configuration flatness of lagrangian control systems with fewer controls than degrees of freedom abstract a lagrangian control system is said to be configuration flat if its states are determined by configuration flat outputs depending on configuration variables only this paper gives a necessary condition and two types of sufficient conditions for lagrangian control systems with n degrees of freedom and m controls with m n to be configuration flat and further makes a remark on the choice of output variables for configuration flatness two examples are given in which the sufficient conditions are utilized for finding configuration flat outputs

trellis coded differentially coherent tcdc mpsk with carrier phase noise the authors consider trellis coded m ary phase shift keying mpsk when used with differentially coherent demodulation over a carrier phase noise dominated channel a tight upper bound to the probability of error is introduced this bound shows the presence of an irreducible probability of error when compared to coherently demodulated trellis coded mpsk the irreducible probability of error of the differentially coherent scheme is much lower this improved robustness to carrier phase noise is obtained at the expense of signal to noise ratio snr coding gain numerical results for two ungerboeck codes with differentially coherent mpsk demodulation show poor snr coding gain a modification of ungerboeck codes which makes them more suitable for use with differentially coherent demodulation is shown to increase the snr gain while maintaining good robustness to carrier phase noise

continuous phase modulation part i full response signaling the continuous phase modulation cpm signaling scheme has gained interest in recent years because of its attractive spectral properties data symbol pulse shaping has previously been studied with regard to spectra for binary data and modulation index 0 5 in this paper these results have been extended to the m ary case where the pulse shaping is over a one symbol interval the so called full response systems results are given for modulation indexes of practical interest concerning both performance and spectrum comparisons are made with minimum shift keying msk and systems have been found which are significantly better in e b n 0 for a large signal to noise ratio snr without expanded bandwidth schemes with the same bit error probability as msk but with considerably smaller bandwidth have also been found significant improvement in both power and bandwidth are obtained by increasing the number of levels m from 2 to 4

coded continuous phase modulation using ring convolutional codes rate 1 2 convolutional codes over the ring of integers modulo m are combined with m ary continuous phase modulation cpm schemes whose modulation indices are of the form h 1 m an m ary cpm scheme with h 1 m can be modeled by a continuous phase encoder cpe followed by a memoryless modulator mm where the cpe is linear over the ring of integers modulo m the fact that the convolutional code and the cpe are over the same algebra allows the state of the cpe to be fed back and used by the convolutional encoder a modified euclidean distance function that substantially simplifies the search for good codes has been derived and used to find new codes numerical results show that this approach consistently improves the performance as compared to coded schemes using binary convolutional codes with the same decoding complexity

brief freedom in coordinate transformation for exact linearization and its application to transient behavior improvement this paper deals with the use of extra freedom in the exact linearization technique firstly the freedom in choosing the coordinate transformation and nonlinear state feedback for the exact linearization is clarified secondly a controller design strategy for the transient behavior improvement in the presence of impulsive disturbances is shown finally numerical and experimental examples exhibit the effectiveness of this method

coding cpfsk for differential demodulation a model is developed for finding codes for differentially demodulated continuous phase frequency shift keying with modulation index h 1 m where m is the size of the symbol alphabet the results of codes searches show that there is very little loss in squared euclidean distance when comparing differential codes with coherent codes

constructive controllability algorithms for motion planning and optimization presents algorithms for planning feasible and minimum energy paths the algorithms rely on series expansions to characterize planning problems for polynomial control systems the resulting inversion problem is solved through an iterative contraction or a power series inversion while the design methodology is general our focus is on a class of polynomial control systems for which we provide explicit convergence guarantees we demonstrate performance and numerical characteristics using one dimensional and six dimensional systems

optimization of trellis coded tfm via matched codes a matched code is a convolutional code chosen in such a way that when combined with modulation with memory the resulting receiver for the coded modulation has the smallest possible number of states in the paper the matched coding technique is applied to coded tamed frequency modulation tfm schemes and a formal procedure is developed to find the best combination of a code and a modulation the optimization criterion is the maximum free euclidean distance for a given code rate and a given number of states in the viterbi receiver used for the coded modulation a search for the best codes was carried out for code rates 1 2 and 2 3 and for receivers with up to 256 and 64 states respectively good coding gains more than 7 db for rate 1 2 were achieved some of the best codes were catastrophic yet the coded modulation was not the codes obtained using the matched coding approach were in many cases better than those obtained using traditional optimization techniques

design of serial concatenated msk schemes based on density evolution we consider the design of convolutional codes and low density parity check ldpc codes with minimum shift keying msk when the receiver employs iterative decoding and demodulation the main idea proposed is the design of coded schemes that are well matched to the iterative decoding algorithm being used rather than to hypothetical maximum likelihood decoding we first show that the design is crucially dependent on whether the continuous phase encoder cpe is realized in recursive form or in nonrecursive form we then consider the design of convolutionally coded systems and low density parity check codes with msk to obtain near capacity performance with convolutional codes we show that it is possible to improve the performance significantly by using a mixture of recursive and nonrecursive realizations for the cpe for low density parity check codes we show that codes designed for binary phase shift keying are optimal for msk only if the nonrecursive realization is used for the recursive realization we design new ldpc codes based on the concept of density evolution we show that these codes outperform the best known codes for msk and have lower decoding complexity

correlative encoded digital fm this paper gives a straightforward method of obtaining an explicit expression for the spectrum of a correlative encoded digital fm signal an investigation of the band occupancy for various encoding schemes with rectangular as well as raised cosine pulse shaping is carried out correlative encodings that are spectrally more efficient than minimum shift keying msk and that promise an improved error performance are shown in addition if a small degradation in error performance is tolerated substantial increases in band efficiency are possible for example with the polynomial 1 2d d 2 4 the signal is spectrally 47 percent more efficient than msk and with an snr performance degradation of only 1 1 db

noncoherently detected trellis coded partial response cpm on mobile radio channels a noncoherent receiver is proposed for partial response trellis coded continuous phase modulation tc cpm on interleaved flat rician fading channels by using a multiple symbol observation interval and a simple metric calculator the power efficiency is improved over a receiver that uses a single symbol observation interval performance bounds on the bit error probability are derived by defining a set of characteristic distances for cpm signals and showing that tc cpm is equivalent to a tcm scheme our results show that with the same observation length the proposed receiver is less than 0 5 db inferior to a coherent receiver for which perfect channel information is needed we also conclude that in terms of joint power bandwidth complexity 2rc is the best candidate for rate 1 2 tcm codes

