SCK LAB MANUAL SAMPLE

Transcription

1 SCK LAB MANUAL SAMPLE VERSION 1.2 THIS SAMPLE INCLUDES: TABLE OF CONTENTS TWO SELECTED LABS FULL VERSION IS PROVIDED FREE WITH KITS Phone: , Fax: URL: REVISION HISTORY Reviion Decription Date 1.0 Firt draft March 20, Preface added and few lab updated May 15, Digital Communication lab added Feb 25, 2014

2 PREFACE There ha been alway exited a gap between how communication ytem are taught in theory and deigned in practice. Over the lat decade or o the practice of communication ytem deign ha gone through a dratic change. The claical approach wa focued on the ue of hardware electronic component to build communication circuit. With the rapid increae in the digital computational power and introduction of Software Defined Radio (SDR) concept, now the focu i on building communication ytem in which main tak are performed by the oftware. The key advantage of thi approach i that now it i poible for an undergrad tudent or a profeional engineer who i learning communication theory to directly apply hi theoretical concept and rapidly build real-time communication ytem. While the communication indutry ha adopted the new SDR technology for quite ome time now, education ector i till lacking behind. Mot of book, lab manual and training equipment are till not up to date with the current trend of the market. Although the trend ha tarted to change over the lat few year but till a lot of work till need to be done. Thi lab manual i an effort to bridge thi gap between theory and practice of communication ytem deign. If we look at the exiting lab equipment, it primarily fall into following two main categorie. 1) Conventional Electronic Communication Trainer: Thee trainer are eay to ue but they don t provide hand on ytem deign experience. Such trainer come with fixed circuitboard and tudent are required to jut change jumper etting to oberve the output on ocillocope or voltmeter. 2) High-end SDR-baed Platform: Thee are relatively high end trainer which do provide ytem deign experience but tudent require pecialized expertie and programming kill to ue them. Thee kill are not uually available with the undergraduate and even graduate tudent. Thi i the reaon why thee platform are not a good option for tudent lab epecially at undergraduate level. Renzym lab equipment i an attempt to fill thi void becaue not only it provide hand on deign experience but alo it doen t require any pecialized programming expertie. Thi lab manual demontrate the deign of different analog communication ytem uing SDR Communication Kit (SCK). SCK i USB powered, plug and play device that enable true SDR development directly from cla room Simulink/LabView imulation. It can be ued to readily build real-time communication ytem by directly applying the concept learnt from theory with a minimum of implementation effort in the hardware. Thi blending of theory and practice i generally miing from mot of the communication coure. Theoretical performance of variou technique can now be quickly compared with their performance in a real-world environment. Furthermore it provide a unique opportunity to the reearcher working on receiver deign to verify their algorithm in variou practical cenario with a minimum of implementation effort.

3 SDR Communication Kit Complex baeband repreentation of paband communication ytem ha been adopted in thi manual. Thi repreentation implifie the ytem deign by eparating proceing of information bearing baeband ignal from the carrier ignal. An excellent decription of thi approach can be found in a book by Michael P. Fitz titled Fundamental of Communication Sytem. The theory of analog communication ytem decribed in Profeor Fitz book ha been ued for deigning related lab in thi lab manual. Although we did provide brief theoretical explanation at the tart of every lab, it i till recommended that thi book hould be conulted by both, intructor and tudent, during the lab. With the help of powerful deign tool like Simulink/Labview now it i poible to exactly implement the theoretical concept in practice. Thi i the reaon why in thi manual theoretical explanation of the concept precede the Simulink implementation in every lab. Complete implementable block diagram have been explained with the help of mathematical equation. Student mut undertand the theory before they attempt to deign a ytem in Simulink. Lab tak are provided wherever neceary for tudent to take their learning experience to the next level by deigning at their own uing what they learned in the previou lab. It i alo important to take a tep-by-tep approach while deigning relatively complex ytem. A common mitake that tudent often make i that they try to build a complete ytem firt before tart teting it. It would make almot impoible to debug for mitake and identify the ource() of error in a big ytem with ten of functional block. Therefore it i of utmot importance for tudent to divide a big ytem into maller ubytem and verify each ytem eparately before connecting them together to make complete ytem. In order to be able to ubdivide a ytem and to be able to verify the output of each individual ytem, one mut have a clear theoretical undertating of the ytem functionality. Without uch undertanding it would be extremely difficult to uccefully deign the complete ytem. Thi manual cover a range of analog modulation cheme often ued in practice. Firt two lab provide introduction to Simulink and how to build and analyze a baic ytem in Simulink. In the third lab complex baeband repreentation of paband ytem i introduced and key baic building block like Baeband to Paband Converter and Paband to Baeband Converter are deigned. Fourth lab deal with the baic Double Sideband Amplitude Modulation (DSB-AM) cheme. SDR Communication Kit (SCK) i introduced in the fifth lab and tudent will learn to interface SCK with computer and end/receive baic phyical ignal uing SCK. Furthermore DSB-AM ytem will alo be built uing a pair of SCK. Lab 6 and 7 will cover two popular cheme of amplitude modulation namely Large Carrier-AM (commonly known a AM) and Single Sideband Carrier AM. Angle modulation i treated in the Lab tarting from 8 to 11 where Phae Modulation (PM) and Frequency Modulation (FM) ytem are covered. Student will build angle modulator and verify the Caron bandwidth rule. Moreover they will deign different modulator for both FM and PM ignal including direct phae detector, dicriminator detector and PLL baed modulator.

