Ghassan Dahman - Academia.edu (original) (raw)

Papers by Ghassan Dahman

2011 Saudi International Electronics, Communications and Photonics Conference (SIECPC), 2011

ABSTRACT In this paper, the information extracted from Single-Input Multiple-Output sounding meas... more ABSTRACT In this paper, the information extracted from Single-Input Multiple-Output sounding measurements is used to study the effect of several aspects of the receive antenna arrays on system performance. The extracted multipath parameters are used to synthesize the MIMO channel matrices of a hypothesized communication system having a fixed microcellular base-station and a handheld terminal moving throughout the environment, and subsequently study the effect of array configuration on mean effective link gain, eigenvalue dispersion and outage capacity under real-world channel conditions. Three configurations of a dual inverted-F receive antenna array in a generic mobile handset were studied. The work in this paper revealed that on average, the effective power gain of a MIMO link has greater effect on the achievable capacity than multiplexing gain.

2019 IEEE Canadian Conference of Electrical and Computer Engineering (CCECE)

In this paper, we investigate the capabilities of Multiple-Input Multiple-Output (MIMO) systems i... more In this paper, we investigate the capabilities of Multiple-Input Multiple-Output (MIMO) systems in increasing the transmission range in tactical backhaul links. We utilize the ITU-R P.530 extensive measurement-based results in order to extract the correlation properties of the long-range line-of-sight (LOS) MIMO channel. Then we use this correlation information to formulate—based on the concept of worst-month outage probability —the improvements that can be achieved by MIMO- MRC (maximum ratio combining) systems. The main findings of this work are as follows. 1) For very low link outage requirement (e.g., 10−510^{-5}10−5 outage probability), a 2×2 MIMO system can increase the communication range by about 160% compared to a Single-Input Single-Output (SISO) system —this range extension is almost double what can be achieved when using a 1×2 (Single-Input Multiple-Output) SIMO-MRC system. 2) For comparably moderate link outage requirement (e.g., 10-3 outage probability), the range extension achieved by MIMO is only around 10% higher than what can be achieved by SIMO, but the strong gain is maintained compared to traditional SISO. We demonstrate that, for tactical backhaul links where high reliability is required, MIMO technology provides superior capabilities allowing for significantly increasing the transmission range.

The exponential growth of traffic in mobile networks is leading to an increased pressure on the i... more The exponential growth of traffic in mobile networks is leading to an increased pressure on the infrastructure of mobile networks and in particular on their backhaul networks. It is more critical than ever to carefully plan backhaul networks. In this paper, we formulate and solve the problem of hierarchical wireless backhaul network design. In our problem, we cover different requirements, namely: topology simplicity, network resiliency and link reliability. We formulate the problem as an Integer Linear Programming (ILP) problem, allowing us to solve the problem to optimality. Furthermore, we provide a graph theory based algorithm that allows to solve the problem overlarge scale. The proposed algorithm exploits the properties of the graph representing the network. The results of our evaluations in various network scenarios demonstrate the efficiency of our ILP formulation and the provided algorithm in keeping the backhaul network simple, resilient and reliable. Using a practical chan...

2011 XXXth URSI General Assembly and Scientific Symposium, 2011

A method previously reported by the authors for identifying simultaneous signals from different T... more A method previously reported by the authors for identifying simultaneous signals from different Tx antennas is applied for double-directional channel sounding between a channel sounder base station (CSBS) and a channel sounder mobile station (CSMS), as well as for single input single output (SISO) channel sounding on relay channels in urban microcell-type Tx/Rx scenarios. Using this method, multiple-orthogonal signals are produced from one pseudo-noise code by using it to modulate RF carriers at pre-calculated offset frequencies. The frequency spectra of the resulting signals are interleaved and they occupy the same overall frequency band, but the spectral lines from different transmitters are separable using Fourier analysis of signals sampled at the CSMS receiver output. In theory, any arbitrary number of links from different transmitters can be measured simultaneously using this method. However, in practice, Doppler spreads limit the number of simultaneous soundings that can be made with acceptable isolation among resulting impulse response estimates. Herein, examples are given of results from double-directional channel sounding using a linear array of 4 Tx antennas at the CSBS and of relay channel sounding with one Tx antenna at the CSBS and one Tx antenna at a channel sounder relay station (CSRS).

2017 XXXIInd General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS), 2017

A Matlab-based ray tracing (RT) simulator is implemented for the analysis of ship-to-ship communi... more A Matlab-based ray tracing (RT) simulator is implemented for the analysis of ship-to-ship communications. The anomalous propagation effect due to the evaporation duct which results in bending and/or trapping the rays is modelled. Based on extensive RT simulations, the received rays are identified and their parameters are estimated. We briefly describe the implementation of the RT simulator and compare the obtained ray tracing results with those obtained from a widely used simulation tool, the PETOOL. We highlight the excellent agreement between the two tools for lineof-sight (LOS) ranges and also highlight that there is significant disagreements between them for beyond-line-of-sight (beyond-LOS) ranges. Then, based on our RT simulator, we provide detailed results describing the effect of the evaporation duct phenomena on the communication link quality in the beyond-LOS zone.

