Information Rate

Consider a communication network in which certain source nodes multicast information to other nodes on the network in the multihop fashion where every node can pass on any of its received data to others. We are interested in how fast each node can receive the complete information, or equivalently, what the information rate arriving at each node is. Allowing a node to encode its received data before passing it on, the question involves optimization of the multicast mechanisms at the nodes. Among the simplest coding schemes is linear coding, which regards a block of data as a vector over a certain base field and allows a node to apply a linear transformation to a vector before passing it on. We formulate this multicast problem and prove that linear coding suffices to achieve the optimum, which is the max-flow from the source to each receiving node.

The convergent and discriminant validities of well-being concepts were examined using multitraitmultimethod matrix analyses (D. T. Campbell & D. W. Fiske, 1959) on 3 sets of data. In Study 1, participants completed measures of life satisfaction, positive affect, negative affect, self-esteem, and optimism on 2 occasions 4 weeks apart and also obtained 3 informant ratings. In Study 2, participants completed each of the 5 measures on 2 occasions 2 years apart and collected informant reports at Time 2. In Study 3, participants completed 2 different scales for each of the 5 constructs. Analyses showed that (a) life satisfaction is discriminable from positive and negative affect, (b) positive affect is discriminable from negative affect, (c) life satisfaction is discriminable from optimism and selfesteem, and (d) optimism is separable from trait measures of negative affect.

In this paper, we introduce a new paradigm for the design of transmitter space-time coding that we refer to as linear precoding. It leads to simple closed-form solutions for transmission over frequency-selective multiple-input multiple-output (MIMO) channels, which are scalable with respect to the number of antennas, size of the coding block, and transmit average/peak power. The scheme operates as a block transmission system in which vectors of symbols are encoded and modulated through a linear mapping operating jointly in the space and time dimension. The specific designs target minimization of the symbol mean square error and the approximate maximization of the minimum distance between symbol hypotheses, under average and peak power constraints. The solutions are shown to convert the MIMO channel with memory into a set of parallel flat fading subchannels, regardless of the design criterion, while appropriate power/bits loading on the subchannels is the specific signature of the different designs. The proposed designs are compared in terms of various performance measures such as information rate, BER, and symbol mean square error.

Chaotic signals have been proposed as broadband information carriers with the potential of providing a high level of robustness and privacy in data transmission 1,2 . Laboratory demonstrations of chaos-based optical communications have already shown the potential of this technology 3-5 , but a field experiment using commercial optical networks has not been undertaken so far.

Energy efficiency is becoming increasingly important for small form factor mobile devices, as battery technology has not kept up with the growing requirements stemming from ubiquitous multimedia applications. This paper addresses link adaptive transmission for maximizing energy efficiency, as measured by the "throughput per Joule" metric. In contrast to the existing water-filling power allocation schemes that maximize throughput subject to a fixed overall transmit power constraint, our scheme maximizes energy efficiency by adapting both overall transmit power and its allocation, according to the channel states and the circuit power consumed. We demonstrate the existence of a unique globally optimal link adaptation solution and develop iterative algorithms to obtain it. We further consider the special case of flat-fading channels to develop an upper bound on energy efficiency and to characterize its variation with bandwidth, channel gain and circuit power. Our results for OFDM systems demonstrate improved energy savings with energy optimal link adaptation as well as illustrate the fundamental tradeoff between energy-efficient and spectrum-efficient transmission.

We consider the capacity of multiple-input multipleoutput systems with reduced complexity. One link-end uses all available antennas, while the other chooses the L out of N antennas that maximize capacity. We derive an upper bound on the capacity that can be expressed as the sum of the logarithms of ordered chi-square-distributed variables. This bound is then evaluated analytically and compared to the results obtained by Monte Carlo simulations. Our results show that the achieved capacity is close to the capacity of a full-complexity system provided that L is at least as large as the number of antennas at the other linkend. For example, for L = 3, N = 8 antennas at the receiver and three antennas at the transmitter, the capacity of the reducedcomplexity scheme is 20 bits/s/Hz compared to 23 bits/s/Hz of a full-complexity scheme. We also present a suboptimum antenna subset selection algorithm that has a complexity of N 2 compared to the optimum algorithm with a complexity of N L .

The information rate of finite-state source/channel models can be accurately estimated by sampling both a long channel input sequence and the corresponding channel output sequence, followed by a forward sum-product recursion on the joint source/channel trellis. This method is extended to compute upper and lower bounds on the information rate of very general channels with memory by means of finite-state approximations. Further upper and lower bounds can be computed by reduced-state methods.

