Title of Invention

A METHOD FOR MOBILE ASSISTED HARD HANDOFF (MAHHO) IN 1X EV-DO CDMA2000 COMMUNICATION SYSTEM

Abstract

This invention is a method, which enable access terminal to assist the access network inter-frequency hard handoff in communication system which comprises determining the serving frequency candidate sectors by the access terminal, determining the other frequency candidate sectors by the access terminal, sending RouteUpdate message to the access network with the status, evaluating the status of every pilot received in the RouteUpdate message by access network and sending TrafficChannelAssignment message to access terminal. The present invention in general relates to the Communication technology. Specifically the present invention relates to the Inter-frequency hard handoff, other frequency search, HDR 1x EVDO communication system, MAHHO. More particularly the present invention encompasses a method for mobile assisted Inter-frequency hard handoff (MAHHO) in 1x EV-DO CDMA2000 communication system.

Full Text

FIELD OF THE INVENTION The present invention in general relates to the Communication technology. Specifically the present invention relates to the Inter-frequency hard handoff, other frequency search, HDR 1x EVDO communication system, MAHHO. More particularly the present invention encompasses a method for mobile assisted Inter-frequency hard handoff (MAHHO) IN1x EV-DO CDMA2000 communication system. DESCRIPTION OF RELATED ART In cellular communication system, a region is divided into cells. Each cell can further be sub-divided into sectors. In CDMA system, each sector is represented by a pilot channel (specified by the pilot's PN [Pseudo Noise] offsetand the pilot's CDMA [Code Division Multiple Access] Channel). A PN offset is one of the 512 codes used to differentiate sectors on base stations for communication with the mobile units. PN stands for pseudo random noise that appears in a repetitive manner. Access terminal uses this pilot channel to synchronize with the base station, to extract phase information for coherent detection and to measure the strength of forward link. As access terminal (AT) moves across, it moves from one sector (cell) to another sector (cell). In connected state, for access terminal to maintain the communication link, access terminal continuously measures the strength of pilots in its current and neighboring sectors. As and when access terminal sees the changes in radio environment (like decrease in active sector's pilot strength and increase in another sector's pilot strength), it reports the measurement results to access network (AN). Upon evaluating access terminal's report, access network can decide to handoff the access terminal (or put access terminal in soft handoff) to (/with) another sector. In 1x-EVDO system, in the connected state, access terminal continuously monitors the radio link between the access terminal and access network by measuring the strength of the pilots transmitted by the current and neighbor sectors. Access terminal maintains the following pilot sets to monitor the radio link between the access network and access terminal. Active Set: The set of pilots (specified by the pilot's PN offset and the pilot's CDMA Channel) associated with the sectors currently serving the access terminal. When a connection is open, a sector is considered to be serving an access terminal when there is a Forward Traffic Channel, Reverse Traffic Channel and Reverse Power Control Channel assigned to the access terminal. When a connection is not open, sector is considered to be serving the access terminal when the access terminal is monitoring that sector's control channel. Candidate Set: The pilots (specified by the pilot's PN offset and the pilot's CDMA Channel) that are not in the Active Set, but are received by the access terminal with sufficient strength to indicate that the sectors transmitting them are good candidates for inclusion in the Active Set. Neighbor Set: The set of pilots (specified by the pilot's PN offset and the pilot's CDMA Channel) that are not in either one of the two previous sets, but are likely candidates for inclusion in the Active Set. Remaining Set: The set of all possible pilots (specified by the pilot's PN offset and the pilot's CDMA Channel) on the current channel assignment, excluding the pilots that are in any of the three previous sets. The access terminal continually searches for pilots in the connected state. The access terminal searches for only the serving frequency pilots in all pilot sets as the procedures illustrating how and when to perform the other frequency search by access terminal are not specified in 1x EVDO communication system. The access terminal measures the strength of every pilot it searches. The strength estimate formed by the access terminal is