AWGN Performance Research Articles

Group-Based CSS Modulation: A Novel Enhancement to LoRa Physical Layer

LoRa is a proprietary technology for IoT (Internet of Things) applications and it has attracted widespread interest from both academia and industry in recent years. As the core technique of LoRa physical (PHY) layer, chirp spread spectrum (CSS) modulation is adopted to support long range communications. In this letter, we propose a novel group-based CSS (GCSS) modulation scheme and introduce a new configurable parameter called group number (GN) as an enhancement to LoRa PHY layer with the aim of achieving a more extensive and flexible trade-off between power and spectral efficiency. Moreover, by exploiting the intrinsic properties of GCSS modulation, we prove that the maximum spectral efficiency can reach up to 0.5 bps/Hz. Simulation results of BER (bit error rate) performance in both AWGN and Rayleigh fading channels are presented to verify the feasibility and advantage of this new modulation scheme.

A Novel Scheme for the Construction of the SCMA Codebook

As a code-domain non-orthogonal multiple access technique, sparse code multiple access (SCMA) is considered as a promising technique for future wireless Internet of Things (IoT) networks. The minimum Euclidean distance (MED) and minimum product distance (MPD) have been highlighted as the key performance indicators of the codebook in additive gaussian white noise (AWGN) and downlink Rayleigh channels respectively. In this paper, based on the mother codebook, a novel codebook design scheme is proposed to achieve better error performance in both AWGN and downlink Rayleigh channels. The problem of constructing the mother codebook is considered as the quadratic assignment problem (QAP), where the Tabu searching algorithm is employed to reduce the complexity of searching for the best permutation result. Then, the rotation matrix is adopted to find the best degrees for the generation of the constellation group, and two algorithms are proposed to assign the obtained constellation in factor graph matrix. Taking the degree optimization and the constellation assignments into joint consideration, an improved unified optimization is further explored to maximize the MED of each user. Besides, a novel polarized modulation scheme is proposed, which places the symbols in the three dimensional (3D) stokes parameters to improve the performance of the system. Finally, simulation results are provided to show the performance of the proposed codebooks, and the comparisons of symbol error performance (SER) in different codebooks are also discussed in detail.

A new scheme to enhance the performance of permutation index\u2013differential chaos shift keying communications system

In this paper, a new scheme based on permutation index–differential chaos shift keying is proposed, modeled, and evaluated in AWGN channel environment. Data is sent by frames, and each frame is headed by a single reference signal and followed by some information-bearing signals. Modulation is performed through permutations of a reference signal according to the mapped data. At the receiver, each incoming information-bearing signal undergoes all inverse permutation possibilities to perform a correlation with the delayed and stored version of the received reference signal. To decode the information bits, the detector selects the highest correlator outputs. The proposed scheme named single reference–permutation index–differential chaos shift keying is an enhanced version of PI-DCSK, and uses a single reference signal for multiple information-bearing ones. Hence, the energy requirement is saved by almost a half. The bit error performance is studied using the baseband system model and analytically tested using Gaussian approximation method. Results show the BER performance outperforms other standard and recently developed differentially coherent chaos systems, including Permutation Index–DCSK by an average of 2.25 dB. Moreover, the analytical form which is developed to predict the bit error rate (BER) is validated by simulation. Results demonstrate the performance in AWGN is closely matching with the simulation results, particularly at high SNR.

An Image Processing Method: Edge-guided Directional Walk Mean Smoothing

Image denoising is an important computer vision task, it is also the basis of many other high-level vision tasks. Recently, various image denoising algorithms have proposed, such as BM3D, sparse representation and deep learning, that have achieved impressive performance in AWGN denoising or blind denoising tasks. However, when dealing with Dongba painting (A traditional painting from China’s ethnic minorities), there are problems that Dongba painting have blurred edges and faded colors, it is important to retain its original style when denoising. In this paper, we propose a novel image post-processing technique termed edge-guided directional walk mean smoothing (EDWMS), it can effectively calculate the mean of pixels along different directions then obtain denoised image with sharp edge. Experiments show that the proposed EDWMS outperforms compared algorithms in both edge sharpness and color saturation.

