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Wireless Mesh Deployment using Wi-Fi
2011. 07. 06.
Jae-Hyun Kim
Wireless Information aNd Network Engineering Research Lab.
School of Electrical and Computer Engineering
Ajou University, Korea
Wi-Fi 기술 방식 자문
Contents
WLAN Introduction
Coverage Extension
Directional Antenna
Carrier Sensing Problem
Wi-Fi Mesh Introduction
IEEE 802.11s
Throughput Enhancement
IEEE 802.11n
Conclusion
2
What is WiFi?
Definition of Wi-Fi
Informal : Wireless Fidelity (look like Hi-Fi)
Formal : never supposed to mean anything at all
Trademark of the Wi-Fi Alliance
Describe only a narrow range of connectivity technologies
including wireless local area network (WLAN) based on the IEEE
802.11 standards
3
What is Wi-Fi?What is IEEE
802.11 standard?
IEEE 802.11 Standard
Define one medium access control (MAC) and several physical layer (PHY) specifications for wireless connectivity for fixed, portable, and moving stations (STAs) within a local area
The base current version of the standard is IEEE 802.11-2007
Provide wireless connectivity to STAs that require rapid deployment
Describes the functions and services to operate within ad-hoc and infrastructure networks
Defines the MAC procedures to support the asynchronous MAC service data unit (MSDU) delivery
Defines several PHY signaling techniques and interface functions that are controlled by the IEEE 802.11 MAC
Defines mechanisms for dynamic frequency selection (DFS) and transmit power control (TPC)
Describes the requirements to provide data confidentiality of user information being transferred over the wireless medium (WM) and authentication
4
Major Task Groups in 802.11
5
PHY & Data Rates in IEEE 802.11
TGFrequency
(GHz)
Bandwidth
(MHz)
Data rate per stream
(Mbps)
MIMO
stream
Maximum data
rate(Mbps)Modulation
Range(m)
Indoor Outdoor
2.4 20 1,2 1 2DSSS,
FHSS20 100
a 5 206,9,12,18,24,36,4
8,541 54 OFDM 35 120
b 2.4 20 5.5, 11 1 11DSSS,
CCK38 140
g 2.4 206,9,12,18,24,36,4
8,541 54
DSSS,
CCK,
OFDM
38 140
n 2.4/5
207.2,14,21.7,28.9,
43.3,57.8,65,72.24 288
OFDM
CCK70 250
4015,30,45,60,90,1
20,135,1504 600
OFDM
CCK70 250
6
IEEE 802.11 (Layers and Functions)
MAC
Access mechanisms, fragmentation, encryption
MAC management
Synchronization, roaming, management information base (MIB), power management
7
Physical layer convergence protocol (PLCP)
Clear channel assessment (CCA) signal (carrier sense)
Physical medium dependent (PMD)
Modulation, coding
PHY management
Channel selection, MIB
Architecture in IEEE 802.11
Infrastructure
8
Ad-Hoc
Components in IEEE 802.11
Station (STA)
Terminal with access mechanisms to the wireless medium and radio contact to the access point
Access point (AP)
Station integrated into the wireless LAN and the distribution system
Basic service set (BSS)
A set of STAs that have successfully synchronized
Distribution system (DS)
A system used to interconnect a set of BSSs
Extended service set (ESS)
An ESS is the union of the BSSs connected by a DS
Not include the DS
The ESS network appears the same to an LLC layer as an IBSS network
STAs within an ESS may communicate and mobile STAs may move from one BSS to another (within the same ESS) transparently to LLC
9
Frequency Bands in IEEE 802.11
Industrial, Scientific and Medical (ISM) Bands
10
• UNLICENSED OPERATION GOVERNED BY FCC DOCUMENT 15.247, PART 15
• SPREAD SPECTRUM ALLOWED TO MINIMIZE INTERFERENCE
• 2.4GHz ISM BAND
- More Bandwidth to Support Higher Data Rates and Number of Channels
- Available Worldwide
- Good Balance of Equipment Performance and Cost Compared with 5.725GHz Band
- IEEE 802.11 Global WLAN Standard
1 2 3 4 5 6FREQUENCY (GHz)
26MHz 83.5MHz 125MHz
2.400 to 2.4835GHz902 to 928MHz 5.725 to 5.850GHz
Spectrum Allocation in IEEE 802.11
Divided into 13 channels(14 channels in Japan) each of width
