Abstract: An apparatus, such as a subscriber unit or a base station within a spread spectrum communication system, may add one or more additional “virtual” paths to a list of candidate paths when assigning demodulation elements. These “virtual” paths are added as candidate paths even though a corresponding peak was not necessarily detected within a received spread spectrum system. The list of paths may include a first path having a time offset approximately equal to a time offset for one of the demodulation elements, and the virtual path having a short time separation from the first path. The time separation between the paths may be, for example, less than 2 chips.

Abstract: Half-duplex mode in V.34 facsimile modems can be exploited using symbol rate re-negotiation to enhance performance and throughput. The enhancement is useful for facsimile servers and for facsimile transmission over Internet Protocol (“FAX-over-IP”) network applications. Extending the modem's symbol rate from the current maximum of 3429 symbols per second standard to a higher rate of symbol transmission can quickly enhance throughput. The technique is useful for fast primary channel retrains and for situations in which symbol rates are to be reduced. The technique is also useful for changing the requested symbol rate with data rate negotiation in situations in which data rate selection for the new symbol rate may not be known.

Abstract: A receiving device for angle-modulated signals performs the channel selection in a digital manner rather than an analog manner. A receive signal is preferably initially converted to an intermediate frequency band, filtered and A/D converted. The receive signal is subsequently converted to the baseband and channels are selected in a digital manner through the use of a digital complex multiplier before the receive signal component of the selected transmission channel is demodulated and the corresponding symbols are detected through the use of a differential demodulator.

Abstract: A method for coherent estimation of the traffic-to-pilot energy ratio is presented. A received preamble is decoded, and then re-encoded. The received preamble is then multiplied by the re-encoded preamble. The results are summed, squared, and then divided by a pilot energy value. In another method, a message carrying energy information can be inserted between a subpacket preamble and a subpacket.

Abstract: A CDMA coded, spread spectrum radio signal containing a strong signal and a weak signal is received, and the interference of the strong signal with the weak signal is computed to enhance the ability to track the weak signal. The codes modulating both signals are known, and the weak signal can be predicted. The interference of the strong signal is calculated as the product of the amplitude of the strong signal and the predicted crosscorrelation of the strong signal with the weak signal. The strong signal may be measured, predicted, or acquired through a combination of both methods. The crosscorrelation may be predicted for a range of weak signal values, and the weak signal selected as the prediction producing the greatest received power.

Abstract: A transmitter for a radio transmission system has an encoder for encoding data according to an error correction code and supplying a digital output stream of bits which are then distributed over a selectable number of carriers belonging to a group of carriers that are uniformly distributed over a transmission channel, so as to constitute a frequency division multiplex. Then the stream is subjected to time interleaving responsive to a distribution given by the bit spreading module which achieves distribution and frequency interleaving operating on the carriers; the stream is then modulated in phase or possibly a phase and amplitude.

Abstract: A discrete loading algorithm maximizes data rate or system performance margin for discrete multitone (DMT) transmission. A preliminary bit assignment for each subchannel is first obtained by optimizing a DMT system with an available bandwidth. The subchannels that receive negative bit assignments are then excluded for further optimization until all the bit assignments are positive. The bit assignment of each subchannel is rounded and a corresponding rounding error is calculated. If the total bit number of the bit assignments are greater than the available bandwidth, the bit assignment of the subchannel having the least rounding error is decreased by one bit. If the total bit number of the bit assignments are smaller than the available bandwidth, the bit assignment of the subchannel having the largest rounding error is increased by one bit.

Abstract: A training method provides an advantageous technique for estimating secondary propagation path parameters based on learning propagation path characteristics for a selected number of secondary propagation path signals. In a multipath environment, a received radio signal comprises multiple received signals, each received through a different signal propagation path. The strongest multipath signal is deemed the main path signal, while the remaining multipath signals are termed secondary path signals. In some types of direct-sequence, spread spectrum communications systems, significant secondary signals must be canceled from the received multipath signal to achieve desired receiver performance, while in other types of systems, such secondary signals may be used to enhance the signal-to-noise ratio of the received signal. In either case, the various multipath signals must be accurately characterized.

Abstract: A tetrahedron modem phase modulates input serial binary data and demodulates input waveforms based on a four dimensional vector set. The phase modulation scheme has four possible state vectors (or symbols), that form a tetrahedron in four dimensional space. This symbol geometry improves the bit error rate performance over conventional PSK methods for a given signal to noise ratio. In addition the tetrahedron modem aids bit synchronization and eliminates phase ambiguity in the receiver. Lastly, the tetrahedron modulator outputs a constant envelope waveform, which may be subjected to non-linear devices and channels without fear of negative effects due to amplitude distortion.

Abstract: Received signals are decoded based on a coupling between bits of the received signals introduced by the channel over which the signal is transmitted or by the transmitter which transmitted the signals. For example, in a higher-order modulation scheme, such as 8-PSK, individual bits grouped in a given symbol are generally coupled rather than fully independent. Accordingly, decoding information on a first one of the bits processed through a forward error correction decoder may be used to adjust the soft information from a demodulator for one or more of the other bits contained in the same symbol for use in processing those bits through the forward error correction decoder. Particularly where interleaving is utilized, a first bit may be processed through the decoder before the soft information on another of the bits is needed, thereby allowing an intermediate decision soft value for the first bit to be used in generating the input value to the decoder for the subsequent bit.

