Research of transceiver system based on wireless communication radio frequency technology

The usage of wireless communication technology has been widespread in daily lives. The crucial function that the IF transceiver system plays makes the reliability of the transceiver a top concern. In order to improve the shortcomings of different transceiver systems, it is necessary to understand the design and working principles of today’s transceiver systems. This article will analyze the transceiver systems of different design types, start from their principles, discuss the respective advantages and disadvantages of different types of systems, and discuss the methods that can be improved. After the above research, it can be concluded that different transceiver systems have their own advantages and disadvantages, but they all have the same problems, and they all need to improve their sensitivity and reduce noise interference to improve work efficiency.


Introduction
Radio frequency is an electromagnetic wave signal of a specific frequency that can propagate in free space.Radio frequency communication technology has the characteristics of a wide frequency band, high information capacity, small size, a large available spectrum, and low interference [1].It is widely used in wireless communication systems.In real life, the cable TV signal is transmitted through a radio frequency communication system.The radio frequency transceiver system handles the reception and transmission of signals in the line communication system.It is located at the forefront of the wireless communication system and is related to the quality of communication.This paper will study and discuss the design of different transceiver systems.Therefore, this paper focuses on Studying the working principle of the radio frequency transceiver system and optimizing its design scheme can effectively improve the quality of wireless communication [2].

Radio frequency transmitter Development status and working principle:
While RF transmitters currently dominate the mobile telephony and communications market, there are also problems.Process size, innovation, power consumption and many other issues still need continuous efforts [3].
Working principle: The transmitter converts the low-frequency baseband signal into a corresponding high-frequency signal through modulation, power amplification, up-conversion, filtering, etc.And sends the processed signal through the antenna [4].

Radio frequency receiver
Similar to the development of the transmitter, it also faces no small challenges.At present, all technologies related to the receiver are realized on the basis of AM and FM radio circuits, and how to improve the sensitivity of the receiver is also a major difficulty in current research.Working principle: When the antenna is receiving, the electromagnetic wave sent by the base station is converted into a weak AC current signal.After high-frequency filtering and amplification, it is sent to the intermediate frequency for demodulation, and the baseband information is received and sent to the logic audio circuit for further processing [5].

Receiver design
The basic design of the radio frequency receiver should be based on the channel and frequency required by the communication system [6].First, determine the following performance indicators according to the working channel and frequency of the RF receiver.First, determine the filter order, amplifier gain and noise reduction coefficient according to the center frequency, that is, the center frequency of the filter in the RF front-end circuit; secondly, set The frequency of the intermediate frequency signal needs to be considered in the mixer, which is consistent with the frequency of the input signal and the frequency of the local oscillator signal.For ease of control, choose the right frequency input voltage source at the same time.Next, design and build the baseband circuit, the down-conversion circuit, and the RF front-end circuit [7].The amplifier and the filter form the RF front-end circuit, the centimeter, the phase shifter and the mixer form the down-conversion circuit, and the baseband circuit is composed of two branch lines cascaded with the baseband amplifier and the channel selection low-pass filter, and the circuit infrastructure.After the construction is completed, the circuit components of the basic parts of each circuit are determined to complete the design of the RF receiver [8].
The main topic of discussion here is the superheterodyne radio frequency receiver.1> Signal path: The signal is picked out by the band-pass filter BPF1 and sent to the high-frequency amplifier after being picked out by the antenna.The amplified signal then enters the mixer and combines with the local oscillator to form an intermediate frequency signal before being sent.After passing via the baseband chip for demodulation and amplification, the filtered intermediate frequency signal from the band-pass filter BPF2 is amplified and filtered by the intermediate frequency amplifier before being output as the relevant sound and data signals [9].
2> Features: The radio frequency signal is a high-frequency signal, the 2G signal ranges from 850MHZ to 2100MHZ, and the channel is only a few hundred KHz.Therefore, it is very difficult to select a channel of hundreds of KHz from a high frequency, and the requirements for the filter are very high.Therefore, we convert the frequency of the signal, and we know that the frequency mixing of the signal is actually a shift of the spectrum in the frequency domain.We set the frequency of the local oscillator signal to change with the change of the input signal, and the frequency of the output signal is fixed, so that the frequency spectrum of the output signal can be moved to a fixed frequency band.That is, move the 100M or 1000M signal to the KHZ or several MHZ intermediate frequency band.At this time, it is easier to choose a channel of several hundred KHZ.And this is also the characteristic of the superheterodyne receiver, that is, the frequency ωLO of the local oscillator signal entering the mixer changes with the frequency ωRF of the received signal, so that the frequency of the output intermediatefrequency signal ωIF remains constant.
Of course, this kind of receiver also has many advantages and disadvantages at the same time: the performance of superheterodyne is better than that of traditional receivers, but it improves the performance at the expense of cost and space.At the same time, due to multiple frequency conversions, the power consumption is relatively large.Corresponding modulation methods may include QPSK/QAM.However, there is also noise interference [10].

