Ergodic Channel Capacity Research Articles

Design and analysis of low-profile quad element wide band MIMO antenna with efficient isolation for C and X-band applications

ABSTRACT A low-profile, quad-element multiple-input/multiple-output (MIMO) antenna of 0.69 λ 0 λ 0 is presented in this study. The proposed design consists of a stub and slot-loaded partial ground plane with a quad rectangular-shaped radiator on top. The four elements are placed orthogonally to one another to reduce mutual coupling and envelope correlation coefficient (ECC). The maximum isolation of the proposed MIMO antenna is 61.5 dB at 9.94 GHz frequency. It achieved impedance bandwidth 5.56 GHz, ranging from 5.74–11.30 GHz. The peak gain of the proposed MIMO antenna is 6.18 dB at 7.3 GHz, with a maximum efficiency of 89.21% at 7.1 GHz. The minimum ECC between ports 1 and 2 over the operating band are observed as 0.0001. To achieve the best outcome, a parametric analysis of the proposed antenna is also performed. Various diversity characteristic metrics, including diversity gain (DG), mean effective gain (MEG), total active reflection coefficient (TARC), channel capacity loss (CCL), and ergodic channel capacity (CC), are thoroughly analysed to determine how well the MIMO antenna performs in terms of diversity. Over the operating band, the measured values provide good agreement with respect to simulated and equivalent circuit model results, indicating a strong candidacy for operation in the investigated bands. The proposed MIMO antenna have the potential for C and X band applications such as WLAN, radio astronomy, satellite communication, and automotive radar.

Performance analysis of the FSO communication system with random jamming over a composite Málaga turbulence fading channel

The performance analysis of a free space optical (FSO) communication system in the presence of random jamming is presented over a Málaga (M) distributed channel model with pointing errors and atmospheric attenuation. Firstly, the probability density function expressions of the transmission channel, signal-to-jamming ratio, and signal-to-noise ratio are derived. Then, considering the probability of the jammer and Gaussian white noise, the closed-form expressions for the ergodic channel capacity, outage probability, and average bit error rate are derived. Moreover, asymptotic expressions for the aforementioned performance metrics are also derived to ascertain the diversity gain of the system. Extensive Monte Carlo simulations are performed to demonstrate the credibility of this theoretical analysis. Results indicate that the adverse impact of random jamming is higher than that of Gaussian noise for the FSO communication system. Besides, this observation highlights the pulsating nature of the jamming effect, showcasing that within high signal-to-jamming ratio regions, a low probability jammer exerts the most significant impact on the FSO system.

The [formula omitted]-[formula omitted] composite distribution with pointing errors: Theory and applications to RIS

The α-F composite fading distribution with pointing errors is investigated in this paper. New expressions for the probability density function and cumulative distribution function of the envelope/instantaneous signal-to-noise ratio (SNR), higher-order moments, and moment generating function of the instantaneous SNR are derived. Based on the aforementioned statistics, expressions for the outage probability, symbol error probability, and ergodic channel capacity are obtained. An asymptotic analysis is also provided. Furthermore, an application of the α-F model with pointing errors in a wireless emerging system, namely reconfigurable intelligent surfaces (RIS), is shown. Several curves, corroborated by Monte–Carlo simulations, are presented for different values that characterize the channel and pointing error parameters.

Performance analytics of adaptive subcarrier intensity modulated free-space optical communications over general Málaga turbulence links

In this paper, we study the performance analysis of free-space optical (FSO) system employing a constant-power variable-rate adaptive subcarrier intensity modulation (SIM) and utilizing phase-shift keying (PSK) over the Málaga atmospheric turbulence with pointing errors. According to a target bit-error rate (BER) and the instantaneous signal-to-noise ratio (SNR), the adaptive strategy adopts the subcarrier PSK modulation order. More precisely, we develop new analytical expressions for the average BER, the upper bound on ergodic channel capacity for non-adaptive modulation, and the attainable spectral efficiency (SE) of an adaptive SIM-FSO communication system. According to the simulation results, it is possible to achieve an increase in SE under weak-to-strong turbulence conditions without the need to increase the average optical power transmitted or compromise the BER requirements.

