at which the selection is to be made is communicated to the transmitting system through any one of a plurality of available links 58 that can be either a radio frequency link or another optical link and can be a much lower speed link the method of synchronizing interleaver depth selection is not specified as part of this invention in one embodiment of this invention fade signal 54 can be derived from bit stream 37 itself in another embodiment of this invention fade signal 54 is derived by periodically inserting a short sequence of a number of symbols into the data path at multiplexer 34 this signal is referred to as a u201c fade detection sequence u201d the frequency of repetition of fade detection sequences is contrived to be short in comparison to the frequency and duration of channel fading but very long in comparison to the data stream bit rate of channel transmission path 38 the fade signal 54 is true when all bits in the fade detection sequence are lost the number of symbols transmitted is contrived to be such that the error rate for a false fade indication based on uncorrelated symbol errors is much less than the link error rate and failure to indicate a fade signal in the presence of highly correlated fading channel dropouts is also low the transmitted symbols are designed to allow the receiver to measure signal strength in one embodiment of.