Long Range (LoRa) technology is widely adopted in Low Power Wide Area Networks due to its robustness, energy efficiency, and long-range capabilities. However, its lightweight ALOHA-based medium access scheme makes it vulnerable to packet collisions, especially in dense deployments with multiple simultaneous transmissions. Efficient multiuser detection strategies are therefore essential to enhance system scalability and reliability. In this paper, we propose a novel multiuser detection scheme for LoRa systems that exploits the time offset information of received packets, obtained through an effective synchronization method, to mitigate mutual symbol interference. The proposed approach incorporates successive interference cancellation, performed at symbol level, that jointly leverages both power and delay characteristics of overlapping signals. Such combined use of temporal and power-domain knowledge enhances the capability to separate superposed transmissions, thereby improving detection performance in multiuser scenarios.

Handling multiple access represents a key challenge of indoor optical wireless communications, even though rarely addressed in the uplink case. Typical solutions in the literature rely on orthogonal access schemes, providing interference-free links to users but suffering from low performance when the number of access requests grows. An alternative is represented by non-orthogonal multiple access, even though its feasibility and effectiveness are generally assessed only for simple scenarios with few users. In this paper, we introduce a space-time division multiple access framework where access points equipped with an angle diversity receiver allow the channel resources to be managed in both space and time domain. Moreover, by resorting to successive interference cancellation, it is possible to serve users in a non-orthogonal fashion. Herein, we propose two novel resource allocation algorithms aimed to maximize the users access rate. Performance results demonstrate the capability of the proposed solution to serve up to 9 users, outperforming the other benchmark orthogonal and non-orthogonal strategies. Additionally, we introduced two mechanisms that, combined with successive interference cancellation, guarantee a reliable detection of superposing signals, with bit error rate below 10-3. Summarizing, the presented multiple access scheme allows users to transmit simultaneously and reliably, thus realizing channel resources saving as well.

Underwater optical communication (UWOC) is a promising technology for effective data transmission, nevertheless challenges like multipath interference, turbulence, and strong attenuation persist. Additionally, multiple access management represents a crucial issue to address for the realization of the so called Internet of Underwater Things networks (IoUT). In particular, uplink medium access control is a largely unexplored field, with performance of both known orthogonal and non orthogonal strategies being assessed only for basic scenarios. This paper introduces a novel uplink space division multiple access framework for underwater optical camera communication (UOCC), integrating image segmentation techniques to distinguish and process multiple users simultaneously. Spatial diversity enables initial users separation by position relative to the receiver, while segmentation enhances signal decoding efficiency at the pixel level. The proposed system is evaluated under realistic underwater conditions, addressing propagation impairments such as Gaussian blurring, intensity saturation and quantization artifacts. Simulation results validate the robustness and scalability of the approach, highlighting its potential to enable reliable multiuser communication in uplink scenarios.

Visible light communication (VLC) has emerged as an alternative to radio-frequency (RF) systems and promising technology for high-speed wireless communications. In this context, spatial Multiple-Input Multiple-Output (MIMO) techniques have been widely investigated to enhance the performance of VLC systems by exploiting the spatial domain for transmitting multiple data streams simultaneously. The conventional focus has primarily been on optimizing transmitter configurations, overlooking the significance of receiver design. In this paper, we shed light on the necessity of incorporating angular diversity receivers in spatial MIMO VLC systems to mitigate channel impairments and improve the overall performance. Through extensive simulations and analysis, we demonstrate the benefits of angular diversity receivers in terms of enhanced signal reception, increased data rates, and improved link robustness in various indoor scenarios. Our findings underscore the importance of considering both transmitter and receiver aspects for the advancement of spatial MIMO VLC technology.

The newly emerging concept of intelligent reflecting surfaces (IRSs) is changing how we think about the optical wireless propagation channel. Through controlling the light propagation within indoor settings, it becomes feasible to influence the optical channel characteristics in order for visible light communications (VLC) systems to attain specific key performance metrics. In this paper, we propose a novel physical layer security (PLS) mechanism for IRS-assisted VLC systems based on utilising a secret IRS activation pattern that is only shared with the legitimate users. We show that our approach can enhance the secrecy performance of the system without the need to acquire information about the locations of the eavesdropper, which is a major practical limitation to many PLS techniques.

