Title of Invention

A METHOD FOR THE SELECTION OF PREFERRED NETWORK SYSTEM IN A MULTI-RAT DEPLOYED ENVIRONMENT

Abstract

The invention is about a method for performing the selection of preferred Radio Access Technology (RAT) network for a multi-mode mobile station (MS) in a multi-RAT deployed environment depending upon MS position / location co-ordinates and RAT coverage profile. The present invention proposes to choose the preferred network system as per the information contained in RAT coverage profile message from the network and position / location co-ordinates of the Mobile Station, instead of the conventional method of performing periodic measurements for all systems, which are more preferable than the current system as per system selection table. RAT coverage profile, which is maintained in a location server includes the coverage profile of various RATs at various locations in that region and is estimated / determined with the help of extensive RF measurements and drive tests. The network acquires the RAT coverage profile pertaining to the position / location coordinates of the MS by querying the location server that contains the extensive network coverage profile for all the systems present at any location in the multi-RAT deployed environment and sends the RAT coverage profile in response to that particular location informed by the MS.

Full Text

FIELD OF THE INVENTION This invention in general pertains to the Wireless communication technology and in particular to cellular systems. Further, this invention relates to a method for a preferred system selection in a multi-RAT (Radio Access Technology) deployment scenario. More particularly, this invention relates to a method for performing the selection of preferred Radio Access Technology (RAT) network for a multi-mode mobile station (MS) in a multi-RAT deployed environment depending upon MS position location co-ordinates and RAT coverage profile. DESCRIPTION OF RELATED ART In a typical cellular system, a wider region is divided into cells and each cell is covered by a BTS (Base Transfer Station). Usually an operator deploys only one RAT (Radio Access Technology) in all these cells as shown in Fig 1. The RAT or network system can be CDMA2000, GSM, UMTS, 4G etc. In such a single RAT, when the Mobile station (MS) is powered on, it measures the signal strength of various frequencies or codes of the deployed RAT and camp on to it Then MS receives all system information by listening to overhead messages from the network, which consists of Mobile Switching Center (MSC) and Base station (BS) that is responsible for air-interface connection with MS. Also MS registers with the network (NW) by sending registration message. Once the registration is made MS becomes ready to receive or originate calls to exchange user traffic. In order to originate a call MS should send an origination message. Then NW assigns appropriate resources to MS. These actions enable MS and NW to perform service negotiation and start exchanging user traffic. The advent of new RATs having extra capabilities in terms of more capacity, higher data rates, optimize qualities for various services, better QoS (quality of service), etc bestows the operators with various choices and hence makes them concerned about the need to deploy the new RATs in order to capitalize on the various advantages/features of the newly developed and standardized RATs. The operators can either deploy new RAT in the entire region of their operation at once or can go for phase wise deployment. If the first option is exercised, old RAT has to be totally phased out thus making the existing mobile stations unusable. Also the process is very costly. In the case of "Phase wise deployment" of new RATs, the implementation is done by overlaying the new RAT on the existing RAT in selective regions depending on the demands for the new capabilities and services. This choice is preferable as it has many advantages like less initial cost, on-demand basis, less risk etc. Consequently as time progresses there will be so many RATs available with various capabilities and optimized for various services based on the user's requirements and therefore results in a multi-RAT environment where there are many RATs existing and are widely deployed by various operators. One of such deployment scenarios is shown in Figure 2. When there are many RATs in a regional, it has to be ensured that the mobile station (MS) is always on a RAT, which is preferable for the MS to camp on in its IDLE state i.e. the state when there is no connection established with network for user data exchange. Therefore the MS should check whether the present RAT is the preferred RAT in the region and also take decision to switch from non-preferred RAT to a preferred RAT, which is listed in system selection table as higher in priority when compared to the currently camped RAT. The working of the prior art system determination method is diagrammatically represented in Figure 3. It can be seen that when MS is powered on, it enters into System determination module and looks for the preferred RAT based on system selection table or user setting. If the preferred system is found, MS camps on to that system and keeps performing RF/channel and usual procedures for the current system and stays on it. Also when MS is on preferred system, whenever RF channel power of preferred RAT is below some threshold, then MS can search for other available RATs in the order of preference (as per system selection table) and camp onto the available RAT. If the current network is not the most preferred system, MS periodically searches for the better system observing the priority in the selection table and shifts to the better system if found. To summarise the teachings of the prior art, when the MS is in a non-preferred RAT network then it keeps measuring periodically the RF channel power of RATs in the order of preference. If the RF channel power of any other RAT, which is more preferable than the current RAT is determined, then MS can simply tune to the preferred RAT network. Once it is tuned to the preferred RAT, then MS can simply monitor the preferred RAT's RF channel power for IDLE