WO2014020504A1 - Wireless communication method, apparatus and computer program - Google Patents

Abstract

Uplink buffer occupancy(304), and a link imbalance between a serving and a neighbour cell operating in the same frequency and the same radio access technology, are determined for a user equipment UE. Based at least on those,the UE is controlled to transition directly from an idle state with the serving cell to a connected state with the neighbour cell (308,310B). In one embodiment the UE checks its own buffer occupancy, link imbalance and downlink channel quality against thresholds to decide whether to transition directly. In another embodiment the UE sends to the serving cell at least its buffer occupancy and link imbalance, and the serving cell sends to the UE a redirect message that identifies the neighbour cell as a target cell for the direct transition. The neighbour cell may be a small cell operating at a lower transmit power than the (macro) serving cell.

Description

WIRELESS COMMUNICATION METHOD,

APPARATUS AND COMPUTER PROGRAM

Cross Reference to Related Application

This application claims the benefit under 35 U.S.C. § 119 and 37 CFR § 1.55 to

UK patent application no. 1213517.4, filed on July 30, 2012, the entire content of which is incorporated herein by reference.

Technical Field

The present invention relates to a wireless communication method, apparatus and computer program. The exemplary and non- limiting embodiments of this invention relate generally to wireless communication systems, methods, devices and computer programs, and specific examples relate to cell selection/re-selection in a heterogeneous network with macro and small cells operating on the same frequency.

Background

Continuing expansion of mobile communications by the general public is rendering the available radio spectrum more crowded and this trend is expected to accelerate in the near term as greater volumes of data are wirelessly exchanged. One recent approach to increase the network operators' capacity to handle this increased traffic is to deploy heterogeneous networks (HetNet). In a HetNet there is a conventional cell commonly termed a macro cell, and within its coverage area are one or more small cells sometimes termed pico or femto or local cells that operate with various levels of coordination with the macro cell. The term pico cell is used herein to refer in general to such a small cell, and these pico cells can also be used to extend the coverage area of the macro cell, either to extend range or plug coverage holes.

The macro cell typically transmits with a much higher power than the pico cells and so the macro coverage area is much larger than that of the pico. Some HetNet deployments have the macro cell and the pico cells on different frequency bands such as a primary versus secondary component carriers, while others have one or more pico cells operating on the same frequency band as the macro cell. These teachings are relevant to the latter deployment where the frequency band is shared, sometimes termed a co-channel HetNet. The Third Generation Partnership Project (3 GPP) has formally investigated co- channel HetNets; see document Rl-110687 by Qualcomm Inc. entitled Interference issues in heterogeneous Networks for HSPA [3 GPP TSG WG1 Meeting #64; Taipei, Taiwan; 21-25 Feb 2011]. HSPA in the title refers to the High Speed Packet Access radio access technology which is a 3G enhancement, but the interference issues identified there are in general applicable to other radio access technologies such as for example the Long Term Evolution (LTE) of the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) technology. Introduction of the low power pico nodes to the macro cell brings challenges in terms of reliability of the uplink (UL) control channel as well as the interference management between low power pico nodes and high power macro nodes. Specifically, there is a UL imbalance caused by the transmit power difference between the pico and macro cell which can cause unreliable UL control channel decoding in the serving cell; there can be excessive UL interference from the macro cell to the low power pico cell; and there can be excessive UL interference in the other direction from the pico cell to the macro cell.

These teaching are in general directed to properly selecting which cell to attach in the presence of such interference in a co-channel HetNet environment, regardless of the radio access technology in use. Summary

According to a first aspect of the present invention, there is provided a method for operating a wireless communications device, the method comprising: determining for a user equipment an uplink buffer occupancy and a link imbalance between a serving cell and a neighbour cell operating in the same frequency and the same radio access technology; and based on the determined uplink buffer occupancy and link imbalance, controlling the user equipment to transition directly from an idle state with the serving cell to a connected state with the neighbour cell.

According to a second aspect of the present invention, there is provided apparatus for communicating, the apparatus comprising a processing system constructed and arranged to cause the apparatus at least to: determine for a user equipment an uplink buffer occupancy and a link imbalance between a serving cell and a neighbour cell operating in the same frequency and the same radio access technology; and based on the determined uplink buffer occupancy and link imbalance, control the user equipment to transition directly from an idle state with the serving cell to a connected state with the neighbour cell.

