The advent of spectrum sharing has increased the need for robust interference rejection methods. The Citizens Broadband Radio Service (CBRS) band is soon to be occupied by LTE waveforms and License Assisted Access (LA...
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The advent of spectrum sharing has increased the need for robust interference rejection methods. The Citizens Broadband Radio Service (CBRS) band is soon to be occupied by LTE waveforms and License Assisted Access (LAA) will have LTE signals coexisting with other signals in the 5 GHz band. In anticipation of this need, we present a method for interference rejection of cyclostationary signals, which can also help avoid interference through better detection of low power co-channel signals. The method proposed in this thesis consists of a frequency-shift (FRESH) filter which acts as a whitening filter, canceling the interference by exploiting its cyclostationarity. It learns the cyclostationary characteristics of the interferer blindly, through a property restoration algorithm which aims to drive the spectrum to white noise. The property restoration algorithm, inspired by the constant modulus algorithm (CMA), is applied to each frequency bin to determine the optimal coefficients for the proposed CMA FRESH whitening filter (CFW). The performance of the CFW in interference rejection is compared to a time-invariant version, and proposed use cases are analyzed. The use cases consist of the rejection of a high powered, wider bandwidth interferer which is masking the signal-of-interest (SOI). The interferer is rejected blindly, with no knowledge of its characteristics. We analyzed signal detection performance in the case that the SOI is another user with much lower power, for multiple types of SOIs ranging from BPSK to OFDM. We also deal with the case that the SOI is to be received and demodulated; we recover it and compare resulting bit error rates to state of the art FRESH filters. The results show significantly better signal detection and recovery.
This paper presents a novel diversity receiver of MPSK signal in fading channel in the presence of the carrier frequency offset. As a part of this receiver, a new algorithm for the estimation of the combining coeffici...
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This paper presents a novel diversity receiver of MPSK signal in fading channel in the presence of the carrier frequency offset. As a part of this receiver, a new algorithm for the estimation of the combining coefficients (ECC algorithm) is introduced. Having in mind that the QPSK modulation is one of the most used modulation formats in many wireless communication standards (LTE, WiFi, WiMax), the performance of the proposed receiver is analyzed in more detail for the QPSK modulation. In the presence of Rayleigh fading, representing the most severe fading condition, this algorithm shows significantly better performance comparing to the same receiver structure that uses conventional constant modulus algorithm (CMA1 or CMA2). The proposed diversity receiver structure with ECC algorithm operates within a wide carrier frequency offset range with a very small variation of the performance. For this reason, it can be applied in 4G mobile communication systems.
It is well known that the constant modulus algorithm (CMA) presents a large steady-state mean-square error (MSE) for high-order quadrature amplitude modulation (QAM) signals. In this paper, we propose a low-complexity...
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It is well known that the constant modulus algorithm (CMA) presents a large steady-state mean-square error (MSE) for high-order quadrature amplitude modulation (QAM) signals. In this paper, we propose a low-complexity hybrid adaptive blind equalization algorithm, which augments the CMA error function with a novel constellation matched error (CME) term. The most attractive advantage of the proposed algorithm is that it is computationally simpler than concurrent CMA and soft decision-directed (SDD) scheme (CMA+SDD), and modified CMA (MCMA), while the approximation of steady-state MSE of the proposed algorithm is same with CMA+SDD, and lower than MCMA. Extensive simulations demonstrate the performance of the proposed algorithm.
The blind equalization of minimum-shift keying (MSK) in coherent optical communication is investigated. After the classical constant modulus algorithm (CMA) equalization step, the output of the equalizer does not nece...
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The blind equalization of minimum-shift keying (MSK) in coherent optical communication is investigated. After the classical constant modulus algorithm (CMA) equalization step, the output of the equalizer does not necessarily coincide with a delayed and rotated version of the input MSK signal. In our MSK coherent optical system, a blind equalization criterion is proposed to eliminate the latter indeterminacy. Simulation results show that the 10-Gb/s MSK system successfully recovers MSK signal from various transmission impairments. (C) 2014 Society of Photo-Optical Instrumentation Engineers (SPIE)
The main disadvantage of constant modulus algorithm (CMA) equalizer is that the output error is very large for the transmitted signals with non-constantmodulus. So a new dual-mode CMA equalizer is proposed. This equa...
