Adaptive Multicarrier CDMA Space-Time Receivers - Adaptive Signal Processing in Wireless Communications - page 269

Amplitude

Frequency-domain spreading
Data bits +1
Spreading sequence -1+1-1+1-1

Frequency

T

Time

FD-MC-CDMA system
(a)

Amplitude

Time-domain spreading
Data bits +1+1-1
Spreading sequence -1+1-1+1

Frequency

T C

T MC

Time

MC-DS-CDMA system
(b)

FIgure 10.1 Spectr a of different multicarrier CDMA schemes : (a) FD-MC-CDMA, (b) MC-
DS-CDMA, (c) MT-CDMA.

subcarriers may encounter different amplitude attenuations and phase shifts, which can
consequently destroy the orthogonality of the subcarriers.

10.2.2 Time-Domain Spreading Multicarrier CDMA:
MC-DS-CDMA
In [11], a multicarrier DS-CDMA system named MC-DS-CDMA has been proposed. The
MC-DS-CDMA transmitter spreads the serial-to-parallel converted data streams using
a given spreading code in the time domain so that the resulting spectrum of each sub-
carrier can satisfy the orthogonality condition with the minimum frequency separation
[11]. This scheme was originally proposed for an uplink communication system, because