The processing system may comprise at least one processor and at least one memory including computer program code configured to cause the apparatus to operate as described above.

According to a third aspect of the present invention, there is provided a computer program comprising a set of instructions comprising: code for determining for a user equipment an uplink buffer occupancy and a link imbalance between a serving cell and a neighbour cell operating in the same frequency and the same radio access technology; and code for controlling the user equipment, based on the determined uplink buffer occupancy and link imbalance, to transition directly from an idle state with the serving cell to a connected state with the neighbour cell. There may be provided a computer-readable memory tangibly storing a set of instructions as described above.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments of the invention, given by way of example only, which is made with reference to the accompanying drawings. Brief Description of the Drawings

Figure 1 shows a schematic diagram illustrating a co-channel HetNet with a user at a location where the downlink signals it sees from a macro and a pico cell are not balanced with the uplink signals it sends to them, and is an example HetNet deployment in which these teachings can be used to advantage;

Figure 2 shows a logic flow diagram summarising how a user equipment at the location of Figure 1 would behave when setting up a connection under prior art rules specified for the HSPA radio access technology;

Figure 3 shows a logic flow diagram that illustrates, from the perspective of the UE for the first embodiment below and from the perspective of the macro/serving cell for the second embodiment below, the operation of an example of a method, and a result of execution of computer program instructions embodied on a computer readable memory, in accordance with the exemplary embodiments of these teachings;

Figure 4 shows a logic flow diagram that illustrates examples of embodiments of the present invention; and Figure 5 shows a non-limiting example of a simplified block diagram of examples of a UE, macro/serving cell and a pico/low power cell, which are exemplary electronic devices suitable for use in practising some example embodiments of this invention. Detailed Description

While the examples below are in the context of the HSPA radio access technology and use channel names specified therein, these are non-limiting examples only. The specific examples used in these teachings may be easily adapted for other radio access technologies such as various cellular systems (LTE and EUTRAN for example). Figure 1 illustrates an example HetNet deployment which highlights a problem in the prior art approach for a user, or more specifically a user equipment (UE) 10, attaching to a cell according to the HSPA procedures, and is also a radio environment in which these teachings can be used to advantage. One key to understanding the problem with the prior art procedures is to recognise that there is an imbalance in the downlink (DL) and UL signals at certain locations of the UE 10 due to the transmit power difference between the high power macro cell 20 and the low power pico cell 22. More generally these network entities are referred to as base stations (BSs) or access nodes, and may in some instances be implemented as remote radio heads, relay stations, and the like.

In HSPA the serving cell selection as well as the active set management are mainly based on the downlink (DL) received signal strength, and as noted above the transmit power of each cell 20, 22 largely determines the coverage area of the cell. Normally, a high transmit power node will cover a larger area than the low transmit power nodes. But from the UL perspective the strength of the signal being received at each node 20, 22 does not rely on that node's DL transmit power. The result is that the introduction of the low power nodes 22 could potentially cause a large UL imbalance in the sense that, in UL, cells other than the serving cell could receive much stronger signals from the UE than the serving cell. In this case it is likely that there will be excessive UL interference from the high power macro node 20 to the low power pico node 22.

Another problem arises where the UE 10 has a large volume of UL traffic for transmission, which may cause a high level of interference from when the UE 10 performs its cell selection for setting up a radio resource control (RRC) connection. In current iterations of HSPA, the cell selection (re-selection) criteria which are broadcast by the BS are typically based on the best DL signal, and as such these criteria are agnostic to the traffic type and traffic volume. For a UE 10 located near the low power pico cell 22 as in Figure 1 and for the case where the UE 10 also has a large volume of UL traffic, this would cause high interference to the small/pico cell in case the UE 10 selects the best DL for RRC connection establishment which in the case of Figure 1 is the macro cell 20.

The current procedures in HSPA are not suitable to address these interference issues. Specifically, the current 3 GPP specifications provide for the UE behaviour summarised at the logic flow diagram at Figure 2. When the UE 10 has UL traffic to send, the UE 10 would always establish its RRC connection based on the cell that the UE selected (or re-selected) with the RRC state transition for the UE's mode from the idle mode to the RRC-connected mode.