2021 IEEE 94th Vehicular Technology Conference (VTC2021-Fall), 2021

In this paper, we analyze the weather information for 14 waterbodies from geographical areas with... more In this paper, we analyze the weather information for 14 waterbodies from geographical areas with different meteorological characteristics. We estimate the sub-hourly instances of the evaporation duct height (EDH) throughout a period of 10 years. Then, considering the frequency range 1 to 6 GHz, based on the parabolic equation method, we analyze the quality for a presumed shore-to-ship link throughout 100 km range. We evaluate the maximum range that can be supported for different reliability requirements and we focus specifically on analyzing the gain that can be obtained when antenna height and/or band diversity are used. It was found that for high reliability requirements, the antenna height at the shore is the main factor on deciding the maximum communication range that can be maintained. On the other hand, for applications that tolerate delay and work seasonally on an opportunistic basis, the evaporation duct statistics is the main factor deciding the likelihood of increasing the link range and establishing over-the-horizon communications.

2016 IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), 2016

We investigate antenna correlation of an Mantenna massive multiple-input multiple-output (MIMO) s... more We investigate antenna correlation of an Mantenna massive multiple-input multiple-output (MIMO) setup with the purpose of obtaining a low-rank representation of the instantaneous massive MIMO channel. Low-rank representation bases using short-term and long-term antenna correlation statistics are defined, and their performance is evaluated with data sets obtained from channel measurements in both indoor and outdoor environments at 2.6 GHz. Our results indicate that the shortterm bases can capture a larger amount of the channel energy compared to the long-term ones, but they have a limited timespan, one coherence time or less. On the other hand, the long-term bases are stable over time-spans of a few seconds. Hence, they can be obtained relatively easily. We also investigate a rank-p vector-scalar LMMSE channel estimator that exploits antenna correlation. Our results show that the investigated estimator can achieve a performance similar to that of full-rank LMMSE at a (2p + 1)/M times lower cost. The investigated estimator may be used in conjunction with estimators that exploit correlation in the frequency and time domains or, alternatively, in situations in which these estimators cannot be used, e.g., when pilot separation is larger than the channel coherence bandwidth or time.

2016 IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), 2016

In this paper, the effect of polarization on the downlink achievable sum-rate of multi-user Coope... more In this paper, the effect of polarization on the downlink achievable sum-rate of multi-user Cooperative Multi-Point (CoMP) systems is studied using synchronous multi-link channel measurements with two different antenna arrangements. In the first setup, four dual-polarized antenna patches with inter-patch distance varied from half wavelength to 8 m are considered at the base station (BS). In the second setup, two BSs located 60 m apart are used, each is provided with dual-polarized antennas spaced half a wavelength apart. Based on the BS antenna element selection, scenarios with different antenna polarizations at the BSs are considered. We consider four virtual users each is equipped with two antennas (V and H-polarized) with half-wavelength inter-element distance. The users are equally spaced with inter-user distance of about 0.5 m and moving in different routes. For each setup, the 8 × 4 MIMO multi-user channels are used to evaluate the achievable sum-rate of the system, where the ...

The possibility of using radio over fiber (RoF) analog transmissions to characterize the wireless... more The possibility of using radio over fiber (RoF) analog transmissions to characterize the wireless propagation channel of distributed antenna systems is investigated. In particular, the coherence time of kilometer-long, fiber-based networks is analyzed. Joint measurements of the phase noise of parallel links to the same site (intra-site) and to different sites (inter-site) in such a network are presented. The coherence time of the phase noise and phase noise difference between links is evaluated by means of the Allan time deviation. Measurements are performed at a frequency of 2.3 GHz under both stationary and non-stationary temperature conditions, for a duration of ten hours. In the setup analyzed, the phase noise was found to be white, with a phase drift component that determines the coherence time of the link. Coherence times between two to six minutes have been measured for a phase offset of 10 degrees Celcius. Values of the correlation coefficient r for intra-site phase noise pr...

ICC 2021 - IEEE International Conference on Communications, 2021

The problem of selecting the modulation and coding scheme (MCS) that maximizes the system through... more The problem of selecting the modulation and coding scheme (MCS) that maximizes the system throughput, known as link adaptation, has been investigated extensively, especially for IEEE 802.11 (WiFi) standards. Recently, deep learning has widely been adopted as an efficient solution to this problem. However, in failure cases, predicting a higher-rate MCS can result in a failed transmission. In this case, a retransmission is required, which largely degrades the system throughput. To address this issue, we model the adaptive modulation and coding (AMC) problem as a multi-label multi-class classification problem. The proposed modeling allows more control over what the model predicts in failure cases. We also design a simple, yet powerful, loss function to reduce the number of retransmissions due to higher-rate MCS classification errors. Since wireless channels change significantly due to the surrounding environment, a huge dataset has been generated to cover all possible propagation conditions. However, to reduce training complexity, we train the CNN model using part of the dataset. The effect of different subdataset selection criteria on the classification accuracy is studied. The proposed model adapts the IEEE 802.11ax communications standard in outdoor scenarios. The simulation results show the proposed loss function reduces up to 50% of retransmissions compared to traditional loss functions.

The increase in demand for high-data rates on the move in the complex urbanenvironment requires e... more The increase in demand for high-data rates on the move in the complex urbanenvironment requires either the allocation of new spectrum such as availablecontiguous spectrum in the mm-wave band or the use of novel configurationssuch as the application of massive multiple-input multiple-output (MIMO)technology. To enable the design of efficient wireless networks, an understandingof the propagation phenomena in the diverse urban environments isfundamental. In this chapter, we present results of studies related to fourthgeneration (4G) and future 5G radio systems both outdoor and outdoor-toindoor.Classifications include rural and highway, BS to pedestrian users,vehicular-to-vehicular, vehicular-to-infrastructure, container terminals, vegetation,and high-speed mobility such as trains. Results for path loss (PL)and shadow fading are presented from various studies of stochastic anddeterministic channel models based in outdoor, indoor-to-outdoor, hotspots,vehicular, and train environments. Re...