computed as the sum of the ratios of received pilot energy per chip, Ec, to total received spectral density, l0 (signal and noise) for at most k multi-path components, where k is the maximum number of multi-path components that is demodulated simultaneously by the access terminal. The access terminal sends a RouteUpdate message to the access network in the connected state to request addition or deletion of pilots from its Active Set based on its measurements of the pilot strengths of sectors in its neighborhood. The access terminal includes in the RouteUpdate message the pilot PN phase, pilot strength, and drop timer status for every pilot in the active set and the candidate set. Access Network evaluates the status of every pilot received in the RouteUpdate message. Access Network sends TrafficChannelAssignment message to Access Terminal if it decides to change the active set based on its evaluation of the RouteUpdate message. The access terminal updates its active set on receiving the TrafficChannelAssignment message and sends the access network a TrafficChannelComplete message. The access network updates its active set on receiving the TrafficChannelComplete message. Figure 1 Messages exchanged between AT(Access Terminal) and AN (Access Network) in related art. The following are the steps of the existing art: 1. In the connected state, access terminal determines the serving frequency candidate sectors by monitoring the signal strength* of the forward pilot channel (specified by the pilot's PN offset and the pilot's CDMA channel) transmitted by sectors in all pilot sets which belongs to the serving frequency. Note: The access terminal searches for only the serving frequency pilots in all pilot sets as the procedures illustrating how and when to perform the other frequency search by access terminal are not specified in 1x EVDO communication system. 2. Access terminal sends** RouteUpdate message to the access network with the status (e.g. pilot strength, pilot PN phase, and drop timer) of ■ every pilot in the active set pilots in the candidate set corresponding to the serving frequency 3. Access network evaluates the status of every pilot received in the RouteUpdate message. Access network sends*** TrafficChannelAssignment message to access terminal if it decides to change the active set based on its evaluation of the RouteUpdate message. * The strength estimate formed by the access terminal shall be computed as the sum of the ratios of received pilot energy per chip, Ec, to total received spectral density, lo (signal and noise) for at most 'k' multi-path components, where (k' is the maximum number of multi-path components that can be demodulated simultaneously by the access terminal. ** In the connected state, RouteUpdate messages from the access terminal are based on changes in the radio link between the access terminal and the access network, obtained through pilot strength measurements at the access terminal. *** The Access Network sends a TrafficChannelAssignment message to the Access Terminal in response to changing radio link conditions, as reported in the Access Terminal's RouteUpdate messages. Note: The detailed procedure for moving the pilots from candidate set to neighbor set and vice versa and sending the RouteUpdate messages are given in the 3GPP2 standard (C.S0024-Av1.0). There are following limitations in the existing art: The above method works fine when all cells in that region are deployed with the same frequency as the access terminal's current serving frequency. The above method doesn't address the scenario wherein the neighboring sectors/cells are deployed with another frequency (i.e. frequency different from the access terminal's current serving frequency. So if access terminal is moving from the current sector/cell to another sector/cell which has different frequency (frequencies other than the serving frequency), then access terminal looses the connection. If access terminal attempts to measure the pilots on the other frequency, then access terminal will lose the data that is coming on the forward traffic channel. Standard doesn't specify the procedure on how to measure pilot strengths which are transmitted on other frequencies and hence the access network cannot initiate inter frequency hard handoff as it does not have the status of the pilots which belongs to other frequency. Figure 2 shows a Flow chart for the operation of related art. AT continually searches and measures the strength of serving frequency pilots. Then a check is made to confirm whether addition or deletion of pilot from active set required or not. If addition or deletion is required, AT sends RouteUpdate message to AN. Then a check is made to confirm whether Traffic Channel Assignment message is received or not. If the message is received, AT Updates it's active