22 MHz
11
MAC Entity in IEEE 802.11
MAC Sublayer
12
MAC Entity in IEEE 802.11
Distributed coordination function (DCF)
Contention-based channel access
Carrier sense multiple access/collision avoidance (CSMA/CA)
Carrier sense
Physical carrier sense - CCA
Virtual carrier sense - Request to send/clear to send (RTS/CTS)
Point coordination function (PCF)
Polling-based channel access
Enhanced Distributed channel access (EDCA)
Support prioritized QoS
Differentiated by inter frame space (IFS), contention window (CW) size
HCF controlled channel access (HCCA)
Support parameterized(reservation-based) QoS
Allocate transmission opportunity (TxOP)
13
MAC Entity in IEEE 802.11
DCF
PCF
14
DIFS Contention Window
Slot time
Busy Medium
Defer Access
Backoff-Window Next Frame
Backoff slot reduced when channel is idle
SIFS
PIFSDIFS
Sense channel during DIFS
Beacon D1+Poll
NAV
SIFS
SIFS
U1+Ack
D2+Ack+Poll
SIFS
U2+Ack
SIFS
SIFS
CF-End
Uplink
Downlink
Contentio Free Period (CFP) for PCF
Contention
Period (CP)
for DCF
Contention Free Period Repetition Interval (CFPRI) or Superframe
Reset NAV
CF_MAX_DurationDx - downlink frame to STA x
Ux - uplink frame from STA x
PIFS
MAC Entity in IEEE 802.11
EDCA
HCCA
15
ACK RTS
CTS
SIFSSIFS
PIFS
AIFS[AC]=DIFS
SIFS
AIFS[AC]
AIFS[AC]
high priority AC
medium priority AC
low priority AC
defer access Contention Windows (counted in slots, 9us)
count down as long as medium is idle, Back off when medium gets bust again
CW=rand[1,CWi+1]
Contention Free Period, CFP(polling through HCF) Contention Period, CP (listen before talk and polling through HCF)
TXOP TXOP TXOPTBTT
QoS CF-PollQoS CF-PollCF-end
Beacon
Transmitted
by (Q)STAs
Transmitted
by HC
TBTTTime
RTS/CTS
Fragmented DATA/ACK
(polled by HC )
RTS/CTS/DATA/ACK
(after DIFS+backoff) RTS/CTS
Fragmented DATA/ACK
(polled by HC )
HC : Hybrid Coordinator AP , TBTT : Target Beacon Transmission Time
Consideration for Coverage Extension
Transmission power is limited in ISM band
Regulate equivalent isotropic radiated power (EIRP) in ISM band
by FCC 47 CFR part 15, subpart B Class B
16
<U.S. public safety transmit power levels by regulatory domain>
The amount of power that a theoretical isotropic antenna (which evenly
distributes power in all directions) would emit to produce the peak power
density observed in the direction of maximum antenna gain.
What is EIRP?
Regulatory Channel starting
frequency(GHz)
Channel spacing Channel set Transmit power limit(mW)
1 5 20 36,40,44,48 40
2 5 20 52,56,60,64 200
3 5 20 149,153,157,161 800
4 5 20 100,104,108,112,116,120,124 200
5 5 20 165 1000
6 4.9375 5 1,2,3,4,5,6,7,8,9,10 25
Consideration for Coverage Extension
Directional Antenna
An antenna which radiates greater power in one or more directions
and reduced interference from unwanted sources
Commercially, increase about 20dBi(Yagi, Corner, Sector, Grid, etc)
Pros and Cons
Divert the RF energy in a particular direction to farther distances
• Increase range in near LOS(hallway, long corridor, isle)
Need to LOS environment
Cannot cover large area as the angular coverage is less
17
Consideration for Coverage Extension
vender categoryGain
(dBi)
3dB beamwidth
(degree)
Max input
power (W)
Price
($)
GNS Wireless
Grid 27 7.5 100 295
Sector 20H : 120
V : 5300 500
Radio Labs
Yagi 12.5 30 150 57
Parabolic 23 10.5 100
18
Consideration for Coverage Extension
Amplifier
Can amplify the receiver power, not the transmitter power
Amplify also the noise
19
Vendor AmplificationTemperature
rangePrice($)
RadioLabs
Tx : 26dBm(+2dB)
Rx : 30dBm(+1dB)
Rx Noise Figure:
3.5dBm
-30ºC~+70ºC 120
Tx : 30dBm(+2dB)
Rx : 10dBm(+1dB)
Rx Noise
Figure:3.5dBm
-40ºC~70ºC 300
Consideration for Coverage Extension
Is it increase the coverage using the directional antenna and the amplifier?
