Expert Notes: How to meet higher frequency division requirements through flexible uplink architecture?

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Expert Notes: How to meet higher frequency division requirements through flexible uplink architecture? [Copy link]

Since March 2021, broadband hybrid fiber-coax (HFC) networks have seen unprecedented demand. Global internet traffic has increased by 25% to 45% during this period. Multiple system operators (MSOs) around the world are evaluating the latest DOCSIS specifications to upgrade their current networks to meet the growing demand.

Currently, the weakest link in most HFC networks is upstream transmission capacity. DOCSIS 3.1 and DOCSIS 4.0 will help MSOs increase upstream capacity and speed. One of the advantages of DOCSIS 3.1 and DOCSIS 4.0 is the ability to provide higher upstream frequency division, thereby achieving greater bandwidth and higher capacity in HFC networks.

This article focuses on the upstream architecture in amplifiers and nodes that supports this higher frequency crossover, and how Qorvo products can help network equipment manufacturers provide flexible network architectures to meet the diverse needs of MSOs.

Current Uplink Capacity and Expansion

With the increasing demand for streaming content, video conferencing and other applications, it is imperative to exceed the traditional 5-42MHz and 5-85MHz upstream frequency division capacity. DOCSIS 3.1 currently supports "high frequency division" of 204MHz, and can also use Orthogonal Frequency Division Multiple Access (OFDMA) technology with up to 96Mhz bandwidth. OFDM can be used in the downlink to achieve a single-user broadcast channel for the cable plant; while OFDMA in the uplink uses a "multiple access" form, allowing multiple customers to share a channel through a form of time division multiple access (TDMA).
OFDM uses multiple orthogonally spaced QAM (quadrature amplitude modulation) subcarriers to form a channel. These subcarriers have narrow bandwidths, up to 4096QAM for OFDM orders and up to 1024QAM for OFDMA orders (higher QAM orders can be selected). OFDM has a higher payload capacity than 256QAM over similar bandwidths. By raising or lowering the modulation order of each subcarrier, it can dynamically adapt to the current channel conditions to maintain signal integrity at the best possible capacity.
Extended Spectrum DOCSIS (ESD, DOCSIS 4.0) and full-duplex technology provide new standards for achieving downstream and upstream capacity expansion goals. Both standards support the expansion of the maximum available bandwidth of the upstream amplifier to 684MHz.

Figure 1: DOCSIS 4.0 ESD spectrum and the division between upstream (US) and downstream (DS).

Figure 2: DOCSIS 4.0 FDX spectrum for upstream (US) and downstream (DS).

As the bandwidth planned for the upstream increases, the performance of the upstream amplifier MMIC will increase accordingly. The overall requirements for composite signal levels, losses and tilt levels need to be considered, and these factors become more of an issue as bandwidth and tilt increase.
Since full-duplex architectures utilize simultaneous operation of upstream and downstream within the same bandwidth, it is easier to rely on bandwidths up to 684MHz, while extended spectrum DOCSIS as a frequency division duplex scheme (FDD) must balance bandwidth requirements between upstream and downstream. It can be intuitively seen in Figure 1 that increasing upstream bandwidth reduces the available bandwidth in the downstream path, while in Figure 3 it can be seen that using existing SC-QAM data rates has a more direct impact on actual throughput compared to the new 1.8GHz ESD division.

Figure 3: Impact of increased upstream bandwidth on SC-QAM data throughput.

If we increase the number of OFDM and OFDMA channels as much as possible within the permitted range of the uplink and downlink frequency band plans (Figure 4), we will find that adding OFDM can indeed increase data capacity, but bandwidth still needs to be weighed at the same time. Therefore, operators will still give up the maximum uplink bandwidth and tend to promote 1Gbit and 2Gbit uplink services and achieve 10Gbit downlink rates through frequency divisions such as 204MHz and 396MHz.

Figure 4: Improving data throughput and uplink bandwidth by using OFDM.

Qorvo Uplink Solutions

Traditional D3.0 upstream applications use narrowband MMICs or transistors when the target bandwidth is 42MHz or 85MHz. To adapt to the growing DOCSIS 4.0 market, the full bandwidth provided by MMICs needs to be up to 684 MHz to meet FDX requirements and support extended spectrum applications.
Qorvo's solution is a modular solution consisting of small size, low power amplifiers as well as attenuators, equalizers and switches, making it easy for customers to place the device where needed in the end application. Qorvo has introduced a series of amplifier products to challenging new markets, as shown in Figure 5.

Figure 5: Qorvo’s modular solution.

Some of Qorvo's products have very low noise figures, which can build excellent driver ICs covering the entire bandwidth. These ICs in SOIC8 packages are pin-compatible, with a gain range of 12dB to 25dB, and can support all available frequency divisions up to 684MHz. Due to the same pin arrangement, the required gain, output power, linearity and NPR characteristics can be easily achieved to meet all upstream application requirements from 5MHz to 684MHz.

In addition to amplifier MMICs, Qorvo also provides control products for upstream device designers. To learn more, click here to view the original article.