Assume for Figure 2 that cell A (which is a high power node such as the macro cell 20) is the best DL cell whereas cell B (which is a low power node such as the pico cell 22) is the best UL cell. This power imbalance between the macro 20 and pico 22 cells can occur when the UE 10 is at a particular physical location relative to those cells 20, 22 as shown in Figure 1. In this case the UE 10 would at block 202 likely select Cell A (macro, 20) for camping. The UE 10 then sees it has UL traffic buffered at block 204 and so at block 206 it will select cell A for its RRC connection setup when transitioning its state from Idle to RRC-Connected. But once the RRC connection is established at block 206, the serving BS which is cell A (macro 20) would become aware of the high interference to cell B (pico 22) based on the UE's measurement reports. In this case, cell A (macro 20) may trigger a handover at block 208 to cell B for the UE 10, which is initiated at block 210. For the HSPA radio access technology this would be a serving HS-DSCH/E-DCH cell change (HS-DSCH is high-speed downlink shared channel and E-DCH is enhanced data channel).

Because the cell selection/re-selection criteria is agnostic to the UE traffic, in the above example it causes the UE 10 to select the unsuitable cell for camping and RRC connection setup. Even though the handover shown at Figure 2 will correct the initial incorrect selection, by that time there is already suboptimal UL performance for the UE 10 and high UL interference to the neighbour low power node 22 prior to the actual handover. And there are additional drawbacks of added/unnecessary signalling overhead and delay associated with handing over to correct the initial incorrect cell selection.

There is another procedure in HSPA for the UE in idle mode to select or reselect a cell, apart from that summarised at Figure 2. 3 GPP TS 25.304 vlO.5.0 (2012-06) specifies at section 5.2.6.1.4 that a UE in idle mode has to fulfil both S-criteria and R- criteria with the broadcast parameters in system information block 4 (SIB4). That same specification defines the R-criterion for cell ranking as follows:

Rs = Q meas,s + Qhysts + Qoffmbms; and

R„ = Q_meas,n - Qoffset_s,n + QoffhlbmS - TOn * ( 1 -Ln) where R_s is for serving cell and R_n is for the neighbour cell; and Qmeas,s and Qmeas,n are the measurements of received signal code power (RSCP) on the common pilot channel (CPICH) or bit energy to noise density (Ec/No) on the CPICH for the serving cell and for the neighbour cell separately.

Briefly, this means that the UE shall reselect the new cell if the new cell is better ranked than the serving cell during the preceding time interval T_reSeiection. But it is possible that the parameter Qoffset_s,_n can have a negative value (for example, to bias the cell reselection towards some specific cells such as for offloading traffic in the HetNet) despite the relatively worse RSCP or CPICH Ec/No. But in this case also the decision-making for cell reselection is done by the UE according to broadcast criteria from the base station, yet the base station is not aware of the UE's UL traffic status prior to the time the UE establishes its RRC connection. The parameter Qoffset_s,_n is a cell-specific parameter which is not optimised for any specific UE. In a HetNet scenario, if there is a good volume of DL traffic for the UE 10 which starts its RRC connection for data transmission, the UE 10 would likely select cell B (pico cell 22) based on the above cell range extension (CRE) in idle mode procedure. But from Figure 1 it is clear that cell B (pico 22) has a poorer DL than cell A (macro 20) and so ideally it should not be selected in this case for the UE's RRC connection. The embodiments below avoid the above initial improper cell selection by the UE when transitioning from idle to a connected state with a cell. First consider Figure 3 which shows a logic flow diagram of an example of the UE behaviour for selecting a cell with which to establish (or re-establish) a connection according to a first embodiment of these teachings. In this embodiment the UE makes the cell selection based on new criteria which the base station broadcasts, and so the cell selection by the UE 10 can be made before the new RRC connection is setup for UE-initiated calls. In this manner it avoids the unnecessary control signalling overhead and the delays mentioned above which arise when the UE 10 chooses the incorrect cell initially and then needs to be handed over.

