The invention relates to a device for exchanging ultra wide band signals, and also relates to a circuit for use in a device, to a system, and to a method. Examples of such a device are receivers, transmitters and tranceivers for exchanging ultra wide band signals, such as wireless interfaces, wireless terminals and wireless stations.

A prior art device is known from US 5,467,091, which discloses in its Figure 6B a device with a high-frequency mixer Ml in a receiving branch and with a high-frequency mixer M2 in a transmitting branch. The high-frequency mixer Ml receives an input signal from an antenna and receives a high-frequency oscillation signal from a synthesizer and generates an output signal destined for an intermediate frequency stage in the form of a dual IF receiver. The high-frequency mixer M2 receives an input signal from, an intermediate frequency stage in the form of switchable clutter oscillators and receives the high-frequency oscillation signal from the synthesizer and generates an output signal destined for a filter transmit bank and an antenna. To tune the device to different frequency channels in the ultra wide band (>1 GHz), the synthesizer generates different high-frequency oscillation signals: For tuning the device to a first frequency channel, a first high-frequency oscillation signal is to be generated, and for tuning the device to a second frequency channel, a second high- frequency oscillation signal is to be generated. The known device is disadvantageous, inter alia, owing to the fact that its hopping synthesizer, when having a classical phase locked loop architecture, needs too much time for switching from one frequency channel to an other. When having a classical single side band mixer architecture, the hopping synthesizer is sufficiently fast, but then generates unwanted tones. These unwanted tones cause distortions that need to be filtered by either many filters (for example a filter per frequency channel) or by one or several expensive filters (for example a filter having an adjustable frequency characteristic). It is an object of the invention, inter alia, to provide a device which can be tuned to different frequency channels of an ultra wide band in a sufficiently fast and relatively distortionless way. Furthers objects of the invention are, inter alia, to provide a circuit, a system, and a method, all for use in (combination with) a device which can be tuned to different frequency channels of an ultra wide band in a sufficiently fast and relatively distortionless way. The device according to the invention for exchanging ultra wide band signals comprises: - a high-frequency stage for tuning the device to an ultra wide band; and a low-frequency stage for tuning the device to a frequency channel of the ultra wide band. By shifting the tuning to the frequency channels of the ultra wide band from (prior art situation) the high-frequency stage to (invention) the low-frequency stage, the disadvantageous prior art hopping synthesizers are avoided. By separating the tuning to the ultra wide band from the tuning to the frequency channels in the ultra wide band, the tuning to the frequency channels can be done in a sufficiently fast and relatively distortionless way. This is a great advantage, especially, but not exclusively, in frequency hopping networks. Further advantages are a lower power consumption, cleaner spectra and the fact that complex hopping synthesizers are replaced by simple oscillating synthesizers. An ultra wide band is a band of frequency channels for example situated above 1 GHz. A high-frequency stage is a stage, in which stage, at the moment, at least one relevant signal has a frequency for example above 1 GHz. A low- frequency stage is a stage, in which stage, at the moment, all relevant signals have frequencies for example below 1 GHz. In general, at the moment as well as for the future, in the high-frequency stage at least one relevant signal has a frequency above X GHz, and in the low- frequency stage all relevant signals have frequencies below X GHz, whereby for example X > 1. An embodiment of the device according to the invention is defined by the high-frequency stage comprising a high-frequency mixer for frequency translating signals by applying a high-frequency oscillation signal, which high-frequency oscillation signal, for operation in the ultra wide band, comprises one fixed high-frequency signal and, for operation in a further ultra wide band, comprises one further fixed high-frequency signal. The fixed and further fixed high-frequency signals for example originate from oscillators. An oscillator for generating a fixed high-frequency signal is easy to make. The switching between two oscillators can be done in a sufficiently fast and relatively distortionless way. It should be noted that EP 1 292 043 discloses in its Figure 1 an intermediate mixer coupled to a fixed frequency local oscillator and an end mixer coupled to a frequency hopped oscillator. This intermediate mixer is a low-frequency mixer which is not used for tuning the device to the frequency channels in the ultra wide band. The tuning to the frequency channels in the ultra wide band is done by the end