טכניקות בתקשורת מרחיבת סרט (Spread Spectrum) Chapter 2a מצגת זו תכלול כנראה דיון של הקהל, אשר יביא ליצירת פריטי פעולה. השתמש ב- PowerPoint כדי לעקוב אחר פריטי פעולה אלה במהלך המצגת. בהצגת שקופיות, לחץ באמצעות לחצן העכבר הימני. בחר באפשרות “מפקח הישיבות”. בחר בכרטיסיה “פריטי פעולה”. הקלד את פריטי הפעולה כאשר הם מופיעים. לחץ על אישור כדי להסיר תיבה זו. פעולה זו תיצור אוטומטית שקופיות לפריטי פעולה בסוף המצגת, והנקודות שהעלית יוזנו בתוכה. טכניקות בתקשורת מרחיבת סרט (Spread Spectrum) Chapter 2a ד"ר משה רן כל הזכויות שמורות לחברת MostlyTek Ltd. אין לצלם, לשכפל או להעתיק בכל צורה שהיא ללא קבלת אישור בכתב מד"ר משה רן Dr. Moshe Ran- Spread Spectrum

Dr. Moshe Ran / Spread Spectrum נושאי לימוד פרק 1 מבוא הסטורי לטכניקות Spread Spectrum הרחבת ספקטרום – לשם מה? חזרה- מושגי יסוד ועקרונות של מערכות תקשורת ספרתיות; רעשים והפרעות במערכות תקשורת, דרישות מערכתיות על התקשורת, השוואת שיטות אפנון ספרתיות, יעילות ספקטרלית. פרק 2 מבוא למערכות מרחיבות סרט (Spread Spectrum) - : קונספט ומודלים למערכות מרחיבות סרט; שיטות הרחבת סרט המבוססות על הרחבה ישירה DS)) דילוגים בזמן TH) ) דילוגים בתדר (FH) פרק 3 סדרות קוד למערכות מרחיבות סרט - LFSR, Gold Sequence, Walsh פרק 4 ביצועים של מערכות עם הרחבת סרט ישירה (DS) ביצועים של מערכות עם דילוגי תדר (FH) ; שיטות גילוי, עקיבה וסנכרון של אותות Spread Spectrum פרק 5 קודים לתיקון שגיאות, ביצועים של מערכות Spread Spectrum עם קודים לתיקון שגיאות, אלגוריתם Viterbi פרק 6 עקרונות CDMA בתקשורת תאית פרק 7 שימושים ואפליקציות של מערכות Spread Spectrum 8 שו"ת 8 שו"ת 8 שו"ת 8 שו"ת 8 שו"ת 8 שו"ת 4 שו"ת Dr. Moshe Ran / Spread Spectrum

Dr. Moshe Ran / Spread Spectrum 1. Introduction Secure communications EW – Electronic Warfare ECCM Communication System Requirements Global System Approach to ECCM Dr. Moshe Ran / Spread Spectrum

1.1 Secure Communication שיטות לתקשורת צבאית חסינה Electronic Warfare (EW) לוחמה אלקטרונית The enemy uses Electronic Counter Measures (ECM) Secure Communication The communicators use Electronic Counter-Counter Measures (ECCM). ECC…CM…. Dr. Moshe Ran / Spread Spectrum

1.2 Electronic Warfare (EW) Interception יירוט אותות תקשורת ("האזנה") LPI – Low Probability of Interception Data Extraction פענוח ופיצוח אותות התקשורת COMMINT, ELINT, HUMINT Jamming חסימת אותות התקשורת Deception הונאה Dr. Moshe Ran / Spread Spectrum

1.3 ECCM אמצעי נגד-נגד לוחמה אלקטרונית Encryption Power Control Adaptive Antenna Array Adaptive Time and Frequency Filtering Spread Spectrum Direct Sequence (DS) Frequency Hopping (FH) Time Hopping (TH) Error Correcting Codes Alternative Routing Dr. Moshe Ran / Spread Spectrum

