How to use digital DPD technology to reduce the cost and increase the efficiency of router chip kits?

Part 01

Cost Advantage

Currently, wireless networks in Chinese households generally have problems such as weak signal coverage and poor wall penetration. Most Wi-Fi wireless devices solve this problem by adding high-power, high-linear PAs to the peripheral circuits to increase the transmission power, but this solution also increases the cost of RF chips and peripheral circuit components. High-power Wi-Fi chips based on DPD technology can increase Wi-Fi signal coverage by 15% and signal edge throughput by 20% without using high-power, high-linear PAs. While maintaining the same performance of Wi-Fi devices, the hardware cost of RF chips and peripheral circuit components can be reduced.

Part 02

Performance Advantages  

Improve transmission power and wall penetration capability

Currently, the Wi-Fi transmission power of routers on the open market generally ranges from 20 to 14 dBm under different modulation modes of MCS0 to 11, which has a large room for improvement in accordance with the SRRC "Technical Requirements for Radio Frequency Transmission in 2400MHz, 5100MHz and 5800MHz Frequency Bands". The transmission power of Wi-Fi chip kit solutions based on DPD technology can be increased to the maximum power limit specified by regulations for each frequency band.

The transmit power remains constant under different MCS modulation and coding strategies

Stable high-speed throughput within the coverage area

When Wi-Fi devices are at the edge of signal coverage, as attenuation increases, throughput will drop significantly, affecting user experience. The high-power Wi-Fi chip solution based on DPD technology can not only significantly improve the coverage capability of Wi-Fi signals through signal pre-distortion technology, but also keep the maximum transmit power basically consistent within the coverage range under different MCS modulation and coding strategies while keeping the signal undistorted, which can ensure that the wireless throughput performance of the device remains unchanged and maintain a stable high rate.

Maintain a constant high rate while improving wall penetration

Part 03

How to make full use of the DPD module?  

1) Choose a low-cost, low-process FEM chip.

2) Set the power supply voltage and control logic of the FEM chip.

3) Debugging the DPD digital pre-distortion parameters to match the nonlinear curve of the FEM chip can compensate for the distortion and ensure the linearity of the final output amplified signal.

4) Debug the peripheral impedance matching circuit to further optimize the signal quality.

5) Verify the consistency of the linear amplification curve of the FEM chip under conditions of high and low temperature changes and bias voltage fluctuations.

Part 04

summary  

The pain point of using Wi-Fi routers in home scenarios is often transmission jams caused by insufficient signal coverage. DPD technology is a peripheral custom circuit and performance tuning method that can replace high-gain antennas, beamforming, and high-linear PAs in Wi-Fi wireless systems. It increases the transmission power for small-coverage, low-capacity home scenarios, and increases the coverage range of constant high transmission rates, creating a new high-power, high-efficiency router product category, and achieving enterprise-level wireless performance at the price level of home-level products.

Of course, digital pre-distortion DPD technology also has its technical implementation difficulties. It requires nonlinear characteristic modeling for broadband PA. The challenge is that the distortion characteristics of PA will change with temperature and bias voltage. In actual applications, it is necessary to match different DPD characteristic modeling for different PA amplifier devices. In other words, it is necessary to continuously refine the characteristic matching of the two types of devices to cooperate with the Wi-Fi baseband chip platform to truly exert its low-cost and high-performance effects.