Performance Analysis of Multi-Hop FSOC over Gamma-Gamma Turbulence and Random Fog with Generalized Pointing Errors

The multi-hop amplify-and-forward free-space optical communication (FSOC) system is studied in random fog using the I-function, considering Gamma-Gamma atmospheric turbulence and Beckmann pointing error. Outage probability, average bit error rate and average ergodic channel capacity are obtained. Channel-state-information assisted relay performs better than fixed-gain relay under high transmitted power. Increasing the hop number significantly improves the performance. More hops are needed in medium fog than in light fog to achieve the same performance. In addition, on a single-hop link, the influence of fog channel on system performance is dominant, while atmospheric turbulence intensity, normalized jitter standard deviation and normalized boresight error have little effect on the system performance. However, on a multi-hop link, atmospheric turbulence intensity, normalized jitter standard deviation and normalized boresight error have serious effects on system performance. Compared with correcting the normalized boresight error, compensating the normalized jitter standard deviation greatly improves the multi-hop FSOC system performance. Furthermore, optimizing beam width can further improves the performance. To ensure good communication, the system should select a low-order modulation scheme.

Performance analysis of satellite link using Gaussian mixture model under rain

SummaryThe evolution of communication systems to the next generation, for example, B5G and 6G, demands an ultrareliable performance regardless of weather conditions. Such ultrareliable system design will require that the effects of adverse weather events on the communication system have to be computed more accurately so that physical layer compensation should be optimally and dynamically adaptive to such events. The performance of satellite links is severely affected by dynamic rain attenuation, and thus, accurate and reliable modeling of performance parameters is essential for dynamic fade countermeasures, especially above 10 GHz. In this work, we model the energy per bit to noise spectral density ratio ( ) using Gaussian mixture (GM) model during rainy events. The developed mathematical expression is used to accurately model the average , bit error rate (BER), outage probability, and ergodic channel capacity of the link. The average BER, upper bound on BER, and average ergodic capacity of an M‐ary phase shift keying scheme (MPSK) using the GM model of are derived to evaluate the performance of the link under such weather impairments. We then show the numerical results and analysis using the GM model of the measured data obtained with the AMoS‐7 satellite at a site located in Israel.

Spreading CDMA via RIS: Multipath Separation, Estimation, and Combination

As a revolutionary technology for future wireless communications, reconfigurable intelligent surface (RIS), characterized by an efficient way of manipulating wireless signals, has been widely investigated in recent years toward enhancing signal quality, energy efficiency, throughput, and so on. However, in RIS-assisted Internet of Things (IoT), a new issue as multipath separation emerges especially when deploying multiple RISs to assist communication, since the devices may have limited signal processing capabilities. For alleviating this problem, we conceive a novel RIS-enabled code division multiple access (CDMA) structure, where each RIS holds a specified time-varying coefficient to tag the channel. Moreover, multipath extraction is further considered, including a practical channel estimation approach along with theoretical derivations in terms of Cramér-Rao lower bound, mean square error, as well as ergodic channel capacity. Simulation results corroborate the feasibility of the conceived RIS-CDMA structure and the effectiveness of the proposed multipath extraction approach.

Performance analysis of a RIS-assisted RoFSO communication system over Malaga distribution for smart city applications.

Radio over free space optics (RoFSO) is one of the potential technologies that can satisfy the requirements of 5G services in a smart city. However, as RoFSO is line-of-sight (LOS) communication, one of its limitations is the occurrence of a skip zone in the targeted areas. In this work, a reconfigurable intelligent surface (RIS) is proposed as the solution to overcome this connection difficulty, which prevents signal blocking by generating LOS connections. These RIS modules extend the communication channel coverage, making it more intelligent and controllable. The performance analysis based on outage probability, ergodic channel capacity, and bit error rate has been performed using heterodyne detection. Malaga distribution has been used to model atmospheric turbulence. The exact closed-form expressions of the probability density function and cumulative distribution function of the end-to-end signal-to-noise ratio are derived. Exploiting these derived statistics, system performance is investigated through the ergodic channel capacity, outage probability, and average bit error rate for M-ary quadrature amplitude modulation and two binary modulation schemes: non-coherent binary frequency-shift keying and coherent binary phase-shift keying. Numerical results are compared among different turbulence conditions, link lengths, and scattering errors. The results show that the proposed RIS-assisted RoFSO technology has the potential to be effective for 5G smart city applications.

