IEEE C802.16m-10/0812r1
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Text Proposal for the situation of DL/UL different pathloss (16.3.9.4.7.2)
Date
Submitted
2010-07-12
Source(s)
Jeongho Park, Hokyu Choi
Samsung Electronics
Re:
Proposed text changes to P802.16m/D6
jeongho.jh.park@samsung.com
Abstract
Purpose
Notice
Release
Patent
Policy
To be discussed and adopted by TGm for the 802.16m D7 Draft
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Text Proposal for the situation of DL/UL different pathloss (16.3.9.4.7.2)
Jeongho Park, Hokyu Choi
Samsung Electronics
References
[1] WiMAX Forum Mobile Radio Specifications (2009-07-05)
I. Introduction
This contribution proposes several remedies to solve the problems which are incurred by Uplink Power Control
under the situation with different pathloss between downlink and uplink.
II. Problem Definition
A. Effect of difference pathloss between downlink and uplink
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IEEE C802.16m-10/0812r1
Current power control would operate well with an assumption that downlink pathloss is identical to uplink
pathloss. For the given parameters which are broadcasted by BS, MS measures the downlin pathloss ‘L’ and
decide the required tone power for the uplink transmission.
If there is no mismatch between DL and UL pathloss, no problem would be expected. That is to say uplink IoT
(interference over thermal noise) level would be under the control and transmission would be satisfied with
error rate.
If there is mismatch between DL and UL pathloss for a specific MS, however, a story is going to be different.
1. DL pathloss > UL pathloss
: Generally, this case does not bring a critical problem. If the MS is at cell edge, it would impact on
adjacent sectors as a stronger interference. As soon as serving BS recognizes the difference of DL and
UL pathloss of the MS, however, BS can send AAI_UL_POWER_ADJ message to make the power fit
the proper level.
2. DL pathloss < UL pathloss
: This case would bring a critical problem. Unless BS fixs this difference through message, any control
transmission including BW REQ would not succeed in being decoded by BS at all only except
synchronous ranging which has power ramping function. Even though s-RNG succeeds in arriving at BS
safely through power ramping, BS does not recognize how many times MS did power ramping.
Moreover BW REQ would continuously fail, eventually the MS would disconnect from the serving BS
and might start the initial entry process from cell search, again.
B. Why does different DL and UL pathloss happen?
The simplest case we can take as an example would be FDD systems. According to [1], the recommended
spectrum for R1.5 as FDD systems operation is 1710~1755(MHz) and 2110~2155(MHz) for uplink and
downlink transmission respectively. The frequency gap between DL and UL is 400MHz, which would result in
different pathloss. Theoretically, lower frequency experiences much smaller pathloss which is proportional to
the square of operation frequency. ( L = [4πrfc/c]2 where r is distance, c is the speed of light and fc is the
frequency )
Another peculiar case as an example is an optical repeater. Optical repeater is connected to BS with wired
optical line which repeats the downlink signals to the MSs which received signal strength from BS is not strong
enough. For example, the optical repeater can be deployed in the underground of buildings or subway stations.
The problem is uplink receiver at optical repeater. Since the noise is added with signals to optical repeater, from
the BS point of view, the noise level would be linearly proportional to the number of optical repeaters which are
connected to the BS. For this reason, optical repeater usually has lower uplink gain in order to prevent the noise
level enhancement at BS. If it does not, the noise level of BS would be enlarged and the SINR of an MS which
is connected to macro BS directly would decrease, which eventually bring the shrink of uplink coverage.
Therefore, it is usually understood that smaller gain compared to downlink is inevitable in optical repeater. The
difference of gain between downlink and uplink is dependent on the environments of systems (total number of
repeater, the location of repeater and so on) and typical difference is from 3 to 10dB.
III. The Scope of Suggested Remedies
In this contribution, one parameter updated by MS is proposed – OffsetMS. This value is common to data or
control including sounding channel transmission.
