[show abstract][hide abstract] ABSTRACT: We apply a recently developed first principles approach that uses transmitted
information in bits per joule to quantify the energy efficiency of information
transmission for an inter-spike-interval (ISI) code. We investigate single
compartment conductance-based model neuron driven by excitatory and inhibitory
spikes, where the rate and synchrony in the presynaptic excitatory population
may independently vary. We find that for a fixed input rate, the ISI
distribution of the post synaptic neuron depends on the level of synchrony and
is well-described by a Gamma distribution for synchrony levels less than 50%.
For levels of synchrony between 15% and 50% (restricted for technical reasons),
we compute the optimum input distribution that maximizes the mutual information
per unit energy. This optimum distribution shows that an increased level of
synchrony, as occurs in the attention process, reduces the mode of input
distribution and the excitability threshold of post synaptic neuron and hence
facilitates a more energy efficient neuronal communication.
[show abstract][hide abstract] ABSTRACT: Studying the development of malignant tumours, it is important to know and
predict the proportions of different cell types in tissue samples. Knowing the
expected temporal evolution of the proportion of normal tissue cells, compared
to stem-like and non-stem like cancer cells, gives an indication about the
progression of the disease and indicates the expected response to interventions
with drugs. Such processes have been modeled using Markov processes. An
essential step for the simulation of such models is then the determination of
state transition probabilities. We here consider the experimentally more
realistic scenario in which the measurement of cell population sizes is noisy,
leading to a hidden Markov model. In this context, extrinsic randomness is
related to noisy measurements, which are used for the estimation of the
transition probability matrix. Intrinsic randomness, on the other hand, is here
related to the error in estimating the state probability from small cell
populations. Using aggregated data of fluorescence-activated cell sorting
(FACS) measurement, we develop a minimum mean square error estimator (MMSE) and
maximum likelihood (ML) estimator and formulate two problems to find the
minimum number of required samples and measurements to guarantee the accuracy
of predicted population sizes using a transition probability matrix estimated
from noisy data. We analyze the properties of two estimators for different
noise distributions and prove an optimal solution for Gaussian distributions
with the MMSE. Our numerical results show, that for noisy measurements the
convergence mechanism of transition probabilities and steady states differ
widely from the real values if one uses the standard deterministic approach in
which measurements are assumed to be noise free.
[show abstract][hide abstract] ABSTRACT: A scheme for detection of abnormality in molecular nano-networks is proposed.
This is motivated by the fact that early diagnosis, classification and
detection of diseases such as cancer play a crucial role in their successful
treatment. The proposed nano-abnormality detection scheme (NADS) comprises of a
two-tier network of sensor nano-machines (SNMs) in the first tier and a data
gathering node (DGN) at the sink. The SNMs detect the presence of competitor
cells as abnormality that is captured by variations in parameters of a
nano-communications channel. In the second step, the SNMs transmit micro-scale
messages over a noisy micro communications channel (MCC) to the DGN, where a
decision is made upon fusing the received signals. The detection performance of
each SNM is analyzed by setting up a Neyman-Pearson test. Next, taking into
account the effect of the MCC, the overall performance of the proposed NADS is
quantified in terms of probabilities of misdetection and false alarm. A design
problem is formulated, when the optimized concentration of SNMs in a sample is
obtained for a high probability of detection and a limited probability of false
[show abstract][hide abstract] ABSTRACT: In this paper, delay-limited transmission of quasi-stationary sources over
block fading channels are considered. Considering distortion outage probability
as the performance measure, two source and channel coding schemes with power
adaptive transmission are presented. The first one is optimized for fixed rate
transmission, and hence enjoys simplicity of implementation. The second one is
a high performance scheme, which also benefits from optimized rate adaptation
with respect to source and channel states. In high SNR regime, the performance
scaling laws in terms of outage distortion exponent and asymptotic outage
distortion gain are derived, where two schemes with fixed transmission power
and adaptive or optimized fixed rates are considered as benchmarks for
comparisons. Various analytical and numerical results are provided which
demonstrate a superior performance for source and channel optimized rate and
power adaptive scheme. It is also observed that from a distortion outage
perspective, the fixed rate adaptive power scheme substantially outperforms an
adaptive rate fixed power scheme for delay-limited transmission of
quasi-stationary sources over wireless block fading channels. The effect of the
characteristics of the quasi-stationary source on performance, and the
implication of the results for transmission of stationary sources are also
IEEE Transactions on Communications 02/2012; · 1.75 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper addresses the problem of efficient data gathering based on distributed source coding (DSC) in wireless sensor networks (WSNs) with a complexity constrained data gathering node (DGN). A particular scenario of interest is a cluster of low complexity sensor nodes among which, one node is selected as the cluster head (CH) or the DGN. Utilizing DSC allows for reducing the required rate of communications by exploiting the dependency between the nodes observations in a distributed manner. We consider a DSC-based rate allocation structure, which takes into account the CH (DGN) memory and computational constraints. Specifically, this is accomplished, respectively, by limiting the number of nodes whose data may be stored at the CH and exploited during decoding, and the number of nodes that can be jointly (de)compressed using DSC. Based on this structure, we investigate two WSN resource optimization problems aiming at: (i) minimizing the total network cost and (ii) maximizing the network lifetime. To these ends, optimal dynamic programming solutions based on a trellis structure are proposed that incur substantially smaller computational complexity in comparison to an exhaustive search. Also, a suboptimal yet high performance solution is presented whose complexity grows in polynomial order with the number of network nodes. Numerical results demonstrate that the proposed rate allocation structure and solutions, even with limited complexity, allow for exploiting most of the available dependency and hence the achievable compression gain.
