Patent Application
20160066176
The present application relates to wireless telecommunication networks and, in particular, to a method to prevent the loss of downlink control signaling caused by transmission collision between downlink control signaling and positioning reference signal.
Location based services (LCS) brings convenience and new services to subscribers of mobile communication networks and therefore generates significant revenues to the operators. LCS requires the integration of wireless network infrastructure, mobile stations (also known as “user equipment”, or “UE” in short), and a range of location-specific applications and content. Besides the utilization of build-in satellite GPS chipset inside a UE, the UE locating technology may utilize the downlink wireless reference signals specifically designed for the UE geographic locating service. One challenge with using the downlink wireless reference signals for locating a UE is that such reference signals may collide with other downlink control signaling, resulting the potential loss of the other downlink control signaling.
The above deficiencies and other problems associated with using the downlink wireless reference signals for locating a UE are reduced or eliminated by the invention disclosed below. In some embodiments, the invention is implemented in a base station (also known as “eNB”) that has one or more processors, memory and one or more modules, programs or sets of instructions stored in the memory for performing multiple functions. Instructions for performing these functions may be included in a computer program product configured for execution by one or more processors.
One aspect of the present application is a method performed at a base station for transmitting ePDCCH to a user equipment. The method includes: selecting a user equipment within a service area of the base station; determining Positioning Reference Signal (PRS) configuration information configured with the user equipment; and choosing a strategy for transmitting ePDCCH to the user equipment in accordance with the determination of the PRS configuration information configured with the user equipment. In some embodiments, if the user equipment is configured with the PRS configuration information and the user equipment is in an OTDOA positioning service session, the base station identifies PRS subframes in accordance with the PRS configuration information and transmits the ePDCCH to the user equipment in any subframe allocated for the user equipment that is not one of the PRS subframes. But if the user equipment is not configured with the PRS configuration information or not in an OTDOA positioning service session, the base station transmits the ePDCCH to the user equipment in any subframe allocated for the user equipment. In some other embodiments, the base station identifies a set of PRS subframes in accordance with the PRS configuration information of all the user equipments within the service area of the base station and transmits the ePDCCH to the user equipment in any subframe allocated for the user equipment that is not one of the set of PRS subframes.
Another aspect of the present application is a base station including one or more processors, memory, and one or more program modules stored in the memory and executed by the one or more processors. The one or more program modules further including instructions for: selecting a user equipment within a service area of the base station; determining Positioning Reference Signal (PRS) configuration information configured with the user equipment; and choosing a strategy for transmitting ePDCCH to the user equipment in accordance with the determination of the PRS configuration information configured with the user equipment. In some embodiments, if the user equipment is configured with the PRS configuration information and the user equipment is in an OTDOA positioning service session, the base station identifies PRS subframes in accordance with the PRS configuration information and transmits the ePDCCH to the user equipment in any subframe allocated for the user equipment that is not one of the PRS subframes. But if the user equipment is not configured with the PRS configuration information or not in an OTDOA positioning service session, the base station transmits the ePDCCH to the user equipment in any subframe allocated for the user equipment. In some other embodiments, the base station identifies a set of PRS subframes in accordance with the PRS configuration information of all the user equipments within the service area of the base station and transmits the ePDCCH to the user equipment in any subframe allocated for the user equipment that is not one of the set of PRS subframes.
For a better understanding, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which:
Like reference numerals refer to corresponding parts throughout the drawings.
Reference will now be made in detail to various implementations, examples of which are illustrated in the accompanying drawings. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure and the described implementations herein. However, implementations described herein may be practiced without these specific details. In other instances, well-known methods, procedures, components, and mechanical apparatus have not been described in detail so as not to unnecessarily obscure aspects of the implementations.
In LTE, downlink positioning reference signal (PRS) is designed to support downlink UE positioning algorithms based on observed time difference of arrival (OTDOA). In OTDOA, a number of (say M, usually M≧4) base stations or so-called eNBs broadcast PRS signals to a UE. One of the eNBs transmitting PRS is considered as the reference eNB for the UE. The UE measures the arrival timing difference between the PRS sent from the reference eNB and the PRS sent from the other non-reference eNBs. The UE sends these M-1 arrival timing differences to a network unit called Enhanced Serving Mobile Location Centre (E-SMLC), which calculates the geo-location of the UE based on the received measurements as well as the geographic coordination of the M eNBs that send the PRS signals. Note that not every eNB is capable of transmitting PRS. In this application, the eNB transmitting the PRS is called “OTDOA-functional eNB”, while the eNB never transmitting PRS is called “non-OTDOA-functional eNB”. The subframe (the minimum transmission time interval unit in LTE) that contains PRS signal is called “PRS-subframe”, while the subframe that does not contain PRS is called “non-PRS subframe”.
