Wcdma Band Gsm Interference Signal Rejection Techniques

As mobile services develop, GSM(Global System for Mobile) system is evolving towards third generation(3G) systems, and will co-exsit with 3G systems and its long term evolution for a long time. Spectrum resource plays an important role in the whole asset of GSM operators. Almost all the operators are considering the issue of the co-existence of GSM network and 3G networks. To lower the investments, most operators hope to directly extend 3G services in the GSM frequency bands assigned. Especially for a certain operators, they can only manage these two different networks in the same frequency bands.CDMA(Code Division Multiple Access)overlay allows CDMA waveforms to share common spectrum with conventional narrow GSM signals. This spectrum-sharing method enhances both the spectrum utilization and the flexibility of that utilization. In view of a smoother evolution, this paper firstly proposes the study of frequency overlay of GSM and WCDMA(Wideband Code Division Multiple Access). And for the successful deploy of the overlay, this paper mainly focuses on the rearsch of the overlay GSM interference suppression in WCDMA signals. From the perspective of WCDMA system and its market development, this proposal will have a bright future.Firstly, on the basis of principles of GSM and WCDMA system, this paper analyzes the feasibility of WCDMA overlay on GSM system. The results present that, by overlaying WCDMA signals on GSM uplink channels, this proposal can make full use of the existing GSM resources and economize lots of investments.Secondly, evaluation analysis of the mutual interference between the overlay WCDMA system and GSM system is carried out in the uplink. By finding the degree of degradation of Eb /N 0 of the received data due to interference coming from another system, the evaluation results indicate that, WCDMA system, just depending on the spread spectrum gain, can not effectively resist the stronger GSM interference. Meanwhile, WCDMA signals also dramatically degrade the quality of GSM signals. Therefore, suitable interference prevention or suppression measures are needed to improve the performance of the frequency overlay system. How to reduce or avoid the interference from the WCDMA system to the GSM system and vice versa is the key to the success of the project. Referring to the multi-user detection technique and an exsiting patent, this paper proposes a signal rebuilding-based iterative interference cancellation receiver, which uses the detected data to rebuild and cancle the mutual interference in an iterative way. In every iteration, it includes three major stages: signal detection,siganl rebuilding and interference cancellation. The number of iteration is determined by the bit error rate(BER). The simulation results obtained show that, this receiver can efficiently eliminate the intracell interference between the overlay WCDMA and GSM system, and improve the performance of the overlay WCDMA system.Applying this receiver into the GSM and WCDMA overlay system can solve the excessive interference caused by the co-exsitent overlay system, and further low the investments and operation risk of network operators.