Although situated within the highly active research field of WiFi sensing, this paper introduces a novel method based on digital receive beamforming using samples of the Channel State Information (CSI) that is able to advance the state-of-the-art. Key contributions include: a) the definition of a new set of features based on the digital receive beamforming technique, and, b) the test of the proposed method over two different environments exploiting a unique training set for both environments. The excellent results achieved in two different environments using the same trained system push the boundaries of the capabilities of current systems.

Combining the use of Extremely High Frequencies (EHF) and Free Space Optics (FSO) for the feeder links of future High Throughput Satellites (HTS) is recognized as a key element to optimize system efficiency in terms of costs, power consumption and to increase the data rate to unprecedented levels (Terabit/s). This paper provides an overview of the main challenges to be faced to make the exploitation of hybrid EHF/FSO links feasible and cost-effective. In this framework, propagation and HW impairments mitigation techniques will play a key role. Therefore, the paper also presents a vision on how the use of SDN/SDR and NFV, extended down to lower layers of the protocol stack, could provide novel, so far unexplored, opportunities for optimizing the performance of such mitigation techniques.

This issue highlights the current and future trends of aerospace communications and networking, including satellites, high-altitude platforms (HAPs), optical deep-space communications, interplanetary communications, aircraft communications, with a look at those "classical" services that still lead the mass market of aerospace applications and will do so into the future.

In this paper an analysis on the use of Adaptive Coding and Modulation (ACM) techniques for EHF satellite communications is presented. In particular, our analysis is focused on W-band channels and includes the main channel impairments in this frequency band, i.e. rain fading and HPA non-linearity. The aim of the analysis is to identify modifications to the ACM mode switching algorithm to optimize their use at those high frequency bands.

The recently allocated 71-76 GHz and 81-86 GHz bands provide an opportunity for Line Of Sight (LOS) links for directional point-to-point “last mile” links. An efficient use of this spectrum may allow wireless to finally “catch up” with wires, leading to systems such as “multi-Gigabit wireless Ethernet,” and “wireless fiber.” However, the transmission at such a frequency range is characterized by several additional challenges compared to lower frequency bands, from the technological and propagation point of view, which makes difficult to use them efficiently. In this scenario, IR-UWB technology might offer some more degrees of freedom for the design of a highly integrated, low cost transceiver. This work has at its core the design and BER (Bit Error Rate) performance evaluation of an IR-UWB architecture based on an 85 GHz (this frequency belongs to W band/75-110 GHz) up-conversion stage of train of Gaussian pulses having a duration lower than 1 ns. Finally, we compare performance of this architecture with the ones of a more traditional continuous wave communications system with FSK (Frequency Shift Keying) modulation. Simulation results show that BER performance, in presence of RF non-linearities, for an IR-UWB transceiver architecture operating at W band (with same data rate and bandwidth) are better than a coherent BFSK scheme working in a similar scenario.

Wireless Personal Area Networks (WPANs) are short-range ad-hoc networks centered around a person that make use of unlicensed bands for data transmission. Two complementary types of standards have been proposed by IEEE working groups for both High Data Rate (HDR) and Low Data Rate (LDR) WPANs. However, because of the unlicensed nature of WPANs, interference issues exist between uncoordinated WPANs. These interference issues are particularly severe when two or more nodes are closely located (e.g. in a multimode LDR/HDR device). This paper proposes a novel collaborative coexistence mechanism named Alternating Wireless Activity (AWA, patent pending) between a HDR WPAN based on the standard IEEE 802.15.3 and a LDR WPAN based on the standard IEEE 802.15.4. The AWA coexistence mechanism does not require any modification to the mentioned standards because it exploits their already available features.

