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With the rapid development of wireless communications, the occupation of time and frequency resources becomes more crowded. The exploitation of space resources is necessary and the diversity combining techniques have substantial applications. Diversity combining achieves great diversity gains and improves the ability to combat multipath fading, among which the maximum ratio combining (MRC) performs as the optimal linear combining approach. However, MRC suffers from detrimental factors such as channel fading and no Gaussian noise in practical scenarios. In this paper, we focus on a comprehensive investigation of MRC. Starting from the MRC principle and system model, we summarize typical scenarios and analyze the channel fading statistics. For the influential factors, we further review related literature on channel correlation, cochannel interference (CCI) and impulsive noise. Major performance criteria and performance bounds are derived and compared. MRC confronts new developing challenges and the major development directions are reviewed. The paper finally discusses recent works and open problems for MRC applications and development. Emerging techniques such as artificial intelligence provide novel solutions for MRC performance improvements. The paper aims to present a summarized insight to assist readers in clarifying the analyzed methodology of MRC, so as to motivate new technology integration and extensive applications of advanced communication systems. [ABSTRACT FROM AUTHOR]

Advancements in technology have positioned Unmanned Aerial Vehicles (UAVs) as current and future computational paradigms. This novel artificial intelligence tool facilitates various applications, including communication, sports, real-time data collection in agriculture, and commercial purposes. Even though UAVs were much known for military usage in navigating hard-to-reach areas and hostile environments for physical human interaction. Considering UAV's application in communications, the maximum adaption of diversity combination properties has been used for some years ago, facing the Bit Error Rate (BER) of selective combing, maximal ratio combining, equal gain combining, direct combining, selective combining, BER of Rayleigh, and Ricean approach. This paper surveys models and current UAV systems to analyze the most common technologies in UAV diversity, combining Rayleigh and Ricean based on the diversity combination properties. Based on the survey, the existing proposed models have not depicted the most reliable and effective model for adopting Rayleigh or Ricean in UAV communication systems and UAV-associated concerns.

Summary: This paper presents the performance of maximum ratio combining (MRC) diversity receiver over shadowed Beaulieu‐Xie (SBX) fading model. The SBX model is used to characterise wireless communication environments that include multiple numbers of line‐of‐sight (LOS) and non‐line‐of‐sight (NLOS) signals. The probability density function (PDF) of the MRC scheme over the SBX channel has been derived. The PDF‐based approach has been used to calculate the outage performance and average bit error rate of several modulation schemes for coherent and non‐coherent signals. It has also been shown how the diversity orders and the fading channel's parameters affect the system's performance. To authenticate the evaluated expressions, Monte‐Carlo simulation results are used for validation. The SBX model is used to characterise wireless communication environments that include multiple numbers of LOS and NLOS signals. [ABSTRACT FROM AUTHOR]

Advancements in technology have positioned Unmanned Aerial Vehicles (UAVs) as current and future computational paradigms. This novel artificial intelligence tool facilitates various applications, including communication, sports, real-time data collection in agriculture, and commercial purposes. Even though UAVs were much known for military usage in navigating hard-to-reach areas and hostile environments for physical human interaction. Considering UAV's application in communications, the maximum adaption of diversity combination properties has been used for some years ago, facing the Bit Error Rate (BER) of selective combing, maximal ratio combining, equal gain combining, direct combining, selective combining, BER of Rayleigh, and Ricean approach. This paper surveys models and current UAV systems to analyze the most common technologies in UAV diversity, combining Rayleigh and Ricean based on the diversity combination properties. Based on the survey, the existing proposed models have not depicted the most reliable and effective model for adopting Rayleigh or Ricean in UAV communication systems and UAV-associated concerns. [ABSTRACT FROM AUTHOR]

This article develops maximum likelihood (ML) detection for post-FFT processing of dual-polarized antenna outputs with a cyclic-prefix OFDM (CP-OFDM) waveform for a frequency selective multipath fading in a 5G mobile-to-mobile setting. The suggested maximum likelihood detector (MLD) comprises a combiner applied to the channel matched filter outputs (designated MLC) followed by a decision rule based on correlation and signal energy. When MLC is coupled with a frequency-domain equalizer, this structure is called MLC+FDE. The designed MLD and MLC+FDE are compared to the traditional combining techniques: maximum ratio combining, equal gain combining, and selection combining. Computer simulations performed over a stochastic channel model with polarization state information. The simulation results show that the difference between MLD and maximum ratio combining (the best performing method), MLC+FDE (almost the best performing method) and selection diversity with frequency-domain equalization (the worst performing method) is 2 dB. This diversity improvement is limited by the correlation between the two channels that characterize the two polarization states. This correlation makes it difficult to achieve reliable transmission through combining alone; some form of error control coding is also needed. When channel estimates are used in place of perfect channel knowledge, an error floor is observed.

