Non-blocking OVSF codes and enhancing network capacity for 3G wireless and beyond systems

摘要

Orthogonal variable spreading factor (OVSF) codes are employed as channelization codes in wideband CDMA. Any two OVSF codes are orthogonal if and only if one of them is not a parent code of the other. Therefore, when an OVSF code is assigned, it blocks all of its ancestor and descendant codes from assignment because they are not orthogonal to each other. Unfortunately, this code-blocking problem of OVSF codes can cause a substantial spectral efficiency loss of up to 25%. This paper presents non-blocking OVSF (NOVSF) codes to increase substantially the utilization of channelization codes without having the overhead of code reassignments. In addition, an encoding algorithm is presented to increase network capacity and support higher data rates when NOVSF codes are employed.