CCNP Wireless CUWSS 642-732 Summary Notes 10 : Designing a mesh network

Design Considerations (especially outdoors)

Consider the data rate required at the edge of the cell

Larger cells offer binary phase shift keying (BPSK) or quadrature phase shift keying (QPSK) data rates at the edge but require fewer hops to wired network.
Smaller cells may offer quadrature amplitude modulation (QAM) (16QAM or even 64 QAM) at the edge hence increased performance BUT
- More APs are needed to cover the area
- More APs means more backhaul traffic leading to need for multiple backhauls to increase throughput and reduce hop count to wired closet.
Approximate AP radius per speed offered and area of the cell
- AP with QPSK at the edge can have 0.619 m radius (in open space)
- 16-QAM rate AP offers 0.324-m radius per cell at the edge
- 64-QAM rate AP offers 0.226-m radius per cell at the edge
Common distances
- MAP to MAP: 100 to 200 m
- Client to MAP: 80 to 150 m
- RAP to first MAP: 200 to 800 m ( If RAP is high, APs at the foot of the building are in the shadow area, and need to go through another MAP to reach the RAP)
- Maximum recommended number of hops to RAP is 4
AP cell area can be approximated as
```
Area = Pi (3.14159) x Square of the radius
```
- For Mesh, neighbouring APs overlap forming a hexagon with aan AP on each side

Area = 2.598 x Square of the radius

Number of APs per Km= 1 / (2.598 x Square of the radius)

Planning for Outdoor Surveys

MAPs are commonly located on light poles and RAPs on towers or rooftops
Issues with mounting on the pole
- The mounting hardware might not fit the pole.
- The antenna might end up too close to the pole.
- Power might not be available all the time.
- The pole might not handle the AP weight and wind load.
- Aesthetics
All outdoor APs must be grounded
Make sure that nothing is blocking the first Fresnel zone, even the mounting point itself.
- Poles placed near the antenna can also affect the antenna radiation pattern and create dead spots in the direction of the pole.
- The minimum distance between the antenna and the pole depends on:
  - Pole thickness
  - Antenna height
  - the street angle, the lower pole antenna radiation may be too low to be in range with the next AP up the street.
  - Frequency to be used (5 GHz APs need more clearance)
- the antenna should be placed far enough so that the pole does not block more than 5 degrees in the antenna field of view.
Outdoor mesh APs should not be used to provide indoor coverage. Indoor APs should be used to relay signal from the mesh AP
Surrounding environment will also affect the design
- Buildings in the path change the cell shape
- Light pole positions determine where MAPs can be placed
APs and antennas in the same physical space interfere with each other even if they are not using the same channel soAPs should be separated to limit interference.
- Vertical separation is more efficient than horizontal separation.