4 CONTENTS Preface Content Lab 1: Simulink Fundamental Lab 2: Baic Signal Proceing Lab 3: Complex Baeband Repreentation of Paband Communication Signal Lab 4: Double-Sideband Suppreed-carrier Amplitude Modulation (DSBSC-AM) Lab 5: Getting Started with SDR Communication Kit Lab 6: Large Carrier Amplitude Modulation Sytem (LC-AM) Lab 7: Single Sideband AM (SSB-AM) uing Tranmitted Reference Baed Demodulation Lab 8: Angle Modulation Lab 9: Angle Demodulation uing Direct Phae Demodulator Lab 10: Angle Demodulation Uing Dicriminator Detector Lab 11: Digital Communication Lab 12: Pule Amplitude Modulation (PAM) Lab 13: Phae Shift Keying (PSK) Lab 14: Frequency Shift Keying (FSK) Lab 15: C/C++ MEX S-Function Lab 16: Symbol Timing Error and Recovery Lab 17: Carrier Error and Recovery Lab 18: Unique Word Phae and Frame Recovery Lab 19: Bit Error Rate (BER)

5 Lab 6: AM) Large Carrier Amplitude Modulation Sytem (LC- 6.1 Lab Objective: In thi lab we will deign Large Carrier Amplitude Modulation (LC-AM) ytem. Key lab objective will be a follow 1) Simulate the analog amplitude modulation through envelop detection i.e. LC-AM. 2) Tet the ame model uing SDR Communication Kit 3) Single Sideband AM uing Tranmitted Reference Baed Demodulation Following Simulink block will be ued in thi lab 1) Sine Wave Block from Signal Proceing Source. 2) Digital Filter Deign block from Signal Proceing Block et. 3) Bandpa to Baeband and Baeband to Paband converter (deigned in previou lab) 6.2 LC-AM Modulator and Non-coherent Demodulator The main advantage of LC-AM over DSBSC-AM i that it can detected by imple envelope detector without any phae etimation. DSBSC-AM meage ignal modulate the 1) Envelope of the bandpa carrier ignal in a continuou manner 2) Phae of the binary bandpa carrier in a binary fahion i.e. the carrier of the phae change from 0 to when meage ignal amplitude goe from +ve to ve. In fact, if the meage ignal never goe negative the envelope of the bandpa ignal and the meage are identical up to a multiplicative contant. Thi deired characteritic i obtained if a DC ignal i added to the meage ignal to guarantee that the reulting ignal alway i poitive. Thi implie the complex envelope i an affine function of the meage ignal, i.e. Where i a poitive number. Thi modulation ha o the imaginary portion of the complex envelope i not ued again in LC-AM. The reulting bandpa ignal and pectrum are given a and Block diagram of LC-AM modulator i hown in Figure 6.1.

