6,193 research outputs found
Joint transmitter and receiver optimization in additive cyclostationary noise
No full textA joint optimization of transmitter and receiver is considered for strictly band-limited linear modulations in additive cyclostationary noise. Under the assumptions that the period of the cyclostationarity of the noise is the same as the inverse of the symbol transmission rate and that the noise has a positive-definite autocorrelation function, the optimum transmitter and receiver waveforms that jointly minimize the mean-squared error at the output of the linear receiver are derived with the data sequence modeled as a wide-sense stationary (WSS) colored random process and the channel modeled as a linear time-invariant system with a general frequency-selective impulse response. Numerical results show that this joint optimization technique leads to a significant performance improvement over the systems with receiver-only optimization and the systems with no transmitter and receiver optimizations.X1128sciescopu
Multiuser constrained water-pouring for continuous-time overloaded Gaussian multiple-access channels
No full textIn this paper, signature waveforms and signal powers are jointly optimized for multiuser communications over strictly bandlimited, continuous-time, overloaded channels corrupted by additive white Gaussian noise (AWGN). The total signal power is minimized subject to general asymmetric signal-to-interferenceplus-noise ratio (SINR) constraints at the output of linear minimum mean-squared error (LMMSE) receivers. Using vectorized Fourier transform (VFT) technique, the optimal solutions as well as a necessary and sufficient condition for the existence of a feasible solution are derived in the frequency domain. It turns out that every optimal solution performs the same as the optimal frequency-division multiple-access (FDMA) system. A geometric procedure called multiuser constrained water-pouring is developed to construct every possible optimal solution, of which profiles of signal power and equivalent bandwidth are, respectively, the same as those of signal power and physical bandwidth of the optimal FDMA system. It is shown that orthogonal signature waveforms are assigned to oversized users and continuous-time equivalents of generalized Welch bound equality (CTE-GWBE) sequences are assigned to non-oversized users.X117sciescopu
Asymptotic Optimality of Binary Faster-than-Nyquist Signaling
No full textIn this letter, the asymptotic information rate of faster-than-Nyquist (FTN) signaling is examined when the data sequence consists of independent and identically distributed (i.i.d.) binary symbols. It is shown that, as the FTN rate tends to infinity, the information rate converges to that of the FTN signaling with i.i.d. Gaussian symbols. This leads to the optimality of the i.i.d. binary FTN signaling in the sense that the channel capacity can be asymptotically achieved by employing a transmit pulse that results in the same power spectral density as the water-filling solution.X111820sciescopu
Continuous-time equivalents of Welch bound equality sequences
No full textThe theory developed on the sequence optimization for equal-power code-division multiple-access (CDMA) systems is generalized in this paper. Unlike previous works, where discrete-time or vector channel models are predominantly employed, the overloaded channels are modeled as strictly band-limited, continuous-time multiple-access channels corrupted by additive white Gaussian noise (AWGN). After being posed as a multiple-input/single-output (MISO) joint transmitter and receiver optimization problem with the total mean-squared error (MSE) as the objective functional to be minimized, the variational problem is solved by using a frequency-domain approach. It is shown that there exist continuous-time equivalents of Welch bound equality (CTE-WBE) sequences as the jointly optimum transmit waveforms and that the matched filters are the jointly optimum receivers. The user capacity of the band-limited channels is characterized by a necessary and sufficient condition for the admissibility of users into the system in terms of the channel load, the received signal-to-noise ratio, and the signal-to-interference-plus-noise ratio (SINR) requirement. It is also shown that CTE-WBE sequences achieve the lower bound on the continuous-time equivalent of total squared correlation (CTE-TSC).X119sciescopu
Asymptotically Optimal Low-Complexity SC-FDE in Data-Like Co-Channel Interference
No full textIn this paper, the design of a low-complexity linear equalizer is considered for single-carrier (SC) block transmission in the presence of inter-symbol interference (ISI) and data-like co-channel interference (CCI). Unlike the linear minimum meansquared error (LMMSE) frequency-domain equalizer (FDE) designed to suppress ISI only, the LMMSE FDE suffers from high computational complexity due to the CCI component in the signal correlation matrix. Motivated by the fact that the double Fourier transform of the autocorrelation function of a wide-sense cyclostationary process consists of impulse fences with equal spacing, a low-complexity FDE is proposed that approximates the frequency-domain correlation matrix of the CCI plus noise by a block matrix with diagonal blocks. It is shown that the proposed FDE is asymptotically optimal in the sense that the average meansquared error (MSE) converges to that of the LMMSE FDE as the block length tends to infinity. It is also shown that the proposed FDE is more numerically stable than the LMMSE FDE when the receive filter is matched to the transmit filter and its output is over-sampled to better capture the cyclostationarity of the CCI. Discussions and numerical results include SC block transmission systems with unique word instead of cyclic prefix, and systems with multiple receive antennas.X11814sciescopu
