With appropriate parameter selection, MFSK can tolerate significant Doppler or delay spreads, especially when augmented with forward error correction. (Mitigating large amounts of Doppler "and" delay spread is significantly more challenging, but it is still possible). A long delay spread with little Doppler spreading can be mitigated with a relatively long MFSK symbol period to allow the channel to "settle down" quickly at the start of each new symbol. Because a long symbol contains more energy than a short one for a given transmitter power, the detector can more easily attain a sufficiently high signal-to-noise ratio (SNR). The resultant throughput reduction can be partly compensated with a large tone set so that each symbol represents several data bits; a long symbol interval allows these tones to be packed more closely in frequency while maintaining orthogonality. This is limited by the exponential growth of tone set size with the number of data bits/symbol.