The upcoming integration of AI in the physical layer (PHY) of 6G radio access networks (RAN) envisions a distributed intelligence for enhanced quality-of-service. However, an AI-Native PHY greatly increases the computational complexity of conventional baseband, challenging sub-ms deployment on edge cells within an affordable power budget. Thus, a new generation of efficient domain specific processing engines is needed for AI-Native RAN with sufficient flexibility to ensure long term sustainability. We present TensorPool, a many-core cluster accelerated for the intensive tensor computations, dominating AI-Native PHYs. TensorPool offers massive parallelism: 256 RISCV32IMAF cores and 16 256 MACs/cycle (FP16) tensor-engines with shared low-latency access to 4MiB L1 scratchpad for maximal data-reuse. Implemented in TSMC’s N7, TensorPool achieves 3643 MACs/cycle (89% tensor-unit utilization) on tensor operations for AI-RAN, 6 × more than a core-only cluster without tensor acceleration, while concurrently improving GOPS/W/mm2 efficiency by one order of magnitude.

The fast-rising demand for wireless bandwidth [1] requires rapid evolution of high-performance baseband processing infrastructure. Programmable many-core processors for software-defined radio (SDR) have emerged as high-performance baseband processing engines, offering the flexibility required to capture evolving wireless standards and technologies [2]–[4]. This trend must be supported by a design framework enabling functional validation and end-to-end performance analysis of SDR hardware within realistic radio environment models. We propose a static binary translation based simulator augmented with a fast, approximate timing model of the hardware and coupled to wireless channel models to simulate the most performancecritical physical layer functions implemented in software on a many (1024) RISC-V cores cluster customized for SDR. Our framework simulates the detection of a 5 G OFDM-symbol on a server-class processor in $9.5 \mathrm{~s}-3 \mathrm{~min}$, on a single thread, depending on the input MIMO size (three orders of magnitude faster than RTL simulation). The simulation is easily parallelized to 128 threads with $73-121 \times$ speedup compared to a single thread.

Artificial intelligence approaches for base-band processing for radio receivers have demonstrated significant performance gains. Most of the proposed methods are characterized by high compute and memory requirements, hindering their deployment at the edge of the Radio Access Networks (RAN) and limiting their scalability to large bandwidths and many antenna 6G systems. In this paper, we propose a low-complexity, model-driven neural network-based receiver, designed for multiuser multiple-input multiple-output (MU-MIMO) systems and suitable for implementation at the RAN edge. The proposed solution is compliant with the 5G New Radio (5G NR), and supports different modulation schemes, bandwidths, number of users, and number of base-station antennas with a single trained model without the need for further training. Numerical simulations of the Physical Uplink Shared Channel (PUSCH) processing show that the proposed solution outperforms the state-of-the-art methods in terms of achievable Transport Block Error Rate (TBLER), while reducing the Floating Point Operations (FLOPs) by 66×, and the learnable parameters by 396×.

Faster-than-Nyquist (FTN) signaling aims at improving the spectral efficiency of wireless communication systems by exceeding the boundaries set by the Nyquist-Shannon sampling theorem. 50 years after its first introduction in the scientific literature, wireless communications have significantly changed, but spectral efficiency remains one of the key challenges. To adopt FTN signaling, intersymbol interference (ISI) patterns need to be equalized at the receiver. Motivated by the pattern recognition capabilities of convolutional neural networks with skip connections, we propose such deep learning architecture for ISI equalization and symbol demodulation in FTN receivers. We investigate the performance of the proposed model considering quadrature phase shift keying modulation and low density parity check coding, and compare it to a set of benchmarks, including frequency-domain equalization, a quadratic-programming-based receiver, and an equalization scheme based on a deep neural network. We show that our receiver outperforms any benchmark, achieving error rates comparable to those in additive white Gaussian noise channel, and higher effective throughput, thanks to the increased spectral efficiency of FTN signaling. With a compression factor of 60% and code rate 3/4, the proposed model achieves a peak effective throughput of 2.5 Mbps at just 10dB of energy per bit over noise power spectral density ratio, with other receivers being limited by error floors due to the strong intersymbol interference. To promote reproducibility in deep learning for wireless communications, our code is open source at the repository provided in the references.

Shared L1-memory clusters of streamlined instruction processors (processing elements - PEs) are commonly used as building blocks in modern, massively parallel computing architectures (e.g. GP-GPUs).Scaling outthese architectures by increasing the number of clusters incurs computational and power overhead, caused by the requirement to split and merge large data structures in chunks and move chunks across memory hierarchies via the high-latency global interconnect.Scaling upthe cluster reduces buffering, copy, and synchronization overheads. However, the complexity of a fully connected cores-to-L1-memory crossbar grows quadratically with PE-count, posing a major physical implementation challenge. We present TeraPool, a physically implementable, >1000 floating-point-capable RISC-V PEs scaled-up cluster design, sharing a Multi-MegaByte >4000-banked L1 memory via a low latency hierarchical interconnect (1-7/9/11 cycles, depending on target frequency). Implemented in 12nm FinFET technology, TeraPool achieves near-gigahertz frequencies (910MHz) typical, 0.80V/25 °C. The energy-efficient hierarchical PE-to-L1-memory interconnect consumes only 9-13.5 pJ for memory bank accesses, just 0.74-1.1× the cost of a FP32 FMA. A high bandwidth main memory link is designed to manage data transfers in/out of the shared L1, sustaining transfers at the full bandwidth of an HBM2E main memory. At 910MHz, the cluster delivers up to 1.89 single precision TFLOP/s peak performance and up to 200GFLOP/s/W energy efficiency (at a high IPC/PE of 0.8 on average) in benchmark kernels, demonstrating the feasibility of scaling a shared-L1 cluster to a thousand PEs, four times the PE count of the largest clusters reported in literature.

Following the scale-up of new radio (NR) complexity in 5G and beyond, the physical layer’s computing load on base stations is increasing under a strictly constrained latency and power budget; base stations must process$\gt$20-Gb/s uplink wireless data rate on the fly, in$\lt$10 W. At the same time, the programmability and reconfigurability of base station components are the key requirements; it reduces the time and cost of new networks’ deployment, it lowers the acceptance threshold for industry players to enter the market, and it ensures return on investments in a fast-paced evolution of standards. In this article, we present the design of a many-core cluster for 5G and beyond base station processing. Our design features 1024, streamlined RISC-V cores with domain-specific FP extensions, and 4-MiB shared memory. It provides the necessary computational capabilities for software-defined processing of the lower physical layer of 5G physical uplink shared channel (PUSCH), satisfying high-end throughput requirements (66 Gb/s for a transition time interval (TTI), 9.4–302 Gb/s depending on the processing stage). The throughput metrics for the implemented functions are ten times higher than in state-of-the-art (SoTA) application-specific instruction processors (ASIPs). The energy efficiency on key NR kernels (2–41 Gb/s/W), measured at 800 MHz,${25}~^{\circ } $C, and 0.8V, on a placed and routed instance in 12-nm CMOS technology, is competitive with SoTA architectures. The PUSCH processing runs end-to-end on a single cluster in 1.7 ms, at <6-W average power consumption, achieving 12 Gb/s/W.