handoff purpose. At any time, if it is found that the RF channel power of preferred RAT is below some threshold, then MS can search for other available RATs in the order of preference as per system selection table and camp onto the available RAT. Even though the selection of preferred RAT is possible, it has many limitations. One of the major drawbacks is that there is no way for MS to recognize that it is in the preferred NW and therefore extensive RF measurements by way of polling are needed. If period of measurement is less, then RF measurements for preferred RAT is too often and hence results in too much of processing power consumption in tuning to new RAT and processing for RF - measurements. Its adverse effect is the reduction in IDLE mode sleep time (when MS is operating in slotted mode) causing more consumption of battery power. Similarly, if period is too high, then measurements for preferred RAT are seldom and consequently MS camps on the non-preferred RAT for too long even though preferred RAT is available. In this case also MS looses the valuable sleep time whenever the preferred RAT Radio Frequency measurement is triggered. In light of the foregoing limitations for network selection in multi RAT scenario, the present invention proposes to choose the preferred network system as per the information contained in RAT coverage profile message from the network and position location co-ordinates of the Mobile Station, instead of performing periodic measurements for all systems, which are more preferable than the current system as per system selection table. RAT coverage profile includes the coverage profile of various RATs at various locations in that region and is estimated / determined with the help of extensive RF measurements and drive tests. Advantageously, the position location co-ordinates representing the precise current location of MS can be estimated with the help of position location technologies such as "Global Position System" (GPS). Also a location server wilt be provided to maintain RAT coverage profile and various other location related information. SUMMARY OF THE INVENTION The primary object of the present invention is to provide a method for selecting the preferred RAT network for a mobile station using RAT coverage profile messages from the network and position location co-ordinates of the Mobile Station. It is another object of the invention to provide a system for the selection of a preferred network system in a multi-RAT deployed environment in which the network acquires the RAT coverage profile pertaining to the position location coordinates of the MS by querying the location server that contains the extensive network coverage profile for all the systems present at any location in the multi RAT environment and sends the RAT coverage profile in response to that particular location informed by the MS. It is yet another object of the invention to provide a quick system selection procedure by directly attempting the best system available with the help of extra information such as RAT info, band class, channel number, CDMA code etc. given in RAT coverage profile message from network. It is a further object of the invention to facilitate the registration of the MS with the system by sending a registration message once the preferred RAT is acquired and to send the power down registration message to the current RAT before leaving the current RAT so as to inform that it is leaving the RAT. It is also an object of the invention to save the battery power and increase sleep time by avoiding unnecessary search for the systems that are not available at that location and also by enabling the network to make the system selection frequency dynamic based on MS location and RAT coverage profile information. Accordingly, the present invention comprises a method for selecting a preferred Radio Access Technology (RAT) Network by a multi-mode Mobile station (MS) while camping on a less priority system in a multi-RAT deployed environment depending upon MS position location co-ordinates and RAT coverage profile, the method comprising the steps of: (a) passing a position location co-ordinates of the mobile station to the current network; (b) receiving the RAT coverage profile of the said location from the network; (c) inspecting the RAT coverage profile in order to check if there is any preferred/better system at the current location; (d) ascertaining whether the signal strength is sufficient in the better system if found; and (e) sending "power down registration" message to the current network, camping on to the newly selected system and placing a registration message. Other advantages and features of the invention will become more readily apparent from the following description of an embodiment of the invention given as a non-restrictive example only and represented in the accompanying drawings. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 shows a typical deployment of a network with single RAT in a given region. Figure 2 depicts a typical deployment of network with multiple RATs in a given region. Figure 3 represents a flow chart for illustrating the MS system determination procedure for the selection of preferred network in prior art. Figure 4 is a Message Sequence chart for MS getting RAT coverage profile information from NW in preferred embodiment of the invention. Figure 5 presents the flow chart for illustrating the MS system determination procedure for the selection of preferred network in preferred embodiment. DETAILED DESCRIPTION OF THE INVENTION The preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. It should be understood however that the disclosed embodiments are merely exemplary of the invention, which may be embodied in various forms. The following description and drawings are not to be construed as limiting the invention and numerous specific details are described to provide a thorough understanding of the present invention, as the basis for the claims and as a basis for teaching one skilled in the art on how to make and/or use the invention. However, in certain instances, well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail. For example, the description