System Design

The system comprises the network management, the base stations and the subscribers.

Industry standard Network Management

The network management server is an industry standard PC available from several different suppliers. It conditions all the links by setting the IP addresses and the channel allocations.

Base stations each cover 10 to 25 km and can be daisy chained over 40 km

One or more base stations can be used depending on the geographical coverage. They should be located to provide a line of sight to the greatest number of subscribers and to have easy access for the backhaul. Typically, a capacity of 1 Mbps is required for every 40 subscribers. The connection can be either direct to the network or via a microwave spur. An alternative is to daisy chain the base stations, which may be up to 40 km apart. In this arrangement, the backhaul need be connected to one station only.

Simple subscriber units

The key to the system is the simplicity of the subscriber equipment. It comprises two units, the outdoor wireless module and the industry standard cable modem. They are connnected together by a single cable and wall plug power supply.

Up to 8,000 subcribers per base station

The downstream capacity is usually the limiting factor, which in turn is determined by the bandwidth available - typically 24 to 30 MHz. DOCSIS transmits 27 Mbps of data in a 6 MHz channel which means there are a minimum of 4 channels.

To avoid mutual interference, only half the channels are used in each 90 degree sector with the other half used in the adjacent sectors. Thus, base stations have a capacity of 216 Mbps. If each subscriber is offered 500 kbps with a 20:1 contention ratio, the capacity is 8,000 subscribers.

The system can also share the spectrum between TV and IP. For example if 12 MHz is allocated to TV, then 12 channels can be transmitted, albeit by reducing the internet capacity to 4,000 subscribers.