System Design for Capacity Limited Networks
Field Area Networks and large SCADA networks run across narrowband channels are often capacity limited (as opposed to coverage limited) due to the large number of devices and high net data rates involved. Hence, the number of base stations required in such a system is determined by a utility’s capacity requirements rather than their coverage requirements.
The conflicting demands of high system performance versus the efficient use of spectrum is a challenge faced by any network designer. In terms of system design, the main limitations faced when creating a network design for a Field Area Network are:
- In narrow slices of spectrum (such as the 700MHz Upper A block) the potential for out-of-band interference is high;
- The ability for co-channel reuse can be significantly impacted by high RF power which can overpower the other signals at that frequency, reducing the opportunity to re-use frequencies and increasing issues with interference.
Our tips for System Design:
Some options to consider when designing a system to fit the needs of a capacity limited network are:
1) Design a second tier in the network, allowing for the reduction of the signal level required at the Tier 1 base stations. Shorter path lengths and lower carrier-to-interference ratio requirements in this second tier ensures a high reuse of channels in this part of the network, leading to greater spectral-efficiency.
2) Divide your total spectrum allocation into multiple channels to also allow for guard bands and far greater frequency reuse. Running more channels will not only assist with mitigating interference but will also allow you to play with modulation rates at different parts of the network.
3) Select radios with integrated band pass duplexers to assist with mitigating interference and use high gain directional antennas at the subscriber ends of the network to boost performance.
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