Hi ,
I've coded in Matlab an OFDMA downlink transmission scheme (OFDM modulation for sure) using QAM for each user, after that i wanted to implement a clipping function to reduce PAPR (PEAK to Average Power Ratio) until here everything gone fine, i fellowed the clipping function by implementing a pulse shaping filtring to reduce ISI (Inter symbol Interference) & to reduce too clipping's effect wich affected the BER (Bit Error rate) at the receiver, i choose a Nyquist filtering, an RRC filter (Raised Cosin Filter), when it comes to apply this filter to my OFDMA system by using the matlab function rcosflt() i got some weird results (BER very high > 50%).
I have doubts how to apply the filter, i explain, i applied the filter at rate of OFDM symbols not at the rate of the QAM symbols inside each OFDM symbol, i don't know if i'm doing it wrong?
I tried a rectangular pulse shaping (rectpulse()) it works on OFDM symbols with good results however this method is hard to implement in practice (infinite bandwidth) so not recommended as in practice a signal exist only for a duration & has a limited bandwidth.
I need help from specialist.My questions:
- How do we apply Nyquist filtering in OFDM signal case & in Matlab?
- How the filter parameters are chosen in OFDM case?
- the RRC should be applied to the OFDM symbol or to QAM symbols themself in the OFDM symbol?
If you want i will post you my Matlab program filtering part.
Thanks in advance.
I've coded in Matlab an OFDMA downlink transmission scheme (OFDM modulation for sure) using QAM for each user, after that i wanted to implement a clipping function to reduce PAPR (PEAK to Average Power Ratio) until here everything gone fine, i fellowed the clipping function by implementing a pulse shaping filtring to reduce ISI (Inter symbol Interference) & to reduce too clipping's effect wich affected the BER (Bit Error rate) at the receiver, i choose a Nyquist filtering, an RRC filter (Raised Cosin Filter), when it comes to apply this filter to my OFDMA system by using the matlab function rcosflt() i got some weird results (BER very high > 50%).
I have doubts how to apply the filter, i explain, i applied the filter at rate of OFDM symbols not at the rate of the QAM symbols inside each OFDM symbol, i don't know if i'm doing it wrong?
I tried a rectangular pulse shaping (rectpulse()) it works on OFDM symbols with good results however this method is hard to implement in practice (infinite bandwidth) so not recommended as in practice a signal exist only for a duration & has a limited bandwidth.
I need help from specialist.My questions:
- How do we apply Nyquist filtering in OFDM signal case & in Matlab?
- How the filter parameters are chosen in OFDM case?
- the RRC should be applied to the OFDM symbol or to QAM symbols themself in the OFDM symbol?
If you want i will post you my Matlab program filtering part.
Thanks in advance.
