1. Multi-band Modulation, Coding, and Medium Access Control
November 2007
doc.: IEEE /27800
November 2007
Multi-band Modulation, Coding, and Medium Access Control
Date:
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

2. November 2007
doc.: IEEE /27800
November 2007
Abstract
Past IEEE 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 to minimize MAC overhead and maximize PHY performance, we suggest some ideas for multi-band PHY and MAC implementation.
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

3. VHT - Very High Throughput
November 2007
doc.: IEEE /27800
November 2007
VHT - Very High Throughput
Next Generation Wireless LANs
Stated Requirements (from previous VHT SG meetings):
Gigabit Throughput (5x Scaling) *
Extended Communication Range †
Reduce Latency (MAC efficiency) †
* = critical requirement
† = important requirement
Conflicting Requirements:
Backwards Compatibility with IEEE n
Interoperability and Coexistence
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

4. Enhancing PHY Throughput
November 2007
doc.: IEEE /27800
November 2007
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)
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

5. Enhancing PHY Throughput Exploiting the Spatial Dimension
November 2007
doc.: IEEE /27800
November 2007
Enhancing PHY Throughput Exploiting 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
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

6. Enhancing PHY Throughput Exploiting the Spatial Dimension
November 2007
doc.: IEEE /27800
November 2007
Enhancing PHY Throughput Exploiting the Spatial Dimension
There exist information theoretic results that suggest maximum number of antennas [Hassibi ‘03]
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

7. Enhancing PHY Throughput Exploiting the Time (Frequency) Dimension
November 2007
doc.: IEEE /27800
November 2007
Enhancing PHY Throughput Exploiting the Time (Frequency) Dimension
Increasing the symbol time is the simplest way to increase throughput
Unfortunately, the necessary bandwidth (5x20 MHz = 100 MHz) allows for at most 1 channel at traditional frequencies (2.45 or 5 GHz)
Internationally available bandwidth to spare at higher frequencies [Daniels ‘07]
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

8. Enhancing PHY Throughput Digital Baseband Improvements
November 2007
doc.: IEEE /27800
November 2007
Enhancing PHY Throughput Digital 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 n
More effective use of feedback
Present in IEEE n, doesn’t take advantage of recent limited feedback research [Choi ‘05], [Mondal ‘05], [Choi ‘06]
20 dB
30 dB
40 dB
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

9. Enhancing PHY Throughput Summary
November 2007
doc.: IEEE /27800
November 2007
Enhancing PHY Throughput Summary
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
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

10. The Multi-band Solution
November 2007
doc.: IEEE /27800
November 2007
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 n multi-RF approach
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

11. M-PHY/M-MAC 2.4 GHz & 60 GHz Modulation and Coding
November 2007
doc.: IEEE /27800
November 2007
M-PHY/M-MAC 2.4 GHz & 60 GHz Modulation and Coding
This is an equivalent strategy used in past IEEE standards
Now require a higher carrier frequency instead of higher SNR for enhanced throughput modulation and coding schemes
Can maintain backwards compatibility with IEEE n and just use higher frequencies for higher level MCSs
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

12. Multi-band versus Multi-mode
November 2007
doc.: IEEE /27800
November 2007
Multi-band versus Multi-mode
Many have proposed 2.45/5/60 GHz multi-mode devices, or an IEEE n/ c combination
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

13. Multi-band versus Multi-mode
November 2007
doc.: IEEE /27800
November 2007
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
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

14. The Multi-band Physical (M-PHY) Layer
November 2007
doc.: IEEE /27800
November 2007
The Multi-band Physical (M-PHY) Layer
Design Examples: A Preview
Training sent on one band, data on another
Lower frequency transmission “helps” higher frequency signal
Increase performance of higher frequency system, by performing synchronization, frequency offset at lower, more reliable symbol rate.
Thus far, such topics have largely been studied from an information theory point of view. [Devroye ‘06]
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

15. The Multi-band Medium Access Control (M-MAC) Layer
November 2007
doc.: IEEE /27800
November 2007
The Multi-band Medium Access Control (M-MAC) Layer
Design Examples: A Preview
Divide MAC functionality over each band to reduce contention
For example, ACK in lower frequency channel
Short, low-latency packets (VoIP) use lower frequency channels
Throughput-demanding packets use higher frequency channels
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

16. November 2007
doc.: IEEE /27800
November 2007
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 moves WLAN into cognitive arena
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin

17. November 2007
doc.: IEEE /27800
November 2007
References
B. Hassibi and B.M. Hochwald, ``How much training is needed in a multiple-antenna wireless link,” IEEE Transactions on Information Theory, vol.49, no.4, Apr. 2003, pages
H. Hashemi, ``Integrated Concurrent Multi-Band Radios and Multiple-Antenna Systems,” 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 , Nov
B. Mondal and R. W. Heath, Jr., ``Algorithms for Quantized Precoded MIMO-OFDM Systems,'' Proc. of the IEEE Asilomar Conf. on Signals, Systems, and Computers, pp Pacific Grove, CA, USA, Oct Nov. 2, 2005.
J. Choi, B. Mondal, and R. W. Heath, Jr., ``Interpolation Based Unitary Precoding for Spatial Multiplexing MIMO-OFDM with Limited Feedback,'' IEEE Trans. on Signal Processing, vol. 54, no. 12, pp , December 2006.
N. Devroye, P. Mitran, and V. Tarokh ``Achievable Rates in Cognitive Radio Channels,'’ IEEE Trans. Inform. Theory, vol.52, no.5, pp , May 2006.
R. C. Daniels and R. W. Heath, Jr., ``60 GHz Wireless Communications: Emerging Requirements and Design Recommendations,'' submitted to the IEEE Vehicular Technology Magazine, April 2007.
R. C. Daniels, UT Austin
R. C. Daniels, UT Austin