30,151 research outputs found
Channel Aided Interference Alignment
Interference alignment (IA) techniques mostly attain their degrees of freedom
(DoF) benefits as the number of channel extensions tends to infinity.
Intuitively, the more interfering signals that need to be aligned, the larger
the number of dimensions needed to align them. This requirement poses a major
challenge for IA in practical systems. This work evaluates the necessary and
sufficient conditions on channel structure of a fully connected interference
network with time-varying fading to make perfect IA feasible within limited
number of channel extensions. We propose a method based on the obtained
conditions on the channel structure to achieve perfect IA. For the case of
user interference channel, it is shown that only one condition on channel
coefficients is required to make perfect IA feasible at all receivers. IA
feasibility literature have mainly focused on network topology so far. In
contrast, derived channel aiding conditions in this work can be considered as
the perfect IA feasibility conditions on channel structure.Comment: 20 pages, 4 figure. arXiv admin note: text overlap with
arXiv:0901.4379 by other author
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Capacity bounds for some Gaussian interference channels
In current wireless networks, co-channel interference is the major limiting factor in achieving high spectral efficiency. The effective interference at receivers can be minimized by using advanced interference management techniques. Given channel conditions, what is the fundamental limit on maximum spectral efficiency we can achieve, and which encoding and decoding techniques achieve this limit? These research questions can be addressed as network information theory problems. In particular, the capacity of Gaussian interference channels is an important open problem dealing with these fundamental questions. Some special cases of the interference channels and their capacity regions are studied in this dissertation.
For a class of partially connected interference channels, approximate capacity regions are characterized. The impact of topology, interference alignment, and the interplay between interference and noise are discussed. The results show that for these channels, genie-aided outer bounds are tight to within a constant gap from capacity. Near-optimal achievable schemes, based on rate-splitting and lattice alignment, are presented.
The Gaussian X-channel is also an important Gaussian interference channel model. Lower and upper bounds on the sum-rate capacity are derived for this channel. The achievable schemes are based on layered lattice coding and compute-and-forward decoding. For different regimes of channel parameters, some combinations of encoding and decoding strategies are designed. For some range of channel parameters, the approximate sum-rate capacity is characterized to within a constant gap.Electrical and Computer Engineerin
A New DoF Upper Bound and Its Achievability for -User MIMO Y Channels
This work is to study the degrees of freedom (DoF) for the -user MIMO Y
channel. Previously, two transmission frameworks have been proposed for the DoF
analysis when , where and denote the number of antennas at
each source node and the relay node respectively. The first method is named as
signal group based alignment proposed by Hua et al. in [1]. The second is named
as signal pattern approach introduced by Wang et al. in [2]. But both of them
only studied certain antenna configurations. The maximum achievable DoF in the
general case still remains unknown. In this work, we first derive a new upper
bound of the DoF using the genie-aided approach. Then, we propose a more
general transmission framework, generalized signal alignment (GSA), and show
that the previous two methods are both special cases of GSA. With GSA, we prove
that the new DoF upper bound is achievable when . The DoF
analysis in this paper provides a major step forward towards the fundamental
capacity limit of the -user MIMO Y channel. It also offers a new approach of
integrating interference alignment with physical layer network coding.Comment: 6 pages, 3 figures, submitted to IEEE ICC 2015. arXiv admin note:
text overlap with arXiv:1405.071
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μ .This dissertation contains the following three contributions to the interesting research topics on diversity techniques and interference alignment (IA) for cooperative communication networks.
*Relay on-off threshold (ROT) for non-orthogonal decode and forward (NDF) protocol with distributed
orthogonal space-time block codes (DOSTBCs)
- Calculate the optimal ROT for NDF protocol with DOSTBCs in high signal to noise power ratio (SNR) region.
- Propose suboptimal ROT for NDF protocol with DOSTBCs in low SNR region.
- Analyze the diversity order of the proposed scheme.
*New IA schemes aided by relays for quasi-static MX2 X channel
- Propose IA scheme aided by one full-duplex relay.
- Propose IA scheme aided by two half-duplex relay.
- Prove that the proposed IA schemes achieve the maximum degrees of freedom (DoF) for quasi-static MX2 X channel.
* Selection diversity on the IA for multi-input and multi-output (MIMO) interference channel
- Propose the selection criterion of beamforming matrices of IA for MIMO interference channel.
- Analyze the diversity order of the proposed scheme.
First, we construct the DOSTBCs using source and relay in the cooperative communication networks. In order to decode the DOSTBCs, the destination uses the linear combining (LC) decoding scheme. In this system models, the symbol error rate (SER) is formulated and the ROT is calculated to minimize the SER. It is proved that the full diversity order of NDF protocol can be achieved by using the relay on-off scheme with the optimal threshold.
