1. Uplink Symbol Structure
March 2007
doc.: IEEE yy/xxxxr0
March 2007
Uplink Symbol Structure
IEEE P Wireless RANs Date:
Authors:
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Carlos de Segovia, France Telecom
Patrick Pirat, France Telecom

2. March 2007
doc.: IEEE yy/xxxxr0
March 2007
Abstract
In the current status of the OFDMA parameter document it is suggested to allocate the same number of pilot and data carriers per OFDM symbol in the upstream as in the downstream sub-frame.
It is proposed here to unbalance upstream and downstream and to increase the pilot/data carrier ratio for upstream as it is done in
Carlos de Segovia, France Telecom
Patrick Pirat, France Telecom

3. Content Current OFDMA parameters
March 2007
doc.: IEEE yy/xxxxr0
March 2007
Content
Current OFDMA parameters
Rationale for unbalanced down and up link pilot density
Burst definition
Upstream service allocation
Carlos de Segovia, France Telecom
Patrick Pirat, France Telecom

4. Current OFDMA parameters
March 2007
doc.: IEEE yy/xxxxr0
March 2007
Current OFDMA parameters
1440 data carriers pilots + 1 DC per OFDM symbol
Downstream
Upstream
Useful symbol/frame 17 7
# Sub-channels 30 60
# Data carriers/SC 48 24
# Pilots/SC 8 4
Carlos de Segovia, France Telecom
Patrick Pirat, France Telecom

5. Rationale for unbalanced up and down links (1)
March 2007
doc.: IEEE yy/xxxxr0
March 2007
Rationale for unbalanced up and down links (1)
Let's consider 1 BS and 2 CPE's:
CPE X makes use of sub-channel X
CPE Y makes use of sub-channel Y BS
Sub-channel X
Sub-channel Y
CPE X
CPE Y
Downstream: all the pilots sent by the BS can be used by both CPEs to estimate sub-channels X and Y
Upsteam: only the pilots sent by CPE X and Y can be used by the BS to respectively estimate sub-channel X and Y
Carlos de Segovia, France Telecom
Patrick Pirat, France Telecom

6. Rationale for unbalanced down and up links (2)
March 2007
doc.: IEEE yy/xxxxr0
March 2007
Rationale for unbalanced down and up links (2)
The upstream channel estimation (between CPE X and BS) only relies on the pilots sent by CPE X.
Sub-channel allocated to CPE X P P P P P
Physical subcarriers
 time P P P P P P P P P P P P P P P
This pilot cannot be used
to estimate channel X
Pilots used by the BS to estimate sub-channel X
Carlos de Segovia, France Telecom
Patrick Pirat, France Telecom

7. Rationale for unbalanced up and down links (3)
March 2007
doc.: IEEE yy/xxxxr0
March 2007
Rationale for unbalanced up and down links (3)
The pilot density should be higher for uplink than for downlink.
In e-2005 the uplink pilot density is 1/3 versus 1/7 for downlink. P P P P
Since WRAN (fixed applications) is less stringent than , we propose to have an uplink pilot density of 1/5 .
Carlos de Segovia, France Telecom
Patrick Pirat, France Telecom

8. March 2007
doc.: IEEE yy/xxxxr0
March 2007
Burst (1)
A burst is a set of sub-carriers (rectangle in the time/frequency domain) allocated to a CPE in a sub-frame.
A burst consists of:
k sub-channels
j consecutive OFDM symbols to enable the BS to estimate the sub-channel associated to the burst.
It is proposed here to have j=5 since the proposed pilot density is 1/5.
It is also proposed to allocate 20 sub-carriers to each sub-channel :
16 data carriers;
4 pilot carriers.
Carlos de Segovia, France Telecom
Patrick Pirat, France Telecom

9. March 2007
doc.: IEEE yy/xxxxr0
March 2007
Burst (2)
The smallest burst consists of 1 sub-channel on 5 OFDM symbols as illustrated below.
Smallest burst
Frequency P P P P P P P P
Logical subcarriers
 time P P P P P P P P P P P P
Carlos de Segovia, France Telecom
Patrick Pirat, France Telecom

10. Features of smallest burst (when 1 burst per sub-frame)
March 2007
doc.: IEEE yy/xxxxr0
March 2007
Burst (3)
Features of smallest burst
Number of bits
carried
Minimum bit-rate
transported
(when 1 burst per sub-frame)
QPSK
160
16 kbit/s
16 QAM
320
32 kbit/s
64 QAM
480
48 kbit/s
Carlos de Segovia, France Telecom
Patrick Pirat, France Telecom

11. Proposed modifications for OFDMA parameters
March 2007
doc.: IEEE yy/xxxxr0
March 2007
Proposed modifications for OFDMA parameters
Uplink OFDMA parameters
Curent
Modified to
US useful symbols 7
5 (or multiple of 5)
US symbols for pilot spreading 5
US pilot carriers per symbol
240
288
US data carriers per symbol
1440
1392
Number of US sub-channel 60 84
Number of US carriers/SC 28 20
Number of US data carriers/SC 24 16
Number of US pilot carriers/SC 4
Carlos de Segovia, France Telecom
Patrick Pirat, France Telecom