REDUCING EFFECTS OF CHANNEL FILTER FREQUENCY DRIFT

TECHNICAL FIELD

The present disclosure relates to a communication arrangement comprising a first transceiver unit and a second transceiver unit. The first transceiver unit comprises a first control unit and a first transmitter arrangement that is adapted to transmit signals by means of at least one carrier frequency to the second transceiver unit that in turn comprises a second control unit and a second receiver arrangement that is adapted to receive said signals.

BACKGROUND

For wireless communication, often multiple frequency channel signals are transmitted from a transmitter to a receiver. For each frequency channel, there is a corresponding transmitter filter and receiver filter; these filters are in the form of waveguide filters and are tuned to match used channel separation and have high rejection outside the channel’s band.

One problem with these filters is frequency drift which for example is caused by varying air humidity and temperature. In order to avoid this frequency drift materials with low temperature drift are used, for example invar. Each filter can also be individually calibrated depending on site location. Both these solutions are relatively expensive. It is desirable to provide a communication arrangement where the negative effects of channel filter frequency drift are reduced.

SUMMARY

It is an object of the present disclosure to provide a communication arrangement where the negative effects of channel filter frequency drift are reduced.

Said object is obtained by means of a first transceiver unit comprising a first control unit and a first transmitter arrangement that is adapted to transmit signals by means of at least one carrier frequency to a second transceiver unit comprising a second receiver arrangement that is adapted to receive said signals. The first transmitter arrangement comprises a transmitter branch for each carrier frequency. The first transceiver unit is adapted to receive information from the second transceiver unit regarding a desired carrier frequency for at least one transmitter branch. The first control unit is adapted to adjust said carrier frequency accordingly.

This confers an advantage of providing a suitable carrier frequency as evaluated at the second transceiver unit. In this way, the filters need not be extremely resilient to changes in temperature and humidity.

According to some aspects, the transmitter branch comprises a corresponding transmitter device and a corresponding transmitter filter.

According to some aspects, the first control unit is adapted to adjust said carrier frequency by means of controlling an IF (Intermediate Frequency) signal and/or a voltage controlled oscillator (VCO) at each transmitter device in question.

This provides uncomplicated ways to adjust the carrier frequency. Said object is also obtained by means of a second transceiver unit comprising a second control unit and a second receiver arrangement that is adapted to receive signals via at least one carrier frequency from a first transceiver unit comprising a first transmitter arrangement that is adapted to transmit said signals. The second receiver arrangement comprises a receiver branch for each carrier frequency. The second control unit is adapted to determine if a received signal spectrum deviates from a desired signal spectrum to a certain degree, and for each such deviation, the second transceiver unit is adapted to transmit information to the first transceiver unit regarding a desired carrier frequency for at least one corresponding signal. This confers an advantage of controlling the carrier frequency to a desired value. In this way, the filters need not be extremely resilient to changes in temperature and humidity. According to some aspects, each receiver branch comprises a corresponding receiver device and corresponding receiver filter.

According to some aspects, the second transceiver unit comprises an equalizer functionality and the second control unit is adapted to determine if a received signal spectrum deviates from a desired signal spectrum by analyzing at least one of:

equalizer gain as a function of frequency; and

equalizer group delay as a function frequency. According to some other aspects, the second control unit is adapted to calculate an FFT (Fast Fourier Transform) for said received signals, and to determine if a received signal spectrum deviates from a desired signal spectrum by analyzing said FFT.

This provides uncomplicated ways to acquire information regarding a desired carrier frequency.

Said object is also obtained by means of a communication arrangement comprising a first transceiver unit and a second transceiver unit, where the first transceiver unit comprises a first control unit and a first transmitter arrangement that is adapted to transmit signals by means of at least one carrier frequency to the second transceiver unit. The second transceiver unit in turn comprises a second control unit and a second receiver arrangement that is adapted to receive said signals. The first transmitter arrangement comprises a transmitter branch for each carrier frequency, where each transmitter branch comprises a corresponding transmitter device and a corresponding transmitter filter. The second receiver arrangement comprises a receiver branch for each carrier frequency, where each receiver branch comprises a receiver device and corresponding receiver filter. The second control unit is adapted to determine if a filter response of at least one transmitter filter and corresponding receiver filter deviates from a desired receiver filter response to a certain degree, and for each such deviation the second transceiver unit is adapted to transmit information to the first transceiver unit regarding a desired carrier frequency for at least one corresponding transmitter branch. The first transceiver unit is adapted to receive said information and where the first control unit is adapted to adjust said carrier frequency accordingly. This confers an advantage of controlling the carrier frequency to a desired value. In this way, the filters need not be extremely resilient to changes in temperature and humidity.

