197 research outputs found
Improving the Spectral Efficiency of Nonlinear Satellite Systems through Time-Frequency Packing and Advanced Processing
We consider realistic satellite communications systems for broadband and
broadcasting applications, based on frequency-division-multiplexed linear
modulations, where spectral efficiency is one of the main figures of merit. For
these systems, we investigate their ultimate performance limits by using a
framework to compute the spectral efficiency when suboptimal receivers are
adopted and evaluating the performance improvements that can be obtained
through the adoption of the time-frequency packing technique. Our analysis
reveals that introducing controlled interference can significantly increase the
efficiency of these systems. Moreover, if a receiver which is able to account
for the interference and the nonlinear impairments is adopted, rather than a
classical predistorter at the transmitter coupled with a simpler receiver, the
benefits in terms of spectral efficiency can be even larger. Finally, we
consider practical coded schemes and show the potential advantages of the
optimized signaling formats when combined with iterative detection/decoding.Comment: 8 pages, 8 figure
FTN Signaling In the Saturation Regime: Spectral Efficiency Improvement
Faster-than-Nyquist (FTN) signaling is investigated in future satellite communication standardization for an improved spectral efficiency considering the increasingly constrained resource. Previous studies showed that FTN lower modulation orders compressed in time-domain could reach the spectral efficiency of uncompressed higher modulation orders. The FTN gain in terms of transmission rate is obtained at the price of a turbo-equalization at the receiver, increasing the complexity. The increased capacity in DVB-S2X’s transmissions is due to innovations increasing the fluctuation of the complex envelop of the transmitted signal. Since the satellite’s payload introduces higher non-linear distortions with increased fluctuations, the growing receiver’s complexity is unavoidable. However, in this non linear regime, the complexity of the FTN receiver is not this detrimental compared with those of a classical Nyquist receiver. For a similar spectral efficiency, its lower Peak to Average Power Ratio (PAPR), making the non-linearities treatment easier, makes this innovation suitable for future satellite communications, especially when the payload is operated in the saturation regime. In this paper, we show that compression offers a gain between 10 and 20 in terms of spectral efficiency when compared to Nyquist signaling, both equalized thanks to the MAP symbol detection based on the Volterra series model of non-linearities
Polar Coded Faster-than-Nyquist (FTN) Signaling with Symbol-by-Symbol Detection
Reduced complexity faster-than-Nyquist (FTN) signaling systems are gaining
increased attention as they provide improved bandwidth utilization for an
acceptable level of detection complexity. In order to have a better
understanding of the tradeoff between performance and complexity of the reduced
complexity FTN detection techniques, it is necessary to study these techniques
in the presence of channel coding. In this paper, we investigate the
performance a polar coded FTN system which uses a reduced complexity FTN
detection, namely, the recently proposed successive symbol-by-symbol with
go-backK sequence estimation (SSSgbKSE) technique. Simulations are performed
for various intersymbol-interference (ISI) levels and for various go-back-K
values. Bit error rate (BER) performance of Bahl-Cocke-Jelinek-Raviv (BCJR)
detection and SSSgbKSE detection techniques are studied for both uncoded and
polar coded systems. Simulation results reveal that polar codes can compensate
some of the performance loss incurred in the reduced complexity SSSgbKSE
technique and assist in closing the performance gap between BCJR and SSSgbKSE
detection algorithms
Spectrally Efficient FDM over Satellite Systems with Advanced Interference Cancellation
For high data rates satellite systems, where multiple carriers are frequency division multiplexed with a slight overlap,
the overall spectral efficiency is limited. This work applies highly overlapped carriers for satellite broadcast and broadband scenarios
to achieve higher spectral efficiency. Spectrally efficient frequency division multiplexing (SEFDM) compresses subcarrier
spacing to increase the spectral efficiency at the expense of orthogonality violation. SEFDM systems performance degrades compared
to orthogonal signals, unless efficient interference cancellation is used. Turbo equalisation with interference cancellation
is implemented to improve receiver performance for variable coding, compression and modulation/constellation proposals that
may be applied in satellite communications settings. Such parameters may be set to satisfy pre-defined spectral efficiency values
for a given quality index (QI) or associated application. Assuming LDPC coded data, the work proposes two approaches to
receiver design; a simple matched filter approach and an approach utilising an iterative interference cancellation structure specially
designed for SEFDM. Mathematical models and simulations studies are presented indicating promising gains to be achieved for
SEFDM transmission with advanced transceiver architectures at the cost of increased complexity at the receiver
Advanced receivers and waveforms for UAV/Aircraft aeronautical communications
