Interference Cancellation in Next Generation CDMA Systems
The adaptive interference cancellation (IC) algorithm has been developed for the next generation CDMA systems. It can be used for a low rate user to cancel the interferences from high rate users. An interference estimate, IE, is designed to estimate the high-rate user’s signal (interference). The estimated interference is then subtracted from the signal before the Walsh demodulation and soft combining. The interference cancellation improves the SNR, and thus the system performance. The SNR measurement & control system block, SM & CS, calculates the SNR and triggers the interference cancellation when it is necessary.
Background & Objective: Variable transmission rate services will be supported simultaneously in the next generation wireless systems. In practice, the power control is used to meet the predefined performance for different users. In an additive white Gaussian noise channel, un-even power is then needed for different rate users to obtain the same bit-error-rate (BER). However, when the power difference between the different rate users becomes large, the performance of the low rate user will be seriously degraded. The adaptive IC is to address this issue by estimate and canceling the interference from the high rate user.
Technical Discussion: By changing the spreading gain for each user, variable rate transmission can be achieved. Data services generally need much lower BER than the voice services, therefore higher power. The power ratio between high rate users and low rate users will be further enlarged when two users are close to each other in location. To maintain a good conversation quality for the voice service while another data service user access to the network with high data rate, becomes very important issue in the CDMA system downlink.
Contact: Jinyun Zhang
Technology Area: Digital Communications
Modification Date: July 31, 2001
