Long-Range Fixed Wireless

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• Wireless technology can be used to configure a bridge between two networks
  • can be a more cost-effective and practical solution than laying cable
  • regulation of the radio spectrum means that the transmitters required to cover long distances must be carefully configured
  • referred to as long-range fixed wireless
• Point-to-point line-of-sight fixed wireless uses ground-based high-gain microwave antennas that must be precisely aligned with one another
  • High-gain means that the antenna is strongly directional
    • Each antenna is pointed directly at the other and can transmit signals at ranges of up to about 30 miles
      • long as they are unobstructed by physical objects
      • antennas themselves are typically affixed to the top of tall buildings or mounted on tall poles to reduce the risk of obstructions

Licenses and Unlicensed Frequencies

• Long-range fixed wireless can be implemented using licensed or unlicensed frequency spectrum
  • Licensed means that the network operator purchases the exclusive right to use a frequency band within a given geographical area from the regulator
    • US regulator is the Federal Communications Commission (FCC)
    • if any interference sources are discovered, the network operator has the legal right to get them shut down
  • Unlicensed spectrum means the operator uses a public frequency band, such as 900 MHz, 2.4 GHz, and 5 GHz
    • Anyone can use these frequencies
      • so interference is a risk
    • To minimize the potential for conflicts, power output is limited by regulatory requirements

Wireless Signal Power Measurement

• A wireless signal’s power has three main components:
  • Transmit power
    • the basic strength of the radio
    • measured in dBm (decibel per milliwatt)
  • Antenna gain
    • the amount that a signal is boosted by directionality—focusing the signal in a single direction rather than spreading it over a wide area
    • measured in decibels isotropic (dBi)
  • Effective isotropic radiated power (EIRP)
    • is the sum of transmit power and gain
    • expressed in dBm
• Lower frequencies that propagate farther have stricter power limits than higher frequencies
  • but, higher EIRPs are typically allowed for highly directional antennas
  • E.g.,
    • in the 2.4 GHz band, each 3 dBi increase in gain can be compensated for by just a 1 dBm reduction in transmit power
    • this allows point-to-point wireless antennas to work over longer ranges than Wi-Fi APs