QPSK Acoustic Software Radio

Orr Srour & Naftali ZonUnder the supervision of

Ami Wiesel

The problem

RF Communication systems, and especially MIMO communication systems are:

expensive have long development time require wide technological knowledge

The need

Besides their public use, in the academic world communication systems are needed for vary of reasons, for example – new algorithms testing.

In many cases, making a real communication system is simply unreasonable.

The goal

Real time communication system. Rapid development Easy to construct, manipulate and

upgrade Modular

The solution

Using ACOUSTIC waves instead of electromagnetic.

Fully software implemented - Simple ordinary computer is enough

We will use the computer as our processing unit (we use Matlab-Simulink), and ordinary speakers and microphones as our antennas.

Systems overview - TOC

Simple SISO receiver/transmitter system Virtually linked SIMO antenna selection Fully SIMO system running the Alamouti

space-time algorithm

System Parameters

We use QPSK modulation Data frequency:

50 symbols/sec = 100 bit/sec Carrier frequency:

800Hz

Communication Protocol

We send data in packets. Each packet is constructed as follows:

Training Sequence Data Sequence

13 symbols 50 symbols

Training Packets

The training sequence are constant predefined series of symbols.

They allow us to distinguish actual data packet from random noise.

They allow us to estimate the propagation channel and reconstruct the data.

Alamouti Transmit Diversity Technique The Alamouti diversity technique allows us

to send data from two antennas to one with the highest theoretical SNR possible, without the need of a delay system or pre-knowledge of the channel.

To do that, the transmission is done using 2 antennas as follows:

Alamouti Transmit Diversity Technique

Where S0 and S1 are two data symbols after QPSK modulation.

Antenna 1Antenna 2

Time tS0S1

Time t + T-S1*S0*

Alamouti Transmit Diversity Technique In order to reconstruct the data, the

following mathematical function is preformed:

0*1*101)10(

110*00)10(

*1

0

0*1

1*0

1~0

~

22

22

nhnhShh

nhnhShh

r

r

hh

hh

S

S

Here h0 and h1 are the two channels propagation factors estimated by the detectors (see below)

“Down to Top” overview – our basic building blocks

We will now introduce our basic building blocks, which will later be shown inside the different type of systems.

Packets Creator

This unit simply receives bits and returns them in packets according to the mentioned protocol.

M-PSK Modulator/Demodulator

These units transform between complex phase symbols and integer symbols

Raised Cosine Filter

This unit both upsamples and filters the input signal, using raised consine filter.

Amplification Vector Creator

When the bits of data are being transmitted, each bit has a unique amplification factor that determines its amplitude.

These bits are sorted in a vector created in the "Amplification Vector Creator unit".

Up Mixer / Down Mixer

The up-mixer block is in charge of shifting the incoming (complex) data into a real carrier signal.

The down-mixer has the opposite functionality.

Amp

Squaring Timing Recovery

The Squaring Timing Recovery block is in charge of sampling the incoming signal at the right time. It uses the knowledge of the number of constant phase samples in the incoming signal.

The Estimator

The estimator block uses the predefined reference training signal in order to estimate the free-air channel propagation factor.

We assume here that the channel can be modeled by a complex number, representing the attenuation, delay and noise the signal has suffered, and that this complex number will not change within the transmission of one data packet.

The Estimator – cont’

All this is done by correlating the incoming signal with the training sequence.

This block:1. rises a trigger flag

representing the reference signal has been discovered and is now over.

2. samples and holds the conjugate phase of the correlation result

3. samples and holds the amplitude of the correlation result.

The Detector

The detector block is in charge of canceling the free-air channel effect of the incoming data.

The Signal Output block

This block is in charge of sampling the actual data and regrouping the different packets into one long vector.

Antenna Selection Amplification For the antenna selection system only

This block is in charge of the creation of the amplification vector for the two antennas, in accordance to the "antenna selection" parameter received from the receiver.

EstimatorFor the antenna selection system only

This block uses two ordinary estimators blocks (mentioned in the SISO system), each for different reference sequence.

In addition to the ordinary estimator outputs, it also outputs the ID of the antenna which had the strongest signal in the receiver.

To AlamoutiFor the Alamouti system only

This block is in charge of transforming the input data into 2 antennas input data, transformed by the Alamouti Diversity Technique mentioned before.

Solve by AlamoutiFor the Alamouti system only

This block has the opposite functionality to the previous mentioned "To Alamouti" block. Its purpose is to demodulate the input signal using the Alamouti Diversity Technique.

Putting it all together

The SIMO Transmitter

Wave Out

Sig

Sig1

Out

Up Mixer

-C-

RefAmp

Square root

Raised CosineTransmit Fi l ter

Data Ready Packets

Packets Creator

M-PSK

M-PSKModulatorBaseband

-C-

Data In

AmpFact

Ref Amp

Amp

Ampli fication Vector Creator

1

AmpFact

Putting it all together

The SIMO Receiver

Putting it all together

The SIMO Receiver

Putting it all together

The Antenna Selection

Putting it all together

The Antenna Selection

Putting it all together

The Alamouti Transmitter

Receiver

Wave In

insig

To Workspace

Est_h0

Est_h1

Sig

Trigger

Output

Solve By Alamouti

Data Input

IsInit

SignalOutput

-C-

Ref1

-C-

Ref0

Square root

Raised CosineReceive Filter1

M-PSK

M-PSKDemodulator

BasebandOR

LogicalOperator

Inp Out

DownMixer

Ref 0

Sig

Ref 1

h0h1

Signaltrigger1trigger0

Detector

Putting it all together

The Alamouti Receiver

Wave Out

Amp1

Input

Amp2

Out

UpMixer

DataIn

DataAnt1

DataAnt2

To Alamouti

-C-

Ref_h1

-C-

Ref_h0

In1

In2

Out1

Prepare Data

1

Data In2

1

Data In1

-C-

Data In

AmpFact

Ref Amp

Amp

Amplification Vector Creator1

AmpFact

Ref Amp

Amp

Amplification Vector Creator

Putting it all together

The Alamouti Receiver

Future Applications

short-range communication system on a single chip (using ultrasound waves)

submarine communication systems implementation of MIMO sonar system

Questions