6 Figure 6.1: LC-AM Modulator The demodulator of LC conit of imple envelope detector. The output of bandpa to be baeband converter at the receiver, in the abence of noie, can be written a We can ee that envelope of ignal can be ued to recover meage ignal,, by ignoring the phae,, becaue it doen t change it value. The envelope of the i given below Meage ignal can be recovered from thi envelope by applying a highpa filter, DC remover, a hown in Figure 6.2. Figure 6.2: LC-AM Demodulator LC-AM differ from DSBSC-AM in that a DC term i added to the complex envelope. Thi DC term i choen uch that or equivalently the envelope of the bandpa ignal never pae through zero. Thi implie that or equivalently Thi contant, here denoted the modulation coefficient, i important in obtaining good performance in a LC-AM ytem. Typically the time average of i zero the average power There are two part to the tranmitted/received power: (1) The power aociated with the added carrier tranmiion (2) The power aociated with the meage ignal tranmiion It i deirable to maximize the power in the meage ignal tranmiion and a factor that characterize thi plit in power in LC-AM i denoted the meage to carrier power (MCPR).

7 It how in order to maximize the modulation coefficient,, hould be maximized. But it i not poible to increae it beyond a certain level and for audio tranmiion practically remain between 10-15%. Thi i the penalty which we have to pay for implified envelope detection baed detection. 6.3 Deign in Simulink A Simulink deign of LC-AM modulator and demodulator for inuoidal meage ignal i hown in Figure 6.3. Student are required to imulate an LC-AM ytem with the following parameter. Input meage amplitude, Sampling frequency, Carrier Amplitude, Carrier frequency, Hz Hz Student hould calculate appropriate value of modulation co-efficient,, and and hould make it part of lab report. A careful deign of highpa filter, DC remover, i alo required at the demodulator. Figure 6.3: LC-AM Sytem in Simulink Student hould verify their reult by comparing the demodulator output ignal with the input meage ignal a hown in Figure 6.4.

8 Figure 6.4: Meage ignal and LC-AM demodulator output Furthermore energy pectrum of the baeband ignal,, and paband ignal,, hould be verified by uing pectrum cope a hown in Figure 6.5. Figure 6.5: Spectrum plot for baeband and paband ignal 6.4 Speech Tranmiion Uing SDR Communication Kit In thi ection we try to etup an LC-AM link for audio ignal uing SDR Communication kit. A decribed earlier, we need two SCK connected with two different computer; one acting a modulator and other a receiver or demodulator. Simulink model for modulator and demodulator will alo plit into two eparate Simulink model. The etup would look like a hown in figure below

9 Simulink Model Tx-ide Rx-ide Simulink Model USB SDR Kit SDR Kit USB Figure 6.6: Tranmiion Setup uing SCK When connected, SCK hould appear a a default ound card to the computer. It hould be checked from the audio device propertie and SCK hould be elected a default ound card. At the tranmitter end, modulator output hould be ent to the SCK by uing To audio device block which can be found in commonly ued block. SCK can alo be elected a default output audio device from To audio device block propertie. LC-AM modulator providing output to SCK i hown in Figure 6.7. Figure 6.7: LC-AM Modulator with SCK Pleae alo note that block From Multimedia File ued in Figure 6.7 to provide input meage ignal to the LC-AM modulator. Uing thi block any audio file can be provided a input ignal. File will keep on repeating after during the imulation. It i important to calculate audio ignal bandwidth before tranmiion and alo adjut the variable like carrier frequency, modulation coefficient, ampling frequency (it hould be matched with the audio file ampling rate). Simulink. Output of the demodulator can be ent to audio device by connecting it to To audio device block a hown in Figure 6.8.

10 Figure 6.8: LC-AM Demodulator with SCK Matlab i computationally intenive oftware o in order to have a mooth non-interrupted tranmiion pleae remover all the plotting block like time Scope or Spectrum Scope etc.

11 Lab 14: Frequency Shift Keying (FSK) 14.1 : FSK Modulator FSK modulator can be categorized into two type; dicontinuou phae FSK (DPFSK), continuou phae FSK (CPFSK). DPFSK i alo known a noncoherent FSK and CPFSK i alo known a coherent phae FSK. The categorization i hown in Figure FSK Dicontinuou Phae FSK Continuou Phae FSK Figure 14.1: FSK Categorization Dicontinuou phae FSK and continuou phae FSK modulated ignal are hown in Figure A hown in figure, DPFSK modulated ignal ha dicontinuitie at ymbol boundarie. Thee dicontinuitie increae ignal bandwidth. Similarly CPFSK i alo hown in the figure; where the phae i coherent at ymbol boundarie. Dicontinuou Phae FSK/Noncoherent FSK Continuou Phae FSK(CPFSK)/Coherent FSK Figure 14.2: FSK Modulated Signal

