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.

The outcomes in terms of very high data rates, low latencies, almost full-time availability and wide coverages promised by the fifth generation (5G) networking technology should cope with the increasing customers demand for high quality multimedia content and services. The attempt to fulfill 5G pledges has seen the move to explore other groundbreaking technologies. These will include, among the others, the exploitation of millimeterwave (mmWave) bandwidths in both satellite and terrestrial communications, the novel paradigm of Software Defined Networking (SDN), the use of smart satellite gateways, etc. This paper aims at proposing an SDN-based seamless integration of ultra-broadband short-range wireless network segments, namely information showers with fixed fiber-based terrestrial network infrastructures for internetworking and mmWave geostationary satellite links in order to provide multi-gigabit multimedia content delivery to nomadic users. The impact of different parameters (including tropospheric conditions, latency and technical faults) on network performance have been fully appreciated by means of realistic emulations in Mininet environment. Preliminary results evidenced the clear advantages in terms of increased throughput and reduced latencies of the proposed SDN-based approach.

Millimeter wave (mm-Wave) communications has been considered as a strong candidate for future wireless standards, due to the large available bandwidth in the order of gigahertz. As a result, a plethora of future services and application-oriented scenarios can be conceived, under suitable propagation conditions. Accurate physical layer (PHY) design plays a vital role in the deployment of robust transmission systems able to efficiently exploit the large bandwidth portions available in the mm-Wave frequencies. In this paper, we propose Space-Time Shift Keying (STSK) MIMO coding combined with Cyclic-Prefixed Single Carrier (CP-SC) block transmission for broadband data exchange over frequency-selective mm-Wave channels. STSK facilitates exploiting transmit and receive diversity resulting in enhanced performance, when compared with state-of-the-art MIMO techniques only relying on receive diversity, such as Spatial Modulation (SM). In this paper, we assess the performance of CP-SC-STSK and CP-SC-SM in the presence of phase noise and imperfect channel estimation, considering 2 and 4 elements MIMO systems and Line of Sight (LoS) indoor versus non-LoS (nLoS) outdoor 73 GHz multipath channels. We show that the STSK-based solution using MMSE Frequency-Domain Equalization (FDE) is very robust against the aforementioned impairments and clearly outperforms CP-SC-SM at the price of a slight increase of receiver complexity and a throughput reduction of 50% when 4 × 4 MIMO systems are considered.

Constant-Envelope (CE) multicarrier techniques have been recently proposed in order to enable the use of multicarrier waveforms in channels characterized by severe nonlinear distortions. They are based on a phase modulation applied to the multicarrier signal, generated in the time domain by means of a real-valued DFT. Such techniques, known as CE-OFDM and CE-SC-FDMA, demonstrated their superior performance with respect to conventional OFDMA and SC-FDMA, when applied to nonlinear satellite channels, at the price of reduced spectral efficiency. An open issue still to be evaluated is related to the impact of phase noise on the performance of CE multicarrier systems. This is especially important in view of the use of EHF bands for broadband satellite communications. This paper aims at analyzing the effects of phase noise on CE-OFDM and CE-SC-FDMA, highlighting the different behavior of conventional and CE multicarrier signals in the presence of such impairment. Then, simulation results will be discussed considering two different phase noise masks. The performed analysis demonstrates that CE multicarrier signals have globally better performance when both phase noise and nonlinear distortions are considered. Moreover, the sensitivity to the phase noise is strongly dependent from the modulation order and the angular modulation index.

The increasing demand for broadband service delivery by satellite connections is still a challenge particularly due to the nature of the satellite channel. Multi-carrier techniques such as OFDM, OFDMA and SC-FDMA, which have successfully been deployed in terrestrial networks to achieve broadband access, present some limitations when applied to the satellite context. The main reason is their vulnerability to nonlinear distortions. In this paper we propose a novel multicarrier technique, called Constant-Envelope Single-Carrier FDMA (CE-SC-FDMA). In this technique, a nonlinear phase modulation is applied to an SC-FDMA signal rather than to an OFDM signal, as proposed by prior state-of-the-art contributions. At the receiver side, the phase demodulation is applied before the conventional SC-FDMA detection. Simulation results show that the proposed CE-SC-FDMA outperforms OFDM, SC-FDMA and CE-OFDM over nonlinear satellite channels. This improved robustness to nonlinear distortions makes CE-SC-FDMA a good candidate for future broadband satellite communication systems.

