Boris Gremont

Spatio-temporal rain attenuation model for application to fade mitigation techniques

We present a new stochastic-dynamic model useful for the planning and design of gigahertz satellite communications using fade mitigation techniques. It is a generalization of the Maseng-Bakken and targets dual-site dual-frequency rain attenuated satellite links. The outcome is a consistent and comprehensive model capable of yielding theoretical descriptions of: 1) long-term power spectral density of rain attenuation; 2) rain fade slope; 3) rain frequency scaling factor; 4) site diversity; and 5) fade duration statistics using a novel method based on Markov Chains. We also present a simple rain attenuation synthesizer matching the predictions of the theoretical model.

Comparative analysis and performance of two predictive fade detection schemes for Ka-band fade countermeasures

The design of Ka-band satellite fade countermeasure (FCM) systems is conditioned by the detection/prediction algorithm to be included within practical DSP-based FCM controllers. It depends upon the ability of systems to efficiently integrate the dynamic and stochastic nature of the Ka-band fading process which is dominated by rain attenuation and amplitude scintillation. The paper analyzes the modeling and statistical performance of two predictive fade detection algorithms. Prediction is introduced as a way to minimize the impact of the finite response time on the BER/throughput of practical FCM systems. Both fixed (FDM) and variable (VDM) detection margin strategies are introduced and compared in terms of their margin requirements, FCM utilization factor, and channel capacity utilization. The VDM is shown to be more efficient than its fixed counterpart. The long-term BER availability and average user data throughput of a VDM/fixed-FEC/adaptive transmission rate FCM are then evaluated for a typical low-power low-rate Ka-band in-bound VSAT link.

Extra-high frequency line-of-sight propagation for future urban communications

Spectrum congestion at conventional microwave frequencies has forced communication system designers to explore and investigate higher and higher frequencies, well into the millimetric band. This part of the radio spectrum is currently underutilized and offers a very wide bandwidth and permits higher data rates as well as more channels. This paper presents measurements, analysis and modeling of propagation losses for a 97-GHz line-of-sight terrestrial link. The link was established in an urban environment over a path length of 6.5 km and operated over a period of more than a year. An overview of path geometry, experimental equipment and data acquisition, and data processing is first given. The annual distribution of the measured rain attenuation at 97 GHz is discussed in connection with that of the rainfall rate at the receiving point, and compared with the current ITU-R rain attenuation prediction model. Extensive experimental results on rain fade durations, long-term fade statistics and amplitude scintillations carried out using data recorded from this link are also presented. The experimental results concerning rain attenuation modeling indicate that the agreement between the measured rain attenuation values and those computed on the basis of the ITU-R rain attenuation prediction model is not entirely satisfactory. However, the results presented in this paper are only based on data collected over a period of one year, thus the difference between reported and modeled rain attenuation distributions may be attributed to expected year-to-year variations in rain fall rate and its associated attenuation distributions. Therefore, the experimental results appear to indicate that further research is necessary to fully validate the ITU-R rain attenuation model at higher millimeter wave frequency band over longer period of time. Nevertheless, the experimental results have established a considerable degree of confidence in the feasibility of millimeter wave link systems with short distance and low power requirements.

Spatial and temporal variation of wideband indoor channels

Extensive studies of the impact of temporal variations induced by people on the characteristics of indoor wideband channels are reported. Singular Value Decomposition Prony algorithm has been used to compute the impulse response from measured channel transfer functions. The high multipath resolution of the algorithm has allowed a detailed assessment of the shapes of individual multipath clusters and their variation in time and space in indoor channels. Large- and small-scale analyses show that there is a significant dependency of the channel response on room size. The presence of people in the channel has been found to induce both signal enhancements and fading with short-term dynamic variations of up to 30 dB, depending on the number of people and their positions within the room. A joint amplitude and time of arrival model has been used to successfully model measured impulse response clusters.

A Review of Channel Simulators for Heterogeneous Microwave Networks

A review is performed of the current simulation tools able to produce simultaneous dynamic fading, due to a range of mechanisms, experienced by heterogeneous networks of SHF and EHF radio links. The primary focus is fading due to rain. A taxonomy of tools is proposed, based on the methods used to generate fields of meteorological parameters. The capabilities, deficiencies, and futures of these tools are discussed, and a series of research questions are proposed.

Rain granularity effects on bandwidth demand for faded DVB-RCS systems

Broadband satellite communication networks, operating at Ka band and above, play a vital role in today’s worldwide telecommunication infrastructure. The problem, however, is that rain can be the most dominant impairment factor for radio propagation above 10 GHz. This paper studies bandwidth and time slot allocation problem for rain faded DVB-RCS satellite networks. We investigate how using finer rain granularity can improve bandwidth utilization in DVB-RCS return links. The paper presents a mathematical model to calculate the bandwidth on demand. We formulate the radio resource allocation as an optimization problem and propose a novel algorithm for dynamic carrier bandwidth and time slots allocation, which works with constant bit rate type of traffic. We provide theoretical analysis for the time slot allocation problem and show that the proposed algorithm achieves optimal results. The algorithm is evaluated using a MATLAB simulation with historical rain data for the UK.

On the frequency scaling of rain attenuation for space communications

We present a statistical model of the scaling factor of rain attenuation encountered in dual-frequency satellite communication systems. The new model considers the impact of the random variations of rain drop size distribution on tropospheric slant path rain attenuation. The model is validated and calibrated using known empirical results.

Integration of Fade Mitigation within centrally managed MF-TDMA/DVB-RCS networks

This paper addresses the integration of a Fade Mitigation Technique FMT within a centrally managed MF-TDMA satellite network in the context of guaranteed QoS delivery. Burst Length Control BLC is introduced as a suitable FMT and the methodology of its design and implementation within the existing DVB-RCS standard is described and simulated. The proposed technique provides compensation for rain attenuation at the expense of capacity utilisation. Within any fixed partition of the MF-TDMA space, by considering the space-time properties of rain attenuation, suitable geographical multiplexing of rain-attenuated and non-attenuated links allows the optimisation of the channel capacity utilisation while still exploiting the statistical multiplexing of the sources on the return channels.

Loop-Back Detection Technique for Uplink Power Control

We present a novel detection technique for uplink power control on satellite links that avoids the use of models of the frequency scaling of rain attenuation. The proposed method is then shown to outperform classical ULPC techniques. The technique is particularly applicable to the real-time detection/compensation of rain attenuation for feeder satellite links. Nomenclature A = 1 ^ ) ( u cnr the clear-sky up-link carrier-to-noise ratio for the link Hub1-to-Satellite u A , d A = uplink, downlink rain attenuation in dB u a , d a = uplink, downlink rain attenuation in ratio B = 1 ^ ) ( d cnr the clear-sky down-link carrier-to-noise ratio for Satellite-to-Hub1 B′ = 2 ^ ) ( d cnr the clear-sky down-link carrier-to-noise ratio for Satellite-to-Hub2 t CNR) ( = the total carrier-to-noise ratio in dB 1 ) ( t cnr = the total carrier-to-noise ratio in ratio for link1 (Hub1-to-Satellite-to-Hub1) 2 ) ( t cnr = the total carrier-to-noise ratio in ratio for link2 (Hub1-to-Satellite-Hub2) 1