Performance Analysis of Active RIS-Aided Systems in the Face of Imperfect CSI and Phase Shift Noise

The linear minimal mean square error (LMMSE) estimator for active reconfigurable intelligent surface (RIS)-aided wireless systems is formulated. Furthermore, based on the moment-matching method, we employ the Gamma distribution to approximate the distribution of the instantaneous received signal-to-interference-plus-noise ratio (SINR), and then derive the closed-form outage probability and ergodic channel capacity in the presence of realistic channel estimation errors, the thermal noise of RIS amplifiers and the RIS phase shift noise. Our theoretical analysis and simulation results show that the introduction of RIS amplifiers is equivalent to increasing of the transmit power, and also present the performance degradation resulting from the channel estimation error and the RIS phase noise.

Performance Analysis of Intelligent Reflecting Surface-Aided Decode-and-Forward UAV Communication Systems

In this article, we consider a scenario of a decode-and-forward (DaF) wireless system supporting the communication of an unmanned aerial vehicle (UAV) with a ground-control-station (GCS) through an intelligent reflecting surface (IRS). Particularly, the UAV moves according to the three-dimensional (3D) random way point model at low altitude in a complex urban environment. However, a stationary relay-station (RS) decodes and forwards the UAV’s signal over an IRS-aided virtual line-of-sight (LoS) link to a GCS. The highly dynamic and terrain-dependent UAV-to-RS channel follows the Beaulieu-Xie fading model. However, the RS-to-IRS and IRS-to-GCS links enjoy clear LoS; thus, follow the Rice fading model. We derive new closed-form expressions for the probability density functions (PDFs) and the cumulative distribution functions (CDFs). Then based on the derived statistical expressions, several performance metrics including outage probability, average bit error rate, and ergodic channel capacity are derived in closed-forms. Additionally, simple and accurate approximated expressions in the high signal-to-noise ratio regime are also provided. The analytical results are validated through some representative numerical examples and supported by Monte-Carlo simulation results.

Joint channel model for fog and atmospheric turbulence and performance analysis of unmanned aerial vehicles’ free-space optical communication

To study the joint effects of turbulence and fog on free-space optical (FSO) communication, a joint fog-turbulence-pointing error probability model for FSO is derived based on the random fog channel, Malaga turbulence model, and pointing error model. The closed-form expressions for the average signal to noise ratio (SNR), outage probability, average bit error rate (BER), ergodic channel capacity, and moment generating function in FSO communication under intensity modulation/direct detection are derived based on the joint model. Based on the unmanned aerial vehicle (UAV) working scenario, applying these expressions, the performance analysis of the inter-UAVs optical wave communication is implemented under the conditions for different beam widths, turbulence intensity and fog density and the pointing error caused by position, orientation, and jitter deviations. The calculated results are in good agreement with the Monte Carlo simulations. The analytical results for the average BER and outage probability show that the increase in beam width can significantly degrade the BER and outage probability, for the UAVs optical communication link. The analysis for the ergodic channel capacity shows that it increases with the increase of average transmission power; however, it increases slowly with the increase of beam width. And the increase in turbulence intensity, fog density, and drone jitter will degrade the communication performance of the system. Our study lays an important theoretical foundation for the development of FSO communication and UAV communication performance improvement in joint fog and turbulent environment.

Eight-Port Modified E-Slot MIMO Antenna Array with Enhanced Isolation for 5G Mobile Phone

An eight-element antenna system operating at sub 6 GHz is presented in this work for a future multiple-input multiple-output (MIMO) system based on a modified E-slot on the ground. The modified E-slot significantly lowers the coupling among the antenna components by suppressing the ground current effect. The design concept is validated by accurately measuring and carefully fabricating an eight-element MIMO antenna. The experimentation yields higher element isolation greater than −21 dB in the 3.5 GHz band and the desired band is achieved at −6 dB impedance bandwidth. The E-shape slot occupies an area of 17.8 mm × 5.6 mm designed on an FR-4 substrate with dimensions of 150 mm × 75 mm × 0.8 mm. We fed the I-antenna element with an L-shape micro-strip feedline, the size of the I-antenna is 20.4 × 5.2 mm2, which operates in the (3.4–3.65 GHz) band. Moreover, our method obtained an envelope correlation coefficient (ECC) of <0.01 and an ergodic channel capacity of 43.50 bps/Hz. The ECC and ergodic channel capacity are important metrics for evaluating MIMO system performance. Results indicate that the proposed antenna system is a good option to be used in 5G mobile phone applications.

