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Spatial diversity can be used over satellite-to-ground optical links to mitigate turbulence induced fading. In this paper, bit-error rate (BER) performances of satellite-to-ground downlink optical communication are evaluated for fiber-based coherent detection receiver system with spatial diversity. The performance analysis is carried out with M-ary phase shift keying (M-PSK) and M-ary quadrature amplitude modulation (M-QAM) schemes. Maximum ratio combining (MRC), equal gain combining (EGC), and selection combining (SC) are evaluated as diversity combining methods. We consider Gamma-Gamma distributed model for the signal irradiance and non-central chi-square distribution for the random fluctuation of fiber-coupling efficiency. BER performances of fiber-based coherent detection receiver system with downlink spatial diversity are analyzed for 8PSK and 8QAM modulation schemes and compared with receiver system with single aperture under the same conditions. BER performances of fiber-based receiver systems with spatial diversity are also studied for MPSK and MQAM with different constellation M. It is observed that 8PSK and 8QAM modulated fiber-based receiver systems with spatial diversity can significantly improve the BER performance with EGC and MRC receiver system. For SC diversity, additional number of apertures does not mean better communication performance under the case of low zenith angles. The research work of this paper has laid a analytical foundation for the application of satellite-to-ground downlink multiple apertures receiver system with fiber-based coherent detection MPSK and MQAM modulations.

Digital Audio Broadcasting (DAB) is a terrestrial audio broadcast system supporting Single Frequency Networks (SFN). SFNs are beneficial for the distribution of services in large areas, but do not support local services, i.e. different services from different transmitters, without distortion. However, some audio service providers rely on local services. A local service insertion technique for DAB SFNs that supports existing receivers was developed, tested and presented in a field trial in Braunschweig, Germany. The results showed that the local reception area is influenced by the remaining co-channel interference between various local services. In this paper, simulations and field trial measurements investigating dual-branch diversity to combat the co-channel interference are presented. An increase in robustness against co-channel interference of about 5 dB is found in comparison to single antenna reception.

In high-density wireless local area networks (WLANs), if a number of neighboring nodes simultaneously use limited radio frequency resources, a large amount of interference may reduce the reliability of data transmission significantly. To enhance the transmission reliability by exploiting neighboring APs, we consider a centralized WLAN with a control node (CN), which performs a simple link-layer cooperative processing for overheard transmissions from multiple APs. While APs in the conventional WLAN protocol simply discard erroneous data frames and those transmitted from non-associated stations, the proposed medium access control (MAC) protocol uses redundant wireless links between the stations and non-associated APs in high-density WLANs. In the proposed MAC protocol, CN corrects erroneous uplink data frames by using a simple diversity combining scheme, which is based on a majority voting algorithm. To evaluate the performance of the proposed MAC protocol, we perform simulation studies and empirical experiments using software-defined radio equipment.

The macro diversity (MD) system consisting of macro-diversity (MD) selection combining (SC) receiver and two micro-diversity (mD) maximal ratio combining (MRC) receivers is considered in this paper. The diversity combining receivers operating over correlated Gamma shadowed Rician multipath fading environment is analyzed. Moment generating function (MGF) of mD MRC receivers output signals is calculated in a closed-form. Furthermore, the expression for MGF function of macro-diversity SC receiver output signal envelope is performed. This result can be used for calculation the bit error probability of proposed macrodiversity system with several modulation schemes. Numerical results are presented graphically to show the influence of number of diversity branches, Rician severity parameter, Gamma shadowing severity parameter and correlation coefficient of shadowing on observed system performance.

Public safety incidents typically involve a significant amount of group traffic and have a stringent requirement of connection reliability. Hence multicast could potentially improve network and user performance significantly, which triggered our study on Long-Term Evolution (LTE) Multicast Broadcast Single Frequency Network (MBSFN). In this paper, we first derive a realistic MBSFN Signal-to-Interference-plus-Noise Ratio (SINR) analytical model, with multiple antennas, multipath channel, and equalizer considered. Then through comprehensive system level simulations, we compare MBSFN and unicast in terms of resource efficiency v.s. throughput, as well as outage probability. We also study the impacts of MBSFN size and quantify the MBSFN SINR improvement due to diversity combining and interference reduction, respectively.

