In a previous post we took a look at initial leak testing of UmSITE hardware, which lead to an improved gasket solution being used in order to meet the desired level of ingress protection. In this post we take a look at UmSITE operation at extreme high and low temperatures, to ensure that there is minimal degredation in performance.

Setup

For testing at temperatures up to +65C a chamber was constructed from insulation panels, using a 75W incandescent lamp as the heat source. A fan equipped with a variac for speed control ensured an even distribution of air temperature, without excessive circulation. A thermocouple was used to measure the air temperature inside the chamber.

Testing at down to -40C was carried out using an environmental chamber. Again a thermocouple was used to confirm the air temperature inside.

An RF splitter was used to feed the first ARFCN to both PAs simultaneously, enabling testing with both channels being driven constantly at full TX power. RF performance was then measured using an Agilent E4406A VSA Transmitter Tester. Power supplies were included in tests to ensure that they also performed well up to their 65C rating.

Next we’ll look at UmSITE-TM10 (2x10W TX) performance at 65C, followed by the UmSITE-TM3 (2x3W TX) at -40C.

UmSITE-TM10

In this first screen capture we can see that the measured spectral mask (yellow) remains a healthy 1.46dB below the limit set out in the GSM specification, allowing for some variation.

The next capture shows the RF envelope, with time on the X axis and power on Y. At more typical ambient temperatures the TX output is ~41dBm (13 watts), and so a degradation of only 0.6dBm up at an ambient temperature of 65C means that the PA is still doing a great job!

Note that originally OpenBTS would not always pass the RF envelope test and so Fairwaves funded work on the OsmoTRX transceiver code to improve this.

In this screen capture we can see the phase error, which contributes to link quality.

1 degree peak and 5 degrees RMS phase error is pretty much the industry standard.

David Burgess has put together an excellent concise write-up on the importance of frequency control in GSM. In short, the specification requires 50ppb precision. At 900MHZ this is approximately 50Hz and since tests were conducted indoors and without a GPS antenna connected, the error was up at 36Hz. However, with the UmTRX onboard GPS reference active we typically see <10Hz offset.

This final image from the TM10 tests shows that we have no second harmonic, which means that the duplexer is doing a good job at filtering out-of-band transmissions.

Next we’ll take a look at the Temperature measurements from the sensors on the SBC and UmTRX.

First, with normal CPU load:

$ sensors

Adapter: Virtual device
temp1: +67.0°C (crit = +100.0°C)

coretemp-isa-0000
Adapter: ISA adapter
Core 0: +82.0°C (crit = +100.0°C)
Core 1: +83.0°C (crit = +100.0°C)

$ uhd_usrp_probe

Creating the usrp device with: addr=192.168.10.2...
-- Opening a UmTRX device... 192.168.10.2
-- user_mtu.recv_mtu = 1472
-- user_mtu.send_mtu = 1472
-- TempA: 70.250000 C
-- TempB: 69.187500 C
-- VoltagePR1: 0.090000 V
-- VoltagePF1: 0.080000 V
-- VoltagePR2: 0.070000 V
-- VoltagePF2: 0.060000 V
-- Voltagezero: 0.000000 V
-- VoltageVin: 28.140000 V
-- VoltageVinPA: 28.400000 V
-- VoltageDCOUT: 28.100000 V
-- PA low=`` PA dcdc_r=`255`
-- Detected UmTRX 2.3.1

Note:

• A & B temperature sensors are located next to the LMS6002D transceiver ICs
• The power supply is coping well and delivering 28V!

With 100% CPU load (with burnP6):

$ sensors

Adapter: Virtual device
temp1: +68.0°C (crit = +100.0°C)

coretemp-isa-0000
Adapter: ISA adapter
Core 0: +91.0°C (crit = +100.0°C)
Core 1: +92.0°C (crit = +100.0°C)

UmSITE-TM3

Now we’ll take a look at UmSITE-TM3 operation down at -40C.

In this first screen capture we can see that the TX output is a healthy 5 watts.

The next shows that there is an increased phase error, but this is still within the GSM specification limit of 5 degrees RMS and 20 degrees peak.

Once again the spectral mask is within spec.

Finally, the IQ plot (similar to the second above) confirms that everything is as it should be.

Which all results in a happy Andrey Sviyazov!

The post UmSITE passes temperature tests with flying colours appeared first on Fairwaves.

The demo will take place at the Canonical booth in Hall 8.1 at App Planet Stand CC8.20. As part of this visitors will be able to use a  handset with a Truphone SIM to place a call via a Fairwaves UmSITE base station, to a UK phone number on the Truphone network. The call will be routed via the Metaswitch Project Clearwater IMS platform and an IVR system running on TeleStax’s RestComm. It promises to be a pretty compelling demonstration of the power and flexibility of open source and open standards in mobile communications.