Limited
IEEE 802.11 is basically operated by the slot
Slot Time : time granularity in IEEE 802.11 Slot Time : FHSS(50μs), DSSS(≤20μs), OFDM(≤9μs)
aCCATime : FHSS(27μs), DSSS(≤15μs), OFDM(≤4μs)
aRxTxTurnaroundTime : FHSS(20μs), DSSS(≤5μs), OFDM(≤2μs)
aAirPropagationTime : 1μs Distance < 300m
+aMACProcessingDelay : ≤2μs
20
Consideration for Coverage Extension
aSlotTime이 증가할 경우
Propagation delay의 증가에 따른 성능의 변화
Contention Window가 Node의 수에 최적화되어 있을 경우
Basic DCF를 사용할 경우
21
참고문헌 G. Bianchi, “Performance Analysis of the IEEE 802.11 Distributed Coordination Function”,
IEEE Journal on Selected Area in Communications, Vol. 18, No. 3, pp. 535-547, Mar. 2000
max 1/
, /21 1
cK
s c
E PS K T
T K T K e
min 1
1/
1
1 1s c
K
D T TK e
minD
sT
cT
E P
maxS : maximum throughput
: minimum delay
: consumed time to successfully transmit
: consumed time by the collision
: average payload size
: propagation delay
Consideration for Coverage Extension
성능 분석 결과
Throughput 감소
Propagation delay(σ)이 1μs증가하면 평균 1.1%의 throughput 감소
Delay는 점짂적으로 증가
Propagation delay(σ)이 1μs증가하면 평균 0.8us의 delay 증가
22
300 600 1000 2000 10000 1500010
15
20
25
30
35
40
45
50
Distance(m)
Thro
ughput(
Mbps)
300 600 1000 2000 10000 150009
9.05
9.1
9.15
9.2
9.25
9.3
9.35
9.4
9.45
9.5
Distance(m)
Del
ay(m
sec)
Consideration for Coverage Extension
Need to wireless backhaul using PtP device
23
Vendor Data Rate Range Frequency Cost($)
Motorola105Mbps
(Ethernet)
LoS : 250km
Near LoS : 40km
NLoS : 10km
5.4GHz5,995
(w ant.)
300Mbps
(Ethernet)
LoS : 250km
Near LoS : 40km
NLoS : 10km
5.8GHz3,295
(w/o ant.)
Bridge
Wave
1.25Gbps
(Ethernet) Up to 11.5km 80GHz 33,000
Proxim
wireless125Mbps 1km 60GHz
Wi-Fi Mesh Network using IEEE 802.11s
It will provide an IEEE 802.11 Wireless DS that supports both
broadcast/multicast and unicast delivery at the MAC layer
using radio-aware metrics over self-configuring multi-hop
topologies.
The objectives
Increased range/coverage & flexibility in use
Reliable performance
Seamless security
Power efficient operation
Multimedia transport between devices
Backward compatibility
Interoperability for interworking
24
Network Architecture in IEEE 802.11s
Mesh point (MP)
Relay frames each other in a router-like hop-by-hop fashion
Mesh access point (MAP)
Mesh relaying + AP service for clients
Mesh portal point (MPP)
Acting as a bridge to other networks
25
MP
MPP
MP
MP
STAs
802.11s Mesh links
Legacy 802.11s links
MAP
` `
`
Multi Channel Operation in IEEE 802.11s
Single interface
Simple channel allocation
Share the resources for the client access, backhaul ingress, backhaul egress Increase the latency, Decrease the throughput
Low cost
Multiple interface
Advanced channel allocation
All radio on a device should use the same mode
WLAN mesh network is a layer 2 network
Each radio can operate on different band(Max. = 4 in OFDM)
26<Simple interface example> <Multiple interface example>
Key Functionality of Mesh Networks
Mesh Topology Creation
Self-configuring neighbor discovery
Channel selection
Link establishment with neighbor MPs (Authentication/Association)
L2 Routing
Mesh path selection and forwarding based on MAC addresses
Radio-aware metrics for routing
Hybrid wireless mesh protocol (HWMP)
On-demand and proactive routing
MAC Enhancement
for supporting QoS(basically EDCA), and increasing the network
throughput
Security
27
MAC Enhancement in IEEE 802.11s
EDCA as the basis for the .11s media access mechanism
Re-use of latest MAC enhancement from 802.11
Compatibility with legacy devices
Interaction of forwarding and BSS traffic
Handling of multi-hop mesh traffic and single-hop BSS traffic within
one device impacts network performance
Dependent on system fairness and prioritization policies
Treated as an implementation choice
MAC enhancement for mesh
Intra-mesh congestion control
Simple hop-by-hop congestion control mechanism implemented at
