This example shows how to set up a wireless digital video broadcasting system simulation that includes RF beamforming. The baseband transmitter, receiver and channel are created using Communication System Toolbox. The RF receiver is created using the SimRF™ Circuit Envelope library and the transmit and receive arrays are created using Phased Array System Toolbox. A 16 element (4 X 4) planar phased array at the receiver is used with receive modules with individual phase shifters on each channel for the purpose of beamforming.
This example requires the following products:
Communications System Toolbox
DSP System Toolbox
Phased Array System Toolbox
The system consists of:
*Baseband Transmitter subsystem which is responsible for generating a 64-QAM, 2 MHz bandwidth signal that adheres to the DVB-C standard.
*A planar transmit array which provides control over number of elements, transmit frequency, and radiation pattern.
*Channel effects in the form of path loss and noise.
*A 16 element phased array at the receiver arranged in a 4 X 4 grid which provides control over operating frequency, element radiation pattern, receive direction and calculation of beamformer weights.
*RF receiver with a 16 channel receive module comprised of LNA and phase shifters. The network of 2:1 power combiners is constructed using the S-Parameters block from the SimRF Circuit Envelope library. Each block will use measured data available in a Touchstone(.s3p) file. There are 2 options available to characterize the behavior of this block; the first approach would utilize the data file directly while the second approach involves providing a rational model of the data. To use the second approach we would utilize the rationalfit function in RF Toolbox™, save the appropriate parameters in the base workspace and use them in the S-Parameters block of interest. In this example we will use the data file directly(i.e. the first approach).
*Baseband Receiver subsystem which is responsible for extracting the transmitted signal. The receiver also includes some simple models for correcting effects of phase offsets and gain control. The transmitted and received constellations, bit error rate calculations and spectrum at various stages in the system are available as diagnostics. The transmitter and receiver arrays depend on Phased Array System Toolbox and are implemented in the form of MATLAB functions. The receive side phased array provides an option for performing beamforming.
model = 'simrfV2_wirelessdvb_beamforming'; open_system(model);
The transmit side planar array is chosen to have 16 elements and transmits along the main beam (at 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.
While the simulation is running, modify the receive direction by changing the 'Receive Direction' dialog parameter for the 16-element receive phased array in the Transmit-Receive Arrays, Channel subsystem. The angle chosen results in a decrease in signal strength due to the proximity to a null in the array radiation pattern.
set_param([model '/Receive Antenna Array'],'Locn','[20;25]') sim(model);
Utilize the RF beamforming capability to adjust the phase shifts on each channel. Stop the simulation and enable the 'Beamforming' option in the 4 X 4 phased array on the receive side. This will result in the appropriate phase shifts being applied to the 16 phase shifters in the RF Receiver subsystem. Restart the simulation and observe increase in received signal level
set_param([model '/Receive Antenna Array'],'beamForm','on') sim(model);
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