12 : DPFSK Modulator Binary DPFSK modulator i given in Figure The multiplexer witche between the inuoid at and. In general and are not the ame, therefore the modulated ignal i not continuou at ymbol boundarie. BFSK pectrum i given in Figure 14.4, that viualize the relation between and. 0 ( ) 1 ( ) M U X ( ) Binary Data Source Figure 14.3: Continuou Time Binary DPFSK Modulator Conider, Therefore, Thi produce the inuoid, For better detection the frequencie are choen to be at maximum eparation i.e. achieved by making then orthogonal. The two frequencie are orthogonal if the following equation i equal to zero When, i equal to zero. Thi mean that frequencie are orthogonal for multiple of,

13 The required frequency hift for coherent CPFSK bai ignal to be orthogonal can be expreed a. Thi mean all the frequencie hift are multiple of half the ymbol rate and frequency eparation i. 1 c 0 0 c 1 Figure 14.4: BFSK Spectrum : CPFSK Modulator For a binary FSK two waveform are ued to tranmit a bit a given below ( 14.1) For a CPFSK the phae at the ymbol tranition boundarie hould be continuou. To do o the modulator mut remember the phae during ymbol tranition. Thi i achieved by repreenting the modulated ignal in term of current and previou ymbol. A continuou phae BPSK modulator i given in Figure ,0,1 data The look up table output i +1,-1+1 LUT DAC VCO a(k) x(t) Figure 14.5: VCO Baed FSK y(t) DAC produce a bipolar quare wave with amplitude. DAC output can be expreed a Where, The VCO output i expreed a

14 ( 14.2) Where to be to produce a unit energy pule hape. Conider look up table output during, then the phae term in ( 14.2) become Where, I contant, reulting in ( 14.3) Subtituting ( 14.3) in ( 14.2) produce Suppoe then For For ( 14.4) ( 14.5) A een ( 14.4) and ( 14.5) are of the form given in ( 14.1). Now conider output during the DAC output i, be the look up table Then the phae term of VCO output become

15 Where Thi produce the VCO output to be The frequency hift i normalized by ymbol rate, producing, Thi make the VCO output to be, Where, or i choen o that the two bai ignal of coherent CPSK are orthogonal. Correlation function i ued to check orthogonality a hown below. When, i equal to zero. Thi mean that frequencie are orthogonal for multiple of, The required frequency hift for coherent CPFSK bai ignal to be orthogonal can be expreed a.

16 Thi mean all the frequencie hift are multiple of quarter the ymbol rate and frequency eparation i. The minimum frequency hift that produce orthogonal ignal i. FSK with i called Minimum Shift Keying (MSK). In term of modulation index ( ), when i equal to zero, Thi mean that frequencie are orthogonal for multiple. For MSK. Uing proper frequencie or modulation index the following ignal can be orthogonal bai ignal for BSK. Or, Modulator for orthogonal BSK i given in Figure φ 0 ( ) data LUT0 LUT1 DAC DAC 0( ) 1( ) ( ) φ 1 ( ) Figure 14.6: Continuou Time Binary Orthogonal FSK Modulator Dicrete time CPFSK modulated ignal i repreented a Where, Therefore,

17 For, modulation index i, Therefore, Where i ampled verion of Thi produce a dicrete time CPSK modulator given in Figure data LUT ( ) N FIR Filter d c z 1 co() DAC ( ) VCO 14.2 : FSK Demodulator Figure 14.7: Dicrete Time CPFSK Modulator FSK demodulator ha two type, coherent demodulator and noncoherent demodulator. In coherent demodulation theoretically it i aumed that the demodulator know the phae of received ignal, practically the phae of the received ignal i etimated uing phae recovery algorithm. In noncoherent demodulation the demodulator doe not require the phae of the received ignal, therefore noncoherent demodulation i preferred over coherent demodulation. DPKSF ignal have dicontinuou phae at ymbol boundarie i.e. phae change at ymbol boundarie therefore, DPKSF received ignal can only be demodulated noncoherently. CPFSK ha continuou phae at ymbol boundarie therefore, CPFSK received ignal can be demodulated coherently or noncoherently : FSK Coherent Demodulator Dicrete time BFSK coherent demodulator i given in Figure The received ignal i ampled uing an ADC. The ampled ignal i project onto and producing an etimate of and. The projection are downampled by, producing of and.

