Patents Assigned to Comsat
  • Patent number: 6711140
    Abstract: A method and apparatus for providing frame acquisition and synchronization for ATM transmissions in terrestrial wireless and satellite systems. During acquisition (1020), the transmitter (15) fills the entire payload of a frame with a pattern that is used by the receiver (18) to determine the location of the frame boundary. As to synchronization (1020), a procedure is utilized for using frame sequence number field in the header and Reed-Solomon decoding result (1012) for correction and maintaining frame synchronization.
    Type: Grant
    Filed: April 25, 2000
    Date of Patent: March 23, 2004
    Assignee: Comsat Corporation
    Inventors: Anil K. Agarwal, Sampath Kumar
  • Patent number: 6661781
    Abstract: An apparatus and method for providing bandwidth on demand service in a wireless communication system having at least one user station, including a frequency divider for dividing a selected bandwidth into a plurality of frequency subdivisions. Also included is a unit for assigning a first number of frequency subdivisions to the individual user stations having a first total bandwidth, commensurate with the volume of transmission traffic. There also is a unit for changing the first number to a second number having a second total bandwidth commensurate with the change of the volume of transmission traffic.
    Type: Grant
    Filed: November 19, 1999
    Date of Patent: December 9, 2003
    Assignee: Comsat Corporation
    Inventors: Dattakumar M. Chitre, Soheil I. Sayegh
  • Patent number: 6618435
    Abstract: A method and device for measurement and reduction of frequency offset in a communication network having a master reference terminal and at least one terminal exchanging reference and control bursts includes steps for adjusting demodulator frequency in the terminal responsive to a first frequency error between a first nominal frequency value and a respective reference burst received by the terminal, and adjusting modulator frequency at the terminal responsive to a second frequency error between a second nominal frequency value and a control burst generated by the master reference terminal and transmitted to the terminal.
    Type: Grant
    Filed: November 23, 1999
    Date of Patent: September 9, 2003
    Assignee: Comsat Corporation
    Inventors: Anil K. Agarwal, Charles Richard Thorne
  • Patent number: 6560303
    Abstract: The present invention provides a method to achieve frame synchronization from a received data sequence before the carrier phase and frequency offset recovery for any MPSK modulated signals on the basis of maximum likelihood theory. Two overhead configurations are considered in developing the frame synchronization algorithms. One overhead configuration consists of a unique word followed by a preamble, and the other consists of unique word only. For the first overhead, the frame synchronization can be decoupled from carrier recovery because the preamble following the unique word is a known sequence pattern. In this case, the maximum-likelihood frame synchronization rule is simply a complex correlation. In second overhead, the unique word is immediately followed by random traffic data and thus the coupling effects are generated between frame synchronization and carrier recovery. These coupling effects are not dominant, however, and may be neglected in actual practice.
    Type: Grant
    Filed: October 26, 2000
    Date of Patent: May 6, 2003
    Assignee: Comsat Corporation
    Inventors: Yigang Fan, Prakash Chakravarthi
  • Publication number: 20030021364
    Abstract: The present invention relates to burst mode digital communication systems where data transmission is preceded by a preamble for acquisition of carrier and clock synchronization using maximum likelihood (ML) principle. The preamble is sampled and the set of samples obtained is processed using the optimization algorithms of the present invention to provide the ML timing estimate. The optimization algorithms in the present invention consist of three parts. The first part deals with isolating the desired optimal estimate from non-optimal extremes satisfying the same necessary condition, and provides the initial conditions for activating the binary search schemes. The second part performs the binary search for the optimal timing estimate that guarantees the convergence. On the basis of the obtained iterative sequence, the last part constructs a more rapidly convergent sequence to obtain the ML symbol timing estimate.
    Type: Application
    Filed: May 8, 2001
    Publication date: January 30, 2003
    Applicant: COMSAT CORPORATION
    Inventors: Yigang Fan, Prakash Chakravarthi
  • Patent number: 6477669
    Abstract: A method for adaptive control of a forward error correction code for transmission between a terrestrial cell/packet switch at a first terminal and a satellite/wireless network connecting to a second terminal, including the steps of: calculating a byte error rate associated with communication signals received by the first terminal, determining a forward error correction code length based on the byte error rate, and transmitting the forward error correction code length to the second terminal.