and candidate sets and AT sends TrafficChannelComplete message to AN. SUMMARY OF THE INVENTION In view of the above limitations the invention proposes a new art which will enable access terminal to assist the access network in deciding the handoff to other frequencies. Since access terminal (or Mobile station) assists access network in deciding about hard handoff (i.e. handoff between different frequencies), this procedure can be called as Mobile Assisted Hard handoff (MAHHO). The following solution is proposed to assist the access network in performing the inter-frequency hard handoff in 1x-EVDO communication system: 1. Access terminal determines the serving frequency candidate sectors by monitoring the signal strength* of the forward pilot channels (specified by the pilot's PN offset and the pilot's CDMA channel) transmitted by each sector in all the pilot sets list which belongs to the serving frequency. 2. Access terminal determines the other frequency candidate sectors by monitoring the signal strength* of the forward pilot channels transmitted by the sectors in the neighbor list which belongs to the frequencies other than the serving frequency. The procedures illustrating when and how to perform the other frequency search are given with reference to figures 3, 4 and 5 in the detailed description of this invention. 3. Access terminal sends** RouteUpdate message to the access network with the status (e.g. pilot strength, pilot PN phase, and drop timer) of ? every pilot in the active set ? pilots corresponding to the serving frequency candidate sectors ? pilots corresponding to the other frequencies candidate sectors 4. Access network evaluates the status of every pilot received in the RouteUpdate message. Access network sends*** TrafficChannelAssignment message to access terminal if it decides to change the active set based on its evaluation of the RouteUpdate message. * The strength estimate formed by the access terminal shall be computed as the sum of the ratios of received pilot energy per chip, Ec, to total received spectral density, l0 (signal and noise) for at most 'k' multi-path components, where 'k' is the maximum number of multi-path components that can be demodulated simultaneously by the access terminal. ** In the connected state, RouteUpdate messages from the access terminal are based on changes in the radio link between the access terminal and the access network, obtained through pilot strength measurements at the access terminal. *** The access network sends a TrafficChannelAssignment message (TCAM) to the access terminal in response to changing radio link conditions, as reported in the access terminal's RouteUpdate messages. This invention explains a method of enabling an access terminal to assist an access network inter-frequency hard handoff in communication system comprising the steps of: a.) determining plurality of serving frequency candidate sectors by the access terminal; b.) performing different frequency candidate sector search by the access terminal; c.) determining an other frequency candidate sectors by the access terminal; d.) sending a RouteUpdate message to the access network with a status of every pilot received; e.) evaluating the status of every pilot received in the RouteUpdate message by access network; and f) sending a TrafficChannelAssignment message to the access terminal. This invention further explains a method, of enabling access terminal to assist the access network inter-frequency hard handoff in communication system wherein access terminal performs different frequency search when : a. pilot strength of active set members is being decreased consistently and there is no feasible candidate on the serving frequency; b. OFSseach_timer is expired; or c. Sector switching or hard handoff is not in progress These and other objects, features and advantages of the present invention will become more readily apparent from the detailed description taken in conjunction with the drawings and the claims. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1: shows Messages exchanged between AT and AN in related art Figure 2: depicts a flow chart for the operation of related art Figure 3: shows Messages exchanged between AT and AN in the invention Figure 4: depicts a Flowchart for Other Frequency Search Procedure Figure 5: depicts a Flowchart for procedure to stop data transmissions by AN DETAILED DESCRIPTION OF THE INVENTION The preferred embodiments of the present invention will now be explained with reference to the accompanying drawings. The following description and drawings are illustrative of the invention and are not to be construed as limiting the innovation. Numerous specific details are described to provide a through understanding of the present invention. However in certain instances well-known or conventional