Beam Hopping Research Articles

Environment-Aware Coverage Optimization for Space-Ground Integrated Maritime Communications

To satisfy the growing demand for broadband maritime communications, space-ground integrated maritime communication networks (MCNs) arise, which are envisioned to take full advantage of both satellites and terrestrial shore-based networks. In practice, due to the frequent beam hopping of satellites and the limited number of geographically available onshore base-station sites, the space-ground integrated MCN usually presents a highly non-cellular network structure, leading to both challenging blind zones and coverage areas with severe interference. In this paper, we optimize the coverage performance by exploiting the marine environment information. Particularly, the transmit antenna correlation is estimated using the location and mobility information of scatterers on the sea, such as lighthouses, reefs, islands, and vessels. The position and attitude information of satellites are also utilized for interference estimation. Based on that, we optimize the input covariance and precoding matrix to maximize the ergodic sum capacity for all mobile terminals within the coverage. It is a complicated non-convex problem, especially because the ergodic sum capacity is difficult to be expressed straightly without the expectation operator. We introduce an upper bound of the ergodic sum capacity using the path loss and the transmit antenna correlation estimated from the environment information, and then propose an iterative algorithm to solve the problem by solving a set of convex subproblems. The proposed environment-aware scheme is evaluated using the real-world geographic information of a coastal area of China. Simulation results demonstrate that the proposed scheme can greatly improve the ergodic sum capacity and the energy efficiency compared with existing approaches, and achieve dynamic coverage to match the non-cellular network structure.

Deep reinforcement learning‐based beam Hopping algorithm in multibeam satellite systems

Beam hopping (BH) is the key technology to improve the system throughput and decrease the transmission delay in multibeam satellite systems. The objective of this study is to find a policy to maximise the expected long-term resource utilisation. The BH illumination plan (BHIP) optimisation problem aimed at minimising the transmission delay is formulated and modelled as a partially observable Markov decision process. To tackle the issue of unknown dynamics and prohibitive computation, an artificial intelligence method named deep reinforcement learning (DRL) is first proposed to solve the BHIP problem in multibeam satellite systems. The proposed DRL-BHIP algorithm considers a series of realistic conditions, including the traffic demands in spatial distribution and temporal variation, ModCod constraints, antenna radiation pattern and inter-beam interference. The state reformulation concept is adopted to characterise the traffic spatial and temporal features. Simulation results show that the proposed DRL-BHIP algorithm can decrease the transmission delay and improve the system throughput compared with existing algorithms.

Resource Allocation for Cognitive Satellite Communications Downlink

Cognitive satellite communications (SatCom) is considered to be able to alleviate the bottleneck of spectrum resource shortage due to traditional spectrum allocation. This paper focuses on a special scenario where the frequency band of SatCom is recommended by the terrestrial terminal according to its spectrum sensing results. Further speaking, frequency bands preferred by terminals in each coverage beam of the satellite may be random, which on the whole forms diverse recommended channels problem that poses a great challenge to traditional multi-beam satellites. To make reasonable use of available resources in this scenario, this paper targetedly proposes a beam hopping (BH) scheme, which is capable of providing services on each frequency band. Based on the BH scheme, two 4-D [i.e., time, frequency, power, and dedicated spot (DS) beam] resource allocation (RA) schemes are presented, which adopt maximizing throughput (MT) and minimizing demand-supply variance (MDSV) as objectives, respectively, corresponding to the fact that satellite resources may be relatively rich or scarce. Both of the RA problems belong to mixed-integer nonlinear programming. By decomposing them, three levels of problems, namely, frequency band selection (FBS) problem, dedicated beam allocation (DBA) problem, and time-power allocation (TPA) problem are successively formed. For the FBS and DBA problems, we correspondingly propose heuristic algorithms to quickly distribute frequency bands and dedicated beams. Whereas for the TPA problem, Lagrangian dual algorithm and water-filling-assisted Lagrangian dual algorithm are respectively adopted to solve the convex problem for MT and the nonconvex problem for MDSV. Taking also spectrum sensing errors into account, numerical simulations show that the proposed schemes and algorithms perform well, and a significant gain can be achieved in cognitive SatCom.

QoS-equilibrium slot allocation for beam hopping in broadband satellite communication systems

In broadband satellite communication systems, beam hopping (BH) is more and more welcome to compensate the low-power-efficiency wide beam and the low-spectrum-efficiency multiple spot beams simultaneously. As a flexible coverage method, BH demands efficient hopping strategy to reach the desired quality of service (QoS). In this paper, we consider the QoS equilibrium, in particular the delay fairness, among different cells illuminated by one hopping beam through designing the hopping strategy on the condition of capacity satisfaction. Due to the physical limitation that hopping speed is much slower than packet arrival speed, the ideal first-come-first-serve packet scheduling is not realizable, which compels us to pursuit the optimal slot scheduling instead. In this paper, we consider a long-term delay fairness problem by per-period slot allocation for BH, using instantaneous and statistical information. To deal with the complex stochastic programming problem, we introduce the time-sharing principle to uncouple the variables and adopt stochastic gradient theory to deduce the suboptimal close-form solution. Our contributions are in three folds: firstly, it is the first time to consider the delay fairness not the traditional capacity fairness for BH; secondly, a general per-period decision scheme is proposed for the unique slot allocation in the perspective of queuing; thirdly, a suboptimal close-form solution for the per-period slot allocation is obtained, which could also cope with burst traffic cases. In simulation, we verify our method's advantage in terms of delay fairness comparing with the existing similar works.

