Performance Analysis of a Decision-Feedback Coherent Code Tracking Loop for Pilot-Symbol-Aided DS/SS Systems

This paper examines the bit error rate (BER) of a direct sequence spread spectrum (SS) system that uses bandlimited white Gaussian noise (BLWGN) as a spreading code. The performance of this bandlimited-SS system is examined in both additive white Gaussian noise (AWGN) and single tone jamming environments. The BLWGN spreading code is inferior to conventional codes in AWGN channels, but is more robust when a narrow band interference signal is present.

Cooperative spectrum sensing (CSS) can improve the spectrum sensing performance by introducing spatial diversity in cognitive radio networks (CRNs). However, such cooperation also introduces the delay for reporting sensing data. Conventional cooperation scheme assumes that the cooperative secondary users (SUs) report their local sensing data to the fusion center sequentially. This causes the reporting delay to increase with the number of the cooperative SUs, and ultimately affects the performance of CSS. In this article, we consider the reporting delay and formulate the optimization problem of CSS with sensing user selection to maximize the average throughput of the CRN in both the additive white Gaussian noise (AWGN) environment and the Rayleigh fading environment. It is shown that selecting all the SUs within the CRN to cooperate might not achieve the maximal average throughput. In particular, for the AWGN environment, the sensing user selection scheme is equivalent to selecting the optimal number of cooperative SUs due to all the SUs having the same instantaneous detection signal-to-noise ratio (SNR). For the Rayleigh fading environment, the maximal average throughput is achieved by selecting a certain number of cooperative SUs with the highest instantaneous detection SNRs to cooperate. Finally, computer simulations are presented to demonstrate that the average throughput of the CRN can be maximized through the optimization.

The optical ZCZ code, which is a set of pairs of binary and biphase sequences with zero correlation zone, can provide code division multiple access (CDMA) communication system without co-channel interference. The M-ary amplitude shift keying spread spectrum (M-ary/ASK-SS) system using this code can detect a desired sequence without interference of undesired sequences. We have proposed the compact construction of a matched filter bank for this code, which is called the compact-type matched filter bank. However, M-ary/ASK-SS system using this filter bank might go down the bit error rate (BER) performance because input-output characteristics of this filter bank for this code with zero correlation zone 4n - 2 are nonlinear characteristics. In this paper, we clarify that BER performance in the M-ary/ASK-SS system over the additive white Gaussian noise (AWGN) channels is not influenced by nonlinear characteristics of this filter bank by the theoretical formula of BER characteristics and the computer simulation. The BER performance in the ASK-SS system using compact-type matched filter under the AWGN environment go down compared to that using direct-type matched filter as expected. But the BER performance in the M-ary/ASK-SS system using this compact-type matched filter bank under the AWGN environment is almost equal compared to that using parallel-type matched filter bank. In fact, this compact-type matched filter bank is effective in the M-ary/ASK-SS system.

The problem of optimal coherent detection of frequency-shift keying (FSK) signals transmitted over an additive colored Gaussian noise channel with imbalance gains in different frequencies (IGDF-ACGN channel) is studied. The structure of the optimal coherent detector is derived. Theoretical analysis and computer simulation results show that the detector is optimal in either additive colored Gaussian noise environment or additive white Gaussian noise environment.

In this paper, a promising spectrum sensing technique is proposed using Neyman Pearson (NP) based energy detection scheme for cognitive radio (CR) systems, where the secondary user is running in full duplex (FD) mode under residual self-interference (SI). First, NP based likelihood ratio test is carried out in additive white Gaussian noise (AWGN) environment and the closed form expressions for performance metrics are derived analytically. Next, minimum mean square error based estimator correlator for spectrum sensing under AWGN scenario is proposed, where PU signal having uncertain/arbitrary covariance structure is considered affirming a more realistic scenario in a heterogeneous network. Finally, the proposed detection scheme is extended to a practical Rayleigh fading scenario in FD CR under residual SI, where closed form analytical expressions for performance metrics are also derived. The simulated and analytical results are found in good compliance with each other.