Blocks 302 and 304 of Figure 3 are not unlike respective blocks 202 and 204 of Figure 2; the flow diagram begins at block 302 with the UE 10 in an idle state and camped with cell A (for example the macro cell 20 of Figure 1), and when the UE 10 sees at block 304 that it has UL traffic in its buffer for transmission it proceeds to block 306. This is where Figure 3 diverges from Figure 2, for in Figure 3 the UE 10 assesses whether re-selection is triggered, where re-selection means the RRC connection is to be set up with a different cell than the one with which the UE is camped in the idle state. In this example the UE is camped on the macro cell 20 and any re-selection to a different cell for the RRC connection, if such a re-selection is triggered at block 306, would be to the pico cell 22 shown at Figure 1.

This re-selection triggering at block 306 utilises the new criteria broadcast by the base station, in this case the serving macro node 20 of Figure 1. In various embodiments this new broadcast criteria comprises a threshold for link imbalance level between camping cell and neighbour cells and a threshold for layer 3 (L3) buffer status at the UE. The new broadcast criteria may further comprise one or more of the following:

• Minimum requirements for DL channel quality (CPICH EcNo or CPICH RSCP).

• RRC establishment cause (a cause code or cause index). • Call type.

• UE capability (in this case the network indicates that UEs with certain capabilities should reselect to cell B). Since the UE makes its re-selection decision at block 306 based on the criteria broadcast by the base station whether to reselect to a small cell (cell B/pico cell 22 in this example) or remain on a large cell (cell A/macro cell 20 in this example), the solution of Figure 3 implies that the radio network controller (R C) indicates which neighbour cells are small/low power cells in the broadcast neighbour cell list that it provides to the base station/ macro cell 20.

Completing Figure 3 then, if the UE 10 sees at block 306 that with this new criteria a cell re-selection is triggered, then the UE's behaviour continues then to block 308 at which the UE selects cell B (pico cell 22) and sets up an RRC connection with it at block 310B. If instead with the new criteria a cell re-selection is not triggered at block 306, then the UE 10 behaviour continues then to block 310A at which the UE selects the same cell A (macro cell 20) with which it is camped to set up its RRC connection. The above is a non- limiting example: if for some reason the UE 10 is camped in the idle state on cell B (pico cell 22) it can re-select to cell A (macro cell 20) according to Figure 3 if the cell re-selection triggering criteria are met.

Initially the base station broadcasts the criteria for cell reselection, which is used when the UE 10 with UL traffic initiates a call. When the UE 10 initiates that call (depending on which of the above criteria is/are in use in the cell), the UE 10 will then check its measured results in the idle mode and also its L3 buffer status to decide at block 306 whether there is the need to trigger cell re-selection for its upcoming RRC connection establishment. In case the criteria are fulfilled, the UE 10 would then make the cell re-selection to a new cell at block 308, followed by RRC connection setup in the new cell at block 310B. Otherwise, the UE would start the RRC connection in the current cell at block 31 OA. Consider a few examples where block 306 triggers the UE 10 to reselect a new cell. The UE may make the reselection if the UE's UL traffic is higher than the broadcast threshold criteria of the UE's L3 buffer status. The UE may make the reselection if the radio link balance is higher than the threshold specified by the base station's broadcast criteria (for example, the pathloss difference that the UE measures between the current cell and the neighbour cell). Or in another example the UE may make the reselection if the DL channel quality of the neighbour cell (for example, the CPICH EcNo and/or the CPICH RSCP) satisfies the minimum requirements specified by the base station's broadcast criteria.

There are various means by which the network can indicate to the UE 10 which subset of the neighbour cell list are the small/low power cells. For example, the pico cell scrambling code range could be signalled, or each entry in the neighbour cell list corresponding to a small cell could have a Boolean flag associated with it. In another example the network may utilise a configurable pico cell index to the intra- frequency neighbour cell list; every cell in the neighbour list has an index but those cells listed after the configurable index are assumed by the UE 10 to be the small/low power cells.

