user equipment it is assumed that at point a on the horizontal axis server 2 a is already included in the active set of servers at position 9 a the power received from server 2 b represented by curve 8 b crosses threshold 10 a and neglecting effects related to time constants server 2 b is added to the active set at position 15 a however the received power from server 2 b falls below the threshold 10 a on the assumption of a zero hysteresis system and so the server 2 b is dropped from the active set it will therefore be appreciated that the server 2 b is held within the active set over the region 14 a now considering the case of a slow moving or static user equipment it is again assumed that at point a on the horizontal axis server 2 a is already included in the active set of servers at position 9 b the power received from server 2 b represented by curve 8 b crosses threshold 10 b and server 2 b is added to the active set at position 15 b the received power from server 2 b falls below the threshold 10 b and so the server 2 b is dropped from the active set it can be seen that this case the server 2 b is held within the active set over the region 14 b which is smaller than 14 a the server.