iagram. Initially, there are some unused channel input slots until the shift registers in the interleaver fill up. After sixty channel sym- bols are transmitted the convolutional interleaver outputs are X47, X19, X5, X66, X52, The convolutional deinterleaver inverts the action of the interleaver as shown in Figure 3A.3. Observables are fed in with each channel output going to a different shift register. Again, we have the property that a jamming pulse of b coded symbol duration where b VI I will result in these jammed sym- bols at the deinterleaver output being separated by at least N symbols. From this it is clear that the convolutional interleaver requires roughly IN/2 symbols of memory compared to 2IN for the block interleaver mem- ory for synchronous transmission. A fair comparison, however, must consider the fact that shift registers of varying lengths may be considerably more costly in terms of numbers of required integrated circuits than, for example, a random access memory (RAM) of larger size. Also, note that the deinter- leaver memories for both approaches are often several times larger than the interleaver memory. This is because of the fact that channel output symbols are often quantized with more bits than the channel input symbols. For BPSK modulations, for example, each coded channel input symbol is one bit while the usual channel outputs are three bit quantized to eight levels. With the deterministic interleaver and deinterleaver techniques described above, a jammer might cleverly pulse jam selected channel ssymbols in such a way that the deinterleaver outputs a burst of jammed symbols. This would dramatically degrade a coding system designed for independent channel dis- turbances. A pseudorandom interleaver/deinterleaver system can overcome this vulnerability. A pseudorandom interleaver/deinterleaver is one where a pseudorandom sequence generator is used at the transmitter and receiver to pseudoran- domly choose between many possible interleaver/deinterleaver structures. Typically for block inter