Visible Light Communication (VLC) is expected to enable a wide range of applications in the next generation wireless networks. These applications are recognized as sensitive and prone to dangerous threats. So far, VLC research activities have been more focused on developing high data rate solutions and more robust systems for both indoor and outdoor applications, with a reduced focus on the security aspects. This is mostly due to the fact that VLC systems are based on short range and occurs in line of sight and it is then considered inherently secure by design. The specific characteristics of VLC systems make the traditional countermeasures adopted in radio-frequency-based systems not applicable, with a concrete need to conceive ad hoc solutions. Basing on these premises, in this work we consider a physical layer perspective by analyzing the intrinsic properties of visible light signals so as to develop a secure by design VLC system to be used in downlink. By exploiting the light bias, we guarantee an improved security level in respect of eavesdropper attack by granting also a good illumination level. A key aspect of this work is that the proposed solution does not rely on external devices or extra hardware.

The simultaneous task of data transmission and illumination achievable with Visible Light Communication is continuing to raise the interest of research and industry community. The joint use of the same infrastructure for illumination and communication may enable new location-based services, by implementing sensing functionalities. In this paper, we propose a new multi-dimensional modulation scheme combining different techniques, in order to increase the spectral and energy efficiency, while meeting the optical power emission constraints. Specifically, Pulse Position Modulation Pulse Amplitude Modulation and Frequency Shift Keying are effectively combined in a joint fashion, in order to exploit time, amplitude and frequency information. The innovation of using a smart combination of those modulation formats is based on the exploitation of specific features of the different approaches. In particular, we combine time, amplitude and frequency features to enhance the robustness of the system, without sacrificing the data rate performance as for coded systems. The major implication of such approach is twofold. In this way, we grant a constant illumination level per symbol and, moreover, we outperform in terms of reliability coded modulations for the same level of spectral efficiency. Theoretical results, validated through experimental evaluations, demonstrate that the combined approach achieves very good performance.

Long Range (LoRa) defines a particular chirp spread spectrum modulation employed for signaling in the LoRaWAN network. LoRa is recognized as one of the most effective technologies for the Internet of Things communication scenario, providing high reliability, wide coverage and low energy consumption for devices. The achievement of such performance is tied to the capability of LoRa receivers to accurately detect the signal even at low signal-to-noise ratio conditions. Dealing with signal demodulation, coherent and non-coherent detection represent the most widespread approaches. In this contribution, we present a new detection mechanism that exploits the geometrical properties of linear chirp to perform symbol demodulation, without requiring the energy consuming operations related to coherent and non-coherent detection. Furthermore, we demonstrate how the proposed approach can be fruitfully exploited not only for symbol demodulation, but also for LoRa packet synchronization and spreading factor recognition. By showing some numerical results, we compare the reliability level of the presented scheme through bit error rate with respect to the one offered by conventional detection methods.

The use of Optical Wireless Communications is largely adopted in both indoor and outdoor applications. Recently, it is also extending to underwater scenarios, as an alternative technology to the acoustic one, which is traditionally adopted. Knowing more precisely the position of artifacts, technical/scientific instruments and operators in the marine environment increases the operational potential and consequently, the interest in the progress of knowledge is guaranteed. Furthermore, the possibility of operating in both shallow and deep waters and the opportunity to be a new underwater navigation system increases the possibility of success of underwater activities, in the context of the Internet of Underwater Things (IoUT). This paper introduces an underwater all-optical IoT network architecture for both communication and positioning tasks. We initially discuss the main issues for data transmission via underwater visible light communications, and present an IoUT schematic based on Light Emitting Diode (LED) devices accordingly deployed on the seabed and illuminating a given space of interest. Then, a simple but accurate fingerprinting-based localization approach is presented, able to estimate the position of an object moving within the space of interest (e.g., a diver or an Autonomous Underwater Vehicle). The positioning error is auto-adjusted in case of variable channel coefficients, mainly due to changes in water turbidity space distribution. The achieved results have been assessed in case of two different paths, where variable distances from the positioning/communication LEDs are assumed.

