Experiment: In search of NB-IoT, 4G & 5G signals on the air

21 Sep

It seems that at least every decade, wireless telecommunications makes a significant leap in the form of a new generation of air-interface technology which puts the latest developments in radio technology into the consumer’s hands. Right now, we are actually on the precipice of two new technologies which have the potential to improve quality of service over 4G/LTE-A technologies in densely populated areas and extend service to low-cost low-powered sensor nodes – the two technologies being 5G and NB-IoT respectively.

I was prompted to take a closer look at these technologies when a fellow colleague mentioned them in passing over a lunchtime conversation which coincided with the RoadTest for a Siretta SNYPER-LTE cellular network analyser. While I put an application in, unfortunately, I was not successful which was a bit of a disappointment, but at least I could still look at the spectrum with my Tektronix RSA306 Real-Time Spectrum Analyser.

Getting Ready for NB-IoT and 5G

Narrowband IoT (shortened to NB-IoT) is an LTE technology designed for low-power wide-area network (LPWAN) applications. It brings a lower-rate, narrower-bandwidth service which reduces cost and complexity of compatible radios and reduces power budget. This means it competes with the likes of LoRa, Sigfox and other similar technologies. Its technical specs include a 250kbit/s throughput, single-antenna configuration with 180kHz bandwidth in half-duplex mode and device transmit powers of 20/23dBm.

The big draw of NB-IoT compared to the other competing technologies is that it can be enabled simply by updating BTS firmware and configurations. Telcos are already in a prime position, having the hardware, network infrastructure, dedicated/protected spectrum and business already established while competing networks often are still building out coverage using unlicensed bands. Furthermore, the NB-IoT standard solves key interoperability, cost and power budget issues with full-function cellular modules which may accelerate the adoption of IoT devices using this form of connectivity.

Not wanting to be left behind, in Australia, Optus, Vodafone and Telstra have trialled NB-IoT in 2016 and 2017. Of them, the latter two have deployed NB-IoT service, with full service by October 2017 (Vodafone)/January 2018 (Telstra) while further extending coverage. Optus, however, does not seem to have a commercial NB-IoT service at this time. Despite this, the number of NB-IoT capable equipment is still relatively scarce in the consumer space, with development boards only recently becoming available.

In contrast, 5G seems more widely publicised as the successor to LTE, offering higher speeds and lower latencies which are often claimed to be the enabler of many new wireless applications (although this is yet to be seen). There has been a lot of confusion as to the capabilities and coverage as 5G services can be deployed in the sub-6GHz band where performance is often said to be like an “improved” LTE-A, as well as millimeter-wave bands which offer much wider bandwidth and throughput, but has very poor propagation characteristics. Present-day 5G handsets are not “standalone” yet, operating in “NSA” mode which relies on 4G network radio hardware. This may persist for a few years and is perhaps, not surprising, as many of the MVNOs still do not offer VoLTE and thus LTE-capable phones are still falling back to 3G for circuit-switched calling.

Regardless of the practicalities of deploying a technology that is still in evolution, both Telstra and Optus have made some rather public announcements of introducing 5G services in select areas in a fight for bragging rights which seems reminiscent of the 4G LTE roll-out. Notably absent is Vodafone, who perhaps are being more careful after investing heavily in their LTE refresh after Vodafail, although their joint venture with TPG has secured some spectrum.

In the Sydney area, the present Telstra map looks like this, showing isolated pockets of 5G coverage:

Meanwhile, it would seem that Optus has split their Sydney area maps into districts, where it seems one or two towers in a few select suburbs have been upgraded, likely to support their limited 5G Wireless Broadband service which is attempting to challenge the NBN.


While it doesn’t look like there are many active sites, this is because there is a lot of work being done to prepare for the sites to be active.

Near to where I live, this Telstra tower had a crane servicing the tower for about four days. I would suspect this is to prepare for the activation of 5G – especially when you see the following ads being taken out in the notices section of local papers:


This does imply that Telstra uses Service Stream, while Optus uses Metasite to work on some of their sites.

I suppose it makes sense that deployment is already underfoot, especially seeing that now, early 5G-capable handsets are starting to appear which may provide the added performance and prestige that the high-end of the market might demand (and be willing to pay for). However, aside from cost, there have been some reported downsides with some 5G handsets having shorter battery life due to greater power consumption.

