Browsing by Author "Lu, Hsiao-feng (Francis)"

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A Feedback-Aided Rate-Split Decode-and-Forward Protocol for Static Cooperative Communications
(2016-01-01)
Lu, Hsiao-feng (Francis)
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電機工程學系
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Department of Electrical and Computer Engineering
A two-phase, rate-split, static nonorthogonal decode-and-forward protocol for the cooperative relay network consisting of a source, multiple half-duplex relays and a destination, all having single antenna, is proposed in this paper. In the proposed protocol, the desired transmission rate R is split into rates R-1 and R-2; then the source sends rate R-1 during the first phase and rate R2 during the second. Explicit expressions for R-1 and R-2, are also given. It is shown that the proposed protocol achieves the optimal cooperative diversity derived from the information theoretic cut set bound in high SNR regime. Compared to the compress-and-forward protocol, the proposed protocol is much simpler for practical implementation, holds the same for any number of relays and requires only local channel-state-information at each node, except for a small feedback of rate R-1 as well as a selection index of relays.
Accumulate Codes Based on 1+D Convolutional Outer Codes
(2009-02-01)
Chiu, Mao-Ching
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Lu, Hsiao-feng (Francis)
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電信工程研究所
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Institute of Communications Engineering
A new construction of good, easily encodable, and soft-decodable codes is proposed in this paper. The construction is based on serially concatenating several simple 1+D convolutional codes as the outer code, and a rate-1 1/(1 + D) accumulate code as the inner code. These codes have very low encoding complexity and require only one shift-forward register for each encoding branch. The input-output weight enumerators of these codes are also derived. Divsalar's simple bound technique is applied to analyze the bit error rate performance, and to assess the minimal required signal-to-noise ratio (SNR) for these codes to achieve reliable communication under AWGN channel. Simulation results show that the proposed codes can provide good performance under iterative decoding.
An Error Event Sensitive Tradeoff Between Rate and Coding Gain in MIMO MAC
(2015-11-01)
Ernvall, Toni
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Lahtonen, Jyrki
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Lu, Hsiao-feng (Francis)
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Vehkalahti, Roope
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電機資訊學士班
This paper investigates the design of codes for multiple-input multiple-output (MIMO) multiple access channel (MAC). If a joint maximum-likelihood decoding is to be performed at the receiver, then every MIMO-MAC code can be regarded as a single-user code, where the minimum determinant criterion proposed by Tarokh et al. is useful for designing such codes and for upper bounding the maximum pairwise error probability (PEP), whenever the codes are of finite rate and operate in finite signal-to-noise ratio range. Unlike the case of single-user codes where the minimum determinant can be lower bounded by a fixed constant as code-rate grows, it was proved by Lahtonen et al. that the minimum determinant of MIMO-MAC codes decays as a function of the rates. This decay phenomenon is further investigated in this paper, and upper bounds for the decays of minimum determinant corresponding to each error event are provided. Lower bounds for the optimal decay are established and are based on an explicit construction of codes using algebraic number theory and Diophantine approximation. For some error profiles, the constructed codes are shown to meet the aforementioned upper bounds, hence they are optimal finite-rate codes in terms of PEPs associated with such error events. An asymptotic diversity-multiplexing gain tradeoff (DMT) analysis of the proposed codes is also given. It is shown that these codes are DMT optimal when the values of multiplexing gains are small.
Analysis and Practice of Uniquely Decodable One-to-One Code
(2013-01-01)
Liu, Chin-Fu
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Lu, Hsiao-feng (Francis)
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Chen, Po-Ning
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電機資訊學士班
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Undergraduate Honors Program of Electrical Engineering and Computer Science
In this paper, we consider the uniquely decodable one-to-one code (UDOOC) that is obtained by inserting a comma indicator, termed the unique word (UW), between consecutive one-to-one codewords for separation. As such, we analyze a class of UDOOCs and present practical algorithms for encoding and decoding such codes. Specifically, for various cases of UWs, we investigate the number of length-n codewords of UDOOCs and their asymptotic growth rates in n. The proposed encoding and decoding algorithms of UDOOCs can be implemented in parallel at low computational complexity without storing the codebook. Simulation results show that for proper choices of UWs, UDOOCs can achieve better compression efficiency than Lempel-Ziv codes even when the source is not statistically independent.