Long Range (LoRa) represents an efficient low power solution for the Internet of Things. Specifically, LoRa defines a physical layer technology, while access control and network issues are handled by the LoRaWAN protocol. Channel access is essentially unslotted ALOHA, so LoRaWAN performance suffer from packet collision events. Such problem becomes more penalizing in dense network scenarios, where the large number of devices simultaneously connected makes the collision probability significantly grow. The largest part of solutions proposed to overcome LoRaWAN inefficiency is oriented to collision avoidance. Differently, we firstly present an algorithm for mitigating the interference among superposing LoRa signals, allowing collided packets to be detected anyway. Then, we propose a novel combining mechanism, implemented at the LoRaWAN network server, that exploits the information carried by the same packet, but received by different gateways, to achieve a more robust decoding. Hence, packet detection is reliably performed even in the presence of interference, thus reducing the need of retransmission and providing energy saving for end devices. Furthermore, simulation results show that the proposed solutions allow the end users to transmit exploiting low spreading factors, thus reducing the channel use that will be fundamental when dealing with larger scale network scenarios.

Energy-constrained slot-amplitude modulation (ECSAM) enables light dimming, eliminates light flicker and constrains the peak optical power while providing robust communication links. However, the complexity of the maximum-likelihood (ML) based ECSAM receiver increases exponentially with required spectral efficiency. This paper provides a comprehensive performance evaluation of ECSAM for the indoor visible light communication (VLC) channel with multipath propagation under realistic illumination constraints and imperfect channel estimation. A sub-optimal receiver that employs a slot-by-slot detection algorithm followed by a slot-correction mechanism for reducing the receiver complexity is proposed. Additionally, the method for optimal selection of parameters when designing the signal waveform is presented. The analytical upper bound on the symbol error rate of ECSAM is derived using the union-bound technique. The results show that the error performance of the sub-optimal receiver are comparable to that of the optimal ML receiver. Compared with conventional power or bandwidth efficient VLC modulation techniques such as multiple pulse position modulation (MPPM) and pulse amplitude modulation (PAM), ECSAM provides complete flexibility in modifying the signal constellation for a desired dimming level to maximise the spectral efficiency and provide a robust bit error rate performance especially in the multipath propagation channel induced intersymbol interference.

This paper proposes an advanced multi-pulse multi-light emitting diodes (LEDs) modulation technique to improve the efficiency for indoor visible light communication systems. The technique is referred to as spatial multiple pulse position modulation (SMPPM), and it is developed by combining a high spectral efficiency space shift keying (SSK) with a high energy efficiency multiple pulse position modulation (MPPM). During a symbol transmission, multiple active pulse slots and active LED indices are utilized as two degrees of freedom to modulate information which in turn provides the balance between the complexity, achievable spectral efficiency and energy efficiency. The analytical expression for symbol error rate (SER) of SMPPM in a multiple input multiple output system with multi-path propagation from reflection is derived theoretically using union bound technique and validated by means of Monte-Carlo simulations. Error performance of SMPPM is then evaluated extensively for different transceiver parameters and pulse configurations. Error rate distribution in a typical indoor workspace is plotted and analyzed. The SMPPM system achieves significantly higher spectral efficiency with respect to the conventional MPPM, SSK and spatial pulse position modulation (SPPM).

We are at the dawn of an era in information and communication technology with unprecedented demand for connected and automated everything. Both Shannon theories and industrial advances have clearly evidenced that more densely packed networks and a much wider operating bandwidth are key drivers for meeting the escalating wireless network demands. Recently, there have been substantial research efforts on the exploitation of higher frequency bands, in particular the millimetre wave and optical wireless bands. After a decade of active research and development, and along with the maturity of device technology, Visible Light Communications (VLC) has emerged as a very promising technology to enable next generation digital innovations and support wide range of applications. This special issue on VLC focuses on three core thrusts of the discipline:Localisation, CommunicationandNetworking. The overall aim of the special issue is to inspire multi-disciplinary international communities to work together in order to achieve further research advances. Indeed, a total of 96 high quality papers were received from both academia and industry. After a careful peer-reviewing process, 17 papers were selected based on their combined novelty, rigour, and impact. Owing to the highly selective nature of JSAC, many other interesting papers were not selected for the special issue, but we hope that these papers might appear elsewhere.

A novel cooperative least mean square adaptation rule is proposed with application to fractionally spaced blind channel equalization schemes used in quadrature amplitude modulation data links. A novel cost function based on second-order statistics only of the received signal is defined and jointly used with another chosen among classical blind cost functions such as decision directed and other Bussgang-type ones. Numerical results show that severe misconvergence observed in classical blind equalization algorithms is drastically mitigated using the here described technique.

