In CDMA systems using block spreading techniques, where a data-block modulates a spreading sequence to produce a transmitting symbol, a user inherent orthogonal carrier-frequency modulating system is proposed. This method contributes to accommodating as many users as the processing gain L and to reducing the guard sequence overhead. Applying a MIMO configuration without using coding and multiple constellation on PSK modulation to this system, especially using N pieces of receive antennas is considered. This block spreading system is capable of accommodating as many users per orthogonal carrier as N, by using a method of concatenating the N symbols received at N antennas. This means that the aggregate data rate per chip increases N in the maximum. Further it is shown that a fairly good error rate performance is achieved by selecting the practical aggregate data rate to be about 80% of the maximum rate.
A new signal demodulation system for CDMA receivers is proposed. This system has an effective function of canceling the interference noise components in the received symbol frames. For a target symbol frame to be detected, the differential frames are produced, each of which is made by subtracting one of the neighboring symbol frames from the target frame. The interference noise being left in some of the differential frames is much less than that in the target frame. By demodulating only such noise cancelled differential frames that have been estimated with effective analyzing sequences, the information conveyed on the target frame with a heavy interference can be detected. The simulation indicates powerful canceling performance for all the possible interference disturbance is achieved.
To improve the diversity gain performance in CDMA-MIMO systems, multi-user detection with decorrelating detectors (DD) is examined. Without using error-correcting codes, it is confirmed that tremendous performance improvements may be achieved by enhancing the regularity of the decorrelating matrix by inserting dummy response insertion and by utilizing multiple dimensions of the matrix component vector made of plural receive antenna outputs. These improvements increase both the actual process gain and the maximum number of active users.
For mobile systems higher than 3G, multi-rate data service is becoming an important issue. This paper proposes a multi-rate block-spreading CDMA system as an efficient scheme which is capable of intra-cell-interference free operation and inter-cell-interference reduction by a factor of reciprocal of the spreading factor. With a use of an accurate pilot transmission scheme, it is shown that a high frequency utilization efficiency can be achieved for various mixed data rate services.
