n say that soft block- ing occurs when the total interference level exceeds the background noise level by a given quantity. Then from the logic for capacity started in Chapter 7 we define the total interference as: (8.5) where M is the number of users in the same cell, Eb equals the energy per bit of the sig- nal, R is the baseband data rate, N is the thermal noise power, and n is the loading factor defined in Chapter 7 [20], i.e. the interference ratio brought in by the MSs served by other cells to interference generated by MSs served by the home cell. Then, if we get soft blocking when Itotal exceeds the background noise level by a given quantity 1/x, we can prevent soft blocking if (8.6) If we define x = N/I total, we can define the soft capacity as a function of the maximum allowable interference level for our simple model, which would not necessary apply in practice, but can serve to understand the concept of load control, (8.7) To conclude the load control, we next define hard blocking. Here we assume that the actual ratio of Itotal to background noise is negligible, i.e. there exists very low probabil- ity for soft blocking. To define hard blocking we first define the actual load and the conditional load. The first refers to the real load passing through a network in action, while the 2nd refers to the actual load plus the administrative traffic such as soft handovers. Then we introduce a traffic factor as traffic raffic_tactor (8.8) conditional load Then, the actual load is actual_load=traffic_factorxconditional_load (8.9) The UMTS Network and Radio Access Technology Thus, we have a simple way to quickly determine the number of voice channels, e.g. we can use the actual load in conjunction with Erlang's C formula for the blocking rate. This formula implies that a subscriber who is blocked will re-originate calls until he/she goes through. This blocking probability is equivalent to the probability that the call has been delayed, and it can be expressed as: (8.10) 8.4.2.2 Conclusions Enhancing and managing 