2.4 ghz timing difficulties

Good day -

Since my last post, we've added 2.4 ghz to another tower with what I would have thought was a higher noise floor (but it in fact is around -80).  There are certainly higher noise floors around the customer radios.

We have four 90 degree sectors and have set the timing percentage for 75/25.  These sectors were performing pretty good before enabling all four and setting up timing (on the flexible scheduler)

Now our weakest customers (which honestly are not that weak) are showing some upload trouble.  Here is a sample link test

* the radio is set for a MIR of 10000/10000

* the radio's receive signal from the tower is -45

* the tower's receive signal from the radio is -62

Today, honestly, this isn't bad, but it is also 10 in the morning local time

4 second test:

Downlink - 67.692 Mbps ;Uplink - 2.508 Mbps

 

10 second test:
Downlink - 80.438 Mbps ; Uplink -3.727 Mbps

 

During the peak evening hours I have seen he downlink remain at approximately 60 meg but the uplink drops to under a meg - - .8 or less.  ( i may post tonight ).  I have also seen more drops on the two weaker radios - other radios have been connected 5+ days.

 

In doing reading, would changing to MCS0 on the management traffic help this at all?

I know changing to 50/50 would help, but that would also take a lot of our download traffic.

That might be our only option :(

 

Any suggestions are appreciated.  Thanks in advance!

 

 


@cyberbroadband wrote:

We have four 90 degree sectors and have set the timing percentage for 75/25.  These sectors were performing pretty good before enabling all four and setting up timing (on the flexible scheduler)

 


Hi, 

Are you trying to frequency reuse? If so, Flexible scheduler cannot be used for frequency reuse. You will have to use one of the fixed ratios (75/25, 50/50 or 30/70). I apologize in advance if I have misunderstood you. 

Thanks,

Sriram

I am sorry I was not more clear.  Prior to adding sector 3 and 4 yes we were using the flexible scheduler.  Since moving to frequency reuse we are using 75/25.  My question is what can we do to improve the upload on these weaker customers?  Would using MCS0 for management improve or is moving to 50/50 our best option?


@cyberbroadband wrote:

I am sorry I was not more clear.  Prior to adding sector 3 and 4 yes we were using the flexible scheduler.  Since moving to frequency reuse we are using 75/25.  My question is what can we do to improve the upload on these weaker customers?  Would using MCS0 for management improve or is moving to 50/50 our best option?


Ok, thanks for clarifying. It was I who misunderstood you. One more quick clarification: you mean MIR of 100000/10000? MIR of 10000/10000 will be 10/10 Mbps so I'm not sure how you are doing 60+ Mbps on the Downlink. Perhaps you are turning off MIR to run the link tests?

MCS0 is used only for management messages. It may help with the drops but it will not imrpove data throughput. 

Would you be able to share the frequency plan between the four sectors? i.e Frequency Carrier and Channel Bandwidth? And I assume you are using the Cambium sector antennas or a third party antenna with a good F/B ratio?

It would be best to understand why this particular SM's uplink is poor. What is the Uplink MCS spread (under Monitor->Performance) looking like for this SM? Can you post a screenshot? Before you do that, Reset the stats on that page, run a fresh link test and then take a screenshot. 

What is the Subscriber Module Target Receive Level (under Configuration->Radio->Power Control on the AP) set to? If its set to -60, can you bump it up to -55? NOTE: You must change the back sector to this value also to avoid self interference. 

I realize this is highly disruptive but would you be able to do a Spectrum Analysis on the AP? Perhaps during a maintenance window?

50/50 would increase the capacity on the uplink. However, if there is interference at the AP causing this, then increasing the uplink frame time may not help.

You mentioned that this issue started happening after adding sector 3&4. I would go back and double check all the settings to ensure the front and back sectors are properly configured for frequency reuse. i.e DL/UL ratio, frame size, Tx power of the AP and Subscriber Modules Target receive Level are all identical between the front and back sector and one sector is set to "Front Sector" and the other sector is set to "Back Sector" for the Frequency Reuse parameter under Configuration->Radio->Access Point Configuration.

Thanks,

Sriram

Yes - quite a few requests here but i will do as many as i can!

I misread the MIR on one of the SMs (it is being used as a backhaul to another access point).  The MIR for that radio is/was actually 100000/100000.

Thank you for the answer on MCS0.

here are the four sectors:

west

access point

tdd

united states

range unit - miles

maxregs=30

maxrange=20

autochannelsection=disabled

channelbandwidth=20

frequency 2437 (wanted to use 2412 but one customer will not connect on that channel)

frequency reuse=front sector

altfreqcarrier1bandwidth=20mhz

altfreqone=none

altfreqcarrier2bandwidth=20mhz

altfreqtwo=none 

transmitteroutputpower=27

antennagain=8

targetreceivelevel=  -53

downlinkratio=75/25

framesize=5ms

downlinkmaxrate=mcs15/64qam5/6

managementtrafficrate=mcs1

colocation mode =enabled

syncsource=gps

syncholdtime=3600

north

access point

tdd

united states

range unit - miles

maxregs=30.....(this was incorrectly set for 60!!)   now fixed.