In order to support the OTDOA measurements, the UE also receives assistance data, including but not limited to, the PRS configuration parameters associated with the eNBs. The UE performs these measurements during a given period of time (typically up to 8 or 16 periods of the PRS signals) and reports to the E-SMLC these estimated time differences together with an estimate of the measurement quality. The E-SMLC then, using these time difference estimates, the knowledge of the eNBs' positions and transmit time offsets, estimates the position of the UE. In other words, a UE-assisted positioning technique includes at least two steps: (i) the UE makes some radio signal measurements, and (ii) the network determines the UE location (e.g., latitude and longitude) by processing the measurements reported by the UE.
The PRS are sent in a configurable number of consecutive subframes, which could be just one subframe or as many as 5 subframes. The E-UTRAN configures the PRS bandwidth (e.g., a certain number of resource blocks) and the periodicity of the PRS (e.g., one PRS occurrence every 160 subframes). Within a subframe containing the PRS, the PRS are transmitted on more subcarriers and more OFDM symbols when compared to the regular eNB-specific reference signals being sent on an antenna. Utilization of more time-frequency resources within a subframe by the PRS can improve the quality of the UE measurements compared to the use of only the basic eNB-specific reference signals. A pseudo-random sequence is sent on the PRS, and, this sequence is a function of numerous factors such as PCI (Physical layer Cell Identity), slot number, OFDM symbol number, and the value of Cyclic Prefix. The UE observes the PRS from different eNBs in the neighborhood and makes certain measurements. Examples of such measurements include RSTD (Reference Signal Time Difference), which is the relative timing difference between a neighbor eNB and the reference eNB. The E-UTRAN processes these OTDOA measurements from the UE in an implementation-specific and non-standardized manner to estimate the UE's location.
As noted above, in order for the UE to receive and measure the PRS, the UE should be firstly configured with PRS parameters, either explicitly or implicitly. In LTE, these parameters include:
The OTDOA positioning protocol defined in LTE has two kinds of protocol transparency:
These two kinds of protocol transparency may cause some problems when working with enhanced Physical Downlink Control CHannel (ePDCCH).
In some embodiments, a subframe in LTE is partitioned into two regions in the time domain: the first 2-4 OFDM symbols in the subframe construct the PDCCH (physical downlink control channel) region, while the rest of OFDM symbols in the subframe construct the PDSCH (physical downlink shared channel) region. The PDCCH region typically carries the physical layer control signaling including the downlink/uplink scheduling command, and the PDSCH region is used to carry downlink traffic data. The PRS is transmitted in the PDSCH region, but not in the PDCCH region. With the release 11 of LTE, ePDCCH was created. Note that ePDCCH can carry the same control information as conventional PDCCH, including downlink/uplink scheduling command. Like PRS, ePDCCH is transmitted in the PDSCH region but not in the conventional PDCCH region. But UE does not check both PDCCH and ePDCCH in the same subframe to find UE-specific downlink/uplink scheduling command. Instead, each UE is configured with one ePDCCH-monitoring bitmap of 20 or 40 bits, which informs the UE of the subframes the UE should monitor for ePDCCH and the rest subframes it should monitor for PDCCH.
In a typical wireless communication system (such as LTE) with the UE positioning function enabled, one UE can receive control signaling (such as PDCCH or ePDCCH) from its serving eNB and also the PRS signal from its OTDOA-functional eNB. One example of such UE reception is shown in
When there is a signal collision, PRS transmission and reception are prioritized over ePDCCH transmission and reception because PRS is the common signal that supports cell-wise UE positioning functionality, which would result the loss of the ePDCCH.
In light of the above, the serving eNB 100 can avoid the signal collision by ceasing its ePDCCH transmission in that subframe if it gains any of above two types of information. Otherwise, the eNB 100 transmits the ePDCCH which is dropped by the UE 300, as shown in
The previous analysis indicates that, if the serving eNB 100 can obtain any of following two types of PRS configuration information, it can avoid transmitting ePDCCH in the subframe where the UE 300 attempts to detect PRS signal from the eNB 200 so that the loss of ePDCCH is avoided:
Note that the information type-a above is per-UE wise. What the eNB obtains is the PRS configuration information for one particular UE. As shown in
As shown in
As shown in
In some other embodiments, the direct communication with the corresponding UE can also be accomplished by UE actively sending the indication message to the eNB without any request from eNB. This indication message informs the receiving eNB of the most recent PRS configuration information and/or OTDOA positioning session status inside UE. Similarly, if no indication message is received by eNB for a particular UE, the eNB assumes that UE is not configured with any PRS or that the UE is not in any OTDOA positioning service session, which means the UE does not attempt to receive any positioning reference signal from any eNB. In this case, the eNB can send ePDCCH without being concerned about signal collision.
Note that the information type-b above is per-serving-area wise. What eNB obtains is the super-set of all PRS configuration information for any UE whose ePDCCH could be served by this eNB. The eNB can obtain information type-b by either consulting E-SMLC that makes all PRS configurations for all UEs within the geographic area or exchanging information with other eNBs.