each MP
Common channel framework (Optional)
Support for multi-channel MAC operation
28
Need for Congestion Control
Mesh characteristics
Heterogeneous link capacities along the path of a flow
Traffic aggregation: Multi-hop flows sharing intermediate links
Issues with the 11/11e MAC for mesh:
Nodes blindly transmit as many packets as possible, regardless of
how many reach the destination
Results in throughput degradation and performance inefficiency
29
2
1
7
6
3
High capacity linkLow capacity link
Flow
4
5
Intra-Mesh Congestion Control Mechanisms
Local congestion monitoring
Each node actively monitors local channel utilization
If congestion detected, notifies previous-hop neighbors and/or the neighborhood
Congestion control signaling
Congestion control request (unicast)
Congestion control response (unicast)
Neighborhood congestion announcement (broadcast)
Local rate control
Each node that receives either a unicast or broadcast congestion notification message should adjust its traffic generation rate accordingly
Rate control (and signaling) on per-AC basis – e.g., data traffic rate may be adjusted without affecting voice traffic
Example: MAPs may adjust BSS EDCA parameters to alleviate congestion due to associated STAs
30
CCF for Multi-Channel MAC Operation
A framework that enables single and multi-channel MAC
operation for devices with single and multiple radios
Common channel is:
Unified Channel Graph on which MPs and MAPs operate
The channel from which MPs switch to a destination channel and
return back
MPs with multiple radios may use a separate common channel for
each interface
CCF supports optional channel switching in different forms
After RTX/CTX exchange on common channel, MP pairs switch to a
destination channel and then switch back
Groups of MPs may switch to a negotiated destination channel
Neighbors discover support for CCF during association.
Using the Mesh Capability IE in the beacon
31
Multi-Channel CCF for Single Radio: Channel Switching
32
RTX
MP1
MP2
MP3
MP4
Common
Channel
Data
Channel n
Data
Channel m
CTX
SIFS
CTX
SIFS
RTX
DIFS
DIFS
DATA
Switching
Delay
ACK
SIFS CTX
SIFS
RTX
DIFS
Switching
Delay
DATA
Switching
DelayDIFS
ACK
SIFS
Network Topology
MP boot sequence
Neighbor discovery
A MP performs passive or active scanning
Classify the node‟s physical neighbor according the profile
• Ignore node, Neighbor MP, Candidate peer
Channel selection
The channel of a MP is set to the highest channel precedence value
Link establishment
Determine the directionality
Link state measurement
The superordinate node of the link measures the bit rate and packet
error rate
Path selection and forwarding
Using airtime cost
AP initialization (optional)
33
Network Participation
34
57
12
6
4
3
Mesh Identifier:WLANMesh_Home
Mesh Profile:(link state, airtime
metric)
X
Capabilities:Path Selection: distance vector, link
state
Metrics: airtime, latency
1. Mesh Point X discovers
Mesh (WLANMesh_Home)
with Profile (link state,
airtime metric)
2. Mesh Point X associates /
authenticates with
neighbors in the mesh,
since it is capable of
supporting the Profile
3. Mesh Point X begins
participating in link state
path selection and data
forwarding protocol
One active protocol/metric in one mesh, but allow for alternative protocols/ metrics in different meshes
8
Hybrid Wireless Mesh Protocol
Extensible framework
Default metric
Airtime cost
Default protocol
Radio metric ad-hoc on demand distance vector (RM-AODV)
Optional protocol
Radio aware optimized link state routing (RA-OLSR)
Different meshes may have different active path selection
protocols
Path selection messages
Transported at the link layer
Using IEEE 802.11 management frames
35
Airtime Link Metric Function
Airtime cost
The amount of channel resources consumed by transmitting the
frame over a particular link.
