1,772 research outputs found
Architectures and Key Technical Challenges for 5G Systems Incorporating Satellites
Satellite Communication systems are a promising solution to extend and
complement terrestrial networks in unserved or under-served areas. This aspect
is reflected by recent commercial and standardisation endeavours. In
particular, 3GPP recently initiated a Study Item for New Radio-based, i.e., 5G,
Non-Terrestrial Networks aimed at deploying satellite systems either as a
stand-alone solution or as an integration to terrestrial networks in mobile
broadband and machine-type communication scenarios. However, typical satellite
channel impairments, as large path losses, delays, and Doppler shifts, pose
severe challenges to the realisation of a satellite-based NR network. In this
paper, based on the architecture options currently being discussed in the
standardisation fora, we discuss and assess the impact of the satellite channel
characteristics on the physical and Medium Access Control layers, both in terms
of transmitted waveforms and procedures for enhanced Mobile BroadBand (eMBB)
and NarrowBand-Internet of Things (NB-IoT) applications. The proposed analysis
shows that the main technical challenges are related to the PHY/MAC procedures,
in particular Random Access (RA), Timing Advance (TA), and Hybrid Automatic
Repeat reQuest (HARQ) and, depending on the considered service and
architecture, different solutions are proposed.Comment: Submitted to Transactions on Vehicular Technologies, April 201
Differential Distributed Space-Time Coding with Imperfect Synchronization in Frequency-Selective Channels
Differential distributed space-time coding (D-DSTC) is a cooperative
transmission technique that can improve diversity in wireless relay networks in
the absence of channel information. Conventionally, it is assumed that channels
are flat-fading and relays are perfectly synchronized at the symbol level.
However, due to the delay spread in broadband systems and the distributed
nature of relay networks, these assumptions may be violated. Hence,
inter-symbol interference (ISI) may appear. This paper proposes a new
differential encoding and decoding process for D-DSTC systems with multiple
relays over slow frequency-selective fading channels with imperfect
synchronization. The proposed method overcomes the ISI caused by
frequency-selectivity and is robust against synchronization errors while not
requiring any channel information at the relays and destination. Moreover, the
maximum possible diversity with a decoding complexity similar to that of the
conventional D-DSTC is attained. Simulation results are provided to show the
performance of the proposed method in various scenarios.Comment: to appear in IEEE Transaction on Wireless Communications, 201
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