Reed-Solomon, Viterbi, and Turbo Codes in IMT2000

For IMT2000, Reed-Solomon block codes, Viterbi convolutional codes, and turbo codes
are employed. The combination of Reed-Solomon and Viterbi coding can give an
improvement in S/N for a given BER of 6 to 7 dB. Turbo coding used on the 1 × 10-6
traffic adds a further 1.5- to 3 dB improvement. Total coding gain is ~ 8 dB.
The benefit of coding gain is only obtained above the coding threshold, that is, when
a reasonable amount of Eb/No is available (rather analogous to wideband FM demodulator
gain—the capture effect). Turbo coding needs 300 bits per TTI (Transmission
Time Interval) to make turbo coding more effective than convolutional coding. This
means turbo coding only works effectively when it is fed with a large block size (anything
up to 5114 bits blocks). This adds to the delay budget and means that turbo coding
is nonoptimum for delay-sensitive services.