Smart mm-Wave Beam Steering Algorithm for Fast Link Re-Establishment under Node Mobility in 60 GHz Indoor WLANs

Smart mm-Wave Beam Steering Algorithm for Fast Link Re-Establishment under Node Mobility in

60 GHz Indoor WLANsAvishek Patra, Ljiljana Simić and Petri Mähönen

Institute for Networked Systems, RWTH Aachen University, Aachen, Germany

OUTLINE

INTRODUCTION TO MM-WAVE NETWORKS

BEAM STEERING PROBLEM

MOTIVATION FOR SMARTER SOLUTION

60 GHz CONNECTIVITY PRE-STUDY

SMART MM-WAVE BEAM STEERING ALGORITHM

SIMULATION SCENARIOS

RESULTS

CONCLUSIONS & FUTURE WORKS

INTRODUCTION TO MM-WAVE NETWORKS

• large unlicensed spectrum in mm-wave bands, e.g. 60 GHz

• exploiting mm-wave bands for multi-Gbps wireless connectivity in WLAN, e.g. IEEE 802.11 ad

FILLER

• Challenges:

• high signal attenuation inherent at mm-wave frequencies!

FILLER

• Solution:

• highly directional beamforming antennas

⇒ increase transmission range 1

• But in mm-Wave WLAN…

1) directional link formation = only when Tx and Rx antenna sectors are both steered in correct directions

2) sector misalignments OR signal interruption ⇒ link breakage

3) node mobility ⇒ more link breakagesFILLER

FILLER

⇒ link establishment and maintenance much more challenging using directional antennas cf. vs. traditional omnidirectional antennas

2

CONTD.INTRODUCTION TO MM-WAVE NETWORKS

• low latency, fast beam steering to re-establish links essential for seamless connectivity and maintaining QoS

FILLER

• State of the Art:

Simple exhaustive sequential scanning of Tx and Rx antenna sectors, e.g. in IEEE 802.11 ad

FILLER

• Our work:

Smart beam steering algorithm with reduced Tx-Rx sector pair search space

3

CONTD.INTRODUCTION TO MM-WAVE NETWORKS

if RSS > Threshold for given AP-UE sector pair:

⇒ link established

⇒ “feasible sector pairs”

e.g. S and S

4

...

user equipment (UE)

S4

S3S2S1

S I

S i ...

S1

S JS j

S3 S2S4

...

i

j

APΘ = 360°I

UEΘ = 360°J

APΘ

UEΘ...

Pair = {S , S }3 4

access point (AP)

AP, f UE, fFeasible sector


3 4

• links may be LOS or NLOS

FILLER

depends on the material properties of the surrounding indoor environment

FILLER

• a given AP-UE pair may have multiple feasible sector pairs


5

8

UE1

UE3

UE2

5

6

4

AP

LOS = if no blockage and close enough

NLOS = reflected signals, penetrations

CONTD.

⇒


• (re-) establishing link = searching until a feasible sector pair is found

FILLER

• link (re-) establishment latency ∝ # sector pairs searched before formation of link

FILLER

• Existing proposals: Exhaustive sequential scanning (# sector pairs searched = total # sector pairs), e.g. IEEE 802.11 ad

• Finds optimal feasible sector pair

• But… high latency (∝ total # sector pairs)

6

CONTD.

MOTIVATION FOR SMARTER SOLUTION

• link re-establishment latency increases with increase of antenna directionality

• especially under node mobility conditions FILLER

⇒ highly detrimental to QoSFILLER

Our aim: maintaining seamless connectivity and QoS in 60 GHz WLAN requires frequent faster beam re-steering methodsFILLER

Our work: develop faster beam steering algorithm by smartly restricting feasible sector pair search space

7


• Algorithm idea…

“Smart beam steering algorithm for link re-establishment that searches for a new feasible sector pair over a reduced search space in the vicinity of the previously known valid sector orientation (previous feasible sector pair).”

