A low-complexity 2D signal space diversity solution for future broadcasting systems

Abstract

International audience—DVB-T2 was the first industrial standard deploying rotated and cyclic Q delayed (RCQD)modulation to improve performance over fading channels. This enablesimportantgains compared toconventional quadrature amplitude modulations(QAM) under severe channel conditions.However, the corresponding demodulation complexitystill prevents its use forwider applications. This paper proposes several rotation angles for different QAM constellations anda corresponding low-complexity detection method. Results show that the proposed solution simplifies both the transmitter and the receiver with often betterperformancethan the proposed angles in DVB-T2. Compared with the lowest complexity demappers currently used in DVB-T2, the proposed solution achieves an additional reduction bymore than 60%. Index Terms— DVB-T2, Rotated and Cyclic Q Delayed (RCQD) Modulations, Signal Space Diversity (SSD), Fading Channel, Quadrature Amplitude Modulations (QAM), Max-Log, ComputationalComplexity

Uniformly Projected RCQD QAM: A Low-Complexity Signal Space Diversity Solution Over Fading Channels With or Without Erasures

“…Different from the sphere decoders [24] used for MIMO systems, the radius of the proposed spheredemapper indicates the number of constellation points to be considered and guarantees to perform successful soft demapping. We also go beyond [22] by proving that for the fading case with one erased component, the nearest constellation point to the observation symbol (also known as the ML point) is always found. We demonstrate that in this case the demapper has the same performance as the Max-Log algorithm.…”

“…According to (22): |x I,3 − x I,1 | = 2 sin α, which contradicts the condition that x 2 is one of the nearest symbol to x 1 in terms of the distance |x I,2 − x I,1 |. Therefore, for any rotated symbol, its nearest neighbor projected on the in-phase component is at the distance d 1D,min = 2 sin α.…”

“…In contrast to previous works [2, 3, 4, 10, 11, 17, 18, 19, 20, 21] which focused only on the transmitter side, [22] put forth a series of rotation angles to greatly simplify the demapper's design and led recently to a proposal of hardware implementation [23]. This series of angles was independently proposed by [28,29] without considering the demapping and complexity issues.…”

“…This series of angles was independently proposed by [28,29] without considering the demapping and complexity issues. In addition, neither [22], nor [28,29] give any proof of the properties introduced by this series of angles. In this paper, we first elaborate on [22] to systematically prove all of the algebraic properties introduced by the considered series of angles and show how they allow the simplification of the demapper.…”

“…In addition, neither [22], nor [28,29] give any proof of the properties introduced by this series of angles. In this paper, we first elaborate on [22] to systematically prove all of the algebraic properties introduced by the considered series of angles and show how they allow the simplification of the demapper. In particular, the fact that the studied rotated constellations keep the uniformity of the non-rotated constellations, enables simple mutual conversions between each projected point over the I or Q axis and its corresponding 2D QAM constellation point.…”