In the second part of this dissertation, two new IA schemes aided by relays for quasi-static MX2 X channel are proposed. The first proposed scheme uses one full-duplex relay and it can achieves the maximum DoF. However, at the full-duplex relay, the transmit signal can be strong self-interference, called echo and thus it is difficult to implement practically. To resolve this problem, at the second proposed IA scheme, two half-duplex relays are used and it is proved that the second proposed IA scheme can also achieve the maximum DoF of MX2 X channel.
Finally, the selection scheme for IA is proposed for MIMO interference channel. Most of IA schemes are focused on DoF but there is only a few research results for diversity order which is a crucial measure of reliability. Therefore, we propose a selection criterion to minimize SER and analyze the diversity order of the proposed scheme in the MIMO interference channel.Abstract i
Contents iv
List of Tables vii
List of Figures viii
1. Introduction
1.1. Background
1.2. Overview of Dissertation
1.3. Terms and Notations
2. Diversity Techniques and Interference Alignment
2.1. MIMO Communications
2.2. Space-Time Coding and Selection Diversity
2.3. Cooperative Communications
2.4. Interference Alignment
3. Relay On-Off Threshold for NDF Protocol with Distributed
Orthogonal Space-Time Block Codes
3.1. Introduction
3.2. System Models and Linear Combining Decoding
3.2.1. System Models of NDF Protocol
3.2.2. Linear Combining Decoding
3.3. Relay On-Off Threshold and Diversity Analysis
3.3.1. Relay On-Off Threshold
3.3.2. Relay On-Off Threshold for LC Decoding
3.3.3. Decision of Suboptimal Relay On-Off Threshold in
Low SNR Region
3.3.4. Diversity Analysis
3.4. Numerical Analysis
3.5. Conclusion
4. New Interference Alignment Scheme Aided by Relays for
Quasi-Static X Channels
4.1. Introduction
4.2. Preliminaries: X Channel and Interference Alignment
4.3. The Proposed Schemes and System Models
4.3.1. Two Proposed Schemes
4.3.2. System Models for the Proposed Schemes
4.4. Achievability of the Proposed IA Schemes
4.4.1. IA Scheme with a Full-Duplex Relay
4.4.2. IA Scheme with Two Half-Duplex Relays
4.5. Achievability of the Proposed IA Schemes for the 2ΓM X Channel
4.6. Numerical Analysis
4.7. Conclusion
5. Selection Diversity on the Interference Alignment for MIMO Interference Channels
5.1. Introduction
5.2. Characteristic Function of Multivariate Rayleigh Random
Variables
5.3. Combining IA and Selection Schemes for 3-User MIMO Interference
Channel
5.3.1. System Model and IA for 3-User MIMO Interference
Channel
5.3.2. Orthogonalization of Beamforming Matrices
5.3.3. Selection of Beamforming Matrices
5.4. Diversity Analysis
5.5. Simulation Results
5.6. Conclusions
6. Conclusions
Bibliography
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Interference alignment for one-hop and two-hops MIMO systems with uncoordinated interference
Providing higher data rate is a momentous goal for wireless communications systems, while interference is an important obstacle to reach this purpose. To cope with this problem, interference alignment (IA) has been proposed. In this paper, we propose two rank minimization methods to enhance the performance of IA in the presence of uncoordinated interference, i.e., interference that cannot be properly aligned with the rest of the network and thus is a crucial issue. In this scenario, perfect and imperfect channel state information (CSI) cases are considered. Our proposed approaches employ the l2 and the Schatten-p norms to approximate the rank function, due to its non-convexity. Also, we propose a new convex relaxation to expand the feasible set of our optimization problem, providing lower rank solutions compared to other IA methods from the literature. In addition, we propose a modified weighted-sum method to deal with interference in the relay-aided MIMO interference channel, which employs a set of weighting parameters in order to find more solutions
A Systematic Approach for Interference Alignment in CSIT-less Relay-Aided X-Networks
The degrees of freedom (DoF) of an X-network with M transmit and N receive
nodes utilizing interference alignment with the support of relays each
equipped with antennas operating in a half-duplex non-regenerative mode
is investigated. Conditions on the feasibility of interference alignment are
derived using a proper transmit strategy and a structured approach based on a
Kronecker-product representation. The advantages of this approach are twofold:
First, it extends existing results on the achievable DoF to generalized antenna
configurations. Second, it unifies the analysis for time-varying and constant
channels and provides valuable insights and interconnections between the two
channel models. It turns out that a DoF of \nicefrac{NM}{M+N-1} is feasible
whenever the sum of the
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