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EXCLUSION BAND FILTERING TO REMOVE ICI DUE TO NON-OFDM/A SIGNALS WITHIN THE FFT CAPTURE BAND OF AN OFDM/A RECEIVER

IP.com Disclosure Number: IPCOM000246343D
Publication Date: 2016-Jun-01
Document File: 12 page(s) / 1M

Publishing Venue

The IP.com Prior Art Database

Related People

Rick Meller: AUTHOR [+3]

Abstract

Application of a filter prior to the Fast Fourier Transform (FFT) of a DOCSIS 3.1 receiver attenuates the non-OFDM/A signals occupying the exclusion bands within the FFT capture bandwidth and reduces the Modulation Error Ratio/Signal-to-Noise Ratio (MER/SNR) degradation due to spectral leakage. This was shown to provide much better performance than the traditional method of just adding guard band separation in the DOCSIS 3.1 required case of spectral co-existence. The filter coefficients need only be computed once or once per exclusion band definition change as configured by the MSO. An implementation can be a receive only approach exploiting the exclusion band information available/known to the OFDM/A receivers, this requires D3.1 receive silicon changes to incorporate the new filtering function. It is also possible to tag each exclusion band for filtering/not filtering.

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EXCLUSION BAND FILTERING TO REMOVE ICI DUE TO NON-OFDM/A SIGNALS WITHIN THE FFT CAPTURE BAND OF AN OFDM/A RECEIVER

AUTHORS:

   Rick Meller Koen Van Renterghem Xing Gao

CISCO SYSTEMS, INC.

ABSTRACT

    Application of a filter prior to the Fast Fourier Transform (FFT) of a DOCSIS 3.1 receiver attenuates the non-OFDM/A signals occupying the exclusion bands within the FFT capture bandwidth and reduces the Modulation Error Ratio/Signal-to-Noise Ratio (MER/SNR) degradation due to spectral leakage. This was shown to provide much better performance than the traditional method of just adding guard band separation in the DOCSIS 3.1 required case of spectral co-existence. The filter coefficients need only be computed once or once per exclusion band definition change as configured by the MSO. An implementation can be a receive only approach exploiting the exclusion band information available/known to the OFDM/A receivers, this requires D3.1 receive silicon changes to incorporate the new filtering function. It is also possible to tag each exclusion band for filtering/not filtering.

DETAILED DESCRIPTION

    Orthogonal Frequency Division Multiplexed (OFDM/A) signals are received via a Fast Fourier Transform FFT process. In DOCSIS 3.1, exclusion bands are contained within the receiver's FFT capture band. These exclusion bands can/will contain non- OFDM/A signals for required revenue generating services that create substantial Modulation Error Ratio/Signal-to-Noise Ratio (MER/SNR) degradations to the OFDM/A received signal by way of the FFT process. These degradations are a serious issue for

Copyright 2016 Cisco Systems, Inc.

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DOCSIS 3.1 due to the very large modulation densities DOCSIS 3.1 must support (e.g. up to 16384-QAM).

    The traditional approach to dealing with the OFDM/A signal degradation due to non-OFDM/A signals is to move the OFDM/A channel completely away from the non- OFDM/A signal in time or in frequency. This cannot be done in DOCSIS 3.1 due to the very large bandwidth of the OFDM/A channels and the legacy signal's channel line-up requirements that are always on. Another approach if both OFDM/A and non-OFDM/A must share the spectrum is to increase the guard band separation between the two, however, this is spectrally inefficient since the guard band separation needs to be quite large for the kind of performance needed for D3.1 high order constellations, (e.g., up to 16384-QAM).

FIG. 1

    FIG. 1 shows a CW tone at the same integrated power level of the OFDM signal at exactly a frequency that falls in the center bin of 4096 of the receive FFT in the exclusion band. No noticeable degradation to the OFDM 512 QAM constellation is observed.

Copyright 2016 Cisco Systems, Inc.

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FIG. 2

    FIG. 2 shows a CW tone at the same power level of the OFDM signal at a frequency that falls exactly between bin 4096 and 4097 (4096.5) of the receive FFT in the exclusion band. There is obviously large degradation to the 512 QAM constellation...