WO2014024123A1

WO2014024123A1 - Fast cell reselection

Info

Publication number: WO2014024123A1
Application number: PCT/IB2013/056414
Authority: WO
Inventors: Tero Henttonen; Brian Alexander MARTIN
Original assignee: Renesas Mobile Corporation
Priority date: 2012-08-06
Filing date: 2013-08-05
Publication date: 2014-02-13
Also published as: GB201213964D0; GB2504698A

Abstract

A user equipment UE determines from a connection reject message received from a serving cell currently serving the user equipment, at least one layer comprising a frequency layer or a radio access technology layer, then measures received signal strength of cells that are neighbors of the serving cell at available layers after de- prioritising the determined at least one layer associated with the serving cell, and ordering the neighbor cells based on the measuring. The UE then initiates a procedure to establish a connection with a highest-ordered one of the neighbor cells. In one specific embodiment the determined layer(s) are identified in an information element of the connection reject message. In one embodiment the de-prioritising triggers the UE to do a cell selection to measure the received signal strength from neighbor cells, and in another embodiment it sets a threshold purposely to exceed measured received power from its serving cell to force the signal strength measurements.

Description

FAST CELL RESELECTION

Cross Reference to Related Application

This application claims the benefit under 35 U.S.C. § 119(a) and 37 CFR § 1.55 to UK patent application no. 1213964.8, filed on August 6, 2012, the entire content of which is incorporated herein by reference.

Technical Field

The exemplary and non-limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs and, more specifically, relate to cell reselection in response to a connection reject message from a user equipment's wireless network, and related signaling.

Background

Congestion in cellular radio networks is a continuing concern as both the number of users and especially the volume of data being handled continues to increase. In a typical cell there will be a number of user equipments (UEs) in a connected state with the cell and a number of other UEs in an idle state. Only those in the connected state can send and receive user data, those in the idle state listen at prescribed times in case there is an incoming call to them. While different radio access technologies (RATs) use different terms for the idle and the connected states, the salient difference is that the UE in a connected state have an allocated data channel and those in an idle state do not.

A problem arises when a UE in the idle state wishes to establish a connection to the cell on which it is camped when that cell is congested. To address this, the third Generation Partnership project (3GPP) has identified the need to perform selection from the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) to another RAT or to another E-UTRAN frequency when the cell (eNodeB or alternatively eNB) is congested, or when another frequency or RAT may be more suitable for the particular service being requested. In the E-UTRAN system this requires modification of the Radio Resource control (RRC) Connection Reject procedure, which can currently not be used to re-direct a UE to another cell or frequency. In current practice the congested eNB can either reject the connection request, or grant it and immediately hand over the newly connected UE to another cell or frequency. But when the eNB is congested it may not be possible to provide an R C Connection to the UE in order to redirect using RRC Connection Release. Even if the eNB could provide the new UE connection, this simply adds to its congestion. A more thorough examination of this problem in E- UTRAN is set forth at document R2-121063 entitled: LS on RR failures and network reselection (3GPP TSG RAN WG2 Meeting #77bis; Jeju, Korea; 26-30 March 2012). Summary

The foregoing and other problems are overcome, and other advantages are realized, by the use of the exemplary embodiments of this invention.

In a first exemplary embodiment of the invention there is provided a method for controlling a user equipment, the method comprising: determining, from a connection reject message received from a serving cell currently serving the user equipment, at least one layer comprising a frequency layer or a radio access technology layer; measuring received signal strength of cells that are neighbors of the serving cell at available layers after de-prioritising the determined at least one layer associated with the serving cell, and ordering the neighbor cells based on the measuring; and initiating a procedure to establish a connection with a highest-ordered one of the neighbor cells.

In a second exemplary embodiment of the invention there is an apparatus for controlling a user equipment. This apparatus includes at least a processing system, which may be embodied by at least one memory storing computer program code and at least one processor. In this embodiment the processing system is configured to cause the apparatus at least to: determine, from a connection reject message received from a serving cell currently serving the user equipment, at least one layer comprising a frequency layer or a radio access technology layer; measure received signal strength of cells that are neighbors of the serving cell at available layers after de-prioritising the determined at least one layer associated with the serving cell, and order the neighbor cells based on the measuring; and initiate a procedure to establish a connection with a highest-ordered one of the neighbor cells. In a third exemplary embodiment of the invention there is a computer readable memory comprising a set of instructions, which, when executed by a user equipment, causes the user equipment to perform the steps of determining, from a connection reject message received from a serving cell currently serving the user equipment, at least one layer comprising a frequency layer or a radio access technology layer; measuring received signal strength of cells that are neighbors of the serving cell at available layers after de-prioritising the determined at least one layer associated with the serving cell, and ordering the neighbor cells based on the measuring; and initiating a procedure to establish a connection with a highest-ordered one of the neighbor cells.

