Browsing by Author "Hollanti, Camilla"

Now showing 1 - 9 of 9

An Algebraic Tool for Obtaining Conditional Non-Vanishing Determinants
(2009)
Hollanti, Camilla
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Lu, Hsiao-Feng (Francis)
;
Vehkalahti, Roope
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電信工程研究所
;
Institute of Communications Engineering
An algebraic tool from the theory of central simple algebras is proposed to obtain families of complex matrices satisfying the conditional non-vanishing determinant (CNVD) property. Such property is of great use in e.g. the design of multiuser space-time (ST) codes, in which context it is not always crucial for the transmission matrix to be invertible. On the other hand, whenever it is invertible, it is important that it has a non-vanishing determinant. Also any submatrix of any subset of users multiplied with its transpose conjugate should preferably have a non-vanishing determinant, provided it is non-zero. In recent submissions by Lu et al. it has been shown that, with suitable multiplexing, such property yields a construction of space-time codes that achieve the optimal diversity-multiplexing tradeoff (DMT) of the multiple-input multiple-output (MIMO) multiple access channel (MAC) and outperform the previously known ST codes.
Construction Methods for Asymmetric and Multiblock Space-Time Codes
(2009-03-01)
Hollanti, Camilla
;
Lu, Hsiao-Feng (Francis)
;
電信工程研究所
;
Institute of Communications Engineering
In this paper, the need for the construction of asymmetric and multiblock space-time codes is discussed. Above the trivial puncturing method, i.e., switching off the extra layers in the symmetric multiple-input multiple-output (MIMO) setting, two more sophisticated asymmetric construction methods are proposed. The first method, called the block diagonal method (BDM), can be converted to produce multiblock space-time codes that achieve the diversity-multiplexing tradeoff (DMT). It is also shown that maximizing the density of the newly proposed block diagonal asymmetric space-time (AST) codes is equivalent to minimizing the discriminant of a certain order, a result that also holds as such for the multiblock codes. An implicit lower bound for the density is provided and made explicit for an important special case that contains e.g., the systems equipped with 4Tx+2Rx antennas. Further, an explicit scheme achieving the bound is given. Another method proposed here is the Smart Puncturing Method (SPM) that generalizes the subfield construction method proposed in earlier work by Hollanti and Ranto and applies to any number of transmitting and lesser receiving antennas. The use of the general methods is demonstrated by building explicit, sphere decodable codes using different cyclic division algebras (CDAs). Computer simulations verify that the newly proposed methods can compete with the trivial puncturing method, and in some cases clearly outperform it. The conquering construction exploiting maximal orders improves upon the punctured perfect code and the DjABBA code as well as the Icosian code. Also extensive DMT analysis is provided.
Diversity-Multiplexing Tradeoff-Optimal Code Constructions for Symmetric MIMO Multiple Access Channels
(2009)
Lu, Hsiao-feng (Francis)
;
Hollanti, Camilla
;
電信工程研究所
;
Institute of Communications Engineering
An explicit, systematic code construction for the symmetric MIMO (multi-input multi-output) multiple access (MAC) channel with any number of users and any numbers of transmit and receive antennas is presented in this paper. The users are assumed to transmit at the same level of multiplexing gain. This newly constructed code is proved to achieve the optimal MIMO-MAC diversity-multiplexing tradeoff.
Efficiently sphere-decodable physical layer transmission schemes for wireless storage networks
(2016-05-05)
Lu, Hsiao-feng (Francis)
;
Barreal, Amaro
;
Karpuk, David
;
Hollanti, Camilla
;
資訊工程學系
Three transmission schemes over a new type of multiple-access channel (MAC) model with inter-source communication links are proposed and investigated in this paper. This new channel model is well motivated by, e.g., wireless distributed storage networks, where communication to repair a lost node takes place from helper nodes to a repairing node over a wireless channel. Since in many wireless networks nodes can come and go in an arbitrary manner, there must be an inherent capability of inter-node communication between every pair of nodes. Assuming that communication is possible between every pair of helper nodes, the newly proposed schemes are based on various smart time-sharing and relaying strategies. In other words, certain helper nodes will be regarded as relays, thereby converting the conventional uncooperative multiple-access channel to a multiple-access relay channel (MARC). The diversity-multiplexing gain tradeoff (DMT) of the system together with efficient sphere-decodability and low structural complexity in terms of the number of antennas required at each end is used as the main design objectives. While the optimal DMT for the new channel model is fully open, it is shown that the proposed schemes outperform the DMT of the simple time-sharing protocol and, in some cases, even the optimal uncooperative MAC DMT. While using a wireless distributed storage network as a motivating example throughout the paper, the MAC transmission techniques proposed here are completely general and as such applicable to any MAC communication with inter-source communication links.
Efficiently sphere-decodable physical layer transmission schemes for wireless storage networks
(2016-05-05)
Lu, Hsiao-feng (Francis)
;
Barreal, Amaro
;
Karpuk, David
;
Hollanti, Camilla
;
電機工程學系
Three transmission schemes over a new type of multiple-access channel (MAC) model with inter-source communication links are proposed and investigated in this paper. This new channel model is well motivated by, e.g., wireless distributed storage networks, where communication to repair a lost node takes place from helper nodes to a repairing node over a wireless channel. Since in many wireless networks nodes can come and go in an arbitrary manner, there must be an inherent capability of inter-node communication between every pair of nodes. Assuming that communication is possible between every pair of helper nodes, the newly proposed schemes are based on various smart time-sharing and relaying strategies. In other words, certain helper nodes will be regarded as relays, thereby converting the conventional uncooperative multiple-access channel to a multiple-access relay channel (MARC). The diversity-multiplexing gain tradeoff (DMT) of the system together with efficient sphere-decodability and low structural complexity in terms of the number of antennas required at each end is used as the main design objectives. While the optimal DMT for the new channel model is fully open, it is shown that the proposed schemes outperform the DMT of the simple time-sharing protocol and, in some cases, even the optimal uncooperative MAC DMT. While using a wireless distributed storage network as a motivating example throughout the paper, the MAC transmission techniques proposed here are completely general and as such applicable to any MAC communication with inter-source communication links.
