February 2007
Doc.: IEEE802.22-07-0072r1
OFDMA Single Channel Harmonization
IEEE P802.22 Wireless RANs
Authors:
Name
Company
Address
Eli Sofer
Runcom Technologies
Yossi Segal
Runcom Technologies
Doron Ezri
Runcom Technologies
Michael
Erlichson
Runcom Technologies
2 Hachoma St., 75655
Rishon Lezion, Israel
2, achoma St. 75655
Rishon Lezion, Israel
2, achoma St. 75655
Rishon Lezion, Israel
2, achoma St. 75655
Rishon Lezion, Israel
Date: 2007.8.02
Phone
email
+972 3 9428892
[email protected]
+972 3 952 8440
[email protected]
+972 3 952 8440
[email protected]
+972 3 952 8440
[email protected]
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>
Submission
Runcom Technologies Ltd.
Slide 1
1
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
• Adequacy of CAZAC PN sequences
• Attributes of PN sequences needed to support
WRAN deployment with Reuse factor 1/3
• Partial simulations results on O-PUSC
Submission
Runcom Technologies Ltd.
Slide 2
2
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Adequacy of proposed CAZAC scheme
• the PAPR of preamble is an important property. However, the preamble PAPR
should be examined in view of the payload PAPR. That is, decreasing the Preamble
PAPR beneath the expected payload PAPR would not lead to any advantage on the
system level.
• The very low 1-2 dB PAPR suggested by the CAZAC approach would give
almost no advantage over another series with PAPR in the vicinity of 4-5dB.
•Although the CAZAC waveforms are simple to generate (similarity to the
sounding waveforms of the 802.16e) the decoding/reception complexity is
extremely high. This is easy to show by means of comparison with BPSK
modulated preamble. The estimation process begin with multiplying the incoming
preamble (in the frequency domain) with a series of PN sequences (stored at the
UT memory). Obviously, the multiplication of a digital series with a sequence of
+1, -1 (BPSK) is far more attractive and simpler than the multiplication with a
series of complex value numbers (suggested by CAZAC approach)
•
Submission
Runcom Technologies Ltd.
Slide 3
3
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Adequacy of proposed CAZAC scheme
• CAZAC approach would imply a complex HW required to carryout a large
number of complex multiplications ( the number is identical to number of
pilots within the preamble). The negligible gain of CAZAC preamble on the
system level does not justify the massive HW requirements.
• we recommend use of binary PN sequences.
Submission
Runcom Technologies Ltd.
Slide 4
4
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Attributes of PN sequences needed to support
WRAN deployment with Reuse factor 1/3 (use of
aggregated channels)
Submission
Runcom Technologies Ltd.
Slide 5
5
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Support for Channel aggregation
In multi-cell deployment, the popular deployment is with Hexagon like cells.
This allows the use of multiple different allocation within the cell (Reuse factor
< 1)
Reuse 1/3 deployment calls for decimated preamble with factor 3. This means
that each segment uses a different set of pilot in Preamble (e.g. every 3n+k, K=
0,1,2). This preamble structure makes sure that the transmitted preamble by all 3
segments remain orthogonal (in the frequency domain)
Simulation studies also show that in many scenarios (especially in the low CINR
regime) the capacity of a cell with reuse less than 1 (e.g. 1/3) is higher than that
in the elementary Reuse 1.
We believe that similar deployment ideas will be predicted in the 80-2.22
standard.
It is therefore important to adhere to the decimation with factor 3 for use as the
802.22 preambles.
Submission
Runcom Technologies Ltd.
Slide 6
6
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Preamble Binary PN Sequences
• Preamble with 3 repetitions (for three different sectors)
• 3 different Binary PN Sequences each shifted by one subcarrier
(k= 0,1,2), allocated for three different sectors, supports resuse 1/3
(Aggregated channels)
• Interference mitigation among sectors, differentiation among
sectors
0
3
6
9
12
15
18
21
24
27
30
33
+1
1
4
7
10
13
17
20
23
26
29
32
-1
Sub carriers
Submission
Runcom Technologies Ltd.
Slide 7
7
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Reuse 1/3
Different PN sequence, each to one of the three sectors
Seg

Seg
Seg
Submission
Runcom Technologies Ltd.


