Study On Characteristics And Suppression Method Of Wireless Networks

With the rapid development of mobile communication technology, the competition in mobile communication market is growing. Because different kinds of communication systems are adopted by many operators, the limited wireless spectrum resource becoming more and more crowded. Almost all the network operators wish to use the existing GSM network system resources to construct CDMA system. The two systems co-exist in the same frequency space, therefore the mutual interference result in a sharp decline in the service quality. In addition, considering GSM uplink frequency close to the CDMA downlink frequency band, the network of mutual interference of intersystem can also affect the normal operation of the systems.Therefore, availably interference suppression is of great importance in the scheme that the frequency band of GSM and CDMA is common or adjacency. There are many methods to cancel the intersystem interference, for example, increasing protection band, improving isolation between antennas, employing high order FIR digital filters. However, little amount of researches about the specific interference suppression algorithm. This paper Design interference suppression scheme, the methods of Interference Cancellation and Adaptive array signal processing is employed.Firstly, the physical layer signal processing of GSM and CDMA is researched and simulated in an environment characterized AWGN channels. The mixed signal at GSM receiver is reconstructed, which includes the desire signal (GSM signal) and interference signal (CDMA signal).Secondly, on the basis of Interference Cancellation, the LMS algorithm, Envelope filtering algorithm both are introduced in the interference cancellation scheme. In the case that the GSM base station equipped with one antenna, the CDMA signal is canceled successfully. Simulation result shows the output signal-interference ratio reaches5dB.Finally, this paper proposes the interference suppression scheme with multi antennas in GSM base station, from the perspective of Adaptive array signal processing. Considering the difference between the arrive angle of GSM and CDMA signal, Spatial filter and spatiotemporal filter are employed in the multi-antennas scheme. Simulation result shows the output signal-interference ratio reaches lOdB. Moreover, the performance of DOA estimation is simulated and is analyzed; the results show the stability of TLS-ESPRIT is the best of the DOA estimation applied for uniform linear arrays. Based on uniform circular arrays, the MUSIC and RB-MUSIC algorithms estimated the direction accurately, however, with the interference and noise power increase, the estimate error grows.