Flexible Assignment of OVSF Codes for Data Calls in CDMA Wireless Networks

In this paper, an efficient design is proposed to utilize full capacity of the orthogonal variable spreading factor (OVSF) code tree. The design favors time bound calls and scattered capacity when not used by time bound calls is utilized for data calls. The call establishment delay for delay sensitive time bound calls is significantly reduced due to less number of code searches, as only a part of code tree is searched for low rate or high rate calls. The design favors time bound calls which are given higher priority compared to data calls. If there is no vacant code for time bound calls, one of the ongoing data call is stored in buffer and the code released is assigned to time bound call. The data call will get the vacant code later at the completion of some of the ongoing call. Also, the data call rate can be increased or decreased depending upon the vacant code availability in the code tree. Further, the code tree allocates different portions for low rate and high rate calls. Due to the variable rate options, data calls utilize vacant codes scattered in code tree. Simulation results are shown to verify superiority of our design.