5G - Test Equipment Concept Design                             Home : www.sharetechnote.com





In this post, I will talk about a kind of ideal test equipment (my dream) for 5G device. Actually this is not only for 5G and it can be any cellular technology, but I talk of this mostly under the context of 5G because 4G test equipment market is already almost saturated and I don't think there would be drasitic redesign activities. Followings are some of the topics (aspects) which I want to touch on.



Requirement (Getting Tougher)


As 5G requirements for Network and UE gets tougher, it can easily be anticipated that the requirement for the device test equipment will get tougher as well. Followings are some of the features that will be strongly required for 5G.

  • Highly Flexible (covering both strict conformance test and diverse/flexible application test)
  • Very Low Cost
  • Strong/Versatile debugging features
  • Robust/reliable Automation
  • Portability

Is this new requirement ? Haven't we been under pressure with all of these all the time ?

Yes, it is true. But the amount of pressure will be enourmous. The scope of cost and flexibility would be something beyond what we can imangine now. Every equipment vendor have high expectation of IoT being an important part of 5G, but it doesn't seem that they take any serious consideration of the nature of IoT market.

There will be incomparable number of IoT device manufacturer comparing to the current mobile phone manufacturer which is good news for the equipment vendor. However, the size and budget of IoT device manufacturer will be incomparably small comparing to the current mobile phone vendor or chipset vendor. They should not expect to see multi-million or at least sub million dollar equipment to all of IoT device makers. Therefore, it is about time for equipment vendors to come out with brilliant/disruptive idea to reduce the cost of the equipment and still providing all the features required for testing.

One thing that was not requested before but might be a strong requirement would be 'Portability' (Compact and Easy to carry around). We will see more and more devices embedded in a vehicle or a lot of IoT devices installed in remote place. At the phase of initial test before those devices gets installed in final place, we can test it at the bench as we usually do with mobile phone for now, but how about test/verification or troubleshoot after the installation ? I think it would be much easier to bring the equipment to the installation place rather than uninstall/disassmble the installed device.



Conceptual Architecture of UE Test Equipment


Even though we will call it 5G device (or whatever 3GPP will name it), it will be required for the device to support all or most of the existing (legacy) technology. As a result, the test requirement will also be required to support all the legacy technology. My personal 10000 feet overview of the equipment architecture is as follows.



Followings are some of the key features of this imaginary test equipment :

  • Most of the radio protocol (except High Throughput/Short TTI 5G) is based on SDR. This would give the equipment vendor great flexibility of implementation/revise/upgrade and at the same time help reduce the cost.
  • Low level Radio Stack and higher layer C-Plane node and core network parts are implmented as independent software module. This kind of architecture is similar to real network architecture, but many of current mainstream test equipment is not designed like this. In most case, they implement the very minimal part of core network capability and integrate it as a part of Radio Protocol Stack. I will talk more on the advantage and disadvantage of this architecture later.
  • The equipment should be easility connected to public IP network that provide UE with easy access to public network.
  • The equipment should be able to be connected to external core network (e.g, external MME/MSC simulator or external EPC or even live network EPC).



How about Conformance Test ?


Even though the architecture illustrated above would be my dream equipment, I think I should admit that it can cover all of the test scenario we need to go through.  One important area is Conformance Test. Even though the above architecture would be ideal for application layer test or reproducing real life problem (live network problem), it would be tricky to perform the conformance test cases.  Most of the conformance test cases has a couple of characteristics as listed below.

  • Test cases should go through a specific/predefined protocol sequence
  • In most cases, conformance test case is less tolerant to variation of protocol sequence.
  • Most of test equipment vendor are not writing their own protocol conformance test cases, they are just translating TTCN code from ETSI into the form that can be executed by their own hardware. The TTCN code structure would not be easily translated for the equipment architecture as shown above.
  • Not designed to connect to multiple UEs simultaneously

Due to these factors, most of the test equipment being used for Conformance (especially for protocol conformance) is based on following architecture. As you see here, there is no NAS/Core Network components. Each of the radio stack is directly controlled by the test case and NAS/Core Network part is simulated by radio message directly created by the test cases.




Modular Architecture for Both Software and Hardware


I hope to see all of this within a common frame (there might be some exceptions for IoT though. We may think of portable hardware frame for IoT. The equipment vendor may go with different hardware frame to meet the price and portability requirement in IoT industry, but it would be better to use the same software even with such a low cost / small sized equipment).

You may say 'I understand we may need two different software module, but why do we need two different Hardware module and bother to replace it depending on use model ?'. It is purely because of the cost. For users, it would be the best to use a single / best performing hardware to cover everything and there is no technical restriction for this. Development / Manufacturing cost for different hardware is a harsh reality. We cannot get everything in single penny.




Connectivity vs Testing


When do we need a Cellular network simulator ? As a person who are playing with various kind of cellular network simulator as part of job and as a hobby, I have roughly two cases (two types of motivation) that make me want to have this kind of network simulator. One is just to have 'Connectivity' and the other one is to have 'Testing Capability'.


Connectivity : By Connectivity, I mean 'simple Radio Access capability with interface to ethernet interface to local server or public internet. We don't need to configure very details of Network part (e.g, Radio Bearer, QoS and detailed Power control etc). We just need a simple/low cost box that is like WLAN AP (Access Point). If I just plug in the equipment (e.g, LTE Network simulator) to ethernet socket and turn on my UE (mobile phone) and I can get access to YouTube video or any public web site, this is enough in terms of connectivity. Technically you can implement this kind of equipment at very low cost, but we couldn't get this kind of simple and low-cost equipment mainly because main stream test equipment vendor didn't make this kind of equipment. However, with evolution of SDR (Software Defined Radio) in recent years, now we have several low cost solutions that gives pretty good Connectivity especially in LTE. Some solutions are Open source mostly based on low cost hardware like Ettus N series and a Linux PC and some solutions are available under the category of 'Private LTE Network'. In near future, you would have very small LTE network with the size of a smartphone based on the hardware like Ettus Embedded Series. (You can google 'SDR LTE' or 'Private LTE' and easily find various solutions for now). This would be a good news for those who want to have private LTE connectivity with some degree of user defined configuration and does not have enough budget to go with high end test equipment, but this may be a threat to main stream equipment ventor.


Testing : If you are interested in performaing more details test and the details of each and every lines of protocol sequence and radio bearer configurations, you may need some of high-end test equipment supplied by main stream test equipment vendor.

    i) Maximum throughput for latest category and Carrier aggregation with more than 3 CC (e.g, 600 Mbps and higher throughput)

    ii) Multiple Radio Access technology in one box (e.g, Not only LTE but also other legacy technology like 2G/3G)

    iii) Various Negative Test/Corner Case test capability

    iv) Real time logging and analysis along with high throughput

    v) RF accuracy even at very low Cell Power (meaning maintaining good SNR even at low cell power)


In user's perspective, of course we want to both types of equipment. However, reality would not go as we hope. Maijor issues are 'cost' and 'mind set'. As I mentioned above, you get the equipment with a relatively low cost if you only need a simple connectivity (cellular data pipe), but you would need to consider huge investment if you want to have detailed testing and analysis/troubleshoot capability. It is mainly because it requires high-end hardware design and a lot of cost to develop, maintain and support those testing capability. Usually there are only several equipment vendors who can afford to such a big investment and it doesn't seem to be that those mainstream equipment vendor wants to release low cost equipment. However, I think time will come when the mainstream equipment vendor should look look into low cost /more accessible equipment because the SDR based/low cost solution provided by some company or open source organization is rapidly expending their capability and they will see more and more pressures directly from end users as well.