Transmitter design
Average carrier frequency is one of the key performance metrics that influence RF transmitter design.
The RF transmitter is designed to complete the corresponding modulation processing through the power amplifier, change the structure of the signal frequency, and send the processed signal frequency through the antenna.The design of the shooting face transmitter includes the design of the amplifier circuit and the design of the crystal oscillator circuit: When designing the amplifier circuit, the appropriate triode should be selected to meet the static operating point current of the triode, and the resistance value should be adjusted reasonably to ensure the working voltage in the circuit.The commonly used crystal oscillating circuit is a parallel crystal oscillating circuit.The quality of the crystal and the structure of the oscillator affect the vibration performance of the circuit.Among them, the Clapp oscillation circuit works the most steadily, and the loop is weakened by the capacitance due to the influence of the electrode tube.It belongs to the three-point oscillator with capacitive feedback, so the frequency stability of the Clapp oscillation circuit is high, and it is often used in the design of RF transmitters [11].
The offset phase-locked loop transmitter is the main topic here: the offset phase-locked loop is made up of four parts: an offset mixer, an identification phase frequency detector (PFD), a loop filter (LPF), and a transmit VCO.The baseband signal TX I/Q is modulated before the intermediate frequency IF VCO to obtain the transmitted intermediate frequency modulated signal.This signal is then sent to the phase frequency detector (PFD) of the OPLL.The frequency and phase detector is a three-terminal device.After phase comparison with the input signal from the offset mixer at the other end, the phase error signal Err is output (the phase error signal Err is actually a control signal that modulates the final TX VCO) .The signal is filtered by LPF to remove high-frequency noise and AC signal to obtain a pulsed DC signal, which contains TX I/Q information.Then use this signal to modulate the VCO, and then modulate the signal containing the baseband information to the transmit carrier to obtain the carrier signal TX VCO.This signal is divided into two channels, one of which is amplified by the back-end PA, and finally transmitted through the antenna; the other part is sent to the offset mixer and mixed with the RF VCO of the radio frequency to complete the negative feedback [12].
When the loop is stable, fIF=fRF -fTX can be obtained, and the negative feedback circuit is stable.
Since the FPD has two inputs, each input signal can cause a change in the output signal: First, when switching channels, the baseband controls the frequency of the RF VCO to change the Err control signal, which in turn affects the change of the TX VCO output signal.
Second, when the baseband I/Q signal with information changes, the Err control signal will also change, affecting the final TX VCO output change, so that the signal change is finally transmitted through the antenna.
There is an OPLL architecture in which a frequency divider is added via a negative feedback circuit to ultimately generate a multiplied output RF VCO signal, however the OPLL indicated above is undoubtedly the most typical type.But in the final analysis, the signal frequency conversion, adjustment, and tracking are all done through the offset phase-locked loop.Figure 3 shows that Transmitter Circuit Block Diagram.Both the benefits and drawbacks of this sort of transmitter are readily apparent.For example, the offset phase-locked loop architecture allows the negative feedback signal TX VCO to get the minimum dynamic phase error and locking time, which promotes the transmitter's rapid stability.The benefits increase the system's sturdiness and have a positive impact on interference suppression.In line with this, all different types of transmitter topologies have relatively significant design costs because of how complicated the circuit is.

