Joint frequency and scrambling code allocation for TD-SCDMA cellular network optimization

Frequency allocation and scrambling code allocation are challenging issues for TD-SCDMA networks. Proper allocation schemes should not only meet traffic volume requirement and networking constraints, but suppress intercell interference effectively as well. This paper investigates joint frequency and scrambling code allocation, in order to take full use of the freedom degrees owned by these two resources and thus suppress interference to the greatest extent. A complete model of intercell interference is established, taking radio propagation condition, traffic distribution, frequency orthogonality and code correlation into consideration. A novel two-step joint allocation algorithm is proposed, with joint frequency and scrambling code family allocation in the first step and then scrambling code selection in the second step. Therefore, the minimum interference is achieved by the joint allocation, and computational complexity is greatly reduced by the two-step implementation. Numerical results show that in interference suppression point of view, our proposed joint allocation outperforms the sequential allocation commonly used in engineering.