According to some aspects, the first control unit is adapted to adjust said carrier frequency by means of controlling an IF (Intermediate Frequency) signal or a voltage controlled oscillator (VCO) at each transmitter device in question. This provides uncomplicated ways to adjust the carrier frequency.

According to some aspects, the second transceiver unit comprises an equalizer functionality and the second control unit is adapted to determine if said filter response deviates from a desired filter response by analyzing at least one of:

equalizer gain as a function of frequency; and

equalizer group delay as a function frequency.

According to some other aspects, the second control unit is adapted to calculate an FFT (Fast Fourier Transform) for said received signals, and to determine if said filter response deviates from a desired filter response by analyzing said FFT.

This provides uncomplicated ways to acquire information regarding a desired carrier frequency. There are also disclosed herein methods associated with the above-mentioned advantages.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure will now be described more in detail with reference to the appended drawings, where:

Figure 1 schematically shows a wireless communication node;

Figure 2 schematically shows a communication arrangement; Figure 3A schematically shows a nominal filter response and received signal spectrum; Figure 3B schematically shows a distorted filter response, a received signal spectrum and a modified signal;

Figure 4 schematically shows a nominal received signal spectrum and a distorted received signal spectrum;

Figure 5 schematically shows a nominal equalizer gain and a distorted equalizer gain;

Figure 6 schematically shows a nominal equalizer delay and a distorted equalizer delay;

Figure 7 shows a flowchart for methods according to the present disclosure; and

Figure 8 shows a flowchart for methods according to the present disclosure.

DETAILED DESCRIPTION

With reference to Figure 1 , there is a first node N1 and a second node N2, where the first node N1 comprises a first transceiver unit 1 and the second node N2 comprises a second transceiver unit 2, where these transceiver units 1 , 2 are comprised in a communication arrangement 10.

With reference to Figure 2, schematically showing the communication arrangement 10, the first transceiver unit 1 comprises a first control unit 3 and a first transmitter arrangement 4 that is adapted to transmit signals by means of three carrier frequencies to the second transceiver unit 2. The second transceiver unit 2 in turn comprises a second control unit 9 and a second receiver arrangement 5 that is adapted to receive said signals. Thus, for communication from the first transceiver unit 1 to the second transceiver unit 2, the first transmitter arrangement 4 comprises a transmitter branch 16, 17, 18 for each carrier frequency, where each transmitter branch 16, 17, 18 comprises a corresponding transmitter device TX1 a, TX1 b, TX1 c and a corresponding transmitter filter 6, 7, 8 that is connected to a corresponding branch circulator 48, 49, 50. The second receiver arrangement 5 comprises a receiver branch 31 , 32, 33 for each carrier frequency, where each receiver branch 31 , 32, 33 comprises a receiver device RX2a, RX2b, RX2c and corresponding receiver filter 11 , 12, 13 that is connected to a corresponding branch circulator 51 , 52, 53.

Correspondingly, for communication from the second transceiver unit 2 to the first transceiver unit 1 , the second transceiver unit 2 comprises a second transmitter arrangement 34 that is adapted to transmit signals by means of three carrier frequencies to the first transceiver unit 1. The first transceiver unit 1 in turn comprises a first receiver arrangement 35 that is adapted to receive said signals.

The second transmitter arrangement 34 comprises a transmitter branch 36, 37, 38 for each carrier frequency, where each transmitter branch 36, 37, 38 comprises a corresponding transmitter device TX2a, TX2b, TX2c and a corresponding transmitter filter 39, 40, 41 that is connected to a corresponding branch circulator 54, 55, 56. The first receiver arrangement 35 comprises a receiver branch 42, 43, 44 for each carrier frequency, where each receiver branch 42, 43, 44 comprises a receiver device RX1 a, RX1 b, RX1 c and corresponding receiver filter 45, 46, 47 that is connected to a corresponding branch circulator 57, 58, 59.