The development of wireless personal area networks is one of the key challenges in the new frontier of communications. The standardization activities of the IEEE802.15.6 and IEEE802.15.4f workgroups along with the proposed 368-369 ECMA specifications open new roads to optimize performance in ultrawideband (UWB) communication links and services. In this perspective, new communications require high reliability, high throughput for multimedia content delivery, very low latency, and bit error rates are required. In this regard, this contribution deals with a turbo-like mechanism that, starting from an interference acquisition phase, proceeds with data-aided channel estimation and synchronization to data detection of ultrawideband impulse-radio (UWB-IR) terminals operating over broadband channels affected by multipath fading and in the presence of imperfect orthogonal access. The performance of the proposed transceiver has been evaluated in terms of both required number of pilot symbols for the channel estimation/data synchronization and bit error rate resulting from the channel estimation and interference analysis. Moreover, the performance related to system efficiency (i.e., data transmitted with respect to the whole information needed for estimation purposes) is evaluated by showing the balance between achieved transmission rate and bit error rate. Numerical comparisons have been performed as well as tests on real data and partial implementation of the proposed scheme.

This paper addresses the problem of texture images recovery from compressively sampled measurements. Texture images hardly present a sparse, or even compressible, representation in transformed domains (e.g. wavelet) and are therefore difficult to deal with in the Compressive Sampling (CS) framework. Herein, we resort to the recently defined Graph-based transform (GBT), formerly introduced for depth map coding, as a sparsifying transform for classes of textures sharing the similar spatial patterns. Since GBT proves to be a good candidate for compact representation of some classes of texture, we leverage it for CS texture recovery. To this aim, we resort to a modified version of a state-of-the-art recovery algorithm to reconstruct the texture representation in the GBT domain. Numerical simulation results show that this approach outperforms state-of-the-art CS recovery algorithms on texture images.

A critical issue of a Cognitive Radio Network is the interference generated by secondary users simultaneously accessing and transmitting over the primary user spectrum band. In this paper, we introduce and study a distributed and opportunistic access scheme for MIMO ad-hoc cognitive radio networks identified as OPTIM-COG (OPporTunistic Interference control for Mimo COGnitive radio). OPTIM-COG is based on simple power stimuli issued by PU transmitters. These stimuli are basic control messages exchanged, at a known power, by both primary transmitter and primary intended receiver for their internal power control. A periodic repetition of this power stimulus and the power control generated in the primary network are used by secondary nodes to get their transmission opportunities. These opportunities are determined with a twofold goal: on the one hand the secondary node will transmit to its secondary receiver only if the quality of the already established primary connection does not decrease below a minimum level, on the other hand the resulting opportunistic access exploits the MIMO performance improvements. We describe the fully distributed version of this access scheme and we theoretically demonstrate, via a game theoretical formulation, that the resulting power allocation is the unique Nash Equilibrium. Performance results present secondary user access maps in the 2D plan, where both MIMO benefits as well as the presence of multiple active secondary links can be represented. Both the cases of a perfect interference measurement and imperfect channel estimation are evaluated.

Nowadays, the use of Visible Light Communications is growing towards several applications, due to the many benefits of this technology. By efficiently modulating visible light, it is possible to reach very high data rates, while at the same time providing illumination. As a result, traditional indoor systems, like open offices and homes, become smarter, providing high efficient services i.e., localization, positioning and navigation. In this paper, we propose a simple method for indoor localization service provided by infrared LED devices. The positioning estimation can be calculated by exploiting the uniform deployment of LED-based transmitters, and the information of the impulse responses. The comparison to the impulse responses time samples of a room map, opportunely built according to the transmitters' deployment, allows to estimate the position of a mobile device inside the room. The estimation error can be then reduced on the basis of the number of LED devices used.

Vertical handover (VHO) procedure facilitate service continuity in an heterogeneous wireless scenario under varying network as well as channel conditions. Decision criteria for VHO are, mainly, designed to maximize a combination of network parameters in order to guarantee an acceptable service level and maximize network operators and/our users expectation. The objective of this paper is to formalize the VHO decision criteria as a QoS constrain bound problem and propose two strategies that permits to achieve QoS constrains without wasting resources. The former that minimize the power consumption and the latter that minimize the number of VHO. Numerical results are provided in order to compare the two strategies.