Supporting Ultra-Reliable Low-Latency Communication (URLLC) in the Internet of Things (IoT) era is challenging due to stringent constraints on latency and reliability combined with the simple circuitry of IoT nodes. Diversity is usually required for sustaining the reliability levels of URLLC, but there is an additional delay associated to auxiliary procedures to be considered, specially when communication includes low-cost IoT devices. Herein, we analyze Selection Combining (SC) and Switch and Stay Combining (SSC) diversity schemes as plausible solutions for enabling ultra-reliable low-latency downlink communications to low-cost IoT devices. We demonstrate the necessity of considering the time spent in auxiliary procedures, which has not been traditionally taken into account, while we show its impact on the reliability performance. We show there is an optimum number of receive antennas, which suggests that under certain conditions it might be required to turn off some of them, specially under the SC operation. We highlight the superiority of SSC with respect to SC as long the associated Signal-to-Noise Ratio threshold is properly selected. We propose using a fixed threshold relying only on long-term channel fading statistics, which leads to near-optimum results., Comment: Accepted at ICC'20 Workshop - ULMC6GN, 6 pags, 3 figures

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.

In this work, we develop a deep learning (DL) based robust data detection algorithm for a receive-diversity system, where the data is corrupted by Gaussian and different non-Gaussian noise and interference in different diversity branches. A fully-connected deep neural network (DNN) is designed for this purpose and is trained with different noisy datasets offline. The developed DNN is then applied in real-time for data detection process. We emphasize that the detector does not require the noise distribution to be known for its operation. Furthermore, by the use of simulations, we show that the proposed DL-based detector performs much better than the conventional maximal ratio combining (MRC) detector for non-Gaussian noise. Moreover, simulation results point out that the proposed detector is robust enough to operate in time-varying noisy environment.

Hybrid free space optical (FSO)/radio frequency (RF) systems have been proved to be reliable for high-data-rate wireless backhauls. In this article, we present a unified performance analysis of the hybrid FSO/RF transmission system which transmits identical data in both links and implements two popular diversity combining schemes, namely, selection combining (SC) and maximal ratio combining (MRC), in the receiver. Specially, for the FSO link, the Gamma-Gamma turbulence with pointing errors under heterodyne detection (HD) and intensity modulation/direction detection (IM/DD) is considered in our analysis while the general κ - μ shadowed fading which unifies popular RF fading models is employed for the analysis of the RF link. As a result, unified closed-form expressions of outage probabilities and average bit error rates for different modulation schemes are derived. A preliminary extension of the RF link to multi-input–multi-output (MIMO) transmission is also analyzed. Analytical and Monte Carlo simulation results are provided to characterize the performance of the hybrid FSO/RF link which is compared to the single FSO link and the single RF link. The agreement between the analytical and simulation results confirms the unification of various FSO channels and RF fading scenarios into a single closed-form expression.

This paper presents, multiple relay selection strategy and comparison of different diversity combining techniques at the receiver in Non Orthogonal Multiple Access (NOMA) based wireless cooperative networks .Three different diversity combining strategies Selection Combining(SC) ,Equal Gain Combining (EGC) and Maximal Ratio Combining(MRC) were examined under Rayleigh fading channel conditions and Amplify and Forward relaying strategy. Analytical results were developed to demonstrate Symbol Error Rate (SER) performance. The simulation results revealed the benefit of selecting the MRC scheme instead of SC and EGC which were applied to combine the multiple received signals from selected relays .The effective Signal to Noise Ratio (SNR) for all the wireless channel links are calculated and multiple relay selection is done by choosing relays having maximum effective SNR. Performance analysis on MRC scheme was carried out for Fixed Power Allocation and Optimal power allocation using Lagrangian method and the results affirmed better performance for optimal power allocation technique.

