Title of Invention

METHOD OF POWER OPTIMIZATION FOR RANDOM ACCESS PROCEDURE UNDER QUASI-STATIONARY ENVIRONMENT

Abstract

The proposed new approach is in the area of random access procedure used during initial cell access and for packet call in Quasi connected state (No dedicated link available, Ex: - In 3GPP based WCDMA, CELL_JACH state) for mobile equipment in a mobile communication system. In the proposed new approach, UE minimizes the transmission of preambles by estimating the preamble power for which UE is more likely to reach the network, based on statistics collected from previous random access procedure. For the estimation algorithm to work accurately and effectively, the channel should be slow changing. By minimizing the number of preamble transmissions, UE can now save its own power proportional to the number of preamble transmission avoided, increase sleep time in quasi connected state thereby increasing standby time, and reduce UL interference and reduce collision probability there by increasing system capacity. The proposed approach serves as an optimization over the existing random access procedure. The proposal can be used in any random access procedure which uses multiple preamble transmissions with increasing power, to access network.

Full Text

\FIELD OF THE INVENTION The present invention, in general relates to the field of Random access procedure used during initial cell access and during Quasi connected state (where no dedicated link available) by a mobile equipment in a mobile communication system. More particularly, the present invention relates to system and method of Power optimization for random access procedure under quasi-stationary environment. DESCRIPTION OF RELATED ART Random access procedure described in 3GPP TS 25.214 uses Open loop power control (OLPC) where in the User equipment (UE) just does a rough estimate of the uplink (UL) power to be used based on UL interference and downlink (DL) path loss. On the contrary in closed loop power control (CLPC), UE uses just the required amount of power to maintain the link. The link adaptation procedures in CLPC are quite robust. As described in 3GPP TS 25.214, UE calculates the initial TX power for the random access procedure based on formula below. Preamble Initial Power Po = Primary CPICH TX power - CPICH_RSCP + UL interference + Constant value-→ (equationi) As depicted in Figure 1, UE transmits first preamble with the preamble initial power Po calculated by equation (1) above and then if there is no response from the network, increases the power by a uniform Ap and transmits successive preambles with increasing transmit power until one of the following conditions are met. 1. The network sends response for the Jth preamble with transmit power Pj 2. Maximum preambles configured by the network is reached 3. The maximum transmit power for the UE as per its power class is reached. The publication WO 2004100565 titled “Fast random access method for EUDCH of WCDMA” describes a fast random access method for enhanced uplink dedicated channel (EUDCH) users. In this method user equipment (UE) calculates preamble initial power and preamble transmission power by EUDCH power offset and EUDCH power ramp step. In this scheme, the values of new elements i.e., EUDCH power offset and EUDCH power ramp step are set by the network. The publication discusses about the calculation for the initial preamble transmission power for random access procedure. Each time calculation of the preamble transmission power is performed by replacing the current power ramp step with the EUDCH power ramp step. This patent publication WO2004038951 titled ‘Random access for wireless multiple-access communication” systems describes a method for accessing the wireless multiple-access communicatiori system. The method first determines the current operating state of a terminal. One random access channel is selected from the existing random access channels which comprises fast random access channel (F-RACH) or slow random access channel (S-RACH), and message is sent on the selected random access channel for accessing the system. Various types of channels i.e., fast and slow random access channels and how to access the communication system in different operating states is described. LIMITATIONS In the current procedure ( Figure 1) UE transmits multiple preambles to attain the optimal power level required to reach network. The J-1 preambles transmitted for which there was no response from network are just a waste of power. When a PS call is active on quasi connected state, due to bursty nature of the traffic, it keeps transmitting relatively large amount of control and data packets to the network through Random Access Channel. Unlike closed loop power control, random access procedure uses open loop power control, which always uses higher power than required to reach the network. In a situation where UE is frequently reconfigured to quasi connected state, current random access procedure is very inefficient in terms of power consumption. As per 3GPP TS 25.214 whenever UE uses preamble initial power Po calculated based on equation (1), it ignores cell specific propagation conditions, which it acquired in its previous random access attempt. Once UE made an access on a cell and received a response from network, UE could now make a rough estimate about the actual propagation conditions using the actual preamble power Pj and use this acquired information for its further random access transmission attempts unless channel conditions around UE changed across successive attempts. Current implementation suffers from the following disadvantages. 