MW Planning

After MW survey planning is carried out. Survey data gives clear picture about terrain, LoS, obstructions etc. Whether your link is point-to-point or point-to-multipoint, the first thing to do is to verify that it will have not only clear line of sight, but at least 60 percent of the first Fresnel zone clear of obstructions as well. The longer the distance, the more important this is. If the Fresnel zone is blocked, then you will get a lower signal level on the distant end than expected. But even if your Fresnel zone is partially blocked, it is still possible to get a link, provided that your system was designed to have a strong signal at the other end of the link. In planning long-range microwave links where you are not sure that you have unobstructed line-of-site and clear Fresnel zone, an MW survey should be done. There are many software packages like TNS uses path loss tool, available that have terrain data and can create a path profile from a set of latitude/longitude coordinates. By putting survey data the tool gives more realistic results.

But assuming that you do have clear line-of-site and 60 percent of the first Fresnel zone clear (or nearly clear), how can you know if you will have a good link or not? How much gain do your antennas need to have? How much coax cable loss is too much? Or given your fixed base station antenna with a pre-set gain, how far can you reach with the different types of client antennas? And which clients will need amplification?

By doing an fade margin calculation, you can test various system designs and scenarios to see how much fade margin (or "safety cushion") your link will theoretically have. It presumes that the antennas are aimed at each other properly (i.e., they are in each others' main lobe). To calculate fade in the example, start with the transmit power (+24 dBm), subtract the coax cable loss (1 dB), and add the transmit antenna gain (24 dBi). This gives you the effective isotropic radiated power: EIRP = TX Power - Coax Cable Loss + TX Antenna Gain. Then subtract the FSL (130 dB), add the receiver antenna gain (24 dBi), subtract the coax cable loss (1dB) and you get the signal reaching the receiver: RX Signal = EIRP - FSL + RX Antenna Gain – Coax Cable Loss Compute the difference between the received signal and the radio's receiver sensitivity to determine the fade margin. In this example, the received signal is –60 dBm and the receiver's sensitivity is –83 dBm giving a theoretical fade margin of 23 dB.

In practice, the fade margin is not the only determining factor. It's the actual SNR at the receiver that makes a link reliable. If you are getting noise or interference on your channel, your SNR will deteriorate. This could be an issue if you are co-locating at a site with other radios operating in the same band. You need to find out what frequency spectrum these radios are occupying. If these transmitter have energy or sideband noise on your receive channel and their antennas are close to yours, you will likely get interference from them, perhaps to the point where your link will not work.

TNS has expert resources to carry out MW planning of backbone and access links. We have wide experience to carry out planning in difficult hilly terrains also. MW survey and planning group is headed by experience manager with vast industry experience on MW planning and had carried out planning for different terrains of India. The team supported by experience engineers equipped with tools and Path loss software tool to carry out the planning. We give main emphasis on availability of topographical maps before starting any activity on survey and planning.