Ultra reliable low latency communication (URLLC), a use case of 5G, requires high reliability and low end-to-end latency simultaneously. While 5G physical layer enablers like short packet communication and flexible numerology along with one-shot transmission can achieve low latency, multi-connectivity based on macrodiversity is a potential solution for achieving high reliability in single transmission. This paper discusses the various architectures available for implementing macrodiversity based multi-connectivity for achieving URLLC. 3C based packet duplication architecture, diversity combining architecture using maximal ratio combining (MRC) and Coordinated multi-point (CoMP) architecture for interference suppression at cell edge are considered in this paper. Monte-carlo simulations prove that 3C and MRC architecture perform best in terms of reliability and radio resource usage efficiency, respectively.

A theoretical analysis is presented to evaluate the bit error rate performance of a UWB RFID system using hybrid receive diversity combining technique. Expression is developed for output SNR and the PDF of the SNR at the output of the hybrid receive combiner which consists of selection combiner followed by an equal gain combiner considering Rayleigh fading channel. The performance results for a RFID reader receiver are evaluated for several reader-to-tag round trip distance and degree of diversity. Significant improvement is noticed in receiver sensitivity and boost in the range of a RFID system due to dual diversity combining at a given transmitter power and BER. For example, the range of the system can be increased from 5 m to 40 m by using the combining technique.

This paper presents a linear complexity iterative rake detector for the recently proposed orthogonal time frequency space (OTFS) modulation scheme. The basic idea is to extract and combine the received multipath components of the transmitted symbols in the delay-Doppler grid using linear diversity combining schemes like maximal ratio combining (MRC), equal gain combining and selection combining to improve the SNR of the combined signal. We reformulate the OTFS input-output relation in the vector form by placing some null symbols in the delay-Doppler grid thereby exploiting the block circulant property of the channel matrix. Using the new input-output relation we propose a low complexity iterative detector based on the MRC scheme. The bit error rate (BER) performance of the proposed detector will be compared with the state of the art message passing detector and orthogonal frequency division multiplexing (OFDM) scheme employing a single tap minimum mean square error (MMSE) equalizer. We also show that the frame error rate (FER) performance of the MRC detector can be improved by employing error correcting codes operating in the form of a turbo decision feedback equalizer (DFE)., Comment: Accepted in IEEE Wireless Communications and Networking Conference (WCNC), 2020

The multipath fading independency between different Global Navigation Satellite System (GNSS) frequency bands and space-separated antennas can be used to improve robustness of high-precision GNSS receivers in harsh urban environments. This research focuses on a new sensitive and robust fading monitoring architecture for GNSS diversity branches, and implementation of the method on an Adaptive Diversity reception-based Tracking Loop (ADTL). Firstly, fluctuations in the amplitude and phase of multipath fading signals are characterized. Performance of different design parameters in the fading monitoring method is analyzed in details. Next, diversity combining strategies including the non-linear Selective Combining (SC) and the Maximum-Ratio Combining (MRC) are utilized in ADTL for different fading conditions. Experimental results with Monte-Carlo simulation and real GNSS fading signals demonstrated that: (1) the proposed novel method can achieve robust and sensitive fading monitoring with response delay less than 20 ms; (2) Compared with traditional Phase Lock Loops (PLLs), the ADTL algorithm significantly reduced the navigation bit error rate due to half-cycle sudden-phase change caused by phase losing of lock.

This paper presents performance and its simulation results of pseudonoise (PN) code acquisition scheme with MIMO scheme for an ultra-wideband time-hopping/code-division-multiple-access (UWB TH/CDMA) system. The transmission channel is modelled as a frequency selective lognormal fading channel. In almost practical PN code acquisition system, the existence of more than two synchronous cells in the uncertainty region of the search process is possible due to multipath effect. Therefore, based on deriving the detection probability, false alarm rate, miss detection probability, and mean acquisition time, the acquisition performance is analyzed under the hypothesis of multiple synchronous states (cells) in the uncertainty region of the PN code. And the code acquisition performance is evaluated when the correlator outputs are noncoherently combined by using equal gain combining (EGC) scheme. In this procedure, the closed form for the conditional probability of decision variable is derived using the Gauss-Hermite quadrature formula. The performance comparison of the scheme mentioned above shows that the code acquisition performance with the diversity combining technique, especially when increasing the number of antenna, is more robust than that using no diversity. And code acquisition performance comparison also shows that if the detection threshold is set inappropriately, the performance might be degraded, even if an antenna diversity method is applied. It is also shown that Tx diversity can improve the acquisition performance but not as much as Rx diversity does. And Rx diversity can be applied to the acquisition system for additional diversity gain if the complexity of the receiver can be accepted.

