WO2013185304A1

WO2013185304A1 - Inter-frequency cell detection

Info

Publication number: WO2013185304A1
Application number: PCT/CN2012/076826
Authority: WO
Inventors: Na WEI; Haiming Wang; Chunyan Gao; Erlin Zeng; Wei Bai; Pengfei Sun
Original assignee: Renesas Mobile Corporation
Priority date: 2012-06-13
Filing date: 2012-06-13
Publication date: 2013-12-19

Abstract

Signaling between a first node operating on a first frequency band and capable to transmit a discovery signal on a second frequency band, and a second node operating on the second frequency band is provided. The first and second frequency bands are different from each other. The first and second node are configured to provide access to a mobile communications system. The signaling comprises negotiating a detection range based on a desired detection range for the discovery signal of the first node on the second frequency band, the discovery signal serving to discover the first node by user equipments.

Description

INTER-FREQUENCY CELL DETECTION

DESCRIPTION BACKGROUND OF THE INVENTION Field of the invention

The present invention relates to inter-frequency cell detection.

Related background Art

Prior art related to this technical field can e.g. be found in:

[1] TR 36.839 vO.5.0: "Evolved Universal Terrestrial Radio Access (E-UTRA); Mobility Enhancements in Heterogeneous Networks".

[2] R2-120654: "Inter-frequency Small Cell Identification".

[3] R2-121133 : "Inter-frequency small cell identification with selected broadcast signals". The following meanings for the abbreviations used in this specification apply:

ABS almost blank subframe

CA carrier aggregation

CC component carrier

CE control element

CSI-RS channel state information-reference signal

DCI downlink control information

DL downlink

DoA direction of arrival

DRX discontinuous reception

eNB enhanced node B

HO handover

LP linear prediction

LTE long term evolution

LTE-A long term evolution advanced MAC medium access control

MBSFN multicast broadcast single frequency network

MIB master information block

QoS quality of service

PDCH packet data channel

PDSCH physical downlink shared channel

PL pathloss

PSS primary synchronization signal

PUCCH physical uplink control channel

RF radio frequency

RRH remote radio head

RSRP reference signal received power

SSS secondary synchronization signal

UE user equipment

UL uplink

With respect to heterogeneous network mobility enhancement, inter-frequency cell deployment is studied. For inter-frequency cell detection evaluation, a scenario has been considered where one (macro) frequency layer provides full coverage and where pico cells are provided on a second frequency layer for offloading purposes including means to improve perceived QoS in hot spot locations.

For detecting candidate small cells on the second frequency layer it has been proposed that the small cell may have the capability to transmit some signals

(discovery signals) on the frequency band of the macro cell. These signals can be measured by the UE and reported to the serving macro cell, which in turn can cause the serving macro ceil to configure measurements on the frequency band of the small cell.

The benefits of this solution are that:

- it does not rely on inter-frequency measurements to detect small cells;

- it does not rely on UE remembering the location of small cells via fingerprints or other methods; and

- the small cell can be detected immediately. However, the above solution has the following drawbacks:

- hardware cost and complexity in the small cell;

- pilot pollution caused by discovery signals; and

- not applicable to all scenarios, e.g. if a significant fraction of UEs does not support the RF band of the small cell.

SUMMARY OF THE INVENTION

The present invention aims at solving the above drawbacks. For example, the invention aims at reducing hardware cost and complexity in the small cell, and avoiding pilot pollution caused by discovery signals.

Moreover, the invention aims at enabling a proper reuse of measurements performed by the small cell in one frequency band, in another frequency band for mobility purposes.

This is achieved at least in part by the methods and apparatuses as defined in the appended claims. The invention may also be implemented as a computer program product.

In the following the invention will be described by way of exemplary

embodiments thereof with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a signaling diagram illustrating a method of inter-frequency cell detection according to an exemplary embodiment of the invention.

Fig. 2 illustrates a simplified block diagram of various electronic devices that are suitable for use in practicing the exemplary embodiments of this invention.

DESCRIPTION OF THE EMBODIMENTS According to an exemplary embodiment of the invention, a coordinated first ceil detection signal transmission in a frequency band of a second cell is proposed for enhancing inter-frequency cell detection. In order to reduce intra-frequency interference for UEs, e.g. pilot pollution caused by discovery signals, the following coordinating signaling between a first node, e.g. a small node/cell or a macro node/cell/eNB, and a second node, e.g. a macro node/cell/eNB or a small node/cell may be performed. The coordination signaling will be described with reference to Fig. 1.