Slide 8
8
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Coverage - Simulations
 Multi Sector Coverage, 3 Sectors, 3 Frequencies, achieves
2.8Bits/s/Hz/Cell, 22.5Mbps/Sector
Submission
Runcom Technologies Ltd.
Slide 9
9
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
DL preamble and Ranging process
Submission
Runcom Technologies Ltd.
Slide 10
10
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Ranging Process
• The CDMA like synchronization is achieved by allocating
several of the usable Sub-Channels for the Ranging process, the
logic unit they consist is called a Ranging Sub-Channel.
• Onto the Ranging Sub-Channel users modulate a Pseudo Noise
(PN) sequence using BPSK modulation
• The Base Station detects the different sequences and uses the
CIR that he derives from the sequences for:
– Time and power synchronization
– Decide on the user modulation and coding
Submission
Runcom Technologies Ltd.
Slide 11
11
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Effectiveness of DL Preamble and Ranging
Example
•
•
•
•
•
Subscriber Units at the Current OFDMA Symbol = 3
Sub-Channels Allocated to Subscriber-Unit #1 = 12
Sub-Channels Allocated to Subscriber-Unit #2 = 9
Sub-Channels Allocated to Subscriber-Unit #3 = 6
Number Of New Subscriber-Units Requesting Services = 3
All Subscriber-Units Suffer Different Multi-Paths
and different Attenuation's
Submission
Runcom Technologies Ltd.
Slide 12
12
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
• Constellation at the Base Station
Submission
Runcom Technologies Ltd.
Slide 13
13
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
• Users Separation
Submission
Runcom Technologies Ltd.
Slide 14
14
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Example - Results
• User Estimation 1
Constellation to Estiamte
Estimated vec
2
2
1.5
1.5
1
1
0.5
0.5
0
0
-0.5
-0.5
-1
-1
-1.5
-1.5
-2
-2
-2
-1.5
-1
-0.5
Submission
Runcom Technologies Ltd.
0
0.5
1
1.5
2
-2
Slide 15
15
-1.5
-1
-0.5
0
0.5
1
1.5
2
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Results
• User Estimation 2
Estimated vec
Constellation to Estiamte
2
2
1.5
1.5
1
1
0.5
0.5
0
0
-0.5
-0.5
-1
-1
-1.5
-1.5
-2
-2
-2
-1.5
-1
-0.5
Submission
Runcom Technologies Ltd.
0
0.5
1
1.5
2
-2
Slide 16
16
-1.5
-1
-0.5
0
0.5
1
1.5
2
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Results
• User Estimation 3
Constellation to Estiamte
Estimated vec
2
2
1.5
1.5
1
1
0.5
0.5
0
0
-0.5
-0.5
-1
-1
-1.5
-1.5
-2
-2
-2
-1.5
-1
Submission
Runcom Technologies Ltd.
-0.5
0
0.5
1
1.5
2
Slide 17
17
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Results
• Finding New Subscriber-Units Requesting Services, Using the
Ranging Pilots (CDMA/OFDM Techniques)
Despreading on All Users
300
• Synchronization is achieved
using DL preamble within
accuracy of few micro seconds
250
200
• Preamble processing gain is
27dB, adding to that 9dB
boosted pilots, overall 36dB
150
100
50
0
0
20
40
60
80
100
120
140
Time accuracy at UT (o.1 Microsecond/step)
Submission
Runcom Technologies Ltd.
Slide 18
18
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Simulations results on O-PUSC (Partial)
Submission
Runcom Technologies Ltd.
Slide 19
19
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Scope
The purpose is to present performance of OPUSC
scheme to various types of channel estimation methods.
The simulations were ran with OPUSC frame structure
for two profiles of WRAN channels.
Submission
Runcom Technologies Ltd.
Slide 20
20
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Simulations parameters:
•
•
•
•
•
•
•
Bandwidth =6MHz.
FFTSize=2048.
FEC Size=480;
Modulation =QPSK
CTC coding.
Coding rate=1/2.
Guard Interval=256.
Submission
Runcom Technologies Ltd.
Slide 21
21
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
OPUSC Frame Structure
1 OPUSC
Frame
Pilot
2048
subcarriers
Submission
Runcom Technologies Ltd.