We propose and experimentally demonstrate, for the first time, a system which integrates millimeter-wave (MMW) and free-space-optics (FSO) analog radio-over-fiber (A-RoF) channels, and provides enhanced reliability in 5G and beyond mobile fronthaul (MFH) links. The integrated system utilizes a novel coordinated mapping and combining (CMC) technique that senses the signal quality in each data block and apportions the load accordingly. Furthermore, the technique takes advantage of the abundant bandwidth in both MMW and FSO links and is compatible with orthogonal frequency division multiplexing (OFDM). In the CMC design, the data blocks at the transmitter side are interleaved and repeated in both the frequency domain and the time domain, and then the duplicated blocks are combined with adaptive weight coefficients at the receiver side. We demonstrate experimentally that the proposed CMC t echnique improves power margins and enhances the robustness of the adaptive diversity combining technique (ADCT)-based FSO/MMW links by mitigating system impairments caused by frequency/time burst interference and power fading attributable to adverse weather conditions. In experiments, compared with the ADCT-based system, we find a 9 dB gain in received optical power tolerance and a 5.8 dB lower EVM floor under a deliberately injected 20-MHz LTE frequency interference burst.

In this paper, the performance of an energy detector in cognitive radio, using different diversity combining techniques, is evaluated. Among many diversity combining techniques, maximal ratio combining (MRC) gives the best results but at the cost of the highest complexity. To design a simpler receiver, it is suggested to use less complex combining techniques, i.e. switched diversity, which provides one of the least complex solutions to combat fading. The paper analyzes two switched diversity schemes, switch examine combining (SEC), and switch examine combining with post examining selection (SECp). A closed form expression determining the probability of detection using MRC, SEC and SECp is derived for various numbers of branches. Detection performance with different diversity combining techniques is compared and the complexity trade-off is observed.

Due to severe inter-cell interference (ICI), the signal-to- interference-and-noise ratio (SINR) suffers from very significant fluctuation in indoor multi-cell visible light communication (VLC) systems, which greatly limits the overall system performance. In this paper, we propose and evaluate a generalized angle diversity receiver (ADR) structure to reduce SINR fluctuation in indoor multi-cell VLC systems. The generalized ADR consists of one top detector and multiple inclined side detectors. In an indoor multi-cell VLC system using the generalized ADR, the inclination angle of the side detectors is optimized in order to minimize the SINR fluctuation over the receiving plane, where the impact of receiver random rotation is considered. An optimized ADR with different numbers of detectors is analyzed with different LED layouts and diversity combining techniques in a typical indoor environment. Analytical results show that the SINR fluctuation is gradually reduced when more detectors are equipped in the optimized ADR. In an indoor two-cell VLC system, much more significant SINR fluctuation reduction is achieved by using select-best combining (SBC). However, nearly the same SINR fluctuations are obtained in an indoor four-cell VLC system when using SBC and maximal-ratio combining (MRC). By applying the optimized ADR, up to 15.9 and 32.4-dB SINR fluctuation reductions can be achieved in comparison to a conventional single-element receiver (SER) in indoor two-cell and four-cell VLC systems, respectively. NRF (Natl Research Foundation, S’pore)

This paper investigates the effect of exponential antenna correlation on the secrecy performance of Nakagami-m fading correlated channels in the presence of an eavesdropper. Diversity combining techniques are imposed to reduce the effect of that exponential correlation. The closed-form analytical expressions (CFAEs) for the ergodic secrecy capacity (EGC), probability of non-zero secrecy capacity (PNZSC) and the secure outage probability(SOP) are derived to facilitate the investigation clearly. Our results show that the effect of exponential antenna correlation in Nakagami-m fading channel significantly affects the security. But the antenna diversity is the best solution to reduce that effect maintaining a tradeoff between the number of antennas and the intensity of correlation. Finally, the validity of analytical expressions are checked via Monte-Carlo simulations.

