THE OVERLAY OF INTELLIGENT FDSS ON GSM SYSTEM (DOWNLINK AND UPLINK ANALYSIS)
Keywords:GSM, Downlink capacity, Uplink capacity, FDSS, Overlay
The overlay of an intelligent frequency diversity spread spectrum system (FDSS) on the (GSM) system is studied. The worst-case condition is considered for the downlink. Moreover, the effect of spectrum sidelobes outside the FDSS principal spectrum is considered. The downlink and uplink capacity of both systems are given using a model of 36 hexagonal cells. The performance of the (GSM) and (FDSS) users is investigated. Results show that the downlink is insensitive to the power ratio (P1/P2) while the uplink is very sensitive to the variation of this power ratio. Also, the results show that the uplink is the link that limits the capacity of the mixed system when the power ratio (P1/P2) is 5 or higher. An original GSM system with 48 users/cell can be substituted by a mixed system, which has an GSM system capacity of 24 users/cell and FDSS system capacity of 172 users/cell. If a notch filter with 20 dB attenuation is used, the FDSS uplink capacity increases to 191 FDSS users/cell and the downlink will be the link that limits the capacity of the overlaid system to 24 GSM users/cell and 182 FDSS users/cell. The FDSS uplink capacity will be 191 FDSS users/cell if the power control is used.
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