The exploitation of extremely high-frequency (EHF) bands (30-300 GHz) for broadband transmission over satellite links is currently a hot research topic. In particular, the Q-V band (30-50 GHz) and W-band (75-110 GHz) seem to offer very promising perspectives. This paper aims at presenting an overview of the current status of research and technology in EHF satellite communications and taking a look at future perspectives in terms of applications and services. Challenges and open issues are adequately considered together with some viable solutions and future developments. The proposed analysis highlighted the need for a reliable propagation model based on experimental data acquired in orbit. Other critical aspects should be faced at the PHY-layer level in order to manage the tradeoff between power efficiency, spectral efficiency, and robustness against link distortions. As far as networking aspects are concerned, the large bandwidth availability should be converted into increased throughput by means of suitable radio resource management and transport protocols, able to support very high data rates in long-range aerospace scenarios.

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 the recent years, MIMO MC-CDMA techniques have been proposed in order to increase system capacity over frequency-selective wireless channels. The key feature of MIMO MC-CDMA is the capability of exploiting diversity jointly in time, frequency and in the space domains. Very promising results have been achieved by STBC-MIMO MC-CDMA using receiver schemes targeted to maximize the signal-to-noise plus interference ratio (SINR) at the output of the diversity combiner. Such a concept turns on the minimum mean squared error (MMSE) combining criterion. Nevertheless, it is known by literature that MSE cost function is not always optimal in digital communications. In this work, we are proposing an adaptive multi-user detection approach based on a minimum-BER (M- BER) concept for a synchronous STBC-MIMO MC-CDMA system transmitting data over time-varying multipath fading channels. The practical implementation of the M-BER receiver relies on an adaptive least-mean-square (LMS)-like algorithm, periodically aided by a training sequence and working in decision-directed modality during a coherence time window. Experimental results have shown a performance improvement yielded by the proposed adaptive M-BER MUD with respect to MMSE adaptive MUD achieved by spending an affordable computational effort.

This letter aims at proposing the use of evolutionary computation methodologies (i.e., genetic algorithms) in order to solve the problem of the maximum-likelihood estimation of orthogonal frequency-division multiplexing symbols in the presence of nonlinear distortions. Experimental results can prove the effectiveness of the proposed detection algorithm achieved with a reasonable computational load

In this work, a novel minimum-mean squared-error (MMSE) multi-user detector is proposed for MC-CDMA transmission systems working over mobile radio channels characterized by time-varying multipath fading. The proposed MUD algorithm is based on a genetic algorithm (GA)-assisted per-carrier MMSE criterion. The GA block works in two successive steps: a training-aided step aimed at computing the optimal receiver weights using a very short training sequence, and a decision-directed step aimed at dynamically updating the weights vector during a channel coherence period. Numerical results evidenced BER performances almost coincident with ones yielded by ideal MMSE-MUD based on the perfect knowledge of channel impulse response. The proposed GA-assisted MMSE-MUD outperforms state-of-the-art adaptive MMSE receivers based on deterministic gradient algorithms, especially for high number of users

In this work, a novel methodology for the efficient multiplexing and streaming of MPEG4 video over wireless networks is presented and discussed. The proposed cross-layer adaptation jointly exploits variable-bitrate (VBR) multi-carrier code-division multiplexing (MC-CDM) and MPEG4 fine-grain-scalability (FGS) in order to provide unequal error protection to the transmitted video stream. A shared bandwidth is partitioned into orthogonal sub-channels in order to multiplex different layers of MPEG4-coded signals. Lower layers are assigned a higher number of sub-channels (and hence an increased frequency diversity) as compared to FGS enhancement layers, in order to provide a differentiated protection against channel degradations. Results achieved in terms of PSNR show that the VBR MC-CDM technique can provide better results than conventional MPEG4 single-layer multicarrier spread spectrum transmission.

In this letter, a real-world working case of interfering signals coming to an antenna array with random arrivals modeled as a Poisson process is considered. A procedure based on a suitable genetic algorithm for adaptive array control is assessed by means of numerical simulations. Selected results clearly demonstrate the effectiveness and flexibility of the proposed procedure.