The channel properties have a large influence on user separability in massive multi-user multiple... more The channel properties have a large influence on user separability in massive multi-user multiple-input multiple-output (massive MIMO) systems. In this paper we present spatio-temporal characteristics obtained from massive MIMO channel measurements at 2.6 GHz. The results are based on data acquired in both indoor and outdoor scenarios where a base station equipped with 64 dual-polarized antenna elements communicates simultaneously with nine single-antenna users. In the outdoor scenarios the base station is placed at two rooftops with different heights and the users are confined to a five-meter diameter circle and move rando mly at pedestrian speeds. In the indoor scenarios, the users are located close to each other in a lecture theater and the base station is placed at various locations in the room. We report on the observed distribution of the delay spreads and angular spreads. Furthermore, the multi-user performance in terms of singular value spread of the MU-MIMO channel is also ...

One of the most crucial aspects is modern commercial and tactical wireless networks is the capabi... more One of the most crucial aspects is modern commercial and tactical wireless networks is the capability of the network’s backhaul to forward that massive amount of traffic to the core network. Hence, the careful planning for a resilient and cost-efficient backhaul is compulsory. In this letter, we formulate and solve the problem of hierarchical wireless backhaul design. In our problem, we cover different requirements, namely: link reliability, network resiliency, and low management overhead. We have formulated the problem as Integer Linear optimization Problem (ILP). The results of our simulation in various network scenarios demonstrate the efficiency of our formulation in keeping the backhaul network simple, reliable and resilient. Using practical channel propagation model and nodes density that model wide range of cities, our results show that even with high resiliency requirements, the network traffic can be backhauled with only 5-10% of the nodes for the considered densities.

IEEE Access, 2020

It is well established that the performance of communication systems is improved when deploying m... more It is well established that the performance of communication systems is improved when deploying multiple antennas at one or both of the transmit/receive sides; and the amount of the gained improvement depends on the level of multipath richness of the propagation channel. In ship-to-ship overwater channels, quantifying such an improvement is not an easy task due to the effect of evaporation duct on imposing complex range-and height-dependent patterns of the received signal level. In this study, based on the parabolic equations (PE) method and using realistic evaporation duct distributions, we conduct extensive simulations in order to quantify the link-level improvement achieved when using 2 × 2 vertically-spaced Multiple-Input Multiple-Output (MIMO) systems against 1 × 2 Single-Input Multiple-Output (SIMO) and Single-Input Single-Output (SISO) systems. Then, we analyze the implication of such link improvement on the performance of a system comprised of a network of randomly distributed ships. When evaluating the outage throughput at the 2 nd percentile using realistic system parameters, it was found that 2×2 MIMO-MRC (maximum ratio combining) systems with 1 m antenna spacing are able to improve the outage throughput by threefold compared to SISO systems. This improvement increases to one order of magnitude when the antenna spacing increases to 10 m. It was also found that, in all cases, assuming using the same vertical spacing, 1 × 2 SIMO-MRC systems capture about 60% of the improvement achieved by 2 × 2 MIMO-MRC systems. On the other hand, 1 × 2 SIMO-DIV (diversity combining) systems are very sensitive to antenna spacing, and when assuming using the same vertical spacing, they can capture from 20% and up to 55% of the improvement achieved by 2 × 2 MIMO-MRC systems if the antenna spacing increases from 1 m to 10 m, respectively. INDEX TERMS Evaporation duct, multiple-antenna ship-to-ship communications, radio-wave overwater propagation.

IEEE Access, 2018

Spatially distributed transmission points connected to the same source, known as distributed ante... more Spatially distributed transmission points connected to the same source, known as distributed antenna systems, can improve system performance compared with single-link traditional systems. However, the anticipated gain depends heavily on the cross-correlation properties of the large-scale parameters (LSPs) of the different links. Usually, measured LSPs-except the large-scale fading-have non-Gaussian distributions. Therefore, in order to study their multi-link cross-correlation properties, scenario-and parameterspecific ad-hoc transformations are applied, such that the LSPs have Gaussian distributions in the transform domain [1], [2]. In this paper, we propose using the Box-Cox transformation as a general framework for homogenizing this conversion step. The Box-Cox transformation is, by nature, not distribution specific; therefore, it can be used regardless of the empirical distributions of the studied LSPs. We demonstrate the applicability of the proposed framework by studying multi-link fully-coherent propagation measurements of four base stations and one mobile station in a suburban microcell environment at 2.6 GHz. The interand intra-link cross-correlation of four LSPs-the large-scale fading, the delay, azimuth, and elevation spreads-are analyzed and their distributions are modeled. Based on our analysis, it is found that for the investigated environment: 1) the LSPs of the different links can be modeled using unimodal and bimodal Gaussian distributions; and 2) the inter-and intra-link cross-correlation coefficients of the different studied LSPs can be modeled using the Truncated Gaussian distribution. The proposed models are validated using the Kolmogorov-Smirnov test, and their parameters are provided. INDEX TERMS Distributed antenna systems, inter-link cross-correlation, intra-link cross-correlation, largescale parameters, multi-link systems.

