A Low Interference Time-Slicing Code Assignment for the 2D-Spread MC-DS-CDMA Systems

In addition to some design flexibilities, the low interference property of code division multiple access (CDMA) makes multi-carrier direct sequence CDMA (MC-DS-CDMA) suitable for possible unlicensed transmissions in the licensed bands. Introducing the concept of time division multiple access (TDMA) into MC- DS-CDMA may further create a new dimension dealing with the interference problem. In this paper, we proposed a time slicing code assignment for the two-dimensional (2D) spread MC-DS- CDMA. The time slicing technique distributes interference equally over transmission time intervals (TTIs) by assigning users different frequency-domain spreading code groups and transmitting in their corresponding TTIs. Combing with the previous interference avoidance code assignment and power control mechanism for the 2D-spread MC-DS-CDMA, the proposed time slicing scheme is proved to be capable of eliminating interference more efficiently. In terms of the call admission rate, the improvement can be as large as 10% in one of the considered cases. A good operating point of time slicing can also maintain a high throughput, while achieving lower call dropping rate and lower power consumption. The results of this paper can provide some important and interesting hints for the system designers.