24 research outputs found
On the Degrees-of-freedom of the 3-user MISO Broadcast Channel with Hybrid CSIT
The 3-user multiple-input single-output (MISO) broadcast channel (BC) with
hybrid channel state information at the transmitter (CSIT) is considered. In
this framework, there is perfect and instantaneous CSIT from a subset of users
and delayed CSIT from the remaining users. We present new results on the
degrees of freedom (DoF) of the 3-user MISO BC with hybrid CSIT. In particular,
for the case of 2 transmit antennas, we show that with perfect CSIT from one
user and delayed CSIT from the remaining two users, the optimal DoF is 5/3. For
the case of 3 transmit antennas and the same hybrid CSIT setting, it is shown
that a higher DoF of 9/5 is achievable and this result improves upon the best
known bound. Furthermore, with 3 transmit antennas, and the hybrid CSIT setting
in which there is perfect CSIT from two users and delayed CSIT from the third
one, a novel scheme is presented which achieves 9/4 DoF. Our results also
reveal new insights on how to utilize hybrid channel knowledge for multi-user
scenarios
Retroactive Anti-Jamming for MISO Broadcast Channels
Jamming attacks can significantly impact the performance of wireless
communication systems. In addition to reducing the capacity, such attacks may
lead to insurmountable overhead in terms of re-transmissions and increased
power consumption. In this paper, we consider the multiple-input single-output
(MISO) broadcast channel (BC) in the presence of a jamming attack in which a
subset of the receivers can be jammed at any given time. Further,
countermeasures for mitigating the effects of such jamming attacks are
presented. The effectiveness of these anti-jamming countermeasures is
quantified in terms of the degrees-of-freedom (DoF) of the MISO BC under
various assumptions regarding the availability of the channel state information
(CSIT) and the jammer state information at the transmitter (JSIT). The main
contribution of this paper is the characterization of the DoF region of the two
user MISO BC under various assumptions on the availability of CSIT and JSIT.
Partial extensions to the multi-user broadcast channels are also presented.Comment: submitted to IEEE Transactions on Information Theor
System-Level Modelling and Beamforming Design for RIS-assisted Cellular Systems
Reconfigurable intelligent surface (RIS) is considered as key technology for
improving the coverage and network capacity of the next-generation cellular
systems. By changing the phase shifters at RIS, the effective channel between
the base station and user can be reconfigured to enhance the network capacity
and coverage. However, the selection of phase shifters at RIS has a significant
impact on the achievable gains. In this letter, we propose a beamforming design
for the RIS-assisted cellular systems. We then present in detail the
system-level modelling and formulate a 3-dimension channel model between the
base station, RIS, and user, to carry out system-level evaluations. We evaluate
the proposed beamforming design in the presence of ideal and discrete phase
shifters at RIS and show that the proposed design achieves significant
improvements as compared to the state-of-the-art algorithms
A Novel Beamformed Control Channel Design for LTE with Full Dimension-MIMO
The Full Dimension-MIMO (FD-MIMO) technology is capable of achieving huge
improvements in network throughput with simultaneous connectivity of a large
number of mobile wireless devices, unmanned aerial vehicles, and the Internet
of Things (IoT). In FD-MIMO, with a large number of antennae at the base
station and the ability to perform beamforming, the capacity of the physical
downlink shared channel (PDSCH) has increased a lot. However, the current
specifications of the 3rd Generation Partnership Project (3GPP) does not allow
the base station to perform beamforming techniques for the physical downlink
control channel (PDCCH), and hence, PDCCH has neither the capacity nor the
coverage of PDSCH. Therefore, PDCCH capacity will still limit the performance
of a network as it dictates the number of users that can be scheduled at a
given time instant. In Release 11, 3GPP introduced enhanced PDCCH (EPDCCH) to
increase the PDCCH capacity at the cost of sacrificing the PDSCH resources. The
problem of enhancing the PDCCH capacity within the available control channel
resources has not been addressed yet in the literature. Hence, in this paper,
we propose a novel beamformed PDCCH (BF-PDCCH) design which is aligned to the
3GPP specifications and requires simple software changes at the base station.
We rely on the sounding reference signals transmitted in the uplink to decide
the best beam for a user and ingeniously schedule the users in PDCCH. We
perform system level simulations to evaluate the performance of the proposed
design and show that the proposed BF-PDCCH achieves larger network throughput
when compared with the current state of art algorithms, PDCCH and EPDCCH
schemes
How to choose a neural network architecture? – A modulation classification example
Which neural network architecture should be used for my problem? This is a common question that is encountered nowadays. Having searched a slew of papers that have been published over the last few years in the cross domain of machine learning and wireless communications, the authors found that several researchers working in this multi-disciplinary field continue to have the same question. In this regard, we make an attempt to provide a guide for choosing neural networks using an example application from the field of wireless communications, specifically we consider modulation classification. While deep learning was used to address modulation classification quite extensively using real world data, none of these papers give intuition about the neural network architectures that must be chosen to get good classification performance. During our study and experiments, we realized that this simple example with simple wireless channel models can be used as a reference to understand how to choose the appropriate deep learning models, specifically neural network models, based on the system model for the problem under consideration. In this paper, we provide numerical results to support the intuition that arises for various cases. © 2020 IEEE
Graph Neural Networks-Based User Pairing in Wireless Communication Systems
Recently, deep neural networks have emerged as a solution to solve NP-hard
wireless resource allocation problems in real-time. However, multi-layer
perceptron (MLP) and convolutional neural network (CNN) structures, which are
inherited from image processing tasks, are not optimized for wireless network
problems. As network size increases, these methods get harder to train and
generalize. User pairing is one such essential NP-hard optimization problem in
wireless communication systems that entails selecting users to be scheduled
together while minimizing interference and maximizing throughput. In this
paper, we propose an unsupervised graph neural network (GNN) approach to
efficiently solve the user pairing problem. Our proposed method utilizes the
Erdos goes neural pipeline to significantly outperform other scheduling methods
such as k-means and semi-orthogonal user scheduling (SUS). At 20 dB SNR, our
proposed approach achieves a 49% better sum rate than k-means and a staggering
95% better sum rate than SUS while consuming minimal time and resources. The
scalability of the proposed method is also explored as our model can handle
dynamic changes in network size without experiencing a substantial decrease in
performance. Moreover, our model can accomplish this without being explicitly
trained for larger or smaller networks facilitating a dynamic functionality
that cannot be achieved using CNNs or MLPs