An Efficient SCMA Codebook Optimization Algorithm Based on Mutual Information Maximization

An efficient codebook optimization algorithm is proposed to maximize mutual information in sparse code multiple access (SCMA). At first, SCMA signal model is given according to superposition modulation structure, in which the channel matrix is column‐extended. The superposition model can well describe the relationship between the codebook matrix and received signal. Based on the above model, an iterative codebook optimization algorithm is proposed to maximize mutual information between discrete input and continuous output. This algorithm can efficiently adapt to multiuser channels with arbitrary channel coefficients. The simulation results show that the proposed algorithm has good performance in both AWGN and non‐AWGN channels. In addition, message passing algorithm (MPA) works well with the codebook optimized according to the proposed algorithm.

N the Performance of Cooperative Spectrum Sensing of Cognitive Radio Networks in AWGN and Rayleigh Fading Environments

For the purpose of enhancing the spectrum efficiency, cognitive radio (CR) technology has been recently proposed as a promising dynamic spectrum allocation paradigm. In CR, spectrum sensing is the key capability of secondary users in a cognitive radio network that aims for reducing the probability of harmful interference with primary users. However, the individual CRs might not be able to carry out reliable detection of the presence of a primary radio due to the impact of channel fading or shadowing. This paper studies the cooperative spectrum sensing scheme as means of optimizing the sensing performance in AWGN and Rayleigh channels. Results generated from simulation provide evidence of the impact of channel condition on the complementary receiver operating characteristic (ROC). Based on the results, it was found that with constant local SNRs at the secondary users, the probability of missed detection (Pm) of cooperative spectrum sensing in a cognitive radio network, calculated using a closed form expression, can be significantly minimized. Thus, the paper illustrates that improvement of the detection performance of the CR network can be achieved by establishing a centralized cooperation among neighboring cognitive radio users. Finally, verification of the validity of the fusion schemes utilized for combining the individual CR decisions is provided.

Exploiting cyclic prefix redundancy in OFDM to improve performance of Tanner: graph based decoding

Redundancy, which is added in transmitter in standard OFDM in the form of a cyclic prefix is usually discarded in the receiver. However, it can be interpreted as a repetition code, which repeats only part of the symbols. Therefore it is a rather weak error control code. Nevertheless the receiver could be modified to implement a signal processing technique using this redundancy, which allows increasing error correcting capability of an outer code. A powerful outer code is usually present in any transmission adhering to some of the modern digital communication standards such as IEEE 802.16 WiMax or ETSI LTE specification family. The details on such a modification and some corresponding simulations results were presented in Palenik and Farkas (SDR'10 Technical Conference and Product Exposition, Washington DC, 2010). This manuscript is an extended version of Palenik and Farkas (SDR'10 Technical Conference and Product Exposition, Washington DC, 2010). Additional new simulation results are presented, which investigate the effects of varying prefix size on overall system error performance in both AWGN and Rayleigh fading channels. A discussion on practical usability and limitations of described receiver modification is also presented.

Exact analytical expression of schmidl-cox signal detection performance in AWGN

In this letter we investigate the performance of Schmidl-Cox signal detection, a widely used approach in practical OFDM systems whose performance is usually evinced by resorting to Gaussian approximations. We show that, by a slight modification of the normalization factor, we are able to derive a basically equivalent approach whose performance can be expressed in exact analytical form. A particularly simple expression is found for the false alarm probability, allowing system designers a straightforward selection of optimal parameters.

A Low-Complexity Detector for Large MIMO Systems and Multicarrier CDMA Systems

We consider large MIMO systems, where by 'large' we mean number of transmit and receive antennas of the order of tens to hundreds. Such large MIMO systems will be of immense interest because of the very high spectral efficiencies possible in such systems. We present a low-complexity detector which achieves uncoded near-exponential diversity performance for hundreds of antennas (i.e., achieves near SISO AWGN performance in a large MIMO fading environment) with an average per-bit complexity of just O(N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ), where N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</sub> and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> denote the number of transmit and receive antennas, respectively. With an outer turbo code, the proposed detector achieves good coded bit error performance as well. For example, in a 600 transmit and 600 receive antennas V-BLAST system with a high spectral efficiency of 450 bps/Hz (using BPSK and rate-3/4 turbo code), our simulation results show that the proposed detector performs to within about 7 dB from capacity. This practical feasibility of the proposed high-performance, low-complexity detector could potentially trigger wide interest in the theory and implementation of large MIMO systems. We also illustrate the applicability of the proposed detector in the low-complexity detection of high-rate, non-orthogonal space-time block codes and large multicarrier CDMA (MC-CDMA) systems. In large MC-CDMA systems with hundreds of users, the proposed detector is shown to achieve near single-user performance at an average per-bit complexity linear in number of users, which is quite appealing for its use in practical CDMA systems.

