Power line interference compensation in PCM upstream transmissions

#None

#The present invention relates generally to the removal of line noise in a PCM upstream data communications system. More particularly, the present invention relates to a method for filtering and compensating power line interference in PCM upstream data transmissions.

#Personal computers connecting to networks through the public switched telephone system (PST) typically use a modem to dial-up a network connection through analog telephone lines. These client, or end user, modems transmit data signals converted to digital source through an analog channel through a network. Due to the increase in data, voice, and facsimile traffic over the telecommunications infrastructures methods to increase the digital and analog transfer rates through modems over telephone lines are extremely useful and necessary to adhere to International Telecommunication Union (ITU) standards.

#Preferred embodiments of the invention are discussed hereinafter in reference to the drawings, in which:

#FIG. 1 is a diagram of a PCM a communications network;

#FIG. 2 is a diagram of a PCM upstream channel;

#There is described herein a technique for equalizer designs and channel error detections for a PCM upstream data transmission between a digital PCM server modem and a PCM analog client modem.

#When connecting two modems over the public switched telephone network (PSTN), digital data from a central office (CO) often must be translated from digital signals at the server modem into analog tones for transmission over a local analog line to a client modem. At each client modem, the received analog waveform is sampled and quantized by an analog to digital convertor (A/D). A PCM upstream network with a voice-band modem 12 connection is illustrated in FIG. 1. The network 10 includes a V.92 PCM client modem from an end user's personal computer 14 connected to an analog telephone line 16, or channel. The analog channel 16 is connected to a telephone company central office (CO) 18 wherein the analog levels are quantized using a μ- or A-law codec 20. There is also a digital network 22 which is interconnected to the CO 18 and to the digital transmission channel, which may comprise a T1, E1, or ISDN line 24. A V.92 server modem 26 completes the connection in the upstream direction. Data may transmit in either the downstream direction (server to client modem) 28 or the upstream direction 30 (client to server modem).

#For digital symbols transmitted over the analog channel to be reasonably free of intersymbol interference over the frequency spectrum used by the symbols, modems employ adaptive filters called equalizers. Equalization is a technique used to compensate for distortion in analog signal lines. One of the distortions which is compensated for is intersymbol interference. Equalizers in a receiver neutralize intersymbol interference which would cause high bit error rates if left uncompensated. Equalization is accomplished by passing the digital signal through a filter whose tap coefficients are adjusted so that the combination of channel plus equalizer is some known response. When the channel is properly equalized, data can be recovered reliably from the received symbols. Modems equalize the incoming signals by employing various types of equalizers include linear equalizers, decision-feedback equalizer, and trellis-based Viterbi equalizers. The equalizer taps of a minimum mean-square-error decision-feedback equalizer (MMSE-DFE) can be directly computed by Givens rotations without back-substitution and matrix-vector multiplication, as discussed in the paper “An Improved Fast Algorithm for Computing the MMSE Decision-Feedback Equalizer” by Bin Yang, Int. J. Electron. Commun., 51 (1999) No. 1, 1-8, which is incorporated herein by reference.