Slide 22
22
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Additional assumptions:
• The simulation were ran without frequency shift
and without phase noise.
• Since in the OPUSC scheme the pilots in each
symbol are allocated not in all subcarriers, we
used linear interpolation to perform channel
estimation.
Submission
Runcom Technologies Ltd.
Slide 23
23
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Channel parameters:
Profile 1
Path1
Path2
Path3
Path4
Path5
Path6
Excess delay,
msec
0
3
8
11
13
21
Relative
amplitude
0
-7 Db
-15 Db
-22 Db
-24 Db
-19 Db
Doppler
frequency
0
0.1 Hz
2.5 Hz
0.13Hz
0.17Hz
0.37Hz
.
Profile 2
Excess delay,
msec
Path1
Path2
Path3
Path4
Path5
Path6
-3
0
2
4
7
11
Relative
amplitude
-6 Db
0
-7 Db
-22 Db
-16 Db
-20 Db
Doppler
frequency
0.1 Hz
0
0.13Hz
2.5 Hz
0.17Hz
0.37Hz
Submission
Runcom Technologies Ltd.
Slide 24
24
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Channel parameters
The point spread function(PSD) of each tap
is defined as follows:
S( f ) 
1
1  ( f / f dop )
Submission
Runcom Technologies Ltd.
2
, f dop  f  f dop .
Slide 25
25
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Reference Performance: Profile 1 (BER)
10
10
BER
10
10
10
10
10
10
OPUSC allocation QPSK 1/2 FEC 480 Profile 1
0
3 symbols
9 symbols
15 symbols
Perfect channel
-1
-2
-3
-4
-5
-6
-7
1
2
Submission
Runcom Technologies Ltd.
3
4
5
SNR [dB]
Slide 26
26
6
7
8
9
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Reference Performance: Profile 1 (PER)
10
OPUSC allocation QPSK 1/2 FEC 480
0
3 symbols
9 symbols
15 symbols
Perfect channel
PER
10
10
10
10
-1
-2
-3
-4
1
2
Submission
Runcom Technologies Ltd.
3
4
5
SNR [dB]
Slide 27
27
6
7
8
9
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Reference Performance: Profile 2 (BER)
10
OPUSC allocation QPSK 1/2 FEC 480 Profile 2
0
3 symbols
9 symbols
10
BER
10
10
10
10
10
-1
-2
-3
-4
-5
-6
2
Submission
Runcom Technologies Ltd.
3
4
5
6
SNR [dB]
Slide 28
28
7
8
9
10
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Reference Performance: Profile 2 (PER)
10
OPUSC allocation QPSK 1/2 FEC 480 Profile 2
0
3 symbols
9 symbols
PER
10
10
10
10
-1
-2
-3
-4
2
Submission
Runcom Technologies Ltd.
3
4
5
6
SNR [dB]
Slide 29
29
7
8
9
10
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Conclusions:
• The presented graphs show us that we have BER=1e-5
with SNR=9.5. In order to improve the channel
estimation we suggest to aggregate number of frames (3
and 5). From the first graph we see that the aggregation
of 5 frames improves the performance in approx. 3.5db to
compare with 1 frame and is close to the perfect channel
performance.
Submission
Runcom Technologies Ltd.
Slide 30
30
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Water filling concept
Tiles transmission on preferred frequencies
User1
Tiles spread
User2
Threshold
Threshold
Different thresholds for different modulation schemes and coding rates
Channel behavior , different users
Submission
Runcom Technologies Ltd.
Slide 31
31
Eli Sofer, Runcom
February 2007
Doc.: IEEE802.22-07-0072r1
Conclusions
• Preamble with 3 reps is recommended (for 3 different
segments), accommodating different deployment
scenarios and multi-cell scenarios.
• PUSC simulation results so far are poor unless used
tiles are transmitted in favorable CINR.
• The concepts presented by ETRI are almost identical
to the transmission scheme (US & DS) of the 802.16.e.
The changes are mostly semantic. We propose to adopt
the concepts presented by ETRI (not necessarily the
details.
Submission
Runcom Technologies Ltd.
Slide 32
32
Eli Sofer, Runcom