1) Unnecessary battery drain for transmitting J-1 preambles which impacts battery life. 2) UE needs to stay awake for longer time in quasi connected state as random access procedure becomes longer. 3) Causes higher UL interference, reducing system capacity. 4) Increases the probability of collisions with other users who are attempting random access, which again translates to more random access attempts and hence reduced system capacity. However it would not be feasible to maintain a dedicated link either because 1) The procedures in maintain a dedicated link are an overkill to handle such low traffic and 2) It would be a waste of channel bandwidth as some other user having a higher instantaneous bandwidth requirement could make better use of this channel. SUMMARY OF INVENTION In the proposed new approach, UE minimizes the transmission of preambles by estimating the preamble power for which UE is more likely to reach the network, based on statistics collected from previous random access procedure. For the estimation algorithm to work accurately and effectively, the channel should be slow changing. By minimizing the number of preamble transmissions, UE can now save its own power, reduce UL interference and reduce collision probability there by increasing system capacity. Accordingly, this invention explains a method of power optimization for random access procedure under quasi-stationary environment comprising the steps of: (a) reducing the number of successive transmission of preambles to achieve optimized power level to reach network by a user equipment; (b) realizing the reduction in number of preamble transmissions by estimating the amount of preamble power for UE to reach the network, based on a previous random access procedure; (c) making an access on a cell with preamble initial power for the random access procedure based on uplink (UL) interference and downlink (DL) path loss; (d) sending a response for further access attempts by the network; (e) updating the acquired actual preamble power by the UE after receiving each response from the network; and (f) avoiding transmission of preamble by starting with the actual preamble power of the previous random access attempt by UE. Accordingly, this invention further explains a system of power optimization for random access procedure under quasi-stationary environment comprising: (a) a user equipment, reducing the number of successive transmission of preambles to achieve optimized power level to reach network; (b) means for realizing the reduction in number of preamble transmissions by estimating the amount of preamble power for UE to reach the network, based on a previous random access procedure; (c) means for making an access on a cell with preamble initial power for the random access procedure based on uplink (UL) interference and downlink (DL) path loss; (d) means for sending a response for further access attempts by the network; (e) means for updating the acquired actual preamble power by the UE after receiving each response from the network; and (f) means for avoiding transmission of preamble by starting with the actual preamble power of the previous random access attempt by UE. These and other objects, features and advantages of the present invention will become more apparent from the ensuing detailed description of the invention taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS Figure 1 depicts Current Random access procedure. Figure 2 depicts Random access procedure after using proposed algorithm. Figure 3 depicts Random variation in RSCP. Figure 4 depict Exponential variation in RSCP. Figure 5 depict Flowchart of the proposed algorithm. Figure 6 depicts Preamble transmit power with and without use of proposed algorithm. Figure 7 depict RACH attempts distribution based on number of preambles. Figure 8 depict Comparison of number of preambles transmitted. DETAILED DESCRIPTION OF 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. The present technique generally relates to mobile communication, and more particularly to a method for power optimization for random access procedure under quasi stationary environment. A method for power optimization for random access procedure under quasi