[show abstract][hide abstract] ABSTRACT: In a cooperative relay network, a relay (R) node may facilitate data transmission to the destination (D) node when the latter node cannot correctly decode the source (S) node data. This paper considers such a system model and presents a cross-layer approach to jointly design adaptive modulation and coding (AMC) at the physical layer and the truncated cooperative automatic repeat request (C-ARQ) protocol at the data-link layer for quality-of-service (QoS)-constrained applications. The average spectral efficiency and packet loss rate of the joint C-ARQ and AMC scheme are first derived in closed form. Aiming to maximize the system spectral efficiency, AMC schemes for the S-D and R-D links are optimized, whereas a prescribed packet-loss-rate constraint is satisfied. As an interesting application, joint link adaptation and blockage mitigation in land mobile satellite communications (LMSC) with temporally correlated channels is then investigated. In LMSC, the S node data can be delivered to the D node when the S-D is in the outage, therefore provisioning the QoS requirements. For applications without instantaneous feedback, an optimized rate selection scheme based on the channel statistics is also devised. Detailed and insightful numerical results are presented, which indicate the superior performance of the proposed joint AMC and C-ARQ schemes over their optimized joint AMC and traditional ARQ counterparts.
IEEE Transactions on Vehicular Technology 10/2011; · 2.06 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper presents performance analysis and cross-layer design approaches for hybrid ARQ (HARQ) protocols in wireless networks, which employ adaptive modulation and coding (AMC) in conjunction with adaptive cooperative diversity and are subject to time-correlated fading channels. We first consider a point-to-point scenario, i.e., non-cooperative HARQ with AMC. Utilizing a Markov channel model which accounts for the temporal correlation in the successive transmission of incremental redundancy by the HARQ protocol, we derive the system throughput and the packet loss probability based on a rate compatible punctured convolutional code family. Next, we consider a cooperative HARQ (CHARQ) scheme in which a relay node, also equipped with AMC, retransmits redundancy packets when it is able to decode the source information packet correctly. For this scenario, we also derive the throughput and packet loss performance. Finally, we present a cross-layer AMC design approach which takes into account the hybrid ARQ protocol at the link layer. The results illustrate that including AMC in the HARQ protocols leads to a substantial throughput gain. While the performance of the AMC with HARQ protocol is strongly affected by the channel correlation, the CHARQ protocol provides noticeable performance gains over correlated fading channels as well.
IEEE Transactions on Wireless Communications 04/2011; · 2.42 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this paper, channel optimized distributed multiple description vector
quantization (CDMD) schemes are presented for distributed source coding in
symmetric and asymmetric settings. The CDMD encoder is designed using a
deterministic annealing approach over noisy channels with packet loss. A
minimum mean squared error asymmetric CDMD decoder is proposed for effective
reconstruction of a source, utilizing the side information (SI) and its
corresponding received descriptions. The proposed iterative symmetric CDMD
decoder jointly reconstructs the symbols of multiple correlated sources. Two
types of symmetric CDMD decoders, namely the estimated-SI and the soft-SI
decoders, are presented which respectively exploit the reconstructed symbols
and a posteriori probabilities of other sources as SI in iterations. In a
multiple source CDMD setting, for reconstruction of a source, three methods are
proposed to select another source as its SI during the decoding. The methods
operate based on minimum physical distance (in a wireless sensor network
setting), maximum mutual information and minimum end-to-end distortion. The
performance of the proposed systems and algorithms are evaluated and compared
IEEE Transactions on Signal Processing 01/2011; · 2.81 Impact Factor
[show abstract][hide abstract] ABSTRACT: This paper presents novel joint link adaptation and user selection (JLAUS) schemes to maximize a weighted sum of the average rates of wireless links sharing a spectrum, while their possibly different minimum required average rates and quality of service constraints are provisioned. The schemes take into account the instantaneous SNR of all links and select a link for transmission and set its rate and power in a jointly optimized manner. The links operate based on adaptive modulation and coding and power control over heterogeneous wireless fading channels. Two JLAUS schemes are presented. The first scheme provides a framework for integrated analysis and design of link adaptation and user selection and relies on a partitioning of the space of link SNRs into regions. In this setting, the second scheme offers a particular JLAUS design, which enjoys a polynomial design complexity. The design is performed before the transmission starts, based on closed form solutions. The proposed schemes can be easily applied to a multiple access or a broadcast network. Numerical results demonstrate how the proposed JLAUS schemes outperform the benchmark schemes, or effectively meet various user requirements.
