Common Problems and Solutions for CDMA network optimization (1)

CDMA network optimization has its own characteristics. The unique soft switching mode of CDMA makes the signal control of the base station more important than other mobile communication systems, which also increases the control difficulty. If the signal control is improper, this vulnerability may cause problems such as channel pollution, strong interference, and network performance degradation. In actual projects, network problems should be summarized and summarized, combined with on-site surveys, road tests and OMC report analysis to find the reasons, and accumulated network optimization engineering experience to build a high-quality network.

This article defines a good RF environment that meets the following performance parameters:

Good FFER (<2%) (forward frame rate by mistake)

Good Ec/Io (>-9dB) (pilot signal-to-noise ratio)

Normal (<+ 5dBm) (Mobile Station transmit power)

Good Mrx (>-85dBm) (mobile station receiving power)

Forward link interference

Indicator indicators: High FFER (> 5%), low Ec/Io (<-12dB), normal (<+ 15dBm), and good (>-95dBm ).

First, the list of adjacent sets is lost. Even if the PN is not included in the list of adjacent sets, if the SRCH_WIN_R value is large enough, the mobile platform can detect the PN of the remaining set during the call. If the intensity is sufficient, the system will upgrade to the candidate set. However, this PN can only exist in the Candidate Set and send PSMM messages, but cannot be upgraded to the activation set. This PN will cause interference to the forward link, so that the FFER and Ec/Io of the activated PN are decreased accordingly, resulting in disconnection. After the disconnection, the mobile device usually initiates registration on a strong PN that does not exist in the adjacent set list before the disconnection.

Solution: add the PN to the list of adjacent sets of the active slice. If the PN is already in the list of adjacent sets, the priority is increased.

The second is sudden strong PN interference. This occurs during soft switchover. When the mobile station moves in a certain sector of a BTS, the sector is blocked by the terrain and buildings. The mobile station searches for a sector belonging to another BTS and sends a request to add it to the activation set. At this time, the original sector suddenly emerged from the original blocking, and the mobile station was overwhelmed by the huge power of the original sector. However, before the PN is added to the activation set, the performance of the FFER and Ec/Io of the call suddenly drops.

Solution: Soft switchover is introduced to eliminate sudden strong PN interference cells. by increasing the pilot power, the sudden PN can be smoothly soft-switched. You can also adjust the antenna direction angle, guide power and other measures to transmit the signal to the original blocked area to cause coverage, or reduce the switching parameter T_ADD. You can also increase the SRCH_WIN_x window so that the phone can find the PN. The method for eliminating burst PN is to first reduce the pilot power, clear the burst PN, or optimize it by adjusting the antenna direction, downtilt angle, replacing the antenna and other physical methods.

The third is total PN interference. If the two adjacent sectors of two different base stations in the same region have the same PN, the Mobile Station will request to add the PN to the activation set when it finds that the PN is strong enough. The MM in CBSC establishes a switching link based on the list of adjacent sets. Whether the mobile phone can switch to the correct BTS depends on the BTS seen by MM at this time. If a switchover error occurs, the call quality will deteriorate further, causing a disconnection. Using NLP software, we can find that the number of soft switching requests for two sectors with the same PN exceeds 1%.

Solution: Change the PN value of one base station. Regular re-adjustment of PN is a long and difficult task, but it is very good for the system.