1.4 communication System Requirements Functional Requirements Data Flow Operation and Special Features EW Threat Interception Data Extraction Jamming Deception Collocation Requirements Users Number Relative Location Mode of Channel Use Resources Budget Weight and Volume Frequency Range Dr. Moshe Ran / Spread Spectrum

1.5 Global System Approach to ECCM System Control Time and Frequency Management Alternative Routing Communication Protocols כאן מחפשים פרוטוקולים לא סטנדרטיים בד"כ Communication Controller Error Correcting Codes and Interleaving Cryptography Modem and Spread Spectrum Modulation Direct Sequence Frequency Hopping IF/RF and Antennas Power Control FDMA or TDMA Directional Antennas Adaptive Antennas Arrays Dr. Moshe Ran / Spread Spectrum

2. Introduction to Spread Spectrum Systems Definition Spread Spectrum System Concept PN Waveforms Time-Frequency waveforms Spread Spectrum Process Dr. Moshe Ran / Spread Spectrum

2.1 Spread Spectrum System Definition A System is considered to be a spread spectrum system if: a. The effective bandwidth WSS is much larger then the data rate Rb. b. the receiver is able to select the channel (or the waveform) where the signal is present and disregard the energy of the unused channels (or the waveforms). c. The waveforms are random or pseudo random, known to the communication but unknown to the enemy. Dr. Moshe Ran / Spread Spectrum

2.2 Spread Spectrum System Concept DATA SOURCE JAMMER LINK SELECTOR TR #1 #2 #K COMMON CLOCKS AND KEYS RCV #1 RCV #2 RCV #K DIVERSITY COMBINER USER Dr. Moshe Ran / Spread Spectrum

A Basis for a Jamming Game Assume : “Communication space” is divided between K Transmitters. Wss [Hz] total available BW Ts is transmitted signal period Complex envelope of k-th Tx signal Scenario of Orthogonal communication complex of multiplicity K Dr. Moshe Ran / Spread Spectrum

A Basis for a Jamming Game (cont.) Observed signal at i-th receiver Strategy for i-th Rx: project the signal onto the set of basis functions for the i-th Tx signal space Dr. Moshe Ran / Spread Spectrum

A Basis for a Jamming Game (cont.) In the absence of J(t) and ni(t) - the i-th Rx can correctly discover the data symbols used by i-th Tx Both J(t) and ni(t) can be expanded in terms of orthonormal basis Dr. Moshe Ran / Spread Spectrum

A Basis for a Jamming Game (cont.) In general No useful jamming signal Total energy in the Jamming signal Jammer has full knowledge of timing [0, Ts] ; Jammer has full knowledge of the set The EJ can be partitioned into K parts, the i-th part representing the energy to jam the i-th Rx Dr. Moshe Ran / Spread Spectrum

A Basis for a Jamming Game (cont.) Thus, Additive partitions is direct result of the orthogonality requirement. Similarly, total Tx energy is the sum of K signals each related with the i-th Tx Dr. Moshe Ran / Spread Spectrum

(1) Energy Allocation Strategies Within the orthogonal communication system complex of multiplicity K, consider strategies to allocate: Es “communicator” energy EJ “Jammer” energy to the K links. Communicator strategy: Randomly select Each receiving units. The remaining links are not used. KS diversity factor. Strategy fully known to communicator Rx. Jammer strategy: Randomly select receivers out of K to jam. Each receiving units. The remaining links are not used. Dr. Moshe Ran / Spread Spectrum

(2) Energy Allocation Strategies Communicator Rx collects all Es units of transmitted energy in Ks receivers (and further uses diversity combiner). Communicator also collects jamming energy. What is the Pr that exactly N communicator receivers will be jammed?! - the multiplicity of orthogonal system complex, should be as large as possible. Communicator can select Ks = 1 to minimize . Using only 1 out of K available links is - “pure spread-spectrum strategy” Dr. Moshe Ran / Spread Spectrum