Radio Access Networks (RAN) workloads are rapidly scaling up in data processing intensity and throughput as the 5G (and beyond) standards grow in number of antennas and sub-carriers. Offering flexible Processing Elements (PEs), efficient memory access, and a productive parallel programming model, many-core clusters are a well-matched architecture for next-generation software-defined RANs, but staggering performance requirements demand a high number of PEs coupled with extreme Power, Performance and Area (PPA) efficiency. We present the architecture, design, and full physical implementation of Terapool-SDR, a cluster for Software Defined Radio (SDR) with 1024 latency-tolerant, compact RV32 PEs, sharing a global view of a 4 MiB, 4096-banked, L1 memory. We report various feasible configurations of TeraPool-SDR featuring an ultra-high bandwidth PE-to-L1-memory interconnect, clocked at 730 MHz, 880 MHz, and 924 MHz (TT/0.80 V/ <?TeX $25 \,\mathrm{ \mathrm{^{\circ }\mathrm{\mathrm{C}}}}$?> Math 1 ) in 12 nm FinFET technology. The TeraPool-SDR cluster achieves high energy efficiency on all SDR key kernels for 5G RANs: Fast Fourier Transform (93 GOPSW− 1), Matrix-Multiplication (125 GOPSW− 1), Channel Estimation (96 GOPSW− 1), and Linear System Inversion (61 GOPSW− 1). For all the kernels, it consumes less than 10 W, in compliance with industry standards.

Non-Terrestrial Networks (NTNs) will be an es-sential element in Beyond -5G (BSG) and 6G ecosystems, with the purpose of enabling seamless and global coverage, as well as supporting high data rate services. To achieve that, Full Frequency Reuse (FFR) schemes, along with digital beamforming techniques to cope with the Co-Channel Interference (CCI), are considered as promising strategies in 6G NTN. In this paper, we address the design of Cell-Free (CF) MIMO algorithms in NTN composed of multiple swarms of Non-GeoSynchronous Orbit (NGSO) nodes, in which each swarm performs distributed digital beamforming schemes. Furthermore, aiming at increasing the directivity of on-board antenna arrays for each NGSO node and enhancing the interference mitigation, we propose a Limited Field of View (LFoV) planar array architecture built up of smaller planar subarrays. We evaluate the performance of distributed beamforming schemes including both Channel State Information (CSI)-based, e.g., digital Minimum Mean Square Error (MMSE), and position-based such as analog Conventional Beamforming (CBF). We provide a numerical analysis of the performance in terms of per-user spectral efficiency. The results show that our proposed sub arrayed architecture designed for federated CF-MIMO beamforming outperforms the reference approach without subarraying in the proposed NTN system architecture.

This paper describes the integration of Terrestrial and Non-Terrestrial Networks, wherein space-based network entities collaborate with traditional and emerging terrestrial communication frameworks to furnish pervasive, resilient, and three-dimensional wireless connectivity worldwide toward the 6th Generation of communication networks. This integration supports heterogeneous services, such as enhancing coverage, user experience, system capacity, service reliability, and availability, while also providing high-speed connectivity in remote or disaster-affected areas, improving existing 5th Generation technologies. Various Use Cases are detailed, highlighting the pivotal roles that Non-Terrestrial Networks play in distinguishing between urban/suburban and rural environments, with particular emphasis on transportation ecosystems. Through this analysis, Key Performance Indicators and requirements are delineated to characterize the requisite service quality for these diverse Use Cases. The paper further presents an overview of potential and standards-compliant integrated Terrestrial/Non-Terrestrial architectures, delineating their roles both in backhauling and access across different layers of Non-Terrestrial systems and elements. These insights are derived from studies conducted within the Integrated Terrestrial And Non-Terrestrial Networks (ITA-NTN) project, part of the European Union initiative defined as the Italian National Recovery and Resilience Plan (NRRP) RESTART Research Program.

Through the transition from 5G to 6G, a significant rise in the number of Internet of Things (IoT) devices is anticipated, enabling pervasive and uninterrupted connectivity for several applications, in different verticals. Coping with the substantial influx of IoT devices and fulfilling the high capacity demands of different IoT technologies, such as NB-IoT, will necessitate the involvement of Non-Terrestrial Networks (NTNs), which will serve as crucial complements to terrestrial systems, enhancing the availability, resilience, and coverage of the network and will guarantee cost/benefit for some services and will fully satisfy some key requirements. Nevertheless, a primary obstacle to be faced when integrating IoT terrestrial communication systems in NTN, in particular with Non-Geostationary (NGSO) satellites, lies in the short visibility time of the flying platform due to its high speed. The latter introduces criticalities in various communication phases, including the Random Access (RA) procedure. In a highly congested scenario, the large Round Trip Delay and a limited visibility window, which varies for each user within the satellite’s coverage area, contribute to reducing the number of users successfully concluding the RA procedure. In this paper, to enhance the percentage of users who successfully conclude the RA, we introduce the concept of Coverage Enhancement Levels in time and a novel backoff mechanism, namely Smart Backoff, that leverages the beam coverage visibility period of individual users to adjust the random backoff interval. The numerical results obtained from our proposed scheme substantiate significant improvements compared to the standard backoff scheme. Specifically, our approach yields an increase of up to 16% per channel in the percentage of users who successfully complete the RA process.

5G Radio access network disaggregation and soft-warization pose challenges in terms of computational performance to the processing units. At the physical layer level, the baseband processing computational effort is typically offloaded to specialized hardware accelerators. However, the trend toward software-defined radio-access networks demands flexible, programmable architectures. In this paper, we explore the software design, parallelization and optimization of the key kernels of the lower physical layer (PHY) for physical uplink shared channel (PUSCH) reception on MemPool and TeraPool, two manycore systems having respectively 256 and 1024 small and efficient RISC-V cores with a large shared L1 data memory. PUSCH processing is demanding and strictly time-constrained, it represents a challenge for the baseband processors, and it is also common to most of the uplink channels. Our analysis thus generalizes to the entire lower PHY of the uplink receiver at gNodeB (gNB). Based on the evaluation of the computational effort (in multiply-accumulate operations) required by the PUSCH algorithmic stages, we focus on the parallel implementation of the dominant kernels, namely fast Fourier transform, matrix-matrix multiplication, and matrix decomposition kernels for the solution of linear systems. Our optimized parallel kernels achieve respectively on MemPool and TeraPool speedups of 211, 225, 158, and 762, 880, 722, at high utilization (0.81, 0.89, 0.71, and 0.74, 0.88, 0.71), comparable a single-core serial execution, moving a step closer toward a full-software PUSCH implementation.