[show abstract][hide abstract] ABSTRACT: This paper addresses the problem of efficient data gathering in wireless sensor networks with a complexity constrained data gathering node. Due to the complexity constraint, the data gathering node employs an asymmetric DSC that (de)compresses the data of a given node exploiting its dependency with a limited number of other nodes. This is characterized in a DSC rate allocation structure that is referred to as limited-order DSC. Within this structure, we investigate the problem of rate allocation for the nodes to maximize the network lifetime. To this end, an algorithm is proposed that is proven optimal with polynomial complexity in terms of number of network nodes. Numerical results demonstrate that the algorithm, even with limited complexity, allows for exploiting most of the achievable compression gain.
[show abstract][hide abstract] ABSTRACT: In this paper, the interference statistics and the probability of outage in a clustered Poisson field of interfering nodes are analyzed. In this architecture, a large number of users communicate directly with each other through their closest cluster heads. It is assumed that the location of the users and the cluster heads are two independent two-dimensional homogeneous Poisson point processes over an unbounded plain. A common bandwidth is shared among all users and the transmitted signals undergo path loss and Log-normal shadowing. A perfect power control is assumed in a user to cluster head transmission. We analyze the performance of this wireless network by calculating the probability of outage over a cluster head. To this end, we derive analytical formulas for the mean and the variance of the total amount of interference. Further, we show that the total interference received by the cluster head precisely follows Log-normal distribution. The accuracy of Log-normal assumption as well as the obtained analytical results are verified by simulations.
Telecommunications (ICT), 2010 IEEE 17th International Conference on; 05/2010
[show abstract][hide abstract] ABSTRACT: In this paper, we consider a primary and a cognitive user transmitting over a wireless fading interference channel. Both primary and cognitive links are subject to delay-QoS constraints. The achievable throughput subject to a given delay-QoS constraint can be quantified as the effective capacity of a link. We consider a system in which the primary user transmits with a constant power and utilizes an adaptive modulation and coding (AMC) scheme subject to its required bit error rate (BER). A link (power and rate) adaptation scheme is proposed for the interfering cognitive radio to maximize its effective capacity, while a minimum required effective capacity for the primary user is provisioned. A BER performance requirement and a power constraint are also considered for the cognitive radio. The resulting problem is then cast as a nonlinear discrete optimization problem for which a fast and efficient suboptimum solution is presented. Comparisons with the scheduled (non-interfering) adaptive cognitive transmission demonstrate the efficiency of the proposed interfering transmission scheme.
Telecommunications (ICT), 2010 IEEE 17th International Conference on; 05/2010
[show abstract][hide abstract] ABSTRACT: This paper addresses the problem of efficient data gathering in wireless sensor networks with a complexity constrained data gathering node. A particular scenario of interest is a cluster of sensor nodes among which one is selected as the cluster head. Distributed source coding allows for exploiting the dependency between the nodes observations and reducing the required rate of communications. We consider a rate allocation structure, which incorporates the decoder complexity constraints, by limiting the number of nodes whose data may be stored and exploited during decoding. Based on this structure, we investigate the problem of rate allocation for the nodes to minimize the total cost, where the cost of a node is a general function of its rate and related parameters. To this end, an optimal dynamic programming solution based on a trellis structure is proposed. Also, a suboptimal yet high performance solution is presented whose complexity grows in polynomial order as the number of network nodes increases. Numerical results demonstrate that the proposed solutions, even with limited complexity, allow for exploiting most of the available dependency and hence the achievable compression gain.
