Imperfect Channel State Information

Practical transceivers have hardware impairments, which may affect the data rate of a system. In this paper, two way relaying with hardware losses is considered and is different from previous methods, which considers only ideal hardware case. Here both hops are subjected to independent and non-identical distributed nakagami-m fading variants with Amplify-and-Forward (AF) protocol and Decode-and-forward (DF) protocol. Hardware impairments are calculated at source, relay and destination. The outage probability is calculated with a function effective end-to-end signal-to-noise-anddistortion ratio (SNDR). In a similar way ergodic capacity also achieved. For low SNR values losses will be less but substantial. And for high SNR values losses will increase without bounds. But for SNDR case, increasing SNR makes some constant value of threshold, which is inversely proportional to the SNDR, called SNDR ceiling. Finally, this paper suggests the design guidelines for selecting hardware equipmen...

In this work, we investigate the problem of secure broadcasting over block-fading wiretap channels with limited channel knowledge at the transmitter. More particularly, we analyze the effect of having a finite rate feedback on the throughput of multiuser broadcast wiretap channels. We consider that the transmitter is only provided by a b-bits feedback of the main channel state information (CSI) sent by each legitimate receiver, at the beginning of each fading block, over error-free public links with limited capacity. Also, we assume that the transmitter is aware of the statistics of the eavesdropper's CSI but not of its channel's realizations. Under these assumptions of CSI uncertainty, we characterize the ergodic secrecy capacity of the system when a common message is broadcasted to all legitimate receivers, the ergodic secrecy sum-capacity when multiple independent messages are transmitted, and the ergodic secrecy capacity region for the broadcast channel with confidential messages (BCCM). In all three scenarios, we show that as long as the transmitter has some knowledge of the main CSI, obtained even through a 1-bit CSI feedback, a non-zero secrecy rate can still be achieved. The impact of having the feedback sent over a binary erasure channel (BEC) is also investigated for the BCCM case. Here again, and even with the possibility of having the feedback bits erased, a positive secrecy rate can still be achieved as long as the erasure event is not a probability-one event. An asymptotic analysis of the obtained results is provided for the high SNR regime, and the scaling law of the system, when the number of legitimate receivers is large, is also presented.

Opportunistic interference alignment (OIA) is a well known precoding technique that uses interference alignment to improve the rate of secondary user (SU) simultaneously nullifying the interference that SU causes to a primary user (PU). In this paper, we analyse the efficacy of OIA technique in multiuser multiple input multiple output (MU-MIMO) underlay cognitive radio network (eRN) for generalized K-tL fading channel and Rayleigh fading with lognormal shadowing (K fading) channel models. Numerical results are presented for the achievable data rates of both PU and SU links in two fading environments.

This work presents outage analysis of a hybrid communication system, where radio frequency (RF) and free space optical (FSO) communication links transmit in parallel to the then cascaded underwater wireless optical communication (UWOC) link forming a RF/FSO-UWOC cooperative system. Optical wireless communication (OWC) is being used as a viable communication technology by researchers due to its advantages such as fast speed, cost effectiveness, and highly secure transmission. The proposed architecture connects the terrestrial and the underwater regions to form an end-to-end cooperative system. This hybrid RF/FSO back-haul link makes the system more reliable as the optical link is highly susceptible to weather conditions. The channel models considered are Nakagami-m distributed fading, Double Generalized Gamma (DGG) distributed atmospheric turbulence along with Rayleigh distributed misalignment losses and mixture of Exponential Generalized Gamma (EGG) distributed oceanic turbulence fo...

In this paper, we analyze the performance of twoway amplify-and-forward (AF) relaying with best relay selection scheme in the presence of hardware impairment at the relays. We first obtain the tractable closed-form expressions of the statistical characteristics for end-to-end signal-to-noise ratio (SNR). To reveal significant insights into the system performance, we also computed the asymptotic SEP, which is shown extremely tight in the high SNR regime and low hardware impairments level. Our analysis enables us to evaluate the impact of non-ideal hardware on the performance of two-way relaying networks and highlight as a benchmark for system designer.

