Spectral precoding and windowing are two effective approaches to reduce out-of-band radiation (OBR) in multicarrier systems. Their performance comes at the price of reduced throughput and additional computational complexity, so there is strong motivation for simultaneously using both techniques. We present a novel design that jointly optimizes the precoder and window coefficients to minimize radiated power within a user-selectable frequency region. Results show that the proposed design achieves a better OBR/throughput/complexity tradeoff than either of these individual techniques separately.

%B IEEE Communications Letters %V 26 %P 3044-3048 %8 12/2022 %G eng %N 12 %R 10.1109/LCOMM.2022.3203521 %0 Conference Paper %B European Signal Processing Conference (EUSIPCO) %D 2022 %T Orthogonal precoding with memory for sidelobe suppression in OFDM %A Khawar Hussain %A R. López-Valcarce %K rodin %K spectrum shaping %XOrthogonal precoding is a very effective approach to reduce out-of-band radiation (OBR) in multicarrier systems in order to avoid adjacent channel interference. This is achieved at the cost of introducing precoder redundancy, which results in throughput loss. Introducing memory in the precoding operation has the potential to improve performance without sacrificing additional spectral efficiency, in exchange for extra computational complexity. We present a novel orthogonal memory precoder which minimizes OBR within a user-selectable frequency region and allows for controlling spectral overshoot. Decision-feedback decoding avoids symbol error rate degradation at the receiver.%B European Signal Processing Conference (EUSIPCO) %G eng %0 Journal Article %J IEEE Transactions on Communications %D 2021 %T Mask-Compliant Orthogonal Precoding for Spectrally Efficient OFDM %A Ravinder Kumar %A Khawar Hussain %A R. López-Valcarce %K rodin %K spectrum shaping %K winter %X

Orthogonal precoding constitutes a powerful technique to reduce spectrum sidelobes of multicarrier signals. This reduction is bought at the cost of introducing precoder redundancy, which results in some throughput loss and additional precoding/decoding complexity. When the goal is to meet some spectral emission mask constraints, it is desirable to avoid unnecessary sidelobe suppression in order to keep precoder redundancy at a minimum. In this context, we introduce a general framework under which we develop a novel Lagrange multiplier-based mask-compliant orthogonal precoder design targeting minimal redundancy. We also adapt to this framework two previously proposed

designs based on spectral notches and minimum out-of-band emission, respectively, to explicitly incorporate mask constraints. Simulation results are provided to show the effectiveness of the proposed designs under different practical masks for multicarrier wireless systems.

%B IEEE Transactions on Communications
%V 69
%P 1990-2001
%8 03/2021
%G eng
%N 3
%R 10.1109/TCOMM.2020.3041351
%0 Conference Paper
%B IEEE Int. Workshop Signal Process. Adv. Wireless Commun. (SPAWC)
%D 2021
%T Memory Tricks: Improving Active Interference Cancellation for Out-of-Band power reduction in OFDM
%A Khawar Hussain
%A R. López-Valcarce
%K rodin
%K spectrum shaping
%X Although active interference cancellation (AIC) is an appealing approach to reduce out-of-band radiation (OBR) in multicarrier systems without distorting data subcarriers, it usually requires a large number of reserved subcarriers to be effective. Introducing memory in AIC precoding may help alleviate this drawback in exchange for some increase in computational complexity. We propose a novel memory AIC precoder which, in contrast to previous schemes, minimizes OBR within a user-selectable frequency region and allows for controlling spectral overshoot.

%B IEEE Int. Workshop Signal Process. Adv. Wireless Commun. (SPAWC) %C Lucca, Italy (Virtual event) %G eng %0 Conference Paper %B IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP) %D 2020 %T Optimal window design for W-OFDM %A Khawar Hussain %A R. López-Valcarce %K spectrum shaping %K winter %XWindowing is an effective approach to reduce out-of-band radiation (OBR) in multicarrier systems in order to avoid adjacent channel interference. However, commonly used window functions are chosen in an ad hoc manner and fixed. We present an optimal window design for windowed-OFDM minimizing OBR within a given frequency region. The proposed technique is flexible in that it allows to specify the range of frequencies involved in the minimization and to apply spectral weighting. The optimal window can be computed offline.

%B IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP)
%8 05/2020
%G eng
%1 Accepted.

%0 Conference Paper %B 2nd XoveTIC Conference %D 2019 %T Flexible spectral precoding for OFDM systems %A Khawar Hussain %A R. López-Valcarce %K spectrum shaping %K winter %XSpectral precoding is a popular approach to reduce out-of-band radiation (OBR) in

multicarrier systems in order to avoid adjacent channel interference. However, it introduces

distortion in the data, appropriate decoding is required at the receiver side. Thus, trading off

between implementation complexity, OBR reduction and error rate is important. We present a novel

linear precoder design with flexibility to trade off OBR reduction, precoding/decoding complexity,

and error rate at the receiver. Moreover, the constraint can be imposed on each subcarrier individually

to provide more flexibility. The precoding matrices have low rank, which translates into significant

computational savings. In this way, the requirements of different systems can be satisfied with

varying complexity levels

%B 2nd XoveTIC Conference
%C A Coruña (Spain)
%8 09/2019
%G eng
%R 10.3390/proceedings2019021024
%0 Conference Paper
%B IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP)
%D 2019
%T Flexible spectral precoding for sidelobe suppression in OFDM systems
%A Khawar Hussain
%A Ana Lojo
%A R. López-Valcarce
%K spectrum shaping
%K winter
%X Spectral precoding is a popular approach to reduce out-of-band radiation (OBR) in multicarrier systems in order to avoid adjacent channel interference. Since precoding will introduce signal distortion, appropriate decoding is required at the receiver side. We present a novel linear precoder design with flexibility to trade off OBR reduction, precoding/decoding complexity, and error rate at the receiver. The precoding matrices have low rank, which translates into significant computational savings. In this way, the requirements of different systems can be satisfied with varying complexity levels.

%B IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP) %I IEEE %C Brighton, UK %P 4789 - 4793 %8 04/2019 %G eng %R 10.1109/ICASSP.2019.8683162 %0 Conference Paper %B European Signal Processing Conference (EUSIPCO) %D 2019 %T OFDM spectral precoding with per-subcarrier distortion constraints %A Khawar Hussain %A R. López-Valcarce %K spectrum shaping %K winter %XSpectral precoding is effective in reducing out-of-band radiation

(OBR) in multicarrier systems, but it introduces distortion

in the data, requiring a suitable decoder at the receiver.

Thus, trading off OBR reduction, implementation complexity,

and error rate is of paramount importance. We present a precoder

design which minimizes OBR under constraints on the

distortion at each individual data subcarrier. By judiciously

choosing the distortion profile, the decoding task can be significantly

alleviated, with a sizable improvement in terms of

implementation complexity with respect to previous designs.

%B European Signal Processing Conference (EUSIPCO)
%C A Coruña, Spain
%8 09/2019
%G eng