Automatic modulation classification based on high order cumulants and hierarchical polynomial classifiers

Two three‐dimensional (3D) 16‐ary signal constellations having extended lattice structures are presented in this paper. The theoretical symbol error probabilities (SEPs) of the new constellations in additive white Gaussian noise (AWGN) and Rayleigh fading channel are derived. Computer simulation confirms that the closed‐form expressions for average SEPs of the constellations in the AWGN channel are very accurate. The theoretical SEP upper bounds in the Rayleigh fading channel are very tight. Since the presented constellations have larger minimum Euclidean distance (MED) than the conventional one, error performance can be improved up to 0.9 dB in an AWGN environment. Hence, the proposed constellations and their theoretical analysis can be used as a reference for the development of a wireless communication system with 3D signal constellations.

The spectrum sensing of a wideband frequency range is studied by dividing it into multiple subbands. It is assumed that in each subband either a primary user (PU) is active or absent in a additive white Gaussian noise environment with an unknown variance. It is also assumed that at least a minimum given number of subbands are vacant of PUs. In this multiple interrelated hypothesis testing problem, the noise variance is estimated and a generalised likelihood ratio detector is proposed to identify possible spectrum holes at a secondary user (SU). Provided that it is known that a specific PU can occupy a subset of subbands simultaneously, a grouping algorithm which allows faster spectrum sensing is proposed. The collaboration of multiple SUs can also be considered in order to enhance the detection performance. The collaborative algorithms are compared in terms of the required exchange information among SUs in some collaboration methods. The simulation results show that the proposed detector outperforms the energy detector in the presence of noise variance mismatch above 2.3 dB. Some involved trade-offs in the spectrum sensing using the proposed detector are discussed.

We propose a method of discerning components in multicomponent, stationary and nonstationary signals by application of edge detection techniques to the time-frequency (TF) plane. The approach is based upon the use of a robust to noise computer vision edge detection algorithms, which can be used to precisely mark the position of the component in the TF plane independent of its length, frequency or shape. The results show the proposed method correctly detects positions of stationary signals with low error even in signals heavily corrupted by Additive White Gaussian Noise (AWGN) and other color noise environments, tested for Signal-to-Noise Ratio (SNR)of OdB and 6dB. Positions of nonstationary components in the TF plane are detected with error of less than 6%. Results with synthetic signals and a real-life signal (bat-echolocation) indicate that the method can be used in identifying components in noisy environments using a computationally less costly method that outperforms previously proposed adaptive methods by offering faster computational speed and smaller processor workload. Closer to optimal detection can be achieved with a combination of edge detection operators and thresholded image segmentation procedures.

In this paper, a new differentially coherent chaos-based communication scheme is proposed and named as Differentially Encoded-Differential Chaos Shift Keying (D-DCSK). The system utilizes the correlation relationship between chaotic segment and its shifted version. At the transmitter, transitions between successive bits are detected by XOR operation. Based on XOR output, the chaos source generates either a new segment or repeated copy of the previous segment. At the receiver, a reference bit is initialized, and each received segment is correlated with the previous over one bit duration. Correlation value is compared with a threshold and information bits are decoded by comparing threshold output with an updated reference bit. Bit-Error-Rate (BER) performance of D-DCSK is compared with conventional correlation delay shift keying (CDSK), and Chaotic ON-OFF keying (COOK) schemes in Additive White Gaussian Noise (AWGN) environment and with different values of spreading factors. In addition to the simplicity of the structure, results show that the proposed scheme outperforms other systems at higher values of the spreading factor.

