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Transcript of Scheduling and capacity estimation in LTE - ITC 23 · PDF fileScheduling and capacity...
![Page 1: Scheduling and capacity estimation in LTE - ITC 23 · PDF fileScheduling and capacity estimation in LTE Olav Østerbø, ... LTE is the new, ... building on current](https://reader036.fdocuments.us/reader036/viewer/2022082212/5a72baf37f8b9ab6538dc595/html5/thumbnails/1.jpg)
Scheduling and capacity estimation in LTE
Olav Østerbø, Telenor CD (Corporate Development)
ITC-23, September 6-8, 2011, San Francisco
![Page 2: Scheduling and capacity estimation in LTE - ITC 23 · PDF fileScheduling and capacity estimation in LTE Olav Østerbø, ... LTE is the new, ... building on current](https://reader036.fdocuments.us/reader036/viewer/2022082212/5a72baf37f8b9ab6538dc595/html5/thumbnails/2.jpg)
Agenda
Introduction
Obtainable bitrate as function of SINR
Radio channel propagation model
Radio signal fading model
Analytical models for LTE radio network performance
Numerical examplesNumerical examples
Conclusions
ITC-23, September 6-8, 2011, San Francisco2
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Introduction
LTE is the new, (following up of HSPA) mobile access technology specified by 3GPP:
• Flat all-IP architecture
• Flexible in frequency bands (700 MHz-2.6 GHz)
• Flexible carrier bandwidths (1.4, 3, 5, 10, 15 and 20 MHz)
• Increased spectrum efficiency based on OFDMA for • Increased spectrum efficiency based on OFDMA for uplink, SC-FDMA for downlink
– Typical cell capacity (20 MHz bandwidth), 20 – 40 Mbps for downlink link and 5 – 15 Mbps for uplink
• Momentum in the industry, building on current investments in the GSM/UMTS
ITC-23, September 6-8, 2011, San Francisco3
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Obtainable bitrate as function of SINR
Bitrate function B=B(SINR)
• Upper bound Shannon: B/f=Log2(1+SINR)
• Discrete; B/f based on CQI-table (3GPP TS 36.213) and Linear relation between SINR[dB] and CQI-index
• Approximate/Truncated modified version of Shannon's formula:
B/f=MIN[T, C Log2(1+γSINR)]
6
D ---- Shannon
CQI index modulation code rate x 1024 efficiency
0 out of range
1 QPSK 78 0.1523
0 5 10 15 20 25SINR@dBD
1
2
3
4
5
de
si
la
mr
oN
tu
ph
gu
or
hT
@tib s
zHD ---- Modified Shannon
---- LTE CQI table
ITC-23, September 6-8, 2011, San Francisco4
1 QPSK 78 0.1523
2 QPSK 120 0.2344
3 QPSK 193 0.3770
4 QPSK 308 0.6016
5 QPSK 449 0.8770
6 QPSK 602 1.1758
7 16QAM 378 1.4766
8 16QAM 490 1.9141
9 16QAM 616 2.4063
10 64QAM 466 2.7305
11 64QAM 567 3.3223
12 64QAM 666 3.9023
13 64QAM 772 4.5234
14 64QAM 873 5.1152
15 64QAM 948 5.5547
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Radio channel propagation model
Signal-to-noise ratio:GP
SINR w=
r
Signal-to-noise ratio:
sending power
Path loss (model):
C and A constants, Xt shadowing usually assumed to be normal
distributed with zero mean and given standard deviation
Noise sum the internal (or own-cell) noise power and is the external (or other-cell) interference.
wPN
GPSINR w=
1010LG = tXrACL +−= )(log10
extNNN += int
ITC-23, September 6-8, 2011, San Francisco5
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Radio signal fading model
SINR on the form:
Stochastic part of SINR:
Slow fading (shadowing): Lognormal
Fast fading: Rayleigh, i.e. neg. exp. distributed
: Suzuki distributed with CDF
)(λα hrSt
et XXS ln=lnX
eX
tS dtt
edttsexS
t
xtt
t
xtsu ∫∫
∞
=
−−∞
=
− ==0
2
))(ln(
ln
0
2
2
2
1)()(
~ σ
σπ
)ln()1(11~ 2
))(ln(22
2
2
σσσ Txke kkTxt
t−
∑∫∞
−−
Truncated version:
1 2 3 4 5x
0.5
1
1.5
2
2.5
3
sHxL
1 2 3 4 5
x
0.25
0.5
0.75
1
1.25
1.5
1.75
2
sHxL
2.0=σ
6.0=σ
0.1=σ
0.2=σ
0.5=σ
2.0=σ
2.0=σ
6.0=σ
0.1=σ
0.2=σ
0.5=σ 2.0=σ
Lognormal Suzuki
ITC-23, September 6-8, 2011, San Francisco6
)2
)ln(
2(
!
)1(
2
1
2
1),(
~
0
2
0
2 2
σσ
σπ
σσ Txkerfcex
kdt
t
eTxS
k
kk
kT
t
su +−== ∑∫∞
==
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Analytical models for LTE radio network performance
• Spectrum efficiency through the bit-rate distribution per Recourse Block (RB) for users that are either randomly or located at a particular distance in a cell.
• Cell throughput/capacity and fairness by taking the scheduling into account.
– Scheduling based on metrics which depends (only) on own SINR and distance and distance
– Specific models for the common (basic) scheduling algorithms, Round Robin, Proportional Fair and Max-SINR.