Later on down the track, I suppose the network may be refreshed with new BTS hardware and antennas to support mmWave and standalone-5G deployments, while high-end users are likely to have replaced their handsets to take advantage of these advances. Mainstream users (such as myself) will still have to wait a few years for it to “trickle down”, but the benefits may be felt as the LTE network has some load shifted over to 5G. That would be especially welcome where I am as the NBN is still not here and LTE congestion is a real phenomenon.

On the Air

So I thought it would be a good idea to get out the spectrum analyser to see what the signals nearby looked like on a band-by-band basis.

700MHz (Band 28)

The “digital dividend” band which was opened up by the change to all-digital TV broadcasting is also often known as 4GX (Telstra) or 4G Plus (Optus). Band 28 support has also become the “in-joke” of OzBargainers whenever anyone posts a deal about a mobile phone, as it wasn’t a widely-supported band by most budget-mainstream phones (especially imported ones).

In this band, there is a 10MHz carrier at 763MHz (Optus) and a 20MHz wide carrier at 778MHz (Telstra). Because these are FDD-LTE, the receive carrier is equivalent width at 708MHz and 723MHz respectively. But do you see that on the right side?

The carrier at about 787.200MHz is the Telstra NB-IoT service, plainly visible on a spectrum analyser. The choice of the 700MHz band would ensure greater propagation than a higher band, but whether this frequency is well-supported by all NB-IoT radios is perhaps unknown.

850MHz (Band 5)

The 850MHz band was home to Telstra’s “NextG” 3G service as well as Vodafone’s LTE service (as they don’t have any 700MHz allocation).

In the low part of the band, we can see some digital trunking radio which still lives near the 850MHz band. The 10MHz wide Vodafone LTE carrier (875MHz, paired with 830MHz) can be seen next to two 5MHz Telstra NextG 3G carriers (885MHz paired with 840MHz). The carriers which have “rounded” shoulders are easily distinguished as 3G.

900MHz (Band 8)

The 900MHz band was formerly home to mostly GSM services, but since the 2G shutdown, it has been refarmed for 3G use mainly by Optus with Vodafone LTE (and in some places, Telstra).

The 8MHz wide Optus allocation is at the lower end of the band 947.6MHz paired with 902.6MHz, split across two carriers. The Vodafone allocation at 955.9MHz is 8MHz wide and paired with 910.9MHz according to ACMA, which seems to be split across several carriers. There is an interesting “shard” on the right hand side – this appears to be Vodafone’s NB-IoT service.

Its frequency is approximately 959.800MHz and has a very similar spectral characteristic to the Telstra carrier identified earlier.

1800MHz (Band 3)

The 1800MHz band was the home of 4G at its introduction and is one of the bands where every carrier has some allocation.


The first carrier belongs to Telstra which has a 12MHz allocation at 1811.25MHz paired with 1716.25MHz which is carrying a 10MHz wide carrier. This is followed by Vodafone with 15MHz at 1827.5MHz paired with 1732.5MHz and 1842.5MHz paired with 1747.5MHz which they seem to be using as 10+20MHz. Rounding out the band is Optus with 15MHz at 1857.5MHz paired with 1762.5MHz.

2100MHz (Band 1)

The 2100MHz band is the upper band which was used by early 3G handsets, but has also been refarmed for LTE to some extent, making it rather messy to look at.


Vodafone has a 14MHz band allocation at 2117.5MHz paired with 1927.5MHz which seems to have a 15MHz LTE carrier in it. This is followed by a 20MHz allocation to Optus centred at 2140Mhz paired with 1950MHz which seems to be carrying a 10MHz LTE carrier and a 3G carrier. This is followed by a 5MHz Telstra 3G carrier at 2127.5Mhz paired with 1937.5Mhz, then a 10MHz wide Telstra LTE carrier at 2155MHz paired with 1965Mhz. Rounding the upper part of the band seems to be a pair of 3G carriers from Vodafone which sits in a 9MHz bandwidth allocation at 2165Mhz paired with 1975MHz.

2300MHz (Band 40)

Band 40 is exclusively used by Optus by their TDD-LTE service used initially to serve data connection to their home wireless broadband product users, but now, seems to allow connection from any capable device. As this is TDD, there is no paired frequency as both directions share the same frequencies.