This paper presents an analysis of optical buffers based on slow-light optical delay lines. The focus of this paper is on slow-light delay lines in which the group velocity is reduced using linear processes, including electromagnetically induced transparency (EIT), population oscillations (POs), and microresonator-based photonic-crystal (PC) filters. We also consider slow-light delay lines in which the group velocity is reduced by an adiabatic process of bandwidth compression. A framework is developed for comparing these techniques and identifying fundamental physical limitations of linear slow-light technologies. It is shown that slow-light delay lines have limited capacity and delay-bandwidth product. In principle, the group velocity in slowlight delay lines can be made to approach zero. But very slow group velocity always comes at the cost of very low bandwidth or throughput. In many applications, miniaturization of the delay line is an important consideration. For all delay-line buffers, the minimum physical size of the buffer for a given number of buffered data bits is ultimately limited by the physical size of each stored bit. We show that in slow-light optical buffers, the minimum achievable size of 1 b is approximately equal to the wavelength of light in the buffer. We also compare the capabilities and limitations of a range of delay-line buffers, investigate the impact of waveguide losses on the buffer capacity, and look at the applicability of slow-light delay lines in a number of applications. Index Terms-Electromagnetically induced transparency (EIT), optical delay lines, optical memories, optical propagation in dispersive media, photonic crystals (PCs), slow light.

The amount of information a sensory neuron carries about a stimulus is directly related to response reliability. We recorded from individual neurons in the cat lateral geniculate nucleus (LGN) while presenting randomly modulated visual stimuli. The responses to repeated stimuli were ...

Background: Prostate cancer gene 3 (PCA3) encodes a prostate-specific mRNA that has shown promise as a prostate cancer diagnostic tool. This report describes the characterization of a prototype quantitative PCA3-based test for whole urine. Methods: Whole-urine specimens were collected after digital rectal examination from 3 groups: men scheduled for prostate biopsy (n ‫؍‬ 70), healthy men (<45 years of age with no known prostate cancer risk factors; n ‫؍‬ 52), and men who had undergone radical prostatectomy (n ‫؍‬ 21). PCA3 and prostate-specific antigen (PSA) mRNAs were isolated, amplified, and quantified by use of Gen-Probe DTS400 ® Systems. Prostate biopsy results were correlated with the PCA3/PSA mRNA ratio, and PSA mRNA concentrations were used to normalize PCA3 signals and confirm the yield of prostate-specific RNA. Assay precision, specimen stability, and mRNA yield were also evaluated. Results: The specimen informative rate (fraction of specimens yielding sufficient RNA for analysis) was 98.2%. In this clinical research study, ROC curve analysis of prebiopsy specimens yielded an area under the curve of 0.746; sensitivity was 69% and specificity 79%. Serum PSA assay specificity was 28% for this same group. PCA3 and PSA mRNAs were undetectable in postprostatectomy specimens except for one man with recurrent prostate cancer. Assay interrun CVs were <12%. Both mRNAs were stable in processed urine up to 5 days at 4°C and after 5 freeze-thaw cycles. Conclusion: The APTIMA ® PCA3 assay combines simple specimen processing with precise assays and existing instruments and could add specificity to the current algorithm for prostate cancer diagnosis.

Traditional approaches to transmit information reliably over an error-prone network employ either Forward Error Correction (FEC) or retransmission techniques. In this paper we propose some network coding schemes to reduce the number of broadcast transmissions from one sender to multiple receivers. The main idea is to allow the sender to combine and retransmit the lost packets in a certain way, so that with one transmission, multiple receivers are able to recover their own lost packets. For comparison, we derive a few theoretical results on the bandwidth efficiencies of the proposed network coding and traditional Automatic Repeat-reQuest (ARQ) schemes. Both simulations and theoretical analysis confirm the advantages of the proposed network coding schemes over the Automatic Repeat-reQuest (ARQ) ones.

