4,923 research outputs found
Optical Time-Frequency Packing: Principles, Design, Implementation, and Experimental Demonstration
Time-frequency packing (TFP) transmission provides the highest achievable
spectral efficiency with a constrained symbol alphabet and detector complexity.
In this work, the application of the TFP technique to fiber-optic systems is
investigated and experimentally demonstrated. The main theoretical aspects,
design guidelines, and implementation issues are discussed, focusing on those
aspects which are peculiar to TFP systems. In particular, adaptive compensation
of propagation impairments, matched filtering, and maximum a posteriori
probability detection are obtained by a combination of a butterfly equalizer
and four 8-state parallel Bahl-Cocke-Jelinek-Raviv (BCJR) detectors. A novel
algorithm that ensures adaptive equalization, channel estimation, and a proper
distribution of tasks between the equalizer and BCJR detectors is proposed. A
set of irregular low-density parity-check codes with different rates is
designed to operate at low error rates and approach the spectral efficiency
limit achievable by TFP at different signal-to-noise ratios. An experimental
demonstration of the designed system is finally provided with five
dual-polarization QPSK-modulated optical carriers, densely packed in a 100 GHz
bandwidth, employing a recirculating loop to test the performance of the system
at different transmission distances.Comment: This paper has been accepted for publication in the IEEE/OSA Journal
of Lightwave Technolog
A low multiplicative complexity fast recursive DCT-2 algorithm
A fast Discrete Cosine Transform (DCT) algorithm is introduced that can be of
particular interest in image processing. The main features of the algorithm are
regularity of the graph and very low arithmetic complexity. The 16-point
version of the algorithm requires only 32 multiplications and 81 additions. The
computational core of the algorithm consists of only 17 nontrivial
multiplications, the rest 15 are scaling factors that can be compensated in the
post-processing. The derivation of the algorithm is based on the algebraic
signal processing theory (ASP).Comment: 4 pages, 2 figure
Generating optimized Fourier interpolation routines for density function theory using SPIRAL
© 2015 IEEE.Upsampling of a multi-dimensional data-set is an operation with wide application in image processing and quantum mechanical calculations using density functional theory. For small up sampling factors as seen in the quantum chemistry code ONETEP, a time-shift based implementation that shifts samples by a fraction of the original grid spacing to fill in the intermediate values using a frequency domain Fourier property can be a good choice. Readily available highly optimized multidimensional FFT implementations are leveraged at the expense of extra passes through the entire working set. In this paper we present an optimized variant of the time-shift based up sampling. Since ONETEP handles threading, we address the memory hierarchy and SIMD vectorization, and focus on problem dimensions relevant for ONETEP. We present a formalization of this operation within the SPIRAL framework and demonstrate auto-generated and auto-tuned interpolation libraries. We compare the performance of our generated code against the previous best implementations using highly optimized FFT libraries (FFTW and MKL). We demonstrate speed-ups in isolation averaging 3x and within ONETEP of up to 15%
Adaptive DSP Algorithms for UMTS: Blind Adaptive MMSE and PIC Multiuser Detection
A study of the application of blind adaptive Minimum Mean Square Error (MMSE) and Parallel Interference Cancellation (PIC) multiuser detection techniques to Wideband Code Division Multiple Access (WCDMA), the physical layer of Universal Mobile Telecommunication System (UMTS), has been performed as part of the Freeband Adaptive Wireless Networking project. This study was started with an analysis of Code Division Multiple Access (CDMA) and conventional CDMA detection. After that blind adaptive MMSE and PIC detection have been analyzed for general CDMA systems. Then the differences between WCDMA and general CDMA were analyzed and the results have been used to determine how blind adaptive MMSE and PIC can be implemented in WCDMA systems. Blind adaptive MMSE has been implemented inWCDMASim, aWCDMA simulator and some preliminary simulation results obtained with this simulator are presented. These simulation results do not yet show the performance that was expected of blind adaptive MMSE detection based on simulation results obtained in previous research. The cause for these unexpected results is not yet known and will be the subject of further research.\ud
Implementation of PIC detection in WCDMASim was found to require changes to the architecture of the WCDMASim simulator. Implementation of these changes and solving the problems with blind adaptive MMSE detection are considered for future work
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