New Relay-Based Transmission Protocols for Wireless Distributed Storage Systems
(2014-01-01)
Hollanti, Camilla
;
Lu, Hsiao-feng (Francis)
;
Karpuk, David
;
Barreal, Amaro
;
電機資訊學士班
Communication over a fading channel in a wireless storage system makes repair transmissions prone to physical layer errors. The repair transmission can be modeled as a multiple access channel (MAC), where multiple helpers are simultaneously communicating to the newcomer node. The existing optimal MAC space-time (ST) codes are, however, practically useless due to exponentially high decoding complexity when the number of helper nodes is big and the number of antennas at the newcomer node is low. To tackle this problem, two new repair transmission protocols based on ST-coding and relaying strategies are given in this paper. The diversity-multiplexing gain tradeoff (DMT) of the system together with sphere-decodability and low transmitter and receiver complexity in terms of the number of antennas required at each end are used as the main design criteria, thus naturally establishing a tradeoff between DMT, complexity, and the decoding delay. Both schemes are converting the MAC into a relay channel by increasing the decoding delay, which enables them to outperform the DMT of a simple time sharing protocol and the MAC DMT for certain multiplexing gains.
New Space-Time Code Constructions for Two-User Multiple Access Channels
(2009-12-01)
Lu, Hsiao-feng (Francis)
;
Vehkalahti, Roope
;
Hollanti, Camilla
;
Lahtonen, Jyrki
;
Hong, Yi
This paper addresses the problem of constructing multiuser multiple-input multiple-output (MU-MIMO) codes for two users. The users are assumed to be equipped with n(t) transmit antennas, and there are n(r) antennas available at the receiving end. A general scheme is proposed and shown to achieve the optimal diversity-multiplexing gain tradeoff (DMT). Moreover, an explicit construction for the special case of n(t) = 2 and n(r) = 2 is given, based on the optimization of the code shape and density. All the proposed constructions are based on cyclic division algebras and their orders and take advantage of the multi-block structure. Computer simulations show that both the proposed schemes yield codes with excellent performance improving upon the best previously known codes. Finally, it is shown that the previously proposed design criteria for DMT optimal MU-MIMO codes are sufficient but in general too strict and impossible to fulfill. Relaxed alternative design criteria are then proposed and shown to be still sufficient for achieving the multiple-access channel diversity-multiplexing tradeoff.
Optimal Diversity-Multiplexing Tradeoff and Code Constructions of Some Constrained Asymmetric MIMO Systems
(2010-05-01)
Lu, Hsiao-Feng (Francis)
;
Hollanti, Camilla
;
電機工程學系
;
Department of Electrical and Computer Engineering
In multiple-input-multiple-output (MIMO) communications, the notion of asymmetric channel refers to the situation when the number of transmit antennas is strictly larger than the number of receive antennas. Such channels can often be found in MIMO downlink transmissions. While existing cyclic-division-algebra (CDA)-based codes can still be employed to achieve the optimal diversity-multiplexing tradeoff (DMT) at high signal-to-noise ratio (SNR) regime, such codes cannot be directly decoded using, for example, the pure sphere decoding method. Although other means of decoding methods such as minimum mean square error generalized decision feedback equalizer (MMSE-GDFE) with lattice search and regularized lattice decoding are available, an alternative approach is to constrain the number of active transmit antennas in each channel use to be no larger than the number of receive antennas. The resulting system is coined constrained asymmetric MIMO system. Two general types of asymmetrical channels are considered in this paper, namely, 1) when there are two receive antennas and the number of transmit antennas is arbitrary, and 2) when the number of transmit antennas is one larger than the number of receive antennas. Explicit optimal transmission schemes as well as the corresponding code constructions for such constrained asymmetric MIMO channels are presented, and are shown to achieve the same DMT performance as their unconstrained counterparts.
Space-Time Storage Codes for Wireless Distributed Storage Systems
(2014-01-01)
Hollanti, Camilla
;
Karpuk, David
;
Barreal, Amaro
;
Lu, Hsiao-Feng (Francis)
;
電機資訊學士班
Distributed storage systems (SDSSs) have gained a lot of interest recently, thanks to their robustness and scalability compared to single-device storage. Majority of the related research has exclusively concerned the network layer. At the same time, the number of users of, e.g., peer-to-peer (p2p) and device-to-device (d2d) networks as well as proximity based services is growing rapidly, and the mobility of users is considered more and more important. This motivates, in contrast to the existing literature, the study of the physical layer functionality of wireless distributed storage systems. In this paper, we take the first step towards protecting the storage repair transmissions from physical layer errors when the transmission takes place over a fading channel. To this end, we introduce the notion of a space-time storage code, drawing together the aspects of network layer and physical layer functionality and resulting in cross-layer robustness. It is also pointed out that existing space-time codes are too complex to be utilized in storage networks when the number of helpers involved is larger than the number of receive antennas at the newcomer or data collector, hence creating a call for less complex transmission protocols.