摘要:
An apparatus and method for demodulating an FM RF signal is presented. An Adaptive Differentiate Cross Multiply (ADCM) system in which the energy estimate of the desired on-channel RF is generated using adaptive filtering. The adaptive filter includes low pass filtering of the instantaneous energy estimate. The bandwidth of the LPF is adjusted in real time based on the received signal strength energy estimate, the periodicity of any changes in the energy estimate, AGC setting for the receiver, and/or the type of sub-audible signaling applied to the RF signal if known. After the bandwidth is set, the optimum filtered energy estimate is applied to the system to demodulate the received information free from distortion artifacts associated with IQ imbalance. A normalized signal in the ADCM system is clipped by a limiter whose clipping threshold is equal to a maximum gain of differentiators in the ADCM system.
摘要:
A method of detecting an on-channel signal and synchronizing signal detection with correcting for DC offset errors in a direct conversion receiver is presented. A received signal is digitized, and a state machine operates to detect the presence of an on-channel signal. If the signal is not detected, a mixed mode training sequence is initiated in which the DC offset errors in both an analog and digital received signal path are corrected. While training, processing of the digitized samples by a digital signal processor and a host controller is suspended (while they are put into battery save mode) and the gain provided to subsequently received signals is minimized. The DC offset correction circuitry is bypassed and put into battery save mode at predetermined periods when DC offset correction is not performed.
摘要:
An adaptive dc compensation technique (100) eliminates dc error for both digital and constant envelope modulation protocols (108). For analog modulation, a dc averaging technique utilizes piece-wise continuous dc averaging (110) that calculates discrete dc error values over a variable number of samples (112) and updates the dc compensation value as a fixed value for a specified sample length (114). The piece-wise “update-and-hold” technique (110) results in a pseudo high pass filter response with an equivalent corner. For digital modulation, a continuous high pass filter section of the receiver is enabled (120).
摘要:
A method for transmitting a communication generated by an originating device to a target device using a repeating device is provided. In the method the communication is transmitted from the originating device and received at the repeating device. A repeater request sequence is transmitted from the originating device and retransmitted from the first repeating device to the target device before the repeater request sequence is received at the first repeating device.
摘要:
Methods of enabling late entry into an on-going spread spectrum call are described. A late join frame replaces, and has the same size as, a traffic frame. A late join slot in the late join frame contains sufficient information in preamble and sync subframes to permit a target to join the call. The traffic slots in the late join frame replicate data such that call quality of the call is substantially unaffected if one of the remaining traffic frames is not received. The preamble and sync subframes frequencies may be the same as, or different from, preamble and sync frames frequencies during a call establishment phase of the call. If different, the preamble and sync subframes frequencies are selected from one or more frequencies. Use of the preamble and sync subframes frequencies is compensated for when selecting the traffic slot frequencies to obtain uniform utilization of the spectrum.
摘要:
A method for correcting I/Q imbalance in a received signal is disclosed. The method includes the steps of grouping (202) the received signal into a predetermined number of clusters, and determining (204) at least one coefficient value by feeding the predetermined number of clusters into a nested loop. The method further includes computing (206) a compensation value based on the at least one coefficient value, and correcting (208) the I/Q imbalance in the received signal by using the compensation value.
摘要:
Briefly, according to the invention, a receiver (100) for receiving and decoding a carder signal is described. A carrier signal is modulated with an information signal which has one of a plurality of formats. The receiver includes a circuit (104) for receiving and demodulating the carrier signal to produce a demodulated signal. The receiver (100) also includes a digital signal processing subsystem (108) for calculating the correlation function of the demodulated signal and based on this correlation function classifies the format of the demodulated signal. A decoder (118) is further included in the receiver (100) to decode the demodulated signal once it has been classified.
摘要:
A radio system for locating a radio transceiver configured to exchange voice or data with a plurality of base stations on a narrowband channel is described. The system includes the radio transceiver that exchanges voice or data on the narrowband channel with a base station of the plurality of base stations and also to periodically transmit a chirp signal to the plurality of base stations. The radio system also includes the plurality of base stations each with a matched filter configured to receive the periodically transmitted chirp signal and to triangulate a location of the radio transceiver using the received chirp signal.
摘要:
A public/private communication system is provided which includes a public communication device 100, a private communication device (102) and a radio accessory extension (RAE) 200 coupled therebetween. The RAE (200) of the present invention provides audio and/or display capability which allows the public communication device to operate as a private communication accessory. Methods (300, 400 500) provide for the configuration and prioritization of private and public calls through the three devices to ensure that private calls will take priority and public calls will be received on the public communication device and handled appropriately.