According to a second embodiment of these teachings, the network itself can redirect the UE 10 to select the neighbour intra- frequency cell. In conventional HSPA the network can enforce a cell redirection during the UE's RRC connection establishment but only to an inter-frequency cell or a cell in another radio access technology. Specifically, in HSPA the network receiving from the UE 10 an RRC CONNECTION REQUEST message can then issue an RRC CONNECTION REJECT message on the downlink common control channel (CCCH) to direct the UE 10 to another UTRA carrier or to another system. But this is not available to the network for neighbour cells that are intra-frequency cells in the same radio access technology, which is the scenario of Figure 1, and so cannot solve the problem of an incorrect same- frequency cell selection for connection establishment (or re-establishment) in the same radio access technology (RAT) system. In an example of this second embodiment, during RRC connection setup for UE initiated calls the UTRAN can direct the UE 10 to the same frequency cell in the same RAT based on the UE measurement reports about the traffic status and any link imbalance carried in the RRC connection request message. Specifically, upon receiving an RRC CONNECTION REQUEST message, the UTRAN can check the information element (IE) "Measured Results on RACH" (RACH is the random access channel) to derive the link imbalance between cells. The UTRAN can further decide whether to make an intra- frequency cell redirection, taking into account additional information, which by these teachings are included in the UE's measured results, such as for example call type, UE capability, RRC establishment cause, and/or L3 buffer status. So in these teachings for the second embodiment, the UE's measurement report, and specifically the IE "Measured Results on RACH", includes one or more of the following information: the UE's L3 buffer status information, and/or whether the UE supports intra- frequency cell redirection.

The network's RRC CONNECTION REJECT message is modified according to this second embodiment to include an indication of the target cell that the UE 10 is to reselect for RRC connection establishment. In an embodiment this additional indication is included in the IE "Redirection information".

Consider a more comprehensive example for this second embodiment. When the UE 10 initiates a call, the UE 10 sends the RRC CONNECTION REQUEST message with its measured results about the UE's L3 buffer status to the currently serving base station. Upon receiving the UE's RRC CONNECTION REQUEST message, the UTRAN can then check the measured results to decide whether to make an intra-frequency cell redirection, taking into account the information such as link imbalance, L3 buffer status, call type, UE capability, and RRC establishment cause. If the UTRA network deems that an intra-frequency cell redirection is needed, the UTRAN would then send to the UE 10 the RRC CONNECTION REJECT message, by which the UTRAN may direct the UE 10 to the suitable neighbour cell 22. In this case, the base station 20 can explicitly indicate to the UE 10 the cell (pico 22) to be re-selected for the UE's RRC connection establishment. The second embodiment can be easily adopted into current signalling processes without adversely impacting any backward compatibility of UEs that lack the capability to practise it, for example in the next specification release by adding to the existing signalling messages an extension IE which contains the new measurement elements.

In general, the first embodiment is quite useful to perform the suitable cell reselection at the early stage, whereas the second embodiment can be fully under the control of the base station. Both of them have their own distinct advantages. As noted above, while the above examples are in the context of the HSPA system these teachings can be readily applied to other radio access technologies, such as for example an LTE HetNet deployment of small cells 22 within the coverage area of a macro cell 20.

Exemplary embodiments of these teachings provide the technical effect that they are simple solutions to implement in existing infrastructure to avoid UL interference at an early stage; the first embodiment can have the cell reselection take place even before the UE transmits its RACH preambles. Both embodiments help avoid a wrong cell selection for the UE transitioning from idle to a connected state, and so they result in power savings at the UE as well as reducing signalling overhead and latency as compared to the prior art where the wrong cell was selected and a handover had to be accomplished to correct that initial error.

The logic flow diagram of Figure 4 illustrates some highlights of both the first embodiment from the perspective of the UE 10 and the second embodiment from the perspective of the serving cell. 20. Blocks 402 and 404 are from either device's perspective, after which the embodiments and perspectives diverge.

Specifically, at block 402 there is determined for a UE 10 an UL buffer occupancy and a link imbalance between a serving and a neighbour cell operating in a same frequency and a same radio access technology. Then at block 404, based on the determined UL buffer occupancy and link imbalance, the UE is controlled to transition directly from an idle state with the serving cell to a connected state with the neighbour cell.

In the above example embodiments the serving cell is a macro cell and the neighbour cell is a small cell operating at a lower transmit power than the macro cell; and further the link imbalance comprises a pathloss difference between the serving cell with the user equipment and the neighbour cell with the user equipment.

While the above examples were in the context of the radio access technology comprising high speed packet access HSPA, in another embodiment the radio access technology comprises Long Term Evolution of Evolved Universal Terrestrial Radio Access Network E-UTRAN.

