In this paper, we propose a new concept of receiver structure with diversity reception technique to realize multi-service simultaneous reception, which shares diversity branches between receiving communication services. In the proposed receiver structure, each diversity branch selects the receiving services dynamically according to channel states, and each communication service is always selected by at least one branch to realize multi-service simultaneous reception. A basic algorithm is also described to select combinations of a diversity branch and a receiving communication service. The total number of branches decreases and the effective number of branches per communication service increases, by sharing the branches between communication services in the proposed receiver. Simulation results are shown that the proposed diversity receiver achieves both complexity reduction and performance improvement.

In an orthogonal frequency division multiplexing (OFDM) system, the bit error performance is degraded in the presence of multiple propagation paths whose excess delays are longer than the Guard Interval (GI), because the orthogonality between subcarriers cannot be maintained. Therefore, the GI has to be long enough for an expected delay spread of the channel. On the other hand, a long GI causes a decrease in transmission efficiency. In this paper, we propose a new OFDM demodulation method with a variable effective symbol duration, in order to improve the bit error performance in the presence of multipaths whose excess delays are longer than the GI. The proposed method can realize more stable radio communication systems under a multipath propagation environment even if a propagation path whose excess delay is longer than the GI exists. In other words, the proposed method can improve transmission efficiency without performance degradation by a shortened GI under the same environment. The principle of the proposed method is explained, and the bit error probability of the proposed method is analyzed theoretically in an AWGN channel and a multipath fading channel. The performance of the proposed method is then evaluated by computer simulation. The results show that the proposed method improves the system availability under more various multipath fading environments without changing the system parameters.

In an orthogonal frequency division multiplexing (OFDM) system, the bit error performance is degraded in the presence of multiple propagation paths whose excess delays are longer than the Guard Interval (GI), because the orthogonality between subcarriers cannot be maintained. In this paper, we propose a new OFDM demodulation method with a variable-length effective symbol and a multi-stage inter-carrier interference (ICI) canceller, in order to improve the bit error performance in the presence of multipaths whose excess delays are longer than the GI. The influence of the inter-symbol interference (ISI) is eliminated by the variable-length effective symbol, and then the ICI component is reduced by the multi-stage ICI canceller. The principle of the proposed method is explained, and the performance of the proposed method is then evaluated by computer simulation. The results show that the proposed method improves the system availability under more various multipath fading environments without changing the system parameters.

A novel timing synchronizing scheme is proposed for use in inter-vehicle communication (IVC) with an autonomous distributed intelligent transport system (ITS). The scheme determines the timing of packet signal transmission in the IVC network and employs the guard interval (GI) timing in the orthogonal frequency divisional multiplexing (OFDM) signal currently used for terrestrial broadcasts in the Japanese digital television system (ISDB-T). This signal is used because it is expected that the automotive market will demand the capability for cars to receive terrestrial digital TV broadcasts in the near future. The use of broadcasts by automobiles presupposes that the on-board receivers are capable of accurately detecting the GI timing data in an extremely low carrier-to-noise ratio (CNR) condition regardless of a severe multipath environment which will introduce broad scatter in signal arrival times. Therefore, we analyzed actual broadcast signals received in a moving vehicle in a field experiment and showed that the GI timing signal is detected with the desired accuracy even in the case of extremely low-CNR environments. Some considerations were also given about how to use these findings.

The reception quality of terrestrial digital broadcasting when the directional pattern of a mobile terminal is controlled has been experimentally evaluated using test signal. It was found that the reception probabilities with a controlled directional pattern were significantly improved over the case when an omni-directional antenna was used.