Multi-Beam Reflector Antenna System Combining Beam Hopping and Size Reduction of Effectively Used Spots

This paper describes a concept combining beam hopping and size reduction of effectively used spots that can be implemented on multiple-beam antennas to improve their performance, namely the carrier-to-interference ratio, the minimum directivity, and the roll-off. The expected impact on antenna RF performance is demonstrated based on simplified models. A more-realistic focal-array-fed reflector antenna is also presented, based on a cell-reuse scheme of 12 reduced to four (one-third of the coverage receiving all the available bandwidth according to a cell-reuse scheme of four at a given instant), with performance in line with the simplified model. This specific design enabled improving the antenna's performance without drastically increasing its complexity: the minimum directivity and C/I were respectively 1.67 dB and 3.65 dB higher when compared to a standard antenna implementation with a cell-reuse scheme of four.

Multibeam satellite frequency/time duality study and capacity optimization

In this paper, we investigate two new candidate transmission schemes, non-orthogonal frequency reuse (NOFR) and beam- hopping (BH). They operate in different domains (frequency and time/space, respectively), and we want to know which domain shows overall best performance. We propose a novel formulation of the signal-to-interference plus noise ratio (SINR) which allows us to prove the frequency/time duality of these schemes. Further, we propose two novel capacity optimization approaches assuming per-beam SINR constraints in order to use the satellite resources (e.g., power and bandwidth) more efficiently. Moreover, we develop a general methodology to include technological constraints due to realistic implementations, and obtain the main factors that prevent the two technologies dual of each other in practice, and formulate the technological gap between them. The Shannon capacity (upper bound) and current state-of-the-art coding and modulations are analyzed in order to quantify the gap and to evaluate the performance of the two candidate schemes. Simulation results show significant improvements in terms of power gain, spectral efficiency and traffic matching ratio when comparing with conventional systems, which are designed based on uniform bandwidth and power allocation. The results also show that BH system turns out to show a less complex design and performs better than NOFR system specially for non-real time services.

Performance evaluation of distributed‐antenna communications systems using beam‐hopping

AbstractDigital beamforming (DBF) techniques are capable of improving the performance of communications systems significantly. However, if the transmitted signals are conflicted with strong interference especially in the direction of the transmitted beams, these directional jamming signals will severely degrade the system performance. In order to efficiently mitigate the interference of the directional jammers, in this contribution a beam‐hopping (BH) communications scheme is studied. In the BH communications scheme, only one pair of the beams is used for transmission and it hops from one to the next according to an assigned BH pattern. In this contribution, a range of expressions in terms of the average signal to interference plus noise ratio (SINR) performance have been derived, when both the uplink and downlink are considered. The average SINR performance of the BH scheme and that of the conventional single‐beam (SB) as well as multiple‐beam (MB) assisted beam‐processing schemes have been investigated. Our analysis and results show that the BH scheme is capable of efficiently combating the directional jamming, with the aid of utilizing the directional gain of the beams generated by both the transmitter and the receiver. Furthermore, the BH scheme is capable of reducing the intercept probability of the communications. Therefore, the BH scheme is suitable for communications when several distributed antenna arrays are available around a mobile. Copyright © 2005 John Wiley & Sons, Ltd.

Performance Analysis of Distributed-Antenna Communication Systems Using Beam-Hopping Under Strong Directional Interference

In order to efficiently mitigate the interference of directional jammers, we investigate a beam-hopping (BH) communication scheme, which includes slow beam-hopping (SBH) and fast beam-hopping (FBH) schemes. In the BH communication scheme, only one pair of the beams is used for transmission and it hops from one to the next according to an assigned BH pattern. In this contribution, a range of expressions in terms of the symbol error rate (SER) performance of the BH and conventional single-beam (SB) schemes have been derived, when both the downlink and uplink are considered. The SER performance of the BH scheme is compared with that of the SB scheme, for M-ary phase-shift keying (MPSK) and M-ary quadrature amplitude modulation (MQAM) signals under composite log normal shadowing/Nakagami-m fading channels. Our analysis and results show that the proposed BH scheme is suitable for communications, when several distributed antenna arrays are available around a mobile.

GIGABIT SATELLITE NETWORK FOR NASA’S ADVANCED COMMUNICATION TECHNOLOGY SATELLITE (ACTS)

The advanced communication technology satellite (ACTS) gigabit satellite network provides long-haul point-to-point and point-to-multipoint full-duplex SONET services over NASA's ACTS. at rates up to 622 Mbit/s (SONET OC-12), with signal quality comparable to that obtained with terrestrial fiber networks. Data multiplexing over the satellite is accomplished using time-division multiple access (TDMA) techniques coordinated with the switching and beam hopping facilities provided by ACTS. Transmissions through the satellite are protected with Reed-Solomon encoding. providing virtually error-free transmission under most weather conditions. Unique to the system are a TDMA frame structure and satellite synchronization mechanism that allow: (a) very efficient utilization of the satellite capacity: (b) over-the-satellite dosed-loop synchronization of the network in configurations with up to 64 ground stations: and (c) ground station initial acquisition without collisions with existing signalling or data traffic. The user interfaces are compatible with SONET standards, performing the function of conventional SONET multiplexers and. as such. can be: readily integrated with standard SONET fiber-based terrestrial networks. Management of the network is based upon the simple network management protocol (SNMP). and includes an over-the-satellite signalling network and backup terrestrial internet (IP-based) connectivity. A description of the ground stations is also included.

Trends of the antenna systems on-board new generation telecommunications satellites

Point to multipoint and multipoint to multipoint satellite telecommunications require the cost-effective exploitation of on-board power and bandwidth resources. This leads to the implementation of advanced antenna concepts such as Contoured Beam, Multiple Beam and Beam Hopping Antennas. The paper discusses the advantages of these antennas in order to meet the new system requirements. Whilst attention is focussed on the reflector antenna configurations, different hardware solutions are also presented such as phased arrays, imaging reflectors and active antennas.