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IEEE C802.16m-10/0812r1
1. Offset update during Initial ranging procedure
Initial power control has its own power control equation for its starting tone power. However, if UL pathloss is
smaller than DL pathloss, the transmission will fail and power will be increased by 2dB (power ramping). After
successful procedure, several power ramping might have been performed. This power ramping amount needs to
be considered for normal power control equation because it is necessary for other uplink transmission channel
too.
Before cases happen, let’s say the current offset value is noted as OffsetMS_Old. Then offset value shall be
updated as follows :
- case 1) Whenever Power Ramping happens,
OffsetMS
= OffsetMS_Old +2
- case 2) Whenever “Power level adjustment” field in RNG-ACK is detected by MS with the value of PRNG_ACK,
OffsetMS
= OffsetMS_Old + PRNG_ACK
Or we can merge all cases happening during initial ranging procedure.
If there have been total N times power ramping and M times RNG-ACK reception with power level adjustment
field until MS succeeded in initial ranging, MS shall update OffsetMS as follows:
OffsetMS
= OffsetMS_Old + 2*N + Sum{(PRNG_ACK) for all M}
Here OffsetMS_old is zero because MS has not received any AAI_UL_POWER_ADJ message before it starts
initial ranging procedure.
2. Offset update during synchronized ranging procedure
Currently, Tx power of synchronized ranging channel is based on equation (291) [1]. And s-RNG has power
ramping feature for its failure case. If UL pathloss is smaller than DL pathloss, power ramping would happen
during s-RNG procedure for successful reception. After successful s-RNG procedure, MS needs to reflect the
amount of power ramping on its normal power control.
Before synchronized ranging happens, let’s say the offset value is noted as OffsetMS_Old. After s-RNG is
completed successfully offset value shall be updated as follows :
If there have been total N times power ramping and M times RNG-ACK reception with power level adjustment
field until MS succeeded in synchronized ranging procedure, MS shall update OffsetMS as follows:
OffsetMS
= OffsetMS_Old + 2*N + Sum{(PRNG_ACK) for all M}
Here OffsetMS_old could have some values because MS would be in connected mode before it started with
synchronized ranging procedure.
3. Power ramping concept for BW REQ preamble code transmission
Currently, BW REQ preamble code transmission does not include power ramping feature. If we think of
repeater case which has different DL and UL gain, however, it is necessary to consider power ramping during
BW REQ preamble code transmission. Or we must guarantee synchronized ranging procedure before BW REQ
preamble transmission.
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IEEE C802.16m-10/0812r1
As shown in Figure 1, if MS moves into the location covered by repeater during its sleep mode, and if downlink
pathloss between location A and B are not so much different, there is no way for BS to recognize that MS went
under the area controlled by repeater. Let’s say the repeater has 5dB small gain for UL. Then no matter how
many MS tries to do BW REQ preamble code transmission for the given parameter of target SINR for BW REQ,
the MS will fail to get response after BW REQ. Eventually, the MS would disconnect from the serving BS and
might start initial entry procedure from the cell searching process again.
In order to prevent this situation, it would be better to have power ramping feature during BW REQ preamble
code transmission.
Base station
MS @ A
Repeater
MS @ B
Figure - 1 Movement of MS from location A to location B
4. Offset update after successful BW REQ preamble code transmission
If BW REQ has power ramping feature for its transmission failure, the amount of power ramping should be
taken into account for UL Tx power.
Let’s say the offset value is noted as OffsetMS_Old before BW REQ preamble transmission happen. Then offset
value shall be updated as follows :
- case 1) If Power Ramping happens,
OffsetMS
= OffsetMS_Old +2
5. Offset report to BS
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IEEE C802.16m-10/0812r1
Since proposals talk about UL Tx power correction mainly determined by MS, BS does not figure out how
much correction was done by MS. Therefore the amount of correction needs to be feedback to BS for BS’s
scheduling. Once BS recognize the amount of correction, BS can reset the value and compensate the same
amount by OffsetData and OffsetControl.
Currently, report triggering condition is defined as below.
