cdma综述外文翻译-通信工程(编辑修改稿)

cdma综述外文翻译-通信工程(编辑修改稿)内容摘要：

t。 this noise represents the interference generated by other base stations that are using the same frequency band. In the receiver section, the ining signal is first filtered by the Receive Filter block, which implements a filter matched to the transmit filter. The filters in this demo are designed to maximize the signal power within the desired frequency band. Then the filtered signal is sent to the IS95A Rev Ch Detector library block, which contains the reverse channel rake receiver. The rake receiver consists of three rake fingers that are set to different delays to handle up to three multipaths. Each active rake finger performs the despreading of the input data with the short PN sequence, followed by despreading with the long code. This is followed by the correlation with the entire set of 64 Walsh codes. The energies in the I and Q ponents are added, and the results from the fingers are added together. This is processed by the Walsh demodulator, which generates decisions in groups of 6 bits, the size used for modulation. The Walsh demodulator outputs both soft decisions and bipolarvalued hard decisions. both are gated by the data burst randomizer signal. The Error Rate Calculation block pares the transmitted bits and the received decisions, and produces the raw (that is, without channel coding) bit error rate. This rate is displayed in the model window during the simulation. Visible Results of the Demo The demo shows the raw bit error rate (BER) for the reverse channel. The BER depends on the channel conditions and the number of rake receiver fingers active. As the signaltonoise ratio or the channel conditions are changed, the effect of these on the raw BER can be seen by running the model for these different conditions. Changing Demo Parameters This section suggests some ways that you can alter the parameters in the demo after you understand the model. The simulation duration in this demo is set to 2 seconds. Because the frame duration in IS95A is second, this model processes 100 frames. This gives a sufficient time for the BER measurements to converge at reasonable SNR settings. To run the simulation for a longer or shorter time, select Parameters from the Simulation menu and change the Stop time to times the number of frames you want to simulate. To change the data rate, doubleclick on the Data Source icon. Then doubleclick on the Mobile Station Transmitter Data Rate icon and change the Data Rate parameter. Choices are Full, Half, Quarter, and OneEighth rates. To change the long code mask, doubleclick on the Spreading and Modulation icon. Then doubleclick on the IS95A Rev Ch Walsh Modulation and Spreading icon, and enter a new value for the Long code mask parameter. This parameter can be any nonnegative integer less than 2421. The block uses the binary representation of this number to generate the code. The value for the Long code mask parameter is also required in the IS95A Rev Ch Detector library block. Experiment with。