(3) Energy Allocation Strategies The strategy to use any of K orthogonal links increases Es/EJ at receiving antenna to K* (Es/EJ) Energy gain, EG, against jamming That is, EG is the ratio of the signal space dimension (what the Jammer needs to jam) to the total dimensions actually used by communicator over KS links. For pure spread Spectrum strategy Dr. Moshe Ran / Spread Spectrum

2.3 Spread Spectrum Pseudo Random Waveforms a. Frequency Hopping where is a pseudo random sequence of frequencies is a random sequence of phases is the time duration of one hop and b. Direct Sequence is the time duration of one chip and is a complex discrete pseudo random sequence Dr. Moshe Ran / Spread Spectrum

2.3 Spread Spectrum Pseudo Random Waveforms (cont.) c. Time Hopping where is the time duration of one time hop and is the start time of one time hop d. Hybrid methods: DS-FH, TH-DS, TH-FH, ….. e. Pure random: Spread Spectrum Transmitted Reference (TR) Spread Spectrum Stored Reference (SR) f. Matched filter (MF): generating a wideband Tx signal by pulsing a filter having a long, wideband PN controlled impulse response Dr. Moshe Ran / Spread Spectrum

2.4 Time and Frequency Occupancy of Spectrum Waveforms Frequency Hopping: when Ts>Th “fast FH” WSS Frequency Fast FH TIME Dr. Moshe Ran / Spread Spectrum

2.5 Complex Spectrum Spreading Process a. Multiplication where are complex discrete pseudo random process waveforms and is complex data waveform For example is a direct sequence and is a frequency hopping sequence. Data Source Data modulator Spreading function generator Dr. Moshe Ran / Spread Spectrum

2.5 Spectrum Spreading Process (cont.) b. Switching The previous method is susceptible to “repeater Jamming”: transmitting a replica with different modulation. This reduces multiplicity K factor of a SS system to unity. Here, data signal is quantized to M-levels Per each level – a distinct one–out–of M possible code sequences is transmitted. Dr. Moshe Ran / Spread Spectrum

c. Compress and Shift (delay modulation) Reorganization of modulated data into the transmission intervals of a time hopping signal. Dr. Moshe Ran / Spread Spectrum

2.6 Receiver and demodulation aspects Basically, Rx computes the inner product (matched filter, correlation receiver) One or both of the complex signals appears as real IF or RF signal SS receiver needs sync. circuits to determine the inner product Dr. Moshe Ran / Spread Spectrum

Overview of Spread Spectrum – Sync. Baseband processing baseband correlation Baseband matched filters Bandpass processing IF multiplication, bb integration IF multiplication and integration (“bp” correlator) Recovery of requires 3 levels of sync. Dr. Moshe Ran / Spread Spectrum

Levels of Spread Spectrum – Sync. Correlation interval sync: Correlator requires pulse START and STOP correlation. In “bp” implementation this provides timing for the sampling and initialization of “bp” filters at the beginning of correlation.. In DS correlation sync related with the symbol clock period. In FH (fast hopping) each symbol lasts several hops. Interval sync pulse indicates Th . No meaning to correlate over range with random phase transitions. SpSp generator sync: Timing signal to control the local SpSp generator with the incoming SpSp signal. In DS this requires sync to the chip rate 1/Tc. In FH - to 1/Th Carrier sync: For ideal “bp” to “bb” operation the frequency and phase of local oscillator should be in sync. to received signal. In DS both carrier and phase sync is available. In FH – only freq is attained Dr. Moshe Ran / Spread Spectrum

Dr. Moshe Ran / Spread Spectrum Bibliography R. C. Dixon, Spread Spectrum Systems. New Work: John Wiley, 1976 M. K Simon et. Al., Spread Spectrum Communication, Vol. I,II,III, Rockville Maryland: Computer Science Press,1985. R. Ziemer, Peterson, Introduction to Spread Spectrum Communications, Prentice Hall,1995 2Ed J. K. Holmes, Coherent Spread Spectrum System, New Work: John Wiley & Sons, 1982 ISBN 0-471-03301-4. R. Skaug, J. F. Hjelmstad, Spread Spectrum in Communication, London: Peter, Peregrinus Ltd., 1985, ISBN 0-86941-034-0. D. J. Torrieri, Principles of Military Communication System, Dedham, Massachusetts: Artech House Inc., 1981 ISBN 0-89006-102-5. Dr. Moshe Ran / Spread Spectrum

