Pilot Spacing Research Articles

From the flight of Yu.A. Gagarin to the contemporary piloted space flights and exploration missions

The first human flight to space made by Yu. A. Gagarin on April 12, 1961 was a crucial event in the history of cosmonautics that had a tremendous effect on further progress of the human civilization. Gagarin's flight had been prefaced by long and purposeful biomedical researches with the use of diverse bio-objects flown aboard rockets and artificial satellites. Data of these researches drove to the conclusion on the possibility in principle for humans to fly to space. After a series of early flights and improvements in the medical support system space missions to the Salyut and Mir station gradually extended to record durations. The foundations of this extension were laid by systemic researches in the fields of space biomedicine and allied sciences. The current ISS system of crew medical care has been successful in maintaining health and performance of cosmonauts as well as in providing the conditions for implementation of flight duties and operations with a broad variety of payloads. The ISS abounds in opportunities of realistic trial of concepts and technologies in preparation for crewed exploration missions. At the same, ground-based simulation of a mission to Mars is a venue for realization of scientific and technological experiments in space biomedicine.

A policy of anticipation as a strategic objective of space biology and medicine at the present stage

This article reflects the ongoing debates in Russia regarding paths of innovative development and the role that fundamental science has played in the development of technology critical for national security and for its breakthrough potential. Alternative routes of technical development include variations in priority support for those points of growth, in which Russia has attained and steadily held the leading position, occupying a prominent place in the international division of labor. Russia’s space program is a good example of the successful implementation of a national program and provides a demonstration of the country’s leadership role in this area of human activities. This article presents an analysis of the factors and circumstances in Russia that predetermined, in the early, “Gagarin” period of piloted space flights, its winning of the leading position. They also determined the vector of the development of manned space flight for many years to come. Even taking into account the host of issues with the implementation of the International Space Station (ISS) utilization program and the planning of manned flights to the Moon and Mars, the unique experience of preparations and the conducting of research and tests with humans in space—the enormous groundwork in fundamental biomedical research over the past 50 years of piloted flights—provides the basis for an optimistic prognosis for gaining headway with essentially new, ambitious space projects. The key question is whether the proactive strategy of prioritized development and the affirmation of the role of manned space flights as the most integrated and science-intensive sector of innovative achievement will be realized. The development of the space industry depends upon the answer, not only at the present stage but in the long-term as well, as does the fate of the national fundamental space sciences, an integral part of which is space biomedicine.

Pilot Symbol Parameter Optimization Based on Imperfect Channel State Prediction for OFDM Systems

The optimization of pilot symbol parameters can improve the spectral efficiency of adaptive modulation for orthogonal frequency division multiplexing (OFDM) systems, since pilot symbols impose an overhead on the system consuming power and bandwidth. An optimal pilot symbol assisted adaptive modulation (PSAAM) scheme for OFDM systems is proposed that maximizes spectral efficiency by adapting the power and constellation size of each subcarrier based on employing imperfect channel state information (CSI) at the transmitter. The pilot symbol power and spacing is also optimized in this scheme. A suboptimum scheme that decreases computational complexity without perceivable loss in performance is also presented. The optimality of minimum mean square error (MMSE) channel prediction for OFDM systems expressed in terms of a lower bound on spectral efficiency is approached. It is proved that the rectangular pilot pattern with equi-spaced and equal power pilot tones achieves the minimum MSE of the channel prediction in addition to having the advantage of simplifying PSAAM design. Numerical results show the importance of optimal pilot parameter adjustment for rapidly fading channels.

Eigen-Coherence and Link Performance of Closed-Loop 4G Wireless in Measured Outdoor MIMO Channels

Employing feedback in multiple-input-multiple-output (MIMO) systems offers the potential to significantly increase data rates over open-loop schemes. However, the impact the propagation channel has on the behavior and performance of the scheme must be considered and, where appropriate, the signaling designed to suit. In this paper, measured outdoor MIMO propagation data is used to evaluate initially the distributions and statistics of the coherence of the eigenmodes of the channel, for a wide range of mobility scenarios and user devices. Then, the impact on link performance of the differing coherences in time and frequency is evaluated in terms of the feedback delay and spectral spacing of pilots in a practical feedback scheme used in mobile WiMAX. It is found that not only mobility and physical environment, but also the directivity of the antenna array affect the eigen-coherence and also, therefore, the performance of a feedback scheme. Bit-error rate and information capacity are both shown to be sensitive to increased feedback delay and pilot spacing, however, the closed-loop system always outperforms its open-loop counterpart.