The branch circulators 48, 49, 50; 57, 58, 59 of the first transceiver unit 1 are connected to a first common circulator 60 that in turn is connected to a first antenna arrangement 61. The branch circulators 51 , 52, 53; 54, 55, 56 of the second transceiver unit 2 are connected to a second common circulator 62 that in turn is connected to a second antenna arrangement 63.

The branches of each transceiver corresponds to frequency channels. Each branch is adapted for a certain frequency band, or channel, having a certain centre frequency, and all filters are in the form of channel filters. The frequency bands lie relatively close to each other, and the circulators and the filters are all used for avoiding leakage of undesired signals in a well-known manner.

With reference to Figure 3A, there is a filter response 64 and a transmitted signal spectrum 65 shown for a signal generated at a first transmitter device TX2a at a first transmitter branch 16 of the first transceiver unit 1 and received at a first receiver branch 31 at the second transceiver unit 2. Here, the filter response 64 that is centred around a carrier frequency f _c depends on the filter characteristics of the corresponding filters 6, 11 in said branches 16, 31. Should the filter characteristics change, as shown in Figure 3B where a changed filter response 64’ is centred around a changed carrier frequency f _c ’ due to frequency drift, the received signal spectrum will be distorted as evident from Figure 3B.

According to the present disclosure, the second control unit 9 is adapted to determine if the filter response for said filters 6, 11 deviates from a desired receiver filter response to a certain degree. If that is the case, as shown in Figure 3B, the second transceiver unit 2 is adapted to transmit information to the first transceiver unit 1 regarding a desired carrier frequency for the first transmitter branch 16. The first transceiver unit 1 is adapted to receive said information and the first control unit 3 is adapted to adjust said carrier frequency accordingly.

This is illustrated in Figure 3B, where the first transmitter device TX2a is controlled to generate a modified signal 65’ that is centred around the changed carrier frequency fc’. In this way, the received signal spectrum will no longer be distorted, as evident from Figure 3B. The first control unit 3 is adapted to adjust the carrier frequency by means of controlling an IF (Intermediate Frequency) signal and/or a voltage controlled oscillator (VCO) at the first transmitter device TX1 a.

In order to determine that the filter response for said filters 6, 11 deviates from a desired receiver filter response to a certain degree, different strategies are possible.

According to a first example, the second transceiver unit 2 comprises an equalizer functionality that according to some aspects is implemented in the second control unit 9. As shown in Figure 4, there is a nominal received signal spectrum 66 and a distorted signal spectrum 67 that has been distorted by means of filter frequency drift as discussed above.

Figure 5 shows the corresponding equalizer gains over frequency; a nominal equalizer gain 19a corresponding to the nominal received signal spectrum 66 and a distorted equalizer gain 19b corresponding to the distorted received signal spectrum 67. The equalizer functionality will always strive to compensate the filter attenuation by gaining up the attenuated side so the gain will be asymmetrical compared to a non-distorted spectrum. By instructing the first control unit 3 to adjust the carrier frequency in question in the direction to the side with lowest gain, in this example towards a higher frequency, the gain unbalance will be smaller and when the gain is symmetrical there is an optimum frequency offset.

Figure 6 shows corresponding equalizer group delays over frequency; a nominal equalizer group delay 20a corresponding to the nominal received signal spectrum 66 and a distorted equalizer group delay 20a corresponding to the distorted received signal spectrum 67. The equalizer group delay 20a, 20b are used for detecting frequency drift in the same way as equalizer gain. In general, several channels are used, one for each branch of a transceiver unit, and each channel frequency offset can be calculated according to above. By using information from all available channels when calculating each channel frequency offset provides a more robust algorithm. According to a second example, the second control unit (9) is adapted to calculate an FFT (Fast Fourier Transform) for the received signals, and to determine if said filter response deviates from a desired filter response by analyzing said FFT.

According to a third example, each one of the first transceiver unit 1 and the second transceiver unit 2 comprises a temperature sensor 14a, 14b and a humidity sensor 15a, 15b. The second control unit 9 is adapted to determine if said filter response deviates from a desired filter response by comparing sensor inputs from said sensors 14a, 14b; 14c, 14d with a predetermined list of filter responses versus different temperatures and/or humidity values. The first transceiver unit 1 transfers the sensor inputs of its sensors 14a, 15a to the second transceiver unit 2 in any suitable manner, for example via a radio link.

