January 2001
doc.: IEEE 802.11-01/066r1
Options for PBCC 22 Proposal
Anuj Batra Ph.D., Chris Heegard Ph.D., Eric J. Rossin Ph.D.,
Matthew B. Shoemake Ph.D., and Srikanth Gummadi
Texas Instruments
12500 TI Boulevard, MS 8653
Dallas, TX 75243
(214) 480-4220, [email protected]
Submission
Slide 1
Anuj Batra et al., Texas Instruments
January 2001
doc.: IEEE 802.11-01/066r1
Increasing Throughput with a
High Performance Preamble
Submission
Slide 2
Anuj Batra et al., Texas Instruments
January 2001
doc.: IEEE 802.11-01/066r1
Current Preamble and Header (P/H)
• Long PLCP PPDU Format:
PLCP PREAMBLE
144 BITS @ 1Mbps
PLCP HEADER
48 BITS @ 1Mbps
PSDU
192 ms
• Short PLCP PPDU Format:
SHORT PLCP PREAMBLE
72 BITS @ 1Mbps
SHORT PLCP HEADER
48 BITS @ 2Mbps
PSDU
96 ms
• Preamble and header contains no information - overhead
Submission
Slide 3
Anuj Batra et al., Texas Instruments
January 2001
doc.: IEEE 802.11-01/066r1
Motivation for a Shorter P/H
• For short packets:
– preamble and header spans a large portion of the packet
– Large P/H wastes valuable resources and decreases the
network throughput
• Can reduce overhead by:
– defining a new preamble, and
– increasing the data rate for the header
Submission
Slide 4
Anuj Batra et al., Texas Instruments
January 2001
doc.: IEEE 802.11-01/066r1
New High Performance P/H
PREAMBLE
TIMING SYNC
FRAME SYNC
CHANNEL EST
88 symbols @ 11Msps 72 symbols @ 11Msps 168 symbols @ 11Msps
HEADER
48 BITS @ 5.5Mbps
PSDU
5.5 – 33 Mbps
~38 ms
•
Timing Synchronization Sequence: tones
– complex tone at f0 = ±8.25 MHz
– allows for easy detection of packet, carrier frequency offset, symbol timing
– requires that the clocks to be locked
•
Frame Synchronization Sequence: PN sequences
– can be used to determine the location within packet
– can also be used for receiver diversity – select the antenna with best gain
•
Channel Estimation Sequence: deterministic sequence
– first 160 symbols of a length 255 PN sequence
– sequence is generated by using a minimal polynomial over GF(4)
Submission
Slide 5
Anuj Batra et al., Texas Instruments
January 2001
doc.: IEEE 802.11-01/066r1
Key Points of High Performance P/H
• Increases throughput by reducing overhead
• Designed to work at SNRs as low as 3–4 dB
• Preamble can be used to estimate the channel
• Supports most legacy rates: 5.5 and 11 Mbps
• Also supports newer rates: 16.5, 22, 33 Mbps
• High performance Preamble/Header can also be clocked at 16.5 MHz
(more later)
Submission
Slide 6
Anuj Batra et al., Texas Instruments
January 2001
doc.: IEEE 802.11-01/066r1
Throughput with ACK
30
Rates: 5.5, 11, 16.5, 22, 33 Mbps
192 ms
96 ms
38 ms
25
20
15
10
5
0
Submission
0
500
1000
1500
Slide 7
2000
2500
Anuj Batra et al., Texas Instruments
January 2001
doc.: IEEE 802.11-01/066r1
Throughput with NO ACK
35
Rates: 5.5, 11, 16.5, 22, 33 Mbps
192 ms
96 ms
38 ms
30
25
20
15
10
5
0
Submission
0
500
1000
1500
Slide 8
2000
2500
Anuj Batra et al., Texas Instruments
January 2001
doc.: IEEE 802.11-01/066r1
Increasing the Data Rate to 33Mbps
in Wireless Ethernet via Clock
Switching
Submission
Slide 9
Anuj Batra et al., Texas Instruments
January 2001
doc.: IEEE 802.11-01/066r1
Clock Switching
• The existing IEEE 802.11b standard, and the TI proposed 22 Mbps
extension to the standard, is based upon an 11 Msps symbol rate and a
bandwidth occupancy of 20 MHz. In terms of modern digital
communications techniques such as pulse shaping and adaptive
equalization, a more aggressive symbol rate in the same bandwidth is
practical. However, in order to deal with inter-operability with
existing networks, the structure of the preamble, including the symbol
rate of the preamble, must not change. A viable method to address
these issues is to transmit an 11Msps preamble followed by a higher
symbol rate encoded data rate. Means and issues involving the switch
in the clock are addressed in this presentation. The suggested increase
in rate by 50% to 16.5 Msps yields a data rate of 33 Mbps.
• Reference: IEEE 802.11-00/386
Submission
Slide 10
Anuj Batra et al., Texas Instruments