As shown in
As shown in
During the information exchange with other eNBs, the eNB informs other eNBs of its latest knowledge of all UEs' PRS configurations it knows up-to-date. The information exchange starts with the OTDOA-functional eNBs reporting the configuration information of PRS they actually transmit. Then every time each eNB (not only OTDOA-functional eNB but also non-OTDOA-functional eNB) obtains the new knowledge of PRS configuration, it informs the new knowledge to other eNBs. In some embodiments, all the information exchanges between eNBs are performed on X2 interface.
Note that the two types of information have their own advantage over each other. For example, the obtaining of information type-a, which is per-UE wise, has the advantage that the information obtained is just sufficient for the eNB to ensure that the ePDCCH, which would otherwise have been transmitted to that UE, is not lost in a PRS subframe. In contrast, the obtaining of information type-b, which is per-serving-area wise, may result in more-than-necessary ePDCCH blocking. For example, assume the set of PRS subframes configured to a particular UE is represented by ΨUE, while the PRS subframes known by eNB via information type-b is represented by ΨeNB. In general, ΨeNB can be a super-set of ΨUE. Then the ePDCCH to the UE should have been received by the UE without any problem in the subframe x, where subframe x belongs to ΨeNB but not ΨUE, but the ePDCCH is indeed not transmitted by the eNB because the eNB blocks transmission of ePDCCH based on ΨeNB instead of ΨUE.
On the other hand, the obtaining of information type-b has the advantage that the supporting information flow does not occur very frequently, because the PRS transmissions in OTDOA-functional eNBs are very stable and rarely need to be reconfigured. Therefore the signaling overhead across the network backhaul to support the information type-b is minimal and the eNB behavior is easy to predict and control. In contrast, for information type-a may result in frequent signaling exchange over the network backhaul or even over the air interface, because the UE can be frequently reconfigured with new PRS due to the UE mobility and/or the UE can dynamically enter and quit from the OTDOA positioning service session. In some embodiments, an eNB obtains both types of information based on its specific need. For example, the eNB starts with obtaining the information type-b so that it can quickly gain knowledge of the PRS configuration information of the UEs within its service area. After that, the eNB may switch to obtain the information type-a when, e.g., a new UE is present in the service area. By doing so, the total bandwidth usage at the eNB can be reduced.
Throughout this application, it is assumed to have no technical difference between description “UE is configured with PRS” and the description “UE detects PRS based on the corresponding PRS configuration information”. If UE quits from OTDOA positioning service session, the PRS configuration that previously configured to this UE is no longer valid, and the UE is considered by this application to have no PRS configuration.
The above disclosures are merely preferred implementations of the present application, but are not intended to limit the scope of the claims of the present application. Any equivalent change made according to the claims of the present application modification still falls within the scope of the present application.
While particular implementations are described above, it will be understood it is not intended to limit the invention to these particular implementations. On the contrary, the invention includes alternatives, modifications and equivalents that are within the spirit and scope of the appended claims. Numerous specific details are set forth in order to provide a thorough understanding of the subject matter presented herein. But it will be apparent to one of ordinary skill in the art that the subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the implementations.
Although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, first ranking criteria could be termed second ranking criteria, and, similarly, second ranking criteria could be termed first ranking criteria, without departing from the scope of the present application. First ranking criteria and second ranking criteria are both ranking criteria, but they are not the same ranking criteria.
The terminology used in the description of the invention herein is for the purpose of describing particular implementations only and is not intended to be limiting of the invention. As used in the description of the invention and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term “and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. It will be further understood that the terms “includes,” “including,” “comprises,” and/or “comprising,” when used in this specification, specify the presence of stated features, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, operations, elements, components, and/or groups thereof.
As used herein, the term “if” may be construed to mean “when” or “upon” or “in response to determining” or “in accordance with a determination” or “in response to detecting,” that a stated condition precedent is true, depending on the context. Similarly, the phrase “if it is determined [that a stated condition precedent is true]” or “if [a stated condition precedent is true]” or “when [a stated condition precedent is true]” may be construed to mean “upon determining” or “in response to determining” or “in accordance with a determination” or “upon detecting” or “in response to detecting” that the stated condition precedent is true, depending on the context.
Although some of the various drawings illustrate a number of logical stages in a particular order, stages that are not order dependent may be reordered and other stages may be combined or broken out. While some reordering or other groupings are specifically mentioned, others will be obvious to those of ordinary skill in the art and so do not present an exhaustive list of alternatives. Moreover, it should be recognized that the stages could be implemented in hardware, firmware, software or any combination thereof.
The foregoing description, for purpose of explanation, has been described with reference to specific implementations. However, the illustrative discussions above are not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in view of the above teachings. The implementations were chosen and described in order to best explain principles of the invention and its practical applications, to thereby enable others skilled in the art to best utilize the invention and various implementations with various modifications as are suited to the particular use contemplated. Implementations include alternatives, modifications and equivalents that are within the spirit and scope of the appended claims. Numerous specific details are set forth in order to provide a thorough understanding of the subject matter presented herein. But it will be apparent to one of ordinary skill in the art that the subject matter may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the implementations.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2014/034310 | 4/16/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61812649 | Apr 2013 | US |
