Smart mm-Wave Beam Steering Algorithm for Fast Link Re-Establishment under Node Mobility in 60 GHz Indoor WLANs
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The document presents a smart beam steering algorithm designed to improve link re-establishment speed under node mobility in 60 GHz indoor WLANs. By reducing the feasible sector pair search space, the algorithm achieves significant reductions in search space and latency, while maintaining nearly optimal link quality. Simulation results demonstrate an average of 86% reduction in search space compared to traditional methods.
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Smart mm-Wave Beam Steering Algorithm for Fast Link Re-Establishment under Node Mobility in 60 GHz Indoor WLANs
- 1. Smart mm-Wave Beam Steering Algorithm for Fast Link Re-Establishment under Node Mobility in 60 GHz Indoor WLANs Avishek Patra, Ljiljana Simić and Petri Mähönen Institute for Networked Systems, RWTH Aachen University, Aachen, Germany
- 2. 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
- 3. 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
- 4. • 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 breakages FILLER FILLER ⇒ link establishment and maintenance much more challenging using directional antennas cf. vs. traditional omnidirectional antennas 2 CONTD.INTRODUCTION TO MM-WAVE NETWORKS
- 5. • 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
- 6. if RSS > Threshold for given AP-UE sector pair: ⇒ link established ⇒ “feasible sector pairs” e.g. S and S 4 ... user equipment (UE) S4 S3 S2S1 S I S i ... S1 SJ S j S3 S2 S4 ... i j APΘ = 360° I UEΘ = 360° J APΘ UEΘ ... Pair = {S , S } 3 4 access point (AP) AP, f UE, f Feasible sector BEAM STEERING PROBLEM 3 4
- 7. • 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 BEAM STEERING PROBLEM 5 8 UE1 UE3 UE2 5 6 4 AP LOS = if no blockage and close enough NLOS = reflected signals, penetrations CONTD. ⇒
- 8. BEAM STEERING PROBLEM • (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.
- 9. MOTIVATION FOR SMARTER SOLUTION • link re-establishment latency increases with increase of antenna directionality • especially under node mobility conditions FILLER ⇒ highly detrimental to QoS FILLER Our aim: maintaining seamless connectivity and QoS in 60 GHz WLAN requires frequent faster beam re-steering methods FILLER Our work: develop faster beam steering algorithm by smartly restricting feasible sector pair search space 7
- 10. SMART MM-WAVE BEAM STEERING ALGORITHM • 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 pair FILLER 8
- 11. SMART MM-WAVE BEAM STEERING ALGORITHM • idea based on a look at the 60 GHz connectivity… 9 (a) Exhaustive sequential scan (b) Our Work Previous feasible sector pairs
- 12. • study AP-UE link formation in indoor scenarios • determining all feasible sector pairs between AP and UE FILLER 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 60 GHz CONNECTIVITY PRE-STUDY
- 13. 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
- 14. 60 GHz CONNECTIVITY PRE-STUDY -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
- 15. 0 2 4 6 8 10 0 1 2 3 4 5 6 7 8 9 10 0 2 4 6 8 10 0 1 2 3 4 5 6 7 8 9 10 60 GHz CONNECTIVITY PRE-STUDY CONTD. 13 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:
- 16. * 1 hop = 1 m • studying beam steering requirements (from previous to new feasible sector pair) for 1–3 hop* UE movements FILLER 0 5 10 15 20 0 0.2 0.4 0.6 0.8 1 CDF home AP+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 home AP+UE98%-ile case 60 GHz CONNECTIVITY PRE-STUDY CONTD. 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
- 17. SMART MM-WAVE BEAM STEERING ALGORITHM • 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.
- 18. SMART MM-WAVE BEAM STEERING ALGORITHM 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
- 19. SIMULATION SCENARIOS • 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
- 20. 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 SIMULATION SCENARIOS 18 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10home walks office walks conference hall walks CONTD.
- 21. 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
- 22. A. Straight walk Home layout: 0 1 2 3 4 5 6 7 8 9 10 0 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 10 0 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
- 23. RESULTS 21 CONTD. 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 A. Straight walk Home layout: Case 2: AP – 10⁰ UE – 90⁰ 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
- 24. RESULTS A. Straight walk in home layout: 22 Avg. search reduction* Avg. RSS difference ** Case 1 90% ~ 0.03 dB Case 2 75% ~ 0.00 dB * Total # of sector pairs = 144 (both cases) ** RSS (optimal sector pair) – RSS (selected sector pair) CONTD.
- 25. RESULTS 23 CONTD. 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 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 optimal sector pair, RSS opt Received power using selected sector pair, RSS , for direction– unaware UE SBS Received power using selected sector pair, RSS , for direction– aware UE SBS Minimum received power threshold, Selected sector pair search space size, |P| , for direction– aware UE SBS Complete sector pair search space size, |M| ( |M|= |P| )EX Case 1: AP – 30⁰ UE – 30⁰
- 26. RESULTS 24 CONTD. 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 0 1 2 3 4 5 6 7 8 9 10 0 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 optimal sector pair, RSS opt Received power using selected sector pair, RSS , for direction– unaware UE SBS Received power using selected sector pair, RSS , for direction– aware UE SBS Minimum received power threshold, Selected sector pair search space size, |P| , for direction– aware UE SBS Complete sector pair search space size, |M| ( |M|= |P| )EX B. Random walk Home layout: Case 2: AP – 10⁰ UE – 90⁰
- 27. 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 difference Orientation unaware UEs Case 1 75% ~ 1.44 dB Case 2 83% ~ 0.00 dB Orientation aware UEs Case 1 86% ~ 1.44 dB Case 2 86% ~ 0.00 dB CONTD.
- 28. C. Overall result (search space and latency reduction) 1 2 3 4 5 6 0 30 60 90 120 150 Conference Hall Home Office Home Office Conference Hall θ 30AP θ 30UE θ 10AP θ 90UE Walk A Walk B Walk C Walk D Overall 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)
- 29. C. Overall result (link optimality) RESULTS 27 CONTD. 1 2 3 4 5 6 0 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 A Walk B Walk C Walk D Overall Average (RSS - RSS ) (RSS-RSS)[dB] opt SBS optSBS 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
- 30. 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 scenarios 28