Code scattering and reduction in OVSF code blocking for 3G and beyond mobile communication systems

Abstract

Scattered vacant codes in Orthogonal Variable Spreading Factor (OVSF) code based 3G and beyond WCDMA wireless networks leads to code blocking which further gives call blocking. The paper proposes four single code assignment schemes to reduce code scattering. The use of assignment scheme depends upon the type of input calls. The code reservation assignment (CRA) is used to efficiently handle one or higher rate class calls. It assigns priority number to the children of priority class codes such that the future availability of vacant codes in the priority layer is the highest. The remaining three code assignment schemes favors low to medium calls. The code assignment using group leaders uses busy codes (capacity) under predefined leaders to handle future calls. The code blocking in group leader approach can be reduced further if the used capacity of all the parents of the eligible vacant codes is examined and the code whose parent has maximum used capacity is used for new call. In adjacent vacant codes grouping scheme, the eligible vacant codes are listed to find code with least adjacent vacant codes. If unique result does not exists, the code (among the codes producing same adjacent vacant codes) with the least elapsed time of the busy neighbors is used for incoming call.