LTE fast on iPhone 12 but slow on other devices (band 7?)

September 17, 2021 4:15 AM

The iPhone says it is using "band 7" An LTE router reports "mcsDownCarrier1Code0:5 mcsDownCarrier1Code1:30 PLMN 45400" An Android phone says it's using "lte band 1800+" The specs of the Android phone and the router says that they support LTE 4G band 7. So why are they so slow compared to the iPhone?

Further detail:

iphone, csl:

dl_freq 3150
dl_bw 50
ul_bw 50
phy_cell_id 400
sys_mode_lte
phy_cell_id 400
channel_type dl_dcch
cell_id 26899479
freq_band _ind 7 (2600mhz??)
num_mnc_digits 2
kctcellmonitordeplytype 5g nsa(1)

kctcellmonbandwidth 100
kctcellmonitorid 25637...(changed)
" mcc 454
"pid 400
"tac 1133
uarfcn 1385

Router:

Device name
B316-855
Hardware version
WL1B316M

CELL_ID
26899478
CQI
CQI0:5 CQI1:127
RSRQ
-14.0dB
RSRP
-93dBm
RSSI
-59dBm
SINR
-3dB
Wireless transmit power
PPusch:4dBm PPucch:-9dBm PSrs:11dBm PPrach:6dBm
TDD subframe ratio
SubframeAssign:0 SubframePatterns:0
Uplink mod/demod of MCS
mcsUpCarrier1:8
Downlink mod/demod of MCS
mcsDownCarrier1Code0:5 mcsDownCarrier1Code1:30
PLMN
45400

CSL Android:
cell 26899478 (ECI E-Utran cell id)
1133 TAC
switched to 27093... when a truck went by
lte band 1800+, 3, earfcn 1385
-93 rsrp @ -12db

CSL simcard in router = bad (2-5mbit)
CSL simcard in Android phone = bad (2-5mbits)

ChinaMobile in ALL devices = good (20mbits or better)

posted by TheGreenRye to Computers & Internet (4 answers total)

As you've observed, they're using different bands. The iPhone is using LTE band 7 which is at 2600MHz. The Android phone is using band 3 which is at 1800MHz. So they're talking to completely different cells on the other end of the link.

The internet speeds you get don't just depend on which band and cell you're connected to though. If there are lots of users and the network provider's upstream bandwidth is congested, you will get slower speeds even if the over-the-air interface is working at the highest bitrates and widest channel bandwidths available. This is usually the limiting factor in practice.

Cheap high-quota or "unlimited" data plans often give poor speeds because their users' traffic is prioritised below that of users with higher-cost plans, on the upstream network beyond the cell site.

If you get good bandwidth from ChinaMobile, use them!
posted by automatronic at 5:16 AM on September 17, 2021 [2 favorites]

Response by poster: Why are the Android and router using the slow band even though they support the fast band like the iPhone? If only I could force them to use the faster band?
posted by TheGreenRye at 9:34 PM on September 17, 2021

They'll do what they're told to do by the basestation. If it tells them to migrate to a different band or cell they will do so. It's not something you have control over. It's done based on observed signal quality, and policies on the basestation side.

Maybe the iPhone has an antenna that's more effective at 2600MHz than the other devices, so it gets better signal there and gets assigned to that band when the others don't. Maybe the network provider has a deal with Apple and prioritises iPhones to make them seem faster than other brands.

It looks like that Huawei router has connectors for external antennas, so you could try putting a better antenna on it that's optimised for 2600MHz.

If you had an option to disable band 3 on the Android phone or the router, that would force the matter and might put them on band 7. I've worked at a low level with LTE modems and done that sort of thing, but generally that level of control isn't exposed to the user on consumer devices.
posted by automatronic at 11:22 PM on September 17, 2021 [1 favorite]

Response by poster: An update:

I think it was just a coincidence regards band 7/5 that whenever I tested it, band 7 seemed to be faster.

A separate issue that also confused it was the WiFi. I had tested it with an ethernet cable and it wasn't faster. But Even though I tested that 3 times, it was just a coinsidence with network congestion. I've tested it a lot more with ethernet to the LTE router and it's much faster and reliable!!

The iPhone is still a lot faster though! The SIMcard isn't supposed to support 5G but this one of the only other things left to explain this. I don't think the network is prioritising iPhones because tethering VIA the iPhone is also fast too.
posted by TheGreenRye at 9:20 PM on April 3, 2022