controllability and motion algorithms for underactuated lagrangian systems on lie groups we provide controllability tests and motion control algorithms for underactuated mechanical control systems on lie groups with lagrangian equal to kinetic energy examples include satellite and underwater vehicle control systems with the number of control inputs less than the dimension of the configuration space local controllability properties of these systems are characterized and two algebraic tests are derived in terms of the symmetric product and the lie bracket of the input vector fields perturbation theory is applied to compute approximate solutions for the system under small amplitude forcing in phase signals play a crucial role in achieving motion along symmetric product directions motion control algorithms are then designed to solve problems of point to point reconfiguration static interpolation and exponential stabilization we illustrate the theoretical results and the algorithms with applications to models of planar rigid bodies satellites and underwater vehicles

robust point stabilization of underactuated mechanical systems via the extended chained form this paper addresses point stabilization for the extended chained form ecf a control system that may be used to model a number of mechanical underactuated systems a control law is proposed based on well known hybrid open loop feedback techniques which exponentially stabilizes the origin of a dynamic extension of the ecf and ensures a degree of robustness to additive disturbance terms that may represent for instance model uncertainties numerical simulations are included to illustrate the performance of the presented stabilizers

catastrophic continuous phase modulation schemes and their noncatastrophic equivalents continuous phase modulation cpm schemes are bandwidth and energy efficient constant envelope modulation schemes that can be viewed as a continuous phase encoder cpe followed by a memoryless modulator mm where the cpe is of convolutional type it is observed that cpm schemes can be catastrophic in the sense that pairs of input sequences that differ in an infinite number of positions can be mapped into pairs of signals with finite euclidean distance this can happen in spite of the fact that the cpe is never catastrophic when considered as a stand alone convolutional encoder the necessary and sufficient condition for a general cpm scheme to be catastrophic is given each member of the two major families of cpm schemes namely the lrec and the lrc has been classified as a catastrophic or noncatastrophic scheme for the catastrophic schemes the probability that a catastrophic event occurs is determined a canonical precoder which transforms each scheme of both families into an equivalent noncatastrophic scheme is derived the equivalent noncatastrophic scheme has the same number of states as the original one moreover it has the property that if two input sequences differ in the ith position the corresponding output signals have nonzero euclidean distance in the ith interval

nonlinear control of mechanical systems with an unactuated cyclic variable numerous robotic tasks associated with underactuation have been studied in the literature for a large number of these in the plane the mechanical models have a cyclic variable the cyclic variable is unactuated and all shape variables are independently actuated this paper formulates and solves two control problems for this class of models if the generalized momentum conjugate to the cyclic variable is not conserved conditions are found for the existence of a set of outputs that yields a system with a one dimensional exponentially stable zero dynamics i e an exponentially minimum phase system along with a dynamic extension that renders the system locally input output decouplable if the generalized momentum conjugate to the cyclic variable is conserved a reduced system is constructed and conditions are found for the existence of a set of outputs that yields an empty zero dynamics along with a dynamic extension that renders the system feedback linearizable a common element in these two feedback problems is the construction of a scalar function of the configuration variables that has relative degree three with respect to one of the input components the function arises by partially integrating the conjugate momentum the results are illustrated on two balancing tasks and on a ballistic flip motion

uniform distance and error probability properties of tcm schemes the class of uniform trellis coded modulation tcm techniques is defined and simple explicit conditions for uniformity are derived uniformity is shown to depend on the metric properties of the two subconstellations resulting from the first step in set partitioning as well as on the assignment of binary labels to channel symbols the uniform distance property and uniform error property which are both derived from uniformity but are not equivalent are discussed the derived concepts are extended to encompass transmission over a not necessarily gaussian memoryless channel in which the metric used for detection may not be maximum likelihood an appropriate distance measure is defined that generalizes the euclidean distance it is proved that uniformity of a tcm scheme can also be defined under this new distance the results obtained are shown to hold for channels with phase offset or independent amplitude only fading examples are included to illustrate the applicability of the results

unit memory codes for continuous phase modulation in an awgn channel the combination of unit memory codes and continuous phase modulation in an additive white gaussian noise channel is considered our motivation is based on the fact that when rouanne and costello s 1988 free distance lower bound is applied to unit memory codes an improved lower bound is obtained specific constructions are considered for 4 level modulation schemes with full response and weak partial response heuristic design rules are used for defining the subsets of codes within which an exhaustive search is conducted the coding gains of the best codes within these subsets are better than those of best previously known multi memory codes

serially concatenated continuous phase modulation with convolutional codes over rings in this paper we investigate serially concatenated continuous phase modulation sccpm with convolutional codes cc over rings the transmitted signals are disturbed by additive white gaussian noise the properties for systems with both infinite and finite block lengths are investigated for an infinite length system we check the convergence threshold using the extrinsic information transfer chart for a finite length system we use union bound techniques to estimate the error floors in the union bound analysis we consider both the order and the position of nonzero permuted symbols a simple method for determining a cpm error event through the sum of the input symbol sequence is shown thus we can determine if the output symbol sequence of an error event in the ring cc can form an error event in cpm two properties concerning the interleaver gain ig are investigated a recursive search algorithm for the maximal ig is shown compared with previous sccpm with a binary cc the proposed system shows an improvement concerning the convergence threshold or error floors

impact of interactions on human dynamics abstract queueing theory has been recently proposed as a framework to model the heavy tailed statistics of human activity patterns the main predictions are the existence of a power law distribution for the interevent time of human actions and two decay exponents 1 and 3 2 current models lack however a key aspect of human dynamics i e several tasks require or are determined by interactions between individuals here we introduce a minimal queueing model of human dynamics that already takes into account human human interactions to achieve large scale simulations we obtain a coarse grained version of the model allowing us to reach large interevent times and reliable scaling exponents estimations using this we show that the interevent distribution of interacting tasks exhibit the scaling exponents 2 3 2 and a series of numerable values between 3 2 and 1 this work demonstrates that within the context of queueing models of human dynamics interactions change the exponent of the power law distributed interevent times beyond the study of human dynamics these results are relevant to systems where the event of interest consists of the simultaneous occurrence of two or more events

