Abstract: A solution to the problem of frequency offset in a digital communication system. On the transmitter side, interleaving is applied to a stream of symbols to which an error correcting code has been applied. The interleaving is such that symbols of the stream are divided into two groups, e.g, alternating symbols are assigned to different groups. The result of interleaving is a burst where symbols of a first one of the group are transmitted in ascending order and symbols of a second one of the group are transmitted in descending order. In one embodiment, the second group comes first in the burst, then one or more synchronization symbols followed by the first group.

Abstract: An existing TDRSS satellite communication system is incorporated, together with low-power ground-based remote transceivers of special design, and additional beamforming and steering elements at the ground terminals, to make possible digital communication between low power field transceivers and satellite ground terminals. The satellite communication system transmits to its ground terminals a composite signal, comprising amplified, phase-coherent signals received by an array of broad-coverage antennas on the satellite. The field transceiver transmits a pseudonoise coded signal spread across all or a portion of the satellite's receive bandwidth. At the ground terminals, the downlinked composite signal is processed by a beamformer to define a narrow, high-gain beam between the satellite and low-power transceiver. Signal processing gain and beamformer gain in combination serve to elevate the received, demodulated signals well above the noise level at the receiver.

Abstract: A method and apparatus for estimating a carrier frequency of an incoming signal. The carrier frequency estimator determines the phase difference between the phases for two successive modulation symbols when the two successive modulation symbols are within a particular magnitude range having at least two evenly spaced modulation phase states. The carrier frequency estimator includes a magnitude selector for selecting modulation symbols within the particular magnitude range and a phase subtractor coupled to the magnitude selector for determining phase differences between the successive modulation symbol phases. A signal receiver of the present invention uses the phase differences for tuning a locally generated frequency for tracking a carrier frequency of an incoming radio frequency (RF) signal.

Abstract: An information broadcast system having a broadband broadcast system selected from cable and satellite for broadcasting requested information from a selected information source, including the Internet, to one or more selected subscriber stations includes an independent backhaul channel for communicating information request signals from a subscriber station to one or more central processing stations. The system includes a data broadcast station for transmitting requested data from the selected data source and central station via the data broadcast station to the one or more selected subscriber stations. The high-data rate broadcast station forwards requested data from a data source to the data broadcast station. A backhaul satellite communication system, independent of the broadband broadcast system, has a backhaul satellite ground terminal for coupling information request signals from backhaul satellite communication system to high data broadcast station terminal.

Abstract: The present invention is directed to the use of bandwidth efficient OCDMA in a multipath environment. The high rate PN code greatly attenuates multipath components that are delayed enough to have significant impact on the degree of orthogonality that may be achieved. By offsetting the carriers by the RW chipping rate and using precise network timing to align all accesses to a small fraction of a high rate PN chip duration, it is possible to fully utilize the available bandwidth. The procedure for achieving this time base alignment has been previously disclosed in U.S. patent application Ser. No. 980,957.

Abstract: A digital mode receiver for the reception of signals from multiple independent subscribers, as on a cable television bidirection broadband data transmission system, adapted for subscriber inquiries and two-way data transmission. Each burst comprises a fixed preamble portion and a variable data portion. The received burst is sampled and fed to a sample storage buffer. The preamble portion's output is used to initialize an equalizer, and to synchronize carrier and modulation clock. By repeating the processing of the preamble and optionally all or part of each burst, accuracy of detection of the variable data is improved, so that it is feasible to receive individual bursts without burst-to-burst coordination, while using a short preamble for increased efficiency.

Abstract: A method and apparatus are provided which enables all return links from the remote stations in a star configured CDMA system to be maintained in time synchronization. This method employs special synchronization codes in conjunction with a standard CDMA chip time tracking apparatus, such as a Delay Lock Loop. Each of these special synchronization codes possesses an extremely low cross-correlation property with each of the other codes in the set of synchronization codes. The low cross-correlation property exists for time offsets up to plus and minus one CDMA chip period which permits the use of a standard chip timing discriminator apparatus, such as an early-late gate, within the Delay Lock Loop. Given the extremely low cross-correlation of these special synchronization codes, a significant improvement is achieved in time tracking performance and/or return link signal efficiency over prior art.

Abstract: Disclosed are digital processing techniques for efficiently receiving, sampling and recovering multiple direct-sequence spread-spectrum signals by multiplexing key signal processing elements across many logical channels. Global Positioning System (GPS) receivers serve to illustrate the technique. They receive many signals, each with independent timing, phase, amplitude, and data modulation, which may arrive on multiple carrier frequencies and at multiple spreading rates. To employ digital processing techniques, the carrier or carriers are reduced to one or more digital sample streams. Digital processing (e.g., products, sums, decisions, etc.) is then used to estimate, or recover, the received signal and its characteristics. When these functions can be partitioned by processing rate, the usual case, the lower-rate functions can be efficiently shared with negligible efficiency loss.

Abstract: A fast algorithm for performing maximum likelihood detection of data symbols transmitted as phases of a carrier signal.

Abstract: Interactive internet activities are a very popular means for gathering information for business, personal, medical, entertainment and other purposes. Most internet interaction is asymmetrical in nature in that a client's requests for information are much smaller (in data size) than the resulting information delivered by the server. Although the client/internet link is inherently asymmetrical, there remains a great deal of interaction and overhead required between the client and the server that increases the bandwidth needs for the client's upstream request channel. There are many advantages to reducing this upstream traffic volume and thereby making the internet interaction even more asymmetrical. Such compression of request data could allow more clients to utilize a single upstream data path instead of separate paths.