Popular small satellites host individual sensors or sensor networks in space but require ground stations with directional antennas on rotators to download sensors' data. Such ground stations can establish a single downlink communication with only one satellite at a time with high vulnerability to system outages when experiencing severe channel impairments or steering engine failures. To contribute to the area of improving the reception quality of small satellites signals, this paper presents a simple receive diversity scheme with proposed processing algorithms to virtually combine satellite downlink streams collected from multiple omnidirectional receivers. These algorithms process multiple received versions of the same signal from multiple geographically separated receiving sites to be combined in one virtual ground station. This virtual ground station helps detect the intended signal more reliably based only on a network of simple and cooperating software-defined radio receivers with omnidirectional antennas. The suggested receive diversity combining techniques can provide significant system performance improvement if compared to the performance of each individual receiving site. In addition, the probability of system outages is decreased even if one or more sites experience severe impairment consequences. Simulation results showed that the bit error rate (BER) of the combined stream is lower than the BER of the best quality receiving site if considered alone. Moreover, virtual ground stations with cooperative omnidirectional reception at geographically separated receivers also allow data to be received from multiple satellites in the same frequency band simultaneously, as software-defined receivers can digitize a wider portion of the frequency band. This can be a significant conceptual advantage as the number of small satellites transmitting data grows, and it is reasonable to avoid the corresponding necessary increase in the number of fully equipped ground stations with rotators. [ABSTRACT FROM AUTHOR]

Equivalent discrete-time models for a variety of spatial combining techniques operating in a frequency-selective multipath fading channel are derived. The equivalent discrete-time models are used to perform computer simulations of the post-equalizer bit error rate over a frequency-selective multipath channel whose derivation preserved polarization state information. Two sets of computer simulations were performed. In the first set, the performance of co-located cross-polarized antenna elements was investigated. The results showed that maximum likelihood combining maximizes polarization diversity, but that maximum ratio combining and selection combining were very competitive in the case where the cross-polarized antennas produce one strong channel and a relatively weak channel. Elliptical combining, using a 90° hybrid coupler, produced the worst results. The second set of simulations used a combination of spatial and cross-polarized antenna elements, for a total of eight antenna elements. The simulation results showed that maximum likelihood combining was best, followed by maximum ratio combining, equal gain combining, and selection combining. Again, elliptical combining was the worst, leading to the conclusion that other combining techniques are preferred in frequency-selective fading environments.

To address the explosive traffic demands, the capacity of the fading channel is increasingly becoming a prime concern in the designing of the wireless communication system. The channel capacity is an extremely important quantity, since it allows the transmission of the data through the channel with an arbitrarily small probability of error. In other words, capacity dictates the maximum rate of information transmission, called as 'capacity' of channel, determined by the intrinsic properties of the channel and is independent of the content of the transmitted information. In this paper, we present a comprehensive survey of the existing work related to the channel capacity model over various fading channels. With an elaborated explanation of the theory of channel capacity, definitions of channel capacity based on the channel state information are reviewed. To compliment this, review of the technique to enhance the channel capacity is discussed and reviewed. An effective capacity model to overcome the channel capacity limitation is also explained. Furthermore, as the secure transmission of data is of utmost importance, to address this physical layer security model is also reviewed. We also summarize the work related to channel capacity in various types of wireless networks. We finally cover the future research directions, including less explored aspects of the channel capacity that can be studied to design efficient communication systems. [ABSTRACT FROM AUTHOR]

The Arctic Ocean and its various shallow passages are rapidly changing due to global warming. The development of a large-scale wireless network that collects and distributes oceanographic data remotely would be an extremely valuable asset to researchers. This concept, however, is completely dependent upon the ability to acoustically transmit digital information under water over long ranges, which is not currently available. In this work, we investigate the performance of four transceivers that are based on frequency-hopping binary frequency-shift keying and multilevel phase-shift keying (M-PSK) signaling in the 300 $-$ 400-Hz acoustic band. The transceivers use low-rate coding that provides bit rates from 1.8 to 13.3 b/s (bits per second). Their bit error rates are computed based on real data recorded in Barrow Strait (NU). During the 2019 experimental activities, the transmitter was towed by a supporting vessel at an average speed of 4 kn. The receiver, a vertical hydrophone array, was at distance between 14 and 33 km. Additionally, the received signals experienced extended multipath propagation and strong in-band impulsive interferences. For a single-hydrophone receiver, our postprocessing analysis shows reliable bit rates up to 6.7 b/s. When processing uses the array and performs multichannel decision feedback equalization (DFE), the maximum designed rate, i.e., 13.3 b/s, is confirmed. Further analysis reveals that the experimental links could support higher data rates. Our results demonstrate that 2-PSK signaling combined with single-channel DFE and 4-PSK signaling combined with multichannel DFE could reliably achieve 100 and 200 b/s, respectively. [ABSTRACT FROM AUTHOR]

