| 1. |
- Skoglund, Pontus, et al.
(author)
-
Investigating population history using temporal genetic differentiation
- 2014
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In: Molecular biology and evolution. - : Oxford University Press (OUP). - 0737-4038 .- 1537-1719. ; 31:9, s. 2516-2527
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Journal article (peer-reviewed)abstract
- The rapid advance of sequencing technology coupled with improvements in molecular methods for obtaining genetic data from ancient sources holds the promise of producing a wealth of genomic data from time-separated individuals. However, the population genetic properties of time-structured samples have not been extensively explored. Here, we consider the implications of temporal sampling for analyses of genetic differentiation, and use a temporal coalescent framework to show that complex historical events such as size reductions, population replacements, and transient genetic barriers between populations leave a footprint of genetic differentiation that can be traced through history using temporal samples. Our results emphasize explicit consideration of the temporal structure when making inferences, and indicate that genomic data from ancient individuals will greatly increase our ability to reconstruct population history.
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| 2. |
- Alickovic, Emina, et al.
(author)
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Predicting EEG Responses to Attended Speech via Deep Neural Networks for Speech
- 2023
-
In: 2023 45TH ANNUAL INTERNATIONAL CONFERENCE OF THE IEEE ENGINEERING IN MEDICINE & BIOLOGY SOCIETY, EMBC. - : IEEE. - 9798350324471 - 9798350324488
-
Conference paper (peer-reviewed)abstract
- Attending to the speech stream of interest in multi-talker environments can be a challenging task, particularly for listeners with hearing impairment. Research suggests that neural responses assessed with electroencephalography (EEG) are modulated by listener's auditory attention, revealing selective neural tracking (NT) of the attended speech. NT methods mostly rely on hand-engineered acoustic and linguistic speech features to predict the neural response. Only recently, deep neural network (DNN) models without specific linguistic information have been used to extract speech features for NT, demonstrating that speech features in hierarchical DNN layers can predict neural responses throughout the auditory pathway. In this study, we go one step further to investigate the suitability of similar DNN models for speech to predict neural responses to competing speech observed in EEG. We recorded EEG data using a 64-channel acquisition system from 17 listeners with normal hearing instructed to attend to one of two competing talkers. Our data revealed that EEG responses are significantly better predicted by DNN-extracted speech features than by hand-engineered acoustic features. Furthermore, analysis of hierarchical DNN layers showed that early layers yielded the highest predictions. Moreover, we found a significant increase in auditory attention classification accuracies with the use of DNN-extracted speech features over the use of hand-engineered acoustic features. These findings open a new avenue for development of new NT measures to evaluate and further advance hearing technology.
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| 3. |
- Andersson, Agnes, et al.
(author)
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Headache Before and After Endoscopic Transsphenoidal Pituitary Tumor Surgery: A Prospective Study
- 2022
-
In: Journal of Neurological Surgery Part B-Skull Base. - : Georg Thieme Verlag KG. - 2193-6331 .- 2193-634X. ; 83:suppl. 2
-
Journal article (peer-reviewed)abstract
- Objective Headache is a common symptom among patients with pituitary tumors, as it is in the general population. The aim of the study was to investigate headache as a symptom in patients with pituitary tumors before and 6 months after endoscopic transsphenoidal surgery (TSS). Design This is a prospective observational cohort study. Setting This study was conducted at university tertiary referral hospital. Participants A total of 110 adult patients underwent endoscopic TSS for pituitary tumors. Main Outcome Measures The Migraine Disability Assessment (MIDAS) questionnaire was used before and 6 months after surgery for the assessment of headache. Clinical variables with potential influence on headache were analyzed. Results Sixty-eight (62%) patients experienced headaches at least once during the 3 months before surgery. Thirty (27%) patients reported disabling headache before surgery, with younger age being an independent associated factor ( p <0.001). In patients with disabling headache before surgery, the median (interquartile range) MIDAS score improved from 78 (27-168) to 16 (2-145; p =0.049), headache frequency decreased from 45 (20-81) to 14 (4-35) days ( p =0.009), and headache intensity decreased from 6 (5-8) to 5 (4-7) ( p =0.011) after surgery. In total, 16 of the 30 (53%) patients reported a clinically relevant improvement and five (17%) a clinically relevant worsening. Four (5%) patients developed new disabling headache. No predictor for postoperative improvement of headache was identified. Conclusion In this prospective study, the results show that disabling headache improves following endoscopic TSS in a subset of patients with pituitary tumors. However, no predictive factors for improvement could be identified.
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| 4. |
- Andersson, Mattias, et al.
(author)
-
Polar codes for bidirectional broadcast channels with common and confidential messages
- 2012
-
In: International Symposium on Wireless Communication Systems (ISWCS), 2012. - : IEEE conference proceedings. - 9781467307604 ; , s. 1014-1018
-
Conference paper (peer-reviewed)abstract
- We consider the bidirectional broadcast channel with common and confidential messages. We show that polar codes achieve the capacity of binary input symmetrical bidirectional broadcast channels with confidential messages, if one node's channel is a degraded version of the other node's channel. We also find a new bound on the cardinality of the auxiliary random variable in this setup.
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| 5. |
- Andersson, Mattias, et al.
(author)
-
Polar Coding for Bidirectional Broadcast Channels with Common and Confidential Messages
- 2013
-
In: IEEE Journal on Selected Areas in Communications. - 0733-8716 .- 1558-0008. ; 31:9, s. 1901-1908
-
Journal article (peer-reviewed)abstract
- The integration of multiple services such as the transmission of private, common, and confidential messages at the physical layer is becoming important for future wireless networks in order to increase spectral efficiency. In this paper, bidirectional relay networks are considered, in which a relay node establishes bidirectional communication between two other nodes using a decode-and-forward protocol. In the broadcast phase, the relay transmits additional common and confidential messages, which then requires the study of the bidirectional broadcast channel (BBC) with common and confidential messages. This channel generalizes the broadcast channel with receiver side information considered by Kramer and Shamai. Low complexity polar codes are constructed that achieve the capacity region of both the degraded symmetric BBC, and the BBC with common and confidential messages. The use of polar codes allows an intuitive interpretation of how to incorporate receiver side information and secrecy constraints as different sets of frozen bits at the different receivers for an optimal code design. In order to show that the constructed codes achieve capacity, a tighter bound on the cardinality of an auxiliary random variable used in the converse is found using a method by Salehi.
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| 6. |
- Bilal, Ibrahim, et al.
(author)
-
An Optimized Linear Scheme for Stabilization Over Multi-User Gaussian Networks
- 2013
-
In: 2013 Information Theory And Applications Workshop (ITA). - New York : IEEE. - 9781467346481 ; , s. 290-297
-
Conference paper (peer-reviewed)abstract
- Remote stabilization of linear dynamical systems over Gaussian networks is studied. Two linear time invariant systems (plants) with arbitrary distributed initial states are monitored by two separate sensors. The sensors communicate their measurements to two remotely situated controllers over a Gaussian interference, possibly with the assistance from a relay node. The common goal of the sensors, relay, and controllers is to stabilize the plants in mean-square sense. An optimized linear delay-free sensing and control scheme is proposed and sufficient conditions for mean-square stability are derived. These conditions reveal the relationship between plants' stability and communication channel parameters. It is shown that the proposed linear scheme can significantly outperform the existing estimation based control scheme in multi-user Gaussian networks.
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| 7. |
- Bilal, Ibrahim, et al.
