U-TDOA/TOA Positioning for IEEE 802.16m Document Number: IEEE C802.16m-10/0221 Date submitted: March. 05, 2010 Source: Chien-Hwa Hwang, Pei-Kai Liao, Yih-Shen Chen MediaTek Inc. Venue: IEEE 802.16 Session #66, Orlando, USA Re: Letter Ballot #31 on the Draft Amendment (IEEE P802.16m/D4) Base Contribution: This is base contribution Purpose: For TGm members’ discussion and approval Notice: This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.16. Patent Policy: The contributor is familiar with the IEEE-SA Patent Policy and Procedures: <http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and <http://standards.ieee.org/guides/opman/sect6.html#6.3>. Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and <http://standards.ieee.org/board/pat >. 1 Motivation One of the most powerful ways to personalize mobile services is based on location. One of the most obvious technologies behind location based service (LBS) is positioning Strict requirements on user positioning accuracy are imposed on existing location services such as wireless Enhanced 911 and new upcoming services It is imperative to verify whether IEEE 802.16m network is able to meet the positioning accuracy requirements 2 LBS Performance Requirements According to IEEE 802.16m SRD [3], IEEE 802.16m systems should provide support for LBS. IEEE 802.16m systems should satisfy the requirements in the following table LBS Requirements Feature Requirement Location determination latency < 30 sec Handset-based position accuracy (in meters) 50 meters (67%-tile of the CDF of the position accuracy) 150 meters (95%-tile of the CDF of the position accuracy) Network-based position accuracy (in meters) 100 meters (67%-tile of the CDF of the position accuracy) 300 meters (95%-tile of the CDF of the position accuracy) Comments Need to meet E911 Phase II Requirements 3 Reasons for Network-based Positioning (1/2) No AAI_LBS-ADV message is required In handset-based positioning, it takes about 328 bits for broadcasting even when there are not many AMSs requesting LBS No need for AMS to feedback the measurement results TOA measurement results Location estimation results if it is conducted in AMS Lower complexity in AMS Lower complexity of cell coordination No need to implement location estimation algorithm if it is conducted in ABS Fewer involved ABSs for interference control Less impact on HARQ timing Handset-based positioning may require one dedicated DL subframe for better LBS performance to meet E911 requirement and it may impact HARQ timing 4 Reasons for Network-based Positioning (2/2) For scenarios wherein there are many AMSs requesting LBS in a short time or with high accuracy, handset-based positioning is a better choice However, for other scenarios, network-based positioning is more efficient and introduces less complexity to the system 5 Problems in D4 In D4, only the following text about network-based positioning is mentioned and the description is not clear “AMS and ABS capability to enable measurement of RTD based on ranging channel transmission (U-TDOA and TOA) (see Subclause 6.3.25)” There are currently two types of ranging channel and the above text does not specify which type According to D4, both types of ranging channel allocation are contention-based so it’s unlikely for AMS to meet E911 requirement due to intra-cell interference Only the allocation for initial ranging, handover ranging, periodic ranging is mentioned in D4 and all are contention-based 6 Definition of Terminology TOA measurement algorithm The algorithm used to measure the TOA of the positioning reference signal sent by the target AMS to the serving/neighbor ABSs. The TOA measurements can be transformed to the distances between the target AMS and the serving/neighbor ABSs. Positioning algorithm The algorithm which computes the position of the target AMS using TOA measurements. If TOA measurements are used for the computation of position, it is called UTOA positioning algorithm. If relative differences of TOA measurements are used for the computation of position, it is called U-TDOA positioning algorithm. 