1. Introductory TGah Proposal
Month Year
doc.: IEEE yy/xxxxr0
January 2011
Introductory TGah Proposal
Date:
Authors:
Ron Porat, Broadcom
Ron Porat, Broadcom

2. January 2011
Summary
We propose re-banding and down clocking of TGac for the purpose of Tgah
To achieve low data rates, we propose two simple methods:
Repetition
Preamble extension
For the TGah MAC we propose optional HCCA mechanism
Ron Porat, Broadcom

3. January 2011
TGah Scope
This amendment defines an Orthogonal Frequency Division Multiplexing (OFDM) Physical layer (PHY) operating in the license-exempt bands below 1 GHz, e.g., MHz (Europe), 950 MHz -958 MHz (Japan),  MHz, MHz, MHz, and MHz (China), 917 – MHz (Korea) and MHz (USA), and enhancements to the IEEE Medium Access Control (MAC) to support this PHY, and provides mechanisms that enable coexistence with other systems in the bands including IEEE and IEEE P g.
The data rates defined in this amendment optimize the rate vs. range performance of the specific channelization in a given band.
This amendment also adds support for:
transmission range up to 1 km
data rates > 100 kbit/s
while maintaining the WLAN user experience for fixed, outdoor, point to multi point applications.
Ron Porat, Broadcom

4. TGac Basis for TGah Proposal
January 2011
TGac Basis for TGah Proposal
We propose to use TGac features as a basis for TGah
Preliminary TGac Draft was presented during the November 2010 IEEE meeting
11-10/1361r2 Proposed TGac Draft Amendment
Adoption by the Task Group is pending (to become Draft 0.1)
MU-MIMO – for low frequencies the antennas will be more correlated and reduce the ability to do spatial multiplexing hence making this feature much more important.
Beamforming
802.11n has many options and there was no industry convergence
802.11ac has only one beamforming option for SU and MU
LDPC
Enhanced MAC features agreed upon in TGac
Ron Porat, Broadcom

5. Challenges and Issues January 2011
The requirements of TGah may get us closer to wide area networks, hence OFDM parameters may need to be adjusted accordingly
Need to create a system operating from low to high available bandwidth
600KHz to 20MHz
Need to extend OFDM rates down to at least what currently is supported by b
Higher delay spread can exist not just in S1G frequencies but also in 2.4GHz for Metro-WiFi deployment.
TGah design provides an opportunity to define a system more suitable for such deployments
Ron Porat, Broadcom

6. Basic PHY parameters for TGah
January 2011
Basic PHY parameters for TGah
PHY parameters are derived from the delay spread and Doppler that need to be supported
What is the right delay spread we need to support?
LTE uses 15KHz subcarrier BW and CP=4.7uS (there is an option for long CP=16uS) for all BW between 1.25MHz to 20MHz
WiMAX uses 11KHz subcarrier BW and CP=11uS (other options exist) for all BW between 1.25MHz to 20MHz
g uses 10.4KHz and CP=24uS for all BW between 160KHz to 1.2MHz
802.11ac uses 312.5KHz and CP=400nS (or 800nS) for all BW between 20MHz to 160MHz
Reference [1] discusses delay spread measurements in 3G cellular systems and concludes that the typical RMS delay spread is 0.2uS
Reference [2] conducted delay spread measurements in the 900MHz frequency and reports 1-2uS maximum delay spread
Ron Porat, Broadcom

7. January 2011
Proposal
Leverage three ac PHY definitions with lower PHY clocks to achieve larger delay spread tolerance which is also similar across different system BW
Specifically use FFT sizes:
256 for 20MHz and 10MHz BW
128 for 5MHz and 2.5MHz BW
64 for 1.25MHz BW
64 (or 32) for 0.625MHz BW
Ron Porat, Broadcom

8. Parameters Table January 2011 * To be investigated Ron Porat, Broadcom
BW (MHz)
FFT Size
Tone Spacing (KHz)
CP (1/8) uS
CP (1/4) uS 20
256 78
1.6
3.2 10 39
6.4 5
128
2.5
19.5
12.8
1.25 64
0.625* or 32
25.6
* To be investigated
Ron Porat, Broadcom

9. January 2011
OFDM low rates
Currently 2.4GHz deployments rely on b for the lowest rates (1-11Mbps)
The lowest rate of the OFDM waveform is 6Mbps
The lowest rate of OFDM is not reliable due to weak preamble (especially with BF)
Propose to add OFDM lower rates by using simple repetition.
64 FFT can support repetitions 2,4,13,52
128 FFT can support repetitions that divide 4x27
256 FFT can support repetitions that divide 2x9x13
Ron Porat, Broadcom

10. Improved Preamble/Control Channel
January 2011
Improved Preamble/Control Channel
The current ac/a/n preamble is not robust enough to support the lowest rates (even without Beamforming).
It is the limiting factor for using the OFDM lowest rates.
802.11ah PAR does not include b modulations (CCK/DSSS)
Significantly reduces range as the CCK signal provides
Low PAPR
Low data rate thus lower SNR requirement
Simple option to improve OFDM preamble performance is to increase preamble length
Ron Porat, Broadcom

11. Usage of Centralized MAC
January 2011
Usage of Centralized MAC
Some of the applications envisioned for TGah may benefit from more centralized MAC:
Smart utility networks – high density of nodes with low link budget may cause CSMA/CA to fall apart
Usage of WiFi for providing broadband wireless access – QoS should be guaranteed in high density and CSMA/CA may fall apart
Metro-WiFi applications – for example deployments of WiFi hotzones by AT&T in NYC, SF and elsewhere
Enable centralized MAC using HCCA mechanism
The hybrid coordinator (HC) coordinates channel access by polling stations. Stations do not compete for access to the channel medium
Allows improved network coordination
Ron Porat, Broadcom

12. January 2011
References
[1] How typical is the "Typical Urban" channel model? Ericsson Research
[2] g-channel-characterization-for-sun.ppt
Ron Porat, Broadcom