Title of Invention

A METHOD FOR SELECTING BEST SERVING SECTOR IN A HIGH DATA RATE CDMA SYSTEM

Abstract

This invention to provides a method for selecting the best serving sector in a high data rate COMA system by avoiding fast toggling between sectors and maximizing the throughput on the forward link. The serving sector is selected such that it achieves site selection transmit diversity in high data rate COMA communication system using a signal level and timing hysterisis. Access terminal compares the signal levels of the active sectors with the signal level of the current serving sector. Access terminal updates the selection parameters for each active sector using the signal level and timing hysterisis and determines the possible candidates for serving sectors based on the selection parameters. If there is more than one candidate for serving sector, access terminal uses the weighted average of the signal strength accumulated during timing hysterisis such that the sector with the larger weighted average of accumulated signal strength is selected as the best serving sector.

Full Text

FIELD OF THE INVENTION This invention in general relates to the communication technology. Specifically this invention relates to a method for selecting a serving sector in a high data rate CDMA data communication system. More particularly this invention relates a method for selecting best serving sector in a high data rate CDMA system. DESCRIPTION OF THE RELATED ART In a typical high data rate CDMA data communication system a large geographical area is divided into cells. Each cell is further divided into sectors and inside each cell there Is a base station. An access terminal typically communicates with the network through the sectors. At any given instant of time, access terminal communicates with one or more sectors, which may belong to one or more cells. In the conventional CDMA wireless system, data traffic including the voice is routed to each sector that Is actively communicating with the user. As a result, access terminal receives traffic from all the active sectors. In the high data rate CDMA data communication system, like 1XEVDV, 1XEVD0 or HSDPA data traffic, is routed by only one sector that maximizes the forward link throughput. Access terminal continuously monitors all the active sectors, among which it selects the best serving sector and informs the network about its selection. This selection of best serving sector is also referred to as the "site selection transmit diversity". In the state of the art approach access terminal selects the serving sector, which has the strongest forward link signal amongst all active sectors and the access terminal informs the network about its selection via a feedback channel. Following steps are performed by access terminal to select the serving sector: Step1: Access terminal monitors the signal strength of forward link signal of all the active sectors. Step2: Access tenninal determines the serving sector by comparing the forward link signal strength of all active sectors. The sector with the strongest forward link signal strength is selected as the serving sector. Step3: Access terminal informs the network about its selection via a feedback channel. The process is repeated again for monitoring the signal strength of the fonvard signal of all the active sectors. The problem with the prior art is that the procedure detailed above leads to rapid switching between sectors. Each time a switching occurs, data that was going to be sent to access terminal must be sent to the corresponding data queue of that sector. Moreover access terminal cannot receive the data until data queue is ready. Such rapid transitions can cause severe network overhead and outage for the access terminal. Also if a serving sector is selected based on pilot strength at one particular instant then there is possibility that pilot strength looked high because of false signal strength calculation or because of surge. In effect signal strength of the selected serving sector will reduce after sometime. Based on the foregoing the invention proposes a method, which enables the access terminal to ideally select a sector so that throughput is maximized on the fonvard link and fast toggling between the sectors Is avoided. SUMMARY OF THE INVENTION It is therefore the primary object of the invention to provide a method for selecting the best serving sector in a high data rate CDMA system by avoiding fast toggling between sectors and maximizing the throughput on the forward link. It is another object of the invention to provide a method to select a serving sector in order to achieve site seiection transmit diversity in high data rate CDMA communication system using a signal level and timing hysterisis. It is yet another object of the invention to provide a method for updating the selection parameters for each active sector using the signal level and timing hyterisis and for determining the possible candidates for serving sectors based on the selection parameters. It is also an object of the invention to provide a method to use the weighted average of the signal strength accumulated during liming hysterisis such that the sector with the larger weighted average of accumulated signal strength is selected as the best serving sector if there is more than one candidate for serving sector. Accordingly, the invention provides a method for selecting a best serving sector in a high data rate CDMA system using signal level and timing hysterisis, the method comprising the steps: a) measuring the forward link signal strength from each sector in the active set of pilots and the current sen/ing sector; b) comparing signal levels received from the said active sectors with the signal level of current serving sector in order to determine the difference; c) updating the selection parameters for each of the active sectors using the said difference based on signal level and timing hysterisis; and d) identifying the best serving sector from active sectors using the selection and comparison parameters 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. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS Figure 1 portrays a typical high data rate CDMA system. Figure 2 illustrates a procedure for selecting a best serving sector according to the invention. Figure 3 depicts a procedure for updating seiection parameters using signal level and timing hysterisis. Figure 4 shows a procedure for identifying a best serving sector when thee are more than one suitable candidates. 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 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. Before describing the various aspects and details of the present invention it will be useful to describe the context in which the invention is used. Consequently a typical high data rate CDMA system is Illustrated in Errorl Reference source not found.. The system consists of three cells, cell 1, cell2 and ceil3. Each cell comprises of three sectors. Cell 1 comprises of sectors x1, y1 and z1. Cell 2 comprises of sectors x2, y2 and z2. Cell 3 comprises of sectors x3, y3 and z3. The access terminal "A" is communicating with three active sectors x1, y1 and z3. The current serving sector is x1. Data traffic is routed from base station BS1 to sector x1and then from sector x1 to access terminal "A". Access terminal "A" monitors the forward link signal strength of active sectors x1, y1 and z3 continuously. Suppose at any instance the fonvard link signal strength of the sector z3 is the strongest. Access terminal will immediately select this sector and will inform the network about its selection. So now the data traffic is routed from BS3 to sector z3 and then from sector z3 to access terminal "A". Now suppose the sector x1 has the strongest forward (ink signal at one instance such that access terminal "A" selects the sector x1 as the serving sector. In a next instance sector z3 has the strongest forward link signal. Just a few moments later sector x1 again has the strongest forward link signal. It is possible that rapid switching between two or more sectors can occur. Each time a switch occurs, data that was going to be sent to access terminal "A", must be sent to the corresponding data queue of that sector. This results in rapid switching that is undesirable. Now the procedure in Errorl Reference source not found, contains steps for determining the best serving sector to achieve site selection transmits diversity for access terminal. The procedure in Errorl Reference source not found. may be implemented in hardware or software at access terminal. When operating in a CDMA HDR system the procedure in Errorl Reference source not found, is called once in each HDR slot while access terminal is in connected state i,e. communicating with the access network. The procedure in Error! Reference source not found, consists of following steps: Step 200: The procedure begins in this step and proceeds to next step. Step 201: In this step, access terminal measures the forward link signal strength from each sector in the active set of pilots. Access terminal also measures the forward link signal strength of current serving sector. step 202: In this step, access terminal updates the sector selection parameters for each sector in the active set using the timing and signal level hysterisis. This step is illustrated in more detail in Error! Reference source not found.. Step 203: In this step access terminal determines the possible candidates for serving sectors using the selection parameters for each sector in the active set. If there is more than one possible candidate for serving sector, access terminal uses the comparison parameters to identify the best serving sector This step is illustrated in more detail in Errorl Reference source not found.. Step 204: The procedure in Errorl Reference source not found, ends in this step. Now the procedures for updating of selection parameters i.e. step 202 of procedure in Errorl Reference source not found, is illustrated in Errorl Reference source not found.. In each HDR slot this procedure is called for each sector in the active set to update the selection parameters. The access terminal maintains the following selection parameters for each sector in the active set: DIFF: It is the difference between the forward link signal strength of a sector in the active set and the current sewing sector. SELECTION_COUNT: This parameter gives the number of times the DIFF value was greater than the TH_STRENGTH. This parameter is incremented when the FAD1NG_CNT is zero and the DIFF value is greater than the TH^STRENGTH. A sector becomes a probable candidate for serving sector, whenever this parameter of that sector transitions from a zero to non-zero value. This parameter is reset after the selection of best serving sector. FADING_COUNT: This parameter gives the number of times the DIFF value is less than the TH_STRENGTH, for a sector, which is a probable candidate for serving sector. This parameter is incremented when the SELECTION_COUNT value is non-zero and the DIFF value is less than the TH_STRENGTH. This parameter is reset after the selection of best serving sector. The procedure in Error! Reference source not found, consists of following steps: Step 300: The procedure begins in this step and proceeds to next step. Step 301: In this step access terminal determines the difference between the forward link signal strength of the sector in the active set and the forward link signal strength of the cunrent serving sector i.e. access terminal determines DIFF value for a sector in the active set. Step 302: In this step access terminal determines whether the DIFF value of the sector is greater than