This document describes a student's thesis project on implementing an OFDM communication system using three DSP boards to represent the transmitter, channel, and receiver. The goals of the project were to accurately synchronize data packets in the OFDM system and simulate the wireless channel and effects of noise. At the transmitter, a preamble signal and additive white Gaussian noise were added to simulate the full system and enable synchronization. The receiver used delay and correlation algorithms for packet detection. Performance was analyzed by measuring bit error rate and packet missing rate over simulated wireless channels with varying signal-to-noise ratios. The system was able to reconstruct the original voice signal, demonstrating its potential for various communication applications.

1. Process of packets synchronization and simulation of the wireless channel
in the OFDM system - National Taipei University of Technology
Student: Chien-Cheng Lai Supervisor : Yuan-Fu Liao
Orthogonal Frequency Division Multiplexing transmission(OFDM)
system construction of the subject refers to DVB-T(Digital Video
Broadcast- Terrestrial) Standard, using three TI DSP boards-DSK
6416 which are separated transmitter, channel and receiver
individually in the way of software(C programming) to implement a
complete OFDM communication system that comes with real-time
ability.
1.Abstract 2.Content
The point of the subject is that synchronization process packets of
OFDM System can be coped with accurately. Wireless channel
simulation between transmitter and receiver and preamble signal were
added in order to simulate the affection of whole communication
system and the implementation of synchronization in front of packets
encoded by the method of multi-layer(Additive White Gaussian Noise,
AWGN) and detecting packets by delay and correlation algorithm at the
transmitter.
inbuf1
RX
End
3840 3840 inbuf
0 7680
Delay & correlation algorithm
Packet detection
start_of_the_packet
If Else
Down 4 rxxI =rxxQ=1636symbols
Remove GI(4 symbols)
64 FFT
Demapping(480symbols)
Convolution decode->120 symbols
Deinter_leaver
RS decode->66symbols
GSM 6.10 decode
LPF(fs=96k,fc=1k)
38400
3.OFDM Flowcharts and Diagram
Receiver Flowchart
Transmitter Flowchart
.
Channel
Transmitter
Receiver
Microphone
AWGN
Speaker
Additive White Gaussian Noise on the channel, AWGN
Data Timing Diagram of the Transmitter Noise Data timing Diagram of the ReceiverOFDM Communication System Picture
4. QAM Table Simulation
Ideal 16 QAM Table
Receiver QAM Table of none passing noise channel
5.OFDM Communication System via AWGN Channel
Missing Rate of Packets via AWGN on the Receiver
BER(Bit Error Rate) of OFDM System Chart
6、Conclusion
The original voice has been restored from decoded signal via the OFDM system, as an
infrastructure of communication system. By reducing BER(Bit Error Rate), the system will be
applied for various communication system which makes it more complete.
3840
Start
Insert pilots
64IFFT
GI addition(4 symbols)
txI=txQ=Preamble 160
Up4 ofdm_upI_tmp[4*i+3]
LPF(fs=96k,fc=24k) 1636symbols
ofdm_I_tmp=408symbols=ofdm_Q_tmp
2 Preamble IQIQIQ 2
720 3664
outbuf
LPF (fs=96k,fc=4k)
GSM 6.10 encode
RS(15,9) ->120 rs_symbols
Convolution encode (2,1,2)
Inter_leaver
QAM I=Q= 240symbols
392
TX
Transmitter Channel
Receiver
Microphone
Speaker
Preamble
Data
SNR Packets Missing Rate of Receiver
10dB 0.0625%
15dB 0.05%
20dB 0.0375%
25dB 0.025%
30dB 0.025%