There has recently been significant interest in feedback stabilization problems with communication constraints including constraints on the available data rate. Signal to noise ratio constraints are one way in which data-rate limits arise, and are the focus of this paper. In both continuous and discrete-time settings, we show that there are limitations on the ability to stabilize an unstable plant over a signal-to-noise ratio constrained channel using finite dimensional linear time invariant (LTI) feedback. In the case of state feedback, or output feedback with a delay-free, minimum phase plant, these limitations in fact match precisely those that might have been inferred by considering the associated ideal Shannon capacity data rate over the same channel. In the case of LTI output feedback, additional limitations are shown to apply if the plant is nonminimum phase. In this case, we show that for a continuous-time nonminimum phase plant, a periodic linear time varying feedback scheme with fast sampling may be used to recover the original signal-to-noise ratio requirement at the cost of robustness properties. The proposed framework inherently captures channel noise effects in a simple formulation suited to conventional LTI control performance and robustness analysis, and has potential to handle time delays and bandwidth constraints in a variety of control over communication problems.

in consulting for both industry and government. He has taught a broad range of subjects in both mechanical and electrical engineering curricula. His research interests are in adaptive and learning systems, nonlinear control, and modelling. At present, his research interests are in modelling and controlling of large-scale systems. His main areas of interest are in signal processing, particularly with radar applications, waveform design and radar theory, and sensor management. He also works in various areas of mathematics, including harmonic analysis and number theory.

The effects of store characteristics on customers' mood, on their satisfaction, and on their purchasing behavior are investigated. Two furniture stores differing with regard to their atmosphere, i.e. their condition, information rate and layout, were selected. Customers' mood -measured at the beginning, in the middle and at the end of their shopping -was shown to Ž . improve in the pleasant and to deteriorate in the less pleasant store n s 76 for each store . Satisfaction with the store was greater in the pleasant store. Regression analyses showed that this was due to a direct effect of store atmosphere as well as to an indirect effect mediated by customers' mood. Customers in the pleasant store spontaneously spent more money on articles they simply liked. This effect was only due to customers' mood.

Hybrid fiber-wireless networks incorporating WDM technology for fixed wireless access operating in the sub-millimeter-wave and millimeter-wave (mm-wave) frequency regions are being actively pursued to provide untethered connectivity for ultrahigh bandwidth communications. The architecture of such radio networks requires a large number of antenna base-stations with high throughput to be deployed to maximize the geographical coverage with the main switching and routing functionalities located in a centralized location. The transportation of mm-wave wireless signals within the hybrid network is subject to several impairments including low opto-electronic conversion efficiency, fiber chromatic dispersion and also degradation due to nonlinearities along the link. One of the major technical challenges in implementing such networks lies in the mitigation of these various optical impairments that the wireless signals experience within the hybrid network. In this paper, we present an overview of different techniques to optically transport mm-wave wireless signals and to overcome impairments associated with the transport of the wireless signals. We also review the different designs of subsystems for integrating fiber-wireless technology onto existing optical infrastructure.

This article describes the development and validation of an instrument to assess cognitively mediated functional abilities in older adults, Everyday Cognition (ECog). The ECog is an informant-rated questionnaire comprised of multiple subscales. Confirmatory factor analysis (CFA) was used to examine its factor structure. Convergent validity was evaluated by comparing it to established measures of everyday function. External validity was evaluated by comparing ECog results across different clinical groups [cognitively normal, mild cognitive impairment (MCI), dementia]. CFA supported a seven-factor model including one global factor and six domain-specific factors (Everyday Memory, Language, Visuospatial Abilities, Planning, Organization, and Divided attention). The ECog correlated with established measures of functional status and global cognition, but only weakly with age and education. The clinical groups performed differently in each domain. In addition to the global factor, the Eve...

Since battery technology has not kept up with the demand for battery capacity on mobile devices, power optimization techniques are becoming increasingly important in wireless system design. Power optimization schemes are critical to interference management in wireless systems as interference usually results from aggressive spectral reuse and high power transmission and severely limits system performance. In this paper, we develop energy-efficient power optimization schemes for interference-limited communications.

We present experimental demonstrations using direct-detection and optical-orthogonal frequency division multiplexing (DD-OOFDM) for the compensation of chromatic dispersion in long-haul optical fiber links. Three transmitter designs of varying electrical and optical complexity are used for optical single sideband (OSSB) transmission and the theory behind each design is discussed. The data rates achieved for the three systems are 10, 12, and 20 Gbit/s for fiber distances between 320 and 400 km. A discussion of system overheads is provided together with simulations of the required optical signal-to-noise ratio (OSNR).