TH_STRENGTH or not. If the DIFF value is greater than TH_STRENGTH then procedure continues to step 303. Othenwise, the procedure continues to step 306. Step 303:ln this step access terminal determines whether the FADING_COUNT value of the sector equals zero, if the FADING^COUNT value equals zero, the procedure continues to step 304. Otherwise, the procedure continues to step 305. Step 304: In this step access terminal increments the SELCT10N_C0UNT value of the sector, stores the DIFF value and procedure continues to step 310. Step 305: In this step access terminal resets the FADING_COUNT value of the sector to zero and procedure continues to step 310. Step 306: In this step access terminal determines whether the value of SELECTION_COUNT equals zero or not. If the value of SELECTION_COUNT equals zero then the procedure continues to step 310. Otherwise, the procedure continues to step 307. Step 307: In this step access terminal increments the value of FADING_COUNT of the sector and procedure continues to step 308. Step 308: In this step access terminal determines whether the value of FAD1NG_C0UNT of the sector equals MAX_FADING_COUNT or not. If the value of FADING_COUNT equals IVIAX_FADING_COUNT, then the procedure continues to step 309. Otherwise, the procedure continues to step 310. Step 309: In this step access terminal resets the value of FAD1NG_C0UNT of the sector to zero and decrements the value of SELECTION_COUNT of the sector by PENALTY_COUNT. Step 310: The procedure in Errorl Reference source not found, ends in this step. The procedure in Errorl Reference source not found, illustrates the best sector selection based on selection parameters step of procedure in Errorl Reference source not found, i.e. step 203. This procedure is called once each HDR slot to identify a best serving sector. The procedure in Error! Reference source not found, consists of the following steps. Step 400: The procedure begins in this step and proceeds to next step. Step 401: In this step access terminal marks the sectors whose SELCTI0N_C0UNT value equals MAX_SELECTION_COUNT. The access terminal chooses the best serving sector from the merited sectors. Step 402: In this step access terminal uses the comparison parameters to select the best serving sector form the marked sectors. Following comparison parameters are used for identifying the best serving sector from the marked sectors: DRC Lock bit information: This is used only in 1X EVDO system. This bit is received from all the sectors in the active set. It indicates the reliability of the reverse link. If the DRC Lock bit received from a sector which is marked in step 401 is "0" i.e. reverse link is not reliable then un-mark this sector. Here the Weighted Average of the Pilot Signal Strength is calculated for each of the marked sectors in the active set. The sector with the maximum value of weighted average is selected as the best serving sector. The equation used to calculate weighted average of pilot signal strength is given below: The procedure continues to step 403 after identifying the best serving sector. Step 403: In this step access terminal resets the FAD1NG_C0UNT and SELECT10N_C0UNT values for all the sectors in the active set and the procedure continues to step 404. Step 404: The procedure in Error! Reference source not found, ends in this step. 1. 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 THEIR DEFINITIONS Access Network: The network equipment providing data connectivity between a packet switched data network (typically the Internet) and the access terminals. Access Terminal: 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. 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: Access terminal is in this state when there is a connection (for user data exchange) established with network. Forward Pilot Channel: The portion of the Forward Channel that carries the pilot. HDR: High Data rate Sector: The part of the access network that provides one CDMA channel. Slot: duration of time specified by 1.67 ms in HDR system, and 1.25 ms for EVDV. WE CLAIM 1. A method for selecting a best serving sector by an access terminal in a high data rale CDMA system using signal level and timing hysterisis, the method comprising the steps: a) measuring the forward link signai strength from each sector in the active set of pilots and the current serving sector; b) comparing signal levels received from the said active sectors with the signal level of current serving sector in order to determine the difference; c) updating the selection parameters for each of the active sectors using the said difference based on signal level and timing hysterisis; and d) identifying the best serving sector from active sectors using the selection and comparison parameters. 2. The method as claimed in claim 1 wherein access terminal uses the weighted average of the signal strength accumulated during timing hysterisis such that the sector with the larger weighted average of accumulated signal strength is selected as the best serving sector when there is more than one suitable sectors. 3. A method, for selecting a best serving sector by an access terminal in a high data rate CDMA system using signal level and timing hysterisis substantially as herein above described and illustrated with reference to the accompanying drawings.

Documents:

1483-che-2004 abstract-duplicate.pdf

1483-che-2004 abstract.pdf

1483-che-2004 claims-duplicate.pdf

1483-che-2004 claims.pdf

1483-che-2004 correspondence-others.pdf

1483-che-2004 correspondence-po.pdf

1483-che-2004 description (complete)-duplicate.pdf

1483-che-2004 description (complete).pdf

1483-che-2004 drawings-duplicate.pdf

1483-che-2004 drawings.pdf

1483-che-2004 form-1.pdf

1483-che-2004 form-13.pdf

1483-che-2004 form-19.pdf

1483-che-2004 form-26.pdf

1483-che-2004 form-3.pdf

1483-che-2004 form-5.pdf