or identification of fields in each message are not critical for illustrating the idea, while the description of the message is understood when one goes through the steps of the related art. Similarly Timers and other negative scenarios are not captured in the diagrams, as these are not critical for illustrating the idea. The description is intended to serve merely as the basis for the claims and as a basis for teaching one skilled in the art how to make or use the invention. Also it should be noted that in this document "RAT" and "System" are used interchangeably and therefore "preferred RAT" and "preferred System" mean the same. Further, the description assumes that the MS has position location capability like GPS functionality and is capable of operation in multimode i.e. it supports Multiple RATs and their frequencies. The description also assumes that NW has enough information on which region is covered by what all RATs/NWs. This RAT coverage profile can be determined with the help of various measurements and database is maintained at network side. In order to facilitate the better understanding of the invention, a brief description of the prior art method for selection of preferred network is herein described below with reference to Figures 1,2 and 3. Fig 1 illustrates a typical deployment of a network with single RAT in a given region whereas in figure 2 is shown a deployment of network with multiple RATs in a given region. Accordingly for the purpose of illustration, four locations in the figure 2 are shown representing the locations of the mobile station at different times while roaming. Here it is assumed that MS has camped on to CDMA2000 system RAT at the time of power-up as per its system selection table. The order/preference of systems in system selection table is assumed to be: UMTS, CDMA2000, GSM and Wi-Fi. Now the selection of the preferred RAT in each location (as MS is moving from one location to another location) is detailed below. Location-1: This position location is covered by only one RAT i.e. CDMA2000 and MS are currently camped onto CDMA2000. Since only CDMA2000 is available, MS continues to camp onto the CDMA2000 system. But MS periodically sends its position location information to NW in order to get NW coverage profile in the region with respect to position changes. Location-2: This position location is covered by two RATs viz. CDMA2000 and GSM and MS is currently camped onto CDMA2000. MS periodically sends its position location information to NW in order to get NW coverage profile in the region with respect to position changes. Upon seeing the NW coverage profile request from MS, NW checks the available RATs at current MS location and sends message to MS informing the presence of both CDMA2000 and GSM NW. Based on the information; MS takes the decision to continue with CDMA2000 as it is more preferred system than GSM as per system selection table. Location-3: This position location is covered by two RATs i.e. CDMA2000 and UMTS and MS is currently camped onto CDMA2000. MS periodically sends its position location information to NW in order to get NW coverage profile in the region with respect to position changes. In these conditions, upon seeing the NW coverage profile request from MS, NW checks the available RATs at current MS location send message to MS containing information about the availability of UMTS and CDMA2000. This time, MS selects UMTS based on the table given above and try to acquire the system. Once UMTS is acquired MS will not send NW coverage profile request to NW as long as MS is camped on to UMTS, as UMTS is the most preferred system. Location-4: This position location is covered by three RATs viz. CDMA2000, UMTS and Wi-Fi and MS is currently camped onto UMTS. Since MS is already camped on to most preferred system (i.e. UMTS in this example), MS will not send NW coverage profile request to NW. The working of the prior art system determination method is diagrammatically represented in figure 3.It can be seen that when MS is powered on, it enters into System determination module and looks for the preferred RAT based on system selection table or user setting. If the preferred system is found it camps on to that system and keeps performing RF/channel measurements on that preferred system. Then the MS performs measurements and usual procedures for the current system and stays on to it if it is the most preferred system. If the current network is not the most preferred system it periodically searches for the better system observing the priority in the selection table and shifts to the better system if found. If MS doesn't find the preferred system it exits from searching for the preferred RAT, and search for less preferred RAT. Also if signal strength is not adequate then MS can select a RAT, which is available at current location that could be less preferable and as per system selection table. Now the operation of the present invention is illustrated with reference to Figure 5. It can be seen that the MS camps onto the most preferred system when determined and utilizes the services of the network. If MS sees that RF/channel power of most preferred system is at unacceptable level consistently for some time, then MS tries to acquire the less preferred system as per system selection table order and camps onto the available system. It means that if MS is on and it moves from most preferred area to less preferred area while on a voice/data call then call may be disconnected. According to a preferred embodiment of the invention, when the MS camps on to the less preferred system, MS continues to perform RF channel (eg: pilot channel in CDMA2000) power measurements in the selected system and informs about its position location co-ordinates (for eg: GPS co-ordinates) to NW. In response to this message NW sends the RAT coverage profile that contains RATs covered at that particular location to MS. These messages can even be transmitted in Short messaging Service (SMS) with operator specific tele-service IDs. The period for this communication between MS and NW can be decided or dynamically configured from the NW from time to time based on RAT deployment scenario