mixer. This end mixer is a high- frequency mixer. The frequency hopped oscillator is a synthesizer having the disadvantages discussed above. An embodiment of the device according to the invention is defined by the fixed high-frequency signal being a 3960 MHz signal and the further fixed high-frequency signal being a 7128 MHz signal, and which ultra wide band comprises three frequency channels at 3432 MHz, 3960 MHz and 4488 MHz, and which further ultra wide band comprises four frequency channels at 6336 MHZ, 6864 MHZ, 7392 MHZ and 7920 MHz. These ultra wide bands are the most interesting bands of a frequency area which is expected to become an industrial standard under the communication standard IEEE802.15.3a. Between these ultra wide bands, an other ultra wide band is situated, but in this other band further communication standards are active, such as IEEE802.il a. A Multi-Band Orthogonal Frequency Division Multiplexing Alliance (MBOA) proposal assumes frequency hopping through the frequency channels within 9 nsec. while remaining in the frequency channel around 300 nsec. An embodiment of the device according to the invention is defined by the low- frequency stage comprising a low-frequency mixer for frequency translating signals by applying a low-frequency oscillation signal, which low-frequency oscillation signal, for a frequency channel, comprises a low- frequency signal and, for a further frequency channel, comprises a further low- frequency signal. The low-frequency signal tunes the device to the frequency channel, and the further low- frequency signal tunes the device to the further frequency channel. An embodiment of the device according to the invention is defined by the low- frequency signals being 528 MHz signals with inverted phases. Then, the device can be tuned to the frequency channels of the first ultra wide band situated around 3960 MHz (comprising three frequency channels at 3432 MHz, 3960 MHz and 4488 MHz) and to the frequency channels of the second ultra wide band situated around 7128 MHz (comprising four frequency channels at 6336 MHZ, 6864 MHZ, 7392 MHZ and 7920 MHz). An embodiment of the device according to the invention is defined by the low- frequency stage comprising a converter having a bandwidth equal to or larger than a bandwidth of combined frequency channels of the ultra wide band. In this case, between the high-frequency stage and the converter, a low-frequency mixer is no longer necessary. The tuning to the frequency channels of the ultra wide band is done in the converter, where the frequency channels, but now in baseband, are available next to each other. An embodiment of the device according to the invention is defined by the stages forming part of a receiver, which receiver comprises an antenna coupled to an input of the high-frequency stage and which low- frequency stage comprises an analog-to-digital converter coupled to an output of the high-frequency stage. As described above, the analog- to-digital converter may be coupled to the output of the high-frequency stage (high-frequency mixer) directly (possibly via one or more filters, amplifiers etc.) or indirectly via the low- frequency mixer (and possibly via one or more filters, amplifiers etc.). An embodiment of the device according to the invention is defined by the stages forming part of a transmitter, which low- frequency stage comprises a digital-to-analog converter coupled to an input of the high-frequency stage and which transmitter comprises an antenna coupled to an output of the high-frequency stage. As described above, the digital-to- analog converter may be coupled to the input of the high-frequency stage (high-frequency mixer) directly (possibly via one or more filters, amplifiers etc.) or indirectly via the low- frequency mixer (and. possibly via one or more filters, amplifiers etc.). The circuit according to the invention for use in a device for exchanging ultra wide band signals comprises a high-frequency stage and a low-frequency for example in the form of an integrated circuit. The system according to the invention comprises at least two devices for exchanging ultra wide band signals, which devices comprise high-frequency stages and low- frequency stages. Preferably, a device comprises a terminal device and an other device comprises a station device, for example in a frequency hopping network. Embodiments of the circuit according to the invention and of the system according to the invention and of the method according to the invention correspond with the embodiments of the device according to the invention. The invention is based upon an insight, inter alia, that the tuning to frequency channels of an ultra wide band is a process, which process, in a high-frequency environment, is either slow or causes distorsion, and is based upon a basic idea, inter alia, that this process can be shifted from the high-frequency environment to a low- frequency environment. The invention solves the problem, inter alia, to provide a device which can be tuned to different frequency channels of an ultra wide band in a sufficiently fast and relatively distortionless way, and is advantageous, inter alia, in that the process of tuning the device to different frequency channels of an ultra wide band is sufficiently fast and relatively distortionless. Further advantages are a lower power consumption, cleaner spectra and the fact that complex hopping synthesizers are replaced by simple oscillating synthesizers.