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Performance Analysis of MIMO Relay Networks with BeamformingJanuary 2012 (has links)
abstract: This dissertation considers two different kinds of two-hop multiple-input multiple-output (MIMO) relay networks with beamforming (BF). First, "one-way" amplify-and-forward (AF) and decode-and-forward (DF) MIMO BF relay networks are considered, in which the relay amplifies or decodes the received signal from the source and forwards it to the destination, respectively, where all nodes beamform with multiple antennas to obtain gains in performance with reduced power consumption. A direct link from source to destination is included in performance analysis. Novel systematic upper-bounds and lower-bounds to average bit or symbol error rates (BERs or SERs) are proposed. Second, "two-way" AF MIMO BF relay networks are investigated, in which two sources exchange their data through a relay, to improve the spectral efficiency compared with one-way relay networks. Novel unified performance analysis is carried out for five different relaying schemes using two, three, and four time slots in sum-BER, the sum of two BERs at both sources, in two-way relay networks with and without direct links. For both kinds of relay networks, when any node is beamforming simultaneously to two nodes (i.e. from source to relay and destination in one-way relay networks, and from relay to both sources in two-way relay networks), the selection of the BF coefficients at a beamforming node becomes a challenging problem since it has to balance the needs of both receiving nodes. Although this "BF optimization" is performed for BER, SER, and sum-BER in this dissertation, the solution for optimal BF coefficients not only is difficult to implement, it also does not lend itself to performance analysis because the optimal BF coefficients cannot be expressed in closed-form. Therefore, the performance of optimal schemes through bounds, as well as suboptimal ones such as strong-path BF, which beamforms to the stronger path of two links based on their received signal-to-noise ratios (SNRs), is provided for BERs or SERs, for the first time. Since different channel state information (CSI) assumptions at the source, relay, and destination provide different error performance, various CSI assumptions are also considered. / Dissertation/Thesis / Ph.D. Electrical Engineering 2012
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Signal design for multi-way relay channelsSharifian, Shaham 20 December 2016 (has links)
Today’s communication systems are in need of spectrally efficient and high throughput
techniques more than ever because of high data rate applications and the scarcity
and expense of bandwidth. To cope with increased data rate demands, more base
stations are needed which is not cost and energy efficient in cellular networks. It
has been shown that wireless relay networks can provide higher network throughput
and increase power efficiency with low complexity and cost. Furthermore, network
resources can be utilized more efficiently by using network coding in relay networks.
A wireless relay network in which multiple nodes exchange information with the
help of relay node(s) is called a multi-way relay channel (MWRC). MWRCs are
expected to be an integral part of next generation wireless standards. The main
focus of this dissertation is the investigation of transmission schemes in an MWRC to
improve the throughput and error performance. An MWRC with full data exchange
is assumed in which a half-duplex relay station (RS) is the enabler of communication.
One of the challenges with signal demodulation in MWRCs is the existence of
ambiguous points in the received constellation. The first part of this dissertation
investigates a transmission scheme for full data exchange in MWRC that benefits from
these points and improves its throughput by 33% compared to traditional relaying.
Then an MWRC is considered where a RS assists multiple nodes to exchange messages.
A different approach is taken to avoid ambiguous points in the superposition of
user symbols at the relay. This can be achieved by employing complex field network
coding (CFNC) which results in full data exchange in two communication phases.
CFNC may lead to small Euclidean distances between constellation points, resulting
in poor error performance. To improve this performance, the optimal user precoding
values are derived such that the power efficiency of the relay constellation is highest
when channel state information is available at the users. The error performance of
each user is then analyzed and compared with other relaying schemes.
Finally, focusing on the uplink of multi-way relay systems, the performance of an
MWRC is studied in which users can employ arbitrary modulation schemes and the
links between the users and the relay have different gains, e.g. Rayleigh fading. Analytical
expressions for the exact average pairwise error probability of these MWRCs
are derived. The probability density function (PDF) and the mean of the minimum
Euclidean distance of the relay constellation are closely approximated, and a tight
upper bound on the symbol error probability is developed. / Graduate
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