Gsm Band In Wcdma Interference Signal Rejection Techniques

A major factor that will influence the future wireless communications is the contradictions between the higher transfer rate and the more limited spectrum resources. In order to save the spectrum resources and reduce the investment cost, an idea that different signals could be transmitted within the same frequency band has been proposed. For this idea, the representative of the third generation mobile communication system-WCDMA can be transmitted in the same frequency band as the representative of the second generation of mobile communications systems-GSM.When we transmit GSM sinal and WCDMA signal in the same frequency band, the two different signals will interfere with each other. If the interference is very serious, it will cause a worse quality of service. There are many methods about reducing the coexistence interference, such as establishing the base station at the same place, increasing the isolation of antennas, and optimazing the design of the network. But there are few papers researching about the specific interference suppression algorithm.WCDMA signal will exist in the same frequency band as the GSM signal transmitted The paper introduced an method based on the iterative signal rebuilt and cancellation to reduce the interference. Another method based on Smart AGC has already been proposed to reduce the interference by this paper.The GSM uplink receiver model has been given to transmit the GSM and WCDMA signal in the same frequecey band. We can obtain the rebuilding signal using direct pilot symbol averaging, weighted multi-slot averaging, and other channel estimation methods for the proposed model. The rebuilding signal will be extracted from the signals received.We simulated the reconstruction of WCDMA signal based on the weighted multi-slot averaging channel estimation method. It can be observed that the amplitude curve of the rebuilding signal is mostly the same as the curve of the original signal from the simulation results. The maximum difference about the amplitude can be controlled less than thirty percent of the original signal. A simulation has also been made about the bit error rate as iterating the rebuilding signal and cancellation twice. It also can be found that the bit error rate will approach that of no interference with increasing the number of iterations from the simulation results. The performance of this method is worse than that of no interference about 0.6 dBA technology named Smart AGC has been studied in this paper. The key to operation of Smart AGC is a broad band power measurement of the composite input signal which is then used to control a nonlinear amplifier characteristic. The restrictive conditions with the optimal bias threshold should meet has been derived for the single tone interference. The method based on maximum likelihood estimation has been researched about the suppression of the single tone interference. The BER performance of the method is compared with that of Smart AGC. Finally, the BER performance of iterative interference suppression is compared with that of Smart AGC to suppress WCDMA interference. It can be observed that the method based on the principle of Smart AGC has a worse performance than that of the iterative interference suppression method from the simulation results. The BER performance of the method based on the principle of Smart AGC is worse than that of the iterative interference suppression about 0.8dBThe research results on the interference suppression can be applied in the existed communication systems and future communication, which has great theoretical importance and economic value.