Signal processing challenges for applying software radio principles in future wireless terminals: an overview

Abstract

SUMMARYThe general idea of software radio is to develop highly integrated radio transceiver structures with high degree of flexibility and multimode capabilities, achieved through increased role of digital signal processing software in defining the functionalities which have traditionally been implemented with analog RF techniques. This paper explores the software radio concept from the receiver architecture and signal processing points of view, with mainly the wireless terminal application in mind. We first discuss the critical issues in alternative receiver architectures with simplified analog parts and increased configurability. We also introduce certain advanced digital signal processing techniques which could potentially relieve some of the essential problems and pave the way towards DSP-based, highly integrated, and highly configurable terminals. Big emphasis is on efficient digital multirate signal processing methods and complex (I/Q) signal processing.

Quadrature ΣΔ Modulators for Cognitive Radio—I/Q Imbalance Analysis and Complex Multiband Principle

“…The main principle and impact of I/Q mismatch is quite extensively documented in the scientific literature [23,24,29,32] in ordinary receiver context. In this section, the main objective is to obtain an analytical model for the imbalance effects in case of a quadrature modulator used in an ADC.…”

RF Impairment Compensation for Future Radio Systems

“…This typically leads to rms jitter requirements on the order of a few picoseconds, especially if the dynamic range of the sampler input signal is high [6]. From a jitter point of view, having an input signal with strong out-of-band energy is by far the most problematic case, in which the jitter noise of the strong signal or signals can easily block the weaker signal bands entirely.…”

“…From a jitter point of view, having an input signal with strong out-of-band energy is by far the most problematic case, in which the jitter noise of the strong signal or signals can easily block the weaker signal bands entirely. Notice that based on (15.22), increasing the sampling frequency helps to decrease the jitter requirements, since the jitter noise is distributed over a wider frequency range [6,70,71].…”

A Novel Approach to Blind I/Q Mismatch & Carrier Offset Compensation

“…These levels of image attenuation are clearly insufficient in low-IF-type receivers where the image band can carry a signal with much higher power level than the desired signal. Some digital signal processing (DSP)-based approaches to improve this image attenuation in IF receivers are presented, for example, in [7][8][9][10]. In direct-conversion receivers, the image signal is inherently a self-image (the desired signal itself at negative frequencies), and the analog front-end image attenuation might be sufficient with low-order modulations.…”

“…Thus, architectures with more simplified analog front-ends with less RF processing are generally needed. In addition, it has recently been demonstrated [7][8][9] that various non-idealities and distortion effects due to the simplification of the analog front-end can in general be compensated by advanced DSP techniques. This is also the central theme in this paper.…”