This paper proposes a novel slow transmit power control (TPC) algorithm which exploits a cross layer approach in order to optimize the energy efficiency of a single link. This optimization process has been applied to a short range wireless link (i.e. IEEE 802.15.3-based transmission) and it takes into account the signal fluctuations due to the multipath fading of typical indoor environments. Analytical results have shown that the proposed TPC can improve the battery life duration of 25% with respect to a non optimized strategy, without losing transmission quality

This paper aims at clarifying the role of the outer loop power control for CDMA satellite systems with on-board power constraints. If the inner loop of the power control is perfect, the channel turns into a AWGN channel and there is no need of the outer loop. In satellite CDMA systems, due to the longer propagation delay with respect to a terrestrial system, the inner loop of power control is only partly able to track power variations due to fast fading. Moreover, the Rice factor, which characterizes the channel statistics, can widely vary even if the user does not move but just because of the change of the elevation angle. Because of that, a wide range of target SNIR (and larger than in typical terrestrial systems) may be necessary to get the same BER performance. Therefore, the outer loop power control turns out to be essential to minimize the dynamic of the power link margins and avoid capacity degradations induced by the systematic use of static link margins. A semi-analytical model for the capacity evaluation has been developed, which is specifically intended for the power-limited satellite-to-mobile link with multi satellite reception. We found that the capacity gain with respect to a pure SNIR-based strategy (i.e., only inner loop) can reach the 40% of the total capacity in a single reception scheme. A smaller, but still noticeable capacity gain of the order of 20 - 30% is observed in presence of satellite diversity. Therefore, any dimensioning of CDMA satellite systems should not neglect this component of the power control.

The issue of the performance degradation of transmission control protocol/Internet Protocol (TCP/IP) over wireless links due to the presence of noncongestion-related packet losses has been addressed with a physical layer approach. The effectiveness of automatic repeat request techniques in enhancing TCP/IP performance depends on the tradeoff between frame transmission delay and residual errors after retransmissions. The paper shows how a truncated power control can be effectively applied to improve that tradeoff so that a higher transmission reliability is provided without increasing the frame transmission delay through the radio link layer and without increasing the energy consumption. An analytical framework has been developed to show the feasibility and effectiveness of the proposed power control. The analytical results, which are carried out assuming a constant multiuser interference level, show that the proposed algorithm turns out to be very effective when the time variability of the channel is high, which-in case of constant interference level-means that the Doppler frequency is high. Simulations carried out in a variable interference scenario show that the proposed strategy is very effective in improving the end-to-end throughput of a TCP connection. Moreover, these improvements are higher when the traffic is more bursty, like in typical Internet data applications such as e-mail and web surfing.

The DAta and Video Interactive Distribution (DAVID) satellite mission belongs to the small missions for science and technology programme of the Italian Space Agency and is intended to pioneer the use of W-band for an experimental collection of a high volume of data and its forwarding, through Ka-band links, to the Internet. The satellite launch is envisaged in 2004. The system presents various technological innovations and will also collect data from very remote scientific laboratories in Antarctica, allowing also remote control of the experiments.

The issue of the performance degradation of TCP protocols over wireless links due to the presence of non-congestion related packet losses has been addressed at the physical layer. The feasibility and effectiveness of a proper power management strategy that allows the performance to be improved without increasing the transmission delay and/or increasing the energy consumption has been analyzed. In particular, the dependence of the key parameters of the proposed solution with respect to the correlation of the fading channel has been evaluated. Furthermore, it is shown that the proposed strategy can be effectively exploited to remove local retransmissions at the link layer.

Abstract The concept of adaptivity is of paramount importance in the design of future communication systems, in which a careful exploitation of the limited available resources (bandwidth, power, etc.) is required. The potential of channel‐adaptive transmission has been already recognized 30 years ago, but it did not receive much interest at that time. In the last decade, the advent of feasible software radio systems, and hence, the availability of fast flexible and reconfigurable transceivers has renewed interest in adaptive techniques, which include adaptive modulation and coding, adaptive antennas and adaptive equalization techniques. This paper focuses on adaptive modulation and adaptive error control mechanisms. Basic concepts are highlighted and an overview on the achieved results and new trends in this research area are presented. Some results from information theory are also presented, which show the limitations of these techniques and motivate further research on the practical and design issues that have to be addressed to enable performance to reach close to the theoretical limit. Copyright © 2002 John Wiley & Sons, Ltd.

