Submission

doc.: IEEE 11-13/0536r0May 2013

Wookbong Lee, LG ElectronicsSlide 1

HEW SG PHY Considerations For Out-door Environment

Date: 2013-05-12

Name Affiliations Address Phone email Wookbong Lee LG Electronics Gyeonggi-do, Korea +82-31-450-

1883 wookbong.lee@lge.com

Jinyoung Chun LG Electronics jiny.chun@lge.com

Jinsoo Choi LG Electronics js.choi@lge.com

Dongguk Lim LG Electronics dongguk.lim@lge.com

HanGyu Cho LG Electronics hg.cho@lge.com

Authors:

Submission

doc.: IEEE 11-13/0536r0May 2013

Wookbong Lee, LG ElectronicsSlide 2

Abstract

This document includes PHY considerations for HEW development especially for Outdoor Environment.

Submission

doc.: IEEE 11-13/0536r0May 2013

Wookbong Lee, LG ElectronicsSlide 3

Introduction

• IEEE 802.11a/b/g/n/ac have been developed focusing on

indoor usage cases.

• Even though the indoor usage case will be one of the ma-

jor environment for HEW project, we also need to con-

sider outdoor environment as well. [1]

• Outdoor channel environment is quite different from in-

door channel model as measured and modelled in [2][3].

• In this contribution, we analyze major characteristics of

outdoor channel model (urban macro cell (UMa)).

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

Delay Spread• Following figures shows CDF of the maximum excess

delay for UMa channel model at 2.4GHz

Slide 4

May 2013

User Loca-tion

Average SNR (dB)

95% Max Excess

Delay (ns)

30m 42.6 806

100m 27.3 1330

500m 0.3 1540

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

delay [us]

CD

F

2.4GHz, UMa

30m100m300m

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

Delay Spread• Following figures shows CDF of the maximum excess

delay for UMa channel model at 5GHz

Slide 5

May 2013

User Loca-tion

Average SNR (dB)

95% Max Excess

Delay (ns)

30m 36.5 804

100m 21 1344

500m -4 1546

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

delay[us]

CD

F

5GHz,UMa

30m100m300m

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

Impact of Larger Delay Spread

• Performance loss due to larger inter-symbol-interference.

• There is no other solution than increasing CP length in this case.

• Just increasing CP length brings throughput loss due to larger PHY overhead. (See Appendix for more details)

• During the development of IEEE 802.11af or .11ah, members come up with increasing CP length by increasing FFT size for a given bandwidth to maintain physical layer overhead.

─ For example, the subcarrier spacing of .11af is 41.7kHz (in case of U.S. channel) and that of .11ah is 31.25kHz while the subcarrier spacing of .11a/n/ac is 312.5kHz.

• With same logic, we can increase CP length by increasing FFT size for a given bandwidth (20MHz, 40MHz, 80MHz or 160MHz).

Slide 6

May 2013

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

Impact of Larger Delay Spread

Slide 7

May 2013

User Location @ 100m

Performance gain over FFT 64 (%)

FFT 128 22.2%

FFT 256 39.4%

FFT 512 47.7%

0 50 100 150 200 250 3000

10

20

30

40

50

60

70

User Distance [m]

Th

rou

gh

pu

t [M

bp

s]

UMa, 2.4GHz

FFT 64FFT 128FFT 256FFT 512

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

Impact of Larger Delay Spread

Slide 8

May 2013

User Location @ 100m

Performance gain over FFT 64 (%)

FFT 128 16.0%

FFT 256 27.2%

FFT 512 32.7%

0 50 100 150 200 250 3000

10

20

30

40

50

60

70

User Distance [m]

Th

rou

gh

pu

t [M

bp

s]

UMa, 5GHz

FFT 64FFT 128FFT 256FFT 512

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

Channel Variation

• In outdoor channel, per tone channel is varying faster than that in indoor channel due to faster environmental change as well as more channel tap (more multi-path)

