The Application Of Orthogonal Frequency Division Multiplexing Narrow-band Carrier In Communication Of Electric Control Valve

With the development of layered water injection technology in oil areas,to increase the production/injection efficiency,ground system needs to achieve the accurate control of multiple electric control values which installed in different stratum.When the signal is transmitted between ground and electric control value device at high speed,some problems will occur due to the complicated transmission channel environment,such as signal attenuation,noise interference,multi-path propagation,etc.All of these will affect the quality of communication.However,current communication technologies used in down-hole can not fully satisfy the requirements of transmission rate and reliability,particularly in high transmission rate,where transmission errors are more likely to occur.Orthogonal Frequency Division Multiplexing(OFDM)as a special method of multi-carrier modulation has higher transmission rate.And OFDM is suitable for the environment with poor channel characteristics due to its excellent performance of withstanding multi-path interference and signal fading.In this paper,in order to against the transmit errors between ground system and electric control value equipment,a scheme of narrow-band carrier communication in wells with anti-interference is established through combining the OFDM technology used in power line carrier with channel coding technology from the view of carrier modulation.Firstly,according to the OFDM system parameters and the carrier scheme,methods of carrier modulation and demodulation are designed detailedly,including preamble,channel encoding and decoding,encoding mapping and demapping,modulation and demodulation of OFDM symbol,addition and removal of cyclic prefix,synchronization detection,etc.Thereafter,based on the hardware scheme,the circuits,such as power supply,DSP master controller and analog front end,are developed in detail,including components selection,schematics design,analysis and calculation of circuits functions,design and production of PCB,etc.Secondly,different simulations of this carrier system are deployed using MATLAB software,consisting of transmission rate,output signal characteristics,synchronous detection,system performance in disturbance and fading environment,effect of channelcoding,etc.Subsequently,the DSP software of technologies related to the carrier communication is programmed using CCS code development platform and DSP controller.Also,the software debugging results are compared with MATLAB simulation results to verify the validity of software.Finally,a communication protocol is formulated,and the feasibility of system is verified through indoor experiments.The experimental results demonstrate that the hardware and software of OFDM carrier system presented in this paper are able to achieve the point to point communication and multi-machine communication with satisfying results.