It is known that multicarrier code-division multiple-access (MC-CDMA) systems suffer from multiaccess interference (MAI) when the channel is frequency-selective fading. In this paper, we propose a Hadamard - Walsh code-based MC-CDMA system that achieves zero MAI over a frequency-selective fading channel. In particular, we will use appropriately chosen subsets of Hadamard - Walsh code as codewords. For a multipath channel of length L, we partition a Hadamard - Walsh code of size N into G subsets, where G is a power of two with G ≥. We will show that the N/G codewords in any of the G subsets yields an MAI-free system. That is, the number of MAI-free users for each codeword subset is N/G. Furthermore, the system has the additional advantage that it is robust to carrier frequency offset (CFO) in a multipath environment. It is also shown that the MAI-free property allows us to estimate the channel of each user separately and the system can perform channel estimation much more easily. Owing to the MAI-free property, every user can enjoy a channel diversity gain of order L to improve the bit error performance. Finally, we discuss a code priority scheme for a heavily loaded system. Simulation results are given to demonstrate the advantages of the proposed code and code priority schemes.
- Carrier frequency offset (CFO)
- Hadamard-Walsh code
- Interference free
- Large-area synchronized (LAS) code
- Multiaccess interference (MAI)-free
- Multicarrier code-division multiple-access (MC-CDMA)
- Multiuser detection (MUD)