A Multi-User Multi-Rate OFDMA Transmission System based on Orthogonal Subcarrier Grouping

In this work, we shall propose an OFDMA system based on the allocation of orthogonal subcarrier groups to multi- rate user classes. This system can be regarded as an evolution of GO-OFDMA used for single-rate data transmission. A user data stream is split into a multiple substreams, whose number depends on the user data rate. Then, each substream is spread by a distinct spreading code and, finally, transmitted in OFDM modality over the selected subcarrier set. The main advantage obtained with respect to classical OFDMA lies in the possibility of exploiting diversity in code domain and frequency domain (like it happens in MC-CDMA). Experimental results in terms of BER evidenced an interesting trend of the proposed GO-OFDMA system towards a noticeable BER improvement achieved for highest-data rate users with respect to VSL MC-CDMA. Therefore, the proposed GO-OFDMA system seems to provide a less conservative management of radio resources that is more in favor to "broadband" users, while penalizing "narrowband" users, whose BER is slightly degraded with respect to that one achieved by VSL MC-CDMA.