Abstract: An apparatus and method for suppressing intermodulation noise in a radio frequency power amplifier. Intermodulation noise suppression is achieved by use of an amplitude limiter connected to the signal source and a shaping filter connected between the amplitude limiter and the power amplifier. The shaping filter may be a band-stop notch filter which attenuates intermodulation noise in a selected radio band or a bandpass filter which attenuates all out-of-band intermodulation noise. The intermodulation noise suppression of this invention causes the signal entering the power amplifier to be characterized by (1) a low peak-to-average envelope distribution and (2) low spectral content in the radio frequency bands to be protected.

Abstract: A method of paging assigns a unique digital address to mobile stations with each unique digital address being mapped into an orthogonal signal set which is then transmitted to all mobile stations. Each mobile station then correlates a received orthogonal signal function against an orthogonal function corresponding to its address. More particularly, each orthogonal signal set comprises a binary orthogonal signal set such as a set of Rademacher-Walsh functions. Other well known orthogonal function sets can be employed. For example, an mbit address can be partitioned into g binary sequences and each sequence is then uniquely mapped into one of 2.sup.m/g orthogonal functions.

Abstract: A star configured multiple access radio communication system wherein a hub station communicates, in time division multiplex mode, with a plurality of remote subscriber stations by a forward link signal path and the remote subscriber stations communicate with the hub on a return link signal path and wherein all received return link signals are time synchronous, and all signals possess the same time division multiplex structure in which a portion of the signal is dedicated to time synchronization. Each remote subscriber station has a synchronization burst sequence generator, each generated burst sequence is constructed such that the time tracking and synchronization process of each return link is relatively unaffected by all other remote stations. At the hub station there is a delay discrimi-nator for each remote subscriber, each delay discriminator includes a first and a second channel. The first channel has a one symbol delay device, a matched filter, and a squaring circuit.

Abstract: A time division multiple access (TDMA) burst receiver and a method for recognizing and providing a time-of-arrival of a TDMA burst transmission having a selected preamble. The TDMA burst receiver includes a blanker for blanking the TDMA burst transmission when the signal level exceeds a pre-selected noise threshold, a signal threshold detector for providing a first tentative time-of-arrival when a correlation of the TDMA burst transmission and the selected preamble exceeds a first threshold and a second tentative time-of-arrival only when the correlation exceeds a second threshold within a selected time period following the first tentative time-of-arrival, and a state machine for providing an operational time-of-arrival corresponding to the first tentative time-of-arrival when the second tentative time-of-arrival is not received and the second tentative time-of-arrival when the second time-of-arrival is received.

Abstract: A system for the delivery of wireless broadband integrated services digital network (ISDN) using asynchronous transfer mode (ATM).

Abstract: A local multipoint distribution system having a head end coupled to a plurality of base stations with each base station constituting a cell. Each base station has a plurality of sector beam antennas, each sector beam antenna illuminating a predetermined sector of the cell with RF communication signals. A plurality of RF subscriber stations for each sector of a cell, with each subscriber station having a high gain antenna with a narrow beam width oriented toward the sector beam antenna oriented toward its assigned sector. Time division multiple access control is provided at each subscriber station operated such that each subscriber transmits at a time different from the other subscribers in its sector so that the subscribers in a given sector do not interfere with each others' transmissions, respectively. The power level transmitted by the subscribers are adjusted or controlled so that the subscriber signals arrive at the respective base stations at about the same power level.

Abstract: Air traffic surveillance and communication system for air traffic controllers includes a plurality of ground based first digital radio transceivers, each first digital radio transceiver being located in specific geographic sectors, respectively, and having a first frequency channel for supporting party-line digital voice, and a second frequency channel dedicated to supporting a digital data channel for down-linking dependent surveillance data and for both up-link and down-link data communications. The first and second frequency channels are paired such that each time a frequency change is commanded by the ground both the first and second frequency channels will be automatically tuned to a new air-ground frequency pair.

Abstract: A frequency control system and method for minimizing frequency drifts in subscriber terminals in a point-to-multipoint system is described enabling the use of low cost oscillators in the Subscriber terminals by measuring the frequency offset of the subscriber terminal's receiver to estimate its oscillator frequency drift which is then used to correct the subscriber terminal's transmitter frequency and also by feedback of a frequency correction from the base station to the subscriber.

Abstract: A spread spectrum CDMA communication system in which a base station communicates with a plurality of subscriber terminals and the base signal transmitted by the base station is comprised of a set of substantially orthogonal functions which are overlaid with a pseudo-noise (PN) sequence forming a coded spreading sequence for an information signal, each orthogonal function of the set carries data for a single user in the system. Information signals are modulated onto the carrier to form a transmit signal and the coded spreading sequence on the transmit signal for broadcasting, each subscriber terminal having a receiver for coherently demodulating the base station signal. A plurality of correlators, each respectively tuned to different functions of the orthogonal signal set, are each followed by an appropriate nonlinearity for removing the data modulation. The summed output of the correlators is used to improve the estimate of carrier phase over that obtained with a single correlator.

Abstract: A networking protocol for wireless point (base station) to multipoint (user) networks where the users are stationary which utilized time-division multiplexing the in the direction of the base station to the user, heretofore called the downstream direction, and time-division multiple access in the direction of the user to the base station, heretofore called the upstream direction, where medium access control actively assigns time slots in the upstream direction to accommodate varying demands for bandwidth by multiple users, where upstream frame timing is synchronized to the downstream frame timing, where time slots carry individual ATM cells, where the first time slot of the downstream frame carries a frame start ATM cell, where upstream time slot synchronization is maintained to within .+-.