Wireless LAN Site Survey for satellite installation with some information courtesy of Dr Richard Butler RGU
WLAN with consistent reliable wireless access.
Investigate customer facility
Radio frequency
Install location
Number of connections to be served 15000 in Inverurie and 240,000 in Aberdeen
Throughput
WLAN coverage
Determine feasibility of desired coverage think about Omni directional
Radio frequency interference
Optimum installation locations
Spacing between APs
Wired connectivity limits
Process
Gather tools and configuration
Research and investigate industry specific concerns and requirements
Line of sight for satellite signals blocked by curvature of Earth need for inter satellite Communications and multiple satellites
Gather the recommended equipment list or survey kit like microwave dishes and transponder gear on the ground
Implement the site survey
Document the site survey in video
Considerations - data rates, proportional to sensitivity and range
Antenna type and placement the yagi antenna and omnidirectional.
Physical requirements open areas provide better range than closed or filled areas trees block wireless signals
Obstructions shelves pillars metallic reflective surfaces
Building materials drywalls allow greater range than concrete blocks
Line of sight for outdoor applications need clear line of sight
Design requirements, high availability achieved through system redundancy, redundant Access Points on separate frequencies
Proper coverage area design Accounts for roaming
Automatic data rate negotiation think TCP Transport Control Protocol windowing when signal strength weakens
Proper antenna selection
Possible use of repeater to extend coverage to areas where Access Point cannot be located
Design requirements
Scalability accomplished by supporting multiple Access Points per coverage area
Using multiple frequencies and non-overlapping channels for Access Points performing load balancing
Manageability accomplished by enterprise Wireless LAN devices that support remote management protocols
Interoperability achieved through adherence to standards 80211b through 802.11e
Participation interoperability associations for example WIFI alliance
Specifics - applications and data collection be aware of applications users might be using
Load and coverage
Bandwidth and throughput
Mobile users
Power consumption of battery devices
Constant awake mode CAM
Fast power save mode Fast PSP
Max power save mode Max PSP
Interference
Encryption none, 40 and 128 bit
The survey
Step 1 - make a detailed layout of the building lots of photos of mountain side for satellite installation
Step 2 - decide on the method of powering the access point AC Alternating Current accessible or a battery pack. Flat land high up for electricity substation
Step 3 - prepare a description of the desired coverage area
Step 4 - prepare a description of the desired usage of email internet applications, the number of users per Access Point etcetera, potential load of Access Point.
Calculate throughput of each user typical applications.
Good direction and gain with yagi antennas.
Step 5 - select the same model of Radio Frequency equipment that the customer will use.
Antenna
An antenna is electrical conductor - transmission radiates electromagnetic energy into space, reception receives electromagnetic energy from space. Two way Communications same antenna transmission and reception.
Refraction bending radio waves
Wireless LAN impairments
Refraction radio waves bounce back off surface. Occurs when signal encounters a surface that is large relative to wavelength of signal.
Multi path obstacles reflect signals so that multiple copies with varying delays are received
Attenuation and attenuation distortion also signal loss
Free space loss
Noise
Atmospheric absorption consider the weather at different times of year
Fading
Scattering wireless signals scatter out this leads to data loss. Scattering occurs when incoming signal hits an object whose size in the order of the wavelength or less.
Diffraction occurs at the edge of an impenetrable body that is large compared to wavelength of radio wave
The effects of multi path propagation - multiple copies of a signal may arrive at different phases. If phases add destructively the signal level relative to noise declines making detection more difficult.
Intersymbol interference one or more delayed copies of a pulse may arrive at the same time as the primary pulse for a subsequent bit.
Wireless signal noise
Thermal noise due to attenuation of electrons
Present in all electronic devices and transmission media Cannot be eliminated
Function of temperature Particularly significant for satellite communication
Intermodulation noise - occurs if signals with different frequencies share the same medium Interference caused by a signal produced at a frequency that is the sum or difference of original frequencies
Crosstalk unwanted coupling between signal paths
Impulse noise irregular pulses or noise spikes
Short duration and of relatively high amplitude caused by external electromagnetic disturbances or faults and spikes in the communications system
Atmospheric absorption water vapor and oxygen contribute to attenuation and Fading