With the evolution process of the 5G into the 6G, there will be an exponential growth of the Internet of Things (IoT) devices, offering ubiquitous and continuous connectivity services in all areas of our life. In order to deal with such huge amount of IoT devices, and to satisfy the large capacity requirements of the most advanced of them, non-terrestrial networks (NTNs) will play a pivotal role to assist and complement the terrestrial systems. However, one of the major challenges of the NTN channel is represented by the large delay which hampers the different communication phases, such as the Random Access (RA) procedure. In this paper, we provide an assessment of the system level performances, in terms of access delay and access success probability, of the Narrowband IoT (NB-IoT) devices in typical satellite scenarios defined by the 3GPP. In particular, we provide a detailed analysis under different network densities, for various combinations of the related configuration parameters, and for different system architectures supporting the NB-IoT over NTN. The analysis led to a useful comparison of the RA performances obtained with 3GPP compliant configurations for access parameters and satellite configuration with the aim to maximize the access success probability and minimize the access time in a NB-IoT NTN system.

Satellite Communications systems are a promising solution to extend and support terrestrial networks in un- or under-served areas. In Release 17, 3GPP initiated a Study Item for IoT over Non-Terrestrial Networks (NTN) to assess and adapt the NB-IoT air interface to the NTN characteristics. One of the main objective of the study is the evaluation of the Random Ac-cess procedure and the estimation of the up-link synchronization parameters at the satellite. In this context, it is essential that the detection algorithms of the NB-IoT preamble, at the receiver, satisfy the user detection requirements as well as the timing synchronization accuracy. This is not a trivial task, especially in satellite channels where the carrier frequency offset (CFO) is more severe than that of terrestrial links. In order to cope with this problem, we propose a new algorithm based on a non-decimated dyadic wavelet transform. This method is able to detect the incoming preambles and to estimate their time of arrival, without having to compensate the CFO first. The performance of the proposed algorithm is compared with a classical estimation approach based on the Fast Fourier Transform, substantiating the significant advantage obtained in the considered NTN scenarios.

Machine Type Communications (MTC) and Internet of Things (IoT) applications are growing exponentially and are forecast to play an even more important role in Future Networks and Systems. The Third Generation Partnership Project (3GPP) introduced the Narrowband IoT (NB-IoT) air interface as a response to the IoT use case requirements. However, it is widely accepted that the terrestrial network alone is not able to serve the requirement of the IoT market of a truly ubiquitous coverage. To this aim, several initiatives are currently addressing the inclusion of a satellite component into the telecommunication infrastructure to extend its coverage to those areas that are unserved or underserved by the terrestrial network. The recently approved 3GPP study item on NB-IoT over Non-Terrestrial Network (NTN) is the most important of these initiatives. The study item, starting at the beginning of 2021, will assess the performance of the NB-IoT air interface over satellite and will identify which adaptations are needed to enable its use. In this context, our work provides an assessment of the system level performance, in terms of the link budget parameters, of the NB-IoT air interface in typical satellite scenarios. In particular, we provide a detailed discussion of the system architecture supporting the NB-IoT over NTN, a description of the link budget computation methodology, and the numerical results of the link budget analysis in both single-satellite and multi-satellite scenarios.

During the last few years, the interest around Machine-Type Communications (MTC) and Internet of Things (IoT) is growing exponentially. The Third Generation Partnership Project (3GPP), acknowledging the importance of this trend, has introduced a number of key features to support IoT. Specifically they provided progressively improved support for Low Power Wide Area Network (LPWAN) introducing the so called Narrowband IoT (NB-IoT) in 2017 for better serving IoT use cases. Furthermore, the integration of Non Terrestrial Networks (NTN) in the New Radio (NR) is playing an important role, enabling many different use cases for the forthcoming 5G system. This work aims at analyzing the feasibility of integrating NB- IoT with satellite communication systems; the main issues are investigated with a particular focus on the impact of doppler shift on NB-IoT waveform. Possible solutions are proposed, empowering the utilization of the NB-IoT terrestrial standard within satellite channel.

Satellite Communication systems represent a solid solution to extend and complement terrestrial networks in un-/under-served areas. The recent standardisation endeavours within 3GPP led to the Non-Terrestrial Networks (NTN) study item for New Radio, aimed at deploying satellite systems either stand-alone or as integration to terrestrial networks in mobile broadband and machine-type communication scenarios. In this context, the main focus is currently related to: i) evaluating the system level performance; and ii) understanding the impact at link level of typical satellite channel impairments on the PHY/MAC procedures. In this paper, we focus on the former; in particular, we provide: i) a detailed discussion on the current system architecture and assumptions; ii) we thoroughly describe the methodology to perform link budget computations; and iii) we show the numerical results for GEO and LEO systems.

This special issue is devoted to Satellite Communication advances so as to gather the most important contributions in this field from academia and industry. In particular, the importance of this issue is also due to the fact that the last issue appearing on IEEE JSAC about SatCom is dated back to 2004 and therefore many important technology advances have been testified in the meantime, actually revolutionizing the satellite industry. In particular, important innovations have been brought to the design of both ground and space segments, spanning physical layers up to upper layers of the protocol stack.

This special issue is devoted to the satellite communications (SatCom) advances so as to gather the most important contributions in this field from academia and industry. In particular, the importance of this issue is also due to the fact that the last issue appearing on IEEE JSAC about SatCom is dated back to 2004 and therefore many important technology advances have been testified in the meantime, actually revolutionizing the satellite industry. In particular, important innovations have been brought to the design of both ground and space segments, spanning physical layers up to upper layers of the protocol stack.

In this paper, we propose two novel schemes to solve the problem of finding a quasi-optimal number of coded packets to multicast to a set of independent wireless receivers suffering different channel conditions. In particular, we propose two network channel virtualization schemes that allow for representing the set of intended receivers in a multicast group to be virtualized as one receiver. Such approach allows for a transmission scheme not only adapted to per-receiver channel variation over time, but to the network- virtualized channel representing all receivers in the multicast group. The first scheme capitalizes on a maximum erasure criterion introduced via the creation of a virtual worst per receiver per slot reference channel of the network. The second scheme capitalizes on a maximum completion time criterion by the use of the worst performing receiver channel as a virtual reference to the network. We apply such schemes to a GEO satellite scenario. We demonstrate the benefits of the proposed schemes comparing them to a per-receiver point-to-point adaptive strategy.