Brief Description of the Drawings

Figure 1 is a schematic diagram of a UE proximal to four neighbour cells which is an exemplary radio environment in which these teachings can be used to advantage.

Figure 2 is a signaling diagram illustrating messages and functions for a UE, a serving cell and a highest-ranked neighbour cell according to a first non- limiting embodiment of these teachings.

Figure 3 is a signaling diagram illustrating messages and functions for a UE, a serving cell and a highest-ranked neighbour cell according to a second non- limiting embodiment of these teachings.

Figure 4 is a simplified block diagram of a user equipment in communications with the serving cell and one of the neighbour cells of Figures 1-3, which are exemplary electronic devices suitable for use in practicing the exemplary embodiments of these teachings. Detailed Description

Currently two potential solutions have been proposed to the 3GPP for solving the connection redirect problem set forth in the background section. Document R2- 122609 entitled: Redirection/Reselection on RRC Connection Reject (3GPP TSG-RAN WG2 Meeting #72; Prague, Czech Republic; 21-25 May 2102) proposes that the network reply to the UE's RRC Connection Request with a RRC Connection Reject message that redirects the UE to an alternative cell or frequency on which to establish its desired connection. This has met some resistance since in current procedures, when receiving the idle state UE's RRC Connection Request message the network would have no knowledge of what specific frequency bands the UE supports and so there is a possibility of redirecting the UE to a frequency layer with which it is incompatible. For convenience, each different frequency and RAT may be considered a different layer on which a cell operates with the UEs that it is serving, or may serve.

The second potential solution is set forth at document R2-121118 entitled: UE reaction on RRC Connection Rejection (3 GPP TSG-RAN WG2 Meeting #77bis; Jeju, Korea; 26-30 March 2012) and concerns de-prioritising the current camped frequency using the RRC Connection Reject message, which consequently raises the priority of other neighbour frequencies or RATs which the UE searches.

This second potential solution has its own unresolved issues. For example, assigning the current frequency the lowest absolute priority leaves all other layers with a higher priority, but the current measurement performance requirement is that the UE should perform a search every N x 60 seconds, where N is the number of inter- frequency or inter-RAT layers configured for the UE. The UE following these requirements may take several minutes to establish its connection on another frequency/RAT layer. Further, this second proposal sets a time limit for the deprioritisation which means the problem will re-assert itself after the time expires and the (congested) camped frequency again becomes the highest priority (which follows from the point above where the UE's search takes quite a long time).

One resolution suggested for these issues is to include a note in the governing radio specifications that the UE should reselect as soon as possible, but this does not enable any faster reselection and is not an objectively testable requirement. The UE might start performing a higher priority search immediately after the RRC Connection Reject message but procedurally there is still a requirement to modify the performance requirements in the relevant radio specifications. The 3GPP is a responsive organization but even so this would take awhile to implement. The teachings below resolve the above deprioritisation issues within the existing radio specification framework of E-UTRAN. Figure 1 is a schematic diagram of a UE with four cells and representing an exemplary radio environment in which these teachings can be used to advantage. Assume the UE 20 is in an idle state while traversing through the cell controlled by the serving eNB 22 and listens periodically for pages by that serving eNB 22 on a first frequency and a first RAT. The UE 20 is moving in the direction of the arrow toward the neighbour base stations 23, 24 and 25 which each operates on a neighbour frequency and/or a neighbour RAT, different from the first frequency and first RAT. They are termed base stations since if in another RAT they may not be properly characterized as eNBs, but any or all may be eNBs if in the same/first RAT as the serving eNB 22. The first frequency has become congested and the idle-state UE 20 sends to the serving eNB 22 a RRC Connection Request message in order to establish a connection to make a call. The serving eNB 22 prefers not to congest its first frequency further and would rather the UE 20 established that RRC connection with some other neighbour base station 23, 24, 25.