IEEE Access, 2020

In this paper, we derive a closed-form expression for the evaluation of the average vectorsymbol ... more In this paper, we derive a closed-form expression for the evaluation of the average vectorsymbol error rate (VER) of group detection followed by maximum-likelihood (GD-ML) receivers in large multiuser multiple-input multiple-output (MU-MIMO) systems with transmit side correlated Rayleigh channels. We assume M antennas at the base station (BS), N closely-located, single-antenna user equipment (UEs) with load factor λ = N M , and N 1; consequently, we evaluate the performance of GD-ML receivers as the load factor grows to unity. The derived expression requires a negligible correlation at the receive side of the communication channel. Hence, from a practical point-of-view, when considering scenarios with a large number of UEs, the derived analytical expression is generally more applicable for systems with a distributed massive number of BS antennas. Numerical results are provided to validate our derived expression. We observe that the GD-ML with N u group size achieves a diversity order proportional to M − N + N u. Moreover, we show that for small group sizes, the analytical and simulation results remain close, and at moderate to high signal-to-noise ratio (SNR), the derived expression very closely matches the simulations, whereas this match becomes perfect as the users' side correlation increases. We also demonstrate that GD-ML outperforms the zero-forcing (ZF) and minimum mean-squared error (MMSE) receivers, in terms of VER; where for high λ, GD-ML exploits the maximum spatial multiplexing gain. Moreover, in terms of floating-point operations (FLOPs), we show that GD-ML receivers have almost the same complexity as ZF and MMSE where the ML detection stage adds a negligible complexity compared to the channel matrix inversion operation. INDEX TERMS Group detection (GD), maximum likelihood (ML) detection, multiple-input multiple-output (MIMO), vector-error rate VER.

IEEE Access, 2017

This paper presents results from an extensive measurement campaign of multiuser channels with lar... more This paper presents results from an extensive measurement campaign of multiuser channels with large-scale antenna arrays (MULAs) in a subway station environment. Based on the measurements, two spatial separation metrics are characterized. The variance of user separability and temporal behavior are investigated. Furthermore, a MULA channel model with transmit correlation is proposed, which ensures that the MULA channels can be generated with a given degree of compatibility. The proposed MULA model is validated by comparing the distributions of the sum rate capacity and the condition number to measurements. INDEX TERMS Channel measurement, large-scale antenna, multiuser , MIMO channel model, subway station.

Radio Science, 2018

Atmospheric ducts, which are caused by the rapid decrease in the refractive index of the lower at... more Atmospheric ducts, which are caused by the rapid decrease in the refractive index of the lower atmosphere, have been recognized as the dominant propagation mechanism for long range maritime links. Recent advances in radio technology are making reliable high-capacity overwater links a reality. A ray-tracing simulation model was developed to obtain reliable prediction of maritime link performance beyond 30 km for realistic conditions. A series of static and mobile long range maritime multiple-input multiple-output links were tested with representative antenna heights at 1.39 (Band 3 or L-Band) and 4.5 GHz (Band 4 or C-Band) during periods with various levels of ducting activities, for example, sunset and sunrise times. Measured link performance and observed ducting occurrences are compared to predictions to validate the model ability to accurately predict and explain link performance for various ducting conditions. The test results agree with the model predictions and illustrate the various Received Signal Level degradation, enhancement, and fluctuations that can be expected in long range maritime links below 6 GHz. We also report on short-term (few to several minutes) fluctuations of the received signal level at the two measurement frequency bands during high ducting activity periods. Measurements and theoretical analysis of the effect of ducting on the quality of maritime communication links indicate that both reflection-induced and ducting-induced disruptions are different and more frequent in higher-frequency bands. This work opens interesting perspectives on providing more robust and more predictable communications in the presence of ducting. This paper draws on 1 week of extensive maritime propagation tests and on recent ray-tracing modeling work that took place in order to get a better understanding of modern broadband radio behavior under

IEEE Wireless Communications Letters, 2019

Based on analyzing two-day ship-to-shore propagation measurements performed simultaneously at two... more Based on analyzing two-day ship-to-shore propagation measurements performed simultaneously at two frequency bands (1.39 GHz and 4.5 GHz), we extract the small-scale fading (SSF) and show that the higher the frequency, the larger the amplitudes of the SSF. Consequently, we introduce a modification to the 2-ray model so that the behavior of the SSF at different frequency bands is captured. We model the effect of the randomness and the unknown dynamic details of the propagation environment as a zero-mean Gaussian random variable which is then superimposed on the length of the rays in the traditional 2ray model. For the measured environment, it is found that a standard deviation in the sub-centimeter range is able characterize these unknown details and almost replicate the behavior of the observed SSF at these two bands.

IEEE Wireless Communications Letters, 2018

In this contribution, we propose a method extending the deep-fading outage probability results of... more In this contribution, we propose a method extending the deep-fading outage probability results of the ITU-R P.530 [1] to the SIMO-MRC (maximum ratio-combining) and MIMO-MRC cases. By deducing the similarity between the analytical expressions of correlated Rayleigh fading and the ITU-R P.530 formulations, we utilize the ITU-R P.530 correlation information and the results of [2], [3] in order to estimate the outage probability of SIMO-MRC and MIMO-MRC systems. Finally, we demonstrate the significant reduction (of several orders of magnitude) in the worst month deep-fading outage probability that can be achieved using SIMO-MRC and MIMO-MRC for different fading depths and antenna spacings. Index Terms-ITU-R P.530 deep-fading outage probability, LOS antenna diversity, SIMO and MIMO MRC improvements.

