Abstract: A method 600 of selecting an ARQ method for retransmitting a data frame based on an accumulated signal to noise ratio (SNR) of systematic bits in the data frame at a receiving unit 508. The sending unit 500 tracks the accumulated SNR of systematic bits by using channel SNR measurement reports sent by the receiving unit 508. The method utilizes Chase combining of re-transmitted systematic bits (via Partial incremental redundancy transmissions) until the accumulated SNR of the systematic bits has reached a suitable value, and then switches to sending only parity bits (via Full incremental redundancy) in retransmissions. In addition, the method alters the allocation of resources, such as code power, to provide only that necessary for successful decoding of the transmitted frame. The sending unit 500 informs the receiving unit 508 of the type of transmission, number of the transmission and/or resource allocation associated with the data frame.

Abstract: A transmitter uses adaptive array weights to modify a gain and a phase of a communication signal to produce a plurality of element communication signals coupled to antenna elements in an adaptive array antenna. The communication signal is transmitted along with an element pilot signal that is coupled to one of the elements in the adaptive array antenna. In a receiver, the communication signal is received, and the element pilot signal is received. Thereafter, the adaptive array weights used at the transmitter are estimated in response to comparing characteristics of the received element pilot signal to characteristics of the received communication signal.

Abstract: A digital receiver (200) and transmitter (300), wherein the digital receiver includes a plurality of antennas (202) for receiving uplink radio frequency signals; a plurality of analog to digital converters (210) for converting the received radio frequency signals into digital signals; a switched digital down converter (214) for down converting one of the digital signals to a baseband IF signal; and a channel processor (228) for recovering one of a plurality of communication channels contained within the baseband IF signal.

Abstract: An apparatus that includes a logarithm based processor (216) having at least one digital logarithm converter (202) and a power amplifier (208) responsive to the logarithm based processor (216).

Abstract: An apparatus for amplifying a signal that includes a digital processor (12) producing a first digital signal (20) and a second digital signal (22), a pulse width modulator (32) receiving the first digital signal (20) and producing a pulse width modulated signal, an amplitude restoration module (37) responsive to the pulse width modulator (32), the amplitude restoration module (37) producing an amplitude envelope signal, a frequency upconverter (16) receiving the second digital signal (22) and producing a frequency modulated signal, and a power amplifier (18) responsive to the frequency upconverter and the amplitude restoration module (37). The power amplifier receives the frequency modulated signal and the amplitude envelope signal and produces an amplified output signal.

Abstract: A digital radiotelephone system employs vocoders to convert between analog speech and a digital format suitable for transmission via radio. Under most circumstances, the highest data rate is selected for optimum audio quality. When the system occupancy exceeds a particular threshold, as detected at the fixed site of the system, some or all of the vocoders are instructed to switch to a lower data rate to provide for an increase in the number of communication channels. Further, a portable subscriber unit may autonomously change its vocoder data rate depending upon the charge state of its battery.

Abstract: A multi-channel digital transceiver (400) receives uplink radio frequency signals and converts these signals to digital intermediate frequency signals. Digital signal processing, including a digital converter module (426), is employed to select digital intermediate frequency signals received at a plurality of antennas (412) and to convert these signals to baseband signals. The baseband signals are processed to recover a communication channel therefrom. Downlink baseband signals are also processed and digital signal processing within the digital converter module (426) up converters and modulates the downlink baseband signals to digital intermediate frequency signals. The digital intermediate frequency signals are converted to analog radio frequency signals, amplified and radiated from transmit antennas (420).

Abstract: An information gap in an ADPCM signal is detected in one or both of a transmitter or receiver. This detection can be accomplished using a voice activity detector. When an information gap is detected, a clock signal to the encoder and/or decoder is interrupted. Alternatively, null frames can be inserted into the encoder and/or decoder. When null frames are used, it is preferable to insert comfort noise into the signal output from the decoder.

Abstract: A method of synchronizing to a signal includes first performing a rough synchronization and then a fine synchronization to a sync word. The fine synchronization includes comparing a stored portion of the sync word to a received portion. By adjusting the timing and then performing additional correlations, the timing for the best correlation can be obtained. The bit clock is then adjusted so that subsequent data samples can be taken as close to bit center as possible.

Abstract: A radio (100) transmits and receives encrypted signals having unencrypted key identifiers, allowing other radios having the corresponding key identifiers and encryption keys to communicate with radio (100). Prior to transmitting an encrypted message, radio (100) selects a unique key identifier automatically and uses the corresponding encryption key to encrypt the message that will be transmitted. Radio (100) transmits the key identifier in an unencrypted format with the encrypted message in order to allow other radios to determine the encryption key used in encrypting the message. When receiving an encrypted message, radio (100) uses the predetermined process stored in the radio (100) to properly select the proper encryption key for use in decrypting the incoming message.

Abstract: A trunked communication system (400) transmits and receives encrypted signals over the system control channel (402). The trunked system (b 400) includes a plurality of radios (300) which can communicate with the communication system via control channel (402). By using control information signals and system information signals radios (300) can determine if it they are capable of decrypting the encrypted control information signals sent over the control channel (402). This is done by first determining if the encryption identification field found in the unencrypted system information signal matches an encryption identification field found in radio (300). If a match is found between the radio's encryption identification and the encryption identification field in the system identification signal radio (300) loads the encryption into the encryption circuitry in order to successfully decrypt the control information signals.

Abstract: A method of voice communication is provided to avoid disruption in the received voice signal. A compressed voice signal is received occupying 100% of the audio time during a lesser percentage (352) of the radio frequency (RF) time (302). An informational signal is also received during at least a portion of a remainder (354) of the RF time. Scanning for another channel, receiving data or embedded control signals may occur during at least a portion of the remainder (354) of the RF time saved.

Abstract: A communication device (10) comprises an input for receiving a first audio signal (12) and an input (36) for receiving a second audio signal. The communication device (10) also includes a circular buffer (34) for storing the output digital audio signal (12) and for producing an output audio signal (20). The communication device (10) determines whether at least a portion of the output audio signal (20) is present in the second audio signal. If such a portion is present, the communication device (10) subtracts the portion of the output audio signal (20) from the second audio signal, to produce a third audio signal (26). A threshold detector, responsive to the third audio signal, produces a first control signal, when the level of the third audio signal increases to at least a first predetermined level, and a second control signal, when the level of the third audio signal decreases to a value lower than a second predetermined level, where the second predetermined level is lower than the first predetermined level.

Abstract: A sampled input signal is quantized to lie within a predetermined magnitude range. The quantized input signal is coupled to a bandpass filter which selects the digital signal to be processed. The bandlimited signal is then coupled to a feedback automatic gain control circuit which removes the slow variations in the envelope of the input signal. The output of the feedback AGC circuit is then coupled to a feedforward AGC circuit which removes the fast variations in the envelope of the input signal. The feedback AGC and the feed forward AGC circuits share a common envelope detector, that is composed of a squaring operation and low pass filter operation. The feedback AGC circuit also reduces the dynamic range of the input signal which is required of the feed forward AGC circuit. The processed signal is then demodulated with a quadrature FM detector. The output of the FM detector may be low pass filtered, and coupled to a D/A converter to produce an audio message signal.