Figure 1 is a straightforward deployment so the reader may more clearly understand the teachings herein. In other relevant radio scenarios one or more neighbour frequencies may also be operated by the serving eNB 22. One or more of the neighbour base stations 23-25 may also be embodied as a remote radio head operated by the serving eNB 22. One of the neighbour cells may operate on the first frequency and the second RAT. So as not to foreclose these other possibilities the description below teaches in terms of the first and neighbour frequencies and RATs, the first frequency and first RAT being that on which the UE 20 is camped and either or both of the neighbour frequency or neighbour RAT being one on which the UE 20 is not.

Figures 2-3 are signaling diagrams illustrating by non-limiting example two specific approaches to resolve the above issues within the existing E-UTRAN framework so as to enable the UE 20 to perform a fast reselection to another frequency or RAT. Both show only one of the neighbour base station 23 (shown as neighbour eNB 23 but in another embodiment it may be operating in a neighbour/second RAT), and use fl to represent the first frequency and f2 to represent the neighbour frequency utilized by the neighbour cell 23 (or neighbour/second RAT). The description explains where more than one neighbour cell might be involved, but the exchanges between the UE 20 and any additional neighbour cells are similar to that shown for the illustrated neighbour cell 23.

Figure 2 illustrates a first embodiment according to these teachings and begins with the idle state UE 20 sending to the network/serving cell 22 a RRC connection request message 202. The serving cell 22 sends to the UE 20 a RRC Connection Reject message 204 which includes a new information element (IE) to de-prioritise the current frequency fl . This IE may optionally also de-prioritise other frequencies beyond fl, may additionally de-prioritise the first RAT, and/or may also have a timer to specify the time interval during which the deprioritisation will be in effect. This RRC Connection Reject message 204 with the new IE triggers the UE 20 to perform at block 206 a cell selection (but excluding the deprioritised frequency/frequencies and/or RAT), as opposed to remaining on the current cell and performing reselection evaluation.

The cell selection enables the UE 20 to immediately measure and rank the available frequencies, excluding the frequency/frequencies and/or RAT which was deprioritised. In the cell search procedure the UE acquires time and frequency synchronization with a cell by first listening to its primary synchronization signal (i.e. PSS in LTE, PSC in UMTS) and then listening to its secondary synchronization signal (i.e. SSS in LTE, SSC in UMTS). After detecting both primary and secondary synchronization signals, the UE will have acquired the physical layer identity (in LTE) or the CPICH scrambling group (in UMTS) of that cell, along with knowledge of the cell's common reference symbol pattern (for LTE; in UMTS, another step is still needed after this, to detect the exact scrambling code out of the detected CPICH scrambling code group). For cell reselection detailed at 3GPP TS 36.304 the ranking also takes into account the absolute priority of the layers. In the E-UTRAN system a given cell transmits both PSS and SSS twice per 10 ms radio frame, so the UE can identify the frame timing of a cell from only the PSS with a maximum ambiguity of 5 ms and acquire the full physical cell identity (PCI) as fast as possible. From the PSS the UE 20 can also lock its local oscillator frequency to the base station carrier frequency, find an identity within the cell, and can also obtain partial knowledge about the cell's reference signal structure. The UE 20 can also listen to the secondary synchronization signal (SSS) to detect the cell identity group and to determine the frame timing more precisely. The UE 20 can then coarsely rank the cells by measuring received signal strength of the PSS or of the SSS, or the UE 20 can more comprehensively measure the cell for ranking by measuring the reference signals which each cell transmits (for example, by measuring reference signal received power RSRP and/or reference signal received quality RSRQ of the common reference signals CRSs). The UE 20 can learn the reference signal structure from the PSS and SSS. The cell search procedure is thus a fast way for the UE 20 to find and rank the neighbour cells whether they are inter- frequency or inter-RAT .

Figure 2 assumes that the neighbour eNB 23 operating on frequency f2 is the highest ranked neighbour from the UE's cell selection process. At message exchange 208 the UE 20 then performs some procedure on the second layer f2 with that neighbour eNB 23, such as for example establishing a connection via a random access channel (RACH) procedure. If the timer has not expired and the UE 20 has selected a cell (eNB 23 in Figure 2), normal cell reselection procedures apply with the priorities as adjusted from the RRC connection reject message 204 and with the cell selection of block 206 until the timer expires.

