Here P can be determined specifically in the following two approaches without any limitation thereto.
In a first approach, for example, N=50, there are 500 frequency domain resource elements in total, and the resource granularity is 50, so one bit indicates a resource element, and there are 500/50=10 bits, so that the third frequency domain position of the frequency domain resources occupied by the downlink control channel resource set corresponding to the user equipment shall be notified in P=10 bits. Alternatively P can be determined according to the maximum bandwidth to be indicated, or another preset bandwidth.
In a second approach, for example, N=10, so the third frequency domain position of the frequency domain resources occupied by the downlink control channel resource set corresponding to the user equipment can be notified in ceil(log 2(Q*(Q+1)/2))=ceil(log 2(50*(50+1)/2))=11 bits, where Q is the number of the resource granularities in the downlink transmission bandwidth.