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Eminence
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Good documentation for R11e-LTE ?

Thu Aug 23, 2018 8:55 pm

Where can I find good documentation for this LTE card (I have it in my WAP)? Especially a list of AT dialog commands?

The problem I have is that it keeps on connecting to the same BTS and doesn't change (switch to another one) even if the data stops flowing (as a result I have Internet working 'ok' for about 10-15 minutes then a longer pause and then again it works). I think this may be due to this BTS being suboptimal for my location (my location is quite elevated and many BTSes are visible, the modem keeps on locking to one that is relatively far away). I would like to be able to a) list visible BTSes and b) select which one to connect to. Or maybe change the parameters of the selection algorithm. I hope this is possible, but for that I need good documentation for this LTE modem card (what is on Mikrotik wiki is not sufficient).
 
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mkx
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Re: Good documentation for R11e-LTE ?

Thu Aug 23, 2018 11:50 pm

It is against the idea of single-frequency network (SFN) to allow device to "lock" to certain base station. Let alone allowing user to do that un-educated choice. So there isn't a AT command to lock device to arbitrarily chosen base station.

LTE is a SFN where all cells operate on exactly same frequency. Which means that every device, placed between two towers, while "talking" to one cell, creates interference (noise) of same level to the other cell and thus reduces the second cell's capacity. If it would happen that device is closer to second cell while still talking to the first cell, it would generate huge interference in second cell and consequently almost kill cell performance for the well-behaving users.
To avoid that, there are plenty of procedures for mobility (changing the serving cell) standardized and implemented in every device and every network's base station. Most of intelligence is put in base stations as they normally don't have limited power supply.

The description above is true for uplink (device transmits, base stations listen), but things are very similar for downlink (base stations transmit, devices listen).

In OP's case things are worse due to large number of cells "visible" to LTE card. There is a proper solution to the problem, but it might be impractical to implement: use directional antenae (that's plural!) for LTE device. For basic LTE two antennae are necessary, both should point to the same direction, only polarisation should differ by 90 degrees. Both antennae should point roughly at the best base station ...
Sometimes it's better not to point them directly but rather slightly off-direction. Depending on antenna design even directional antennae have quite wide beam, usually around 50-60 degrees (along the axis plus minus 30 degrees). If many base stations are generally in the same direction, just using directional antennae will not reduce interference. Antennae must point half of beamwidth to either side of group of basestations so that signal of the left- or right-most base station is still within main beam of antenna while most base stations are out of it and their interference is thus attenuated.
 
Eminence
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Re: Good documentation for R11e-LTE ?

Fri Aug 24, 2018 1:04 am

There is such an AT command, discussed here.

As for your discussion - this is interesting. Didn't know LTE is single-frequency. That would explain a lot. Actually, my device uses a station [1] that is much further away than the other station [2] I have in mind. However, it may be so that the station 1 is visible directly to the antenna while station 2 despite being closer is not directly visible. My station (device) is a couple of kilometers away from station 1 and therefore other stations closer to it transmit over my station (my location is 200-150m above the terrain station 1 is located on). I wonder how LTE designers thought this should function in a mountainous terrain.

I would switch to 3G and see if that changes things.
 
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mkx
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Re: Good documentation for R11e-LTE ?

Fri Aug 24, 2018 10:09 am

A long story short ...