Popular small satellites host individual sensors or sensor networks in space but require ground stations with directional antennas on rotators to download sensors’ data. Such ground stations can establish a single downlink communication with only one satellite at a time with high vulnerability to system outages when experiencing severe channel impairments or steering engine failures. To contribute to the area of improving the reception quality of small satellites signals, this paper presents a simple receive diversity scheme with proposed processing algorithms to virtually combine satellite downlink streams collected from multiple omnidirectional receivers. These algorithms process multiple received versions of the same signal from multiple geographically separated receiving sites to be combined in one virtual ground station. This virtual ground station helps detect the intended signal more reliably based only on a network of simple and cooperating software-defined radio receivers with omnidirectional antennas. The suggested receive diversity combining techniques can provide significant system performance improvement if compared to the performance of each individual receiving site. In addition, the probability of system outages is decreased even if one or more sites experience severe impairment consequences. Simulation results showed that the bit error rate (BER) of the combined stream is lower than the BER of the best quality receiving site if considered alone. Moreover, virtual ground stations with cooperative omnidirectional reception at geographically separated receivers also allow data to be received from multiple satellites in the same frequency band simultaneously, as software-defined receivers can digitize a wider portion of the frequency band. This can be a significant conceptual advantage as the number of small satellites transmitting data grows, and it is reasonable to avoid the corresponding necessary increase in the number of fully equipped ground stations with rotators.

Wireless data transmission in the hydroacoustic channel under non-line-of-sight (NLOS) propagation conditions, for example, during a wreck penetration, is difficult to implement reliably. This is mostly due to the multipath propagation, which causes a reduction in the quality of data reception. Therefore, in this work an attempt has been made to develop a reliable method of wireless underwater communication test it under the NLOS conditions. In our method, we used multiple frequency-shift keying (MFSK) modulation, sending a single bit on two carriers, and diversity combining. The method was tested in laboratory conditions which simulated underwater signal propagation during the penetration of the wreck. The propagation conditions were investigated by determining the impulse responses at selected measurement points using the correlation method. Additionally, for comparison, the data transmission quality was determined by the bit error rate (BER) under the same conditions using direct sequence spread spectrum (DSSS) and binary phase shift keying (BPSK) modulation. The obtained results confirmed the usefulness of the application of the developed method for wireless data transmission in a hydroacoustic channel under NLOS conditions.

Summary: In this paper, the closed‐form expressions for outage probability, channel capacity, and average symbol error probability are derived for amplify‐and‐forward multihop relay network. Based on approximation of multihop relay by dual‐hop relay systems, the analytical expressions are obtained for the case when maximal ratio combining technique is employed at each relay while destination node uses selection combining technique. The impact of system and channel parameters on the system performances is investigated, and numerical results are graphically presented. The derived analytical expressions are verified by numerical simulation. [ABSTRACT FROM AUTHOR]

Featured Application: Less power consumption, robust, and faster near vertical incidence skywave remote sensing platforms. Every year more interest is focused on high frequencies (HF) communications for remote sensing platforms due to their capacity to establish links of more than 250 km without a line of sight and due to them being a low-cost alternative to satellite communications. In this article, we study the ionospheric ordinary and extraordinary waves to improve the applications of near vertical incidence skywave (NVIS) on a single input multiple output (SIMO) configuration. To obtain the results, we established a link of 95 km to test the diversity combining of ordinary and extraordinary waves by using selection combining (SC) and equal-gain combining (EGC) on a remote sensing platform. The testbench is based on digital modulation transmissions with power transmission between 3 and 100 W. The results show us the main energy per bit to noise spectral density ratio (Eb/N0) and the bit error rate (BER) differences between ordinary and extraordinary waves, SC, and EGC. To conclude, diversity techniques show us a decrease of the power transmission need, allowing for the use of compact antennas and increasing battery autonomy. Furthermore, we present three different improvement options for NVIS SIMO remote sensing platforms depending on the requirements of bitrate, power consumption, and efficiency of communication. [ABSTRACT FROM AUTHOR]

In wireless communication system, various parameters such as average symbol/bit error probability (ASEP/ABEP), outage probability and average channel capacity, etc. are studied for its performance analysis. In this paper, the performance of L-Hoyt/Gamma (HG) composite fading channel with Maximum Ratio Combining (MRC) employing micro-diversity is analyzed. Closed-form expressions for distribution function, moments, outage probability and channel capacity are derived in terms of hypergeometric functions. Further, the expressions of ASEP/ABEP for all formats of coherent and non-coherent modulation techniques involving Q-functions and Marcum Q-function are derived over the composite fading channel. Monte-Carlo simulations are performed to validate our analytical results. The analytical results produced here can be useful in several wireless applications where multipath and shadowing are characterized by Hoyt/Gamma distribution.

