Kazuyuki Shimezawa

Multipath division turbo equalization with block inter-carrier interference cancellation in cellular system with amplify-and-forward relaying

This paper proposes multipath division turbo equalization with block inter-carrier interference cancellation (MD-BIC) for orthogonal frequency division multiplexing (OFDM). When the multipath delay difference exceeds the cyclic prefix (CP) length, the OFDM transmission performance suffers severely due to inter-symbol interference (ISI) and inter-carrier interference (ICI). Cellular systems with amplify-and-forward (AF) relay stations, for example, might cause a long delay due to their process delays. Therefore, mobile terminals served by AF relay systems should compensate for the influence of ISI and ICI. MD-BIC divides a series of paths into several blocks by using a log likelihood ratio (LLR) that is computed in the decoding process. The delay difference within each block is limited so as not to exceed the CP length. This means that ISI and ICI are mitigated in each block. Computer simulations demonstrate that the proposed scheme can achieve excellent performance in the severe multipath channels where the delay difference is greater than the CP length.

A novel SC/MMSE turbo equalization for multicarrier systems with insufficient cyclic prefix

In this paper, we propose a multipath division SC/MMSE turbo equalizer for multicarrier systems with insufficient cyclic prefix (CP). In the proposed scheme, the received paths, which include paths that exceed the length of the CP, are divided into several blocks. Therefore, inter-symbol interference and inter-carrier interference, which are caused by large delayed paths, can be mitigated by making the paths in each block shorter than or equal to the CP length through multipath division. Moreover, path diversity gain can be obtained when paths in each block are combined by the MMSE filter. Therefore, this proposed turbo equalization can realize the reduction of both ISI and ICI with low complexity. In order to evaluate the effectiveness of the proposed scheme, we perform computer simulation. The simulation results show that the proposed scheme can drastically improve PER characteristics.

Cyclic Shifted-and-Extended Codes Based on a Quasi-Orthogonal Sequence for a CDM Transmission Scheme

We have developed a code-division-multiplexing (CDM) transmission scheme for future road-vehicle communication systems, which uses cyclic shifted-and-extended (CSE) codes generated from a basic code with superior auto-correlation characteristics. This paper proposes to use a Quasi-Orthogonal (QO) sequence as the basic code. Its auto-correlation values are zero except at zero and middle shifts. When the CDM transmission is performed by the CSE codes based on the QO sequence, a desired correlation value is, at a receiver, interfered by the auto-correlation value at middle shift. Therefore, an elimination technique for the interfered correlation value is proposed and realizes zero cross-correlation characteristics within the cyclical shift interval. The new CDM transmission scheme based on the proposed scheme is evaluated by computer simulations in terms of the bit-error-rate performance.

A high-speed DSRC system assisted by an overfill CDM for future seamless road-vehicle communication systems

In order to realize a future seamless high-speed road-vehicle communication system, we have proposed using the code division multiplexing (CDM) radio transmission scheme by using cyclic shifted-and-extended (CSE) codes as spread codes. As the CSE codes are generated by cyclically shifting and extending a conventionally used code, the number of codes generated from a code is limited to the length of the shift interval and the tolerable period of delayed waves also depends on the length. In this paper, based on CSE codes, we propose a method to minimize the length of the shift interval and a cancellation technique with a simple calculation in order to eliminate the interference from delayed waves caused by the reduction of the length of shift interval. The concept of the proposed scheme and the BER performances in AWGN, two-paths, and multipath fading environment are described in this paper. As a result, the maximum transmission rate of CSE-based-CDM transmission per one-code using the newly proposed transmission scheme is 3 times as large as that using conventional CSE codes and DQPSK-CDM transmission scheme.

Performance of MC-CDM Systems with Iterative Inter-Code Interference Canceller and Frequency-Domain Interleaver

This paper presents a suitable frequency-domain interleaving method for a multi-carrier code division multiplexing (MC-CDM) system using an inter-code interference (ICI) canceller. We consider two interleaving methods: namely, symbol-interleaving and chip-interleaving. For MC-CDM, the suitable interleaving method is decided by frequency diversity gain and ICI. In this paper, we evaluate the performance of MC-CDM systems that employ ICI canceller and different interleaving methods by computer simulation. Simulation results show that the chip-interleaving method and an ICI canceller can achieve superior MC-CDM performance.

Cyclic shifted-and-extended codes based on almost perfect autocorrelation sequences for CDM transmission scheme

For future cellular communication systems, we have developed a code-division-multiplexing (CDM) transmission scheme based on cyclic shifted-and-extended (CSE) codes generated from a basic code with superior autocorrelation characteristics in order to realize seamless communication in a high-speed mobile environment. In this paper, an almost perfect autocorrelation sequence is used as the basic code and its autocorrelation values are zero except at zero and middle shifts. Moreover, we propose an elimination technique for interference caused by the correlation value at the middle shift. The proposed technique can realize perfect correlation characteristics within the cyclical shifted chips by adding a simple calculation at a receiver. The proposed scheme is evaluated by computer simulations in terms of the bit-error-rate performance for various code lengths of the basic code.

A CDM transmission scheme with cancellation technique for accumulated cross-correlation values

We propose adding a code-division-multiplexing transmission scheme with a cyclic shifted-and-extended codes and many-valued modulation scheme to a conventional DSRC-based road vehicle communication system in order to realize seamless communication in high mobility environment. Then, cross-correlation values accumulate by a combination of polarity of transmission data in parallel channels, and the accumulated cross-correlation values make transmission performance to degrade. Therefore, we propose the CDM transmission scheme with a cancellation technique for the accumulated cross-correlation values. Moreover, we calculate transmission performances of the proposed scheme by computer simulations. As a result, the proposed scheme can realize high-quality data transmission in fast fading environment.