Slide 9

May 2013

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

Impact of Larger Channel Variation

Slide 10

May 2013

• Channel variation of one tone per one OFDM symbol ─ Observation during the PPDU max Time

In 802.11 ac, aPPDUMaxTime is 5.484 ms

0 400 800 1200 1600 2000 2400 2800 3200 3600 4000 4400 4800 5200 5600 600060000.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.21.2

Second [us]

Mag

nitu

de

Channel variation comparison in max PPDU size

InH

UMa

0 400 800 1200 1600 2000 2400 2800 3200 3600 4000 4400 4800 5200 5600 60006000-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.60.6

Second [us]

Pha

se (ra

dian

)

Channel variation comparison in max PPDU size

InH

UMa

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

Impact of Larger Channel Variation

Slide 11

May 2013

• Channel variation of one tone per 1ms─ It is possible to check that channel is very fast change in outdoor

•

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 1000.9

1

1.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

Second [ms]

Mag

nitu

de

Channel variation comparison between InH and UMa

InH

UMa

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

4

Second [ms]

Pha

se (ra

dian

)

Channel variation comparison between InH and UMa

InH

UMa

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

Design Consideration Points for HEW

Slide 12

May 2013

Observed fea-tures

Things to be resolved Enabling technologies

Larger delay spread

Need to minimize per-formance loss due to larger inter-symbol-in-terference

•Larger CP length by increasing CP portion versus symbol duration- Pros: Robustness against delay spread in outdoor - Cons: Throughput loss from increased CP portion

•Larger CP length by increasing FFT size - Pros: Robustness against delay spread in outdoor and no direct throughput loss- Cons: Possible impact on PPDU design by diff. OFDM nu-merology

Larger chan-nel variation

Need to compensate per-formance loss due to dis-torted channel informa-tion

•Channel estimation improvement- Accurate channel estimation (e.g. pilot, midamble)•Channel feedback improvement- Efficient feedback (e.g. Effective SINR (ESINR) feedback, codebook based channel information, fast feedback channel)•Techniques to mitigate fading- Enhancement of link quality (e.g. effective error correction and retransmission mechanism)

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

Appendix

May 2013

Slide 13

Submission

doc.: IEEE 11-13/0536r0

Performance result for just increasing CP

Slide 14 Wookbong Lee, LG Electronics

May 2013

0 50 100 150 200 250 3000

10

20

30

40

50

60

User Distance [m]

Th

rou

gh

pu

t [M

bp

s]

UMa, 2.4GHz

CPx1CPx2CPx4CPx8

0 50 100 150 200 250 3000

10

20

30

40

50

60

User Distance [m]

Th

rou

gh

pu

t [M

bp

s]

UMa, 5GHz

CPx1CPx2CPx4CPx8

Submission

doc.: IEEE 11-13/0536r0May 2013

Wookbong Lee, LG ElectronicsSlide 15

Channel Model

ScenarioUMa

LoS NLoS

Delay Spread (log10(s)) (-7.03,0.66)* (-6.44,0.39)*

K-factor (K) (dB) (9,3.5)* N/A

Delay distribution Exp Exp

Delay scaling parameter 2.5 2.3

Number of cluster 12 20

Per cluster shadowing std ζ (dB) 3 3

LoS probability as a function of distance, d(m)

37,5.0

3718,2718exp

18,1

d

dd

d

PLOS )36/exp()36/exp(1)1,/18min( dddPLOS

* (μ,σ)For SNR evaluation, we assume noise figure 5dB, cable loss 2dB, signal power 1W for 20MHz.See page 30-41 of reference [2]

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

Channel Model

Slide 16

May 2013

Scenario

Path loss (dB)Note: fc is given in GHz

and distance in m!

