Transcript OFDMA for wireless communications - part IV

OFDM(A) Competence Development – Part IV
Per Hjalmar Lehne, Frode Bøhagen, Telenor R&I
R&I seminar, 23 January 2008, Fornebu, Norway
[email protected]
[email protected]
Outline
• Part I: What is OFDM?
• Part II: Introducing multiple access: OFDMA, SC-FDMA
• Part III: Wireless standards based on OFDMA
• Part IV: Radio planning of OFDMA
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OFDMA Radio Planning
• No difference in the principal planning procedure
compared to GSM and UMTS
• Steps in a planning procedure:
1. Find the input parameters
2. Define cell edge quality
3. Calculate coverage
Input parameters:
 power
 frequency
reuse scheme
 etc…
Define edge
quality
If coverage or
capacity do
not meet
requirements
Results:
 Path loss
 Cell range
Covera
ge
4. Calculate capacity
Results:
 Cell capacity
 Throughput
distributions
Capacit
y
Subcarrier orthogonality
=> OFDMA planning has more
resemblance with GSM planning than
UMTS planning
Done
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Frequency Reuse
•
Frequency reuse is a source to co-channel-interference (CCI)
•
Traditional GSM planning uses relatively large FRF
(Example: FRF = 7)
•
For new OFDMA systems smaller FRFs are suggested (typical
FRFs of 1 or 3)
Smaller FRF => Inter cell interference for
OFDMA systems closer to UMTS than GSM
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Reuse Factor = 1
•
Referred to as universal frequency reuse
•
Reuse 1 => always highest spectral efficiency
•
Usually combined with interference randomization
– Frequency hopping
– Frequency domain scrambling
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Reuse Factor = 3
• Increased spatial separation between co-channels
– Eliminates CCI at the sector boundaries
– Significantly decreases CCI between neighbour cells
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Fractionally Frequency Reuse
• Procedure
1. Users are designated into multiple classes (e.g. cell centre and
cell edge)
2. Different frequency resources are assigned for different user
classes
3. Transmissions across BSs and sectors are coordinated so that
maximal interference avoidance is achieved
f1+ f2+ f3
f1
f2
f3
frequency
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Fractionally Frequency Reuse
• Time coordination
DL subframe
Preamble
Centre cell
with FRF =1
Whole cell
with FRF =3
UL subframe
Centre cell
with FRF =1
Whole cell
with FRF =3
• Power coordination
• Result: Frequency reuse factor between 1 and 3
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Link budget
• Studying OFDMA link budgets reveals
– No big surprises
– Interference margins between 1-6 dB suggested
• Example: E-UTRA link budget (outdoor)
Uplink
Downlink
Data rate
kbps
64,0
a
b
c
d
Transmitter - UE
Max. TX power
TX antenna gain
Body loss
EIRP
dBm
dBi
dB
dBm
24,0
0,0
0,0
24,0 =a + b - c
e
f
g
h
i
j
k
l
m
Receiver - Node B
Node B noise figure
Thermal noise
Receiver noise floor
SINR
Receiver sensitivity
Interference margin
Cable loss
RX antenna gain
MHA gain
dB
2,0
dBm -118,4 = k(Boltzmann) x T(290K) x B(360kHz)
dBm -116,4 =e + f
dB
-7,0 From simulation (Nokia)
dBm -123,4 =g + h
dB
2,0
dB
2,0
dBi
18,0
dB
2,0
Maximum path loss
dB
163,4 =d - i - j + k + l - m
Data rate
Mbps
a
b
c
d
Transmitter - Node B
HS-DSCH power
TX antenna gain
Cable loss
EIRP
dBm
dBi
dB
dBm
e
f
g
h
i
j
k
l
m
Receiver - UE
UE noise figure
dB
Thermal noise
dBm
Receiver noise floor
dBm
SINR
dB
Receiver sensitivity
dBm
Interference margin
dB
Control channel overhead
dB
RX antenna gain
dBi
Body loss
dB
Maximum path loss
dB
1,0
46,0
18,0
2,0
62,0 =a + b - c
7,0
-104,5
-97,5
-10,0
-107,5
3,0
1,0
0,0
0,0
= k(Boltzmann) x T(290K) x B(9MHz)
=e + f
From simulation (Nokia)
=g + h
165,5 =d - i - j + k + l - m
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Summary: OFDMA radio planning
• No principal difference in radio planning for OFDMA
compared to existing systems (WCDMA/TDMA/FDMA)
• Interference properties of OFDMA
– Limited inter-cell-interference due to orthogonal subcarriers
(similar to GSM)
– Large intra-cell-interference due to small FRF (similar to UMTS)
– Interference margins suggested 1 - 6 dB
• Fractionally frequency reuse suggested to trade off
fairness with efficiency
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