CS代写 IEEE 802.11 for Niche Applications 802.11af/ah/ad/ay – cscodehelp代写

IEEE 802.11 for Niche Applications 802.11af/ah/ad/ay

1. IEEE 802.11af
2. IEEE 802.11ah

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3. IEEE 802.11ad
4. IEEE 802.11ay

TVWS, Long-distance, Rural
IoT, low energy 700MHz 900MHz
Mainstream WiFi: personal devices, wireless local area networks
Cable replacement, Data center, backhaul
802.11 Standards
2.4GHz 5GHz 6GHz 60GHz
a/n/ac/ax/be be

IEEE 802.11af
2014 (a.k.a. White

802.11af Overview
1. Television Channels 2. Whitespaces
3. Whitespace Database & Protocols
4. Data rates and MCS

Air Television Channels
10 m 30 MHz
1 m 300 MHz
3 GHz 30 GHz
q Television channels use Very High Frequency (VHF) and Ultra High Frequency (UHF) bands
q Each channel uses 6 MHz in USA, 8 MHz in Europe, and 7
MHz at some places FM Radio
Channel 2 3 4 5 6 7 8 12 13 14 15 37 38 82 83
Freq. 54 60 66 72 76 82 88 174180 204 210216470 476 608614 620 884890 VHF Channels UHF Channels
q At least one channel is skipped between two analog stations in
neighboring areas to avoid interference
Radio Astronomy

Digital Television
q Converting pixels to bits
Þ Can easily encrypt, multiplex, mix with data
q Change Standard Definition (SD), High Definition (HD)
q Do not need empty channels between neighbors
q Need about 19 Mbps Þ Can transmit 6-8 channels in 6-8 MHz. q US FCC stopped analog transmissions on June 12, 2009
q A lot of TV spectrum became available Þ Digital Dividend
q Big demand for this “new” spectrum in 700 MHz band:
Ø Cellular, Emergency Services, ISM, everyone wants it
Ø Government raised $19.5 billion from auction to cellular
companies and saved some for unlicensed use

700 MHz Band
q Lower attenuation (1/7th to 1/9th of 1800/1900/2100 MHz) Þ Lower transmission power
Þ Longer mobile battery life
q Larger Cell radius Þ Smaller number of towers
q Long distance propagation Þ Good for rural areas.
Ref: More, “The 700 MHz Band: Recent Developments and Future Plans,”
(Rural Areas)

Spectral White Spaces
q Any spectrum at a given area at a given time available for use on a non-interfering basis:
Ø Unallocated spectrum
Ø Allocated but under-utilized
Ø Channels not used to avoid interferences in adjacent cells
Ø Digital Dividend Time
White Spaces
Ref: C. Gomez, “White Spaces for Rural Broadband,” April 2013, http://www.itu.int/ITU-D/asp/CMS/Events/2013/PacificForum/ITU-APT-S3_Cristian_Gomez.pdf

Spectrum Usage Example
Ref: C. Stevenson, et al., “Tutorial on the P802.22.2 PAR for: Recommended Practice for the Installation and Deployment of
IEEE 802.22 Systems” http://www.ieee802.org/802_tutorials/06-July/Rec-Practice_802.22_Tutorial.ppt ©2020
White Spaces

TVWS Databases
q FCC has authorized 10 companies to administer TVWS databases.
Ø Get info from FCC database
Ø Register fixed TVWS devices and wireless microphones Ø Synchronize databases with other companies
Ø Provide channel availability lists to TVWS devices
q Europe requires devices to check every two hours

White Spaces Near WUSTL, St. Louis, USA
q 17 channels. Zipcode 63130.
Ref: Google Spectrum Database (not available anymore), https://www.google.com/get/spectrumdatabase/channel/ ©2020

802.11af Database Operation
q Geolocation Database (GDB)
q Registered Location Secure Server (RLSS):
Ø Provide faster response to access points (APs) locally in a campus.
Ø May be Internet Service Provider (ISP) owned. q Geolocation Database Dependent (GDD) entities:
Ø GDD Enabling: Access Point
Ø GDD Dependent: Other stations
RLQP Station 1
Station 2 Station n
Ref: A. Flores, et al., “IEEE 802.11af: A Standard for TV White Space Spectrum Sharing,”

Registered Location Query Protocol (RLQP)
q Protocol for exchange of white space map (WSM) among RLSS, APs, and stations, aka, Channel Schedule Management (CSM)
CSM Request
CSM Response
Contact Verification Signal (CVS)
Channel Availability Query (CAQ)
Network Channel Control (NCC) Request Network Channel Control (NCC) Response Disassociate