The present disclosure is not limited to the example described above, but may vary within the scope of the appended claims. For example, a filter response is in this context dependent on the combined filter characteristics for one channel, of course the individual filters no not have to change to an equal amount. It is conceivable that only one of the filter is responsible for the frequency drift. When a control unit 9 is adapted to determine if a filter response of at least one transmitter filter 6, 7, 8 and corresponding receiver filter 11 , 12, 13 deviates from a desired receiver filter response to a certain degree, it is combined deviation of each transmitter filter and corresponding receiver filter that is referred to. The individual filters may probably, as stated above, deviate to different degrees. In the above, an example has been described for one transmitter branch TX1A at the first transceiver unit 1 and one receiver branch RX2A at the second transceiver unit 2. Of course, the present disclosure can be implemented for all branches in both directions, i.e. also when the second transceiver unit 2 transmits signals to the first transceiver unit 1. The present disclosure is, however, at least implemented for one transmitter branch and a corresponding receiver branch at any type of communication arrangement 10. Each transceiver unit can comprise any suitable number of branches for transmission and reception. There is however at least one transmitter branch comprised in one transceiver unit and at least one receiver branch comprised in another transceiver unit.

Each antenna arrangement may comprise any suitable type of antenna, such as single column array antennas, multi-column array antennas and single element antennas such as for example reflector antennas. Each antenna arrangement may thus comprise one or more antenna elements; for example in the form of reflector antennas, patch antennas, slit antennas and/or dipole antennas. The antenna arrangements may comprise the same, similar or different types of antennas.

In the Figures, only those elements essential for describing the present matter in a clear manner are shown. Of course, wireless communication nodes and transceiver units comprise several more components such as for example devices for power, communication and control, which are not shown here. All such components are considered as well-known in the art, and are neither shown, nor discussed, for reasons of clarity.

All or some of the circulators can be changed with any suitable type of power combiner/splitter device.

With reference to Figure 7, the present disclosure relates to a method for a first transceiver unit 1 comprising:

21 : transmitting signals by means of at least one carrier frequency to a second transceiver unit 2 via at least one corresponding transmitter branch 16, 17, 18;

The method further comprises:

22: receiving information from the second transceiver unit 2 regarding a desired carrier frequency for at least one transmitter branch 16, 17, 18; and

23: adjusting said carrier frequency accordingly.

With reference to Figure 8, the present disclosure relates to a method for a second transceiver unit 2 comprising:

24: receiving signals via at least one carrier frequency from a first transceiver unit 1 ; and

25: determining if a received signal spectrum deviates from a desired signal spectrum to a certain degree;

wherein, for each such deviation, the method comprises:

26: transmitting information to the first transceiver unit 1 regarding a desired carrier frequency for at least one corresponding signal.

According to some aspects, the determining 25 if a filter response of at least one receiver filter 11 , 12, 13 deviates from a desired filter response comprises:

27: analyzing at least one of:

equalizer gain as a function of frequency 19a, 19b; and

equalizer group delay 20a, 20b as a function frequency. According to some aspects, the determining 25 if a filter response of at least one receiver filter 11 , 12, 13 deviates from a desired filter response comprises:

28: calculating an FFT, Fast Fourier Transform, for the received signals; and where the determining 25 of if received signal spectrum deviates from a desired signal spectrum comprises:

29: analyzing said FFT.

According to some aspects, the determining 25 if a received signal spectrum deviates from a desired filter response comprises:

30: comparing sensor inputs regarding temperature and/or humidity with a predetermined list of filter responses versus different temperatures and/or humidity values.

Generally, the present disclosure also relates to a first transceiver unit 1 comprising a first control unit 3 and a first transmitter arrangement 4 that is adapted to transmit signals by means of at least one carrier frequency to a second transceiver unit 2 comprising a second receiver arrangement 5 that is adapted to receive said signals, where the first transmitter arrangement 4 comprises a transmitter branch 16, 17, 18 for each carrier frequency, wherein the first transceiver unit 1 is adapted to receive information from the second transceiver unit 2 regarding a desired carrier frequency for at least one transmitter branch 16, 17, 18, where the first control unit 3 is adapted to adjust said carrier frequency accordingly.

