GB2460819A

GB2460819A - Controlling reselection from access points in a telecommunications network

Info

Publication number: GB2460819A
Application number: GB0809576A
Authority: GB
Inventors: Youssef Chami
Original assignee: Vodafone Group PLC
Current assignee: Vodafone Group PLC
Priority date: 2008-05-28
Filing date: 2008-05-28
Publication date: 2009-12-16
Also published as: EP2294873B1; ES2385728T3; US20110111759A1; WO2009144501A1; US8805377B2; EP2294873A1; GB0809576D0; ATE543358T1

Abstract

A GSM or UMTS mobile telecommunications network comprises of macro stations (42) and one or more additional access points (20). The access point (20) is connected to the network core by an IP transport broadband connection. The access point (20) is configured to appear to the mobile terminal (1) as a conventional base station by supporting the GSM or UMTS transport protocol. No modifications are required to a standard GSM and UMTS mobile terminal. A subscriber may be provided with a designated "home" access point (20) to provide coverage in their premises (38). The reselection parameters are selectively changed to alter the likelihood of the neighbouring base station being chosen instead of the "home" access point (20).

Description

CONTROLLING RESELECTION FROM ACCESS POINTS TN A

TELECOMMUNICATIONS NETWORK

The present invention relates to a base station reselection method for a mohi)e terminal camped on a predetermined ce1l to a base station and to a telecommunications system.

Conventional access to the features and services provided by GSM and UMTS networks involves signalling between the mobile terminal and a standard base station (macro base station) that has a dedicated connection to an MSC and provides coverage in the cell occupied by the mobile terminal using cellular telecommunication (e.g. GSIM or UMTS) transport protocols.

There have recently been proposals to allow access to the features and services provided by GSIvl and UMTS networks by providing additional special base stations (femto base stations). referred to as access points (APs), for example at a subscriber's home or office, in order to increase network capacity and improve coverage. These access points communicate with the core network via IP based comrnunications such as a broadband IP network, arid are typically routed via the Internet, Many different names have been given to AN, such as home access points (H.APs), microbase stations, pico-hase stations, pco-celis and femto-cells, hut all names refer to the same apparatus. APs provide short range.

localized coverage, and are typically purchased by a subscriber to be installed in their house or business premises.

It has also been proposed to use APs in the Long Term Evolution (LIE) telecommunications network currently being developed, but not vet implemented. LTE is likely to he the next network implementation after -C-, it) L)'J.

An advantage of using an access point connected to the core network via an IP network is that existing broadband Digital Subscriber Line (DSL) 1 i F- trrtr rtk t k= ti;'h rI

I

During the call set up procedure, the core network will receive the MS1SDN of the subscriber arid the cell ID of the base station with which the subscriber is communicating. In order to confirm at which rate to change the subscriber, the core network checks whether the subscriber is using one of the home base stations wInch cover his house. This check is made by consulting the Location Based Charging (LBC) Module and by comparing the MSISI)N and cell Ii) identified in the call with those stored in the database. If the cell ID for the MSISDN is the ID of one of the subscriber's logged home base stations, the subscriber is recognised as calling from within hts home and is charged at a reduced rate, otherwise he is charged at his standard rate.

With this in mind, APs provide another opportunity for network providers to offer reduced rates to subscribers. For instance, subscribers may benefit from a different caH tariff when using their mobile terminal through an AP acting as a base station.

[he present inventor has found that when a home base station (either an A? or a macro base station) is provided at a particular location, the subscriber's mobile device may select other base stations when at that location. This may happen, tbr example, if there is a nearby macro base station that perhaps in some parts of the subscriber's home provides better radio coverage/quality than the home base station.

Mobile networks such as 20 (OSM), 30 (LIMIS) and LTE telecommunications networks have an active state of communication with their mobile terminals and an inactive/idle state of communication with their terminals. When in the active state, as the mobile terminals move between different cells of the network, the communication session is maintained by performing a "handover" operation between the cells, in the inadiveidJe state, as a mobile terminal moves between different cells of the network. the mobile terminal performs "cell reselection" to select the most

S

For 2(1 and. 30, a mobile terminal is in active communication when it has a CS (Circuit Switched) connection established, In 2.50, GPRS PS (Packet Switched). active communication can he defined as the OPRS Ready state. in 30 UMTS PS, active communication can he defined as the RRC connected mode state that is CELL-DCH.