Capacity Analysis and Pilot-Data Power Allocation for MIMO-OFDM With Transmitter and Receiver IQ Imbalances and Residual Carrier Frequency Offset

We analyze the ergodic capacity and capacity bound of a multiple-input–multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system suffering from frequency-selective in-phase and quadrature-phase (IQ) imbalances along with residual carrier frequency offset (CFO). In the literature, capacity analysis of systems with IQ imbalance has been done only for the single antenna case and has considered either frequency-flat IQ imbalances at both transmitter and receiver sides without CFO or only receiver-side IQ imbalances with CFO. Additionally, these works dealt with IQ imbalance by treating the mirror tone interference as an additional source of noise, which is not optimal. In this paper, we consider a generalized system model that includes a multiantenna system with frequency-selective IQ imbalances at both the transmitter and the receiver sides, in addition to the presence of CFO, and perform capacity analysis considering joint detection of the signal and its self-interference. In addition, for the imperfect channel estimation case, existing works in the literature optimize for pilot spacings and pilot designs. Pilot-data power allocation is an additional degree of freedom that is available to further optimize the system and has not been addressed before. Therefore, we analyze the pilot-data power allocation that maximizes the capacity bound and obtain a closed-form solution for the optimal power allocation at high signal-to-noise ratio (SNR) regime. We then study how the IQ imbalance and residual CFO severity affect capacity, symbol error rate (SER), and capacity bound maximizing power allocation. Finally, we derive the optimal power allocation when the channel is slow varying and remains constant over a block of several OFDM symbols. The derived results are validated through Monte Carlo simulations.

Crew roles and interactions in scientific space exploration

Future piloted space exploration missions will focus more on science than engineering, a change which will challenge existing concepts for flight crew tasking and demand that participants with contrasting skills, values, and backgrounds learn to cooperate as equals. In terrestrial space flight analogs such as Desert Research And Technology Studies, engineers, pilots, and scientists can practice working together, taking advantage of the full breadth of all team members' training to produce harmonious, effective missions that maximize the time and attention the crew can devote to science. This paper presents, in a format usable as a reference by participants in the field, a successfully tested crew interaction model for such missions. The model builds upon the basic framework of a scientific field expedition by adding proven concepts from aviation and human space flight, including expeditionary behavior and cockpit resource management, cooperative crew tasking and adaptive leadership and followership, formal techniques for radio communication, and increased attention to operational considerations. The crews of future space flight analogs can use this model to demonstrate effective techniques, learn from each other, develop positive working relationships, and make their expeditions more successful, even if they have limited time to train together beforehand. This model can also inform the preparation and execution of actual future space flights.

Cross-layer combining of adaptive pilot-symbol-assisted modulation with truncated automatic repeat request in the presence of imperfect channel state information at both the receiver and the transmitter

In this study the authors provide an adaptive cross-layer design that maximises the spectral efficiency under prescribed quality of services (QoSs) such as error rate and delay. The considered scheme combines adaptive modulation at physical layer with a truncated automatic repeat request at data link layer in the presence of both channel estimation and prediction errors. Both the channel estimation and prediction are done based on adaptive pilot-symbol-assisted modulation in which both pilot spacing and power allocation on pilot symbols are optimised in order to maximise the spectral efficiency. We provide closed-form expression for average spectral efficiency and average packet error rate over Rayleigh fading channel. Numerical results demonstrate that our adaptive cross-layer design improves the spectral efficiency while meeting the prescribed QoS. We have shown that the channel prediction is more important than the channel estimation in order to improve the spectral efficiency in a practical situation. Also we have found that the increment of spectral efficiency decreases on increasing the maximum number of retransmissions, and thus in order to reduce the delay and buffer size at the data link layer, the maximum number of retransmissions are limited to a small number in practice.

