Application of virtual segment interleaving to high speed land vehicle diffCDMA and transmission characteristics of the low chip rate diffCDMA over multi-ray Rayleigh fading channel

As is well known, CDMA possesses such advantages as high capacity, low power transmission, and system flexibility, but it suffered from broadband occupancy of wasting finite frequency resource owing to innocent spectrum spreading. Narrowing the frequency bandwidth occupied by the channels is an efficient method of developing high capacity digital transmission as one of the most important key technologies promising effective frequency usage. Narrowing the frequency bandwidth both of the primary and secondary modulation has been discussed in an effort to realize high capacity and speed diffCDMA. The phase continuity primary DQPSK, which has already been reported as a solution for 2 Mbps/8 Mcps diffCDMA, is reviewed here to realize the higher reliability and frequency efficiency of 2 Mbps/4 Mcps diffCDMA. Virtual segment interleaving is discussed as a way of reducing the chip rating as one of the important solutions for effective frequency usage without the problems of system reliability and complexity. Both continuous phase primary modulation and continuous chip shaping are also enhanced in this proposal for 2 Mbps/4 Mcps diffCDMA.