Abstract: Transmitting a signal from a transmitter. A method includes identifying a threshold spectral flux density for a given physical location. The method further includes, as a result of identifying the threshold spectral flux density, transmitting a signal at a power level causing the signal to be below the spectral flux density at the given physical location, the signal being transmitted at a data rate. The method further includes receiving feedback from a receiver indicating the signal-to-noise ratio of the signal at the receiver. The method further includes adjusting the data rate of the signal based on the feedback. The method further includes continuing transmitting the signal at the adjusted data rate and power level.

Abstract: Transmitting a signal from a transmitter. A method includes identifying a threshold spectral flux density for a given physical location. The method further includes, as a result of identifying the threshold spectral flux density, transmitting a signal at a power level causing the signal to be below the spectral flux density at the given physical location, the signal being transmitted at a data rate. The method further includes receiving feedback from a receiver indicating the signal-to-noise ratio of the signal at the receiver. The method further includes adjusting the data rate of the signal based on the feedback. The method further includes continuing transmitting the signal at the adjusted data rate and power level.

Abstract: An antenna system includes a heptagonal antenna array having one center antenna element and seven circumferentially surrounding antenna elements offering improved near and far sidelobe rejection, which is well suited for mechanically-gimbaled and time delayed electrical steering antenna applications.

Abstract: An emergency locating system can include emergency transceivers and locator transceivers. The emergency transceivers can be capable of transmission of spread-spectrum encoded messages, and can be actuated by a user to send a distress message. A locator transceiver can be capable of receiving the distress messages and performing two-way ranging to determine a distance between the locator transceiver and the emergency transceiver.

Abstract: An apparatus and method for correlating a signal over a correlation interval while accommodating spreading code frequency offset is described. In one embodiment, the apparatus includes a plurality of correlators, where each correlator forms a correlation result corresponding to a unique code frequency offset hypothesis. Each correlator selects samples from a tapped delay line at a tap position moved along the delay line at a rate corresponding to the correlator unique code frequency offset hypothesis.

Abstract: An emergency locating system can include emergency transceivers and rescue transceivers. The emergency transceivers can be capable of repeat transmission of a distress message using a variable power level and variable spreading factor. A receive transceiver can be capable of receiving the distress messages and sending a confirmation message to the emergency transceiver. The emergency transceiver can be capable of receiving the confirmation message and terminating transmission of the distress message.

Abstract: Method and apparatus are disclosed for obtaining improved performance when using Forward Error Correction (FEC) with channels experiencing block fading or burst jamming over some number of contiguous symbols. One suitable application is when the channel is periodically obstructed due to the rotation of a propeller blade, resulting in a periodic block fading channel. During operation zero symbols are inserted into the received signal stream, prior to the FEC decoder at times that are estimated or otherwise determined to correspond to periods of jamming or severe fading. The zero symbols effectively “erase” the severely degraded symbols. The zero symbols are less detrimental to the FEC decoder than the severely degraded symbols, especially when the channel interleaving/de-interleaving operations result in the zero symbols being temporarily distributed over a large block of received symbols.

Abstract: An antenna system includes a heptagonal antenna array having one center antenna element and seven circumferentially surrounding antenna elements offering improved near and far sidelobe rejection, which is well suited for mechanically-gimbaled and time delayed electrical steering antenna applications.

Abstract: A technique for resolving access contention in a parallel turbo decoder is described. The technique includes associating a plurality of buffer memories with the subdecoders so that accesses to banks of a shared interleaver memory can be rescheduled. Accesses can be rescheduled to prevent simultaneous accesses to a single bank of the shared interleaver memory based on an interleaver pattern.

Abstract: A first node seeking entry into a secure spread spectrum communications network sends a discovery burst at a low rate, and sends traffic bursts at a higher rate to exchange data rate for range. A receiving node receives discovery bursts via an omni-directional link and transmits and receives traffic bursts via directional links. As a node within the network detects a fading signal, it transmits a discovery burst at low rate on both its uplink and downlink channels. Other nodes may reply via the original uplink channel, and the fading node updates a list of candidate nodes through which it can relay through the network to its intended recipient by reversing the link direction of its original uplink and original downlink channels.

Abstract: An antenna system includes a heptagonal antenna array having one center antenna element and seven circumferentially surrounding antenna elements offering improved near and far sidelobe rejection, which is well suited for mechanically-gimbaled and time delayed electrical steering antenna applications.