Sensor networks have become more popular in recent years, now featuring plenty of options and capabilities. Notwithstanding this, remote locations present many difficulties for their study and monitoring. High-frequency (HF) communications are presented as an alternative to satellite communications, being a low-cost and easy-to-deploy solution. Near vertical incidence skywave (NVIS) technology provides a coverage of approximately 250 km (depending on the frequency being used and the ionospheric conditions) without a line of sight using the ionosphere as a communication channel. This paper centers on the study of the ionosphere and its characteristic waves as two independent channels in order to improve any NVIS link, increasing its robustness or decreasing the size of the node antennas through the appliance of specific techniques. We studied the channel sounding of both the ordinary and extraordinary waves and their respective channels, analyzing parameters such as the delay spread and the channel’s availability for each wave. The frequency instability of the hardware used was also measured. Furthermore, the correlation coefficient of the impulse response between both signals was studied. Finally, we applied polarization diversity and two different combining techniques. These measurements were performed on a single frequency link, tuned to 5.4 MHz. An improvement on the mean bit energy-to-noise power spectral density (Eb/N0) was received and the bit error rate (BER) was achieved. The results obtained showed that the extraordinary mode had a higher availability throughout the day (15% more availability), but a delayed spread (approximately 0.3 ms mean value), similar to those of the ordinary wave. Furthermore, an improvement of up to 4 dB was achieved with the usage of polarization diversity, thus reducing transmission errors.

Outage probability analysis of diversity reception over lognormal fading channels is challenging because the cumulative distribution function (CDF) of a sum of lognormal random variables (RVs) does not yield a closed-form expression. Furthermore, traditional asymptotic analysis techniques fail for lognormal fading channels. The well-applied approximation techniques, such as Fenton, Wilkinson, and Schwartz and Yeh approximations, become unreliable when the signal-to-noise ratio (SNR) is high. In this paper, we derive closed-form bounds of outage probability for dual-branch equal-gain combining system over non-identically distributed lognormal fading channels. The bounds are shown tight from low-to-high SNR regimes, which provides an efficient way to evaluate the EGC system without resorting to expensive Monte Carlo simulation or numerical integration. Furthermore, the new analytical expressions can be used to test at what SNR the existing approximation techniques become inaccurate, and can also be used as criteria for system design. [ABSTRACT FROM AUTHOR]

A new diversity combining receiver is proposed for asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM). With the aid of symmetry recovering the odd and even signals of ACO-OFDM are distinguished directly in time domain without complex operation such as inverse fast Fourier transform (IFFT). Simulation results show that the diversity combining receiver we proposed gives a signal-to-noise ratio (SNR) improvement of 2 ∼ 3 dB. The receiver proposed also has the same SNR gain as the conventional diversity combining receiver distinguishing the odd and even signals in frequency domain. [ABSTRACT FROM AUTHOR]

Correlation among antenna branches has become a major concern in multi-antenna systems, especially in small devices with closely spaced antennas. Since physically distancing the antennas seems impractical, a decorrelator implementation at the receiver will be very beneficial. In this paper, such a decorrelation scheme employed prior to the selection combining (SC) diversity technique is studied. Using the fundamental principles, we derive expressions for the statistics of decorrelating the identical and correlated dual antenna SC receiver in Nakagami- m fading channels. Numerical results show that the probability density function (PDF) of the difference of identical and correlated Nakagami- m bivariate could be perfectly represented by a semi-standard normal distribution with zero mean and constant variance depending on the bivariate's parameters. This observation could help simplify the design of the decorrelator receiver. Performance of the decorrelator is also verified by evaluating the outage probability which shows improvement. [ABSTRACT FROM AUTHOR]

Multiantenna receivers are often deployed in cognitive radio systems for accurate spectrum sensing. However, correlation among signals received by multiple antennas in these receivers is often ignored which yields unrealistic results. In this paper, the effect of this correlation is accurately quantified by deriving analytical expressions for the average probability of detection. Alternative simpler expressions are also derived. These are done for selection combining (SC) and switch and stay combining (SSC) diversity techniques in dual arbitrarily correlated Nakagami- $m$ fading channels. Then, it is repeated for triple exponentially and identically correlated Nakagami- $m$ fading channels with SC diversity technique. Analysis results show that the interbranch correlation impacts the detector performance significantly, especially in deep fading scenarios. Also, SC outperforms SSC as expected. However, the difference between them becomes very small in low fading and highly correlated scenarios, which indicates that the simpler SSC scheme can as well be deployed in such situations. [ABSTRACT FROM AUTHOR]

This paper presents a general expression for the bit-error rate performance of quadrature amplitude modulation (QAM), considering arbitrary branch selection combining (SC) receiver over two-wave diffuse power Fading Channels. The impact on the performance of the M branch-SC receiver, caused by the fading parameters Δ and K, has been analysed for different QAM constellations. The expressions have been numerically evaluated and the results obtained have been verified using Monte Carlo Simulation. [ABSTRACT FROM AUTHOR]

