摘要:
Apparatus and methods of compensating for distortions introduced in communication signals received over a telephone network. An adaptive linear equalizer (LE) pre-filter is used for filtering incoming sampled communication signals received via the telephone network transmission medium. An adaptive decision feedback equalizer (DFE) is used in conjunction with the LE to provide error filtering as a hybrid equalizer system to determine which of a plurality of communication states of the sampled communication signals as an accurate estimate of the originally transmitted signals over the transmission medium, responsive to the filtered communication signals from the LE. An error signal is generated relative to the difference between the determined states of the decision mechanism of the DFE and the filtered communication signals from the LE. Further, an error filter provides a filtered output of the generated error signal, wherein the error filter has an error filter characteristic defined in accordance with the known telephone network transmission medium. The LE for the received sampled communication signals has a LE pre-filter characteristic defined in accordance with the filtered output of the error filter, using a recursive least-mean-square (LMS) technique.
摘要:
A method in which correctable I/Q imbalance errors in a complex receiver can be detected and compensated for digitally without the use of special calibration signals. Differential D.C. offset errors are compensated by averaging the incoming I.sub.d and Q.sub.d digital signals and subtracting from them an expected value of differential D.C. offset, for example, computed from the long term average of the I and Q signals to create I' and Q' signals. Differential gain imbalance errors are corrected by calculating a root means square average of the I' and Q' digital signals and applies to them compensation coefficients K.sub.x and K.sub.y determined from either the RMS average or from a Stochastic Gradient Algorithm. The DSP compensates for the quadrature phase errors by calculating a compensation matrix which is independent of the frequency of the carrier and applies the compensation matrix to the I' and Q' digital signals. The compensation matrix for quadrature phase errors is completely independent of the frequency of the input carrier signal supplied to the complex receiver, and is not dependent on the use of a calibration signal. The compensation may be performed as a step in calibration of the complex receiver, or continuously.
摘要:
The present invention provides a method of generating a signal that may be used to determine the characteristic response of a communication channel that utilizes the public Digital Telephone Network (DTN). The channel includes the DTN, which may have Network Digital Attenuators (NDA) and/or Robbed Bit Signalling (RBS), and a Digital-to-Analog Converter (DAC), (also known as a codec), as well as the analog characteristics of the local loop, typically a twisted pair of copper wires. The present invention provides a method and apparatus to determine the optimal sampling instant of the received data stream. The present invention provides a probing signal that is well-suited for use in determining the channel's response to a known sequence of PCM codes used as data symbols. This is especially useful in so-called PCM modulation schemes that utilize the DTN, where knowledge of network and DAC distortion predicates the selection of available PCM codes used to represent data. This information is also useful when the data receiver, or PCM modem, makes determinations of which codes were actually sent.
摘要:
The present invention provides a method of generating a signal that may be used to determine the characteristic response of a communication channel that utilizes the public Digital Telephone Network (DTN). The channel includes the DTN, which may have Network Digital Attenuators (NDA) and/or Robbed Bit Signalling (RBS), and a Digital-to-Analog Converter (DAC), (also known as a codec), as well as the analog characteristics of the local loop, typically a twisted pair of copper wires. The present invention provides a method and apparatus to determine the optimal sampling instant of the received data stream. The present invention provides a probing signal that is well-suited for use in determining the channel's response to a known sequence of PCM codes used as data symbols. This is especially useful in so-called PCM modulation schemes that utilize the DTN, where knowledge of network and DAC distortion predicates the selection of available PCM codes used to represent data. This information is also useful when the data receiver, or PCM modem, makes determinations of which codes were actually sent.
摘要:
The present invention provides a method of generating a signal that may be used to determine the characteristic response of a communication channel that utilizes the public Digital Telephone Network (DTN). The channel includes the DTN, which may have Network Digital Attenuators (NDA) and/or Robbed Bit Signalling (RBS), and a Digital-to-Analog Converter (DAC), (also known as a codec), as well as the analog characteristics of the local loop, typically a twisted pair of copper wires. The present invention provides a method and apparatus to determine the optimal sampling instant of the received data stream. The present invention provides a probing signal that is well-suited for use in determining the channel's response to a known sequence of PCM codes used as data symbols. This is especially useful in so-called PCM modulation schemes that utilize the DTN, where knowledge of network and DAC distortion predicates the selection of available PCM codes used to represent data. This information is also useful when the data receiver, or PCM modem, makes determinations of which codes were actually sent.
摘要:
A signal for exception processing is provided. The signal includes a first sequence of PCM codewords. Each PCM codeword in the sequence has a magnitude corresponding to a maximum point within an active constellation. The signal further includes a timing mark following the first sequence. In addition, a client device is provided. The client device includes a receiver and a detector coupled to the receiver. The receiver is coupled to an analog subscriber loop and has a decision feedback equalizer. The receiver provides a decision corresponding to data sent by a digital data source. The detector monitors the decision of the receiver to determine when an exception has been requested by the digital data source. Further, a method of requesting a change in a mode of operation of a client device when the client device is operating in a data mode is provided. The data mode includes receiving signal points selected from an active constellation and deciding which points have been received to thereby recover data. The method includes the step of transmitting, to the client device, a predetermined sequence of points from the active constellation. Each of the points in the predetermined sequence has the same index relative to a maximum point within the active constellation. The method further includes the steps of receiving the transmitted sequence, and detecting the predetermined sequence.
摘要:
An electronic transmit/receive device employs an equalized envelope derived timing system to compensate for differential time delay occurring at upper and lower bandedges of the received signal. The received signal is split into a complex signal and the envelope derived timing system is utilized to perform amplitude and delay distortion compensation on the received signal. The amplitude and delay distortion compensation is performed by employing bandedge filters which preferably take the form of Finite Impulse Response (FIR) filters.
摘要:
Methods and apparatus for routing messages between an end node and an access node via another access node are described. Physical layer identification information is used when identifying a remote, e.g., adjacent, access node as a message destination. Thus, when a connection identifier based on one or more physical layer identifiers is available to a wireless terminal, e.g., from one or more downlink signals received from a destination access node, the wireless terminal can use the connection identifier corresponding to the destination node to route a message via an access node with which it has an established uplink connection. Such connection identifier information can be used even when other addressing information, e.g., network layer address information, associated with the destination access node, may not be available to the wireless terminal.
摘要:
Methods and apparatus for using end nodes, e.g., wireless terminals, to discover base stations and communicate information about discovered access nodes, e.g., base stations, to other access nodes in a system are described. As the wireless terminal roams in the system and new access nodes are encountered, one or more physically adjacent access nodes will be informed of the presence of the new access node as a result of communications with the wireless terminal. A message indicating an access node's inability to route a message to another access node which is known to a wireless terminal may trigger the wireless terminal to begin the process of updating access node routing and neighbor information.
摘要:
A base station uses a common link layer controller for multiple physical attachment points to facilitate concurrent wireless connections between different sector physical attachment points and a wireless terminal using the same link layer link. A wireless terminal maintains multiple simultaneous wireless connections for the same link layer link. A packet of user data is fragmented into a plurality of grouping of MAC frames, thus a packet portion can be communicated over a connection. A single packet is sometimes communicated with different portions conveyed over different wireless connections. Automatic repeat request, using the common link layer controller, allows for retransmission of a packet portion over a different connection than it was initially transmitted over. A wireless terminal sends connection request messages including lists of link layer identifiers associated with the wireless terminal. A base station responds with an indication of whether logical link state was already present.