Efficient M-QAM Transmission Using Compacted Magnitude Modulation Tables

Abstract

Magnitude Modulation is a technique proposed with success for QPSK and OQPSK in order to maximize power and bandwidth of small satellite earth stations, by reducing PAPR of the modulated signal at the HPA input. To meet the ever growing demand for higher data rates, higher order modulations have been considered. This paper shows that it is possible to use the magnitude modulation concept for the M-QAM case, even considering the huge number of symbol combinations. The constellation and RRC symmetries are explored, allowing considerable reduction on look-up table computation complexity and storage requirements. Experimental results show considerable gains (>2dB) in PAPR and back-off reduction for 16-QAM with negligible BER losses.

Magnitude modulation for VSAT's low back-off transmission

“…Based on the following proposition [5], only states whose central symbol belongs to X 1 st need to be computed and stored in a LUT. This leads to a reduction on the number of states to be considered by a factor of 2 for RC-RS case and by a factor of 4 for the remaining LUT-MM approaches.…”

“…[3], [4]. MM coefficients are computed a priori by an iterative algorithm [5], [6], and stored in a LUT.…”

“…Resulting from RRC being driven by a sequence of data symbols varying not only in phase but also in magnitude, the control of envelope's peakpower at RRC output is more complex. In order to cope with the additional complexity, new clipping limits were proposed [5] and the method's capability to avoid phase modulation was improved [6]. In addition, we also show that a considerable reduction on LUT's computation complexity and storage requirements can be achieved by exploring the constellation's symmetry and the RRC's linear phase characteristic.…”

Soft-iterative magnitude demodulation

“…In order to avoid phase distortion the MM factors mn are usually taken in R + , i.e. MM performs a polar scaling [3] of sn, with the pulse-shaped signal being given by…”

“…Temporal subscript n can be dropped, since under assumption (3) the statistical distribution that mn follows depends only on the constellation symbol S i and not on the particular instant n 3. A complex number a + jb can be interpreted as a vector with coordinates (a, b), and so the scalar vector product as applied to complex numbers is defined as (a + jb) · (c + jd) ac + bd.Globecom 2014 -Signal Processing for Communications Symposium…”