(author)
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Feedback stabilization over a Gaussian interference relay channel
- 2013
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In: 2013 IEEE 14th Workshop on Signal Processing Advances in Wireless Communications, SPAWC. - : IEEE. - 9781467355773 ; , s. 560-564
-
Conference paper (peer-reviewed)abstract
- A transmission scheme for mean square stabilization of two linear systems over a Gaussian interference relay channel is studied. A delay-free linear sensing and control strategy is proposed and an achievable stability region is derived. It shows that the stability region can be significantly enlarged by deploying a relay node in such a multi-user Gaussian channels. Furthermore we observe that the separation structure between estimation and control is inadequate in high interference regime.
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| 8. |
- Bilal, Ibrahim, et al.
(author)
-
Managing interference for stabilization over wireless channels
- 2012
-
In: Intelligent Control (ISIC), 2012 IEEE International Symposium on. - : IEEE. - 9781467345989 ; , s. 933-938
-
Conference paper (peer-reviewed)abstract
- The remote stabilization of a first order linear plant over a wireless channel is studied. The plant is assumed to have an arbitrary distributed initial state and the wireless channel between the plant's sensor and the controller is modeled as a white Gaussian channel subject to an external interference signal. In order to combat the interference a dedicated sensor (relay) node is deployed adjacent to the interferer, which relays the interference information to both the plant's sensor and the controller. The sensor and the controller utilize this information to mitigate interference. We use delay-free linear sensing and control scheme in order to derive sufficient conditions for mean square stability. The achievable stability region significantly enlarges with the relay assisted interference cancelation scheme. Moreover the effect of interference can be completely eliminated if the encoder knows all the future values of the interference.
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| 9. |
- Cao, Le Phuong, 1983-
(author)
-
Optimal Transmit Strategies for Multi-antenna Systems with Joint Sum and Per-antenna Power Constraints
- 2019
-
Doctoral thesis (other academic/artistic)abstract
- Nowadays, wireless communications have become an essential part of our daily life. During the last decade, both the number of users and their demands for wireless data have tremendously increased. Multi-antenna communication is a promising solution to meet this ever-growing traffic demands. In this dissertation, we study the optimal transmit strategies for multi-antenna systems with advanced power constraints, in particular joint sum and per-antenna power constraints. We focus on three different models including multi-antenna point-to-point channels, wiretap channels and massive multiple-input multiple-output (MIMO) setups. The solutions are provided either in closed-form or efficient iterative algorithms, which are ready to be implemented in practical systems.The first part is concerned with the optimal transmit strategies for point-to-point multiple-input single-output (MISO) and multiple-input multiple-output (MIMO) channels with joint sum and per-antenna power constraints. For the Gaussian MISO channels, a closed-form characterization of an optimal beamforming strategy is derived. It is shown that we can always find an optimal beamforming transmit strategy that allocates the maximal sum power with phases matched to the complex channel coefficients. An interesting property of the optimal power allocation is that whenever the optimal power allocation of the corresponding problem with sum power constraint only exceeds per-antenna power constraints, it is optimal to allocate maximal per-antenna power to those antennas to satisfy the per-antenna power constraints. The remaining power is distributed among the other antennas whose optimal allocation follows from a reduced joint sum and per-antenna power constraints problem with fewer channel coefficients and a reduced sum power constraint. For the Gaussian MIMO channels, it is shown that if an unconstraint optimal power allocation for an antenna exceeds a per-antenna power constraint, then the maximal power for this antenna is used in the constraint optimal transmit strategy. This observation is then used in an iterative algorithm to compute the optimal transmit strategy in closed-form.In the second part of the thesis, we investigate the optimal transmit strategies for Gaussian MISO wiretap channels. Motivated by the fact that the non-secure capacity of the MISO wiretap channels is usually larger than the secrecy capacity, we study the optimal trade-off between those two rates with different power constraint settings, in particular, sum power constraint only, per-antenna power constraints only, and joint sum and per-antenna power constraints. To characterize the boundary of the optimal rate region, which describes the optimal trade-off between non-secure transmission and secrecy rates, related problems to find optimal transmit strategies that maximize the weighted rate sum with different power constraints are derived. Since these problems are not necessarily convex, equivalent problem formulation is used to derive optimal transmit strategies. A closed-formsolution is provided for sum power constraint only problem. Under per-antenna power constraints, necessary conditions to find the optimal power allocation are provided. Sufficient conditions, however, are available for the case of two transmit antennas only. For the special case of parallel channels, the optimal transmit strategies can deduced from an equivalent point-to-point channel problem. In this case, there is no trade-off between secrecy and non-secrecy rate, i.e., there is onlya transmit strategy that maximizes both rates.Finally, the optimal transmit strategies for large-scale MISO and massive MIMO systems with sub-connected hybrid analog-digital beamforming architecture, RF chain and per-antenna power constraints are studied. The system is configured such that each RF chain serves a group of antennas. For the large-scale MISO system, necessary and sufficient conditions to design the optimal digital and analog precoders are provided. It is optimal that the phase at each antenna is matched tothe channel so that we have constructive alignment. Unfortunately, for the massive MIMO system, only necessary conditions are provided. The necessary conditions to design the digital precoder are established based on a generalized water-filling and joint sum and per-antenna optimal power allocation solution, while the analog precoder is based on a per-antenna power allocation solution only. Further, we provide the optimal power allocation for sub-connected setups based on two properties: (i) Each RF chain uses full power and (ii) if the optimal power allocation of the unconstraint problem violates a per-antenna power constraint then it is optimal to allocate the maximal power for that antenna. The results in the dissertation demonstrate that future wireless networks can achieved higher data rates with less power consumption. The designs of optimal transmit strategies provided in this dissertation are valuable for ongoing implementations in future wireless networks. The insights offered through the analysis and design of the optimal transmit strategies in the dissertation also provide the understanding of the optimal power allocation on practical multi-antenna systems.
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| 10. |
- Cao, Le Phuong, et al.
(author)
-
Transmit Beamforming for Single-User Large-Scale MISO Systems With Sub-Connected Architecture and Power Constraints
- 2018
-
In: IEEE Communications Letters. - : IEEE. - 1089-7798 .- 1558-2558. ; 22:10, s. 2096-2099
-
Journal article (peer-reviewed)abstract
- This letter considers optimal transmit beamforming for a sub-connected large-scale MISO system with RF chain and per-antenna power constraints. The system is configured such that each RF chain serves a group of antennas. For the hybrid scheme, necessary and sufficient conditions to design the optimal digital and analog precoders are provided. It is shown that, in the optimum, the optimal phase shift at each antenna has to match the channel coefficient and the phase of the digital precoder. In addition, an iterative algorithm is provided to find the optimal power allocation. We study the case where the power constraint on each RF chain is smaller than the sum of the corresponding per-antenna power constraints. Then, the optimal power is allocated based on two properties: each RF chain uses full power and if the optimal power allocation of the unconstraint problem violates a per-antenna power constraint then it is optimal to allocate the maximal power for that antenna.
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| 11. |
- Cao, Phuong, et al.
(author)
-
Optimal Transmission Rate for MISO Channels with Joint Sum and Per-antenna Power Constraints
- 2015
-
In: IEEE International Conference on Communications (ICC), London, June 08-12, 2015. - 9781467364324 ; , s. 4727-4732
-
Conference paper (peer-reviewed)abstract
- We consider multiple-input single-output (MISO) Gaussian channels with joint sum and per-antenna power constraints. A closed-form solution of the optimal beamforming vector is derived which achieves the maximal transmission rate. The result shows that if the sum power constraint only optimal power allocation violates a per-antenna power constraint then the joint power constraint optimal power allocation is at the intersection of the sum power constraint and the per-antenna power constraints.