The standardization of 5G systems is entering in its critical phase, with 3GPP that will publish the PHY standard by June 2017. In order to meet the demanding 5G requirements both in terms of large throughput and global connectivity, Satellite Communications provide a valuable resource to extend and complement terrestrial networks. In this context, we consider a heterogeneous architecture in which a LEO mega-constellation satellite system provides backhaul connectivity to terrestrial 5G Relay Nodes, which create an on- ground 5G network. Since large delays and Doppler shifts related to satellite channels pose severe challenges to terrestrial-based systems, in this paper we assess their impact on the future 5G PHY and MAC layer procedures. In addition, solutions are proposed for Random Access, waveform numerology, and HARQ procedures.

To face the challenges of the new era of heterogeneous networks, mobile satellite systems need to provide an increased level of flexibility. As a consequence, a more effective use of the available resources and the exploitation of interference mitigation techniques are considered necessary to tackle the issue. The limits of a traditional configuration are even more noticeable in specific areas of high traffic requests i.e., in hot spots. In this paper, focusing on the forward link of a typical mobile interactive satellite system operating in L-band, where a large imbalance in traffic demand between the multiple beams is common, new configurations that aim at improving the performance of the system are studied. The proposed approach, based on a higher frequency reuse factor and the application of precoding techniques, boosts the system in terms of total capacity and provides higher flexibility, without making any change whatsoever to the space segment. A general analytic formulation of the problem and a pragmatic solution are provided for hot spot scenarios. Simulations are carried out to validate the proposed solution.

Small cells will play an important role in the fifth generation mobile networks. As recent works pointed out, a significant improvement in energy efficiency can be obtained if small base stations (SBSs) are provided with storage capabilities. In this paper, we study the problem of caching optimization in the presence of interference with and without cooperation between the SBSs. We consider a setup in which two SBSs and one macro base station (MBS) are connected through a wireless backhaul link. Cooperation is applied following the Han-Kobayashi rate splitting approach and its variation including common information. Our results show that applying cooperation to caching systems yields significant gains in terms of power and provide indications on how much interference can be tolerated which, in turn, has impact on the network design both in terms of frequency reuse planning and SBS deployment.

The need for increased data rates has led towards the development of advanced broadband satellite systems able to achieve higher capacity for providing Internet and backbone services in remote areas. Aside of the more conventional geostationary orbit (GEO), Medium Earth Orbit (MEO) satellite constellations are envisaged due to their advantages in terms of shorter link path and low latency; MEO satellite constellations are currently operating at Ka-band and are already showing signs of spectrum saturation in high demand areas in their coverage. In search of additional spectrum, in this paper, we employ the Q-band by investigating the performance of a multi-satellite MEO constellation network in terms of system capacity considering sophisticated propagation and physical layer tools. In particular, within the proposed Q-band solution, a higher throughput can be achieved with respect to a corresponding Ka-band system, by reaching up to 100% gain in terms of system capacity in a clear sky conditions.

Wireless communication systems are predicted to appear massively in the future human life. In case of 5G communications, high expectations in terms of Quality of Service and reliability are foreseen. However, the development of future systems has to cope with a better exploitation of the available resources. As a matter of fact, system coexistence and frequency sharing are two of the most promising approaches to achieve spectrum efficiency. Cognitive Radio (CR) is a key enabler of these approaches, which are also arising in Satellite Communications (SatComs). In this paper, a carrier allocation based scheduling algorithm inspired by genetic algorithms (GA) is proposed by taking into account different environment conditions and service requirements of the users of the cognitive satellite system.

The increasing request of communication capacity for the introduction of modern multimedia services has collided with the problem of the spectrum shortage. One of the most known approach is represented by cognitive radios, which are supposed to exploit already deployed frequency bands in use by an incumbent system. Among other cognitive radio features, detection and estimation of the incumbent user are essential for implementing the cognitive radio system avoiding any interference. This is particularly important in SatCom cognitive scenarios due to transmission power impairments. In this paper, we focus on a joint interference and noise estimation algorithm aiming at detecting and estimating incumbent interference, for allowing the coexistence of the two systems. The behavior of the algorithm is analytically derived, and numerical results obtained through computer simulations confirm the effectiveness of the proposed approach.

The increasing request of bandwidth for multimedia advanced services is one of the major issues of modern wireless systems. The spectrum shortage has been faced in several ways; among others the cognitive radio approach, aiming to exploit the unused spectrum resources already assigned to incumbent users, is maybe the most known. However, even if its application has been extensively proposed for wireless terrestrial communications, it remains a still unexplored area concerning Satellite Communications. The aim of this paper is to propose an Energy Detector based Radio Environment Mapping for the spectrum awareness functionality of a hybrid terrestrial/satellite scenario where the satellite components aim at exploiting the resources unused by terrestrial communications. The proposed approach allows to take advantage of cooperation between multiple sensing nodes evaluating spatial detection and false alarm probabilities besides their relationship with device detection and false alarm probabilities.

The modern approach in wireless multimedia communications is toward the adaptation of transmission parameters subject to internal and external requirements and constraints, represented by, e.g., the user QoS, the propagation environment, the traffic behavior, the external interferences. One of the most challenging issues that arises during the parameters adaptation is the temporal behavior due to the continuous change of the external context; in that sense it is important to focus the attention on the timing constraints that impact on the system capability of adapting the transmission parameters in a reliable way. The satellite communications (SatCom) are especially affected by the delay problems, due to the high propagation Round Trip Time (RTT). Herein we analyze the temporal behavior of the Land Mobile Satellite (LMS) environment, aiming to define a reliability index for different operational speeds and scenarios.

In the last years we are seeing the increasing presence of multimedia applications together with a wide variety of terminals, from the PCs to the notebooks, from the smartphones to the tablets. In order to exploit such advanced services, ubiquitous and broadband connections are required. While urban or suburban areas can be covered by using terrestrial wireless broadband networks, there are several rural or low populated areas with narrowband access. To this aim, satellite community has developed in the last years two communications standards specifically suited for mobile communications, i.e., DVB-SH and DVB-RCS NG. Among others they consider adaptive waveforms techniques for increasing the system reliability and throughput aiming to exploit the variable channel behavior. Adaptive coding and modulation (ACM) belongs to this family of algorithms, by adapting the modulation and coding scheme based on the channel behavior. In this paper we focus on a state adaptive algorithm suited for mobile applications.