In this paper, digital chaotic communications in multiple-input-multiple-output (MIMO) wireless multipath fading channels is considered. A noise reduction-differential chaos shift keying (NR-DCSK) scheme is employed to modulate data symbols at each transmit antenna which transmits signals omni-directionally. In the transmitter side, we use β/P chaotic samples as reference sequences which is then repeated P times to generate the required reference sequence of length β. At the receiver side, a moving average filter of size P is used to reduce the noise variance of the received signal so as to enhance the system performance. The resulting filtered signal is then correlated and combined using diversity combining techniques to yield the transmitted symbol. It is shown that with spatial diversity gains, the enhancement in bit error rates (BER) of the proposed system is much better than the conventional M-DCSK based MIMO Chaotic Communication systems. Moreover, a closed-form expression for BER of the proposed system is derived over AWGN and Rayleigh fading channel conditions. Comparison of simulation results with theoretical BER expressions of additive white Gaussian noise (AWGN) and Rayleigh fading channels for various system parameters like signal to noise ratio, Spatial diversity orders, combining techniques have been carried out to test the performance enhancement of the proposed NR-DCSK based MIMO system. [ABSTRACT FROM AUTHOR]

When transmitting data in a hydroacoustic channel under difficult propagation conditions, one of the problems is intersymbol interference (ISI) caused mainly by the effect of multipath propagation. This phenomenon leads to a decrease in transmission parameters, and sometimes completely prevents it. Therefore, we have made an attempt to use diversity combining with Recursive Least Squares (RLS) adaptive filtering to improve the quality of data transmission in a hydroacoustic channel with strong reflections. The method was tested in simulation and during measurements in a real environment. The influence of the method on data transmission in the hydroacoustic channel was examined in detail. The obtained results allow us to draw conclusions regarding the purposefulness of use of diversity combining and RLS adaptive filtering in order to improve the quality of data transmission by reducing the effect of ISI.

This paper investigates the performance analysis of diversity combining over flat fading channels subject to additive impulsive noise. Specifically, the impulsive noise follows the symmetric α-stable (SαS) distribution. Tradi- tionally, this is a difficult problem since the analytical ex- pression for the probability density function of a general SαS distribution remains unknown. In order to tackle this diffi- culty, we adopt Fourier power transform to obtain an exact bit error rate (BER) expression for the Genie-aided receiver as well as a BER upper bound for the conventional linear matched filter receiver, without taking any approximation. Monte-Carlo simulations are performed to validate our ana- lytical results. The simulation results show that our proposed BER expressions are valid in the whole geometric signal- noise-ratio (GSNR) ranges, thus outperforming the previous results valid only at high GSNR values.

Every year more interest is focused on high frequencies (HF) communications for remote sensing platforms due to their capacity to establish links of more than 250 km without a line of sight and due to them being a low-cost alternative to satellite communications. In this article, we study the ionospheric ordinary and extraordinary waves to improve the applications of near vertical incidence skywave (NVIS) on a single input multiple output (SIMO) configuration. To obtain the results, we established a link of 95 km to test the diversity combining of ordinary and extraordinary waves by using selection combining (SC) and equal-gain combining (EGC) on a remote sensing platform. The testbench is based on digital modulation transmissions with power transmission between 3 and 100 W. The results show us the main energy per bit to noise spectral density ratio (Eb/N0) and the bit error rate (BER) differences between ordinary and extraordinary waves, SC, and EGC. To conclude, diversity techniques show us a decrease of the power transmission need, allowing for the use of compact antennas and increasing battery autonomy. Furthermore, we present three different improvement options for NVIS SIMO remote sensing platforms depending on the requirements of bitrate, power consumption, and efficiency of communication.

This paper proposes a new receiver based on frequency-domain diversity combining (FDDC) for an asymmetrically clipped optical orthogonal frequency-division multiplexing (ACO-OFDM) system. Compared with its time-domain diversity combining (TDDC) counterpart, the FDDC receiver is capable of more effectively exploiting the frequency selectivity of the channel to further improve the detection performance, which is proved by postcombining signal-to-noise-ratio (SNR) analysis. An enhanced version of the FDDC receiver, which is called eFDDC, is also proposed subsequently. It allows for optimal selection among multiple sets of candidate symbol vectors based on signum matrix estimation. Simulation results show that the proposed FDDC and eFDDC receivers outperform the TDDC receiver. With a sufficient number of candidate symbol vector sets, the eFDDC receiver even outperforms a kind of iterative receiver, which is known to have superior performance in current literature, yet the complexity of eFDDC is lower due to the avoidance of matrix inversion. Those facts suggest that the FDDC and eFDDC receivers are strong receiver candidates for the ACO-OFDM system.

