By Richard S. Prodan, Ph.D., Comcast Cable
Full Duplex Data-Over-Cable Service Interface Specifications (DOCSIS®)(FDX) technology has been realized in a custom system on a chip (SoC) successfully implemented in an operational FDX remote PHY (R-PHY) node design. A new implementation of this SoC is also being adapted for use in an FDX amplifier utilizing the same echo cancellation technology employed in the node. FDX amps will begin to replace conventional mid-split amps and will support concurrent bidirectional communication within the same bandwidth. These amps are more complex to configure for FDX operation. Completely new and more complicated procedures for configuring these amplifiers are needed to install these amps. Additionally new procedures to maintain proper operation of these new amplifiers will be needed. Embedded digital signal processing within DOCSIS 4.0 FDX amplifiers provides the ability to automatically configure the amp for FDX operation, replacing the manual alignment process in conventional amps today. Optimal results for cascades of amps can be obtained resulting in near perfect amp alignment that is otherwise not possible. The heart of these FDX amps use digital signal processing (DSP) in a custom SoC that digitizes all inbound and outbound signals with flexible processing of the required amplifier gain, equalization, and echo cancellation. Several test points and a wideband Fast Fourier Transform (FFT) processor for spectrum analysis are included in the SoC in addition to the required DSP for digital filtering, echo cancellation, and FFT signal processing. These digital test points can be processed by the wideband FFT for spectrum analysis. Such processed spectral data can be communicated through an embedded cable modem (eCM) in the SoC, as well as the loading of data as the result of processing this spectrum data for configuring proper amplifier operation. The alignment process for technicians can therefore be simplified through automation via a communication link between the amp and a configuration server using internal amp measurements that are described in this paper. This paper discusses a method for automatically configuring an FDX amplifier for optimal operation using the spectral analysis capability and DOCSIS communication in the SoC. Additionally, a method for discovering the network topology of the amplifiers in a tree and branch network is derived. Such methodologies can also be used to initially set up and periodically check for continued proper operation of installed and configured amplifiers.