Living and Dealing with RF Impairments in Communication Transceivers

Abstract

Abstract-This paper provides an overview of the sources and effects of the RF impairments limiting and rendering the performance of the future wireless communication transceivers costly as well as hindering their wide-spread use in commercial products. As transmission bandwidths and carrier frequencies increase effect of these impairments worsen. This paper studies and presents analytical evaluations of the performance degradation due to the RF impairments in terms of Bit-ErrorRate and Image Rejection Ratio. The paper also give highlights of the various aspects of the research carried out in mitigating the effects of these impairments primarily in the digital signal processing domain at the baseband as well as providing lowcomplexity hardware implementations of such algorithms incorporating a number of power and area saving techniques.

RF Impairment Compensation for Future Radio Systems

“…This, in turn, then relaxes the RF filtering requirements and thus simplifies the transceiver implementation in that sense. As practical examples, both the direct-conversion and low-IF radio architectures, discussed in more detail later, are based on the I/Q mixing principle [4,11,[16][17][18]20].…”

“…Based on the signal models in (15.6) and (15.7), the overall effect of I/Q imbalances on both the transmitter and receiver sides is to cause mirror-frequency crosstalk. Practical levels of mirror-frequency attenuation using state-of-the-art analog electronics are on the order of 25 to 40 dB [4,11,16,18]. In general, attenuation levels close to 40 dB are already very challenging to achieve using purely analog techniques.…”

“…One important imperfection is related to the random fluctuations or instability of the oscillator frequency and phase. This is typically called phase noise, 5 1 and basically causes additional or unwanted phase "modulation" to the waveforms transmitted and received [4,7,10,11,17,30,31]. At the modeling level, given an ideal oscillator of cos(ω 0 t) (real case) or exp( jω 0 t) (complex or I/Q case), such random phase fluctuations appear as additional additive phase terms, written here as x LO,R (t) = cos(ω 0 t + n (t)) (15.8) or…”

Design and low-power implementation of an adaptive image rejection receiver

“…However, analog implementations of I/Q signal processing is vulnerable to RF-impairments [1]- [11], resulting in imperfect image rejection, which is not sufficient for communications applications. With large signal constellations of M-QAM/PSK even modest RF-impairments result in detrimental performance degradation.…”

“…However, hybrid and digital solutions have also been reported in the literature which attempts to improve IRR [1] - [8]. An unsupervised adaptive self-calibrating image rejection receiver was proposed and its performance evaluated in [8] utilising the Digital Image Rejection Processor (DIRP).…”