An OFDMA/CDMA-based bandwidth resource allocation scheme for future broadband mobile networks

We propose a new transmission and multiple access method for future broadband wireless networks. The scheme combines the advantages of orthogonal frequency division multiple access (OFDMA) and code division multiple access (CDMA) to cope simultaneously with both frequency spread produced by the Doppler effect, and time spread caused by the multipath channel. Through the code orthogonalization of neighboring (close) OFDM subcarriers, the method mitigates the intercarrier interference generated by high speed users while keeping the advantages offered by OFDMA to diminish the intersymbol interference produced by multipaths. In this way, the method optimizes the reliability of the communication channel provided to every user according to its speed, position and channel characteristics. The allocation of subcarriers and orthogonal codes to users is carried out dynamically with time by considering parameters such as required bitrate, speed, level of interference, multipath effects and physical location. The results show that a substantial reduction of intercarrier interference can be achieved by using our proposed method, which makes it a good candidate for highly-mobile networks based on OFDMA.