Ultra Wide Band (UWB) communication systems operate in the frequency range between 0 and 10.6 GHz so they induce the Scientific Community to solve the problem of coexistence with concurrent telecommunication services. This is the leading reason why both the Federal Communications Commission (FCC) and the European Telecommunications Standards Institute (ETSI) gave strict indications about the spectral limits to be respected and require the transmitter and receiver to be compliant with these spectral masks. To this end, it is mandatory to carefully shape the UWB pulse, for this can be accurately designed so as to avoid severe performance reduction while guarding inter-systems coexistence. The UWB technology and, more, the pulse shaping allow to apply the cognitive paradigm where the transmitter and receiver are the actors of this functionality since the performance are tied to channel features and interference presence. The widespread choice of Gaussian-like pulses has proven, however, largely suboptimal from a power emission point of view since they fail to optimize performance. Goal of this contribution is to show how to achieve a good compromise between spectral emission, rate and synchronization errors robustness, via a modified version of the Parks-McClellan method, considering channel impairments due to its frequency-selective nature and to the inter-pulse interference.

Power Line Communication (PLC) systems are currently envisioned as a possible solution for distributing multimedia contents and allowing Internet access with a capillary (already built) network without demanding further infrastructure. The real challenge for PLCs consists in providing connectivity where Public Switch Telephone Network (PSTN)-based Internet Access and/or Wi-Fi/WiMAX seem to be unable to solve the problem of Digital Divide. In this paper we introduce a new metric, i.e. the goodput, to balance transmission rate and bit error rate (BER) in resource allocation issues for Power Line Communication systems. In detail, we state the well-known integer bit-loading problem as a goodput maximization with constraints on the power consumption and the maximum decoding time. The use of Trellis Coded Modulation (TCM) allows to pursue the goodput maximization weighing error probability and transmission rate which would have otherwise been in trade-off. Numerical results are presented to stress how our solution improves system performances, both in ideal conditions and with additional impairments such as crosstalk and impulsive noise, with respect to the conventional Maximum Rate (MR) and Minimum BER (MB) approaches and to validate the suitability of TCMs in comparison with higher complexity codes.

The interference induced by UWB communication on systems operating in the frequency range between 0 and 10.6 GHz is the main reason why the essential role in these systems' design is played by the pulse shape selection. That's why an accurate shaping choice can lead to avoid severe performance reduction and to guard systems coexistence. To this end, FCC (and ETSI in the near future) gave strict indications about the spectral limits to be respected, so as to define, as the purpose of UWB systems realization, the compliance with this spectral mask. The, widely used, choice of Gaussian-like pulses is, however, largely suboptimal from a power emission point of view since they are unable to maximize the signal-to-noise ratio (SNR). Goal of this contribution is to achieve a good compromise, in a cognitive way, between spectral emission, rate and synchronization errors robustness, via a modified version of the Parks-McClellan method, considering channel impairments due to its frequency-selective nature, to the inter-pulse interference and in-band interference.

Emerging media overlay networks for wireless applications aim at delivering Variable-Bit-Rate (VBR) encoded media contents to nomadic end-users by exploiting the (fading-impaired and time-varying) access capacity offered by the "last-hop" wireless channel. In this application scenario, a still open question concerns the design of control policies maximizing the average throughput over the wireless last-hop, under constraints on the maximum connection bandwidth allowed at the Application (APP) layer, the queue-capacity available at the data-link (DL) layer, and the average and peak transmit energies sustained by the Physical (PHY) layer. The main feature of the approach we follow relies on the maximization (on a per-slot basis) of the throughput averaged over the fading statistics and conditioned on the queue-state. The resulting optimal controller is rate-based and operates in a cross-layer fashion that involves the APP, DL and PHY layers of the underlying protocol stack. This means that the proposed controller dynamically allocates connection bandwidth at the APP Layer, throughput at the DL layer and transmit energy at the PHY layer by basing on both current queue and channel states. The carried out numerical tests give insights about the connection bandwidth-vs.-queue delay tradeoff attained by optimal controller.