Figure 2 assumes the UE 20 established a new connection with the neighbour eNB 23 on f2, Then the timer expires, and at block 210 the UE 20 performs cell selection again but this time the frequency/frequencies/RAT that was deprioritised for the earlier cell selection at block 206 is no longer deprioritised. Assuming the UE 20 is still in the coverage area of the serving cell 22 and not yet too close to the coverage edge, then typically frequency fl will be the highest ranked cell after the new cell selection at block 210. Note that when the timer expires and the original frequency fl is returned to a high rank at block 210, the UE triggers cell selection again instead of the normal reselection measurements. The UE 20 then performs a procedure at message exchange 212 with the highest ranking cell as determined by the most recent cell selection done at block 210. For example, the UE 20 may send a new RRC Connection Request to the serving cell 22 at message exchange 212 if the UE has been returned to the idle mode with eNB 23 and again needs a connection. If the UE 20 remains in the connected mode with eNB 23 it will maintain that connection and will do the cell selection at some later time.

Now consider the second exemplary embodiment at Figure 3 which begins similar to Figure 2; the idle state UE 20 sends to the network/serving cell 22 a R C Connection Request message 302 and the serving cell 22 sends to the UE 20 a RRC Connection Reject message 304 which includes a new information element (IE) to de- prioritise the current frequency fl . That new IE is detailed above for Figure 2.

The RRC Connection Reject message 304 with the new IE triggers the UE 20 to set the absolute priority of the serving cell layer (frequency fl) to be lower than the priority of the other layers. Specific for the current E-UTRAN system the UE 20 does this in the non-limiting Figure 3 embodiment by setting a high value for the parameter SnonintraSearchP and/or the parameter SnonintraSearchQ. In one specific implementation the UE 20 sets the value of SnonintraSearchP and/or SnonintraSearchQ to infinity (or some other arbitrary value).

As defined at section 5.2.4.7 of 3 GPP TS 36.304 vl 1.0.0 (2012-06), the parameter SnonintraSearchP specifies the Srxiev (received signal power, based on the reference symbols in LTE) threshold in dB for E-UTRAN inter- frequency and inter- RAT measurements, and the parameter SnonintraSearchQ specifies the S_quai (received signal quality, also based on reference symbols in LTE) threshold in dB for E-UTRAN inter- frequency and inter-RAT measurements. Paragraph 5.2.4.2 of that same TS 36.304

Specifies that if the Serving Cell fulfills Srxiev > SnonintraSearchP and Squal > SnonintraSearchQ then the UE may choose not to perform measurements of E-UTRAN inter- frequency and inter-RAT frequency cells of equal or lower priority, otherwise the UE shall perform measurements of inter-frequencies or inter-RAT frequency cells of equal or lower priority. But the above allows a faster reselection because as specified in 3 GPP TS 36.133 the rate of measurement is adjusted based on the above parameters, so when the current layer is deprioritized in this manner the resulting faster measurements lead to a faster reselection.

So when temporarily modifying the current frequency priority, one or both of those parameters/thresholds are changed to a high (or infinite) value. It follows that Srxiev will be less than (or equal to) the new higher threshold SnonintraSearchP, and so the above-cited clause from TS 36.304 causes the UE 20 to start performing measurements of all the other layers at a faster rate. Importantly, these neighbour cell measurements are configured according to a tighter performance requirement since they are normally used to assure basic coverage for the UE, as opposed to expanding the services that may be available to the UE (which have more relaxed tolerances since the assumption for service-based measurements is that basic coverage is not at risk of being lost).

Like Figure 2, the non-limiting embodiment of Figure 3 has the neighbour cell 23 as an eNB so it is on the same/first RAT with the serving cell 22. Figure 3 assumes that after resetting the priority at block 306 following its de-prioritising of the current frequency or RAT that was indicated in message 304), the neighbour cell 23 operating on frequency £2 is now the highest priority cell/layer. At message exchange 308 the UE 20 then performs some procedure on the second layer £2 with that neighbour eNB 23, such as for example establishing a connection via a RACH procedure.

