Interference Alignment and DOF Analysis of Interference and Interference Broadcast Channels

175 Pages·2016·2.78 MB·English

Interference Alignment and DOF Analysis of
Interference and Interference Broadcast
Channels
by
Jhanak Parajuli
A thesis submitted in partial fulfillment
of the requirements for the degree of
Doctor of Philosophy
in Electrical Engineering
Approved Dissertation Committee:
Prof. Dr. Eng. Giuseppe Abreu
(Jacobs University Bremen)
Prof. Dr. Ing. Werner Henkel
(Jacobs University Bremen)
Dr. Antti To¨lli
(CWC, University of Oulu)
Date of Defense: September 22, 2016.
Computer Science & Electrical Engineering, Jacobs University Bremen
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Dedication
“Behind every child who believes in himself/herself is a parent who believed first.”
Matthew Jacobson
I dedicate this thesis to my parents:
Jayaram Parajuli
and
Chuna Devi Parajuli.
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Acknowledgements
I would like to express my deep thanks and sincere gratitude to all who have helped me in
one way or other during my complete Ph.D program. I am very very grateful to my Ph.D.
supervisor Prof. Dr. Giuseppe Abreu, whose constant motivation, strong support, quality
guidance, valuable discussions and strict requirements could make my work a success. I am
very thankful for the convenient and friendly academic environment that he provided during
my Ph.D and masters studies at Jacobs University Bremen. I could really grow academically
during this time. Thanks to the university for such a wonderful environment . I am also very
grateful to Prof. Dr. Ing. Werner Henkel and Dr. Antti To¨lli, who have agreed to be on my
dissertation committee.
I am also thankful to the European Union FP7 project BUTLER (uBiquitous, secUre
inTernet-of-things with Location and contEx-awaReness) and H2020 project HIGHTS (High-
precision positioning for cooperative Intelligent Transport systems) for providing me economic
assistance, without which I could not imagine my Ph.D degree. My special thanks to Dr.
Stefano Severi for his constant efforts to work on new projects which made it really easy
for me and I could focus on my Ph.D work. I am very thankful to my previous and present
work-group and colleagues Samip, Satya, Tayo, Simona, Yohannes, Remun, Ali, Andrei,
Cristian, Jonathan and all other who are involved in our work-group in one way or the other.
Fruitful discussions during our group meeting always helped me a lot.
My sincere thanks to my Nepali friends in Jacobs University, Samip, Asman, Anup, Riwaj,
Shailesh, Dileep, Chhabi, Ujjwal, Dev and my friends outside the university Shankar, Ashish,
Sudha, Bishal, Gyanendra, Aabhushan, Jwalanta , Gunjan and Binod who supported me in
every possible ways they could and helped me feel homely every time. A very very sincere
thanks to my very nice and lovely host family in Bremen (Gerlind, Axel and Marius) who
helped me a lot during my initial days in Bremen. I always appreciate their help.
My special thanks to the MIT open courseware, edX and coursera that allows a framework
to take a number of online courses and make myself clear on the topics which I had not
understood before. It was really very helpful many times. Also, a very special thanks to the
badminton club members in the university and members of my house in Cigarrenmanufaktur,
especially to Shailesh, Viri, Satya and Harsha.
Last but not the least, I am very thankful to my parents, who always devoted their life for
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giving me better education and helping me in every possible ways they could; and to all my
family members, my brothers, sisters, brother-in-laws and sister-in-laws for providing me a
strong mental and economic support when needed. Thanks to all my well-wishers and to all
those who helped me and I forgot to mention here.
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Statutory Declaration
I, Jhanak Parajuli, hereby declare, under penalty of perjury, that I am aware of the
consequences of a deliberately or negligently wrongly submitted affidavit, in particular the
punitive provisions of 156 and 161 of the Criminal Code (up to 1 year imprisonment or a
§ §
fine at delivering a negligent or 3 years or a fine at a knowingly false affidavit).