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| 12. |
- Cao, Phuong, et al.
(author)
-
Optimal Transmission with Per-antenna Power Constraints for Multiantenna Bidirectional Broadcast Channels
- 2016
-
In: The Ninth IEEE Sensor Array and Multichannel Signal Processing Workshop.
-
Conference paper (peer-reviewed)abstract
- This paper considers the optimal transmit strategy for multi-antenna bidirectional broadcast channels with per-antenna power constraints. First, an equivalent formulation of the weighted rate sum maximization problem is provided. This allows us to come up with an effective solution to characterize the boundary of the capacity region which relies on the weighted rate sum optimal rate pair. To that end, an iterative algorithm to find the optimal transmit strategy is derived, the convergence to the optimum is proved, and a closed-form solution of the corresponding off-diagonal elements of the optimal transmit strategy is provided. Further, we provide a parametrization of the curved section of the capacity region. Finally, the theoretical results and algorithm performance are illustrated by numerical examples.
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| 13. |
- Cao, Phuong, et al.
(author)
-
Optimal Transmit Strategy for MISO Channels with Joint Sum and Per-antenna Power Constraints
- 2016
-
In: IEEE Transactions on Signal Processing. - : IEEE. - 1053-587X .- 1941-0476.
-
Journal article (peer-reviewed)abstract
- In this paper, we study an optimal transmit strategy for multiple-input single-output (MISO) Gaussian channels with joint sum and per-antenna power constraints. We study in detail the interesting case where the sum of the per-antenna power constraints is larger than sum power constraint. A closed-form characterization of an optimal beamforming strategy is derived.It is shown that we can always find an optimal beamforming transmit strategy that allocates the maximal sum power with phases matched to the complex channel coefficients. The main result is a simple recursive algorithm to compute the optimal power allocation. Whenever the optimal power allocation of the corresponding problem with sum power constraint only exceeds per-antenna power constraints, it is optimal to allocate maximal per-antenna power to those antennas to satisfy the per-antenna power constraints. The remaining power is divided amongst the other antennas whose optimal allocation follows from a reduced joint sum and per-antenna power constraints problem of smaller channel coefficient dimension and reduced sum power constraint. Finally, the theoretical results are illustrated by numerical examples.
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| 14. |
- Cao, Phuong, et al.
(author)
-
Precoding Design for Massive MIMO Systems with Sub-connected Architecture and Per-antenna Power Constraints
- 2018
-
Conference paper (peer-reviewed)abstract
- This paper provides the necessary conditions to design precoding matrices for massive MIMO systems with a sub-connected architecture, RF power constraints and per-antenna power constraints. The system is configured such that each RFchain serves a group of antennas. The necessary condition to design the digital precoder is established based on a generalized water-filling and joint sum and per-antenna optimal power allocation solution, while the analog precoder is based on a per-antenna power allocation solution only. We study the analytically most interesting case where the power constraint on the RF chain is smaller than the sum of the corresponding per-antenna power constraints. For this, the optimal power is allocated based on two properties: Each RF chain uses full power and if the optimal power allocation of the unconstraint problem violates a per-antenna power constraint then it is optimal to allocate the maximal power for that antenna.
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| 15. |
- Cervia, Giulia, et al.
(author)
-
(epsilon, n) Fixed-Length Strong Coordination Capacity
- 2021
-
In: 2021 IEEE Information Theory Workshop (ITW). - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- This paper investigates the problem of synthesizing joint distributions in the finite-length regime. For a fixed block-length n and an upper bound on the distribution approximation epsilon, we prove a capacity result for fixed-length strong coordination. It is shown analytically that the rate conditions for the fixedlength regime are lower-bounded by the mutual information that appears in the asymptotical condition plus Q(-1) (epsilon) root V/n, where V is the channel dispersion, and Q(-1) is the inverse of the tail distribution function of the standard normal distribution. A full version of this paper is accessible at: https://arxiv.org/pdf/2101.06937.pdf
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| 16. |
- Cervia, Giulia, et al.
(author)
-
Fixed-Length Strong Coordination
- 2019
-
In: 2019 IEEE Information Theory Workshop, ITW 2019. - : Institute of Electrical and Electronics Engineers Inc.. - 9781538669006
-
Conference paper (peer-reviewed)abstract
- We consider the problem of synthesizing joint distributions of signals and actions over noisy channels in the finite length regime. For a fixed blocklength n and an upper bound on the distance ϵ, a coding scheme is proposed such that the induced joint distribution is \varepsilon-close in L1 distance to a target i.i.d. distribution. The set of achievable target distributions and rate for asymptotic strong coordination can be recovered from the main result of this paper by having n that tends to infinity.
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| 17. |
- Cervia, Giulia, et al.
(author)
-
Remote Joint Strong Coordination and Reliable Communication
- 2020
-
Conference paper (peer-reviewed)abstract
- We consider a three-node network, in which two agents wish to communicate over a noisy channel, while control- ling the distribution observed by a third external agent. We use strong coordination to constrain the distribution, and we provide a complete characterization of the “remote strong coordination and reliable communication” region.
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| 18. |
- Chen, Yiqi, et al.
(author)
-
On Strong Secrecy for Multiple Access Channel with States and causal CSI
- 2023
-
In: 2023 IEEE International Symposium on Information Theory, ISIT 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 2744-2749
-
Conference paper (peer-reviewed)abstract
- Strong secrecy communication over a discrete memoryless state-dependent multiple access channel (SD-MAC) with an external eavesdropper is investigated. The channel is governed by discrete memoryless and i.i.d. channel states and the channel state information (CSI) is revealed to the encoders in a causal manner. An inner bound of the capacity is provided. To establish the inner bound, we investigate coding schemes incorporating wiretap coding and secret key agreement between the sender and the legitimate receiver. Two kinds of block Markov coding schemes are studied. The first one uses backward decoding and Wyner-Ziv coding and the secret key is constructed from a lossy reproduction of the CSI. The other one is an extended version of the existing coding scheme for point-to-point wiretap channels with causal CSI. We further investigate some capacity-achieving cases for state-dependent multiple access wiretap channels (SD-MAWCs) with degraded message sets. It turns out that the two coding schemes are both optimal in these cases.
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| 19. |
- Do, Hieu, et al.
(author)
-
A new inner bound for the interference relay channel
- 2012
-
In: 2012 46th Annual Conference on Information Sciences and Systems, CISS 2012. - : IEEE. - 9781467331401 ; , s. 6310756-
-
Conference paper (peer-reviewed)abstract
- This paper proposes a new coding scheme for the discrete memoryless interference channel with a dedicated relay. The scheme is built upon rate-splitting encoding, layered noisy network coding, and joint decoding. The result is extended to two Gaussian channels. For the Gaussian channel whose relay is connected to the destinations via orthogonal links we indirectly show that the proposed scheme achieves a bounded gap to the capacity region under certain channel conditions. For the Gaussian channel wherein the relay receives and transmits in the same spectral resource with the transmitters the numerical results show that the proposed scheme achieves higher sum rate than other compress-forward-based schemes. This work, together with our previous work [1], shows that noisy network coding can be extended by the well-known rate-splitting technique of the interference channel to achieve a bounded gap to the capacity region of some multi-unicast networks.
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| 20. |
- Do, Hieu, et al.