As for Figure 2, Figure 3 assumes the UE 20 established a new connection with the neighbour cell 23 in the procedure of message exchange 308 before the timer expires. Then, when the timer expires at block 310, the UE 20 sets the absolute priority of the serving cell fl back to its original value and now sets high the value of the threshold SnonintraSearchP for the new cell 23 (£2) so the UE 20 is again forced to make measurements of inter-frequency and inter-RAT neighbours. Assuming the UE 20 is still in the coverage area of the serving cell 22 and not yet too close to the coverage edge, then typically frequency fl will be the highest priority cell after the new absolute priorities are calculated at block 310. So when the timer expires and the original frequency f 1 is returned to a high priority, the UE temporarily sets the threshold of the currently camped frequency (i.e., £2 since the assumption above is that the procedure at message exchange 308 established a new connection on £2 with cell 23) to a high value in order to quickly find another layer, which in the Figure 3 non- limiting example is the original layer fl since the UE 20 is assumed to still be in the same area. The message exchange 312 then has the UE 20 performing some procedure with the new highest- priority layer f 1 , such as a RRC Connection Request or RACH procedure to establish a connection if as with Figure 2 the further assumption is that the UE 20 enters again the idle mode with cell 23 and then wants to establish yet another new connection. The adjustments needed to implement the above teachings for the E-UTRAN system involves a new rule to trigger the above behaviour in the circumstances shown by example at Figures 2-3 (modifying the threshold for reselection measurements and/or triggering a cell selection rather than a reselection), and UEs operating in the E- UTRAN system are already compatible with that behaviour (under different circumstances when they are in an idle state). For example, such a rule can be written into 3 GPP TS 36.331 or 36.304.

Certain embodiments of these teachings provide the technical effect of re-using for a new purpose and under different conditions the conventional E-UTRAN implementation of cell selection/reselection measurements. Implementing these teachings in the E-UTRAN system is seen to impose no adverse impact to the E- UTRAN performance requirements while providing the advantage of a faster reselection by the UE upon receiving a R C Connection Reject message when the current frequency is deprioritised, as compared to the proposed deprioritisation method outlined at document R2-121118. Additionally, the UE behaviour according to these teachings is both objectively testable and predictable.

The elements shown at Figures 2-3 for the serving eNB 22 and for the UE 20 may be considered as representing a logic flow diagram for those respective devices, and further may be considered to represent the operation of a method, and a result of execution of a computer program stored in a computer readable memory, and a specific manner in which components of an electronic device such as a UE or network access node (or one or more components thereof) are configured to cause that electronic device to operate. The various different steps shown in Figures 2-3 may also be considered as a plurality of coupled logic circuit elements constructed to carry out the associated function(s), or specific result of strings of computer program code stored in a memory.

The steps of Figures 2-3 and the functions they represent are non-limiting examples, and may be practiced in various components such as integrated circuit chips and modules, and that the exemplary embodiments of this invention may be realized in an apparatus that is embodied as an integrated circuit. The integrated circuit, or circuits, may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor or data processors, a digital signal processor or processors, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this invention.

Where the inter- frequency layers (same RAT, different frequency) and the intra- frequency layers (different RAT, same or different frequencies) are understood as layers, the RRC Connection Reject message can be understood as de-prioritizing one or more layers of which the serving frequency is one of those one or more de-prioritized layers. The more general features of Figures 2-3 may, from the UE's perspective (that is, a method for controlling a UE), can then be summarized as:

• determining from a connection reject message 204, 304 received from a serving cell currently serving the user equipment, at least one layer (fl in the examples) comprising a frequency layer or a radio access technology layer

• measuring received signal strength of cells that are neighbors of the serving cell at available layers after de-prioritising the determined at least one layer associated with the serving cell and ordering the neighbor cells based on the measuring, and

• initiating a procedure 208, 308 to establish a connection with a highest-ordered one of the neighbor cells (the neighbor cell 23 at frequency layer f2 in the examples).

In both Figures 2-3, each of the at least one layer, which is identified in an IE of the connection reject message.

Specific to the Figure 2 embodiment, the above measuring of the received signal strength comprises performing cell selection of the neighbor cells at the available layers after the de-prioritising, in which the cell selection is triggered by the UE 20 in response to receiving the IE in the connection reject message 204. As further detailed above for the Figure 2 embodiment, the received signal strength for each cell at the available layers is measured on at least a primary synchronization signal.

For the case in which the connection rejection message includes a timer, then the Figure 2 embodiment further includes, after expiration of the timer: performing a new cell selection of cells at the available layers without de-prioritising the determined at least one layer associated with the previously serving cell; ordering again the cells at the available layers from the new cell selection; and initiating a procedure to establish a connection with a highest-ordered cell of the ordered-again cells.

