| Wireless video transmission is an old research focus.It is the objective of several generations of telecommunication engineers that making people enjoy the high-quality and reliable wirless video communication conveniently at any time any place.This objective is not completely realized nowadays.The key point is wireless transmission.It is impossible to realize a very perfect wireless video transmission system through existing industrry and manufacturing. Therefore, tradeoff must be made between video's quality,transmission distance, portability,price ,user capacity etc.in existing transimission systems to tailor to different applications. The project is proposed under this background and the prime task is to design and implement a wireless video transmission system though upgrading a 400-512MHz center frequence adjustable ,half-duplex,FM audio transceiver.The features of this system are listed below:(1)The system is developed based on a mature UHF FM transceiver.The wireless transmission distance can reach more than ten miles;(2)H.264 and MPEG4 Image coding source which have high image compression ratio.Users can adjust sharpness and fram rate upon certain transmission bit rate to adapt to different application;(3)Adopt FSK modulation and support several bit rate scheme (up to 256kbit/s) to establish multi-user system flexibly;(4)Self-developed PCB accomplishes the functions of FM modem,signal shaping, carrier extraction,control etc.(5)High economic value and practicality.The audio UHF FM transceiver is very popular.It is convenient and low cost to realize long distance wireless image transmission by upgrading the existing transceiver and adding a PCB and some image acquisition devices (such as camera and screen). Because of the long transmission distance without the support of base stations,the product applies in particular to the image monitoring, public security, building construction, or scientific research, communications and other fields in remote areas.It takes nearly ten months from proposing the initial concept to establishing the wireless data transmission system.This thesis is a summary of that ten months work and the key issues of developing the system.Firstly,the thesis introduce the structure and key parameters of the audio transceiver we used and then introduce the scheme of upgrading the transceiver and the design of the self-developed baseband PCB in detail including contrast of different design scheme.Then demonstrating the performance by error bit ratio and receiver sensitivity,discussing the scheme of estabishing a multi-user system.The thesis proposes a innovative approach to change IF by setting a offset between transmitter's and receiver's center frequence so as to benefit FM demodulation.The performance and key signal waveforms are analyzed theoretically.In conclusion,this thesis present an entire narrow-band wireless video transmission system.Experiment proved that when the system received signal power more than -130 dBm, the error rate data is in a negative seven to ten orders of magnitude. In the laboratory,the scheme proposed in this thesis has been implemented.At the end of this thesis,the defects of the system are discussed and some advices are proposed for future system development. |
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