In 30 UMTS PS, CELL/URA PCI! and CELL EACH can he defined as inactive states. In GPRS, the Standby state can he regarded as an inactive stateS Either one or both of the CS and PS active communications may occur in the mobile terminal.

For a 30 mobile terminal, in the active mode the terminal is in the RRC connected mode The RRC connected mode includes the following States: CELL OCR state is characterized by: A dedicated physical channel is allocated to the UE in uplink and.

downhnk.

The UE is known on cell level according to its current active set I)edicated transport channels, downi ink and uplink (TDD) shared transport channels and a combination of these transport channels can be used by the liE.

CELL FAC1I-I state is characterized by: dedicated physical channel is allocated to the liE.

The liE continuously monitors a EACH (forward access channel) in the downlink.

* The UB is assigned a default common or shared transport channel in the uplink (e.g. BACH) that It can use anytime according to the access procedure for that transport channel * The position of the liE is known by UfltAN on cell level according to the cell where the UE last made a cell update.

* In TDD ma one or several USCU or DSCH transport channels may have been established.

CELL_PCI! state is characterized by: * No dedicated physical channel is allocated to the liE. The UE selects a PCI! (paging channel) with the algorithm, and uses VBX for monitoring the selected PCI! via an associated PCI!.

* Nouplinkactivityispossiblt * The position of the UE is known by UTRAN on cell level according to the cell where the UE last made a cell update mCELLJACH * Nodedica1edchannelisallocatedtotheUtTleUEseiectsaPCH, and uses DRX for monitoring the selected PCI! via an associated PCH.

* No uplink activity is possible.

* The location of the liE is known on UTRAN muting area level accordIng to the URA assigned to the liE during the last URA update in CELL-FACH state.

In the CELL_DCH state a network-driven handover is performed when necessary, as described in 3GPP lB 25-331. In this state a mobile terminal scans the pilot channels of up to 32 intra-frequency coils neighbouring its current cell. The mobile terminal rorms a list of the best cells for possible handovr based on the received signal strength and/or quaity (i.e. the error rate in the received signal). The information in this list is passed to the t T'1) .. r - 1 1 I +1 Broadcast Channel (BCFI) in the system information block 3 (STB3) or system information block 4 (51134). Notably. these are the time interval "Ireseledlion" and the hysteresis value "Qhyst", In order to avoid too fast a switch between cells based on quickly changing network conditions, a switch from the original cell to the neighbouring cell only takes place if the neighbouring cell was better than the original cell by the factor for the time "Treselection". This behaviour of a mobile end device is described in detail on the technical specification 3GPP TS 25304. Multiple frequency layers and mobility state determination are provided in a similar manner for LTE/SAE networks.

When a subscriber is at their borne location, the reselection measurements continue to be made in the normal way and cell reselection may occur.

When a base station other than the home base station is selected, this is unsatisfactory for several reasons, Firstly, if the home base station is an AR. the capacity of the macro network will he used unnecessarily.

Secondly. the subscriber will not receive the discounted "home" rate when using a base station other than the macro network. This is a particular problem as the subscriber is unlikely to he aware of which base station is selected.

One solution would be to increase the power of the home base station but this has the disadvantages of increasing interference to neighbouring base stations and reducing bandwidth.

An object of' embodiments of the presett invention is to provtde an alternative solution, without these disadvantages.

According to a first aspect of the present invention, there is provided a base station reselection method for a mobile terminal camped on a predetermined base station, which mobile terminal performs a cell reseicction function in accordance with reselection parameters, the method including determining the radio characteristics of at least one neighbouring base station and selectively varying the reselection parameters in dependence upon the determined radio characteristics of the neighbouring base station to alter the likelihood that the neighbouring base station will be selected by' the mobile terminal.

The arrangement may be such that the predetermined base station may be selected for longer without having to increase its power.

The predetermined base station may be a "home" macro base station or "home' access point (femtocefl).

The method may further include determining the radio characteristics of the predetermined cell with. respect to the mobile terminal.

