5Qs on 5G: Rohde & Schwarz sits our test on testing

The latest to take our quick 5G questionnaire is Arnd Sibila, Technology Marketing Manager, Rohde & Schwarz. Arnd brings a test perspective to 5G, with R&S involved in supporting many of the research initiatives current in Europe and globally at the moment. The crucial questions are, will 5G require new test capabilities, and if so, what are they? 

What is R&S’s role in the development of 5G?

As 5G requirements are becoming clearer, it also becomes apparent that these requirements are extremely challenging and therefore quite diverse technologies and concepts need to be discussed. There is a need to improve the understanding of potential new air interfaces at frequencies above current cellular network technologies, from 6 GHz right up to 90 GHz, as well as advanced antenna technologies such as massive MIMO and beamforming.

Rohde & Schwarz  is committed to supporting the wireless communications industry with the solutions needed to meet the challenging requirements and to investigate, develop and standardise 5G.

What are the key testing challenges for 5G?

For the cellular industry, spectrum above 6 GHz is a new area and there is a need to understand the new ideas and concepts under discussion. Consequently researchers require flexible test and measurement solutions to generate and analyse wideband signals with carrier frequencies ranging from 6 GHz to more than 60 GHz.

Channel measurements/channel sounding is one specific topic of the “high frequency/ high bandwidth” challenge described above. The new spectrum discussed in various research projects ranges from 6 GHz to more than 60 GHz. The entire industry needs to learn how signals in emerging high-frequency bands with very wide bandwidths propagate through the radio channel. Channel sounding is a process that allows a radio channel to be characterised by decomposing the radio propagation path into its individual multipath components. This information is essential for developing robust modulation schemes to transmit data over the channel.

Currently, quite a few channel measurement studies address specific frequency bands and specific environments, but the industry still needs to define channel models at frequencies well above 6 GHz . Therefore research institutes, universities, mobile network operators, and major infrastructure and terminal / chip set providers are conducting extensive channel measurement campaigns in order to define channel models for standardisation bodies like 3GPP.

Antenna Array characterization/Massive MIMO/beamforming: In particular at higher frequencies, the significantly increased propagation path loss has to be compensated by higher antenna gains. Additionally, adaptive beamforming algorithms – even on a per user device basis – are required and can be implemented using active antenna technology. Antenna Arrays are not only emerging with 5G, but they are a means to improve system performance of 4G / LTE networks at deployed frequencies such as 2.6GHz.

New BS antenna array test concepts (Over-The-Air (OTA)) need to be developed for static beamforming measurement as well as dynamic beamforming verification

For testing Antenna Arrays, access to connectors of antenna elements is only possible in the design phase of an antenna array, but potentially not later when the array has to be characterized. Consequently new BS antenna array test concepts (Over-The-Air (OTA)) need to be developed for static beamforming measurement as well as dynamic beamforming verification.

What 5G research initiatives have you been involved in so far that you can talk about?

There are several research activities underway globally. Rohde&Schwarz is active in the following:

  • Horizon 2020 – 7-year EU research and innovation program (2014 – 2020). It is the 8th Framework Program (FP8) funded by the European Union (EU). R&S participates in the mmMAGIC project (mm-wave Based Mobile Radio Access Network for Fifth Generation (5G) Integrated Communications).
  • 5GPPP, the 5G Infrastructure Public Private Partnership project is a EUR 1.4 billion joint initiative between the European ICT industry and the European Commission
  • 5G Innovation Centre: R&S is founding member of the 5GIC project hosted by the University of Surrey (5G research center in the UK).
  • China: R&S is member of the Future Forum
  • Korea: R&S is member of the 5G Forum, the Korean industry-academy-R&D cooperation system
  • Germany: R&S supports the 5G Lab Germany (TU Dresden)

What modifications and developments has R&S made to products and solutions to enable 5G R&D?

Test and measurement solutions from Rohde & Schwarz are perfectly suited for the demanding research projects involved with 5G. The R&S FSW signal and spectrum analyzer provides unmatched measurement capabilities up to 67 GHz without the need for external down conversion components. Above 67 GHz a family of harmonic mixers (R&S FS-Z75/Z90/Z110) is available to reach absolute frequencies as high as 110 GHz. The R&S FSW supports an in-build demodulation up to 500 MHz bandwidth, which can be extended to enable 2GHz signal analysis with an external Rohde & Schwarz oscilloscope. Additional software options complement the flexible solution. The R&S FSW-K70 option flexibly analyses digitally modulated single carriers down to the bit level and the R&S FS-K96 OFDM analysis software enables modulation measurements on general OFDM signals.

For demanding signal simulations, the R&S SMW200A vector signal generator provides high quality signals up to 40 GHz including inbuilt channel emulation capabilities. The R&S SMW200A configured as a two-path instrument offers 20 GHz maximum frequency on each RF output. This configuration is ideally suited to provide both LO and IF to an external up-converter out of and controlled by a single instrument. Therefore signal generation for frequencies higher than 40 GHz can easily be realized. The internal ARB functionality supports playback of e.g. Matlab designed waveforms with a bandwidth of up to 160 MHz. The in-build I/Q modulator supports 2 GHz bandwidth when connecting an external baseband generator to the analog I/Q ports, such as the R&S AFQ100B UWB signal and I/Q modulation generator that provides a bandwidth of 528 MHz (RF).

For antenna array characterization in the design phase (where access to antenna elements is available) the Multiport Vector Network Analyser R&S ZNBT is well suited. Upgradable to 24 ports this amount of antenna elements can be simultaneously tested (incl. active return loss) since all ports can be stimulated simultaneously so that crosstalk between antenna elements can be identified, which is the important mode of operation in real networks.

Over-the-Air (OTA) test concepts for antenna arrays need to be developed for static as well as dynamic beamforming verification. These OTA test concepts are currently in discussion with our key customers. Without full control of the beam steering processed by the base station test modes need to be defined. 3GPP RAN4 started specification of OTA requirements, which will need to be enhanced in particular to cover dynamic beamforming verification. A strong alignment and cooperation between infrastructure suppliers, operators and T&M suppliers like Rohde & Schwarz is essential.

5G will bring additional air interface technologies (waveform, multiple access schemes, coding mechanisms, etc.) that will also drive the need for inter-technology interference measurements

 Will 5G see a different environment in terms of testing methodologies, product development and acceptance, or do you think it will be similar to LTE?

LTE will still play a major role for macro cellular network coverage also in the years to come and there will be evolutionary approaches to 5G that will integrate LTE into SW defined air interface concepts under the 5G umbrella.

5G will bring additional air interface technologies (waveform, multiple access schemes, coding mechanisms, etc.) that will also drive the need for inter-technology interference measurements (like e.g. in-device coexistence tests).

In particular the Antenna Array characterization and verification requirements will drive a completely new area for testing. Huge number of antenna elements per array and the lack of access to antenna connectors will require Over-The-Air test methods.

The trend towards C-RAN (Cloud based RAN) is even increasing this importance. The traditional Base Station functions will be split into a baseband part (eventually moved into the cloud (server based / “baseband hoteling”, etc.)) and an Active Antenna Array part (including active RF components like the power amplifier) that will be connected via a fiber interface.

Security relevant aspects like concentrated radiated power (e.g. by pencil-like beams) will become possible and potentially require verification as part of a certification procedure.

Summing up the above, comprehensive test functionality including LTE / LTE-Advanced (potentially even covering technologies like WLAN) will need to be enhanced by new 5G testing aspects.