Abstract: An Orthogonal Frequency Division Multiplexing (OFDM) transmission utilizes random phases across the OFDM sub-carrier components and differential encoding so that the phase information (i.e., phase values) does not have to be explicitly transmitted to a receiver. The OFDM data symbols are differentially encoded so that the phase information on the symbols that are multiplied together in the differential encoder is the same. Assuming use of a differential phase shift keying (DPSK) system, a phase sequence is used having “V” random phase values, where ?n,k is the phase value in the nth sub-carrier in the kth OFDM symbol and is periodic in n with V as the period. A current input symbol is then differentially encoded relative to the Vth previous encoded output from the encoder so that the phase values on the symbols multiplied together in the differential encoding process are the same.

Abstract: A CDM satellite transmission system is disclosed that broadcasts programming content, such as audio and video information, using one or more geo-synchronous satellites based on Code Division Multiple Access technology. Forward error correction coding and interleaving are used prior to broadcasting the signals over the CDM channel to account for signal loss due to short-term fading. The CDM satellite transmission system provides a tuning channel corresponding to each program channel that reduces the delay when a mobile receiver is first tuned to a selected program channel. The tuning channel utilizes a shorter interleaver length, if any, than the corresponding primary program channel. The CDM satellite transmission system transmits a delayed version of a program signal with the on-time version of the audio output to accommodate uninterrupted reception in the event of such a blockage.

Abstract: A method and apparatus which reduces the start-up delay that may occur when switching programs in audio and/or video streaming applications while maintaining high quality steady-state performance thereof. A program source (e.g., an audio and/or video data stream) is encoded and transmitted as two or more separate bit streams (e.g., sequences of data packets), the transmission of one of these bit streams being delayed by a given amount of time relative to the transmission of the other bit stream(s). At the receiving end of the transmission channel, the two or more bit streams are buffered by receive buffers having different sizes (thereby resulting in different time delays when the contents thereof are decoded), wherein the time delay difference corresponds (inversely) to the relative delay times prior to transmission.

Abstract: A system and method is disclosed for improving diversity in a multiple transmitter or multiple receiver orthogonal frequency division multiplexing (OFDM) system. Signal diversity is improved by introducing phase offsets at the transmitters and/or the receivers. The phase offsets are unique to each transmitter or receiver. The unique phase offsets are applied to individual symbols of the OFDM signal in the frequency domain.

Abstract: A method and apparatus for performing automatic speech recognition (ASR) in a distributed ASR system for use over a wireless channel takes advantage of probabilistic information concerning the likelihood that a given, portion of the data has been accurately decoded to a particular value. The probability of error in each feature in a transmitted feature set is employed to improve speech recognition performance under adverse channel conditions. Bit error probabilities for each of the bits which are used to encode a given ASR feature are used to compute the confidence level that the system may have in the decoded value of that feature. Features that have been corrupted with high probability are advantageously either not used or are weighted less in the acoustic distance computation performed by the speech recognizer.

Abstract: A method and apparatus for reducing deep fading of signals in satellite-based communications systems employing terrestrial repeater stations by shifting the phase of the signals transmitted from each terrestrial repeater station by a different amount so that the signals are transmitted from each terrestrial repeater station and received at a receiver at different phases, thereby effectuating time diversity in such signals to reduce deep fading of the signals. The method and apparatus can be used in CDMA and OFDM systems.

Abstract: A CDM satellite transmission system that broadcasts programming content, such as audio or video information, using two geo-synchronous satellites and a plurality of terrestrial repeaters based on Code division multiple access [(CDMA)] technology is disclosed. A plurality of programming channels is multiplexed onto a carrier frequency using Code division multiple access [(CDMA)] technology. A delayed version of the signal is transmitted with the on-time version of the programming content to accommodate uninterrupted reception in the event of a blockage. The on-time and delayed version of each information channel is transmitted by each of the satellites and repeaters, providing additional diversity gains. Thus, the satellites and terrestrial repeaters occupy the entire available bandwidth. CDM transmissions are used where the pseudo-noise sequences are the same, or linear translates of one another.

Abstract: An Orthogonal Frequency Division Multiplexing (OFDM) transmission utilizes random phases across the OFDM sub-carrier components and differential encoding so that the phase information (i.e., phase values) does not have to be explicitly transmitted to a receiver. The OFDM data symbols are differentially encoded so that the phase information on the symbols that are multiplied together in the differential encoder is the same. Assuming use of a differential phase shift keying (DPSK) system, a phase sequence is used having “V” random phase values, where &thgr;n,k is the phase value in the nth sub-carrier in the kth OFDM symbol and is periodic in n with V as the period. A current input symbol is then differentially encoded relative to the Vth previous encoded output from the encoder so that the phase values on the symbols multiplied together in the differential encoding process are the same.

Abstract: First and second source signal streams each associated with a program source are produced. A first error correction code having a first correction delay is applied to the first source signal stream, thus producing a first error-corrected source signal stream that is transmitted for reception by a receiver. A tuning signal stream corresponding to the second source signal stream is transmitted for reception by the receiver at a determined timing relative to transmission of the first error-corrected signal stream. When first tuning to a program transmission channel, the receiver initially processes the tuning signal to obtain at least a recognizable reproduction of the program source, with little if any delay attributable to error correction coding of the first source signal stream.

Abstract: The present invention is a fast fading packet diversity transmission method and system for reducing the effects of multipath fading on slow fading channels. One embodiment of the present invention includes a modulator for modulating information packets and a plurality of M multipliers for transmitting the modulated information packets from M antennas with up to M sets of M fixed phase offsets. Another embodiment of the present invention transmits a first group of information packets from M antennas with up to M sets of M fixed phase offsets and a second group of information packets with M slow time varying phase offsets.