36
pt
tpcaa
er
BOOc
1
1
Parameter Description 802.11a 802.11b
Oca Channel access overhead 75μs 335μs
Op Protocol overhead 110μs 364μs
Bt Number of bits in test frame 8224 8224
r Transmission bit rate for Bt
ept Error rate for Bt
Radio Metric AODV
Basic features
Source node broadcasts a RREQ message flooded by all nodes
When a RREQ is received, the node creates a reverse path to the source
The forward path is established when a RREP is received
Difference
RREQ for multiple destinations are aggregated in same message
Path select algorithm select the interface with highest available capacity
Airtime-cost
To adapt channel fluctuation
Periodically refresh routes to maintain the route
Keep the candidate route (secondary path)
Intermediate nodes does not generate a RREP even if they have a route to the destination
37
A
S
C
B
E
D
AODV
A
C
B
E
D
RMAODV
S
HWMP Example #1: No Root, Destination Inside the Mesh
38
Example: MP 4 wants to communicate with MP 9
1. MP 4 first checks its local forwarding table for
an active forwarding entry to MP 9
2. If no active path exists, MP 4 sends a RREQ to
discover the best path to MP 9
3. MP 9 replies to the RREQ with a RREP to
establish a bi-directional path for data
forwarding
4. MP 4 begins data communication with MP 9
59
710
6
4
3
2
1
8
X
On-demand path
HWMP Example #2: Non-Root Portal, Destination Outside the Mesh
39
Example: MP 4 wants to communicate with X
1. MP 4 first checks its local forwarding table for an active forwarding entry to X
2. If no active path exists, MP 4 sends a RREQ to discover the best path to X
3. When no RREP received, MP 4 assumes X is outside the mesh and sends messages destined to X to Mesh Portal(s) for interworking
Learned via IE in beacons, probe response
4. MP 1 forwards messages to other LAN segments according to locally implemented interworking
59
710
6
4
3
2
1
8
X
On-demand path
HWMP Example #3: Root Portal, Destination Outside the Mesh
40
Example: MP 4 wants to communicate with X
1. MP 4 first checks its local forwarding tablefor an active forwarding entry to X
2. If no active path exists, MP 4 mayimmediately forward the message on theproactive path toward the Root MP 1
3. When MP 1 receives the message, if it doesnot have an active forwarding entry to X itmay assume the destination is outside themesh and forward on other LAN segmentsaccording to locally implementedinterworking
Note: No broadcast discovery required whendestination is outside of the mesh
59
710
6
4
3
2
1
8
X
Proactive path
Root
HWMP Example #4: With Root, Destination Inside the Mesh
41
Example: MP 4 wants to communicate with MP 9
1. MP 4 first checks its local forwarding table for an active forwarding entry to MP 9
2. If no active path exists, MP 4 mayimmediately forward the message on the proactive path toward the Root MP 1
3. When MP 1 receives the message, it flags the message as “intra-mesh” and forwards on the proactive path to MP 9
4. When MP 9 receives the message, it mayissue an on-demand RREQ to MP 4 to establish the best intra-mesh MP-to-MP path for future messages
59
710
6
4
3
2
1
8
X
Proactive path
Root
On-demand path
Reference Model for 802.11s Interworking
42
802.11sMeshPoint
802.11sMeshPoint
802.11sMeshPoint
802.11sMeshPoint
802.11sMeshPoint
802.11sMeshPoint
802.11sMeshPoint
802.11sMeshPoint
802.11s
MAC802
MAC
Bridge
802.11s
MAC802
MAC
BridgeMesh Portal Mesh Portal
L3 Router L3 Router
The 802.11s MAC entity appears as a single port to an 802.1 bridging relay or L3 router.
802.11s mesh portals expose the WLAN mesh behavior as an 802-style LAN segment
(appears as a single loop-free broadcast LAN segment to the 802.1 bridge relay and higher
layers).
Achieving 802 LAN Segment Behavior
43
Bridge Protocol
Bridge
Relay 802.11s
MAC(including
L2 routing)
802 MAC
1
11
59
710
6
2
4
3
13
14
12
Support for connecting an 802.11s mesh to an 802.1D bridged LAN• Broadcast LAN (transparent forwarding)
• Overhearing of packets (bridge learning)
• Support for bridge-to-bridge communications
802 LAN
802 LAN
Layer-2 Mesh
Broadcast LAN
• Unicast delivery
• Broadcast delivery
• Multicast delivery
Interworking: Packet Forwarding
44Abr
ah
1
11
59
710
6
2
4
3
13
14
12A.1
15
A.2
A.3
B.1 B.2
Destination
inside or outside
the Mesh?