2011 Saudi International Electronics, Communications and Photonics Conference (SIECPC), 2011

ABSTRACT In this paper, the information extracted from Single-Input Multiple-Output sounding meas... more ABSTRACT In this paper, the information extracted from Single-Input Multiple-Output sounding measurements is used to study the effect of several aspects of the receive antenna arrays on system performance. The extracted multipath parameters are used to synthesize the MIMO channel matrices of a hypothesized communication system having a fixed microcellular base-station and a handheld terminal moving throughout the environment, and subsequently study the effect of array configuration on mean effective link gain, eigenvalue dispersion and outage capacity under real-world channel conditions. Three configurations of a dual inverted-F receive antenna array in a generic mobile handset were studied. The work in this paper revealed that on average, the effective power gain of a MIMO link has greater effect on the achievable capacity than multiplexing gain.

2019 IEEE Canadian Conference of Electrical and Computer Engineering (CCECE)

In this paper, we investigate the capabilities of Multiple-Input Multiple-Output (MIMO) systems i... more In this paper, we investigate the capabilities of Multiple-Input Multiple-Output (MIMO) systems in increasing the transmission range in tactical backhaul links. We utilize the ITU-R P.530 extensive measurement-based results in order to extract the correlation properties of the long-range line-of-sight (LOS) MIMO channel. Then we use this correlation information to formulate—based on the concept of worst-month outage probability —the improvements that can be achieved by MIMO- MRC (maximum ratio combining) systems. The main findings of this work are as follows. 1) For very low link outage requirement (e.g., 10−510^{-5}10−5 outage probability), a 2×2 MIMO system can increase the communication range by about 160% compared to a Single-Input Single-Output (SISO) system —this range extension is almost double what can be achieved when using a 1×2 (Single-Input Multiple-Output) SIMO-MRC system. 2) For comparably moderate link outage requirement (e.g., 10-3 outage probability), the range extension achieved by MIMO is only around 10% higher than what can be achieved by SIMO, but the strong gain is maintained compared to traditional SISO. We demonstrate that, for tactical backhaul links where high reliability is required, MIMO technology provides superior capabilities allowing for significantly increasing the transmission range.

The exponential growth of traffic in mobile networks is leading to an increased pressure on the i... more The exponential growth of traffic in mobile networks is leading to an increased pressure on the infrastructure of mobile networks and in particular on their backhaul networks. It is more critical than ever to carefully plan backhaul networks. In this paper, we formulate and solve the problem of hierarchical wireless backhaul network design. In our problem, we cover different requirements, namely: topology simplicity, network resiliency and link reliability. We formulate the problem as an Integer Linear Programming (ILP) problem, allowing us to solve the problem to optimality. Furthermore, we provide a graph theory based algorithm that allows to solve the problem overlarge scale. The proposed algorithm exploits the properties of the graph representing the network. The results of our evaluations in various network scenarios demonstrate the efficiency of our ILP formulation and the provided algorithm in keeping the backhaul network simple, resilient and reliable. Using a practical chan...

2011 XXXth URSI General Assembly and Scientific Symposium, 2011

A method previously reported by the authors for identifying simultaneous signals from different T... more A method previously reported by the authors for identifying simultaneous signals from different Tx antennas is applied for double-directional channel sounding between a channel sounder base station (CSBS) and a channel sounder mobile station (CSMS), as well as for single input single output (SISO) channel sounding on relay channels in urban microcell-type Tx/Rx scenarios. Using this method, multiple-orthogonal signals are produced from one pseudo-noise code by using it to modulate RF carriers at pre-calculated offset frequencies. The frequency spectra of the resulting signals are interleaved and they occupy the same overall frequency band, but the spectral lines from different transmitters are separable using Fourier analysis of signals sampled at the CSMS receiver output. In theory, any arbitrary number of links from different transmitters can be measured simultaneously using this method. However, in practice, Doppler spreads limit the number of simultaneous soundings that can be made with acceptable isolation among resulting impulse response estimates. Herein, examples are given of results from double-directional channel sounding using a linear array of 4 Tx antennas at the CSBS and of relay channel sounding with one Tx antenna at the CSBS and one Tx antenna at a channel sounder relay station (CSRS).

2017 XXXIInd General Assembly and Scientific Symposium of the International Union of Radio Science (URSI GASS), 2017

A Matlab-based ray tracing (RT) simulator is implemented for the analysis of ship-to-ship communi... more A Matlab-based ray tracing (RT) simulator is implemented for the analysis of ship-to-ship communications. The anomalous propagation effect due to the evaporation duct which results in bending and/or trapping the rays is modelled. Based on extensive RT simulations, the received rays are identified and their parameters are estimated. We briefly describe the implementation of the RT simulator and compare the obtained ray tracing results with those obtained from a widely used simulation tool, the PETOOL. We highlight the excellent agreement between the two tools for lineof-sight (LOS) ranges and also highlight that there is significant disagreements between them for beyond-line-of-sight (beyond-LOS) ranges. Then, based on our RT simulator, we provide detailed results describing the effect of the evaporation duct phenomena on the communication link quality in the beyond-LOS zone.

