Research And Design Of Wireless Communication System With Smart Antenna Array

After entered21st century, smart antenna, combining antenna array and digital signalprocessing technology, has become one of the key technologies of the third generation (3G)mobile communication. The digital beamforming (DBF) of smart antenna can formdirectional beam and pattern null so as to suppress interference effectively and improve thesystem capacity and communication quality. Moreover, smart antenna technology has beenwritten into mobile communication technology standards of WCDMA, CDMA2000andTD-SCDMA. Hence, the research and development of wireless communication system withsmart antenna array have huge theoretical significance and practical value. In this dissertation,according to the requirement of practical application, the key technologies of communicationsystem with smart antenna array for mobile platform, including antenna array, adaptivebeamforming (ABF), anti-interference, digital transmitter and receiver, and so on, are studied,fabricated and measured. The author’s major works and innovative contributions are asfollows:1. A novel low cost transmitter based on field programmable gate array (FPGA) isdeveloped. It can implement the transmitting function of direct radio frequency modulationwireless serial port communication. The basic work procedure is that FPGA receives theinstruction from upper personal computer (PC), transforms its formation and codes itsequentially and then to modulate carrier wave. The whole design uses the FPGA as the coreand includes a digital lock phase loop, a modulator and a dual digital to analog converter(DAC). Moreover, digital quadrature phase shift keying (QPSK) is adopted in the system.Depending on the powerful performance of the FPGA, the new design has realized thefunctions of digital and analog modulation and spreading spectrum respectively. It can alsorealize the function of frequency hopping.2. Based on a dual polarized planar antenna array, the techniques of beamforming,polarization diversity and microwave phase shifting are researched. According to theapplication character of mobile platform, a structure and algorithm combining digitalmicrowave beam switching and digital beamforming for planar antenna array is developed. Adigital microwave phase shifter is used to steer the microwave beam in vertical plane. Anddigital signal processing technology is used to synthesize beam in horizontal plane. A realplatform is fabricated and the measured results are given to show its validity. 3. An adaptive beamforming and anti-interference module is designed and implemented.For time division multiple access (TDMA) technology is adopted, the data of every user aretransmitted and received at a fixing time slot with a protection interval between any twoadjacent time slots. In the protection interval, multiple signal classification (MUSIC) methodis used to estimate the direction of arrival (DOA). Then minimum variance distortlessresponse (MVDR) beamforming method is utilized to form beam and null the interferences inhorizontal plane. The measured results show that for the inputted4digital signals of theuniform linear antenna array, while the main beam directed to the azimuth of0°, thedeveloped system can form beam null of-30dB at the azimuth of56°, and the gain of thesidelobe is no more than-10dB.4. Based on70MHz intermediate frequency signal, a digital intermediate frequencyreceiver is researched and developed. The intermediate frequency signal is analog-to-digitalconverted firstly and then is digitally down converted (DDC) to baseband signal. The receivedorthogonal polarized signals are combined by weights to enhance the signal in digitalpolarization diversity processing. Rowing window method is adopted here to realize signalsynchronization. Finally, the decoded signal is sent through the serial port to personalcomputer (PC) to display on screen. A real digital receiver is fabricated and the measuredresults show that the bit error rate is no more than10-5.5. A new design of direct radio orthogonal modulation wireless transmitter based onfield programmable gate array (FPGA) is proposed. The new design makes the base-banddigital signal processor directly connect to the radio orthogonal modulator. Software of digitalcoding and modulating is developed. Under the control of FPGA, a microwave phase shiftercan implement2,4,8,16,32or64PSK flexibly. Results of tests show the bit error ratio (BER)of the new design reaches the BER level of the traditional orthogonal modulation scheme, butmore simple and cost-down.6. A new processing method for the planar antenna array is presented. Estimation ofdirection of arrival (DOA) of this method can be implemented by fully digital processingand beam can be formed in two ways. All parts of the system are digitally designed as far aspossible, which enhances the flexibility and adaptability and makes control and update simpleand convenient for the system.