A first node 10 may request transmitting a cell detection signal on a second node frequency band to a second node 10 e.g. via an X2 interface, which means that the first node 10 is capable of transmitting on the second node frequency band. The signaling can include a certain size of a dedicated resource for transmitting the cell detection signal (discovery signal) and a certain transmission periodicity of the dedicated resource. Alternatively, the second node 20 may request this information (desired detection range) if the second node 20 is the initiator of the coordination signaling. In other words, according to an option 1, in step SI the first node 10 (e.g. the small node or the macro node/eNB) requests resources from the second node 20 (e.g. the macro node/eNB or the small node) along with information about a desired detection range. Alternatively, according to an option 2 in which the second node 20 is the initiator, in step Sla the second node 20 requests the information from the first node 10, and in step Slb the first node 10 transmits this information to the second node 20. It is to be noted that in case the first node 10 represents the small node/cell, the second node 20 represents the macro node/cell/eNB. Alternatively, the first node 10 may represent the macro node/cell/eNB and the second node 20 may represent the small node/cell.

In a negotiation step 2, the second node 20 assigns resource and periodicity for the discovery signal based on the request or based on its own decision, and signals the result to the first node 10. The signaling can include the dedicated resource in the second node frequency band for first node's detection signal transmission and may be a certain MBSFN subframe, scheduled PDSCH resource, and a dedicated CSI-RS configuration, e.g. cell specific or group specific CSI-RS configuration info for measurement. Moreover, the signaling may include the assigned transmission periodicity. The exact content of the discovery signal may reuse a PSS/SSS/MIB format, or may use some other PDCH design for a more condensed resource.

Alternatively, there is a fixed dedicated resource in certain time and frequency domain, and the second node 20 can configure or de-configure it based on the negotiation with the first node 10.

It is to be noted that the first node 10 may be an RRH connected to the second node 20 via RRH, or a pico cell connected to the second node via X2. In case the first node is an RRH, the signaling exchange of steps 1 and 2 between the first node 10 and the second node 20 is not applicable, since the second node will generate a discovery signal for RRH itself accordingly. In case the first node is a pico cell, the second node can be the initiator, and step SI can be optional.

It is further to be noted that according to macro cell eNB's application, ABSs or LP-ABSs may be assigned by the second node for the dedicated resource.

As described above, in step S2 the second node 20 may acknowledge the requested dedicated resource per request, or make a proposal on new resource and periodicity. The feedback is sent to the first node 10. The second node 20 may initiate this without the first node's request (option 2).

The second node 20 coordinates its transmission so there is no interference with the discovery signal, and in step S3 informs its (all or part of) serving UEs (UEs 30 and 40 in the example of Fig. 1) to detect the first node 10 in the

time/resource (negotiated detection range) reserved for the first node 10. In other words, the second node 20 (e.g. the macro cell eNB or the small cell) broadcasts the negotiated resource to potential second node UEs which are configured to make intra-frequency measurement. The signaling can include a second node's discovery type. In step S4, the first cell 10 transmits the discovery signal on the assigned resource with the given periodicity.

The first node 10 may perform an average interference measurement (step S5), which is collected over its served UE or selected UE on a defined time window, and may report the measurement result to the second node 20 (step S6). In case the first node coverage is very small, it may be sufficient to report one average value. In case a more accurate interference measurement is desired, the first node 10 may make an estimation based on a certain group of UEs, for example with similar geometry (or RSRP), and/or DoA, etc., and report a few values for different ranges of UEs.

In this respect, one issue is a pathloss difference of two frequencies. Depending on the difference of two frequencies, the pathloss difference can be huge.

Secondly, an interference level is independent in two frequencies. Therefore, in step S5, the first node 10 may calculate an average PL offset value due to a difference in frequency, which may be used to compensate on RSRP

measurement. The calculation may be made on the basis of small cell estimation based on macro cell pathloss model and small cell pathloss model. The

calculation may also be based on serving UEs measurement which were or are being served by the second node, for example with similar geometry (or RSRP), and/or DoA, etc., and report one or a few values for different ranges of UEs.

