11 07 2780-01-0vht multi band modulation coding and medium access control
TRANSCRIPT
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R. C. Daniels, UT AustinSlide 1
Multi-band Modulation, Coding, and
Medium Access ControlDate: 2007-11-12
Authors Affiliations Addre ss Phone email
Robert C. Daniels The University of Texas
at Austin
Robert W. Heath, Jr. The University of Texasat Austin
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R. C. Daniels, UT AustinSlide 2
Abstract
Past IEEE 802.11 WLAN networks have used
improvements in digital baseband algorithms
(modulation, coding, etc.) and spatial multiplexing with
multiple transmit and receive antennas to increase
physical layer throughput. In this talk, we suggest that
next generation WLAN systems must exploit large
quantities of spectrum available at higher frequencies
to achieve satisfactory throughput. In order tominimize MAC overhead and maximize PHY
performance, we suggest some ideas for multi-band
PHY and MAC implementation.
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R. C. Daniels, UT AustinSlide 3
VHT - Very High Throughput
Next Generation Wireless LANs
Stated Requirements (from previous VHT SG meetings):
Gigabit Throughput (5x Scaling) *
Extended Communication Range
Improve MAC efficiency
* = critical requirement
= important requirement
Conflicting Requirements: Backwards Compatibility with IEEE 802.11n
Interoperability and Coexistence
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November 2007
R. C. Daniels, UT AustinSlide 4
Enhancing PHY Throughput
Exploitable dimensions in wireless (E-Mag) technology
Space Higher Degree of Spatial Multiplexing
Polarization Cross Polarized Multiplexing
Time Broaden Bandwidth
Digital baseband improvements
Larger constellation sizes (256-QAM)
Advanced channel coding strategies (LDPC/Turbo)
Effective use of channel feedback (Digital Precoding)
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November 2007
R. C. Daniels, UT AustinSlide 5
Enhancing PHY ThroughputExploiting the Spatial Dimension
We can always add more antennas, but will spatial
multiplexing throughput gain scale?
Spatial multiplexing is limited by condition of the wireless channel
Throughput compromised by extra training in data and sounding*
Other drawbacks with large numbers of antennas
Cost
Size constraints on mobile devices
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November 2007
R. C. Daniels, UT AustinSlide 6
Enhancing PHY ThroughputExploiting the Spatial Dimension
There exist information theoretic results that suggest
maximum number of antennas [Hassibi 03]
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doc.: IEEE 802.11-07/2780r1
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November 2007
R. C. Daniels, UT AustinSlide 7
Enhancing PHY ThroughputExploiting the Time (F requency) Dimension
Increasing the symbol time is the simplest way toincrease throughput
Unfortunately, the necessary bandwidth (5x20 MHz =
100 MHz) allows for at most 1 channel at traditionalfrequencies (2.45 or 5 GHz)
Internationally available bandwidth to spare at higherfrequencies [Daniels 07]
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R. C. Daniels, UT AustinSlide 8
Enhancing PHY ThroughputDigital Baseband Improvements
Higher constellation order (256-QAM)
Places more demands on the phase tracking and SNR
Advanced channel coding (LDPC/Turbo)
Already optionally present in IEEE 802.11n
More effective use of feedback
Present in IEEE 802.11n, doesnt take advantage of recent limitedfeedback research [Choi 05], [Mondal 05], [Choi 06]
30 dB20 dB 40 dB
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doc.: IEEE 802.11-07/2780r1
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November 2007
R. C. Daniels, UT AustinSlide 9
Enhancing PHY ThroughputSummary
Adding more antennas has limitations
Practical maximum spatial multiplexing gain (< 8)
More antennas is not the solution
Digital baseband additions only partially solve problem
Solution: Significantly more bandwidth needed
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R. C. Daniels, UT AustinSlide 10