Analysis and comparison of different designs
3.3.1.Receiver.In addition to superheterodyne receivers, there are many types of zero-IF receivers.Compared with the superheterodyne, the structure of the zero-IF receiver is simpler, and the zero-IF receiver is also called a direct down-conversion receiver.In this scheme, the local oscillator signal frequency ωLO directly and completely follows the signal frequency ωRF, that is, ωLO=ωRF, from which the intermediate frequency signal ωIF=ωLO-ωRF=0, which is also the origin of the name zero intermediate frequency.Since ωLO=ωRF, the high-frequency carrier signal of the output signal after mixing is completely canceled, and the baseband signal is directly restored.
As the frequency is directly down converted to the baseband frequency, there is no need for numerous additional circuits for processing at intermediate frequencies.This considerably simplifies the circuit, makes integration easier, and lowers the cost.Figure 4 shows that Zero-IF receiver design architecture diagram.Advantages and disadvantages: The advantage of this is that the structure is very simple and the cost is correspondingly low.However, since the local oscillator signal and the transmitted signal are signals of the same frequency, there is a situation in which the two interfere with each other.The leakage of the transmitted signal will affect the accuracy of the local oscillator.

Testing and transmitting efficiency analysis
When testing the receiver and transmitter, it is necessary to complete the test content such as transmitter gain and leakage, receiver input third-order intercept point, gain step size, and noise figure.First, check that the voltage is 5V, then use an instrument to detect the signal across the receiver.The noise detected at the output is attenuated and no signal is detected at the input.According to the two detection frequency ranges, the receiver gain variation range is determined, and the transmit gain is controlled.Secondly, connect the noise source to the input port of the noise analyzer to calibrate the noise analyzer.After completion, connect the noise signal at the output of the receiver to a noise analyzer to obtain the noise figure at the maximum gain of the receiver.Finally, the system power of the transmitter determines the propagation distance of the electromagnetic signal, and the leakage value of the RF transmitter must be strictly controlled to prevent it from affecting the signal-to-noise ratio of the transmitting system [13].   1 and Table 2 that in terms of performance, the superheterodyne is better than the zero-IF receiver, and the offset phase-locked loop is better than the direct conversion transmitter, but at the same time, similarly, the cost and space of the former will be larger.Structural and operational aspects will also be more complex.

Conclusion
The RF transceiver system's operating system, present state of development, and analysis are covered in this paper.At the same time, it clarifies the different architecture design requirements, test principles and key points of different types of transceiver systems.It also analyzes the advantages and disadvantages of different types of transceivers.The advancement of science and technology has promoted the rapid development of radio frequency technology in wireless communication.Radio frequency technology has been widely used in people's lives.Wireless communication has changed people's living and working habits, and realized direct communication between people and equipment.People's dependence on wireless communication systems becomes stronger and their requirements become higher.The working performance and application performance of the wireless communication system are the key to the system design.Researchers still need to research on this issue since it is currently the key design challenge to increase receiving sensitivity, adjacent channel selectivity, noise figure, and dynamic range while increasing operating efficiency.

Figure 3 .
Figure 3. Transmitter Circuit Block Diagram.Both the benefits and drawbacks of this sort of transmitter are readily apparent.For example, the offset phase-locked loop architecture allows the negative feedback signal TX VCO to get the minimum dynamic phase error and locking time, which promotes the transmitter's rapid stability.The benefits increase the system's sturdiness and have a positive impact on interference suppression.In line with this, all different types of transmitter topologies have relatively significant design costs because of how complicated the circuit is.

Figure 5
shows the internal block diagram of the direct conversion transmitter.

Figure 5 .
Figure 5.The internal block diagram of the direct conversion transmitter.Looking closely at the picture above, we can see that the direct conversion transmitter is actually reversing the signal flow to the zero-IF receiver.The baseband I/Q signal is directly mixed with the radio frequency local oscillator signal, and the up-conversion of the radio frequency section is completed in one step.Therefore, the transmitting frequency of the radio frequency is the frequency of the local oscillator.The transmitter of a certain platform of the MTK61 series adopts the direct conversion architecture.Advantages and disadvantages:The advantage of this is that the structure is very simple and the cost is correspondingly low.However, since the local oscillator signal and the transmitted signal are signals of the same frequency, there is a situation in which the two interfere with each other.The leakage of the transmitted signal will affect the accuracy of the local oscillator.

Table 1 .
The multifaceted comparison of different RX.

Table 2 :
The multifaceted comparison of different TX.