Narrowband signal transport sub-system for distributed antenna system
Certain aspects involve narrowband signal transport sub-systems for a distributed antenna system (“DAS”). The narrowband signal transport sub-system includes one or more filter banks that are communicatively coupled to a port of a unit in the DAS. The input port can receive a broadband downlink signal that includes multiple carriers. Each filter bank can generate a set of narrowband downlink signals corresponding to a carrier from the broadband downlink signal. Each filter bank can include demodulators and filters. The demodulators can generate respective frequency-shifted downlink signals from the carrier. Each frequency-shifted downlink signal can have a respective frequency shift from the carrier's frequency that is based on a respective bandwidth for the carrier. Each filter can have a passband corresponding to the bandwidth of a narrowband channel associated with the carrier and can generate one of the narrowband downlink signals by filtering a respective one of the frequency-shifted downlink signals.
1. A narrowband signal transport sub-system for a distributed antenna system, the narrowband signal transport sub-system comprising:
an input port configured to receive a broadband downlink signal comprising a plurality of carriers; and
a filter bank configured to generate a set of narrowband downlink signals from the broadband downlink signal, wherein the set of narrowband downlink signals corresponds to a carrier from the plurality of carriers, the filter bank comprising:
demodulators communicatively coupled to the input port and configured to generate respective frequency-shifted downlink signals from the carrier, each of the frequency-shifted downlink signals having a respective frequency shift from a frequency of the carrier, wherein the respective frequency shift is based on a bandwidth of a narrowband channel associated with the carrier, and
filters communicatively coupled to the demodulators and configured to output the set of narrowband downlink signals, wherein each of the filters has a passband corresponding to the bandwidth of the carrier and is configured to generate a respective narrowband downlink signal of the set of narrowband downlink signals by filtering a respective one of the frequency-shifted downlink signals.
2. The narrowband signal transport sub-system of claim 1 , wherein each frequency shift is based on the bandwidth divided by a step width, the step width comprising a difference in frequency between adjacent narrowband downlink signals in the set of narrowband downlink signals.
3. The narrowband signal transport sub-system of claim 2 , wherein the filter bank is configured such that the step width minimizes a ripple in an additional passband for the set of narrowband downlink signals.
4. The narrowband signal transport sub-system of claim 1 , wherein each of the filters comprises a respective bandpass filter having a respective center frequency corresponding to a respective additional center frequency of the respective frequency-shifted downlink signal.
5. The narrowband signal transport sub-system of claim 1 , wherein the filter bank further comprises decimators that are communicatively coupled to respective outputs of the filters, wherein each decimator is configured to reduce a sampling rate of a respective narrowband downlink signal outputted from a respective one of the filters.
6. The narrowband signal transport sub-system of claim 1 , wherein the filter bank is included in a master unit that is configured to communicate signals between base stations and remote units of the distributed antenna system.
7. The narrowband signal transport sub-system of claim 1 , further comprising an additional filter bank, wherein the additional filter bank comprises modulators configured to up-convert respective narrowband downlink signals from the set of narrowband downlink signals.
8. The narrowband signal transport sub-system of claim 7 , wherein the filter bank further comprises decimators configured to reduce a sampling rate of the set of narrowband downlink signals outputted by the filters, wherein the additional filter bank comprises interpolators configured to increase the sampling rate of the set of narrowband downlink signals.
9. The narrowband signal transport sub-system of claim 7 , further comprising a combiner configured to combine the set of narrowband downlink signals into a combined broadband downlink signal.
10. A method for generating narrowband signals from a multicarrier signal communicated via a distributed antenna system, the method comprising:
receiving a broadband downlink signal comprising signal components for carriers; and
for each of the carriers:
generating a set of frequency-shifted downlink signals having respective frequency shifts from a frequency of the carrier, wherein each of the frequency shifts is determined based on a bandwidth of a narrowband channel associated with the carrier, and
generating narrowband downlink signals by filtering the frequency-shifted downlink signals using filters having respective passbands corresponding to the bandwidth for the carrier.
11. The method of claim 10 , wherein each frequency shift is based on the bandwidth of the carrier divided by a step width, wherein the step width comprises a difference in frequency between adjacent narrowband downlink signals.
12. The method of claim 11 , further comprising selecting the step width such that a ripple in an additional passband for a set of the narrowband downlink signals is minimized.
13. The method of claim 10 , wherein each of the filters comprises a respective bandpass filter having a respective center frequency corresponding to a respective additional center frequency of the respective frequency-shifted downlink signal.
14. The method of claim 10 , further comprising reducing a sampling rate of the narrowband downlink signals and transmitting the narrowband downlink signals to a remote unit of the distributed antenna system.
15. The method of claim 14 , further comprising increasing, by the remote unit, the sampling rate of the received narrowband downlink signals.
16. The method of claim 15 , further comprising combining, by the remote unit, the narrowband downlink signals into a combined broadband downlink signal.
17. A distributed antenna system configured to generate narrowband signals from a multicarrier signal, the distributed antenna system comprising:
a remote unit; and
a distributed antenna unit comprising filters having respective passbands corresponding to bandwidths for carriers, the distributed antenna unit configured to be communicatively coupled to the remote unit and a base station, the distributed antenna unit configured to:
receive a broadband downlink signal comprising signal components for the carriers, and
for each of the carriers:
generate a set of frequency-shifted downlink signals having respective frequency shifts from a frequency of the carrier, wherein each of the frequency shifts is determined based on a bandwidth of a narrowband channel associated with the carrier, and
generate narrowband downlink signals by filtering the frequency-shifted downlink signals using at least one of the filters having a respective passband corresponding to the bandwidth for the carrier.
18. The distributed antenna system of claim 17 , wherein the distributed antenna unit is configured with the frequency shift such that the frequency shift is based on the bandwidth of the carrier divided by a step width, wherein the step width comprises a difference in frequency between adjacent narrowband downlink signals.
19. The distributed antenna system of claim 18 , wherein the distributed antenna unit is configured with the frequency shift such that a ripple in an additional passband for a set of the narrowband downlink signals is minimized.
20. The distributed antenna system of claim 17 , wherein each of the filters comprises a respective bandpass filter having a respective center frequency corresponding to a respective additional center frequency of the respective frequency-shifted downlink signal.