|
On intrabuilding Power line networks, Donaldson et al [6] observed typical FEC coding gains of 15 dB at 10 –3 decoded Bit Error Rate (BER). (Our own experiments also show spectacular results.) This is a very significant improvement of noise tolerance, (Signal-to-noise ratio) as well as other impairments tolerance like sudden impedance variation. “Stated differently, FEC coding typically enhances decoded Bit Error Rate values three order of magnitude relative to systems not implementing any Forward Error Correction techniques.” [6]
FEC is a well known and relatively simple technique that significantly increases communication reliability in noisy channels like Power line. In PLC communication, FEC enhanced products should also mean much less unsatisfied customer call-back, less installation and debugging time, less (if any) filters to install in front of noisy loads, etc. FEC could mean thousands and thousands of Dollars savings per year to PLC manufacturers/dealers/installers. FEC has the potential to dramatically increase customer satisfaction, translating into increased sales.
But FEC is not totally "free"! It involves adding redundant data, meaning that more bits per message must be carried out. In other words, it decreases the throughput (number of effective data bits delivered per second) in noiseless environments, where FEC would not be mandatory. But power line is not such an environment. In noisy networks, FEC can even increase the net throughput over non-FEC systems, by reducing the need for packet repeating. In severe situations, (particularly in presence of line synchronous impairments, causing error bursts) FEC enabled products can often deliver data where other non-FEC products simply crash. On the other hand, implementing a FEC algorithm in a power line modem IC is likely to be free: FEC implementation is relatively simple and should not require a significant increase of the die size of a transceiver or modem IC.
Regrettably, many manufacturers and consumers have good reason to believe that PL communications are unreliable. Indeed, older and less sophisticated technologies-as well as more recent ones that do not implement an adequate FEC technique-contribute to a large extent in the spreading of the belief that PL communications are synonymous with unreliability.
Yet the PL medium is of paramount interest and does allow for adequate reliability to meet application requirements, as long as one keeps in mind that this medium is among the most challenging and thus demands the design of communication technologies suited to the task at hand, therefore including an FEC technique.
- Given the very significant reliability increase obtained from FEC,
- Considering that a power line is probably the most error-prone communication medium,
- Given the fact that cost of FEC is null when added into a PLC transceiver IC,
- Considering the benefits and savings that FEC brings to customers, installers, distributors and manufacturers of PLC products,
- Given the economic losses potentially incurred with non-FEC systems,
is it advisable, or is it simply affordable for anyone to offer Power Line Carrier products that do not implement an efficient Forward Error Correction algorithm? From an economic and marketing perspective, FEC is not only free, it can save lots of money, it increases customer satisfaction, helping generate more sales.
We believe that everyone will benefit from having FEC included into PLC transceivers.
References :
[6] M.H.L. Chan, D. Friedman and R.W. Donaldson, "Performance enhancement using forward error correction on power line communication channels." SM 93 367-3 PWRD presented at the IEEE/PES Summer Meeting, Vancouver B.C., July 1993
|