Pioneering space research in the ussr and mathematical modelling of large problem of radiation transfer

This review is to recall to scientists of the older generation about some historical pages of our memory and about many famous researchers, teachers and colleagues. As to the younger researchers and foreign colleagues, it will be useful for them to get to know about pioneer advancements of the Soviet scientists in the field of information and mathematical supply for cosmonautic problems on the eve of the space era. Main attention is paid down to the scientific experiments conducted on the piloted space vehicles and the research collectives who created the information and mathematical tools for the first space projects. The role of Mstislav Vsevolodovich Keldysh, the Major Theoretician of cosmonautics, is in particular emphasized, who determined in the most degree the basic directions of development of space research and remote sensing of the Earth and planets that are shortly called as REMOTE SENSING.

Analytic performance evaluation of MIMO OFDM with pilot‐aided channel estimation on doubly selective channels

AbstractIn this work, the effects of channel estimation errors on the performance of a maximum likelihood detector (MLD) in a MIMO OFDM system are assessed. The analysis is conducted in the framework of a long‐term evolution (LTE) air interface and is based on a robust pilot aided channel estimator. The correlation coefficient between the estimate and the real channel is computed and the impact of interpolation errors on the detector is evaluated as a function of key design parameters such as the pilot spacing and the number of transmit antennas. The effect of partial knowledge of the channel statistics at the receiver side is studied with special emphasis on the role of the delay and Doppler spread of the channel. Our analysis accounts for both time and frequency selectivity of the channel and thus also for the intercarrier interference arising in a typical time varying propagation scenario. Copyright © 2010 John Wiley & Sons, Ltd.

On the performance evaluation of an LTE SFBC system with Wiener channel estimation in frequency-selective channels

The uncoded performance of an Alamouti space-frequency block code operating in a frequency-selective channel is studied in the presence of channel estimation errors. The Alamouti Maximum Likelihood (ML) symbol detector with linear combining is considered at the receiver. Imperfect channel estimates are provided by a realistic as well as robust Wiener interpolator. A closed-form expression of the uncoded error probabilities of a space-frequency block code employing an Alamouti with linear combining is derived. Our analysis is conducted in the framework of a Long-Term Evolution air interface. The impact of channel estimation errors on the uncoded performance of the system is evaluated as a function of key system parameters, such as the anticipated power delay profile at the channel estimator, the actual, i.e. true, power delay profile, the pilot spacing and the Wiener filter length. The role of partial knowledge of the channel statistics is investigated as well. Finally, we derive a lower bound from our closed-form expression and calculate the bit error outage of the linear Alamouti combiner in presence of log-normal fading signal-to-noise ratio (SNR).

The problem of artificial gravity in piloted space exploration missions

The review deals with the problem of using artificial gravity in piloted space missions, its history and relevance to the proclaimed goals of remote space exploration. It contains a brief discussion of deconditioning and loss of acceleration tolerance developing in cosmonauts despite a variety of preventive procedures. Key issues pertaining short-arm centrifuge (SAC) design and in-flight utilization are acceleration tolerance, effectiveness and g-prescriptions. The Russian and international literature on SAC experience in ground-based investigations with simulated microgravity effects (immersion, HDT) gives credence to this approach to counteracting the negative physiological effects of microgravity. Open issues and goals to be gained are described.