Wireless mesh networks (WMNs) are envisioned for extending the coverage of WLANs by interconnecting the underlying access points (APs) via high-capacity wireless backbones. Since the ultimate goal of a WMN is to provide Internet connectivity to residential clients, WMN traffic is mainly routed over the backbone either toward the Internet gateways (IGWs) or from the IGWs to the APs. In principle, the transport capacity of a WMN can further be upgraded by equipping the underlying backbone routers with multiantenna (MA) radio modules. Motivated by the above consideration, in this paper, we focus on the optimized node selection (e.g., path-routing) over MA mesh backbones when the target is to maximize the end-to-end routed information rate subject to a constraint on the total power available for the relays. Under the assumption of Rayleigh-distributed block fading, we assume that point-to-point capacity-achieving space-time codes (STCs) are used for the single-hop link. At first, we tackle the routing problem when neither interference mitigation (IM) nor transmit beamforming (TB) is performed at the relay nodes, and then, we extend the analysis to the cases when IM and/or TB are also carried out. The effects of channel-state-information (CSI) possibly available at the relay nodes are also investigated. So doing, we are able to gain insight about the combined effect of spatial multiplexing and IM capabilities of the overall MA architecture on both end-to-end capacity and access medium performance of the considered WMN.

Main goal of this work is to give insight on the possible performance improvement arising in the wireless local and/or ad-hoc access from the synergic cooperation of two emerging paradigms, e.g., multi-antenna and cognitive radios. As application scenario, we consider both the faded uplink of a WLAN working in infrastructure-mode, where noncooperative Multi-Antenna cognitive radios attempt to join to a (possibly multi-antenna) access point (AP) and an ad-hoc scenario where each node can communicate with each free node. The target can be twofold and two different approaches are considered. The first is the competitive maximization of own access throughput in the presence of multiple-access Interference (MAI) induced by the other accessing terminals, the second one is the BER minimization. Being the radios cognitive, they are capable to autonomously learn the ambient-context and, then, self-configure their access strategy via suitable power-allocation that is time-frequency-code-space signal-shaping. Furthermore, a generalized approach is developed that allows the node to access with a (possibly hybrid) scheme to the medium by combining different x-DMA strategies under QoS-guaranteed access policy.

In this contribution, the problem of the synchronization for ultra wideband impulse radio (UWB-IR) systems, through the adoption of a multi-antenna platform working on multipath faded channels, is afforded. In this regard, we propose a novel UWB-IR synchronizer devoted to jointly estimate (according to the maximum likelihood (ML) criterium) the arrival times and their (Poisson distributed) number, composing a typical UWB-IR multipath faded channel. Such estimate is effected without any knowledge on the value of the channel paths (noncoherent ML synchronizer). The architecture of such synchronizer is based on a single-input multiple-output (SIMO) platform, instead of a multiple-input multiple-output MIMO one, according to a previous result in the literature. Related performance of this joint ML estimation is expressed in closed via the Cramer-Rao bound (CRB) and is tested by simulations, under acquisition and tracking conditions.

In this contribution we develop a multiple-input multiple-output (MIMO) impulse radio ultra wide band (IR-UWB) transceiver for orthogonal signalling over (baseband) muhipath faded MIMO channels. The proposed maximum-likelihood receiver results to be "partially coherent", since it is optimized to work without any information about channel coefficients, and it is based on the knowledge of the arrivals' times of the transmitted signals' replicas. The behavior of the proposed transceiver has been evaluated via three suitable versions of the Union-Chernoff Bound related to several indoor and outdoor propagation scenarios, and these limits are considered to introduce a novel family of unitary orthogonal space-time block codes (e.g., the space-time OPPM (STOPPM) codes), that are able to attain maximum diversity and coding gains.

The emerging proxy-based wireless content delivery networks (CDNs) should to be designed to download huge-size files over fading-affected channels. However, from a radio resource management point of view, several basic problems still need to be solved for such wireless delivery systems to operate efficiently. Specifically, due to the fading nature of the downlink channel, a still open basic problem is how to design optimal energy-allocation (for example, scheduling) policies that minimize the requested download time when constraints on the total available energy and peak energy are simultaneously active. In this contribution, this problem is solved for application scenarios where the downlink channel is slotted and continuous-state, the carried out traffic is elastic, and the resulting conveyed throughput is measured by any desired increasing concave rate function. Specifically, the optimal energy-allocation policy minimizing the download time is computed in closed form, and its performance is compared against that of a basic on-off heuristic energy scheduler on some Rayleigh-faded multi-antenna delivery systems of practical interest. The carried out performance comparisons point out that the presented optimal policy typically may outperform the heuristic one up to two orders of magnitude, especially when the delivery system is strongly energy limited.