Specific to the Figure 3 embodiment, the above de-prioritising comprises: setting absolute priority of the determined at least one layer associated with the serving cell lower than each other layer not de-prioritized by the received connection reject message; and setting a value of a threshold parameter to exceed received signal power measured from a serving frequency layer, where the serving frequency layer of the serving cell is the de-prioritized layer or one of the de-prioritized layers. As detailed further above for the Figure 3 embodiment, the threshold parameter is SnonintraSearchP which is set to infinity or some other arbitrarily high value, and the received signal power measured from a serving frequency layer is Srxiev.

For the case in which the connection rejection message includes a timer, then the Figure 3 embodiment further includes, after expiration of the timer: while the value of the threshold parameter remains set to exceed the received signal power measured from a new serving frequency layer of a new serving cell, setting again absolute priority of all of the layers including at least the one layer associated with the previously serving cell that was de-prioritized by the received connection reject message; measuring again received signal strength of the cells at all of the layers; ordering again the cells at all of the layers from the again measured received signal strength; and initiating a procedure to establish a connection with a highest-ordered cell of the again ordered cells.

Reference is now made to Figure 4 for illustrating a simplified block diagram of various electronic devices and apparatus that are suitable for use in practicing the exemplary embodiments of this invention. In Figure 2 there is a serving cell/serving network access node 22 such as a base transceiver station (the eNB 22 of Figures 1-3 for the E-UTRAN system) which is adapted for communication over a wireless link 21 A with an apparatus 20 such as a mobile terminal or UE 20 in the idle state/mode. Figure 3 also illustrates a neighbour cell 23 such as that shown in Figures 1-3 which has a wireless link 21B with the UE 20, and that link 2 IB is unidirectional downlink for the idle-mode UE taking measurements and bi-directional for connection establishment as detailed above. Also as noted above, the serving cell 22 and the neighbour cell 23 represent different frequency and/or RAT layers. While not shown, the serving cell 22 and the neighbour cell 23 may each be further communicatively coupled via respective data and control links to a higher network node such as a mobility management entity/serving gateway MME/S-GW in the case of the E-UTRAN system, or to different higher network nodes for the case they are in different RATs. There may be a direct interface between the serving cell 22 and the neighbour cell 23, or if they are in different RATs they may be connected only via a control link between their respective but different high network nodes.

The UE 20 includes processing means such as at least one data processor (DP) 20A, storing means such as at least one computer-readable memory (MEM) 20B storing at least one computer program (PROG) 20C, communicating means such as a transmitter TX 20D and a receiver RX 20E for bidirectional wireless communications with the serving cell 22 and at least for receiving signals from the neighbour cell 23 via one or more antennas 20F. Within the memory 20B of the UE 20 but shown separately as reference number 20G is also a computer program for de-prioritising one or more layers identified in a connection reject message, for ordering the layers after that de- prioritising, and taking fast measurements of the ordered layers as is detailed above in the various embodiments.

The serving cell 22 also includes processing means such as at least one data processor (DP) 22A, storing means such as at least one computer-readable memory (MEM) 22B storing at least one computer program (PROG) 22C, and communicating means such as a transmitter TX 22D and a receiver RX 22E for bidirectional wireless communications with its associated user devices 20 via one or more antennas 22F and a modem. The serving cell 22 also has stored in its memory at 22G software to de- prioritise the one or more layers via an IE inserted into the connection eject message it sends to the UE 20, as is detailed by example above.

The neighbour cell/neighbour network access node 23 is similarly functional with blocks 23A, 23B, 23C, 23D, 23E and 23F, which are similar in function to those blocks having a same suffix and described for the serving cell/serving network access node 22.

While not particularly illustrated for the UE 20 or cells 22, 23, those devices are assumed to include as part of their wireless communicating means a modem which may in one exemplary but non limiting embodiment be inbuilt on an RF front end chip so as to carry the respective TX 20D/22D/23D and RX 20E/22E/23E.

