TAC and CID from different? towers - weaker signal connects, stronger signal doesn't

[jmanecke]

I'm having trouble getting a connection at my cabin where I want to mount an antenna. There is only one tower in range (EDIT - there may be more than one - see follow up below). I get a good connection 200 feet away, but both locations appear equal from an RF measurements perspective (RSSI, RSRP, RSRQ, SINR). If anything, the location that won't connect is better on these measurements. The puzzling part is I see one TAC and CID in one place but another 200 feet away.

First some details. I have two locations, one where I get a connection (called YES) and one where I don't (called NO). I want to get a connection at the NO location. I'm using the exact same device at both locations.
Physical Layout

• both locations are 2.62 miles from the tower
• YES and NO are along the same arc from the tower (same distance to the tower)
• distance between locations is 200ft
• altitude of antenna at each location is approximately equal (within +/- 5ft)
• tower is in valley below locations, about 1000ft lower in altitude
• only tower around, next nearest is over 5 miles and not LOS
• rural area, wooded mountains, leaves on the trees
• both locations have similar amount of trees along LOS to tower

Location NO is on a wooden pole about 15ft above the roof line of my cabin
Location YES is on the roof of my car on the side of the driveway slightly uphill of the cabin
(edited above, had this backwards when I first posted )

T-mobile tower and T-mobile SIM.
MC7455 Modem, We826-T2 router, stock antennas
Also tried with a Google Fi SIM and saw the same results. Was connecting to the same T-mobile tower with the Fi SIM.

Below is the output of at!lteinfo and at!gstatus? from both locations. Realized today I only copied part of the output from the NO location, hopefully I've got the important bits.

Location: YES
at!lteinfo

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!LTEINFO: 
Serving:   EARFCN MCC MNC   TAC      CID Bd D U SNR PCI  RSRQ   RSRP   RSSI RXLV
             5035 310 260 44799 01911916 12 2 2   1 133 -15.9 -103.4  -73.5 --
IntraFreq:                                          PCI  RSRQ   RSRP   RSSI RXLV
                                                    133 -15.9 -103.4  -73.5 --
                                                    166 -12.5 -104.7  -83.7 --
                                                     99 -17.6 -110.6  -83.7 --
InterFreq: EARFCN ThresholdLow ThresholdHi Priority PCI  RSRQ   RSRP   RSSI RXLV
              901            0           0        0 448 -18.1 -127.1 -100.0   0
GSM:       ThreshL ThreshH Prio NCC ARFCN 1900 valid BSIC RSSI RXLV
WCDMA:     UARFCN ThreshL ThreshH Prio PSC   RSCP  ECN0 RXLV
CDMA 1x:   Chan BC Offset Phase Str
CDMA HRPD: Chan BC Offset Phase Str

at!gstatus?

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!GSTATUS: 
Current Time:  1434		Temperature: 48
Reset Counter: 1		Mode:        ONLINE         
System mode:   LTE        	PS state:    Attached     
LTE band:      B12    		LTE bw:      5 MHz   
LTE Rx chan:   5035		LTE Tx chan: 23035
LTE CA state:  ACTIVE      		LTE Scell band:B2     
LTE Scell bw:10 MHz  		LTE Scell chan:901
EMM state:     Registered     	Normal Service 
RRC state:     RRC Connected  
IMS reg state: No Srv  		

PCC RxM RSSI:  -75		RSRP (dBm):  -103
PCC RxD RSSI:  -76		RSRP (dBm):  -108
SCC RxM RSSI:  -92		RSRP (dBm):  -127
SCC RxD RSSI:  -91		RSRP (dBm):  -127
Tx Power:      16		TAC:         AEFF (44799)
RSRQ (dB):     -11.9		Cell ID:     01911916 (26286358)
SINR (dB):      1.8

Locaiton NO (partial command output)
at!lteinfo

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!LTEINFO: 
Serving:   EARFCN MCC MNC   TAC      CID Bd D U SNR PCI  RSRQ   RSRP   RSSI RXLV
             5035 310 260 44672 019D0516 12 2 2  15 166 -13.2  -97.9  -70.7  26
             

at!gstatus?

