Inter-FA Scanning Simplification for AMS (15.2.6.13)
Document Number: IEEE C802.16m-09/1883
Date Submitted: 2009-08-29
Source:
I-Kang Fu, Kelvin Chou, YihShen Chen, Paul Cheng
MediaTek Inc.
E-mail: IK.Fu@mediatek.com
kelvin.chou@mediatek.com
Venue:
IEEE 802.16 Session#63 at Jeju, Korea.
Base Contribution:
This is base contribution.
Purpose:
Propose to be discussed and adopted by TGm for the use in Project 802.16m/D1
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Motivation
•
Much longer time is required to complete the scanning over more FAs and cells
–
The scanning process in single FA system already takes a long time
• Number of cells in 16m system is expected to be higher than 16e system
–
Multi-carriers + femtocells = much more scanning targets…..
• Number of FA (carriers) in 16m system will also be more than 16e system
• These result in the difficulty for AMS to arrange its scanning operation to complete scanning
in time
Problem Analysis
•
When the FA number is increased, the time to complete scanning is also increased.
–
–
It takes longer time to collect enough time domain statistics if the scanning opportunities doesn’t increase
The following example take multi-carrier configuration as an example for simple description
Problem Analysis
•
For the multi-carrier AMS implemented by single RF (i.e. with single large FFT), the
same problem on multi-carrier scanning also exists.
Problem Analysis
•
Therefore, the increase on the number of the carriers and cells will result in higher
difficulty for AMS to complete scanning over each carriers for each ABS.
– If the scanning opportunities is the same, the scanning result will be unreliable by higher
variance.
• This is because of the less averaging duration when scanning each ABS over each carrier
• This will degrade the algorithm performances which rely on scanning results as their input
• This will be more significant for the MS with higher speed or for the network with more cells
(especially pico-/femto-cells) deployed into the network
– If the scanning opportunities is increased in response to the number of carriers, the
achievable user throughput will be degraded due to less transmission opportunities.
• This will also result in the difficulty for ABS scheduling, especially when the number of users is
increased.
• Autonomous scanning cannot resolve this problem since the MS can only perform background
scanning over the same carrier as the one used for data transmission
Investigation
•
The received preamble power by AMSj mainly depends on the preamble
transmission power by ABSi over each carrier
– The received preamble signal power from ABSi by AMSj can be represented by the
following equation:
PR,i,j,k = PT,i,k + Gi,j(θi,j) – PL(di,j,k) – χi,j dBm,
(1)
where
PR,i,j,k : Received power of the preamble signal from ABSi by AMSj over carrier k.
PT,i,k : Transmission power on preamble signal by ABSi over carrier k.
Gi,j : antenna gain of the signal transmitted from ABSi to AMSj .
θi,j : the direction of AMSj the with respective to the steering direction of ABSi.
PL(di,j,k) : path loss experienced by the signals transmitted from ABS i to AMSj.
χi,j : shadow fading experienced by the signals transmitted from ABS i to AMSj.
– The multi-path fading effect is not shown in the equation (1) because the scanning
operation will take average over the preamble measurement results.
Investigation
– Because the impact by choosing different carrier is the difference on center frequency,
Gi,j(θi,j) and χi,j in equation (1) are not function of the carrier index k.
– For the path loss over the signals transmitted from ABSi to AMSj, the typical path loss
function can be represented by the following equation:
PL(di,j,k) = Alog10(di,j) + B + Clog10(fc(k)/5) dB
• The parameters {A, B, C} will be different for different environments. For example, the following
path loss model may be used for Rural macro cell environment with LOS condition:
PL(di,j,k) = 40log10(di,j)+10.5-18.5log10(hBS)-18.5log10(hMS)+1.5log10(fc(k)/5) dB
,where
hBS : (m) BS antenna height, hMS : (m) MS antenna height, fc(k) : (GHz) center frequency of carrier k
• In general, the bandwidth of each carrier is from 5MHz~20MHz. Therefore, the separation from the
center frequencies of the adjacent carrier will be within 20MHz for most cases.
• If the carriers supported by ABS and AMS are adjacent in frequency domain, the pathloss
difference due to different carrier will be very small and can be neglected.
• If the carriers supported by BS and MS are separated in frequency domain (e.g. one carrier in
2.5GHz and another at 3.5GHz), the path loss difference will be larger (e.g. around 3dB). But
it can be pre-calculated once the MS can know parameter “C” in advance.
Investigation
– Therefore, the main factor to impact the PR,i,j,k under different k is the PT,i,k.
• The propagation loss in different carrier will not change significantly. The main difference
comes from the BS transmit power over each carrier.