The IEEE 802.16 is a standard for broadband wireless communication in Metropolitan Area Networks (MAN). To meet the QoS requirements of multimedia applications, the IEEE 802.16 standard provides four different scheduling services: Unsolicited Grant Service (UGS), real-time Polling Service (rtPS), non-real-time Polling Service (nrtPS), and Best Effort (BE). The paper is aimed at verifying, via simulation, the effectiveness of rtPS, nrtPS, and BE (but UGS) in managing traffic generated by data and multimedia sources. Performance is assessed for an IEEE 802.16 wireless system working in Point-to-Multipoint (PMP) mode, with Frequency Division Duplex (FDD), and with full-duplex Subscriber Stations (SSs). Our results show that the performance of the system, in terms of throughput and delay, depends on several factors. These include the frame duration, the mechanisms for requesting uplink bandwidth, and the offered load partitioning, i.e., the way traffic is distributed among SSs, connections within each SS, and traffic sources within each connection. The results also highlight that the rtPS scheduling service is a very robust scheduling service for meeting the delay requirements of multimedia applications.

Novel objectives such as very low outage, high capacity, and high throughput are major challenging problems in radio resource management of mobile communication systems. More specifically, in radio resource scheduling (RRS), the aim is how to optimize available resources such as transmission power and data rate to achieve certain targeted objectives. Conventional RRS algorithms are based on optimizing one objective while keeping others as constraints. This paper proposes a novel distributed RRS algorithm based on analytic multi-objective optimization. The proposed algorithm relaxes the constraints and jointly optimizes all the required objectives. Infinity set of optimal solutions, called Pareto optimal, is obtained. Each solution in the set is optimal in a specific sense. The decision maker selects the required solution that fulfills the network requirements and conditions. Some of the conventional RRS algorithms are special cases of our multi-objective based algorithm. Detailed mathematical analysis of the proposed algorithm is given. Simulation results show the behavior of the proposed algorithm as well as its advantages over conventional algorithms.

Optimal finite impulse response (FIR) transmit and receive filterbanks are derived for block-based data transmissions over frequency-selective additive Gaussian noise (AGN) channels by maximizing mutual information subject to a fixed transmitpower constraint. Both FIR and pole-zero channels are considered. The inherent flexibility of the proposed transceivers is exploited to derive, as special cases, zero-forcing (ZF) and minimum mean-square error receive filterbanks. The transmit filterbank converts transmission over a frequency-selective fading channel, affected by additive colored noise, into a set of independent flat fading subchannels with uncorrelated noise samples. Two loading algorithms are also developed to distribute transmit power and number of bits across the usable subchannels, while adhering to an upper bound on the bit error rate (BER). Reduction of the signal-to-noise ratio (SNR) margin required to satisfy the prescribed BER is achieved by coding each subchannel's bit stream. The potential of the proposed transceivers is illustrated and compared to discrete multitone (DMT) with simulated examples.

In this paper, we present two simple Monte Carlo methods for estimating the achievable information rates of general finite state channels. Both methods require only the ability to simulate the channel with an a posteriori probability (APP) detector matched to the channel. The first method estimates the mutual information rate between the input random process and the output random process, provided that both processes are stationary and ergodic. When the inputs are i.i.d. equiprobable, this rate is known as the Symmetric Information Rate (SIR). The second method estimates the achievable information rate of an explicit coding system which interleaves m independent codes onto the channel and employs multistage decoding. For practical values of m, numerical results show that this system nearly achieves the SIR. Both methods are applied to the class of partial response channels commonly used in magnetic recording.

An information-theoretic approach for studying synchronization phenomena in experimental bivariate time series is presented. &quot;Coarse-grained&quot; information rates are introduced and their ability to indicate generalized synchronization as well as to establish a &quot;direction of information flow&quot; between coupled systems, i.e., to discern the driving from the driven (response) system, is demonstrated using numerically generated time series from unidirectionally coupled chaotic systems. The method introduced is then applied in a case study of electroencephalogram recordings of an epileptic patient. Synchronization events leading to seizures have been found on two levels of organization of brain tissues and &quot;directions of information flow&quot; among brain areas have been identified. This allows localization of the primary epileptogenic areas, also confirmed by magnetic resonance imaging and pasitron emission tomography scans.

