Block Type. The first type of inter/de-interleaving technique to be discussed is called block interleaving.
Here a block of data is stored and waiting to be transmitted. The block size is sometimes
described the same way the sizes of matrices are defined.
A typical block interleaver is shown below (Fig. 5.3) and contains N rows and Mcolumns, describing
an N by M (N M) matrix. The number of rows, N, is commonly called ???interleaver depth.??? This
value is chosen based on the FEC code word size and the error protection needed in the communication
system link. Each element (or cell) of the N M matrix is either a bit or a symbol, depending on
its location in the communication system.
In this example the FEC encoder output bit stream is inserted into each row until all N rows have
been filled. At this point the coded data to be transmitted is read out by the columns.
Now turning our attention to the receiver we describe the block de-interleaving operations. Here a
matrix of the same N Msize is constructed by writing the received bits into each column. Once the matrix
is full, data is read out of each row (see Fig. 5.4). This de-interleaved bit stream enters the FEC decoder.
One can easily see the additional time delays the information signal incurred as a result of the
interleaving and de-interleaving.
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