Research On Multi-rate Modem Of Broadband Radio

In recent years,wireless communication continues to develop and its applications are becoming more and more widespread.The performance of various aspects of wireless communication systems is also receiving more and more attention.It must not only meet the characteristics of low latency and anti-jamming,but also achieve multi-rate transmission.As an effective communication tool,broadband radio plays a decisive role in wireless communication.Therefore,this paper mainly designs and implements a multi-rate modem in a broadband radio system based on wireless channel processing technology.The physical layer is responsible for wireless data transmission.It uses single-carrier frequency domain equalization,Turbo codes,and direct-sequence spread techniques to form multi-rate transmission frames that accommodate different lengths and different channel qualities.First of all,the technologies related to data processing in the broadband radio system are explained in detail.The direct-spreading technology spreads through 11 Barker codes to broaden the spectrum and enhance the system's anti-jamming capability.The single-carrier frequency domain equalization technology can effectively eliminate the effects of multi-path fading.Turbo coding of data can effectively reduce the bit errors caused by noise and interference to digital signals.The performance of Turbo codes can almost be approximated by the Shannon limit,and thus it has been widely applied in the field of wireless communications.Secondly,to design and simulate multi-rate modems.According to the system function index,the baseband physical frame is designed,and the data frame includes five types of ultra-short frame,short frame,common frame,long frame,and ultra-long frame,which correspond to different frame header information and data information respectively,and their frame lengths are also different.The physical layer data processing algorithms for different types of frames are simulated,multipath and Gaussian white noise are added to the simulation channel,which verifies the performance of the system and lays a foundation for further implementation.Finally,to implement and test multi-rate modems.Firstly,the interface module between the physical layer and the control layer is designed and implemented,and the interface is tested to ensure the reliability of data transmission.Through the interface module,the control information and data information of upper layer can be obtained,and the control information is parsed to obtain the corresponding frame type indication and rate indication,and then the framing is performed according to different frame type structures,and the preamble part is spread and BPSK modulated.According to the rate indication,the data part is turbo coded at the corresponding code rate,and QPSK modulation is performed.Then the modulated signal is up-sampled and shaped and filtered to send the baseband shaped signal out.At the receiving end,the data is captured synchronously and then de-spread is performed to obtain the corresponding control information.According to the control information,the frame type of the received signal is determined.According to different frame types,the data part and the training sequence are retrieved and then to perform frequency offset,phase correction,and frequency domain equalization to eliminate the effects of channel.Turbo decoding is then performed to obtain data information.Then the data information is transmitted to the upper layer through the interface module to complete the FPGA implementation.Finally,the actual transceiver test on the system development platform composed of ZYNQ-7030 and AD9361 verified the feasibility of the system.