details are not described in order not to unnecessarily obscure the present invention in detail. Figure 3 shows Messages exchanged between AT and AN which will assist in performing Inter Frequency Hard HandOff (IFHHO) in the invention. AN initially sends a neighbor list message to AT. AT then stores the list of neighbor sectors. AT measures the strength of pilots on serving frequency and also AT measures the strength of pilots on other frequencies. A RouteUpdate Message is sent from AT to AN. AN evaluates the status of each pilot received in RouteUpdate message and a TrafficChannelAssignment Message (TCAM) is sent by AN to AT. AT updates the active and candidate sets and performs IFHHO if a new channel record is included in the TCAM message and a TrafficChannelComplete Message is sent from AT to AN. AN Procedures No changes are required in the procedures of access network. AT Procedures Following procedures are added on access terminal side: ? Procedures which determines when the access terminal should perform other frequency search ? Procedures to perform Other Frequency Search (OFS) OFS Frequency Procedures (It determines when the access terminal should perform OFS): During the OFS, data cannot be received and transmitted by AT on the serving frequency. So other frequency search should be done only when it is necessary. AT performs OFS when the following conditions are satisfied, ■ After searching all the serving frequency members of the neighbor set once, pilot strength of active set members is being decreased consistently and there is no feasible candidate on the serving frequency. Or OFSseach_timer iS expired. Note: OFSseach_tmer = N* time required to search all the serving frequency members of the neighbor set once. Here, 'AT is a configurable parameter for configuration ■ Sector switching or hard handoff is not in progress. Other Frequency Search Procedures (It determines how the access terminal should perform other frequency search i.e the frequencies other then the serving fequency): Figure 4 shows a Flowchart for Other Frequency Search Procedure. Access terminal performs the following steps in sequence when the OFS procedure is invoked: 1. AT suspends the sector switching algorithm. 2. AT suspends generating RouteUpdate message from Route Update Protocol (RUP). 3. AT deactivates Control Channel MAC Protocol (CCMP). 4. AT deactivates Overhead Message Protocol (OMP). 5. AT makes sure that data packets will not be sent by AN during the OFS interval as it will not be monitoring the serving frequency during the OFS interval. Figure 5 shows a Flowchart for procedure to stop data transmission from AN. In order to ensure this, AT performs the following steps: The DRC message includes a data rate portion and a sector portion. Both data rate and sector information are typically required to process a data transmission. The data rate portion is referred to as a DRC value, and the sector portion is referred to as a DRC cover Stepl: AT sets DRC(Data Rate Control) Cover to NULL COVER. (AT initializes DRC - needs confirmation from the client) Step2: AT waits until the following conditions are met at time "T" which satisfies the equation: (T+1-FrameOffset) mod DRCLength = 0, where "T" is the system time in slots: a) DRC Cover is NULL COVER b) Packet reception is not in progress: There is no pending slots of the packet being received (For multi slot packets, slots of same packet are transmitted with 4 slot interlacing) c) The DRC Cover transmitted before the slot T is a Non NULL COVER but the DRC value is NULL. Or The DRC Cover transmitted before the slot T is also NULL COVER. 6. AT switches off the transmitter. 7. AT stops handoff drop timers corresponding to its current active set and candidate set members. 8. AT tunes to the other frequency. AT takes the samples of the pilot for OFSinterval- Pilot strengths of the sectors on this frequency are determined offline from the pilot samples collected during the OFSmtervai- Note: OFSinterval will be determined through simulations at the time of implementation. But it can typically take the value of 96 chips (at the rate of 1.2288 Mega chips per second). 9. AT tunes back to the serving frequency. 10. AT enables handoff drop timers corresponding to its current active set and candidate set members. 11. AT switches on the transmitter. 12. AT evaluates samples of other frequency to check if there is any better pilot available on that frequency. This is done with the help of pilots in neighbor list. There can be separate correlator circuit in access terminal to perform this calculations offline. 13. AT starts the sector switching algorithm. 14. AT starts generating RouteUpdate message from Route Update Protocol (RUP). 15. AT activates Control Channel Mac Protocol (CCMP). 