Furthermore I declare that I have written this PhD thesis independently, unless where
clearly stated otherwise. I have used only the sources, the data and the support that I have
clearly mentioned.
This PhD thesis has not been submitted for the conferral of a degree elsewhere.
Bremen, October 10, 2016.
Signature
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Abstract
Multi-user wireless communication system is interference limited and determining the capacity
region for such network is a challenging problem. Information theoretically, even the capacity
region of a two-user Gaussian interference channel (IC) remains an open problem since
1970s. However, recently a new cooperative interference management technique, called the
interference alignment (IA), has been proposed and shown to achieve the optimum degrees of
freedom (DOF) in interference networks such as multiple access channel (MAC), broadcast
channel (BC), IC and the X-channel (XC). Since DOF is the first order approximation of the
capacity at high signal to noise ratios (SNRs), IA has been a topic of tremendous interests to
the wireless communication engineers and information theorists.
Interference alignment is a technique in which all the interfering signals observed from
different transmitters are aligned onto the same direction or onto a common subspace while
maintaining independence with the desired signal in a particular receiver. In a K-user single
input single output (SISO) interference network with K > 2, IA allows all K 1 interference
−
signals to be aligned over only 1 dimension as opposed to K 1 dimensions in other spectrum
−
sharing techniques like frequency division multiple access (FDMA) and time division multiple
access (TDMA). Thus, each user can achieve maximum of 1 DOF, which is much higher than
2
1 in traditional FDMA and TDMA systems.
K
Aligning K 1 independent interference signals observed from different sources onto a
−
single direction becomes mathematically challenging as K increases. Initial ideas in [1]
considered infinite uses of the channel and proved that 1 DOF is mathematically achievable
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for any SISO-IC. Later, it is observed that for the multiple input multiple output (MIMO)
settings, the spatial dimensions can be exploited and infinite channel uses are not required
for the alignment, but the interference can be aligned by designing proper precoding matrices
at all the transmitters [2].
However, one of the main drawbacks of these approaches are the requirement of instanta-
neous channel state information at the transmitter (CSIT) and the explosion of parameters
as K increases. In fact, a robust generalized IA algorithm for any interference network still
remains an open problem.
In this thesis, we aim to address some of these existing challenges in the interference
management of multi-user networks by providing following three fold contributions:
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Improvement of the existing IA algorithms: Using cooperation among the receivers, it
•
is shown that a proper precoding and zero-forcing matrix can be designed iteratively by
decreasing the interference power and increasing the desired signal power simultaneously
foraK-userMIMO-IC.Suchprecodingmatricesimprovesthesystemcapacitymeasured
in bits per second per channel use than previously existing algorithms. Simulation
results are provided.
Relaxation of the requirement of CSIT: A space-time transmission scheme is designed
•
which uses only the delayed CSIT instead of instantaneous CSIT and such scheme is
shown to achieve greater than one DOF in any multi-cell multiple input single output
(MISO) BC. Such interference broadcast channel (IBC) requires both the inter cell
interference (ICI) and the inter user interference (IUI) be canceled properly. It is shown
that by proper transmission strategy, the achievable DOF converges to 8 when the
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number of users per cell becomes very large.
Proposition of a new alignment technique: A new grouping based IA technique is
•
proposed where the receivers within a group cooperatively align the interference from a
common source onto an overlapping space. By doing so, the receivers can take benefit
from the unused spatial dimensions of each other. Such concept of alignment is termed
as vertical alignment. Proper precoding matrices are designed to align the ICI onto a
common overlap space in two cell MIMO BC and optimal overlapping dimensions are
determined for ring and star topologically arranged three user MIMO IC.
DOF analysis of three user MIMO IC with any arbitrary number of transmit and receive
antennas is a challenging problem and very few works are done in this regard. By
determining the optimal overlapping between any two adjacent receivers, a relatively
new and simple chain based DOF analysis technique is proposed, where the DOF can
be expressed in terms of the length of such chain. The scheme is termed as receiver
chain alignment (RCA).
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