Dynamic power headroom threshold for mobile rate determination in a CDMA network

Until recently, the focus in 3G networks has been on the forward link since this typically requires a higher bandwidth than the reverse direction. We focus on the reverse link since this also needs to have a sufficiently high bandwidth to support reverse link bandwidth intensive applications. H-ARQ can be used to improve throughput efficiency since errors are corrected at the physical instead of at the MAC layer. However, when this is used, the mobile must take into account possible future re-transmissions when deciding on the transmission rate of the first transmission. This requires reserving enough transmission power headroom in case additional power is needed for a subsequent re-transmission. This depends on the variability of the reverse channel conditions which in turn depends on the mobility of the mobile as well as the reverse link load of the sector. In this paper, we propose setting the power headroom dynamically instead of using a static value as is presently done. Simulation results demonstrate the effectiveness of our approach.