Abstract: An invention for providing diversity for direct sequence spread spectrum wireless communication systems is presented. The invention provides a receiver technique in which M antennas are utilized at the receiver. Distinct weighting signals are applied to information signals received at each of the M antennas, with the weighing signals being, for example, distinct changes in either phase or amplitude. Applying weighing signals to each of the information signals received at the M receiver antennas results in constructive addition of derived signal vectors at predetermined intervals, which eliminates deep fading at the receiver. Each different time varying weighting signal is determined independently of the corresponding information signal and the combined received input signal.

Abstract: A system for inducing rapid fading in wireless communication systems, such as digital radio and television transmission is described. Orthogonal polarization combined with time varying offsets are combined to insure rapid fading and result in improved signal reception.

Abstract: The invention provides a method and apparatus for transmitting digital signaling formation to a receiver using a plurality of antennas. The invention involves applying a channel code to a digital signal producing one or more symbols. A plurality of symbol copies is made and each copy is weighted by a distinct time varying function. Each antenna which are located at two or more base stations transmits a signal based on one of the weighted symbol copies. Any channel code may be used with the invention, such as a convolutional channel code or block channel code. Weighting provided to symbol copies may involve application of an amplitude gain, phase shift, or both. The present invention may be used in combination with either or both conventional interleavers and constellation mappers.

Abstract: A method and apparatus for performing adaptive hybrid automatic repeat request (ARQ) coding in which the coding is modified based on the acknowledgements returned by the receiver. In accordance with one illustrative embodiment of the present invention, the state of the channel is implicitly determined by the transmitter based upon the frequency of acknowledgments (ACKs and NACKs) arriving from the receiver. For example, since a NACK implies a weak received signal strength, the code rate of the FEC is advantageously reduced in response to such an acknowledgement. On the other hand, the code rate of the FEC is advantageously increased in response to an ACK. In accordance with another illustrative embodiment of the present invention, the acknowledgement returned by the receiver is modified to convey the number of errors in the corresponding received data packet.

Abstract: The present invention is an improved switched antenna diversity transmission system for use with an ARQ error protection protocol. The transmitter of the present invention includes an error detection encoder for encoding information packets with an error detection code, a modulator for modulating the encoded information packets, and a first antenna for transmitting the modulated information packets over a first forward channel of a wireless communication medium to the receiver. The transmitter further includes a switch for switching from the first antenna to a second antenna for transmitting the information packets over a second forward channel of a wireless communication medium in response to a negative acknowledgment from the receiver transmitted over a feedback channel of the wireless communication medium.

Abstract: The present invention is an improved transmission system for JPEG images. The present invention may include a separator for separating the JPEG image into Type-I and Type-II information and a transmitter for transmitting the Type-I and Type-II information over a wire or wireless communication medium to a receiver with unequal error protection, wherein the more error sensitive Type-I information is provided with more powerful error protection than the less sensitive Type-II information which makes up the bulk of the JPEG image. The present invention may further include a combiner for combining the Type-I and Type-II information received by the receiver in a JPEG format suitable for the data sink.

Abstract: The present invention provides an improved wireless transmitter and method for transmitting incremental redundancy. In one illustrative embodiment of the present invention, switched antenna diversity is used in conjunction with punctured error correction codes to provide an independently fading channel for the punctured bits. In this embodiment, the transmitter includes an error correction encoder which outputs a punctured packet and punctured bits encoded from the information packet. The transmitter further includes a modulator for modulating the punctured packet and punctured bits, a first antenna for transmitting the modulated punctured packet to a receiver, and a second antenna for transmitting one or more of the punctured bits to the receiver, in response to a negative acknowledgment received by the transmitter. The first and second antennas in this embodiment are positioned to provide first and second channels having independent fading characteristics.

Abstract: The present invention is a storage and retrieval system for JPEG images. In one illustrative embodiment the system includes an apparatus for storing a JPEG image in or on a storage medium with unequal error protection, comprising a separator for separating the JPEG image into Type-I and Type-II information, an error correction encoder for encoding the Type-I information with more error protection than the Type-II information, and a storage recorder for recording the encoded Type-I and Type-II information in or on the storage medium. The system further includes an apparatus for reading the encoded Type-I and Type-II information from the storage medium.

Abstract: A technique for reducing multiple access interference (MAI) experienced by receivers of transmissions from a transmitter, e.g., a base station, in a direct-sequence code division multiple access communication system, e.g., a cellular radio system, is disclosed. The technique provides for the precoding of user signature sequences for use in spreading information signals to be transmitted. The use of precoded signature sequences significantly reduces the average level of MAI experienced by the receivers. Despreading of received signals by receivers may be accomplished with the original (i.e., non-precoded) signature sequences. Thus, no changes to receivers are required. The technique includes a feature for determining a set of sequences for both transmitter and receiver from a smaller set of orthogonal sequences.

Abstract: The invention provides a method and apparatus for transmitting digital signal information to a receiver using a plurality of antennas. The invention involves applying a channel code to a digital signal producing one or more symbols. A plurality of symbol copies is made and each copy is weighted by a distinct time varying function. Each antenna transmits a signal based on one of the weighted symbol copies. Any channel code may be used with the invention, such as a convolutional channel code or block channel code. Weighting provided to symbol copies may involve application of an amplitude gain, phase shift, or both. The present invention may be used in combination with either or both conventional interleavers and constellation mappers.