921 research outputs found
Hardware Precoding Demonstration in Multi-Beam UHTS Communications under Realistic Payload Characteristics
In this paper, we present a new hardware test-bed to demonstrate closed-loop precoded communications for interference mitigation in multi-beam ultra high throughput satellite systems under realistic payload and channel impairments. We build the test-bed to demonstrate a real-time channel aided precoded transmission under realistic conditions such as the power constraints and satellite-payload non-linearities. We develop a scalable architecture of an SDR platform with the DVB-S2X piloting. The SDR platform consists of two parts: analog-to-digital (ADC) and digital-to-analog (DAC) converters preceded by radio frequency (RF) front-end and Field-Programmable Gate Array (FPGA) backend. The former introduces realistic impairments in the transmission chain such as carrier frequency and phase misalignments, quantization noise of multichannel ADC and DAC and non-linearities of RF components. It allows evaluating the performance of the precoded transmission in a more realistic environment rather than using only numerical simulations. We benchmark the performance of the communication standard in realistic channel scenarios, evaluate received signal
SNR, and measure the actual channel throughput using LDPC codes
European H2020 Project WORTECS Wireless Mixed Reality Prototyping
This paper presents European collaborative project WORTECS objectives and reports on the development of several radio and optical wireless prototypes and a demonstrator targeting mixed reality (MR) application. The aim is to achieve a net throughput of up to Tbps in an indoor heterogeneous network for the MR use case, which seems to be a high throughput "killer application" beyond 5G. A special routing device is associated with the demonstrator to select the most suitable wireless access technology. Post introduction to the project, an overview of the demonstrator is presented with details of the current progress of the prototypes
Hardware Demonstration of Precoded Communications in Multi-Beam UHTS Systems
In this paper, we present a hardware test-bed to demonstrate closed-loop precoded communications for interference mitigation in the forward link of the multi-beam ultra-high throughput satellite systems. The hardware demonstrator is a full-chain closed-loop communication system with a multi-beam DVB-S2X compliant gateway, a satellite payload and MIMO channel emulator and a set of DVB-S2X user terminals with real-time CSI estimation and feedback. We experimentally show the feasibility of Precoding implementation in satellite communications based on the superframe structure DVB-S2X standard. Using the test-bed we have a possibility to run real-time precoded DVB-S2X communication and benchmark its performance under realistic environment. The hardware demonstrator is suitable to perform realistic benchmarks of Block- and Symbol-level Precoding techniques for multicast and unicast user scheduling scenarios
Knowledge-based vision for space station object motion detection, recognition, and tracking
Computer vision, especially color image analysis and understanding, has much to offer in the area of the automation of Space Station tasks such as construction, satellite servicing, rendezvous and proximity operations, inspection, experiment monitoring, data management and training. Knowledge-based techniques improve the performance of vision algorithms for unstructured environments because of their ability to deal with imprecise a priori information or inaccurately estimated feature data and still produce useful results. Conventional techniques using statistical and purely model-based approaches lack flexibility in dealing with the variabilities anticipated in the unstructured viewing environment of space. Algorithms developed under NASA sponsorship for Space Station applications to demonstrate the value of a hypothesized architecture for a Video Image Processor (VIP) are presented. Approaches to the enhancement of the performance of these algorithms with knowledge-based techniques and the potential for deployment of highly-parallel multi-processor systems for these algorithms are discussed
High-speed civil transport issues and technology program
A strawman program plan is presented, consisting of technology developments and demonstrations required to support the construction of a high-speed civil transport. The plan includes a compilation of technology issues related to the development of a transport. The issues represent technical areas in which research and development are required to allow airframe manufacturers to pursue an HSCT development. The vast majority of technical issues presented require flight demonstrated and validated solutions before a transport development will be undertaken by the industry. The author believes that NASA is the agency best suited to address flight demonstration issues in a concentrated effort. The new Integrated Test Facility at NASA Dryden Flight Research Facility is considered ideally suited to the task of supporting ground validations of proof-of-concept and prototype