For the embodiment detailed at block 408 in which the device performing the logic flow diagram of Figure 4 is the UE, that UE receives a first threshold and a second threshold from the serving cell and controls itself to transition directly from the idle state with the serving cell to the connected state with the neighbour cell as stated in block 404 specifically based on the uplink buffer occupancy exceeding the first threshold and the link imbalance exceeding the second threshold, and also based on a downlink channel quality between the UE and the neighbour cell exceeding a minimum quality threshold. In the above example for the first embodiment, the first and the second threshold are received by the UE in broadcast system information. The minimum quality threshold may be received in broadcast system information also, or it may be static (for example, specified in a published standard) and not specifically signalled to the UE by the serving or neighbour cell. As noted in the more detailed examples above, the downlink quality can be a condition of transitioning directly from the idle state with the serving cell to the connected state with the neighbour cell for other embodiments as well. This is true also for the RRC establishment cause, call type, and UE capability; any one or combination of these may be used in addition to the criteria summarised at blocks 404 and 408. For the embodiment detailed at block 410 in which the device performing the logic flow diagram of Figure 4 is the serving cell for the user equipment, that serving cell determines the uplink buffer occupancy and the link imbalance from measurements received from the UE. In this case, the serving cell controls the UE to transition directly from the idle state with the serving cell to the connected state with the neighbour cell as stated at block 404 specifically by sending to the UE a redirect message that identifies the neighbour cell as a target cell. In the particular example above, that redirect message comprises an RRC-CONNECTION REJECT message which identifies the neighbour cell as the target cell, and the serving cell sends to the UE that RRC-CONNECTION REJECT message in response to receiving from the UE an RRC-CONNECTION REQUEST message that includes the measurements.

The logic flow diagram of Figure 4 described above may be considered to illustrate the operation of a method for operating a wireless communications device such as the UE 10 or the serving cell 20, 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 are configured to cause that electronic device to operate, whether such an electronic device is the UE 10, the serving cell 20, or one or more components therefore such as a modem, chipset, or the like.

Such blocks and the functions they represent are non-limiting examples, and may be practised in various components such as integrated circuit chips and modules, and the exemplary embodiments of this invention may be realised 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. Such circuit/circuitry embodiments include any of the following: (a) hardware- only circuit implementations (such as implementations in only analog and/or digital circuitry) and (b) combinations of circuits and software (and/or firmware), such as: (i) a combination of processor(s) or (ii) portions of processor(s)/software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone/UE and/or the serving cell/base station/access node, to perform the various functions summarised at Figure 4 and (c) circuits, such as a microprocessor(s) or a portion of a microprocessor(s), that require software or firmware for operation, even if the software or firmware is not physically present. This definition of "circuitry" applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term "circuitry" would also cover an implementation of merely a processor (or multiple processors) or portion of a processor and its (or their) accompanying software and/or firmware. The term "circuitry" also covers, for example, a baseband integrated circuit or application specific integrated circuit/processor for a mobile phone/user equipment or a similar integrated circuit in a server, a cellular network device, or other network device.

Reference is now made to Figure 5 for illustrating a simplified block diagram of examples of various electronic devices and apparatus that are suitable for use in practising some example embodiments of this invention. In Figure 5, a wireless network represented by the serving cell 20, or more generally an access node, is adapted for communication over a wireless link 15A with an apparatus such as a portable radio device such as the user equipment UE 10. The serving cell 20 also has a wired or wireless link 30B with the small/pico cell 22. The network may also provide connectivity via data/control path 30 with a broader network (e.g. a cellular network and/or a publicly switched telephone network PSTN and/or a data communications network/Internet), such as via a radio network controller RNC (not shown) or a mobility management entity/serving gateway (not shown) depending on the radio access technology in use.

The UE 10 includes processing means such as at least one data processor (DP) 1 OA, storing means such as at least one computer-readable memory (MEM) 10B storing at least one computer program (PROG) IOC, and communicating means such as a transmitter TX 10D and a receiver RX 10E for bidirectional wireless communications with the network access point/serving cell 20 and with the pico/small cell 22 via wireless link 15B using one or more antennas 10F. Also stored in the MEM 10B at reference number 10G is the UE's means for obtaining the new triggering criteria, and for transitioning from the idle state to the connected state with the new pico/low power cell 22.

