Making sense of operating frequencies on cellular modules

26 Aug

When an engineer looks to deploy a cellular device for collecting remote data (M2M) they need to consider where the device will be deployed and which cellular frequencies are in use from the cellular operator.  This post will look at cellular frequencies used within Australia.

One of the areas of greatest confusion is around cellular frequencies. We are regularly asked – “which frequencies do I need my M2M wireless device to operate on when deploying cellular based equipment?”.  It is not surprising there is so much confusion around this issue.  Things are changing rapidly in the frequency space in Australia and around the world and keeping well informed is proving a challenge, even for the tech savvy engineer. The introduction of LTE is only going to further confuse the understanding for the casual observer.

If we look back to the recent past, all 2G networks (GSM/GPRS) operated across two frequencies in Australia – 900Mhz  as the main operating band, and 1800Mhz for increased capacity. (Readers may remember that Telstra also offered a CDMA network for the country areas, which operated in the 800Mhz band).  When choosing a GSM cellular device a user only had to ensure that the module supported 900Mhz and 1800MHz GSM.

When 3G was rolled out across Australia the networks all had different operating frequencies for the new higher speed data services.  There were a range of reasons for this including established operating frequency standards from around the world,  marketing differentiation, and convenience to re-use existing infrastructure to minimise upgrade costs and extend coverage quickly.

OPTUS and Vodafone chose to start with 2100Mhz on their 3G network rollouts as this was a standard in other 3G rollouts around the world and was good from a roaming perspective and device availability.  Telstra chose the less used 850Mhz frequency range (at least at the time of rollout) for its Next G 3G network.  The lower operating frequency allowed the signal to be transmitted further giving greater coverage with less tower infrastructure.  This suited the rural rollout requirements to replace CDMA and also meant that the existing CDMA antennas might be used, saving some expense and time. Telstra also offered a 2100Mhz network in the city and larger towns through their arrangement with the “3” network in Australia.   At this time M2M users would often be confused as to why their existing quad band 2G devices would not work on the new 850Mhz NEXT G network as their module stated it supported the 800Mhz band.  The issue here is the change in the “air interface” standard on the radio technology from TDMA, used on the 2G networks to a new standard on the 3G networks called WCDMA.

Over time Vodafone expanded and added 850Mhz frequency to their 3G rollout,  and OPTUS added 900Mhz frequency to expand capacity and coverage. Some confusion came into the market again with people asking why their 2G 900Mhz module or device did not work on the new 900Mhz 3G network and the answer is the change in air interface technology from TDMA on 2G to WCDMA on 3G.

In the initial 3G rollouts it was very important to choose a device that supported your required 3G frequencies and also had 2G-frequency support for fall-back in areas that did not have suitable 3G coverage.  Today many 3G modules support all Australian 3G/NextG frequencies with fall-back to GSM/GPRS.

Whilst 4G or “LTE” is not yet a major consideration for the majority of M2M applications , there are immerging M2M applications and developer segments where the faster data networks are of a significant benefit to deliver solutions. 4G/LTE networks use yet another radio interface and require the user to select an appropriate device that has the correct 4G/LTE frequencies (including LTE bands). Today in Australia almost all LTE services are deployed on 1800Mhz frequency (band 3).  OPTUS has also deployed an LTE network operating on 2.3Ghz TDD LTE  in Canberra, a standard that today is not compatible with most LTE modules an devices.   Like the transition from 2G to 3G it pays to ensure there is also the correct 3G frequency support for fall back where there is insufficient 4G coverage. Newer radio modules often support a range of 4G, 3G and even 2G frequencies as manufacturers try to cover all the variations a user may encounter.

The 1800Mhz frequency being rolled out for LTE was originally deployed on the GSM/GPRS networks in Australia.  This frequency is being re-farmed to LTE as 2G devices have moved off the older 2G networks and been replaced by 3G devices.  Recently we have observed more re-farming of the older GSM frequencies for reuse for faster data networks as traffic moves off the older GSM networks. In 2014 and 2015 we will see further frequencies deployed for LTE. Recently the government held auctions for the 700Mhz frequency, which is being released with the analogue TV closure.   700Mhz LTE deployments on band 28 are expected in the later part of 2014 as is the use of the 2600Mhz frequency.  There are at least 7 LTE frequencies in use (plus variations) and no current LTE modules or device is available in the market today that supports all LTE expected frequencies.

In conclusion it is important to thoroughly investigate the specification of the module/cellular device and the network (s) you intent to operate in to avoid disasters with your communication deployments.

Source: http://blog.m2mconnectivity.com.au/2013/08/26/making-sense-of-operating-frequencies-on-cellular-modules/

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