Radio Network Planning for Outdoor WLAN-Systems · · 2016-01-28Radio Network Planning for Outdoor WLAN-Systems Jarkko Unkeri ... network planning tools like Atoll and SitePlanner

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Radio Network Planning forOutdoor WLAN-Systems

Jarkko [email protected]

54029P

S-72.333 Postgraduate Course in Radio Communications

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S-72. 333 Postgraduate Course in Radio Communications27.4.2004

Outline

• Introduction• WLAN Radio network planning challenges• Objectives for network planning• Planning process

• Coverage planning• Capacity planning• Frequency planning

• Summary and discussion

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• Outdoor WLAN-Systems are getting more popular– Outdoor Hot-Spots; Train stations, Squares,– Campus areas– Industry and logistics (e.g. surveillance, harbours)– Residential areas– City-wide networks; Fixed Wireless Access (FWA), Hot-Spots etc.

• WLAN outdoor usage is quite challenging– IEEE 802.11b radio interface is mainly specified for office

environment, where distances and number of users are small– Unlicenced frequency band

Low transmit powers, interference...

Introduction

Need for carefull network planning

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WLAN radio network planning challenges

• Challenges of WLAN radio technology• short distance (LOS: <1km) due to low transmit power

medium gain antennas (13 dBi) to get better sensitivity andoptimal antenna alignment to use effectively transmit power

• near-far problem due to lack of transmit power controloptimal radiation pattern and alignment of base station antenna (the farer the client, the higher the antenna gain)

• hidden node problem during the uploadingsectorized cell (multiradio site) mimimizes cases, where clients can’t hear each other.RTS/CTS handshaking protocol

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Objectives for network planning

• Capacity• There should be enough capacity to support the subscriber traffic

with sufficiently low blocking and delay

• Coverage• To obtain the ability of the network to ensure the availability of the

service in the entire service area

• Quality• Linking the capacity and the coverage and still provide the required

QoS

• Costs• To enable an economical network implementation when the service

is established and a controlled network expansion during the life cycle of the network

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Equipment selection

• Equipment selection is important because e.g. receiver sensitivities might vary a lot between different chipset manufacturers

• The use of OFDM improves spectral efficiency, improves resistance to frequency selective fading, decreases ISI and lowersmultipath distortion. The main advantages of DSSS (802.11b) are that it tolerates noise more efficiently and the client devices are very popular and inexpensive

802.11b 802.11g 802.11aFrequency band (outdoor) [GHz] 2,4 - 2,483 2,4 - 2,483 5.47 - 5.725Maximum data rate [Mbit/s] 11 54 54Physical layer modulation DSSS OFDM OFDM

Receiver sesitivity [dBm] 5.5 Mbps: -89 11 Mbps: -89

36 Mbps: -82 54 Mbps: -76

36 Mbps: -83 54 Mbps: -77

Maximum transmit power (EIRP) [dBm] 20 20 30Number of channels (outdoor) 13 13 11(Values are based on ETSI regulations)

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Planning process

Requirements for coverage

Requirements for capacity

Requirements for quality

Area type / radio propagation

Dimensioning

Capacity and coverage planning

Network performance visualisation

OptimisationMeasured network

performance

-Rough number of base stations and sites

-Base station configurations

Adjustment of radio parameters

-Site selection

-Base station configurations

-Cell specific parameters for radios

-Capacity and coverage analysis

-Quality of service analysis

Input Output

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Input for the network planning

• Capacity• Available backhauls?

• Offered client end capacity?

• Population in the service area?

• Estimated Internet penetration?

• Load factor?

• Coverage• Area type?

• Maps, also 3D?

• Need for 100 % Coverage?

• Access type (Fixed, mobile)?

• Frequency• Other networks in the area

(or other essential interference)?

• Other• Special needs for capacity,

coverage or QoS?

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Dimensioning ProcessDimensioning Process

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Coverage planning (1/2)

• Due to uncertainty of signal levels in NLOS situations, the LOSconnection to client is typically needed. For example trees between base station and client shall be avoided, because attenuation can vary tens of decibels depending on weather andseason

• The client end equipments plays important role in WLAN radionetwork planning (Client antenna gain, receiver sensitivity...)

• Radio wave propagation depends on environment:

Typical path-loss exponents:Free space 2Urban area cellular 2.7 - 3.5Shadowed urban cell 3 - 5

Rayleigh fading

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Coverage planning (2/2)

• Radio coverage can be simulated based on 3D map using radionetwork planning tools like Atoll and SitePlanner that are popularin cellular world

• Simple link budget calculations can be used to estimate the acceptable propagation loss:

where Pt is transmit power, Pr is receiver sensitivity, M is fading margin, Lois the free space loss, Lkt and Lkr are cable losses, Gt and Gr are antenna gains.

where λ is the wavelength and d is the distance between antennas.• The link budget should be calculated for both directions

(uplink/downlink)

Pr=Pt+ Gt-Lkt-L0+Gr-Lkr-M [dB]

2

04log10

⋅⋅⋅=

λπ dL

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Multipath propagation

• In a radio connection the signal is often received from different paths reflected, penetrated, diffracted and scattered=> Changes in amplitude, phase and polarization in the

received signal

Figure 5:Multipath propagation

Signals in phase: Amplified signal

Signals out of phase: Distorted signal

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Base station antenna gain vs.coverage

• Higher antenna gain results inmore directivitynarrower beam (horizontal + vertical)larger antenna structure

• Directional antennas are also used to restrict some of incoming multipath echoes

• Reasonable omni-directional antenna gain no higher than 6 dBiotherwise elevation beam unreasonable narrow resulting in null sectors

Cell size extension by sectorization Antenna gain vs. range

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Sectorized antenna systemvs. omni-directional

• Gives up to four times larger effective coverage per site• Decreases probablity for typical WLAN outdoor network

problemshidden node, near-far, null sectors

• Sectorized system gives more even signal strength troughout the cell (down-tilting, shaped beam antennas)

• Omni antenna cannot be directed (cell size management)

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Capacity planning

Corporate 802.11WLAN

HotZones802.11 WLANs

PtMP WLL/802.16

SDH/PDH (PtP) Link Fiber• The use of interference free solutions in transmission network confirms the network operability– Wired solutions: Fiber, xDSL etc.– Wireless solutions: SDH/PDH,

WLL, 802.16 etc.