The macro node/serving cell 20 also 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, and communicating means such as a transmitter TX 20D and a receiver RX 20E for bidirectional wireless communications with the UE 10 via one or more antennas 20F. The serving cell 20 also has a program stored in its local memory for obtaining the measurements of UL buffer occupancy and link imbalance from the UE and for sending the UE a redirect message according to the second embodiment and as summarised at 20G.

Figure 5 also shows for the pico/low power cell 22 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 the UE 10 over the link 15B via one or more antennas 22F.

While not particularly illustrated for the UE 10 or serving cell 20 or pico cell 22, those devices are also assumed to include as part of their wireless communicating means a modem which may be inbuilt on an RF front end chip within those devices 10, 20, 22 and which also carries the TX 10D/20D/22D and the RX 10E/20E/22E.

At least one of the PROGs 10C/10G/20C/20G in the UE 10 and/or in the serving cell/macro cell 20 is assumed to include program instructions that, when executed by the associated DP 10A/20A, enable the device to operate in accordance with the exemplary embodiments of this invention, as detailed above particularly with respect to Figure 4 and the first and second embodiments detailed above. In this regard the exemplary embodiments of this invention may be implemented at least in part by computer software stored on the MEM 10B, 20B which is executable by the DP 10A of the UE 10 and/or by the DP 20A of the macro cell 20, 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 may not be the entire UE 10 or macro cell 20, 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, modem, system-on-a-chip SOC or an application specific integrated circuit ASIC.

In general, the various embodiments of the UE 10 can include, but are not limited to, personal portable digital devices having wireless communication capabilities, including but not limited to user equipments, cellular telephones, navigation devices, laptop/palmtop/tablet computers, digital cameras and Internet appliances, as well as machine-to -machine devices which operate without direct user action.

Various embodiments of the computer readable MEMs 10B, 20B 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 DPs 10A, 20A include but are not limited to general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), and multi-core processors.

The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisaged. It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments. Furthermore, equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.

Claims

1. A method for operating a wireless communications device, the method comprising:

determining for a user equipment an uplink buffer occupancy and a link imbalance between a serving cell and a neighbour cell operating in the same frequency and the same radio access technology; and

based on the determined uplink buffer occupancy and link imbalance, controlling the user equipment to transition directly from an idle state with the serving cell to a connected state with the neighbour cell.

2. A method according to claim 1 , in which the serving cell is a macro cell and the neighbour cell is a small cell operating at a lower transmit power than the macro cell.

3. A method according to claim 1 or claim 2, in which the link imbalance comprises a pathloss difference between the serving cell with the user equipment and the neighbour cell with the user equipment.

4. A method according to any of claims 1 to 3, in which the radio access technology comprises High Speed Packet Access HSPA.

5. A method according to any of claims 1 to 3, in which the radio access technology comprises Long Term Evolution of Evolved Universal Terrestrial Radio Access Network E-UTRAN.

6. A method according to any of claims 1 to 5, in which the wireless communication device is the user equipment which receives a first threshold and a second threshold from the serving cell,

wherein the user equipment is controlled to transition directly from the idle state with the serving cell to the connected state with the neighbour cell based on:

the uplink buffer occupancy exceeding the first threshold; the link imbalance exceeding the second threshold; and

a downlink channel quality between the user equipment and the neighbour cell exceeding a minimum quality threshold.

7. A method according to claim 6, in which the first and the second threshold are received by the user equipment in broadcast system information.

8. A method according to any of claims 1 to 5,

in which the wireless communication device is the serving cell for the user equipment which determines the uplink buffer occupancy and the link imbalance from measurements received from the user equipment;

wherein the serving cell controls the user equipment to transition directly from the idle state with the serving cell to the connected state with the neighbour cell by sending to the user equipment a redirect message that identifies the neighbour cell as a target cell.

9. A method according to claim 8, in which the redirect message comprises an RRC-CONNECTION REJECT message which identifies the neighbour cell as the target cell,

wherein the serving cell sends to the user equipment the RRC-CONNECTION

REJECT message in response to receiving from the user equipment an RRC- CONNECTION REQUEST message which includes the measurements.

