Detailed description of WCDMA uplink parameter optimization method (1)

Introduction

As the main wireless transmission technology of the third generation mobile communication system (3G), the WCDMA uplink adopts the BPSK coherent demodulation technology assisted by the pilot channel. Although accurate channel estimation can be obtained through the pilot channel, it increases the energy of each data signal to be sent. While keeping the total signal energy unchanged, increasing the power of the pilot channel can improve the accuracy of channel estimation, but it also increases the interference with other users. At the same time, as the power of the channel increases, the power allocated to the data channel will inevitably decrease, resulting in a decrease in the signal-to-noise ratio during demodulation. On the other hand, although reducing the power of the channel can reduce the interference and improve the power of the data channel, thus improving the signal-to-noise ratio during demodulation, the accuracy of channel estimation will be reduced, especially when the mobile station moves at high speed.

It can be seen that the Power Ratio (Pilot-to-data Channel Power Ratio) between the Pilot Channel and the data Channel has a great impact on the system performance and is an important parameter to be optimized urgently. In addition, since the accuracy of channel estimation affects the error probability of the system, it is obviously highly correlated with the determination of the optimal power ratio. Because the channel estimator of the actual system generally uses the moving average filter, therefore, the main purpose of this article is to analyze how to determine the optimal power ratio and the optimal average length of the moving average filter under the minimum error probability criterion.

Transmission Structure of the WCDMA uplink

Figure 1 shows the baseband transmission structure of the WCDMA uplink dedicated physical channel (DPCH. DPCCH (DPCCH) is a dedicated data channel (DPDCH) that carries user data and other control information, so in order to simplify the processing, we think it is a continuous channel in the following analysis ). They are added after being spread to the Chip rate by different real-time Wd codes and Wc codes, and then disturbed by Sdpch and n, which are specified by the nth user. Beta indicates the power ratio of the Pilot Channel to the data channel. Generally, it is smaller than 1 to reduce the interference to dpdch on the I channel and other users.

The wireless communication environment can be regarded as a frequency-selective secondary fading channel. For the convenience of the following analysis, we assume that the channel has 1 equal power path, and each path is irrelevant. At the receiver's input end, considering that different users of the WCDMA uplink are performing asynchronous operations, you can overlay the received signal by the thermal noise and other user multi-access interference (MAI) the noise is regarded as a white Gaussian noise, and its unilateral power spectrum is set to N0. Because the multi-path Interference (IPI) is negligible compared with the thermal noise and multi-path interference, we will not consider the interference caused by signal multi-path propagation here, assuming that the receiver knows the accurate latency information for each path.