Portal(s)
forward
the message
Use path
to the
destination
Interworking: MP view
1. Determine if the destination is inside or
outside of the Mesh
a. Leverage layer-2 mesh path discovery
2. For a destination inside the Mesh,
a. Use layer-2 mesh path discovery/forwarding
3. For a destination outside the Mesh,
a. Identify the “right” portal, and deliver packets via
unicast
b. If not known, deliver to all mesh portals
45
Interworking support
Each MP maintains a layer-2 forwarding table, and there are
three kinds of format to present next hop field
The MAC address : the destination is inside the Mesh
The identity of the MPP : the destination is outside the Mesh
A broadcast address : the destination is outside the Mesh and we
don‟t know what the correct MPP is
46
New components in IEEE 802.11n
PHY enhancements
High modulation : OFDM modulation with additional coding
methods, preambles, multiple streams and beam-forming
Multiple input multiple output (MIMO) : spatial multiplexing
Channel aggregation : two adjacent 20 MHz channels are
combined to create a single 40 MHz channel
MAC Enhancements
Frame aggregation : aggregation in MAC or PHY to efficiently pack
smaller packets into a single MPDU
Block acknowledgement : A performance optimization in which an
IEEE 802.11 ACK frame need not follow every unicast frame and
combined acknowledgements may be sent at a later point in time
47
PHY enhancements
Multiple Input Multiple Output (MIMO)
Transmit and receive with multiple radios simultaneously in same
spectrum
Compare to traditional single input single output radio (with
optional receive diversity)
48
channelRadio
Radio
D
S
P
Bits
TX
Radio
Radio
Radio
D
S
P
Bits
Radio
RX
channelRadioDSPBits
TXRadio DSP Bits
RX
MIMO Method
Spatial multiplexing (SM) throughput ↑
Space-time block coding (STBC) diversity ↑
Transmit beamforming (TxBF) directivity ↑, overall throughput ↑
49
A
B
A
B
A
B
Spatial Division Multiplexing
Multiple independent data streams are sent between the
transmit and receive antennas to deliver more bits in the
specified bandwidth
Cross-paths between antennas are automatically decoded by
the receiver, assuming sufficient “richness” in the propagation
environment
50
Radio
Radio
D
S
P
More Bits
TX
Radio
Radio
Radio
D
S
P
More Bits
Radio
RX
MAC Enhancement
The basic MAC Exchange
Block ACK
With block ACK, we don‟t need to ACK each MPDU
Frame Aggregation
With frame aggregation, multiple MAC frames are assembled into
a single PHY frame
Provides a Latency vs. Throughput tradeoff
51
RTS
CTS
MPDU
ACK
MPDU
ACK
RTS
CTS
MPDU MPDU
BACK
RTS
CTS
A-MPDU
BACK
Frame Aggregation
MAC service data unit aggregation (A-MSDU)
Group logical link control packets (MSDUs) with the same 802.11e
Quality of Service, independent of source or destination
MAC protocol data unit aggregation (A-MPDU)
occurs later, after MAC headers are added to each MSDU
52
MAC
Proce-
ssing
F1
F2
F3
MAC
header
F1
F2
F3
MAC
Proce-
ssing
F1
F2
F3
MAC
header
F1
F2
F3
MAC
header
MAC
header
A-MSDU A-MPDU
Backward compatibility
Backward compatibility to a/b/g & Coexistence
802.11n supports three compatibility modes
Non-HT mode (Legacy mode)
- Compatible with 802.11a/b/g
HT-mixed mode
- For high throughput operation and coexistence
HT-Greenfield mode
- For high throughput operation but not detectible by legacy devices
The new PHYs require enhanced protection mechanisms to avoid
interfering with existing older station (i.e. a/b/g)
53
Consideration for Throughput Enhancement
Random Network
Source-destination의 방향성이 없는 네트워크
Theoretical upper limit of the per node throughput capacity
Theoretically achievable capacity to ever node in a random static
wireless ad hoc network
Assumed by Ideal global scheduling and routing
With the use of real MAC, routing, and transport protocols and
a realistic traffic pattern, the achievable capacity in a WMN, in
practice, is much less than the theoretical upper limit
54
1/O n
<참고문헌>
P. Gupta and P.R. Kumar, „„The Capacity of Wireless Networks.‟‟ IEEE Transactions on Information Theory, vol. 46, no. 2, pp.
388–404, March 2000.