At least one of the PROGs 20C, 22C in the UE 20 and in the serving cell 22 is assumed to include program instructions that, when executed by the associated DP 20A, 22A, enable the device to operate in accordance with the exemplary embodiments of this invention as detailed more fully above. In this regard the exemplary embodiments of this invention may be implemented at least in part by computer software stored on the MEM 20B, 22B which is executable by the DP 20A, 22A of the respective devices 20, 22; or by hardware; or by a combination of tangibly stored software and hardware (and tangibly stored firmware). Electronic devices implementing these aspects of the invention need not be the entire UE 20, or serving cell 22, but exemplary embodiments may be implemented by one or more components of same such as the above described tangibly stored software, hardware, firmware and DP, or a system on a chip SOC or an application specific integrated circuit ASIC or a digital signal processor DSP or a modem or a subscriber identity module commonly referred to as a SIM card.

Various embodiments of the UE 20 can include, but are not limited to: cellular telephones; data cards, USB dongles, laptop computers, personal portable digital devices having wireless communication capabilities including but not limited to laptop/palmtop/tablet computers, digital cameras and music devices, and Internet appliances.

Various embodiments of the computer readable MEM 20B, 22B, 23B include any data storage technology type which is suitable to the local technical environment, including but not limited to semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, removable memory, disc memory, flash memory, DRAM, SRAM, EEPROM and the like. Various embodiments of the DP 20A, 22A, 23A include but are not limited to general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and multi-core processors.

Various modifications and adaptations to the foregoing exemplary embodiments of this invention may become apparent to those skilled in the relevant arts in view of the foregoing description. While the exemplary embodiments have been described above in the context of the E-UTRAN system with other RATs as possibly other layers, it should be appreciated that the exemplary embodiments of this invention are not limited for use with only this one particular type of wireless communication system, and that they may be used to advantage in other wireless communication systems such as for example the GSM or GERAN or wideband code division multiple access (WCDMA) version of UTRAN, as some non- limiting further examples.

Some of the various features of the above non-limiting embodiments may be used to advantage without the corresponding use of other described features. The foregoing description should therefore be considered as merely illustrative of the principles, teachings and exemplary embodiments of this invention, and not in limitation thereof.

Claims

1. A method for controlling a user equipment, the method comprising: determining, from a connection reject message received from a serving cell currently serving the user equipment, at least one layer comprising a frequency layer or a radio access technology layer;

measuring received signal strength of cells that are neighbors of the serving cell at available layers after de-prioritising the determined at least one layer associated with the serving cell, and ordering the neighbor cells based on the measuring; and

initiating a procedure to establish a connection with a highest-ordered one of the neighbor cells.

2. The method according to claim 1 , in which each of the at least one layer is identified in an information element of the connection reject message.

3. The method according to claim 2, in which measuring the received signal strength comprises performing cell selection of the or each neighbor cell at the available layers after the de-prioritising, in which the cell selection is triggered by the user equipment in response to receiving the information element in the connection reject message.

4. The method according to any of claims 1 to 3, in which the received signal strength for each cell of the available layers is measured on at least a primary synchronization signal.

5. The method according to claim 4, the method further comprising, after expiration of a timer received in the connection rejection message:

performing a new cell selection of cells at the available layers without de- prioritising the determined at least one layer associated with the previously serving cell; ordering again the cells at the available layers from the new cell selection; and initiating a procedure to establish a connection with a highest-ordered cell of the ordered again cells.

6. The method according to claims 1 or 2, wherein de-prioritising the determined at least one layer associated with the serving cell comprises:

setting absolute priority of the determined at least one layer associated with the serving cell lower than each other layer not de-prioritized by the received connection reject message; and

setting a value of a threshold parameter to exceed received signal power measured from a serving frequency layer of the serving cell, where the serving frequency layer is the de-prioritized layer or one of the de-prioritized layers.

7. The method according to claim 6, wherein the threshold parameter is SnonintraSearchP, which is set to an arbitrarily high value and the received signal power measured from a serving frequency layer is S_rxiev.

8. The method according to claims 6 or 7, the method further comprising, after expiration of a timer received in the connection rejection message:

while the value of the threshold parameter remains set to exceed the received signal power measured from a new serving frequency layer of a new serving cell, setting again absolute priority of all of the layers including at least the one layer associated with the previously serving cell that was de-prioritized by the received connection reject message;

measuring again received signal strength of the cells at all of the layers;

ordering again the cells at all of the layers from the again measured received signal strength; and

initiating a procedure to establish a connection with a highest-ordered cell of the again ordered cells.