16. AT activates Overhead Message Protocol (OMP). Note: All these procedures can be achieved within the framework of the existing standard. Advantages: 1. Access terminal assisting Access network in doing inter-frequency hard handoff by measuring the pilot strengths on other frequencies 2. Inter-frequency handoff without losing data on forward traffic channel 3. very cost effective and no NW (Network) modifications are needed in this procedure 4. All this procedure fits in the existing EV-DO defined standards frame work i.e. no changes are required in the existing signaling messages In the description herein, numerous specific details are provided, such as examples of components and/or methods, to provide a thorough understanding of embodiments of the present invention. One skilled in the relevant art will recognize, however, that an embodiment of the invention can be practiced without one or more of the specific details. In other instances, well-known operations are not specifically shown or described in detail to avoid obscuring aspects of embodiments of the present invention. It will also be appreciated that one or more of the elements depicted in the drawings/figures can also be implemented in a more separated or integrated manner, or even removed or rendered as inoperable in certain cases, as is useful in accordance with a particular application. The foregoing description of illustrated embodiments of the present invention, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed herein. While specific embodiments of, and examples for, the invention are described herein for illustrative purposes only, various equivalent modifications are possible within the spirit and scope of the present invention, as those skilled in the relevant art will recognize and appreciate. As indicated, these modifications may be made to the present invention in light of the foregoing description of illustrated embodiments of the present invention and are to be included within the spirit and scope of the present invention. Thus, while the present invention has been described herein with reference to particular embodiments thereof, a latitude of modification, various changes and substitutions are intended in the foregoing disclosures, and it will be appreciated that in some instances some features of embodiments of the invention will be employed without a corresponding use of other features without departing from the scope and spirit of the invention as set forth. Therefore, many modifications may be made to adapt a particular situation to the essential scope and spirit of the present invention. It is intended that the invention not be limited to the particular terms used in following claims, but that the invention will include any and all embodiments and equivalents falling within the scope of the appended claims. GLOSSARY OF TERMS AND DEFINITIONS THEREOF Access Network (AN): The network equipment providing data connectivity between a packet switched data network (typically the Internet) and the access terminals. Access Terminal (AT): A device providing data connectivity to a user. An access terminal may be connected to a computing device such as a laptop personal computer or it may be a self-contained data device such as a personal digital assistant. An access terminal is equivalent to a mobile station. CCMP: Control Channel MAC Protocol CDMA: Code Division Multiple Access Channel: The set of channels transmitted between the access network and the access terminals within a given frequency assignment. A Channel consists of a Forward Link and a Reverse Link. Connected state: AT is in this state when there is a connection (i.e traffic channels) (for user data exchange) established with NW DRC: Date Rate Control EV-DO: Evolution Data Optimized Forward Pilot Channel: The portion of the Forward Channel that carries the pilot. IFHHO (Inter-Frequency Hard Handoff): IFHHO implies reconfiguring physical network MAHHO: Mobile Assisted Hard HandOff NW: NetWork OFS: Other Frequency Search OMP: Overhead Message Protocol PN: Pseudo Noise RUP: Route Update Protocol Sector: The part of the access network that provides one CDMA channel. Slot: A duration of time specified by 1.66... ms. 1x EV-DO: CDMA2000 1x evolution-Data Optimized system. TCAM: Traffic Channel Assignment Message WE CLAIM 1. A method, of enabling an access terminal to assist an access network inter- frequency hard handoff in communication system comprising the steps of: a. determining plurality of serving frequency candidate sectors by the access terminal; b. performing different frequency candidate sector search by the access terminal; c. determining an other frequency candidate sectors by the access terminal; d. sending a RouteUpdate message to the access network with a status of every pilot received; e. evaluating the status of every pilot received in the RouteUpdate message by access network; and f. sending a TrafficChannelAssignment message to the access terminal. 