If you’re attending MWC be sure to drop by the booth, and if you’d like to arrange a meeting please get in touch.

The post Mobile World Congress 2015 Demo appeared first on Fairwaves.

Speaking of comments, a question that came up — and which we frequently get asked! — is, why not just use VoIP over WiFi? After all, most handsets tend to have WiFi, are capable of running a SIP client and this would seem like an obvious solution.  Well, there are numerous reasons why such an approach is far from optimal:

• WiFi is typically short range. Sure, you can achieve longer distances with high gain antennas and powerful equipment at both ends of a link, but this is impractical for mobile. However, Fairwaves GSM solutions can cover a range of 2-4km now, and 10km will soon be possible.
• Commodity WiFi equipment simply isn’t designed for applications such as this and — due to using weak CPUs which can only sustain low packet per second rates — will only be able to support a relatively low number of calls reliably. GSM on the other hand is designed from the outset for voice, scaling and reliability.
• GSM consumes far less power. Remember how a handset without a touchscreen, apps and data would last for a week on a single charge? Well, it’s possible to achieve multiple days on a modern handset if you put it into GSM-only mode and disable data. Turn on WiFi and it’s a whole other story!
• Finally, in many countries you need a spectrum licence in order to operate outdoor WiFi networks.

So, as you can see, GSM certainly makes more sense than VoIP+WiFi for mobile voice, and even more so in rural areas where power supply may be a relatively scarce/premium resource and the greater distances that can be covered by a single site the better. In fact, for the very same reasons, in such applications GSM is typically preferable to more modern, albeit more power hungry and shorter range, 3G and 4G systems.

In closing it should be noted that there are applications where VoIP+ WiFi is the right solution. Such as rural fixed telecoms, as championed by the good folks at Village Telco. A mention should also go to the Serval Project, whose WiFi mesh network-based approach is well suited to use in support of disaster relief efforts.

The post Wired article and the VoIP over WiFi question appeared first on Fairwaves.

Given that the UmSITE-TM3 BTS is designed for mounting outdoors on top of masts and towers, it clearly needs to be able weather the elements and not fail during a heavy downpour. So, in addition to the UmTRX transceiver being tested across a range of operating temperatures, the assembled UmSITE-TM3 is also subjected to an air under water test to check for leaks.

In this video we can see that the UmSITE-TM3 sample received back from the fab failed in the first of these such tests.

The foam gasket material used was suspected to be the culprit. After the initial disappointment and subsequently much testing with alternative materials of different hardness, a silicon gasket material was finally settled upon.

As can be seen below, the UmSITE-TM3 now passed this basic bubble test.

Testing such as this is something that is done as a matter of course and repeatedly, to ensure that there will no preventable failures in production, and the above two videos just go to show how vitally important testing is!

The post First UmSITE-TM3 Sample Passes Leak Test appeared first on Fairwaves.

A recent article in Popular Mechanics explains how “the device fuses a dial-up modem with a motor from a cell phone and a souped-up version of a common blood glucose meter.” Going on to say that in use, “A drop of blood is applied onto a chemically active test strip, and the more glucose is in the blood, the stronger the electrical signal is from the strip. The idea with uMED is that a person equipped with the right test strips and a device that can analyze them, a person could rapidly carry out an extraordinary variety of electrochemical tests with just one detector.”

As if that wasn’t enough, the uMED is seemingly also Arduino-compatible and as such can easily be reprogrammed for use with new tests, by someone with minimal training. Furthermore, the device doesn’t even require a network data service, since it incorporates a modem and uses a voice channel as a bearer, thereby ensuring compatibility with every generation of mobile network technology.

The growing case for universal network coverage

Mobile communications has always been about so much more than simply convenience and the benefits it brings in an emergency, whether that be at a personal, community or national level, is clear. However, innovations such as uMED go on to even further underline how mobile communications infrastructure has a vital part to play in not only transforming, but saving lives.

Unfortunately, there still remain a great many areas of the world that are without network coverage. And in fact if we look at Mexico alone this amounts to a staggering 50,000 or so rural localities.

This is where open source network infrastructure — which lends itself to agile deployment, with drastically reduced costs and supporting far more flexible business models — can help. Making it possible to connect communities such as the Mexican village of Yaviche, improving the quality of life and in some cases perhaps even saving lives.

Image source: Alex Nemiroski

The post The $25 cell phone connected device saves lives appeared first on Fairwaves.