1,721,219 research outputs found
Feeder Link Precoding for Future Broadcasting Services: Architecture and Performance
Full text link5G systems are becoming a reality and the evolution towards Beyond 5G (B5G) and 6G systems is already being defined, also to cope with the ever increasing capacity demanded by on-ground users. This will pose challenging requirements on the feeder link of future satellite systems, which risks to become a bottleneck for the overall system performance. In this paper, we propose a novel architecture of linear precoding for the feeder link of a broadcast satellite system operating with full frequency reuse to significantly enhance the achievable capacity. The architecture has been simulated and tested in a challenging multi-frequency scenario, where Ku, Ka, Q/V, and W band have been considered for transmission. The numerical performance analysis and the open issues related to the practical realisation of the proposed architecture are also thoroughly discussed
Measuring Service Continuity in Integrated TN/NTN for 5G-Advanced and 6G
No full textService continuity has been defined in 3GPP TS 22.261 as the " uninterrupted user experience of a service that is using an active communication when a UE undergoes an access change without, as far as possible, the user noticing the change". Such definition remains open, is not associated with KPIs and thus, cannot be used to compare the many architecture and business options that can be envisaged to deploy and operate 3D networks. In this paper, we propose a generic three-phased approach, with KPIs, to quantify the seamless performance of TN / NTN switching. We also discuss the purpose, applicability and order of magnitude of each KPI, based on concrete examples
Federated Cell-Free MIMO in Non-Terrestrial Networks: Architectures and Performance
Full text linkWhile 5G networks are being rolled out, the definition of 5G-Advanced features and the identification of disruptive technologies for 6 G systems are being addressed by the scientific and academic communities to tackle the challenges that 2030 communication systems will face, such as terabit-capacity and always-on networks. In this framework, it is globally recognised that Non-Terrestrial Networks (NTN) will play a fundamental role in support to a fully connected world, in which physical, human, and digital domains will converge. Notably, one of the main challenges that NTN have to address is the provision of the high throughput requested by the new ecosystem. In this paper, we focus on Cell-Free massive Multiple Input Multiple Output (CF-MIMO) algorithms for NTN. In particular: i) we discuss the architecture design supporting centralised and federated CF-MIMO in NTN, with the latter implementing distributed MIMO algorithms from multiple satellites in the same formation (swarm); ii) we design a location-based CF-MIMO algorithm, which does not require Channel State Information (CSI) at the transmitter; and iii) we design normalisation approaches for federated CF-MIMO in NTN, to cope with the constraints on non-colocated radiating elements. The numerical results substantiate the good performance of the proposed algorithm, also in the presence of non-ideal information
Clustering strategies for multicast precoding in multibeam satellite systems
Full text linkNext generation multibeam SatCom architectures will heavily exploit full frequency reuse schemes along with interference management techniques, eg, precoding or multiuser detection, to drastically increase the system throughput. In this framework, we address the problem of the user selection for multicast precoding by formulating it as a clustering problem. By introducing a novel mathematical framework, we design fixed/variable size clustering algorithms that group users into simultaneously precoded and served clusters while maximising the system throughput. Numerical simulations are used to validate the proposed algorithms and to identify the main system-level trade-offs
Geographical Scheduling for Multicast Precoding in Multi-Beam Satellite Systems
No full textCurrent State-of-The-Art High Throughput Satellite systems provide wide-Area connectivity through multi-beam architectures. Due to the tremendous system throughput requirements that next generation Satellite Communications (SatCom) expect to achieve, traditional 4-colour frequency reuse schemes are not sufficient anymore and more aggressive solutions as full frequency reuse are being considered for multi-beam SatCom. These approaches require advanced interference management techniques to cope with the significantly increased inter-beam interference both at the transmitter, e.g., precoding, and at the receiver, e.g., Multi User Detection (MUD). With respect to the former, several peculiar challenges arise when designed for SatCom systems. In particular, multiple users are multiplexed in the same transmission radio frame, thus imposing to consider multiple channel matrices when computing the precoding coefficients. In previous works, the main focus has been on the users' clustering and precoding design. However, even though achieving significant throughput gains, no analysis has been performed on the impact of the system scheduling algorithm on multicast precoding, which is typically assumed random. In this paper, we focus on this aspect by showing that, although the overall system performance is improved, a random scheduler does not properly tackle specific scenarios in which the precoding algorithm can poorly perform. Based on these considerations, we design a Geographical Scheduling Algorithm (GSA) aimed at improving the precoding performance in these critical scenarios and, consequently, the performance at system level as well. Through extensive numerical simulations, we show that the proposed GSA provides a significant performance improvement with respect to the legacy random scheduling
DS-CDMA Code Acquisition in the Presence of Correlated Fading Part I: Theoretical Aspects
No full textThis 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 multi dwell 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 flowgraph 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 PartII companion paper
DS-CDMA Code Acquisition in the Presence of Correlated Fading Part II: Application to Cellular Networks
No full textThis 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 multi dwell testing procedure is adopted. Notably, a procedure for the optimization of the multi dwell 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
Neural Network based Non Orthogonal Random Access for 6G NTN-IoT
No full textInternet of Things (IoT) devices have become increasingly more pervasive and distributed. To provide connectivity to the massive amount of IoT devices and to satisfy the need of an ubiquitous and resilient coverage, Non-Terrestrial Network (NTN) will be pivotal to assist and complement terrestrial systems. In particular, due to the fact that IoT communication is mainly characterized by sporadic uplink data reports, non-continuous satellite coverage, provided by cost efficient incomplete LEO constellations, is a baseline approach for most of the foreseen IoT-NTN architectures. In such configurations, all the terminals within a satellite beam must be served during the short satellite visibility window, thus generating congestion because of IoT devices simultaneously trying to access the same resources. When the number of colliding terminals increases, the number of successful access decreases, and the average time to complete the access increases. A possible countermeasure to this problem is represented by Non-Orthogonal Multiple Access scheme, which requires the knowledge of the number of users transmitting on the same resources. In this paper, we address this problem by proposing a Neural Network (NN) algorithm to cope with the uncoordinated random access performed by a massive number of Narrowband-IoT devices. Our proposed method classifies the number of colliding users and for each of them estimates the Time of Arrival (ToA). The performance assessment, under Line of Sight (LoS) and Non LoS conditions in sub-urban environments with two different satellite configurations, shows significant benefits of the proposed NN algorithm with respect to traditional methods for the ToA estimation
NB-IoT over Non-Terrestrial Networks: Link Budget Analysis
No full textMachine 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
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