US 20090286542A1 (19) United States (12) Patent Application Publication (10) Pub. No.: US 2009/0286542 A1 ROBERTS et al. (43) Pub. Date: Nov. 19, 2009 (54) METHOD AND APPARATUS FOR Publication Classification TRANSTONING FROMA FIRST RAT TO A (51) Int. Cl. SECOND RAT H04.736/00 (2009.01) (75) Inventors: Gideon ROBERTS, Surrey (GB); H04M I/00 (2006.01) Sukhdev SAINI, Surrey (GB) (52) U.S. Cl. ...................................... 455/436: 455/552.1 Correspondence Address: CONLEY ROSE, PC. 5601 GRANITE PARKWAY, SUITE 750 (57) ABSTRACT PLANO, TX 75024 (US) A method, in a wireless communications device having a first (73) Assignee: RESEARCH IN MOTION protocol stack for use with a first radio access technology and LIMITED, Waterloo (CA) a second protocol stack for use with a second radio access technology, the method for transitioning from a first radio (21) Appl. No.: 12/463,124 access technology to a second radio access technology, the method comprising: maintaining a list of available commu (22) Filed: May 8, 2009 nication cells associated with the second radio access tech nology, and transferring information associated with more Related U.S. Application Data than one available communication cell associated with the (60) Provisional application No. 61/052,085, filed on May second radio access technology from the first protocol stack 9, 2008. to the second protocol stack. 2O1 Start 2O2 Maintain List of available UMTS cells 2O3 Identify transition from GPRS to UMTS required 2O4. Transfer List of available UMTS cells from GPRS protocol stack to UMTS protocol stack Attempt to connect to a 2O5 first listed available UMTS Cell Attempt to connect 2O7 Attempt to further listed Successful? available UMTS cell END 208 Patent Application Publication Nov. 19, 2009 Sheet 1 of 4 US 2009/0286542 A1 112 110 Fig. 1 Patent Application Publication Nov. 19, 2009 Sheet 2 of 4 US 2009/0286542 A1 Maintain List of available UMTS cells 2O3 ldentify transition from GPRS to UMTS required 204 Transfer List of available UMTS cells from GPRS protocol stack to UMTS protocol stack Attempt to connect to a 205 first listed available UMTS Cell Attempt to connect 2O7 Attempt to further listed Successful? available UMTS Cell Fig. 2 Patent Application Publication Nov. 19, 2009 Sheet 3 of 4 US 2009/0286542 A1 Star" 302 Maintain List of available GPRS Celts 303 identify transition from UMTS to GPRS required 304 Transfer List of available GPRS Cells from UMTS protocol stack to GPRS protocol stack Attempt to connect to a 305 first listed available GPRS cell 306 Attempt to connect 307 Attempt to further listed Successful? available GPRS Cell 308 END Fig. 3 Patent Application Publication Nov. 19, 2009 Sheet 4 of 4 US 2009/0286542 A1 Og6||IOq[B?IÐS -OJO?W JOSS93OJd y'61-I US 2009/0286542 A1 Nov. 19, 2009 METHOD AND APPARATUS FOR 0008 FIG. 1 is a schematic diagram showing an overview TRANSTONING FROMA FIRST RAT TO A of a network and a UE device; SECOND RAT 0009 FIG. 2 is a flow diagram showing, at a high level, a process performed by the UE during an inter-RAT cell rese CROSS-REFERENCE TO RELATED lection as described herein; APPLICATIONS 0010 FIG. 3 is a flow diagram showing, at a high level, a 0001. The present application claims priority to U.S. Pro process performed by the UE during an alternative inter-RAT visional Patent Application No. 61/052,085, filed May 9, cell reselection; and 2008, by Gideon Roberts, et al, entitled “Method and Appa 0011 FIG. 4 is a block diagram illustrating a mobile ratus for Transitioning From a First RAT to a Second RAT device, which can act as a UE in accordance with the (31496-US-PRV 4214-08000), which is incorporated by approach described herein. reference herein as if reproduced in its entirety. DETAILED DESCRIPTION OF THE DRAWINGS TECHNICAL FIELD 0002 This application relates to telecommunication sys 0012 Consider a wireless mobile device, generally tems in general, having for example application in UMTS referred to as user equipment (UE), which complies with the (Universal Mobile Telecommunications System) and in par 3GPP specifications for the UMTS protocol. The 3GPP ticular relates to a method and apparatus for transitioning 25.304 specification, V 7.1.0, incorporated herein by refer from a first Radio Access Technology (RAT) to a second ence and referred to herein as the 25.304 specification, Radio Access Technology (RAT). addresses the subject of User Equipment (UE) procedures in idle mode and procedures for cell reselection in connected BACKGROUND mode. (0013 Section 5.2 of the 25.304 specification defines cell 0003. In a typical cellular radio system, mobile user equip selection and reselection in idle mode. This applies to UES ment (UE) communicates via a radio access radio network that support at least a UMTS (3G) network. Different types of (RAN) to one or more core networks. User equipment (UE) measurements are