2021 IEEE 94th Vehicular Technology Conference (VTC2021-Fall), 2021

In this paper, we analyze the weather information for 14 waterbodies from geographical areas with... more In this paper, we analyze the weather information for 14 waterbodies from geographical areas with different meteorological characteristics. We estimate the sub-hourly instances of the evaporation duct height (EDH) throughout a period of 10 years. Then, considering the frequency range 1 to 6 GHz, based on the parabolic equation method, we analyze the quality for a presumed shore-to-ship link throughout 100 km range. We evaluate the maximum range that can be supported for different reliability requirements and we focus specifically on analyzing the gain that can be obtained when antenna height and/or band diversity are used. It was found that for high reliability requirements, the antenna height at the shore is the main factor on deciding the maximum communication range that can be maintained. On the other hand, for applications that tolerate delay and work seasonally on an opportunistic basis, the evaporation duct statistics is the main factor deciding the likelihood of increasing the link range and establishing over-the-horizon communications.

2016 IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), 2016

We investigate antenna correlation of an Mantenna massive multiple-input multiple-output (MIMO) s... more We investigate antenna correlation of an Mantenna massive multiple-input multiple-output (MIMO) setup with the purpose of obtaining a low-rank representation of the instantaneous massive MIMO channel. Low-rank representation bases using short-term and long-term antenna correlation statistics are defined, and their performance is evaluated with data sets obtained from channel measurements in both indoor and outdoor environments at 2.6 GHz. Our results indicate that the shortterm bases can capture a larger amount of the channel energy compared to the long-term ones, but they have a limited timespan, one coherence time or less. On the other hand, the long-term bases are stable over time-spans of a few seconds. Hence, they can be obtained relatively easily. We also investigate a rank-p vector-scalar LMMSE channel estimator that exploits antenna correlation. Our results show that the investigated estimator can achieve a performance similar to that of full-rank LMMSE at a (2p + 1)/M times lower cost. The investigated estimator may be used in conjunction with estimators that exploit correlation in the frequency and time domains or, alternatively, in situations in which these estimators cannot be used, e.g., when pilot separation is larger than the channel coherence bandwidth or time.

2016 IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications (PIMRC), 2016

In this paper, the effect of polarization on the downlink achievable sum-rate of multi-user Coope... more In this paper, the effect of polarization on the downlink achievable sum-rate of multi-user Cooperative Multi-Point (CoMP) systems is studied using synchronous multi-link channel measurements with two different antenna arrangements. In the first setup, four dual-polarized antenna patches with inter-patch distance varied from half wavelength to 8 m are considered at the base station (BS). In the second setup, two BSs located 60 m apart are used, each is provided with dual-polarized antennas spaced half a wavelength apart. Based on the BS antenna element selection, scenarios with different antenna polarizations at the BSs are considered. We consider four virtual users each is equipped with two antennas (V and H-polarized) with half-wavelength inter-element distance. The users are equally spaced with inter-user distance of about 0.5 m and moving in different routes. For each setup, the 8 × 4 MIMO multi-user channels are used to evaluate the achievable sum-rate of the system, where the ...

The possibility of using radio over fiber (RoF) analog transmissions to characterize the wireless... more The possibility of using radio over fiber (RoF) analog transmissions to characterize the wireless propagation channel of distributed antenna systems is investigated. In particular, the coherence time of kilometer-long, fiber-based networks is analyzed. Joint measurements of the phase noise of parallel links to the same site (intra-site) and to different sites (inter-site) in such a network are presented. The coherence time of the phase noise and phase noise difference between links is evaluated by means of the Allan time deviation. Measurements are performed at a frequency of 2.3 GHz under both stationary and non-stationary temperature conditions, for a duration of ten hours. In the setup analyzed, the phase noise was found to be white, with a phase drift component that determines the coherence time of the link. Coherence times between two to six minutes have been measured for a phase offset of 10 degrees Celcius. Values of the correlation coefficient r for intra-site phase noise pr...

ICC 2021 - IEEE International Conference on Communications, 2021

The problem of selecting the modulation and coding scheme (MCS) that maximizes the system through... more The problem of selecting the modulation and coding scheme (MCS) that maximizes the system throughput, known as link adaptation, has been investigated extensively, especially for IEEE 802.11 (WiFi) standards. Recently, deep learning has widely been adopted as an efficient solution to this problem. However, in failure cases, predicting a higher-rate MCS can result in a failed transmission. In this case, a retransmission is required, which largely degrades the system throughput. To address this issue, we model the adaptive modulation and coding (AMC) problem as a multi-label multi-class classification problem. The proposed modeling allows more control over what the model predicts in failure cases. We also design a simple, yet powerful, loss function to reduce the number of retransmissions due to higher-rate MCS classification errors. Since wireless channels change significantly due to the surrounding environment, a huge dataset has been generated to cover all possible propagation conditions. However, to reduce training complexity, we train the CNN model using part of the dataset. The effect of different subdataset selection criteria on the classification accuracy is studied. The proposed model adapts the IEEE 802.11ax communications standard in outdoor scenarios. The simulation results show the proposed loss function reduces up to 50% of retransmissions compared to traditional loss functions.

The increase in demand for high-data rates on the move in the complex urbanenvironment requires e... more The increase in demand for high-data rates on the move in the complex urbanenvironment requires either the allocation of new spectrum such as availablecontiguous spectrum in the mm-wave band or the use of novel configurationssuch as the application of massive multiple-input multiple-output (MIMO)technology. To enable the design of efficient wireless networks, an understandingof the propagation phenomena in the diverse urban environments isfundamental. In this chapter, we present results of studies related to fourthgeneration (4G) and future 5G radio systems both outdoor and outdoor-toindoor.Classifications include rural and highway, BS to pedestrian users,vehicular-to-vehicular, vehicular-to-infrastructure, container terminals, vegetation,and high-speed mobility such as trains. Results for path loss (PL)and shadow fading are presented from various studies of stochastic anddeterministic channel models based in outdoor, indoor-to-outdoor, hotspots,vehicular, and train environments. Re...

