Direct-conversion RF receiver design

Abstract

Direct-conversion radio-frequency receiver architecture promises superior performances in power, size, and cost over existing superheterodyne-based receivers. The use of direct-conversion receiver (DCR) architecture, however, has been limited due to two well-known problems, namely, the 1=f noise and the direct-current offset noise, to which conventional architectures are less sensitive. This paper analyzes these noise effects on reception performance of a DCR with alternating-current (ac) coupling filter in the receive path. A mathematical treatment of the performance of a DCR is provided. A performance bound of a DCR given its 1=f noise roll-off frequency and ac-coupling filter cutoff frequency is first obtained using vector coding. Then, the performance of a more practical adaptive reception method using a linear equalizer is discussed. Adaptability is especially important in rapidly time-varying channels such as in the wireless environment. Linear equalizer is effective at signal-to-noise ratios (SNRs) below 9 dB, but its performance degrades significantly at larger SNR. To achieve high performance at large SNR (9 dB), a spectrum shaping method using line codes for direct-conversion reception is proposed. This method achieves near-optimum direct-conversion reception at high SNR while maintaining low complexity and adaptability at the receiver.

A General Approach for Image and Co-Channel Interference Suppression in Diversity Wireless Receivers Employing ICA

“…Traditionally, image rejection in a superheterodyne wireless receiver is performed through analog filtering, which makes the front end costly and difficult to integrate [8]. With the rapid growth of the wireless communications market, this problem has become more serious, because the receivers are required to work at a newly allocated high-RF band.…”

“…Alternative structures, namely zero-intermediate frequency (IF) and low-IF receivers, have been proposed to alleviate the image problem by the adoption of inphase/quadrature phase (I/Q) processing [3], [8]. These structures have a considerable advantage in terms of the hardware complexity, cost, and achievable degree of integration.…”

“…For low-IF receivers, the consequence of the I/Q mismatches is insufficient image suppression [13]. Although the problem is less serious for zero-IF receivers [3], zero-IF architecture suffers from severe distortions near dc, namely, the flicker noise and the dc offset [8]. Therefore, the introduction of an IF stage in the receiver is still preferable in most applications.…”

Early Experiments with W-band Satellite Links

“…The ground terminal EIRP requires a RF power for which an untrivial solution is proposed: to put in parallel 2 to 4 Impatt-amplifiers each having an output RF power between 200 and 400 mW. Besides a commonality with the satellite payload amplifier modules, the solution overcomes the key problem that in W-band, no small power TWTAs (Traveling Wave Tube) are still easily available [7], [8] o More noteworthy than the hardware will be the software part of the ground terminal, in particular that devoted to the orbital prediction, the Doppler frequency corrections from the satellite ephemerides, the baseband signal modulation/demodulation -and coding/decoding if any-part of which is assumed to be performed in software…”

“…In particular the RF power reduction is of outstanding importance at MMW frequencies, where the RF power generation is both difficult, costly and risky [7] [8].…”