In this paper, we propose an algorithm to remove movement noise from second derivative of photoplethysmography (SDPPG) signals. SDPPG is widely used in healthcare applications because of its easy and comfortable measurement. However, an SDPPG signal is vulnerable to movement, which degrades the signal. Degradation of SDPPG signal shapes can result in incorrect diagnosis. The proposed algorithm detects movement noise in a measurement signal using wavelet transform, and removes movement noise by selecting the best signal from among multiple signals measured at different locations. Experiment results show that the proposed algorithm outperforms the previous filter-based algorithm, and that movement noise with 30% time duration can be reduced by up to 70.89%. [ABSTRACT FROM AUTHOR]

In this paper, an improved receiver based on diversity combining is proposed to improve the bit error rate (BER) performance of layered asymmetrically clipped optical fast orthogonal frequency division multiplexing (ACO-FOFDM) for intensity-modulated and direct-detected (IM/DD) optical transmission systems. Layered ACO-FOFDM can compensate the weakness of traditional ACO-FOFDM in low spectral efficiency, the utilization of discrete cosine transform in FOFDM system instead of fast Fourier transform in OFDM system can reduce the computational complexity without any influence on BER performance. The BER performances of layered ACO-FOFDM system with improved receiver based on diversity combining and DC-offset FOFDM (DCO-FOFDM) system with optimal DC-bias are compared at the same spectral efficiency. Simulation results show that under different optical bit energy to noise power ratios, layered ACO-FOFDM system with improved receiver has 2.86, 5.26 and 5.72 dB BER performance advantages at forward error correction limit over DCO-FOFDM system when the spectral efficiencies are 1, 2 and 3 bits/s/Hz, respectively. Layered ACO-FOFDM system with improved receiver based on diversity combining is suitable for application in the adaptive IM/DD systems with zero DC-bias. [ABSTRACT FROM AUTHOR]

In wireless communication system, various parameters such as average symbol/bit error probability (ASEP/ABEP), outage probability and average channel capacity, etc. are studied for its performance analysis. In this paper, the performance of L-Hoyt/Gamma (HG) composite fading channel with Maximum Ratio Combining (MRC) employing micro-diversity is analyzed. Closed-form expressions for distribution function, moments, outage probability and channel capacity are derived in terms of hypergeometric functions. Further, the expressions of ASEP/ABEP for all formats of coherent and non-coherent modulation techniques involving Q-functions and Marcum Q-function are derived over the composite fading channel. Monte-Carlo simulations are performed to validate our analytical results. The analytical results produced here can be useful in several wireless applications where multipath and shadowing are characterized by Hoyt/Gamma distribution. [ABSTRACT FROM AUTHOR]

In this paper, a dual-hop amplify-and-forward relay system is considered with an eavesdropper where each link undergoes independent, non-identical, flat Rayleigh fading. The eavesdropper is capable of diversity combining the direct and relayed communication from the source using maximal ratio combining (MRC) and selection combining (SC). Closed-form upper and lower bounds on secrecy outage probability are derived. Closed-form approximate secrecy outage probability and ergodic secrecy rate is also obtained when source-relay link average signal-to-noise ratio (SNR) is high. Asymptotic analysis is presented when dual-hop links have equal or unequal average SNR. It is found that SC has both the secrecy outage and ergodic secrecy rate performances are better than MRC. To achieve the same secrecy outage performance of SC, MRC requires relatively higher SNR at lower rate. MRC also requires relatively higher SNR to achieve same secrecy rate performance of SC when eavesdropper link quality degrades. It is observed that lower bound for secrecy outage is tight and tends towards secrecy outage as SNR increases. It is interesting to find that either one of the dual-hop link can limit the performances even if the other link average SNR is infinitely high. [ABSTRACT FROM AUTHOR]

This paper presents a simple equal gain combining technique for cyclostationarity detection based spectrum sensing in cognitive radio networks. The presented technique is based on maximum cyclic autocorrelation function (MCAS) technique with a low computational cost relative to other cyclostationarity detection based spectrum sensing techniques. MCAS judges whether an orthogonal frequency division multiplexing signal is included in received signals, by comparing the peak and non-peak values of a cyclic autocorrelation function (CAF). In this paper, the signal-to-noise ratio (SNR) of the CAF, which is composed of the peak and non-peak values of the CAF, is employed. The presented technique attempts to improve the performance of spectrum sensing by combining CAFs obtained at each receive antenna and by obtaining a stable CAF SNR. Moreover, the presented technique is implemented on a software defined radio based testbed for the evaluation. The developed testbed is mainly composed of a Universal Software Radio Peripheral/GNU Radio which is one of the software defined radio receiver, and the spectrum sensing technique is experimentally demonstrated in an anechoic chamber using the 470-710 MHz frequency band allocated to ISDB-T (terrestrial digital broadcasting) in Japan. The effectiveness of the presented techniques is validated by these results. [ABSTRACT FROM AUTHOR]

Spatial diversity is an effective method to mitigate the effects of fading, and when used in conjunction with low-density parity-check (LDPC) codes, it can achieve excellent error-correcting performance. Noise added at each branch of the diversity combiner is generally assumed to be additive white Gaussian noise, but there are many applications where the received signal is impaired by noise with a non-Gaussian distribution. In this paper, we derive the exact bit-error probability of different linear combining techniques on Rayleigh fading channels with impulsive noise, which is modeled using symmetric alpha-stable distributions. The relationship for the signal-to-noise ratios of these linear combiners is derived and then different non-linear detectors are presented. A detector based on the bi-parameter Cauchy–Gaussian mixture model is used and shows near-optimal performance with a significant reduction in complexity when compared with the optimal detector. Furthermore, the threshold signal-to-noise ratio of LDPC codes for different combining techniques on these channels is derived using density evolution and an estimation of the waterfall performance of LDPC codes is derived that reduces the gap between simulated and asymptotic performance. [ABSTRACT FROM AUTHOR]

