of the network (coverage). As a rule of thumb, every dB of sensitivity or selectivity lost in a handset translates into a required 10% increase in network density to maintain equivalent coverage/capacity. Handset sensitivity and selectivity is therefore directly related to the overall investment and running cost of the network. The impact of production volume on RF performance therefore needs to be carefully quantified. The metric is not simply volume but volume over time, effectively a 'maturity threshold' that has to be reached in order to support an adequate supply of performance competitive price competitive handsets. So we need to define the 'volume thresholds' and 'maturity thresholds' needed to achieve a supply of 'economically efficient' handsets. Economically efficient handsets are handsets that have reached a volume threshold at which their component costs do not significantly decrease with additional volume. This implies that an acceptable return of investment has been achieved both in terms of component development investment and the engineering effort needed to turn those components into finished competitive product. However, we are also saying that economically efficient handsets must also have reached a volume and maturity threshold at which handset RF performance is effectively as good as it can be, given the capabilities of the technology used, in other words a maturity performance threshold. 4.4.2 The Impact of Volume Thresholds and Maturity Performance Thresholds on RF Performance - A GSM Example In 1992, when GSM single-band 900-MHz phones first became available, it was a major design and production challenge to make phones that would meet the basic conformance sensitivity specification of -102 dBm. There were similar problems meeting other RF performance parameters, for example adjacent channel selectivity and phase errors on the transmit path. Only just achieving the conformance requirement significantly increases production costs. This is because the variation in component tolerances from p