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments(s) described hereinafter. In the drawings: Fig. 1 shows diagrammatically a device according to the invention in the form of a receiver comprising a high-frequency mixer stage; Fig. 2 shows diagrammatically a device according to the invention in the form of a receiver comprising a high-frequency mixer stage and a low- frequency mixer stage; Figs. 3A-D show spectra before and after high-frequency and low- frequency mixer stages for an ultra wide band; Figs. 4A-D show spectra before and after high-frequency and low-frequency mixer stages for a further ultra wide band; Fig. 5 shows diagrammatically a device according to the invention in the form of a transmitter comprising a high-frequency mixer stage; Fig. 6 shows diagrammatically a device according to the invention in the form of a transmitter comprising a high-frequency mixer stage and a low-frequency mixer stage; Fig. 7 shows diagrammatically a first embodiment of a prior art mixer for use in a high-frequency or low- frequency mixer stage; and Fig. 8 shows diagrammatically a second embodiment of a prior art mixer for use in a high-frequency or low- frequency mixer stage.

The device 1 according to the invention shown in Fig. 1 in the form of a receiver comprises a high-frequency stage 5 and a low- frequency stage 7 and a processor 11. The high-frequency stage 5 comprises a high-frequency mixer stage 50. The high-frequency mixer stage 50 comprises two mixers 51 and 52 of which the inputs are coupled to each other and to an output of a unit 54. The unit 54 for example comprises an amplifier and a filter. An input of the unit 54 is coupled to an antenna 13. An oscillator input of the mixer 51 is coupled to an oscillator 53 for receiving an in-phase high-frequency oscillation signal, and an oscillator input of the mixer 52 is coupled to the oscillator 53 for receiving a quadrature high- frequency oscillation signal. Outputs of the mixers 51 and 52 are coupled via units 71 and 72 to a unit 73 which is further coupled to a unit 74. These units 71-74 form part of the low- frequency stage 7. The units 71 and 72 for example comprise filters, amplifiers and analog- to-digital converters. The unit 73 for example comprises a synchronizer, a common pilot remover and a fast fourier transformator. The unit 74 for example comprises a pilot remover, a de-interleaver, a viterbi decoder and a descrambler. The processor 11 for example controls the units 54, 71-74 and the oscillator 53. The device 2 according to the invention shown in Fig. 2 in the form of a receiver comprises the high-frequency mixer stage 5 and the processor 11 already described for Fig. 1 and a low-frequency stage 8. The low-frequency stage 8 comprises a low-frequency mixer stage 80 and a unit 70 comprising the units 71-74 already described for Fig. 1. An output of the mixer 51 is coupled to inputs of mixers 81 and 82 of the low-frequency mixer stage 80, and an output of the mixer 52 is coupled to inputs of mixers 83 and 84 of the low- frequency mixer stage 80. Outputs of the mixers 81 and 84 are coupled to inputs of a summing unit 86. An output of the summing device 86 is coupled to an input of the unit 70. Outputs of the mixers 82 and 83 are coupled to inputs of a summing unit 87. An output of the summing device 87 is coupled to a further input of the unit 70. Oscillator inputs of the mixers 81 and 83 are coupled to an oscillator 85 for receiving an in-phase low- frequency oscillation signal, and oscillator inputs of the mixers 82 and 84 are coupled to the oscillator 85 for receiving a quadrature low- frequency oscillation signal. The processor 11 for example controls the units 54,70 and the oscillators 53,85. The operation of the device 1 is explained in view of Fig. 3 A. A first ultra wide band is situated around 3960 MHz signal and a second ultra wide band is situated around 7128 MHz signal. The first ultra wide band comprises a first frequency channel at 3432 MHz, a second frequency channel at 3960 MHz and a third frequency channel at 4488 MHz. The second ultra wide band comprises a first frequency channel at 6336 MHZ, a second frequency channel at 6864 MHZ, a third frequency channel at 7392 MHZ and a fourth frequency channel at 7920 MHz. Each frequency channel has a bandwidth equal to 528 MHz. Ultra wide band signals situated in the first ultra wide band arrive at the antenna 13 and are down converted to zero IF (Intermediate Frequency) by the high- frequency mixer stage 50. Thereto, the mixers 51 and 52 receive their in-phase and quadrature oscillation signals comprising high-frequency signals at 3960 MHz. Fig. 3A shows the ultra wide band signals before being down converted at the left side, and after being down converted at the right side. After being down converted, the first frequency channel is positioned from -792 MHz to -264 MHz, the second frequency channel is positioned from —264 