Nowadays, several studies are launched for the design of reliable and safe communications systems that introduce Unmanned Aerial Vehicle (UAV), this paves the way for UAV communication systems to play an important role in a lot of applications for non-segregated military and civil airspaces. Until today, rules for integrating commercial UAVs in airspace still need to be defined, the design of secure, highly reliable and cost effective communications systems still a challenging task. This thesis is part of this communication context. Motivated by the rapid growth of UAV quantities and by the new generations of UAVs controlled by satellite, the thesis aims to study the various possible UAV links which connect UAV/aircraft to other communication system components (satellite, terrestrial networks, etc.). Three main links are considered: the Forward link, the Return link and the Mission link. Due to spectrum scarcity and higher concentration in aircraft density, spectral efficiency becomes a crucial parameter for largescale deployment of UAVs. In order to set up a spectrally efficient UAV communication system, a good understanding of transmission channel for each link is indispensable, as well as a judicious choice of the waveform. This thesis begins to study propagation channels for each link: a mutipath channels through radio Line-of-Sight (LOS) links, in a context of using Meduim Altitude Long drones Endurance (MALE) UAVs. The objective of this thesis is to maximize the solutions and the algorithms used for signal reception such as channel estimation and channel equalization. These algorithms will be used to estimate and to equalize the existing muti-path propagation channels. Furthermore, the proposed methods depend on the choosen waveform. Because of the presence of satellite link, in this thesis, we consider two low-papr linear waveforms: classical Single-Carrier (SC) waveform and Extented Weighted Single-Carrier Orthogonal Frequency-Division Multiplexing (EW-SC-OFDM) waveform. channel estimation and channel equalization are performed in the time-domain (SC) or in the frequency-domain (EW-SC-OFDM). UAV architecture envisages the implantation of two antennas placed at wings. These two antennas can be used to increase diversity gain (channel matrix gain). In order to reduce channel equalization complexity, the EWSC- OFDM waveform is proposed and studied in a muti-antennas context, also for the purpose of enhancing UAV endurance and also increasing spectral efficiency, a new modulation technique is considered: Spatial Modulation (SM). In SM, transmit antennas are activated in an alternating manner. The use of EW-SC-OFDM waveform combined to SM technique allows us to propose new modified structures which exploit exces bandwidth to improve antenna bit protection and thus enhancing system performances
Advanced transceivers for spectrally-efficient communications
In this thesis, we will consider techniques to improve the spectral
efficiency of digital communication systems, operating on the whole transceiver
scheme. First, we will focus on receiver schemes having detection algorithms
with a complexity constraint. We will optimize the parameters of the reduced
detector with the aim of maximizing the achievable information rate. Namely, we
will adopt the channel shortening technique. Then, we will focus on a technique
that is getting very popular in the last years (although presented for the
first time in 1975): faster-than-Nyquist signaling, and its extension which is
time packing. Time packing is a very simple technique that consists in
introducing intersymbol interference on purpose with the aim of increasing the
spectral efficiency of finite order constellations. Finally, in the last
chapters we will combine all the presented techniques, and we will consider
their application to satellite channels.Comment: PhD Thesi
Multidimensional Index Modulation for 5G and Beyond Wireless Networks
This study examines the flexible utilization of existing IM techniques in a
comprehensive manner to satisfy the challenging and diverse requirements of 5G
and beyond services. After spatial modulation (SM), which transmits information
bits through antenna indices, application of IM to orthogonal frequency
division multiplexing (OFDM) subcarriers has opened the door for the extension
of IM into different dimensions, such as radio frequency (RF) mirrors, time
slots, codes, and dispersion matrices. Recent studies have introduced the
concept of multidimensional IM by various combinations of one-dimensional IM
techniques to provide higher spectral efficiency (SE) and better bit error rate
(BER) performance at the expense of higher transmitter (Tx) and receiver (Rx)
complexity. Despite the ongoing research on the design of new IM techniques and
their implementation challenges, proper use of the available IM techniques to
address different requirements of 5G and beyond networks is an open research
area in the literature. For this reason, we first provide the dimensional-based
categorization of available IM domains and review the existing IM types
regarding this categorization. Then, we develop a framework that investigates
the efficient utilization of these techniques and establishes a link between
the IM schemes and 5G services, namely enhanced mobile broadband (eMBB),
massive machine-type communications (mMTC), and ultra-reliable low-latency
communication (URLLC). Additionally, this work defines key performance
indicators (KPIs) to quantify the advantages and disadvantages of IM techniques
in time, frequency, space, and code dimensions. Finally, future recommendations
are given regarding the design of flexible IM-based communication systems for
5G and beyond wireless networks.Comment: This work has been submitted to Proceedings of the IEEE for possible
publicatio
- …