An Implementation of Nonlinear Multiuser Detection in Rayleigh Fading Channel

A blind nonlinear interference cancellation receiver for code-division multiple-access- (CDMA-) based communication systems operating over Rayleigh flat-fading channels is proposed. The receiver which assumes knowledge of the signature waveforms of all the users is implemented in an asynchronous CDMA environment. Unlike the conventional MMSE receiver, the proposed blind ICA multiuser detector is shown to be robust without training sequences and with only knowledge of the signature waveforms. It has achieved nearly the same performance of the conventional training-based MMSE receiver. Several comparisons and experiments are performed based on examining BER performance in AWGN and Rayleigh fading in order to verify the validity of the proposed blind ICA multiuser detector.

A Coding and Modulation Scheme for HDTV Services in DMB-T

In this paper a channel coding and modulation scheme for providing HDTV broadcasting services is presented, which adopts BICM structure as inner code in connection with 64QAM constellation and OFDM transmission. A new mapping method is designed to maximize the minimum Euclidean distance between signal points divided by feedback bits, thus an iterative algorithm between demodulator and decoder can be performed to acquire performance improvement. Analysis, simulation and laboratory test results have proved that the proposed system has good SNR performance in both AWGN and multipath channels.

A simulation comparison of multiuser receivers for cellular CDMA

Multiuser detection has gained significant notoriety as a potential advanced enabling technology for the next generation of CDMA systems. Due to the limitations of the conventional correlation receiver, the capacity of a single cell using CDMA is limited by self-interference and is subject to the near-far problem. To overcome these drawbacks, several advanced receiver structures have been proposed. Unlike the conventional receiver which treats multiple access interference (MAI) as if it were AWGN, multiuser receivers treat MAI as additional information to aid in detection. Although each of the multiuser types have been the subject of much literature, there is little published work comparing all structures on the basis of common assumptions. We present a comparison of five of the most discussed receiver structures: the decorrelator, the minimum mean square error (MMSE) receiver, the multistage parallel interference cancellation receiver, the successive interference cancellation receiver, and the decorrelating decision feedback receiver. Comparisons are based on both theoretical analysis and simulation results, examining bit error rate (BER) performance in AWGN, Rayleigh fading, and near/far channels. Additionally, receiver structures are compared on the basis of computational complexity as well as robustness to code phase misalignment. Finally, we present simulation results for noncoherent architectures of the aforementioned receivers.

F-QPSK-a superior modulation technique for mobile and personal communications

A brief review of the principles and properties of F-QPSK (quadrature phase shift keying) modulation is given. Its spectral efficiency is compared with that of Gaussian minimum-shift keying (GMSK) using adjacent channel interference (ACI) as a parameter. It is established that in a noncellular environment, hardlimited F-QPSK has a spectral efficiency of 1.42 b/s/Hz, which is up to 51% more spectrally efficient than GMSK BT=0.5 for ACI=20 dB. F-QPSK's BER performance in AWGN and Rayleigh fading channels is shown to be superior to that of GMSK. The spectral efficiency of the modulations in cellular/microcellular environments where frequency is reused in geographically separate cells to achieve higher capacity is compared. It is shown that the application of F-QPSK in such environment would leads to a 95% increase of system capacity compared to GMSK. It is concluded that the power and spectrally efficient F-QPSK make it an excellent candidate for future high-capacity personal communication system (PCS) networks. >

Design and analysis of a fast frequency-hopped DBPSK communication system. I. Error performance in AWGN plus partial-band noise jamming

The purpose of the paper is to present the design and performance analysis of a fast frequency-hopped (FFH) spread spectrum communication system employing differential binary phase-shifted-keying (DBPSK) modulation and differentially coherent demodulation. The receiver utilizes a hop time tracking loop to lock the hop clock. The authors present an analysis of the average bit error probability of the overall system when it is operating in additive white Gaussian noise plus partial-band noise jamming. The effect of channel phase distortion is also studied. >