86 research outputs found
Performance of an Echo Canceller and Channel Estimator for On-Channel Repeaters in DVB-T/H Networks
This paper investigates the design and performance of an FIR echo canceller for on-channel repeaters in DVB-T/H network within the framework of the PLUTO project. The possible
approaches for echo cancellation are briefly reviewed and the main guidelines for the design of such systems are presented. The main system parameters are discussed. The performance of an FIR echo canceller based on an open loop feedforward approach for channel estimation is tested for different radio channel conditions and for different number of taps of the FIR filter. It is shown that a minimum number of taps is recommended to achieve a certain mean rejection ratio or isolation depending on the type of channel. The expected degradation in performance due to the use of fixed point rather than floating point arithmetic in hardware implementation is presented for different number of bits. Channel estimation based on training sequences is investigated. The performance of Maximum Length Sequences and Constant Amplitude Zero Autocorrelation (CAZAC) Sequences is compared for different channels. Recommendations are given for training sequence type, length and
level for DVB-T/H on-channel repeater deployment
Analysis of DVB-H network coverage with the application of transmit diversity
This paper investigates the effects of the Cyclic Delay Diversity (CDD) transmit diversity scheme on DVB-H networks. Transmit diversity improves reception and Quality of Service (QoS) in areas of poor coverage such as sparsely populated or obscured locations. The technique not only povides robust reception in mobile environments thus improving QoS, but it also reduces network costs in terms of the transmit power, number of
infrastructure elements, antenna height and the frequency reuse factor over indoor and outdoor environments. In this paper, the benefit and effectiveness of CDD transmit diversity is tackled
through simulation results for comparison in several scenarios of coverage in DVB-H networks. The channel model used in the simulations is based on COST207 and a basic radio planning
technique is used to illustrate the main principles developed in this paper. The work reported in this paper was supported by
the European Commission IST project—PLUTO (Physical Layer DVB Transmission Optimization)
OFDM based air interfaces for future mobile satellite systems
This thesis considers the performance of OFDM in a non-linear satellite channel and mechanisms for overcoming the degradations resulting from the high PAPR in the OFDM signal in the specific satellite architecture. It was motivated by new S-DMB applications but its results are applicable to any OFDM system via satellites. Despite many advantages of OFDM, higher PAPR is a major drawback. OFDM signals are therefore very sensitive to non-linear distortion introduced by the power amplifiers and thus, significantly reduce the power efficiency of the system, which is already crucial to satellite system economics. Simple power amplifier back-off to cope with high OFDM PAPR is not possible. Two transmitter based techniques have been considered: PAPR reduction and amplifier linearization.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Capacity and spectrum efficiency analysis of an asymmetric PMR system with DAB downlink
Cataloged from PDF version of article.Different trunked Private Mobile Radio (PMR) systems have been designed
over the last several decades, all of which have symmetric downlink and uplink
channel capacities. Due to this symmetry, those systems may not be spectrally
efficient in case of different types of services which are only supported by
PMR systems, such as group (acknowledged or unacknowledged) and
broadcast calls, either voice or data. In this thesis, a new asymmetric trunked
PMR system comprising an OFDM based broadband, wide-area downlink and
a narrowband cellular uplink, is proposed to achieve a higher capacity and
higher spectral efficiency than current digital trunked PMR systems have. This
thesis concentrates on the system capacity analysis of the proposed system
associated only with the downlink part for voice communications, as well as
the spectrum efficiency comparison of the proposed system with the Terrestrial
Trunked Radio (TETRA) system, which is accepted as the spectrally most
efficient PMR system. In this study, we study the performance and capacity of
the proposed system using Digital Audio Broadcasting (DAB) downlink. In
particular, we study the capacity of such a system for voice calls using voice
activity detection and statistical multiplexing. Moreover, we show that, the
capacity of the system can significantly increase, if the incoming calls, which cannot find an available channel, are allowed to wait a certain amount of time
before occupying a channel. The system is shown to have high trunking
efficiency since all users are assumed to use the pool of channels available in
the wideband downlink. Spectral efficiency of the proposed system and a
standard TETRA system are compared using numerical case studies against
different traffic loads, cell sizes and number of clusters. The optimum point,
with respect to number of clusters, up to which the proposed system is more
efficient, is determined. It is shown that for a realistic PMR scenario the
proposed system is more efficient up to 5 clusters, i.e. 35 cells, and therefore it
can be concluded that the proposed system can be used efficiently in realistic
situations.Şengül, ErsinM.S
Satellite Channel Impairments: link performace degradation and countermeasures
Le forme d’onda introdotte nel DVB-S2 promettono il raggiungimento di efficienze spettrali prossime al limite di Shannon. Tuttavia, gli impairments tipici del canale satellitare degradano inevitabilmente le prestazioni nominali, definite sul canale AWGN. In questo lavoro, l’impatto delle non-linearità tipiche della catena di trasmissione satellitare viene valutato quantitativamente, attraverso metodi numerici. Si esplora Inoltre il guadagno ottenibile attraverso tecniche di predistorsion
Hybrid Satellite-Terrestrial Communication Networks for the Maritime Internet of Things: Key Technologies, Opportunities, and Challenges
With the rapid development of marine activities, there has been an increasing
number of maritime mobile terminals, as well as a growing demand for high-speed
and ultra-reliable maritime communications to keep them connected.
Traditionally, the maritime Internet of Things (IoT) is enabled by maritime
satellites. However, satellites are seriously restricted by their high latency
and relatively low data rate. As an alternative, shore & island-based base
stations (BSs) can be built to extend the coverage of terrestrial networks
using fourth-generation (4G), fifth-generation (5G), and beyond 5G services.
Unmanned aerial vehicles can also be exploited to serve as aerial maritime BSs.
Despite of all these approaches, there are still open issues for an efficient
maritime communication network (MCN). For example, due to the complicated
electromagnetic propagation environment, the limited geometrically available BS
sites, and rigorous service demands from mission-critical applications,
conventional communication and networking theories and methods should be
tailored for maritime scenarios. Towards this end, we provide a survey on the
demand for maritime communications, the state-of-the-art MCNs, and key
technologies for enhancing transmission efficiency, extending network coverage,
and provisioning maritime-specific services. Future challenges in developing an
environment-aware, service-driven, and integrated satellite-air-ground MCN to
be smart enough to utilize external auxiliary information, e.g., sea state and
atmosphere conditions, are also discussed
Low complexity channel estimation for OFDM based satellite systems
EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Femtocell deployment; next generation in cellular systems
The final Bachelor’s Thesis that is shown below has such a final purpose of
giving an overview of the inclusion of the so-called Femtocells (or Home Node
B) in the current cellular systems. The main objective is to give a clear but
simple idea about the concepts of Femtocells, as well as to explain the
benefits and disadvantages of the mass uses of these services both for
consumers and associated companies with this phenomenon.
In this text it is also possible to find a brief review of wireless technologies
throughout the history of telecommunications, as well as an introduction to the
more current wireless technologies, with a special interest in the concept of
cellular systems.
In the last chapter a simple mathematical explanation of the key issue of
interference between Femtocells and macrocellular networks is presented,
with a brief argument about possible solutions
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