stationary environment is described. In this scheme, user equipment (UE) reduces the number of successive transmission of preambles to achieve optimized power level to reach network. This reduction in number of preamble transmissions is realized by estimating the amount of preamble power for UE to reach the network, based on the previous random access procedure. This approach works best for slow changing channel propagations or quasi stationary environment. An access is made on a cell with preamble initial power for the random access procedure based on uplink (UL) interference and downlink (DL) path loss. This method exploits the information collected in terms of actual preamble power for which network sends a response for its further access attempts. After each response received from the network, UE updates the acquired actual preamble power. UE avoids transmission of preamble by starting with the actual preamble power of the previous random access attempt and saves a proportional amount of power. Once an access is made on a cell with preamble initial power Po calculated using Equation (1), proposed new approach exploits the information acquired in terms of actual preamble power Pj for which network sent a response, for its further access attempts. On each response received from the network, UE updates the acquired Pj. The procedure is shown in Figure 2, where UE avoids transmission of preambles by starting with the preamble power Pj of the previous random access attempt and saves power proportional to the number of avoided preambles. This algorithm works best when the channel propagations are slowly changing. So this algorithm should be turned on only for slow changing channel profile and turned off for fast changing channel profile. To model an Uplink channel based on DL channel, we should use Received signal power or pathloss as measurement quantity. Radio signals are typically subject to the following kind of channel conditions. 1) Path-loss 2) Shadowing 3) Multi-path fading (Slow and fast) Ignoring Multi-path fading component for this discussion, as it is difficult to estimate it in case of UL random access scenario, shadowing and path-loss lead to the following kind of variations in RSCP. Both these variations in RSCP are to be detected and the usage of proposed algorithm should be stopped until UE is quasi stationary. Random Variation in RSCP To detect that UE is moving through a Shadowing Channel (Figure 3), UE can maintain a running average of RSCP samples for a time window in multiples of measurement occasions. If the deviation of the difference between consecutive samples is higher than a benchmarked threshold value, UE can be considered as fast moving under a shadowing environment. In this case we can turn off the usage of the proposed method. Exponential variation in RSCP To detect that the UE is moving through a path-loss channel (Figure 4), UE can maintain a running window of RSCP samples for a time window in multiples of measurement occasions. The gradient of the curve shown in Figure 4 over the measurement window indicates a path-loss channel. Gradient can simply be calculated by taking the difference between 2 consecutive samples for a range of samples collected over time. If this gradient pattern is observed, UE can be considered as fast moving under a path-loss environment. Gradient can be positive or negative based on the direction of the mobile with respect to network. In this case we can turn off the usage of the proposed method. The proposed method as shown in a flowchart representation in Figure 5 is detailed below. I. If UE is not in the same cell as previous random access attempt, use regular random access procedure II. If UE moved to connected state through a dedicated channel allocation between 2 consecutive random access attempts, use regular random access procedure III. If UE was declared fast moving between 2 consecutive random access attempts, use regular random access procedure IV. If UE was declared OUT of SERVICE between 2 consecutive random access attempts, use regular random access procedure V. Maintain a running average of RSCP collected over a time window in multiples of measurement occasions depending on the state of the UE (Ex - DRX cycle for Idle mode and FACH measurement occasions for CELL_FACH in WCDMA) VI. Calculate the deviation of the difference between consecutive values collected over the averaging window. If the deviation is greater than kΔpt declare the UE to be fast moving or channel is fluctuating and use regular random access procedure, k is a factor chosen depending on the power ramp step size and up to how much RSCP variation this algorithm should work for. VII. Calculate the gradient between 2 consecutive RSCP values for all RSCP samples collected over the averaging window. If the gradient for each pair is continuously positive or negative, declare the UE to be fast moving or channel is fluctuating and