Whe.n the determined radio characteristics of the neighbouring cell are better than a tlu'eshold the reselection parameters may he varied to alter the likelihood that the neighbouring base station will be selected by the mobile terminal. in the embodiment, when the determined characteristics of the neighbouring cell are better than a threshold and the determined characteristics of the predetermined cell are better than a threshold, the reselection parameters are varied to make it less likely that the neighbouring base station will he selected by the mobile That is, in this scenario, the predetermined/home base station is made "more attractive" or "more sticky" to the mobile terminal. The mobile terminal is instructed to begin measurements for cell reselection later (when the predetermined base station is of lower coverage/quality than is conventionally the case).

Conversely, iii the embodiment, when the predetermined characteristics of the neighbouring cell are better than a threshold and the determined characteristics of the predetermined cell are worse than a threshold, the reselection parameters are varied to make ft more 1 ikely that the neighbouring base station wifl he selected by the mobile terminal. That is, n hi nrin t1i hn-w' ttcvn k rti ttr tvi" nr Qoffset2. In the embodiment, by varying the amount by which the radio characteristics of the neighbour base station must he better than these of the predetermined base station, the likelihood of reselection to the neighbour base station can be adjusted.

The determination of the radio characteristic may be performed by the predetermined base station. Alternatively, the detennination of the radio characteristics may he performed by the mobile ten.ninal and reported to t.he predetermined base station..

The predetermined base station may vary' the reselection parameters and transmit these to the mobile terminal as Â�system information".

in the embodiments,. only the reselection parameters of a mobile terminal 1 5 registered for use with the predetermined base station are adjustable. For example, the predetermined base station may he the registered home" base station for the particular mobile terminal.

The reselection parameters may apply to both inter and intra carrier reselection, and may comprise "sintcrsearch" and "sintrascarch" parameters.

the present invention also relates to a base station and to a system as defined in the clams.

For a better understanding of the present invention embodiments will now be described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic drawing of key elements of a mobile telecommunications network Figure 2 shows a modified mobile telecommunications network for receiving 1? based communications from an access point in addition to communications from a conventional base station; Figure 3 shows an access point located in a subscribers premises that is also served by a conventional base station; Figure 4 shows how reselection parameters on a home access point are varied in dependence upon the neighbouring cell coverage/quality; and Figure 5 shows a high-level flow chart of the steps performed to provide adaptive reselection in accordance with. an embodiment of the invention.

Key elements of a mobile telecommunications network, and its operation, will now briefly be described with reference to Figure 1.

Each base station (135) corresponds to a respective cell of its cellular or mobile telecommunications network and receives calls from and transmits calls to a mobile terminal in that cell by wireless radio communication iii one or both of the circuit switched Or packet switched domains. Such a subscriber's mobile terminal is shown at 1. The mobile terminal may be a handheld mobile telephone, a personal digital assistance (PDA) or a laptop computer equipped with a datacard, in a USM mobile telecommunications network, each base station comprises a base transceiver station (RI'S) and a base station controller (BSC). A BSC may control more than one BTS. The WFSs and RSCs comprise the radio access network.

in a UMTS mobile telecommunications network, each base station comprises a node B and a radio networ.k controller (RNCI. An RNC may control more than one node B. The node B's and itNCs comprise the radio access network.

In the proposed LTE mobile teleconiniunications network, each base station \ t I t't Y'I -t 1 1 number, by means of which callers initiate calls to the sUbscriber. This number is the MSISDN, The network includes a home location register (HLR) 10 which, for each S subscriber to the network, stores the IMSI and the corresponding.MS1SDN together with other subscriber data, such as the current or last known MSC or SGSN of the subscriber's mobile terminal.

When mobile terminal 1 is activated, it registers itself in the network by 1(1 transmitting the IMSI (read from its associated SIM card) to the base station 3 associated with the particular cell in which the terminal I is located. In a traditional network, the base station 3 then transmits this JMSI to the MSC 2 with which the base station 3 is. registered. In a network using the functionality described in 3C3PP IS 2323$, the base station follows 1 5 prescribed rules to select which MSC to use. and then transmits this IMSI to the selected MSC.

