Microwave links come in two categories, point-to-point links (P2P) and point-to-multipoint links (P2MP). Designing for either type requires some serious planning.

Microwave transmission refers to the technology of transmitting information by the use of radio waves whose wavelengths are conveniently measured in small numbers of centimeters; these are called microwaves. This part of the radio spectrum ranges across frequencies of roughly 1.0 gigahertz (GHz) to 30 GHz. These correspond to wavelengths from 30 centimeters down to 1.0 cm

The next higher part of the radio electromagnetic spectrum, where the frequencies are above 30 GHz and below 100 GHz, are called “millimeter waves” because their wavelengths are conveniently measured in millimeters, and their wavelengths range from 10 mm down to 3.0 mm.

A microwave link can be used for cellular tower interconnections, which were common with the older 3G GSM or CDMA link. A next generation microwave link can be a 4G LTE, 4G LTE Advanced, and soon a 5G link.

A microwave link can be point to point or point to multipoint.

A Multi-hop Routing Between Cities

A satellite link technically speaking is also a microwave link. Although, most refer to satellite as a different sort of connection, yet it uses similar technology and is operated in the microwave spectrum. There are many kinks of links that can be called microwave links. However, any wireless network below 1 GHz is not called microwave, these networks are normally called VHF or UHF or by some other name that fits the licensing name, such as 902 MHz to 928 MHz ISM Band (Industrial, Scientific, Medical). Microwaves are any frequency greater than 1 GHz.

When required, we can bounce microwave links to get around obstructions, however, this is not a common practice today as it was at one time. Today, two links are built to relay the traffic past the obstructions.

To design a microwave link we do work in the office and out in the field. Both are required. Rarely is it sufficient to be successful to plan from the office only. A visit to the view the path firsthand is required.

INITIAL KICK-OFF TASKS

Produce a preliminary network design by:

  • Meet with the customer to define the application. 
    • Learn everything that you can about the nature and the type of content that they wish to transmit,
    • What is the bandwidth required?
    • Is the pathway in one or two directions?
    • Is the data flow symmetrical or asymmetrical?
    • How robust does it need to be?  Can the user tolerate outages?
    • What is known about the perspective sites?
    • What about future expansion of the communication traffic and the need for additional bandwidths?
  • Determining the local frequency availability and regulations relating to frequency management and microwave path availability,
  • Selecting suitable sites,
  • Establishing line-of-sight,
  • Calculating path prediction with a software tool,
  • Overlay the path on a topographical map.
The Start of the First Hop in a Multi-hop Path

PREPARATION TASKS

  • Determine the technical strategy, if possible, before starting the process of conducting a site survey
  • Secure hard-copy government topographical (topo) maps of the area with a scale of 1:50,000 and 1:250,000
  • Secure a street and road paper map of the area
  • Secure aviation paper maps of the area
  • Secure marine paper charts of the area, if applicable
  • Locate the end and intermediate points of the path and identify the latitude, longitude and elevation data
  • Document this waypoints in a MS Word document
  • Search the tower database for collocation opportunities
  • Review the DOT Fight supplement for aviation coordinates and data
  • Create a map overview with the path overlaid in MS Visio and incorporate into the MS Word report document
  • Run a path profile and calculate any obstructions and Fresnel clearance issues
  • Determine the path performance and reliability
  • Set the performance specification for the link and size power, antennas, etc.
  • Check local weather conditions (related to the visit itself and from the perspective of signal attenuation)
  • Plan site access issues (gate keys, permissions, escorts, jurisdictions, health and safety [radiation])
  • Assemble the site survey kit for the field work
    • GPS, with fresh batteries
    • Binoculars (spotting scope or high power binoculars)
    • Digital camera (telephoto lenses and high quality, low light photography with suitable polarizing and UV filters are sometimes required depending upon the path length)
    • Compass – electronic fluxgate, magnetic (high grade), magnetic (low grade)
    • Inclinometer
    • Tape measure (50’ or 100’ preferred, 25’ minimum)
    • Topo maps and lat / long snapshot sheet
    • Pencil and pad for notes
    • Backpack carrying bag
    • Suitable clothing (weather – temperature and rain) and safety equipment (shoes, hard hat, etc.)
  • Ensure that all required preparation work is completed before departing for the field work
  • “Fly the path” on Google Earth
A Relay Tower Point in a Multi-hop Path

FIELD TASKS

  • Follow the signal flow from source to destination
  • Locate the first site and capture GPS readings (latitude / longitude / elevation)
  • Observe path orientation (azimuth) and record any concerns (obstructions)
  • Search for, and record, any potential sources for terrestrial interference (heat pumps, air conditioners, mercury vapor lights, old or degraded high tension power lines / right of way, Doppler radar (ships, aviation weather, etc.), flight paths
  • Determine if line of sight is achievable
  • Is power available at this site?
  • Is a shelter available at this site?  If yes, is there space for your installation? 
  • If the equipment is pre-wired off-site, can a populated equipment rack be successfully delivered to the site with a delivery truck (roads, access concerns)
  • Can the equipment racks be moved into the shelter (doorway access, walk the path)
  • Do you have interior space for the racks
  • How will the racks be anchored?
  • Is there interior wall space for mounting any hardware systems?
  • How will the racks be grounded?  What is the grounding strategy for the site?
  • Make notes, sketch drawings and photograph the site
  • Move to the next location, and repeat process
The Final Receive Site for a Multi-hop Path

POST FIELD SURVEY TASKS

  • Consolidate information
  • Document field notes into formal report and presentation
  • Archive the photographs and label with meaningful names (create a naming convention)
  • Validate latitude and longitude used for path calculations with field data
  • Reconfirm the path calculations
  • Review all applicable standards documents for compliance (Industry Canada, CRTC, Safety Code 6, FCC, CSA, SMPTE, IETF, IEEE, etc.)
  • Define a data traffic model that will travel over the pathways to ensure capacity
  • Define a data storage model, if applicable
  • Define the traffic and it characteristics
  • Define security requirements for the traffic
  • Define the QoS and VLAN for the traffic
  • Identify the potential for RF interference and atmospheric impacts
  • Define the baseband and IF signal loss calculations for the technology interconnections
  • Prepare the reports and present the findings
A Profile View of an RF Path with Signal Level Degradation Prediction