1. Backward compatibility of CDD preambles
January 2005
doc.: IEEE /xxxxr0
January 2005
Backward compatibility of CDD preambles
Date: xx
Authors:
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Tsuguhide Aoki, Toshiba Corporation, et. al.
Tomoko Adachi, Toshiba Corporation, et. al.

2. January 2005
doc.: IEEE /xxxxr0
January 2005
Abstract
The backward compatibility of the WWiSE and TGnSync preambles is examined by laboratory test.
Results show that the WWiSE preamble is not fully backwards compatible, and that the TGnSync preamble is much more robust.
Tsuguhide Aoki, Toshiba Corporation, et. al.
Tomoko Adachi, Toshiba Corporation, et. al.

3. Preamble structures (first 3 fields)
January 2005
Preamble structures (first 3 fields)
.11a preamble
Tx1
L-STF
L-LTF
L-SIG
TGn Sync preamble (2TX)
Tx1
L-STF
L-LTF
L-SIG
Tx2
L-STF(50ns)
L-LTF(50ns)
L-SIG(50ns)
WWiSE preamble (2TX Mixed-mode)
Tx1
L-STF
L-LTF
L-SIG
Tx2
L-STF(400ns)
L-LTF(3100ns)
L-SIG(3100ns)
Values shown in brackets indicate the amount of CDD delay
Tsuguhide Aoki, Toshiba Corporation, et. al.

4. Problem with WWiSE preamble
January 2005
Problem with WWiSE preamble
Some legacy devices use the auto-correlation technique for synchronization whilst other legacy devices use the cross-correlation technique.
The large cyclic shift (400nsec) on the WWiSE L-STF can affect the time synchronization of legacy devices that use the cross-correlation technique.
L-STF
L-LTF
L-SIG
L-STF(400ns)
L-LTF(3100ns)
L-SIG(3100ns)
Tx1
Tx2
WWiSE preamble (2TX Mixed-mode)
Tsuguhide Aoki, Toshiba Corporation, et. al.

5. Cross-correlation in Legacy devices
January 2005
Cross-correlation in Legacy devices
Cross-correlation of .11a L-STS with .11a L-STS
Period = 800ns
Cross-correlation of WWiSE L-STS with .11a L-STS
Period = 400ns
Potential issues with cross-correlation receivers with WWiSE preamble
Tsuguhide Aoki, Toshiba Corporation, et. al.

6. Test setup Test packets generated in C simulator
January 2005
Test setup
Test packets generated in C simulator
TX signals are convolved with a simulated TGn channel
Signal generator is used for up-conversion
C simulator
Agilent E4438C
Tx1
Rx1
Single input
single output
signal generator
Packet
generator
TGn
Channel model
Tx2
Normalized
Tsuguhide Aoki, Toshiba Corporation, et. al.

7. Measurement Setup TGn simulator Aeropeek NX RATE
January 2005
Measurement Setup
TGn simulator
Aeropeek NX
RATE
LENGTH
Compare the RATE and LENGTH
RATE
LENGTH
Wireless
5.19GHz
10cm apart
Omni transmit antenna
WLAN card
under test
Agilent E4438C
Enhanced Signal Generator (ESG)
Tsuguhide Aoki, Toshiba Corporation, et. al.

8. Preamble performance with Auto-correlation Legacy RX
January 2005
Preamble performance with Auto-correlation Legacy RX
Tsuguhide Aoki, Toshiba Corporation, et. al.

9. Preamble performance with Cross-correlation Legacy RX
January 2005
Preamble performance with Cross-correlation Legacy RX
Tsuguhide Aoki, Toshiba Corporation, et. al.

10. Preamble performance with Auto-correlation Legacy RX
January 2005
Preamble performance with Auto-correlation Legacy RX
Tsuguhide Aoki, Toshiba Corporation, et. al.

11. Preamble performance with Cross-correlation Legacy RX
January 2005
Preamble performance with Cross-correlation Legacy RX
Performance limitation with a WWiSE preamble
Error Floor!
Tsuguhide Aoki, Toshiba Corporation, et. al.

12. Implication of using WWiSE preambles
January 2005
Implication of using WWiSE preambles
Legacy devices with a cross-correlation RX will not correctly decode a WWiSE preamble
Hence, such legacy devices will not defer to a WWiSE HT transmission, potentially creating collisions in the BSS
BSS throughput would drop, and latency would increase
WWiSE preamble is not legacy compatible
Lab test reinforces TGn Sync’s decision to use a 100% backwards compatible legacy preamble
Tsuguhide Aoki, Toshiba Corporation, et. al.

13. January 2005
Backup
Tsuguhide Aoki, Toshiba Corporation, et. al.

14. Test procedure Test packets created in C simulator.
January 2005
Test procedure
Test packets created in C simulator.
Rate= 6Mbps, Date=42bytes, broadcast address and data packet.
IFS = 1msec
100 packets created in C simulator, each convolved with randomly generated TGn channel and saved in the ESG.
Total packets transmitted in 20 seconds.
Tsuguhide Aoki, Toshiba Corporation, et. al.

15. Test procedure (cont’d)
January 2005
Test procedure (cont’d)
Measure the Rate and Length (bytes) in the Signal Field at Aeropeek, and compare them with the predetermined value.
Aeropeek: can observe Signal field and MAC information decoded by the WLAN card.
Calculate Signal Field Error Rate (SFER) by using Rate and Length.
Tsuguhide Aoki, Toshiba Corporation, et. al.

16. January 2005
Aeropeek NX
Tsuguhide Aoki, Toshiba Corporation, et. al.