MSC 2 now accesses the appropriate storage location in the HER 10 present in the core network 140 and extracts the corresponding subscriber MSISDN and other subscriber data from the appropriate storage location, and stores it temporanly ii a storage location n a visitor location register (/Lk) 14, In this way, therefore the particular subscriber is effectively registered with a particular MSC (MSC 2), and the: subscrihe?s information is temporarily stored in the VLR (VLR 14) associated with that MSC.

Each of the MSCs of the network (MSC 2 and MSC $) has a respective VLR i4 and II) associated with. it and operates in the same way as already described when a subscriber activates a mobile terminal in one of the cells corresponding to one of the base stations controlled by' that M.SC.

\Vhen the subscriber using mobile terminal 1 wishes to make a calL they enter the telephone number of the called party in the usual manner. This L 1 -" cellular telecommunications transport protocols used tbr signaling in conventIonal CJSM or UMTS networks used between, the mobile terminal 1 and the A? 20 to IT' based signalling.

S The connection 23 between the access point 20 and the core network 140 may use the PSTN telephone network, Typically a DSL cable connection connects the access point 20 to the PSTN network, The data is transmitted between the access point 20 and the core network 140 by 11? transport/DSL transport (a hackhaul connection).

The access point 20 may be connected to the core network 12 by means other than a DSL cable and the PSTN netwo& For exanwle, the access point 20 may be connected to the core network 140 by a dedicated cable connection that is independent of the PSTN, or by a satellite connection between the access point 20 and the network core 140.

Using an access point 20 connected to the core network via an 1? network.

does have advantages. Existing broadband DSL connections can be used to link mobile terminals with the network core 140 without using the capacity 2.0 of thc mobile telecommunications network radio access network. or where there is no conventional radio access network coverage. For example, UMTS coverage could be provided by an access point 20 whcre there is no conventional UMTS coverage (perhaps only (JSM coverage).

A? 20 may he configured to serve a WLAN located in a home or office, in addition to GSM/'UMTS/L'TE networks, The WLA'N could belong to the subscriber of the mobile terminal 1, or be an independently operated WLAN.

The owner of A? 20 can program the A? so that it is either "open" or "c1osed'. whereby an open A? is able to carry communications from any i7 mobile device in the GSM/UMTS network, and a closed AP is only able to carr communications from specific predesignated mobile devices.

Arrangements for controlling use of APs by mobile devices are disclosed in

D

With this background in mind, a first embodiment of the invention will now be described in relation to Figure 3.

Figure 3 shows an AP 20 installed in the subscriber's home or workplace 38. The coverage area, indicated by dashed line 40 of the NP 20 will typically be smaller than that of macro base station 42 but generally will he sufficient to cover the whole area of the premises 38. Generally one or more macro base stations, including macro base station 42 as in Figure 3, will also cover the Ipremises.

The AP 20 is connected to a DSL line at the premises 3$. All communications from the AP 20 are transmitted along the DSL and to an internet Service Provider (ISP). Typically, the ISP will receive communications from multiple APs, and so will include a Digital Subscriber Line Access Multiplexer (DSLA.M) and a data switch, for multiplexing a. plurality of custorncr communications and routing them to an MSC/SGSN.

If the power and/or quality of the radio signal received at the mobile terminal i for the home AP 20 becomes relatively low then the cell reselection process is triggered. In this process the power arid/br quality of the neighbouring base stations (including base station 42) is evaluated in the manner described above. if a neighbouring base station provides mproved radio quality, then the reselection process can be completed in a conventional nmnner, also briefly described above.

The ibliowing parameters are used to control the reseleetion process: Sintersearch The Sintersearch information element is described in 3GPP TS 25331 and S 3GPP TS 21304, and is sent in 51.83. Sintersearch controls whether the mobile device I must make measurements of inter4requency ccl Is while camped on a particular "serving cell". If the quality of the serving cell is above Sintersearch., then the UP will not measure other inter-frequency cells while camped.

The Sintersearch value is conventionally the same for all base stations (including APs) in a network.

S intrasearch The Sintrasearch information element is described in 3CPP TS 25331 and 30PP TS 25304, and is sent in 5183. Sintraseareb. controls whether the mobile terminal 1 must make measurements of intra-frequeney cells while camped. If the quality of the serving cell is above Sintrasearch, then the UP will not measure other intrafrcqucncy cells while camped.

The Sintrasearch value is conventionally the samc for all base stations (including APs) in a network.