We describe a new receiver for layered asymmetrical clipped optical orthogonal frequency-division multiplexing (LACO-OFDM) in which diversity combining is used at each layer to improve the performance. In each layer of LACO-OFDM, some subcarriers carry data and others carry only the components which result from clipping. In the new receiver at each layer, a nonlinear process is used to recover this clipped signal and use it for diversity combining. Simulation results show that the new receiver outperforms a conventional receiver by up to 2 dB when two layers are used. The performance of LACO-OFDM with diversity combining is compared with other forms of optical OFDM. The results show that at high bit rates LACO-OFDM with diversity combining is the most power efficient system, while ACO-OFDM with diversity combining but without layering is the best for low bit rates. In addition, the diversity combining receiver is compared to the recently proposed receiver for LACO-OFDM based on the noise cancellation. Results show that the diversity combining and noise cancellation have the same performance over flat channels. However, over frequency selective channels, the diversity combining receiver has better performance. [ABSTRACT FROM PUBLISHER]

In this letter, we present a novel diversity combining receiver for demodulating layered asymmetrically clipped optical orthogonal frequency division multiplexing. The receiver consists of a soft successive interference cancellation (SIC) module which cancels the inter-layer interference (ILI) using the minimum mean square error (MMSE) estimates of the information symbols, and a diversity combining module which extracts the diversity components from the clipping noise. We show that the soft SIC module alone can effectively suppress the ILI, leading to bit error rates (BERs) resembling those of a genie receiver which is free of error propagation. It is also shown that the diversity combining receiver which combines the MMSE estimates with their diversity components outperforms the genie receiver by up to 2 dB at the BER of 10^-6 . [ABSTRACT FROM PUBLISHER]

In amplify and forward cooperative relaying system, the knowledge of individual channel state information (CSI) is essential for coherent decoding and optimal design. To assist in the estimation of the individual channels, we proposed an in-band pilot strategy, where some cooperative data at the relay are discarded to insert pilots that can be utilized to estimate the relay to destination link. The new cooperative strategy implies that relay not only helps the source to transmit cooperative data, meanwhile, assisting the destination to acquire the individual CSI at the cost of cooperative information. Although some useful data are lost due to insertion of in-band pilots, the detection performance can be maintained with a simple iterative reconstruction method. Furthermore, if the direct link is available, the received signals from both the source and the relay can be combined to achieve spatial diversity. Simulation results are presented to assess the performance of the proposed schemes. [ABSTRACT FROM PUBLISHER]

In this paper, we propose an algorithm to remove movement noise from second derivative of photoplethysmography (SDPPG) signals. SDPPG is widely used in healthcare applications because of its easy and comfortable measurement. However, an SDPPG signal is vulnerable to movement, which degrades the signal. Degradation of SDPPG signal shapes can result in incorrect diagnosis. The proposed algorithm detects movement noise in a measurement signal using wavelet transform, and removes movement noise by selecting the best signal from among multiple signals measured at different locations. Experiment results show that the proposed algorithm outperforms the previous filter-based algorithm, and that movement noise with 30% time duration can be reduced by up to 70.89%.

This paper investigates the performance analysis of diversity combining over flat fading channels subject to additive impulsive noise. Specifically, the impulsive noise follows the symmetric a-stable (SaS) distribution. Traditionally, this is a difficult problem since the analytical expression for the probability density function of a general SaS distribution remains unknown. In order to tackle this difficulty, we adopt Fourier power transform to obtain an exact bit error rate (BER) expression for the Genie-aided receiver as well as a BER upper bound for the conventional linear matched filter receiver, without taking any approximation. Monte- Carlo simulations are performed to validate our analytical results. The simulation results show that our proposed BER expressions are valid in the whole geometric signal-noiseratio (GSNR) ranges, thus outperforming the previous results valid only at high GSNR values. [ABSTRACT FROM AUTHOR]

Analysis of communication systems with combiners, assuming flat fading channels, is well-known. However, this analysis for a chaos-based DSSS system with a frequency selective channel, giving proper mathematical model and derived expressions for the probability of error, practically does not exist. This paper presents the theoretical model of a chaos-based DSSS system assuming frequency selective channel that is composed of a primary channel and a number of secondary channels. In order to investigate the consequences of delays on signal transmission in these channels, this paper uses presentation of signals in discrete time domain and theoretical frame of discrete time stochastic processes. The channel is represented by a modified Saleh–Valenzuela model, which results in a number of delayed signal replicas at the receiver side. For the sake of explanation, the delays are assumed to remain in a chip interval. For the sake of comparison, the theoretical models and derived expressions are confirmed by the simulation of the system. [ABSTRACT FROM AUTHOR]

