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Bit error rate (BER) performances for CL-EM and NCD-EM in coded OFDM system. The number of pilot symbols is 8. Modulation is 16-QAM. The channel has 6 taps.
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Expectation-maximization (EM) based iterative algorithms are investigated in order to estimate the impulse response of a frequency-selective multipath channel in a coded OFDM system. Two ways of choosing the EM complete data are compared: a complete data built from observations and transmitted symbols (CL-EM) and a complete data chosen by decomposi...
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A new blind channel estimation approach for orthogonally coded multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems is proposed. The main idea of our technique is, using specific properties of the orthogonal space-time block codes (OSTBCs), to estimate the finite impulse response (FIR) channel parameters in...
Channels with a long but sparse impulse response arise in a variety of wireless communication applications, such as high definition television (HDTV) terrestrial transmission and underwater acoustic communications. By adopting the ℓ1-norm as the sparsity metric of the channel response, the channel estimation is formulated as a complex-valued convex...
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Citations
The estimation accuracy of conventional parameter estimation methods, including the maximum likelihood (ML) estimator and subspace-based estimation methods, diverges from the Cramer-Rao lower bound (CRLB) under low signal-to-noise (SNR) ratio conditions. Conventional stochastic resonance (SR) technique has shown appealing weak signal improvement advantages under low SNR, but it still needs a priori information such as the probability density functions (pdfs) of weak signal and channel noise. In this study, to address the channel parameter estimation for weak signal conditions, a novel channel parameter estimation algorithm based on dynamic stochastic resonance networks (SRN) is introduced. Since the signal statistical properties are altered by the SRN processing, the CRLB of the wireless channel parameter estimation employing the SRN-enhanced signal is derived, and then the corresponding ML estimator is presented. Theoretical analyses show that the CRLB is lower than those from the original signal and stochastic-resonance-enhanced signal. Computer simulations are performed to verify the effectiveness of the theoretical CRLB expressions. Both simulation and real experimental results indicate that the proposed SRN processing approach outperforms the conventional SR processing through achieving the CRLB improvement, the ML estimation performance enhancement under low SNR conditions, and the hardware complexity reduction.
This paper presents the implementation and experimental evaluation of a short-packet physical-layer network coding (PNC) system. Implementation of short-packet PNC systems is challenging. First, short packets may have only a few pilot symbols for synchronization and channel estimation purposes. Increasing the number of pilots increases the overhead; decreasing the number of pilots, on the other hand, degrades the packet error rate performance. Second, many short-packet systems are meant for applications with very stringent delay requirements. Employing advanced but complex PNC channel decoding may result in unacceptable delay due to the processing delay. This work presents a low-complexity and low-overhead physical-layer design of OFDM-based short-packet PNC systems, implemented over the software-defined radio platform. Our design makes use of only a small number of pilots (without separate OFDM preamble symbols) to address issues such as slot synchronization, packet detection, carrier frequency offsets, and mismatched channel state information. Our design employs reduced-complexity XOR channel decoding based code-aided parameter estimation (that includes synchronization and channel estimation) to compensate for the limitations imposed by having a small number of pilots. This is the first demonstration that provides a practical framework for applying PNC to short-packet communications.
Multisatellite cooperative random access (MSC-RA) scheme is proposed in low earth orbit (LEO) satellite networks. In the scheme, a packet structure based on single carrier interleaved frequency division multiple access (SC-IFDMA) is designed to overcome the effect of users’ propagation delays on the received signals at satellite nodes, which ensures the synchronization of received signals. The transmission model from multiple terminals to multiple satellite nodes in a slot can be equivalent to a virtual multi-input multioutput model, and MSC detection is employed to decode multiple collided packets. The MSC detection can be applied to slotted ALOHA (SA), contention resolution diversity slotted ALOHA (CRDSA), CRDSA-3, and irregular repetition slotted ALOHA (IRSA) protocols, which are dubbed MSC-SA, MSC-CRDSA, MSC-CRDSA-3, and MSC-IRSA, respectively. At the gateway station, the MSC detection and iterative interference cancellation processing are alternately conducted for multiple collided packets at satellite nodes. The performance of these MSC-RA schemes is evaluated via mathematical analysis and computer simulation in terms of throughput, stability and energy efficiency. Simulation results show that MSC-SA, MSC-CRDSA, MSC-CRDSA-3, and MSC-IRSA schemes significantly outperform conventional ones, and the MSC-CRDSA scheme is superior to MSC-SA, MSC-CRDSA-3 and MSC-IRSA schemes.
