WO2013037826A1 - Session setup in an energy-efficient cellular wireless telecommunications system - Google Patents

Session setup in an energy-efficient cellular wireless telecommunications system Download PDF

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Publication number
WO2013037826A1
WO2013037826A1 PCT/EP2012/067843 EP2012067843W WO2013037826A1 WO 2013037826 A1 WO2013037826 A1 WO 2013037826A1 EP 2012067843 W EP2012067843 W EP 2012067843W WO 2013037826 A1 WO2013037826 A1 WO 2013037826A1
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WO
WIPO (PCT)
Prior art keywords
sa
terminal
cell
cells
la
Prior art date
Application number
PCT/EP2012/067843
Other languages
French (fr)
Inventor
Ljupco Jorguseski
Jacob Cornelis Van Der Wal
Job Cornelis Oostveen
Haibin Zhang
Adrian Victor Pais
Original Assignee
Koninklijke Kpn N.V.
Nederlandse Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Tno
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Publication date
Priority to EP11181151.9 priority Critical
Priority to EP11181151 priority
Application filed by Koninklijke Kpn N.V., Nederlandse Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Tno filed Critical Koninklijke Kpn N.V.
Publication of WO2013037826A1 publication Critical patent/WO2013037826A1/en

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Classifications

    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W52/00Power management, e.g. TPC [Transmission Power Control], power saving or power classes
    • H04W52/02Power saving arrangements
    • H04W52/0203Power saving arrangements in the radio access network or backbone network of wireless communication networks
    • H04W52/0206Power saving arrangements in the radio access network or backbone network of wireless communication networks in access points, e.g. base stations
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04WWIRELESS COMMUNICATION NETWORKS
    • H04W88/00Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/02Terminal devices
    • H04W88/06Terminal devices adapted for operation in multiple networks or having at least two operational modes, e.g. multi-mode terminals
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02DCLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THIR OWN ENERGY USE
    • Y02D70/00Techniques for reducing energy consumption in wireless communication networks
    • Y02D70/10Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT]
    • Y02D70/12Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT] in 3rd Generation Partnership Project [3GPP] networks
    • Y02D70/122Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT] in 3rd Generation Partnership Project [3GPP] networks in 2nd generation [2G] networks
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02DCLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THIR OWN ENERGY USE
    • Y02D70/00Techniques for reducing energy consumption in wireless communication networks
    • Y02D70/10Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT]
    • Y02D70/12Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT] in 3rd Generation Partnership Project [3GPP] networks
    • Y02D70/124Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT] in 3rd Generation Partnership Project [3GPP] networks in 3rd generation [3G] networks
    • Y02D70/1242Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT] in 3rd Generation Partnership Project [3GPP] networks in 3rd generation [3G] networks in Universal Mobile Telecommunications Systems [UMTS] networks
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02DCLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THIR OWN ENERGY USE
    • Y02D70/00Techniques for reducing energy consumption in wireless communication networks
    • Y02D70/10Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT]
    • Y02D70/12Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT] in 3rd Generation Partnership Project [3GPP] networks
    • Y02D70/126Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT] in 3rd Generation Partnership Project [3GPP] networks in 4th generation [4G] networks
    • Y02D70/1262Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT] in 3rd Generation Partnership Project [3GPP] networks in 4th generation [4G] networks in Long-Term Evolution [LTE] networks
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02DCLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THIR OWN ENERGY USE
    • Y02D70/00Techniques for reducing energy consumption in wireless communication networks
    • Y02D70/10Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT]
    • Y02D70/14Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT] in Institute of Electrical and Electronics Engineers [IEEE] networks
    • Y02D70/142Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT] in Institute of Electrical and Electronics Engineers [IEEE] networks in Wireless Local Area Networks [WLAN]
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02DCLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THIR OWN ENERGY USE
    • Y02D70/00Techniques for reducing energy consumption in wireless communication networks
    • Y02D70/10Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT]
    • Y02D70/16Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT] in other wireless communication networks
    • Y02D70/164Techniques for reducing energy consumption in wireless communication networks according to the Radio Access Technology [RAT] in other wireless communication networks in Satellite Navigation receivers
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02DCLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THIR OWN ENERGY USE
    • Y02D70/00Techniques for reducing energy consumption in wireless communication networks
    • Y02D70/20Techniques for reducing energy consumption in wireless communication networks independent of Radio Access Technologies
    • Y02D70/21Techniques for reducing energy consumption in wireless communication networks independent of Radio Access Technologies in machine-to-machine [M2M] and device-to-device [D2D] communications

Abstract

The invention relates to a telecommunications system comprising a decision unit, an larger area LA-cell, and a plurality of smaller area SA-cells. A method is provided for a terminal to facilitate establishment of a data connection between the terminal and at least one of the SA-cells including the step of, while the terminal is in an idle mode and is camping on the LA-cell, the terminal determining properties of a signal received from each of one or more SA-cells of the plurality of SA-cells, the properties being indicative of propagation conditions between the each of the one or more SA-cells and the terminal. The method further includes the step of, while the terminal is in the idle mode, the terminal providing a report to the decision unit, via the LA-cell, the report comprising at least information indicative of at least a portion of the determined properties for at least one of the one or more SA-cells.

Description

Session setup in an energy-efficient cellular wireless telecom¬ munications system

FIELD OF THE INVENTION

Generally, the invention relates to the field of wire¬ less telecommunications. More specifically, the invention relates to the field of establishing a data connection between a terminal and a cell in an energy-efficient cellular wireless network .

BACKGROUND OF THE INVENTION

A cellular wireless access telecommunications network (system) typically includes multiple base stations, also known as, for example, base terminal station in GSM, NodeB in WCDMA (UMTS), and evolved NodeB or eNB in LTE . A base station includes at least transmitting and receiving equipment to support wire¬ less communication with a (possibly mobile) terminal, in

standardisation more formally known as UE (User Equipment) . The range that can be covered with the transmitter/receiver in a base station is limited. The area that can be served by the transmitter/receiver of a base station is referred to as its "coverage area" or as the "cell." As used herein, the term

"cell" refers to both the base station itself and to its associ¬ ated coverage area.

A cell (base station) in a cellular network is typically connected to the remainder of the network via one or more backhaul links, for example, via optical fibre, via copper wire or wirelessly. A base station further includes processing capa¬ bilities, for example for the wireless transmission and

reception and for handling the protocols specified between the base station and the terminal and between the base station and the network, including other cells.

In a cellular network, different cells may have different sizes, indicated e.g. as macrocells, microcells, picocells or femtocells in decreasing order of cell size. Cells may show a partial overlap with nearby cells or a smaller cell (e.g.

picocell) may be entirely overlapped by a larger cell (e.g. mac- rocell) . Multiple cells may thus form a cellular network provid¬ ing near contiguous coverage in a very large area.

In a cellular network it is common that each cell (base station), when in operation, transmits broadcast signals. Such signals are known as, for example, BCH (Broadcast CHannel) in GSM, as CPICH (Common Pilot CHannel) in WCDMA (UMTS) and as RSs (Reference Signals) in LTE . The same or separate broadcast sig¬ nals are used to indicate a cell's (base station's) presence and to broadcast information about the cell (system information) , for example, the cell identity and information about the config¬ uration of the cell and/or about the cell's resources, such as e.g. which channel to use in order to initiate contact with the cell. Such broadcast signals allow terminals to make measure¬ ments on the broadcast signals, e.g. to determine the strength of the signal received by the terminal, and to receive the cell's system information. The broadcast signals are usually transmitted as long as the cell is in operation. The transmit power involved in broadcasting these signals may consume up to 20% of the cell's maximum transmit power, also when the cell does not actually exchange data with a terminal in the cell or when there is no terminal at all in the cell.

In a cellular wireless network it is common to distinguish a terminal to be in an xidle mode' or in an xactive mode' . In the active mode, the terminal is able to exchange data (e.g. sending/receiving an e-mail or making a phone call) via a cell in which the terminal is located. This requires resources in the network (e.g. frequencies and/or codes) and also requires the terminal and the network to provide power for the purpose. In the idle mode the terminal is not able to exchange data and, therefore, does not require the above resources and consumes less power. A terminal in the idle mode only regularly listens to signals broadcast by the cells and selects a xbest cell' , for example the cell with the signal that the terminal receives as strongest. A terminal in the idle mode also monitors the paging channel transmitted by the selected cell for a paging message addressing the terminal. Such an (idle mode) terminal is said to xcamp on' the selected cell. When, for example because of termi- nal mobility, a different cell is identified as best cell, the terminal may re-select the different cell as xbest cell' and camp on the newly selected cell. It should be noted that a ter¬ minal in the idle mode normally does not inform the cell and/or the network about which cell the terminal is camping on, also not when re-selecting a different cell as best cell. When the terminal re-selects to a cell which is found to be in a differ¬ ent location area (LA or RA - routing area) , which the terminal may determine from the cell's system information, then the ter- minal initiates contact with the network via the newly selected cell to perform an LA or RA update procedure, and subsequently returns to the idle mode. Thus, the network is made aware of the LA/RA the idle terminal is located in. A LA/RA commonly compris¬ es multiple cells, as configured by the network operator.

Consequently, the network is not aware on which cell an idle mode terminal is camping on, it is only aware in which LA/RA an idle terminal is (expected to be) located.

In a cellular wireless access telecommunications net¬ work a terminal and the network need to set up a session when the terminal requests a service or is being paged. This involves a terminal in the idle mode making a transition to the active mode. In an LTE network, for example, a session setup is a two- step process, the result of which is illustrated in FIG. 1. If service is initiated by the network, the network performs a pag- ing procedure, where a paging message is broadcast in all cells where the network expects the terminal to be camping on (RA/LA) . When the terminal receives a paging message addressing the ter¬ minal, or if service is initiated by the terminal without having been paged, in a first step the terminal performs a random ac- cess channel (RACH) procedure towards the cell it currently is camping on to establish a Radio Resource Control (RRC) connec¬ tion. When successful, in the second step, the RRC connection with that cell is used to negotiate resources for and to estab¬ lish a data connection between the terminal and that cell. Then the wireless exchange of user data between the terminal and the cell is possible. 3GPP TS 36.213 and 3GPP TS 36.331 describe these procedures in more detail. As is illustrated in FIG. 1, for the LTE network as well as for other legacy networks such as e.g. GSM and UMTS, all transmissions, be it signalling or data, occur between the terminal and a single cell which is the same cell that the terminal was camping on when it was in idle mode.

Recently, a new, more energy efficient, network archi¬ tecture is being developed. One aspect in the new architecture is the use of relatively small cells. High bit rate data connec¬ tions can be much more efficiently provided with a larger number of (at least partially overlapping) small cells (e.g. micro- cells, picocells, femtocells) than with a fewer number of larger cells (e.g. macrocells) . A further aspect in the new architec¬ ture is that the power consumption of a cell is envisioned to scale, as much as possible, with the service actually provided (e.g. with the number of active terminals served, with the bit rate provided to a terminal, with the distance covered by the connection to a terminal, etc.) . One approach for realizing this vision includes putting those cells that do not actually serve an active terminal into a power-save mode, e.g. switching those cells almost completely off. Another, complementary, approach includes significantly reducing or refraining from transmitting broadcast signals that are common in conventional networks. The transmission of these broadcast signals causes a large overhead, in particular for cells operating at less than full load.

