An apparatus of a user equipment, UE, the UE configured to perform inter-frequency and inter-public land mobile network, PLMN, discovery, the apparatus comprising one or more processors and memory configured to: process a serving PLMN system information block, SIB, 19, received from an eNodeB, for a carrier frequency of a serving PLMN of the UE; acquire inter-frequency and inter-PLMN discovery system information acquisition assistance signaling information from the SIB19; process a non-serving PLMN SIB19 for one or more carrier frequencies of a non-serving PLMN using the inter-frequency and inter-PLMN discovery system information acquisition assistance signaling information; and identify inter-frequency and inter-PLMN discovery announcement rate information and monitoring control configuration information for the one or more carrier frequencies of the non-serving PLMN to enable the UE to perform device-to-device, D2D, discovery with a UE in the non-serving PLMN according to the inter-frequency and inter-PLMN discovery announcement rate information and monitoring control configuration information; characterized in that the one or more processors and memory are further configured to: use a higher layer signaling of transmission probabilities for the inter-frequency and inter-PLMN discovery announcement rate information and monitoring control configuration information, wherein the higher layer signaling configures: a transmission, TX, discovery pool for transmission of discovery messages on the one or more carrier frequencies of the non-serving PLMN such that the UE transmits on every K-th period of the discovery pool configured in the one of a plurality of carrier frequencies, where K is a positive integer greater than 1; or a time interval for inter-frequency discovery announcement or monitoring on top of an existing discovery pool configurations, wherein the time interval is dependent on a PLMN identity. process a serving PLMN system information block, SIB, 19, received from an eNodeB, for a carrier frequency of a serving PLMN of the UE; acquire inter-frequency and inter-PLMN discovery system information acquisition assistance signaling information from the SIB19; process a non-serving PLMN SIB19 for one or more carrier frequencies of a non-serving PLMN using the inter-frequency and inter-PLMN discovery system information acquisition assistance signaling information; and identify inter-frequency and inter-PLMN discovery announcement rate information and monitoring control configuration information for the one or more carrier frequencies of the non-serving PLMN to enable the UE to perform device-to-device, D2D, discovery with a UE in the non-serving PLMN according to the inter-frequency and inter-PLMN discovery announcement rate information and monitoring control configuration information; characterized in that the one or more processors and memory are further configured to: use a higher layer signaling of transmission probabilities for the inter-frequency and inter-PLMN discovery announcement rate information and monitoring control configuration information, wherein the higher layer signaling configures: a transmission, TX, discovery pool for transmission of discovery messages on the one or more carrier frequencies of the non-serving PLMN such that the UE transmits on every K-th period of the discovery pool configured in the one of a plurality of carrier frequencies, where K is a positive integer greater than 1; or a time interval for inter-frequency discovery announcement or monitoring on top of an existing discovery pool configurations, wherein the time interval is dependent on a PLMN identity. a transmission, TX, discovery pool for transmission of discovery messages on the one or more carrier frequencies of the non-serving PLMN such that the UE transmits on every K-th period of the discovery pool configured in the one of a plurality of carrier frequencies, where K is a positive integer greater than 1; or a time interval for inter-frequency discovery announcement or monitoring on top of an existing discovery pool configurations, wherein the time interval is dependent on a PLMN identity.