The channel properties have a large influence on user separability in massive multi-user multiple... more The channel properties have a large influence on user separability in massive multi-user multiple-input multiple-output (massive MIMO) systems. In this paper we present spatio-temporal characteristics obtained from massive MIMO channel measurements at 2.6 GHz. The results are based on data acquired in both indoor and outdoor scenarios where a base station equipped with 64 dual-polarized antenna elements communicates simultaneously with nine single-antenna users. In the outdoor scenarios the base station is placed at two rooftops with different heights and the users are confined to a five-meter diameter circle and move rando mly at pedestrian speeds. In the indoor scenarios, the users are located close to each other in a lecture theater and the base station is placed at various locations in the room. We report on the observed distribution of the delay spreads and angular spreads. Furthermore, the multi-user performance in terms of singular value spread of the MU-MIMO channel is also ...

One of the most crucial aspects is modern commercial and tactical wireless networks is the capabi... more One of the most crucial aspects is modern commercial and tactical wireless networks is the capability of the network’s backhaul to forward that massive amount of traffic to the core network. Hence, the careful planning for a resilient and cost-efficient backhaul is compulsory. In this letter, we formulate and solve the problem of hierarchical wireless backhaul design. In our problem, we cover different requirements, namely: link reliability, network resiliency, and low management overhead. We have formulated the problem as Integer Linear optimization Problem (ILP). The results of our simulation in various network scenarios demonstrate the efficiency of our formulation in keeping the backhaul network simple, reliable and resilient. Using practical channel propagation model and nodes density that model wide range of cities, our results show that even with high resiliency requirements, the network traffic can be backhauled with only 5-10% of the nodes for the considered densities.

IEEE Access, 2020

It is well established that the performance of communication systems is improved when deploying m... more It is well established that the performance of communication systems is improved when deploying multiple antennas at one or both of the transmit/receive sides; and the amount of the gained improvement depends on the level of multipath richness of the propagation channel. In ship-to-ship overwater channels, quantifying such an improvement is not an easy task due to the effect of evaporation duct on imposing complex range-and height-dependent patterns of the received signal level. In this study, based on the parabolic equations (PE) method and using realistic evaporation duct distributions, we conduct extensive simulations in order to quantify the link-level improvement achieved when using 2 × 2 vertically-spaced Multiple-Input Multiple-Output (MIMO) systems against 1 × 2 Single-Input Multiple-Output (SIMO) and Single-Input Single-Output (SISO) systems. Then, we analyze the implication of such link improvement on the performance of a system comprised of a network of randomly distributed ships. When evaluating the outage throughput at the 2 nd percentile using realistic system parameters, it was found that 2×2 MIMO-MRC (maximum ratio combining) systems with 1 m antenna spacing are able to improve the outage throughput by threefold compared to SISO systems. This improvement increases to one order of magnitude when the antenna spacing increases to 10 m. It was also found that, in all cases, assuming using the same vertical spacing, 1 × 2 SIMO-MRC systems capture about 60% of the improvement achieved by 2 × 2 MIMO-MRC systems. On the other hand, 1 × 2 SIMO-DIV (diversity combining) systems are very sensitive to antenna spacing, and when assuming using the same vertical spacing, they can capture from 20% and up to 55% of the improvement achieved by 2 × 2 MIMO-MRC systems if the antenna spacing increases from 1 m to 10 m, respectively. INDEX TERMS Evaporation duct, multiple-antenna ship-to-ship communications, radio-wave overwater propagation.

IEEE Access, 2018

Spatially distributed transmission points connected to the same source, known as distributed ante... more Spatially distributed transmission points connected to the same source, known as distributed antenna systems, can improve system performance compared with single-link traditional systems. However, the anticipated gain depends heavily on the cross-correlation properties of the large-scale parameters (LSPs) of the different links. Usually, measured LSPs-except the large-scale fading-have non-Gaussian distributions. Therefore, in order to study their multi-link cross-correlation properties, scenario-and parameterspecific ad-hoc transformations are applied, such that the LSPs have Gaussian distributions in the transform domain [1], [2]. In this paper, we propose using the Box-Cox transformation as a general framework for homogenizing this conversion step. The Box-Cox transformation is, by nature, not distribution specific; therefore, it can be used regardless of the empirical distributions of the studied LSPs. We demonstrate the applicability of the proposed framework by studying multi-link fully-coherent propagation measurements of four base stations and one mobile station in a suburban microcell environment at 2.6 GHz. The interand intra-link cross-correlation of four LSPs-the large-scale fading, the delay, azimuth, and elevation spreads-are analyzed and their distributions are modeled. Based on our analysis, it is found that for the investigated environment: 1) the LSPs of the different links can be modeled using unimodal and bimodal Gaussian distributions; and 2) the inter-and intra-link cross-correlation coefficients of the different studied LSPs can be modeled using the Truncated Gaussian distribution. The proposed models are validated using the Kolmogorov-Smirnov test, and their parameters are provided. INDEX TERMS Distributed antenna systems, inter-link cross-correlation, intra-link cross-correlation, largescale parameters, multi-link systems.