• Bottlenecks should be avoided in transmission network

• Typical WLAN network topologies– 5 GHz (.11a) for wireless

links– 2.4 GHz (.11b/g) for Client

Access

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802.11 throughput

• In 802.11b/g/a the data transmission is half-duplex• Effective data rates should be taken into account when planning

capacity• The maximum number of users/AP depends on the offered client

end capacity• The throughput of .11g reduces significantly if .11b is used

simultaneously (RTS/CTS or CTS overhead)Table 1. Theoretical Maximum Application-level Throughput

StandardNumber of Non-

Interfering Channels ModulationMaximum Link Rate

Theoretical Maximum TCP Rate

Theoretical Maximum UDP Rate

802.11b 3 CCK 11 Mbps 5,9 Mbps 7,1 Mbps802.11g (with 802.11b) 3 OFDM/CCK 54 Mbps 14,4 Mbps 19,5 Mbps802.11g (.11g only) 3 OFDM/CCK 54 Mbps 24,4 Mbps 30,5 Mbps802.11a 19* OFDM 54 Mbps 24,4 Mbps 30,5 Mbps802.11a Atheros Turbo Mode 6 OFDM 108 Mbps 42,9 Mbps 52,8 Mbps* 13 non-overlapping channels in United States and up to 19 non-overlapping channels in Europe depending on localregulations

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Frequency planning (1/3)

• The number of non-overlapping channels sets the limitations forchannel planning

• Isolation between antennas, radio units at the same site and neighbouring cells should be calculated to estimate needed channel difference

• Isolation consists of things like propagation loss, radiation patternof antennas and receiver adjacent channel rejection

• In the worst case, when transmitting (20 dBm) and receiving(-90 dBm) is occuring at the same time, 110 dB isolation isneeded

• Isolation can be increased also by using different polarisations(e.g. if 802.11g is used for wireless links between 802.11b AP’s)

• Antenna type selection has effects also to interference– Low sidelobe levels, high High cross polarization discrimination, High

front-to-back ratio

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• Receiver adjacent channel rejection– The adjacent channel rejection for .11b and .11g shall be

equal to or better than 35 dB between any two channels with> 25 MHz separation in each channel group

Needed carrier to interference ratio @ 11 Mbit/s

-50

-40

-30

-20

-10

0

10

1 2 3 4 5 6 7Channel difference

C/I

[dB

]

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• Interference scanning is required in the area– Spectrum analyzer is also needed because there might exist

some other interference than from other WLAN systems e.gcordless telephones, wireless cameras etc.

• Centralized management and monitoring of radio channels andinterference is needed in large networks (e.g SNMP based tool)

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Summary

• The outdoor usage of WLAN systems is quite challenging– Interference, hidden-node, near-far...

• With proper radio network planning the effects of these problems can be minimized– Base station site selection– Antenna type selection– Proper capacity calculations– Proper frequency planning

• It should be noticed that WLAN regulations varies from country toanother especially at 5 GHz band

• Centalized management and monitoring of radio parameters are needed in networks with multiple Access Points

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References

[1] H. Holma, A. Toskala, WCDMA for UMTS Radio Access for ThirdGeneration Mobile Communications, John Wiley& Sons, 2000.

[2] M. S. Gast, 802.11 Wireless Networks, The Definitive Guide, O’Reilly, April 2002.

[3] T.S. Rappaport, Wireless Communications, Upper Saddle River (NJ), Prentice Hall PTR, 1996.

[4] J. Heiskala, J. Terry, OFDM Wireless LANs: A Theorethical and Practical Guide, Sams Publishing 2002.

[5] J. Geier, Wireless LANs; Implementing High Performance IEEE 802.11 Networks, 2nd ed., Sams Publishing 2002.

[6] 802.11 Wireless LAN Performance, Atheros Communications Inc. , April 2003. Available: http://www.atheros.com/pt/atheros_range_whitepaper.pdf

[7] ORiNOCO AP-4000 Tri-Mode Access Point Technical Specifications, Proxim Corp., 2004. Available: http://www.proxim.com/products/wifi/ap/ap4000/techspecs.html

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Homework

• Calculate using the simple link budget the needed receiver antenna gain to achieve 11 Mbit/s data rate. The connection length is 0,5 km and typical 802.11b equipments are used.– AP antenna gain: 12 dBi– LOS situation with free fresnell-zone– 6 dB fade margin expexted– 5 m RF cable in both ends– AP side cable attenuation: 0,12 dB/m (1/2” RF)– Client end cable attenuation: 1,4 dB/m (RG 58)– Tx power adjustable in AP side: 7, 10, 13 or 16 dBm– Tx power at client end: 15 dBm

Documents

Radio Network Planning for Outdoor WLAN-Systems · · 2016-01-28Radio Network Planning for Outdoor WLAN-Systems Jarkko Unkeri ... network planning tools like Atoll and SitePlanner