Systematic Performance Analysis of Hybrid FSO/RF System over Generalized Fading Channels with Pointing Errors

Hybrid free space optical (FSO)/radio frequency (RF) system has attracted extensive attention because of its advantages of both the FSO and RF links. From the viewpoint of overall system performance, this paper presents a systematic analysis method of communication performance and security performance of the hybrid FSO/RF system with the Málaga turbulence channel and the α−μ fading channel. The hybrid FSO/RF system adopts the diversity method of maximum ratio combining (MRC) to receive signals. The new expressions of communication performance parameters (i.e., the bit error rate, the outage probability, the ergodic channel capacity) of the only FSO system and the hybrid system are obtained. Then, the new expressions of the security performance parameters (i.e., the security outage probability and the strictly positive secrecy capacity) of the hybrid system with the FSO or RF links eavesdropping are derived, respectively. Our derived analytical expressions present an efficient tool to investigate the impact of system parameters on the overall performance of the hybrid system, namely modulation scheme, turbulence intensity, pointing errors, target rate, and eavesdropper output signal-to-noise ratio. The simulation results show that compared with the only FSO system, the hybrid system can significantly improve the communication performance of the system; the communication performance of the hybrid system using coherent binary phase shift keying (CBPSK) modulation is obviously better than the other two modulation technologies; with the deterioration of atmospheric environment (increasing turbulence intensity and pointing errors), the communication performance and security performance of the hybrid system will decline; both RF link eavesdropping and FSO link eavesdropping have a greater impact on the security performance of the hybrid systems; whether it is FSO link eavesdropping or RF link eavesdropping, the reduction of target rate and output signal-to-noise ratio of the eavesdropper can improve the security performance of the hybrid system.

LoS MIMO transmission for LEO satellite communication systems

To provide global service with low latency, the broadband low earth orbits (LEO) satellite constellation based communication systems have become one of the focuses in academic and industry. To allow for wideband access for user links, the feeder link of LEO satellite is correspondingly required to support high throughput data communications. To this end, we propose to apply line-of-sight (LoS) multiple-input multiple-output (MIMO) transmission for the feeder link to achieve spatial multiplexing by optimizing the antenna arrangement. Unlike the LoS MIMO applications for static scenarios, the movement of LEO satellites make it impractical to adjust the optimal antenna separation for all possible satellite positions. To address this issue, we propose to design the antenna placement to maximize the ergodic channel capacity during the visible region of the ground station. We first derive the closed-form probability distribution of the satellite trajectory in visible region. Based on which the ergodic channel capacity can be then calculated numerically. The antenna placement can be further optimized to maximize the ergodic channel capacity. Numerical results verify the derived probability distribution of the satellite trajectory, and show that the proposed LoS MIMO scheme can significantly increase the ergodic channel capacity compared with the existing SISO one.

Capacity-Oriented Envelope Correlation Coefficient for Multiple Antennas of Mobile Devices

In this article, a capacity-oriented envelope correlation coefficient (ECC) that incorporates a preferred channel model for assessing a multiple antenna system of a multiple-input-multiple-output (MIMO) mobile device is proposed. Originated from the rudimentary law of ergodic channel capacity, the ECC for multiple antennas (ECC-M) is proven to holistically reflect the impact of radiation patterns and total efficiencies of multiple antennas on channel capacity. The closed-form ECC-M expressions for Rayleigh fading channel model and ray-based spatial channel model are studied, leading to an easy-to-use ECC-M expression that approximately incorporates a realistic channel model. The correlation of the proposed ECC-M to the channel capacity is demonstrated through the Monte Carlo (MC) simulation of three four-element MIMO antenna testbeds in two channel models, showing that the antenna total efficiency and a realistic channel model involved in the ECC-M play an important role in assessing the performance of multiple antennas. It is justified that the difference in channel capacities of two multiple antenna systems is highly relevant to their ECC-Ms at high signal-to-noise ratios (SNRs). The proposed ECC-M is also experimentally validated through over-the-air (OTA) throughput measurement, revealing that the ECC-M can effectively assess the OTA performance of multiple antenna systems for MIMO terminal devices.

MIMO system capacity based on different numbers of antennas

This paper analyzed and compared the ergodic channel capacities of several typical channel systems (SISO, SIMO, MISO, MIMO) in independent identically distributed flat Rayleigh fading channels. The theoretical and simulation results show that the ergodic capacity of the MIMO channel increases linearly with the number of antennas.