Asymptotic Frequency-Shift Properizer for Block Processing of Improper-Complex Second-Order Cyclostationary Random Processes
No full textIn this paper, the block processing of a discretetime (DT) improper-complex second-order cyclostationary (SOCS) random process is considered. In particular, it is of interest to find a preprocessing operation that enables the adoption of conventional signal processing techniques and algorithms developed for the filtering of proper-complex signals and that leads to computationally efficient near-optimal postprocessing. An invertible linear-conjugate linear (LCL) operator named the DT frequency shift (FRESH) properizer is first proposed. It is shown that the DT FRESH properizer converts a DT improper-complex SOCS random process input to an equivalent DT proper-complex SOCS random process output by utilizing the information only about the cycle period of the input. An invertible LCL block processing operator named the asymptotic FRESH properizer is then proposed that mimics the operation of the DT FRESH properizer but processes a finite number of consecutive samples of a DT improper-complex SOCS random process. It is shown that the output of the asymptotic FRESH properizer is not proper but asymptotically proper and that its frequency-domain covariance matrix converges to a highly structured block matrix with diagonal blocks as the block size tends to infinity. Two representative estimation and detection problems are presented to demonstrate that asymptotically optimal low-complexity postprocessors can be easily designed by exploiting these asymptotic second-order properties of the output of the asymptotic FRESH properizer.X1177sciescopu
An Optimal Orthogonal Overlay for a Cyclostationary Legacy Signal
No full textIn this paper, the design of an overlay system is considered that operates on a channel already occupied by a legacy system. It is assumed that the legacy transmitter generates a cyclostationary signal, and that the legacy receiver is equipped with a linear filter followed by a uniform sampler. Under a zero-interference constraint at the legacy receiver, the mean-squared error at the overlay receiver is minimized to find the optimal overlay system that employs linear modulation and demodulation. For the trade-off between performance and rate of the overlay system, the problem is formulated to allow a transmission rate that is a fraction of the fundamental cycle frequency of the legacy signal. The notion of a virtual legacy receiver is devised to incorporate cases with non-identical frequency bands for the transmission and reception of the overlay signal. Using the vectorized Fourier transform technique, the problem is reformulated, the solution is derived, and a necessary and sufficient condition for the existence of the optimal solution is found, all in the frequency domain. Numerical results show that the proposed scheme significantly improves the spectral efficiency by effectively exploiting the cyclostationarity of the legacy signal.X111111sciescopu
On RAKE receivers for ultra-wideband binary block-coded PPM in dense multipath channels
No full textUltra-wideband communications with a balanced orthogonal binary block-coded pulse-position-modulation scheme are considered over dense multipath channels. The structure and the performance of all-RAKE (A-RAKE) and selective-RAKE (S-RAKE) receivers are studied under the minimum bit-error rate (MBER), the maximum signal-to-noise ratio (MSNR), and the maximum-energy-capture (MEC) criteria. For the A-RAKE reception, the amount of the pulse-position shift is identified as the key design parameter that significantly affects the BER performance of the MBER and, equivalently, the MSNR receivers. It is also shown that the amount of energy capture does not well characterize the BER performance of the RAKE receiver in a very dense multipath channel. For the S-RAKE reception, although suboptimal, the RAKE receivers that allow template-matched filtering are mainly studied. The condition for the equivalence of the MSNR S-RAKE receiver to the MEC S-RAKE receiver is derived. It is shown that the amount of the pulse-position shift is again the key design parameter that determines whether the MSNR S-RAKE receiver is equivalent to the MBER S-RAKE receiver. Various schemes for finger-location selection are also studied, and a heuristic selection scheme is proposed for digital implementation of the RAKE receivers.X117sciescopu
cDNA cloning and characterization of an antimicrobial peptide from earthworm. Lumbricus rubellus
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