Abstract:
A method for automatically selecting optimum frequencies for transmitting data from remote terminals (120, 315a-315c) upstream to a system manager (310) is provided. The system manager (310) initially selects a set of frequencies from a larger set of available frequencies and transmits a comand downstream to each remote terminal (120, 315a-315c) indicating which frequencies to use. Each remote terminal (120, 315a-315c) transmits data messages on each selected frequency in response to addressed commands generated by the system manager (310). The system manager (310) receives and counts the data messages on each of the frequencies, and, after a statistically significant number of messages are received, removes from use the frequency with the lowest number of data messages received. This frequency is replaced with either (1) a previously untried frequency, or if all frequencies have been tried, (2) a previously tried frequency with the highest number of data messages received.
Abstract:
A communications system (30') may include a transmitting device (31') for transmitting a modulated signal therefrom based upon input data, and a receiving device (32') for receiving the modulated signal from the transmitting device. The transmitting device (31') may include a modulator (35'), a baseband injected pilot carrier (BPIC) generator (33') for generating BPIC data, and a framer (48' ) for interleaving BPIC data with the input data to define data frames input to the modulator. The receiving device (32' ) may include a demodulator (41'), a frame recoverer (49'), and a BPIC detector (40' ) cooperating with the demodulator for demodulating the modulated signal from the transmitting device (31') based upon the BPIC data and cooperating with the frame recoverer for recovering the data frames also based upon the BPIC data.
Abstract:
A method and apparatus for digitally demodulating QPSK signals includes a first portion in which the digitally sampled data burst is resampled with a plurality of predetermined timing hypotheses. The timing offset is determined according to an analysis of the resampled data. The digitally sampled data burst is then resampled according to the timing estimation. Modulation of the resampled data burst is then removed by twice squaring the complex I/Q pairs. The data with the modulation removed is then subjected to a Chirp-Z Transform to move the data into the frequency domain. The highest spectral power is used to determine the frequency offset. The phase offset is determined and the resampled data burst is derotated and dephased according to the phase offset and the frequency offset.
Abstract:
A method and apparatus is provided for facilitating coherent communication reception. A received reference symbol coded spread-spectrum communication signal is despread with a spreading code to derive a stream of reference samples (152) and a stream of data samples (158). The channel response is estimated by utilizing the stream of reference samples (152). An offset frequency detector (443) determines an offset to be applied to the received signal via a frequency locked loop (456), while a timing control (176) compensates for slow timing drift and fast fading based on power estimates derived from the stream of reference samples (152) and/or the stream of data samples (158). A rate estimator determines the rate at which the information was encoded, and the rate information is used to optimize the timing control (176), frequency offset detector (443) and channel estimator (154). Thus an improved detection of estimated data symbols from the stream of received data samples (158) is provided.
Abstract:
Automatic level calibration apparatus for transmitting data from a cable television terminal to the headend of a cable television system comprises programmable transmitter apparatus of the terminal, programmable receiving apparatus at the headend and a calibration controller. Responsive to an addressed command from the headend, the programmable transmitter apparatus returns a sequence of levels at a particular calibration frequency. The programmable receiver apparatus determines an indication of the received signal strength of each of the levels of the sequence of levels. The controller determines an optimum level for transmissions from the terminal.
Abstract:
A method formodulating and demodulating PSK signals, and particularly a device BPSK for demodulating BPSK signals comprising: - a signal splitter (1) through which an input signal (10) with two bits which encode a type of transition technique, selected from direct multiplication, constant envelope with positive frequency shift and constant envelope with negative frequency shift, is injected into four second-harmonic injection-locked oscillators (ILO 1 , ILO 2 , ILO 3 , ILO 4 ); - the four second-harmonic injection-locked oscillators (ILO 1 , ILO 2 , ILO 3 , ILO 4 ), locked to the input signal (10) in absence of bit transitions; - two conversion mixers (M1, M2) to obtain respectively the output signals (BHF, BLF), both down-conversion mixers (M1, M2) comprising a mixer (2) and a low-pass filter (3); - means for detecting whether there is a bit transition in the output signals(BHF, BLF) and if so, determining the type of transition technique used for modulating the input signal (10).
Abstract:
A communications system (30') may include a transmitting device (31') for transmitting a modulated signal therefrom based upon input data, and a receiving device (32') for receiving the modulated signal from the transmitting device. The transmitting device (31') may include a modulator (35'), a baseband injected pilot carrier (BPIC) generator (33') for generating BPIC data, and a framer (48' ) for interleaving BPIC data with the input data to define data frames input to the modulator. The receiving device (32' ) may include a demodulator (41'), a frame recoverer (49'), and a BPIC detector (40' ) cooperating with the demodulator for demodulating the modulated signal from the transmitting device (31') based upon the BPIC data and cooperating with the frame recoverer for recovering the data frames also based upon the BPIC data.