Uncoordinated space-frequency pilot design for multi-antenna wideband opportunistic communications

©2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The statistical side information of interference channels is exploited in this paper to derive a novel uncoordinated on-line pilot design strategy for opportunistic communications. Assuming a time division duplex (TDD), or frequency division duplex (FDD) with feedback, wireless network and reciprocity, we prove that the space-frequency pilot design technique in terms of minimum cross-interference to external-network users reduces to a classical minimum-norm problem. The advantages of this novel methodology are time-domain invariance to noise-subspace rotations, a maximally flat angle-frequency response, and robustness in front of frequency calibration errors. Simulation results are reported to assess the performance of the proposed strategy and the advantages of its low-resolution quantization in low signal-to- noise ratio (low-SNR) regimes.Peer ReviewedPostprint (published version

Dimension spreading for coherent opportunistic communications

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.The waveform optimization problem for opportunistic communications is addressed, based on sensing the second-order statistics of the existing transmissions. We propose a minimum-norm waveform optimization that exhibits robustness to the worst-case subspace mismatch, minimizes the spectral overlapping with the existing transmissions, is rotationally invariant, and has maximally white spectrum. The derived solution can be seen as a different kind of signal dimension-based spreading. In addition, the effects of the residual interference caused to the existing transmissions are studied. Numerical results are provided to assess the performance of the proposed solution in the frequency domain for the asymptotic case. The level of induced interference is compared to traditional null space techniques.Peer ReviewedPostprint (published version