1. Performance Evaluation of U-TDOA Positioning for IEEE 802.16m (15.8.2)
IEEE Presentation Submission Template (Rev. 9)
Document Number: IEEE C802.16m-09/2294r1
Date submitted: Nov. 6, 2009
Source: Chien-Hwa Hwang, Pei-Kai Liao, Yih-Shen Chen MediaTek Inc.
Venue: Session #64: November 2009 Atlanta, USA
Re: Letter Ballot #30a on the Draft Amendment (IEEE P802.16m/D2)
Base Contribution: This is base contribution
Purpose: Discussion and approval
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2. 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 m/D2 [2]

3. 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 m network is able to meet the positioning accuracy requirements

4. IEEE 802.16m SRD - LBS Performance Requirements
According to IEEE m SRD [3], IEEE m systems should provide support for LBS. IEEE m systems should satisfy the requirements in the following table
LBS Requirements
Feature
Requirement
Comments
Location determination latency
< 30 s
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)
Need to meet E911
Phase II Requirements
Network-based position
100 meters (67%-tile of the
300 meters (95%-tile of the

5. Description of TOA Estimation Algorithm
A format 0 non-synchronized ranging signal is used by the AMS
The code index of the Zadoff-Chu sequence adopted by the AMS is known to the serving and neighbor ABS’s
The block diagram of TOA estimation is shown in the figure below
Rx Signal
Timing
LPF
RCP
Removal
FFT
Extraction of
Ranging Code
Zero
Padding
IFFT
Peak
Test
Obtain
RCP: Ranging Cyclic Prefix

6. Simulation Assumptions
3 ABS’s (1 serving ABS + 2 neighbor ABS’s) form an equilateral triangle with a side length of 1.5 kilometers
Carrier frequency: 2.5 GHz
Carrier bandwidth: 10 MHz
FFT size: 1024
CP ratio: 1/8
Number of OFDM symbols per subframe: 6
P802.16m/D2 non-synchronized ranging channel, format 0
1 Tx antenna, 2 Rx antennas
Modified ITU Pedestrian B Channel, velocity: 3km/hr
One other user is doing ranging in the same subband with probabilities 1, 0.333, 0.1
Other subcarriers (besides subcarriers for ranging) are transmitting data
Positioning algorithm: TDOA
Distance-dependent pathloss: L (in dB) = log10 R (R in km)
The power of AWGN is 10dB less than the power of intercell interference
Frequency reuse factor = 1
Frames of serving and neighbor ABS’s are synchronized

7. Sources of Interference
The serving and neighbor ABS’s suffer from
AWGN
Intracell interference: interference exists because subcarrier orthogonality cannot be maintained when non-synchronized ranging signal is used
Intercell interference
Another user in the serving cell is doing periodic/aperiodic ranging with a certain probability
Serving
ABS
Neighbor

8. Simulation Results
Collision probability is defined as the probability that another user in the serving cell is doing periodic/aperiodic ranging
One or two times TOA estimates are executed to perform U-TDOA positioning
SIR is fixed as 5dB; AWGN power is 10dB less than interference power

9. Simulation Results: 1 TOA Estimate

10. Simulation Results: 2 TOA Estimates

11. Conclusion
During the execution of LBS, there may be other users in the same cell doing periodic/aperiodic ranging. This degrades the performance of positioning
Intracell interference due to loss of orthogonality when sending ranging signals and intercell interference from neighboring cells also deteriorate the performance
The ranging channel based U-TDOA positioning is NOT able to meet strict Enhanced 911 Phase II requirements in above-mentioned interference limited multipath environment

12. Text Proposal

13. References
[1] IEEE C80216m-09/2086, “Evaluation of D-TDOA Positioning”
[2] IEEE P802.16m/D2. “DRAFT Amendment to IEEE Standard for Local and metropolitan area networks—Part 16: Air Interface for Broadband Wireless Access Systems—Advanced Air Interface” /
[3] IEEE m-07/002r9, “IEEE m System Requirement Document (SRD)”/