MHz to +264 MHz, and the third frequency channel is positioned from +264 MHz to +792 MHz. The analog-to-digital converter 71,72 must have a bandwidth equal to or larger than 729 MHz to be able to convert the ultra wide band signals after being down converted. The demodulation of the wanted frequency channel is done in the digital domain. So, the device 1 in view of Fig. 3 A is tuned to one or more frequency channels of the first ultra wide band by properly selecting one or more down converted frequency channels in the baseband. The operation of the device 2 is explained in view of Fig. 3B-3D. The ultra wide bands and frequency channels are situated before being down converted as already described for Fig. 3 A. Ultra wide band signals situated in the first ultra wide band arrive at the antenna 13 and are down converted to zero IF (Intermediate Frequency) by the high- frequency mixer stage 50. Thereto, the mixers 51 and 52 receive their in-phase and quadrature oscillation signals comprising high-frequency signals at 3960 MHz. Fig. 3B-3D show at the right side the ultra wide band signals after being down converted. In case of the second frequency channel being the wanted frequency channel, Fig. 3B right side, the low- frequency mixer stage 80 is by-passed or driven inactive (for example by generating in-phase and quadrature low-frequency oscillation signals equal to DC). The second frequency channel is positioned from -264 MHz to +264 MHz. The analog-to-digital converter 70 must have a bandwidth equal to or larger than 264 MHz to be able to convert these ultra wide band signals after being down converted. The demodulation of the wanted frequency channel is done in the digital domain. In case of the third frequency channel being the wanted frequency channel, Fig. 3C right side, the low-frequency mixer stage 80 is driven with in-phase and quadrature low- frequency oscillation signals comprising low-frequency signals at 528 MHz. Then, the third frequency channel is converted down to zero IF by the combination of the high- frequency mixer stage 50 and the low- frequency mixer stage 80. The third frequency channel is then positioned from -264 MHz to +264 MHz. The analog-to-digital converter 70 must have a bandwidth equal to or larger than 264 MHz to be able to convert these ultra wide band signals after being down converted, etc. In case of the first frequency channel being the wanted frequency channel, Fig. 3D right side, the low-frequency mixer stage 80 is driven with in-phase and quadrature low- frequency oscillation signals comprising low- frequency signals at 528 MHz. These oscillation signals are the phase inversions of the oscillation signals used for the third frequency channel (for example by exchanging the in-phase and the quadrature connections). Then, the first frequency channel is converted down to zero IF by the combination of the high-frequency mixer stage 50 and the low-frequency mixer stage 80. The first frequency channel is then positioned from -264 MHz to +264 MHz. The analog-to-digital converter 70 must have a bandwidth equal to or larger than 264 MHz, etc. So, the device 2 in view of Fig. 3B-3D is tuned to one or more frequency channels of the first ultra wide band by properly controlling the low- frequency mixer stage 80. For receiving ultra wide band signals situated in the first ultra wide band, the high- frequency oscillation signal comprises, for operation in the ultra wide band, one fixed high- frequency signal (3960 MHz). For operation in the second ultra wide band, the high- frequency oscillation signal comprises one further fixed high-frequency signal (7128 MHz). Thereto, the processor 13 must switch the oscillator 53 from 3960 MHz to 7128 MHz. This can be done by applying two oscillators and by selecting one of the two. The switching between two oscillators can be done in a sufficiently fast and relatively distortionless way. For the second ultra wide band, the operation of the device 1 is explained in view of Fig. 4A. The ultra wide bands and frequency channels are situated before being down converted as already described for Fig. 3 A. Ultra wide band signals situated in the second ultra wide band arrive at the antenna 13 and are down converted to zero IF (Intermediate Frequency) by the high-frequency mixer stage 50. Thereto, the mixers 51 and 52 receive their in-phase and quadrature oscillation signals comprising high-frequency signals at 7128 MHz. Fig. 4A shows the ultra wide band signals before being down converted at the left side, and after being down converted at the right side. After being down converted, the four frequency channels are positioned around 0 MHz. The analog-to-digital converter 71,72 must have a bandwidth equal to or larger than 1056 MHz to be able to convert the ultra wide band signals after being down converted. The demodulation of the wanted frequency channel is done in the digital domain. So, the device 1 in view of Fig. 4A is tuned to one or more frequency channels of the second ultra wide band by properly selecting one or more down converted frequency channels in the baseband. The operation of the device 2 is explained in view of Fig. 4B-4D. The ultra wide bands and frequency