Quality Measure The 3GPP TS 25331. "Cell selection and reselection quality measure" inibrmation element may be RSCP (Received Signal Code Power) and/or the ratio Pc/No (the ratio of the energy per chip. Ec, received by the mobile terminal to the spectral noise power density. No, received b the mobile terminal I, with allowance made for non-orthognohibty).

ffygresisLLtÂ�=hysti_pQoffretl) Qhystl (see 3GPP TS 25331) specifies the hysteresis value to he used by the mobile device 1 if the Quality Measure is CPICH RSCP. Reselection of a neighbouring cell only takes place if the neighbouring cell is better in coverage than the home AP2O by the factor Qoffseti for a predetermined time ("Treselection').

I'tysteresis 2 (Ohyst2 or Qoffset 2) Qhyst2 (see 3GPP TS 25331) specifies the hysteresis value to be used by the mobile device 1 if the Quality Measure is CPICH hello. Reselection of a neighbouring cell only takes place if the neighbouring cell is better in quality than the home AP2O by the flietor Qoffset2 for a predetermined time ("Tres election").

In accordance with an important feathre of the embodiment, Sintersearch, Sintrasearch, Qofiset I and Qoffset 2 may he varied for the mobile terminal 1 while the home AP 20 is selected.

The effect of varying these values is as follows:-Sintrasearch o When this value is increased by the AP 20. the mobile terminal 1 starts intra$requency cell reselection earlier (i.e. when the quality of the serving cell is higher than conventionally).

o When this value is decreased by the AP 20, the mobile terminal starts infra-frequency cell reselection later (i.e. when the quality of the serving cell is lower than conventionally), Sintersearch o When this value is increased by the AlP' 20, the mobile terminal I starts interfrequency cell reselection earlier (i.e. when the quality of the serving cell is higher than convemionally).

o When this value is decreased by the serving cell, the mobile terminal starts inter-frequency cell reselecuon later (i.e. when the quality of the serving cell is lower than conventionally) Qoffset 1 (s,n); applies to R (reselection) rule with CPICFI

RSCP

o When this value is increased by the serving cell the mobile terminal i has a lower probability of selecting a neighbouring cell.

o When this value is decreased by the serving cell, the mobile terminal I has a higher probability of selecting a neighbouring cell.

Qoffset2(s,n): applies to R (reseleedon) rule with CPICH Bc/lu o When this value is increased by the serving cell, the mobile terminal 1 has a lower probability of selecting a neighbouring cell.

o W7} this value is decreased by the serving cell, the mobile terminal 1 has a higher probability of selecting a neighbouring cell.

Olfset I and 2 are only used together with the Siritersearch parameter for the interfrequency mobility, The parameters Qoffsetl and 2 are unchanged for the inirafrequency case. However, the network operator may choose to change these parameters to ease the idle mode mobility from the femto cell to neighbouring 3G macro base staLion on the different carrier in ease of high interference.

The home A? 20 includes a detector module 44 for measuring RSCP and/or Fe/To of the neighbouring base stations (including macro base stations and other ARs) which use the same carrier or a different carrier when the Sintersearch and Sintrasearch parameters so indicated.

The home AP 20 is also aware of the RSCP and/or Fe/lu between itself and mobile terminal I. The home A? 20 is therefore able to eharacterise its RSCP and/or Fe/To with respect to the mobile terminal as Thigh" or low".

The AP20 is also able to eharaeterise the RSCP andior Fe/To of the neighbouring base stations on the same carrier and on a different carrier as "high" or "tow" (at the location of the AP2O).

The home AP2O includes programming means 46. in dependence of these characteristics, the home AP 20 operates the programming means 46 to then instruct the mobile tennnal I to adjust the parameters Sintersearch, Sintraseareh, offsetl and Qoffset2 in the manner summarised in the table below, Measured Measured Measured Sinter-Sintra-Qoffset Qoffset Echo Echo Echo Search Search 1* 2* and/or and/or and/or RSCP of RSCP of RSCP of Current Targeted Targeted Home base 3G Femto 3G Femto station or Macro or Macro cell on cell on Same Different -____________ Carrier Carrier ________ ________ ________ ________ 1 Low Low High 4, 4, 2 Low High Low f ____ ____ 3 Low Low Low 4 High Low High 4, _____ _____ _____ High High Low 4, 6 High High High 3 4, f t -4=+ Parameter value stays f Parameter value goes up 4, Parameter value goes down Note: * s., *) The Qoffsetl & 2 maybe left unchanged if the SinterSearch value is aggressively reduced. Each of the above parameters can be used in isolation or a in conjunction with other parameters. * 0S * 5.

