May 31, 2023

    It’s hard to believe that Data Over Cable Service Interface Specification, also known as DOCSIS, was introduced over 20 years ago!  Unlike some of the hottest tech introduced in the 90s, like Netscape and AOL, DOCSIS has stood the test of time and has made many advancements since its humble beginnings.

    The purpose of DOCSIS is to allow high-bandwidth data transfer over existing hybrid fiber-coaxial infrastructure. Over the years, the upstream and downstream rates have increased due to advancements in multiplexing technologies, which help balance throughput and prevent interference.

    Given the approval of DOCSIS 4.0, we can expect support and equipment for it to be available sometime in 2024. This new version defines four new splits that expand the spectrum range, which could lead to exciting new applications. Upload-heavy activities like live streaming and content creation will be considerably faster. However, it also poses a challenge for developers building amplifiers for upstream applications, as they will now need to support much higher throughput values.

    This blog post provides excerpts from the Qorvo Design Summit webinar, Using Flexible Architecture to Meet DOCSIS 4.0 Higher Upstream Requirements, which explains DOCSIS 4.0 and its new upstream options, as well as discusses the data throughput and bandwidth considerations. It's definitely worth checking out, especially if you're into next-generation technologies and the advances that are driving them.

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    DOCSIS 4.0 spectrum options

    The DOCSIS 4.0 spectrum options are substantially improved over its previous iteration, DOCSIS 3.1. With this latest version, users can now enjoy download speeds of up to 10 Gbps and upload speeds of up to 6 Gbps, which is a significant boost in speed and a major upgrade in terms of latency reduction. To facilitate these faster speeds, DOCSIS 4.0 also includes Extended Spectrum Technology, which expands the upstream spectrum to 684 MHz and the downstream spectrum to 1.8 GHz. This expanded spectrum creates a much larger pathway for data travel, allowing for even faster and more efficient data transfer.

    Extended Spectrum provides four new split options in DOCSIS 4.0, adding flexibility to implementations with additional ultra-high splits. Using frequency division duplexing (FDD), upstream and downstream are separated. The nature of the specific use cases will determine which splits are advantageous for upstream and downstream requirements. 

    Testing the splits

    Network losses and appropriate levels for inputs and outputs are still being defined as trials take place to test equipment performance, allowing operators to perform real-world testing of infrastructure components and the relative performance of different splits.

    Using 96 MHz block Orthogonal Frequency Division Multiple Access (OFDMA) lets multiple customers share a channel for upstream access with time-division multiple access format techniques. Operators can pick the split that best suits their needs. The 204 MHz and 396 MHz splits are likely to be the most popular providing a reasonable balance of 2.5 – 3.0 Gbps upstream and plus 10Gbit/sec downstream rates.


    Figure 1. DOCSIS 4.0 ESD Data Throughput

    Upstream Testing

    With the upstream bandwidths expanding as high as 684 MHz for FDX, 5-42 and 5-85 MHz are being reserved for current plans and equipment compatibility. Operators gearing up for field trials will be able to optimize amplifiers for future deployments. Efforts are underway to automate testing for Bit Error Rate (BER), Carrier to Intermodulation Noise (CIN), Carrier to Intermodulation Noise (CTN), and Carrier to Composite Noise (CCN). The noise power ratio (NPR) can also be tested for bandwidths from 42 MHz through 300 MHz using an automated test set (no capability above 300 MHz currently). Filter evaluation is taking place with plans to use SC-QAM signals up to 684 MHz.

    A variety of filters to perform noise measurements have been obtained to deliver low, mid, and high selections applying to each split. Once again, automation of the test process is being prioritized. Figure 2 shows a block diagram of the existing Modulation Error Ratio (MER) test station that has been set up, supporting input for CPSG from 54 – 684 MHz and SFD from 5 – 51 MHz. A motherboard for automation is currently under development.



    Figure 2. Upstream Modulation Error Ratio (MER) Station

    Overall, DOCSIS 4.0 is expected to bring significant improvements to the cable network infrastructure and enable a wide range of applications that require faster internet speeds, increased capacity and improved network efficiency. Designing amplifiers for DOCSIS 4.0 requires careful consideration of several requirements: higher frequency ranges, higher output power levels and improved noise performance. The Qorvo Design Summit webinar, Using Flexible Architecture to Meet DOCSIS 4.0 Higher Bandwidth Upstream Requirements, offers a more detailed explanation of how to meet these higher upstream requirements.


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