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System mode:   LTE        	PS state:    Not Attached     
LTE band:      B12    		LTE bw:      5 MHz   

PCC RxM RSSI:  -72		RSRP (dBm):  -96
PCC RxD RSSI:  -78		RSRP (dBm):  -102
Tx Power:      0		TAC:         AE80 (44672)
RSRQ (dB):     -9.3		Cell ID:     019D0516 (27067670)
SINR (dB):     13.6

Note the difference in the TAC and CID. That is the confusing part. I'm not fully versed in TAC and CID values, but I thought they were unique to an antenna on a tower. Can't understand why they change. There was no place I ever saw an output of at!lteinfo that showed both. It was always only one or the other. One TAC/CID connected (AEFF / 01911916), one did not (AE80 / 019D0516). At the NO location, I only ever saw TAC: AE80 / CID 019D0516. At the YES location, I did sometimes see TAC: AE80 / CID 019D0516 at startup or after a reboot, with no connection. After a minute it would switch to TAC: AEFF / CID 01911916 and connect.


Questions
- why does it connect at one location but not the other despite what appears to be similar signal strength measures?
- what is the significance of TAC and CID

My long-term plan is to mount external antennas (preferably on the cabin) and I know that will improve things. Right now I'm just trying to understand why one location works but another doesn't.

[swwifty]

This is gonna be a tough one to troubleshoot, but I have a few questions first to clarify.

If I understand correctly, why do you want a connection uphill from your cabin at your car? Did you mean to say things the other way around? I would think you' want the connection that seems to be working at the cabin? From the signal stats you shared the connection looks fairly weak on any band but band 12, so I suspect you have a lot of obstructions, or do you have clear LOS to the tower? I'd suggest getting some external antennas to try out. I actually have some available for free (minus shipping costs) in the classifieds of this forum.

A TAC in LTE is a calling area that is related to mobile phones. The more important thing to pay attention to is Cell ID. That is unique per cell, and there can be 3+ cells easily on one tower. I prefer to look at the PCI ID found in the output of "at!lteinfo" as those are unique over a large geographic area and can help you see when you are actually connected to a different cell.

[jmanecke]

I messed up. You are correct, I do have them switched. Proofreading, Uggh. Edited the original post.

I want a connection at the cabin where it won't connect. I started off by mounting the router on on a temporary pole on the roof. When that wasn't connecting, I began moving around to different places so I could confirm that the device would connect and see where the signal was best. First I moved to areas around the cabin using a 100ft extension chord. When none of those worked, I used a car-charger and tried places along the driveway/road.

There are trees in the LOS path from both locations. The land falls away as you move toward the tower, but I'd say there's about 600-800 feet of foliage before you get to a clear path. It's early fall and the trees have about 70% of their leaves remaining. I expected to only get B12. I was surprised to see B2 (1900MHz) as CA from the YES location.

I know I can always mount the antenna at the YES location as it's all on my property, but I would have to run cable to there. I'm really trying to figure out why it won't connect at the NO location.

Thanks for your help.

[jmanecke]

After doing some research on cellmapper, I located the two CIDs I'm seeing. I also did plots to both towers using the ubiquiti link tool. For both plots, tower is on the left, my location is on the right.

The CID I receive when I can't connect (from the NO location) is on a tower 20 miles away. The location on cellmapper is not validated, so it could be off a bit. I wasn't able to find the specific tower on google maps satellite view. Looking at the plot, there's a few obstructions. There are ridges in the area of that tower where you could have an unblocked LOS. This makes me think the tower location in cellmapper may not be accurate.

Path to TAC: AE80 / CID 019D0516 - tower in Franklin, WV - does not connect


The CID I'm connecting to (from the YES location) is on the tower nearest me (2.62 miles away). There's a ridge that barely obstructs the path, but some of the fresnel zone makes it.

Path to TAC: AEFF / CID 01911916 - tower in Harman, WV - this connects


I'm surprised that the CID I see from the NO connection location (TAC: AE80 / CID 019D0516) in at!lteinfo has such a strong signal considering how far away it is. Comparing the readings I see against the signal strength chart in the Troubleshooting Connections thread https://wirelessjoint.com/viewtopic.php?f=21&t=14 the signal levels seem reasonable:

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MEASURE  VALUE   QUALITY
RSRP(M)  -96     Good
RSRP(D   -102    Good
RSRQ     -9.3    Good
SINR     13.6    Excellent

Based on these values, I would expect to get a connection. Once I get some directional antennas I can better confirm which direction the signals are coming from.

[swwifty]

I would recommend trying some external antennas and see what happens if you are serious about getting a better connection at your cabin. Those little omni antennas are nearly worthless to be honest.