The Multi-band Solution
Simple Idea
Lower frequencies for lower throughput
Higher frequencies for higher throughput
VHT focus
Range extension with lower frequencies
Throughput extension with higher frequencies
Both RF chains funnel data through digital baseband
Joint PHY and MAC for all carrier frequencies
Improves on IEEE 802.11n multi-RF approach
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November 2007
R. C. Daniels, UT AustinSlide 11
Multi-band Modulation and Coding
This is an equivalent strategy used in past IEEE 802.11 standards Now require a higher carrier frequency instead of higher SNR for
enhanced throughput modulation and coding schemes
Can maintain backwards compatibility with IEEE 802.11n and just use
higher frequencies for higher level MCSs
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R. C. Daniels, UT AustinSlide 12
Multi-band versus Multi-mode
Many have proposed 2.45/5/60 GHz multi-mode
devices, or an IEEE 802.11n/802.15.3c combination
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R. C. Daniels, UT AustinSlide 13
Multi-band versus Multi-mode
Multi-band devices can be based off a single reference
local oscillator
Concurrent multi-band operation [Hashemi 03]
frequency, phase offsets and ADC or
DAC consistent among all RF units
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R. C. Daniels, UT AustinSlide 14
The Multi-band Physical (M-PHY) Layer
Design Examples: A Preview
Training sent on one band, data on another
Increase performance of higher frequency system, by
performing synchronization, frequency offset at lower,
more reliable symbol rate.
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R. C. Daniels, UT AustinSlide 15
Multi-band Synchronization Example
Multi-band frame synchronization and frequency offset
estimation simulated on Hydra - an IEEE 802.11n
prototype (http://hydra.ece.utexas.edu)
MCS 0/1/2 (BPSK/QPSK)
Dotted lines show improvement
Training at 20 dB
Data SNR shown on graph Simulated multipath channel
Frequency offset added
http://hydra.ece.utexas.edu/http://hydra.ece.utexas.edu/ -
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R. C. Daniels, UT AustinSlide 16
The Multi-band Medium Access Control
(M-MAC) Layer Design Examples: A Preview
Divide MAC functionality over each band to reduce contention
Short, low-latency packets (VoIP) use lower frequency channels
Throughput-demanding packets use higher frequency channels
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R. C. Daniels, UT AustinSlide 17
Summary
Inevitably more bandwidth necessary for next
generation of WLAN (VHT)
Concurrent operation of PHY and MAC functions
jointly on different bands reduces overhead and latency
Multi-band Modulation, Coding, and MAC movesWLAN into cognitive arena
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R. C. Daniels, UT AustinSlide 18
References
B. Hassibi and B.M. Hochwald, ``How much training is needed in a multiple-antennawireless link, IEEE Transactions on Information Theory, vol.49, no.4, Apr. 2003, pages951-964.
H. Hashemi, ``Integrated Concurrent Multi-Band Radios and Multiple-AntennaSystems, PhD Thesis, Caltech University, 2003.
J. Choi and R. W. Heath, Jr., ``Interpolation Based Transmit Beamforming for MIMO-OFDM with Limited Feedback,'' IEEE Trans. on Signal Processing, vol. 53, no. 11, pp.4125-4135, Nov. 2005.
B. Mondal and R. W. Heath, Jr., ``Algorithms for Quantized Precoded MIMO-OFDMSystems,'' Proc. of the IEEE Asilomar Conf. on Signals, Systems, and Computers, pp.381-385 Pacific Grove, CA, USA, Oct. 30 - Nov. 2, 2005.
J. Choi, B. Mondal, and R. W. Heath, Jr., ``Interpolation Based Unitary Precoding forSpatial Multiplexing MIMO-OFDM with Limited Feedback,'' IEEE Trans. on SignalProcessing, vol. 54, no. 12, pp. 4730-4740, December 2006.
N. Devroye, P. Mitran, and V. Tarokh ``Achievable Rates in Cognitive RadioChannels,' IEEE Trans. Inform. Theory, vol.52, no.5, pp. 1813-1827, May 2006.
R. C. Daniels and R. W. Heath, Jr., ``60 GHz Wireless Communications: EmergingRequirements and Design Recommendations,'' submitted to the IEEE VehicularTechnology Magazine, April 2007.