In this paper, we investigate the performance analysis of dual hop relaying system consisting of asymmetric Radio Frequency (RF)/Free Optical Space (FSO) links. The RF channels follow a Rayleigh distribution and the optical links are subject to Gamma-Gamma fading. We also introduce impairments to our model and we suggest Partial Relay Selection (PRS) protocol with Amplify-and-Forward (AF) fixed gain relaying. The benefits of employing optical communication with RF, is to increase the system transfer rate and thus improving the system bandwidth. Many previous research attempts assuming ideal hardware (source, relays, etc.) without impairments. In fact, this assumption is still valid for low-rate systems. However, these hardware impairments can no longer be neglected for high-rate systems in order to get consistent results. Novel analytical expressions of outage probability and ergodic capacity of our model are derived taking into account ideal and non-ideal hardware cases. Furthermore, we study the dependence of the outage probability and the system capacity considering, the effect of the correlation between the outdated CSI (Channel State Information) and the current source-relay link, the number of relays, the rank of the selected relay and the average optical Signal to Noise Ratio (SNR) over weak and strong atmospheric turbulence. We also demonstrate that for a non-ideal case, the end-to-end Signal to Noise plus Distortion Ratio (SNDR) has a certain ceiling for high SNR range. However, the SNDR grows infinitely for the ideal case and the ceiling caused by impairments no longer exists. Finally, numerical and simulation results are presented.

In this paper, the energy harvesting in mixed multiple-input-single-output radio frequency (RF)/free space optical (FSO) networks is studied. Assuming underlay mode, the secondary user (SU) source with limited battery communicates with its destination via a hybrid SU relay. The SU source harvests energy from both the hybrid relay and the primary network. The hybrid SU relay node is equipped with two antennas; one for energy transmission to the secondary user and the other for data reception. The SU source transmits its data over an RF link to the relay. Then, the relay decodes the SU data before retransmitting it to the SU destination over an optical link. The RF/FSO channels are assumed to follow Nakagami-m/Málaga-M fading models with pointing errors on the FSO link. Closed-form expressions for the exact outage probability, average bit error rate, and ergodic capacity are derived. For high signal-to-noise ratio values, closed-form expressions for the asymptotic outage probability and average bit error rate are derived. Based on the asymptotic results, a power allocation model is proposed to enhance the system outage performance. Some simulation and numerical results are employed to validate the derived expressions.

We analyze the outage performance of coherent partial decode-forward (pDF) relaying over Rayleigh fading channels in both half-and full-duplex transmissions. In coherent DF relaying, the relay either partially or fully decodes the source message, then coherently forwards the decoded message with the source to the destination. This coherent transmission creates a beamforming gain from the source and relay to the destination which improves the transmission rate. We analyze the impact of this beamforming gain on the outage performance, considering outage events at both the relay and the destination. We derive analytical expressions for the overall outage probability, assuming full CSI at receivers and only limited CSI at transmitters. We further show that at high SNR, coherent pDF relaying converges to full DF relaying and achieves the full diversity order of 2. These analyses provide a fundamental understanding of the reliability of coherent pDF relaying and form the basis for analyzing performance in larger network settings. Numerical results show that partial decoding at the relay outperforms full decoding for low SNR and high target rates in the half-duplex mode. Comparison with existing results further shows that source-relay coherent transmission and joint decoding at the destination both improve the outage performance.

In this paper, we analyze the performance of twoway amplify-and-forward (AF) relaying with best relay selection scheme in the presence of hardware impairment at the relays. We first obtain the tractable closed-form expressions of the statistical characteristics for end-to-end signal-to-noise ratio (SNR). To reveal significant insights into the system performance, we also computed the asymptotic SEP, which is shown extremely tight in the high SNR regime and low hardware impairments level. Our analysis enables us to evaluate the impact of non-ideal hardware on the performance of two-way relaying networks and highlight as a benchmark for system designer.