With non-GEO constellations the primary means of counteracting the shadowing and the blockage effects is through the use of the satellite diversity, i.e. multiple satellites in the constellation are simultaneously visible to user. The probability system availability is improved by increasing the probability at least one satellite is in clear line of sight. In the selection diversity (SD) scheme the user is served by one satellite selected on the basis of the better signal to noise ratio. In CDMA systems the spatial diversity provided by the satellite diversity can be more effectively exploited by combining signal replica coming from satellites in view with the aim at increasing the system capacity. Actually, the performance of signal combining/selection diversity schemes depend on the specific propagation scenario and it is not always effective to combine signal replica. In this paper hybrid selection/combining diversity schemes are proposed and a performance comparison in terms of system availability and capacity enhancement is carried out. Furthermore, an analytical methodology of the downlink of DS-CDMA systems which takes into account the power constraints of a satellite environment is described and applied for the capacity assessment of the proposed satellite diversity schemes.

A novel methodology is proposed for computing the outage probability in mobile radio systems in the presence of log-normal shadowing. A relevant feature is that the proposed analysis assumes a general correlation for any pair of links. Various approaches are considered to compute the statistics of user signal-to-interference ratio (SIR), namely Schwartz and Yeh's method, Wilkinson's method, and Fenton's method. By a simple reformulation of the problem, these methods can be used to calculate in a straightforward way the parameters of the SIR. The accuracy of the methods is checked in a number of situations of interest. Moreover, when the same correlation is assigned to any pair of links, the novel analysis is more accurate than previously proposed approaches.

In this paper, the problem of computing cochannel interference statistics in signal strength measurements in mobile radio systems is presented. In a cellular environment with cross-correlated log-normal shadowings, extensions of Wilkinson's method and Schwartz and Yeh's (1982) method are proposed for evaluating the statistics of differences between signal strengths that a mobile terminal measures on the links to any pair of base stations in the presence of cochannel interferers. The derived statistics are then used in the performance analysis of relative signal strength handover algorithms. Results provided by the two methods are compared with simulation results, in order to assess their accuracy, and computational issues are addressed. From numerical results, it is also seen that handover algorithm performance has a noticeable dependence on both cross correlation among shadow fadings and the interference level. Finally, it is seen that previous approaches to derive cochannel interference statistics in the presence of log-normal shadowing can be obtained as particular cases.

The traffic performance of integrated cellular mobile and satellite networks is analyzed. Using a previously proposed traffic model for a hierarchical architecture, a parametric analysis is carried out in the ranges of interest for application scenarios of satellite systems under development (e.g. Iridium and Globalstar). In particular, the effect of the following parameters is considered for some constellations: (a) the ratio between the highest and the lowest value of the spatial traffic density in the area covered by a satellite spot; and (b) the percentage of the satellite spot area covered also by the underlying terrestrial cellular networks. A traffic capacity estimation is carried out for the generic satellite spot, using channel reservation (guard channels) for those users who directly access the satellite. Moreover, an improved traffic model is presented, which accounts for frequent inter-spot handovers in low Earth orbit satellite systems.

The paper proposes a design methodology for the development of wideband wireless local area networks. The approach moves from a modeling environment where the value of a properly defined cost-to-benefit of the system is adopted to measure the design effectiveness. A possible design tool consists of performance charts where the design requirements are related to the model parameters and hence, to the system parameters. The general design formulation and the performance charts are presented.

A performance analysis of packet cellular networks in the presence of shadowing is presented. Starting from the theories of level crossing and large excursions of Gaussian processes, a statistical characterization of occurrence and duration of fading intervals is first obtained. Then, by considering also the statistics of activity-inactivity intervals of the mobile terminal, the probability function of the sequences of dropped packets is derived. Results are presented in terms of fading intervals statistics and probability function of dropped packet sequences for voice sources, in the presence and in the absence of a terminal buffer. A radio link design approach is also proposed and a design example is discussed.

A urban cellular system providing a mixed coverage has been simulated, aiming at a proper trade-off between network capacity and probability of handover failure. In particular a single macrocell has been overlaid to a four-cluster microcell coverage, according to a hierarchical architecture. The system has been investigated in terms of handover performance, achieving a benefit from both handover requests at reserved channels for the overflow handover traffic at macrocell level.>

An EHF satellite system for land-mobile applications to be integrated with a terrestrial cellular system is described. An approach to evaluate the carrier-to-cochannel interference occurring in multispot satellite coverage adopting frequency reuse is introduced, and results from the analysis are shown. Criteria for spectrum efficiency evaluation are also outlined along with traffic and link budget estimates. Possible options for payload implementation and mobile terminal design are presented.>