After the Agilent MXG N5182A has been upgraded with hardware, RF performance has been greatly improved. For the digital signal processing section, Agilent introduced an ARB plus real-time filter on the MXG N5182A to achieve baseband signal generation. This concept is described in detail below.
First, RealTIme mode, traditional ARB mode and enhanced ARB modeThere are two traditional vector signal generation modes in the industry: real-time signal generation and waveform file playback (ARB). Agilent's two vector signal generators ESG E4438C and MXG N5182A are representative of these two modes. ESG E4438C has the powerful function of RealTIme signal generation, and supports ARB mode at the same time; and MXG N5182A only supports ARB mode at the beginning of the launch, in order to better meet the needs of production line customers.
At the same time, Agilent has improved the traditional ARB mode of the MXG. Without reducing the process of signal generation and digital signal processing, the final output of the RF signal keeps the original high quality while reducing the signal source hardware to play. The requirements of memory space are indeed technological innovations. We can understand the main difference between RealTIme mode, traditional ARB mode and enhanced ARB mode from the following picture.
Figure 1, WCDMA uplink RMC12.2k signal generation process
In Fig. 1, the WCDMA uplink RMC12.2k signal generation process is taken as an example to describe the entire process of generating a standard WCDMA signal from an appropriate signal source, including the original data through channel coding, framing, oversampling, DAC digital-to-analog conversion, up-conversion, and finally Launched from the radio port.
As can be seen from the figure above, the ESG Realtime mode is the use of DSP for real-time signal framing and digital signal processing. All the processes are done in real time by the hardware inside the signal source. Therefore, from the point A marked in the figure, all are hardware implementation.
The traditional MXG ARB mode, the MXG1, is implemented in software before the DAC's digital-to-analog conversion, labeled as point C (software can be Agilent's Signal Studio software, C or Matlab software). After DAC digital-to-analog conversion, completed by MXG hardware. Therefore, the location of the memory is the position of point C in the figure. According to the signal generation principle, the number of digital signal points here is 78489600 points.
The improved MXG ARB mode, ie, the MXG2 in the figure, before the oversampling, ie the marked B point in the figure, is implemented by software (the software can be Agilent Signal Studio software, C language or Matlab software). After oversampling, it is done in real time by the MXG hardware. Therefore, the location of the memory is at point B in the figure. According to the principle of signal generation, the number of digital signal points here is 39244800 points. Therefore, a 64-MSample playback memory is sufficient for signal storage and playback.
Second, RF performance comparisonHere we will compare the RF performance of the WCDMA signal generated by the Realtime mode and the improved ARB mode mentioned above to see that the improved ARB mode has very good RF performance.
Signal parameters: WCDMA UpLink RMC 12.2k
Frequency: 1GHz
Amplitude: -10dBm
Source: ESG E4438C, MXG N5182A
Spectrum Analyzer: PXA N9030A
ESG (Real time)MXG with Realtime filter
ACPR (dBc) @5MHz offset (Noise Correction off)-65.20-68.82
EVM0.670.44
1.721.01
The following is a list of several MXG vector signal source performance indicators related to base station receiver sensitivity testing.
Figure 2, MXG N5182A launch WCDMA UpLink RMC12.2k performance - ACLR
Figure 3, MXG N5182A launch WCDMA UpLink RMC12.2k performance - EVM
Figure 4, MXG N5182A Launches WCDMA UpLink RMC 12.2k Performance - Code Domain
Third, the conclusionThrough the above principle description and results display, the MXG improved ARB signal generation and processing methods are fully embodied. That is, the real-time filter plus waveform method can fully satisfy the performance requirements of modern base station receiver sensitivity tests for vector signal sources. At the same time, this concept of innovative performance is a good fusion of Realtime mode and ARB mode, which not only maintains the original economic and flexible features of the ARB mode signal source, but also expands the ARB mode's waveform playback space, making the MXG N5182A has enough room for development to meet the ever-increasing testing needs of customers.
From the figure, it can be found that the main difference between the MXG ARB mode before and after the improvement is that the improved MXG will oversampling the link and incorporate it back into the signal source hardware processing link and use the DSP real-time generation that is used in the ESG E4438C Realtime mode. Waveforms in the same way, in the MXG using real-time FPGA to filter the signal twice, which not only achieves the signal performance required for digital signal processing, but also reduces the previous level of storage space requirements, making the pre-level 64MSample Playback memory doubles utilization efficiency.
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