used in different RATs and modes for cell comprises various types of equipment such as mobile tele selection and reselection. The performance requirements for phones (also known as cellular or cell phones), laptops with the measurements are specified in 3GPP TS 25.133 “Require wireless communication capability, personal digital assis ments for Support of Radio Resource Management (FDD) tants (PDAs) etc. These may be portable, hand held, pocket and 3GPP TS 25.123 “Requirements for Support of Radio sized, installed in a vehicle etc and communicate Voice and/or Resource Management (TDD), both incorporated herein by data signals with the radio access network. reference. The non-access stratum can control the RAT(s) in 0004. In the following, reference will be made to UMTS which the cell selection should be performed, for instance by and to particular standards. However it should be understood indicating RAT(s) associated with the selected Public Land that this disclosure is not intended to be limited to any par Mobile Network (PLMN), and by maintaining a list of for ticular mobile telecommunications system or standard. bidden registration area(s) and a list of equivalent PLMNs. 0005. The radio access network covers a geographical area The UE selects a suitable cell and the radio access mode based divided into a plurality of cell areas. Each cell area is served on idle mode measurements and cell selection criteria. by at least one base station, which in UMTS may be referred 0014. In order to speed up the cell selection process, stored to as a Node B. Each cell is identified by a unique identifier information for several RATs may be available in the UE. which is broadcast in the cell. The base stations communicate When camped on a cell, the UE shall regularly search for a at radio frequencies over an air interface with the UEs within better cell according to the cell reselection criteria. If a better range of the base station. Several base stations may be con cell is found, that cell is selected. The change of cell may nected to a radio network controller (RNC) which controls imply a change of RAT. The non-access stratum is informed various activities of the base stations. The radio network if the cell selection and reselection results in changes in the controllers are typically connected to a core network. received system information. For normal service, the UE has 0006 UMTS is a third generation public land mobile tele to camp on a suitable cell, tune to that cell's control channel(s) communication system. Various standardization bodies are so that the UE can receive system information from the known to publish and set standards for UMTS, each in their PLMN. respective areas of competence. For instance, the 3GPP (0015 Section 5.2.5.1 of the 25.304 specification defines (Third Generation Partnership Project) has been known to the UE activity in a camped normally state for the case of publish and set standards for GSM (Global System for connection to a UMTS cell. When camped normally, the UE Mobile Communications) based UMTS, and the 3GPP2 performs necessary measurements for the cell reselection (Third Generation Partnership Project 2) has been known to evaluation procedure. The UE also executes the cell reselec publish and set standards for CDMA (Code Division Multiple tion evaluation process when appropriately triggered. The Access) based UMTS. Within the scope of a particular stan cell reselection evaluation process may be triggered by a UE dardization body, specific partners publish and set standards internal trigger or when information on the broadcast control in their respective areas. channel (BCCH) used for the cell reselection evaluation pro cedure has been modified. BRIEF DESCRIPTION OF THE DRAWINGS 0016. Problems with inter-RAT cell reselection in a UE 0007 Embodiments will now be described, by way of have been identified, particularly in the case of an inter-RAT example only, with reference to the attached drawings, in cell reselection from a 2GRAT (such as GSM or GPRS) to a which: 3GRAT (such as UMTS). There are thus proposed strategies US 2009/0286542 A1 Nov. 19, 2009 for a method and apparatus for transitioning from a first RAT GPRS protocol stack to the UMTS protocol stack. At 205 the to a second RAT. A number of such strategies are detailed UE attempts to connect to a first listed available UMTS cell. below. At 206 a determination is made as to whether the attempt was 0017. Other aspects and features of the proposed strategy successful. If the attempt was not successful, then the UE will become apparent to those ordinarily skilled in the art attempts to connect to a further available UMTS cell as listed upon review of the following description of specific embodi in the list transferred from the GPRS protocol stack to the ments of a method and apparatus for transitioning from a first UMTS protocol stack.