In this paper, we examine differential modulation for the decode-and-forward (DF) based cooperative free-space optical (FSO) network. We consider multiple relays for transmitting differential binary phase-shift keying (DBPSK) data from an optical source to destination along with a direct path between the two. The relays utilize the selective relaying protocol where the source data is forwarded to the destination only in the case of error-free decoding by the relays. We derive the unified expression of probability density function (PDF) of the signal-to-noise ratio (SNR) for generalized- ( ) distribution with pointing error (PE) considering both intensity modulation/direct detection (IM/DD) and heterodyne detection techniques. The derived unified PDF of SNR for   distribution is mathematically combined with the unified PDF of SNR for the Gamma-Gamma (GG) distribution. This combining enables us to obtain a single closed-form expression for a particular performance metric, which is applicable to both   and GG distributions with PE and both IM/DD and heterodyne detection techniques. More specifically, we derive the average bit error rate (ABER) and outage probability (OP) for the considered multiple-relay-based DF-FSO network. Furthermore, we analyze the asymptotic BER and asymptotic outage performances for the considered system at high SNR of source to relay links and obtain the diversity order, analytically. The impact of different power allocation schemes on ABER and OP is determined by utilizing the power allocation factor. The derived results clearly demonstrate the impact of severe atmospheric conditions, PE, the type of detection scheme, and the number of relays on the network performance. All the derived analytical results are verified through simulations.

Most studies on multi-hop communication systems are actually based on the assumption that hardware parts are built with high quality transmit/receive radio frequency chains. In practice, low cost hardware components are employed, which are prone to hardware manufacturing defects. This paper focuses on the design of the transmitter, relay stations (RSs) and receiver for multi-hop communication systems under hardware defects. This paper analyzes the hardware defects and their impacts on the multi-hop communication system performance. In addition, the impact of self-interference at the RSs is considered. The effect of hardware defects is modeled using distortion noises. A closed-form expression for the signal to noise and distortion ratios (SNDRs) is mathematically derived, and then the performance metrics (i.e., SNDR, outage probability (OP) and ergodic capacity) are calculated, accounting for hardware defects. In addition, exact form expression of the average bit error probability is derived. To facilitate comparison, performance metrics of the proposed multi-hop relaying system and ideal system are illustrated. We also propose a linear minimum mean square error (LMMSE) and self-interference cancellation technique to mitigate the hardware defects. The results reveal that hardware defects can degrade the system performance. In addition, SNDR ceiling is inversely proportional to the summation of the square of hardware defect level. Also, the proposed mitigation technique can enhance the system performance.

In this paper, we analyze the performance of twoway amplify-and-forward (AF) relaying with best relay selection scheme in the presence of hardware impairment at the relays. We first obtain the tractable closed-form expressions of the statistical characteristics for end-to-end signal-to-noise ratio (SNR). To reveal significant insights into the system performance, we also computed the asymptotic SEP, which is shown extremely tight in the high SNR regime and low hardware impairments level. Our analysis enables us to evaluate the impact of non-ideal hardware on the performance of two-way relaying networks and highlight as a benchmark for system designer.

In this paper, we analyze the performance of twoway amplify-and-forward (AF) relaying with best relay selection scheme in the presence of hardware impairment at the relays. We first obtain the tractable closed-form expressions of the statistical characteristics for end-to-end signal-to-noise ratio (SNR). To reveal significant insights into the system performance, we also computed the asymptotic SEP, which is shown extremely tight in the high SNR regime and low hardware impairments level. Our analysis enables us to evaluate the impact of non-ideal hardware on the performance of two-way relaying networks and highlight as a benchmark for system designer.

In this paper, we analyze the performance of twoway amplify-and-forward (AF) relaying with best relay selection scheme in the presence of hardware impairment at the relays. We first obtain the tractable closed-form expressions of the statistical characteristics for end-to-end signal-to-noise ratio (SNR). To reveal significant insights into the system performance, we also computed the asymptotic SEP, which is shown extremely tight in the high SNR regime and low hardware impairments level. Our analysis enables us to evaluate the impact of non-ideal hardware on the performance of two-way relaying networks and highlight as a benchmark for system designer.