S

Based on the measured cell information (Echo and/or RSCP values), in accordance with the table, the following actions are performed: If a neighbouring cell coverage/quality is "high" and the home A? 20 coverage/quality is "high" then home AP 20 modifies cell selection and reselection parameters to make the home AP 20 look "more attractive" to the mobile and broadcasts them through system information to the mobile terminal 1.

in row 4 of the Table the home AP2O coverage/quality is "high", the coverage/quality of th.e neighbouring cell on a different cattier is also "high'>and the coverage/quality of the neighbouring cell on the same carrier is "low", V/hen this occurs> the sintersearch value is reduced which, as indicated above causes the mobile terminal I to start inter-frequency cell reselection measurements later. Moreover, the decision to reselect the macro cell can be delayed by increasing the Qo ffser 1 and Qoffset2. Reselection will therefore generally (though not necessarily) occur later. In Row 4 the sintrasearch value remains unchanged.

In row 5, the coverage/quality of the A? 20 is "high" the coverage/quality of the neighbouring cell on the same carrier is "high" and the coverage/quality of the neighbouring cell on a di1Trerit carrier is "low>'. The sintrasearc.h value is reduced which, as indicated above> results in the mobile terminal starting intra$requency cell reselection measurements later and therefore generally (though not necessarily) performs cell reselection later. in Row 5 the sintersearch value remains unchanged. The Qoffseti and Qoffset 2 values are unchanged. Further, in Row 5, the decision to peri'orm the re-selection to the neighbouring macro cell can be delayed using a variable Faramter (PCompensation) as introduced in 3GPP 25331 In row 6 of the above Table the coverage/quality of the home A? 20 is "high', as is the coverage/quality of the neighbouring cell on the same carrier and cii a different carrier. in column 6 both sintcrsearch and sintrasearch are decreased, which means that the mobile terminal starts inter4'requency and intra-frequency cell reslection measurements later. Qoffset I and Qoffset2 arc increased so tha.t the mobile terminal has a lower probability of selecting a neighbouring cell on a different carrier.

If the neighbouring cell coverage/quality is "high" and home AP 20 coverageiquality is "low", the home A? 20 modifies the cell selection and reselection parameters to make the home A? 20 look "less attractive" to the mobile 1 and broadcasts them through system information to the mobile terminal I. The Sintersearch and SintraSearch values are increased to cause the mobile terminal to start measuring the surrounding 30 macro cells earlier and/or the QoITsetI /2 values are reduced to make reselection by the mobile more likely.

In row 1 of the above Table the coverage/quality of the home A? 20 is "low", the coverage/quality of the neighbouring cell on a different carrier is "high" and the coverage/quality on the same carrier is "low". The sintersearch value is increased so that the mobile terminal starts inter$requency cell reselection measurements earlier.

Qoffsetl and Qoftset are reduced to speed up the reseleetion process to neighbouring inter frequency macro cell. The Sintrasearch value remains unchanged, in row 2 of the above Table the coverage/quality of the home A? 20 is "low", the coverage/quality of the neighbouring cell on the same carrier is "high" and the coverage/quality on the different can-icr is "low". The sintrascarch value is increased so that intra-frcquency cell reslection measurements are started earlier, so that it is more likely that a cell reselection will occur. Qoffsetl, Qoffset2 and Sintersearch values remain unchanged No oilier actions will he required for the remaining conditions.

in row 3 of the above Table the coverageiquahty of the home AP 2Q the neiohhgsnrinn c.eFI nn th cnnne rcrrier n-t-i thn nsxpltheiiring refl At step 0 an auvo<onfiguranon function of the home AP 20 is activatetf At step I a periodic check is performed during which the home AP 20 measures the neighbouring base station (Feintocells macroceils etc) Ec/lo and RSCP vahies on 30 (or RSSI for OSM).

