On Unequal Error Protection Reed-Muller Codes
Dojun Rheel
Abstract
It is well known that Reed-Muller (RM) codes are not an linear unequal error protec- tion (LUEP) code because the set of minimum-weight vectors span Reed-Muller codes (punctured or not) (1,2). In this paper, we showed that most of RM codes are LUEP codes if RM codes are encoded with recursively decomposed trellis oriented generator ma- trix (TOGM) and maximum-likelihood trellis decod- ing (MLTD) is used. I. INTRODUCTION Uneqaul error protection codes protect some information bits against a great number of errors than other information bits. LUEP codes were first introduced by Masnick and Wolf (3). Boyarinov and Katsman (4) found conditions for linear codes to be LUEP. Let C be and (n, IC, d) linear code. It is shown in (l) that if the minimum-weight vectors of a linear code C does not span it, then C is an LUEP code. It is well known that their set of minimum-weight vectors span RM codes (punctured or not) (2). Therefore, RM codes are not LUEP codes in algebraic decoding. In the soft-decision maxi- mum likelihood decoding, bit-error-rate of RM code depends on the weight distribution of code. If non-systematic GM is used for encoding the RM code and soft-decision maximum likelohood decoding is used in decoding, different set of in- formation bits has a different bit-error-rate since each other has different weight distribution. Therefore, even though RM code is not an LUEP code in algebraci decoding, RM code is an LUEP code in soft-decision maximum likelihood decoding if systematic GM is not used for encoding. Especially, in this paper, LUEP RM codes are constructed by using recursively decomposed TOGM for encoding. Sim- ulations show that bit-error-rate of some information bits is almost twice better than that of the other information bits. By using the recursive decomposition, a simple trellis diagram with parallel structure for the RM code is devised. In ML trellis decoding, information bits are retrieved directly from the labeling of the trellis.