design of coded cpfsk modulation systems for bandwidth and energy efficiency consideration is given to the problems related to the design of m ary continuous phase frequency shift keying cpfsk systems with modulation index h j m combined with eternal rate r binary convolution encoders the following questions are raised and answered 1 how should different encoder modulator systems be compared and how can comparable systems be recognized from the system parameters i e m h and r 2 what are the limits on the information rate per unit bandwidth versus signal to noise ratio when reliable transmission is required 3 how does one choose the system parameters m h and r when the overall system has to achieve a specified performance and 4 how does one design the external rate r binary convolutional encoder to put in front of the m ary cpfsk modulation system with h j m a simple approximation for the bandwidth of a cpfsk signal is given and shown to be sufficiently accurate for system design purposes the design of the external convolutional encoder is carried out in a novel way that leads to fewer states in the combined encoder modulator system and thus yields improved performance for a given demodulation decoding complexity compared to previous approaches for the design of coded cpfsk systems

coded continuous phase modulation with low complexity noncoherent reception coded continuous phase modulation based on a feedback free modulator with noncoherent detection is discussed low complexity receiver processing is achieved by using only two or three linear filters for demodulation and applying noncoherent sequence estimation with reduced state viterbi decoding and simple branch metric calculation overall the proposed noncoherent receiver provides significant advantages over previously presented approaches

minimum euclidean distance for combinations of short rate 1 2 convolutional codes and cpfsk modulation continuous phase frequency shift keying cpfsk is a constant amplitude modulation method with good spectral sidelobe properties good error probability properties can be obtained with coherent maximum likelihood detection in this paper we study the euclidean distance properties of signals formed by a conventional rate 1 2 convolutional encoder followed by a binary or 4 level cpfsk modulator the minimum euclidean distance is calculated for these signal sets as a function of the modulation index and the observation interval length the optimum detector is discussed for rational modulation index values the best obtainable codes are found for the case of short rate 1 2 codes with binary or 4 level cpfsk modulation lists of the best codes are given among the results are that the noncatastrophic rate 1 2 convolutional codes with optimum free hamming distance do not in general give the best euclidean distance with cpfsk

suboptimum detection of trellis coded cpm for transmission on bandwidth and power limited channels the authors consider a communication scheme based on continuous phase modulated cpm signals used in conjunction with trellis coded modulation tcm for transmission over a channel affected by gaussian noise and fading this scheme provides a power saving due to the coding gain of tcm and a reduced bandwidth occupancy due to the features of cpm signals moreover cpm provides constant envelope signals to keep the complexity of the receiver manageable and to be able to use interleaving deinterleaving techniques to spread the fade bursts suboptimal detection schemes must be used two such schemes based on coherent and noncoherent detection of cpm are considered their performance is evaluated by computing the computational cutoff rate of the discrete channel generated by cpm

convolutional coding combined with continuous phase modulation background theory and specific coding designs for combined coding modulation schemes utilizing convolutional codes and continuous phase modulation cpm are presented in this paper the case of r 1 2 coding onto a 4 ary cpm is emphasized with short constraint length codes presented for continuous phase fsk double raised cosine and triple raised cosine modulation coding buys several decibels of coding gain over the gaussian channel with an attendant increase of bandwidth performance comparisons in the power bandwidth tradeoff with other approaches are made

linear receivers for correlatively coded msk in this paper we show that many spectrally efficient modified msk schemes termed generalized msk although not representable as oqpsk may nevertheless be suboptimally demodulated using an i q receiver with a proper choice of carrier phase offset correlatively coded msk schemes with i q receivers are studied and it is concluded that duobinary msk and 1 2d d 2 4 msk represent good performance bandwidth tradeoffs among first and second order correlative coding polynomial schemes the optimal design of these receivers are considered subject to the constraint of a finite duration impulse response especially for asymptotic cases of arbitrarily small and large snr filter design based on a zero intersymbol interference constraint for pam based approximations of the signals is also considered the optimized linear i q receivers for 1 d 2 msk and 1 d 2 4 msk are presented these receivers are only 0 28 and 1 24 db poorer than the optimal viterbi receivers at high snr

control of underactuated spacecraft with bounded inputs bounded feedback control laws are designed for stabilization and tracking of underactuated spacecraft the flat outputs of the system are computed and are used to generate reference trajectories for the tracking problem

trellis coded constant envelope modulations with linear receivers we present two multilevel constant envelope continuous phase modulation cpm schemes with four dimensional 4 d trellis coding the receiver is composed of a simple quadrature demodulator followed by a symbol rate sampler and a viterbi decoder matched to the code trellis the first modulation is a quaternary cpm scheme whose phase transitions over a symbol interval are those of spl pi 4 shift quaternary phase shift keying qpsk the demodulator filter is optimized so as to minimize the combined effect of intersymbol interference isi and noise at the decision instants we use wei s 1987 16 state 4 d trellis code and redefine the set partitioning tree so as to maintain the same minimum distance between parallel transitions as in quadrature amplitude modulation qam signal sets the resulting modulation outperforms minimum shift keying msk by as much as 3 5 db in addition to reducing the 30 db signal bandwidth by 20 next we introduce an octonary 8 level cpm scheme whose phase transitions are those of spl pi 8 shift 8psk the same trellis code and receive filter optimization are also applied to this modulation which is shown to achieve better error rate performance than msk while saving some 60 of the transmitted signal bandwidth

multiple symbol trellis coding of cpfsk this paper describes a technique related to the design of a trellis encoder combined with the full response m ary continuous phase frequency shift keying cpfsk with modulation index 1 m a new representation of cpfsk waveforms in n signaling intervals is proposed as a function of an n 1 d vector we also decompose the generation of the proposed cpfsk waveform into two stages an n consecutive continuous phase encoder ncpe and a memoryless modulator mm this decomposition makes it possible to design binary convolutional encoders with various code rates cascaded to the ncpe specific optimal outer convolutional encoders of two and three consecutive full response four ary cpfsk with modulation index 1 4 are designed following ungerboeck s 1982 set partitioning approach these codes achieve asymptotic coding gains up to 4 77 db for the two consecutive case with code rate 3 4 and asymptotic coding gains up to 5 45 db for the three consecutive case with code rate 5 6

