Strengths of Infrared Over Microwave Radio

1
Strengths of Infrared Over Microwave Radio

• Spectrum for infrared virtually unlimited
• Possibility of high data rates
• Infrared spectrum unregulated
• Equipment inexpensive and simple
• Reflected by light-colored objects
• Ceiling reflection to get entire room coverage
• Doesnt penetrate walls
• More easily secured against eavesdropping
• Less interference between different rooms

2
Drawbacks of Infrared Medium

• Indoor environments experience infrared
  background radiation from sunlight and indoor
  lighting
• this radiation appears as noise to infrared
  receiver to counter which
• Transmitters of higher power required
• And the range is limited
• Higher power is limited by concerns of eye safety
  and excessive power consumption

3
Three transmission Techniques for IR Data
Transmission

• Directed Beam Infrared
• The range depends on the emitted power and degree
  of focusing. The range can be in kms (for outdoor
  installation with LOS)
• The figure in next slide shows a token ring LAN.
  Work stations are connected to a hub which is
  connected to a transceiver.
• Omni directional
• Have a single base station that is within LOS of
  all other stations. Usually the BS is mounted on
  the ceiling. The BS transmits omni directional
  signals while other stations transmit directional
  beam aimed at the ceiling base unit.
• Diffused
• Here all IR transceivers are focused and aimed at
  a point on a diffusely reflecting ceiling. The
  signals strike the ceiling and are reradiated or
  reflected omni directionally and picked up by all
  of the receivers in the area.

4
Token ring LAN using point-to-point infrared links
5
Directed Beam Infrared

• Used to create point-to-point links
• Range depends on emitted power and degree of
  focusing
• Focused IR data link can have range of kilometers
• Cross-building interconnect between bridges or
  routers

6
The ceiling transceivers transmits omni
directionally while other stations beam their
signal directly at the ceiling unit
7
Omni directional

• Single base station within line of sight of all
  other stations on LAN
• Station typically mounted on ceiling
• Base station acts as a multiport repeater
• Ceiling transmitter broadcasts signal received by
  IR transceivers
• IR transceivers transmit with directional beam
  aimed at ceiling base unit

8
Here all transceivers are aimed at the ceiling
which reflects the signals back down to cover the
entire area.
9
Diffused

• All IR transmitters focused and aimed at a point
  on diffusely reflecting ceiling
• IR radiation strikes ceiling
• Reradiated omni directionally
• Picked up by all receivers

10
The above picture has a number of ceiling mounted
BSs, one in each room. Each BS provides
connectivity for a number of stationary and
mobile stations. Using ceiling wiring, the BSs
are connected back to a server that connects this
network to WAN or a wired LAN.