Coding Schemes With Constant Sphere-Decoding Complexity and High DMT Performance for MIMO Multiple Access Channels With Low-Rate Feedback
(2014-01-01)
Tang, Ti-wen
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Tien, Hsiao-ting
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Lu, Hsiao-feng (Francis)
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電機資訊學士班
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Undergraduate Honors Program of Electrical Engineering and Computer Science
In a MIMO MAC where the base station has fewer receive antennas than the transmit antennas of all users, sphere (lattice) decoding for the existing MIMO-MAC codes requires an exhaustive search of exponentially large size before processing the root of a sphere-decoding tree. In this paper, two coding schemes are proposed and are shown to yield a constant sphere-decoding complexity, independent of the numbers of users and transmit antennas. The schemes require a channel feedback, but only at an extremely low rate. The first scheme is based on user selection, and the second scheme selects jointly users and transmit antennas, using a fast antenna selection algorithm recently proposed by Jiang and Varanasi. It also involves a design of rate-assignments that maximizes the overall DMT performance. It is shown that both schemes yield DMT performances far superior to the optimal MIMO-MAC DMT without channel feedback in certain multiplexing gain regime. Simulation results confirm that in some cases the second proposed scheme can provide an astonishing SNR gain of 14.5 dB at outage probability 10(-6) compared to the optimal coding schemes without feedback.
Diversity-multiplexing Gain Tradeoff: a Tool in Algebra?
(2011)
Vehkalahti, Roope
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Lu, Hsiao-feng (Francis)
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電機工程學系
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Department of Electrical and Computer Engineering
Since the invention of space-time coding numerous algebraic methods have been applied in code design. In particular algebraic number theory and central simple algebras have been on the forefront of the research. In this paper we are turning the table and asking whether information theory can be used as a tool in algebra. We first show how diversity-multiplexing gain tradeoff (DMT) bounds of Zheng and Tse will give us information of the spread of determinants in matrix lattices and then apply these results to analyze unit groups of orders of division algebras. The results considering unit groups are not new or the best possible but we do find that this interesting relation between algebra and information theory is quite surprising and worth pointing out.
Diversity-Multiplexing Tradeoff in MIMO Gaussian Interference Channels
(2010)
Lu, Hsiao-feng (Francis)
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交大名義發表
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National Chiao Tung University
In this paper we analyze the generalized degrees of freedom (GDOF) and the DMT performances of both the symmetric and asymmetric MIMO Gaussian interference fading channel with a fixed-power-split HK scheme for two transmit-receive pairs. Exact characterizations of both the GDOF and DMT performance measures are given. It is shown in the SIMO case that when the number of receive antennas is at least two, full region of GDOF can be achieved, as if the non-intending transmitter does not exist. The same conclusion is applied to the DMT measure as well. In particular, if the channel is symmetric, both receivers are able to achieve the single-user performance regime.
Diversity-Multiplexing Tradeoff-Optimal Code Constructions for Symmetric MIMO Multiple Access Channels
(2009)
Lu, Hsiao-feng (Francis)
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Hollanti, Camilla
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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.
DMT Optimal Codes Constructions for Multiple-Access MIMO Channel
(2011-06-01)
Lu, Hsiao-feng (Francis)
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Hollanti, Camilla Johanna
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Vehkalahti, Roope Iikanpoika
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Lahtonen, Jyrki
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電機工程學系
Explicit code constructions for multiple-input multiple-output (MIMO) multiple-access channels (MAC) with K users are presented in this paper. The first construction is dedicated to the case of symmetric MIMO-MAC where all the users have the same number of transmit antennas n(t) and transmit at the same level of per-user multiplexing gain r. Furthermore, we assume that the users transmit in an independent fashion and do not cooperate. The construction is systematic for any values of K, n(t) and r. It is proved that this newly proposed construction achieves the optimal MIMO-MAC diversity-multiplexing gain tradeoff (DMT) provided by Tse et al. at high-SNR regime. In the second part of the paper we take a further step to investigate the MAC-DMT of a general MIMO-MAC where the users are allowed to have different numbers of transmit antennas and can transmit at different levels of multiplexing gain. The exact optimal MAC-DMT of such channel is explicitly characterized in this paper. Interestingly, in the general MAC-DMT, some users might not be able to achieve their single-user DMT performance as in the symmetric case, even when the multiplexing gains of the other users are close to 0. Detailed explanations of such unexpected result are provided in this paper. Finally, by generalizing the code construction for the symmetric MIMO-MAC, explicit code constructions are provided for the general MIMO-MAC and are proved to be optimal in terms of the general MAC-DMT.
Efficiently sphere-decodable physical layer transmission schemes for wireless storage networks
(2016-05-05)
Lu, Hsiao-feng (Francis)
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Barreal, Amaro
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Karpuk, David
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Hollanti, Camilla
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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.
Improving the DMT Performances of MIMO Linear Receivers
(2011)
Tang, Ti-wen
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Chen, Min-kun
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Lu, Hsiao-feng (Francis)
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傳播研究所
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Institute of Communication Studies
In this paper, we investigate the diversity multiplexing tradeoff (DMT) performance of MIMO linear receivers with general colored Gaussian input. By varying the rank of the covariance matrix of the channel input and allowing temporal coding across multiple channel uses, we find the DMT performance of MIMO linear receivers can be significantly improved and be much better than the currently known.