Abstract: An operator independent, transparent wireless modem management system is disclosed. According to an embodiment of the invention, the modem management system comprises the steps of receiving a short message service message at the wireless modem and examining the short message service message for modem management information. If the short message service message comprises modem management information, then the wireless modem processes the short message service message. A wireless modem for accomplishing the same is also disclosed.

Abstract: A sequential decoder for decoding convolutional code is provided. The sequential decoder includes a computing device comprising a Fano technique. The Fano technique includes a plurality of variables that are normalized to change a point of reference of the technique. One of the variables is a current node metric. The variables are normalized such that the current node metric is set to approximately zero. Methods for using this decoder in applications that include periodic, hard deadlines such as real-time applications are also presented.

Abstract: The performance of a RAKE receiver for indoor multipath WLAN applications on direct sequence spread spectrum signals having relatively short codeword lengths is enhanced by embedding a decision feedback equalizer structure in the signal processing path through the receiver's channel matched filter and codeword correlator. The decision feedback equalizer serves to cancel both inter-codeword interference (ISI) or “bleed-over” between codewords, and intra-codeword chip interference (ICI) or smearing of the energy within the chips of a respective codeword.

Abstract: A receiver includes a filter for filtering a received signal to produce a filtered signal. A converter converts the filtered signal to a baseband signal that is substantially free of an initial frequency offset and inter-symbol interference (ISI), responsive to a frequency-offset estimate and a restorative signal that compensates for the ISI. A detector detects symbols in the baseband signal to produce a decision signal. A restorative signal generator generates, from the decision signal, the restorative signal responsive to the frequency-offset estimate, such that the restorative signal compensates for the ISI.

Abstract: The apparatus for frequency deviation estimation comprises two CIR estimating units (0) that receive a signal containing a known sequence therein and a plurality of correlation units that calculate the cross correlation between a known sequence recognized on a receiving side and the known sequence contained in the received signal. Each of the CIR estimating units (0) estimate the CIR according to correlation values obtained at prescribed timings from the correlation units. A frequency deviation calculating unit calculates frequency deviation according to the CIR. Therefore, the CIR can be determined with a lesser amount of calculation, so that the hardware can be simplified and the power consumption can be reduced.

Abstract: A high-speed receiver, adapted to receive signals over an input line in the presence of narrowband radio frequency interference (RFI). The receiver includes a RFI canceller module, which is coupled to receive samples of the interference from the input line. The module includes an adaptive bandpass filter, which is adapted to track a dominant frequency of the interference, and to generate a filtered output in a narrow frequency range centered on the dominant frequency. A corrector is coupled to receive the filtered output from the adaptive bandpass filter and to generate, responsive thereto, an estimate of the interference in the signals received by the receiver. A subtractor is adapted to subtract the estimate of the interference from the signals received by the receiver so as to generate a corrected output signal.

Abstract: Techniques for increased pilot detection accuracy are disclosed, which provide the benefits of increased acquisition speed, increased data rate, decreased power, and improved overall system capacity. In one aspect, pilot energy calculations corresponding to PN offsets surrounding the PN offset of a local pilot energy maximum are combined with that local pilot energy maximum resulting in a compensated, more accurate local pilot energy maximum. In another aspect, the combination of nearby energy calculations is combined with the local pilot energy maximum via a function with pre-calculated compensation factors. The pre-calculated compensation factors can be determined to minimize mean-squared error in the resultant compensated local pilot energy maximum. These factors can be calculated based on a matched filter. The techniques described herein apply equally to both access points and access terminals.

Abstract: A system and method for generating an ultra-wide band communication signal having data occurring a specific frequencies precisely excised at baseband. The data to be transmitted is transformed into a function of time where the data to be excised can be removed in the time domain. After the data has been successfully removed in the time domain, the data is then transmitted in the frequency domain in which no data is transmitted at the frequencies where the data was precisely excised.

Abstract: An apparatus comprising a quadrature network, an RF combining circuit and a weighting network. The quadrature network may be configured to generate a first and a second signal in response to an input signal. The RF combining circuit may be configured to generate an output signal comprising the input signal variably phase shifted from a selectable fixed phase starting point in response to the first signal, the second signal and one or more weighting signals. The weighting network may be configured to generate the weighting signals in response to a voltage control signal and one of four possible output selections. The voltage control signal may be configured to control the variable phase shift.

Abstract: A ring oscillator includes an even-numbered plurality of ring coupled delay stages. Each delay stage includes a differential amplifier, a voltage clamping circuit, and a current source. The differential amplifier receives first and second input signals from a preceding delay stage. The differential amplifier provides a first output signal and a complementary second output signal at first and second nodes, respectively. The voltage clamping circuit is coupled between the first and second nodes to limit a peak-to-peak voltage swing of each of the first and second output signals. The current source is coupled to the differential amplifier and varies a bias current in accordance with a delay bias voltage.