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Introduction

This is folder of Matlab code of digital SI cancellation for the full-duplex system. I use Matlab to not only simulate SIC to verify the digital cancellation algorithm but also visualize and test the results from USRP. Basically, they can be classified into 3 parts: SIC for sine wave, SIC for QPSK signal and test code for TX, RX from USRP.

For the detail of digital SIC algorithm, please refer to the digital cancellation part of Full Duplex Radio[1].

SIC for sine wave

This part contains code for the simulation and test for single sine wave and is located in dg_sic_sine folder. Main source files are dgSIC_sine_0.m, dgSIC_sine_rx_1.m and dg_sic.m, mat_generation.m are functions that most related to them. It also contains some data file.

The example of this part is digSIC_sine_rx_1.m, which can run from Matlab and show the result given necessary file.

  • digSIC_sine_0.m is for the simulation for single sine wave. It generates single sine wave as TX and sine wave with AWGN and ISI as RX. By running it, we can test the algorithm and get about 50 dB linear cancellation.

  • digSIC_sine_rx_1.m is for the test of SIC algorithm in Matlab. It obtains TX and RX signals from UHD transceiver for single sine wave and then calls dg_sic() and mat_generation() to do the cancellation. It can both do the linear and the nonlinear cancellation by changing the parameter dim. Since it is for offline cancellation, the program only works for TX/RX signal with length of signal_length. A signal consists of preamble(not necessary for sine wave), pilot and data and I use an estimator which scans from i-k to i+k-1. Their length are defined as estimator_length, pilot_length.

    By default, it will read from sine_data.mat to get TX and RX signal and do the cancellation.

  • dg_sic.m is the SIC function for dig_sine_rx_1.m. It does synchronization for TX and RX signal, does the cancellation (linear and nonlinear are both allowed) and plot the result using general function figure_sic.m.

SIC for QPSK signal

This part contains code for QPSK cancellation like main_qpsk_r.m, main_qpsk_for_c.m, dg_sic_qpsk.m and qpsk_generation.m and data files like tx_file, rx_file.

The example of this part is main_qpsk_for_c.m, which can run from Matlab.

  • main_qpsk_r.m is used for test of SIC algorithm in Matlab. Like digSIC_sine_rx_1.m, it obtains TX and RX signals from UHD transceiver for QPSK signal and then does the cancellation. Note that it need setting for the file path. Different from single sine wave, it needs manually setting the delay between TX and RX by choosing tx_beg through TX and RX plot. So the usage of this code is as following:

    1. uncomment the part for writing TX into file, set a break point after that and run the program;
    2. run UHD transceiver for QPSK (qpsk_transceiver1.cpp) and get the RX signal;
    3. comment writing TX part and use part below to read RX signal, do the cancellation and show the result.

  • main_qpsk_for_c.m is similar to main_qpsk_r.m and the only difference is that it doesn't generate TX signal itself and read both TX and RX QPSK signal from UHD transceiver, which makes it more convenient for the test of QPSK cancellation. After visualizing the TX and RX, we can find the delay manually and set the start of buffer st1, st2. You can also change the length of signal, pilot, estimator and preamble.

    By default, it reads binary file tx_file, rx_file as an example of QPSK cancellation.

  • qpsk_generation.m is a function used to generate QPSK waveform from a symbol stream. Given roll-off coefficient beta, span of symbol and samples per symble, it can generate corresponding QPSK waveform by interpolation and convolution with raised cosine filter. It is used in main_qpsk_r.m.

  • dg_sic_qpsk.m is the SIC function for QPSK signal. It uses specified signal of TX as preamble to do the synchronization, which only works when TX, RX are not far from each other.

Test code for TX, RX from USRP

Source files that have prefix "test" are test code for signals from USRP like TX, RX and cleaned signal. Generally, they read from a path where UHD program writes data into file and then visualize the cancellation result or TX/RX signals.

The example of this part is test_trans_canc_rt.m.

  • test_in.m is only for visualization of initial TX and RX signal. Since it is harder to find the problem after the program processes the signal, I use this code to observe the original signal. However, if you want to visualize a signal in your own path, you have to modify the path. What I usually do is to add an option to the path, txname, rxname arrays.

    Notice that it reads data in 2 rows for most UHD programs write complex signal into file before. And it only plots the real part of the signal by using 1st row of a1 and a2, which can be easily changed.

  • test_trans_canc.m is for visualization of pilot, data and spectrum of TX, RX and cleaned signal (x, y, y_clean). Notice that it reads data in 1 row since UHD cancelers write only real data into file. Like above, you need to modify the build_path and filename to add new data file to visualize.

  • test_trans.m is early version of test_trans_canc.m, which can only plot data and spectrum of sine wave.

  • test_trans_canc_rt.m is for continuous visualization of spectrum of TX, RX and cleaned signal and I often use it to see the result of real time cancellation. Settings for build_path and filename are the same as above. When id = 5, it will use data file from mt_data file and display the result of real-time UHD cancellation continuously and the cancellation in dB will be printed.

Other functions

  • figure_sic.m is used to plot all the TX and RX results: channel h, preamble, pilot, data and spectrum. It is often called by simulation code where preamble and h can be easily obtained.

  • mat_generation.m is used to generate TX matrix given nonlinear dimension.

  • pickpeaks.m is a function to find the several biggest peaks and is used in the synchronization part of dg_sic.m and dg_sic_qpsk.m. It is a source file from Mathworks and thank Antoine Liutkus for his work. For more details, refer to pickpeaks(V, select, display)[2].

  • plot_sic.m is a function to plot the spectrum result of TX, RX (SI) and y_clean (residual SI). It is called in figure_sic.m.

  • sic_db.m is a function to calculate the precise cancellation result in a certain band in dB. It is called in test_trans_canc.m and test_trans_canc_rt.m.

Reference

[1] Bharadia, D., McMilin, E., & Katti, S. (2013). Full duplex radios. ACM SIGCOMM Computer Communication Review, 43(4), 375-386.

[2] Antoine Liutkus. Scale-Space Peak Picking. [Research Report] Inria Nancy - Grand Est (Villers-lès-Nancy, France). 2015.