Powerline-channel adopted layer-design and link-layer for reliable data transmission

Narrow Band PLC uses often MAC-protocol stacks designed for wireless systems like IEEE 802.15.4 (used by Prime, PLC-G3 and IEEE 1901.2). Due to the different behavior of the power line channel mainly OFDM based PHY-Layers, significant modulations and decoding times are used. The resulting computation delay is equivalent to 3-5 OFDM symbol times, which has an equivalent effect on the system as a propagation delay. The short ACKs for confirmation are full packages with several OFDM-symbols. The impulsive noise on the channel requires certain packet duration to reach sufficient reliability. Therefore a stop and wait protocol with immediate acknowledgement of each packet cannot reach an efficient channel usage. Additionally it is necessary for reliable PLC systems to accept links with PER (packet error rates) of 20% and more. The theoretical maximum throughput of a channel with PER of 20 % is still 80%. Very often narrowband PLC standardized protocols fail under this condition. This paper presents an adopted Layer-Design to combine all data flows to a node in a single stream and organize a reliable data transmission even for channel with PER of 90% and more. A pipeline structure allows an efficient medium usage and realizes a selective repeat approach. The confirmation is transferred piggy back in packages in opposite direction. Even for the retransmission of a packet the transmission mode and the route can be changed. This approach allows fast reactions on changed network situations without interruption of any link, which is an important requirement to fulfill reliability and real-time requirements for grid control.