The new architecture envisions distinguishing between different types of cells. A first type of cells, in this text referred to as xSA-cell' is primarily optimised to support the wireless exchange of data with active terminals. The energy- efficiency improvements as outlined above are focused on the SA-cells. A second type of cells, in this text referred to as xLA-cell' is primarily optimised for other functions in a cellu¬ lar network, including those also found in conventional

networks. Thus, it is envisioned to reduce the overhead in the system to that attributed to the LA-cells.

An LA-cell typically covers a larger area, for example comparable to that of a conventional macrocell. The LA-cells to¬ gether provide near contiguous coverage in the area desired to be covered, much like in a conventional network. An LA-cell may transmit broadcast and system information, much like a conventional cell; an idle terminal may camp on an LA-cell and may al- also initiate a signalling connection with the LA-cell, e.g. to perform an LA/RA update or to detach from the network.

An SA-cell covers a smaller area, for example compara¬ ble to that of a conventional microcell, picocell or femtocell. The SA-cells together may support a certain bit rate in the near-contiguous area desired to be covered. An SA-cell only transmits signals when and in so far it is needed; it may be re¬ garded to be normally ' of f or in a power-save or stand-by mode. An idle terminal also does not camp on an SA-cell. Although such a network has been referred to as a "Beyond Cellular Green Generation" (BCG2) network, this term may change in the future. Therefore, in the context of the present application, a network having such architecture will be referred to as an "energy- efficient cellular wireless network."

The result of a session setup in an energy-efficient cellular network is illustrated in FIG. 2. If session setup is network-initiated, this is preceded by the terminal receiving a paging message via the LA-cell it is camping on. As shown, the session setup in an energy-efficient cellular network may be sub-divided into two parts. The first part includes the estab¬ lishment of a signalling connection between the terminal and the LA-cell it currently is camping on, which may include a RACH procedure and RRC connection set-up, similar to legacy networks. After a signalling connection between the terminal and the

LA-cell has been established, the second part includes the es¬ tablishment of a data connection (data session) with an

appropriate SA-cell.

Note that, in an energy-efficient network according to this architecture, it may sometimes not be possible to identify an appropriate SA-cell immediately. This may happen e.g. because all SA-cells in the vicinity of the terminal may be in a power- save mode and do not transmit a suitable signal. It may also be the case that some SA-cell is active and that the terminal de¬ tects a suitable signal from the SA-cell, but that the active SA-cell cannot optimally support the requested data session from an energy saving perspective (e.g. there is an inactive SA-cell in a better position, e.g. much closer to the terminal) . It may also be the case that some SA-cell is active but that the active SA-cell cannot optimally support the requested data session from a quality of service (QoS) perspective (e.g. the active SA-cell cannot support the data session with the requested bit rate, while other inactive SA-cell (s) can) .

As can be seen from FIGs. 1 and 2, setting up a session in a network according to this new architecture is different from that in legacy networks. One difference is that the termi¬ nal issues a request message to a xbest cell' an idle terminal is camping on but that this cell is, normally, not going to serve the terminal (i.e., the data connection for exchanging the actual user data is set up with another cell) . Another difference is that the SA-cell' s RAT (Radio Access Technology) to support the data connection need not be the same as the

LA-cell's RAT to support the terminal in idle mode, which allows optimization of one or both RATs separately for their respective primary purposes. Yet another difference is that, in the new ar¬ chitecture, the xbest cell' to support the data connection still needs to be found. Consequently, as a part of the session setup procedure in an energy-efficient network, an appropriate cell (SA-cell) needs to be selected to support the data connection with the terminal. To ensure high quality and/or user experi¬ ence, the session setup, which includes both identifying an appropriate cell and establishing a data connection with it, is preferably performed quickly.

As the foregoing illustrates, what is needed in the art are methods and systems for facilitating establishment of a data connection between a terminal and a SA-cell in an energy- efficient network, such as e.g. a BCG2 network.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, telecommunications system comprising a decision unit, an LA cell, and a plurality of SA-cells, a method for a terminal facilitate establishment of a data connection between the termi¬ nal and at least one of the plurality of the SA-cells is

disclosed. The method includes the terminal determining proper¬ ties of a signal received from each of one or more SA-cells of the plurality of SA-cells, where the properties are indicative of propagation conditions between the each of the one or more SA-cells and the terminal, and providing a report to the deci¬ sion unit, via the LA-cell. These steps are performed while the terminal is in an idle mode and is camping on the LA-cell. The report includes at least information indicative of at least a portion of the determined properties for at least one of the one or more SA-cells. Preferably, the telecommunications system com¬ prises a cellular wireless access telecommunications system.

In the context of the embodiments of the present inven- tion, the expressions "LA-cell" and "SA-cell" are used to differentiate between two different types of cells.

The first type of cell, the LA-cell (Large Area cell) , refers to a cell that is able to cover a larger area with a smaller bit rate, as compared with the second type of cell. The LA-cell is primarily intended for carrying signaling messages from/to a terminal, e.g. the LA-cell is intended to at least be able to page a terminal . A terminal in idle mode may further be assumed to xcamp' on at least one of these LA-cells. While the LA-cell is not primarily intended to be used to carry wireless user data from/to a terminal, it is not precluded that other signaling than paging or that also some user data is carried via an LA-cell. In the intended coverage area of the wireless access network it may be assumed that at least one LA-cell is fully op¬ erational or, in other words, an LA-cell is xnormally on.'

The second type of cell, the SA-cell (Small Area cell) , refers to a cell that is able to cover a smaller area with a higher bit rate, as compared with the LA-cell. The SA-cell is primarily intended to carry user data from/to a terminal over the established data connection (i.e., the SA-cell is primarily intended to handle connections with active terminals) . Yet, it is not precluded that also some other information and/or some signalling is carried via an SA-cell. In the intended coverage area of the wireless access network it may be assumed that at least one SA-cell is able to provide coverage. An SA-cell is only fully operational when and to the extent that it is needed or, in other words, an SA-cell is xnormally off.'

According to various embodiments of the present inven¬ tion, the SA-cells may occur in any mix of frequency bands and/or radio access technologies (RATs) . It is also not preclud¬ ed that there are differently sized SA-cells (e.g. macro, micro, pico and femto SA-cells, with or without a hierarchical organi- sation) , where larger SA-cells may e.g. more efficiently serve highly mobile terminals.

As used herein, the expression "data connection between a terminal and an SA-cell" refers to a communication path for a wireless exchange of user data between the terminal and the SA- cell. The communication path for user data, including the section between the terminal and the SA-cell, is usually set up according to a set of parameters, for example, depending on what type of user data needs to be exchanged (e.g. for send¬ ing/receiving e-mail, for making a voice or video call, etc.) . The set of parameters, commonly referred to in the art as "QoS parameters" or "QoS profile," may include parameters such as e.g. maximum bitrate, guaranteed (minimum) bitrate, bit error ratio and delay/latency.

In contrast, signalling messages exchanged between the terminal and the LA-cell do not contain user data and are ex¬ changed between e.g. the terminal and various entities in the telecommunication system. Signalling messages may be exchanged without establishing a connection or via a "signalling connection" with a modest bit rate and with a quality sufficient for most signalling information to arrive uncorrupted. A signalling connection, when used, is to a large extent also independent of the parameters of the "data connection" it may be associated with .

Further, it is understood that the terms "user data" and "user terminal" do not necessarily imply a presence of a hu¬ man user and the embodiments of the present invention may also be applicable to e.g. a smartphone checking e-mail without human intervention and to machine-to-machine (M2M) communications. The term "user data" is merely used to differentiate between the ac¬ tual data that is to be exchange over the data connection and the signaling.

As described herein, a terminal may be either in an

"active mode" or an "idle mode." As used herein, the expression "a terminal in an idle mode" refers to a terminal that is nei¬ ther exchanging user data nor able to exchange user data but is camping on a LA-cell and is monitoring possible paging messages for the terminal from the LA-cell. In other words, the expres¬ sion "a terminal in an idle mode" is used to describe a terminal which does not have support for the wireless exchange of user data between the terminal and an SA-cell. In contrast, the ex¬ pression "a terminal in an active mode" refers to a terminal that is either exchanging user data or able to exchange user da¬ ta via at least one SA-cell. In other words, an active terminal supports or is able to support the wireless exchange of user da¬ ta between the terminal and the SA-cell (s) . These notions of idle mode and active mode may be comparable with like notions in standardised conventional networks but do not necessarily coin¬ cide exactly with standardised definitions.

In an embodiment, the signal received from the each of the one or more SA-cells comprises an identification of the cor¬ responding SA-cell.

In an embodiment, when at least one SA-cell of the one or more SA-cells is in a power-save mode, the signal received from the at least one SA-cell comprises an intermittent signal.

In an embodiment, at least two SA-cells of the one or more SA-cells are in a power-save mode and each of the at least two SA-cells transmits the signal to the terminal in a predeter¬ mined pattern, e.g. periodically.

In an embodiment, the terminal is in a power-save mode and the method further comprises the terminal exiting the power- save mode to receive the signal from the each of the one or more SA-cells and/or to determine the properties of the signal re¬ ceived from the each of the one or more SA-cells, where the terminal is configured to exit the power-save mode periodically or upon receiving a paging signal from the LA-cell.

According to another aspect of the present invention, a decision unit for use in the methods described herein is dis- closed. The decision unit is configured at least for receiving the report comprising at least information indicative of at least a portion of the determined properties for at least one of the one or more SA-cells, and, based at least partially on the report, selecting at least one SA-cell of the plurality of SA- cells for establishing the data connection between the terminal and the selected SA-cell.

In an embodiment, the decision unit is further configured for providing an indication to the terminal that the data connection is to be established between the terminal and the se- lected SA-cell, where the indication is provided either via the LA-cell or via the selected SA-cell.

In an embodiment, the decision unit is further configured for providing a trigger to the selected one of the one or more SA-cells to enter an active mode when the selected one of the one or more SA-cells is in a power-save mode.

In an embodiment, the decision unit is configured to receive the report via the LA-cell.

According to another aspect of the present invention, an LA-cell comprising the decision unit as described herein is disclosed. In an embodiment, the LA-cell is configured for providing a paging signal to the terminal.

According to another aspect of the present invention, an SA-cell is disclosed, the SA-cell being configured at least for transmitting the signal.