According to some aspects, each transmitter branch 16, 17, 18 comprises a corresponding transmitter device TX1 a, TX1 b, TX1 c and a corresponding transmitter filter 6, 7, 8.

According to some aspects, the first control unit 3 is adapted to adjust said carrier frequency by means of controlling an IF, Intermediate Frequency, signal and/or a voltage controlled oscillator, VCO, at each transmitter device TX1 a, TX1 b, TX1 c in question.

Generally, the present disclosure also relates to a second transceiver unit 2 comprising a second control unit 9 and a second receiver arrangement 5 that is adapted to receive signals via at least one carrier frequency from a first transceiver unit 1 comprising a first transmitter arrangement 4 that is adapted to transmit said signals, where the second receiver arrangement 5 comprises a receiver branch 31 , 32, 33 for each carrier frequency, wherein the second control unit 9 is adapted to determine if a received signal spectrum deviates from a desired signal spectrum to a certain degree, and for each such deviation, the second transceiver unit 2 is adapted to transmit information to the first transceiver unit 1 regarding a desired carrier frequency for at least one corresponding signal. According to some aspects, each receiver branch 31 , 32, 33 comprises a corresponding receiver device RX2a, RX2b, RX2c and corresponding receiver filter

11 , 12, 13.

According to some aspects, the second transceiver unit 2 comprises an equalizer functionality and the second control unit 9 is adapted to determine if a received signal spectrum deviates from a desired signal spectrum by analyzing at least one of:

equalizer gain as a function of frequency; and

equalizer group delay as a function frequency. According to some aspects, the second control unit 9 is adapted to calculate an FFT, Fast Fourier Transform, for said received signals, and to determine if a received signal spectrum deviates from a desired signal spectrum by analyzing said FFT.

Generally, the present disclosure also relates to a communication arrangement 10 comprising a first transceiver unit 1 and a second transceiver unit 2, where the first transceiver unit 1 comprises a first control unit 3 and a first transmitter arrangement 4 that is adapted to transmit signals by means of at least one carrier frequency to the second transceiver unit 2 that in turn comprises a second control unit 9 and a second receiver arrangement 5 that is adapted to receive said signals, where the first transmitter arrangement 2 comprises a transmitter branch 16, 17, 18 for each carrier frequency, where each transmitter branch 16, 17, 18 comprises a corresponding transmitter device TX1 a, TX1 b, TX1 c and a corresponding transmitter filter 6, 7, 8, and where the second receiver arrangement 5 comprises a receiver branch 31 , 32, 33 for each carrier frequency, where each receiver branch 31 , 32, 33 comprises a receiver device RX2a, RX2b, RX2c and corresponding receiver filter 11 , 12, 13, wherein the second control unit 9 is adapted to determine if a filter response of at least one transmitter filter 6, 7, 8 and corresponding receiver filter 11 , 12, 13 deviates from a desired receiver filter response to a certain degree, and for each such deviation the second transceiver unit 2 is adapted to transmit information to the first transceiver unit 1 regarding a desired carrier frequency for at least one corresponding transmitter branch 16, 17, 18, and wherein the first transceiver unit 1 is adapted to receive said information and where the first control unit 3 is adapted to adjust said carrier frequency accordingly.

According to some aspects, the first control unit 3 is adapted to adjust said carrier frequency by means of controlling an IF (Intermediate Frequency) signal or a voltage controlled oscillator, VCO, at each transmitter device TX1 a, TX1 b, TX1 c in question. According to some aspects, the second transceiver unit 2 comprises an equalizer functionality and the second control unit 9 is adapted to determine if said filter response deviates from a desired filter response by analyzing at least one of:

equalizer gain 19a, 19b as a function of frequency; and

equalizer group delay 20a, 20b as a function frequency.

According to some aspects, the second control unit 9 is adapted to calculate an FFT, Fast Fourier Transform, for said received signals, and to determine if said filter response deviates from a desired filter response by analyzing said FFT. According to some aspects, each one of the first transceiver unit 1 and the second transceiver unit 2 comprises at least one of a temperature sensor 14a, 14b and a humidity sensor 15a, 15b, and where the second control unit 9 is adapted to determine if said filter response deviates from a desired filter response by comparing sensor inputs with a predetermined list of filter responses versus different temperatures and/or hum idity values.