Automatic Content Generation in the Galactic Arms Race Video Game

Simulation and game content includes the levels, models, textures, items, and other objects encountered and possessed by players during the game. In most modern video games and in simulation software, the set of content shipped with the product is static and unchanging, or at best, randomized within a narrow set of parameters. However, ideally, if game content could be constantly and automatically renewed, players would remain engaged longer. This paper introduces two novel technologies that take steps toward achieving this ambition: 1) a new algorithm called content-generating NeuroEvolution of Augmenting Topologies (cgNEAT) is introduced that automatically generates graphical and game content while the game is played, based on the past preferences of the players, and 2) Galactic Arms Race (GAR), a multiplayer video game, is constructed to demonstrate automatic content generation in a real online gaming platform. In GAR <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">,</b> which is available to the public and playable online, players pilot space ships and fight enemies to acquire unique particle system weapons that are automatically evolved by the cgNEAT algorithm. A study of the behavior and results from over 1000 registered online players shows that cgNEAT indeed enables players to discover a wide variety of appealing content that is not only novel, but also based on and extended from previous content that they preferred in the past. Thus, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GAR</i> is the first demonstration of evolutionary content generation in an online multiplayer game. The implication is that with cgNEAT it is now possible to create applications that generate their own content to satisfy users, potentially reducing the cost of content creation and increasing entertainment value from single-player to massively multiplayer online games (MMOGs) with a constant stream of evolving content.

On the pilot spacing constraints for continuous time-varying fading channels

In common wireless systems pilot placing can be interpreted as a way to sample the channel with some degree of accuracy. In this letter we investigate the necessary conditions on the pilots spacing for time-varying fading to guarantee a specified average bit error rate. These constraints are evaluated in closed form for large SNR and small fading dynamics and specialized for varying fading correlation and coded/uncoded binary transmissions.

Demonstrating Automatic Content Generation in the Galactic Arms Race Video Game

In most modern video games, content (e.g. models, levels, weapons, etc.) shipped with the game is static and unchanging, or at best, randomized within a narrow set of parameters. However, if game content could be constantly renewed, players would remain engaged longer. To realize this ambition, the content-generating NeuroEvolution of Augmenting Topologies (cgNEAT) algorithm automatically evolves novel game content based on player preferences, as the game is played. To demonstrate this approach, the Galactic Arms Race (GAR) video game, which incorporates cgNEAT, will be presented. In GAR, players pilot space ships and fight enemies to acquire novel particle system weapons that are evolved by the game. The live demo will show how GAR players can discover a wide variety of weapons that are not only novel, but also based on and extended from previous content that they preferred in the past. The implication of cgNEAT is that it is now possible to create games that generate their own content, potentially significantly reducing the cost of content creation and increasing the replay value of games.

Model-based pilot and data power adaptation in psam with periodic delayed feedback

We consider the optimum design of pilot-symbol-assisted modulation (PSAM) schemes with feedback. The received signal is periodically fed back to the transmitter through a noiseless delayed link and the time-varying channel is modeled as a Gauss-Markov process. We optimize a lower bound on the channel capacity which incorporates the PSAM parameters and Kalman-based channel estimation and prediction. The parameters available for the capacity optimization are the data power adaptation strategy, pilot spacing and pilot power ratio, subject to an average power constraint. Compared to the optimized open-loop PSAM (i.e., the case where no feedback is provided from the receiver), our results show that even in the presence of feedback delay, the optimized power adaptation provides higher information rates at low signal-to-noise ratios (SNR) in medium-rate fading channels. However, in fast fading channels, even the presence of modest feedback delay dissipates the advantages of power adaptation.

Robust low-complexity joint space–time–frequency channel estimation with transmit diversity in mobile wireless channels

In this paper, a robust low-complexity joint space–time–frequency channel estimation with transmit diversity in mobile wireless channels is proposed. Based on the orthogonal frequency division multiplexing (OFDM), the previously known training sequences are firstly blocked, space–frequency complex orthogonally encoded, up-converted and transmitted with diversity in the transmitter. In the receive end, each subchannel frequency response is estimated directly through the inverse pilot space–frequency complex orthogonally decoding. Wiener filtering and interpolating with the time- and frequency-domain correlations of the frequency response of the mobile wireless channels, low-complexity joint space–time–frequency channel estimator is finally constructed. In our proposed scheme, the high-level large-scale matrix inverse operations in traditional multiple input multiple output (MIMO) channel estimations are avoided. Separate and independent channel estimation corresponding to each pair of transmit and receive antennas in the MIMO space–frequency block coding system is achieved with transmit diversity, which can be used to significantly reduce the computation complexity with no degradation in system performance. Moreover, to successfully decoding the known pilot subblock coding matrix, it is only required that the fading channel keep approximately constant in each space–frequency coding subblock during one OFDM symbol block period. Making full use of the best time- and frequency-domain filtering, it makes our proposed scheme even more robust and accurate to estimate and track the channels with rapid time-varying dispersive fading. Numerical results are provided to validate the performance of our proposed channel estimators with diversity in mobile wireless channels.