The configured UEs 30 and 40 make detection and measurement on the assigned resource, and make the RSRP report of the first node 10 and feed it back (not shown in Fig. 1) to the second node 20. The second node 20 receives the measurement report from its serving UEs and makes an HO decision using the further assistant information given by the first node 10 (step S7). It is noted that since the second node 20 (e.g. the macro cell eNB or the small ceil) knows its connected UE's RF competence. If most of the UEs have such RF competence, the second node 20 will enable detection of the first node 10 (if it considers the impact on some UEs is low). If most of the UEs do not have such RF competence, then the second node 20 switches off the above feature and lets the UEs do conventional inter-frequency measurement instead. An advantage of the proposed method of detecting inter-frequency cells/nodes is no or reduced intra-frequency interference for second node UEs by the first node discovery signal due to resource negotiation. In addition, HO measurement accuracy can be improved by the first node feeding back PL offset and

interference information to the second node.

Now reference is made to Fig. 2 for illustrating a simplified block diagram of various electronic devices that are suitable for use in practicing the exemplary embodiments of this invention.

The control unit 100 which may be included in or used by the first node comprises processing resources 11, memory resources 12 and interfaces 13, which are connected by a link 14. The memory resources 12 may store a program. The control unit 100 may perform the processing of the first node 10 shown in Fig. 1 by using its processing resources 11, memory resources 12 and interfaces 13.

The control unit 200 which may be included in or used by the second node comprises processing resources 21, memory resources 22 and interfaces 23, which are connected by a link 24. The memory resources 22 may store a program. The control unit 200 may perform the processing of the second node 20 shown in Fig. 1 by using its processing resources 21, memory resources 22 and interfaces 23. The control unit 100 and the control unit 200 are connected via their interfaces 13, 23 by a link 34, e.g. an X2 interface.

The terms "connected," "coupled," or any variant thereof, mean any connection or coupling, either direct or indirect, between two or more elements, and may encompass the presence of one or more intermediate elements between two elements that are "connected" or "coupled" together. The coupling or connection between the elements can be physical, logical, or a combination thereof. As employed herein two elements may be considered to be "connected" or "coupled" together by the use of one or more wires, cables and printed electrical

connections, as well as by the use of electromagnetic energy, such as electromagnetic energy having wavelengths in the radio frequency region, the microwave region and the optical (both visible and invisible) region, as non- limiting examples. At least one of the programs stored in the memory resources 12, 22 is assumed to include program instructions that, when executed by the associated

processing resources 11, 21, enable the electronic device to operate in

accordance with the exemplary embodiments of this invention, as detailed above. In general, the exemplary embodiments of this invention may be implemented by computer software stored in the memory resources 12, 22 and executable by the processing resources 11, 21, or by hardware, or by a combination of software and/or firmware and hardware in any or all of the devices shown.

Further in this regard it should be noted that the various process step

descriptions above may represent interconnected circuitries.

As used in this application, the term 'circuitry' refers to all of the following :

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) to combinations of circuits and software (and/or firmware), such as (as applicable): (i) to a combination of processor(s) or (ii) to portions of

processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) to circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present.

This definition of 'circuitry' applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term 'circuitry' would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term 'circuitry' would also cover, for example and if applicable to the particular claim element, a baseband integrated circuit or applications processor integrated circuit for a mobile phone or a similar integrated circuit in server, a cellular network device, or other network device

The memory resources 12, 22 may be of any type suitable to the local technical environment and may be implemented using any suitable data storage

technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The processing resources may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on a multi-core processor architecture, as non-limiting examples.

According to an aspect of the invention, an apparatus, e.g. a control unit 100 and/or a control unit 200 shown in Fig. 2, comprises signaling means for providing signaling between a first node operating on a first frequency band and capable to transmit a discovery signal on a second frequency band, and a second node operating on the second frequency band, the first and second frequency bands being different from each other, the first and second node being

configured to provide access to a mobile communications system, the signaling means comprising means for negotiating a detection range based on a desired detection range for the discovery signal of the first node on the second frequency band, the discovery signal serving to discover the first node by user equipments. The apparatus may further comprise means for transmitting a request for resources for transmitting the discovery signal to the second node, the request including information about the desired detection range.

Alternatively, the apparatus may comprise means for transmitting information about the desired detection range upon receiving a request thereon from the second node.

The means for transmitting may transmit the discovery signal based on the detection range negotiated, the detection range comprising a dedicated resource of the second node and a transmission periodicity of the dedicated resource. The apparatus may comprise means for measuring an interference value by collecting information from user equipments attached to the first node and/or estimating a pathloss offset value due to a difference in the first and second frequency bands, and the means for transmitting may transmit the measured interference value and/or estimated pathloss offset value as assistant

information to the second node.

