1) by a factor of π2/3.

In an attempt to improve the performance under frequency selective fading environment, we develop in this paper an orthogonal frequency division multiplex (OFDM) system in which adaptive interleaving is applied. The adaptive interleaving is a method that assigns symbols adaptively to the subcarriers in order to cope with frequency selective fading based on a channel state information (CSI) sent back from the reception end. The concept of adaptive interleaving is to maximize a free Euclidean distance in the limited interleave size. In this paper, we extend the method by an introduction of bit interleaving and multiple trellis coded modulation (MTCM). MTCM assigns two or more symbols to one trellis branch and shows good performance in frequency selective fading. If we could assign those set of symbols with an aid of the adaptive interleaving, the performance improvement can be expected. Another improvement method considered in this paper is the use of bit interleaving. The bit interleaving techniques randomize the effect of channel more efficiently compared to the case of symbols interleaving. Thus the further performance improvement is expected. One draw back is that since the interleaving process is done in bit level, bit interleaving can not be applied to TCM nor MTCM. In this paper, we mainly focus on adaptive bit and symbol interleaving and discuss the performance from the point of interleaving effect, and the error correcting code (convolutional code and MTCM).

The average bit error rate performances of M-ary orthogonal code shift keying (CSK) in Rician fading environments are analyzed in this letter. CSK is a digital modulation scheme that uses a code set as M-ary signals. In CSK, one code is selected from a code set containing M codes according to the information data. A signal is modulated by using this code and the effect of fading can be reduced by applying interleaving to the elements of the codes. In the analysis, the bit error probability is derived in closed form expression by using the Chernoff bound. The analysis results show that the error probability decreases when the code length is increased and that an arbitrarily small error probability is achieved as the code length approaches infinity, provided that Eb/N0 exceeds 1.42 dB.