FIELD OF THE INVENTION
This invention generally relates to communication. More particularly, this invention relates to wireless communication.
DESCRIPTION OF THE RELATED ART
Wireless communication systems have increased in popularity and capability. More features are being added to wireless communication systems on a routine basis. One aspect of wireless communications that remains a challenge is accurately locating a mobile station when global positioning system (GPS) signals are not available. There are situations in which a mobile station having GPS capability is not able to detect enough satellite signals for making an accurate location determination. This is particularly true when a mobile station is being used indoors.
One approach proposed for locating mobile stations that does not rely upon GPS signals includes triangulating based upon multiple base station signals received by a mobile station. There are limitations to this technique in that there are many locations where a mobile station is not able to detect enough base stations. Additionally, signals from a base station in another cell are often not reliably received by a mobile station.
SUMMARY
An exemplary method of communicating includes using coordinated scheduling of downlink transmissions in a plurality of cells. The coordinated scheduling includes a serving node in one of the cells currently serving a mobile station pausing downlink transmission on at least one selected resource when a non-serving node in a neighboring one of the cells not currently serving the mobile station transmits a downlink communication intended for the mobile station on the selected resource.
An exemplary communication system includes a serving node in a cell that is currently serving a mobile station. The serving node pauses downlink transmissions to the mobile station on at least one selected resource when a non-serving node in a neighboring cell transmits a downlink communication intended for receipt by the mobile station on the selected resource.
The various features and advantages of the disclosed example will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically illustrates selected portions of an example communication system.
FIG. 2 is a flowchart diagram summarizing an example approach.
FIG. 3 is a flowchart diagram summarizing an example feature of one example embodiment.
FIG. 4 schematically illustrates a resource block allocation to provide coordinated scheduling of downlink transmissions that is useful with an example embodiment.
DETAILED DESCRIPTION
FIG. 1 schematically shows selected portions of an example wireless communication system 20 involved in mobile station positioning using a triangulation technique. One particular communication arrangement that is well suited for the example approach is the LTE Rel-9 communication system. The disclosed example technique is not necessarily limited to any particular wireless communication system arrangement. A base station or node (e.g., eNode B) 22 provides wireless communication service within a cell 24. In the example of FIG. 1, the node 22 serves a mobile station 26. In other words, the cell 24 is the serving cell for the mobile station 26.
The example system includes a non-serving node or base station 30 in a neighboring cell 32. Another non-serving node or base station 34 is in another neighboring cell 36. Given the current location of the mobile station 26, for example, it is capable of detecting downlink transmissions from the nodes 30 and 34.
When it is desirable to determine location information regarding the mobile station 26, it is possible to estimate a distance relative to each base station using downlink transmissions from the nodes 22, 30 and 34 received by the mobile station 26 for that purpose. Known time difference of arrival techniques allow for using known triangulation techniques to determine a location of the mobile station 26. One example situation in which such location information is desirable is if an emergency service (i.e., E911) call is placed from the mobile station 26. Providing proper response to an emergency service call requires determining the location of the caller. Location information may be needed or desired in other situations, also.
The example of FIG. 1 includes a radio resource management (RRM) module 40 that coordinates scheduling of downlink transmissions from the nodes 22, 30 and 34 to increase the ability of the mobile station 26 to receive reliable signals from the non-serving nodes 30 and 34. Given that the node 22 is currently serving the mobile station 26, any transmissions from that node will interfere with the ability of the mobile station 26 to detect signals from the non-serving nodes 30 and 34. The RRM module 40 coordinates timing of transmissions from the nodes on at least one selected resource to increase the ability of the mobile station 26 to reliably receive downlink transmission from each of the nodes so that an accurate location determination can be made.
For purposes of discussion, a single RRM module 40 is schematically shown in FIG. 1. Depending on the arrangement of the particular communication system, each node is likely to have its own RRM functionality that is capable of communicating with the RRM functionality of the other nodes in adjacent or nearby cells. This is true in LTE systems, for example. In some examples there may be a centralized or regional RRM functionality that performs the task of coordinating the scheduling among the serving cell and the neighboring cells. Given this description, those skilled in the art will realize what type of controllers and functionality will best meet the needs of their particular situation.
FIG. 2 includes a flowchart diagram 50 that summarizes one example approach. At 52, a triggering event is detected. One example triggering event is an emergency service call from the mobile station 26. Other requests for making a location determination are used as a triggering event in some examples. At 54, neighboring cells are identified. The neighboring cells will be non-serving cells that the mobile station 26 may detect a downlink transmission from given its current disposition. In one example, the mobile station 26 reports a list of neighboring cells to the serving node 22. This information is used by the radio resource management module 40 to coordinate scheduling for the serving cell in the neighbor cells as shown at 56 in FIG. 2.
As shown at 58, the serving cell node 22 will pause or mute downlink transmission to the mobile station 26 over at least one selected resource during an interval during which at least one of the neighbor cell nodes 30, 34 is transmitting a downlink communication intended for the mobile station 26 over the selected resource. Pausing downlink transmission from the serving cell 24 eliminates a source of interference that would otherwise reduce the likelihood that the mobile station 26 would reliably receive a signal from a non-serving node. Increasing the ability of the mobile station 26 to receive downlink transmissions from the non-serving neighbor cells 32 and 36 increases the likelihood of accurately making a location determination regarding the current position of the mobile station 26.