7 Proposed U-TDOA/TOA Positioning Mechanism (1/4) Scenario #1: Serving cell interference: none Cooperative neighboring cell interference: none One reference signal transmission for one TOA measurement Dedicated radio resource for one AMS so as to suppress intra-cell interference An assignment A-MAP is used to allocate the radio resource to a specific AMS for LBS ranging Dedicated radio resource among cooperative cells so as to suppress inter-cell interference Physical ranging channel for non-synchronized AMSs is utilized as reference signal for uplink TOA measurement Inter-BS coordination is used to silence the radio resource for LBS ranging in cooperative cells More than one TOA measurements can be conducted over a period of time to improve positioning result The number of TOA measurements can be adjusted by serving BS and broadcasted to MSs e,g,: the adjustment is based on current traffic load The number of TOA measurements can be fixed and predefined in the system 8 Proposed U-TDOA/TOA Positioning Mechanism (2/4) Scenario #2: Serving cell interference: none Cooperative neighboring cell interference: yes One reference signal transmission for one TOA measurement Dedicated radio resource for one AMS so as to suppress intra-cell interference Physical ranging channel for non-synchronized AMSs is utilized as reference signal for uplink TOA measurement An assignment A-MAP is used to allocate the radio resource to a specific AMS for LBS ranging No inter-BS coordination is required to silence the radio resource for LBS ranging in cooperative cells More than one TOA measurements can be conducted over a period of time to improve positioning result The number of TOA measurements can be adjusted by serving BS and broadcasted to MSs e,g,: the adjustment is based on current traffic load The number of TOA measurements can be fixed and predefined in the system 9 Proposed U-TDOA/TOA Positioning Mechanism(3/4) AMS transmits the reference signal to all ABSs over this radio resource one time Cooperative BS One transmission, instead of sequential multiple transmissions, to all ABSs per TOA measurement Cooperative BS Serving BS Neighboring BS Timing Adjustment t3 UL Reference Signal Received Granted Slot Serving BS Timing Adjustment t2 UL Reference Signal Received Delayed Granted Slot Propagation Delay Timing Advance t1 UL Reference Signal Transmitted 10 Proposed U-TDOA/TOA Positioning Mechanism (4/4) Network or Serving ABS Initiation MS Serving BS Cooperative BSs Network-based Positioning is initiated by the Network 1 Select cooperative BSs 2 Necessary Information for Positioning Radio Resource Allocation for Positioning 3 Same Time Instant Positioning Reference Signal Reference Signal Detection & TOA Measurement 4 5 Reference Signal Detection & TOA Measurement 5 TOA Measurement Results 6 Repeat Step 3~6 Several Times Repeat Step 3~6 Several Times Positioning 7 Repeat Step 3~6 Several Times 8 Positioning Results 9 11 Conclusion Based on the simulation results shown in the appendix, network-based positioning can meet E911 performance requirement if there is dedicated radio resource for LBS ranging among cooperative cells Suggest to adopt the proposed scenario #1 for IEEE 802.16m 12 Text Proposal 13 Appendix 14 TOA Measurement Algorithm Serving ABS and two neighbor ABSs cooperate to perform positioning Format 0 non-synchronized ranging signal is transmitted by the AMS to be positioned Code index of Zadoff-Chu sequence adopted by the AMS is known to the serving and neighbor ABSs Serving and neighbor ABSs execute TOA measurements for the ranging signal transmitted by the AMS U-TDOA/TOA positioning is computed using algorithm [4] based on TOA measurements of serving and neighbor ABSs Block diagram of TOA measurement algorithm is shown in the