This paper presents a new phase-alignment algorithm for distributed beamforming [1].1This scheme is more energy-efficient than existing solutions, since it requires each node to transmit only once, but it converges at least as fast as all other previously proposed algorithms. In contrast with all other studies of distributed beamforming, where noise had been neglected, here it is explicitly included in the signal model and shown to have a considerable impact on synchronization that cannot be ignored. With and without noise, analytical expressions that characterize the performance of the new algorithm are provided, with emphasis on various limiting regimes of interest.

In the last years the increasing presence of multimedia applications and devices is even requiring higher throughput links with a higher availability. In order to exploit such advanced services, ubiquitous and broadband connections are required. Even if much of populated areas are nowadays covered by terrestrial wireless broadband networks, there is an increasing request of satellite communications able to cover low density populated areas and to fill the coverage gaps. In the last years two novel communication standards specifically suited for mobile satellite communications, i.e., DVB-SH and DVB-RCS NG, have been introduced. Among others, they consider adaptive waveforms techniques for increasing the system reliability and throughput aiming to exploit the variable channel behavior. Adaptive coding and modulation (ACM) belongs to this family of algorithms, by adapting the modulation and coding scheme based on the channel behavior. In this paper we focus on a state adaptive algorithm suited for mobile applications by considering the effect of the mobile speed.

This paper presents a new deterministic closed-loop phase-alignment algorithm based on quantized feedback from the receiver for distributed beamforming. In contrast with previously proposed methods, which entailed repeated transmissions from all the nodes in the network, this new algorithm requires each node to transmit only once during the synchronization cycle. This drastically reduces the amount of power consumed to achieve phase alignment, yet the new algorithm converges at least as fast as all other existing schemes. In contrast with previous analyses of distributed beamforming based on random phase updates, where noise had been disregarded, here it is explicitly included in the models and shown to have a considerable effect that cannot be ignored. With and without noise, analytical expressions that characterize the performance of the new algorithm are provided, with emphasis on various limiting regimes of interest.

This paper presents an assessment of several interference cancellation and gateway cooperation strategies for the return link of a multi-gateway multi-beam broadband satellite system. The aim of the work is to provide theoretical upper bounds to the achievable average per user spectral efficiency and maximum system throughput under different coverage schemes and frequency reuse patterns, considering actual system parameters and antenna design. The trade-off between spectral efficiency and system complexity is also addressed focusing on the amount of information that has to be exchanged amongst different gateways during the iterations of the interference cancellation algorithm.

This papers addresses the design of new energy-efficient Continuous Phase Modulation (CPM) waveforms suitable for being adopted in satellite mesh networks that are characterized by the absence of the Hub, and by small antennas and power amplifiers with moderate to low output saturated power at the user terminal. In particular, a CPM modulation format concatenated with a proper convolutional code for low spectral efficiency values has been selected to implement an efficient waveform for power-limited scenarios. Performance results show the gain obtained with respect to the DVB-RCS2 CPM waveforms at higher spectral efficiency also when transmission techniques, such as Burst Repetition, are considered, and confirm the suitability of the new designed CPM waveforms for satellite hub-less scenarios.

This paper addresses detailed waveform trade-offs for mesh satellite networks. The waveform analysis is carried out considering spectral efficiency, resilience against non linear distortion, channel impairments and interference for both linear and continuous phase modulation schemes defined in the DVB-RCS2 standard.

Coarse beamforming is a space processing scheme which allows for efficient use of the available spectral resources on the feeder link of a multi-beam broadband satellite system. In this framework, spectral occupancy of the multiplexed antenna signals that must be exchanged between the satellite and the gateway is a critical issue, up to the point that a costly multiple gateway infrastructure could be required to restrain bandwidth usage. Alternatively, a hybrid on board/on ground processing architecture is desirable, where the effect of space processing allows to project feed signals on a subspace, thus reducing the required feeder link bandwidth. This foresees a fixed processing scheme on board the satellite, which we refer to as Coarse Beamforming, yielding an overall system which relies on reasonable payload complexity, together with on ground processing flexibility. We explore two Coarse Beamforming techniques for the return link of a multi beam satellite system, and we evaluate the effect of compression in terms of reconstructed signal degradation. We show how, without significant distortion, bandwidth occupancy can be considerably reduced.

In the “Internet of Things” (IoT) vision the physical world blends with virtual one, while machine-to-machine interaction improve our daily life. Clearly, how these virtual objects are exposed to us is critical, so that their user interface must be designed to support the easiness of usage that is driven by the users' needs, which is different from what machines requires. These two requirements must be solved, and an integrated solution should emerge, if we want to bring the IoT to the 50 billions network that is predicted to became in the next years. We believe that these requirements cannot be met by the same communication protocol, and so we propose a new kind of broker, named QEST that can bridge the two worlds, represented by their state-of-the-art protocols: MQTT and REST. In this paper, we demonstrate that our approach allows rapid development of user-facing IoT systems, while grating machines all the performance they need.

In this paper, OFDM data-aided channel estimation based on the decimation of the Channel Impulse Response (CIR) through the selection of the Most Significant Samples (MSS) is addressed. Our aim is to approach the Minimum Mean Square Error (MMSE) channel estimation performance, while avoiding the need for a-priori knowledge of channel statistics (KCS). The optimal set of samples is defined in the instantaneous and average senses. We derive lower bounds on the estimation mean-square error (MSE) performance for any MSS selection strategy. We show how MSS-based channel estimation can approach these MSE lower bounds. We introduce novel MSS strategies oriented towards instantaneous decimation (Instantaneous Energy Selection - IES), and windowed decimation (Average Energy Selection - AES). We also consider decimation via Threshold Crossing Selection (TCS), which we characterize analytically, to derive the optimum threshold in the minimum MSE sense. We also propose a sub-optimal method for threshold setting that does not require KCS. Finally, we provide numerical results in terms of both MSE estimation performance and Bit Error Rate (BER) of a coded OFDM system using the proposed channel estimators, to show that they indeed approach MMSE performance.

We consider a windowed decoding scheme for LDPC convolutional codes that is based on the belief-propagation (BP) algorithm. We discuss the advantages of this decoding scheme and identify certain characteristics of LDPC convolutional code ensembles that exhibit good performance with the windowed decoder. We will consider the performance of these ensembles and codes over erasure channels with and without memory. We show that the structure of LDPC convolutional code ensembles is suitable to obtain performance close to the theoretical limits over the memoryless erasure channel, both for the BP decoder and windowed decoding. However, the same structure imposes limitations on the performance over erasure channels with memory.

