Dear community friends！
What is uplink interference?
Interference is one of the key factors affecting network quality. With the increasing complexity of network structure and frequency allocation, many types of signal sources appear in the network. When these non-service signals fall into the LTE receive frequency band, uplink interference occurs, affecting call quality, call drops, handovers, and overall network coverage and capacity.
Today, I want to share with you a case of checking uplink interference.
Common Interference Types
intra-system interference
FDD Intra-RAT Intermodulation Interference
TDD remote interference
TDD air interface out-of-synchronization interference
The frame offset configuration is incorrect.
Neighboring Cell Terminal Level Interference
Co-channel interference
Inter-system interference
Inter-RAT spurious interference
Inter-system intermodulation harmonic interference
Inter-RAT blocking interference
External interference Instrument interference
Problem Description
A carrier in country X received a complaint that the network quality of the terminal equipment at site XX was poor near the site.
Problem Analysis
After arriving at the site, use the UE to perform the test. The UE has network signals, but the network quality is poor. It is preliminarily determined that uplink interference exists at the site.
Solution
Step 1. Determine the interference source.
The data obtained through the base station or the NMS are discrete digital signals. Generally, data sources can be presented in two forms: time domain or frequency domain. The time-domain data of uplink interference is a trend chart of the power of received signals that changes with time. The frequency-domain data is a trend graph of the power of the received signal as a function of the frequency.
A manner of obtaining a signal time domain/frequency domain spectrum may be mainly obtained by using a frequency scanner or Fourier transform.
Frequency sweeper: The frequency sweeper uses the built-in digital filter to scan frequencies one by one to obtain frequency-domain information within the RF bandwidth. After scanning all frequencies, the frequency sweeper starts scanning again on the first frequency until the scanning stops.
Figure 1 Schematic diagram of the frequency sweeper
Fourier transform: The frequency represents the rate of change of the digital signal, and by extending the digital signal in the form of a Fourier series, the power of different frequencies can be obtained. As previously described, the digital signal is a discrete digital signal, and therefore the Fourier transform actually used is a discrete Fourier transform (DFT). Meanwhile, the inverse discrete Fourier transform (IDFT) can inversely transform the frequency domain into the time domain. Therefore, spectrum diagrams in two dimensions, frequency domain and time domain, are obtained.
Figure 2 Fourier Transform Schematic Diagram
The use of a frequency sweeper is recommended as this is the most effective way to determine external interference.
Use a frequency sweeper to check the site. It is found that the co-channel interference of the site is severe. Check the area around the site. Determine that the interference source is a neighboring site.
Co-channel interference
Co-channel interference refers to the interference caused by the same carrier frequency of unwanted signals as the carrier frequency of wanted signals and the interference caused to the receiver that receives useful signals of the same frequency.
In mobile communication systems, frequency reuse technology is often used to improve frequency utilization and increase system capacity. Frequency reuse means that multiple cells in a given coverage area use the same frequency group after a certain distance. These cells are called intra-frequency cells. Interference between intra-frequency cells is called co-channel interference.
Step 2. Optimize co-channel interference.
Optimization Method
1. Decrease the power of the neighboring cell and weaken the signal strength of the neighboring cell.
2. SFN networking is used.
3. Interference randomization.
4. The time domain is staggered.
The customer chooses to reduce the power of neighboring cells based on the actual situation. In this way, the co-channel interference is greatly reduced and services are restored.
Welcome to learn!
