735 research outputs found
Constrained Phase Noise Estimation in OFDM Using Scattered Pilots Without Decision Feedback
In this paper, we consider an OFDM radio link corrupted by oscillator phase
noise in the receiver, namely the problem of estimating and compensating for
the impairment. To lessen the computational burden and delay incurred onto the
receiver, we estimate phase noise using only scattered pilot subcarriers, i.e.,
no tentative symbol decisions are used in obtaining and improving the phase
noise estimate. In particular, the phase noise estimation problem is posed as
an unconstrained optimization problem whose minimizer suffers from the
so-called amplitude and phase estimation error. These errors arise due to
receiver noise, estimation from limited scattered pilot subcarriers and
estimation using a dimensionality reduction model. It is empirically shown
that, at high signal-to-noise-ratios, the phase estimation error is small. To
reduce the amplitude estimation error, we restrict the minimizer to be drawn
from the so-called phase noise geometry set when minimizing the cost function.
The resulting optimization problem is a non-convex program. However, using the
S-procedure for quadratic equalities, we show that the optimal solution can be
obtained by solving the convex dual problem. We also consider a less complex
heuristic scheme that achieves the same objective of restricting the minimizer
to the phase noise geometry set. Through simulations, we demonstrate improved
coded bit-error-rate and phase noise estimation error performance when
enforcing the phase noise geometry. For example, at high
signal-to-noise-ratios, the probability density function of the phase noise
estimation error exhibits thinner tails which results in lower bit-error-rate
Interference Localization for Uplink OFDMA Systems in Presence of CFOs
Multiple carrier frequency offsets (CFOs) present in the uplink of orthogonal
frequency division multiple access (OFDMA) systems adversely affect subcarrier
orthogonality and impose a serious performance loss. In this paper, we propose
the application of time domain receiver windowing to concentrate the leakage
caused by CFOs to a few adjacent subcarriers with almost no additional
computational complexity. This allows us to approximate the interference matrix
with a quasi-banded matrix by neglecting small elements outside a certain band
which enables robust and computationally efficient signal detection. The
proposed CFO compensation technique is applicable to all types of subcarrier
assignment techniques. Simulation results show that the quasi-banded
approximation of the interference matrix is accurate enough to provide almost
the same bit error rate performance as that of the optimal solution. The
excellent performance of our proposed method is also proven through running an
experiment using our FPGA-based system setup.Comment: Accepted in IEEE WCNC 201
Filtered OFDM systems, algorithms and performance analysis for 5G and beyond
Filtered orthogonal frequency division multiplexing (F-OFDM) system is a promising waveform for 5G and beyond to enable multi-service system and spectrum efficient network slicing. However, the performance for F-OFDM systems has not been systematically analyzed in literature. In this paper, we first establish a mathematical model for F-OFDM system and derive the conditions to achieve the interference-free one-tap channel equalization. In the practical cases (e.g., insufficient guard interval, asynchronous transmission, etc.), the analytical expressions for inter-symbol-interference (ISI), inter-carrier-interference (ICI) and adjacent-carrier-interference (ACI) are derived, where the last term is considered as one of the key factors for asynchronous transmissions. Based on the framework, an optimal power compensation matrix is derived to make all of the subcarriers having the same ergodic performance. Another key contribution of the paper is that we propose a multi-rate F-OFDM system to enable low complexity low cost communication scenarios such as narrow band Internet of Things (IoT), at the cost of generating inter-subband-interference (ISubBI). Low computational complexity algorithms are proposed to cancel the ISubBI. The result shows that the derived analytical expressions match the simulation results, and the proposed ISubBI cancelation algorithms can significantly save the original F-OFDM complexity (up to 100 times) without significant performance los
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