International Global Navigation Satellite Systems Association
IGNSS Conference 2016
Colombo Theatres, Kensington Campus, UNSW Australia
6 – 8 December 2016
Receiver Losses when using Quadrature Bandpass
Sampling
Andrew G Dempster and Ediz Cetin
Australian Centre for Space Engineering Research,
School of Electrical Engineering and Telecommunications,
UNSW Australia
+61-2-93856890, a.dempster@unsw.edu.au
+61-2-93854206, e.cetin@unsw.edu.au
ABSTRACT
Use of Quadrature Bandpass Sampling (QBPS) in GNSS receivers gives
several advantages over quadrature-sampled superheterodyne architectures.
The sampling process has the important secondary function of providing
frequency down-conversion (exploiting aliasing) that avoids the use of front-
end RF mixers and oscillators. However, the process is not perfect and does
incur some losses. This paper examines the use of naïve reconstruction of the
QBPS quadrature samples and a simple compensation scheme such as a
constant delay of the in-phase channel, and the losses that these methods
incur. The paper concludes that for satellite navigation systems, losses
incurred due to the use of these simple methods are small enough not to
degrade receiver performance.
KEYWORDS: GNSS receivers, sampling, bandpass sampling, quadrature
bandpass sampling, image rejection ratio
1. INTRODUCTION
Bandpass sampling [1], where signals with high carrier frequency are sampled at much lower
frequencies related to signal bandwidth, has been used in multiband GNSS receiver design
[2]. Quadrature bandpass sampling (QBPS) [3] is an extension to this idea which produces
sequences similar to those produced by sampling in-phase and quadrature versions of a
downconverted signal. Our motivating example is multi-band GNSS [4]. The fact that these
sequences are “similar” but not identical to those produced by an analogue front end is what is
examined in this paper – what are the penalties paid for this approximation, and can they be
tolerated. Following the methods we introduced in [5], we find the answer to these questions
is “small” and “yes”.