(author)
-
An Achievable Rate Region for the Gaussian Z-interference Channel with Conferencing
- 2009
-
In: 2009 47TH ANNUAL ALLERTON CONFERENCE ON COMMUNICATION, CONTROL, AND COMPUTING, VOLS 1 AND 2. - NEW YORK : IEEE. ; , s. 75-81
-
Conference paper (peer-reviewed)abstract
- This paper presents an achievable rate region for a 2-user Gaussian Z-interference channel with a noiseless and bidirectional digital communication link between the receivers. The region is achieved by utilizing the rate-splitting encoding technique, and the decode-and-forward and compress-and-forward strategies. In the very strong interference regime, the capacity region is achieved. In the weak interference regime, the asymptotic sum rate is characterized and shown to be possibly unbounded, which is in contrast to a recent result by Yu and Zhou for a similar scenario, however, with a unidirectional communication link between the receivers.
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| 21. |
- Do, Hieu, et al.
(author)
-
Capacity bounds for the Z channel
- 2011
-
In: IEEE Information Theory Workshop (ITW), 2011. - 9781457704383
-
Conference paper (peer-reviewed)abstract
- We present a new achievable rate region for the discrete memoryless Z channel (DM-ZC) using Marton coding with rate splitting. The region is shown to include previously known achievable rate regions. Secondly we study a class of degraded Z channels, the bijective degraded Z channel (BDZC). An outer bound for the BDZC is proved, which is shown to meet the inner bound for the deterministic settings. For the Gaussian Z channel with weak crossover link, we show that if Gaussian inputs are optimal then a coding scheme based on Marton coding without rate splitting achieves to within half a bit per real dimension from the boundary of the capacity region.
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| 22. |
- Do, Hieu, et al.
(author)
-
Capacity Region of a Class of Interfering Relay Channels
- 2013
-
In: 2013 IEEE Information Theory Workshop (ITW). - : IEEE. - 9781479913237 ; , s. 6691350-
-
Conference paper (peer-reviewed)abstract
- This paper studies a new model for cooperative communication, the interfering relay channels. We show that thehash-forward scheme introduced by Kim for the primitive relay channel is capacity achieving for a class of semideterministic interfering relay channels. The obtained capacity result generalizes and unifies earlier capacity results for a class of primitive relay channels and a class of deterministic interference channels.
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| 23. |
- Do, Hieu, et al.
(author)
-
Coding for the Z Channel With a Digital Relay Link
- 2010
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In: 2010 IEEE Information Theory Workshop, ITW 2010 - Proceedings. - 9781424482627 - 9781424482634
-
Conference paper (peer-reviewed)abstract
- This paper considers a discrete memoryless four-node network where two nodes want to send three independent messages to the other two nodes. The two receiving nodes are allowed to cooperate by means of a unidirectional noiseless link with finite capacity. A coding scheme is proposed which combines rate splitting, block Markov multi-level superposition coding with binning and joint decoding. The general achievable rates are then specialized to degraded channel and Gaussian channel, where it is shown that the sum capacity for the Gaussian channel is achieved under certain conditions. Results in this paper recover and unify previously known results for the discrete memoryless Z channel without cooperation, and results for the Gaussian Z-interference channel with a digital relay link.
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| 24. |
- Do, Hieu, 1980-
(author)
-
Fundamental Aspects of Cooperative Interference Management
- 2013
-
Doctoral thesis (other academic/artistic)abstract
- Today and future wireless networks are facing one of their greatest limiting factors:interference. This is due to the unprecedented increase in the number of connecteddevices. Therefore, in order to meet the ever increasing demand for data rate andquality of services, more advanced techniques than what we have today are requiredto deal with interference. This thesis takes a step towards interference managementin multiuser wireless systems by means of relaying and cooperation. We study fourfundamental building blocks in network information theory, propose new codingschemes, and derive limits on the capacity regions.The first problem we consider is the one-sided interference channel with bidirectional and rate-limited receiver cooperation. We propose a coding scheme that tailors two versions of superposition coding with classical relaying protocols. Theproposed scheme unifies and recovers previous results for the unidirectional coop-eration, yet in simpler forms. Analytical and numerical results confirm the benefitsof cooperation and illuminate the ideas behind the coding strategy.The second problem generalizes the first one by allowing the existence of bothcrossover links in the channel. We propose a coding scheme for this channel byextending noisy network coding to encompass rate-splitting at the encoders. Theachievable rate region is shown to be the same as a region achieved by explicitbinning. As a corollary, we prove that noisy network coding achieves the capacityregion of the Gaussian channel within 1 bit, under strong interference. Our resultis among the first to show constant-gap optimality of noisy network coding for amultiple-unicast problem, and to demonstrate equivalence in terms of achievablerates of two different coding approaches for a noisy interference network.We follow up by introducing a dedicated relay into the interference channelwhich simultaneously helps both receivers. For this third problem, the interferencechannel with a relay, we propose new coding schemes based on layered codes for long- and short-message quantize-forward techniques. The short-message schemesshow improvements in the achievable rates compared to other known coding tech-niques, especially when the channel is asymmetric, while relaxing the excessive delayissue of the long-message scheme. The analysis also reveals the trade-off betweenachievable rates, encoding and decoding delays, and complexity.In the fourth problem, we propose a new model for cooperative communication,the interfering relay channels, which consists of two neighboring relay channelsinducing interference to each other. Each relay, by utilizing a finite-capacity andnoise-free link to its own receiver, helps the receiver decode the desired message.We characterize the exact and approximate capacity region and sum-capacity forvarious classes of channels. The established results generalize and unify severalknown results for the relay and interference channels.The methods and results shown in this thesis aim at providing insight intopotential techniques for cooperative interference management in real-world systems.
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| 25. |
- Do, Hieu, et al.
(author)
-
Gaussian Interfering Relay Channels
- 2013
-
In: 2013 Asilomar Conference on Signals, Systems and Computers. - : IEEE Computer Society. - 9781479923908 ; , s. 1968-1972
-
Conference paper (peer-reviewed)abstract
- We extend the primitive relay channel (PRC) in-troduced by Cover and Kim to a more general scenario wheretwo Gaussian PRC’s cause interference to each other. We show that extended hash-and-forward relaying with proper power allocation can achieve bounded gaps to the capacity region of the Gaussian channel in different regimes of channel parameters.
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| 26. |
- Do, Hieu, et al.
(author)
-
Layered quantize-forward for the two-way relay channel
- 2012
-
In: Information Theory Proceedings (ISIT), 2012 IEEE International Symposium on. - : IEEE. - 9781467325790 ; , s. 423-427
-
Conference paper (peer-reviewed)abstract
- This paper proposes two new coding schemes for the discretememoryless two-way relay channel. The main target is to show thebenefits of compress-forward without Wyner-Ziv binning and oflayered relaying in networks wherein a relay is to help multipledestinations, that may have unequal channel quality and/or haveaccess to different side information. Numerical results for aGaussian channel show that the new coding schemes outperformvariants of compress-forward relaying and offer a good trade-offbetween achievable rates and complexity and decoding delay. The ideacan also be applied to other relay networks.
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| 27. |
- Do, Hieu, et al.
