Spectral sharing across 2G-3G systems

3G schemes with large bandwidth occupancy (e.g. UMTS) are gradually being introduced in response to the growing demand for non-voice services. Meanwhile, 2G systems (e.g., GSM, IS-95) still represent the main source for profit of carriers, and continues to exist for years to come. As a result, a coexistence of 2G and 3G systems is emerging that is likely to last for at least a few years. To optimize spectral efficiency, we show how a 2G/3G sharing strategy enables corporations to make optimal use of the 2G/3G spectral bands that they own. Specifically, we propose an efficient 2G/3G spectral sharing satisfying the following criteria: (1) the sharing strategy provides flexible system capacity over noncontiguous bandwidth, (2) it is able to dynamically update quantities of borrowed spectrum and borrowing duration, and (3) it ensures both lender and borrower to optimize their spectral efficiency and revenues. Specifically, assuming that 2G and 3G networks are DS-CDMA based, we propose an efficient technique supporting spectral sharing across networks by: (1) utilizing a new family of orthogonal spreading codes labeled carrier interferometry (CI) codes, capable of serving as a flexible replacement for the usual Hadamard-Walsh (HW) code; and (2) replacing the usual sinc(/spl middot/) and raised cosine chip shape by a multi-carrier chip shape. Simulation results show a significant beneficial effect via the proposed spectral sharing, e.g., increased capacity of 50% and 100% (in terms of numbers of users) with no loss in BER performance.