The following is a simulation of the DMT system, similar to implementation as done in ADSL systems. The bandwidth has been divided into 32 sub-channels of equal width. Each sub-channel has been allocated bits in the range of 1-15 bits/symbol/Hz.
In a finite length DMT system, the effective length of the channel impulse response, ?V? will cause inter-block interference. To counter the effects of ISI, cyclic prefix is applied to the modulated block after a parallel to serial conversion. The length of cyclic prefix will be the same as ?V?. In this simulation a cyclic prefix of length 5 has been used.
The simulation is performed with three channel responses 1) an ideal channel 2) channel with effective length ?V+1? and 3) channel with effective length greater than ?V+1?. In all cases the channel is modeled as a low pass FIR filter with varying magnitude with frequency. |