use regular random access procedure VIII. If the above points permit UE to use the proposed new continue as below IX. Store the following parameters of the previous successful random access procedure attempt a) Calculated Preamble Initial Power P0, prev using equation (1) b) RSCP used to calculate (a) c) UL interference used to calculate (a) d) PSC of the cell on which the random access procedure was attempted e) Number of preambles taken to converge at the optimal power to reach network, Nprev f) The preamble power for which ACK was received during last random access procedure, Pj, prev X. Calculate the optimal power level for current random access attempt as below a) Calculate Preamble Initial Power for current attempt Po, cur, from equation (1) as usual b) Calculate k1, k2 and k3 independent safety factors whose values can be dynamically changed to suite the step size Δp and instantaneous channel conditions (Ex: - dependent on the deviation of the difference between the of the DL RSCP samples). K1 also depends on Nprev. If Nprev = 1, choose k1 such as to increase the number of preamble transmissions by 1, else use k1 as usually calculated. C) If DIFF (POl Prev, Po, Cur) first preamble power and converge at the optimal power using the regular random access procedure d) Else if Po, cur >= Po, Prev + Δp, use MAX(Pj, prev - k2ΔXp, Po, cur) as the first preamble power and converge at the optimal power using the regular random access procedure e) Else if Po, cur + Δp • Option 1: Use Po, cur as the first preamble power and converge to the optimal power using dynamic step sizes to minimize number of preambles • Option 2: Use MAX [Po, cur, (PJ, Prev - k3Δp - (Po, Prev - Po, cur))] power for the first preamble and converge at the right power using existing random access procedure f) Store the actual preamble power Pj, cur and number of preamble attempts Ncur for which response is received from the network Figure 6 shows a comparison of the preamble transmit power between the existing algorithm specified in 3GPP TS 25.214 and the proposed changes in this document. The data are collected over real field trials for a WCDMA system. Δp is 2dB and the values of k1, k2 and k3 are considered to be equal and of value equal to [2 * Δp + Deviation of the difference in RSCP samples]. Value of k is (2 * Δp) for this field trial. The curve labeled "PO-Revised" show the new Po values calculated HSing the proposed algorithm and the curve labeled “Pj” shows the actual value for which response was received from network, starting at values plotted in curve “PO-Revised” as starting values. Clearly the “PO-Revised” curve shows a gain over the “PO” curve for random variations in UL channel conditions, which are at times uncorrelated with variations in DL channel conditions. Figure 7 shows a Bar chart representation of the distribution of the Random access attempts, classified based on the number of preambles used to receive response from network. A description of each bar in the bar chart is given in Table 1 below. It is clear from the Figure 7 that by using the newly proposed algorithm there is no impact on UL interference. UE still continues to start RACH transmission at a lower power and ramps up to the required power to reach the network, while reducing the number of preambles transmitted. Figure 8 shows that by using the proposed algorithm, the number of preamble transmission is reduced by 40%, there by offering significant power savings for the UE. Table 1: Description of labels used in Figure 6 ADVANTAGES 1) UE will get ACK/ NACK for lesser number of preambles and it will save unnecessary transmission of preambles. This would conserve UE power. 2) Since UE avoids transmission of many preambles, it would be causing lesser interference, as compared to existing approach 3) Decreases the probability of collisions with new users who are attempting random access procedure afresh. 4) By using the preamble power for which UE received ACK/ NACK in the previous attempt and coupling it with the existing random access procedure, a better estimate of the Uplink channel can be made compared to existing procedure, and hence UE can predict more accurately the nearest preamble power that would reach the network. UE will get ACK/ NACK for lesser number of preambles than earlier approach and hence it will save transmission of unnecessary preambles. This would conserve UE power and saves power proportional to the number of avoided preambles. 5) Since UE used fewer preambles for random access transmission, the random access procedure got concluded quicker than it would have compared to existing approach. Hence UE can go to sleep earlier compared to existing approach and hence would sleep for longer duration. This increases standby time. Ex: For a WCDMA system as described in 3GPP 25.211, UE can finish the random access procedure earlier by [(4096 + 3 * 2560 chips) * Num preambles avoided]. 