figure below Ranging Signal LPF RCP Removal FFT RCP: Ranging Cyclic Prefix Extraction of Ranging Code Zero Padding Ranging Code IFFT Peak Test Obtain Timing Timing 15 Simulation Assumptions System Parameters Bandwidth, FFT size, CP ratio 10 MHz, 1024 points, 1/8 Carrier frequency 2.5 GHz OFDMA symbols per subframe 6 Ranging signal format Format 0 non-synchronized ranging channel in IEEE 802.16m, Draft 3 [2] Equipment Model ABS Number of RX antennas 2 Antenna gain 17dBi, q 3dB = 70°, Max. attenuation 20dB Noise figure 5dB Cable loss 2dB AMS Number of TX antennas 1 Antenna gain Omni, 0dBi Maximum Tx power 23dBm Deployment Parameters Cell layout Hexagonal grid, Warp around Inter-site distance 1500 m Shadowing factor Lognormal shadowing std. dev. 8dB, Correlation distance of shadowing 50 m Channel model Modified ITU Pedestrian B Channel, velocity 3km/hr Path loss model PL (dB) = 130.19 + 37.6 log10 (R [km]) Penetration loss 10dB Frequency reuse factor 1 Others Positioning algorithm Algorithm for nonlinear least squares problems in Reference [4] 16 Interference Model For serving and neighbor ABSs Signal to thermal noise ratio (SNR) is fixed as 10dB Intercell interference to thermal noise ratio (IoT) is Gaussian with mean [0, 3.5, 7] dB and variance 2dB Based on SNR and IoT setting, average signal to intercell interference plus thermal noise ratio (SINR) is [7, 4.9, 2.2] dB Intracell interference appears because subcarrier orthogonality between nonsynchronized ranging signal and regular OFDM signal cannot be maintained In the cell of serving ABS Other subbands (besides the subband for ranging) are carrying data In the cells of neighbor ABSs Ranging subband is occupied by another AMS (sending data) with probability [0, 0.5], called interference collision rate Other subbands (besides the subband for ranging) are carrying data 17 Mechanism to Enhance Positioning Accuracy Some mechanism can be utilized to enhance the accuracy of positioning Scheme 1 d := estimated distance of the target AMS to the serving ABS by TOA measurement algorithm If d is smaller than a threshold, e.g. 50 meters, then the position of the serving ABS is utilized as the target AMS position Scheme 2 (xTDOA, yTDOA) := estimated position of the target AMS by U-TDOA positioning algorithm (xTOA, yTOA) := estimated position of the target AMS by U-TOA positioning algorithm If the distance from (xTDOA, yTDOA) to the serving ABS is smaller than d, then (xTDOA, yTDOA) is declared as the target AMS position; otherwise, (xTOA, yTOA) is used. 18 Simulation Results (1/3) Average intercell interference to noise ratio (IoT) = 0dB; 2 ranging channels Empirical CDF of X 1 0.9 0.8 0.7 0.6 F(X) 0.5 0.4 0.3 0.2 interference collision rate = 0 interference collision rate = 0.5 0.1 0 0 50 100 150 200 250 300 350 400 X: Positioning Error (in meters) 450 500 19 Simulation Results (2/3) Average intercell interference to noise ratio (IoT) = 3.5dB; 2 ranging channels Empirical CDF of X 1 0.9 0.8 0.7 0.6 F(X) 0.5 0.4 0.3 0.2 interference collision rate = 0 interference collision rate = 0.5 0.1 0 0 50 100 150 200 250 300 350 400 X: Positioning Error (in meters) 450 500 20 Simulation Results (3/3) Average intercell interference to noise ratio (IoT) = 7dB; 2 ranging channels Empirical CDF of X 1 0.9 0.8 0.7 0.6 F(X) 0.5 0.4 0.3 0.2 interference collision rate = 0 interference collision rate = 0.5 0.1 0 0 50 100 150 200 250 300 350 400 X: Positioning Error (in meteres) 450 500 21 References [1] IEEE C80216m-09/2086, “Evaluation of D-TDOA Positioning” [2] IEEE P802.16m/D4. “DRAFT Amendment to IEEE Standard for Local and metropolitan area networks—Part 16: Air Interface for Broadband Wireless Access Systems—Advanced Air Interface” / January 2010 [3] IEEE 802.16m-07/002r9, “IEEE 802.16m System Requirement Document (SRD)”/ 2009-09-24 [4] Fletcher, R., (1971): A Modified Marquardt Subroutine for Nonlinear Least Squares. Rpt. AERE-R 6799, Harwell 22