Signal processing in satellite applications is usually performed either on-ground or on-board, i.e. at the gateway station or in the payload. Within the framework of the European Space Agency (ESA) SatNEx III study, a hybrid approach has been considered by splitting the processing between the satellite and the gateway, aiming to strike a better balance between performance and payload complexity. The design of a high-capacity multi-beam system has been carried out, to assess the potential applicability of a hybrid space-ground processing architecture (Digisat) for satellite broadband systems; this is achieved via hybrid space-ground beamforming, MIMO and MIMO-MUD, Precoding, as well as Digital Feeder link techniques.

In the satellite communications component of the future Internet, peer-to-peer mesh connectivity of satellite terminals is an impellent necessity. In particular, delay sensitive applications such as real-time multimedia, collaborative conferencing and cellular backhauling are appealing use-cases for adopting mesh network topologies. Moreover, the use of a single satellite hop for directly connecting remote terminals (as opposed to a double-hop connection required in star topologies) reduces the satellite traffic load and leads to savings in operational costs of the satellite network. In this paper, we propose a multi-beam satellite mesh network based on a semi-transparent or fully regenerative satellite with different on board switching capabilities. In particular, four network solutions have been assessed in terms of flexibility, complexity and capacity, trading-off between network performance and implementation cost.

This paper takes a broad view on the history and the present status of satellite communications and broadcasting. The necessary starting point of this overview is the visionary papers produced by Sir Arthur C. Clarke and John Pierce. This was the real dawn of the satellite communication era. This paper attempts to explain the “fil rouge” of the evolution of satellite technologies across six decades, analyzing successes and failures of past satellite missions, and concluding with a picture of future satellite communications.

The mobile satellite broadcasting arena is witnessing a constant increase in demand for improved transmission quality and higher number of services in order to remain on par with the corresponding terrestrial counterparts. A promising way forward in this regard is the migration from the conventional single polarization per beam to an advanced dual polarization per beam architecture for effective spectrum exploitation; this also enables the application of advanced multiple antenna (MIMO) techniques. The present paper moves from DVB-SH the current state-of-the-art for mobile satellite services towards a more advanced system architecture doubling the overall system capacity with a minimum power increase. It turns out that a multiplexing gain equal to two comes at a cost of about 6 dB for the conventional single polarization system, whereas for the advanced system the corresponding cost is about 3.5 dB.

In this paper we propose the usage of Single Carrier Frequency Division Multiple Access (SC-FDMA) in the Broadband Satellite Return Channel. Notably, SC-FDMA is able to improve the physical layer spectral efficiency with respect to single carrier systems, which has been used so far in the Return Channel Satellite (RCS) standards. However, it requires a strict synchronization and it is also sensitive to phase noise of local radio frequency oscillators. For this reason, we propose an effective pilot tone arrangement within the SC-FDMA frame, and a novel Joint Multi-User (JMU) estimation method for the SC-FDMA. As shown by numerical results, the proposed scheme manages to satisfy strict synchronization requirements and to guarantee a proper demodulation of the received signal.

This paper addresses the problem of robust frame synchronization for TDM/TDMA systems in the presence of frequency errors, accomplished through data-aided recognition of the Unique Word (UW) preamble in the transmission flow. Robust detection design is performed applying, through approximations, the Maximum Likelihood (ML) criterion coupled to Post Detection Integration (PDI), to obtain a novel detector identified as Balanced-GPDI (B-GPDI). This new approach considerably outperforms other schemes available in the literature, at the cost of a moderate complexity increase. This is possible thanks to an optimized use of coherent accumulation, which enhances the correlation term in the decision variable, along with highly accurate modeling of the energy correction factor. To limit complexity increase and memory requirements, several approximations of the exact B-GPDI are proposed and discussed in the paper, to provide the designer with practical solutions that are still able to outperform other approaches in specific application scenarios. In particular, approximations for low and high Signal-to-Noise Ratio (SNR) are presented. Different application scenarios are considered in the paper for numerical analysis. In particular, the cases of forward link Continuous Transmission (CTX) and return link Burst Transmission (BTX) are addressed.

This paper investigates the concept of single frequency satellite networks (SFSNs), whereby multiple satellite beams that have no form of mutual phase coherence are unified through baseband signal processing to achieve uniform coverage across wide areas. We present a realistic application scenario and its link budget analysis, which allows to highlight the advantages with respect to a classic single beam approach. Our technique is based on the use of orthogonal frequency division multiplexing and on the creation of synthetic multipath at the gateway, realizing a form of delay diversity. The synthetic power delay profile is beam specific, and it is the key instrument that allows to avoid destructive interference amongst the signals transmitted from the multiple beams. The main benefit is that homogeneous coverage is guaranteed with a generic multi-beam antenna, that can be easily reconfigured according to traffic and service needs.

Providing low-latency high-quality data services to mobile terminals has become a mandatory requirement for all mobile broadband standards. Therefore, effective countermeasures against mobile channel impairments, like small- and largescale fading, are of the utmost importance whenever traditional physical layer channel codes do not provide sufficient resilience or request too much hardware resources. Among the possible countermeasures, the paper investigates the application of packet layer coding, which basically consists in applying forward error control techniques at upper layer (UL-FEC). In the paper the UL-FEC decoder performance analytical model already developed by authors is generalized and extended to include nonperiodic shadowing and small-scale fading. Analytical results are then validated through numerical simulation considering a real application scenario.

Some recently proposed robust methods for time domain timing and frequency synchronization in OFDM systems incorporate the use of cross-correlation based threshold detection in their timing adjustment and joint time-frequency algorithms. In this paper, we analyze the threshold criterion used and derive its theoretical performance. This translates into a better characterization of these OFDM synchronization algorithms, leading to a closer match between design expectations and practical performance. Computer simulations show a strong agreement between theoretical predictions and numerical results.

In this paper, we address the problem of OFDM data-aided channel estimation based on the selection of the most significant samples (MSS) of the channel impulse response (CIR), i.e. those samples which contain most of the useful energy. We provide a novel and complete analytical characterization for MSS selection based on threshold crossing, which yields a closed form for the estimate mean-square error (MSE), that we use to derive analytically the optimum threshold in the minimum MSE sense. The optimum threshold value is matched to the specific channel power profile, but this information is hardly available to the receiver. For these reason, we also propose a suboptimal method for threshold setting that does not require any knowledge of channel statistics. We show that the performance of this sub-optimal method is very close to the optimum case, as well as to Wiener channel estimation in the case of sparse multipath channels. Our proposed method outperforms previous approaches based on heuristically set thresholds.