They have four separate 20MHz wide carriers, with compatible devices using carrier aggregation to achieve higher speeds. I believe their total allocation was 98MHz, but the upper section (near 2.4GHz) remains unused possibly due to interference from/to 2.4GHz ISM band devices. I actually get pretty decent 100Mbit/s service using 2x2CA on this band when it’s not congested and is one reason why Optus outperforms Vodafone by a big margin where I am.

2600MHz (Band 7)

Band 7 seemed initially confined to high density areas such as train stations, but now covers a wider area. This band has equal 20MHz carriers where I am at the moment.


Telstra owns 40Mhz of bandwidth at 2650Mhz paired with 2530Mhz. Optus has 20Mhz of bandwidth 2680Mhz paired with 2560Mhz. It is said that TPG has 10Mhz of spectrum in Band 7, but I don’t think I’ve seen the signal from where I am.

3400-3700MHz (5G/Sub-6)

Given that all of these bands are already used – where is 5G going to fit in the “sub-6” scheme? According to the best news I could get, we would be deploying 5G into the 3400-3700MHz range. Higher frequencies normally mean poorer penetration, so that was probably not the best news for indoor coverage. Worse still, it is basically taking over the spectrum from the pre-WiMAX wireless internet service Unwired (later, VividWireless).


While I wasn’t in a coverage area, I decided to see if I could see the signal … ultimately from home, all I saw was bleed-through noise from 4G carriers in the 2600Mhz band.

I decided to carry my gear into the city, to a location where it is covered by both Optus and Telstra 5G to see if the signal can be seen.

The sweep is 1GHz wide which took some time, with peak hold on the traces, but the 5G signal was fairly weak with lots of noise from perhaps intermodulating signals. The lower 5G carrier isn’t so obvious – the upper one is slightly more visible.

Ultimately, it took until the 18th September 2019 for the details to turn up in ACMA’s RRL database – Optus is at 3458.8Mhz with a 60MHz slice with Telstra is at 3605MHz with a 60MHz slice, both operating transmit/receive on the same set of frequencies.

Wait a Minute?

If we remember what happened on the introduction of Unwired, the choice of these frequencies is rather unfortunate for satellite enthusiasts. The extended C-band (large dish) services rely on the frequency range of about 3400-4200MHz with regular C-band occupying 3700-4200MHz.

With the carriers being within the extended C-band range transmitted terrestrially, it is very likely that a small amount of spill-over will cause LNBs (which have very high gains as they were designed to receive the very weak signals from geostationary satellites) to saturate and operate non-linearly causing reception problems for certain frequency ranges or perhaps the whole band altogether. The width of the carriers at 60MHz gives a real possibility it can wipe out a few MCPC services in one fell swoop.

While there are not many services that reach Australia in the extended portion of the band, even OCS “band-stack” LNBs which operate from 3700-4200MHz may not be sufficiently engineered to reject the signals, which are a lot closer than back in the Unwired days when ~3500MHz with a bandwidth of 10MHz was used.

While the “big ugly dish” is becoming less relevant in a world of IPTV and video-on-demand, it seems rather disappointing that yet another one of the technologies I’ve grown to understand is becoming “extinct”.

It’s also interesting to see that the NBN has been trialling fixed wireless in the 3.5GHz band (B42), so there may well be a collision between 5G sub-6GHz deployment and NBN LTE Fixed Wireless services … which would only increase the potential headaches to a C-band satellite user.


The radio bands are chock-full of 3G and LTE carriers, with NB-IoT and 5G recently joining the mix after the death of GSM. But it seems our insatiable appetite for mobile data bandwidth means that we will soon have even more spectrum than ever before, in the form of millimeter wave 5G radio interfaces. It will still be a number of years until they become mainstream despite the limited propagation characteristics and until then, it seems that sub-6GHz will be the “interim” technology that carries the 5G flag even though it is operating at microwave frequencies that are not the most favourable for propagation.

Unfortunately, it seems when the 5G sub-6GHz services are switched on, users of C-band satellite systems may experience the same problems they did when Unwired was in use. It seems that the relentless march of technology continues … for better or for worse.

Source: https://goughlui.com/2019/09/21/experiment-in-search-of-nb-iot-4g-5g-signals-on-the-air/
21 09 19

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