5G Channel Sounding Reference Solution

5G Channel Sounding, Reference Solution

Accelerate 5G Channel Sounding Research with mmWave, Ultra-broadband and MIMO Solution

Introduction

Current LTE/LTE-Advanced standards lack the performance needed to keep up with market demand for higher data throughput, greater cell capacity and more reliability. Thus, new 5G cellular standards are being developed to achieve the desired performance goals and to co-exist with 4G technologies. New wireless channels are being considered at frequencies below 6 GHz such as 3.6 and 5 GHz. However, there is very limited spectrum available below 6 GHz so mmWave frequencies that can incorporate wide-bandwidth transmissions are being investigated for next generation cellular systems. New air interface standards being investigated above 6 GHz include 15, 28, 32, 38, 45, 72 GHz and higher.

In order to define new channel models at mmWave frequencies, research and design engineers need to understand how the radio signal will propagate at the given frequencies. Key obstacles at these higher frequencies include path loss, Doppler Effect, environmental effects such as oxygen absorption and rain, and channel sounding techniques are used to analyze the impact of these obstacles on signal transmissions. These techniques use mathematical models to extract the characteristics of the wireless channel to determine the channel performance at a given frequency. The Keysight Technologies, Inc. Channel Sounding Reference Solution combines Keysight’s metrology grade, off-the-shelf hardware plus software for 5G channel sounding measurements and optional services enabling in-depth analysis of potential 5G channels.

5G Channel Sounding Test Challenges

Evaluation of time-varying, multi-path frequency bands requires highly complex, multi-channel instrumentation that includes precise timing and synchronization and advanced software to capture and characterize a potential channel. Key measurements include:

–Frequency response by amplitude and unwrapped phase and group delay

–Absolute path loss and power delay profile (PDP)

–Angle of Arrival (AoA)

–Angle of Departure (AoD)

Key test challenges faced by design and research engineers include:

–Ability to generate and analyze wideband, MIMO signals at mmWave frequencies

–Ability to do calibrations for wideband transmitter and receiver test that include vector pre-corrections, IQ freq response and IQ imbalance, channel to channel skews

–Significant time to collect and manage huge amounts of data

–Tx/Rx timing and synchronization to get accurate measurements

5G Channel Sounding Reference Solution

To help address these test challenges, the 5G Channel Sounding Reference Solution combines hardware, software and measurement expertise providing the essential components of a 5G channel sounding test platform. This enables engineers and researchers to use, enhance and modify the test platform as required to meet specific test needs such as scaling channel count, transmitting and measuring in the mmWave frequencies, wide transmission and analysis bandwidth, and capture of data for post processing.

With parallel acquisition at the receiver, the multiple signals are captured and sent to the digitizer FPGAs for processing. The Reference Solution software includes an option to perform real-time correlation and processing of the Channel Impulse Response (CIR) data in the M9703A digitizer FPGA, speeding up the data collection process and drastically reducing the amount of data that needs to be collected. Post processing channel parameter estimations can also be made using custom algorithms in SystemVue.

Calibration and synchronization are critical to achieving accurate measurements such as absolute delay, AoA, AoD. In addition to the system-wide calibrations, the phase coherent measurement channels include channel to channel corrections for phase and magnitude skew. The Reference Solution enables precise synchronization between the Tx and Rx by using the high precision 10 MHz LO (provided by Rubidium clocks) and triggering.

The 5G channel sounding Reference Solution supports applications up to a 44 GHz frequency range with 2 GHz stimulus and 1 GHz analysis bandwidth up to 8 channels. Custom solutions to support higher frequency ranges, wider analysis bandwidths and a larger number of channels are also available. If this is required for your application, please contact your Keysight representative.

Reference Solution Architecture

The following shows a simplified block diagram of the 5G Channel Sounding Reference Solution. This solution is scalable and flexible. It can be scaled to address more channels by adding additional downconverters and digitizers or higher frequencies using Keysight “up/down converters” per channel.

5G Channel Sounding Software

Channel sounding characterization requires several steps. Software is used for the following:

–To control instruments, make highly synchronized measurements and generate accurate absolute delay results

–To generate a channel sounding signal and auto correlate to get CIR data

–To use mathematical models for post processing of the data and extract channel parameters

–To perform system-wide calibrations to ensure accurate results

Channel sounding signal

A channel sounding signal is a critical part of the sounding system. Keysight provides several options for generating channel sounding signals using its signal generation tools such as SystemVue, Waveform Creator, or Signal Studio. Keysight’s professional services team also creates custom sounding signals.

CIR and channel parameter extractions

The Reference Solution includes software to capture, correlate and process the CIR data, which can be taken offline for channel parameter extractions. Different algorithms can be used to extract the channel parameters - each with its own benefits and drawbacks. Keysight offers custom channel parameter extractions based on the SAGE algorithm using the SystemVue platform.

Simulation with new channel models

Once the channel modeling is complete, the SystemVue 5G libraries can be used to provide link-level simulation of new channel models with scaling schemes for MIMO channels, as well. The integrated simulation environment allows users to investigate, implement and verify new designs through hardware in the loop.