Because of the potential for bias and error in questionnaire responding, many personality inventories include validity scales intended to correct biased scores or identify invalid protocols. The authors evaluated the utility of several types of validity scales in a volunteer sample of 72 men and 106 women who completed the Revised NEO Personality Inventory (NEO-PI-R; P. T. Costa & R. R. McCrae, 1992) and the Multidimensional Personality Questionnaire (MPQ; A. Tellegen, 1978/1982) and were rated by 2 acquaintances on the observer form of the NEO-PI-R. Analyses indicated that the validity indexes lacked utility in this sample. A partial replication (N = 1,728) also failed to find consistent support for the use of validity scales. The authors illustrate the use of informant ratings in assessing protocol validity and argue that psychological assessors should limit their use of validity scales and seek instead to improve the quality of personality assessments. Most personality assessment relies on the use of questionnaires. Respondents are typically presented with a series of items and asked to indicate whether or to what extent each item accurately describes their personality. Questionnaires are also used to gather informant ratings of personality traits. In both cases, the method assumes that respondents understand the procedure and are both willing and able to provide reasonably accurate responses. Usually respondents are: The accumulated construct validity of all personality questionnaires is compelling evidence of the soundness of this method of measurement. But it has been clear for decades that questionnaire responses are also susceptible to a variety of distortions. Respondents may misunderstand the instructions or misread the questions. They may be uncooperative and respond at random, or without careful thought. They may not have insight into their own personality traits, or they may answer defensively. They may make deliberate attempts to present a favorable or unfavorable picture of themselves. They may agree or disagree with items indiscriminately, or they may overuse or avoid extreme responses. If such distortions

The magnetic field experiment to be carried on the Voyager 1 and 2 missions consists of dual low field (LFM) and high field magnetometer (HFM) systems. The dual systems provide greater reliability and, in the case of the LFM's, permit the separation of spacecraft magnetic fields from the ambient fields. Additional reliability is achieved through electronics redundancy. The wide dynamic ranges of ~:0.5 G for the LFM's and +20 G for the HFM's, low quantization uncertainty of +0.002 3' (Y = 10 -s G) in the most sensitive (-+-8 y) LFM range, low sensor RMS noise level of 0.006 % and use of data compaction schemes to optimize the experiment information rate all combine to permit the study of a broad spectrum of phenomena during the mission. Objectives include the study of planetary fields at Jupiter, Saturn, and possibly Uranus; satellites of these planets; solar wind and satellite interactions with the planetary fields; and the large-scale structure and microscale characteristics of the interplanetary magnetic field. The interstellar field may also be measured.

One of the most consistent findings in rating scale research with children and adolescents is the modest agreement among different informants' ratings. The present study systematically explored patterns of agreement among teachers, parents/caregivers, and students in domains of social skills and problem behaviors using the Social Skills Improvement System-Rating Scales (SSIS-RS; F. M. Gresham & S. N. Elliott, 2008). Two subsamples from the normative sample of the SSIS-RS were used. The first sample of participants consisted of 168 students who had all 3 informants (parent, teacher, and self) complete the SSIS-RS scales, which was necessary to assess agreement across different raters. The second sample consisted of 164 students who had raters in a similar or same role (father-mother, teacher-teacher). The results replicated an extensive literature showing that cross-informant agreements for social skills and problem behaviors are weak to moderate. The current study invoked multitraitmultimethod logic to interpret the correlations among raters derived from different informants and showed that the convergent validity coefficients were consistently stronger than the discriminant validity correlations. Implications for assessment practices and future research are discussed.

Molecular communication is a new paradigm for communication between biological nanomachines over a nano-and microscale range. As biological nanomachines (or nanomachines in short) are too small and simple to communicate through traditional communication mechanisms (e.g., through sending and receiving of radio or infrared signals), molecular communication provides a mechanism for a nanomachine (i.e., a sender) to communicate information by propagating molecules (i.e., information molecules) that represent the information to a nanomachine (i.e., a receiver). This paper describes the design of an in vitro molecular communication system and evaluates various approaches to maximize the probability of information molecules reaching a receiver(s) and the rate of information reaching the receiver(s). The approaches considered in this paper include propagating information molecules (diffusion or directional transport along protein filaments), removing excessive information molecules (natural decay or receiver removal of excessive information molecules), and encoding and decoding approaches (redundant information molecules to represent information and to decode information). Two types of molecular communication systems are considered: a unicast system in which a sender communicates with a single receiver and a broadcast system in which a sender communicates with multiple receivers. Through exploring tradeoffs among the various approaches on the two types of molecular communication systems, this paper identifies promising approaches and shows the feasibility of an in vitro molecular communication system.