Experimental results demonstrating the use of diversity combining in an optical wireless system using asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) are presented. A standard white lighting LED of the type often used in visible light communications (VLC) is used as the transmitter. The experiments show that diversity combining gives an improvement of 2–3 dB, and that uncorrected DC offset in the receiver can cause diversity combining to fail, but that DC correction methods are effective. It is shown that diversity combining changes the frequency distribution of noise received on the even subcarriers. [ABSTRACT FROM PUBLISHER]

To achieve better mitigation of both cochannel interference (CCI) and intersymbol interference, a new structure using generalized estimation of multipath signals in conjunction with maximal-ratio combining diversity for wireless communications over multipath channels is introduced. In this structure, the signal replicas received from multiple paths are first independently produced by a bank of blind spatial filters and then constructively combined by a diversity combining receiver for final signal estimate. The new scheme can be applied on single antenna array or between multiple antenna subarrays. It will be shown, from both theoretical analysis and numerical experiments, that the new scheme provides both space diversity gains and path diversity gains while suppressing the CCIs. [ABSTRACT FROM AUTHOR]

The work presents the investigation of Gaussian Minimum Shift Keying (GMSK) and Binary Phase Shift Keying (BPSK) transmission schemes with Department of Electrical and Electronics Engineering. E-mail: falade.alaba@yahoo.com. Phone: +2347053244999.both Maximum Ratio Combining (MRC) and Equal Gain Combining (EGC) diversity combining techniques over Rayleigh flat fading (RFF) channels in a digital mobile wireless system. The System model for the received signal was developed under L-propagation paths and then simulated. Randomly generated symbols and image data was used as the Information signal. The results obtained showed that BPSK had a higher error probability value than the corresponding GMSK scheme. The results also showed that due to GMSK high immunity to noise and other interfering signals, it provides a better performance than BPSK signalling scheme. MRC was observed to perform better in terms of mitigation of the interference induced by the Rayleigh channel than EGC diversity combining technique. The quality of the images received with both signalling schemes were in agreement with the Bit Error Rate (BER) results. [ABSTRACT FROM AUTHOR]

This paper proposes a new receiver based on frequency-domain diversity combining (FDDC) for an asymmetrically clipped optical orthogonal frequency-division multiplexing (ACO-OFDM) system. Compared with its time-domain diversity combining (TDDC) counterpart, the FDDC receiver is capable of more effectively exploiting the frequency selectivity of the channel to further improve the detection performance, which is proved by postcombining signal-to-noise-ratio (SNR) analysis. An enhanced version of the FDDC receiver, which is called eFDDC, is also proposed subsequently. It allows for optimal selection among multiple sets of candidate symbol vectors based on signum matrix estimation. Simulation results show that the proposed FDDC and eFDDC receivers outperform the TDDC receiver. With a sufficient number of candidate symbol vector sets, the eFDDC receiver even outperforms a kind of iterative receiver, which is known to have superior performance in current literature, yet the complexity of eFDDC is lower due to the avoidance of matrix inversion. Those facts suggest that the FDDC and eFDDC receivers are strong receiver candidates for the ACO-OFDM system. [ABSTRACT FROM PUBLISHER]

We consider an amplify-and-forward relay system with a source node (S), a relay node (R), and a destination node (D) with an arbitrary number of cochannel interferers at the relay. Each node is equipped with a single antenna and operates under the frequency selective circumstance. For such a system, we propose a system scheme to suppress the relay cochannel interference (CCI) at both the relay and the destination, where the relay performs noise selective nulling in the training block to make the relay training sequence avoid suffering from the thermal noise and CCIs at R, and the destination combines the data blocks from the S→R→D link and the S→D link. Simulation results show that the proposed system scheme achieves better channel estimation and symbol detection performance than the original one. [ABSTRACT FROM AUTHOR]

Missed-detection probability expressions for energy detectors often involve infinite series and do not provide quick insights into the effects of operating conditions. To overcome these limitations, we develop novel asymptotic analyses by proposing an approximate probability density function (PDF) of a random variable $\beta$, which, in general, can characterize fading channels in diverse operating conditions. The coefficients of the proposed approximate PDF of $\beta$ are obtained by matching the coefficients of the approximate PDF's series expansion (or coefficients of the approximate PDF's moment generating function (MGF)) with those of the exact PDF (or MGF) of $\beta$. By using the proposed approximation, a unified closed-form asymptotic missed-detection probability is derived. Its usefulness is then demonstrated for fading channels without and with antenna diversity, for cooperative detection, and in co-channel interference. For each case, the sensing gain, which reveals the effect of the operating conditions on the detection performance, is determined explicitly. Furthermore, the asymptotic complementary area under the receiver operating characteristic curve, an alternative performance metric, is derived, and found to reveal the sensing gain. Numerical results verify the accuracy of our derived asymptotic expressions over a wider signal-to-noise ratio (SNR) range compared to the existing asymptotic solution, which is accurate only for high SNRs. [ABSTRACT FROM PUBLISHER]