Other

Motorola Corporation

Comtech Systems Inc.

Datum Systems, Inc.

Peter Monsen

Thomas Peter Emmons, Jr

James William Startup

Robert Anthony Peters

Norbert Kleiner

Duke Edward Hanson

Richard Hollingsworth Cannon

David Bagby

A transmitter/receiver apparatus and method provide adaptive data rate fading compensation that utilize dual-polarization transmissions at a constant modulation-symbol rate over a forward-scatter radio link and that employ adaptive receiver techniques that operate efficiently at the noisy uncoded signal-to-noise ratio threshold of present-day forward-error correction codes over the range of multipath widths in such forward-scatter environments. The dual-polarization transmissions support both dual transmission and dual diversity configurations. The adaptive receiver techniques include adaptive channel matched filtering and adaptive equalizing at the modulation-symbol rate.

Apparatus and methods for adaptive data rate communication in a forward-scatter radio system

A method and apparatus are provided for demodulating a received signal containing modulated desired-signal digital data and relayed-interference that results from a nonlinear-distorted interference signal. Estimation of the nonlinear-distorted interference from a pre-distortion interference signal and subsequent cancellation within the received signal of the distorted interference produces a residual-interference signal that is subsequently demodulated to produce estimates of the desired-signal data. The estimation is adapted for changing nonlinear distortion effects.

Method and apparatus for demodulation of a desired signal by constellation-independent cancellation of nonlinear-distorted interference

The present disclosure provides methods and apparatuses for nonlinear channel identification and estimation of the distorted signals in digital data transmission systems that include signals traversing a dispersive nonlinear channel that produces noisy distorted signals. The identification and estimation are accomplished with an amplitude-based signal expansion and are adapted for changing nonlinear distortion effects using a Least-Means Square direct solution that includes a precomputed matrix.

Method and apparatus for nonlinear-channel identification and estimation of nonlinear-distorted signals

The present disclosure provides methods and apparatuses for demodulating discrete-time desired signals in a period-Tbandpass desired signal in the presence of interference that results from a period-T bandpass interference signal that has been nonlinear distorted. Estimation of the nonlinear-distorted interference and subsequent cancellation from a received signal, that includes the interference and desired signal, produces residual-interference signals. The demodulation of the residual-interference signals uses an equalization technique when Tis not equal to T. The estimation, cancellation, and demodulation are adapted for changing nonlinear distortion effects.

Method and apparatus for demodulation of a desired signal in the presence of nonlinear-distorted interference

A method and apparatus at a local terminal are described for demodulating a remote-terminal signal located at a subband offset frequency in a frequency subband of relayed interference from a transponder satellite link. The demodulation of the remote-terminal signal is accomplished by transferring the digital data that produced the local-terminal transmit signal to the local-terminal receiver. The digital data is time-delayed and converted to a narrowband offset-constellation signal that cancels the relayed interference in an adaptive equalizer. Providing cancellation in the subband of the relayed interference produces larger interference cancellation factors than those obtained in conventional broadband cancellation systems. A phase-noise error signal is also generated and used to increase cancellation levels limited by phase noise generated in the satellite link frequency converters. Additionally the receiver converter frequencies are chosen such that errors in estimating the subband offset frequency do not affect cancellation in the adaptive equalizer.

Method and apparatus for subband signal demodulation in a transponder satellite communication link containing a component of relayed interference

In a duplex radio link digital data information is transmitted to a remote terminal at a constant symbol rate in accordance with a selected data rate mode that is a function of direct sequence spreading gain, error correction code rate, and signal constellation type. The data rate is adapted by selecting a data rate mode that is a function of a data packet arrival rate and a link quality measure fed back from the remote terminal. The data packet arrival rate is controlled as a function of the link quality measure and the current data packet arrival rate. In systems with multiple transmit diversity channels, independent data is sent over each of the transmit diversity channels. In an idealized feedback communication example, a single antenna troposcatter system in a Ku-band application is shown to have 15.5 times the data rate capability of a conventional two-antenna system at S-band.

Technique for adaptive data rate communication over fading dispersive channels

In high data rate communication applications where digital data information is error-corrected coded and interleaved and transmitted with spectral limitations over fading dispersive channels, a method and receiver is described that incorporates channel estimation and decision-feedback equalization. Channel estimation is accomplished within a receiver time block with locally generated reference symbol sequences. The parameters of the decision-feedback equalizer (DFE) are computed directly from the channel estimates. The DFE is an optimum finite length realization that includes effects from spectrum control filtering, a space-time block coder (STBC) on multiple transmit antennas, multiple receiver diversity signals, and the fading dispersive channel. The DFE includes a matched filter, forward filter, backward filter, and detector. A symbol combiner within the matched filter produces a P+1 dimensional signal that provides ideal cancellation of P intersymbol interferers in the forward filter. When P is selected to meet an intersymbol interference (ISI) criterion, all desired signal energy is collected and all ISI can be ideally cancelled. The DFE processes received signals within the receiver time block to produce information symbol estimates that are subsequently deinterleaved and error-correction decoded to recover the transmitted digital data information. Deinterleaving over multiple receiver time blocks further compensates for channel estimation variations from block to block. Additionally the STBC and DFE are used in a quadruple angle diversity technique requiring only a single antenna at each terminal of a troposcatter link to provide performance approaching that of a nonfading satellite link.

