This patent application is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "FIG. 1 depicts a diagram of the salient components of wireless telecommunications system 100 in accordance with the prior art. Wireless telecommunications system 100 comprises: wireless terminal 101, base stations 102-1, 102-2, and 102-3, wireless switching center 111, assistance server 112, location client 113, and Global Positioning System ('GPS') constellation 121. Wireless telecommunications system 100 provides wireless telecommunications service to all of geographic region 120, in well-known fashion.
"The salient advantage of wireless telecommunications over wireline telecommunications is the mobility that is afforded to the users. On the other hand, the salient disadvantage of wireless telecommunications lies in that fact that because the user is mobile, an interested party might not be able to readily ascertain the location of the user.
"Such interested parties might include both the user of the wireless terminal and remote parties. There are a variety of reasons why the user of a wireless terminal might be interested in knowing his or her location. For example, the user might be interested in telling a remote party where he or she is or might seek advice in navigation.
"In addition, there are a variety of reasons why a remote party might be interested in knowing the location of the user. For example, the recipient of an E 9-1-1 emergency call from the wireless terminal might be interested in knowing the location of the wireless terminal so that emergency services vehicles can be dispatched to that location.
"There are many techniques in the prior art for estimating the location of a wireless terminal. In accordance with some techniques, the location of a wireless terminal is estimated, at least in part, from signal measurements that are reported by the wireless terminal. The reported measurements are of signals measured by the wireless terminal that are transmitted by one or more base stations and, in some cases, by GPS satellites.
"Wireless terminal 101 reports measurements to telecommunications system 100, which measurements can then be used for location estimation purposes. Independent of location estimation, however, terminal 101 monitors the strength of signals transmitted by multiple neighboring base stations, such as base station 102-1 through 102-3, in order to ensure that the terminal is always communicating with the base station that provides the strongest signal. If, at some point, another base station is found to provide a stronger signal, the call that involves the user of terminal 101 might need to be handed over to the other base station. Terminal 101 can then ask the system to initiate a handover. This technique is known as a 'mobile-assisted handover' (MAHO).
"In addition to other signals that provide connectivity for the wireless terminals, each of base station 102-1 through 102-3 also transmits a signal that is designed to be relatively tolerant of interference. Such signals are known by various names such as 'pilots' in systems that are based on code division multiple access (CDMA), or 'cell-specific reference signals' (CRS) in systems that are based on 3.sup.rd
"The cell-specific reference signals enhance the detectability of signals from neighboring cells and make MAHO possible."
In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventor's summary information for this patent application: "There are system functionalities other than mobile-assisted handover (MAHO), such as some location estimation techniques, that benefit from the ability to accurately detect signals from neighboring cells and, specifically, from the ability to estimate parameters of such signals. The problem with relying solely on cell-specific reference signals for non-MAHO functionalities, however, is that these reference signals were designed for detection by a wireless terminal primarily when the signal is transmitted by the base station of the serving cell of the wireless terminal or by a base station of a cell that is adjacent to the serving cell. Consequently, cell-specific reference signals that are transmitted from base stations that are further away from the wireless terminal can be difficult to detect and, hence, often unreliable for use in at least some non-MAHO functionalities in the prior art. Location estimation that relies on measurements by a wireless terminal is one such functionality.
"In addition to providing for the transmission of cell-specific reference signals, the Long-Term Evolution (LTE) standard also provides a capability for estimating the location of wireless terminals, based on a technique referred to as 'observed time difference of arrival' (OTDOA). OTDOA requires relative timing measurements to be made by the terminal. To support this capability, LTE requires that each base station transmit, at regular intervals, a signal known as a 'positioning reference signal' (PRS). A PRS is designed to enable precise estimation of its time of arrival when received by a wireless terminal. In a typical use of these signals, a wireless terminal compares propagation time differences of signals from multiple base stations to estimate its own location.
"The present invention enables a wireless terminal to measure reference signals with improved interference characteristics over at least some techniques in the prior art. The present invention is based on the observation by its inventors that the positioning reference signals used in the LTE standard, though optimized for precise estimation of time of arrival, also happen to have good characteristics for interference mitigation. In other words, the interference caused by positioning reference signals is less than the interference caused by other signals in the LTE standard, and it is easier to mitigate by using well-known and commonly used interference-mitigation techniques.