Atmospheric turbulence is one of the main causes of degrading the quality of service in free-space optical (FSO) systems. The use of diversity techniques in an FSO system can minimize the fading effect which is caused by atmospheric turbulence. When diversity combining is applied at both the transmitter and the receiver ends, the system can mitigate the degradation more effectively. In this paper, we consider a $$2\times L$$ multiple-input multiple-output FSO system with on–off keying modulation where the link is affected by gamma–gamma fading. Alamouti space–time coding is implemented at the transmitter, while the receiver employs switch-and-examine combining. Analytical expressions for different performance metrics such as outage probability, average bit error rate and average capacity are derived using a moment-generating function-based approach. Numerical results are provided and are compared with Monte Carlo simulations.

In the spectrum sharing mode, the transmitting power of the secondary user (SU) is optimally controlled, such that no additional interference occurs at the primary user (PU). In this paper, the secrecy outage performance is analyzed for such cognitive underlay decode-and-forward (DF) threshold-based relay network. The relayed and the direct signals are combined at the secondary eavesdropper and destination. Unlike other works to date, we have used both selection combining (SC) and maximal ratio combining (MRC) diversity schemes at the destination and eavesdropper with all possible permutations, and the best possible combination for cognitive system secrecy has been validated. Further, we consider threshold-based relaying where, the relay can successfully decode and re-transmit, only if the received signal-to-noise ratio (SNR) meets the particular threshold. We show that the diversity scheme, the threshold SNR, the secrecy rate, and the interference power all have a significant impact on cognitive system secrecy. We have also shown that the secrecy performance is more sensitive to changes in the quality of direct link between source to eavesdropper than source to destination, especially at the higher secrecy rates. The accuracy of the analytical expressions is corroborated by the computer simulation results.

The authors investigate the performance and reliability improvement of multiple relay cooperative free space optical (FSO) communication over direct link. Multiple gain combiner (MGC) method has been introduced as a diversity combining method which assures to provide a close to optimum performance as compared to maximal ratio combining (MRC). As compared to MRC, the proposed MGC technique does not require prior channel information and adaptive gain adjustment. Bit error rate (BER) performance improvement with different combining techniques, including MGC, in cooperative FSO system for different channel environments has been included in this study. BER performance for multiple relays for various combining techniques: selection combining, equal gain combining, MRC and MGC have been compared and it is seen that the performance of MGC is close to optimum MRC. High availability of the system is achieved by using multiple relays in the cooperative system. Markov model analysis for availability and mean time between failures of FSO systems in multiple relays cooperative communication has been done to verify the reliability improvement of a cooperative system with increasing number of relays.

In this paper, we analyze a newly introduced fading channel model that consists of several specular and diffused scatter components. This model unifies the non-central chi, generalized Ricean and κ – μ models into a single fading model. A closed form expression for the generalized moment generating function (MGF) for this model is derived. This novel result acts as a base for calculating various other performance metrics of communication systems like n th moment of signal to noise ratio (SNR), amount of fading (AF) and outage probability. We also derive closed form expressions for performance of energy detection in Single input Single Output (SISO) systems as well as in the case of diversity combining. This includes probability of detection, probability of false alarm and the area under receiver operating characteristic (ROC) curve. Further, closed form expressions of average bit error rate (ABER) have been derived for SISO and Multiple Input Multiple Output (MIMO) based Orthogonal Frequency Division Multiplexing (OFDM) system over fading channel using MGF approach. The results obtained from derived expressions are verified with the help of benchmark results and Monte Carlo simulations.

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.

