11/01/2015
Hybrid OFDM and CDMA
Compromise between
the main advantage of OFDM, high spectral efficiency
and
the main advantage of CDMA, robustness to interference
Two main approaches:
The code sequence is spread over the sub-carriers
[parallel]
The code sequence modulates a single sub-carrier
[serially]
Multiple access can be performed in the code and frequency domain.
LTE and next generation mobile networks
2014
Hybrid OFDM and CDMA
MC-CDMA
∆f = 1/TS
The chips corresponding to the same symbols are spread over different sub-channels of the
same multi-carrier block.
LTE and next generation mobile networks
2014
1
11/01/2015
Hybrid OFDM and CDMA
Here the chips corresponding to the same symbol are allocated to different multi-carrier blocks of
the same sub-channel.
MC-DS-CDMA
∆f = 1/TC
MT-CDMA
∆f = 1/TS (or different)
LTE and next generation mobile networks
2014
Hybrid OFDM and CDMA
MC-DS-CDMA vs. MC-CDMA and DS-CDMA
MC-DS-CDMA typically requires lower chip rate spreading codes than DS-CDMA
thanks to the presence of multiple subcarriers ( lower processing rate).
MC-DS-CDMA necessitates a lower number of subcarriers than MC-CDMA due to
DS spreading on each subcarrier’s signal ( lower PAPR).
MC-DS-CDMA has the highest level of flexibility and degrees of freedom in the
system design. The orthogonality is built in the time and frequency domains.
LTE and next generation mobile networks
2014
2