In an embodiment, the SA-cell is in a power-save mode and the SA-cell is configured for transmitting the signal in re¬ sponse to receiving a trigger from the LA-cell or from the decision unit to transmit the signal. In a further embodiment, the trigger is provided to the SA-cell in response to the LA- cell receiving a service request message from the terminal. Such a trigger may, at least partially, be based on one or more of a terminal location estimate, an estimate of the accuracy of the terminal location estimate, and activity status of the SA-cells in the vicinity of the estimated terminal location.

In an embodiment, the SA-cell is configured for includ¬ ing in the signal an identification of the SA-cell.

In an embodiment, the signal comprises an intermittent signal when the SA-cell is in a power-save mode.

In an embodiment, when the SA-cell is in a power-save mode, the SA-cell is configured for transmitting the signal in a predetermined pattern, e.g. periodically.

According to other aspects of the present invention, a terminal, a computer program with portions (possibly distribut¬ ed) for performing the various functions described herein, a data carrier for such software portions, and a telecommunica¬ tions system are disclosed. The telecommunications system may include two or more of the terminal, the decision unit, the LA- cell, and the SA-cell as described herein.

According to yet one more aspect of the present inven¬ tion, in a telecommunications system comprising a decision unit, an LA-cell, and at least two SA-cells, a method for a terminal in an active mode to facilitate handover of a first data connec¬ tion to a second data connection is disclosed. The first data connection is a data connection between the terminal and a first SA-cell of the at least two SA-cells. The second data connection is a data connection between the terminal and a second SA-cell of the at least two SA-cells. The method includes the terminal determining properties of a first signal received the first SA- cell, the properties being indicative of propagation conditions between the first SA-cell and the terminal. The method also in¬ cludes the terminal determining properties of a second signal received the second SA-cell, the properties being indicative of propagation conditions between the second SA-cell and the termi¬ nal. The method further includes the terminal providing a report to the decision unit, via the LA-cell, the report comprising at least information indicative of at least a portion of the deter- mined properties for the first and second SA-cells.

Hereinafter, embodiments of the invention will be described in further detail. It should be appreciated, however, that these embodiments may not be construed as limiting the scope of protection for the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic illustration of the result of a session setup in legacy networks;

FIG. 2 is a schematic illustration of the result of a session setup in an energy-efficient network, according to an embodiment of the present invention; and

FIG. 3 is a schematic illustration of a telecommunica¬ tions system, according to an embodiment of the present

invention ;

FIG. 4 is a schematic illustration of coverage areas of the LA-cell and a plurality of SA-cells in a telecommunications network, according to one embodiment of the present invention;

FIG. 5 sets forth a flow diagram of method steps for selecting one or more SA-cells when the terminal measures sig¬ nals from the SA-cells, according to one embodiment of the present invention;

FIG. 6 sets forth a flow diagram of method steps for selecting one or more SA-cells when the terminal transmits an information request message, according to one embodiment of the present invention; and

FIG. 7 sets forth a flow diagram of method steps for selecting one or more SA-cells when the terminal transmits an information request message, according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 3 illustrates a telecommunication system 10 according to one embodiment of the present invention. As shown, the telecommunication system 10, which is preferably a cellular wireless access telecommunication system, includes at least a decision unit 11, an LA-cell 12, and SA-cells 13 and 14. FIG. 3 also illustrates a user terminal 15. For clarity reasons, only the most relevant elements of the telecommunication system are illustrated in FIG. 3. Other elements, not shown in FIG. 3, may also be present and are within the scope of the present inven¬ tion. Such "other elements" may include e.g. additional SA- cells, additional LA-cells, additional terminals, further ele- ments to the telecommunication system and the backhaul links connecting each cell with the telecommunication system and/or with each other.

Below, a general description of each of the decision unit 11, the LA-cell 12, the SA-cells 13, 14, and the terminal 15 is provided. A more detailed description of the functionality of each of these elements is provided in the discussion of the different solutions, following the general description.

The decision unit 11 is a unit which may exchange mes¬ sages with at least the terminal 15 and, possibly, with the SA- cells 13,14. In some embodiments, as described in greater detail below, the decision unit 11 may be configured to select one or more SA-cells with which the terminal 15 may establish a data connection. To that end, in one embodiment, the decision unit 11 may include at least a communications interface for exchanging messages, a memory for storing data (possibly received in the messages) and/or computer program instructions, and a processor for processing data, running computer programs, etc. In other embodiments, the decision unit 11 may be implemented in software or in firmware. In yet other embodiments, the decision unit 11 may be implemented as any combination of hardware, software, and firmware .

In the illustrative embodiment of FIG. 3 the decision unit 11 is shown to be a part of the LA-cell 12. However, in other embodiments, the decision unit 11 may be not included in the LA-cell 12, but be a stand-alone unit, be included in a fur¬ ther network node, or be distributed between two or more network nodes (e.g. a part of the functionality of the decision unit 11 may be implemented within the LA-cell 12, while another part may be implemented in a further network node, not shown in FIG. 3) . Unless indicated otherwise, discussions provided herein with re¬ spect to the decision unit 11 apply both to the embodiments where the decision unit 11 is a part of the LA-cell 12 and where the decision unit 11 is implemented outside of the LA-cell 12.

The LA-cell 12 is an LA-cell cell configured to at least be able to enable terminal 15 to camp on LA-cell 12 and to page the terminal 15 in a conventional manner known in the art. According to some embodiments of the present invention, the LA- cell 12 is also configured to receive service request messages (SRMs) from the terminal 15 indicating that a data connection needs to be established between the terminal 15 and one of the SA-cells for supporting wireless traffic (i.e. wireless exchange of user data), not shown in FIG 3. While the LA-cell 12 is not primarily intended to be used to carry wireless user data from/to the terminal 15, it is not precluded that other signal¬ ling than paging or that also some user data traffic is carried via the LA-cell 12, for example low bit rate traffic (such as a voice call) for the full duration or for a part of the duration of the data session (call) .

In comparison with the SA-cells 13 and 14, the LA-cell 12 is configured to cover a larger geographical area with a smaller bit rate. The geographical area where an idle terminal selects the LA cell to camp on is referred to as the coverage area of the LA-cell. In a properly dimensioned cell, a terminal within that area is usually also capable of successfully receiv¬ ing the system information and signalling messages from the LA- cell (for example a paging message) . This is assumed to also ap¬ ply in the reverse direction, i.e. when a terminal, camping on an LA-cell, transmits a signalling message (for example a ser¬ vice request message) to the LA cell it is camping on, the LA cell is usually capable of successfully receiving the message. In the intended coverage area of the wireless access network it may be assumed that at least one LA-cell (in FIG. 3, the LA-cell 12) is fully operational or xnormally on' and is capable of sup¬ porting exchange of signalling messages with the terminals. In a simplest embodiment, this may mean that the LA cell 12 is always fully functional ( λοη' ) . In other embodiments, power-saving op¬ tions suitable for LA-cells may be applied to the LA-cell 12, meaning that the LA-cell 12 would not necessarily always be λοη' .

The terminal 15 may be a terminal operated by an actual human user, such as e.g. a mobile phone with which the user can make a voice call or browse the Internet, but may also be a smart phone or a blackberry operating without human intervention (e.g. sending/receiving e-mail), and may also be an M2M device, such as e.g. a smart electricity meter or a camera surveillance device .

The terminal 15 may be in an active mode or in an idle mode. As used herein, the terminal 15 is said to be in an idle mode while there is no support for a wireless exchange of user data or traffic between the terminal 15 and the SA-cells 13 or 14. As used herein, the terminal 15 is said to be in an active mode when it is able to exchange data with at least one of the SA-cells 13, 14. Note that while these notions of idle mode and active mode may be comparable with the meaning of like terms in standardized conventional networks, as used herein, they do not necessarily coincide exactly with such standardized definitions.

Further, the terminal 15 may support some form of pow¬ er-saving options (i.e., be in a power-save mode or in an operational mode, where the terminal consumes less power in the power-save mode than in the operational mode) . Since the differ¬ entiation between power-save and operational modes is based on the amount of power consumed by the terminal, while the differ¬ entiation between idle and active modes is based on the presence of the support for wireless exchange of user data with the SA- cells, a terminal may e.g. be in the operational mode but still be an idle terminal (or the terminal in the operational mode may be in active mode) . Similarly, a terminal in a power-save mode can be either active or idle, depending on whether the terminal supports wireless exchange of user data with at least one of the SA-cells. Most common, however, would be a situation where an idle terminal in a power-save mode "wakes up" (i.e. exits the power-save mode and enters the operational mode) to perform cer¬ tain actions to facilitate establishment of a data connection with at least one SA-cell, after which the terminal becomes "ac- tive" (and operational) . Since the embodiments of the present invention deal with a session setup for the terminal (i.e. es¬ tablishment of a data connection with one or more SA-cells) , in the following description, the differentiation is mainly made between idle and active modes of the terminal.

The terminal 15 in an idle mode may be assumed to xcamp' on at least the LA-cell 12, which may also be realized in a conventional manner. For example, the LA-cells may broadcast a pilot signal or a beacon signal which can be received by the terminal 15 which then uses the information contained in the re¬ ceived signal to select or re-select the LA-cell to camp on. In FIG. 3, the signals transmitted by LA-cell 12 and received by the terminal 15 are illustrated as a solid arrow. In an embodi¬ ment, the terminal 15 may be capable of informing the network about the change of location/routing area in order to facilitate the paging function of the LA-cell 12, not shown in FIG. 3.

The SA-cells 13 and 14 are data cells, primarily in¬ tended to carry user data traffic from/to the terminal 15 over the data connections established for that purpose. However, it is not precluded that also some other information and/or some signalling is carried via one or more of the SA-cells.

Each of the SA-cells 13 and 14 are intended to be capa¬ ble of covering smaller areas with a higher bit rate, as opposed to the LA-cell 12. In a typical deployment scenario, the areas that can possibly be covered by nearby SA-cells may show a con¬ siderable overlap. In the intended coverage area of the wireless access network it may be assumed that at least one of the SA- cells 13, 14 is able to provide coverage. An SA-cell is only fully operational when and to the extent that it is needed or, in other words, is xnormally off . An SA-cell is assumed to sup¬ port at least one form of power-saving, e.g. a power-save mode or stand-by mode. To that end, an exemplary embodiment of FIG. 3 illustrates that the SA-cell 13 is an SA-cell in a power-save mode (indicated in FIG. 3 as a white triangle), while the SA- cell 14 is an SA-cell in an active mode (indicated in FIG. 3 as a dark triangle) . In FIG. 3, the signals transmitted by active SA-cell 14 and received by the terminal 15 are illustrated as a solid arrow, while a possible signal transmitted by SA-cell 13, which is in power-save mode, and received by the terminal 15 is illustrated as a dashed arrow.

Each of the terminal 15, the LA-cell 12, and the SA- cells 13, 14 may include at least one or more of a processor, a memory unit, and a communications interface configured for car¬ rying out functionalities of these units described herein.