In hybrid free space optical/radio frequency (FSO/RF) systems, switching between the optical and RF links depends on the optical and RF signal to noise ratio (SNR) threshold levels; therefore, the correct choice of these threshold levels is essential to make best use of the complementary nature of optical and RF links. Optimal selection of these threshold levels is the prime objective of this paper. A hybrid FSO/RF system using modified switching scheme with two optical and one RF threshold is considered. Here, we propose an algorithm to obtain the optimized thresholds, which yield minimum bit error rate (BER) for a given outage probability under a constraint on maximum transmitted power. The optimized thresholds are dependent on the average optical and RF SNR. Hybrid FSO/RF system use both optical as well as RF power. The average system SNR is computed by considering the actual optical and RF power consumption. Also the performance of the hybrid FSO/RF system is studied with respect to average system SNR using optimized optical and RF thresholds. This analysis reveals the existence of a critical operating point of average optical SNR, beyond which the system should be preferably operated to ensure minimum BER.

In this paper, we investigate the information theoretic performance of parallel relaying in free-space optical (FSO) communications over Gamma-Gamma fading channels. We consider an intensity modulation/direct-detection (IM/DD) FSO system with a single relay and a line-of-sight link between the source and the destination. Considering both amplify-andforward and decode-and-forward relaying, we develop performance characterizations of each relaying mode in terms of outage probability, diversity gain, coding gain, and diversitymultiplexing tradeoff (DMT). Our results demonstrate that parallel relaying improves the performance of FSO systems by bringing diversity advantages. In addition, both relaying modes achieve the same DMT and diversity gain while their coding gains can be different depending on underlying channels' characteristics. Index Terms-Free-space optical communications; parallel relaying; diversity gain; coding gain; diversity-multiplexing tradeoff. I. INTRODUCTION With its appealing features such as wide bandwidth in unregulated spectrum and low-cost implementation, free-space optical (FSO) communication has recently attracted a growing attention for a wide range of applications [1]. A major performance-limiting factor for terrestrial FSO links is atmospheric turbulence-induced fading. This has motivated many researchers to investigate temporal and spatial diversity techniques such as channel coding, sequence detection, and multiple-input multiple-output (MIMO) communications for performance improvements against the degrading effects of fading [2]-[8]. An alternative method to exploit diversity advantages is cooperative diversity, also known as user cooperation, which has been originally introduced for radio-frequency (RF) wireless communication [9]-[11]. In RF wireless systems, cooperative diversity takes advantage of the broadcasting nature of RF transmission in which the signal transmitted by the source node is overheard by other than destination nodes. The source node along with those nodes which overhear and are willing to share their resources (which are defined as "relays") create a virtual antenna array. Such a cooperative scheme is able to extract spatial diversity advantages in a distributed manner.

We propose a queueing model for free space optics-radio hybrid channel. Hybrid channel is presented by a pair of alternating channels (free-space optical link and radio frequency channel). Time when optical link is/is not used mainly depends on the weather conditions and is approximated by the mixture of two exponential distributions. We consider a queueing system with alternating service rates and apply the matrix-analytical approach to obtain stationary distribution of system states and performance characteristics.

In this paper, we investigate the performance analysis of dual hop relaying system consisting of asymmetric Radio Frequency (RF)/Free Optical Space (FSO) links. The RF channels follow a Rayleigh distribution and the optical links are subject to Gamma-Gamma fading. We also introduce impairments to our model and we suggest Partial Relay Selection (PRS) protocol with Amplify-and-Forward (AF) fixed gain relaying. The benefits of employing optical communication with RF, is to increase the system transfer rate and thus improving the system bandwidth. Many previous research attempts assuming ideal hardware (source, relays, etc.) without impairments. In fact, this assumption is still valid for low-rate systems. However, these hardware impairments can no longer be neglected for high-rate systems in order to get consistent results. Novel analytical expressions of outage probability and ergodic capacity of our model are derived taking into account ideal and non-ideal hardware cases. Furthermore, we study the dependence of the outage probability and the system capacity considering, the effect of the correlation between the outdated CSI (Channel State Information) and the current source-relay link, the number of relays, the rank of the selected relay and the average optical Signal to Noise Ratio (SNR) over weak and strong atmospheric turbulence. We also demonstrate that for a non-ideal case, the end-to-end Signal to Noise plus Distortion Ratio (SNDR) has a certain ceiling for high SNR range. However, the SNDR grows infinitely for the ideal case and the ceiling caused by impairments no longer exists. Finally, numerical and simulation results are presented.

