sdr_matlab_ofdm_802.11a's Introduction

SDR_Matlab_OFDM_802.11a

This simple OFDM demo is based on IEEE 802.11a OFDM format for testing SDR hardware.

Using Software Designed Radio (SDR) to transmit OFDM signals at 5 GHz.

Transmitter and Receiver hardware : Zedboard (Xilinx Zynq®-7000) + AD9361 (Analog Device-FMCOMMS3)

Software needed :

Matlab R2016a
support package for Xilinx Zynq-Based Radio (R2016a version)

Before executing this code, please follow this tutorial to install support package for Xilinx Zynq-Based Radio in Matlab.

Code Structure :

Please open multiple Matlab windows to run Hardware_TX.m and Hardware_RX.m respectively.

Hardware_TX.m

TX_signal.mat

OFDM_TX.m

data_Payload_1.mat
data_Payload_2.mat
oversamp.m

Hardware_RX.m

OFDM_RX.m

Long_preamble_slot_Frequency.mat
setstate0.m

RX_test

RX.mat
RX2.mat

GUI :

GUI_TX

GUI_RX

Video Demo : https://www.youtube.com/watch?v=gNmMxtsWckw

System Model :

OFDM Block Diagram

Code Function :

Implemented

Data Signal Mapping
Packet Detection
Coarse/Fine Frequency Offset Estimation & Compensation
Channel Estimation & One-Tap Equalizer
Data De-Mapping

Not implemented yet

AGC (Auto Gain Control)
Fine Symbol Timing Estimation
Convolutional Decoding
De-Interleaving
Frame check calculation (It assumes every packet is the same length)

TX System Model

Short Preamble

Long Preamble

Payload

TX signal

TX RX Hardware Parameters

Center Frequency	5 GHz
Baseband Sample Rate (Bandwidth)	20 MHz
Ts (Sampling time)	50 ns
Samples Per Frame	3000
PC Host IP address	192.168.3.1
TX IP address	192.168.3.2
RX IP address	192.168.3.3

The way to change Hardware IP / Mac address

Edit newip.sh file in SD card

# Flush existing config
ip addr flush dev eth0
ip link set dev eth0 down
# Set up new config
ip addr add 192.168.3.3/24 dev eth0
ip link set eth0 address 00:0A:35:00:01:23
ip route add default via 192.168.3.1
ip link set dev eth0 up

Then, use router DHCP hand setting mode to distribute network configuration parameters :

RX System Model

"Delay and Correlate" algorithm for Packet Detection

Packet Detection (normal case) , Threshold=0.75

Packet Detection (problem case & deselect the imperfect packet)

Coarse CFO Estimation & Compensation

Fine CFO Estimation & Compensation

Channel Estimation & Equalizer

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sdr_matlab_ofdm_802.11a's Issues

Parameter Settings in file "OFDM_RX.m"

Recently, I am reading the core code about the frame detection described in your repository called SDR_Matlab_OFDM_802.11a_2.4GHz. But some parameters setting confuse me. To be exact, i do not understand the intention of parameter Length_over_Threshold and why the value of Length_over_Threshold should be 230.

For another, the nexe code block confuses me.

for x=1:length(Packet_Front_idx)-1
    if M_n(Packet_Front_idx(x)+Length_over_Threshold)>Threshold;
        idx=Packet_Front_idx(x)+L+1; 
    end 
end

If you are free, I would be more than thankful to receive your answers to my questions.

How to measure Doppler Frequency not Carrier Frequency Offset(CFO)?

I could follow the contents as given and run the code with the zedboard. I need to measure Doppler Frequency or the propagation time from tx to rx. Can you give some tips to measure about it?

By the way, the Doppler frequency is related to CFO as estimated on the code, but the size of it is quite big around over 30,000Hz. Should I check the FFT of the received signal?

some sentences in the code block

Threshold_graph=Threshold*ones(1,length(M_n));
Threshold_graph(idx-L-1)=1.15;

I face some problems in understanding the intention of these two sentences. If you are free, would you please give me some guidance? thank you ahead of time.

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