    Type: Grant
    Filed: January 18, 2000
    Date of Patent: November 5, 2002
    Assignee: Comsat Corporation
    Inventors: Anil K. Agarwal, Dattakumar M. Chitre
  • Patent number: 6462711
    Abstract: The invention is a multi-layer printed circuit antenna and a method for developing the antenna for which a screen printing technology is used to deposit conducting material forming the circuit layout directly on low-cost dielectric material, followed by a post-processing step performed on the printed circuit to increase circuit conductivity. In one embodiment, the dielectric material used is a thin layer supported by low-loss, foam-like material for spacing between the antenna layers. In another embodiment, a thick high-density, low-cost low-loss dielectric material acts as both the printing surface and the spacer between the antenna layers. The thick high-density, low-cost low-loss dielectric material allows for saving one layer in every printed circuit. The screen printing or additive process is less expensive than its etching or subtractive counterpart due to the process itself and due to the lower cost of materials.
    Type: Grant
    Filed: April 2, 2001
    Date of Patent: October 8, 2002
    Assignee: Comsat Corporation
    Inventors: Amir Ibrahim Zaghloul, Eric Christopher Kohls
  • Patent number: 6459898
    Abstract: In a satellite network with on-board switching and bandwidth on demand, traffic monitoring is required to facilitate billing data collection and to avoid congestion at the satellite. In addition to traffic monitoring, performance monitoring is necessary to quickly respond to link degradation or possible equipment anomalies. Monitoring terminals specially equipped with traffic measuring and policing and link performance measuring capabilities are used to monitor traffic and performance. The monitoring terminal is located in each satellite beam to perform the monitoring functions for that beam. The monitoring terminals are low-cost terminals that receive down-link traffic in their respective beam, and record statistics on a per transmit-terminal or per virtual connection basis. Records are periodically transmitted to a central location where they are processed for billing, enforcing traffic contracts, and taking actions against link degradations.
    Type: Grant
    Filed: November 19, 1999
    Date of Patent: October 1, 2002
    Assignee: Comsat Corporation
    Inventors: Ferit Yegenoglu, Thomas Inukai
  • Patent number: 6377914
    Abstract: A speech coding algorithm interpolates groups speech frames into speech frame pairs, and quantizes each frame of the pair according to a different algorithm. The spectral amplitudes of the second frame are quantized by dividing them into two portions and quantizing one portion and then quantizing a difference between the two portions. The spectral amplitudes of the first frame of the pair are quantized by first converting to a fixed dimension, then interpolating between previous and subsequent frames, then selecting interpolated values in accordance with a mean squared error approach.
    Type: Grant
    Filed: March 12, 1999
    Date of Patent: April 23, 2002
    Assignee: Comsat Corporation
    Inventor: Suat Yeldener
  • Patent number: 6377920
    Abstract: A voicing probability determination method is provided for estimating a percentage of unvoiced and voiced energy for each harmonic within each of a plurality of bands of a speech signal spectrum. Initially, a synthetic speech spectrum is generated based on the assumption that speech is purely voiced. The original and synthetic speech spectra are then divided into plurality of bands. The synthetic and original speech spectra are compared harmonic by harmonic, and a voicing determination is made based on this comparison. In one embodiment, each harmonic of the original speech spectrum is assigned a voicing decision as either completely voiced or unvoiced by comparing the difference with an adaptive threshold. If the difference for each harmonic is less than the adaptive threshold, the corresponding harmonic is declared as voiced; otherwise the harmonic is declared as unvoiced. The voicing probability for each band is then computed based on the amount of energy in the voiced harmonics in that decision band.
