Abstract: Methods and apparatus to perform erasure forecasting in communication systems are disclosed. A disclosed example apparatus comprises a forward error correction (FEC) decoder to decode a first codeword and to provide a first error indication for the first codeword, an erasure forecaster to make an erasure decision for a second codeword based on the first error indication, and an erasure forecasting state table including a first field associated with first interleaved data and a second field associated with second interleaved data, the second codeword containing a first element from the first interleaved data and a second element from the second interleaved data.

Abstract: A method for designing an equalizer and tracking performance for upstream PCM in a digital communications network is described. The invention optimizes upstream data rate rates for data transmissions in a network between a client modem a server modem. During training, the upstream channel impulse response is identified compensating for any robbed bit signalling. The upstream transmit equalizer is computed in closed form based on the identified channel. An equalizer in the receiver is also used to track timing and channel variations. The invention approximates bit error rate performance by looking for code violations in the trellis code decoder and tracking their frequency. The bit error rate is used to determine if the current modem parameters need to be re-designed.

Abstract: A method selects the data rate for pulse code modulation upstream transmission by determining an approximate transmit power before the upstream transmission reaches a transmit equalizer based on a recorder power output and a distance halfway between an outermost constellation point and a point following the outermost point. The determined approximate transmit power is multiplied by the power of the transmit equalizer to determine a post-equalizer transmit value. A data rate is selected which is less than a predetermined regulatory limit.

Abstract: A method for constellation design in a telecommunications network using pulse code modulation to transmit data signals upstream between client and server voice-band modems. The invention selects a constellation for transmission over an analog channel of an equivalence class of data points using pulse code modulation based on the presence or absence of robbed bit signaling and interference from echo levels. The constellation is designed by determining noise in a PCM channel using a cumulative distribution function for echo, determining the extent of said noise for an array of possible constellation points, and selecting constellation points such that the largest negative noise of a first point remains above the largest positive noise level of a neighboring second point. Constellations are created off-line and stored for retrieval during modulation depending on the level of the echo.

Abstract: A method for constellation design in a telecommunications network using pulse code modulation to transmit data signals upstream between client and server voice-band modems. The invention selects a constellation for transmission over an analog channel of an equivalence class of data points using pulse code modulation based on the presence or absence of robbed bit signaling and interference from echo levels. The constellation is designed by determining noise in a PCM channel using a cumulative distribution function for echo, determining the extent of said noise for an array of possible constellation points, and selecting constellation points such that the largest negative noise of a first point remains above the largest positive noise level of a neighboring second point. Constellations are created off-line and stored for retrieval during modulation depending on the level of the echo.

Abstract: The present invention relates to a method for filtering and compensating power line interference and DC distortion in PMC upstream data transmissions. To reduce effects of power line interference and DC distortion, the preferred embodiment of the present invention implements extremely narrow IIR notch filters, nominally at 0 Hz, 60 Hz, and 180 Hz (and optionally at 300 Hz) if interference at these frequencies is detected. These filters cause very little distortion. Then, because power line frequencies may drift from their nominal frequencies of the filters are adapted to track the exact frequencies. To effectiveliy eliminate the distortion caused by the IIR filter, the data mode transmit equalizes is adjusted.

Abstract: A method for designing an equalizer and tracking performance for upstream PCM in a digital communications network is described. The invention optimizes upstream data rate rates for data transmissions in a network between a client modem a server modem. During training, the upstream channel impulse response is identified compensating for any robbed bit signalling. The upstream transmit equalizer is computed in closed form based on the identified channel. An equalizer in the receiver is also used to track timing and channel variations. The invention approximates bit error rate performance by looking for code violations in the trellis code decoder and tracking their frequency. The bit error rate is used to determine if the current modem parameters need to be re-designed.

Abstract: For PCM upstream, the analog modem must transmit a filtered sequence of symbols so that the samples of the signal at the input to the codec at the central office (CO) are at a predetermined set of levels. This requires that the analog modem use an 8 kHz symbol rate synchronized to the CO clock. Typical telephone channels have nulls at DC and at 4 kHz. Therefore, for best performance, the signal transmitted by the analog modem should be spectrally shaped to match the channel. The present invention utilizes a generalized Laroia-Tretter-Farvardin (LTF) precoder similar to the one used in V.34. This precoder structure allows spectral shaping and could also allow for constellation shaping gains. Using this precoder structure with spectral shaping has the potential to improve data rates by 3-3.5 kbps.