(page 746, line 41~)
-------------------------------------------------------------------------------------------------------------------------| M(nlast) – M(n) |  txPowerReportThreshold
(298)
and
n – nlast  txPowerReportMinimumInterval
(299)
or
n – nlast  txPowerReportPeriodicalInterval
(299)
Where M is defined in Equation (301)
M = L + SINRTarget(Reported)
(301)
L is the pathloss defined in Equation (291)
nlast is the frame index when the last AMS status reporting message was sent
n is the current frame index
-------------------------------------------------------------------------------------------------------------------------If we adopt the concept the offset decided by MS which reflects the pathloss difference between downlink and
uplink, equation (301) needs to be changed like the following :
M = L + SINRTarget(Reported) + OffsetMS(Reported)
(301)
Where
nlast is the frame index when the last AMS status reporting message was sent
n is the current frame index
Also OffsetMS needs to be reported to serving BS for BS’s efficient scheduling.
Since power ramping is based on 2dB, power adjustment via RNG-ACK is based on 1dB and offsetControl field
of CDMA allocation A-MAP IE is based on 0.5dB, 0.5dB step report would be good.
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IEEE C802.16m-10/0812r1
IV. Proposed Text
Remedy #1:page 57, Modify table 662 as follows:
-------------------------------------------------Text Change Start ----------------------------------------------------Table 662 – Uplink Power Status Report Header Format
Syntax
Uplink Power
Status Report
Header(){
FID
Type
Length
Size(bit)
Notes
4
5
3
Flow Identifier. Set to 0001.
MAC signaling header type = 0b00101
Indicates the length of the signaling header in
bytes:
0b101: 5 bytes
Indicates whether the AMS has updated its
ULPC parameters from AAI_SCD:
0: No ULPC parameters changed comparing
to previous reporting.
1: The confirmation of new ULPC parameters
from AAI_SCD applied.
Only valid if ULPC Parameters Updating
Indicator == 0b1.
The value is the same as “Change configuration change” in the latest AAI_SCD message.
txPowerPsdBase ( PSD(base) ) is coded using
8 bits in 0.5 dBm steps ranging from -74 dBm
(coded 0x00) to 53.5 dBm (coded 0xFF).
txSirDownlink (SIRDL) is coded using 109
bits in 1/168dB steps ranging from -12dB
(coded 0x000) to 51.9375875 (coded 0x31ff).
Shall be filled by 0 for byte alignment
OffsetAMS using 0.5dB step ranging from 15.5dB (coded 0x00) to 16dB (coded 0x3F)
ULPC Parameters
Updating Indicator
1
Change
Configuration
Change
4
txPowerPsdBase
8
txSirDownlink
109
Reserved
OffsetAMS
56
}
-------------------------------------------------Text Change END -----------------------------------------------------
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IEEE C802.16m-10/0812r1
Remedy #2: Modify from line 41 in page 746 to line 18 in page 747 :
-------------------------------------------------Text Change Start ----------------------------------------------------| M(nlast) – M(n) |  txPowerReportThreshold
(298)
n – nlast  txPowerReportMinimumInterval
(299)
n – nlast  txPowerReportPeriodicalInterval
(300)
and
or
Where M is defined in Equation (301)
M = L + SINRTarget(Reported) + OffsetAMS(Reported)
(301)
L is the pathloss defined in Equation (291)
nlast is the frame index when the last AMS status reporting message was sent
n is the current frame index
OffsetAMS (Reported) is the OffsetAMS value at the moment of ‘Reported’
txPowerReportThreshold is a 4 bit unsigned integer value in 0.5 dB steps, the specific value “0b1111”
shall be interpreted as “infinite”;
txPowerReportMinimumInterval and txPowerReportPeriodicalInterval are coded by 4 bit unsigned
integer values d representing 2d frames, the specific value d = 0b1111 shall be interpreted as “infinite”
The
status
reporting
configuration
parameters
txPowerReportThreshold,
txPowerReportMinimumInterval and txPowerReportPeriodicalInterval are sent from ABS to AMS in the
AAI_UL_PSR_CFG message (defined in 16.2.3.33).