FIG. 4 is a schematic illustration of coverage areas of an LA-cell and a plurality of SA-cells in a telecommunications network, according to one embodiment of the present invention.

As shown in FIG. 4, an LA-cell 22, which could be the LA-cell 12 illustrated in FIG. 3, may have a relatively large coverage ar¬ ea, shown with a dashed circle 23. Each of the plurality of SA- cells, shown as triangles, such as the triangles 24, could be the SA-cells 13, 14 illustrated in FIG. 3. The SA-cells 24 may have different, relatively smaller coverage areas, shown with solid circles, such as circles 25. FIG. 4 further illustrates idle mode terminals 26 and active mode terminals 27 (the active mode terminals indicated as bold outlined terminals) . Each of the terminals 26 and 27 could be the terminal 15 illustrated in FIG. 3 and could be within one or more of the coverage areas 25. The idle mode terminals 26 within the coverage area 23 of the LA-cell 22 are said to be camping on the LA-cell 22. The SA- cells 24 having coverage areas 25 shown in white are intended to illustrate the SA-cells in the power-save mode, while the SA- cells 24 having coverage areas 25 shown in dark grey are intend¬ ed to illustrate the SA-cells in the active mode and have ongoing data sessions with one or more active terminals 27. Of course, in other embodiments, the coverage areas 23 and 25 do not have to be circular.

Solution # 1: Session setup via the terminal in idle mode measuring signals transmitted by SA-cells

In the context as illustrated in FIGs. 3 and 4 and de- scribed above, the terminal 15 is first assumed to be an idle terminal which intends to become active, either because it re¬ ceives a page (e.g. from the LA-cell the terminal camps on, e.g. the LA-cell 12) or because the terminal 15 (possibly via the us¬ er of the terminal or via an application running on the

terminal) indicates the desire to exchange user data. Embodi¬ ments of the present invention address the problem of selecting (assigning) a suitable SA-cell (one already active or one cur¬ rently in power-save mode) for that terminal.

For reference, in a conventional network, the terminal would initiate active mode via the cell that it is currently camping on (and, when applicable, via which the terminal re- ceived a page) and also the resulting data connection for carrying user data traffic is supported by the same cell (not excluding a handover or directed retry to a different cell) . In contrast, the following provides solutions for an energy- efficient network as illustrated in FIG. 3 where signaling mes- sages between the terminal and the network are exchanged using the LA-cell, but a data connection for exchanging user data is established with one of the SA-cells.

Embodiments of this solution are based on the idea that at least some of the SA-cells in a telecommunications network are configured to emit signals which the terminal 15 is able to receive while the terminal is in the idle mode. While still in the idle mode and camping on the LA-cell 12, the terminal 15 is further configured to analyze the received signals. More specif¬ ically, the terminal 15 in the idle mode is configured to determine properties representing propagation conditions of the received signals, such as e.g. a signal strength and/or a path loss estimate for the signal. The terminal 15 is also configured to provide a report to the decision unit 11, via the LA-cell 12, containing at least the information regarding at least some of the determined properties for at least some of the SA-cells for which the terminal 15 received and analyzed the signals. Based, at least partially, on the information contained in the report received from the terminal 15, the decision unit 11 is then able to make a selection of at least one of the SA-cells in the tele- communications network to serve the terminal 15. In other words, the decision unit 11 is able to select one or more SA-cells with which the terminal 15 could establish the data connection for exchanging user data.

In this manner, the terminal 15 facilitates establish¬ ment of the data connection between the terminal 15 and one of the SA-cells by providing to the decision unit 11 information regarding the propagation conditions between the terminal 15 and various SA-cells. When the decision unit 11 has such information available, a selection of the most appropriate SA-cell for es¬ tablishing the data connection may be performed quicker and/or more accurately.

FIG. 5 sets forth a flow diagram of method steps for selecting one or more SA-cells when the terminal 15 measures signals from the SA-cells, according to one embodiment of the present invention. While the method steps are described in con- junction with FIG. 3, persons skilled in the art will recognize that any system configured to perform the method steps, in any order, is within the scope of the present invention.

The method begins in step 31, where one or more SA- cells in the network transmit signals intended for the terminal 15. In step 32, the terminal 15 is configured to receive and process at least some of the signals transmitted by the SA- cells.

According to the embodiments of the present invention, not only active SA-cells may emit signals that the terminal 15 may receive and analyze, but also SA-cells in a power-save mode. The latter is particularly advantageous for energy-efficient networks because transmitting signals (e.g. pilot and system in¬ formation) can amount to a substantial portion of the cell's maximum transmit power, such that a cell without any traffic or a cell carrying little traffic is very energy-inefficient. How¬ ever, according to some embodiments of the present invention, an SA-cell in a power-save mode may also be configured to emit a signal that the terminal 15 can receive and analyze. To that end, the SA-cell in a power-save mode may be configured to only emit a so-called "presence signal," e.g. a signal emitted inter¬ mittently, for a fraction of the time. For example, such a SA- cell may be configured to emit the signal for 1 second, followed by 9 seconds of not emitting the signal, corresponding to a fraction l/10th. Varying the duty cycle (i.e. the ratio between the "on" and "on"+"off" times for emitting the signal) in this manner allows reducing the power of the emitted presence signal to roughly the same fraction, as opposed to a conventional ap¬ proach where a transmission would be substantially 100% of the time. In one embodiment, the maximum duty cycle for an intermit¬ tent signal emitted by an SA-cell could be e.g. l/8th, which could result in an 8-fold power saving in comparison with the same signal emitted continuously.

The signals emitted by the SA-cells should be suitable for the terminal 15 in an idle mode to detect and analyze. This means that the signals should be lasting sufficiently long and should be decodable by the terminal. The signals should prefera- bly be sufficiently frequent to allow the terminal 15 to receive and analyze the intermittent signal without excessive waiting time, should be emitted e.g. once per second.

In addition, the signals should be such that the termi¬ nal can differentiate between the signals received from the different SA-cells. In one embodiment, the differentiation may be done by each SA-cell emitting a signal that is uniquely cod¬ ed. In another embodiment, each SA-cell may include its

identification in the signal. In yet another embodiment, each SA-cell may emit signals via a different channel and the termi- nal 15 may be configured to "listen" to these different

channels. Further, if the SA-cells emit their signals intermit¬ tently, the terminal 15 may also differentiate between the SA- cells based on the time the signal is received (provided that there is synchronization between the terminal and the SA-cells and the terminal has access to information indicative of the times when the signals from each respective SA-cells should be expected to be received) . Of course, a combination of these em¬ bodiments and other manners for differentiating between the signals received from different SA-cells are also possible and within the scope of the present invention.

In one embodiment, identification of the SA-cell pro¬ vided in any one of the manners described above could be a globally unique identification which allows global differentia¬ tion between each SA-cell. However, such a globally unique identification is not always necessary. In other embodiments, the identification may be such that it uniquely identifies a particular SA-cell in e.g. a particular, relevant geographical area (e.g. the SA-cell which provides at least partial coverage in the coverage area of the LA-cell) .

In an embodiment particularly useful for the SA-cells in power-save mode, the transmission of the signals by the SA- cells may be configured to take place in a predetermined pattern (e.g. periodically) . An idle terminal in a power-save mode may then be configured to synchronize its "wake-up" times for re¬ ceiving and analyzing the signals of at least the most relevant of these SA-cells.

With a predetermined transmission pattern of the SA- cells, it may be an option to organize the transmission instanc¬ es of the presence signals of the SA-cells (at least the ones of particular relevance to the terminal, e.g. those in the vicinity of each other) such that these transmissions, as far as possi- ble, do not consistently coincide. This may be beneficial for several reasons. One reason is that it may enable the terminal to more easily differentiate between the signals received from the different SA-cells. Another reason is that it may allow the terminal to make assessments of several SA-cell presence signals in a quick succession, e.g. one SA-cell at the time, and without interference from presence signals of other SA-cells nearby the terminal (possibly with received signal strengths in the same range as from the first SA-cell) .

An alternative option for the predetermined transmis- sion pattern of the SA-cells could be to organize the

transmission instances of the presence signals of the SA-cells so that the transmissions would substantially coincide. This op¬ tion is viable if a terminal is able to perform measurements on several SA-cell presence signals at the same time, which re- quires more processing power in the terminal. This would allow the terminal to make several SA-cell presence signal assessments at a time and then go back to the power-save mode again. In one embodiment, an idle terminal in a power-save mode may exit the power-save mode at some predetermined times in order to receive and measure the signals from the SA-cells. The terminal may do so e.g. periodically or upon receiving a paging signal from the LA-cell indicating to the terminal that, for ex¬ ample, a data connection needs to be established or that a report is requested for e.g. network management purposes and/or for terminal localization. In another embodiment, an idle terminal may be configured to only start monitoring the signals from the SA-cells when the terminal needs to establish a data connec¬ tion. Such an embodiment would allow saving power during the time when the terminal is in idle mode, but may result in in¬ creased latency before the terminal is able to transmit the relevant information to the decision unit, thus increasing the latency in establishing the data connection. For many applications, e.g. checking and retrieving new e-mails, such an

increase in latency would have no significant effect on the ap¬ plication .

In yet another embodiment, one or more of the SA-cells in a power-save mode may be triggered by the LA-cell to emit the signal to be received by the terminal. This may be done in re¬ sponse to e.g. the LA-cell receiving a service request message from the terminal or when (or before) the LA-cell pages the ter¬ minal. If the terminal is also in a power-save mode, the LA-cell could synchronize the trigger for the SA-cells to transmit the signals with a trigger for the terminal to receive and analyze the signals. This embodiment also holds for the one or more SA- cells in a power-save mode being triggered by the decision unit 11, which could either be a part of the LA-cell 12 or be an en- tity outside of the LA-cell 12.

A trigger for the SA-cells to transmit the signals could be based, at least partially, on one or more of a terminal location estimate, an estimate of the accuracy of the terminal location estimate, and activity status of the SA-cells in the vicinity of the estimated terminal location. In one embodiment, the terminal location estimate and the estimate of the accuracy of the location estimate could be provided to the LA-cell by the terminal because the terminal has a built-in GPS receiver which is typically able to provide both a position estimate and an in¬ dication of the accuracy of the position estimate. In another embodiment, these values may be derived by the LA-cell from the contents of a service request message received from the termi¬ nal. This may be done e.g. by the terminal providing signal levels of all kinds of signals received (e.g. active SA-cell signals, WiFi hotspot signals, LA-cell signals, etc.) The LA- cell (or a separate location estimating unit associated with the LA-cell) may then process this information into a position esti¬ mate and an accuracy estimate.

The terminal 15 may be configured to maintain a list of at least the most recent and most relevant results for the meas¬ ured signals together with the indication of the corresponding SA-cells.

