585 research outputs found
Flexible OFDM schemes for bursty transmissions
International audienceIn this paper, -OFDM, a generalization of the OFDM modulation, is proposed to enhance the outage capacity of bursty transmissions. This new flexible modulation scheme is easily implemented and only requires a symbol rotation of angle after the IDFT stage. The induced rotation slides the DFT window and provides frequency diversity in block fading channels. Interestingly, the results show a substantial gain in terms of outage capacity and BER in comparison with classical OFDM modulation schemes. The framework is extended to multiuser/multi-antenna OFDM based standards. Simulations, in the context of 3GPP LTE, called hereafter -LTE, sustain our theoretical claims
Frame Structure Design and Analysis for Millimeter Wave Cellular Systems
The millimeter-wave (mmWave) frequencies have attracted considerable
attention for fifth generation (5G) cellular communication as they offer orders
of magnitude greater bandwidth than current cellular systems. However, the
medium access control (MAC) layer may need to be significantly redesigned to
support the highly directional transmissions, ultra-low latencies and high peak
rates expected in mmWave communication. To address these challenges, we present
a novel mmWave MAC layer frame structure with a number of enhancements
including flexible, highly granular transmission times, dynamic control signal
locations, extended messaging and ability to efficiently multiplex directional
control signals. Analytic formulae are derived for the utilization and control
overhead as a function of control periodicity, number of users, traffic
statistics, signal-to-noise ratio and antenna gains. Importantly, the analysis
can incorporate various front-end MIMO capability assumptions -- a critical
feature of mmWave. Under realistic system and traffic assumptions, the analysis
reveals that the proposed flexible frame structure design offers significant
benefits over designs with fixed frame structures similar to current 4G
long-term evolution (LTE). It is also shown that fully digital beamforming
architectures offer significantly lower overhead compared to analog and hybrid
beamforming under equivalent power budgets.Comment: Submitted to IEEE Transactions for Wireless Communication
Priority-based initial access for URLLC traffic in massive IoT networks: Schemes and performance analysis
At a density of one million devices per square kilometer, the10’s of billions of devices, objects, and machines
that form a massive Internet of things (mIoT) require ubiquitous connectivity. Among a massive number of
IoT devices, a portion of them require ultra-reliable low latency communication (URLLC) provided via fifth
generation (5G) networks, bringing many new challenges due to the stringent service requirements. Albeit a surge
of research efforts on URLLC and mIoT, access mechanisms which include both URLLC and massive machine
type communications (mMTC) have not yet been investigated in-depth. In this paper, we propose three novel
schemes to facilitate priority-based initial access for mIoT/mMTC devices that require URLLC services while also
considering the requirements of other mIoT/mMTC devices. Based on a long term evolution-advanced (LTEA) or 5G new radio frame structure, the proposed schemes enable device grouping based on device vicinity
or/and their URLLC requirements and allocate dedicated preambles for grouped devices supported by flexible
slot allocation for random access. These schemes are able not only to increase the reliability and minimize the
delay of URLLC devices but also to improve the performance of all involved mIoT devices. Furthermore, we
evaluate the performance of the proposed schemes through mathematical analysis as well as simulations and
compare the results with the performance of both the legacy LTE-A based initial access scheme and a grant-free
transmission scheme.acceptedVersio
Achieving Ultra-Low Latency in 5G Millimeter Wave Cellular Networks
The IMT 2020 requirements of 20 Gbps peak data rate and 1 millisecond latency
present significant engineering challenges for the design of 5G cellular
systems. Use of the millimeter wave (mmWave) bands above 10 GHz --- where vast
quantities of spectrum are available --- is a promising 5G candidate that may
be able to rise to the occasion.
However, while the mmWave bands can support massive peak data rates,
delivering these data rates on end-to-end service while maintaining reliability
and ultra-low latency performance will require rethinking all layers of the
protocol stack. This papers surveys some of the challenges and possible
solutions for delivering end-to-end, reliable, ultra-low latency services in
mmWave cellular systems in terms of the Medium Access Control (MAC) layer,
congestion control and core network architecture
- …