Design And Verification Of Long-distance Transmission RF Unit By WIFI Analog Signal

In order to reduce the cost of large-area coverage of a local area network,a WiFi chip implemented by long-distance transmission of analog signals is one of the key technologies to promote its commercialization.This paper built a RF unit to analyze the feasibility of the WiFi chip.The RF unit uses a network cable for long-distance transmission at a maximum distance of 100 m.Among them,less spectrum,high thermal noise,and selective fading in the frequency domain are the main challenges brought by network cable long-distance transmission.According to the 802.11 n and 802.11 ac protocol specifications,paper researches and verifies the key technologies of long-range transmission of RF units for WiFi analog signals.The main tasks include:First,it discusses three solutions for the distributed architecture of long-distance transmission of WiFi analog signals.Analyze and compare the advantages and disadvantages of the Super-heterodyne frequency conversion scheme,Complex I-Q frequency conversion scheme,and Generating low-IF frequency by Baseband directly scheme.Considering the implementation difficulty and cost of the solution,it was determined that the RF unit adopts the Super-heterodyne frequency conversion scheme.Second,complete the RF unit design based on overall needs and RF index analysis results.Firstly,according to the performance indicators of commercial AP and the 802.11ac/802.11 n protocol specifications,the overall requirements for the long-distance transmission of radio frequency units for WiFi analog signals are refined.Then,analyze and summarize the key RF indicators such as the transmitting EVM,non-linearity,receiving dynamic range,and noise figure of the RF circuit.At last,select appropriate RF devices to complete the detailed design of the RF transceiver channel,clock unit,real-time control unit,channel configuration unit and control unit,and budget for the relevant RF indicators of each unit.Third,build a test environment to complete the index test.In the system test environment of the RF unit,the performance of the transmission channel is as follows: EVM(27)-36.2dB for 802.11 n WiFi signals with a bandwidth of 20 MHz and EVM(27)-38.65 dB for 802.11 ac WiFi signals with a bandwidth of 80 MHz.The performance of the receiving channel is as follows: The dynamic range of 802.11 ac WiFi signal reception with a bandwidth of 20 MHz is-20~-80.3dBm.In an open environment,the air interface streaming rate is stable at 138 Mbps for 802.11 n 4×3 MIMO and 720 Mbps for 802.11 ac 4×3 MIMO.Finally,according to the test results,suggestions are made for the next research on the long-distance transmission of WiFi analog signals.This paper designs and implements a long-range transmission of WiFi analog signal RF unit,which have 4 chaneels to transmit and receive 802.11 n and 802.11 ac WiFi signals,the maximum bandwidth is 20 MHz and 80 MHz respectively,and the maximum transmission distance of network cable is 100 m.The thesis provides verification for the long-distance transmission of WiFi analog signals using network cables,and provides a reference value for the feasibility analysis of chip-based solutions.Its implementation and verification provide certain technical support for chip design and verification.