In this contribution Time-Hopping (TH) codes are developed based upon the theory of congruences. These codes can be used for coherent multiuser asynchronous spread spectrum communication systems. They represent a compromise between Costas codes, which have nearly ideal auto-ambiguity properties, and congruential codes presenting nearly ideal cross-properties. The presented code applied not in ranging applications but communications system presents good performance in terms of Bit Error Rate (BER) for UltraWide Band Impulse Radio (UWB-IR) systems. Examples of typical auto- and cross-ambiguity functions are given to illustrate the performance of the presented codes jointly with BER evaluation.

This contribution analyzes the problem of multi-user interference suppression via estimation and subtraction. In particular it is shown that spatial diversity helps the suppression capability of a Base Station and this has an important impact on performance. By fact, we show that the best solution does not consist in transmit at maximum energy level but, in order to allow interference estimation and cancellation, a trade off has to be solved. So, interference suppression can give arise to performance improvements both for achieved throughput (that can be "enhanced") and for error probability (that can be reduced).

In this contribution, the problem of download time minimization, by considering channel state, is solved for application scenario where the downlink channel is slotted and continuous-state, while the resulting conveyed throughput is measured by any desired increasing concave rate-function. Specifically, the optimal energy-allocation policy minimizing the download-time is found and its performance is compared against that of a basic on-off type heuristic scheduler for some Rayleigh-faded multi-antenna downloading systems of practical interest

The paper focuses on competitively optimal power-control and signal-shaping for "ad-hoc" networks composed of multiple-antenna noncooperative transmit/receive terminals affected by spatially colored multi-access interference (MAI). The target is the competitive maximization of the information throughput of each link active over the network. For this purpose, the MAI-impaired network is modeled as a noncooperative strategic game, and sufficient conditions for the existence and uniqueness of the Nash equilibrium are provided. Specifically, the main contribution of the paper may be so summarized. First, we develop fully. distributed and scalable power-control and signal-shaping algorithms allowing the implementation of asynchronous space-division multiple access strategies (SDMACSs) able to guarantee the competitive maximization of the users' throughput under both best effort and contracted QoS access policies. Second, we give evidence that the developed SDMACSs outperform (in terms of aggregate throughput) the conventional centralized ones (such as TDMA/FDMA/CDMA), especially in operating scenarios affected by strong MAI.

The paper focuses on competitively optimal power-control and signal-shaping for "ad-hoc" networks composed of multiple-antenna noncooperative transmit/receive terminals affected by spatially colored multi-access interference (MAI). The target is the competitive maximization of the information throughput (measured in bits/slot) sustained by each link active over the network. For this purpose, the MAI-impaired network is modeled as a noncooperative strategic game, and sufficient conditions for the existence and uniqueness of the Nash equilibrium are provided. We develop fully distributed and scalable power-control and signal-shaping algorithms allowing the implementation of asynchronous space-division multiple access strategies (SDMACSs) able to guarantee the competitive maximization of the users' throughput under both best effort and contracted QoS access policies. We give evidence that the developed SDMACSs outperform (in terms of aggregate throughput) the conventional centralized ones (such as TDMA/FDMA/CDMA), especially in operating scenarios affected by strong MAI. We study the convergence property of the presented SDMACSs and show that, when the throughput set requested by the users is not achievable by the network, then the developed SDMACSs are able to move the working point of the system to the nearest one sustainable by the network. By exploiting the distributed feature of the presented SDMACSs, we propose two connection admission procedures (CAPs) able to optimize (in a competitive sense) the tradeoff between aggregate networking throughput and connection requirements advanced by the users.

In this letter, we introduce a simple co-decoding scheme for ultra wideband (UWB) impulse radio systems impaired by multiuser interference (MUI). The proposed scheme exhibits an adaptive capability with respect to MUI degrading effects and, depending on the MUI level, it may switch from a hard-detection operating mode to a soft-detection one. So doing, the presented scheme is able to gain resistance against near-far effects. Several numerical tests support the conclusion that the presented scheme outperforms conventional ones currently planned for noise-limited UWB systems up to orders of magnitude in MUI-limited application scenarios.