Orthogonal frequency division multiplexing (OFDM) provides an effective and low complexity means of eliminating inter-symbol interference for transmission over frequency selective fading channels. In OFDM systems, channel state information (CSI) is required for the OFDM receiver to perform coherent detection or diversity combining, if multiple transmit and receive antennas are deployed. In practice, CSI can be reliably estimated at the receiver by transmitting pilots along with data symbols. In this paper, we investigate and compare various efficient pilot-based channel estimation schemes by neural network technologies for OFDM systems. We present further the application of functional link neural fuzzy network (FLNFN) for channel estimation in the investigated OFDM systems. We compared bit error rates of the proposed neural network with that of the other neural network technologies, the least square (LS) algorithm, and the minimum mean square error (MMSE) algorithm. Our results demonstrate that the proposed FLNFN algorithm can enhance the performance of channel estimation in existing OFDM channel environments.

Increasing number of antennas are closely packed in emerging multiantenna systems and correlation among them can no longer be ignored. In this paper, such a multiantenna spectrum sensing system is investigated considering dual, triple, four and up to infinite number of correlated antenna branches. Constant, arbitrary and exponential correlation among the antenna branches are considered. Closed form expressions for the detection probability, in terms of the confluent hypergeometric function, is derived assuming maximal ratio combining (MRC) and equal gain combining (EGC) diversity techniques in Nakagami-m multipath fading channel. Numerical results quantify the interbranch correlation that impacts the detector performance significantly. However, results also show that this effect could be compensated by employing the appropriate diversity combining technique and by increasing the diversity branches. Furthermore, we find that at high m values (Rician like channel), low false alarm probability and highly correlated environments, EGC which is a simpler scheme performs as good as MRC which is a more complex scheme.

IEEE 802.16j MMR WiMAX network introduces multi-hop relay architecture, which involves cooperative relay stations focusing on increasing the network throughput and coverage. Relay selection algorithms can be used to choose the optimal relay, which help in reducing the computational complexity during the signal processing operation of the wireless network. In this research work, a conventional amplify-forward (AF)/decode-forward (DF) assisted multi-relay IEEE 802.16j WiMAX network is considered. The effects of relay selection algorithms on the performance metrics such as symbol error rate (SER) and channel capacity are investigated in detail through simulation-based study. Further, the performance of this network utilizing the proposed relay selection algorithms, namely threshold based max_min and threshold based harmonic mean of SNR, are compared with the existing max_min and harmonic mean of SNR based algorithms. Standard diversity combining techniques such as maximal ratio combining (MRC) and selection combining (SC) are used for combining the transmitted signal at the receiver. In addition, the impact of relay locations on the performance metrics are explored. It is observed that both the proposed threshold based max_min and threshold based harmonic mean of SNR based relay selection algorithms outperform the max_min and harmonic mean of SNR based algorithms, as both the SER and channel capacity for the considered multi-relay WiMAX network is improved significantly. Further, this extensive study and analysis will be beneficial for the design of MMR WiMAX networks.

In a cloud-based network architecture, the central unit (CU) at the cloud coordinates wireless nodes such as the remote access units (RAUs) at the edges of the network and manages most functions for providing wireless connectivity services to clients. The CU facilitates efficient communication resource management such as radio frequency or transmission power of RAUs by global resource coordination. In this paper, we propose a cloud-based Wi-Fi network architecture consisting of a CU and RAUs as an improvement on the conventional Wi-Fi architecture with traditional access points (APs). We then propose a method for uplink data transmission in a cloud-based Wi-Fi network. In a conventional Wi-Fi network with independently operating APs, APs close to each other may not be able to utilize the same frequency band efficiently because of significant amounts of interference. However, in a cloud-based Wi-Fi network, the CU coordinates RAUs so that they can operate in the same frequency band by transmitting or receiving signals through the shared wireless medium to improve spectral efficiency. For each frequency band, the proposed system utilizes a diversity combining that combines multiple signals and introduces a single improved signal with high signal-to-noise ratio for uplink transmission in the cloud-based Wi-Fi network. In our proposed uplink transmission method for a cloud-based Wi-Fi network, we utilize diversity combining with the immediate acknowledgement (ACK) transmission method that transmits the ACK frame to the client immediately before decoding. The proposed uplink data transmission method mitigates the performance degradation caused by the fronthaul propagation delay between the CU and RAUs, without significant modification of the IEEE 802.11 standard. Using an IEEE 802.11n standard-compliant simulation and experiments with software-defined radio equipment, we verify the goodput performance of the proposed method for a cloud-based Wi-Fi network architecture.