Optimized rate-adaptive PSAM for MIMO MRC systems with transmit and receive CSI imperfections

The impact of imperfect channel state information (CSI) on the performance of transmit-beamforming (TB) over multiple-input multiple-output (MIMO) Rayleigh fading channels when using constant-power rate-adaptive pilot symbol assisted modulation (PSAM) is investigated. Specifically, imperfect CSI is accounted for with respect to both estimation and prediction errors, thereby allowing to quantify the performance degradation of the adaptive PSAM-based TB system due to both channel estimation and prediction errors. Such errors entail a mismatch between the optimal transmit/receive beamforming weights and the transmission rate implied by the true CSI on the one hand, and the actual values of these quantities as determined based on the estimated and predicted CSI, on the other hand. The compound effect of both estimation and prediction errors on the overall system performance is assessed in terms of the achievable average spectral efficiency, average bit error probability and outage probability, for which approximate closed-form expressions are derived for arbitrary numbers of transmit and receive antennas. Furthermore, the latter metrics are used to optimize the PSAM parameters, namely the power allocation between data and pilot symbols as well as the pilot spacing in order to maximize the achievable average spectral efficiency while adhering to a fixed target bit error probability.

Pilot design for OFDM with null edge subcarriers

Pilot symbol assisted modulation (PSAM) orthogonal frequency division multiplexing (OFDM) has proven to be a popular technique for high-speed communication through multipath fading channels. In this paper we examine PSAM pilot design optimization in OFDM systems that employ edge null subcarriers for spectral shaping. Specifically, we show that the commonly used even pilot spacing design is suboptimal in terms of symbol estimate mean squared error (MSE) performance when a sufficient number of null subcarriers are present. We pursue a parametric design of the pilot spacings and use convex optimization techniques in order to find a pilot design that results in near-optimal symbol estimate MSE performance. Finally, we present several example PSAM OFDM pilot designs including one example based on the IEEE 802.16 standard to demonstrate performance improvements over the conventional even-spacing pilot design when null edge subcarriers are present.

Parameter Optimization for Amplify-and-Forward Relaying Systems with Pilot Symbol Assisted Modulation Scheme

Cooperative diversity is a promising technology for future wireless networks. In this paper, we consider a cooperative communication system operating in an amplify-and-forward (AF) mode with a pilot symbol as-sisted modulation (PSAM) scheme. It is assumed that a linear minimum mean square estimator (LMMSE) is used for the channel estimation at the receiver. A simple and easy-to-evaluate asymptotical upper bound (AUB) of the symbol-error-rate (SER) is derived for uncoded AF cooperative communication systems with quadrature amplitude modulation (QAM) constellations. Based on the AUB, we propose a criterion for the parameter optimization in the PSAM scheme. We discuss how the pilot spacing and the length of the Wiener ?lter should be chosen under the constraint of a tradeoff between pilot overhead, estimation accuracy, and receiver complexity. We also formulate an power allocation problem for the considered system. It is shown that the power allocation problem can optimally be solved by means of a gradient search method. Numerical simulations are presented to verify the correctness of the theoretical results and to demonstrate the benefits of the parameter optimization.

A method for analyzing the performance of comb-type pilot-aided channel estimation in power line communications

In this paper, we propose an original method for analyzing the performance of comb-type pilot-aided channel estimation for power line communications. Our method is based on a unified mathematical decomposition of the channel estimation error, which takes both the signal-to-noise ratio of the pilot sub-carrier locations and the interpolation kernel used into account. We demonstrate that the channel estimation error is composed of two terms that evolve differently according to the pilot spacing and the interpolation technique used. The error due to additive noise over channel transmission is formulated by a simple easily used analytic expression. Our results for some practical situations show that good performances can be achieved with a simple linear interpolation.