Summary Bullets:
- PCS Maximizes Fiber Utilization: The PSE-3 DSP relies on PCS modulation to increase available bandwidth per fiber close to its theoretical maximum.
- PSE-3 Simplifies Network Operations: PCS enables the PSE-3 to tune its wavelength capacity from 100G to 600G, using a single modulation format, baud rate, and channel size.
Nokia’s new Photonic Service Engine 3 (PSE-3) is designed to improve optical performance, flexibility, and programmability across a wide range of wavelength capacities. To achieve this, the new DSP chipset utilizes probabilistic constellation shaping (PCS) – a modulation technique which improves optical reach performance by approximately 1 dB, or roughly 25% (compared to the most advanced optical systems today). This brings the optical system performance, according to Nokia, within a fraction of a dB of Shannon theoretical limits.
The use of PCS has a number of practical repercussions. It increases fiber utilization by increasing wavelength capacity close to its theoretical limit. In practice, it means that rather than using coarse steps between pairs of modulation schemes and wavelength capacities (like 100G QPSK, 200G 16 QAM), with PCS, operators can choose much finer steps that more closely match the wavelength capacity and reach limitations on a given optical route. It also means that on existing routes, operators can push their capacity higher than initial design limitations. For example, on routes that are suitable for 100G QPSK, but unsuitable for 200G 16QAM, operators can opt for a value that is between these two figures.
Nokia gave the following indicative estimates for wavelength performance which will be available with PSE-3-based products:
- 450G-600G – 200-500 km (metro);
- 300G-450G – 500-1,200 km (regional);
- 200G-300G – 1,200-2,500km (long haul).
Increased spectral efficiency achieved with PCS, in turn, reduces the number of transponders needed to reach maximum fiber performance. In two studies Nokia quoted in documentation following the PSE-3 launch (a 75-node continental U.S. network and a 50-node network in Germany), using probabilistically shaped 64QAM modulation (PS-64QAM) reduced the number of transponders needed by 25% and 30%, compared to using 100-250G multi-modulation transponders. This potentially translates into significant cost savings, but also much improved space and power efficiency. Another advantage that PSE-3 based transponders will enjoy is simplified operations and planning, stemming from the use of a single modulation scheme, baud rate, and channel size across the whole network.
The first product that will feature PSE-3 will be Nokia’s DCI-oriented platform, the 1830 PSI-M, with expected availability in Q3 2018, pointing to Nokia’s ambitions to gain a higher profile in the highly contested and growing DCI market.
By pushing the flexibility of optical transmission close to the limit, PSE-3 based products will also require change in the way client interfaces are used, as – logically – flexible line rates will need to be matched with flexible client rates. This will be facilitated by adoption of Flexible Ethernet (FlexE) interfaces. Taken together, FlexE and PCS (governed by an SDN solution) can allow dynamic changes to the entire system throughput, furthering the flexibility and versatility of optical transmission.
With its PCS modulation scheme, PSE-3 brings new direction to optical networking, and will further spur the race to maximum spectral efficiency in optical systems. Its performance advantages will need to be proven in live networks and practical operation, but so far, the efficiency gains, operational simplification, and potential cost savings position Nokia very favorably in highly competitive optical marketplace.