LINEAR BLOCK CODER USING ROM

LINEAR BLOCK CODER USING ROM

When the codeword corresponding to each uncoded word has been deter­mined, the results can be stored in a memory. Such a memory, in this case

a read­ only memory (ROM), is shown in Fig. 2.2.The bits x_ml  x_m2 . . . x_mk of the uncoded word are presented as an address to the memory. At the memory location speci­fied by that address we have stored the n bits corresponding to the coded word. The uncoded word bit serial bit stream x_i is converted to a parallel bit array (i.e., all bits available at the same time) by a serial to parallel converter (i.e., a shift register). The converter is driven by a clock at the uncoded bit rate f_b. When the bits x_ml  x_m2 . . . x_mk are all available, a READ command is given to the ROM and a LOAD command to the parallel to series converter (i.e., another shift register with a parallel load facility). The coded word c_m1 c_m2 … c_mn is thus loaded into the converter. The converter then presents the bits serially at its output. The clock rate for this second converter is f_c which is

the bit rate for the coded bits, where f_c/f_b = n / k