In step 33, the terminal 15 is configured to provide a report to the decision unit 11 regarding at least some of the determined properties the SA-cells that the terminal analyzed. The terminal 15 may be configured to provide the report to the decision unit 11 via the LA-cell 12. Such an embodiment may be advantageous because the LA-cell may be configured to add infor¬ mation to the report passed to the decision unit, such as e.g. an identification of the LA-cell. In addition, the decision unit 11 having the identification of the LA-cell may further facili- tate identification of the SA-cells about which the report contains information.

In one embodiment, the terminal 15 may provide the re¬ port periodically, even when there is no immediate need for establishing the data connection. Such an embodiment has the ad- vantage that the decision unit 11 may have sufficient

information available for selecting the most appropriate SA-cell to serve the terminal when the data connection does need to be established. It may also provide the network with more accurate information about the terminal location than just the loca- tion/routing area, which information may be relevant for e.g. statistical purposes. In another embodiment, the terminal 15 may only provide the report upon receiving a paging signal from the LA-cell or when the terminal wants to become active (i.e. when a data con¬ nection needs to be established) . In the latter case, the termi- terminal may be configured to send a service request message

(SRM) to the network via the LA-cell and may include the report in the SRM. Thus, the report is then provided to the decision unit as a part of a connection setup procedure.

As previously described, the report includes at least information regarding at least some of the determined properties for at least some of the SA-cells for which the terminal 15 re¬ ceived and analyzed the signals. In other words, out of all of the SA-cells in the telecommunications network (or at least the plurality of the SA-cells in the vicinity of the terminal) , the terminal may receive signals from only some of these cells. The terminal may then analyze not all of the received signals, but only some of those (e.g. because some signals may be impossible to analyze or because they may be associated with the SA-cells that the terminal is not interested in establishing a data con- nection with) . Further, the terminal may decide to include in the report not all of the information regarding the propagation conditions for all of the analyzed SA-cells, but only the infor¬ mation for some of the analyzed SA-cells and/or only part of the determined information. For example, the terminal may decide to not include the signal strengths for the most relevant SA-cells, but to include the determined path loss estimates, e.g. because the path loss is considered to be more relevant to the decision unit and/or to limit the size of the report and/or when results for many SA-cells have been determined.

In one embodiment, the report may also include one or more of the following: an identification of each SA-cell for which information is provided, identifications of the SA-cells for which the signals were received but for which the infor¬ mation is not provided in the report, an indication of which SA- cells are active and which are in a power-save mode, and a 1-bit flag indicating that there is no coverage provided by a particu¬ lar SA-cell at the location where the service is requested. If the report is received by the decision unit 11 when a data connection needs to be established (i.e. when the termi¬ nal has been paged or the terminal indicates a desire to

establish a data connection) , the decision unit 11 then may pro- ceed, in step 34, to use at least some of the information provided in the report to select one or more SA-cells with which the terminal may establish the data connection. For example, in one embodiment, the decision unit 11 may take into consideration path loss estimates provided in the report and select the SA- cell with the lowest path loss estimate (e.g. the SA-cell clos¬ est to the terminal) as the cell for serving the terminal. The decision unit 11 may, however, also take other information into consideration when making the selection, such as e.g. power and/or load considerations on the candidate SA-cells, capabili- ties of the SA-cells and the terminal (including e.g. the supported RATs) , the type of the required service, and the ur¬ gency of establishing the data connection (i.e., whether

establishing the service is time-critical or not) . For example, the most suitable SA-cell for the terminal could be not neces- sarily the SA-cell with the lowest path loss to the terminal because it may be more suitable to keep the closest SA-cell in a power-save mode (the indication of which could be provided in the report) and to select a different, e.g. already active, SA- cell for serving the terminal. In another example, it could be that the closest SA-cell is already heavily loaded and that a different, more distant, SA-cell is more suitable. In yet anoth¬ er example, it could be that the closest SA-cell supports a less energy-efficient RAT than a different, more distant, SA-cell. In yet one more example it could be that the SA-cell indicated in the report as having the highest signal strength and/or the low¬ est path loss estimate does not have the capabilities for carrying a particular service and, therefore, the "next best" SA-cell is selected from the ones provided in the report that does have the required capabilities. Alternatively, after evalu- ating the report, the decision unit 11 may decide that none of the SA-cells are suitable for carrying the service (this may particularly be the case for time-critical services and/or when the 1-bit flag(s) in the report indicates that there currently is no coverage by any SA-cell at the location where the service is requested) and that the LA-cell instead should serve the ses¬ sion, possibly with a reduced bit rate and/or possibly only temporarily, e.g. until a suitable SA-cell becomes available.

If there is no need to establish the data connection at the time when the report is received, the decision unit 11 may be configured to store the report for later use and evaluation. Alternatively, the decision unit may still go through the pro- cess of selecting one or more SA-cells that could serve the terminal in case there is a need to establish a data connection and store that information, possibly along with the report.

Once one or more SA-cells are selected by the decision unit 11 as the most appropriate SA-cells for establishing the data connection with the terminal, the decision unit 11 may in¬ dicate the selected SA-cells to the terminal. In one embodiment, such indication may be provided via the LA-cell (e.g. in re¬ sponse to receiving a SRM received from the terminal via the LA- cell) . In this embodiment, the decision unit 11 may provide an indication also to the selected SA-cells to inform these

SA-cells that a session set-up is to be expected. In another em¬ bodiment, such indication may be provided via one or more of the selected SA-cells. The latter embodiment assumes that a channel (with mutually known resource details) between the terminal and the selected SA-cell can be made available, along which channel an SA-cell may initiate the set up of a data connection to the terminal. In both these embodiments, the selected SA-cell (s) may be provided with further information related to the terminal and/or the subscription (such as, for example, data connection parameters and/or authentication information and/or encryption keys) in order to facilitate a more speedy session set-up. This information may be supplied by the decision unit and/or may be requested by the decision unit to be supplied from a data base (such as the HLR/VLR (Home Location Register / Visitor Location Register) to the selected SA-cells. If any of the selected SA-cells are in a power-save mode, the decision unit 11 may further be configured to activate the selected SA-cells (possibly via the LA-cell) .

The terminal 15 may further be configured for estab- lishing the data connection (i.e., setting up a traffic channel) with the selected one or more SA-cell. Further, a route for the traffic (and the associated signaling) may be set up connecting the selected SA-cell (s) and the network.

Once the decision unit 11 knows the identities of the selected SA-cells, the decision unit 11 may assist in and pre¬ pare for setting up the route for the traffic connecting the selected SA-cells and the network. This may also be performed by LA-cell 12 when decision unit 11 is within the LA-cell or when the decision unit provides the information to the LA-cell.

In a cellular wireless telecommunication system it may happen that a terminal in active mode, having a connection with a particular cell, moves out of (the coverage area of) that cell and into (the coverage area of) another cell. Then a so-called handover (handoff) may be performed, meaning that the connection between the terminal and the current cell (source cell) is transferred (handed over) to a connection between the terminal and a different cell (target cell) .

Solution #1 as described above may also be used in an energy-efficient wireless network to facilitate a handover of the data connection between an active terminal and the SA-cell it has established the data connection with to another, different, SA-cell.

An active terminal may perform measurements on signals received from various SA-cells as described above, e.g. periodi- cally and/or when the signal received from the SA-cell it has established a data connection with drops below a predetermined threshold and/or when triggered by the network. The terminal may then provide the report to the decision unit via the LA-cell. The decision unit may evaluate the information contained in the report received from the terminal and, taking into account con¬ siderations similar to the ones described above, select a different SA-cell as target SA-cell for a handover. As described above, the decision unit may further in¬ form the terminal and/or the LA-cell and/or the involved (source and target) SA-cells. Solution # 2: Session setup via SA-cells measuring signal transmitted by the terminal in idle mode and the terminal selecting the SA-cell based on the measurements

Similar to the solution # 1 described above, in the context as illustrated in FIGs. 3 and 4, the terminal 15 is as- sumed to be an idle terminal which may, in the future, have to transfer to an active mode, either because it receives a page (e.g. from the LA-cell the terminal camps on, e.g. the LA-cell 12) or because the terminal 15 (possibly via the user of the terminal) initiates exchange of user data. Similar to the solu- tion # 1, embodiments of the solution # 2 also address the problem of selecting (assigning) a suitable SA-cell (one already active or one currently in power-save mode) for that terminal.

Embodiments of solution # 2 are based on the idea that a terminal in the idle mode is configured to emit a signal, re- ferred to herein as an information request message (IRM), intended to be received by one of more of the SA-cells in the telecommunications network. In some ways, the IRM may be compa¬ rable to the SRM, described above, that the terminal 15

transmits to the LA-cell when the terminal wishes to initiate a setup of the signaling connection with the LA-cell. The IRM is used to have the SA-cells receiving the IRM to perform measure¬ ments on the received signal, e.g. to determine the strength with which the signal was received. Similar to the SRM, the IRM may also be used by the terminal to indicate that the terminal wishes to establish a connection and, optionally, to include pa¬ rameters indicative of the requested connection and/or of the terminal's capabilities. Unlike the SRM, the IRM is intended to be received by the SA-cells and is intended to indicate to the SA-cells that the terminal may need to setup a data connection with at least one of them.

Preferably, the IRM is transmitted such that it may be easily received and decoded by an SA-cell, even more preferably also when the SA-cell is in power-save mode. The IRM may be transmitted on a particular separate radio interface which is different from any of the RATs the terminal is capable of em¬ ploying for supporting signaling and/or data connections.

However, it is not precluded that the IRM is transmitted using a RAT the terminal is capable of employing for supporting a sig¬ naling connection and/or a data connection, for example the LA-cell's RAT the terminal is camping on (in which case differ¬ ent frequencies and/or different codes could be used, as known in the art) . The transmission of the IRM further differs from the SRM in that the SRM is directed to and addressed to a par¬ ticular cell (i.e. the LA-cell that the terminal identified and is currently camping on) and has a purpose to e.g. establish a signaling connection with that particular cell. In contrast, the IRM is not directed to nor addressed to any particular cell (the IRM is broadcast) and has a purpose to e.g. identify one or more cells (SA-cells) .

At least some of the SA-cells in the telecommunication system may be able to receive the IRM transmitted by the termi- nal and determine the signal strength with which they received the IRM. At least some of those SA-cells that determined the signal strength of the received IRM can then provide messages to the terminal indicating the determined strength. At least par¬ tially based on such messages received from the SA-cells, the terminal can then make a selection of one or more of the most appropriate SA-cells for establishing the data connection with.

In this manner, the terminal 15 facilitates establish¬ ment of the data connection between the terminal 15 and one of the SA-cells by first enabling the SA-cells to obtain infor- mation indicative of the propagation conditions between the terminal 15 and various SA-cells (e.g., signal strength) and then collecting the obtained information from the SA-cells in order to select an appropriate SA-cell for establishing the data connection. As a result, establishment of the data connection may be performed quicker and/or more accurately.

