Performance Evaluation of U-TDOA Positioning for IEEE 802.16m (16.8.2) IEEE 802.16 Presentation Submission Template (Rev. 9) Document Number: IEEE C802.16m-09/2908 Date submitted: Dec. 31, 2009 Source: Chien-Hwa Hwang, Pei-Kai Liao, Yih-Shen Chen MediaTek Inc. Venue: Session #65: 11-14 January 2010, San Diego, USA Re: Letter Ballot #30b on the Draft Amendment (IEEE P802.16m/D3) Base Contribution: This is base contribution Purpose: 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. 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Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and <http://standards.ieee.org/board/pat >. 1 Introduction Performance of D-TDOA positioning was evaluated in [1] in Hawaii, USA (IEEE Session #63.5) This document defines some specific assumptions required for U-TDOA based positioning evaluation and presents simulation results for U-TDOA positioning that were obtained with specified assumptions This contribution is compliant with the latest version of IEEE 802.16m/D3 [2] 2 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 3 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 meter (67%-tile of the CDF of the position accuracy) 150 meter (95%-tile of the CDF of the position accuracy) Network-based position accuracy (in meters) 100 meter (67%-tile of the CDF of the position accuracy) 300 meter (95%-tile of the CDF of the position accuracy) Comments Need to meet E911 Phase II Requirements 4 TOA Estimation 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 estimations for the ranging signal transmitted by the AMS U-TDOA is computed based on TOAs [4] of serving and neighbor ABSs Block diagram of TOA estimation 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 5 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 TDOA algorithm Algorithm for nonlinear least squares problems in Reference [4] 6 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 std. dev. 3dB 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 Another AMS is doing ranging at the same subband with probability [0, 0.5], called ranging collision rate Other subbands (besides the subband for ranging) are carrying data In the cells of neighbor ABSs Ranging subband is occupied by another AMS with probability [0, 0.5], called interference collision rate Other subbands (besides the subband for ranging) are carrying data 7 Simulation Results (1/3) Intercell interference to noise ratio (IoT) = 0dB; 2 ranging channels Empirical CDF of X 1 0.9 ICR = 0 0.8 ICR = 0.5 0.7 0.6 F(X) 0.5 0.4 ICR: Interference Collision Rate RCR: Ranging Collision Rate 0.3 0.2 ICR = 0; RCR = 0 ICR = 0; RCR = 0.5 ICR = 0.5; RCR = 0 ICR = 0.5; RCR = 0.5 0.1 0 0 50 100 150 200 250 300 350 400 450 500 X: Positioning Error (in meters) 8 Simulation Results (2/3) Intercell interference to noise ratio (IoT) = 3.5dB; 2 ranging channels Empirical CDF of X 1 0.9 ICR = 0 0.8 ICR = 0.5 0.7 0.6 F(X) 0.5 0.4 ICR: Interference Collision Rate RCR: Ranging Collision Rate 0.3 0.2 ICR = 0; RCR = 0 ICR = 0; RCR = 0.5 ICR = 0.5; RCR = 0 ICR = 0.5; RCR = 0.5 0.1 0 0 50 100 150 200 250 300 350 400 450 500 X: Positioning Error (in meters) 9 Simulation Results (3/3) Intercell interference to noise ratio (IoT) = 7dB; 2 ranging channels Empirical CDF of X 1 0.9 ICR = 0 0.8 ICR = 0.5 0.7 0.6 F(X) 0.5 0.4 ICR: Interference Collision Rate RCR: Ranging Collision Rate 0.3 0.2 ICR = 0; RCR = 0 ICR = 0; RCR = 0.5 ICR = 0.5; RCR = 0 ICR = 0.5; RCR = 0.5 0.1 0 0 50 100 150 200 250 300 350 400 450 500 X: Positioning Error (in meters) 10 Conclusion Performance of U-TDOA is deteriorated due to In the serving cell, other AMSs are doing ranging In the cells of neighbor ABSs, some AMSs are sending data using the ranging subband Intercell interference from adjacent cells U-TDOA positioning based on current ranging channel allocation scheme is NOT able to meet strict Enhanced 911 Phase II requirements in interference limited multipath environment It is suggested to have a dedicated positioning radio resource (such as an FDM zone) among cooperative ABSs for U-TDOA and TOA 11 Text Proposal 15.8.2.2 Measurements and Reporting for Location Determination The Location measurement and report capabilities needed to support Basic LBS are the following: •The ABS ability to provide AMS with, and the AMS’s ability to process, the AAI_-LBS-ADV identifying the neighboring ABS’s which need to be scanned by the AMS as well as their locations. •ABS capability to direct AMS to start scanning using a MAC management message, with indication that is for location determination, and to report the results to ABS using a MAC management message. This direction shall include information about which parameter the AMS to measure and report, e.g. RSSI, RD, etc., and it may also include a flag to indicate if Enhanced LBS measurements should be used. •AMS capability to request ABS for scanning time for LBS. •AMS’s capability for downlink scanning of SA-Preambles identified by a MAC management message to measure RSSI and RD. •AMS and ABS capability to enable measurement of RTD based on non-synchronous ranging channel transmission (UL-TDOA and TOA). •ABS’s capability to allocate a dedicated radio resource among cooperative ABSs for non-synchronous ranging channel transmission by AMS •AMS providing scanning report to ABS providing measurements results based on LBS specific direction in a MAC management message. •A The MAC management message shall be used by ABS to trigger measurements in support of location. These a MAC management messages include indication that the purpose of scanning and report is for location calculation. 12 References [1] IEEE C80216m-09/2086, “Evaluation of D-TDOA Positioning” [2] IEEE P802.16m/D3. “DRAFT Amendment to IEEE Standard for Local and metropolitan area networks—Part 16: Air Interface for Broadband Wireless Access Systems—Advanced Air Interface” / December 2009 [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 13