The evolution of mobile networks, driven by usage and technology development, brought some decissions for next generation.
  • 1G was FDMA technology using analogue (FM) modulation. FDMA stands for Frequency Division Multiple Access, which means that every base station used a set of frequency channels ("frequencies") and would assign one of those frequencies to each active user full time. Capacity of the base station was the same as number of frequencies set to be used by the same base station.
    As the total number of frequencies is low, frequencies had to be reused on different base stations. However, if signal from different base stations overlapped, it was not possible to use same frequency on both base stations as there was no interference cancelation built in this standard. Radio network planners had thus hard time to do porper "frequency planning".
    Example of 1G network is NMT (in Europe) with 25kHz wide frequency channels (the whole 450MHz band was divided to 180 such channels), while AMPS was used in US.
  • 2G was usually TDMA technology using digital (e.g. PSK) modulation. TDMA stands for [T]ime Division Multiple Access, which means that every base station used single (or a few) frequency channels and would assign a "time slot" to each active user. Prime example of such network is GSM where frequency channels were 200kHz wide divided to 8 time slots, each time slot has duration of 576.92 μs.
    Still there was no interference cancelation mechanism built-in which means that the same frequency re-use consideration as in 1G networks apply as well. Overall capacity increased compared to 1G, GSM900 (band 8, used in Europe) had 124 channels (later on expanded with additional 48 channels) giving capacity of more than 1300 concurrent active users (compare that to 180 in NMT).
    As data transmission was growing, they added GPRS on top of GSM. GPRS allowed to transmit around 20kbps per timeslot and muti-timeslot could used. Later EDGE came with its 8PSK modulation raising max throughput to 80kbps per timeslot.
    2G could be implemented also as CDMA (IS95 in US). CDMA stands for Code Division Multiple Access, which means that every base station used a single (or a few) frequency channels and would assign "code" to each active user (full time). Used codes are orthogonal in a sense that receiver, when domodulating received signal, would multiply received signal with special wave function of selected (by code) characteristic and would thus filter useful signal from other signals and noise.
  • while 1G and 2G being primarily voice network, data became more and more important, so they standardized 3G networks with high data throughput in their mind. Due to scarche frequency resources they decided to go with SFN (Single Frequency Network) concept. In Europe example of 3G is UMTS, which has official name WCDMA (Wide-band CDMA). It used 5Mhz frequency channels (actually 3.84MHz with side guard bands against inter-channer interference). In this network, every base station used same frequency, but used different scrambling codes. At first, for UMTS they standardized completely new (high) frequency band at 2100 MHz (for Europe) with band width of 60 MHz, allowing for 12 carriers with standard 5 MHz channel width. Later they standardized also 900 MHz frequency band (being already used for GSM) with limited capacity of 35 MHz giving maximum 7 UMTS channels but most of MNOs still operate GSM in that band, hence limited UMTS capacity.
    Use of single frequency introduced problem of inter-base station interference and many mechanisms to fight it were deployed. One such mechanism was kind of spatial diversity where if a device (phone) was receiving signals from two base stations at comparable signal strength level, both base stations would transmit same data to this terminal and terminal would combine both data streams to improve reception. Same technique was used in UL where both base stations would recieve signal from the device and both data streams were combined in radio network controller (RNC). The bad thing about this technique is that capacity of two (or even three) base stations are consumed by single device.
    Use of SFN concept brought a good side effect as well: in mobility, where device moves from one base station to another, device needs to measure signals from other base stations and send measurement reports to RNC. RNC then decides if device needs to hand-over to another base station (if signal of that base station becomes better than signal of currently used one). In MFN networks, device has to perform measurements on different frequency channels which means use of additional receiver (in case of FDMA or CDMA) or re-tuning receiver to another channel during idle periods (in case of TDMA during non-assigned timeslots). In case of SFN receiver can receive signals from other base stations at the same time as receiving data from own base station without any re-tuning, making mibility slightly smoother.
    In case when interference between different base stations was simply too bad, another frequency channel was deployed, reducing interference on both channels. However, mobility between the two frequency channels sucks as receiver again has to perform measurements on both frequencies. As normally transmission in both directions (UL and DL) is contionous in time, new technique (compressed mode) was introduced. In this mode, transmission would only happen half of time (with double speed), giving measurement windows during inactive half of time. The "double speed" part causes troubles specially when devices are in poor radio signal but in good radio signal as well.
  • 4G is OFDM network, meaning all base stations use same frequency (as in 3G), but instead of using spread-spectrum carrier it uses OFDM sub-carriers (tones). OFDM in 4G (LTE) means that base-band unit (brain of the base station) runs scheduller which assigns OFDM sub-carriers to different concurrent devices. Time resolution (TTI, time to transmit) of assignment is 1ms and in each TTI it can assign same set of OFDM sub-carriers to different device. It came also with flexible frequency channel widths (20, 15, 10, 5, 3, 1.4 MHz) and number of standardized frequency bands (giving possibility to re-farm existing frequencies used by legacy networks, such as 1800 MHz band used by GSM).
    To maximize utilization of sub-carriers, devices provide feed-back in form of CQI. Better SINR means higher CQI, higher CQI means cell can use higher order modulations (64QAM v.s. QPSK), higher order MIMO (2x2 MIMO v.s. space diversity) and less robust FEC (7/8 v.s. 1/2), all of them allowing for higher throughput using same number of OFDM sub-carriers and TTIs.
    Interference issues are mostly the same as with WCDMA, but techniques to overcome problems are different. Cells (transmitters), controlled by the same base-band unit (most of times, LTE base station features 3 cells, using antennae pointed in different directions and using 3 distinct transmitters and receivers), can coordinate interference between users in different cells. Example would be that one cell transmits lower half of OFDM sub-carriers to one device while other cell transmits upper half of OFDM sub-carriers to another device during same TTI. Without coordination, both cells would use all OFDM sub-carriers, but those would interfer with each other in the device's receiver giving lower CQI (SINR) and consequently equal or even lower overall throughput. Same technique can be applied also between different base-stations (controlled by different base-band units), however things are more complicated: base-band units need to be absolute time synchronized (this is not a problem in typical US network as CDMA required GPS sync for proper operation, but typical EU network doesn't have GPS installed. IEEE1588v2 time sync is usually used instead, but that has its own prerequisites in backhaul networks), have good inter-base station connectivity (delay less than a few milli secondds) and devices have to support it as well (they have to report interferring cell identities so that serving base-band unit knows which other base-band unit it needs to coordinate with).
All of the above description is focusing on FDD (Frequency Division Duplex) mode of operation. 4G can operate also in TDD (Time Division Duplex) mode which is simliar to WiFi operation. However, due to SFN nature it's absolutely required to have all base stations well synchronized (either using GPS or IEEE1588v2) while this is not basic requirement for FDD networks (but it does help as briefly described above). If base stations are not precisely synchronized, interference problems become much worse as unsynchronized bse stations might transmit during reception frames of neighbouring base stations. As base stations use much higher Tx power than devices (up to 100W base stations v.s. 100mW devices) and due to better Rx sensitivity of base stations, this kind of unsynchronized operation would just kill the whole network.