RLQP (Cont)
q CSM Request: APs ask other APs or RLSS about white space map
q APs broadcast beacons on all channels selected.
q Stations associate with the APs.
q Contact Verification Signal (CVS): APs tell their stations white space map and confirm that stations are still associated
q Contact Availability Query (CAQ): Stations ask AP, if they do not receive the map within a timeout interval
q CAQ Response
q Network Channel Control (NCC) Request: Sent by stations to
APs requesting use of a channel. AP may forward to RLSS.
q NCC Response: Permission to transmit on requested channel
q Stations may be disassociated by APs if necessary ©2020

Protocol to Access White
q IETF working group
q Mechanism to discover white space database
q Protocol to communicate with the database
q Interface Agnostic: 802.11af, 802.15.4m, 802.22, …
q Spectrum agnostic: 6 MHz, 7 MHz, 8 MHz, …
q Master Device: White-Space Device (WSD) connects to database q Slave Device: WSD that get info from master devices
Space (PAWS)
Ref: V. Chen, et al, ed. “Protocol to access White-Space (PAWS) Databases,” Feb 2014,

PAWS (Cont)
q Stations should be able to discover WS Database, its regulatory domain. May be preconfigured similar to DNS or Certification Authorities.
q Listing Server: Web page listing all national database servers. Highly static Þ Can be cached by master
q Master may register with the database (model, serial, owner, …) of itself and its slaves
q Mutual authentication and authorization using certificates or passwords
q Master can then query the database
q The database should be able to push updates on channel
availability changes
q Ensure security of discovery mechanism, access method, and query/response
Ref: A. Mancuso, Ed., at al, “Protocol to Access White-Space (PQWS) Databases: Use Cases and Requirements,” IETF RFC 6953,
May 2013, http://tools.ietf.org/pdf/rfc6953 ©2020

PAWS (Cont)
q Allows WSD to specify geolocation, height, serial number, Certificates, device class, radio access technology (RAT), antenna gain, maximum EIRP, radiation pattern, spectrum mask, owner contact information
q Allows database to specify available spectrum, available area, allowed power levels
q Allows WSD to register its selected spectrum for use q Allows privacy to WSD (encryption)
Ref: V. Chen, et al, ed. “Protocol to access White-Space (PAWS) Databases,” Feb 2014,

PAWS Messages (Cont)
q Listing Request/Response: To/from listing server (not shown)
q Initialization: Exchange capability, location, get rules q Registration: Model, serial, antenna characteristics,
owner, etc
q Available Spectrum: individual or batch request
q Spectrum Use: register used spectrum, location, antenna etc. Get time limits in response.
q Device Validation: Database may ask masters to authenticated slaves

PAWS Messages
Initialization Request Initialization Response Registration Request Registration Response Available Spectrum Query Available Spectrum Response Available Spectrum Batch Query Available Spectrum Batch Response Spectrum Use Notify Spectrum Use Response Device Validation Request Device Validation Response
Master Device

802.11af Channels
q Basic Channel Unit (BCU): One TV Channel W = 6 MHz in USA
q Channel Bonding: Optional
Ø Contiguous: 2W, 4W
Ø Non-contiguous: W+W, 2W+2W

IEEE 802.11af OFDM Data Rates
q Modulation: 256-QAM highest
q Coding: 5/6 highest
q OFDM similar to 40 MHz in 802.11n down-clocked by 7.5x
q 6MHz channel: 144 total subcarriers, 108 Data, 3 DC, 6 pilots, 36 Guard
q 7.5x down clocking
Ø 0.4μs GI in 802.11n -à3μs in 802.11af (0.4×7.5=3) Ø 3.2μs data intervalà3.2×7.5 = 24μs
Ø Total symbol interval = 24+3 = 27μs
q Data rate (single stream, single channel): 26.67 Mbps
q Max. Data rate (4 stream,4 channel): 26.67×16 = 426.7 Mbps

IEEE 802.11af Data Rates in Mbps
Stream, Single Unbonded 6MHz Channel)

ate Example
Question: Calculate 802.11af data rate for MCS=0
For MCS=0, Modulation = BPSK and Coding Rate = 1⁄2 For BPSK, we have 1 bit per data subcarrier
With 108 data subcarrier: 108 coded bits per symbol
With 27 us symbol interval: 1/27 Mega symbols/s
Coded bits per sec: 108/27 Mbps
With 1⁄2 coding rate, effective data rate = 108/(27×2) Mbps = 2 Mbps

Summary of 802.11af
1. Analog to Digital conversion of TV channels has freed up spectrum in 700 MHz band Þ White Space.
2. 700MHz allows long-distance communication, useful for rural areas
3. FCC has allowed license-exempt use of some of the white space in TV bands. Requires software defined radio.
4. IEEE 802.11af White-Fi spec achieve up to 426.7 Mbps using OFDM, 4-stream MIMO,
5. PAWS is the protocol for accessing white space databases.