18 φ 0 ( ) ( ) DAC ( ) (. ) 1( ) Deciion (. ) 0 ( ) φ 1 ( ) Figure 14.8: Dicrete Time BFSK Coherent Demodulator φ Select Index of Larget > 0? 1 > 0 0 > 1 φ 0 Figure 14.9: Deciion Block Figure 14.10: BFSK Deciion Region Deciion are taken on and, deciion region are defined in Figure The deciion block can be implemented uing different method; ome of them are hown in Figure Problem with thi demodulator i that it i difficult to produce phae and frequency coherent replica of the bai function, therefore alternate method are ued for demodulation, where phae coherent replica are not required : FSK Noncoherent Demodulator There are many noncoherent demodulator for FSK, uch a; Differential detection FSK demodulator, Foter Sealy FSK demodulator and Square Law FSK demodulator. Foter Sealy FSK demodulator and Square Law FSK demodulator are dicued in the following ection : Foter Sealy FSK Demodulator Foter Sealy BFSK demodulator i hown in Figure 14.11, it i a noncoherent demodulator, i.e. the demodulator doe not require knowing the phae of the received ignal.

19 ( ) DAC ( ) Bandpa Filter Envelope Detection Deciion Bandpa Filter Envelope Detection Figure 14.11: Foter Sealy BFSK Demodulator Signal at different tage are hown in Figure A een two bandpa filter are ued, one centered at and the other centered at. When frequency content at are preent during a ymbol time the frequency content at are abent a hown by ignal at output of bandpa filter, imilarly when frequency content at are preent during a ymbol time the frequency content at are abent. Thi produce the envelope detector output a hown by ignal in figure. A difference of the envelope detector output produce the deired ymbol value : Square Law FSK Demodulator Continuou Time Square Law demodulator i hown in Figure Continuou Time Square Law demodulator ue a noncoherent projection of the received ignal on to the two bai function by uing quadrature mixer at each of the two poible frequencie. The output are integrated over a ymbol time and quared. The quadrature reult are ummed and paed to the deciion block which chooe the ymbol aociated with the larget output.

20 φ 0 ( ) (. ). 2 (. ). 2 ( ) φ 1 ( ) φ 0 ( ) Deciion (. ). 2 (. ). 2 φ 1 ( ) Figure 14.12: Continuou Time Square Law BFSK Demodulator To ee how thi work, let Be the two poible tranmitted ignal. Now, uppoe the received ignal i Now let compute the ampled output of the four integrator for :

21 Thu And the correct deciion i made. The key to proper performance i the orthogonality of the two poible tranmitted ignal i.e. Dicrete Time implementation Square Law demodulator i hown in Figure φ 0 ( ) (. ). 2 (. ). 2 ( ) DAC ( ) φ 1 ( ) Deciion φ 0 ( ) (. ). 2 (. ) : Deign in Simulink φ 1 ( ) Figure 14.13: Dicrete Time Square Law Demodulator Uing concept decribed in ection 14.1 and 14.2 CPFSK modulator and Square Law detector are given in Figure The modulator i a direct implementation of the dicrete time CPFSK modulator hown in Figure For BFSK the look up table value are et to, where -1 i for bit 0 and 1 i for bit produce a frequency hift and 1 produce a frequency hift. Value of i elected uing the following equation. Where for BFSK i loot up table value. The demodulator i a direct implementation of Square Law FSK demodulator hown in Figure The quadrature inuoid for both path are

22 generated uing the in wave block. The in wave block i configured to produce a complex inuoid, where real part i the inphae coine wave and the complex part i the quadrature phae in wave. The frequency i et to. The deciion block ued here i ame a that ued in PAM and PSK. Figure 14.14: CPSK Modulator and Square Law Demodulator in Simulink The output ignal at different tag at the demodulator are hown below, where Figure how the receiver contellation and Figure how the tranmitter filter output and the upconverted tranmitted ignal. Figure 14.15: Receiver Contellation

23 Amplitude Amplitude Time (ec) Time (ec) Offet= : Lab Tak Figure 14.16: Tranmitter Filter Output and Upconverted Tranmitted Signal 1. Deign a non coherent BFSK modulator and Square Law BFSK Demodulator. 2. Deign a coherent BFSK modulator and Foter Sealy BFSK Demodulator. 3. Deign a coherent 4-FSK modulator and Foter Sealy 4-FSK Demodulator. 4. Deign a coherent 4-FSK modulator and Square Law 4-FSK Demodulator.