摘要:
In a PCM modem system in which equivalence classes are used to communicate information from a transmitter to a receiver, a method is provided to solve the problem of 180° phase reversals in the communications channel which result in a garbled transmission. This is accomplished by remapping the equivalence classes into a form that can be differentially encoded and decoded such that equivalence class identity is not lost during a phase reversal of the channel.
摘要:
A system and method for shifting the relative phases of a PCM data frame and a network RBS frame by one or more symbols is disclosed. The method includes determining whether or not RBS is present. If RBS is present, the slots affected by RBS are identified. Next it is determined what data slots, if any, are affected by encoding. The PCM data frame is shifted so the RBS constraint and the encoding constraint do not coincide at any particular data slot. For one particular PCM upstream modulation scheme, the digital modem adjusts the relative phases of the data-mode frame and network RBS frame such that a minimum number of trellis-modified symbols fall on network RBS affected slots. This information is transmitted to an analog modem. The amount of shift can be conveyed to an analog modem in the same data sequence used to send upstream constellation sets and mapping parameters during an initial training sequence. The present invention improves the performance of any PCM modem that employs a data frame structure in which not all symbols are subject to the same constraints, for example, due to trellis coding.
摘要:
In a PCM modem system, a method and apparatus for optimizing the fractional sampling phase offset in the upstream direction to maximize the upstream data rate utilizes a probing signal from the analog modem generated during startup and having at least two distinct phases of a pure tone, with the probing signal being detected at the digital modem where an optimum sampling phase value is calculated. From this calculated value, a signal representing the appropriate amount to delay the input data stream is transmitted back to the analog modem for adjustment of the fractional sampling phase so that the fractional sampling phase offset at the central office quantizer is optimized.
摘要:
In a full duplex PCM modem system, a method and apparatus is provided for robust measuring of the communications channel in which the digital modem's transmitter is silenced during generation of training signals by the analog modem, with the silencing of the digital modem's transmitter eliminating problems associated with echo during channel measurement at the digital modem. The above method thus eliminates echo during channel estimation and removes any dependencies on the performance of the echo canceller normally used.
摘要:
A method and apparatus is provided for controlling the transmit power of an analog modem when the transmit power level does not match the desired transmit power level, thus conforming to FCC regulations on transmit power and/or eliminating non-linearities associated with higher than required power levels and loss of signal-to-noise ratio and concomitant at loss of data rate if the transmit power levels are less than that desired. In one embodiment, the power level at the analog modem is sensed to ascertain if it is not at the desired transmit power level, with adjustment being provided by transmitting the desired change in the transmit power level to the digital modem, whereupon mapping parameters are redefined by adjusting the number of equivalence classes, thus to adjust transmit power at analog modem.
摘要:
A system and method for adjusting the phase of the analog signal produced by an analog modem connected to a digital modem over a telephone network. The digital portion of the telephone network is locked to the network clock, and the modems have no control over the sampling timing or rate as the analog signal is sampled and quantized by a codec. If the analog signal is shifted in phase relative to the network clock, then the codec may be sampling at unresolvable points on the analog signal, thereby causing errors and a decrease in the usable bandwidth for transmitting data. The analog modem symbol frequency is locked to the clock of the digital network using loop-back timing. A phase estimate is computed using the quantized samples of a known reference signal. Next, a “phase offset” is calculated by comparing the phase estimate to an optimum phase value. Then the digital modem sends the calculated phase offset information to the analog modem. The analog modem then delays its transmitted signal by the phase offset. After the phase of the analog modem's transmitter is adjusted, the analog signal reaches the codec at the phase desired by the digital modem.
摘要:
In a full duplex PCM modem system having an analog and digital modem, a method and apparatus is provided for on-the-fly reconfiguring of analog or digital modem transmitter parameters without switching back to a retrain or startup mode. In one embodiment, the transmitter parameters for the analog modem are modified to take into account channel impairments, in which modified precompensation parameters are sent from the digital modem to the analog modem without switching out of the data mode. In another embodiment, transmit power levels sensed at the analog modem which are non-optimal are adjusted by new parameters sent from the digital modem without having to switch back to the startup mode. In a further embodiment, transmitter parameters in the digital modem are reconfigured to provide more an increased downstream data rate from the digital modem upon sensing improvement in the quality of the downstream channel without switching to the startup mode.
摘要:
A method and apparatus is provided that dynamically allocates processor resources to data transfer-related operations, minimizing the processor resources used for data transfer-related operations and maximizing the processor resources available for other applications. The apparatus comprises a communication device (104), comprising a processing unit (204) and a complexity controller (206), which communication device (104) is capable of executing multiple data transfer-related operations and is highly configurable. The complexity controller (206) monitors a condition of a communication channel (102) and determines the best configuration of communication device (104) in regard to processor resource utilization to meet a given Quality of Service requirement for the condition of channel (102) and to maximize the processor resources available for other applications, such as data terminal equipment user applications (108) or signal processing by other communication devices using the same host processor.