(author)
-
Noisy network coding approach to the interference channel with receiver cooperation
- 2011
-
In: 49th Annual Allerton Conference on Communication, Control, and Computing, 2011.. - 9781457718168 ; , s. 839-846
-
Conference paper (peer-reviewed)abstract
- This work proposes a new coding scheme for thediscrete memoryless two-user interference channel whose receivers can cooperate to decode their desired messages. Thecoding scheme is built upon Han-Kobayashi rate splitting andsuperposition coding at the transmitters, noisy network coding,and non-unique joint decoding at the receivers. As a case studythe general achievable region leads to an inner bound for theGaussian interference channel whose receivers cooperate throughrate-limited orthogonal channels. It is shown that this innerbound is equivalent to the one-round quantize-bin-and-forwardinner bound established by Wang and Tse, thereby showing thatnoisy network coding achieves within 1 bit/s/Hz to the capacityregion when the interference is strong, and achieves within 1 bit/s/Hz to the capacity region of the Gaussian compound multipleaccess channel with conferencing decoders regardless of channelparameters.
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| 28. |
- Do, Hieu, et al.
(author)
-
On Asymmetric Interference Channels with Cooperating Receivers
- 2013
-
In: IEEE Transactions on Communications. - : IEEE. - 0090-6778 .- 1558-0857. ; 61:2, s. 554-563
-
Journal article (peer-reviewed)abstract
- This paper studies a model for communications in wireless networks supported by designated cooperation links. In particular, a 2-user Gaussian one-sided interference channel with two rate-limited and orthogonal communication links between the receivers is considered. A communication protocol for the channel is proposed, which combines rate-splitting and superposition encoding techniques with the conventional decode-forward and compress-forward strategies. It is shown that a careful design of codebooks and coding scheme, which is obtained from intuition based on superposition coding, can greatly reduce the complexity of the strategy. Analytical and numerical results show that the proposed scheme, although not universally optimal, can achieve the capacity region or sum capacity exactly or asymptotically in certain scenarios. Various limits of sum capacity gain due to cooperation are also discussed.
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| 29. |
- Do, Hieu T., et al.
(author)
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Interfering Relay Channels
- 2017
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In: Entropy. - : MDPI AG. - 1099-4300. ; 19:9
-
Journal article (peer-reviewed)abstract
- This paper introduces and studies a model in which two relay channels interfere with each other. Motivated by practical scenarios in heterogeneous wireless access networks, each relay is assumed to be connected to its intended receiver through a digital link with finite capacity. Inner and outer bounds for achievable rates are derived and shown to be tight for new discrete memoryless classes, which generalize and unify several known cases involving interference and relay channels. Capacity region and sum capacity for multiple Gaussian scenarios are also characterized to within a constant gap. The results show the optimality or near-optimality of the quantize-bin-and-forward coding scheme for practically relevant relay-interference networks, which brings important engineering insight into the design of wireless communications systems.
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| 30. |
- Do, Hieu T., et al.
(author)
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Layered Coding for the Interference Channel With a Relay
- 2014
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In: IEEE Transactions on Information Theory. - 0018-9448 .- 1557-9654. ; 60:10, s. 6154-6180
-
Journal article (peer-reviewed)abstract
- This paper studies and derives new results for the interference channel with a relay (ICR). Three inner bounds for the discrete memoryless ICR are proposed, based on three coding strategies that employ layered code at the relay. The first scheme is inspired by layered noisy network coding, proposed by Lim et al. for the two-way relay channel, the second and the third schemes rely on simpler encoding and decoding processes, dubbed layered quantize-forward. Performance of the proposed schemes is investigated for two classes of channels with Gaussian noise: the interference channel with in-band relay reception/out-of-band relay transmission and the interference with in-band relay reception/in-band relay transmission. For the former class of channels, it is shown that the first proposed scheme achieves the same inner bound as the generalized hash-forward scheme with incremental binning. In addition, the inner bound is within 0.5 bit of the capacity region under certain conditions on the channel parameters. For the latter class of channels, new upper bounds on sum-rate are established by extending known upper bounds for symmetric channels. The first inner bound is shown to be within 0.5 bit of the capacity region if the relay's power exceeds a certain threshold, which depends on channel parameters. Numerical examples show that the proposed schemes can achieve significantly higher sum-rates when compared with other compress-forward schemes. Analysis also reveals a tradeoff between achievable rates, coding delay, and complexity of the proposed schemes. Results in this paper provide a better understanding of coding for the ICR, in particular, they show that layered coding is a beneficial element in multiuser networks with relays.
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| 31. |
- Do, Hieu, et al.
(author)
-
The Gaussian Z-interference channel with rate-constrained conferencing decoders
- 2010
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In: 2010 IEEE International Conference on Communications. - 9781424464043 ; , s. 5502610-
-
Conference paper (peer-reviewed)abstract
- We derive achievable rate regions for a 2-user Gaussian Z-interference channel with conferencing decoders. We identify different cases where the rate-limitedness of the conference link from the interference-free receiver to the interfered receiver affects the conferencing strategy as well as the achievable rate region. Furthermore, an outer bound to the capacity region based on cut-set and genie-aided bounds is presented.
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| 32. |
- Do, Tan Tai, et al.
(author)
-
Achievable energy per bit for the multi-pair MIMO bidirectional broadcast channel
- 2012
-
In: European Wireless, 2012. EW. 18th European Wireless Conference. - 9783800834266
-
Conference paper (peer-reviewed)abstract
- This paper presents a transmit strategy for the AWGN multi-pair MIMO bidirectional broadcast channels in the wideband regime. An achievable wideband rate region and an achievable energy per bit region are provided. The transmit covariance matrix at the relay has been designed in order to maximize the wideband weighted rate sum. A closed form of the optimal matrix is derived, which shows that a single beam transmit strategy is optimal. In addition, an energy efficiency versus fairness analysis is considered. Lastly, some discussions on the minimum energy per bit are given.
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| 33. |
- Do, Tan Tai
(author)
-
Fundamental Limits in Wireless Wideband Networking
- 2015
-
Doctoral thesis (other academic/artistic)abstract
- The rapid growth of the wireless communication industry recently does not only bring opportunities but also challenges on developing radio technologies and solutions that can support high data rate as well as reliable and efficient communications. Two fundamental factors that limit the transmission rate are the available transmit energy and the available bandwidth. In this thesis, we investigate fundamental limits on energy and bandwidth efficiencies in wireless wideband networking. The framework and results can be used for performance assessment, design, and development of practical cellular networks.First, we study the energy efficiency of a bidirectional broadcast channel in the wideband regime, i.e., where the bandwidth tends to infinity and the spectral efficiency is disregarded. In particular, we consider a transmit strategy for a Gaussian MIMO bidirectional broadcast channel that maximizes the energy efficiency, i.e., minimizes the energy required to reliably transmit one information bit. A closed-form solution of the optimal transmit covariance matrix is derived, which shows that using a single beam transmit strategy is optimal. Additionally, an extension to a multi-pair Gaussian MIMO bidirectional broadcast channel is studied, in which we propose a simple transmit strategy motivated from the optimal transmit strategy for the single user-pair setup. We show that serving a selected user-pair with full power is optimal in the sense of maximizing the achievable energy efficiency. Discussions on the optimality of the proposed transmit scheme for the multi-pair setup are also provided.Next, we study the bandwidth efficiency of another wireless wideband network, in which the available bandwidth is large but still finite. Accordingly, we consider the bandwidth efficiency limit of an uplink wideband CDMA channel. Various realistic assumptions such as asynchronous transmission, inter-symbol interference, continuous-time waveform transmitted signal, etc. are incorporated into the problem formulation. In order to tackle the problems that arise with those assumptions, we derive an equivalent discrete-time channel model based on sufficient statistics for optimal decoding of the transmitted messages with perfect channel knowledge. The capacity regions are then characterized using the equivalent channel model. In addition, an extension to a system with imperfect channel state information and mismatched filtering at the receiver is considered. Achievable rate regions are characterized considering two different assumptions on decoding strategy, i.e., the optimal decoding based on the actual statistics of channel estimation errors and the sub-optimal approach treating the estimation errors as additive worst-case noise. Moreover, we also present a low-complexity receiver for the uplink wideband CDMA channel, which is based on a decision feedback equalizer structure.
