ACM for OTN Advantages and Enabling Technologies ECOC, Chandra Raj ViaSat Inc

ACM for OTN Advantages and Enabling Technologies ECOC, 2013 Chandra Raj ViaSat Inc

CCM CCM means using a fixed modulation and coding for the link Advantages of CCM Simplicity Disadvantages of CCM Link has to be set-up in accordance with the worst case link conditions Rx OSNR DSP + FEC OSNR limit Margin w.r.t worst case channel CCM is simple but inefficient Copyright 2013 ViaSat, Inc. 4

VCM VCM means selecting a suitable modulation and coding for the link based on pre-known information about the link conditions Advantages of VCM Simpler than ACM as there is not return link / feedback required Disadvantages of VCM Link has to be set-up in accordance with the expected worst case link conditions Margin w.r.t worst case channel (1) Margin w.r.t worst case channel (2) VCM uses pre-knowledge of the link Copyright 2013 ViaSat, Inc. 5

ACM ACM means selecting a suitable modulation and coding for the link based on feedback about the link conditions via a return link Advantages of ACM Highly Efficient (discussed more on the next slide) Disadvantages of ACM Added complexity of needing feedback as well as options to select link setup ACM Updates Link Setup Real Time Copyright 2013 ViaSat, Inc. 6

ACM Advantages Maximize capacity at a given OSNR Pick the highest modulation format and lowest OH that will still close the link with desired margin Most Efficient transmission for a target capacity Pick the modulation format and OH that will close the link with the minimum power or bandwidth or other metric of choice Reduce outage probability Pick more reliable modulation and code when the link quality is degrading ACM can be advantageous in a number of ways Copyright 2013 ViaSat, Inc. 7

Multi - Modulation Support Different modulation formats provides robustness versus capacity trade-off Alternate constellation maps provide different operating characteristics for a given modulation order Differential Encoding versus fully coherent operation provides another set of options Modulation formats provide variety of choices for ACM Copyright 2013 ViaSat, Inc. 9

Multi - Modulation Support Alternate constellation maps provide another avenue for ACM system design Alternate constellation maps provide different performance options in terms of Capacity Phase Noise / Non-linearity tolerance Peak-to-Average power ViaSat has evaluated DSP designs than can support a variety of different constellation options for better overall performance with incremental additional complexity Modulation formats provide variety of choices for ACM Copyright 2013 ViaSat, Inc. 10

Multi OH FEC Supporting multiple OH FEC in the same design can be a key tool for ACM Systems Select higher OH when link is getting worse to ensure higher protection and lower outage probability Select lower OH when link is getting better for higher throughput or lower power ViaSat evaluated designs with 15%, 20%, and 25% OH TPC SDFEC switchable on-the-fly in the same design Synthesis results show only incremental increase in implementation complexity and power Low Complexity Enabler of ACM Copyright 2013 ViaSat, Inc. 11

Bit Error Rate Multi OH FEC Sample SDFEC BER Performance with BPSK / QPSK in AWGN Channel 1.E+00 1.E-01 1.E-02 1.E-03 Uncoded, Coherent 15 % OH Differential 20 % OH Differential 15 % OH Coherent 20% OH Coherent 25 % OH Coherent 1.E-04 1.E-05 1.E-06 1.E-07 1.E-08 1.E-09 1.E-10 1.E-11 1.E-12 1.E-13 1.E-14 1.E-15 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Eb/No (db) Copyright 2013 ViaSat, Inc. 12

Summary ACM is a technique to improve system efficiency and provides a variety of improvements The are a few key technologies needed to facilitate ACM systems ViaSat has demonstrated that some of the key DSP and FEC technologies required for ACM are practically implementable with minimal additional complexity Copyright 2013 ViaSat, Inc. 13