Abstract: A method (20) of orthogonal frequency-division multiplex (OFDM) communication via a plurality of subchannels (30) within a noncontiguous wideband channel (24) is provided. The method (20) determines an SNR for each of the subchannels (30). The method (20) then designates a subchannel (30) as clear (93) when its SNR is greater than a least-SNR threshold (70), as impeded (95) when its SNR is less than the least-SNR threshold and greater than an SNR-evaluation threshold, and as obstructed (111) when its SNR is less than both the least-SNR and the SNR-evaluation thresholds. The method (20) then transmits OFDM data (34) so that each of the clear subchannels receives the OFDM data (34) at a maximum subchannel signal level (40), each of the impeded subchannels receives the OFDM data (34) at an intermediate subchannel signal level (42), and each of the obstructed subchannels receives the OFDM data (34) at zero subchannel signal level (44).

Abstract: A symbol synchronizer (100) is provided for a software-defined communications system (10). The symbol synchronizer (100), when integrated into either a pre- or post-detection diversity signal combiner (108, 208), enables highly accurate signal synchronization with minimal added system complexity. The symbol synchronizer (100) includes a single complex sliding window-matched filter (102) for filtering an input digital signal with a match filtering function based on predetermined signal transfer function characteristics to average out receiver noise from the signal. A signal delay bank (84) includes a plurality of delay blocks each for delaying the digital signal filtered by the single matched filter for a predetermined number of samples. A complex correlator (88) correlates the digital signal filtered by the single complex sliding window matched filter (102) and delayed by the complex correlator (88) with a correlator reference signal, and selects an index of a path having a peak correlator value.

Abstract: A symbol synchronizer (100) is provided for a software-defined communications system (10). The symbol synchronizer (100), when integrated into either a pre- or post-detection diversity signal combiner (108, 208), enables highly accurate signal synchronization with minimal added system complexity. The symbol synchronizer (100) includes a single complex sliding window matched filter (102) for filtering an input digital signal with a match filtering function based on predetermined signal transfer function characteristics to average out receiver noise from the signal. A signal delay bank (84) includes a plurality of delay blocks each for delaying the digital signal filtered by the single matched filter for a predetermined number of samples. A complex correlator (88) correlates the digital signal filtered by the single complex sliding window matched filter (102) and delayed by the complex correlator (88) with a correlator reference signal, and selects an index of a path having a peak correlator value.

Abstract: A wireless access unit (12) for providing an interface between a satellite communications system (32) and a plurality of terrestrial user devices (14-26) in a centralized or distributed architecture includes a spectrum allocation unit (92) for dynamically allocating spectrum to the plurality of terrestrial user devices (14-26) based on a spectral environment about the wireless access unit (12). A spectrum scan unit (60) scans the spectral environment about the wireless access unit (12) and generates a spectrum signal indicative thereof. An environment understanding unit (61) provides signal information corresponding to signal emitters in proximity to the distributed or centralized network. A spectrum table (90) assembles data related to the spectral environment and the proximity emitters for use by the spectrum allocation unit (92) in dynamically allocating spectrum.

Abstract: A communications network (10) having a plurality of wireless nodes (12-28) distributed within a region of interest makes routing decisions based on terrain information for the region of interest. A link quality determination unit (54) determines the quality of individual node-to-node links within the network (10), based on the location of the nodes (12-28) and the terrain about the nodes (12-28). A path selection unit 58 then determines an optimal path through the network 10 based on the link quality information. In one embodiment, communications corridors (102) are defined as preferred subpaths within a network for use in connecting remote nodes.

Abstract: A method for excitation synchronous time encoding of speech signals. The method includes steps of providing an input speech signal, processing the input speech signal to characterize qualities including linear predictive coding (LPC) coefficients, epoch length and voicing and characterizing the input speech signals on a single epoch time domain basis when the input speech signals comprise voiced speech to provide a parameterized voiced excitation function. The method further includes steps of characterizing the input speech signals for at least a portion of a frame when the input speech signals comprise unvoiced speech to provide a parameterized unvoiced excitation function and encoding a composite excitation function including the parameterized unvoiced excitation function and the parameterized voiced excitation function to provide a digital output signal representing the input speech signal.

Abstract: A vocoder device and corresponding method characterizes and reconstructs speech excitation. An excitation analysis portion performs a cyclic excitation transformation process on a target excitation segment by rotating a peak amplitude to a beginning buffer location. The excitation phase representation is dealiased using multiple dealiasing passes based on the phase slope variance. Both primary and secondary excitation components are characterized, where the secondary excitation is characterized based on a computation of the error between the characterized primary excitation and the original excitation. Alternatively, an excitation pulse compression filter is applied to the target, resulting in a symmetric target. The symmetric target is characterized by normalizing half the symmetric target. The synthesis portion performs reconstruction and synthesis of the characterized excitation based on the characterization method employed by the analysis portion.

Abstract: A method for pitch epoch synchronous encoding of speech signals. The method includes steps of providing an input speech signal, processing the input speech signal to characterize qualities including linear predictive coding coefficients and voicing, and characterizing excitation corresponding to the input speech signals using frequency domain techniques when input speech signals comprise voiced speech to provide an excitation function. The method also includes steps of characterizing the input speech signals using time domain techniques when the input speech signals comprise unvoiced speech to provide an excitation function and encoding the excitation function to provide a digital output signal representing the input speech signal.

Abstract: A method for pitch epoch synchronous encoding of speech signals. The method includes steps of providing an input speech signal, processing the input speech signal to characterize qualities including linear predictive coding coefficients and voicing, and characterizing excitation corresponding to the input speech signals using frequency domain techniques when input speech signals comprise voiced speech to provide an excitation function. The method also includes steps of characterizing the input speech signals using time domain techniques when the input speech signals comprise unvoiced speech to provide an excitation function and encoding the excitation function to provide a digital output signal representing the input speech signal.

Abstract: A method for excitation synchronous time encoding of speech signals. The method includes steps of providing an input speech signal, processing the input speech signal to characterize qualities including linear predictive coding (LPC) coefficients, epoch length and voicing and characterizing the input speech signals on a single epoch time domain basis when the input speech signals comprise voiced speech to provide a parameterized voiced excitation function. The method further includes steps of characterizing the input speech signals for at least a portion of a frame when the input speech signals comprise unvoiced speech to provide a parameterized unvoiced excitation function and encoding a composite excitation function including the parameterized unvoiced excitation function and the parameterized voiced excitation function to provide a digital output signal representing the input speech signal.

Abstract: A multi-channel receiver automatically determines the noise floor of each channel and resets the channel threshold based thereon while avoiding undesirable bias from weak non-noise signals. The power probability of uncharacterized input signals (non-noise content unknown) is computed and normalized to have a known probability that the power exceeds a first threshold. A second probability of exceeding a second threshold is determined and compared to a predetermined reference probability for a noise-only signal at the same threshold. If the computed second probability is not higher than the reference probability, then the uncharacterized signal is a noise only signal whose average is the noise floor for the channel. The threshold detection level is then set a predetermined amount above the noise floor. The process is automatic and compensates for receiver aging and ambient noise fluctuations with time and from channel to channel and for other changes.