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)
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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