At step 2 it is determined whether the measurements are above predetermined thresholds relative to the Fe/I o and RSCP values measured by the home AP 20 for communications between the home AP 20 and the mobile terminal 1. If the measurements are not above the predetermined thresholds, then the process returns to step 1 for performance of the periodic check.

However, if the measurements are above the predetermined thresholds, then in step 3 the idle mode parameters of the mobile terminal I arc adjusted in accordance with the principles described above. Control is then returned to step I and the periodic checking is pcrfonned.

in the table arid description above, when it is indicated that a parameter (sinterseareh. sintrasearch, Qoffsetl and/or Qoffset2) stays the same, that parameter may he set to the value set conventionally. When it is indicated that a parameter goes up in value, that parameter may he set to a.

predetermined value that is a predetermined amount more than the conventional value. Similarly, when a parameter value is decreased, that parameter value may he set to a predetermined value that is a predetermined value less than a conventional value. Therefore, there may he only three predetennincd values for each of sintersearch, sintrasearch, Qoffseti and Qoftset2. A predetermined "increased" value, a predetermined Â�decreased value" and a predetermm.ed "conventional" value.

Various modil;eations to the embodiment described arc possible.

For example, in the embodiment the home AP 20 measures the Pc/ic and/or RSCP of neighbouring base stations. In an alternative arrangement. the Pc/b and/or RSCP measurements of the neighbouring base stations may be measured by the mobile terminal 1 and reported to the home AP 20. This is advantageous in that the measurements of the neighbouring cells at the mobile terminal 1 are gathered, which are more relevant to the reselection procedure than the coverage/quality measurements at the home access point 20. However, the disadvantage of this is that the mobile terminal I must be operated to perform the measurements, which will consume power and therefore reduce battery life, and would also require additional signalling between the mobile terminal 1 and the home access point 20.

in the embodiment the base station at the subscriber's premises is an access point (AP). The invention is also applicable where a particular macro base station is designated as a "home" base station. In this context, an advantage is provided because the subscriber tends to have the "home" base station selected when at his premises, and therefore benefits from a favourable charging rate.

Claims

CLAIMS1 A base station reeleetion method fbr a mobile terminal camped on a S predetermint'd base tatic'n. which mobile terminal perfoims a cell rese.lectiori twiction m aeeordanA:e with reseleetton 1.arametc vs. the method includinz determining the radio characteristics of at least one neighbom ing base statjon and sckcti civ varying the rcseieetion parameter' in dependence upon the determined radio rharacteristics of the neighbouring base station to alter the likelihood that the ilci2hhounnv base station will be selected by the mobtie terminal.

2. rme method of claim 1 including determining the radio characteristics of the predetermined cell with respect to the mobile terminal.

3. The method of claim I or 2. wherejn, when the. deten;iined radio characteristics of the neiuhbourin, base station are better than a threthold varying the reseieeticni parameter: to alter the likelihood that the neighbounng base stat ton will be select d b' the mobile terminal.

4. 1 he method of claim 2. vs heiein.. when the predetei mmcd eharactensucs of the ncn.hbouiing flase:taticsn are better than a threshold and the determined chara'tet iucs of the predetermined base station are belier than a threshold vanina the reselection parameters to make it k'.s hkelv that the ttcighb)uring base saticri will be selcctrd b the rnobi le terminal.

1 he method of ckmn 2 or 4. whet cm, when the pi edetermined characteristics of the ncmhbouririg base Â°iatiori aie heutr than a threshold and the deterimned enaraeteri:tics of thepi edeterr iirtesd 1-ase {aton ate t omse han a thre;hoid. varvtna the resriectior: parameters to nulce tt more likely that the neighbouring base station will he selected by the mobile terminal.

6. The method of claim 1,2,3,4 or 5, wherein the determined radio characteristic is coverage, e.g. RSCP.

7. The method of claim 1,2.3.4,5 or 6, wherein the determined radio characteristic is quality, e.g. Echo.

8. The method of any one of claims 2 to 7, wherein the reselection parameters comprise a threshold of the coverage and/or quality of the predetermined base station, below which the mobile tenninal measures the radio characteristics of the neighbouring base station for the purpose of making a reselection decision.

