What happened to the RF?

Blog Post created by AlyssaRao Employee on Jul 7, 2016

This is the second of three posts covering the highlights from the recent webcast, Understanding 5G and How to Navigate Multiple Physical Layer Proposals. In the first post, we talked about the different waveform techniques currently being investigated for 5G. Today I’m going to share a case study of a possible 5G modeling and simulation example at 28 GHz frequency band and 500 MHz bandwidth.

Physical layer designers know that their goal is to consolidate the hardware requirements of a network to enable the successful transmission of data. In order to do that, they need to consider both baseband and RF modeling together. In this example we will consider a 28 GHz frequency band and 500 MHz bandwidth. You can see the setup in the block diagram below.


Block diagram of a 28 GHz frequency band and 500 MHz bandwidth. (Photo credit: Sang-Kyo Shin’s Understanding 5G webcast)

We chose a Filter Band Multicarrer (FBMC) Source for modeling the baseband in the time domain. For 5G opportunities, FBMC is being considered by many as a viable alternative to Orthogonal Frequency Division Multiplexing (OFDM).  FBMC tends to have lower Adjacent Channel Leakage Ratio (ACLR) than OFDM. In this model we combined the Baseband and RF blocks. Both the baseband and RF designers will need to work together for this simulation to be successful. Let's consider the spectrum outputs of each.


FBMC Baseband Spectrum and RF spectrum. (Photo credit: Sang-Kyo Shin’s Understanding 5G webcast)

We already know FBMC already has good performance, and when we consider the FBMC Baseband Spectrum output it looks pretty good. But what happened to the RF?

When we consider the RF spectrum we see out of band leakage. What can we do to meet the spectral requirement of the transmitter signal? Experienced physical layer designers probably know the answer. We need to address the Peak-to-Average Power Ratio (PAPR) problem. This is a common problem for both OFDM and FBMC.  There are many PAPR reduction methodologies being researched in signal processing for 5G today. One of the latest techniques currently being investigated is clipping.  These researchers are using models and simulation such as this one to compare performance. Find out more by watching this webcast.