channels are situated before being down converted as already described for Fig. 3 A. Ultra wide band signals situated in the second ultra wide band arrive at the antenna 13 and are down converted to zero IF (Intermediate Frequency) by the high- frequency mixer stage 50. Thereto, the mixers 51 and 52 receive their in-phase and quadrature oscillation signals comprising high-frequency signals at 7128 MHz. Fig. 4B-4D show at the right side the ultra wide band signals after being down converted. In case of the second and third frequency channels being the wanted frequency channels, Fig. 4B right side, the low- frequency mixer stage 80 is by-passed or driven inactive (for example by generating in-phase and quadrature low-frequency oscillation signals equal to DC). The second and third frequency channels are positioned around 0 MHz. The analog-to-digital converter 70 must have a bandwidth equal to or larger than 528 MHz etc. In case of the fourth frequency channel being the wanted frequency channel, Fig. 4C right side, the low- frequency mixer stage 80 is driven with in-phase and quadrature low-frequency oscillation signals comprising low- frequency signals at 528 MHz. Then, the fourth frequency channel is converted down by the combination of the high-frequency mixer stage 50 and the low-frequency mixer stage 80. The fourth frequency channel is then positioned from 0 MHz to +528 MHz, and the analog-to-digital converter 70 can convert these ultra wide band signals after being down converted, etc. In case of the first frequency channel being the wanted frequency channel, Fig. 4D right side, the low-frequency mixer stage 80 is driven with in-phase and quadrature low- frequency oscillation signals comprising low- frequency signals at 528 MHz. These oscillation signals are the phase inversions of the oscillation signals used for the fourth frequency channel (for example by exchanging the in-phase and the quadrature connections). Then, the first frequency channel is converted down by the combination of the high- frequency mixer stage 50 and the low- frequency mixer stage 80. The first frequency channel is then positioned from -528 MHz to 0 MHz. The analog-to-digital converter 70 can convert these ultra wide band signals after being down converted, etc. So, the device 2 in view of Fig. 4B-4D is tuned to one or more frequency channels of the second ultra wide band by properly controlling the low-frequency mixer stage 80. The device 3 according to the invention shown in Fig. 5 in the form of a transmitter comprises a high-frequency stage 6 and a low-frequency stage 9 and a processor 12. The high-frequency stage 6 comprises a high-frequency mixer stage 60. The high- frequency mixer stage 60 comprises two mixers 61 and 62 of which the outputs are coupled to inputs of a summing device 65. an output of the summing device 65 is coupled to an input of a unit 64. The unit 64 for example comprises an amplifier and a filter. An output of the unit 64 is coupled to an antenna 14. An oscillator input of the mixer 61 is coupled to an oscillator 63 for receiving an in-phase high-frequency oscillation signal, and an oscillator input of the mixer 62 is coupled to the oscillator 63 for receiving a quadrature high-frequency oscillation signal. Inputs of the mixers 61 and 62 are coupled via units 91 and 92 to a unit 93 which is further coupled to a unit 94. These units 91-94 form part of the low-frequency stage 9. The units 91 and 72 for example comprise filters, amplifiers and digital-to-analog converters. The unit 93 for example comprises a synchronizer, a common pilot introducer and a fast fourier transformator. The unit 94 for example comprises a pilot introducer, an interleaver, a viterbi encoder and a scrambler. The processor 12 for example controls the units 64, 91 -94 and the oscillator 63. The device 4 according to the invention shown in Fig. 6 in the form of a transmitter comprises the high-frequency mixer stage 6 and the processor 12 already described for Fig. 5 and a low- frequency stage 10. The low- frequency stage 10 comprises a low- frequency mixer stage 100 and a unit 90 comprising the units 91-94 already described for Fig. 5. An input of the mixer 61 is coupled to an output of a summing device 106, of which inputs are coupled to outputs of mixers 101 and 104 of the low- frequency mixer stage 100, and an input of the mixer 62 is coupled to an output of a summing device 107, of which inputs are coupled to outputs of mixers 102 and 103 of the low-frequency mixer stage 100. Inputs of the mixers 101 and 102 are coupled to an output of the unit 90. Inputs of the mixers 103 and 104 are coupled to a further output of the unit 90. Oscillator inputs of the mixers 101 and 103 are coupled to an oscillator 105 for receiving an in-phase low- frequency oscillation signal, and oscillator inputs of the mixers 102 and 104 are coupled to the oscillator 105 for receiving a quadrature low-frequency oscillation signal. The processor 12 for example controls the units 54,90 and the oscillators 63,105. The operation of the devices 3 and 4 is in correspondance with the operation of the devices 1 and 2 as explained in view of Fig. 3 and 4, apart from the fact