10. Apparatus for communicating, the apparatus comprising a processing system constructed and arranged to cause the apparatus at least to:

determine for a user equipment an uplink buffer occupancy and a link imbalance between a serving cell and a neighbour cell operating in the same frequency and the same radio access technology; and

based on the determined uplink buffer occupancy and link imbalance, control the user equipment to transition directly from an idle state with the serving cell to a connected state with the neighbour cell.

11. Apparatus according to claim 10, in which the serving cell is a macro cell and the neighbour cell is a small cell operating at a lower transmit power than the macro cell.

12. Apparatus according to claim 10 or claim 11 , in which the link imbalance comprises a pathloss difference between the serving cell with the user equipment and the neighbour cell with the user equipment.

13. Apparatus according to any of claims 10 to 12, in which the radio access technology comprises High Speed Packet Access HSPA.

14. Apparatus according to any of claims 10 to 12, in which the radio access technology comprises Long Term Evolution of Evolved Universal Terrestrial Radio Access Network E-UTRAN.

15. Apparatus according to any ofclaims lO to 14, in which the apparatus comprises the user equipment, wherein the user equipment is controlled to transition directly from the idle state with the serving cell to the connected state with the neighbour cell based on:

the uplink buffer occupancy exceeding a first threshold received from a serving cell;

the link imbalance exceeding a second threshold received from the serving cell; and

a downlink channel quality between the user equipment and the neighbour cell exceeding a minimum quality threshold.

16. Apparatus according to claim 15, arranged to receive the first and the second threshold in broadcast system information.

17. Apparatus according to any of claims 10 to 14, in which the apparatus comprises the serving cell for the user equipment which determines the uplink buffer occupancy and the link imbalance from measurements received from the user equipment;

wherein the serving cell controls the user equipment to transition directly from the idle state with the serving cell to the connected state with the neighbour cell by sending to the user equipment a redirect message that identifies the neighbour cell as a target cell.

18. Apparatus according to claim 17, in which the redirect message comprises an RRC-CONNECTION REJECT message which identifies the neighbour cell as the target cell,

wherein the serving cell sends to the user equipment the RRC-CONNECTION REJECT message in response to receiving from the user equipment an RRC- CONNECTION REQUEST message which includes the measurements.

19. A computer program comprising a set of instructions comprising:

code for determining for a user equipment an uplink buffer occupancy and a link imbalance between a serving cell and a neighbour cell operating in the same frequency and the same radio access technology; and

code for controlling the user equipment, based on the determined uplink buffer occupancy and link imbalance, to transition directly from an idle state with the serving cell to a connected state with the neighbour cell.

20. A computer program according to claim 19, in which the serving cell is a macro cell and the neighbour cell is a small cell operating at a lower transmit power than the macro cell.

21. A computer program according to claim 19 or claim 20, in which the link imbalance comprises a pathloss difference between the serving cell with the user equipment and the neighbour cell with the user equipment.

22. A computer program according to any of claims 19 to 21, in which the radio access technology comprises High Speed Packet Access HSPA.

23. A computer program according to any of claims 19 to 21, in which the radio access technology comprises Long Term Evolution of Evolved Universal Terrestrial

Radio Access Network E-UTRAN.

24. A computer program according to any of claims 19 to 23, in which the computer program is for the user equipment, wherein the user equipment is controlled to transition directly from the idle state with the serving cell to the connected state with the neighbour cell based on:

the uplink buffer occupancy exceeding a first threshold received from a serving cell;

the link imbalance exceeding a second threshold received from the serving cell; and

a downlink channel quality between the user equipment and the neighbour cell exceeding a minimum quality threshold.

25. A computer program according to claim 24, in which the first and the second threshold are received by the user equipment in broadcast system information.

26. A computer program according to any of claims 19 to 23,

in which the computer program is for the serving cell for the user equipment which determines the uplink buffer occupancy and the link imbalance from measurements received from the user equipment;

wherein the serving cell controls the user equipment to transition directly from the idle state with the serving cell to the connected state with the neighbour cell by sending to the user equipment a redirect message that identifies the neighbour cell as a target cell.

27. A computer program according to claim 26, in which the redirect message comprises an RRC-CONNECTION REJECT message which identifies the neighbour cell as the target cell,

wherein the serving cell sends to the user equipment the RRC-CONNECTION REJECT message in response to receiving from the user equipment an RRC- CONNECTION REQUEST message which includes the measurements.