Technique for adaptive equalization in band-limited high data rate communication over fading dispersive channels

A radio communication method and system for transmitting multiple-user digital data information in a Code Division Multiple Access (CDMA) format over multipath and mutual-interfering channels to a receiving terminal with diversity antennas and equalization signal processing. At the receiving terminal, diversity antenna signals are grouped into time blocks and replicas are generated of the user-unique CDMA sequence signals for a set of K mutually interfering users. Within each time block the multiuser channel is estimated, equalization parameters are calculated, and decision-feedback equalization is used to produce multiuser estimates associated with a subset &#x3bb; of the K users. These estimates are deinterleaved and error-correction decoded to recover transmitted digital data information for the subset of &#x3bb; users. The invention includes embodiments for a CDMA sequence period that is equal to or longer than the transmitted data symbol interval with applications to current CDMA reverse link and forward link standards. Also embodiments for both decision-directed and reference-directed channel estimation are given.

Technique for adaptive multiuser equalization in code division multiple access systems

A multiple-access digital radio communication system and method with communication links between user terminal transmitters and a central node with a receiver system including a multibeam antenna. User terminal transmitters assigned to one beam coverage region use multiple access channels that are mutually orthogonal for transmitting digital message information that is included in a data group. Assignments are random and are changed for successive data groups. The same multiple access channels are reused in adjacent and other beam coverage regions each with an independent random assignment algorithm. Error-correction coding and interleaving are used in the user transmitter and an adaptive processor is used in the receiver. A reference sequence unique to either each user or each beam coverage region is multiplexed into user data groups for transmission. At the receiver the adaptive processor such as an equalizer or sequence estimator is used to combine multiple antenna beam signals to produce a combined signal associated with each user. The combining in the adaptive processor reduces interference from user terminal transmitters associated with different beam coverage regions but with the same multiple access channel. Deinterleaving and error-correction decoding of the combined signal are used to protect against channel assignments with larege mutual interference levels. The communication system can reuse each orthogonal multiple access channel in all of the other beams, i.e., a reuse factor of unity for each multiple access channel.

Multiple access system and method for multibeam digital radio systems

A multiple access communication system with communication links between one or more central nodes each with a transmitterincluding an antenna with one or more antenna beams, and user terminalslocated in antenna beam coverage area. User terminalsassigned to one beam coverage areause multiple access channels that are mutually orthogonal for receiving digital message information. These multiple access channels are reused by other user terminalsin adjacent and other beam regions. Single-axis error correcting coding, interleaving, channel assignment changes, precoding, and selected 90&#xb0; phase rotationare used in the central node transmitterto reduce potential interference at a user terminalfrom signals using the same orthogonal multiple access channel destined for user terminalsin other beam coverage areas. The communication system can realize complete reuse of all orthogonal multiple access channels in other beam coverage areas, i.e., a reuse factor of unity.

Multiple access technique for downlink multibeam digital radio systems

A multiple-access digital radio communication system and method with communication links between user terminal transmitters and central node with a receiver system including a multibeam antenna. User terminal transmitters assigned to one beam coverage region use mltiple access channels that are mutually orthogonal for transmitting digital message information. These multiple access channels are reused in adjacent and other beam coverage regions. Error-correction coding (), interleaving (), and a single-axis modulator () are used in the user transmitter to increase resistance to potential interference from user terminal transmitters in other coverage regions. At the receiver, an adaptive processor () such as an equalizer or sequence estimator is used to combine multiple antenna beam signals () to produce a combined signal associated with each user. Deinterleaving () and error-correction decoding () of the combined signal is used to complete the recovery of the digital message information.

The present invention utilizes a dual polarization reception system () that utilizes the energy available in orthogonal polarizations to effectively increase link margin, thereby allowing for adequate signal quality reception in difficult environments. A co-polarized and a cross-polarized signal are separately downconverted and demultiplexed. The signals from each demultiplexed output are then sampled and weighted. The weighted samples for each polarity are combined in soft decision combining/decoding circuitry (), and this circuitry determines the most likely state of a received symbol's transmitted value.

Mobile satellite communication system utilizing polarization diversity combining

The present invention utilizes a dual polarization reception system ( ) that utilizes the energy available in orthogonal polarizations to effectively increase link margin, thereby allowing for adequate signal quality reception in difficult environments. A co-polarized and a cross-polarized signal are separately downconverted and demultiplexed. The signals from each demultiplexed output are then sampled and weighted. The weighted samples for each polarity are combined in soft decision combining/decoding circuitry ( ), and this circuitry determines the most likely state of a received symbol's transmitted value.

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Stowe, VT, United States of America

Peter Monsen