This contribution considers the power control and signal-shaping problem for ad-hoc networks composed by multi-antenna non-cooperative terminals affected by spatially colored multiple-access interference (MAI). The multi-antenna interference channel is modeled as a non cooperative and strategic game. Furthermore iterative power control and signal shaping algorithms are presented to efficiently achieve the Nash equilibrium under best effort and "contracted QoS" policies.

This paper focuses on the competitively optimal power-control and signal-shaping for "ad-hoc" networks composed by multiple-antenna noncooperative transmit/receive terminals affected by spatially colored multiple-access interference (MAI). For this purpose, the MAI-impaired network is modeled as a noncooperative strategic game, and sufficient conditions for the existence and uniqueness of the Nash equilibrium are provided. Connection admission procedures are presented with related performance.

In the last years a lot of attention has been paid to multiantenna systems with space-time coding (STC) and to ultra wide band (UWB). In this paper we aim to propose a transceiver scheme in order to evaluate if these two technologies can be considered adequate candidates for next generation WLANs. Merging ultra wide band signals with multiple antenna schemes allows us to achieve very high bit rate and error probability matched to QoS requested by 4GWLANs at low SNR. This contribution presents a simple way to combine ultra wide band and multiple antenna schemes so to improve performance and coverage with respect to the conventional UWB approach in order to promote this approach application scenarios by considering a base band channel model and selective are considered.

In the last few years, ultra-wideband (UWB) systems became an appealing technology for wireless communication applications. Unfortunately, when the transmission channel is affected by intersymbol interference (ISI), system performance of UWB systems equipped with receivers based on conventional matched filters presents error-floor phenomena. Aimed by these considerations, in this letter, we present a novel transmit-receive scheme allowing blind channel estimation and minimum mean-square error linear channel equalization. Essentially, the proposed scheme exploits a very short duration of the UWB pulse for achieving reliable blind deconvolution of the received signal. A nice feature of the resulting system is that blind deconvolution of the received signal is achieved without power and throughput losses. Simulation results support the effectiveness of the proposed scheme, and show that it is able to gain about 8 dB over current UWB receivers based on matched filtering on several test channels impaired by ISI.

In this contribution we propose a simple codec for ultra wideband (UW) radio networks limited by multi-user interference (MUI). The proposed codec exhibits adaptive capabilities with respect to MUI degrading effects and, depending on MUI level, it may switch from a hard-detection operating mode to a soft-detection one. So doing, the presented scheme gains resistance against near-far effect. Several numerical tests show that our scheme outperforms conventional ones currently planned for UWB systems up to several orders of magnitude in MUI-limited wireless local area networks (WLANs).

Multiple-antenna wireless systems with space-time block-codes exploit channel-diversity for improving performance without loss in spectral efficiency. Up to date, most work on this area assumed that perfect channel estimates are available at the receiver so to make feasible fully coherent decoding. However, accurate channel-estimates require long training sequences that lower spectral efficiency. Therefore, in this contribution we focus on architecture, optimized design and performance of multiple-antenna block-coded systems with imperfect channel-estimates. After considering emerging fourth-generation WLANs (4GWLANs) as a possible application scenario, new performance bounds and optimized design criteria are presented together with a new family of robust-space block-codes that "self-match" to channel estimation errors.

We present a novel iterative (turbo) receiver with tunable complexity for reliable detection of (uncoded) payload data transmitted over long intersymbol interference (ISI) channels affected by crosstalk, as those typically encountered in emerging HDSL2 services standardized by ANSI T1.418 recommendation. The proposed receiver combines in an original way "minimum mean square error (MMSE) estimation principle," "turbo-processing principle" and "crosstalk-prediction principle" for achieving both suboptimal maximum a posteriori probability channel equalization and reliable soft-mitigation of ISI tail plus crosstalk. More in detail, according to the turbo-processing principle, at each iteration suitable extrinsic information is extracted from the equalizing and interference-canceling modules and used as "a priori information" for the next iteration. Several simulation results on typical HDSL-like test-loops confirm the superiority of the proposed turbo-detector (TD) over current solutions based on conventional MMSE decision-feedback equalizers and precoders (such as the Tomlinson-Harashima precoder). The numerical tests also point out that performance of the presented TD on typical high bit-rate digital subscriber lines (HDSL) is not limited by error-floor phenomena, even at error-probabilities below 10/sup -7/.