J. Li, C. Blake, D.S.J. De Couto, H.I. Lee, and R. Morris, „„Capacity of Ad Hoc Wireless Networks,‟‟ Proceedings of ACM
Mobicom 2001, pp. 61–69, July 2001.
1/ logO n n
Consideration for Throughput Enhancement
CSMA/CA based MAC protocol
Due to the exposed node problem
String topology
55
String topology 1 hop 2 hop 3 hop 4 hop 5 hop >5 hop
Normalized throughput 1 0.47 0.32 0.23 0.15 0.14
1/hop 1 0.5 0.33 0.25 0.2 0.16
<exposed node problem>
1/1/ dO n
Consideration for Throughput Enhancement
Theoretically achievable capacity
56
2 4 6 8 10 12 14 16 18 200
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Number of Client
No
mal
ized
Th
rou
gh
pu
t
Capacity Upperbound
Ideal case, String topology
CSMA, String topology
CSMA, 2dimensional topology
•Branch의 수가 증가할 수록 throughput 감소 증가•Network topology를 최대한 정방형으로 설계•패킷의 크기가 클수록 throughput 감소가 작음(채널에러가 없는경우)
Consideration for Throughput Enhancement
Arbitrary network
Arbitrary의 의미 „임의로 결정되어 변하지 않는‟의 뜻으로 매 전송마다 동일한 시작 및 목
적지 노드, 전송률, 전송 전력 을 가지는 네트워크로 정의
시스템 모델은 Nc개의 client가 균일하게 분포
Nr개의 mesh router가 존재
Client는 자싞과 가장 가까운 라우터와만 직접 통싞
Capacity upper-bound
MP의 수가 적을 때:
• Per-client throughput: 이 증가할수록 증가
MP의 수가 많을 때:
• Per-client throughput: 이 증가할수록 감소
57
/ log ,r c c g rN O N N N O N
r
c
c
NC
N
rN
/ log ,r c c g rN N N N O N
1
logc
r c
CN N
rN
<참고문헌>
P. Zhou, X. Wang, and R. Rao, “Asymptotic Capacity of Infrastructure Wireless Mesh Networks,” IEEE Transactions on
Mobile Computing, Vol. 7, No. 8, Aug. 2008
Consideration for Throughput Enhancement
Performance
Network topology
Theoretical per node throughput
58
0 10 20 30 40 500.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
0.11
Number of router
No
mal
ized
th
rou
gh
pu
t
50 client
100 client
25 client
STA의 수가 결정되면 최적의MAP(MP)의 수와 MPP의 수가
결정됨
Throughput Enhancement
Multi-radio system (여러 개의 NIC, 최대 4개) 으로 구현
IEEE 802.11n 사용
Frame aggregation, Block ACK, MIMO
상용 장비
BelAir, Cisco, Nortal, SkyPilot
Multi-Hop QoS
Can provide using EDCA, not guarantee
59
IP layer
802.11n
(40MHz)
802.11n
(20MHz)
802.11n
(20MHz)
Upper branch
or gateway
Lower
branchAccess
Consideration for Throughput Enhancement
60
Consideration for Throughput Enhancement
Vendor Model Feature Price($)
BelAir
Network
BelAir200
Wireless Multi-
Service Switch
Router
• Modular architecture
• Supports Wi-Fi,WiMAX and Cellular
• IEEE 802.1p prioritization with 4 queue
• 1-port Ethernet interface
• 4x T1 interface
• IEEE 802.1D MAC bridging
• 802.1x(RADIUS) ,EAP and AES
• MIC2003-13 approvals
4000~9000
(Depending on
the number of
radio module)
Cisco Cisco Aironet
3500 Series
Access Point
• IEEE802.11n
• Dual-band controller-based 802.11a/g/n
• 2x3 multiple-input multiple-output
• Frame aggregation
• 1-port Ethernet interface
• 802.11i, Wi-Fi Protected Access 2 (WPA2),
WPA
2600
SkyPilot SkyPilot®
Connector
DualBand
• IEEE 802.11b/g
• Up to 7.5 miles / 12 kilometers
• AES-128 encryption
• 1-port Ethernet interface
Conclusion
Wi-Fi Mesh using IEEE 802 based technology
Coverage can be extended by directional antenna and amplifier
However, it may limited by the slot size
More than several km Need to point-to-point equipment
In Mesh network, throughput can be reduced in proportion to
the number of node
Multi-Radio system and IEEE 802.11n required
61
Thank you !