FILLER

⇒ use of historical information, i.e. previous feasible sector pair

FILLER

⇒ reduced search in vicinity of previous feasible sector pairFILLER

8


• idea based on a look at the 60 GHz connectivity… 9

(a) Exhaustive sequential scan (b) Our WorkPrevious feasible

sector pairs

• study AP-UE link formation in indoor scenarios

• determining all feasible sector pairs between AP and UEFILLER

o indoor layouts with realistic material properties (for 60 GHz), area of 10 x 10 m2

o AP – centrally located, UE – different locations at every 1 m through indoor layouts

o ray-tracing signal propagation simulation using WinProp

o simulations done for every AP-UE sector pair and every UE location in the indoor layouts

10


FILLER

60 GHz CONNECTIVITY PRE-STUDY CONTD.

Indoor layouts (1) free space, (2) home,

(3) office, and (4) conference hall

Transmission power 0 dBm

Antenna gain (AP + UE) 25 dBi

Receiver sensitivity threshold – 78 dBm

AP Beamwidth Case 1: 30⁰ ; Case 2: 10⁰

UE Beamwidth Case 1: 30⁰ ; Case 2: 90⁰

11


-20-30

-40

-50

-60

-70-80

Received Power[dBm]

12

CONTD.

-20-30

-40

-50

-60

-70-80

Received Power[dBm]

-20-30

-40

-50

-60

-70-80

Received Power[dBm]

-20-30

-40

-50

-60

-70-80

Received Power[dBm]

1. free space

3. office

2. home

4. conference hall

0 2 4 6 8 100

1

2

3

4

5

6

7

8

9

10

0 2 4 6 8 100

1

2

3

4

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10


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Case 1: AP – 30⁰; UE – 30⁰ Case 2: AP – 10⁰; UE – 90⁰

• RSS at UE > Receiver sensitivity threshold ⇒ link established• Complete set of feasible sector pairs for home layout:

* 1 hop = 1 m

• studying beam steering requirements (from previous to new feasible sector pair) for 1–3 hop* UE movements

FILLER0 5 10 15 200

0.2

0.4

0.6

0.8

1

CDF

homeAP+UE

1 – Hop 2 – Hop 3 – Hop 1 – Hop 2 – Hop 3 – Hop

(θ 30 ;θ 30 )AP UE

(θ 10 ;θ 90 )AP UE (θ 10 ;θ 90 )AP UE

(θ 10 ;θ 90 )AP UE (θ 30 ;θ 30 )AP UE

(θ 30 ;θ 30 )AP UE

homeAP+UE98%-ile case


14

• avg. total (AP+UE) beam steering requirement (1-hop movements) for 98% cases ≈ 6

FILLER

• ‘insight’ for smart beam steering algorithm based on reduced search around previous feasible sector pair

Average beam steering requirement

CDF


• Algorithm details…• start new feasible sector pair search for around previous pair

using a reduced search width parameter

• reduced search width parameter = combined search width for AP and UE

• individual search width for AP & UE 1/∝ UE & AP beamwidth respectively

• reduced search sector pairs arranged ∋ sector pairs requiring least movement searched first ⇒ ensures coordination

• if feasible sector pair not found within reduced space, retort to exhaustive sequential scan for unchecked sector pairs

15

CONTD.


16

CONTD.

= 6 for this

work

Initialize reduced search width parameter

Compute AP & UE search widths

Obtain & sort reduced search sector pairs

Select first reduced search sector pair

For selected sector pair,

RSS > threshold? Select next

reduced search

sector pair

All reduced search sector pairs

checked?

NO

NO

Obtain unchecked sector pairs(all sector pairs – reduced search sector pairs)

Select first unchecked sector pair

For selected sector pair,

RSS > threshold? Select next unchecked

sector pair

YES

All unchecked sector pairs

checked?NO

NO

No link for given AP & UE locations

YES

New feasible sector pair found

YES YES


• different indoor layouts – home, office, and conference hall

• mobility simulation through ‘walks’ (AP static, UE moved by 1-hop at a time)

• straight walks and random walks

• for random walks, orientation-unaware UEs and orientation-aware UEs• orientation-unaware UEs – previous feasible sector pair info.

corrupted at turnings

• orientation-unaware UEs – no ambiguity about previous feasible sector pair

17

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

7

8

9

10


18

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

7

8

9

10homewalks

officewalks

conference hall walks

CONTD.

RESULTS

• Performance metrics:

1. Search space and latency reduction – comparing # sector pairs searched vs. total # sector pairs

2. Link optimality – comparing RSS for optimal feasible sector pair and selected feasible sector pair

FILLER

• Results:

A. Straight walk in home layout

B. Random walk in home layout

C. Overall (all straight and random walks in all layouts)

19

A. Straight walk

Home layout:

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

7

8

9

10

Case 1: AP – 30⁰ UE – 30⁰

RESULTS

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

7

8

9

10

CONTD.

