Low-IF 방식을 이용한 8-Ch DBF 수신기의 특성에 관한 연구

Abstract

Wireless communication technologies have greatly progressed in recent years and the markets, especially in the mobile communication have been growing enormously. Moreover the next generation communication services will use higher frequency band, and require more channel capacity and wider bandwidth for a high-speed data communication than nowadays. As a large increase in channel capacity and high transmission rates for wireless communications, the technologies for the power saving and efficient frequency usability are required. To meet the requirements of the next generation wireless communications, a system capable to automatically change the directionality of its radiation patterns in response to its signal environment must be indispensable. The use of spatial resource can noticeably increase the performance such as capacity and quality of a wireless system. The concept of a DBF (Digital Beam Forming) reception system is to control automatically an antenna's reception beam pattern by digital signal processing. The DBF reception system consisted of RF hardware and digital hardware generally. The RF hardware means processing department of reception signal that received from antenna.

Therefore, this thesis describes RF hardware design of 8-Ch DBF reception system for a base-station of mobile communication. In the RF hardware, super-heterodyne method is widely used for wireless communications generally. But DBF reception system used low IF method that existent super-heterodyne method is not. The DBF reception system using low IF method offers significant reduction of circuit complexity by virtue of the elimination of IF circuitry such as IF filters and IF mixers. This DBF reception system consisted of the balanced low noise amplifier, down-converter and power circuit. The used radio frequency (RF), local oscillator (LO) frequency and inter-mediate frequency (IF) are 1.95 GHz, 1.94 GHz and 10 MHz, respectively.

The first stage of DBF reception system designed low noise amplifier. The low noise amplifier operating at 1.92 ～ 1.98 GHz as up-link of IMT-2000 is designed and fabricated. These low noise amplifier is designed as the balanced type by using a compact 90° hybrid coupler.

Secondarily, we designed down-converter for 10 MHz IF conversion and power circuit of receiver. The down-converter consists of band pass filter, mixer, 1940 PLO, 10 MHz TCXO, IF filter, IF amp., IF calibration circuit (phase shift, gain attenuator), de-modulator, etc. The power circuit supplies +15 V, ±8 V, +5 V for the DBF receiver respectively. So we fabricated the 1-Ch DBF receiver with 10 MHz IF and tested performance of receiver. And finally, we fabricated the DBF receiver that composed 8 channels. In DBF reception system, the RF signal is amplified by low noise amplifier and the changed IF on mixer enters by de-modulator. Each of orthogonal I, Q baseband signals output from the de-modulator. These I, Q signals include much information that we want such as direction of signal, data (voice, image), etc.

In the future, DOA (Direction of Arrival) measurement environment was constructed in an anechoic chamber. This measurement system consists of the array antenna, digital signal processing unit, and 8-Ch DBF receiver. And the performance of the receiver will implement DOA estimation experiment.