In this paper, a new differential coherent chaos-based communication system is proposed and named Reference Flipped-DCSK (RF-DCSK). By utilizing the low correlation value between a chaotic segment and its flipped version, each transmitted signal will be the sum of the information bearing signal and the mirrored version of the reference signal. This enhances the bandwidth efficiency of DCSK by doubling bits rate. Additionally, noise performance is improved at typical values of the spreading factor. According to Gaussian approximation method, theoretical expression for Bit-Error-Rate (BER) is derived. The proposed scheme is simulated and compared with Differential Chaos Shift Keying (DCSK), Correlation Delay Shift Key (CDSK) and High Efficiency -Differential Chaos Shift Keying (HE-DCSK) schemes in Additive White Gaussian Noise (AWGN) environment. Effect of spreading factor is studied. Results show that the proposed scheme clearly outperforms other systems.

To improve the efficiency of bandwidth usage, the cognitive radios concept has emerged. Spectrum sensing is a pivotal function in cognitive radio systems so that the secondary users can be able to access the free spectrum holes without interfering with primary users. Energy detection is the most common and easiest spectrum sensing technique for cognitive radios. In this paper, the conventional energy detection receiver operating characteristic curve and performance metrics are simulated under additive white Gaussian noise (AWGN) environment by using Monte Carlo simulation. Also, the performance of energy detection is analyzed under different types of M-ary modulation. The analysis of performance will carry the assumption of noise uncertainty. This performance gain is compared with conventional energy detection without any noise effect. In addition, the relation between a number of samples and signal to noise ratio wall (SNR wall) is provided and simulated. The simulation tool used in the analysis is MATLAB software. Finally, the implementation of energy detection technique in the time domain and frequency domain is designed on Xilinx Spartan-3E (XC3S500E-FG320) Field Programmable Gate Array (FPGA) kit by using Verilog language and Xilinx ISE Simulator version 14.1.

In Japan, the next generation of Integrated Services Digital Broadcasting — Terrestrial (ISDB-T) system is being developed for transmission of large-volume content services such as ultra high definition television (UHDTV). The system uses low density parity check (LDPC) code as the forward error correction (FEC) to improve its robustness. In particular, the performance of the system's FEC should be evaluated not only in additive white Gaussian noise (AWGN) environments, but also in multipath environments. Moreover, it would be desirable for the new FEC to have better performance than the previous one even in multipath environments. Previous research evaluated the transmission performance of LDPC code by using computer simulations of the propagation model. The actual propagation characteristics were not evaluated. In this paper, we describe the transmission performance of convolutional coded orthogonal frequency division multiplexing (CC-OFDM) and LDPC coded OFDM (LDPC-OFDM) in computer simulations using the same OFDM frame structure and propagation channels as measured in an outdoor experiment conducted in an urban area. We show that LDPC code outperforms CC in multipath environments and how the transmission performance depends on the code rate. In addition, we analyze the correlation between transmission performance and propagation channels.

The bit error rate (BER) performance of digital cellular radio systems was investigated in a Nakagami (1960) fading, correlated lognormal shadowing and additive white Gaussian noise (AWGN) environment for noncoherent differential phase shift keying (DPSK) modulation. Two models were used to determine the BER; the first one is based on the cumulative power levels of cochannel interferers while the second one is based on instantaneous cochannel interference power. The relative advantages of the two models were presented for various design parameters. The effects of bit energy to noise ratio, frequency reuse distance, cluster size, correlation coefficient, shadow spread, and fading parameter were studied. The BER was observed to be lower in a correlated shadowing environment compared with the uncorrelated case. The near-far effect was studied by assuming that both the desired and interfering mobiles are randomly located in their corresponding cells.

Wideband spectrum sensing plays a key role in cognitive radio. Detecting wideband signals accurately and efficiently at low SNR regimes has recently attracted much interest from the research community. In this paper, two novel wideband sensing methods are presented, sequential sensing using phase-rotated spectral correlation detector (PSCD) and binary sensing using PSCD, which take advantage of PSCD's detection performance at low SNRs. They are explained in detail with diagrams and pseudo codes. Detection performance of the proposed methods in terms of detection probability and false alarm probability are evaluated in additive white Gaussian noise (AWGN) environment. The time complexity of the methods is also analyzed. Simulated results indicate that our methods outperform the energy detector at low SNRs.