Cost of Ownership
This article discusses the Total Cost of Ownership (or Deployment) in urban multi-point wireless networks. It focuses on the multi-user model e.g. a Wireless ISP. The article argues that service planning, while retaining operational flexibility, is the key factor to low cost deployment. Initial and ongoing costs are identified and the myth of 'low initial cost' is examined and discarded. A related article discusses maximising user density. A future article will look at deployment costs in semi-rural and rural networks. The service will be based on the use of Frequency Hopping (FH) Spread Spectrum wireless technology.
Costs of Ownership or Deployment
Identifying the equipment cost as the key item in determining costs is a common - but catastrophic - mistake in making a decision about a wireless system. The following itemises a list of costs that can be incurred in deploying a wireless network:
- Customer site survey - labor
- Wireless equipment cost
- Antenna costs
- Installation costs - mostly labor
- Maintenance and operational costs - labor
Assuming a fully loaded North American man cost of ~$100 per hour or $800 per day (this is a low-end figure and most organisations will have a cost base of $120+ per hour). By simple inspection of the items above it is clear that labor related costs can significantly exceed initial equipment costs - by a factor of two or three in many cases. It is clear that network planning must focus on reducing or eliminating labor related costs.
Wireless Link Rules
The following rule-of-thumb are critical when designing wireless networks and installations:
- Margin, margin, margin - keep plenty of margin in wireless links 30 - 50% is the minimum safe margin. In general the more the better.
- Multiple routes - where possible allow more than one route for the customer to get to an access or point (or wireless POP). This allows for varying site conditions over time and to compensate for any unique atmospheric conditions that can arise. Any site survey is simply snapshot in time and is not a serious study of site conditions.
- Antenna cable losses are the single biggest losses incurred in any radio installation.
- If you have to calculate anything in an URBAN network you will probably lose money on the connection - this a simple way of saying every installation must use a single engineering model.
Service planning is the key to minimising deployment costs.
Service planning starts with some basic parameters:
- The network will use a co-located multi-cell model to maximise user density.
- The initial network will consist of 3 cell locations - each of which may contain up to 10 co-located cells.
- Each cell will have a maximum radius of 4km (~1.5 miles) with a planned radius of 1 km (~ 0.5 miles) or less when fully deployed.
- Each cell will support up to 10 customer locations.
- Omni-directional antennas will be used throughout - there is no setup overhead and EVERY customer location becomes a possible mesh network location.
- Every installation will be the same - no special engineering will be used. It is cheaper to refuse access to a customer than to engineer special connections.
Air-Frame products are designed to minimise installation costs by:
- Air-Frame may be mounted indoors or outdoors.
- Air-Frame uses LAN power (derives its power over the ethernet connection). this reduces costs as follows:
- Air-Frame has no 'hazardous' power involved outdoor installations - reducing both costs and safety risks. 'Hazardous' power depends on local regulations but normally anything over 48V is regarded as 'hazardous'.
- Air-Frame units may be sited up to 100 meters from the customer site with no wireless losses.
- Air-Frame may be sited optimally for radio reception without considering any other parameter.
- A pair of Air-Frame units 'out-of-the-box' provides 118 dB of power (expressed as TX/RX power - RX sensitivity). With a 30% margin this represent a 4.5 km (~2 mile) cell diameter.
Air-Frame is designed to minimise ongoing costs, specifically:
- By using Frequency Hopping it should always be possible to gain remote access to the Air-Frame unit even in the the most adverse conditions - thus virtually eliminating the need for costly on-site visits.
- Full control is provided over all system characteristics - including radio parameters and access to radio performance - permitting centralised expertise to be focussed on any problem.
- Multiple 'roaming' features are provided to allow the Air-Frame unit considerable control over alternate routing in the case of adverse or hostile conditions.