62
Q & A
Backup slides
MP boot sequence
63
Neighbor discovery
A MP performs passive or active scanning to discover
neighboring MPs
Add nodes of the same profile into MP’s neighbor table
Node’s physical neighbors can be classified to ignore node,
Neighbor MP and Candidate peer
Ignore node: a node that can‟t be communicated with (different
profile nodes)
Neighbor MP: a node that is a neighbor in the Mesh network, but
can‟t setup a link with it (the same profile nodes)
Candidate peer: a node that is a neighbor MP and can setup a link
in the Mesh network, (the same profile nodes)
64
Neighbor discovery
65
802.11 beacon OFDM Mesh ID WLAN mesh capability Neighbor list DTIM Mesh Portal reachability
Beacon
ID
Version
Active protocol ID
Active metric ID
Peer capacity
Power save capability
Channel precedence
A
B
C
DProfile : 1Version: 1
Active protocol ID: 1
Active metric ID: 2
Profile : 2Version: 1
Active protocol ID: 2
Active metric ID: 3
Profile : 2Version: 1
Active protocol ID: 2
Active metric ID: 3
Beacons
Profile : 1Version: 1
Active protocol ID: 1
Active metric ID: 2
Profile : 3Version: 1
Active protocol ID: 2
Active metric ID: 1
Neighbor discovery
66
Neighbor table
MAC adr. Primary
MAC adr.
State Directionality Operating
channel #
Channel
precedence
Bit rate PER RSS
B’s adr #1 #1 Neighbor 1 1 5dp
C’s adr #1 #1 Neighbor 1 1 4dp
A
B
C
DProfile : 1Version: 1
Active protocol ID: 1
Active metric ID: 2
Profile : 2Version: 1
Active protocol ID: 2
Active metric ID: 3
Profile : 2Version: 1
Active protocol ID: 2
Active metric ID: 3
Beacons
Profile : 1Version: 1
Active protocol ID: 1
Active metric ID: 2
Neighbor discovery
67
Neighbor table
MAC adr. Primary
MAC adr.
State Directionality Operating
channel #
Channel
precedence
Bit rate PER RSS
B’s adr #1 #1 Candidate
Peer
1 1 5dp
C’s adr #1 #1 Neighbor 1 1 4dp
A
B
C
D
Peer capacity: # of additional MP
peers that the device can
accommodate
Beacons
Channel Selection
Channel selection mode
Simple unification mode
Single channel unification mode
Advanced mode
Beyond the scope of spec.
Single channel unification mode
The channel of a MP is set to the highest channel precedence
value of candidate peer
68
Channel Selection
69
A‟ Neighbor table
MAC adr. Primary
MAC adr.
State Directionality Operating
channel #
Channel
precedence
Bit rate PER RSS
B’s adr #1 #1 Candidate
Peer
1 1 5dp
C’s adr #1 #1 Candidate
Peer
6 3 4dp
A
B
C
3>1
As a result, A‟s channel is 6
Backup slides
RM-AODV
70
Radio Metric AODV
71
A
S
C
B
E
D{S,D,0}
{S,D,0}
2
3
3
1
3
5
2
2
S S 2
S S 3
Radio Metric AODV
72
A
S
C
B
E
D
2
3
3
1
3
5
2
2
S S 2S A 5
S C 6S S 3
{S,D,2}
{S,D,3}
Radio Metric AODV
73
A
S
C
B
E
D
2
3
3
1
3
5
2
2
S S 2S C 4
S C 6S S 3
Radio Metric AODV
74
A
S
C
B
E
D
2
3
3
1
3
5
2
2
S S 2S C 4
S C 6
S E 8
S S 3
Radio Metric AODV
75
A
S
C
B
E
D
{D,S,5}
2
3
3
1
3
5
2
2
S S 2S C 4
S C 6
D D 2
S E 8
S S 3
E E 3
D E 5
C C 3
D C 8
{D,S,2}
Radio Metric AODV
76
A
S
C
B
E
D
2
3
3
1
3
5
2
2
S S 2S C 4
S C 6
D D 2
S B 6
S S 3
E E 3
D E 5
C C 3
D C 8
Radio Metric AODV
The selected path is S C B D
77
A
S
C
B
E
D
{D,S,3}
2
3
3
1
3
5
2
2
S S 2S C 4
D D 2
S C 6
D D 2
S B 6
S S 3
E E 3
D B 3
B B 1
C C 3
D C 7
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