A novel approach is introduced for the design of a unique word (UW) for frame synchronization in time division multiplexing/time division multiple access (TDM/TDMA) systems. In particular, the UW symbols are distributed in each frame in a specific pattern in order to optimize the UW autocorrelation properties. The distribution patterns are scalable, since they preserve their autocorrelation properties under truncation. The resulting frame structure enables the use of several types of UWs, including the silent-UW (SUW) and the unit-UW (UUW), that are novel approaches for which the optimal Bayes detector is derived. An analytical performance characterization is presented along with comparisons with state-of-the-art alternatives. We show that SUW can significantly outperform the classic UW in the presence of frequency offsets or whenever data interference is the main impairment to cope with, i.e. at moderate to high signal to noise ratios. Interestingly, this performance improvement comes with the further advantage of a considerable complexity reduction. Hence UUW is shown to provide both performance improvement and complexity reduction.

This paper tackles the problem of time synchronization for the mobile extension of DVB-S2/RCS air interfaces. To increase robustness against other system interference, Direct Sequence Spread Spectrum (DS-SS) is selected, which calls for efficient code acquisition. Designed to operate jointly with frame synchronization, a novel high level control logic is proposed for code acquisition, along with robust detectors to cope with the large frequency uncertainty experienced at terminal start-up. The results show that the mean acquisition time is always limited to a few milliseconds, allowing fast acquisition even in the most challenging railway scenario.

The paper investigates coding and encapsulation techniques for the possible extension of the digital video broadcasting-return channel satellite (DVB-RCS) to ensure a global coverage for mobile terminals. specifically, link layer- forward error correction (LL-FEC) appears to be a reliable solution, allowing to improve the C/N performance and to counteract the Doppler effect typical of mobile channels, avoiding scalability and latency issues of Automatic Repeat reQuest (ARQ) approaches. In the paper we evaluate LL-FEC performance when applied to the railway environment. It is shown how this scenario deeply affects the LL-FEC code performance both in the multi protocol encapsulation (MPE), and the generic stream encapsulation (GSE) cases. In order to counteract this performance reduction two different approaches are considered. In the first case, we increase the number of rows of the LL-FEC Reed Solomon (RS) matrix. In the second case we exploit the sliding encoding mechanism. We also introduce a modified version of GSE that shows reduced overhead and improved performance. Results show that DVB-RCS can greatly benefit from LL-FEC RS coding in reducing residual errors that cannot be counteracted at the physical layer for efficiency reasons.

The growing market of Mobile TV requires automated adaptation of standard TV footage to small size displays. Especially extreme long shots (XLS) depicting distant objects can spoil the user experience, e.g. in soccer content. Automated zooming schemes can improve the visual experience if the resulting footage meets user expectations in terms of the visual detail and quality but does not omit valuable context information. Current zooming schemes are ignorant of beneficial zoom ranges for a given target size when applied to standard definition TV footage. In two experiments 84 participants were able to switch between original and zoom enhanced soccer footage at three sizes - from 320x240 (QVGA) down to 176x144 (QCIF). Eye tracking and subjective ratings showed that zoom factors between 1.14 and 1.33 were preferred for all sizes. Interviews revealed that a zoom factor of 1.6 was too high for QVGA content due to low perceived video quality, but beneficial for QCIF size. The optimal zoom depended on the target display size. We include a function to compute the optimal zoom for XLS depending on the target device size. It can be applied in automatic content adaptation schemes and should stimulate further research on the requirements of different shot types in video coding.

The authors deal with the sum–product algorithm (SPA) based on the hyperbolic tangent (tanh) rule when it is applied for decoding low-density parity-check (LDPC) codes. Motivated by the finding that, because of the large number of multiplications required by the algorithm, an overflow in the decoder may occur, two novel modifications of the tanh function (and its inverse) are proposed. By means of computer simulations, both methods are evaluated using random-based LDPC codes with binary phase shift keying (BPSK) signals transmitted over the additive white Gaussian noise (AWGN) channel. It is shown that the proposed modifications improve the bit error rate (BER) performance up to 1 dB with respect to the conventional SPA. These results have also shown that the error floor is removed at BER lower than 10−6. Furthermore, two novel approximations are presented to reduce the computational complexity of the tanh function (and its inverse), based on either a piecewise linear function or a quantisation table. It is shown that the proposed approximations can slightly improve the BER performance (up to 0.13 dB) in the former case, whereas small BER performance degradation is observed (<0.25 dB) in the latter case. In both cases, however, the decoding complexity is reduced significantly.

In all short-medium term business/market forecasts, the efficient provision of digital multimedia broadcasting (DMB) services in mobile systems appears to be of key importance for mobile operators and broadcasters. Several DMB systems are being developed around the world, with several proposed competing standards. In this framework, the DVB (digital video broadcasting) forum is working to define a new air interface, identified as DVB-SSP, to deliver satellite services to portable devices, and several possibilities are being considered as viable options, including the use of DVB-H (handheld). A critical factor to be considered is the resilience to non linear distortion effects. In fact, DVB-H signals are obtained through an OFDM modulation, which traditionally was considered unfit for satellite communications. Recently (S. Cioni et al., 2005), it has been proved that the adoption of strong channel coding techniques in conjunction with the use of non-linear distortion compensation techniques can lead to good OFDM performance even when operating close to amplifier saturation. Following this avenue, this paper investigates the adaptation of the DVB-H physical layer to the satellite environment, and validates the improved robustness of the proposed scheme to non linear distortion

A novel approach is introduced here for the design of the unique word (UW) to be inserted into TDM/TDMA systems for frame synchronization purposes. In particular, the UW is a very simple sequence of ones that are distributed along the frame in order to improve autocorrelation properties. The resulting UW is identified as unit-UW (U-UW). We show in this paper that U-UW leads to an optimum detector with very limited complexity, which does not require any multiplication. A fully analytical performance characterization is also presented and validated through numerical simulations

The paper considers the comparison of orthogonal frequency division multiplexing (OFDM) and high speed downlink packet access (HSDPA) techniques in the physical layer of a satellite system devoted to the provision of digital multimedia broadcasting (DMB) services. In particular, the paper demonstrates that the inherently high spectrum efficiency of OFDM can be retained even in unfavorable propagation channels affected by heavy non-linear and linear distortion, respectively introduced by the on-board high power amplifier and by frequency selective propagation. This encouraging performance, achieved through the proper design and application of coding and pre-distortion techniques, is compared with the standardized HSDPA radio interface for 3G terrestrial mobile networks, and is shown to be in line on non-selective channels. Advantages for OFDM are demonstrated in frequency selective channels, using low complexity equalization in the frequency domain

A novel approach is introduced for the design of the unique word (UW) to be inserted into TDM/TDMA systems for frame synchronization purposes. In particular, the UW is composed by all zero symbols that are distributed along the frame in order to improve the autocorrelation properties. The resulting UW is identified as silent-UW (S-UW). We show in this paper that S-UW leads to an optimum detector with very limited complexity, and with performance that can be significantly better than the classic UW in the presence of frequency offsets or at moderate to high signal-to-noise ratios. A fully analytical performance characterization is presented reporting also comparisons with state-of-the-art alternatives.