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The main disadvantage of constant modulus algorithm (CMA) equalizer is that the output error is very large for the transmitted signals with non-constantmodulus. So a new dual-mode CMA equalizer is proposed. This equalizer operates with switching the algorithm from traditional CMA to multi-modulus CMA and the condition of switching is based on the decision of the equalizer's output. Comparing with the CMA, the proposed method has the lower residual mean square error (MSE). The efficiency of the method is proved by computer simulations.
The constant modulus algorithm (CMA) is recognized as the most widely used algorithm in blind channel equalization practice. However, the CMA cost function exhibits local minima, which often leads to ill-convergence. ...
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The constant modulus algorithm (CMA) is recognized as the most widely used algorithm in blind channel equalization practice. However, the CMA cost function exhibits local minima, which often leads to ill-convergence. This paper proposes a concurrent equalizer, in which a Soft Decision Directed (SDD) equalizer operates cooperatively with a CMA equalizer, controlled through a non-linear link that depends on the system a priory state. The simulation results show that the proposed equalizer has faster convergence rate and lower steady-state mean square error than the CMA equalizer.
In digital communication system, De Castro et al. proposed a combination blind equalization based on a constant modulus algorithm (CMA) and a decision directed (DD) operating concurrently (CMA+DD) which is known to ou...
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In digital communication system, De Castro et al. proposed a combination blind equalization based on a constant modulus algorithm (CMA) and a decision directed (DD) operating concurrently (CMA+DD) which is known to outperform the CMA considerably, however it still only achieves moderate steady-state mean square error (MSE). Then a new CMA based on modified function is discussed in such combination blind equalization scheme. For the 4- PAM and 16-QAM signals, by adjusting the coordinates of received signals the cost function will become exactly zero when the channel is perfectly equalized. So the proposed algorithm can obtain lower steady-state MSE than CMA+DD. Simulation results show that the proposed method achieves satisfactory performance.
In the digital transmission system, constant modulus algorithm (CMA) is a famous blind equalization to overcome the inter-symbol interference without the aid of training sequences. But for the non-constantmodulus sig...
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In the digital transmission system, constant modulus algorithm (CMA) is a famous blind equalization to overcome the inter-symbol interference without the aid of training sequences. But for the non-constantmodulus signals such as higher-order PAM signals, the CMA just achieve moderate steady-state mean square error (MSE) which may not be sufficient for the system to obtain adequate performance. By studying the amplitude relationship between different constellations of PAM signals, a new amplitude transformation method is proposed. According to such method the non-constantmodulus signals can be changed to be constantmodulus, and then using it to the CMA the zero steady- state MSE can be obtained. The efficiency of the proposed method is proved by computer simulations.
In the digital transmission system, constant modulus algorithm (CMA) is a famous blind equalization to overcome the inter-symbol interference without the aid of training sequences. But for the non-constantmodulus sig...
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In the digital transmission system, constant modulus algorithm (CMA) is a famous blind equalization to overcome the inter-symbol interference without the aid of training sequences. But for the non-constantmodulus signals such as higher-order QAM signals, the CMA just achieve moderate steady-state mean square error (MSE) which may not be sufficient for the system to obtain adequate performance. By studying the amplitude relationship between different constellations of QAM signals, a new amplitude transformation method is proposed. According to such method the non-constantmodulus signals can be changed to be constantmodulus, and then using it to the CMA the zero steady- state MSE can be obtained. The efficiency of the proposed method is proved by computer simulations.
Most of the cost functions used for blind equalization are non -con vex and non -linear functions of tap weights, when implemented using linear finite impulse response (FIR) filter structures. Thus, a blind equalizati...
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Most of the cost functions used for blind equalization are non -con vex and non -linear functions of tap weights, when implemented using linear finite impulse response (FIR) filter structures. Thus, a blind equalization scheme with a non -linear structure that can form non -convex decision regions is desirable. In this paper, a scheme for blind equalization of non-stationary channels using complex valued feed-forward neural network is presented. The complex valued activation function, suitable for non-stationary environment is introduced and the learning algorithm based on the constant modulus algorithm (CMA) cost function is derived. The improved performance of the proposed scheme is confirmed through computer simulations.
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