Ternära koder för variabelt felskydd
Ternary codes for unequal error protection is a part of a communication system where different parts of the information to be transmitted can receive different amount of error protection. There are a lot of applications where the channel conditions fluctuate so that reliable or acceptable communication can not be guaranteed. Regardless whether the fluctuations of the channel are intentional or not the idea is to let the coderate decrease so that the error correcting capability can increase for the part of the information to be more protected. By using the support, the nonzero positions of the ternary code, a new binary code can be extracted with properties different from the ternary code in the sense of cardinality and minimum Hamming distance. When the channel conditions are good the receiver decodes the message using ternary decisions and receives all information included in the codeword. When the channel conditions drops the receiver decodes the message using binary decisions to assimilate the information in the support. What the properties of the ternary code should be like to give a good ternary error correcting capability and best possible error correcting capability for the support is one of the questions this thesis will look at. A number of ternary codes used in this thesis are constructed from Mattias Svanströms dissertation ?Ternary Codes with Weight Constraints?, [4]. The properties of the support have been studied and modified in that sense it has given a new binary code with better error correctingcapability and an acceptable coderate. The unequal error protection lies in the modulation scheme. By using knowledge of the weight distribution and the error correcting capability of the ternary code the signal points in the modulation scheme can be optimized in the sense of error probability for ternary or binary decoding. When optimal error probability for the complete system is required optimal signal points for both modulations schemes needs to be considered and the final signal points placed thereafter.