Submission

doc.: IEEE 11-11/1455r0Nov 2011

Fei Tong,Les Smith, CSRSlide 1

802.11ah network outdoor deployment issues

Date: 2011-Nov-03

Name Affiliations Address Phone email Fei Tong CSR Churchill House,

Cambridge business park, CB4 0WZ

0044-1223692160

fei.tong@csr.com

Les Smith CSR Selwyn House, Cambridge business park, CB4 0WZ

0044-1223692483

les.smith@csr.com

Authors:

Submission

doc.: IEEE 11-11/1455r0Nov 2011

Fei Tong,Les Smith, CSRSlide 2

Abstract

This presentation discusses two 802.11ah outdoor deployment issues, limited coverage range and hidden node issue, due to restricted transmission power and low mobile antenna efficiency.

The authors propose to define power classes and adopt multiple AP network topology in 11ah specification.

Submission

doc.: IEEE 11-11/1455r0Nov 2011

Fei Tong,Les Smith, CSRSlide 3

Achieving outdoor coverage

• Outdoor coverage requirement in 11ah• Support up to 1km with 100kbps data rate

• The requirement comes from the characteristic of applications • Geographic distribution of sensors or mobile stations

• Limiting factors for coverage (for a given data rate)• Signal bandwidth (narrow band transmission can reach far, only

consider minimal signal bandwidth 1MHz in this discussion)

• Propagation environment

• Transmission power

• Antenna gain and radiation pattern

Submission

doc.: IEEE 11-11/1455r0Nov 2011

Fei Tong,Les Smith, CSRSlide 4

Tx Power constraints

• Wide range of maximal Tx power constrains in regions• 3 mW or 10 mW depending on channels in South Korea

• 5 mW or 10 mW depending on channels in China

• 1 mW, 20 mW or 250 mW depending on channels in Japan

• 25 mW in Europe

• 1 W in US

Submission

doc.: IEEE 11-11/1455r0Nov 2011

Fei Tong,Les Smith, CSRSlide 5

Mobile station antenna design constraints

• Low frequency mobile antenna efficiency is low• Small low-frequency antennas are often much lower than 0dB

• It is a non-trivial exercise to design relatively small antennas with fractional bandwidths of > 7%

• Space within mobile station is usually very limited and internal components affect the shape of the radiation pattern

• Losses due to coexistence with cellular transceiver• Provide protection from relative high power cellular uplink

transmission• Either from Rx front-end protection circuitry

• Or adding a switch in the 11ah antenna path

Submission

doc.: IEEE 11-11/1455r0

Fei Tong,Les Smith, CSR

Realistic antenna gain

• Best case antenna gain• Vertically polarized, gain +2dB, omni-directional for AP

• Vertically polarized, gain –3dB, omni-directional for hand-held mobile station

• Antenna gain variation due to antenna orientation• For antennas in mobile hand-held applications, the radiation

pattern is essentially omni-directional in one plane only

• As the user moves it around, the relative antenna orientation would result a gain variations of 20dB or more

Slide 6

Nov 2011

Submission

doc.: IEEE 11-11/1455r0

Fei Tong,Les Smith, CSR

Study the received SNR at the cell edge

• Downlink link budget Assumptions• Carrier frequency 900MHz

• Tx power level • 1, 3, 5, 10, 20, 25, 250, 1000 mW

• Best case antenna gain +2dB at AP, -3dB at mobile station

• Noise figure at mobile station 7 dB

• Noise floor -114 dBmW/MHz

• Propagation path loss• Outdoor macro path loss model

• No shadowing loss

Slide 7

Nov 2011

Submission

doc.: IEEE 11-11/1455r0

Fei Tong,Les Smith, CSR

Downlink SNR at different distance

Slide 8

Nov 2011

Submission

doc.: IEEE 11-11/1455r0

Fei Tong,Les Smith, CSR

Discussion on achieving the coverage

• If PHY is simply down-clocked by 10 from 11ac PHY• Minimal data rate will be 325kbps requiring at least 1.5dB SNR

• Adding 8 dB shadowing margin and 3dB implementation loss, required cell edge SNR to achieve minimal data rate will be 12.5dB

• Uplink and downlink link budget are not symmetric• Uplink is 5 dB better than downlink assuming maximal ERP at the

mobile station• Uplink received power: Max ERP – PL + Gap

• Downlink received power: Max ERP – PL + Gsta

• Can not achieve 1km coverage with a single central AP in all regions due to Tx power constrains

Slide 9

Nov 2011

Submission

doc.: IEEE 11-11/1455r0

Fei Tong,Les Smith, CSR

Hidden node issues

• Wide range outdoor deployment may result in high percentage hidden nodes• Low antenna height and antenna gain on mobile stations

• Random mobile antenna orientations

• Averagely longer propagation distance between stations than from AP to mobile stations, especially when coverage is wide

• Hearing other stations’ transmission is critical for carrier sense• Collision avoidance relies on hearing transmission (at least the

preamble) from other stations

• RTS/CTS may not be effective when the percentage of hidden nodes is high (collisions on RTS)

Slide 10

Nov 2011

Submission

doc.: IEEE 11-11/1455r0

Fei Tong,Les Smith, CSR

Study the percentage of hidden nodes

• Carrier frequency 900MHz

• Tx power level 25 mW

• Antenna gain -3dB at mobile station,

• Uniform distributed (0-20dB) antenna orientation loss

• Noise figure at mobile station 7 dB

• Noise floor -114 dBmW/MHz

• Sensitivity for STF detection (-1.5 dB SNR)

• Outdoor macro path loss model

• 8 dB log-normal shadowing loss

• Coverage radius, 250m, 500m and 1000m

Slide 11

Nov 2011

Submission

doc.: IEEE 11-11/1455r0

Fei Tong,Les Smith, CSR

CDF of percentage of hidden nodes

Slide 12

Nov 2011

Submission

doc.: IEEE 11-11/1455r0

Fei Tong,Les Smith, CSR

Discussion on hidden nodes issue

• Mainly due to widely scattering of stations

• For 1km radius, on average stations cannot hear 70% of other stations;

• For 250m radius, stations can hear 90% of other stations

• May result in more collision of transmissions and power consumption due to the prolonged transmission attempt

Slide 13

Nov 2011

Submission

doc.: IEEE 11-11/1455r0

Fei Tong,Les Smith, CSR

Possible solutions

• Define device power classes/capability• Easy to identify devices conforming to regional requirements

• Enable AP to manage devices with different max Tx power

• Allow multiple APs network topology• Enable lower power class device supporting wider coverage

• Study suitability of existing ESS model

• Mitigation techniques required for overlapping BSS’s• High percentage of hidden nodes within the network

• May require coordination between APs using in-band or out-band link

Slide 14

Nov 2011

Submission

doc.: IEEE 11-11/1455r0Nov 2011

Fei Tong,Les Smith, CSRSlide 15

References

1. Minho Cheong, IEEE 802.11-11/0905r4, TGah Functional Requirements and Evaluation Methodology

2. Rolf de Vegt, IEEE 802.11-11/1296r3, Potential Channelization for 802.11ah

3. Ron Porat and SK Yong, IEEE 802.11-11/0968r1, TGah Channel Model