The above is really short, things are actually much more complicated.

Anyhow, mountainous areas are a big problem which can only be solved by proper planning of network (placement of base stations) and, of course, by building more base stations so that in areas with users, there's single base station providing dominant signal. This can be aided by proper selection of devices' antennae and their proper alignment in case of static use (WFA type of use).

Even if OP's use of LTE device falls in FWA category and it would seem that locking device to a particular base station would be benefitial, it's not recommended due to LTE nature (of being mobile network). Signal level vary slightly in short time (seconds) and if many signals from different base stations have comparable level, it can easily happen that signal of bases station, to which device is locked, becomes worse than a few other signals and degradation due to interference overweights lower utilization of that base station.
 
Eminence
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Re: Good documentation for R11e-LTE ?

Fri Aug 24, 2018 3:20 pm

Thanks for a wonderful explanation. I was well acquainted with the GSM up to the introduction of GPRS, but then did not follow further development closely. Which is why I assumed time slots & multiple frequencies were still used. Interestingly, LTE is actively offered by operators here as an alternative to copper last mile for Internet access. Just yesterday Orange told me they would have to build 300m of cable to reach my house, so they won't do it because business case doesn't close for them, but they can offer me LTE access (which I of course refused, I already have it & know it almost doesn't work).

As for my case - I checked with an app on my phone: due to number of cells visible even phones do not work correctly there unless you are completely stationary - if I walk around the device is switching constantly which results in dropped calls. It may be that the network is nor properly configured, but this is beyond my reach. Hence the idea to try & correct it by selecting where my device attaches on my end.
 
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Re: Good documentation for R11e-LTE ?

Fri Aug 24, 2018 3:27 pm

BTW - no matter what for it would have been nice if there was a complete reference of AT commands for this modem. I did some searching and I know by now Mikrotik has never published one. I don't understand why it is kept a secret (after all, Mikrotik must know all the commands in its own device).
 
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mkx
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Re: Good documentation for R11e-LTE ?

Fri Aug 24, 2018 3:41 pm

Interestingly, LTE is actively offered by operators here as an alternative to copper last mile for Internet access.
I guess they use it as last resort to keep customer and to keep costs down (specially bean counters - read: accountants - like that).

Actually this can be a viable solution (not for everybody as you know from your own experience) if done properly. Key thing is to use QoS mechanisms, plenty (compared to previous mobile technologies) are available and they do make big difference.
For example in our mobile network (you may already guessed I work as radio engineer for MNO) we offer triple-play service over LTE as last resort in case where fixed infrastructure is not adequate and bean counters won't finance improvement of fixed infrastructure. We configure QoS profile for both VoIP and IPTV services so that they work properly in times when base stations get congested. And we make sure not to sell this service to too many customers in the area covered by same LTE cell (we do track usage and we block selling service to new customers if load on particular LTE cell raises over threshold). We also deny selling service to customers where LTE signal level is not high enough while for others we demand to install external directional antennae.
Competitors launched similar service but didn't bother with QoS and didn't bother with minimum signal levels nor with external antennae. Everything worked just great for their customers at the beginning, they also pointed at us because we quite often decline new customer or because we bother poor customers with installation of external antenna (oh, holy God, you're making me drill holes in my house and look how ugly those antennae are). However after a few months, when their LTE network received decent load, their IPTV service became flakey and subscribers started to complain. And are complaining louder and louder while our service just works.
 
