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Thursday, July 11, 2013

Ubiquiti Antenna Alignment and Link Performance


Scenario:
This article will cover some of the basics to getting the best performance out of your Wireless Point to Point (or Multipoint) Links. Although this blog is tailored toward optimising your Ubiquiti Wireless Link the principles discussed here are common for most other manufacturers wireless access points as well.



TX Power:
TX Power will vary depending on the distance and Noise Floor of your Link. Typically you should start with you Radios transmitting at their highest TX Power and then once a link has been established reducing the TX Power at each end of your link by approx 3dBm until you get an optimal Receive Signal Strength of between -50dBm and -60dBm for best results. This signal strength will allow your wireless link to maintain the highest data rate even with a typical 10dBm Fade Margin which can be introduced by bad weather among other things.

Noise Floor:
A Noise Floor between -90dBm to -105dBm is desired. If the Noise Floor is higher the -90dBm (say for example -81dBm) this means there is a reasonably high Noise Floor in the area and although your link may still work can cause degraded performance. You can improve your Noise Floor by searching for a different Channel.

Channel Selection:
You should choose a channel that has a Low Noise Floor and that is suitable for your environment. You can find more information on the Radio Spectrum Management Website about the legal Channels and TX Power that you are allowed to use in New Zealand. Here is a brief guide to Channel + TX Power + Link Distance for New Zealand consumers:

Frequency
Total EIRP
Notes
Typical Distance
924MHz
4 watt (36dBm)
Total EIRP with 5MHz channel width.
0 – 20km
2400MHz - 2483.5MHz
4 watt (36dBm)
Total EIRP
0 – 20km
5180MHz - 5250MHz
200mW (23dBm)
Total EIRP (Indoor Use Only).
Not Applicable
5250MHz - 5350MHz
200mW (23dBm)
Total EIRP for Indoor Use or 1 watt (30dBm) total EIRP for Outdoor Use (DFS radar detect must be enabled).
0 – 1km
5470MHz - 5725MHz
1 watt (30dBm)
Total EIRP (DFS radar detect must be enabled).
0 – 5km
5605MHz
DO NOT USE 5605MHz or overlap this channel as this is being used by the MetService Rain Radar equipment.
5725MHz - 5825MHz
200 watts (53dBm)
Total EIRP for Fixed point to point only.
0 – 100km
5725MHz - 5875MHz
4 watts (36dBm)
Total EIRP for Point to Multipoint.
0 – 40km
24GHz - 24.250GHz
1 watt (30dBm)
Total EIRP (Any Modulation).
0 – 10km


Antenna Alignment:
Antenna Alignment is also very important in getting the best performance out of your link. Particularly with Dual Polarity Antennas the Horizontal / Vertical Signal should be no more than 3dBm difference. If the Vertical and Horizontal Poles or Chains are separated by more than 3dBm this can produce uneven TX Rates and bandwidth capacity. i.e. When preforming a Speed test you may find your Download is as expected (i.e. 50Mbps) whilst your Upload (i.e. 17Mbps) is very poor in comparison.

Transmit CCQ:
Your Transmit CCQ (Client Connection Quality) is also a very important factor in link performance. a CCQ of 90-100% is Excellent and typically anything under 60% is considered undesirable. If this is the case you should review all of the above to optimize your CCQ.

Example:
Signal Strength: -45dBm (This is a fairly strong signal, reducing the TX power slightly should decrease the signal to around -50dBm).
Horizontal / Vertical: -47 / -47dBm (This means the Vertical and Horizontal Poles or Chains are equal and therefore both antennas are aligned correctly).
Noise Floor: -96dBm (The Noise Floor on this Frequency or Channel is very clean).
Transmit CCQ: 100% (This indicates the overall connection to the Remote Access Point is Excellent).
TX/RX Rate: 195 Mbps / 195 Mbps (This is the maximum Data Rate for a 30MHz Channel Width, the maximum possible actual throughput over this link is 97.5Mbps TCP).


  

6 comments:

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  3. dear sir,
    i am a isp used rocket m5 with sector anttina (for AP)
    air grid m5 23dbi used for station, signal is -76 to 79 but ccq is very low (50% to 70) speed is very slow litency is high please tell me how to solve this problem. how to connect grid with best ccq & low litency with access point

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    1. Hi there, you may need to increase the tx power (or if already at max level then upgrade antenna), realign antenna or change frequency if your noise floor is not so great.

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