9. The method of any one of claims 2 to 8, wherein the reselection parameters comprise an amount by which the radio characteristics of the neghbour base station must be better than those of the predetermined base station before rcselection by the mobile terminal occurs.

1 0. Thc method of any one of the preceding claims, wherein the predetermined base station comprises a Fcmtoceil.

H. The method of any one of claims 1 to 9, wherein the predetermined base station comprises a macro base station.

12. Th.e method of any one of claims 1 to 11, wherein the mobile terminal measures the radio characteristics of the neighbouring: base station and reports these to the predetermined base station.

13. The method of any one of claims I to 1 2, wherein the determination of the radio characteristics is performed by the predetermined base station.

14. The method of any one of claims 1 to 13, wherein only the reselection parameters of a mobile terminal registered for use with the predetermined base station are adjustable.

1 5. The method of any one of claims 1 to 14, wherein the predetermined base station transmits reselection parameters to the mobile terminal.

16. The method of any one of' claims I to 1 5, wherein the reselection parameters apply to inter and intra carrier reselection, 17. A base station adapted to control the reselection method of a mobile terminal camped on the base station, which mobile terminal performs a cell reselection function in accordance with reselection parameters, the base station including means for determining the radio characteristics of at least onc neighbouring base station, and mobile terminal programming means for scicctiveiy varying the rescicction parameters of the mobile terminal in dependence upon the determined radio characteristics of the neighbouring base staton to alter the likelihood that the neighbouring base staflon will he selected by the mobile termInal.18. The base station of claim 17, including means for determining the radio characteristics of the base station with respect to the mobile terminal.19, The base station of claim 17 or 18, wherein the programming means, when. the determined radio characteristics of the neighbouring base station are better than a threshold, is operable to vary the reselection parameters to alter the likelihood that the neighbouring base station will he selected by the mobile terminal, 20. The base station of claim iS, wherein the programming means, when the predetermined characteristics of the neighbouring base station are better than a threshold and the determined characteristics of the base station are better than a threshold, is operable to vary the reselection parameters to make it less likely that the neighbouring base station will he selected by the mobile terminal.21. The base station of claim 18 or 20, wherein the programming means, when the predetermined characteristics of the neighbouring base station cell are better than a threshold and the determined characteristics of the base station are worse than a threshold, is operable to vary the reselection parameters to make it more likely that the neighbouring base station will he selected by the mobile terminal.22. The base station of claim 17,18,19,20 or 21, wherein thc determined radio characteristic is coverage, e.g. RSCP.23. The base station of claim 17,18,19,2021 or 22, wherein the determined radio characteristic is quality, e.g. bc/Jo.24. The base station of any one of claims 18 to 23, wherein the reselection parameters comprise a threshold of' the coverage and/or quality of the base statiotL below which the mobile terminal measures the radio characteristics of the neighbouring base station for the purpose of making a reselection decision.25. The base station of any one of' claims 18 to 24, wherein the reselection parameters comprise an amount by which the radio characteristics of the neighbour base station must he better than those of the predetermined base station before reseiecton by the mobile terminal occurs.26. The base station of any one of claims 1 7 to 25, wherein the base station comprises a Femtocell.27. The base station of any one of claims 17 to 25, wherein the base station comprises a macro base station.28. The base station of any one of claims 17 to 27, wherein the mobile terminal measures the radio characteristics of the neighbouring cell and reports these to the base station whereby the base station determines the radio characteristics.29. The base station of any one of claims 17 to 28, wherein the determining means includes means fbr measuring the radio characteristics.30. The base station of any one of claims 17 to 29, wherein the programming means transmits reselection parameters to the mobile terminal.3 i. A telecommunications system including a base station as claimed in any one of claims i 7 to 30, the mobile terminal and the neighbouring base station.32. The system of claim 31, operable in accordance with the method of any one of claims 1 to 16.33. A base station reselection method, substantially as hereinbefore described with reference to andior substantially as illustrated in any one of or any combination of Figures 3 to 5 of the accompanying drawings.34. A base station substantially as hereinhefore described with reference to and/or substantially as illustrated iii any one of or any combination of Figures 3 to 5 of the accompanying drawings.35. A telecommunications system substantially as hereinbefore described with reference to and/or substantially as illustrated in any one of or any combination of Figures 3 to 5 of the accothpanying drawings.