Pre-weighting based Contention Resolution Diversity Slotted ALOHA-like (PW-CRDSA-like) schemes with joint multi-user multi-slot detection (JMMD) algorithm are proposed to improve the throughput of random access(RA) in geostationary earth orbit(GEO) satellite networks. The packet and its replicas are weighted by different preweighting factors at each user terminal, and are sent in randomly selected slots within a frame. The correlation of channels between user terminals and satellite node in different slots are removed by using pre-weighting factors. At the gateway station, after the decoding processing of CRDSA, the combinations of remained signals in slots that can construct virtual multipleinput multiple-output(MIMO) signal models are found and decoded by the JMMD algorithm. Deadlock problems that can be equivalent to virtual MIMO signal models in the conventional CRDSA-like schemes can be effectively resolved, which improves the throughput of these CRDSA-like schemes. Simulation results show that the PW-CRDSA-like schemes with the JMMD significantly outperform the conventional CRDSA-like schemes in terms of the throughput under equal packet loss ratio(PLR) conditions (e.g. PLR =10⁻²), and as the number of the transmitted replicas increases, the throughput of the PW-CRDSA-like schemes also increases, and the normalized maximum throughput of the PW-CRDSA-5 scheme can reach 0.95.
Accurate channel estimation is a challenging problem in a long term evolution systems especially in highly selective channels. In this paper, two iterative channel estimation algorithms are proposed to efficiently estimate channels over the orthogonal frequency-division multiplexing (OFDM) symbols containing pilot symbols. The first one is proposed based on a simple interpolation algorithm, named as simple iterative frequency interpolation (SIFI), and improves the system performances with low implementation complexity. The second one is derived from the traditional expectation maximisation (EM) algorithm in OFDM systems. In order to deal with the ‘null’ subcarriers in the guard band and make the algorithm converge, the truncated singular value decomposition method is integrated to truncated singular value decomposition expectation-maximisation (TSVD-EM). Both channel estimation algorithms are followed by a simple linear interpolation in time domain to obtain channel estimates over the whole subframe. Complexities of the proposed algorithms are also analysed and compared. Simulation results show that the SIFI algorithm outperforms the traditional interpolation method with a low complexity, and the TSVD-EM algorithm approaches the best achievable performance with a reduced complexity.Copyright © 2012 John Wiley & Sons, Ltd.
In this paper we compare and test several channel estimation algorithms in the case of LTE (Long Term Evolution) Systems applied in a high mobility environment. In particular, we propose a novel algorithm, based on the observation of OFDM block energy, to perform a semi-blind tracking of the channel between pilot blocks. This algorithm is compared to more traditional approach based on 1D estimation and interpolation. In addition, an Expectation Maximization (EM) is used to improve the overall channel estimation.
In this paper, the truncated singular value decomposition expectation-maximization (TSVD-EM) based channel estimation on single transmit antenna transmission is extended to transmit diversity transmission. Particular attention is given to Long Term Evolution (LTE) systems. In order to obtain the received symbols for each transmit antenna, an approximation is proposed by using the soft symbols and channel estimates from the previous iteration. We prove that the mean square error (MSE) of TSVD-EM on transmit diversity transmission has almost the same constant value at high signal-to-noise ratio (SNR) as on single transmitter antenna case. Simulation results show that the proposed TSVD-EM channel estimation improves system performances remarkably and approaches the performance with perfect channel state information. Even without pilot boosting used in LTE systems, the TSVD-EM achieves the same performances as with pilot boosting.
Atmospheric effects are one of the important factors that affect the physical realism of the infrared (IR) scene generators. IR scene generators obtained by OpenGL library are used in the applications where performance is critical. Modeling atmospheric effects in the IR band using OpenGL's fog model approach is found in the literature. However, the related fog model needs parameters that are independent of the range. In this paper, a novel model that is developed by using the least squares estimation for the both range and wavelength dependent atmospheric transmittance and atmospheric path radiance is proposed and the related model parameters are transformed to usable equivalent parameters for OpenGL platform. It is demonstrated with the simulations that the proposed model has an error less than 5%.