IEEE Access, 2020

In this paper, we derive a closed-form expression for the evaluation of the average vectorsymbol ... more In this paper, we derive a closed-form expression for the evaluation of the average vectorsymbol error rate (VER) of group detection followed by maximum-likelihood (GD-ML) receivers in large multiuser multiple-input multiple-output (MU-MIMO) systems with transmit side correlated Rayleigh channels. We assume M antennas at the base station (BS), N closely-located, single-antenna user equipment (UEs) with load factor λ = N M , and N 1; consequently, we evaluate the performance of GD-ML receivers as the load factor grows to unity. The derived expression requires a negligible correlation at the receive side of the communication channel. Hence, from a practical point-of-view, when considering scenarios with a large number of UEs, the derived analytical expression is generally more applicable for systems with a distributed massive number of BS antennas. Numerical results are provided to validate our derived expression. We observe that the GD-ML with N u group size achieves a diversity order proportional to M − N + N u. Moreover, we show that for small group sizes, the analytical and simulation results remain close, and at moderate to high signal-to-noise ratio (SNR), the derived expression very closely matches the simulations, whereas this match becomes perfect as the users' side correlation increases. We also demonstrate that GD-ML outperforms the zero-forcing (ZF) and minimum mean-squared error (MMSE) receivers, in terms of VER; where for high λ, GD-ML exploits the maximum spatial multiplexing gain. Moreover, in terms of floating-point operations (FLOPs), we show that GD-ML receivers have almost the same complexity as ZF and MMSE where the ML detection stage adds a negligible complexity compared to the channel matrix inversion operation. INDEX TERMS Group detection (GD), maximum likelihood (ML) detection, multiple-input multiple-output (MIMO), vector-error rate VER.

IEEE Access, 2017

This paper presents results from an extensive measurement campaign of multiuser channels with lar... more This paper presents results from an extensive measurement campaign of multiuser channels with large-scale antenna arrays (MULAs) in a subway station environment. Based on the measurements, two spatial separation metrics are characterized. The variance of user separability and temporal behavior are investigated. Furthermore, a MULA channel model with transmit correlation is proposed, which ensures that the MULA channels can be generated with a given degree of compatibility. The proposed MULA model is validated by comparing the distributions of the sum rate capacity and the condition number to measurements. INDEX TERMS Channel measurement, large-scale antenna, multiuser , MIMO channel model, subway station.

Radio Science, 2018

Atmospheric ducts, which are caused by the rapid decrease in the refractive index of the lower at... more Atmospheric ducts, which are caused by the rapid decrease in the refractive index of the lower atmosphere, have been recognized as the dominant propagation mechanism for long range maritime links. Recent advances in radio technology are making reliable high-capacity overwater links a reality. A ray-tracing simulation model was developed to obtain reliable prediction of maritime link performance beyond 30 km for realistic conditions. A series of static and mobile long range maritime multiple-input multiple-output links were tested with representative antenna heights at 1.39 (Band 3 or L-Band) and 4.5 GHz (Band 4 or C-Band) during periods with various levels of ducting activities, for example, sunset and sunrise times. Measured link performance and observed ducting occurrences are compared to predictions to validate the model ability to accurately predict and explain link performance for various ducting conditions. The test results agree with the model predictions and illustrate the various Received Signal Level degradation, enhancement, and fluctuations that can be expected in long range maritime links below 6 GHz. We also report on short-term (few to several minutes) fluctuations of the received signal level at the two measurement frequency bands during high ducting activity periods. Measurements and theoretical analysis of the effect of ducting on the quality of maritime communication links indicate that both reflection-induced and ducting-induced disruptions are different and more frequent in higher-frequency bands. This work opens interesting perspectives on providing more robust and more predictable communications in the presence of ducting. This paper draws on 1 week of extensive maritime propagation tests and on recent ray-tracing modeling work that took place in order to get a better understanding of modern broadband radio behavior under

IEEE Wireless Communications Letters, 2019

Based on analyzing two-day ship-to-shore propagation measurements performed simultaneously at two... more Based on analyzing two-day ship-to-shore propagation measurements performed simultaneously at two frequency bands (1.39 GHz and 4.5 GHz), we extract the small-scale fading (SSF) and show that the higher the frequency, the larger the amplitudes of the SSF. Consequently, we introduce a modification to the 2-ray model so that the behavior of the SSF at different frequency bands is captured. We model the effect of the randomness and the unknown dynamic details of the propagation environment as a zero-mean Gaussian random variable which is then superimposed on the length of the rays in the traditional 2ray model. For the measured environment, it is found that a standard deviation in the sub-centimeter range is able characterize these unknown details and almost replicate the behavior of the observed SSF at these two bands.

IEEE Wireless Communications Letters, 2018

In this contribution, we propose a method extending the deep-fading outage probability results of... more In this contribution, we propose a method extending the deep-fading outage probability results of the ITU-R P.530 [1] to the SIMO-MRC (maximum ratio-combining) and MIMO-MRC cases. By deducing the similarity between the analytical expressions of correlated Rayleigh fading and the ITU-R P.530 formulations, we utilize the ITU-R P.530 correlation information and the results of [2], [3] in order to estimate the outage probability of SIMO-MRC and MIMO-MRC systems. Finally, we demonstrate the significant reduction (of several orders of magnitude) in the worst month deep-fading outage probability that can be achieved using SIMO-MRC and MIMO-MRC for different fading depths and antenna spacings. Index Terms-ITU-R P.530 deep-fading outage probability, LOS antenna diversity, SIMO and MIMO MRC improvements.