• Estimation of the capacity usage for GBR sources in LTE
– Non-persistent allocation, i.e. allocation every TTI to obtain GBR rate
• Cell throughput/capacity for a mix of GBR and Non-GBR (greedy) users
ITC-23, September 6-8, 2011, San Francisco7
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Input parameters to numerical examples
Parameters Numerical values
Bandwidth per Resource Block 180 kHz=12x 15 kHz
Total Numbers of Resource Blocks 100 RBs
Distance-dependent path loss. (Taken from a 3GPP document)
L=C +37.6log10(r), r in kilometers andC=28.1 dB for 2GHz
ITC-23, September 6-8, 2011, San Francisco8
Lognormal Shadowing with standard deviation
8 dB (in most of the cases)
Rayleigh fast fading
Noise power at the receiver -101 dBm
Total send power 46.0 dBm=(40W)
Radio signaling overhead 3/14
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Mean throughput per RB as function of cell radius
0.4
0.5
0.6
0.7
0.8
tu
pr
ep
BR@
ti
bM sD
Located at cell
edge
Random location
Suzuki distributed fading, 2GHz frequency and σ=0dB, 2dB, 5dB, 8dB, 12dB from below.
1 2 3 4 5Distance @KmD
0.1
0.2
0.3
na
eM
ph
gu
or
ht
Random location
Throughput per RB drops for large cells. Approx 0.2 Mbit/s for 2km cell and 0.05 Mbit/s at cell edge with 8dB shadowing.
ITC-23, September 6-8, 2011, San Francisco9
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Multiuser gain as function of cell radius
40
50
60
70
80
yt
ic
ap@
ti
bM sD
-- PF
2GHz frequency, 100 RBs, fading Susuki distributed with shadowing σ=8 dB, number of users =1, 2, 3, 5, 10, 25, 100 from below.
1 2 3 4 5Distance @KmD
10
20
30ll
eC
pa
c -- PF
-- Max-SINR
-- RR
Multiuser gain very large for Max-SINR. PF doubles cell throughput compare to RR for cell of 2 km and 25 users.
ITC-23, September 6-8, 2011, San Francisco10
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Mean Bitrate for a user located at cell edge as function of cell radius.
1 2 3 4 5Distance @KmD
5
10
15
20
25
30
35
40
yt
ic
apa
Cr
ep
re
su@
tib
M sD
1 2 3 4 5
Distance @KmD
5
10
15
20
25
yt
ic
ap
aC
re
pr
es
u@
ti
bM sD
16
D
8
D
RR
PF
Max-
SINR
RR
PF
Max-
SINR
2-users3-users
1 2 3 4 5Distance @KmD
2
4
6
8
10
12
14
yt
ic
ap
aC
re
pr
es
u@
tib
M sD
1 2 3 4 5Distance @KmD
1
2
3
4
5
6
7
yt
ic
ap
aC
re
pr
es
u@
ti
bM sD
RR
PF
Max-
SINR
RR PF
Max-
SINR
5-users10-users
Scheduling: RR, PF and Max-SINR scheduling algorithm , 2GHz frequency and 100 RBs
Max-SINR shows very poor cell edge performance
ITC-23, September 6-8, 2011, San Francisco11
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Mean cell throughput for 10 users scheduled according to PF and a GBR user
0.5 1 1.5 2 2.5Distance @KmD
10
20
30
40
50
60
70
80
ll
eC
yt
ic
ap
ac@
ti
bM sD
0.5 1 1.5 2 2.5
Distance @KmD10
20
30
40
50
60
70
80
ll
eC
yt
ic
ap
ac@
ti
bM sD
70
80
70
80
-- Non-Persistent, cell edge
-- Non-Persistent, random
-- mean PF 10 users
GBR=1 Mbit/s
-- Non-Persistent, cell edge -- Non-Persistent, cell edge
GBR=3 Mbit/s
-- Non-Persistent, cell edge
-- Non-Persistent, random
-- mean PF 10 users
0.5 1 1.5 2 2.5Distance @KmD
10
20
30
40
50
60
70
ll
eC
yt
ic
ap
ac@
ti
bM sD
0.5 1 1.5 2 2.5
Distance @KmD10
20
30
40
50
60
70
ll
eC
yt
ic
ap
ac@
ti
bM sD
GBR=0.3 Mbit/s
-- Non-Persistent, cell edge
-- Non-Persistent, random
-- mean PF 10 users
GBR=0.1 Mbit/s
-- Non-Persistent, cell edge
-- Non-Persistent, random
-- mean PF 10 users
GBR of 3.0, 1.0, 0.3, 0.1 Mbit/s using non-persistent scheduling, for 2 GHz and 100 RB and Suzuki distributed fading with std. σ=8dB.
GBR rates of less than 1 Mbit/s does not reduce the overall throughput very much. GBR rates larger than 1 Mbit/s is not recommended.
ITC-23, September 6-8, 2011, San Francisco12
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Conclusions
• The two most important factors for the radio performance in LTE are fading and attenuation due to distance.
• Numerical examples for LTE downlink shows results which are reasonable;
– In the range 25-50 Mbit/s for 1 km cell radius at 2GHz with 100 RBs .
– Multiuser gain is large for the Max-SINR algorithm but also the PF – Multiuser gain is large for the Max-SINR algorithm but also the PF algorithm gives relative large gain relative to plain RR.
– The Max-SINR has the weakness that it is highly unfair in its behaviour. (Not recommended to use in real operation.)
• The usage of GBR with high rates may cause problems in LTE due to the high demand for radio resources if users have low SINR i.e. at cell edge.
– GBR rate limited to at most 1 Mbit/s per user?
ITC-23, September 6-8, 2011, San Francisco13