10-13-2013 10:23 AM - edited 10-13-2013 10:34 AM
I have two IAP-134's and external Antenna APNT-17 providing point to point connectivity between two buildings and client access. I'm trying to figure out acheivable distance assuming clear line of sight. I'm also looking to figure out backhaul speeds between the AP's and possible client associaion rates. I'm using the Link budget calculator found here http://www.afar.net/rf-link-budget-calculator/ and I was looking for feedback on whether the numbers i used are accurate.
- Frequency – 5240MHz
- IAP-134 Max Transmit Power = 16dBm
- Receive/Send Sensitivity = -82dBm
- Antenna Gain for AP-Ant-17 = 5.0 dBi
- Tx/Rx Cable Loss (5ft) = 0.4dB – APNT-17 has 30 inch antenna cables by default. Added extension cables to extend cables length to 5ft
- Calculated Approximate distance – 0.2 miles/1000 feet.
- Is the calculated approximate distance a number I can confidently use?
- I was unclear as to what Fade Margin to use. I used 12dB. Is this accurate or close to?
- Given the calculated distance, what is the max acheivable backhaul speeds between the AP's? Will they mesh using 20mhz wide or 40MHz wide and therefore give me a 300Mbps backhaul link?
- Assuming the numbers above are accurate, and I also provide client access between these two AP's, what speeds can I expect the clients to associate at?
Many thanks for your time,
10-13-2013 10:03 PM
You've posed a rather complicated question, for several reasons.
If you are attempting to do mesh and client access on the same 5GHz radio then each one is going to impact the other.
Unfortunately, this is nondeterministic both due to varying load from clients and backhaul, as well as the fact that the client-to-AP connection is not likely to perform nearly as well as the AP-to-AP connection. Due to suboptimal antenna pattern on the client side, possible LOS obstruction from ground clutter or a body in the way, and variable orientation from how someone is holding it. And of course 1SS smart devices cannot transmit as fast as multi-stream APs. So the clients are likely to have a much more negative impact on the mesh link than the other way around.
One way to think about this is the maximum achievable goodputs under ideal conditions. Outdoors you are unlikely to achieve 3SS rates due to the multipath environment being much less rich than indoors. In general, we plan on a max of 2SS rates, and then say thank you for those times and physical "sweet spots" where we can get 3SS rates. But this is not common.
A 2SS laptop in an HT20 channel has a max PHY rate of 144Mbps with SGI. It can achieve a max usable goodput of around 80Mbps at short range to a 5dBi dual-polarized antenna, falling to about 60Mbps at 100 meters and 45Mbps at 200 meters.
A 1SS phone/tablet in an HT20 channel has a max PHY rate of 72Mbps with SGI. It can achieve a max usable goodput of around 45Mbps at short range to a 5dBi dual-polarized antenna, falling to about 35Mbps at 100Mbps and 30Mbps at 200 meteres.
By contrast, two IAPs with multi-polarized antennas properly aligned should deliver 85-90Mbps to 100 meters and 75-80Mbps at 200 meters. Assuming we only get 2SS rates in a 20MHz channel.
You asked about HT40 vs. HT20. Generally we don't recommend HT40 due to the increased exposure to interference. Remember, you are using the same channels your indoor network uses, so the two systems are going to interfere with each other to a degree. Unless you hard segment certain channels just for mesh and do not use them for client access anywhere.
Also, HT40 modulations require more SNR to decode than the same modulation in an HT20 channel. So most people run HT20 outdoors.
The link calculator you are using is only for legacy SISO and doesn't incorporate MIMO capabilities like MRC. You should be using the Aruba 3D outdoor planner to model your links and coverage, which is free.