A secret sharing scheme permits a secret to be shared among participants in such a way that only qualified subsets of partecipants can recover the secret, but any non-qualified subset has absolutely no information on the secret. The set of all qualified subsets defines the access structure to the secret. Sharing schemes are useful in the management of cryptographic keys and in multy-party secure protocols. We analyze the relationships among the entropies of the sample spaces from which the shares and the secret are chosen. We show that there are access structures with 4 participants for which any secret sharing scheme must give to a participant a share at least 50% greater than the secret size. This is the first proof that there exist access structures for which the best achievable information rate (i.e., the ratio between the size of the secret and that of the largest share) is bounded away from 1. The bound is the best possible, as we construct a secret sharing scheme for the above access structures which meets the bound with equality.

It has been suggested that one of the most significant reasons for Multi-Protocol Label Switched (MPLS) network deployment is network traffic engineering. The goal of traffic engineering is to make best use of the network infrastructure and this is facilitated by the explicit routing feature of MPLS which allows the potential addressing of many shortcomings associated with current IP routing schemes. This paper describes a software system called Routing and Traffic Engineering Server (RATES) developed for MPLS traffic engineering. It also describes some new routing ideas incorporated in RATES for MPLS explicit path selection. The RATES implementation con-

Multicell processing in the form of joint encoding for the downlink of a cellular system is studied under the assumption that the base stations (BSs) are connected to a central processor (CP) via finitecapacity links (finite-capacity backhaul). To obtain analytical insight into the impact of finite-capacity backhaul on the downlink throughput, the investigation focuses on a simple linear cellular system (as for a highway or a long avenue) based on theWyner model. Several transmission schemes are proposed that require varying degrees of knowledge regarding the system codebooks at the BSs. Achievable rates are derived in closed-form and compared with an upper bound. Performance is also evaluated in asymptotic regimes of interest (high backhaul capacity and extreme signal-to-noise ratio, SNR) and further corroborated by numerical results. The major finding of this work is that even in the presence of oblivious BSs (that is, BSs with no information about the codebooks) multicell processing is able to provide ideal performance with relatively small backhaul capacities, unless the application of interest requires high data rate (i.e., high SNR) and the backhaul capacity is not allowed to increase with the SNR. In these latter cases, some form of codebook information at the BSs becomes necessary.

The sequential Iterative Water-Filling Algorithm (IWFA) proposed by Yu et al. is by now a popular lowcomplexity algorithm to compute the Nash equilibrium point of the power allocation game in a Gaussian frequency-selective multiuser interference channel. The algorithm is based on a distributed sequential updating where, at each iteration, the users choose their power allocation, one after the other. However, this sequential updating strategy may slow down its convergence time excessively when the number of users is high. In this paper, we propose an alternative distributed algorithm, called Simultaneous Iterative Water-Filling Algorithm (SIWFA), where at each iteration, all the users update their power allocations simultaneously, rather than sequentially. This reduces the convergence time considerably, specially when the number of users is large. Our main contribution is to provide a unified set of sufficient conditions for the convergence of both IWFA and SIWFA, that are less stringent than those known in the literature for IWFA. These conditions guarantee the convergence of both algorithms also in the presence of spectral mask constraints imposed on the power allocations of the users. T

Cognitive radio (CR) is the key enabling technology for an efficient dynamic spectrum access. It aims at exploiting an underutilized licensed spectrum by enabling opportunistic communications for unlicensed users. In this work, we first develop a distributed cognitive radio MAC (COMAC) protocol that enables unlicensed users to dynamically utilize the spectrum while limiting the interference on primary (PR) users. The main novelty in COMAC lies in not assuming a predefined CR-to-PR power mask and not requiring active coordination with PR users. COMAC provides a statistical performance guarantee for PR users by limiting the fraction of the time during which the PR users' reception is negatively affected by CR transmissions. To provide such a guarantee, we develop probabilistic models for the PR-to-PR and the PR-to-CR interference under a Rayleigh fading channel model. From these models, we derive closedform expressions for the mean and variance of interference. Empirical results show that the distribution of the interference is approximately lognormal. Based on the developed interference models, we derive a closed-form expression for the maximum allowable power for a CR transmission. We extend the min-hop routing to exploit the available channel information for improving the perceived throughput. Our simulation results indicate that COMAC satisfies its target soft guarantees under different traffic loads and arbitrary user deployment scenarios. Results also show that exploiting the available channel information for the routing decisions can improve the end-to-end throughput of the CRN.

