483 research outputs found
Resource allocation and optimization techniques in wireless relay networks
Relay techniques have the potential to enhance capacity and coverage of a wireless network. Due to rapidly increasing number of smart phone subscribers and high demand for data intensive multimedia applications, the
useful radio spectrum is becoming a scarce resource. For this reason, two way relay network and cognitive radio technologies are required for better utilization of radio spectrum. Compared to the conventional one way relay
network, both the uplink and the downlink can be served simultaneously using a two way relay network. Hence the effective bandwidth efficiency is considered to be one time slot per transmission. Cognitive networks are wireless networks that consist of different types of users, a primary user (PU, the primary license holder of a spectrum band) and secondary users (SU, cognitive radios that opportunistically access the PU spectrum). The
secondary users can access the spectrum of the licensed user provided they do not harmfully affect to the primary user. In this thesis, various resource
allocation and optimization techniques have been investigated for wireless relay and cognitive radio networks
Power efficient designs for 5G wireless networks
In this dissertation, to step forward towards green communication, we study power efficient solutions in three potential 5G wireless networks, namely an asynchronous multicarrier two-way Amplify-and-Forward (AF) relay network, a multi-carrier two-way Filter-and-Forward (FF) network, and a massive Multiple Input Multiple Output (MIMO) network using the Non-Orthogonal Multiple Access (NOMA) scheme. In the first network, two transceivers using the Orthogonal Frequency Division Multiplexing (OFDM) scheme communicate through multiple relays in an asynchronous manner. As an attempt to design a simple solution, we assume the AF protocol at the relays. We jointly design the power allocation and distributed beamforming coefficients to minimize the total transmission power subject to sum-rate constraints. We propose an optimal semi-closed form solution to this problem and we show that at the optimum, the end-to-end channel has only one non-zero tap. To extend the first work to high data-rate scenarios, we consider a second relaying-based network which consists of two OFDM-based transceivers and multiple FF relays. We propose two approaches to tackle a total transmission power minimization problem: a gradient steepest descent-based technique, and a low-complexity method enforcing a frequency-flat Channel Impulse Response (CIR) response at the optimum. As the last network, we consider a massive MIMO-NOMA network with both co-located and distributed structures. We study the joint problem of power allocation and user clustering to minimize the total transmit power subject to QoS constraints. We propose a novel clustering algorithm which groups the correlated users into the same cluster and has an unique ability to automatically switch between using the spatial-domain-MIMO and the power-domain-NOMA. We show that our proposed method can substantially improve the feasibility probability and power consumption performance compared to existing methods
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
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
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
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