118 research outputs found
Signal Processing and Learning for Next Generation Multiple Access in 6G
Wireless communication systems to date primarily rely on the orthogonality of
resources to facilitate the design and implementation, from user access to data
transmission. Emerging applications and scenarios in the sixth generation (6G)
wireless systems will require massive connectivity and transmission of a deluge
of data, which calls for more flexibility in the design concept that goes
beyond orthogonality. Furthermore, recent advances in signal processing and
learning have attracted considerable attention, as they provide promising
approaches to various complex and previously intractable problems of signal
processing in many fields. This article provides an overview of research
efforts to date in the field of signal processing and learning for
next-generation multiple access, with an emphasis on massive random access and
non-orthogonal multiple access. The promising interplay with new technologies
and the challenges in learning-based NGMA are discussed
Asynchronous bi-directional relay-assisted communication networks
We consider an asynchronous bi-directional relay network, consisting of two singleantenna
transceivers and multiple single-antenna relays, where the transceiver-relay
paths are subject to different relaying and/or propagation delays. Such a network can
be viewed as a multipath channel which can cause inter-symbol-interference (ISI) in
the signals received by the two transceivers. Hence, we model such a communication
scheme as a frequency selective multipath channel which produces ISI at the two
transceivers, when the data rates are relatively high. We study both multi- and
single-carrier communication schemes in such networks.
In a multi-carrier communication scheme, to tackle ISI, the transceivers employ
an orthogonal frequency division multiplexing (OFDM) scheme to diagonalize the
end-to-end channel. The relays use simple amplify-and-forward relaying, thereby
materializing a distributed beamformer. For such a scheme, we propose two different
algorithms, based on the max-min fair design approach, to calculate the subcarrier
power loading at the transceivers as well as the relay beamforming weights.
In a single-carrier communication, assuming a block transmission/reception scheme,
block channel equalization is used at the both transceivers to combat the inter-blockinterference
(IBI). Assuming a limited total transmit power budget, we minimize
the total mean squared error (MSE) of the estimated received signals at the both
transceivers by optimally obtaining the transceivers??? powers and the relay beamforming
weight vector as well as the block channel equalizers at the two transceivers
Low-latency Networking: Where Latency Lurks and How to Tame It
While the current generation of mobile and fixed communication networks has
been standardized for mobile broadband services, the next generation is driven
by the vision of the Internet of Things and mission critical communication
services requiring latency in the order of milliseconds or sub-milliseconds.
However, these new stringent requirements have a large technical impact on the
design of all layers of the communication protocol stack. The cross layer
interactions are complex due to the multiple design principles and technologies
that contribute to the layers' design and fundamental performance limitations.
We will be able to develop low-latency networks only if we address the problem
of these complex interactions from the new point of view of sub-milliseconds
latency. In this article, we propose a holistic analysis and classification of
the main design principles and enabling technologies that will make it possible
to deploy low-latency wireless communication networks. We argue that these
design principles and enabling technologies must be carefully orchestrated to
meet the stringent requirements and to manage the inherent trade-offs between
low latency and traditional performance metrics. We also review currently
ongoing standardization activities in prominent standards associations, and
discuss open problems for future research
Timing and Carrier Synchronization in Wireless Communication Systems: A Survey and Classification of Research in the Last 5 Years
Timing and carrier synchronization is a fundamental requirement for any wireless communication system to work properly. Timing synchronization is the process by which a receiver node determines the correct instants of time at which to sample the incoming signal. Carrier synchronization is the process by which a receiver adapts the frequency and phase of its local carrier oscillator with those of the received signal. In this paper, we survey the literature over the last 5 years (2010–2014) and present a comprehensive literature review and classification of the recent research progress in achieving timing and carrier synchronization in single-input single-output (SISO), multiple-input multiple-output (MIMO), cooperative relaying, and multiuser/multicell interference networks. Considering both single-carrier and multi-carrier communication systems, we survey and categorize the timing and carrier synchronization techniques proposed for the different communication systems focusing on the system model assumptions for synchronization, the synchronization challenges, and the state-of-the-art synchronization solutions and their limitations. Finally, we envision some future research directions
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