Telecommunications (ICT), 2010 IEEE 17th International Conference on; 05/2010
[show abstract][hide abstract] ABSTRACT: This paper addresses network code design for robust transmission of sources over an orthogonal two-hop wireless network with a broadcasting relay. The network consists of multiple sources and destinations in which each destination, benefiting the relay signal, intends to decode a subset of the sources. Two special instances of this network are orthogonal broadcast relay channel and the orthogonal multiple access relay channel. The focus is on complexity constrained scenarios, e.g., for wireless sensor networks, where channel coding is practically imperfect. Taking a source-channel and network coding approach, we design the network code (mapping) at the relay such that the average reconstruction distortion at the destinations is minimized. To this end, by decomposing the distortion into its components, an efficient design algorithm is proposed. The resulting network code is nonlinear and substantially outperforms the best performing linear network code. A motivating formulation of a family of structured nonlinear network codes is also presented. Numerical results and comparison with linear network coding at the relay and the corresponding distortion-power bound demonstrate the effectiveness of the proposed schemes and a promising research direction. Comment: 27 pages, 9 figures, Submited to IEEE Transaction on Communication
[show abstract][hide abstract] ABSTRACT: In this study, an approach for robust network coding is introduced for multicast in a directed acyclic network in the presence of network edge failures. The proposed designs aim at combating the resulting path failures, which result in interestingly scalable solutions. A robust network coding scheme (RNC1) is proposed that, devising a rate-path diversity trade-off for the receivers, attains the post-failure capacity of the network with high probability. The scheme is receiver based and can also be applied for correcting random erasures. Next, a rate-guaranteed robust network coding scheme (RNC2) is proposed. The code guarantees the maximum rate for a predetermined number of path failures. The scheme, of course, attains the refined Singleton bound for the edge failure model. A path failure may not necessarily reduce the network capacity, as the remaining intact edges within the network may still facilitate backup paths from the source to the sinks. We introduce RNC3 to employ such backup paths in addition to the original paths and guarantee multicast at a certain rate in the presence of all edge/path failure patterns that do not reduce the capacity below this rate. All the three proposed schemes for multicast are robust to a number of edge failures that may, in general, exceed the refined Singleton bound. Our analyses indicate that the design complexities and the required field sizes grow as a function of the number of network paths, as opposed to the number of network edges because of prior schemes.
[show abstract][hide abstract] ABSTRACT: A Wyner-Ziv Quantizer design method is introduced when the indices at the output of the encoder are transmitted over a noisy channel. The source encoder is considered as a scalar Lloyd quantizer followed by a binning and an index assignment (BIA) mapping. A modified simulated annealing based algorithm is used for BIA mapping design. A minimax solution for Wyner-Ziv problem under channel mismatch condition is also suggested when the channel is assumed to be binary symmetric channel and no information about the statistic of channel is available except the range of bit error rate. Finally the simulation results are presented which show the effectiveness of the proposed algorithm over other common alternative approaches. These results approve the proposed minimax solution too.
2010 Data Compression Conference (DCC 2010), 24-26 March 2010, Snowbird, UT, USA; 01/2010
[show abstract][hide abstract] ABSTRACT: This paper presents performance analysis and cross-layer design approaches for hybrid ARQ (HARQ) protocol in wireless networks which employ adaptive modulation and coding (AMC) at the physical layer and are subject to time-correlated fading channels. Utilizing a Markov channel model which accounts for the temporal correlation in successive parity transmissions by the adaptive rate HARQ protocol, we derive the system throughput and the packet loss probability based on a rate compatible punctured convolutional (RCPC) code family. As an application, we then present a cross-layer AMC design which takes into account the performance gain of the HARQ protocol at the link layer. The results illustrate that including AMC in the HARQ protocol leads to a substantial throughput gain, but the channel correlation strongly diminishes the performance of the HARQ protocol in terms of throughput and packet loss rate.
Proceedings of IEEE International Conference on Communications, ICC 2010, Cape Town, South Africa, 23-27 May 2010; 01/2010
[show abstract][hide abstract] ABSTRACT: In this paper, we consider a primary and a cognitive user transmitting over a wireless fading interference channel. The primary user transmits with a constant power and utilizes an adaptive modulation and coding (AMC) scheme satisfying a bit error rate requirement. We propose a link adaptation scheme to maximize the average spectral efficiency of the cognitive radio, while a minimum required spectral efficiency for the primary user is provisioned. The resulting problem is constrained to also satisfy a bit error rate requirement and a power constraint for the cognitive link. The AMC mode selection and power control at the cognitive transmitter is optimized based on the modified signal to noise plus interference ratio feedback of both links. The problem is then cast as a nonlinear discrete optimization problem for which a fast and efficient suboptimum solution is presented. We also present a scheme with rate adaptive and constant power cognitive radio. An important characteristic of the proposed schemes is that no computation or coordination overhead is imposed on the primary radio due to the cognitive radio activity. Numerical results and comparison with the interweave approach to cognitive radio demonstrate the efficiency of the proposed solutions. Comment: 26 pages, 7 figures submitted to IEEE journal on selected areas in communication