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Application of RF Power Meter in PAPR Analysis and Suppression
2021-09-15
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Author:Frank

The RF peak power meter is a simple, easy-to-use and cost-effective measuring instrument that can be used to measure PAPR (peak-to-average power ratio) and evaluate the effectiveness of PAPR suppression technology.

Everyone knows that the demand for mobile broadband services has been increasing exponentially. In order to solve this demand, enhanced mobile broadband (eMBB) is one of the key basic technologies for the transition to 5G, and higher data rates can also increase the military The communication capability of the communication network. To meet these requirements, engineers are developing technologies that support high-speed data transmission, high mobility, and more efficient use of existing spectrum and network resources. Orthogonal Frequency Division Multiplexing(OFDM) is one of the important technologies in many communication systems. It has advantages in these fields: including 4G (LTE), WLAN (IEEE 802.11a/ac/ax/g/n), Digital wireless technology, cable transmission (DAB and DVB-C2), and even copper broadband access (ADSL)

In OFDM signals, digital data is encoded on multiple frequencies or sub-carriers. Each sub-carrier is modulated at a low symbol rate using a traditional modulation scheme, such as quadrature amplitude modulation (QAM) or phase-shift keying, and occupies a frequency in a sub-band. It is different from other modulation schemes such as frequency division multiplexing (FDM). The subbands can be overlapped to improve the spectral efficiency because each subband is orthogonal to the next subband. This method makes OFDM less sensitive to fading caused by narrow-band co-channel interference, inter-symbol interference, and multipath transmission1.

One of the main disadvantages of OFDM is that multiple sub-carriers will be superimposed on each other to increase and produce high PAPR (see Figure 1). With the requirement for higher data transmission rate, the number of sub-carriers must continue to increase to meet the demand, which will increase PAPR. Figure 2 shows the relationship between PAPR and the number of subcarriers (N)2.
The importance of PAPR

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High PAPR can cause many problems in the amplifier. If the peak power is not set correctly, once the signal enters the non-linear working area of the amplifier, it will cause signal distortion and spectrum expansion or spectrum regeneration. On the other hand, if the input power is reduced (usually referred to as input power back-off (IBO)), it will cause the amplifier's operating efficiency to decrease. In Figure 3, the input signal of the amplifier is backed by 6 decibels and 8 decibels respectively; it can be seen that the input signal back-off by 6 decibels leads to higher spectral regeneration than the back-off by 8 decibels. The spectrum regeneration will cause mutual interference between sub-carriers, resulting in an increase in the bit error rate (BER); however, if the amplifier output power is reduced, the signal-to-noise ratio (SNR) will be reduced, which will also lead to an increase in the bit error rate. . If the main purpose is to blindly increase the data transmission rate, the poor bit error rate will make it counterproductive.

Efficiency is very important in many applications. For mobile phones, the efficiency of their amplifiers will have an impact on battery life. For network operators, the efficiency of base stations will affect their operating expenses. Amplifiers usually work most efficiently near saturation. To illustrate this point.
Reducing PAPR is the only way to reduce the spectrum regeneration rate and maintain high efficiency. According to this principle, in OFDM-based systems, many studies have developed techniques to reduce PAPR to reduce amplifier compression while minimizing the necessary IBO. Rahmatallah and Mohan2 performed an excellent review and weighing of different technologies, and their results are summarized in Table 1. Cutting and filtering are the most commonly used in pcb commercial products because of their simplicity and ease of implementation.