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| 34. |
- Do, Tan Tai, et al.
(author)
-
Massive MIMO Pilot Retransmission Strategies for Robustification Against Jamming
- 2017
-
In: IEEE Wireless Communications Letters. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 2162-2337 .- 2162-2345. ; 6:1, s. 58-61
-
Journal article (peer-reviewed)abstract
- This letter proposes anti-jamming strategies based on pilot retransmission for a single user uplink massive MIMO under jamming attack. A jammer is assumed to attack the system both in the training and data transmission phases. We first derive an achievable rate which enables us to analyze the effect of jamming attacks on the system performance. Counter-attack strategies are then proposed to mitigate this effect under two different scenarios: random and deterministic jamming attacks. Numerical results illustrate our analysis and benefit of the proposed schemes.
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| 35. |
- Do, Tan Tai, et al.
(author)
-
Optimal transmission for the MIMO bidirectional broadcast channel in the wideband regime
- 2011
-
In: IEEE Workshop on Signal Processing Advances in Wireless Communications, SPAWC. - 9781424493326 ; , s. 356-360
-
Conference paper (peer-reviewed)abstract
- This paper presents an optimal transmit strategy for multiple antennas bidirectional broadcast channels in the wideband regime. The transmit covariance matrix at the relay has been designed in order to maximize the wideband weighted sum rate. A closed form of the optimal matrix is derived, which shows that a single beam transmit strategy is optimal. The transmit strategies for some special cases, the wideband capacity region, and the minimum energy per bit versus fairness issues are also discussed.
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| 36. |
- Do, Tan Tai, et al.
(author)
-
Optimal Transmission for the MIMO Bidirectional Broadcast Channel in the Wideband Regime
- 2013
-
In: IEEE Transactions on Signal Processing. - 1053-587X .- 1941-0476. ; 61:20, s. 5103-5116
-
Journal article (peer-reviewed)abstract
- This paper considers a transmit strategy for an AWGN MIMO bidirectional broadcast channel in the wideband regime. In order to characterize the boundaries of the wideband capacity and energy per bit regions, the transmit strategy at the relay is designed to maximize the weighted wideband rate sum. A closed form of the optimal transmit covariance matrix is derived, which shows that a single beam transmit strategy is optimal. The transmit strategies for some special cases are also analyzed. The fairness versus energy efficiency tradeoff is then discussed. In addition, an extension to multipair MIMO bidirectional broadcast channel is studied in which we show that serving a certain pair with full power is optimal in the sense of maximizing the achievable weighted wideband rate sum. Finally, a discussion on the conjecture of the minimum energy per bit for multi-pair systems is provided.
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| 37. |
- Do, Tan Tai, et al.
(author)
-
Uplink Waveform Channel With Imperfect Channel State Information and Finite Constellation Input
- 2017
-
In: IEEE Transactions on Wireless Communications. - : IEEE Press. - 1536-1276 .- 1558-2248. ; 16:2, s. 1107-1119
-
Journal article (peer-reviewed)abstract
- This paper investigates the capacity limit of an uplink waveform channel assuming imperfect channel state information at the receiver (CSIR). Various realistic assumptions are incorporated into the problem, which make the study valuable for performance assessment of real cellular networks to identify potentials for performance improvements in practical receiver designs. We assume that the continuous-time received signal is first discretized by mismatched filtering based on the imperfect CSIR. The resulting discrete-time signals are then decoded considering two different decoding strategies, i.e., an optimal decoding strategy based on specific statistics of channel estimation errors and a sub-optimal decoding strategy treating the estimation error signal as additive Gaussian noise. Motivated by the proposed decoding strategies, we study the performance of the decision feedback equalizer for finite constellation inputs, in which inter-stream interferences are treated either using their true statistics or as Gaussian noise. Numerical results are provided to exemplify the benefit of exploiting the knowledge on the statistics of the channel estimation errors and inter-stream interferences. Simulations also assess the effect of the CSI imperfectness on the achievable rate, which reveal that finite constellation inputs are less sensitive to the estimation accuracy than Gaussian input, especially in the high SNR regime.
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| 38. |
- Do, Tan Tai, et al.
(author)
-
Waveform domain framework for capacity analysis of uplink WCDMA systems
- 2015
-
In: EURASIP Journal on Wireless Communications and Networking. - : Springer. - 1687-1472 .- 1687-1499.
-
Journal article (peer-reviewed)abstract
- This paper investigates the capacity limit of an uplink WCDMA system considering a continuous-time waveform signal. Various realistic assumptions are incorporated into the problem, which make the study valuable for performance assessment of real cellular networks to identify potentials for performance improvements in practical receiver designs. An equivalent discrete-time channel model is derived based on sufficient statistics for optimal decoding of the transmitted messages. The capacity regions are then characterized using the equivalent channel considering both finite constellation and Gaussian distributed input signals. The capacity with sampling at the receiver is also provided to exemplify the performance loss due to a typical post-processing at the receiver. Moreover, we analyze the asymptotic capacity when the signal-to-noise ratio goes to infinity. The conditions to simultaneously achieve the individual capacities are derived, which reveal the impacts of signature waveform space, channel frequency selectivity and signal constellation on the system performance.
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| 39. |
- Ghourchian, Hamid, et al.
(author)
-
Block Source Coding with Sequential Encoding
- 2019
-
In: 2019 IEEE Information Theory Workshop, ITW 2019. - : Institute of Electrical and Electronics Engineers (IEEE). - 9781538669006
-
Conference paper (peer-reviewed)abstract
- We introduce the concept of achievable cumulative rate distribution functions (CRDF) to characterize sequentially encoding processes that ensure a lossless or lossy reconstruction subject to an average distortion using a non-causal decoder. Utilizing tools from majorization theory, we derive necessary and sufficient conditions on the CRDF for a given IID source. It turns out that the optimal achievable distortion level can be adequately characterized by the concave-hull of the CRDF.
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| 40. |
- Ghourchian, Hamid
(author)
-
On Secure and Sequential Source Coding
- 2023
-
Doctoral thesis (other academic/artistic)abstract
- Secure source coding is an important research area in recent years as it deals with the problem of transmitting sensitive information over insecure channels while protecting it from unauthorized access. This is particularly relevant in the context of modern communication systems where the data transmitted is often sensitive in nature and the threat of eavesdropping or data breaches is high. By developing efficient and secure source coding techniques, it is possible to ensure the confidentiality and integrity of the transmitted information, thereby protecting the privacy and security of the users. In addition, secure source coding also plays a critical role in various applications such as sensor networks, wireless communications, and cloud computing. In this thesis, we explore the topic of secure source coding from an information theoretic perspective and focus on two main problems. In the first problem, we have successfully characterized the entire achievable rate-distortion-equivocation region of a specific instance of a classic problem. We investigate the challenge of balancing the trade-off between the rate of data compression, the level of distortion in the compressed data, and the amount of information leaked to an eavesdropper when a private key is shared between the sender and the receiver. Specifically, we concentrate on a scenario where the decoder and eavesdropper have access to different side-informations that are correlated with the source.In the second problem, the focus is on studying secure rate-distortion coding, where data is compressed and transmitted in a block-wise, causal manner, and the decoding is done non-causally. A new concept called cumulative rate distribution functions (CRDFs) is introduced to describe the rate resources that are spent sequentially to compress the sequence, while the concept of cumulative leakage distribution functions (CLFs) is used to characterize the security constraints on the amount of information leakage. Using techniques from majorization theory, necessary and sufficient conditions are derived for the achievable CRDFs for a given independent and identically distributed (IID) source and CLF, and it was found that the concave-hull of the CRDF characterizes the optimal achievable rate distribution. It is also extended to consider the scenario where there is a wiretap channel between the encoder, decoder, and eavesdropper, and inner and outer bounds as well as a closed-solution for a specific case of wiretap channels are found.