Fast frequency hopping (FFH) is a useful anti-jamming method. Many diversity combining methods are used to combat partial-band interference in FFH systems, including linear and non-linear combining receivers. In fifth-generation scenarios, FFH technique may take an important role in OFDM mode. In early works, a non-linear combining receiver in FFH/binary FSK system named division-combining receiver (DCR) was proposed. It was found that the random variables for decision in the DCR are F-distributed under partial-band noise jamming over additive white Gaussian noise channel, which could be used for performance analysis and the probability computation of bit error. In this Letter, the specific presentations of DCR and its F-distribution characteristics are investigated. Simulations show that DCR receiver has a light advantage among non-linear receivers.

To perform spectrum sensing in fading environment is one of the most challenging tasks for a CR system. Diversity combining schemes are used to combat the effect of fading and hence detection proba...

We propose and analyze multi-diversity combining and selection to enhance the performance of relay-assisted mixed radio frequency/free-space optics (RF/FSO) system. We focus on a practical scenario for cellular network where a single-antenna source is communicating to a multi-apertures destination through a relay equipped with multiple receive antennas and multiple transmit apertures. The RF single input multiple output (SIMO) links employ either maximal-ratio combining (MRC) or receive antenna selection (RAS), and the FSO multiple input multiple output (MIMO) links adopt either repetition coding (RC) or transmit laser selection (TLS). The performance is evaluated via an outage probability analysis over Rayleigh fading RF links and Gamma–Gamma atmospheric turbulence FSO links with pointing errors where channel state information (CSI) assisted amplify-and-forward (AF) scheme is considered. Asymptotic closed-form expressions at high signal-to-noise ratio (SNR) are also derived. Coding gain and diversity order for different combining and selection schemes are further discussed. Numerical results are provided to verify and illustrate the analytical results.

In this paper, we consider a cooperative diffusion-based molecular communication (MC) network consisting of single source, single decode-and-forward relay, and single destination. The source and the relay nodes use different types of molecules for information transmission. Considering both the relay and the direct links at the destination node, we have two different received signals that can be used by the destination node to retrieve the data transmitted by the source node. Therefore, diversity arises at the destination node. For detection, we adopt the energy detector applying the diversity combining technique. Since the optimum relay position in relay-aided networks plays a crucial role to enhance their performance, we study the relay location optimization problem. We first derive a closed-form expression for the bit error probability of the proposed detection scheme in which the received energy from the source and the relay nodes are linearly combined at the destination node. Then, in order to find the optimum relay position as well as the optimal destination decision threshold for a given number of molecules released by the source and the relay nodes, we formulate a joint optimization problem whose objective is to minimize the bit error probability of the network. To solve this optimization problem, we propose an iterative algorithm based on the block coordinate descent algorithm and study its convergence behavior. Numerical results show that the error performance can be improved by optimizing the position of the relay node. Our analyses help us in designing a reliable cooperative diffusion-based MC network.

In this work, an angle diversity receiver (ADR) structure is proposed to optimize the uniformity of the received optical power distribution in an indoor visible light communication (VLC) system. Taking the rectangular and hybrid layouts with 16 light-emitting diodes as examples, different inclination angles and the number of side detectors are investigated with three diversity combining techniques in a typical room, where the primary reflection of the wall is considered. Simulation results showed that the inclination angles and the number of side detectors would affect the variance and average of the received optical power, and the variance would decrease with the increase of the number of side detectors. In addition, maximal ratio combining is more suitable for the ADR when the variance and average of the received optical power are considered simultaneously. By applying the ADR with five side detectors, the variances of the received optical power will decrease by 81.34% and 86.09% under the rectangle layout and the hybrid layout, respectively. This work will benefit the design and development of the VLC system.