9. An apparatus for controlling a user equipment, the apparatus comprising a processing system arranged to cause the apparatus to: determine, from a connection reject message received from a serving cell currently serving the user equipment, at least one layer comprising a frequency layer or a radio access technology layer;

measure received signal strength of cells that are neighbors of the serving cell at available layers after de-prioritising the determined at least one layer associated with the serving cell, and order the neighbor cells based on the measuring; and

initiate a procedure to establish a connection with a highest-ordered one of the neighbor cells.

10. The apparatus according to claim 9, wherein each of the at least one layer is identified in an information element of the connection reject message.

11. The apparatus according to claim 10, wherein the processing system is configured to cause the apparatus to measure the received signal strength by performing cell selection of the or each neighbor cell at the available layers after the de-prioritising, in which the cell selection is triggered by the apparatus in response to the user equipment receiving the information element in the connection reject message.

12. The apparatus according to any of claims 9 through 11, wherein the processing system is configured to cause the apparatus to measure the received signal strength for each cell at the available layers on at least a primary synchronization signal.

13. The apparatus according to claim 12, wherein the processing system is configured to cause the apparatus to further, after expiration of a timer received in the connection rejection message:

perform a new cell selection of cells at the available layers without de- prioritising the determined at least one layer associated with the previously serving cell; order again the cells at the available layers from the new cell selection; and initiate a procedure to establish a connection with a highest-ordered cell of the ordered again cells.

14. The apparatus according to claims 9 or 10, wherein the processing system is configured to cause the apparatus to de-prioritise each of the at least one layer by:

15. The apparatus according to claim 14, wherein the threshold parameter is SnonintraSearchP and the processing system is configured to cause the apparatus to set said threshold parameter to an arbitrarily high value, and the received signal power measured from a serving frequency layer is S_rxiev.

16. The apparatus according to claims 14 or 15, wherein the processing system is configured to cause the apparatus to further, after expiration of a timer received in the connection rejection message:

while the value of the threshold parameter remains set to exceed the received signal power measured from a new serving frequency layer of a new serving cell, set again absolute priority of all of the layers including at least the one layer associated with the previously serving cell that was de-prioritized by the received connection reject message;

measure again received signal strength of the cells at all of the layers;

order again the cells at all of the layers from the again measured received signal strength; and

initiate a procedure to establish a connection with a highest-ordered cell of the again ordered cells.

17. A computer readable memory comprising a set of instructions, which, when executed by a user equipment, causes the user equipment to perform the steps of: determining, from a connection reject message received from a serving cell currently serving the user equipment, at least one layer comprising a frequency layer or a radio access technology layer;

initiating a procedure to establish a connection with a highest-ordered one of the neighbor cells

18. The computer readable memory according to claim 17, in which each of the at least one layer is identified in an information element of the connection reject message.

19. The computer readable memory according to claim 18, wherein the set of instructions, when executed by the user equipment causes the user equipment to perform cell selection of the or each neighbor cell at the available layers after the de- prioritising, in which the cell selection is triggered by the user equipment in response to receiving the information element in the connection reject message.

20. The computer readable memory according to any one of claims 17 to 19, wherein the received signal strength for each cell at the available layers is measured on at least a primary synchronization signal.

21. The computer readable memory according to claim 20, wherein the set of instructions, when executed by the user equipment, further causes the user equipment, after expiration of a timer received in the connection rejection message, to: perform a new cell selection of cells at the available layers without de- prioritising the determined at least one layer associated with the previously serving cell; order again the cells at the available layers from the new cell selection; and initiate a procedure to establish a connection with a highest-ordered cell of the ordered again cells.

22. The computer readable memory according to claims 17 or 18, wherein the set of instructions, when executed by the user equipment, causes the user equipment to de-prioritise each of the at least one layer by:

23. The computer readable memory according to claim 22, wherein the threshold parameter is SnonintraSearchP, which is set to an arbitrarily high value and the received signal power measured from a serving frequency layer is Srxiev.

24. The computer readable memory according to claims 22 or 23, wherein the set of instructions, when executed by the user equipment, further causes the user equipment, after expiration of a timer received in the connection rejection message, to: while the value of the threshold parameter remains set to exceed the received signal power measured from a new serving frequency layer of a new serving cell, set again absolute priority of all of the layers including at least the one layer associated with the previously serving cell that was de-prioritized by the received connection reject message;

measure again received signal strength of each cell at all of the layers;

initiate a procedure to establish a connection with a highest-ordered one of the again ordered cells.