At ANGAcom in May 2017, we showed the first worldwide demonstration of Full Duplex DOCSIS3.1 (FDX DOCSIS).
FDX DOCSIS is a truly significant innovation to DOCSIS. A critical mid-life upgrade for the HFC network, FDX DOCSIS will help to position the industry at the forefront of innovation, providing the service provider market with an access network scalable well beyond that of the competition. The FDX DOCSIS innovation is also why Remote PHY is so important to the market, without Remote PHY we would not be able to evolve to a highly distributed network and support FDX to its fullest extent.
Let me expand on what we showed at ANGAcom, we had two cable modems based on the Intel® Puma™ 7 SoC in the setup, one was receiving data in the downstream and the other transmitting in the upstream, both in the same spectrum of 108MHz to 204MHz. What we demonstrated there was our “Echo cancellation” capability which enables the use of the same spectrum, Full Duplex. This was done in collaboration with Intel, and we are again working with Intel on the SCTE demo.
Why did we show a proof of concept that only does 96 MHz symmetrical, when the goal is 576 MHz of shared spectrum? Because current silicon technology on the Remote Phy Device and cable modem have limitations – maxing out at an upstream spectral location of 204 MHz. The 96 MHz shared spectrum in the demo had a downstream rate of 890 Mbps (with 4K QAM) and an upstream rate of 680 Mbps (with 1K QAM). For our SCTE demonstration, we’ll be using the same spectrum and bandwidth, but that’s where the comparison stops.
At SCTE, our FDX DOCSIS demo will include seven cable modems based on the Intel Puma SoC. Why seven? By incorporating seven modems in the demo, we can show you the FDX DOCSIS Interference Groups (IG) including IG discovery capabilities. And it will also demonstrate how normal DOCSIS 3.0 modems can work on the same network as FDX DOCSIS modems, considering the sheer volume of DOCSIS 3.0 modems deployed, this functionality is compelling.
Why is it important to demonstrate Interference Groups? With FDX DOCSIS, the network supports simultaneous bi-directional transmissions across the same spectrum, hence full duplex. And interferences between the full-duplex transmissions must be mitigated for it to work. Remember, DOCSIS is a shared medium, where multiple cable modems connect to the same Converged Cable Access Platform(CCAP) port or network segment. When one cable modem transmits upstream to the CCAP, that upstream signal may interfere with other cable modems that are receiving data from the CCAP (downstream) at the same frequency. This type of co-channel interference (CCI) is different from the DS to US interference, where the source of the interference is known and can be canceled out via echo cancellation at the node, as we showed at ANGAcom. FDX DOCSIS resolves this CM-to-CM CCI issue by grouping cable modems that interfere with each other into Interference Groups. Cable modems in the same Interference Group must transmit or receive along the same direction at any given frequency and time. Cable modems from different IGs have enough “RF isolation” to allow simultaneous upstream and downstream transmissions at the same frequency. Read how John Chapman explains this in a recent Lightreading blog.
How do we determine if there is enough “RF isolation”? Enter the Inference Group Discovery protocol, a new capability introduced in FDX DOCSIS that enables the CCAP to conduct cable modem to cable modem interference measurement via sounding. During sounding, the CCAP selects one or more FDX DOCSIS capable cable modems to transmit test signals on designated frequency locations, while directing other FDX DOCSIS capable cable modems to compute and report the received MER (RxMER) on those frequencies. The CCAP then repeats this procedure until the CCI levels on all relevant frequencies are tested between all possible cable modem combinations. Based on the results, the CCAP forms the Interference Groups.
Although it may sound easy, this is complicated technology. Here’s a quick explanation, to find out more, stop by and see us at SCTE, where we’ll gladly walk you through the demo and answer your questions in more detail.
At SCTE, we are demonstrating the Continuous Wave (CW) sounding method, designed for a deployment scenario where DOCSIS 3.1 cable modems, after a software upgrade, can share the DS spectrum with FDX DOCSIS cable modems. For example, a low-split or mid-split DOCSIS 3.1 cable modem can share the downstream spectrum between 108 to 684 MHz, and a high-split DOCSIS 3.1 cable modem can share the downstream spectrum between 258 to 684MHz. During the CW sounding process, one or multiple FDX cable modems send CW test signals at selected downstream subcarriers, while the rest of the cable modems, including both legacy D3.1 and FDX cable modems, measure the MER using the DOCSIS 3.1 RxMER method.
The IGs we will be demonstrating at the SCTE are another step toward making FDX DOCSIS operational. Please make sure you stop by and see us at our SCTE booth (#987); we are honored to be demonstrating this new FDX DOCSIS capability together in conjunction with Intel.