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| 41. |
- Ghourchian, Hamid, et al.
(author)
-
Secure Block Joint Source-Channel Coding with Sequential Encoding
- 2023
-
In: 2023 IEEE International Symposium on Information Theory, ISIT 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 2732-2737
-
Conference paper (peer-reviewed)abstract
- We extend the results of Ghourchian et al. [1] to joint source-channel coding with eavesdropping. Our work characterizes the sequential encoding process using the cumulative rate distribution functions (CRDF) and includes a security constraint using the cumulative leakage distribution functions (CLF). The information leakage is defined based on the mutual information between the source and the output of the wiretap channel to the eavesdropper. We derive inner and outer bounds on the achievable CRDF for a given source and CLF, and show that the bounds are tight when the distribution achieving the capacity of the wiretap channel is the same as the one achieving the capacity of the channel.
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| 42. |
- Ghourchian, Hamid, et al.
(author)
-
Secure Block Source Coding With Sequential Encoding
- 2021
-
In: IEEE Journal on Selected Areas in Information Theory. - : IEEE. - 2641-8770. ; 2:1
-
Journal article (peer-reviewed)abstract
- We introduce fundamental bounds on achievable cumulative rate distribution functions (CRDF) to characterize a sequential encoding process that ensures lossless or lossy reconstruction subject to an average distortion criterion using a non-causal decoder. The CRDF describes the rate resources spent sequentially to compress the sequence. We also include a security constraint that affects the set of achievable CRDF. The information leakage is defined sequentially based on the mutual information between the source and its compressed representation, as it evolves. To characterize the security constraints, we introduce the concept of cumulative leakage distribution functions (CLF), which determines the allowed information leakageas distributed over encoded sub-blocks. Utilizing tools from majorization theory, we derive necessary and sufficient conditions on the achievable CRDF for a given independent and identically distributed (IID) source and CLF. One primary result of this article is that the concave-hull of the CRDF characterizes the optimal achievable rate distribution.
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| 43. |
- Ghourchian, Hamid, et al.
(author)
-
Secure Source Coding with Side-information at Decoder and Shared Key at Encoder and Decoder
- 2021
-
In: 2021 IEEE Information Theory Workshop, ITW 2021 - Proceedings. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- We study the problem of rate-distortion-equivocation with side-information only available at the decoder when an independent private random key is shared between the sender and the receiver. The sender compresses the sequence, and the receiver reconstructs it such that the average distortion between the source and the output is limited. The equivocation is measured at an eavesdropper that intercepts the source encoded message, utilizing side-information correlated with the source and the side-information at the decoder. We have derived the entire achievable rate-distortion-equivocation region for this problem.
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| 44. |
- Gouverneur, Amaury, et al.
(author)
-
An Information-Theoretic Analysis of Bayesian Reinforcement Learning
- 2022
-
In: 2022 58Th Annual Allerton Conference On Communication, Control, And Computing (ALLERTON). - : Institute of Electrical and Electronics Engineers (IEEE).
-
Conference paper (peer-reviewed)abstract
- Building on the framework introduced by Xu and Raginsky[1] for supervised learning problems, we study the best achievable performance for model-based Bayesian reinforcement learning problems. With this purpose, we define the minimum Bayesian regret (MBR) as the difference between the maximum expected cumulative reward obtainable either by learning from the collected data or by knowing the environment and its dynamics. We specialize this definition to reinforcement learning problems modeled as Markov decision processes (MDPs) whose kernel parameters are unknown to the agent and whose uncertainty is expressed by a prior distribution. One method for deriving upper bounds on the MBR is presented and specific bounds based on the relative entropy and the Wasserstein distance are given. We then focus on two particular cases of MDPs, the multi-armed bandit problem (MAB) and the online optimization with partial feedback problem. For the latter problem, we show that our bounds can recover from below the current information-theoretic bounds by Russo and Van Roy [2].
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| 45. |
- Gouverneur, Amaury, et al.
(author)
-
Thompson Sampling Regret Bounds for Contextual Bandits with sub-Gaussian rewards
- 2023
-
In: 2023 IEEE International Symposium on Information Theory, ISIT 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 1306-1311
-
Conference paper (peer-reviewed)abstract
- In this work, we study the performance of the Thompson Sampling algorithm for Contextual Bandit problems based on the framework introduced by [1] and their concept of lifted information ratio. First, we prove a comprehensive bound on the Thompson Sampling expected cumulative regret that depends on the mutual information of the environment parameters and the history. Then, we introduce new bounds on the lifted information ratio that hold for sub-Gaussian rewards, thus generalizing the results from [1] which analysis requires binary rewards. Finally, we provide explicit regret bounds for the special cases of unstructured bounded contextual bandits, structured bounded contextual bandits with Laplace likelihood, structured Bernoulli bandits, and bounded linear contextual bandits.
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| 46. |
- Hallén, Tobias, et al.
(author)
-
Circulating brain injury biomarkers increase after endoscopic surgery for pituitary tumors.
- 2021
-
In: Journal of clinical neuroscience : official journal of the Neurosurgical Society of Australasia. - : Elsevier BV. - 1532-2653. ; 89, s. 113-121
-
Journal article (peer-reviewed)abstract
- Pituitary tumors and subsequent treatment with endoscopic transsphenoidal surgery (ETSS) may cause injury to suprasellar structures, causing long-term fatigue and neurocognitive impairment. A method to quantify brain injury after ETSS is not available. In this prospective, exploratory study of patients undergoing ETSS for pituitary tumors, a novel approach to detect possible neuronal damage is presented. Plasma concentrations of brain injury biomarkers (glial fibrillary acidic protein [GFAP], tau, and neurofilament light [NFL]) were measured the day before surgery, immediately after surgery, at day 1 and 5, and at 6 and 12months after surgery, using enzyme-linked immunosorbent assays. The association between the increase of biomarkers with preoperative tumor extension and postoperative patient-perceived fatigue was evaluated. Suprasellar tumor extension was assessed from MRI scans, and self-perceived fatigue was assessed using the Multidimensional Fatigue Inventory before and 6months after surgery. Thirty-five patients were included in the analysis. Compared to baseline, GFAP showed a maximal increase at day 1 after surgery (p=0.0005), tau peaked postoperatively on the day of surgery (p=0.019), and NFL reached its maximum at day 5 after surgery (p<0.0001). The increase in GFAP correlated with preoperative chiasmal compression (p=0.020). The increase in tau was correlated with preoperative chiasmal (p=0.011) and hypothalamus compression (p=0.016), and fatigue score 6months after surgery (p=0.016). In conclusion, the concentrations of brain injury biomarkers in blood increased after ETSS for pituitary tumors. The results indicate that postoperative plasma GFAP and tau might reflect astroglial and neuronal damage after ETSS.
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| 47. |
- Hallén, Tobias, et al.
(author)
-
MCM7 as a marker of postsurgical progression in non-functioning pituitary adenomas.