Abstract: The present invention concerns methods and apparatus for use in a spread spectrum communications system. In particular, in a method of the present invention information useful for acquiring a target signal is selected; the information is incorporated in an acquisition signal; the acquisition signal is transmitted; the target signal is spread with a spreading code; and the target signal is transmitted. At a receiving node, the acquisition information useful for acquiring the target signal is recovered from the acquisition signal and used to acquire the target signal. Apparatus in accordance with the present invention implement methods of the present invention. The methods and apparatus of the present invention can be used in node- and network-discovery situations.

Abstract: An apparatus and method for correlating a signal over a correlation interval while accommodating spreading code frequency offset is described. In one embodiment, the apparatus includes a plurality of correlators, where each correlator forms a correlation result corresponding to a unique code frequency offset hypothesis. Each correlator selects samples from a tapped delay line at a tap position moved along the delay line at a rate corresponding to the correlator unique code frequency offset hypothesis.

Abstract: A technique for receiving multiple spread spectrum bursts is disclosed. Each spread spectrum burst is encoded with a common spreading code and may include an individual message and unique signal parameters. The technique includes the detection of the spread spectrum encoded bursts and estimation of the reception signal parameters. A single one of a plurality of burst receivers is assigned to each detected burst to extract the individual message of the detected burst.

Abstract: A system and method for detecting a spread spectrum encoded message within a received signal is described. The spread spectrum encoded message has an unknown code phase, unknown code frequency offset, and unknown carrier frequency offset. A plurality of code phase hypotheses, code frequency offset hypotheses, and carrier frequency offset hypotheses are searched in parallel. The unknown code phase, unknown code frequency offset, and unknown carrier frequency offset may also be estimated.

Abstract: A first node initiating communications with a second node already in a secure network sends a discovery burst having a preamble portion and a payload portion. The preamble portion is sent at a varying frequency between high and low thresholds that are reflective of Doppler uncertainty between the nodes. The second node continuously listens at a frequency, termed an acquisition frequency. A data sequence in the preamble portion, known to the second node, is received and used to determine the receive instant in the preamble portion, and thereby compare against the known frequency ramp to determine the frequency at which the payload portion will be received. Preferably, the first node varies the preamble portion between thresholds more than once within the time span of a single preamble portion, and the preamble and payload portions are spread with different spreading codes. The preamble portion may also be disguised with noise generated by the first node.

Abstract: A method for constructing and selecting non-recursive orthogonal variable spreading factor (OVSF) codes is provided. The method includes: defining a variable B=SFmax/SFmin, where SFmax is a maximum desired spreading factor and SFmin is a minimum desired spreading factor; forming B unique base matrices Gk of dimension SFmin×SFmin, where GiGiT=SFminImin ?i, where T denotes a matrix transpose and Imin is an SFmin×SFmin identity matrix; forming a modulation matrix M of dimension B×B such that MMT=BIB, where IB is a B×B identity matrix; forming an SFmax×SFmax orthogonal variable spread factor (OVSF) code matrix C? as: C ? = [ M 1 , 1 · G 1 M 1 , 2 · G 2 … M 1 , B · G B M 2 , 1 · G 1 M 2 , 2 · G 2 … M 2 , B · G B ? ? ? ? M B , 1 · G 1 M B , 2 · G 2 … M B , B · G B ] , where Mi,j is a scalar from the i-th row and j-th column of the modulation matrix M, Gl . . .

Abstract: A parallel correlator and method includes temporarily storing in a series of P sequence registers, each of length R1, serial bit-sequences of a code of length N=P*R1. In a first-level of processing, certain unique bit sequences are inverted to reduce the number of unique bit sequences by half. Identical bit-sequences are then combined and temporarily stored in a first-level sub-accumulation register. Alternatively, bit sequences differing by only one bit may be combined in a common first-level sub-accumulation register. Further levels of similar processing may be imposed, where each subsequent level taps and inverts only a portion of the bits in the above level of processing, thereby reducing the number of unique bit sequences. Finally, all negative energy is combined in one register position, inverted, and added to all positive energy in the other register positions.

Abstract: A system for the efficient use of CORDIC rotators is provided. The system includes at least one first rotator operating in vector mode and includes a sign storage buffer. The system also includes at least one bit inverter coupled between the first rotator and a second rotator, the second rotator operating in rotation mode.

Abstract: An antenna system includes a heptagonal antenna array having one center antenna element and seven circumferentially surrounding antenna elements offering improved near and far sidelobe rejection, which is well suited for mechanically-gimbaled and time delayed electrical steering antenna applications.