power bandwidth performance of smoothed phase modulation codes constant envelope phase varying sinusoids of the form sqrt 2e t cos omega c t phi t are studied in which the phase function phi t follows some coded pattern in response to data power and bandwidth performance are studied for such patterns the patterns depend on a phase shaping function a modulation index h and a sequence of m ary underlying changes in phase which are chosen at random a cutoff rate like parameter r 0 is computed which guarantees existence of codes at all rates r bits t interval whose error performance varies as exp n r 0 r where n is the code word length in t intervals plots of r 0 are given as a function of interval energy e the shaping function h and m extensive spectral calculations give the spectra of these phased sinusoids and their performance is plotted in the power bandwidth plane the results give strong evidence that phase codes can approximate any power bandwidth combination consistent with shannon s gaussian channel capacity and that linear channels are not required for narrow band transmission

spreading dynamics following bursty human activity patterns we study the susceptible infected model with power law waiting time distributions p ensuremath tau ensuremath tau ensuremath ensuremath alpha as a model of spreading dynamics under heterogeneous human activity patterns we found that the average number of new infections n t at time t decays as a power law in the long time limit n t t ensuremath ensuremath beta leading to extremely slow prevalence decay we also found that the exponent in the spreading dynamics ensuremath beta is related to that in the waiting time distribution ensuremath alpha in a way depending on the interactions between agents but insensitive to the network topology these observations are well supported by both the theoretical predictions and the long prevalence decay time in real social spreading phenomena our results unify individual activity patterns with macroscopic collective dynamics at the network level

configuration flatness of lagrangian systems underactuated by one control lagrangian control systems that are differentially flat with flat outputs that depend only on configuration variables are said to be configuration flat we provide a complete characterization of configuration flatness for systems with n degrees of freedom and n 1 controls whose range of control forces only depends on configuration and whose lagrangian has the form of kinetic energy minus potential the method presented allows us to determine if such a system is configuration flat and if so provides a constructive method for finding all possible configuration flat outputs our characterization relates configuration flatness to riemannian geometry we illustrate the method with two examples

simple mechanical control systems with constraints we apply some recently developed control theoretic techniques to the analysis of a class of mechanical systems with constraints certain simple aspects of the theory of affine connections play an important part in our presentation the necessary background is presented in order to illustrate how the methods may be applied the bulk of this paper is devoted to a detailed analysis of some examples of nonholonomic mechanical control systems we look at the heisenberg system the upright rolling disk the roller racer and the snakeboard

new short constraint length convolutional code constructions for selected rational rates corresp new short constraint length convolutional code constructions are tabulated for rates r n k n k 1 2 cdots n 1 with n 2 3 cdots 8 and for constraint lengths k 3 4 cdots 8 these codes have been determined by iterative search based upon a criterion of optimizing the free distance profile specifically these codes maximize the free distance d f while minimizing the number of adversaries in the distance or weight spectrum in several instances we demonstrate the superiority of these codes over previously published code constructions at the same rate and constraint length these codes are expected to have a number of applications including combined source channel coding schemes as well as coding for burst or impulsive noise channels

configuration controllability of simple mechanical control systems in this paper we present a definition of configuration controllability for mechanical systems whose lagrangian is kinetic energy with respect to a riemannian metric minus potential energy a computable test for this new version of controllability is derived this condition involves an object that we call the symmetric product of particular interest is a definition of equilibrium controllability for which we are able to derive computable sufficient conditions examples illustrate the theory

trellis coding for partial response channels we consider trellis coding techniques for improving the reliability of digital transmission over noisy partial response channels such channels are commonly encountered in digital communication systems and also play a role in devices for data recording concentrating on the channels with characteristics 1 mp d we study methods to obtain codes which increase free euclidean distance between permitted sequences of channel outputs and avoid the occurrence of unlimited runs of identical outputs at the expense of some loss in data rate one technique employs the concept of set partitioning the other is based on using convolutional codes designed for maximum free hamming distance in conjunction with a precoder both methods lead to essentially equivalent codes

invasion percolation and critical transient in the barabasi model of human dynamics we introduce an exact probabilistic description for l 2 of the barabasi model for the dynamics of a list of l tasks this permits us to study the problem out of the stationary state and to solve explicitly the extremal limit case where a critical behavior for the waiting time distribution is observed this behavior deviates at any finite time from that of the stationary state we study also the characteristic relaxation time for finite time deviations from stationarity in all cases showing that it diverges in the extremal limit confirming that these deviations are important at all time doi 10 1103 physrevlett 98 208701

reduced complexity approach to iterative detection of coded soqpsk we develop a reduced complexity approach for the detection of coded shaped offset quadrature phase shift keying soqpsk a highly bandwidth efficient and popular constant envelope modulation the complexity savings result from viewing the signal as a continuous phase modulation cpm we give a simple and convenient closed form expression for a recursive binary to ternary precoder for soqpsk the recursive nature of this formulation is necessary in serially concatenated systems where soqpsk serves as the inner code we show that the proposed detectors are optimal in the full response case and are near optimal in the partial response case due to some additional complexity reducing approximations in all cases the proposed detectors achieve large coding gains for serially concatenated coded soqpsk these gains are similar to those reported recently by li and simon which were obtained using a more complicated cross correlated trellis coded quadrature modulation xtcqm interpretation

design of ring convolutional trellis codes for map decoding of mpeg 4 images we propose a trellis coded modulation system using continuous phase frequency shift keying cpfsk and ring convolutional codes for transmitting the bits generated by an embedded zerotree wavelet encoder improved performance is achieved by using maximum a posteriori decoding of the zerotree symbols and ring convolutional trellis codes are determined for this decoding method the cpfsk transmitter is decomposed into a memoryless modulator and a continuous phase encoder over the ring of integers modulo 4 the latter is combined with a polynomial convolutional encoder over the same ring in the code design process a search is made of the combined trellis where the branch metrics are modified to include the source transition matrix simulation results of image transmission are provided using the optimized system including mismatched channel cases

