Capacity estimation for spectrally-overlaid WCDMA & GSM systems

Much recent interest has been focused upon third-generation cellular systems, particularly wideband code division multiple access (WCDMA). Deployments must consider scarce available spectrum, so researchers have been investigating spectral overlay, as a means of increasing capacity. Spectral overlay may also be a method used during transition from current to future systems. Based upon a method developed in Matolak (2000), we estimate capacities of WCDMA when overlaid upon the Global System for Mobile communication (GSM). This method is an improvement upon the standard technique for approximating multiuser interference (MUI), and is more general than previous work in that it allows for different values of data rate within each system, an arbitrary number of overlaid CDMA systems, inclusion of outside-cell as well as outside-system interferences, and narrowband interferers. We apply the method to GSM and WCDMA, and explore via several examples the capacities achievable as a function of several system parameters, including the number of GSM frequency allocations, relative power levels, and a number of different data rates.