- 2021
-
In: European journal of endocrinology. - 1479-683X. ; 184:4, s. 521-531
-
Journal article (peer-reviewed)abstract
- Current markers predicting tumour progression of pituitary adenomas after surgery are insufficient. Our objective was to investigate if minichromosome maintenance protein 7 (MCM7) expression predicts tumour progression in non-functioning pituitary adenomas (NFPAs).In a cohort study of surgically treated NFPAs, two groups with distinctly different behaviour of a residual tumour were selected: one group requiring reintervention due to tumour progression (reintervention group, n=57) and one with residual tumours without progression (radiologically stable group, n=40). MCM7, Ki-67, estrogen receptor-⍺ expression, mitotic index and tumour subtype was assessed by immunohistochemistry and their association with tumour progression requiring reintervention was analysed.Median (IQR) MCM7 expression was 7.4% (2.4-15.2) in the reintervention group compared with 2.0% (0.6-5.3) in the radiologically stable group (P<0.0001). Cox regression analysis showed an association between high (>13%) MCM7 expression and reintervention (HR 3.1; 95%CI:1.7-5.4; P=0.00012). The probability for reintervention within 6 years for patients with high MCM7 was 93%. Ki-67 expression >3% (P=0.00062), age ≤55 years (P=0.00034) and mitotic index ≥1 (P=0.024) were also associated with reintervention. Using a receiver operating characteristics curve, a predictive model for reintervention with all the above predictors yielded an area under the curve of 82%. All eight patients with both high MCM7 and high Ki-67 needed reintervention.This cohort study shows that expression of MCM7 is a predictor for clinically significant postoperative tumour progression. Together with age, Ki-67 and mitotic index, MCM7 might be of added value as a predictive marker when managing patients with NFPA after surgery.
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| 48. |
- Hallén, Tobias, et al.
(author)
-
Proteomic profiles associated with postsurgical progression in non-functioning pituitary adenomas.
- 2023
-
In: The Journal of clinical endocrinology and metabolism. - 1945-7197.
-
Journal article (peer-reviewed)abstract
- There is a lack of reliable biomarkers capable of predicting postoperative tumor progression of non-functioning pituitary adenomas (NFPAs).To discover proteomic profiles associated with postoperative tumor progression in patients with NFPA.Case-controlled exploratory study.Tertiary university hospital.Tissue samples were obtained from 46 patients with residual tumor following surgery for NFPA of gonadotroph lineage. Two patient groups were compared: patients requiring reintervention due to residual tumor progression (cases; reintervention group, n=29) and patients with a residual tumor showing no progression for a minimum of 5 years (controls; radiologically stable group, n=17).None.Differentially expressed proteins (DEPs) between patient groups.Global quantitative proteomic analysis identified 4074 proteins, of which 550 were differentially expressed between the two groups (fold change>80%, false discovery rate-adjusted P≤0.05). PCA showed good separation between the two groups. Functional enrichment analysis of the DEPs indicated processes involving Translation, ROBO-receptor signaling, Energy metabolism, mRNA metabolism, and RNA splicing. Several upregulated proteins in the reintervention group, including SNRPD1, SRSF10, SWAP-70, and PSMB1, are associated with tumor progression in other cancer types.This is the first exploratory study analyzing proteomic profiles as markers of postoperative tumor progression in NFPA. The findings clearly showed different profiles between tumors with indolent postoperative behavior and those with postoperative tumor progression. Both enriched pathways involving DEPs and specific upregulated proteins have previously been associated with tumor aggressiveness. These results suggest the value of proteomic profiling for predicting tumor progression in patients with NFPA.
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| 49. |
- Hallén, Tobias, et al.
(author)
-
Sinonasal Symptoms and Self-Reported Health before and after Endoscopic Pituitary Surgery-A Prospective Study
- 2022
-
In: Journal of Neurological Surgery, Part B: Skull Base. - : Georg Thieme Verlag KG. - 2193-634X .- 2193-6331. ; 83:suppl. 2
-
Journal article (peer-reviewed)abstract
- © 2021 Thieme Medical Publishers, Inc.. All rights reserved. Objectives Despite the limited invasiveness of endoscopic transsphenoidal surgery (ETSS), some degree of nasal structure destruction is unavoidable. Our objective was to evaluate sinonasal morbidity and self-reported health before and 6 months after ETSS for pituitary tumors, and to identify possible predictive factors for deterioration in sinonasal health. Design Prospective observational cohort study. Setting University tertiary referral hospital. Participants Totally 109 consecutive adult patients undergoing ETSS for pituitary tumors between 2015 and 2019. Main Outcome Measures Sinonasal symptoms and self-reported health before and 6 months after ETSS, assessed by the Sinonasal Outcome Test (SNOT-22) and the EQ-5D questionnaire. Predictive factors for postoperative deterioration in sinonasal symptoms. Results The overall SNOT-22 score did not change, but the score of the rhinologic domain of SNOT-22 worsened from 6.0 ± 5.9 before to 8.0 ± 7.4 6 months after surgery (p = 0.011). The EQ-5D visual analog scale improved from 64.0 ± 22.9 before to 71.1 ± 18.7 6 months after surgery (p = 0.00088). Univariate and multivariable regression analyses showed that prior sinonasal surgery was associated with a significant worsening in rhinologic symptoms 6 months after surgery (p = 0.046 and p = 0.020, respectively). Conclusions Although self-reported overall health improved, significant deterioration of rhinologic symptoms was seen 6 months after ETSS. This information is important for preoperative patient counselling. Further refinement of the surgical technique and follow-up strategies to reduce postoperative sinonasal morbidity could be of value, especially in patients who have undergone prior sinonasal surgery.
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| 50. |
- Hantelius, Victor, et al.
(author)
-
Headache in patients with non-functioning pituitary adenoma before and after transsphenoidal surgery - a prospective study.
- 2024
-
In: Pituitary. - 1573-7403.
-
Journal article (peer-reviewed)abstract
- To study the long-term effect of transsphenoidal surgery (TSS) on headache in patients with non-functioning pituitary adenoma (NFPA) and identify factors predicting headache relief following TSS.We evaluated headache in 101 consecutive patients with NFPA who underwent TSS from September 2015 to December 2021, preoperatively and 12-months post-surgery, by using the Migraine Disability Assessment (MIDAS) questionnaire. Health-related quality of life (QoL) was assessed using the EQ-5D visual analogue scale (EQ-VAS).Of 101 patients, 27 (27%) experienced disabling preoperative headache. Among these, the median total MIDAS score improved from 60 (interquartile range (IQR): 19-140) to 10 (IQR: 0-49) (P=0.004). Additionally, headache frequency over a 90-day period decreased from 45 (IQR: 25-83) to 6 (IQR: 3-36) days (P=0.002), and headache intensity decreased from 5 (IQR: 4-7) to 4 (IQR: 2-7) (P=0.016) at 12-months post-surgery. At 12 months post-surgery, 18 (67%) of 27 patients with preoperatively disabling headache showed clinically relevant improvement of their headache, 4 (15%) showed deterioration, and 5 (19%) remained unchanged. In patients with clinically relevant improvement of their headache, the EQ-VAS score improved from 50 (IQR: 30-7) to 80 (IQR: 65-86) (P<0.001). Of the 74 patients with no preoperative headache, 11 (15%) developed postoperative headache. We identified no clinical factors predicting postoperative headache relief.The study supports that clinically significant and long-lasting improvements of disabling headache and QoL can be achieved with TSS in a substantial number of patients with NFPA.
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