Raptor Codes for Use in Opportunistic Error Correction

In this paper a Raptor code is developed and applied in an opportunistic error correction (OEC) layer for Coded OFDM systems. Opportunistic error correction [3] tries to recover information when it is available with the least effort. This is achieved by using Fountain codes in a COFDM system, which means that each subcarrier contains a Fountain coded packet. The property of a Fountain code that any missing packet can be replaced by any other packet allows the receiver to discard packets with low SNR. As a result ADC resolution and therefore energy consumption can be reduced. In this paper the possibilities of using Raptor codes in an OEC system are investigated. Raptor codes are a type of Fountain codes with an efficient encoding and decoding algorithm. By simulating an OEC system on a wireless indoor channel model, it is shown that Raptor codes can save up to 70% in energy consumption with respect to a traditional system. Furthermore it is found that a feedback channel can reduce energy consumption even more. In this setting 85% of energy consumption can be saved.