597 research outputs found
Time-Domain N-continuous GFDM
Generalized frequency division multiplexing (GFDM) has been a candidate
multicarrier scheme in the 5th generation cellular networks for its flexibility
of transmitter filter in time and frequency. However, for the circularly shaped
transmitter filter, GFDM provides limited performance gain of sidelobe
suppression. In this paper, we propose a scheme, called time-domain
N-continuous GFDM (TD-NC-GFDM), to reduce the discontinuities caused by the
GFDM transmitter filter and achieve promising sidelobe suppression gain. Based
on time-domain N-continuous orthogonal frequency devision multiplexing
(TD-NC-OFDM), TD-NC-GFDM signal can be obtained by superposing a smooth signal
in the time domain. The smooth signal is linearly combined by basis signals in
a new basis set related to GFDM transmitter waveform. To eliminate the
interference caused by the smooth signal, two solutions are proposed. Firstly,
a signal recovery algorithm for reception is adopted at the cost of high
complexity. Thus, secondly, to simplify the TD-NC-GFDM receiver, a
low-interference TD-NC-GFDM is proposed by redesigning the basis signals. A
soft truncation of the basis signals in TD-NC-GFDM is given to design the basis
signals in the low-interference TD-NC-GFDM. Then, the smooth signal is aligned
with the beginning of the GFDM symbol and is added in the front part of the
GFDM symbol. Moreover, for a big number of GFDM subsymbols, theoretical
analysis proves that the signal-to-interference ratio (SIR) in TD-NC-GFDM is
much higher than that in TD-NC-OFDM. Simulation results shows that TD-NC-GFDM
can obtain significant sidelobe suppression performance as well as the
low-interference TD-NC-GFDM, which can achieve the same BER performance as the
original GFDM.Comment: single column, 19 pages, 10 figure
Cyclic Prefix-Free MC-CDMA Arrayed MIMO Communication Systems
The objective of this thesis is to investigate MC-CDMA MIMO systems where
the antenna array geometry is taken into consideration. In most MC-CDMA
systems, cyclic pre xes, which reduce the spectral e¢ ciency, are used. In order
to improve the spectral efficiency, this research study is focused on cyclic pre x-
free MC-CDMA MIMO architectures.
Initially, space-time wireless channel models are developed by considering the
spatio-temporal mechanisms of the radio channel, such as multipath propaga-
tion. The spatio-temporal channel models are based on the concept of the array
manifold vector, which enables the parametric modelling of the channel.
The array manifold vector is extended to the multi-carrier space-time array
(MC-STAR) manifold matrix which enables the use of spatio-temporal signal
processing techniques. Based on the modelling, a new cyclic pre x-free MC-
CDMA arrayed MIMO communication system is proposed and its performance
is compared with a representative existing system. Furthermore, a MUSIC-type
algorithm is then developed for the estimation of the channel parameters of the
received signal.
This proposed cyclic pre x-free MC-CDMA arrayed MIMO system is then
extended to consider the effects of spatial diffusion in the wireless channel. Spatial
diffusion is an important channel impairment which is often ignored and the
failure to consider such effects leads to less than satisfactory performance. A
subspace-based approach is proposed for the estimation of the channel parameters
and spatial spread and reception of the desired signal.
Finally, the problem of joint optimization of the transmit and receive beam-
forming weights in the downlink of a cyclic pre x-free MC-CDMA arrayed MIMO
communication system is investigated. A subcarrier-cooperative approach is used
for the transmit beamforming so that there is greater flexibility in the allocation
of channel symbols. The resulting optimization problem, with a per-antenna
transmit power constraint, is solved by the Lagrange multiplier method and an
iterative algorithm is proposed
MIMO signal processing in offset-QAM based filter bank multicarrier systems
Next-generation communication systems have to comply with very strict requirements for increased flexibility in heterogeneous environments, high spectral efficiency, and agility of carrier aggregation. This fact motivates research in advanced multicarrier modulation (MCM) schemes, such as filter bank-based multicarrier (FBMC) modulation. This paper focuses on the offset quadrature amplitude modulation (OQAM)-based FBMC variant, known as FBMC/OQAM, which presents outstanding spectral efficiency and confinement in a number of channels and applications. Its special nature, however, generates a number of new signal processing challenges that are not present in other MCM schemes, notably, in orthogonal-frequency-division multiplexing (OFDM). In multiple-input multiple-output (MIMO) architectures, which are expected to play a primary role in future communication systems, these challenges are intensified, creating new interesting research problems and calling for new ideas and methods that are adapted to the particularities of the MIMO-FBMC/OQAM system. The goal of this paper is to focus on these signal processing problems and provide a concise yet comprehensive overview of the recent advances in this area. Open problems and associated directions for future research are also discussed.Peer ReviewedPostprint (author's final draft
Measurement-induced quantum synchronization and multiplexing
Measurements are able to fundamentally affect quantum dynamics. We here show
that a continuously measured quantum many-body system can undergo a spontaneous
transition from asynchronous stochastic dynamics to noise-free stable
synchronization at the level of single trajectories. We formulate general
criteria for this quantum phenomenon to occur, and demonstrate that the number
of synchronized realizations can be controlled from none to all. We
additionally find that ergodicity is typically broken, since time and ensemble
averages may exhibit radically different synchronization behavior. We further
introduce a quantum type of multiplexing that involves individual trajectories
with distinct synchronization frequencies. Measurement-induced synchronization
appears as a genuine nonclassical form of synchrony that exploits quantum
superpositions
Seventy Years of Radar and Communications: The road from separation to integration
Radar and communications (R&C) as key utilities of electromagnetic (EM) waves have fundamentally shaped human society and triggered the modern information age. Although R&C had been historically progressing separately, in recent decades, they have been converging toward integration, forming integrated sensing and communication (ISAC) systems, giving rise to new highly desirable capabilities in next-generation wireless networks and future radars. To better understand the essence of ISAC, this article provides a systematic overview of the historical development of R&C from a signal processing (SP) perspective. We first interpret the duality between R&C as signals and systems, followed by an introduction of their fundamental principles. We then elaborate on the two main trends in their technological evolution, namely, the increase of frequencies and bandwidths and the expansion of antenna arrays. We then show how the intertwined narratives of R&C evolved into ISAC and discuss the resultant SP framework. Finally, we overview future research directions in this field
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