Wireless Digital Video Broadcasting with RF Beamforming
This example shows how to model a digital video broadcasting system which includes phased array antennas. The baseband transmitter, receiver and channel are realized with Communication System Toolbox™. The RF receiver is implemented with the RF Blockset™ Circuit Envelope library, and the transmit and receive phased array antennas are constructed using Phased Array System Toolbox™. The 4 x 4 planar phased array feeds a 16 channel receive module that includes phase shifters to enable RF beamforming.
This example requires the following products:
- Communications System Toolbox
- Phased Array System Toolbox
- RF Blockset
The system consists of:
*Baseband Transmitter subsystem is responsible for generating a 64-QAM, 2 MHz bandwidth signal that adheres to the DVB-C standard.
*A planar transmit array with controls for the number of antenna array elements, transmit frequency, radiation pattern and radiation direction.
*Channel effects in the form of path loss and noise.
*A phased array receiver consisting of 16 elements arranged in a 4 X 4 grid. This includes design parameters for operating frequency, element radiation pattern, and receive direction.
*A 16 channel RF receiver module consisting of LNAs and phase shifters. The network of 2:1 power combiners is constructed twice to emulate a typical design process. The initial design employs ideal dividers from the RF Blockset Junctions library used as behavioral combiners, while the second implementation uses actual combiners modeled by S-Parameters blocks from the RF Blockset Circuit Envelope library with measured data supplied via a Touchstone(.s3p) file.
*Transmitter and receiver arrays are implemented using Phased Array System Toolbox and Simulink® MATLAB Functions blocks that generate embedded C code for faster simulation. The receive side phased array mask provides an option for performing beamforming.
*Baseband Receiver subsystem is responsible for extracting the transmitted signal. The receiver includes simple models for correcting effects of phase offsets and gain control.
*Diagnostics are available at various stages in the system using transmitted and received constellations, bit error rate calculations and RF spectrum.
model_ideal = 'simrfV2_wirelessdvb_beamform_ideal'; open_system(model_ideal);
Designing with Ideal Components
An initial design may use ideal components to speed up the overall design process. For example, use ideal dividers from the RF Blockset Junctions library as combiners in the Receive Antenna Array. This removes the need for Phase/Frequency offset compensation in the Baseband Processing Receiver until the hardware is selected.
open_system([model_ideal '/RF Receiver'], 'force');
The Manual Switch in the Baseband Processing Receiver is used to bypass the Phase/Frequency Offset Cancellation block until a manufactured combiner is selected.
open_system([model_ideal '/Baseband Processing Receiver']);
bdclose(model_ideal); clear model_ideal;
Designing with Real Components
Use S-Parameters block to model a real combiner. There are several options available to characterize the behavior of this block; one approach utilizes a data file directly while another approach provides a rational model of the data. For the latter approach, utilize the rationalfit function in RF Toolbox™, save the resulting parameters in the base workspace and use them in the S-Parameters block. In this example the measured data described in a file is used directly. To compensate for the Phase/Frequency effects of the combiner, switch the Manual Switch position in the Baseband Processing Receiver to include the Offset Cancellation block.
model = 'simrfV2_wirelessdvb_beamforming'; open_system(model);
Run the Simulation with Default Settings
The transmit side planar array is chosen to have 16 elements and transmits along the main beam (azimuth = 0 deg. and elevation = 0 deg.) at a frequency of 2 GHz. An isotropic radiation pattern is chosen for each element. Note that the power dividers introduce a phase shift at 2 GHz. This is estimated and corrected in the Baseband receiver subsystem.
Modifying the Receive Direction and Simulate
Modify the receive direction by changing the Receive Direction mask dialog parameter of the 16-element Receive Antenna Array. The angle chosen decreases the signal strength due to the proximity of a null in the array radiation pattern.
set_param([model '/Receive Antenna Array'],'RecDir','[20;25]'); sim(model);
Improve RF Reception with Beamforming
Enable the Beamforming option for the 4 X 4 phased array on the receive side. This mask option will automatically adjust the phase shift of each channel in the RF Receiver subsystem. Run the simulation to observe an increase in the received signal level.
set_param([model '/Receive Antenna Array'],'BeamForm','on'); open_system([model '/RF Receiver'], 'force');
bdclose(model); clear model;
S. Emami, R. F. Wiser, E. Ali, M. G. Forbes, M. Q. Gordon, X. Guan, S. Lo, P. T. McElwee, J. Parker, J. R. Tani, J. M. Gilbert,, and C. H. Doan, "A 60 GHz CMOS Phased-Array Transceiver Pair for Multi-Gb/s Wireless Communications," in IEEE Int. Solid-State Circuits Conf. Tech. Dig., Feb. 2011, pp. 164-165