Abstract: Emergency call handling may, in the near future, require terminal unit location information to be provided to emergency service centers. Exemplary embodiments of the present invention provide techniques which provide for interaction between an adjunct system whose primary function is to provide terminal unit location information and the radiocommunication system. For example, the location information generated by the adjunct system can be used by the radiocommunication system for other purposes, e.g., dynamic channel allocation.

Abstract: A mobile communications device includes at least two receivers and a memory module. The power consumption of the mobile communications device is controlled by selectively awakening and sleeping the receivers as needed to ensure that the desired quality of reception to check the control channel for messages from an associated base station and to handle incoming communications is maintained. The mobile communications device may operate in single receiver mode or dual receiver diversity mode. In the dual receiver diversity mode, the mobile communications device may switch between one of a number of diversity combining techniques based on the quality of reception.

Abstract: A reduced search symbol estimation algorithm includes a forward recursion, a backward recursion, and a combining step. To reduce complexity, during the forward and backward recursions, the number of survivor states retained at each stage is less than the total number of states of the trellis. The survivor states are selected from a group of candidate states, that are connected by branches to survivors from the previous stage of the recursion. The decoder compares the accumulated path metrics for each candidate state and retains a specified number of states that is less than the total possible number of states. For the forward recursion, the retained states or survivor states, denoted as Qk, are stored along with the corresponding state metrics. For the backward recursion, the retained states, denoted as Rk, are stored along with the corresponding state metrics.

Abstract: A detector selector and method are provided for selecting among detectors, where a less complex detector detects known symbols in a received signal, and a bit error rate for the known symbols is used to determine whether the less complex detection method is sufficient. If the less complex detector is not sufficient, a more complex detector is used to detect the signal. Additionally, assured symbols are used as known symbols to increase the accuracy for the determination of whether the less complex detector is sufficient.

Abstract: A receiving apparatus Doppler spread estimator includes a receiver receiving signals over a transmission channel that varies over time due to fading and converting the signals to digital samples for processing. A stationarizer operatively associated with the receiver stationarizes the digital samples. An estimator is operatively associated with the stationarizer for estimating spectral density of the stationarized digital samples. The correlator is operatively coupled to the estimator for correlating the spectral density estimates with functions corresponding to hypotheses of plural Doppler spread values to select one of the Doppler spread values as an estimate of actual Doppler spread.

Abstract: A receiver in a communications system is operated by receiving a radio communications signal transmitted by a station of the communications system and generating a correlation output representing a correlation of the received radio communications signal and a subsequence of a modulation sequence that is selected based on a correlation between the selected subsequence and the modulation sequence. The receiver is then synchronized based on the generated correlation output. The selected subsequence preferably has an optimal out-of-phase correlation with the modulation sequence. According to an aspect of the present invention, the selected subsequence has a minimum out of phase correlation with the modulation sequence in comparison to other subsequences of the modulation sequence. For example, the selected subsequence may have a “minimum maximum” out-of-phase correlation value, a “minimum aggregate” out-of-phase correlation metric, or a combination thereof.

Abstract: Emergency call handling may, in the near future, require terminal unit location information to be provided to emergency service centers. Independent or quasi-independent systems, sometimes referred to as adjunct systems, can be provided to monitor remote unit transmissions and derive location information for mobile units making emergency access therefrom. Techniques for determining which channels each adjunct receive shall monitor are described herein, as well as specific monitoring techniques. Moreover, the adjunct system can use the received information to provide a second speech path to an emergency service center.

Abstract: Techniques for adapting detection schemes used in receivers for receiving radio signals are described. The received signal is processed to determine, for example, an amount of time dispersion present in the radio channel. Based on this determination an appropriate detection scheme is selected for detecting the transmitted symbols. Various techniques for determining the dispersive or non-dispersive nature of the channel are described.

Abstract: A message, e.g., a control message, a short message, a voice message or a data message, is transmitted on at least one of a first communications channel having a first redundancy level or a second communications channel having a second, higher redundancy level. A radio communications signal is received on one of the first communications channel and the second communications channel. The received radio communications signal is demodulated to recover the message using a first demodulation scheme if the radio communications signal is received on the first communications channel and using a second demodulation scheme if the radio communications signal is received on the second communications channel. According to an aspect of the invention, the received radio communications signal is coherently demodulated if the radio communications signal is received over the first communications channel and non-coherently demodulated if the radio communications signal is received over the second communications channel.

Abstract: Combined equalization and decoding of codewords in a coded modulation symbol sequence that has been received from a channel is accomplished in a number of ways. In an intersymbol interference (ISI) cancellation technique, channel impulse response (CIR) estimates corresponding to each received symbol of the coded modulation symbol sequence are determined. Codeword k of the received symbol sequence is then decoded using a maximum likelihood decoding trellis with a path metric that depends upon the CIR estimates and that includes at least one term representing intersymbol interference resulting from symbols of previously decoded codewords. The decoding step is repeated until all of the codewords of the received coded modulation symbol sequence have been decoded.

Abstract: A digital subscriber loop (DSL) modem and methods for controlling a DSL modem are provided which support simultaneous voice and data communications, wherein the voice communication is provided in a first frequency range and the data communication is provided in a second, non-overlapping frequency range. A voice communication is detected in the first frequency range and the output power associated with the data communication in the second frequency range is reduced when a voice communication in the first frequency range is detected. Furthermore, the coding level associated with the data communication in the second frequency range may be increased when a voice communication in the first frequency range is detected. Also, the start frequency associated with data communication in the second frequency range may be increased when a voice communication in the first frequency range is detected.

