Wireless communication often needs to use spectrum analyzer to demodulate the signal and analyze the signal quality. There are usually four methods for analysis: IQ constellation diagram, IQ eye diagram, symbol table and bit error rate table. Today we will introduce how these four analysis methods can help us observe the signal quality.

1、 IQ constellation

Digital modulation is a necessary step to transmit low-frequency information through high-frequency carrier. When we receive the signal, we must demodulate the signal first. IQ constellation is a kind of modulation mapping relationship. By using the orthogonal plane, we spread all the possibilities of modulation – the number of symbols (or state space) after modulation on the orthogonal plane we constructed. In the process of signal modulation, we jump from a point to a point (modulation state). The distance between points is called Euclidean distance, which represents energy. When we observe whether the trace falls on the corresponding grid correctly, we can judge whether the amplitude and phase modulation of the signal is completed.

Using four analysis methods of spectrum analyzer to observe signal quality

Of course, different modulation modes have different constellation shapes. For example, BPSK has only two states, QPSK has four states, and QAM has more states.

2、 IQ eye chart

Eye diagram is often used in time-domain signal testing, by overlapping a certain number of waveforms to observe the effect of clock opening and closing. If the eyes are open, the bit error rate is low and the quality is good; if the eyes are closed, the bit error rate is high, so the circuit design needs to be improved. IQ eye diagram is a powerful tool to observe the change of signal digital modulation process with time. With the change of time, whether the signal modulation process is “eye closed” after the overlap of I-Axis traces can be used to judge the eye diagram quality of in-phase channel. The corresponding q-eye diagram is also called the eye diagram of orthogonal channel. IQ eye diagram is the basis of error vector time measurement.

3、 Symbol table

Symbol is the specific state information of digital modulation, which reflects the actual modulation level change and modulation state. The symbol corresponds to each grid point in the constellation, and the symbol table displays the modulation information obtained after signal demodulation. By comparing the symbol table with the reference table, the BER can be measured.

4、 Bit error rate table

By comparing the symbol reference table, the spectrum analyzer can analyze the bit error rate. By analyzing the data, we can count the error vector amplitude (EVM), amplitude error (magerr), phase error (phasererr) and other results. With the continuous development of communication technology, the corresponding test technology is also put forward higher requirements.

Rsa5065 general source real-time spectrum analyzer is equipped with real-time analysis and frequency sweep analysis functions. It can select vector signal analysis application software (VSA) and EMI measurement application software (EMI). It has excellent performance and indicators. Its frequency range is from 9KHz to 3.2ghz/6.5ghz, and the “TG” model with tracking source is provided, which can be widely used in enterprise research and development, factory production, education and teaching and many other fields.

When observing the signal, rsa5065 can comprehensively use the above four methods to make the engineer’s test more convenient and accurate. It is a powerful tool for wireless communication test which is widely praised by test engineers.

Editor in charge: GT

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