FIG. 6 sets forth a flow diagram of method steps for selecting one or more of the SA-cells 13, 14 when the terminal 15 transmits an information request message, according to one embodiment of the present invention. While the method steps are described in conjunction with FIG. 3, persons skilled in the art will recognize that any system configured to perform the method steps, in any order, is within the scope of the present inven¬ tion.

The method begins in step 41 where the terminal 15 in an idle mode transmits an IRM. In one embodiment, the terminal 15 may be configured to transmit the IRM at some predetermined times and/or at some predetermined pattern, even though there is no immediate need to establish a data connection with any of the SA-cells. In other embodiments, the terminal 15 may be config¬ ured to transmit the IRM when the terminal receives an

indication that the data connection between the terminal and one of the SA-cells should be established. Such an indication could e.g. be a paging message received from the LA-cell 12 on which the idle terminal 15 is camping or be an indication from the us¬ er of the terminal or an application running on the terminal wishing to exchange user data over the established data connec- tion.

In one embodiment, the IRM may be transmitted via a broadcast channel. The IRM is not intended for and not directed towards the LA-cell (as opposed to e.g. a service request mes¬ sage typically used in conventional networks) but is intended for SA-cells which may potentially provide service to the termi¬ nal 15. To that end, the IRM could also include information indicative of the request of the terminal for establishing a da¬ ta connection between the terminal and one of the SA-cells.

The IRM may include at least some means that would ena- ble the SA-cells receiving the message to identify the terminal that sent it so that the SA-cells can differentiate between the IRMs received from different terminals. In one embodiment, the differentiation may be done by the terminal including its (pos¬ sibly partial) identification in the IRM. Instead of or in addition to a direct identification of the terminal (such as the full or partial terminal ID) , the terminal may include a kind of reference (tag or label) in the IRM. Such a reference may enable the SA-cell to discriminate between IRMs received from different terminals. Further, the SA-cell may include (e.g. copy) the re¬ ceived reference (tag or label) in the response message, thus also enabling the terminal to discriminate between response mes- sages relating its own IRM and those that might be received but relate to IRMs transmitted by different terminals. Selecting a randomized number as reference (tag or label) for the IRM may serve this purpose.

The (partial) identification may e.g. be coded in the contents of the IRM and/or may be coded by transmitting the IRM on one or more of multiple frequencies and/or by transmitting the IRM with one or more of multiple channel codes. In another embodiment, the differentiation may be done by the terminal transmitting the IRM at a particular time, for example in one or more of multiple time slots which time slots may be repeated in a predetermined pattern, e.g. periodically. The SA-cell can then differentiate between the terminals based on the times or time windows the IRMs are received (provided that there is synchroni¬ zation between the terminal and the SA-cells) . Of course, a combination of these embodiments and other manners for differen¬ tiating between the signals received from different terminals are also possible and within the scope of the present invention.

In one embodiment, identification of the terminal pro¬ vided in any one of the manners described above could be a globally unique identification which allows global differentia¬ tion between each terminal. However, such a globally unique identification is not always necessary. In other embodiments, the identification may be such that it uniquely identifies a particular terminal in e.g. a particular, relevant geographical area (e.g. the terminal in the coverage area of the SA-cell) .

In yet another embodiment, the terminal may be config¬ ured to include in the IRM an identification of the network to which the terminal belongs. By providing such identification in the IRM, the SA-cell receiving the IRM can differentiate between the IRMs received from terminals belonging to different networks and then choose whether or not to respond. For example, the SA- cell may choose not to respond when the IRM is sent by a termi- nal in a competitor's network. In this case, the provided iden¬ tification does not need to be terminal-specific. It would be sufficient to only identify the network that the terminal belong to .

The IRM may also include an indication of access prior¬ ity. For example, an emergency response terminal or a consumer terminal making an emergency call may include an indication of high access priority or an M2M terminal (e.g. electricity meter) may include an indication of low access priority. By providing such an indication in the IRM, the SA-cell receiving the IRM can differentiate between the IRMs received from terminals and/or purposes having different access priorities and then choose whether or not to respond.

Further, the IRM should be such as to allow the receiv- ing SA-cell to determine the signal strength with which the IRM is received and/or to estimate the path loss between the termi¬ nal and the receiving SA-cell.

Optionally, the IRM may include an indication of the service (s) requested and/or the terminal capabilities, which may be relevant to a SA-cell receiving the IRM in determining to what extent the SA-cell is capable and able to provide the re¬ quested service. The terminal capabilities that could be

identified in the IRM include e.g. one or more of supported fre¬ quency band(s), supported RAT(s), supported mode(s), power with which the IRM is sent by the terminal, supported (maximum) ter¬ minal power, and requested (minimum) bit rate.

In one embodiment, the terminal 15 may transmit the IRM with a relatively high power in order to maximize the likelihood that at least one suitable SA-cell is able to detect the IRM. In one further embodiment, the terminal may transmit the IRM at the maximum terminal's transmitting power. In an alternative embodiment, the terminal 15 may decide to transmit the IRM at still relatively high power, but at less than the maximum transmitting power. This could be sufficient if, for example, the terminal already has measured signals from at least one suitable active SA-cell and, therefore, there is no need to transmit the IRM with more power than to overcome the path loss to the best cur- rently active SA-cell. Such an IRM would only need to reach the SA-cell (s) in power-saving mode that could possibly be better candidate (s) than the best currently active SA-cell. Another ex¬ ample of transmitting the IRM at less than the maximum

terminal's transmitting power could be that the system information provided by a currently active SA-cell or by the serving LA-cell also includes information about the SA-cell density in the area. In such an example, the terminal may limit the trans¬ mitting power for the IRM accordingly.

In an embodiment, the terminal 15 may be configured to transmit the IRM more than once, in a sequence, e.g. to overcome the possibility of corruption by noise, to overcome the possi¬ bility of interference from a similar message from a different terminal, and/or to overcome the sleep period of an SA-cell in power-save mode and listening for only a fraction of the time. In such an embodiment, the terminal may be configured to trans¬ mit subsequent IRMs in the sequence with increased or with increasing power. The terminal may also be further configured to transmit subsequent IRMs with a randomized delay relative to the preceding IRM in the same sequence, in order to avoid subsequent collisions of the IRMs.

In step 42, at least some of the SA-cells may receive the IRM transmitted by the terminal and process the IRM by at least determining the signal strength with which the IRM is re- ceived. The SA-cells may further be configured to estimate the path loss from the terminal to the receiving SA-cell. The

SA-cell may use the estimated path loss for e.g. estimating whether a requested (minimum) bit rate is at all feasible on the wireless path between the terminal and the SA-cell (and, if not, the SA-cell may decide to refrain from responding) .

The SA-cell may be configured to process all of the IRMs that it receives or may choose to ignore some IRMs, such as those requesting a service that the SA-cell is unable to deliver at the moment (e.g. because an unsupported RAT and/or frequency band is requested, and/or because the SA-cell is already highly loaded), and/or those IRMs that have been received with a low signal level and/or with a high estimated path loss. The SA-cell may also be configured to ignore IRMs received from the termi¬ nals not related to the network of the SA-cell (e.g. terminals related to a competitor's network) and/or to ignore IRMs re¬ ceived with an access priority indication lower than a

predetermined threshold. The SA-cell may be able to identify a terminal as belonging to a different network based on the termi¬ nal identification provided in the IRM (for such an embodiment, the identification does not need to be terminal-specific, a net¬ work-specific identification is sufficient) .

It may be noted that, in various embodiments, a wire¬ less access network may contain multiple different types of SA- cells, e.g. SA-cells supporting different (or multiple) frequen¬ cy bands, SA-cells supporting different (or multiple) RATs, SA- cells supporting different (or multiple) modes of operation, and/or SA-cells of different sizes (macro-, micro, pico- and femto-cells) . Still, each of these SA-cells may be configured to have an SA-cell' s monitoring of IRMs which could be performed regardless the SA-cell' s specific capabilities for the data transfer (data connection or traffic channel) . In fact, the ra- dio interface at the terminal for transmitting the IRM and the radio interface at the SA-cells for receiving the IRMs may be designed specifically for the IRMs and may be independent of the SA-cell' s capabilities for data transfer (data connection or traffic channel) . However, in case the frequencies used for the communicating the IRMs and for communicating the actual user data over the established data connection would be significantly different, then the signal strength measurement and/or path loss estimate made using the frequency at which the IRM was sent may be not very well representative for the path loss on the fre- quency to be used for the actual user data transfer (e.g. when the IRM is transmitted in the 900 MHz range while the data con¬ nection is established in the 5 GHz range) . In such cases, a similar IRM may be defined using a different frequency (e.g. in the 3 GHz range) that allows a more representative signal strength/path loss estimate. The terminal 15 may then be config¬ ured to transmit either or both of these IRMs, even

simultaneously, if needed. At least the SA-cells in the power-save mode may be configured to monitor (listen) for the IRMs which may be emitted by the terminals. The SA-cells in the active mode may also be configured to listen for the IRMs, however such listening by the active SA-cells may be not required when the terminal is config¬ ured to monitor the signals of the active SA-cells serving one or more other terminals and when the signals received by the terminal enable the terminal to sufficiently assess the suita¬ bility of these candidate SA-cells. Then, the terminal may maintain a list of suitable active candidate SA-cells for estab¬ lishing the data connection.

In an embodiment, the SA-cells in the power-save mode can be configured to enter the listening mode (i.e. be capable of receiving IRMs) only for a fraction of time, in order to lim- it power consumption. For example, the SA-cell in the power-save mode may enter the listening mode periodically, for e.g. l/10th of the time, thus reducing the power consumed for this purpose to roughly the same fraction (compared to the situation with listening for 100% of the time) . In such embodiments, the lis- tening periodicity, the duration of the IRMs transmitted by the terminal, and/or the number of repetitions of the IRMs in a se¬ quence could be selected such that at least one IRM can be received within a SA-cell' s listening cycle.

In step 43, at least some of the SA-cells that received and measured the IRMs may be configured to wirelessly transmit messages containing their responses to the terminal, e.g. via a channel on the requested RAT and/or frequency, or via a common information request response channel (which could be designed specifically for the purpose) . Such messages could include at least a portion of the measured results to the terminal 15 (e.g. the measured signal strength and/or the estimated path loss de¬ termined by the SA-cell) . The SA-cells may also be configured to include in their messages an indication to what extent the SA- cell is capable and able to provide the requested service. Fur- ther, the SA-cells may be configured to include additional information regarding their current load and/or their currently available resources (e.g. RAT, frequency or frequency band, codes) and/or may further propose specific resources, which re¬ sources the SA-cell provisionally reserves for the case the terminal would select the SA-cell.