IEEE 802.11ah

Sample Application
Data Aggregator/Cloud
15.4g Sensor Network Gateway
Gas Meter Water Meter
Power Meter
802.11ah AP
Wide Area Network (WAN)
Neighborhood Area Network (NAN)
Home Area Network (HAN)
Distributed Automation Device
Distributed Automation Device
Ref: H. Wei, “Self-Organizing Energy Efficient M2M Communications,” http://cc.ee.ntu.edu.tw/~ykchen/1123-HWei.pdf ©2020

802.11ah PHY
1. 802.11ac PHY down clocked by 10X
Ø 2/4/8/16 MHz channels in place of 20/40/80/160 MHz in ac
Ø 20 MHz 11ac and 2 MHz 11ah both have 64 FFT size and 48 data subcarriers + 4 pilots Þ 1/10th inter-carrier spacing
Þ 10X longer Symbols Þ Allows 10X delay spread Þ All times (SIFS, ACKs) are 10x longer
Ø New 1 MHz PHY with 24 data subcarriers
2. Adjacent channel bonding: 1MHz+1MHz = 2 MHz
3. All stations have to support 1MHz and 2MHz
4. Up to 4 spatial streams (compared to 8 in 11ac)
5. 1 MHz also allows a new MCS 10 which is MCS0 with 2x repetition Þ Allows 9 times longer reach than 2.4GHz
6. Beam forming to create sectors
Ref: W. Sun, M. Choi, and S. Choi, “IEEE 802.11ah: A Long Range 802.11 WLAN at Sub 1 GHz,” River Journal, 2013, pp. 1-26,

q If we reduce the clock speed of 802.11ac by a factor of 10, what would be the new symbol rate (symbols/s)?
802.11ac has a symbol duration of 3.6 μs (for 400 ns GI). New symbol duration with a 10x slower clock = 36 μs New symbol rate = 1/(36 x 10-6) = 27,777 sym/s

q In USA, 902-928 MHz has been allocated for 802.11ah. How many different channels can be used if 16 MHz channel option is used?
902-928 MHz has a total bandwidth of 26 MHz. There is only one (non-overlapping) 16 MHz channel possible out of 26 MHz.

802.11 MAC
q Large number of devices per Access Point (AP) Ø Hierarchical Association Identifier (AID)
q Relays are used to allow connectivity outside the coverage area. Limited to 2-hops.
q Power Savings Enhancements:
Ø Allows stations to sleep and save energy.
Ø AP negotiates a Target Wake Time (TWT) for individual stations
q Speed frame exchange allows stations to exchange a sequence of frames for a TXOP.
Ref: E. Khorov, et al., “A survey on IEEE 802.11ah: An enabling networking technology for smart cities,”
Computer Communications, 2014, http://dx.doi.org/10.1016/j.comcom.2014.08.008 ©2020

MAC Protocol Versions
q Protocol Version 0 (PV0) is same as that for b/a/g/n/ac
q Protocol version 1 (PV1) is optimized for IoT Ø Short headers
Ø Null Data packets
Ø Speed frame exchange
Ø Improved channel access

Short MAC Header
q MAC Header shortened by 12-26 Bytes:
Ø Removed: High throughput control, QoS,
Duration field (No virtual carrier sensing)
Ø Optional: 3rd address
Ø 2-byte AID in place of some 6-byte addresses
Ø Frame Control indicates what protocol version is being used Ø Sequence field indicates if 3rd /4th addresses are present
802.11 36B
Frame Control
Duration/ ID
2B 2B 6B 6B 6B 2B 6B 2B 4B
Seq. Control
QoS Control
HT Control
Frame Control
Seq. Control
Frame Control
Seq. Control
0 or 6B 0 or 6B
0or6B 0or6B

q A garbage bin sensor uses 802.11ah to upload 10 bytes of bin-fill-level data once every hour. Compared to legacy 802.11 (a/b/g/n/ac), the bin sensor has to upload how many less bytes per day?
Legacy 802.11 MAC header length = 36 byte
Total bytes uploaded with legacy 802.11 = 24x(10+36) = 1104 bytes/day Total bytes uploaded with 802.11ah = 24x(10+10) = 480 bytes/day (min) 1104 – 480 = 624 less bytes per day

Null Data Packet (NDP)
q RTS/CTS/ACK has no data, but consumes too much MAC overhead
q 802.11ah removes the entire MAC header for these packets and identifies
these packets via the modulation and coding (MCS) scheme at the PHY q ACK, Block ACK, CTS, etc, all use different MCS

Speed Frame Exchange
q Also called “Bi Directional Transmit (BDT)”
q Initiator sends a frame with response indicator set to “long response”
Ø Receiver can send data instead of ACK within a SIFS
Ø Frames are sent until there are no more frames; block ACK at end
Legacy 802.11
Speed Frame Exchange in 802.11ah
Data Ack Data

