re written into the deinterleaver by rows and read out by columns. Note that here a jamming pulse of b coded symbol duration where b < I will result in these jammed symbols at the deinterleaver output sepa- rated by at least N symbols. Thus, if we had a block code of block-length n VI N, there would be only one jammed symbol in a transmitted codeword N = 15 Read in by columns: X1, X2, X3 Read out by rows: X1, x16, 31, Figure 3A.1. Block interleaver example. Basic Concepts and System Models as a result of this jammer pulse. For convolutional codes a simialr result is obtained if N is larger than a constraint length. Clearly I should be chosen to be larger than the channel memory and N should be larger than the code memory measured in number of coded symbols. Synchronization of the block interleaver requires some sort of standard frame synchronization technique. This requires some extra overhead sym- bols which are inserted periodically. Another type of interleaver is the convolutional interleaver proposed by Ramsey [11]. This is illustrated in Figure 3A.2 for the same parameters I = 5 and N = 15. Here the coded symbols are switched between I = 5 tapped shift registers of the interleaver bank. The zero-th element of this bank pro- N = jI = 15 = = Figure 3A.2. Convolutional interleaver example. 11-11j ( 1-2), (1-3)j CHANNEL INCLUDING MODULATOR CODER DEMODULATOR DECODER (1-4) (1-2)j (/-1)j Figure 3A.3. Convolutional interleaver system. Basic Concepts and System Models vides no storage (the symbols are transmitted immediately), while each suc- cessive element provides j = 3 symbols more storage than the preceding one. The input and output commutator switches move together from one regis- ter to the next. Again I is the minimum transmission separation provided for any two coded symbols entering the interleaver with a separation of less than N = jl symbols. In Figure 3A.2 the symbols entering the convolutional interleaver are X1, X2,X3, The interleaver outputs (coded channel input symbols) are shown by the rows of the d