    Type: Grant
    Filed: February 28, 2001
    Date of Patent: April 23, 2002
    Assignee: Comsat Corporation
    Inventor: Suat Yeldener
  • Publication number: 20020039883
    Abstract: This invention describes a method to generate large numbers of spot beams for multiple-beam satellite systems using smaller apertures. This is done by dividing the basic spot beam that has 3 to 4 dB of gain drop within the beam into a number of smaller 1-dB sub-beams. This has the effect of reducing the required peak gain for the antenna by 2-3 dB, thus reducing its size by as much as 50%. The frequency band allocated to the basic beam will be divided among the sub-beams. However, the frequency re-use among the basic beams can be maintained. Frequency allocations have to be coordinated among all beams. This concept is especially applicable to phased arrays using digital beam formers. The DBF complexity is a function of the number of array elements, and is less dependent on the number of beams. Reducing the array size, and consequently reducing the number of elements helps in reducing the complexity, power and mass of the DBF.
    Type: Application
    Filed: July 16, 2001
    Publication date: April 4, 2002
    Applicant: COMSAT CORPORATION
    Inventors: Amir I. Zaghloul, Ozlem Killic, Albert E. Williams
  • Publication number: 20020032029
    Abstract: A telecommunications network including sub-telecommunications networks for transferring information including packet data which comprises one or more mobile stations, a first sub-telecommunications network, and a second sub-telecommunications network interconnected with the first sub-telecommunications network. The network further includes a number of gateway GPRS support nodes, and one or more gateway GPRS support nodes corresponding to each of the first sub-telecommunications network and the second sub-telecommunications network. Each of the gateway GPRS support nodes is operable to provide interworking between the first and the second sub-telecommunications networks and external packet data networks. The network also includes a system controlled in accordance with a procedure for transferring packet data within a multi-country telecommunications network.
    Type: Application
    Filed: July 16, 2001
    Publication date: March 14, 2002
    Applicant: COMSAT CORPORATION
    Inventor: Oguz Angin
  • Publication number: 20020029293
    Abstract: An adaptive intelligent radio module (IRM) is provided in an intelligent radio design for gateways between satellite and terrestrial networks. The intelligent radio module monitors channel signal quality at the channel units of the gateway to determine whether the quality of a channel unit is below a predetermined quality threshold. If the channel quality is greater than or equal to the predetermined quality threshold, then a standard channel unit is employed, and nominal algorithms are used to process the channel. However, if the channel quality is below the quality threshold, then a high performance channel unit is used that employs complex algorithms unique to the particular quality defect of the channel quality. Various additional functions can be performed at the receive side and the transmit side of the channel units monitored by the IRM. Further, the IRM can add or enhance existing algorithms in accordance with new technology.
    Type: Application
    Filed: July 16, 2001
    Publication date: March 7, 2002
    Applicant: COMSAT CORPORATION
    Inventors: Parakash Chakravarthi, Anupama Dharap
  • Patent number: 6337610
    Abstract: Asynchronously-tuned coupled resonator cavities are implemented having a minimum set of inter-resonator couplings, wherein the filter design incorporates only series and parallel couplings. By way of example, 8th order filter topologies having three transmission zeros, no cross-couplings, and only eight series and/or parallel couplings can be achieved.
    Type: Grant
    Filed: November 22, 1999
    Date of Patent: January 8, 2002
    Assignee: Comsat Corporation
    Inventors: Albert Edward Williams, John Irving Upshur, Mohammed Mahbubur Rahman
  • Patent number: 6278754
    Abstract: In a multi-channel demodulator, a detection-transition sample estimation scheme classified samples as left (L) or right (R) of a reference position within a symbol interval (110), or before (B) or after (A) a transition between symbols (120). When a sample is classified as L or B, the classification of the next sample is forced to R or A, respectively. A memory is provided for storing the contents of various registers when switching to processing of a different channel, and for retrieving from the memory stored data corresponding to previous processing of the different channel. Data read from the memory is written to a register downstream of the register from which it was taken when written to the memory. The read cycle of the memory is extended to ensure that a clock is available to load the data from memory into the downstream register after switching to the new channel.
