Longer guard periods allow more distant echoes to be tolerated but reduce channel efficiency. For example, in DVB-T, guard intervals are available as 1/32, 1/16, 1/8 or 1/4 of a symbol period. The shortest interval (1/32) provides the lowest protection and the highest data rate; the longest interval (1/4) provides the highest protection but the lowest data rate. Ideally, the guard interval is set to just above the delay spread of the channel.