memory and burstiness in dynamic networks a discrete time random process is described which can generate bursty sequences of events a bernoulli process where the probability of an event occurring at time t is given by a fixed probability x is modified to include a memory effect where the event probability is increased proportionally to the number of events that occurred within a given amount of time preceding t for small values of x the interevent time distribution follows a power law with exponent 2 x we consider a dynamic network where each node forms and breaks connections according to this process the value of x for each node depends on the fitness distribution x from which it is drawn we find exact solutions for the expectation of the degree distribution for a variety of possible fitness distributions and for both cases where the memory effect either is or is not present this work can potentially lead to methods to uncover hidden fitness distributions from fast changing temporal network data such as online social communications and fmri scans

better rate 1 2 coded continuous phase modulation schemes and the m algorithm continuous phase modulation cpm signals may be precoded by a convolutional code followed by a mapping rule better codes may however be obtained by a more general code formed by a finite state machine we provide improved codes for one such finite state machine a new description of codes and design rules are presented better results are demonstrated for the partial response cpm schemes and previous optimum results are matched for the full response case tests of an m algorithm decoder achieve near maximum likelihood performance with only a fraction of the complexity of the viterbi algorithm

a lie backlund approach to equivalence and flatness of nonlinear systems a new system equivalence relation using the framework of differential geometry of jets and prolongations of infinite order is studied in this setting two systems are said to be equivalent if any variable of one system may be expressed as a function of the variables of the other system and of a finite number of their time derivatives this is a lie backlund isomorphism the authors prove that although the state dimension is not preserved the number of input channels is kept fixed they also prove that a lie backlund isomorphism can be realized by an endogenous feedback the differentially flat nonlinear systems introduced by the authors 1992 via differential algebraic techniques are generalized and the new notion of orbitally flat systems is defined they correspond to systems which are equivalent to a trivial one with time preservation or not the endogenous linearizing feedback is explicitly computed in the case of the vtol aircraft to track given reference trajectories with stability

differential flatness of two one forms in arbitrary number of variables given a differentially flat system of odes flat outputs that depend only on original variables but not on their derivatives are called zero flat outputs and systems possessing such outputs are called zero flat in this paper we present a theory of zero flatness for a system of two one forms in arbitrary number of variables t x1 xn our approach splits the task of finding zero flat outputs into two parts first part involves solving for distributions that satisfy a set of algebraic conditions the second part involves finding an integrable distribution from the solution set of the first part typically this part involves solving pdes our results are also applicable in determining if a control affine system in n states and n 2 controls has flat outputs that depend only on states we illustrate our method by examples

design of differentially flat planar space robots and their planning and control the motion of free floating space robots is characterized by non holonomic constraints i e non integrable rate constraint equations these constraints originate from the principles of conservation of angular momentum it is well known that these rate constraints can also be written to form an input affine drift less control systems trajectory planning of these systems is extremely challenging and computation intensive since the motion must satisfy differential constraints under certain conditions these drift less control systems can be shown to be differentially flat the property of flatness allows a computationally inexpensive way to plan trajectories for a dynamic system between two configurations as well as develop feedback controllers the key contribution of this paper is to systematically study the non holonomic rate constraints for free floating planar open chain robots and determine the design conditions under which the system exhibits differential flatness a design is then proposed that c

structure optimization and realization of ffsk trellis codes the structure of combinations of l k binary trellis encoders and fast frequency shift keying ffsk modulation is studied a novel method for the optimization of these combinations is proposed it is concluded that regardless of the particular realization the best combinations can always be obtained by using a so called matched convolutional code optimum ffsk codes of rates 1 2 and 2 3 for up to 64 and 32 states respectively are reported it is shown that the best matched encoders for ffsk modulation are also matched and best for any ffsk type scheme where the pulse shape is required to satisfy nyquist s third criterion

a decomposition approach to cpm it is shown that any continuous phase modulation cpm system can be decomposed into a continuous phase encoder and a memoryless modulator in such a way that the former is a linear modulo some integer p time invariant sequential circuit and the latter is also time invariant this decomposition is exploited to obtain alternative realizations of the continuous phase encoder and hence of cpm and also to obtain alternative forms of the optimum decoding algorithm when p is a prime p so that the encoder is linear over the finite field gf p it is shown that cascading it with an outside convolutional encoder is equivalent to a single convolutional encoder it is pointed out that the cascade of the modulator the waveform channel which it is assumed is characterized by additive white gaussian noise and the demodulator that operates over one symbol interval yield a discrete memoryless channel that can be studied without the distractions introduced by continuous phase encoding

nonlinear continuous phase frequency shift keying a novel signal space coded cpm continuous phase modulated signaling technique called nonlinear cpfsk continuous phase frequency shift keying signaling which guarantees the maximum constraint length allowed by the number of states is introduced nonlinear cpfsk signals use a suitably selected state transition matrix during all signaling intervals the selected state transition matrix is realized by changing the modulation index of the signals hence the modulation index used during any interval depends on the transmitted symbol as well as on the state of the system binary nonlinear cpfsk signaling schemes are constructed and analyzed numerical results indicate that nonlinear cpfsk signals can achieve attractive minimum distances compared with other existing cpm signaling formats

tracking for fully actuated mechanical systems a geometric framework we present a general framework for the control of lagrangian systems with as many inputs as degrees of freedom relying on the geometry of mechanical systems on manifolds we propose a design algorithm for the tracking problem the notions of error function and transport map lead to a proper definition of configuration and velocity error these are the crucial ingredients in designing a proportional derivative feedback and feedforward controller the proposed approach includes as special cases a variety of results on control of manipulators pointing devices and autonomous vehicles our design provides particular insight into both aerospace and underwater applications where the configuration manifold is a lie group

stabilization of relative equilibria for underactuated systems on riemannian manifolds steady motions of mechanical systems with symmetry are stabilized via a potential shaping and damping control a general methodology based on riemannian geometry tools provides exponential stabilization over the full phase space

nonlinear multi h phase codes for cpfsk signaling two novel trellis coding techniques called nonlinear multi h signaling and nonlinear asymmetrical multi h signaling which achieve higher constraint length than ordinary multi h signals are introduced with cpfsk signals in contrast to ordinary multi h signaling where the modulation index is changed at the end of every symbol interval nonlinear multi h signals are constructed by changing the modulation index based on the previous symbol and the current symbol interval a class of nonlinear asymmetrical multi h signals which change the modulation index based on the current symbol too is then constructed by extending nonlinear multi h signals and combining them with asymmetrical multi h signals binary full response nonlinear multi h and nonlinear asymmetrical multi h cpfsk signals are constructed and analyzed minimum euclidean distances and spectral properties of these signals are calculated at different phase states and various selected modulation index patterns numerical results indicate that nonlinear multi h and nonlinear asymmetrical multi h signals achieve significantly higher distance than other existing multi h formats reported in the literature