Multicarrier code division multiple access (MC-CDMA) techniques were originally proposed at mid of 90's for wideband multi-user communications in wireless environments characterised by hostile propagation characteristics. Problems still to be solved are related to the provision of efficient resource channel allocation in variable-bit-rate transmission. In this work, a strategy for medium access control in MC-CDMA systems for broadband WLAN indoor applications is considered. A great advantage of MC-CDMA lies in the capability of supporting asynchronous multi-user variable-bit-rate (VBR) transmission over multipath channel with conventional detection. This can be helpful in designing an efficient and real-time medium access control (MAC) strategy, since a significant number of VBR users can share the same bandwidth without relevant performance dropouts. Different classes of users will be labeled by the MAC level that has to plan a controlled access to the channel on the basis of the users' requests and to check the possibility of assuring to them a certain QoS degree. The paper presents some simulation results in order to discuss the feasibility of the proposed access control strategy.

One of the most critical problems in asynchronous DS/CDMA reception consists of the effective acquisition of the initial pseudo-noise (PN) synchronism. In particular the multi-user interference (MUI) contrasts the operation to synchronise correctly the system. In this paper, an adaptive PN acquisition scheme based on a statistical hypothesis testing and able to reduce the detrimental effects on the acquisition process of multi-access interference present on the channel is presented. The application considered for the proposed algorithm concerns transmission over an AWGN channel, performed by a DS/CDMA system. The results shown can prove the robustness of the proposed method in presence of different levels of MUI, provided there is a reliable estimation of the channel conditions.

Multimedia services over satellite networks require a large amount of bandwidth for the delivery of variable-bit-rate video and audio signal with adequate quality of service. Hence, the bandwidth allocation has to be efficiently managed. In such a case, CDMA is a flexible multiple access technique since it allows a dynamic configuration of the resources allotted to the users of the system. This paper aims at describing a DSP-based DS/CDMA satellite multimedia system for multimedia applications, working in geo-stationary (GEO) satellite networks. The DSP implementation of the satellite modem is described in detail, both for what concerns the hardware section and the signal processing algorithmic section. The developed prototype, whose test is expected during year 2001, should be considered as a basic platform for developing flexible software radio-based architectures for satellite communications.

This work is aimed at investigating the use of multi-carrier CDMA (MC-CDMA) techniques in variable bit-rate transmission over low-earth-orbit (LEO) satellite channels by means of realistic simulations. It is known from the literature that MC-CDMA techniques are much more resilient with respect to multi-user interference effects in multipath fading channels than single-carrier DS/CDMA ones. Moreover, MC-CDMA exhibits a natural capability to deliver multirate services simply by assigning to each user a variable-cardinality set of subcarriers. The achieved simulation results clearly confirmed the expected improved robustness of MC-CDMA techniques transmitting multirate data streams in frequency selective LEO satellite channels, with respect to state-of-the-art DS/CDMA transceivers.

Interest for advanced video-based surveillance applications has been growing rapidly. This is especially true in the field of railway urban transport where video-based surveillance can be exploited to face many relevant security aspects (e.g. vandal acts, overcrowding situations, abandoned object detection, etc.). This paper investigates an open problem in the implementation of video-based surveillance systems for transport applications, i.e.: the implementation of reliable image understanding modules in order to recognize dangerous situations with reduced false alarm and misdetection rates. We consider the use of a neural network-based classifier for detecting the behavior of vandals in metro stations. The achieved results show that the classifier choice mentioned above allows one to achieve very good performances also in the presence of high scene complexity.

This work presents a real-time post-processing algorithm developed for enhancing the performances of remote JPEG-based video surveillance applications, seriously degraded by transmission over noisy channels. The aim of the algorithm is to distinguish between blocks changes due to variations in the observed scene and noise-altered blocks, which contain errors due to channel noise and can be corrected exploiting the strong spatio-temporal redundancy of the encoded digital source without any side information. Experimental results, obtained through JPEG transmission simulations performed in the context of a remote video-surveillance system devoted to detection of abandoned objects, show a good improvement both in terms of perceptive quality and of the performance of the overall video-surveillance system.