system demonstrations before night demonstrations. An elaborate ground hardware-in-the-loop (iron bird) simulation supported in this facility provides a viable alternative to developing an expensive fill-scale prototype transport technology demonstrator. Drygen's SR-71 assets, modified appropriately, are a suitable test-bed for supporting flight demonstrations and validations of certain transport technology solutions. A subscale, manned or unmanned flight demonstrator is suitable for flight validation of transport technology solutions, if appropriate structural similarity relationships can be established. The author contends that developing a full-scale prototype transport technology demonstrator is the best alternative to ensuring that a positive decision to develop a transport is reached by the United States aerospace industry
Coherent multicarrier lightwave technology for flexible capacity networks (invited)
Highly flexible and survivable networks can be built by allocating optical carriers of heterodyne systems. The basic features of heterodyne systems are reviewed, especially the use of multicarriers, tunability, and selectivity. Then specific application areas that may benefit from flexible multicarrier allocation schemes are discussed. Examples are taken from the RACE Phase II project R2065, coherent optical systems implemented for business traffic routing and access (COBRA). Next, trends and progress in heterodyne systems in general and related key components are summarized, and then examples of ongoing field trials in Europe are discussed. Finally, the coherent multicarrier technology are compared briefly with direct detection multiwavelength technolog
Spectrum Monitoring Algorithms for Wireless and Satellite Communications
Nowadays, there is an increasing demand for more efficient utilization of the radio frequency
spectrum as new terrestrial and space services are deployed resulting in the
congestion of the already crowded frequency bands. In this context, spectrum monitoring
is a necessity. Spectrum monitoring techniques can be applied in a cognitive radio
network, exploiting the spectrum holes and allowing the secondary users to have access
in an unlicensed frequency band for them, when it is not occupied by the primary user.
Furthermore, spectrum monitoring techniques can be used for interference detection in
wireless and satellite communications. These two topics are addressed in this thesis.
In the beginning, a detailed survey of the existing spectrum monitoring techniques according
to the way that cognitive radio users 1) can detect the presence or absence of
the primary user; and 2) can access the licensed spectrum is provided. Subsequently, an
overview of the problem of satellite interference and existing methods for its detection
are discussed, while the contributions of this thesis are presented as well.
Moreover, this thesis discusses some issues in a cognitive radio system such as the reduction
of the secondary user's throughput of the conventional \listen before talk" access
method in the spectrum. Then, the idea of simultaneous spectrum sensing and data
transmission through the collaboration of the secondary transmitter with receiver is
proposed to address these concerns. First, the secondary receiver decodes the signal
from the secondary transmitter, then, removes it from the total received signal and finally, applies spectrum sensing in the remaining signal in order to decide if the primary
user is active or idle. The effects of the imperfect signal cancellation due to decoding
errors, which are ignored in the existing literature, are considered in our analysis. The
analytical expressions for the probabilities of false alarm and detection are derived and
numerical results through simulations are also presented to validate the proposed study.
Furthermore, the threat of interference for the satellite communications services is studied
in this thesis. It proposes the detection of interference on-board the satellite by
introducing a spectrum monitoring unit within the satellite transponder. This development
will bring several benefits such as faster reaction time and simplification of the
ground stations in multi-beam satellite systems. Then, two algorithms for the detection
of interference are provided. The first detection scheme is based on energy detector with
signal cancellation exploiting the pilot symbols. The second detection scheme considers
a two-stage detector, where first, the energy detector with signal cancellation in the pilot
domain is performed, and if required, an energy detector with signal cancellation in the
data domain is carried out in the second stage. Moreover, the analytical expressions for the probabilities of false alarm and detection are derived and numerical results through
simulations are provided to verify the accuracy of the proposed analysis.
Finally, this thesis goes one step further and the developed algorithms are evaluated
experimentally using software defined radios, particularly universal software radio peripherals
(USRPs), while it concludes discussing some open research topics
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