Multi-band Modulation, Coding, and Medium Access Control November 2007 doc.: IEEE 802.11-07/27800 November 2007 Multi-band Modulation, Coding, and Medium Access Control Date: 2007-11-12 R. C. Daniels, UT Austin R. C. Daniels, UT Austin

November 2007 doc.: IEEE 802.11-07/27800 November 2007 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 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

VHT - Very High Throughput November 2007 doc.: IEEE 802.11-07/27800 November 2007 VHT - Very High Throughput Next Generation Wireless LANs Stated Requirements (from previous VHT SG meetings): Gigabit Throughput (5x Scaling) * Extended Communication Range † Improve MAC efficiency † * = critical requirement † = important requirement Conflicting Requirements: Backwards Compatibility with IEEE 802.11n Interoperability and Coexistence R. C. Daniels, UT Austin R. C. Daniels, UT Austin

Enhancing PHY Throughput November 2007 doc.: IEEE 802.11-07/27800 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

Enhancing PHY Throughput Exploiting the Spatial Dimension November 2007 doc.: IEEE 802.11-07/27800 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

Enhancing PHY Throughput Exploiting the Spatial Dimension November 2007 doc.: IEEE 802.11-07/27800 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

Enhancing PHY Throughput Exploiting the Time (Frequency) Dimension November 2007 doc.: IEEE 802.11-07/27800 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

Enhancing PHY Throughput Digital Baseband Improvements November 2007 doc.: IEEE 802.11-07/27800 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 802.11n More effective use of feedback Present in IEEE 802.11n, 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

Enhancing PHY Throughput Summary November 2007 doc.: IEEE 802.11-07/27800 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

The Multi-band Solution November 2007 doc.: IEEE 802.11-07/27800 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 802.11n multi-RF approach R. C. Daniels, UT Austin R. C. Daniels, UT Austin

Multi-band Modulation and Coding November 2007 doc.: IEEE 802.11-07/27800 November 2007 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 R. C. Daniels, UT Austin R. C. Daniels, UT Austin

Multi-band versus Multi-mode November 2007 doc.: IEEE 802.11-07/27800 November 2007 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 R. C. Daniels, UT Austin R. C. Daniels, UT Austin

Multi-band versus Multi-mode November 2007 doc.: IEEE 802.11-07/27800 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

The Multi-band Physical (M-PHY) Layer November 2007 doc.: IEEE 802.11-07/27800 November 2007 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. R. C. Daniels, UT Austin R. C. Daniels, UT Austin

Multi-band Synchronization Example November 2007 doc.: IEEE 802.11-07/27800 November 2007 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 R. C. Daniels, UT Austin R. C. Daniels, UT Austin

The Multi-band Medium Access Control (M-MAC) Layer November 2007 doc.: IEEE 802.11-07/27800 November 2007 The Multi-band Medium Access Control (M-MAC) Layer Design Examples: A Preview Divide MAC functionality over each band to reduce contention 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

November 2007 doc.: IEEE 802.11-07/27800 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

November 2007 doc.: IEEE 802.11-07/27800 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 951-964. 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. 4125-4135, Nov. 2005. 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. 381-385 Pacific Grove, CA, USA, Oct. 30 - 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. 4730-4740, December 2006. N. Devroye, P. Mitran, and V. Tarokh ``Achievable Rates in Cognitive Radio Channels,'’ 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: Emerging Requirements and Design Recommendations,'' submitted to the IEEE Vehicular Technology Magazine, April 2007. R. C. Daniels, UT Austin R. C. Daniels, UT Austin