Performance Evaluation of U-TDOA Positioning for IEEE 802.16m
(16.8.2)
Document Number: IEEE C802.16m-09/2908r2
Date submitted: Jan. 07, 2010
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
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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
Reasons for U-TDOA (1/2)

No AAI_LBS-ADV message is required


No need for AMS to feedback the measurement results



No need to implement location estimation algorithm if it is
conducted in AMS
Lower complexity of cell coordination


TOA, TDOA measurement results
Location estimation results if it is conducted in AMS
Lower complexity in AMS


In D-TDOA, it takes about 328 bits for broadcasting even when
there are not many AMSs requesting LBS
Fewer involved ABSs for interference control
Less impact on HARQ timing

D-TDOA requires one dedicated DL subframe for LBS and it may
impact HARQ timing
5
Reasons for U-TDOA (2/2)

For scenarios wherein there are many AMSs requesting
LBS in a short time or with high accuracy, D-TDOA is a
better choice

However, for other scenarios, U-TDOA is more efficient
and introduces less complexity to the system
6
Problems in D3

In D3, only the following text about U-TDOA 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 D3, 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 D3 and all are contention-based
7
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 of serving and neighbor ABSs using
algorithm of [4]
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
8
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]
9
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

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 (sending data) with probability [0,
0.5], called interference collision rate
 Other subbands (besides the subband for ranging) are carrying data
10
Simulation Results (1/3)
Average 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
ICR = 0; RCR = 0
ICR = 0; RCR = 0.5
ICR = 0.5; RCR = 0
ICR = 0.5; RCR = 0.5
0.2
0.1
0
0
50
100
150
200
250
300
350
400
450
500
X: Positioning Error (in meters)
11
Simulation Results (2/3)
Average 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
ICR = 0; RCR= 0
ICR = 0; RCR= 0.5
ICR = 0.5; RCR= 0
ICR = 0.5; RCR= 0.5
0.2
0.1
0
0
50
100
150
200
250
300
350
400
450
500
X: Positioning Error (in meters)
12
Simulation Results (3/3)
Average 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
ICR = 0; RCR = 0
ICR = 0; RCR = 0.5
ICR = 0.5; RCR = 0
ICR = 0.5; RCR = 0.5
0.2
0.1
0
0
50
100
150
200
250
300
350
400
450
500
X: Positioning Error (in meters)
13
Conclusion

Performance of U-TDOA deteriorates 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

With dedicated ranging channel allocation among cooperative ABSs,
U-TDOA positioning is able to meet E911 requirement

It is suggested to have a dedicated positioning radio resource (such
as an FDM zone) among cooperative ABSs for U-TDOA and TOA
14
Text Proposal
15.8.2.2 Measurements and Reporting for Location Determination
16.8.2.2
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.
15
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
16