A wireless communication device with coexistence of multiple wireless communication systems (102, 104) comprising: a first wireless communication system, comprising: an up-conversion circuit, arranged to up-convert a first transmit, TX, signal in a baseband to generate a second TX signal with a first carrier frequency; and a front-end circuit, arranged to transmit the second TX signal to another wireless communication device, wherein the first carrier frequency is within a band combination that is employed at the first wireless communication system and is supported by said another wireless communication device; the band combination comprising any one or more operating bands employed by the wireless communication system for data transmission; and a second wireless communication system, comprising: a first down-conversion circuit, arranged to down-convert a first receive, RX, signal with a second carrier frequency to generate a second RX signal with a third carrier frequency; and a second down-conversion circuit, arranged to down-convert the second RX signal with the third carrier frequency to generate a third RX signal in the baseband; wherein the first wireless communication system is a 4G Long Term Evolution, LTE, or a 5G sub-6GHz system, and the second wireless communication system is a 5G New Radio, NR, Millimeter Wave, mmWave, system; and wherein the third carrier frequency is chosen to be different to all fundamental frequencies which correspond to the frequencies of the uplink band. a first wireless communication system, comprising: an up-conversion circuit, arranged to up-convert a first transmit, TX, signal in a baseband to generate a second TX signal with a first carrier frequency; and a front-end circuit, arranged to transmit the second TX signal to another wireless communication device, wherein the first carrier frequency is within a band combination that is employed at the first wireless communication system and is supported by said another wireless communication device; an up-conversion circuit, arranged to up-convert a first transmit, TX, signal in a baseband to generate a second TX signal with a first carrier frequency; and a front-end circuit, arranged to transmit the second TX signal to another wireless communication device, wherein the first carrier frequency is within a band combination that is employed at the first wireless communication system and is supported by said another wireless communication device; the band combination comprising any one or more operating bands employed by the wireless communication system for data transmission; and a second wireless communication system, comprising: a first down-conversion circuit, arranged to down-convert a first receive, RX, signal with a second carrier frequency to generate a second RX signal with a third carrier frequency; and a second down-conversion circuit, arranged to down-convert the second RX signal with the third carrier frequency to generate a third RX signal in the baseband; a first down-conversion circuit, arranged to down-convert a first receive, RX, signal with a second carrier frequency to generate a second RX signal with a third carrier frequency; and a second down-conversion circuit, arranged to down-convert the second RX signal with the third carrier frequency to generate a third RX signal in the baseband; wherein the first wireless communication system is a 4G Long Term Evolution, LTE, or a 5G sub-6GHz system, and the second wireless communication system is a 5G New Radio, NR, Millimeter Wave, mmWave, system; and wherein the third carrier frequency is chosen to be different to all fundamental frequencies which correspond to the frequencies of the uplink band.