Capacity enhancement schemes for forward and reverse links of distributed cellular base stations
View Patent ↗Capacity enhancement schemes are described for forward and reverse links of distributed cellular base stations consisting of a central unit and one or more remote units. In general, in one aspect, reverse link capacity is shared among remote units. The capacity sharing can be determined dynamically. The forward link capacity can also be enhanced by estimating the location of the mobile stations.
1. A distributed base station comprising:
a central unit having one or more modems, each modem including one or more input ports;
remote units, at least one of the remote units in communication with the central unit via a transmission medium, the remote units each having one or more RF elements, each RF element having one or more receive antennas;
one or more combining modules configured to select one or more subsets of reverse link signals from the RF elements to be combined before each input port of the modem, wherein RF elements of at least two remote units share a reverse link capacity of at least one of the modems; and
a gain compensation module configured to equalize link gains of signal paths associated with the selected subsets of reverse link signals prior to the selected subsets of reverse link signals being combined by the one or more combining modules.
2. The base station of claim 1 wherein the gain compensation module is further configured to employ a temperature dependent variable gain device.
3. The base station of claim 1 wherein the gain compensation module is further configured to measure an amplified signal power while a test signal is injected at an input of a first RF element.
4. The base station of claim 3 further comprising a test device configured to generate the test signal, wherein the amplified signal power is constant.
5. The base station of claim 3 further comprising a switch configured to disconnect the input from an associated antenna and to connect the input to a first end of a resistor with its second end connected to a ground reference.
6. The base station of claim 5 wherein the test signal comprises thermal noise across the resistor.
7. The base station of claim 1 wherein the combining module is further configured to dynamically change the mapping from the subsets of signals to each modem input port based on changes to the estimated loading in each RF element.
8. The base station of claim 1 wherein the RF elements sharing the reverse link capacity of at least one of the modems are changed dynamically as an estimated loading in each RF element changes.
9. The base station of claim 1 wherein timing advance is used to compensate for transmission delay from the central unit to a first RF element that is not sharing.
10. The base station of claim 1 wherein timing advance is used to compensate for transmission delay from the central unit to a RF element farthest from the central unit that is sharing the reverse link capacity of at least one of the modems with other RF elements and delay compensation is used in other RF elements to equalize forward and reverse link delays.
11. The base station of claim 1 wherein optimal delay compensation and timing advance are used as a function of cell size and RF environment in RF elements sharing the reverse link capacity of at least one of the modems.
12. The base station of claim 1 wherein at least a portion of the remote units are cascaded.
13. The base station of claim 12 wherein cascading is done by TDM.
14. The base station of claim 12 wherein at least a portion of signals are combined at remote units.
15. The base station of claim 1 wherein at least a portion of signals are combined at the central unit.
16. The base station of claim 1 wherein signals transmitted between the central unit and a first remote unit are analog or digital base band signals.
17. The base station of claim 1 wherein signals transmitted between the central unit and a first remote unit are analog or digital IF signals.
18. The base station of claim 1 wherein signals transmitted between the central unit and a first remote unit are RF signals.
19. The base station of claim 1 wherein at least a portion of the RF elements support beam forming.