User's Manual

Rerouting

A rerouting decision is made either due to an active route failure or because a significantly lower cost route is consistently

available. There are four scenarios that cause a reroute operation:

1. A failure in the link or a SkyGateway/SkyExtender system along the selected route.

2. A failure in the link or a SkyGateway/SkyExtender further along the route to the SkyGateway.

3. One or more links along the route degrade in performance, resulting in reduced capacity and, therefore, an increased cost.

4. A lower cost route becomes available. Typically this is through improved link quality or the addition of SkyExtender(s) and/or

SkyGateway(s) to the network.

A link (or node) failure is detected by three consecutive failures to receive a “keep-alive” message. These link keep-alive messages

are transmitted every 1.5 seconds. Therefore, a link is designated as having failed after a maximum of 4.5 seconds. If desired, the

system can be configured to further reduce the maximum time it takes to detect a failure.

A SkyExtender that detects a link failure attempts switching to the next lowest cost route available and activate the associated link.

This activation includes the exchange of scheduling information and takes approximately 1 second. Once that activation is

successfully completed, the SkyExtender then transmits the cost associated with this new route.

If the SkyExtender detecting a link failure has no alternate routes or the activation of the associated link(s) fails, then it transmits an

“infinite” cost message and starts a frequency hunt for another route. Upon receiving an infinite cost message related to an active

route, a SkyExtender will immediately attempt to reroute.

A SkyExtender will change to a lower cost route only when the cost is at least 15 units lower than the current active route.

RF Management

The SkyPilot Carrier-Class Broadband Wireless System affords an unprecedented level of control over radio frequency (RF)

utilization. At the foundation of these capabilities is an innovative 8-way antenna array that supports point-to-point, point-to-

multipoint and omnidirectional communications. The array enables more effective utilization of available spectrum on a network-

wide basis, and even permits granular management of individual links among all nodes.

Eight-way Antenna Array

The SkyGateway, SkyExtender and SkyExtender DualBand systems all have an integral 8-way antenna array providing a full 360°

of coverage in 45° segments. This design enables a granular control over transmission direction, power levels and more, which

together allow the network topology to be optimized for maximum performance with minimal interference.

Within this array, each of the eight antennas provides a focused 45° horizontal beam; all eight antennas together provide

omnidirectional 360° coverage wherever desirable. Internal to each system is a high-speed switching fabric that alternates among

the antennas to provide focused, directional transmissions. When utilized individually, a single antenna establishes a point-to-point

link that can transmit at higher power levels than permitted for point-to-multipoint or omnidirectional communications. This allows

the system to deliver as much as 44.5 dBm / 28.2 W EIRP, resulting in much longer range (up to 10 miles or 16 kilometers

between nodes) and/or greater penetration through obstacles that attenuate the signal.

The directional capabilities of the antenna array also permit more effective utilization of available spectrum by allowing a single

node to communicate at different frequencies with different neighboring nodes. With point-to-multipoint and omnidirectional

systems, by contrast, all nodes must utilize a common frequency. By extension, a mesh network utilizing omnidirectional antennas

must employ the same frequency end-to-end. The SkyPilot directional design overcomes this limitation, which can severely cripple

the performance and scalability of first-generation mesh solutions.

By directing its RF energy in an optimal fashion, the SkyPilot design greatly reduces susceptibility to both internal and external

interference. Mitigating self-interference allows for spectral re-use within the network, which increases aggregate capacity and

permits densities not possible with other wireless broadband solutions. In addition, the system schedules transmissions only on

active sectors (see section on SkyPilot Synchronous Protocol), thereby further enhancing performance and quality of service.