maxrange=20

autochannelsection=disabled

channelbandwidth=20

frequency 2462

frequency reuse=front sector

altfreqcarrier1bandwidth=20mhz

altfreqone=none

altfreqcarrier2bandwidth=20mhz

altfreqtwo=none 

transmitteroutputpower=27

antennagain=8

targetreceivelevel=  -52

downlinkratio=75/25

framesize=5ms

downlinkmaxrate=mcs15/64qam5/6

managementtrafficrate=mcs1

colocation mode =enabled

syncsource=gps

syncholdtime=3600

** i do note the sm receive level is off by one db.  is that an issue?

** i see that is important per the notes section.  i will change. it is now -53

south

access point

tdd

united states

range unit - miles

maxregs=30

maxrange=20

autochannelsection=disabled

channelbandwidth=20

frequency 2462

frequency reuse=back sector

altfreqcarrier1bandwidth=20mhz

altfreqone=none

altfreqcarrier2bandwidth=20mhz

altfreqtwo=none 

transmitteroutputpower=27

antennagain=8

targetreceivelevel=  -50 (changing to -52)

downlinkratio=75/25

framesize=5ms

downlinkmaxrate=mcs15/64qam5/6

managementtrafficrate=mcs1

colocation mode =enabled

syncsource=gps

syncholdtime=3600

east

access point

tdd

united states

range unit - miles

maxregs=30

maxrange=20

autochannelsection=disabled

channelbandwidth=20

frequency 2412

frequency reuse=back sector

altfreqcarrier1bandwidth=20mhz

altfreqone=none

altfreqcarrier2bandwidth=20mhz

altfreqtwo=none 

transmitteroutputpower=27

antennagain=8

targetreceivelevel=  -50 (changing to -52)

downlinkratio=75/25

framesize=5ms

downlinkmaxrate=mcs15/64qam5/6

managementtrafficrate=mcs1

colocation mode =enabled

syncsource=gps

syncholdtime=3600

** i got an error when changing the sm receive level to -52 on the last three sectors but the validation error message was blank.  (all it said was validation results:)

** looks like i must move them all to -52 in order to not get that error.

I did a spectrum analysis of the area when we upgraded to four sectors.  I had everything turned off at that time.  I will attach.

Unfortunately I rebooted all the access points when changing the sm receive level so all the stats have been cleared.  I will retest the one known "weak" sm.  I am waiting to hear from my tech as to which other customers on that sector may have had problems.

I just ran a 10 second link test on the radio in question. 

Downlink
32.092 Mbps
Uplink
0.962 Mbps

I will attach the performance page for the SM

the sm in question is 3f:78

I do appreciate your helping us with this.

I am also attaching information from the SU/SM itself.  Again, I have had reports of other issues on this sector (but no other sectors have been reported as problematic).  Additionally I have not been told which other customers are reporting problems on this sector.  I will pass along that info once I receive it.


Here is the E-detect and monitor -> wireless tabs of the affected SU/SM

I have once again verified all SM receive levels on all access points are -52

I believe after this latest round of changes we are doing a little better.

That su/sm now shows this for speed test results:

Downlink
66.256 Mbps
Uplink
2.066 Mbps

to

Downlink
62.58 Mbps
Uplink
3.252 Mbps

more updates later.

(peak time tomorrow night perhaps) :)

Any suggestions from the data I provided?

The network does appear to be handling these weaker links better now.

do you have your units front and back set correctly?   these are very important (find more detail in the GPS reuse guide)

also, if you've got week clients, and clear noise floor, reducing your target RX power can really improve things.  BUT, and i stress BUT you will need a clean noise floor to do this.  

if you've got subs locked at -75 on the uplink, and your target is -60.  with the cambium sectors (which are great sectors, probably the best you can get for under $500)   that -75 sub will have a noise floor of -90 because of the FTB ratio on the antennas.     if you are able to raise your rx power to -65, without hurting your uplink modulations, that -75 sub will now have a 20 db snr value from your self interference factors.   

if you don't have the noise floor to work with, and you can't drop your RX power levels, try using 10 mhz channel sizes to help your SNR.  you will take a loss in downlink performance, but you could improve your link stability and your end users experience will be much better. 

few more things a lot of people miss, sector tilt. can't stress that enough. you want the upper segment of your antennas vertical beam only reaching as far as it needs to inorder to hear the furthers subscriber. this will help to minimize the noise you are having to deal with.    I personally tilt the antennas to reach a max of 5 miles from our larger sites, and 2 miles on our shorter sites to keep our re-use factor high, and minize un-needed noise and our own noise foot print.  

you can also add things to the subscriber to inprove thier TX signal, the KP reflectors work well, or use a conectorized subscriber unit with a dish.  

as Sakid suggested, the spectrum analyzer will give you a lot of detail and help you to know more of your environment to make the most of what you are dealing with.   you'll want to achieve atleast 15 DB SNR for limited performance, 20 for better, and 28 for best. 

thanks for the additional info.  looked and here are the s/n ratios on the sector in question.

i think we are in pretty good shape.  (of course these change every few seconds with updating)

35/24

35/26

35/25

38/27

36/26

34/23

36/26

35/24

27/25

38/24

36/24

36/24

snr as shown in the cpes give you the floor (the point where the air time is 100% completely consumed like all radios do, you’ll need to figure out what your peak noise values are. The intermittent noise is what’s bothering your setup, not the floor. The radios may experience burst noise 10 to 15 db louder than the reported floor. Sometimes louder yet.

A good example, at a crowded room, with everyone is talking,. There is a constant roar of noise in the background. Sometimes you’ll hear someone laugh loudly over the conversation your having. That loud laugh would be the equivalent of your intermittent noise.

Going by your uplinks snr, you’re trying to use these radios in a very noisy place I’m guessing if your target power is in the 50s