on joint source and channel coding using trellis coded cpm analytical bounds on the channel distortion joint source and channel coding jscc using trellis coded quantization tcq in conjunction with trellis coded continuous phase modulation cpm is studied the channel is assumed to be the additive white gaussian noise awgn channel analytical bounds on the channel distortion for the investigated systems with maximum likelihood sequence detection mlsd are developed the bounds are based on the transfer function technique which was modified and generalized to include continuous amplitude discrete time signals for a memoryless uniform source the constructed bounds for the investigated systems are shown to be asymptotically tight for increasing channel signal to noise ratio snr values for a memoryless nonuniform source the constructed bounds are not as tight as the one for the uniform source however it still can be used as an indication to how the system performs it is concluded that the minimum euclidean distance of the system alone is not enough to evaluate the performance of the considered systems the number of error events having minimum euclidean distance and the total distortion caused by those error events also affect the asymptotic performance this work provides an analysis tool for the investigated systems the analysis method is very general it may be applied to any trellis based jscc schemes

space time coded systems using continuous phase modulation we develop space time trellis coded stc schemes using continuous phase modulation cpm we employ the rimoldi model of cpm to create a decomposed model of stc cpm the decomposition separates the coding from the modulation the space time encoding and the inherent cpm encoding is combined into a single trellis encoder on the ring of integers modulo this is followed by a bank of memoryless modulators the model allows the search for good space time codes to take into account the inherent encoding of the modulation

brief steering of a class of nonholonomic systems with drift terms in the present paper nonholonomic systems with drift terms are studied the discussion is focused on a class of lagrangian systems with a cyclic coordinate we present an approach to open loop path planning in which the system evolution is studied on manifolds of dimension equal to the number of control inputs a control procedure is derived and it is applied to the planar diver

a new performance bound for pam based cpm detectors it is well understood that the pulse amplitude modulation pam representation of continuous phase modulation cpm can lead to reduced complexity detectors with near optimum performance it has recently been shown that the pam representation also extends to cpm schemes with multiple modulation indexes multi h cpm in this paper we present a detector for multi h cpm which is based on the pam representation we also give an exact expression for the pairwise error probability for the entire class of pam based cpm detectors single and multi h optimal and reduced complexity over the additive white gaussian noise awgn channel and show that this bound is tighter than the previously published bound for approximate pam based detectors in arriving at this expression we show that pam based detectors for cpm are a special case of the broad class of mismatched cpm detectors we also show that the metrics for pam based detectors accumulate distance in a different manner than metrics for other cpm detectors these distance properties are especially useful in applications with greatly reduced trellis sizes we give thorough examples of the analysis for different single and multi h signaling schemes we also apply the new bound in comparing the performance of pam based detectors with other reduced complexity detectors for cpm

optimal and suboptimal symbol by symbol demodulation of continuous phase modulated signals in applications requiring soft decision metrics e g systems with interleaved coded modulation symbol by symbol detection is preferred to sequence detection this paper develops the optimum soft output algorithm osa for the demodulation of continuous phase modulated cpm signals since this optimum detector is computationally complex a class of suboptimum symbol by symbol detectors called the reduced state soft output algorithm rs soa is developed by varying certain parameters the rs soa offers an effective tradeoff between performance and complexity as measured by arithmetic operation count and the number of integrators required additionally some simple complexity reduction schemes can be used in conjunction with the osa and the rs soa the properties of the osa and the rs soa and the various complexity reduction schemes are explored in an extensive simulation study

exact asymptotic behavior of digital fm spectra the problem of calculating accurate power spectral densities for an extended class of digital fm schemes is considered this extended class includes partial response as well as multilevel schemes a method suitable for numerical calculation using a computer is developed this new method consists of two parts first the spectral main lobe is calculated then the spectral tail is calculated by a different approach the accuracy of the spectral tail is that of a correction term to an analytical asymptotic tail formula this method yields accurate power spectra down to a level considerably below 100 db numerical results obtained from calculations are given the power spectra can be calculated for an arbitrary modulation index value

block encoding with continuous phase modulation block encoding is considered to increase the minimum distance of cpm signals codes are constructed to prevent merging events with low euclidean distances numerical results presented with full response partial response and trellis coded cpm signals indicate that block coding can significantly increase the minimum distance of the signals nonlinear block codes are also considered

on the computation of π flat outputs for linear time varying differential delay systems abstract we introduce a new definition of flatness for linear differential delay systems with time varying coefficients we characterize and 0 flat outputs and provide an algorithm to efficiently compute such outputs we present an academic example of motion planning to discuss the pertinence of the approach

mlse and soft output equalization for trellis coded continuous phase modulation this paper presents two equalizer structures for trellis coded continuous phase modulation tc cpm on multipath fading intersymbol interference isi channels an equivalent discrete time dt model is developed by combining the tapped delay line tdl model of the frequency selective channel and by oversampling at the receiver the noninterleaved fractionally spaced maximum likelihood sequence estimation mlse equalizer performs continuous phase modulation cpm demodulation trellis coded modulation tcm decoding and channel equalization by exploiting the finite state nature of the isi corrupted tc cpm signal both simulation and analytical results show diversity like improvement when performing joint mlse decoding and equalization for the interleaved soft output equalizer the soft symbol metric is delivered to the tcm decoder by using a forward and backward recursion algorithm three variants of the soft output equalizer are examined we conclude that the backward recursion is essential to partial response cpm schemes and with moderate complexity the soft output equalizer can have a substantial advantage over a noninterleaved mlse equalizer

symbol error probability bounds for coherently viterbi detected continuous phase modulated signals recently the minimum euclidean distance and bandwidth properties of continuous phase modulated cpm signals have been considered it has also been shown that for rational modulation indexes a state description of these signals is possible and that the viterbi algorithm va can be used for demodulation in this paper the performance analysis of cpm systems is extended to obtain bounds on the symbol error probability when the va is used the calculation of these bounds is based on the transfer function technique which has been generalized from numerical comparisons of the upper and lower bounds it is concluded that the minimum euclidean distance is a good performance measure for a broad class of cpm signals even when the symbol error probability is as large as 10 2