that the mixer stages in the devices 3 and 4 perfom up conversions, where the mixer stages in the devices 1 and 2 perform down conversions. The analog-to-digital converter in Fig. 1 and 2 has become a digital-to-analog converter in Fig. 5 and 6. Further, for example in the low- frequency stage 7, after down conversion, the signals of a wanted frequency channel must be selected properly, where, in the low-frequency stage 9, before up conversion, the signals for a wanted frequency channel must be positioned properly. So, the device according to the invention preferably comprises at least one mixer for tuning the device to an ultra wide band. This mixer is, compared to possible other mixers in the device, located closest to the antenna. This mixer converts (or frequency translates) signals by applying a high-frequency oscillation signal, which high-frequency oscillation signal, for operation in the ultra wide band, comprises one fixed high-frequency signal, and possibly, for operation in a further ultra wide band, comprises one further fixed high-frequency signal. The tuning to a frequency channel of the (further) ultra wide band is done, compared to a location of the mixer in the device, at an other location in the device. This other location is at a greater distance from the antenna than the location. At this other location, either at least an other mixer is used, or at least a converter having a sufficient bandwidth is used. In other words, the mixer operating at the highest frequency is only used for tuning the device to an ultra wide band and is not used for tuning the device to a frequency channel of the ultra wide band. And the tuning of the device to the frequency channel is done separately from the tuning of the device to the ultra wide band. A first embodiment of a prior art mixer for use in a high-frequency or low- frequency mixer stage as shown in Fig. 7 comprises six bipolar transistors 201-206. A collector of the transistor 201 is coupled via a resistor 200 to a voltage supply and to a collector of the transistor 203 and forms a negative balanced output. A collector of the transistor 202 is coupled via a resistor 207 to the voltage supply and to a collector of the transistor 204 and forms a positive balanced output. The emitters of the transistors 201 and 202 are coupled to each other and to a collector of the transistor 205. The emitters of the transistors 203 and 204 are coupled to each other and to a collector of the transistor 206. The emitters of the transistors 205 and 206 are coupled to each other and to a current source 208. The basis of the transistors 201 and 204 are coupled to each other for receiving a positive balanced oscillation signal, and the basis of the transistors 202 and 203 are coupled to each other for receiving a negative balanced oscillation signal. The basis of the transistor 201 receives a negative balanced input signal and the basis of the transistor 204 receives a positive balanced input signal. A second embodiment of a prior art mixer for use in a high-frequency or low- frequency mixer stage as shown in Fig. 8 comprises four MOS transistors 300-303. A control electrode of the MOS 300 is coupled to the control electrode of the MOS 303 for receiving a positive balanced oscillation signal. A control electrode of the MOS 301 is coupled to the control electrode of the MOS 302 for receiving a negative balanced oscillation signal. First main electrodes of the MOS 300 and the MOS 301 are coupled to each other for receiving a positive balanced input signal, and first main electrodes of the MOS 302 and the MOS 303 are coupled to each other for receiving a negative balanced input signal. Second main electrodes of the MOS 300 and the MOS 302 are coupled to each other and form a positive balanced output. Second main electrodes of the MOS 301 and the MOS 303 are coupled to each other and form a negative balanced output. Each block shown in Fig. 1,2,5,6 may comprise further filters, amplifiers etc. The in-phase and quadrature signals are just examples, other signals not being based on in- phase and quadrature components may alternatively be used. Sometimes, the ultra wide bands shown in Fig. 3,4 are called groups, and then the frequency channels are called bands. Other bands and frequency channels are not to be excluded. In Fig. 3,4, the vertical stripes are IEEE802.1 Ia communications, therefore, under IEEE802.15.3a, this in between ultra wide band and these frequency channels are not used. The invention may be applied in frequency hopping networks and in non-frequency hopping networks. The balanced prior art mixers shown in Fig. 7,8 are just examples, other possibly non-balanced mixers may be used alternatively. Each mixer shown in Fig. 1,2,5,6 may for example be realised by one of the mixers shown in Fig. 7,8. It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. Use of the verb "to comprise" and its conjugations does not exclude the presence of elements or steps other than those stated in a claim. The article "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. In the device claim enumerating several means, several of these means may be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.