•
The received preamble signal power in carrier k’ can be easily derived by the
scanning result obtained from carrier k by adding the following offsets:
PR,i,,j,k’≈ PR,i,j,k + PT,offset(k, k’) + PLoffset(k, k’)
– PT,offset(k, k’) = PT,i,j,k’ - PT,i,j,k
– PLoffset(k, k’) = C log10(fc(k)/fc(k’)) : the path loss difference between carrier k and k+1,
which is function of the path loss exponent “C” as depicted in previous slide.
• MS can always know fc(k) after synchronize with the serving BS over carrier k, and
it can usually know fc(k’) from multi-carrier configuration information sent by BS.
Then MS can derive the PLoffset(k, k’) once it knows the path loss exponent “C”.
• The received preamble signal power is usually used for reporting to serving BS as the RSSI
(Received Signal Strength Index) result
• If carrier k and carrier k’ are very close in frequency domain (e.g within 100MHz), this path loss
offset value will be very small and can be ignored.
• BS may only need to inform MS the “C” to support multiple band classes scenarios
Investigation
•
The received CINR of carrier k’ can be further derived based on the derived
preamble signal power of carrier k’
CINRi,j,k’ = PR,i,j,,k’ / (IR,i,j,k’ + N)
= PR,i,j,,k’ / (PR,total,j,k’ - PR,i,j,,k’)
,where
IR,j,k’ : received interference power when decoding the signal from ABSi to AMSj over carrier k’
PR,total,j,k’ : total received power by AMSj over carrier k’, including the power of the signals
transmitted from each ABS and the thermal noise power.
– Once the AMSj can obtain the total power received from carrier k’, it can also derive the
received CINR received from ABSi over the carrier k’ before scanning the preamble signal
transmitted by ABSi over the carrier k’.
• AMS only need to measure the total received power from each carrier and perform the aforementioned
derivation, then it can obtain the received CINR from each ABS before scanning their preamble over
each carrier.
Conclusion
•
In order to prevent unnecessary scanning over each FA for each ABS, the
following steps can help AMS easily derive the RSSI and CINR over each
carrier.
1. MS perform scanning over the neighboring BSs in primary carrier
•
•
MS can perform autonomous scanning to prevent service disruption
MS obtains the RSSI of neighboring BSs on primary carrier
2. Serving BS inform MS (1) the A-Preamble transmit power offsets
between each FA in serving/neighboring ABSs (2) and/or the path loss
exponent of the surrounding propagation environment
•
MS can derive the RSSI of the secondary carriers
3. MS measure the total received power over other FAs
4. MS further derive the received CINR of the neighboring BSs based on
the RSSI derived from step 2 and the measurement result by step 3
•
Base on the derivation results, AMS can determine which FAs and ABSs should
be further scanned. But it’s up to AMS implementation algorithm.
Operation Flow Example
AMS
Serving ABS
PT,offset (k, k’) of the
neighboring BSs
Scanning the
neighboring ABSs
Based on the derivation results, AMS
can further perform scanning
operation over the “selected” carriers
and ABSs.
Path loss exponent“C”
AMS derive the RSSI of the
neighboring ABSs in secondary
carriers
Request scanning interval
Grant scanning interval
Measure the total
receive power
AMS derive the received CINR
of the ABS in secondary carriers
Primary Carrier
Primary Carrier
Secondary Carrier k’
- e.g. AMS can only select the ABSs
be scanned over specific carrier if the
RSSI or CINR derivation result is
good (i.e. possible handover target)
Text Proposal to P802.16m/D1
--------------------------------------- Start of the Text ---------------------------------------------[Adopt the following text modification in P802.16m/D1 in page#120, line#54]
Table 707 AAI_MC-ADV Management Message Format
Size (bit)
Description
6
Maximum A-Preamble transmit power level
Field
Transmit Power
[Adopt the following text modification in P802.16m/D1 in page#62, line#28]
BS CINR mean
The BS CINR Mean parameter indicates the CINR measured by the AMS from the serving ABS. The value shall be
interpreted as a signed byte with units of 0.5 dB. The measurement shall be performed on the subcarriers of the frame
preamble that are active in the serving ABS's segment and averaged over the measurement period.
When reporting the BS CINR mean for another FA, AMS is allowed to report the value derived by CINR measurement in
current FA, transmit power difference indicated in AAI_MC-ADV message and the total power measured in another FA.
BS RSSI mean
The BS RSSI Mean parameter indicates the Received Signal Strength measured by the AMS from the serving ABS. The
value shall be interpreted as an unsigned byte with units of 0.25 dB, e.g., 0x00 is interpreted as -103.75 dBm. An MS shall be
able to report values in the range -103.75 dBm to -40 dBm. The measurement shall be performed on the frame preamble and
averaged over the measurement period.
When reporting the BS RSSI mean for another FA, AMS is allowed to report the value derived by RSSI measurement in
current FA and the transmit power difference indicated in AAI_MC-ADV message.
------------------------------------------ End of the Text ----------------------------------------------