hi sudan,
the RLC layer receives one LLC frame
this frame is divided into RLC blocks, with variable size length, depending on the MCS chosen (by RLC layer)
each block is then CODED (convolutional coding) of 1/3 for 8PSK and 1/2 for GMSK.
So if block = 500 bits and 8PSK modulatio is chosen, then coded block = 500*3 = 1500 bits.
And then the PUNCTURING occurs, which erases a certain amount of bits, located a certain places in the coded block.
Therefore, the final size of the RLC Block is strongly reduced, in order to fit into radio timeslots.
try out this book :
books.google.com/books?id=y4_nqAIt_QEC&pg=PA50&lpg=PA50&dq=RLC+block+puncturing&source=bl&ots=JpcwYXioDG&sig=LxLvsZApw5J7NHdQkO1BluDhpns&hl=en&ei=wRapTpOwHILd4QTq9qXZDw&sa=X&oi=book_result&ct=result&resnum=4&ved=0CC0Q6AEwAw#v=onepage&q=RLC%20block%20puncturing&f=false