In wireless communication systems, we often talk about baseband, intermediate frequency, radio frequency, antenna and other physical layers. automatic probe station This paper briefly introduces the digital frequency conversion in the medium frequency part.
Digital conversion is an integral part of the basic architecture of many Chinese digital radio management systems, including the conversion of discrete baseband transmission signal streams to high resolution and radio signals on the transmitter, and the conversion of high resolution radio signals back to baseband processing signals on the receiver.
This paper introduces the basic knowledge of digital conversion (analog-to-digital conversion and digital-to-analog conversion), digital up conversion (DUC) and digital down conversion (DDC) in intermediate frequency and baseband digital conversion.
In communication systems, digital downconversion and DUC are important components of RF front end. private 5g Example of a digital radio transceiver with a superheterodyne architecture. This is a two-stage conversion architecture, in the first stage, the radio frequency (RF) signal is converted down to the intermediate frequency (IF), and then in the second stage, from the intermediate frequency to the baseband signal. The hardware parts of RF, IF and baseband are controlled by software and reconfigurable. This radio transceiver architecture is known as software-defined Radio (SDR).
In the proposed SDR architecture, the RF front end (also known as the analog front end) is the only analog part, which includes the mixer, low noise amplifier (LNA), power amplifier (PA), RF merger, bandpass filter (anti-aliasing), and antenna. The RF front end is responsible for the conversion between RF and IF and sends/receives RF signals. private lte Some advanced RF front ends allow a degree of control through software, such as frequency tuning.
Other parts of the SDR architecture are the digital processing components. In the IF portion, sampling and separation of the IF carrier and conversion from up to down to baseband are done by digital IF processing, which is typically implemented in FPgas. Take the receiving path as an example; If signals are digitized by analog-to-digital converters (ADCs) and converted into baseband signals by digital IF processing. Digital IF processing performs DDC operations such as digital synthesis, digital NCO, digital mixers, IFQ demodulation, and multi-rate decimation filtering. Again, it executes DUC in the reverse order of DDC. Digital systems such as field programmable gate arrays (FPgas) are commonly used to perform IF to baseband conversions because they can handle the strict real-time constraints that come with high-speed sampling and digital conversions. Finally, in the back-end of SDR architecture, the baseband process mainly completes the digital communication functions such as symbol timing recovery, equalization, modulation and channel coding. These functions are usually calculated by digital signal processors (DSP), and the real-time constraints are slightly relaxed.
The development structure of the SDR system is more inclined to enterprises to use the national universal digital information system. Utilizing FPGas and DSPS in SDR will allow the generation of transmitted signals and tuning/detection of received radio signals at the receiver, studying digital operations through analytical software design, rather than the traditional Chinese approach of analog signals requiring specific social functions to be performed by using a single hardware component. Software engineering-defined radio management system work provides a great extension of programmability, reconfigurability, and definability. SDR's goal is to achieve a flexible, versatile and multi-standard radio system for students.
In wireless communications, the Nyquist-Shannon sampling theorem is a widely discussed topic in digital signal processors (DSPS), which states that the sampling frequency f must be greater than or equal to twice the maximum frequency component of the signal. Less than the sampling rate specified by Nyquist will result in a folding or "aliasing" effect, in which the original signal cannot be accurately converted back into an analog signal if needed. This method of converting an analog signal to a digital signal is called low-pass sampling.