The SA-cell may be configured to only transmit a mes- sage regarding some IRMs . For example, the SA-cell may be configured to not transmit a message to the terminal if the SA- cell cannot provide the service requested by the IRM. Alterna¬ tively, the SA-cell could be configured to process and transmit response messages even regarding such IRMs, with an indication that the SA-cell is unable to provide the service and, optional¬ ly, an indication of what the SA-cell is capable of and able to provide, as described above.

In an embodiment, if the SA-cell is able to support the service requested in the received IRM, the SA-cell may provi- sionally reserve the resources according to the requested service and also inform the terminal about it. Such provisional¬ ly reserved resources may be freed up after a suitable period (e.g. when a timer expires) or when the SA-cell is informed that its service is not needed for this particular service request.

In an embodiment, the responding SA-cell may be config¬ ured to apply a small controlled delay between the moment the IRM is received and the moment the corresponding response mes¬ sage is transmitted (and, when applicable, also to control the time between repeated response messages to a sequence of IRMs) . By controlling the delay in dependence of e.g. the strength of the signal with which the SA-cell received the IRM from the ter¬ minal, a potentially better candidate SA-cell can be made to respond earlier than a potentially worse candidate SA-cell, thus supporting the terminal's function of receiving the response messages and of selecting the best candidate SA-cell.

Because more than a single SA-cell may respond at about the same time to the same IRM from the terminal, it is desirable that there is a mechanism to cope with response messages from multiple SA-cells arriving at the terminal overlapping (simulta- neously) or partially overlapping. This may be achieved, for example, by configuring the different (e.g. neighboring) SA- cells to use different channel codes and configuring the termi- nal 15 to simultaneously monitor multiple different channel codes, possibly all of the different channel codes. This may al¬ so be achieved by multiple (repeated) transmissions of a same response message from an SA-cell at separate moments, separated by different (e.g. randomized or SA-cell-dependent ) delays.

In an embodiment of step 43, the SA-cells may be con¬ figured to wirelessly transmit messages containing their

responses to the terminal not directly but via the LA-cell that the terminal is camping on. In such an embodiment, the SA-cells would first transmit their responses to the LA-cell and the LA- cell then would provide to the terminal one or more reports con¬ taining at least some of the information received in the

responses from the SA-cells. For example, the LA-cell may pro¬ vide to the terminal and aggregate reports for all of the SA- cells that provided responses regarding received IRMs .

In an embodiment, based on the responses received from the SA-cells, the terminal 15 may be configured to maintain a list of at least the most recent and most relevant results for the measured signals together with the indication of the corre- sponding SA-cells.

Further, the embodiments of Solution # 2 could be com¬ bined with the Solution # 1 in that the terminal 15 may perform the method steps 41-43 but then, instead of making the selection of the SA-cell itself, provide a report regarding the measure- ments to the decision unit 11, similar to the step 33 described in the Solution # 1. Such a report could include at least some of the information provided to the terminal by the SA-cells that received and processed the IRM transmitted by the terminal. The decision unit 11 could then select one or more SA-cell for es- tablishing the data connection with the terminal based on this report, similar to the step 34 described in the Solution # 1. A person skilled in the art would readily recognize how to adapt the discussions of steps 33 and 34 to this embodiment and, therefore, in the interests of brevity, these discussions are not repeated here.

Continuing with the method illustrated in FIG. 6, in step 44, based, at least partially, on the information received in the response messages from one or more SA-cells, the terminal 15 selects (assigns) one or more SA-cell from the candidates for establishing the data connection. The candidates may include not only the SA-cells that provided their response to the terminal, but also the SA-cells that didn't provide their responses and the SA-cells that didn't even receive the IRM. This could be used e.g. when the terminal is configured to monitor active SA- cells and to evaluate whether the monitored active SA-cells con¬ stitute suitable candidates for establishing the data connection with. In other words, in addition to the information received in the response messages, the terminal 15 may also take into con¬ sideration, when selecting a SA-cell, information regarding other SA-cells that did not provide responses.

The terminal 15 may further be configured for estab- lishing the data connection (i.e., setting up a traffic channel) with the selected one or more SA-cell. Further, a route for the traffic (and the associated signaling) may be set up connecting the selected one or more SA-cell and the network.

Further, the terminal 15 and/or the SA-cells and/or the network may be further configured to inform the non-selected SA- cell (s) , which may then release the provisionally reserved re¬ sources for fulfilling the request. For example, once a data connection has been established between the terminal and the se¬ lected SA-cell, the terminal may provide the SA-cell identities of the non-selected SA-cells to the selected SA-cell and the se¬ lected SA-cell may then inform the non-selected SA-cells

accordingly .

In a cellular wireless telecommunication system it may happen that a terminal in active mode, having a connection with a particular cell, moves out of (the coverage area of) that cell and into (the coverage area of) another cell. Then a so-called handover (handoff) may be performed, meaning that the connection between the terminal and the current cell (source cell) is transferred (handed over) to a connection between the terminal and a different cell (target cell) .

Solution #2 as described above may also be used in an energy-efficient wireless network to facilitate a handover of the data connection between an active terminal and the SA-cell it has established the data connection with to another, different, SA-cell.

An active terminal may emit an IRM as described above, e.g. periodically and/or when the signal received from the

SA-cell it has established a data connection with drops below a predetermined threshold and/or when triggered by the network. The terminal may evaluate the information contained in the re¬ sponse messages received from the SA-cells and, taking into account considerations similar to the ones described above, se¬ lect a different SA-cell as target SA-cell for a handover.

As described above, the terminal may further inform the network and/or LA-cell and/or the involved (source and target) SA-cells .

Solution # 3: Session setup via SA-cells measuring signal transmitted by the terminal in idle mode and the network selecting the SA-cell based on the measurements

Similar to the solutions # 1 and # 2 described above, in the context as illustrated in FIGs. 3 and 4, the terminal 15 is assumed to be an idle terminal which may, in the future, have to transfer to an active mode, either because it receives a page (e.g. from the LA-cell the terminal camps on, e.g. the LA-cell 12) or because the terminal 15 (possibly via the user of the terminal) initiates exchange of user data. Similar to the solu¬ tions # 1 and # 2, embodiments of the solution # 3 also address the problem of selecting (assigning) a suitable SA-cell (one al¬ ready active or one currently in power-save mode) for that terminal .

Similar to the solution # 2, embodiments of solution #

3 are based on the idea that a terminal in the idle mode is con¬ figured to emit the IRM intended to be received by one or more of the SA-cells in the telecommunications network and that at least some of the SA-cells may be able to receive the IRM trans- mitted by the terminal and determine the signal strength with which they received the IRM. At least some of those SA-cells that determined the signal strength of the received IRM can then provide messages to the decision unit reporting the determined signal strength. At least partially based on such messages re¬ ceived from the SA-cells, the decision unit can then make a se- selection of one or more of the most appropriate SA-cells for the terminal to establish the data connection with.

In this manner, the terminal 15 facilitates establish¬ ment of the data connection between the terminal 15 and one of the SA-cells by enabling the SA-cells to obtain information indicative of the propagation conditions between the terminal 15 and various SA-cells (e.g., signal strength) . Since the SA-cells then report the results of their measurements to the decision unit (which could possibly be included within the LA-cell) , the selection of at least one SA-cell for the terminal may be cen¬ trally managed.

FIG. 7 sets forth a flow diagram of method steps for selecting one or more of the SA-cells 13, 14 when the terminal 15 transmits an IRM and the decision unit 11 makes the selection of the most appropriate SA-cell, according to one embodiment of the present invention. While the method steps are described in conjunction with FIG. 3, persons skilled in the art will recog¬ nize that any system configured to perform the method steps, in any order, is within the scope of the present invention.

The method begins in step 51 where the terminal 15 in an idle mode transmits an IRM. In one embodiment, the terminal 15 may be configured to transmit the IRM at some predetermined times and/or at some predetermined pattern, even though there is no immediate need to establish a data connection with any of the SA-cells. In other embodiments, the terminal 15 may be config¬ ured to transmit the IRM when the terminal receives an

indication that the data connection between the terminal and one of the SA-cells should be established. Such an indication could e.g. be a paging message received from the LA-cell 12 on which the idle terminal 15 is camping or be an indication from the us¬ er of (or an application running on) the terminal wishing to exchange user data over the established data connection.

In one embodiment, the IRM may be transmitted via a broadcast channel. The IRM is not intended for and not directed towards the LA-cell (as opposed to e.g. a service request mes¬ sage typically used in conventional networks) but is intended for SA-cells which may potentially provide service to the termi¬ nal 15. To that end, the IRM could also include information indicative of the request of the terminal for establishing a da¬ ta connection between the terminal and one of the SA-cells.

In an embodiment, the terminal may be configured to in¬ clude in the IRM an identification of the network to which the terminal belongs. By providing such identification in the IRM, the SA-cell receiving the IRM can differentiate between the IRMs received from terminals belonging to different networks and then choose whether or not to respond. For example, the SA-cell may choose not to respond when the IRM is sent by a terminal in a competitor's network. In this case, the provided identification does not need to be terminal-specific. It would be sufficient to only identify the network that the terminal belong to.

The IRM may also include an indication of access prior¬ ity. For example, an emergency response terminal or a consumer terminal making an emergency call may include an indication of high access priority or an M2M terminal (e.g. electricity meter) may include an indication of low access priority. By providing such an indication in the IRM, the SA-cell receiving the IRM can differentiate between the IRMs received from terminals and/or purposes having different access priorities and then choose whether or not to respond.

Further, the IRM should be such as to allow the receiving SA-cell to determine the signal strength with which the IRM is received and/or to estimate the path loss between the termi¬ nal and the receiving SA-cell.

Optionally, the IRM may include an indication of the service (s) requested and/or the terminal capabilities, which may be relevant to a SA-cell receiving the IRM in determining to what extent the SA-cell is capable and able to provide the re¬ quested service. The terminal capabilities that could be

indicated in the IRM include e.g. one or more of supported fre¬ quency band(s), supported RAT(s), supported mode(s), power with which the IRM is sent by the terminal, supported (maximum) ter¬ minal power, and requested (minimum) bit rate.

In various embodiments, similar to the solution # 2, the terminal 15 may transmit the IRM with a relatively high pow- er (e.g. at the maximum terminal's transmitting power or at still relatively high power, but lower than the maximum power) in order to maximize the likelihood that at least one suitable SA-cell is able to detect the IRM.

Also similar to the solution # 2, the terminal 15 may be configured to transmit the IRM more than once in a sequence, where the subsequent IRMs in the sequence may be transmitted with increased or with increasing power and/or with a randomized delay relative to the preceding IRM in the same sequence.

In step 52, at least some of the SA-cells may receive the IRM transmitted by the terminal and process the IRM by at least determining the signal strength with which the IRM is received. All of the discussions provided above regarding step 42 of solution # 2 (i.e., the description after the introduction of step 42 and before the introduction of step 43) are applicable to step 52 shown in FIG. 7 and, in the interests of brevity, are not repeated here.