The concept of cognitive radio (CR) has recently received great attention from the research community as a promising paradigm to achieve efficient use of the frequency resource by allowing the coexistence of licensed (primary) and unlicensed (secondary) users in the same bandwidth. In this paper, we propose a novel Nash equilibrium (NE) problem to model concurrent communications of cognitive secondary users who compete against each other to maximize their information rate. The formulation contains constraints on the transmit power (and possibly spectral masks) as well as aggregate interference tolerable at the primary users' receivers. The coupling among the strategies of the players due to the interference constraints presents a new challenge for the analysis of this class of Nash games that cannot be addressed using the game theoretical models proposed in the literature. For this purpose, we need the framework given by the more advanced theory of finite-dimensional variational inequalities (VI). This provides us with all the mathematical tools necessary to analyze the proposed NE problem (e.g., existence and uniqueness of the solution) and to devise alternative distributed algorithms along with their convergence properties.

With the popularity of the IEEE 802.11 standards, many analytical saturation throughput studies for the distributed coordination function (DCF) have been reported. In this paper, we outline a number of issues and criticalities raised by previously proposed models. In particular, a careful look at backoff counter decrement rules allows us to conclude that, under saturation conditions, the slot immediately following a successful transmission can be accessed only by the station (STA) that has successfully transmitted in the previous channel access. Moreover, due to the specific acknowledgment (ACK) timeout setting adopted in the standard, the slot immediately following a collision cannot be accessed by any STA. Thus, the hypothesis of uncorrelation between consecutive channel slots and statistical homogeneity is not generally true. We propose a new backoff decrement model that retains the simplicity of traditional DCF models while being able to take into account such a correlation, and we compare the accuracy of our model with that of previously proposed approaches. interests include wireless networks, particularly multiple access algorithms with qualityof-service provisioning, cross-layer interactions between access solutions and the physical layer, and mobility management and load balancing in wireless packet networks.

Privacy is needed in ad hoc networks. An ad hoc on-demand position-based private routing algorithm, called A02P, is proposed for communication anonymity. Only the position of the destination is exposed in the network for route discovery. To discover routes with the limited routing information, a receiver contention scheme is designed for determining the next hop. pseudo identifiers are used for data packet delivery after a route is established. Real identities (IDS) for the source nodes, the destination nodes, and the forwarding nodes in the end-to-end connections are kept private. Anonymity for a destination relies on the difficulty of matching a geographic position to a real node ID. This can be enforced by the use of secure position service systems. Node mobility enhances destination anonymity by making the match of a node ID with a position momentary. To further improve destination privacy, R-A02P is proposed. In this protocol, the position of a reference point, instead of the position of the destination, is used for route discovery. Analytical models are developed for evaluating the delay in route discovery and the probability of route discovery failure. A simulator based on 77s-2 is developed for evaluating network throughput. Analysis and simulation results show that, while A02P preserves communication privacy in ad hoc networks, its routing performance is comparable with other position-based routing algorithms.

Microwire electrode arrays were implanted in the motor and premotor cortical areas of rhesus macaques. The recorded activity was used to control the three-dimensional movements of a virtual cursor and of a robotic arm in real time. The goal was to move the cursor or robot to one of eight targets. Average information conveyed about the intended target was calculated from the observed trajectories at 30-ms intervals throughout the movements. Most of the information about intended target was conveyed within the first second of the movement. For the brain-controlled cursor, the instantaneous information transmission rate was at its maximum at the beginning of each movement (averaged 4.8 to 5.5 bits/s depending on the calculation method used). However, this instantaneous rate quickly slowed down as the movement progressed and additional information became redundant. Information was conveyed more slowly through the brain-controlled robot due to the dynamics and noise of the robot system. The brain-controlled cursor data was also used to demonstrate a method for optimizing information transmission rate in the case where repeated cursor movements are used to make long strings of sequential choices such as in a typing task.

The present study examines co-occurring psychiatric syndromes in a well-characterized sample of youths with autism spectrum disorders (ASD; n = 177) and their siblings (n = 148), reported independently by parents and teachers. In ASD, parents reported substantial comorbidity with affective (26%), anxiety (25%), attentional (25%), conduct (16%), oppositional (15%), and somatic problems (6%). Teachers reported a much lower prevalence. Autistic severity scores for children with ASD exhibited moderate correlations with general psychopathology within-but not acrossinformants, whereas sibling correlations were significant both within-and across-informants. Results support the role of environmental context in psychiatric symptom expression in children affected by autism and suggest that informant discrepancies may more provide critical cues for these children via specific environmental modifications.

