Combined code reuse scheme with two-dimensional OVSF codes assignment algorithm for uplink multi-user/multi-rate block spread multi-cellularCDMA

The two-dimensional (2D) block spread code division multiple access (CDMA) can avoid the uplink multiple-access interference with low-complexity single-user detection in a slow fading channel and, therefore, is very attractive. In the 2D spreading, orthogonal variable spreading factor (OVSF) is used for spreading; an important problem is how to efficiently assign the limited resource of OVSF codes to users with different data rates, while meeting the requirement of quality of service in a multi-cell environment. In this paper, it is shown that the code reuse can improve the code reuse efficiency and the proposed code reuse scheme combined with code assignment algorithm can allow flexible multi-rate uplink transmission. The computer simulation confirms that the proposed code assignment algorithm improves the code reuse efficiency while achieving lower blocking probability than traditional CDMA.