TAILIEUCHUNG - Phần mềm xác định radio P3

All wireless communication systems have traditionally employed a radio frequency front end (RF FE) (see Figure ), located between the antenna and the baseband subsystem, the latter commonly implemented with digital signal processing technology. While ‘pure’ software radios anticipate analog-to-digital conversion at the antenna, dispensing with the need for this element of the radio, today’s ‘pragmatic’ software defined radios (SDRs), still (and as will be seen later in this chapter, for the foreseeable future) require an RF FE and place stringent demands thereon | Software Defined Radio Edited by Walter Tuttlebee Copyright 2002 John Wiley Sons Ltd ISBNs 0-470-84318-7 Hardback 0-470-84600-3 Electronic 3 Radio Frequency Front End Implementations for Multimode SDRs Mark Cummings enVia All wireless communication systems have traditionally employed a radio frequency front end RF FE see Figure located between the antenna and the baseband subsystem the latter commonly implemented with digital signal processing technology. While pure software radios anticipate analog-to-digital conversion at the antenna dispensing with the need for this element of the radio today s pragmatic software defined radios SDRs still and as will be seen later in this chapter for the foreseeable future require an RF FE and place stringent demands thereon. The requirement for more cost-effective and reconfigurable RF FEs is one of the major needs of the wireless industry. The perspective of our discussion within this chapter is that of commercial SDR pioneers and practitioners seeking economically viable solutions for the commercial wireless marketplace. As such we describe an early multimode RF FE solution the AN2 6 product family a two-band six-mode design discuss alternative architectural options and outline constraints and possible directions for the future evolution of SDR RF front ends. The basic functions of the RF FE are down- up-conversion channel selection interference rejection amplification Down-conversion is required for receivers. A receiver subsystem takes the weak signal from the antenna converts down- up-conversion the signal from the transmission radio frequency high - RF to baseband frequency low - typically low end of the desired signal will approach 0 Hz filters interference rejection out the noise both from external sources 80 Software Defined Radio Enabling Technologies Figure Wireless device generic architecture and internally generated as an unwanted byproduct and unwanted channels channel selection amplifies amplification the

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