Vecima Networks Inc.

Eric Salt

Brian Berscheid

Ha Hoang Nguyen

Quang Nguyen

Zohreh Andalibi

Ha H Nguyen

In embodiments of the presently described subject matter, two efficient PAPR reduction methods for OFDM signals based upon the principle of tone reservation and building upon the clipping noise analysis presented in 'Analysis of clipping noise and tone reservation algorithms for peak reduction in OFDM systems,' L. Wang and C. Tellambura,., vol. 57, pp. 1675-1694, May 2008 are provided, each comprising two stages. The first stage is performed offline to prepare a set of cancellation signals based on the settings of the OFDM system. In particular, these cancellation signals are constructed to cancel signals at different levels of maximum instantaneous power that are above a predefined threshold. The second stage is performed online and in an iterative manner to reduce the peaks of OFDM symbols by using the cancellation signals constructed in the first stage.

Papr reduction for OFDM signals

In a DOCSIS transmission network, it is necessary for an upstream receiver to estimate and correct for errors in the carrier frequency of the transmission based upon observations of a preamble sequence. This task is complicated by the fact that microreflections in the upstream channels cause intersymbol interference, which tends to bias the frequency estimation circuit. An economical, ISI-immune algorithm is provided for estimating the carrier frequency of upstream transmissions. The arrangement improves the reliability of the frequency estimates in the presence of ISI, thereby reducing the overhead and increasing the throughput of the upstream channels.

Frequency offset estimator for upstream cable signals

In an RF signal transmission network such as the reverse channels of a coaxial cable network, there is provided at least one adaptive equalizer for pre- or post-filtering inter-symbol interference in the transmitted signals, the adaptive equalizer having a series of coefficients for which values are required. In order to improve the transmission efficiency the preamble used in these channels is shortened by coarsely estimating the channel using a short 'unique word' placed at the beginning of the equalizer training sequence. The coarse channel estimate is crudely inverted to produce a set of equalizer coefficients which partially equalize the channel. By initializing the adaptive equalizer with these approximate coefficients, it is possible to reduce the length of the training sequence needed for the equalizer to converge.

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Eric Salt