6) Since UE avoids transmission of many preambles, it would be causing lesser interference, as compared to existing approach, and hence would increase system capacity since CDMA/ WCDMA system is a UL interference limited system. 7) Decreases the probability of collisions with new users who are attempting random access afresh, which again would reduce number of preambles transmitted by various mobiles and hence would reduce interference and help increase system capacity. (8) In the worst case, when the multipath environment changes, UE will be using the usual Random access procedure. Hence in any case the proposed approach serves as an optimization over the existing procedure. 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 above. It should also be noted that the host for storing the applications include but not limited to a microchip, microprocessor, handheld communication device, computer, rendering device or a multi function device. 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. GLOSSARY OF TERMS AND DEFINITIONS THEREOF PRACH Physical random access channel RACH Random access channel UL Uplink DL Downlink OLPC Open loop power control CLPC Closed loop power control ACK Acknowledgement NACK Negative acknowledgement AICH Acquisition indicator channel PS Packet switched Po Preamble initial power Pj Actual preamble power for which Network sent a ACK/ NACK Δp Uniform preamble power step size PSC Primary scrambling code MAX Maximum of the quantities supplied DIFF Difference of the quantities supplied RSCP Received signal code power Quasi-connected state A state where UE is in connected state, without any dedicated link available (connected through Shared channels.) Ex: - In WCDMA, CELL_FACH state and CELL_PCH state) k1,k2 and k3 Are independent safety factors, whose value can be dynamically changed to suite step size Δp and instantaneous channel conditions. They work as scaling factors that can be chosen to balance between power optimization in the UE and UL interference. power optimization in the UE and UL interference. WE CLAIM 1. A method of power optimization for random access procedure under quasi-stationary environment comprising the steps of: (a) reducing the number of successive transmission of preambles to achieve optimized power level to reach network by a user equipment; (b) realizing the reduction in number of preamble transmissions by estimating the amount of preamble power for UE to reach the network, based on a previous random access procedure; (c) making an access on a cell with preamble initial power for the random access procedure based on uplink (UL) interference and downlink (DL) path loss; (d) sending a response for further access attempts by the network; (e) updating the acquired actual preamble power by the UE after receiving each response from the network; and (f) avoiding transmission of preamble by starting with the actual preamble power of the previous random access attempt by UE . 2. A method as claimed in claim 1 wherein once an access is made on a cell with preamble initial power Po, the said method exploits the information acquired in terms of actual preamble power Pj for which network sent a response, for its further access attempts. 3. A method as claimed in claim 1 wherein on each response received from the network, UE updates the acquired Pj where the UE avoids transmission of preambles by starting with the preamble power Pj of the previous random access attempt and saving power proportional to the number of avoided preambles. A method as claimed in claim 1 wherein the said method is performed when the channel propagations are slowly changed and stopped when the channel profile is changed fast. 5. A method as claimed in claim 1 wherein shadowing and path-loss lead to the random and exponential variations in RSCP where both these variations in RSCP is detected and the said method is stopped until UE is quasi stationary. 6. A method as claimed in claim 1 wherein if the deviation of the difference between consecutive samples is higher than a benchmarked threshold value, the usage of the said method is tuned off. 7. A method of power optimization for random access procedure claimed in claim 1 wherein the said method involves the steps of: (a) using regular random access procedure if UE is not in the same cell as previous random access attempt; (b) using regular random access procedure if UE moving to connected state through a dedicated channel allocation between 2 consecutive random access attempts; (c) using regular randam access procedure if UE is declared fast moving between 2 consecutive random access attempts; (d) using regular random access procedure if UE is declared OUT of SERVICE between 2 consecutive random access attempts; (e) maintaining a running average of RSCP collected over a time window in multiples of measurement occasions depending on the state of the UE; (f) calculating the deviation of the difference between consecutive values collected over the averaging window; (g) calculating the gradient between two consecutive RSCP values for all RSCP samples collected over the averaging window where if the gradient for each pair is continuously positive or negative, the UE is declared as fast moving or channel is fluctuating and regular random access procedure is used; (h) storing the parameters of the previous successful random access procedure attempt; (i) calculating the optimal power level for current random access attempt; and (j) storing the actual preamble power PJ, cur and numbering of preamble attempts Ncur for which response is received from the network. 