-------------------------------------------------Text Change END -----------------------------------------------------
Remedy #3: Modify from line 39~ to line 65 in page 741:
-------------------------------------------------Text Change Start ----------------------------------------------------The power per subcarrier and per stream shall be calculated according to Equation (291).
P(dBm) = L + SINRTarget + NI + Offset + OffsetAMS
(291)
Where
SINRTarget is the target uplink SINR received by the ABS.
P is the TX power level (dBm) per stream and per subcarrier for the current transmission.
L is the estimated average current DL propagation loss calculated by AMS. It shall include AMS’s Tx
antenna gain and path loss.
NI is the estimated average power level (dBm) of the noise and interference per subcarrier at the ABS, as
indicated in the AAI_ULPC_NI message.
Offset is a correction term for AMS-specific power offset. It is controlled by the ABS through power
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IEEE C802.16m-10/0812r1
control messages. There are two kinds of Offset values that are used for data and control, respectively.
Further details are given in following sections (16.3.9.4.1, 16.3.9.4.2 and 16.3.9.4.3).(291)
OffsetAMS is a correction term determined by AMS whenever it tries non-synchronous ranging,
synchronous ranging or BW REQ preamble code transmission.
The estimated average current DL propagation loss, L, shall be calculated based on the total power received on
the active subcarriers of the frame preamble.
OffsetAMS shall be determined and updated by AMS according to the following rules.
- When AMS starts initial network entry,
OffsetAMS = 0.
- When AMS succeeds in initial/synchronous ranging process after N times power ramping up and M
times of AAI_RNG-ACK messages with power level adjustment field,
OffsetAMS = OffsetAMS_current + 2 * N + PADJ (m)
Where
PADJ (m) is the m-th received power level adjustment field value (m=1, …, M) during ranging
procedure, OffsetAMS_current is the OffsetAMS value before AMS started the process. Note that it is
zero for initial ranging process.
- When AMS succeeds in BW REQ preamble code transmission after N times power ramping up,
OffsetAMS = OffsetAMS_current + 2 * N
- When AMS receives the ‘offsetvalueAMS’ field of AAI_UL_POWER_ADJ message,
OffsetAMS = offsetvalueAMS
-------------------------------------------------Text Change END -----------------------------------------------------
Remedy #4 page 163: Modify from line 9~29 as follows :
-------------------------------------------------Text Change Start ----------------------------------------------------Table 718 – AAI_UL_POWER_ADJ message field Descriptions
M/O
M
Attributes/Arra
y of attributes
offsetData
Size
(bits)
6
M
offsetControl
6
M
offsetvalueAM
S
6
O
channelIndex
8
Value / Note
Conditions
offsetData is the transmit power adjustment value
transmitted by the ABS. It represents the value
among -15.5 to 16 dB with 0.5 dB step
offsetControl is the transmit power adjustment value
transmitted by the ABS. It represents the value
among -15.5 to 16 dB with 0.5 dB step
offsetControl is the transmit power adjustment value
transmitted by the ABS. It represents the value
among -15.5 to 16 dB with 0.5 dB step
Uniquely identifies a fast feedback channel on which
an AMS can transmit fast feedback information.
With this allocation, a one-to-one relationship is
established between channel index and the AMS
N.A.
8
N.A.
N.A.
Present
when ABS
want to
change FF
Channel
Period by
using AAI-
-------------------
IEEE C802.16m-10/0812r1
-----------------------------Text Change END -----------------------------------------------------
Remedy #5 page 743: Include the following proposed text in line 38:
-------------------------------------------------Text Change Start ----------------------------------------------------If AMS does not receive any BR-ACK A-MAP IE at the (n+ BR_ACK_Offset)-th frame who transmitted
a Bandwidth Request preamble sequence at the (n)-th does not receive a response, the AMS considers
it as an implicit-NACK and may restart BR procedure. When it restarts BR procedure for the N-th time
continuously, it shall increase target SINR for BR (SINRtarget for Bandwidth Request,
targetBwRequestSinr) by N PIR,Step dB, where PIR,Step is the step size to ramp up, which is 2 dB.
-------------------------------------------------Text Change END -----------------------------------------------------
9