conversion and matched filter approximations for serial minimum shift keyed modulation serial minimum shift keyed msk modulation a technique for generating and detecting msk using series filtering is ideally suited for high data rate applications provided the required conversion and matched filters can be closely approximated lowpass implementations of these filters as parallel inphase and quadrature mixer structures are characterized in this paper in terms of signal to noise ratio snr degradation from ideal and envelope deviation several hardware implementation techniques utilizing microwave devices or lumped elements are presented optimization of parameter values results in realizations whose snr degradation is less than 0 5 db at error probabilities of 10 6

trellis coded continuous phase frequency shift keying with ring convolutional codes trellis coding techniques are applied to continuous phase frequency shift keying cpfsk a new coding scheme based on convolutional codes on the ring of integers modulo p is shown to be a natural way to apply trellis coding to cpfsk previous work has decomposed cpfsk into two parts a linear encoder with memory called the continuous phase encoder cpe and a memoryless modulator mm where the cpe often has a code structure defined over the ring of integers modulo p the combination of a modulo p convolutional channel encoder ce and the cpe is a linear modulo p encoder design examples are given for rate 1 2 coded quaternary cpfsk with modulation indexes 1 2 and 1 4 and rate 2 3 coded octal cpfsk with modulation index 1 8 combinations are optimized in the normalized minimum euclidean distance sense for a given total number of states in the overall mlse receiver numerical results show that this new coding scheme consistently obtains better performance than previous schemes

individual and group dynamics in purchasing activity abstract as a major part of the daily operation in an enterprise purchasing frequency is in constant change recent approaches on the human dynamics can provide some new insights into the economic behavior of companies in the supply chain this paper captures the attributes of creation times of purchase orders to an individual vendor as well as to all vendors and further investigates whether they have some kind of dynamics by applying logarithmic binning to the construction of distribution plots it s found that the former displays a power law distribution with approximate exponent 2 0 while the latter is fitted by a mixture distribution with both power law and exponential characteristics obviously two distinctive characteristics are presented for the interval time distribution from the perspective of individual dynamics and group dynamics actually this mixing feature can be attributed to the fitting deviations as they are negligible for individual dynamics but those of different vendors are cumulated and then lead to an exponential factor for group dynamics to better describe the mechanism generating the heterogeneity of the purchase order assignment process from the objective company to all its vendors a model driven by product life cycle is introduced and then the analytical distribution and the simulation result are obtained which are in good agreement with the empirical data

unveiling turbo codes some results on parallel concatenated coding schemes a parallel concatenated coding scheme consists of two simple constituent systematic encoders linked by an interleaver the input bits to the first encoder are scrambled by the interleaver before entering the second encoder the codeword of the parallel concatenated code consists of the input bits to the first encoder followed by the parity check bits of both encoders this construction can be generalized to any number of constituent codes parallel concatenated schemes employing two convolutional codes as constituent codes in connection with an iterative decoding algorithm of complexity comparable to that of the constituent codes have been previously shown to yield remarkable coding gains close to theoretical limits they have been named and are known as turbo codes we propose a method to evaluate an upper bound to the bit error probability of a parallel concatenated coding scheme averaged over all interleavers of a given length the analytical bounding technique is then used to shed some light on some crucial questions which have been floating around in the communications community since the proposal of turbo codes

generalized concatenation of encoded tamed frequency modulation a novel construction for encoded tamed frequency modulation tfm is introduced which is based on the principles of generalized concatenation the inner tfm is partitioned into nested subsystems which increases the free euclidean distances in order to obtain a large distance among the nested tfm subsystems the scrambler matrices have to be computed which transfer the original tfm into the equivalent tfm with better partitioning properties then outer convolutional codes with different error correcting capabilities are used to protect the partitioning the new concatenated and generalized concatenated constructions were simulated in an additive white gaussian noise channel a multistep decoding algorithm based on soft output demodulation was used we present various simulation results which show a significant coding gain in comparison with the best known trellis codes having the same trellis state complexity

an improved algorithm for evaluating trellis phase codes corresp a method is described for evaluating the minimum distance parameters of trellis phase codes including continuous phase frequency shift keying cpfsk partial response fm and more importantly coded continuous phase modulation cpm schemes the algorithm provides dramatically faster execution times and smaller memory requirements than previous algorithms results of sample calculations and timing comparisons are included

exact and approximate construction of digital phase modulations by superposition of amplitude modulated pulses amp minimum shift keying and offset qpsk are two well known modulations which can be interpreted as a set of time phase shifted am pulses we show in this paper that any constant amplitude binary phase modulation can also be expressed as a sum of a finite number of time limited amplitude modulated pulses amp decomposition new methods for computing autocorrelation and power frequency spectrum are derived which give very simple results for half integer index modulations we also show that the signal can be built with good accuracy using only one optimized pulse main pulse this synthesis is particularly satisfactory for modulations that have good spectral characteristics and or low index

configuration controllability of mechanical systems underactuated by one control we investigate local configuration controllability for mechanical control systems within the affine connection formalism we rely on previous results on controllability and series expansions for the evolution of mechanical systems starting from rest extending the work by lewis for the single input case we are able to characterize local configuration controllability for systems with n degrees of freedom and n 1 input forces

iterative decoding of serially concatenated cpm in fading channels with noisy channel state information we use the sum product algorithm spa to propose a reduced complexity detector for serially concatenated continuous phase modulated sccpm signals with noisy channel state information csi at the receiver two channel effects phase noise pn and flat fading are tackled using the statistical model and associated factor graph fg of the problem although optimal performance is not assured due to the loopy nature of the fg as well as simplifying assumptions made in the algorithm development simulations show that very significant performance gains are possible and the gap between systems with noiseless and noisy csi can be reduced to about 1 db using the proposed methods the increase in complexity compared to the conventional decoder which treats csi estimates as if they were equal to their true values is small