Dielectric Decoupler for Compact MIMO Antenna Systems

A novel decoupling method based on the superposition principle is proposed for compact multi-input–multi-output (MIMO) antenna systems in this work. A dielectric block is introduced to encompass all radiators in a compact MIMO system and works as a decoupler when the block is appropriately designed. Owing to the presence of dielectric–air boundary (DAB) introduced by the dielectric block, scattered paths show up for electromagnetic (EM) waves inside the block. For any two encompassed primary radiators, mutual couplings via the direct and scattered paths are superposed one on another. Because the scatted wave paths can be controlled by changing the shape and dimension of the DAB, mutual coupling between two encompassed primary radiators can be minimized with a properly designed DAB. To illustrate this decoupling principle, the electric field distribution of a basic Hertzian dipole wrapped in a dielectric decoupler is first studied. Results show that this method can generate several field valleys inside the dielectric block and can lead to good isolation when a second radiator is placed at a valley. A dual-port antenna wrapped in a dielectric decoupler is then proposed for demonstration. By optimizing the DAB shape, this antenna can realize a measured 20 dB isolation bandwidth of 12.6%, covering the whole 3.3–3.7 GHz 5G frequency range 1 (FR1) band. Furthermore, a quad-port decoupled antenna is studied to show the generality of the proposed decoupling method. Using a hollow rectangular dielectric block, isolations among four ports of more than 21.5 dB can be obtained in the 3.3–3.7 GHz band with a 20-dB isolation bandwidth of 18%. The envelope correlation coefficients (ECCs) and calculated ergodic channel capacity (CC) results show that the proposed compact dual-port and quad-port antennas are competitive for MIMO applications.

16-ports indoor base station MIMO array for sub-6 GHz 5G applications

A typical 5G multiple-input and multiple-output (MIMO) system must combine a high number of antennas at both the transmitter and receiver to realize spatial multiplexing capability. In this paper, a wideband 16- element indoor base station (BS) antenna array that can cover 3.3–6.0 GHz is proposed for 5G applications. A π-shaped monopole antenna is designed to cover the Lower band (LTE bands 42/43–N77–N78), the intermediate band (N79), and the higher band (LTE 46). The antenna elements are arranged in a limited space printed on a substrate take the Hexakaidecagon Polygon shape. As the antenna elements are arranged with good isolation, achieving good polarization diversity. The proposed BS array is simulated, fabricated, and tested. The typical results, S-parameters, antenna efficiency, and radiation patterns are investigated. Moreover, to validate the MIMO performances, a very low envelope correlation coefficient (ECC) below 0.02, high antenna efficiency of about 82–93.2% are achieved. The calculated ergodic channel capacity of the 16 × 16 MIMO system reached up to 85 bps/Hz. The proposed antenna array was compared to some other 5G MIMO indoor base station antennas.

Performance analysis of dual-hop mixed radio frequency/free space optical transmission systems based on partially coherent beams over F-distribution channel models

The performance of dual-hop mixed radio frequency (RF)/free space optical (FSO) communication system with partially coherent beams (PCBs) is investigated on the basis of decode-and-forward (DF) protocol. Specifically, both the RF and FSO channels are assumed to follow F-distribution with proper selection of parameters. Taking the path loss, atmospheric turbulence, and pointing errors into consideration, the closed-form expressions for the probability density function (PDF) and cumulative distribution function of the received signal-to-noise ratio are derived in terms of hypergeometric function in RF and FSO links, respectively. Subsequently, the closed-form expressions for outage probability, average bit error rate, and ergodic channel capacity of this system with M-ary phase-shift keying and M-ary quadrature amplitude modulation schemes are obtained on the basis of DF protocol. The results show that shadowing in RF link as well as the pointing error and atmospheric turbulence in FSO link would result in significant performance deterioration in dual-hop mixed RF/FSO system, while PCB can bring significant performance improvement of mixed RF/FSO systems with pointing errors over weak to moderate turbulence. Furthermore, the correctness of the analytical expressions is verified by Monte Carlo simulations. This work would benefit the design and development of the mixed RF/FSO systems.

Performance Analysis of Terahertz Communications in Random Fog Conditions With Misalignment

In this letter, we consider Terahertz (THz) communications in the presence of pointing error impairments (misalignment) and under random fog conditions. We derive closed-form expressions, in terms of I-function, for the probability density function (PDF) and the cumulative distribution function (CDF). Then, the PDF and the CDF are employed to derive closed-form expressions for the outage probability, average symbol error rate (SER), and ergodic channel capacity. Additionally, very tight simple approximations in the high signal-to-noise ratio for the outage probability and average SER are provided. The derived expressions are validated through numerical and Monte-Carlo simulation results.