    Type: Grant
    Filed: March 19, 1999
    Date of Patent: August 21, 2001
    Assignee: Comsat Corporation
    Inventors: James R. Thomas, Soheil I. Sayegh
  • Patent number: 6269333
    Abstract: First and second codeword are selected from respective first and second codebooks having an equal number of codewords and wherein the first and second codewords represent unequal numbers of elements of respective first and second sub-vectors. A codebook populating method for a split vector quantizer relies on comparing centroid calculations for the first codebook. The calculations are performed on eligible pairs of codewords. Eligible codewords are limited to those which satisfy and ordered property based on Line Spectrum Frequencies (LSF). The results of the centroid pair codeword calculations are used to populate the second codebook.
    Type: Grant
    Filed: August 28, 2000
    Date of Patent: July 31, 2001
    Assignee: Comsat Corporation
    Inventor: Channasandra Ravishankar
  • Patent number: 6253171
    Abstract: A voicing probability determination method is provided for estimating a percentage of unvoiced and voiced energy for each harmonic within each of a plurality of bands of a speech signal spectrum. Initially, a synthetic speech spectrum is generated based on the assumption that speech is purely voiced. The original and synthetic speech spectra are then divided into plurality of bands. The synthetic and original speech spectra are compared harmonic by harmonic, and a voicing determination is made based on this comparison. In one embodiment, each harmonic of the original speech spectrum is assigned a voicing decision as either completely voiced or unvoiced by comparing the difference with an adaptive threshold. If the difference for each harmonic is less than the adaptive threshold, the corresponding harmonic is declared as voiced; otherwise the harmonic is declared as unvoiced. The voicing probability for each band is then computed based on the amount of energy in the voiced harmonics in that decision band.
    Type: Grant
    Filed: February 23, 1999
    Date of Patent: June 26, 2001
    Assignee: Comsat Corporation
    Inventor: Suat Yeldener
  • Patent number: 6233552
    Abstract: An adaptive time-domain post-filtering technique is based on the modified Yule-Walker filter. This technique eliminates the problem of spectral tilt in speech spectrum that can be applied to various speech coders. The new post-filter has a flat frequency response at the formant peaks of speech spectrum. Information is gathered about the relation between poles and formants and then the formants and their bandwidths are estimated. The information about the formants and their bandwidths is then used to design the modified Yule-Walker filter based on a least squares fit in time domain.
    Type: Grant
    Filed: March 12, 1999
    Date of Patent: May 15, 2001
    Assignee: Comsat Corporation
    Inventors: Azhar Mustapha, Suat Yeldener
  • Patent number: 6181825
    Abstract: Compression and decompression methods for transmitting facsimile images in which the facsimile image is compressed in both vertical and horizontal directions are implemented using two dimensional maximum differences algorithms. Asymmetrical and fractional image compression are provided by controlling the number of lines, i.e., rows or columns, being compressed and by controlling the bit segment length used during each differences determination. The compressed facsimile image is decompressed by selecting a reference bit in the decompressed facsimile image and expanding the bit in both vertical and horizontal directions in accordance with a binary value of bits near the selected reference bit. A transmission channel adapted to serially perform the encoding and decoding functions is also described.
    Type: Grant
    Filed: December 2, 1994
    Date of Patent: January 30, 2001
    Assignee: Comsat Corporation
    Inventors: Roderick J. Ragland, Spiros S. Dimolitsas, Franklin L. Corcoran, Neil H. Tender
  • Patent number: 6175720
    Abstract: In a method of synchronizing mobile communication devices employed in a non-geostationary satellite communication system according to a paging time plan using geographical paging cells, a geographical region is segmented into a plurality of the geographical paging cells, the mobile communication devices are divided into subgroups according to their location in one of the geographical paging cycles. A plurality of beams are transmitted from non-geostationary satellites to the mobile communication devices positioned within the geographical paging cells according to the paging time plan. The paging time plan requires that each of the beams be transmitted in at least one frame including at least one paging cycle having a plurality of time slots. The time slots occur at fixed intervals relative to time slots occurring in paging cycles of subsequent occurring frames.
    Type: Grant
    Filed: April 10, 1996
    Date of Patent: January 16, 2001
    Assignee: Comsat Corporation
    Inventor: Soheil Sayegh