In case you have missed the previous two parts on Private Mobile Radio (PMR) services on LTE have a look here and here before reading on. In the previous post I've described the potential advantages LTE can bring to PMR services and from the long list it seems to be a done deal. On the other hand there is unfortunately an equally long list of challenges PMR poses for current 2G legacy technology it uses that will not go away when moving on the LTE. So here we go, part 3 focuses on the downsides that show quite clearly that LTE won't be a silver bullet for the future of PMR services:
Glacial Timeframes: The first and foremost problem PMR imposes on the infrastructure are the glacial timeframe requirements of this sector. While consumers change their devices every 18 months these days and move from one application to the next, a PMR system is static and a time frame of 20 years without major network changes was the minimum considered here in the past. It's unlikely this will significantly change in the future.
Network Infrastructure Replacement Cycles: Public networks including radio base stations are typically refreshed every 4 to 5 years due to new generations of hardware being more efficient, requiring less power, being smaller, having new functionalities, because they can handle higher data rates, etc. In PMR networks, timeframes are much more conservative because additional capacity is not required for the core voice services and there is no competition from other networks which in turn doesn't stimulate operators to make their networks more efficient or to add capacity. Also, new hardware means a lot of testing effort, which again costs money which can only be justified if there is a benefit to the end user. In PMR systems this is a difficult proposition because PMR organizations typically don't like change. As a result the only reason for PMR network operators to upgrade their network infrastructure is because the equipment becomes 'end of life' and is no longer supported by manufacturers and no spare parts are available anymore. The pain of upgrading at that point is even more severe as after 10 years or so when technology has advanced so far that there will be many problems when going from very old hardware to the current generation.
Hard- and Software Requirements: Anyone who has worked in both public and private mobile radio environments will undoubtedly have noticed that quality requirements are significantly different in the two domains. In public networks the balance between upgrade frequency and stability often tends to be on the former while in PMR networks stability is paramount and hence testing is significantly more rigorous.
Dedicated Spectrum Means Trouble: The interesting questions that will surely be answered in different ways in different countries is whether a future nationwide PMR network shall dedicated spectrum or shared spectrum also used by public LTE networks. In case dedicated spectrum is used that is otherwise not used for public services means that devices with receivers for dedicated spectrum is required. In other words no mass products can be used which is always a cost driver.
Thousands, Not Millions of Devices per Type: When mobile device manufacturers think about production runs they think in millions rather than a few ten-thousands as in PMR. Perhaps this is less of an issue today as current production methods allow the design and production run of 10.000 devices or even less. But why not use commercial devices for PMR users and benefit from economies of scale? Well, many PMR devices are quite specialized from a hardware point of view as they must be more sturdy and have extra physical functionalities, such as a big Push-To-Talk buttons, emergency buttons, etc. that can be pressed even with gloves. Many PMR users will also have different requirements compared to consumers when it comes the screen of the devices, such as being ruggedized beyond what is required for consumer devices and being usable in extreme heat, cold, wetness, when chemicals are in the air, etc.
ProSe and eMBMS Not Used For Consumer Services: Even though also envisaged for consumer use is likely that group call and multicast service will be limited in practice to PMR use. That will make it expensive as development costs will have to be shouldered by them.
Network Operation Models
As already mentioned above there are two potential network operation models for next generation PMR services each with its own advantages and disadvantages. Here's a comparisons:
A Dedicated PMR Network
- Nationwide network coverage requires a significant number of base stations and it might be difficult to find enough and suitable sites for the base stations. In many cases, base station sites can be shared with commercial network operators but often enough, masts are already used by equipment of several network operators and there is no more space for dedicated PMR infrastructure.
- From a monetary point of view it is probably much more expensive to run a dedicated PMR network than to use the infrastructure of a commercial network. Also, initial deployment is much slower as no equipment that is already installed can be reused.
- Dedicated PMR networks would likely require dedicated spectrum as commercial networks would probably not give back any spectrum they own so PMR networks could use the same bands to make their devices cheaper. This in turn would mean that devices would have to support a dedicated frequency band which would make them more expensive. From what I can tell this is what has been chosen in the US with LTE band 14 for exclusive use by a PMR network. LTE band 14 is adjacent to LTE band 13 but still, devices supporting that band might need special filters and RF front-ends to support that frequency range.
A Commercial Network Is Enhanced For PMR
- High Network Quality Requirements: PMR networks require good network coverage, high capacity and high availability. Also due to security concerns and fast turn-around time requirements when a network problem occurs, local network management is a must. This is typically only done anymore by high quality networks rather than networks that focus on budget rather than quality.
- Challenges When Upgrading The Network: High quality network operators are also keen to introduce new features to stay competitive (e.g. higher carrier aggregation, traffic management, new algorithms in the network) which is likely to be hindered significantly in case the contract with the PMR user requires the network operator to seek consent before doing network upgrades.
- Dragging PMR Along For Its Own Good: Looking at it from a different point of view it might be beneficial for PMR users to be piggybacked onto a commercial network as this 'forces' them through continuous hardware and software updates for their own good. The question is how much drag PMR inflicts on the commercial network and if it can remain competitive when slowed down by PMR quality, stability and maturity requirements. One thing that might help is that PMR applications could and should run on their own IMS core and that there are relatively few dependencies down into the network stack. This could allow commercial networks to evolve as required due to competition and advancement in technology while evolving PMR applications on dedicated and independent core network equipment. Any commercial network operator seriously considering taking on PMR organizations should seriously investigate this impact on their network evolution and assess if the additional income to host this service is worth it.
So, here we go, these are my thoughts on the potential problem spots for next generation PMR services based on LTE. Next is a closer look at the technology behind it, which might take a little while before I can publish a summary here.