New Relay-Based Transmission Protocols for Wireless Distributed Storage Systems
(2014-01-01)
Hollanti, Camilla
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Lu, Hsiao-feng (Francis)
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Karpuk, David
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Barreal, Amaro
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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)
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Vehkalahti, Roope
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Hollanti, Camilla
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Lahtonen, Jyrki
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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 Distributed Codes with Delay Four and Constant Decoding Complexity
(2015)
Lu, Hsiao-feng (Francis)
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電機學院
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College of Electrical and Computer Engineering
A novel transmission scheme based on the nonorthogonal selection decode-and-forward protocol is presented in this paper for cooperative relay networks. The proposed scheme assumes a low rate feedback channel from the destination to the relays. Benefited from the feedback information, an optimal distributed code that has an extremely short delay equal to four is constructed, and the same code can be applied to networks with arbitrary number of relays to yield optimal cooperative diversity gains. The proposed code is sphere-decodable with decoding complexity again independent of the number of relays. In particular, when operating at multiplexing gain >= 1/2, the lattice decoder at the destination has a zero complexity exponent, meaning a constant decoding complexity and independent of transmission rate. Analyses for the decoding complexity of other existing diversity-optimal distributed codes are also provided. It is shown that these codes have a linear growth in delay and an exponential growth in decoding complexity as the number of relays increases.
Optimal Diversity Multiplexing Tradeoff of Constrained Asymmetric MIMO Systems
(2008)
Lu, Hsiao-feng (Francis)
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電信工程研究所
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Institute of Communications Engineering
In a MIMO downlink channel it is often that the number of transmit antennas is strictly larger than the number of receive, and such channel is termed asymmetric MIMO channel. To employ simple decoding techniques in this channel, such as zero-forcing or sphere decoding, the number of active transmit antennas must be constrained to be no larger than the number of receive, and the resulting system is coined "constrained asymmetric MIMO system." For the case of two receive antennas and for any number of transmit antennas, an optimal transmission scheme is presented in this paper and is shown to achieve the same performance as the unconstrained ones in terms of the diversity-multiplexing tradeoff. The construction of optimal constrained codes is also provided.
Rate-Split Based Decode-and-Forward Protocols for Cooperative Communications
(2015)
Lu, Hsiao-feng (Francis)
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電機學院
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College of Electrical and Computer Engineering
In this paper we first establish a general performance upper bound on the diversity-multiplexing tradeoff (DMT) for communication protocols for a half-duplex cooperative network where every node has a single antenna. This bound shows that the dynamic-decode-and-forward (DDF) protocol achieves optimal DMT among all variations of decode-and-forward based protocols when multiplexing gain r <= 1/2. Secondly, when r > 1/2 it shows that the diversity gain must be less than 1 for all protocols and for any number of relay nodes. Our bound also implies that the well-known cut-set-based DMT upper bound is not tight except for the single-relay network and that there are rooms to improve the performance of DDF protocol, thereby settling a long-time open question raised by Azarian et al.. In light of this breakthrough, a novel protocol based on a rate-split is proposed in this paper. Two variations, dynamic and non-dynamic, of the rate-split-based protocol are also presented. It is shown that the dynamic version achieves a DMT better than the DDF protocol, and in particular, meets the cut-set bound in the case of a single-relay network. The other variation, i.e., the non-dynamic one, has a much simpler implementation and reaches its optimal performance in only two channel uses. Moreover, it meets the cut-set bound in the case of a single-relay network.
Selection and Rate-Adaptation Schemes for MIMO Multiple-Access Channels With Low-Rate Channel Feedback
(2015-11-01)
Tang, Ti-Wen
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Tien, Hsiao-Ting
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Lu, Hsiao-feng (Francis)
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電機資訊學士班
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Undergraduate Honors Program of Electrical Engineering and Computer Science
In this paper, two selection schemes are proposed for coded transmission over multiple-input multiple-output (MIMO) multiple-access channels (MAC) to yield a much higher diversity-multiplexing gain tradeoff (DMT) performance. These schemes require a channel feedback, but at an extremely low rate. The first scheme is based on user selection and can be easily implemented in the existing MIMO-MAC systems. Upper bounds on the minimal computational complexity required by sphere decoders to decode DMT-optimal codes for this scheme as well as for MIMO MAC without feedback are given. It is shown that this scheme can offer both a much larger DMT and an exponential reduction on decoding complexity, compared with the latter. The second scheme selects jointly the users and their transmit antennas. It requires an additional design of rate assignments for performance optimization. A very general framework on the design of optimal rate assignments is thus provided. It is shown that this scheme can yield DMT performances far superior to the optimal MIMO-MAC DMT without channel feedback. The simulation results confirm that in some cases, this scheme can provide an astonishing SNR gain of 14.64 dB at outage probability 10(-6) compared with the optimal MIMO-MAC coding schemes without feedback.