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Lab. 13 SISO Wireless System I

In a typical communication system, receiving starts with synchronization.For a packet-based system, it includes

– Packet detection

– Carrier frequency offset (CFO) estimation

– Symbol timingTo recovery the transmit data, we also need

– Equalization To facilitate the operations, preambles are added before the payload data. We will consider a packet-based wireless system with flat-fading channel.

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Define the packet with the following format :

Preamble:– Each packet has 5 short preambles and 1 long preamble.

– Packet format :

– Short preamble Length = 16 samples (for packet detection and CFO

estimation)

– Long preamble Length = 32 samples (for symbol timing and channel

estimation)

S S SS S L Data

S : short preambleL : long preamble

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Transmitter:

Digitalmod.

Addpreamble

Up-sampling

PulseshapingPC

FPGADAC

EMIF

RF

Ethernet

Practice 1: – Implement the four modules of the transmitter in Matlab to

observe each input/output signal.

– Cascade the four modules and observe the input/output signal.

– Practice 2:– Implement the four modules with C.

– Run the DSP to see if the output signal matches the Matlab result (to/from PC).

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Digitalmod.

Addpreamble

Up-sampling

Pulseshaping

PC

Ethernet

Chapter -5

Receiver:

EMIFADC FPGA Packet

detectionCFO

Est./comp.RF

Symboltiming

Matching/down sam.

Channel est./EqualDetectionPC

Ethernet

SR SR

OSRSRSRSR

SR: symbol rateOSR: oversampled rate

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Packet detection:– Calculate autocorrelation of the received signal

– Normalize with the signal power:

– Decision statistic:

– If m(n) exceeds a threshold, a packet is claimed detected.

1*

0

( ) ( ) ( )L

k

C n r n k r n k D

1 12*

0 0

( ) ( ) ( ) ( )L L

k k

p n r n k D r n k D r n k D

2

2

( )( )

( )

c nm n

p n

Chapter -7

Example:– D=16 、 L=16

– Threshold= 0.7

Threshold

Carrier frequency offset (CFO) estimation:– The oscillator frequencies of Tx and Rx are not the same in

general.

– The downconverted signal:

Then,

Compensation:

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*

*

2

j n Dj n

j n Dj n

j D

E x n e x n D e

E x n e x n e

x n e

( )( ) ( )t t rrj n j nj n j nx n e e x n e x n e

1*

0

( )ˆ( ) ( ) ( )

L

k

C nC n r n k r n k D

D

ˆ( ) ( ) j nr n r n e

Symbol timing: – Cross-correlation of received signal and a known reference

signal (preamble)

– Example:

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21*

00

ˆ arg max ( ) ( )L

nk

n r n k t k

t(k): a known reference signal

Practice 3:– Implement the three modules in the receiver with Matlab.

– Observe each input/output signal.

– Cascade the three modules and observe the input/output signal.

Practice 4:– Implement the three modules with C and run the DSP to

see the result is the same as that with Matlab.

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