FIG. 3 includes a flowchart diagram 60 that summarizes an example approach for using coordinated downlink transmissions. This example is useful for locating a mobile station based on the downlink transmissions according to coordinated scheduling. At 62, the downlink transmissions occur according to the coordinated schedule. Transmissions from the serving node 22 are paused or muted at a selected resource during a downlink transmission from either of the non-serving nodes 30 and 34 at the selected resource. At 64, a time difference of arrival of the downlink transmissions received at the mobile station 26 is determined. The time difference of arrival information can be determined in a known manner. Given that the scheduling of the downlink transmissions is coordinated, there will be known time offset information between the different transmissions. Such time offset information is incorporated into the algorithm that determines the time difference of arrival information in one example. At 66, mobile station location information is determined based upon the time difference of arrival information for the downlink transmissions from the serving node 22 and the non-serving nodes 30 and 34, respectively. The coordinated scheduling of those downlink transmissions facilitates better reception by the mobile station 26 of each of those transmissions.
One example includes utilizing a special location service reference signal (LCS-RS) for the time difference of arrival measurements. Using a custom or dedicated signal for such purposes can facilitate recognition by a mobile station.
In one example implementation, the coordinated scheduling is based upon resource block allocation. It is desirable to minimize the amount of wireless communication resources that are jointly allocated among the nodes involved in the coordinated scheduling of downlink transmissions to a mobile station about which location information is desired. FIG. 4 schematically shows an example resource block 70 that is utilized for coordinated scheduling of downlink transmissions among a serving cell (SC), a non-serving or neighboring cell (NC1) and another non-serving or neighboring cell (NC2). The resource block 70 is divided into a plurality of subcarriers represented by the rows and each of the subcarriers is divided up into a plurality of time slots represented by the columns.
As can be appreciated from the illustration, some of the subcarriers are used for downlink transmissions 72 from the serving cell and those are labeled “SC” in the drawing. Transmissions from the non-serving cells also occur on the same subcarriers during different time intervals. All downlink transmissions from one of the neighboring cells NC1 occur as shown at 74 and all downlink transmissions from the other neighboring cell NC2 occur at 76. As can be appreciated from the illustration, the serving cell transmissions SC do not occur on the same subcarrier at the same time as a downlink transmission from either of the non-serving cells on that subcarrier. Downlink transmissions from the serving cell to the mobile station 26 on a subcarrier are muted or paused during an interval including a downlink transmission from one of the non-serving cells on that subcarrier.
A resource block allocation as shown in FIG. 4 is useful in an example where each of the nodes 22, 30 and 34 has two transmit antennas. The illustrated example is also useful for minimizing the number of resource blocks that are required for providing downlink transmissions to the mobile station 26 for the determination of location information. Minimizing the number of resource blocks allocated to the location determinations better utilizes overall wireless communication resources. A single resource block that is jointly allocated among the nodes involved in the location determination is useful for some examples.
The arrangement of FIG. 4 also includes a known pattern of transmission from the neighboring cells. This facilitates correctly estimating the timing offset information among the different signals received by the mobile station 26.
One feature of the example of FIG. 4 is that the LCS-RS pattern reuses the resource elements. For example, the different sub-carriers are reused by selected cells for their LCS-RS transmissions. The same resource element is transmitted at some remote cells to have no interference to those cells. This increases the likelihood that the intended recipient will receive the transmission from the remote cell and ensures sufficiently high resource utilization. Additionally, reusing the resources in this manner decreases the required resolution of LCS-RS detection.
In one example the amount of resource element reuse is less than that shown in the example of FIG. 4. One such example includes power boosting the transmission of the LCS-RS from the non-serving cells (compared to the transmit power used for transmissions to mobile stations served by such cells) to increase the likelihood that the LCS-RS signal will be received.
The illustration of FIG. 4 is one example of coordinated scheduling among a serving cell and non-serving cells for making location determinations. When a mobile station reports more than two neighboring cells, a different pattern for providing an LCS-RS to the mobile station may be utilized. Those skilled in the art who have the benefit of this description will be able to determine how best to coordinate scheduling among the involved nodes by utilizing, for example, resource block allocations so that the serving cell downlink transmissions are muted or paused to avoid interfering with a non-serving cell transmission.
FIG. 4 shows one resource allocation technique that coordinates scheduling and assignment of resource elements such as sub-carriers and time slots. Other examples utilize other resource configurations (e.g., carrier frequencies, time frames, etc.) within the coordinated scheduling approach.
Given this description, those skilled in the art will realize that the example approach may be useful for facilitating communications from a non-serving cell to a mobile station even when the mobile station is not involved in a handoff to that non-serving cell. The mobile station may receive and utilize downlink transmissions from a non-serving cell for a variety of purposes such as locating the mobile station.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims.
Patent Application
20100172310