2. A method as claimed in claim 1 wherein the serving frequency candidate sector determination is done by monitoring the signal strength of the forward pilot channels. 3. A method as claimed in claim 2 wherein the said forward pilot channel is specified by a pilot's PN (Pseudo Noise) offset and the pilot's CDMA channel. 4. A method as claimed in claim 2 wherein the said forward pilot channel is transmitted by each sector in the entire pilot sets list which belongs to the serving frequency. 5. A method as claimed in claim 1 wherein the other frequency candidate sector determination is done by monitoring the signal strength of the forward pilot channels. 6. A method as claimed in claim 5 wherein the said forward pilot channels is transmitted by the sectors in the neighbor list which belongs to the frequencies other than the serving frequency. 7. A method as claimed in claim 1 wherein the said status is pilot strength, pilot PN phase and/or drop timer. 8. A method as claimed in claim 1 wherein the said status send for every pilot received is at least one of the status of every pilot in the active set, status of pilots corresponding to the serving frequency candidate sectors and status pilots corresponding to the other frequency candidate sectors. 9. A method as claimed in claim 1 wherein Access network sends TrafficChannelAssignment message to access terminal if it decides to change the active set based on its evaluation of the RouteUpdate message. 10. A method as claimed in claim 1 wherein the strength estimate formed by the access terminal is computed as the sum of the ratios of received pilot energy per chip, Ec, to total received spectral density, l0 (signal and noise) for at most 'k' multi-path components, where 'k' is the maximum number of multi-path components that can be demodulated simultaneously by the access terminal. 11. A method as claimed in claim 1 wherein in the connected state, RouteUpdate messages from the access terminal are based on changes in the radio link between the access terminal and the access network. 12. A method as claimed in claim 1 wherein the access network sends a TrafficChannelAssignment message to the access terminal in response to changing radio link conditions, as reported in the access terminal's RouteUpdate messages. 13. A method, of enabling access terminal to assist the access network inter- frequency hard handoff in communication system wherein access terminal performs different frequency search when: a. pilot strength of active set members is being decreased consistently and there is no feasible candidate on the serving frequency; b. OFSseach_timer is expired; or c. Sector switching or hard handoff is not in progress. 14. A method as claimed in claim 13 wherein the said different frequency search by access terminal comprise the steps of: a. suspending the sector switching; b. suspending generating RouteUpdate message from Route Update Protocol; c. deactivating Control Channel MAC Protocol; d. deactivating Overhead Message Protocol; e. switching off the transmitter; f. stopping handoff drop timers corresponding to its current active set and candidate set members; g. tuning to the other frequency by access terminal and taking the samples of the pilot for OFSinterval; h. tuning back to the serving frequency ; i. enabling handoff drop timers corresponding to its current active set and candidate set members; j. switching on the transmitter; k. evaluating samples of other frequency to check if there is any better pilot available on that frequency ; I. starting the sector switching; m. generating RouteUpdate message from Route Update Protocol; n. activating Control Channel Mac Protocol; and o. activating Overhead Message Protocol. 15. A method as claimed in claim 14 wherein data packets will not be sent by access network during the other frequency search interval as AT will not be monitoring the serving frequency during the other frequency search interval. 16. A method as claimed in claim 15 wherein to do the different frequency search AT sets DRC Cover to NULL COVER; and AT waits until the conditions are met at time "T" which satisfies the equation: (T+1-FrameOffset) mod DRCLength = 0. 17. A method which enable access terminal to assist the access network inter- frequency hard handoff in communication system such as herein substantially described particularly with reference to the accompanying figures 3 to 5.

Documents:

1477-che-2004-abstract.pdf

1477-che-2004-claims.pdf

1477-che-2004-correspondnece-others.pdf

1477-che-2004-correspondnece-po.pdf

1477-che-2004-description(complete).pdf

1477-che-2004-drawings.pdf

1477-che-2004-form 1.pdf

1477-che-2004-form 13.pdf

1477-che-2004-form 26.pdf

1477-che-2004-form 5.pdf