"In accordance with the illustrative embodiment of the present invention, a telecommunications system comprises a wireless switching center (WSC) and plurality of base stations that are configured to transmit positioning reference signals. The base stations transmit the positioning reference signals in positioning subframe time intervals. Meanwhile, the base stations also transmit cell-specific reference signals continuously, including during the positioning subframe time intervals. In order to ensure that the wireless terminal measures those cell-specific reference signals during periods of lower interference, the base station advantageously imposes a measurement restriction on the wireless terminal, in regard to when it may measure a signal. Such a measurement restriction mechanism is available in LTE, as the inventors have observed, although it was previously used for other applications. As an example, the measurement restriction capability was previously applied to supporting femtocells that were deployed in an area where an LTE-based cellular system provides macrocellular service in the same spectrum. To avoid disruption of the macrocellular system, the femtocells were directed to transmit minimal amounts of radio signal in certain designated time intervals known as 'almost blank subframes' (ABS). The macrocellular system would direct wireless terminals to attempt to detect cell-specific reference signals only in the ABS time intervals. The advantage of doing so was that, during ABS intervals, interference from femtocells was minimized.
"In contrast to the traditional application of the measurement restriction mechanism, such as for femtocell management, the base station of the illustrative embodiment directs the wireless terminal to detect the cell-specific reference signals only in the positioning subframe time intervals. As a result of utilizing the measurement restriction in this way, in combination with the improved interference characteristics of the positioning reference signals themselves, the ability of the wireless terminal to detect the cell-specific reference signals of more distant cells is advantageously improved. This has the added benefit of making available improved measurements to functionalities such as location estimation, thereby improving their performance as well.
"In some embodiments, the base station also transmits a measurement directive to the wireless terminal, in order to explicitly command the terminal to measure the reference signals and to return the corresponding measurement results. In some embodiments, a location estimation system can command the base station to transmit the directive, or can use the measurement results in a location estimation procedure, or both.
"Although the telecommunications system of the illustrative embodiment utilizes the 3GPP LTE set of standards, it will be clear to those skilled in the art, after reading this specification, how to make and use embodiments of the present invention in which other standards are utilized, in addition to or instead of LTE. Such standards include, but are not limited to, Universal Mobile Telecommunications System 'UMTS', Global System Mobile 'GSM,' CDMA-2000, IS-136 TDMA, IS-95 CDMA, 3G Wideband CDMA, IEEE 802.11 WiFi, 802.16 WiMax, and Bluetooth. In such embodiments reference signals, in addition to or instead of cell-specific reference signals and positioning reference signals, may be used, as those who are skilled in the art will appreciate after reading this specification.
"The telecommunications system of the illustrative embodiment features measurement of cell-specific reference signals during the positioning subframe time intervals, in order to improve location estimation performance. It will be clear, however, to those skilled in the art, after reading this specification, how to make and use embodiments of the present invention in order to improve the performance of other functionalities that utilize measurements made by a wireless terminal.
"An illustrative embodiment of the present invention comprises: transmitting, by a base station, a measurement directive to a wireless terminal to measure one or more cell-specific reference signals, wherein a measurement restriction transmitted to the wireless terminal indicates designated time intervals of one or more positioning subframes in which positioning reference signals are transmitted by one or more base stations, and wherein the measurement restriction imposes a restriction on the wireless terminal to measure the one or more cell-specific reference signals coincident with the designated time intervals; and receiving, by the base station, a measurement result from the wireless terminal in response to the measurement directive being transmitted.
BRIEF DESCRIPTION OF THE DRAWINGS
"FIG. 1 depicts a diagram of the salient components of wireless telecommunications system 100 in accordance with the prior art.
"FIG. 2 depicts a diagram of the salient components of wireless telecommunications system 200 in accordance with the illustrative embodiment of the present invention.
"FIG. 3 depicts a block diagram of the salient components of base station 202, as shown in FIG. 2, in accordance with the illustrative embodiment.
"FIG. 4 depicts a block diagram of the salient components of location server 214, as shown in FIG. 2, in accordance with the illustrative embodiment.
"FIG. 5 depicts a flowchart of the salient processes performed in accordance with the illustrative embodiment of the present invention.
"FIG. 6 depicts a flowchart of the salient sub-processes of process 501 as shown in FIG. 5, performed in accordance with the illustrative embodiment of the present invention.
"FIG. 7 depicts a flowchart of the salient sub-processes of process 502 as shown in FIG. 5, performed in accordance with the illustrative embodiment of the present invention.
"FIG. 8 depicts a flowchart of the salient sub-processes of process 504 as shown in FIG. 5, performed in accordance with the illustrative embodiment of the present invention."
URL and more information on this patent application, see: Gordon,
Keywords for this news article include: Telecommunications,
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