Types of Stations
q High-Traffic: Listens to Traffic Indication Map (TIM) in beacons and transmit accordingly within a restricted access window Þ TIM Stations
Ø Remain awake all the time to monitor all beacons
q Periodic Low-Traffic: Negotiate a transmission time allocated in a periodic restricted access windows. Do not listen to beacons Þ Non-TIM Stations
q Very Low-Traffic: Send a poll to AP and get a transmission opportunity in response Þ Unscheduled Stations

Page Segmentation
q Announcing all buffered frames in each beacon Þ 8096 bits would be wasted per beacon interval
q AP segments the TIM stations in segments and announces only one segment at a time.
q Every Delivery TIM (DTIM) interval, AP announces which segments have pending data and downlink, uplink periods.
DTIM Beacon
Segment Count IE
Beacons with TIM for Segment n
Beacon Interval
DTIM Beacon Interval

Channel Access for TIM
q Each station knows what segments they belong to.
q Stations wake up every “DTIM” interval and find out which beacon they should listen to. The beacon has detailed map indicating which station has pending traffic and when stations can contend for access
q If the map indicates, AP has buffered packets for a station, the station uses DCF (distributed coordination function) to send a PS-poll to get the packet
q If a station has a packet to send, it listens to the map and uses DCF to send RTS in the allocated slot (two or more stations may be allocated to the same slotàcollision is possible)
q Small number of stations per slot reduces chances of collisions q Under low load, it becomes TDMA

Response Indication Deferral (RID)
q New virtual carrier sense mechanism replacing NAV (Network Allocation V ector)
q Can not use NAV since there is no duration field
q RID is also a time count down mechanism similar to NAV
Ø NAV is MAC-based, RID is PHY-based q RID is set after reception of PHY header
NAV is set after reception of complete MAC frame
q RID is set based on the 2-bit response indication field in the PHY header (2
bitsà4 combinations)
Ø Normal Response: RID ¬ SIFS + Ack or Block Ack time
Ø NDP Response: RID ¬ SIFS + NDP Frame time
Ø No Response (Broadcast frames): RID ¬ 0
Ø Long Response: RID ¬ SIFS + Longest transmission time (Used with Speed Frame Exchange)

Power Enhancements
q Page Segmentation
q Restricted Access Window q Target Wake Time

Association Identifier
q 802.11 b/g/n/ac use 11-bit identifier Þ 2007 stations
Ø 2000+ bits required in “Traffic Indication Map (TIM)”
q 802.11ah uses 16-bit identifier Þ 8X stations
Ø 8 pages of ~211 stations each. Actually 2007 stations.
Currently only page 0 is allowed. Page 1-7 are reserved.
First 2 bits should be 11 to distinguish AID from duration and others.
1b1b3b 5b 3b 3b
2048 stations
64 stations
8 stations Hierarchical AID
Block Index
Sub-block Index
STA Position Index

Restricted Access Window (RAW)
q Allows a set of slot to be restricted to a group of stations (pages/blocks/subblocks)
Þ Reduces contention
q A TIM station can be allocated slots during restricted access window
(RAW) to transmit/receive packets
q RAW is a part of “Contention Free Period”
q Access may granted for transmission, reception, polling, etc for one or a group of stations
q A RAW schedule is transmitted at the beginning of RAW interval
q A station can tell AP that it has a frame to transmit using a Uplink Data
Indication (UDI) bit
Ø Helps AP to workout which stations need access in the next round
q Dividing stations into groups and dividing time into slots for each group increases the efficiency under heavy load.
Ø At 100% load: RAW gives close to 100%. Regular EDCF gives 0%.

Other RAWs
q Periodic RAW: Period and duration of PRAW are announced by AP for periodic stations
q Sounding RAW: used for sector sounding
q AP Power Management RAW: used by AP to announce the
time when it will be sleeping
q Non-TIM RAW: Protects transmission of non-TIM stations
Ø Prevents TIM stations from hogging the channel
q Triggering Frame RAW: Used to allow stations to send PS-
poll frames indicating their need to transmit

Target Wake Time (TWT)
q Non-TIM stations may sleep for a long timeàwaste for AP to include their buffer information in every beacon
q Non-TIM stations can provide a Target Wake Time (TWT), so the AP does not worry about these stations during their long sleeps
q Because sleeps can be very long, it is difficult to precisely provide waking tie in ms and sec. – àthree parameters: Target-Wake-Time, Minimum-Wake-Duration, and Wake Interval mantissa.
q AP sends a “Null Data Packet (NDP)” to a station at its target wake up time containing buffering status. A station can then send a PS-poll and get its frames.
q AP can also sleep if all stations are sleeping 802.11ah
802.11ah Sta1

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