When you are used that a mobile network consisting of lots of boxes in a huge data center it's a strange feeling when you go to a measurement and testing company like Rohde and Schwarz and you find a whole network from the base station antenna to the servers in the core network condensed in a single box sitting on the table. I've seen devices like this in the past in some labs but never had the time to take a closer look. This year at the Mobile World Congress, I decided to pay Rohde and Schwarz a visit to have a closer look.
The level of detail that can be analyzed is breathtaking. It starts at the physical layer where the tester can veryify that the mobile to be tested modulates the signal correctly and goes up to messaging to the UMTS SGSN or LTE SGW for things like network attach, bearer setup, etc. The tester can even run of the shelf server programs like VLC so video streaming and other sorts of throuput tests can be made with real applications on top.
New network technologies such as LTE are developed step by step, usually starting at the physical layer. So far, I always wondered how one could already test some layers when the software for others has not yet been written. After the demo at the booth I have a much better idea of how that works in practice. So in the first stages, when only layer 1 and parts of layer 2 exists, you pretend on both sides that a bearer, IP address, etc. have previously been negotiated and set those to fixed values. After that you just pump IP packets over the interface to test mobile behavior, modulation, use of sub-channels, etc. Everyhting automated with testcases against the 3GPP test specifications of course. As the protocol stack evolves, more and more components can be included in the test.
Another thing I discovered at the R&S booth was a test environment for network based A-GPS. While the Nokia A-GPS in my N95 connects to a Nokia server on the Internet to download ephemeris information to kick-start the GPRS chip, there is also a network based variant to download the information from the base station. I was not aware that this was going forward but since R&S has a tester that simulates it and a public mobile that uses it, some operators and mobile manufacturers seem to implement it. I need to have a closer look and dig a bit once I am back from MWC.
And finally, I was also shown their mobile testers to debug live networks. Depending on what a network operator or other interested party is prepared to spend, they have mobiles with test and monitoring software (e.g. on an N95) up to boxes that record the complete UMTS band and decode a carrier down to the physical layer. Makes my mouth water.
Thanks for the excellent tour, I thoroughly enjoyed it!