This paper describes a novel quality-of-service (QoS) routing protocol for ad hoc networks based on the OLSR protocol. Our protocol, QOLSR, is designed for wireless networks with stationary or moving nodes, where each node is equipped with 802.11 wireless card. The goal of our protocol is not only to find a route from a source to a destination, but an optimal route that satisfies the end-to-end QoS requirement, often given in terms of bandwidth or delay. We present an analytical model to compute the average delay and permissible throughput on links using the IEEE 802.11 medium access protocol and considering correlations and interferences between nodes. This model takes into account packet's collision probability, node's MAC queuing and service times based on the IEEE 802.11 binary exponential backoff algorithm and the events underneath its operation. Afterwards, our protocol assigns weights to individual links based on the average delay and bandwidth metrics of packets over the link. We present a distributed algorithm for multiple QoS requirements to find the source destination optimal paths in terms of bandwidth and delay using the known partial network topology available on each node. However, these optimal paths in partial network topology are not optimal paths in the whole ad hoc network. We show that this problem is due to the heuristic for the selection of MPRs used in OLSR. We propose innovative heuristics for the selection of MPRs based on QoS measurements that allow QOLSR to find optimal paths on the known partial topology having the same bandwidth performances that those on the whole network. The performance evaluation of our protocol in both static and dynamic ad hoc networks is extensively investigated. Mathematical analysis and simulation results show that the QOLSR protocol yields better performance compared to the best-effort OLSR protocol and significantly improves throughput by using our proposed heuristic. Copyright # 2005 AEIT.

In this paper, we consider an amplify-and-forward wireless relay system where multiple source nodes communicate with their corresponding destination nodes with the help of relay nodes. Conventionally, each relay equally distributes the available resources to its relayed sources. This approach is clearly sub-optimal since each user 1 experiences dissimilar channel conditions, and thus, demands different amount of allocated resources to meet its quality-of-service (QoS) request. Therefore, this paper presents novel power allocation schemes to i) maximize the minimum signal-to-noise ratio among all users; ii) minimize the maximum transmit power over all sources; iii) maximize the network throughput. Moreover, due to limited power, it may be impossible to satisfy the QoS requirement for every user. Consequently, an admission control algorithm should first be carried out to maximize the number of users possibly served. Then, optimal power allocation is performed. Although the joint optimal admission control and power allocation problem is combinatorially hard, we develop an effective heuristic algorithm with significantly reduced complexity. Even though theoretically sub-optimal, it performs remarkably well. The proposed power allocation problems are formulated using geometric programming (GP), a well-studied class of nonlinear and nonconvex optimization. Since a GP problem is readily transformed into an equivalent convex optimization problem, optimal solution can be obtained efficiently. Numerical results demonstrate the effectiveness of our proposed approach.

We derive optimal time-dependent adjustment rules from Shannon's (1948) Information Theory. In a continuous-time LQ prediction problem with a costly rate of information acquisitionprocessing, the optimal prediction evolves smoothly, but jumps at an optimally chosen frequency, when fresh information accrues. A more volatile and persistent target raises the information rate required to maintain a sampling frequency. This cost-e ect moderates and may even reverse the beneÿt-e ect on the value of information, so optimal inertia is unresponsive to and nonmonotonic in the predictability of the environment. Conventional models with a ÿxed cost per observation imply no such cost-e ect, so inertia rises quickly in the predictability of the environment. ?

We investigate the spectral efficiency, achievable by a low-complexity symbol-by-symbol receiver, when linear modulations based on the superposition of uniformly time-and frequency-shifted replicas of a base pulse are employed. Although orthogonal signaling with Gaussian inputs achieves capacity on the additive white Gaussian noise channel, we show that, when finite-order constellations are employed, by giving up the orthogonality condition (thus accepting interference among adjacent signals) we can considerably improve the performance, even when a symbol-by-symbol receiver is used. We also optimize the spacing between adjacent signals to maximize the achievable spectral efficiency. Moreover, we propose a more involved transmission scheme, composed by the superposition of two independent signals and a receiver based on successive interference cancellation, showing that it allows a further increase of the spectral efficiency. Finally, we show that a more involved equalization algorithm, based on soft interference cancellation, allows to achieve an excellent bit-error-rate performance, even when error-correcting codes designed for the Gaussian-noiselimited channel are employed, and thus does not require a complete redesign of the coding scheme.