Shadow

fading std

(dB)

Applicability range,

antenna height default values

Urban Macro (UMa)

LoS

PL = 22.0 log10(d) + 28.0 + 20 log10(fc)

= 4

10m< d1 < d′BP (1)

PL = 40 log10(d1) + 7.8 – 18 log10(h′BS) –18 log10(h′UT) + 2

log10(fc)d′BP < d1 < 5 000 m(1)

NLoS

PL = 161.04 – 7.1 log10 (W) + 7.5 log10 (h) – (24.37 – 3.7(h/hBS)2) log10 (hBS) + (43.42 – 3.1 log10 (hBS)) (log10 (d) 3) +20 log10(fc) – (3.2 (log10 (11.75 hUT))2 4.97)

= 6

10 m < d < 5 000 m

h = avg. building height (20 m)W = street width (20 m)

hBS = 25 m, hUT = 1.5 m

(1)hBS = 25 m, hUT = 1.5 m, d′BP = 4 h′BS h′UT fc/c, h′BS = hBS – 1.0 m, h′UT = hUT – 1.0 m

Submission

doc.: IEEE 11-13/0536r0May 2013

Wookbong Lee, LG ElectronicsSlide 17

Delay profile vs. CP length

• And we need to have proper modeling on how channel and CP impact performance.

• One of possible modeling is as follows [4]:

TFFT is FFT period CP is CP period|αm|2 is power of m-th tapτm is delay of m-th tap including OFDM symbol timing

Submission

doc.: IEEE 11-13/0536r0May 2013

Wookbong Lee, LG ElectronicsSlide 18

Delay profile vs. CP length

• Modified SINR by equations in previous slide matches performance of without ISI

6 7 8 9 10 11 12

10-2

10-1

100

SNR [dB]

PE

R

16QAM 1/2, Perfect channel estimation, Exponential Decaying channel with max tap length = 224, 10%

CP 1/4

CP 1/8 with modi SNRCP 1/8 with SNR

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

Simulation Assumption for Slide 7 and 8

Slide 19

May 2013

FFT1 FFT2 FFT4 FFT8

FFT size 64 128 256 512

Used data subcarriers 52 104 208 416

Symbol length with CP 4us 8us 16us 32us

CP length 0.8us 1.6us 3.2us 6.4us

Center frequency 2.4GHz/5GHz

Bandwidth 20MHz

Channel model UMa 3km/h

Packet structure Preamble +Data frame

Preamble L-STF/LTF/SIG+VHT-SIG-A/STF/LTF/SIG-B =40 us

Data frame SERVICE(2bytes) +MAC header(40bytes) +Data +Tail(6bits) +Padding(Data =8kbyte)

Submission

doc.: IEEE 11-13/0536r0

Wookbong Lee, LG Electronics

HTTP traffic [4]

Main Object Size (Truncated Lognormal: μ=8.37, σ=1.37, Min=100byte, Max=2Mbyte)

Embedded Object Size (Trun-cated Lognormal: μ=6.17, σ=2.36, Min=50byte, Max=2Mbyte)

Number of Embedded Objects per page (Truncated Pareto: α = 1.1, k=2, Max = 53)

Slide 20

May 2013

0 2 4 6 8 100

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

[kbyte]

CD

F

HTTP packet

Mean: 8,728byte

Submission

doc.: IEEE 11-13/0536r0May 2013

Wookbong Lee, LG ElectronicsSlide 21

References

[1] IEEE 802.11-13/0331r5- Laurent Carious et al., “High- effi-ciency WLAN,” March 2013

[2] Report M.2135, “Guidelines for evaluation of radio interface technologies for IMT-Advanced, ” available at http://www.itu.int/pub/R-REP-M.2135

[2] IST-4-027756 WINNER II D1.1.2 V1.2, “WINNER II channel models,” available at http://www.ist-winner.org/deliverables.html

[3] Mickael Batariere, Kevin Baum, and Thomas P. Krauss, “Cyclic Prefix Length Analysis for 4G OFDM Systems,” VTC 2004 Fall

[4] IEEE 802.16m-08/004r5, “IEEE 802.16m Evaluation Methodol-ogy Document (EMD),” Jan. 2012