channel coding with multilevel phase signals a coding technique is described which improves error performance of synchronous data links without sacrificing data rate or requiring more bandwidth this is achieved by channel coding with expanded sets of multilevel phase signals in a manner which increases free euclidean distance soft maximum likelihood ml decoding using the viterbi algorithm is assumed following a discussion of channel capacity simple hand designed trellis codes are presented for 8 phase shift keying psk and 16 quadrature amplitude shift keying qask modulation these simple codes achieve coding gains in the order of 3 4 db it is then shown that the codes can be interpreted as binary convolutional codes with a mapping of coded bits into channel signals which we call mapping by set partitioning based on a new distance measure between binary code sequences which efficiently lower bounds the euclidean distance between the corresponding channel signal sequences a search procedure for more powerful codes is developed codes with coding gains up to 6 db are obtained for a variety of multilevel phase modulation schemes simulation results are presented and an example of carrier phase tracking is discussed

generalized priority queue network dynamics impact of team and hierarchy we study the effect of team and hierarchy on the waiting time dynamics of priority queue networks to this end we introduce generalized priority queue network models incorporating interaction rules based on team execution and hierarchy in decision making respectively it is numerically found that the waiting time distribution exhibits a power law for long waiting times in both cases yet with different exponents depending on the team size and the position of queue nodes in the hierarchy respectively the observed power law behaviors have in many cases a corresponding single or pairwise interacting queue dynamics suggesting that the pairwise interaction may constitute a major dynamic consequence in the priority queue networks it is also found that the reciprocity of influence is a relevant factor for the priority queue network dynamics

a new description of trellis codes a trellis code is a sliding window method of encoding a binary data stream as a sequence of real or complex numbers that are input to a noisy transmission channel ungerboeck has constructed simple trellis codes that provide the same noise immunity as is given by increasing the power of uncoded transmission by factors ranging from two to four his method is to specify an underlying convolutional code and a rule mapping by set partitioning that maps the output of this code onto a fixed signal constallation a new description of a trellis code is given that combines these two steps into one the new description is analytic rather than graphical many practical codes can be described very simply and strict bounds on performance can be obtained a method for differential encoding trellis codes is presented that was suggested by the authors representation

multilevel coded cpfsk systems for awgn and fading channels in this paper we introduce multilevel coded continuous phase frequency shift keying cpfsk systems for both additive white gaussian noise and fading channels based on multilevel coding and multistage decoding techniques these schemes are designed under the constraint m spl ges 2p for m ary cpfsk with modulation index j p in order to maintain the phase continuity property after multilevel coding we use some specific set partitioning rules we construct examples to show that the proposed systems outperform the corresponding conventional one level schemes for the fading case we consider an ideal fading channel where adjacent fading symbols are assumed to be independent and a correlated fading channel where bit interleavers are needed at each coding level the computer simulation results show that the proposed systems have bit error performance and decoder complexity advantages over the corresponding reference codes taken from the literature it is also shown that there is only a slight degradation on the bit error performance for correlated fading compared to the ideal fading case

spectrum distance and receiver complexity of encoded continuous phase modulation a comparison of different classes of encoded continuous phase modulation cpm schemes is presented in terms of joint power bandwidth performance it is found that coded eight level systems are better than coded four level systems and that partial response signalling is better than full response signalling in general the price paid for better performance is increased receiver complexity heuristic design rules have been used to find good codes for cpm in most cases the coding gains found are identical to published results that were generated by exhaustive search indicating that the choice of design rules is quite appropriate in the present study bandwidth efficiency is considered from both the 99 and 99 9 power bandwidth points of view it is found that partial response signalling is even more jointly power and bandwidth efficient for the latter than for the former bandwidth criterion

nonlinear multipulse block coding of cpfsk signals a nonlinear multipulse block coding technique is proposed to improve cpfsk signaling formats the coding technique is developed to prevent merging events with lower distances by separating the respective paths in the time domain coded schemes are constructed with constant h 2 h and trellis coded cpfsk signals the spectral variations and the performance bandwidth tradeoffs of the proposed coded signals are found and compared to those without coding it is concluded from the numerical results that the proposed coding technique can significantly improve the performance bandwidth tradeoff of many cpfsk signaling formats particularly at lower bandwidths

woven coded cpfsk with hierarchical code structure we introduce hierarchical woven coded continuous phase frequency shift keying hierarchical wccpfsk as the serial concatenation of different outer convolutional codes and inner cpfsk we compare it to wccpfsk with identical outer convolutional codes with the proposed code combinations hierarchical wccpfsk achieves superior decoding capability simulations show that it performs better at medium snrs

trellis codes for 4 ary continuous phase frequency shift keying the approach of morales moreno and pasupathy 1988 is extended for the design of trellis codes for 4 ary continuous phase frequency shift keying cpfsk with modulation index h 1 2 the criterion for comparison of codes is the maximum free euclidean distance for a given rate and the number of states of the signal space code for the same number of states of the signal space code these codes improve the free euclidean distance by up to 1 25 db over previously published results finally the implementation of the combined coding and modulation system is discussed

serially concatenated continuous phase modulation with iterative decoding serially concatenated and interleaved continuous phase modulation cpm with iterative decoding is investigated an a posteriori probability app algorithm for cpm is developed based on the classic app algorithm for channel codes the system is analyzed through upper bounds on the average bit error probability for coded and interleaved minimum shift keying the weight spectrum is computed resulting in a transfer function bound this is cumbersome for a general cpm system instead only the most significant error events contributing to the weight spectrum are identified simulations show that firstly these events give a satisfactory view of system performance when equal outer codes are used and secondly that remarkably good performance can be obtained for some simple systems finally power spectral densities and bandwidths are computed allowing for a bandwidth performanee comparison of different combinations

nyquist 3 pulse shaping in continuous phase modulation continuous phase modulation cpm schemes using nyquist 3 pulse shaping and correlative codes are popular candidates for mobile radio applications this paper presents a detailed study of the effects of nyquist 3 pulse shaping on the spectral characteristics of cpm schemes with a modulation index of 1 2 the influence of pulse parameters such as its shape bandwidth coding polynomial and truncation length on spectral characteristics such as main lobe fractional power bandwidths and out of band power levels is thoroughly investigated error performance is also briefly analyzed among uncoded schemes a new scheme using a pulse satisfying both nyquist 3 and nyquist 2 criteria is pointed out as a promising candidate and as a good compromise between spectral and power efficiencies