and based on MS location. By analyzing the RAT coverage profile, MS can determine whether there is any preferred/better system is available at the current location. If a better system is available then MS searches and tunes to the preferred system. Before MS leaves the current RAT, it sends the power down registration message to the current RAT to inform it that it is leaving the RAT. Also once it acquires the preferred RAT registers with the system by sending registration message. These operations can be seen in the message sequence chart in figure 4. According to the invention the RAT coverage profiles are determined by extensive RF measurements and drive tests and are stored in location server, which can contain the extensive network coverage profile for all the systems present at any location in the multi RAT environment. In order to provide the RAT profile information to MS, network acquires the RAT coverage profile by querying the location server. Finding or camping on to new system can be hastened by adding some extra information like band class, channel number and CDMA code etc in the RAT coverage profile message sent by NW. Therefore it is understood that for selecting the best RAT according to the present invention, MS uses the following information: 1. MS capability information including different RATs and band classes supported by MS. 2. System selection table in MS, which consists of different RATs (and their band classes) supported by MS and the corresponding order of preference of RATs. 3. MS position location co-ordinates determined with the help of Global Positioning system or by some other methods. 4. RAT coverage profile at the place where MS is currently located 5. Signal strength of best RAT as seen at MS. It will also be obvious to those skilled in the art that other control methods and apparatuses can be derived from the combinations of the various methods and apparatuses of the present invention as taught by the description and the accompanying drawings and these shall also be considered within the scope of the present invention. Further, description of such combinations and variations is therefore omitted below. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are possible and are apparent to those skilled in the art. Such changes and modifications are to be understood as included within the scope of the present invention as defined by the appended claims unless they depart therefrom. WE CLAIM 1. A method for selecting a preferred Radio Access Technology (RAT) Network by a multi-mode Mobile station (MS) while camping on a less priority system in a multi-RAT deployed environment depending upon MS position location co-ordinates and RAT coverage profile, the method comprising the steps of: (a) passing a position location co-ordinates of the mobile station to the current network; (b) receiving the RAT coverage profile of the said location from the network; (c) inspecting the RAT coverage profile in order to check if there is any preferred/better system at the current location; (d) ascertaining whether the signal strength is sufficient in the better system if found; and (e) sending "power down registration" message to the current network and camping on to the newly selected system after placing registration message. 2. The method as claimed in claim 1 wherein the priority of RATs is determined according to the order in a system selection table in the mobile station. 3. The method according to claim 1 wherein the mobile station does not send RAT coverage profile request when it is camping in a most preferred RAT. 4. The method according to claim 1 wherein if signal strength of the most preferred system is not adequate, then MS selects a RAT, which is available at current location but less preferable compared to the existing RAT. 5. The method according to claim 1 wherein the messages between the mobile station and network is transmitted in Short Messaging Service (SMS) with operator specific tele-services ID. 6. The method as claimed in claim 1 wherein the network acquires the said RAT coverage profile by querying a location server that contains the extensive network coverage profile for all the systems present at any location in the multi RAT environment. 7. The method as claimed in claim 6 wherein the said RAT coverage profiles of the region to be stored in the location server are determined by extensive radio measurements and drive tests. 8. The method as claimed in claim 6 wherein the RAT coverage profile further contains band class, channel number and CDMA code for enabling a quick selection procedure. 9. The method as claimed in claim 1 wherein the said position location co-ordinates are determined by Global Positioning System (GPS) receiver in the mobile station. 10. The method according to claim 1 wherein the mobile station periodically sends its position location information to network in order to get network coverage profile in the region with respect to position changes. 11. The method as claimed in claim 1 wherein the mobile station performs Radio Frequency (RF) measurements on a RAT which is more preferable than the current system if a preferred system is said to be available at that location by network coverage profile information. 12. The method according to any of the claims wherein the RAT employs CDMA2000, GSM, UMTS or Wi-Fi technology. 13. A method for selecting a preferred Radio Access Technology (RAT) Network by a multi-mode Mobile station (MS) while camping on a less priority system in a multi-RAT deployed environment depending upon MS position location co-ordinates and RAT coverage profile, substantially as herein above described and illustrated with reference to the accompanying drawings. Dated this 31st day of December 2004

Documents:

1482-che-2004 claims-duplicate.pdf

1482-che-2004 desscription(complete)-duplicate.pdf

1482-che-2004 form-19.pdf

1482-che-2004-abstract.pdf

1482-che-2004-claims.pdf

1482-che-2004-correspondnece-others.pdf

1482-che-2004-correspondnece-po.pdf

1482-che-2004-description(complete).pdf

1482-che-2004-drawings.pdf

1482-che-2004-form 1.pdf

1482-che-2004-form 13.pdf

1482-che-2004-form 26.pdf

1482-che-2004-form 5.pdf