20

Received power using optimal sector pair, RSS opt

Received power using selected sector pair, RSS SBS

Minimum received power threshold,

Selected sector pair search space size,|P|SBS

Complete sector pair search space size, |M| ( |M|= |P| )EX

RESULTS

21

CONTD.

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6 7 8 9 100

1

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7

8

9

10

A. Straight walk

Home layout:

Case 2: AP – 10⁰ UE – 90⁰


Received power using selected sector pair, RSS SBS


Selected sector pair search space size,|P|SBS


RESULTS

A. Straight walk in home layout:

22

Avg. search reduction* Avg. RSS difference **Case 1 90% ~ 0.03 dBCase 2 75% ~ 0.00 dB

* Total # of sector pairs = 144 (both cases)** RSS (optimal sector pair) – RSS (selected sector pair)

CONTD.

RESULTS

23

CONTD.

0 1 2 3 4 5 6 7 8 9 100

1

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6

7

8

9

10

0 1 2 3 4 5 6 7 8 9 100

1

2

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6

7

8

9

10

B. Random walk

Home layout:

Selected sector pair search space size,|P| , for direction– unaware UE

SBS


Received power using selected sector pair, RSS , for direction–unaware UE

SBS

Received power using selected sector pair, RSS , for direction–aware UE

SBS


Selected sector pair search space size,|P| , for direction–aware UE

SBS


Case 1: AP – 30⁰ UE – 30⁰

RESULTS

24

CONTD.

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

7

8

9

10

0 1 2 3 4 5 6 7 8 9 100

1

2

3

4

5

6

7

8

9

10

Selected sector pair search space size,|P| , for direction– unaware UE

SBS


Received power using selected sector pair, RSS , for direction–unaware UE

SBS

Received power using selected sector pair, RSS , for direction–aware UE

SBS


Selected sector pair search space size,|P| , for direction–aware UE

SBS


B. Random walk

Home layout:

Case 2: AP – 10⁰ UE – 90⁰

RESULTS

B. Random walk in home layout:

max. RSS diff. between orientation unaware and aware UE = 0.17 dB

25

Avg. search reduction Avg. RSS differenceOrientation unaware UEs Case 1 75% ~ 1.44 dB Case 2 83% ~ 0.00 dBOrientation aware UEs Case 1 86% ~ 1.44 dB Case 2 86% ~ 0.00 dB

CONTD.

C. Overall result (search space and latency reduction)

1 2 3 4 5 60

30

60

90

120

150

Conference Hall

Home Office Home Office Conference Hall

θ 30AP θ 30UE θ 10AP θ 90UE

Walk AWalk BWalk CWalk DOverall Average |P|Average |P| θ 30AP θ 30UE ( ; )Average |P| θ 10AP θ 90UE ( ; )|P

|

SBS

SBS

|P|EX

SBS

RESULTS

26

CONTD.

Avg. reduction = 86% (7-fold)

Avg. reduction (Case 1) = 89% (7-fold)

Avg. reduction (Case 2) = 83% (7-fold)

Worst case reduction = 66% (3-fold)

C. Overall result (link optimality)

RESULTS

27

CONTD.

1 2 3 4 5 60

0.03

0.06

0.09

0.12

0.15

0.18

Conference Hall

Home Office Home Office Conference Hall

θ 30AP θ 30UE θ 10AP θ 90UE

Walk AWalk BWalk CWalk DOverall Average (RSS - RSS )

(RSS

- RSS

)[d

B]

opt SBS

opt

SBS

0.03

0.06

1.20

1.50

1.80 Avg. RSS diff. = 0.02 dB

Avg. RSS diff. (Case 1) = 0.02 dB

Avg. RSS diff. (Case 2) = 0.02 dB

Worst case RSS diff. = 1.44 dB

CONCLUSIONS & FUTURE WORKS

• low latency, fast beam steering algorithm that smartly reduces feasible sector pair search space

• search limited based on (static) reduced search width parameter

• 7-fold (avg.) / 3-fold (worst case) reduction in search space and link re-establishment latency

• re-established links nearly optimal (avg. RSS diff. < 0.03 dB)

• incorporation of adaptive reduced search width parameter

• performance in outdoor scenarios28

Smart mm-Wave Beam Steering Algorithm for Fast Link Re-Establishment under Node Mobility in 60 GHz Indoor WLANs

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