Abstract: In a wireless communications system, information is communicated over one of a first communications channel having a first redundancy level or a second communications channel having a second redundancy level based on a determination of communications quality for at least one of the channels. In embodiments of the present invention, communications occur over a first channel, e.g., a “standard” channel until a measure of communications quality for that channel, such as bit error rate or frame error rate, meets a predetermined criterion. When the communications quality meets the predetermined criterion, communications shifts to a “robust” high-penetration channel that utilizes substantially the same amount of spectral resource as the first channel but provides significantly increased redundancy. In other embodiments, a terminal, e.g.

Abstract: In a transmitter for transmitting communication signals across a radio channel, an improved encoder includes a half-rate encoder receiving a digitized speech signal and generating a compressed bit stream at half-rate, and a signal expander receiving the compressed bit stream and generating an expanded bit stream at full-rate for transmission across a radio channel. An improved receiver, receives the transmitted communication signal which is selected from the group consisting of (a) a conventional full-rate encoded digitized speech signal, and (b) a half-rate encoded digitized speech signal including the expanded bit stream. The improved receiver includes a full-rate equalizer, a half-rate equalizer, and a switch initially routing the received digitized speech signal to the full-rate equalizer, wherein the full-rate equalizer demodulates the received digitized speech signal producing a full-rate demodulated signal and dibits of soft information corresponding to the full-rate demodulated signal.

Abstract: Emergency call handling may, in the near future, require terminal unit location information to be provided to emergency service centers. Exemplary embodiments of the present invention provide improved techniques for using a system of monitoring or adjunct stations to provide this location information to the emergency service centers. For example, received signal strength measurements in conjunction with path loss models, alone or in conjunction with either time of arrival (TOA) or time difference of arrival (TDOA) techniques can be selectively used to process received signals and provide location information. Techniques for improving timing estimates are also disclosed.

Abstract: In a transmitter for transmitting communication signals across a radio channel, an improved encoder includes a half-rate encoder receiving a digitized speech signal and generating a compressed bit stream at half-rate, and a signal expander receiving the compressed bit stream and generating an expanded bit stream at full-rate for transmission across a radio channel. An improved receiver, receives the transmitted communication signal which is selected from the group consisting of (a) a conventional full-rate encoded digitized speech signal, and (b) a half-rate encoded digitized speech signal including the expanded bit stream. The improved receiver includes a full-rate equalizer, a half-rate equalizer, and a switch initially routing the received digitized speech signal to the full-rate equalizer, wherein the full-rate equalizer demodulates the received digitized speech signal producing a full-rate demodulated signal and dibits of soft information corresponding to the full-rate demodulated signal.

Abstract: Emergency call handling may, in the near future, require terminal unit location information to be provided to emergency service centers. Exemplary embodiments of the present invention facilitate the provision of this information by reducing a number of monitoring stations needed to track terminal location based upon control channel access. First, mobile units placing emergency calls can be forced to used designated control channels which may differ from control channels to which they are currently listening. Second, mobile units may be required to transmit at greater than specified power levels so that monitoring stations receive their emergency call access.

Abstract: Emergency call handling may, in the near future, require terminal unit location information to be provided to emergency service centers. Exemplary embodiments of the present invention provide improved techniques for using a system of monitoring or adjunct stations to provide this location information to the emergency service centers. For example, either time of arrival (TOA) or time difference of arrival (TDOA) techniques can be selectively used to process received signals and provide location information. Techniques for improving timing estimates are also disclosed.

Abstract: An important consideration in a coded modulation scheme is the choice of the component codes, which has a significant impact on the overall bit error rate performance and which determines the decoding complexity. Methods and apparatus employing product codes are described that can improve the performance of selected classes of information in the coded modulation scheme without affecting the decoding complexity or performance of other classes of information.

Abstract: A system and method for bidirectionally demodulating data symbols transmitted through a communication channel. The method includes sequentially receiving and storing a first plurality of known data symbols, a second plurality of unknown data symbols, and a third plurality of known data symbols. Thereafter, a first block of the unknown data symbols received nearer the first plurality of known data symbols is forward-demodulated. Likewise, a second block of the unknown data symbols received nearer the third plurality of known data symbols is backward-demodulated. The forward- and backward-demodulation of the unknown data symbols determines quality values (figure-of-merits based on at least one of signal power, noise power and a combination of signal power plus noise power) indicative of demodulation qualities of the unknown data symbols that are compared to produce a best direction indication.

Abstract: A low complexity, high performance trellis decoder adapts the complexity of the trellis decoding process based on a current condition of the communications system. A trellis structure of nodes and branches is developed to decode the sequence of symbols received over a communications channel. Each set of nodes in the trellis represents the possible values of a received symbol at one time instant. Each branch defines a specific transition between nodes at different time instants, and each branch has an associated branch metric or weight. A linkage of branches between the nodes and the trellis defines a path through the trellis that represents one possible symbol sequence, and an accumulated metric/weight is generated for each possible path through the trellis. A variable number M survivor paths through the trellis is determined based on their accumulated path metric/weights. The value of the variable M depends on the current condition of the communications system.