Akiyoshi Kawahashi

Advanced CDMA scheme based on interference cancellation

The pseudorandom noise (PN) code is used for a CDMA scheme to spread the spectrum of user data. When the number of users increases, the signals of other users cause interference noises. The fundamental factor of the interference is dependent on the cross-correlation characteristics of the PN code. A scheme for improving the capacity is proposed, based on interference cancellation. The scheme is evaluated on the characteristics of bit-error-rate (BER) vs number of simultaneous users by computer simulations. It is found that around 60 users are available per cell by the proposed method without error correction and voice activity control. Around eight times the capacity of the conventional correlation scheme is achieved. The configuration of the personal station is effectively reduced in size and cost, because the complicated voice activity control is not necessary, and the IC is installed in the base station.

Wideband CDMA system for personal communications

In this paper, a wideband-spreading CDMA (W-CDMA) is proposed to transmit high quality speech and high speed data including Group 3 facsimile and 64 kbps unrestricted data. The maximum capacity is 64 channel per microcell without sectorization and voice activity detection. The proposed scheme is to be the standard of the radio air interface in 1.85 to 1.99 GHz personal communication services.

Advanced CDMA scheme for PCS based on interference cancellation

This paper describes the configuration and characteristics of the advanced CDMA scheme. The scheme realizes the Interference Cancellation (IC) with a Walsh code and a Viterbi decoder using a full soft-decision. The interference signal of other users has been reduced and the Bit Error Rate (BER) performance of this scheme has been improved, bringing the number of simultaneous access users per cell to 64.

Sequential interference cancellation system applying to wideband CDMA systems

This paper considers an interference canceller system (ICS) consisting of tandem/sequential cancellation for DS-CDMA (direct sequence code division multiple access) and its traffic capacity. The ICS receiver consists of coherent detection with a pilot channel to momentarily estimate the amplitude and phase of the propagation path. The analysis is conducted to obtain the conditional distribution function between each stage of the ICS. The analysis results clarify that the number of simultaneous multiple random access subscribers is 40 using a five stage ICS when the spreading ratio is 64.