8. A method as claimed in claim 7 wherein if the deviation is greater than kΔp, the UE is declared as fast moving or channel is considered fluctuating and regular random access procedure is used where k is a factor chosen depending on the power ramp step size and up to how much RSCP variation this method should work for. 9. A method as claimed in claim 7 wherein storing the parameters of the previous successful random access procedure attempt involves storing: (a) calculated Preamble Initial Power Po, prev using Preamble Initial Power Po = Primary CPICH TX power - CPICHJRSCP + UL interference + Constant value; (b) RSCP used to calculate (a); (c) UL interference used to calculate (a); (d) PSC of the cell on which the random access procedure was attempted; (e) number of preambles taken to converge at the optimal power to reach network, Nprev; and (f) the preamble power for which ACK was received during last random access procedure, Pj, Prev 10. A method as claimed in claim 7 wherein calculating the optimal power level for current random access attempt involves: (a) calculating preamble initial power for current attempt Po, cur, from Preamble Initial Power Po = Primary CPICH TX power -CPICH_RSCP + UL interference + Constant value ; (b) calculating k1, k2 and k3 independent safety factors whose values are dynamically changed to suite the step size Ap and instantaneous channel conditions where K1 depends on NpreV and if NPreV = 1, choosing K1 such as to increase the number of preamble transmissions by 1, else using K1 as usually calculated; (c) using MAX (Po, cur, Pjf prev - k1Δp) as the first preamble power and converging at the optimal power using the regular random access procedure if DIFF (POl prev, Po, cur) (d) using MAX(PJt Prev - k2Δp, Po, cur) as the first preamble power and converging at the optimal power using the regular random access procedure if Po, cur >= Po, Prev +Δp; where else if Po, cur + Δp (a) Using Po, cur as the first preamble power and converge to the optimal power using dynamic step sizes to minimize number of preambles; and (b) Using MAX [P0, Cur, (Pj. Prev - k3Δp - (P0, Prev - Po, Cur))] power for the first preamble and converge at the right power using existing random access procedure. 11. A system of power optimization for random access procedure under quasi-stationary environment comprising: (a) a user equipment, reducing the number of successive transmission of preambles to achieve optimized power level to reach network; T (b) means for realizing the reduction in number of preamble transmissions by estimating the amount of preamble power for UE to reach the network, based on a previous random access procedure; (c) means for making an access on a cell with preamble initial power for the random access procedure based on uplink (UL) interference and downlink (DL) path loss; (d) means for sending a response for further access attempts by the network; (e) means for updating the acquired actual preamble power by the UE after receiving each response from the network; and (f) means for avoiding transmission of preamble by starting with the actual preamble power of the previous random access attempt by UE. 12. A method of power optimization for random access procedure under quasi- stationary environment substantially described particularly with reference to the accompanying drawings. 13. A system of power optimization for random access procedure under quasi- stationary environment substantially described particularly with reference to the accompanying drawings.

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2411-CHE-2006 AMENDED CLAIMS 28-02-2013.pdf

2411-CHE-2006 FORM-1 28-02-2013.pdf

2411-CHE-2006 FORM-13 28-02-2013.pdf

2411-CHE-2006 FORM-5 28-02-2013.pdf

2411-CHE-2006 POWER OF ATTORNEY 28-02-2013.pdf

2411-CHE-2006 AMENDED PAGES OF SPECIFICATION 28-02-2013.pdf

2411-CHE-2006 EXAMINATION REPORT REPLY 28-02-2013.pdf

2411-CHE-2006 FORM 1.pdf

2411-CHE-2006 FORM 18.pdf

2411-CHE-2006 OTHER PATENT DOCUMENT 28-02-2013.pdf

2411-che-2006-abstract.pdf

2411-che-2006-claims.pdf

2411-che-2006-correspondnece-others.pdf

2411-che-2006-description(complete).pdf

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2411-che-2006-form 1.pdf

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