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mkx
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Re: Good documentation for R11e-LTE ?

Fri Aug 24, 2018 3:51 pm

As for my case - I checked with an app on my phone: due to number of cells visible even phones do not work correctly there unless you are completely stationary - if I walk around the device is switching constantly which results in dropped calls. It may be that the network is nor properly configured, but this is beyond my reach. Hence the idea to try & correct it by selecting where my device attaches on my end.
I guess it would be possible to isolate one of base stations from the rest using directional antennae enough so that the service would be more stable. It might be that signal of that base station is not one of highest, but the trick is to use antenna's directional characteristics to amplify wanted signal and attenuate the rest thus getting slightly better useful signal and lower the interference. But again, this option requires usage of LTE device with possibility of connecting external antennae, most USB sticks don't offer such possibility. R11e-LTE, if I see it correctly, features two antenna connectors and no "patch antennae" on printed circuit, which should allow to use proper antennae to improve stability and performance of LTE service in your case. When selling tripple play service to our customers, we suggest customers to use these antennae. You might need to use some adapter to connect them to R11e-LTE. Other than being ugly and big (1 metre long), they are very decent antennae and price is acceptable.
 
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Re: Good documentation for R11e-LTE ?

Fri Aug 24, 2018 7:48 pm

Use this page how to lock the R11e-LTE international version to a speciffic cell:
https://wiki.mikrotik.com/wiki/Manual:I ... and_Tricks
 
Eminence
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Re: Good documentation for R11e-LTE ?

Sat Aug 25, 2018 10:37 am

Use this page how to lock the R11e-LTE international version to a speciffic cell:
https://wiki.mikrotik.com/wiki/Manual:I ... and_Tricks
This is not the answer to my question (esp. given that I already listed this site in my posts). I asked for something better, preferably a complete list of available commands - this is clearly not on that page. For example, I would like to know - before I go for any locking - if there are any other parameters I could tune as well as maybe perform something like a scan and list available cells preferably with their signal parameters (all of this data is gathered by the modem - it has to be for it to operate, the question is whether it is made available via the AT commands - the only way to communicate with the modem).
 
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Re: Good documentation for R11e-LTE ?

Sat Aug 25, 2018 3:13 pm

Interestingly, LTE is actively offered by operators here as an alternative to copper last mile for Internet access.
I guess they use it as last resort to keep customer and to keep costs down (specially bean counters - read: accountants - like that).
In their (Orange Poland) case it is the first resort outside of cities - they proposed LTE based before even discussing the wired option. I guess some "wise" strategy coming from the marketing department. I was unofficially told that copper is phased out as not modern enough and they will not extend copper lines even in places where it would have been relatively easy and if fiber is not available in a given area they are to try and get clients on the LTE.
 
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Re: Good documentation for R11e-LTE ?

Mon Aug 27, 2018 11:42 am

we will ad soon an option to scan for the neighbour cells so you could get info for the locking.
 
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Re: Good documentation for R11e-LTE ?

Wed Jan 02, 2019 3:04 pm

we will ad soon an option to scan for the neighbour cells so you could get info for the locking.
Can you tell me where can i find documentation for activate this option? is there in winbox?
 
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sebastia
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Re: Good documentation for R11e-LTE ?

Wed Jan 02, 2019 9:13 pm

It's on the linked page: Cell monitor https://wiki.mikrotik.com/wiki/Manual:I ... ll_Monitor
 
rawlsnake
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R11e-LTE IP issue

Thu Jan 03, 2019 9:19 pm

hi guys. i have a r11e-lte router. for testing purpose i removed its default ip address "192.168.88.0/24" as i was trying to reset the router and access it through winbox but after removing the IP i noticed the winbox is not helping me out to access the router through mac address and since it does not have an IP address on its interface so i also cannot access it via its wlan or any other mean. i tried multiple times to reset the router but default IP is not showing up. what could i do now to access the router. i tried almost everything.

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