In this paper, we analyze the performance of twoway amplify-and-forward (AF) relaying with best relay selection scheme in the presence of hardware impairment at the relays. We first obtain the tractable closed-form expressions of the statistical characteristics for end-to-end signal-to-noise ratio (SNR). To reveal significant insights into the system performance, we also computed the asymptotic SEP, which is shown extremely tight in the high SNR regime and low hardware impairments level. Our analysis enables us to evaluate the impact of non-ideal hardware on the performance of two-way relaying networks and highlight as a benchmark for system designer.

In this paper, we analyze the performance of twoway amplify-and-forward (AF) relaying with best relay selection scheme in the presence of hardware impairment at the relays. We first obtain the tractable closed-form expressions of the statistical characteristics for end-to-end signal-to-noise ratio (SNR). To reveal significant insights into the system performance, we also computed the asymptotic SEP, which is shown extremely tight in the high SNR regime and low hardware impairments level. Our analysis enables us to evaluate the impact of non-ideal hardware on the performance of two-way relaying networks and highlight as a benchmark for system designer.

Dual-hop relay communication systems have received extensive research attention due to their property of improving system reliability, spectral and power efficiency. RF wireless power transfer has also become a popular green technology for remote supply of energy to communication devices. In this paper, an RF wireless power transfer enabled dual hop relay system is analysed over generalised fading scenarios. A closed form expression is derived for the outage probability of the decode and forward as well as amplify and forward systems valid for all fading scenarios. Based on this analysis, the optimum design parameter settings for the system are also presented which serve as a reference point for measuring the outage performance of other variants of the generalised system. The numerical results obtained from derived expressions are compared with Monte-Carlo simulations and are found to be in excellent agreement with each other. INDEX TERMS Amplify and forward, CDF approach, decode and forward, outage probability, generalized fading, wireless power transfer.

Cognitive radio technology has been proposed as a viable solution to the spectrum scarcity problem faced by world today. The technology allows opportunistic spectrum access to the licensed frequency band by unlicensed user without causing any harmful interference to the licensed primary user. In this paper, ergodic channel capacity is investigated for underlay spectrum sharing system under maximum and received power constraint at licensed primary receiver. The time varying discrete time fading channels are assumed to undergo Rayleigh flat fading environment. Numerical simulations have been done to support theoretical results.

In this paper, we present relay-assisted transmission as a powerful fading mitigation tool for free-space optical systems operating in atmospheric turbulence channels. We study both serial (i.e., multi-hop transmission) and parallel (i.e., cooperative diversity) relaying encoupled with amplify-and-forward and decode-and-forward modes. We consider an aggregated channel model which takes into account both path-loss and turbulence-induced log-normal fading. Since fading variance is distance-dependent in free-space optical systems, relay-assisted transmission takes advantage of the resulting shorter hops and yields significant performance improvements. We derive outage probability of the relaying schemes under consideration which are further confirmed through Monte-Carlo simulations. Our outage probability analysis demonstrates that an impressive performance improvement of 18.5 dB is possible with the use of a single relay at a target outage probability of 10 −6 .

On the Performance of Free-Space Optical Systems over Generalized Atmospheric Turbulence Channels with Pointing Errors Imran Shafique Ansari Generalized fading has been an imminent part and parcel of wireless communications. It not only characterizes the wireless channel appropriately but also allows its utilization for further performance analysis of various types of wireless communication systems. Under the umbrella of generalized fading channels, a unified performance analysis of a free-space optical (FSO) link over the Malaga (M) atmospheric turbulence channel that accounts for pointing errors and both types of detection techniques (i.e. indirect modulation/direct detection (IM/DD) as well as heterodyne detection) is presented. Specifically, unified exact closed-form expressions for the probability density function (PDF), the cumulative distribution function (CDF), the moment generating function (MGF), and the moments of the end-to-end signal-to-noise ratio (SNR) of a single lin...