In step 53, at least some of the SA-cells that received and measured the IRMs may be configured to transmit messages containing their responses to the decision unit, e.g. via back- haul links typically found between each of the SA-cells and the network and between the LA-cell and the network and/or via other links providing a same interconnection between SA-cells and the LA-cell, if the decision unit 11 is a part of the LA-cell 12. Such messages could include information regarding at least a portion of the measured results (e.g. the measured signal strength and/or the estimated path loss determined by the

SA-cell) . In addition, the SA-cells may supplement the message with additional information such as the identity of the SA-cells and/or with an indication of the time when the IRM was received by the SA-cell. The SA-cells may also be configured to include in their messages an indication to what extent the SA-cell is capable and able to provide the requested service. Further, the SA-cells may be configured to include additional information re¬ garding their current load and/or their currently available resources (e.g. RAT, frequency or frequency band, codes) and/or may further propose specific resources, which resources the SA-cell provisionally reserves for the case the terminal would select the SA-cell.

If the IRM included information allowing an identifica¬ tion of the terminal provided in any of the manners described in association with solution # 2, then the SA-cell may be config- ured to detect that information and to forward it to the

decision unit 11. If the decision unit 11 receives (potentially a lot of) messages from the SA-cells that relate to requests from different terminals, receiving such information that allows the decision unit to identify the IRM and/or the terminal that transmitted the IRM may be particularly useful. For example, the decision unit 11 may be able to identify the IRM and/or the transmitting terminal by receiving, from the SA-cell, information related to the time of reception of the IRM, to the channel on which or the channel code with which it was received, and/or to the contents of the IRM, which may include, e.g. a

(partial) terminal identification and/or some kind of reference (tag or label) inserted in the IRM by the terminal. This would allow the decision unit to relate all received messages (re¬ ceived with a certain time frame) with a particular combination of partial ID and/or a reference (tag, label) to each other.

Similar to the solution # 2, the SA-cell may be configured to transmit messages to the decision unit only regarding some IRMs . For example, the SA-cell may be configured to not transmit a message to the decision unit if the SA-cell cannot provide the service requested by the terminal. Alternatively, the SA-cell could be configured to process and forward messages even regarding such IRMs, with an indication that the SA-cell is unable to provide the service and, optionally, an indication of what the SA-cell is capable of and able to provide, as described above.

In an embodiment, if the SA-cell is able to support the service requested in the received IRM, the SA-cell may provi- sionally reserve the resources according to the requested ser¬ vice and also inform the decision unit about it and may,

optionally, also inform the terminal. Such provisionally re¬ served resources may be freed up after a suitable period (e.g. when a timer expires) or when the SA-cell is informed that its service is not needed for this particular service request.

In step 54, based, at least partially, on the infor¬ mation received in the messages from one or more SA-cells, the decision unit 11 is configured to select (assign) one or more SA-cell from the candidates for the terminal to establish the data connection with. The candidates may include not only the SA-cells that provided their response to the decision unit, but also the SA-cells that didn't provide their responses and the SA-cells that didn't even receive the IRM. This could be used e.g. when the decision unit is configured to obtain information regarding active SA-cells via e.g. steps 31-33 illustrated in FIG. 5 and described above. When decision unit 11 has such in¬ formation, it is able to evaluate whether the monitored active SA-cells constitute suitable candidates for the terminal to es- tablish the data connection with. In other words, in addition to the information received in the messages from the SA-cells, the decision unit 11 may also take into consideration, when select¬ ing a SA-cell, information regarding other SA-cells that did not provide responses.

Once one or more SA-cells are selected by the decision unit 11 as the most appropriate SA-cells for establishing the data connection with the terminal, the decision unit 11 may in¬ dicate the selected SA-cells to the terminal. In one embodiment, such indication may be provided via the LA-cell (e.g. in re- sponse to receiving a SRM received from the terminal via the LA- cell) . This could be particularly useful when the IRM transmit¬ ted by the terminal and forwarded by the SA-cells to the

decision unit 11 contains a terminal identity suitable to uniquely address the terminal in the LA-cell or when the IRM contains the partial terminal ID and/or reference (tag or label) the terminal used in the IRM, such that the LA-cell/decision unit is able to reconcile the IRM (and therewith possibly the full terminal ID) with the result of the selection. In another embodiment, such indication may be provided via one or more of the selected SA-cells. The latter embodiment assumes that a channel (with mutually known resource details) between the ter- minal and the selected SA-cell can be made available, along which channel an SA-cell may initiate the set up of a data con¬ nection to the terminal. Also in this embodiment the terminal ID or the partial terminal ID and/or the reference (tag or label) may facilitate the terminal to receive and recognize the indica- tion for the terminal.

The terminal 15, in response to receiving the indica¬ tion regarding the selected SA-cell, may further be configured for establishing the data connection (i.e., setting up a traffic channel) with the selected one or more SA-cell. Further, a route for the traffic (and the associated signaling) may be set up connecting the selected one or more SA-cell and the network.

Once the decision unit 11 knows the identities of the selected SA-cells, the decision unit 11 may assist in and pre¬ pare for setting up the route for the traffic connecting the selected SA-cell and the network. This may also be performed by LA-cell 12 when decision unit 11 is within the LA-cell or when the decision unit provides the information to the LA-cell.

Further, the decision unit 11 may be further configured to inform the non-selected SA-cell (s) , which may then release the provisionally reserved resources for fulfilling the request.

If any of the selected SA-cells are in a power-save mode, the decision unit 11 may further be configured to activate the selected SA-cells (possibly via the LA-cell) .

In a cellular wireless telecommunication system it may happen that a terminal in active mode, having a connection with a particular cell, moves out of (the coverage area of) that cell and into (the coverage area of) another cell. Then a so-called handover (handoff) may be performed, meaning that the connection between the terminal and the current cell (source cell) is transferred (handed over) to a connection between the terminal and a different cell (target cell) . Solution #3 as described above may also be used in an energy-efficient wireless network to facilitate a handover of the data connection between an active terminal and the SA-cell it has established the data connection with to another, differ- ent, SA-cell.

An active terminal may emit an IRM as described above, e.g. periodically and/or when the signal received from the

SA-cell it has established a data connection with drops below a predetermined threshold and/or when triggered by the network. The SA-cells receiving the IRM may forward their messages to the decision unit.

The decision unit may evaluate the information contained in the messages received from the SA-cells and, taking into account considerations similar to the ones described above, select a different SA-cell as target SA-cell for a handover.

As described above, the decision unit may further in¬ form the terminal and/or the LA-cell and/or the involved (source and target) SA-cells.

One embodiment of the invention may be implemented as a program product for use with a computer system. The program (s) of the program product define functions of the embodiments (in¬ cluding the methods described herein) and can be contained on a variety of, preferably non-transitory, computer-readable storage media. Illustrative computer-readable storage media include, but are not limited to: (i) non-writable storage media (e.g., read¬ only memory devices within a computer such as CD-ROM disks readable by a CD-ROM drive, ROM chips or any type of solid-state non-volatile semiconductor memory) on which information is permanently stored; and (ii) writable storage media (e.g., floppy disks within a diskette drive or hard-disk drive or any type of solid-state random-access semiconductor memory, flash memory) on which alterable information is stored. The computer program may be run on the processors described herein.

Claims

1. In a telecommunications system comprising a decision unit, an LA-cell base station (LA-cell) , and a plurality of SA- cell base stations (SA-cell) , a method for a terminal to facili¬ tate establishment of a data connection between the terminal and at least one of the plurality of the SA-cells, while at least one of the plurality of the SA-cells is in power saving mode, the method comprising:
while the terminal is in an idle mode and is camping on the LA-cell, the terminal determining properties of a signal re¬ ceived from each of one or more SA-cells of the plurality of SA- cells, the properties being indicative of propagation conditions between the each of the one or more SA-cells and the terminal;
while the terminal is in the idle mode and is camping on the LA-cell, the terminal providing a report to the decision unit, via the LA-cell, the report comprising at least infor¬ mation indicative of at least a portion of the determined properties for at least one of the one or more SA-cells;
while the terminal is in an idle mode and is camping on the LA-cell, the terminal receiving an indication that the data connection is to be established between the terminal and a se¬ lected SA-cell of the plurality of SA-cells, wherein the
selected SA-cell is selected by the decision unit at least par¬ tially based on the report.
2. The method according to claim 1, wherein, for each of the one or more SA-cells, the determined properties comprise a signal strength of the signal received from the each of the one or more SA-cells and/or a path loss estimate.
3. The method according to one or more of the preceding claims, wherein when at least two SA-cells of the one or more SA-cells are in a power-save mode, each of the at least two SA- cells transmits the signal to the terminal in a predetermined pattern .
4. The method according to claim 3, wherein the predetermined pattern for the each of the at least two SA-cells is such that the terminal receives the signals from each of the at least two SA-cells substantially contemporaneously.
5. The method according to claim 3, wherein the prede¬ termined pattern for the each of the at least two SA-cells is such that the terminal receives the signals from each of the at least two SA-cells in a succession.
6. The method according to one or more of the preceding claims, wherein the terminal is in a power-save mode and the method further comprises the terminal exiting the power-save mode to receive the signal from the each of the one or more SA- cells and/or to determine the properties of the signal received from the each of the one or more SA-cells.
7. A terminal comprising means for performing the steps of at least one of the claims 1-6.
8. A computer program comprising software code portion configured, when executed by a processor, for performing the steps of at least one of claims 1-6.
9. A decision unit configured at least for:
receiving from a terminal in idle mode camping on a LA- cell base station (LA cell) a report comprising at least infor¬ mation indicative of at least a portion of the determined properties for at least one of a plurality of SA-cell base sta¬ tions (SA-cell) , and
based at least partially on the report, selecting at least one SA-cell of the plurality of SA-cells for establishing the data connection between the terminal and the selected SA- cell.
10. The decision unit according to claim 9, further configured for providing an indication to the terminal that the data connection is to be established between the terminal and the selected SA-cell.
11. The decision unit according to claim 10, wherein the indication is provided in response to receiving a service request message from the terminal, via the LA-cell, requesting establishment of the data connection.
12. The decision unit according to one or more of claims 9-11, configured for, when at least one SA-cell of the one or more SA-cells is in a power-save mode and in response to receiving a service request message from the terminal, providing a transmit-trigger to the at least one SA-cell to transmit the signal .
13. The decision unit according to claim 12, wherein the transmit-trigger is at least partially based on one or more of a terminal location estimate, an estimate of the accuracy of the terminal location estimate, and activity status of the SA- cells in the vicinity of the estimated terminal location.
14. An LA-cell comprising the decision unit according to one or more of claims 9-13.
PCT/EP2012/067843 2011-09-13 2012-09-12 Session setup in an energy-efficient cellular wireless telecommunications system WO2013037826A1 (en)

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