This paper applies the theoretical framework for the evaluation of code acquisition in the presence of fading developed in the companion Part I paper. Code synchronization for code-division multiple-access (CDMA) cellular networks, such as IS-95 and cdma2000, is considered. A multidwell testing procedure is adopted. Notably, a procedure for the optimization of the multidwell parameters (number of dwells, dwell lengths, thresholds) to achieve minimum acquisition time is introduced and enforced. The effects of fading, interchip interference (ICI), frequency offset, multiple-access interference, and noise are taken into account in the determination of false alarm and detection probabilities. In particular, anomalous ICI despreading and internal interference-cancellation effects are described. Numerical and simulation results, in terms of time for correct acquisition, confirm the accuracy of the proposed approach and show how it can be effectively used in the design and evaluation of a code-acquisition subsystem.

This paper deals with the analysis of the code-acquisition process performed by a mobile terminal in a code-division multiple-access cellular system. The fundamental contribution is the setting of a theoretical framework for code-acquisition analysis, accounting for the presence of fading and shadowing with specified coherence time. A multidwell architecture is considered, accounting for different verification strategies. The MAX/TC detection criterion is used, and the acquisition performance is analyzed, following both the direct and flow-graph approaches. Expressions for the acquisition time probability density function under different assumptions are given, as well as closed-form expressions for the mean and variance of the acquisition time. Practical applications and numerical results are reported in the Part II companion paper.

In this paper we address the study of systems implementing unequal error protection (UEP) by means of the multi level coding (MLC) technique, taking into account the impact of asymmetric constellations and the effect of puncturing. UEP can lead to significant improvements when applied to multimedia broadcast and multicast services (MBMSs), which should represent an important share of the consumer market in the next years. Theoretical considerations and performance assessment of an MLC system implemented by means of turbo codes are undertaken, considering several modulation options.

In recent years large scientific interest has been devoted to joint data decoding and parameter estimation techniques. In this paper, iterative turbo decoding joint to channel frequency and phase estimation is proposed. The phase and frequency estimator is embedded into the structure of the turbo decoder itself, taking into consideration both turbo interleaving and puncturing. Results show that the proposed technique outperforms conventional approaches both in terms of detection capabilities and implementation complexity.

W-CDMA and SW-CDMA (satellite W-CDMA) air interfaces require that a user equipment in a given cell acquires slot and frame synchronization, and identifies the primary scrambling code used by the target cell before starting communications. This synchronization procedure is identified as cell search procedure in W-CDMA and beam search procedure in SW-CDMA. Notwithstanding the extensive commonalities between the two air interfaces, the two procedures are actually different. The paper aims at the evaluation of the false acquisition probability achievable by the two procedures in a scenario in which the receiver may experience both satellite and terrestrial radio propagation conditions. This is a sensible evaluation scenario since, in the delivery of multicast-broadcast multimedia services, the satellite UMTS network represents an efficient complement to terrestrial UMTS, since its coverage is extended to indoor and urban areas through, for example, the use of terrestrial intermediate repeaters. Rayleigh fading, Rice fading, and vehicular multipath propagation channels are used for the performance assessment.

In the paper, the preamble structure of IMT-2000 SW-CDMA air radio interface is considered in the evaluation of the performance of different post detection integration techniques for code acquisition in the return link of a satellite W-CDMA system. In particular, non-coherent post detection integration (NCPDI) and two different options of differential post detection integration (DPDI) techniques, namely DPDI-abs and DPDI-real, are investigated in terms of missed detection and false alarm probabilities. AWGN and Rician channels are considered in the presence of a frequency error. Both analytical and simulation results are provided.

In unknown channels, nonadaptive maximum likelihood sequence detection (NA-MLSD) is far from optimum in the presence of channel-induced uncertainty. To counteract this uncertainty, conventional solutions augment MLSD with external channel estimators. However, for very low SNR values this estimation procedure becomes marginal and the conventional adaptive MLSD (CA-MLSD) approaches perform poorly. We consider joint data decoding and parameter estimation techniques, and in particular per survivor processing (PSP) techniques, as a potentially effective solutions to this problem, at the expense of increased complexity. The performance/complexity tradeoff is addressed for a convolutionally encoded Q-PSK return link of an SHF/EHF satellite system for multimedia services impaired by phase noise and frequency offsets. By contrasting NA-MLSD, CA-MLSD, and PSP, ranges are provided for channel conditions where the tradeoff favors a particular technique. Further, CA-MLSD and PSP are also contrasted in terms of scalar/ vector estimation performance.

Subband perceptual audio coding aims at providing the best subjective quality by decomposing the input signal into adjacent subbands. Every frequency component is then separately coded with a different number of bits in order to properly shape the quantization noise density power spectrum. In this letter, an optimum bit allocation algorithm is presented. As well as being applicable to either uniform or nonuniform frequency decompositions, it allows us to take into account the nonideal selectivity of the reconstruction filters. The effects of leakage for both short and long FIR filters have been investigated referring to a wavelet packet subband decomposition.

The application of per-suvivor processing (PSP) to digital satellite communications at Ka-band and beyond is considered. The PSP approach is used in a convolutionally encoded M-PSK transmission scheme to effectively counteract the degradations caused by phase noise and frequency offsets. Second order tracking loops are considered for per-survivor parameter estimation. A comparison is carried out between conventional adaptive maximum likelihood sequence detection (CA-MLSD) and PSP schemes both in terms of detection and estimation performance. Emphasis is placed on the analysis of the estimation quality one of the most unexplored research areas in the field of PSP-based systems. To this aim, novel definitions for a decision-related tracker and virtual tracker are introduced and their performance analyzed. Monte-Carlo simulations are provided to show the improvement in both estimation and detection quality brought about by PSP with respect to CA-MLSD.

Many future mobile communication networks will include some form of code division multiple access in their radio interface. All such systems must guarantee efficient initial code acquisition at the mobile terminal, both for call start-up and for soft-handoff handling. To this end, a spread pilot tone is generally adopted. In this paper we compare two approaches for pilot design, namely the conventional continuous pilot (CP) and a burst pilot (BP) with fractional duty cycle. We trade-off the two solutions based on acquisition error probability P/sub e/, signal-to-noise ratio (SNR), dwell time T/sub d/, and impact at system level. The main result is that for equal P/sub e/ and T/sub d/ the BP solution yields a considerable gain in requested SNR. However, CP can be forced to achieve the same P/sub e/ objective with the same SNR by allowing a longer T/sub d/, and its impact at system level is considerably milder.