The apparatus may comprise means for requesting information on the desired detection range from the first node.

The means for negotiating may comprise means for reconfiguring the detection range based on the desired detection range, or means for configuring the desired detection range as the detection range. The apparatus may comprise means for coordinating transmission to avoid interference with the discovery signal, and means for informing user equipments attached to the second node on the detection range of the discovery signal.

The apparatus may comprise means for receiving measurement reports from user equipments attached to the second node, and means for deciding on a handover of the user equipments using assistant information from the first node, the assistant information including an interference value measured by the first node by collecting information from user equipments attached to the first node and/or a pathloss offset value due to a difference in the first and second frequency bands, estimated by the first node.

The means for signaling, negotiating, transmitting, receiving, measuring, requesting, reconfiguring, configuring, coordinating, Informing and deciding may be implemented by the processing resources 11, memory resources 12 and interfaces 13 of the control unit 100 and/or the processing resources 21, memory resources 22 and interfaces 23 of the control unit 200.

It is to be understood that the above description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications and applications may occur to those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method comprising :

providing signaling between a first node operating on a first frequency band and capable to transmit a discovery signal on a second frequency band, and a second node operating on the second frequency band, the first and second frequency bands being different from each other, the first and second node being configured to provide access to a mobile communications system, the signaling comprising :

negotiating a detection range based on a desired detection range for the discovery signal of the first node on the second frequency band, the discovery signal serving to discover the first node by user equipments.

2. The method of claim 1, comprising :

transmitting a request for resources for transmitting the discovery signal to the second node, the request including information about the desired detection range.

3. The method of claim 1, comprising :

transmitting information about the desired detection range upon receiving a request thereon from the second node.

4. The method of any one of claims 1 to 3, comprising :

transmitting the discovery signal based on the detection range negotiated, the detection range comprising a dedicated resource of the second node and a transmission periodicity of the dedicated resource.

5. The method of any one of claims 1 to 4, comprising :

measuring an interference value by collecting information from user equipments attached to the first node and/or estimating a pathloss offset value due to a difference in the first and second frequency bands; and

transmitting the measured interference value and/or estimated pathloss offset value as assistant information to the second node.

6. The method of claim 1, the comprising : requesting information on the desired detection range from the first node.

7. The method of claim 6, the negotiating comprising :

reconfiguring the detection range based on the desired detection range; or configuring the desired detection range as the detection range.

8. The method of claim 6 or 7, comprising :

coordinating transmission to avoid interference with the discovery signal; and

informing user equipments attached to the second node on the detection range of the discovery signal.

9. The method of any one of claims 6 to 8, comprising:

receiving measurement reports from user equipments attached to the second node; and

deciding on a handover of the user equipments using assistant ^"information from the first node, the assistant information including an interference value measured by the first node by collecting information from user equipments attached to the first node and/or a pathloss offset value due to a difference in the first and second frequency bands, estimated by the first node.

10. A computer program product including a program for a processing device, comprising software code portions for performing the steps of any one of claims 1 to 9 when the program is run on the processing device.

11. The computer program product according to claim 10, wherein the computer program product comprises a computer-readable medium on which the software code portions are stored.

12. The computer program product according to claim 10, wherein the program is directly loadable into an internal memory of the processing device.

13. An apparatus comprising:

at least one processor; and

at least one memory including computer program code, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform:

14. The apparatus of claim 13, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform :

15. The method of claim 13, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform :

16. The apparatus of any one of claims 13 to 15, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform :

17. The apparatus of any one of claims 13 to 16, the at least one memory and the computer program code configured to, with the at (east one processor, cause the apparatus at least to perform : measuring an interference value by collecting information from user equipments attached to the first node and/or estimating a pathloss offset value due to a difference in the first and second frequency bands; and

18. The apparatus of claim 13, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform :

requesting information on the desired detection range from the first node.

19. The apparatus of claim 18, wherein for the negotiating the at least one memory and the computer program code are configured to, with the at least one processor, cause the apparatus at least to perform :

20. The apparatus of claim 18 or 19, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform:

coordinating transmission to avoid interference with the discovery signal; and

21. The apparatus of any one of claims 18 to 20, the at least one memory and the computer program code configured to, with the at least one processor, cause the apparatus at least to perform :

deciding on a handover of the user equipments using assistant information from the first node, the assistant information including an interference value measured by the first node by collecting information from user equipments attached to the first node and/or a pathloss offset value due to a difference in the first and second frequency bands, estimated by the first node.