3. Anti-jamming Spread Spectrum Systems Processing Gain Common Jammers Classification Anti-jamming System Configuration Interleaving Dr. Moshe Ran / Spread Spectrum

Dr. Moshe Ran / Spread Spectrum 3.1 Processing Gain (PG) = total spread-spectrum signal bandwidth available = data rate in bits per second (3,2) TRANSMITTER RECEIVER JAMMER Dr. Moshe Ran / Spread Spectrum

Basic parameters (independent of SpSp type, coding type etc) Regardless of signal and jammer waveforms we can define bit-energy-to-jammer noise In dB the bit-energy-to-jammer noise Dr. Moshe Ran / Spread Spectrum

Basic parameters- remarks: We assume that jammer power is much higher than thermal noise. Thus Eb/NJ dictates error performance in AWGN channels. PG is defined as the ratio Independent of modulation, coding etc PG definition may not agree with Dr. Moshe Ran / Spread Spectrum

3.2 Common Jammers Classification Wide Band White Noise Jammer Partial Band White Noise Jammer Dr. Moshe Ran / Spread Spectrum

Dr. Moshe Ran / Spread Spectrum CW Jammer Multitone Jammer Dr. Moshe Ran / Spread Spectrum

Common Jammers Classification (cont’d) Pulse Jammer Frequency Follower Jammer Echo Jammer Dr. Moshe Ran / Spread Spectrum

3.3 Anti-jamming System Configuration Data Encoder Interleaver Modulator Spreader JSSI Channel Data Decoder Deinterleaver Demodulator Despreader Coding Channel Figure 1: The antijamming system model. Dr. Moshe Ran / Spread Spectrum

Dr. Moshe Ran / Spread Spectrum 3.4 Interleaving The interleaving process transforms a memory channel to a memoryless channel. The interleaver is scrambling the order of the symbols in the transmitter The deinterleaver is reordering the symbols in the receiver I=6 x51 x21 x11 x1 x52 x22 x12 x2 x53 x23 x13 x3 x54 x24 x14 x4 x55 x25 x15 x5 x56 x26 x16 x6 x57 x27 x17 x7 x58 x28 x18 x8 x59 x29 x19 x9 x60 x30 x20 x10 Block Interleaver: Write symbols column-by-column Read row-by-row N=10 N x I matrix Dr. Moshe Ran / Spread Spectrum

4. Direct Sequence (DS) Spread Spectrum Overview of DS spread spectrum system Parameters of a DS System Spectra in the DS Spread Spectrum System Performance Comparison in the Presence of a Narrow-Band Interference Uncoded DS/BPSK Spectrum System With Pulse Jammer Performance of the Uncoded DS/BPSK System. Worst Case Pulse Jammer Vs. Constant Power Jammer Dr. Moshe Ran / Spread Spectrum

4.1 Overview of DS spread spectrum system 2 3 4 Multiplication by in the transmitter is spreading the signal spectrum. The sequence is despreading the signal spectrum. Usually and the despread signal is equal to the original unspread signal. For the special popular case of a BPSK system the transmitter can be implemented in an equivalent way. BPSK MODULATOR PN GENERATOR PN GENERATOR CHANNEL TRANSMITTER RECEIVER Dr. Moshe Ran / Spread Spectrum

Dr. Moshe Ran / Spread Spectrum PN GENERATOR BPSK MODULATOR PN GENERATOR BPSK MODULATOR Dr. Moshe Ran / Spread Spectrum

Dr. Moshe Ran / Spread Spectrum Plot of DS time signal Dr. Moshe Ran / Spread Spectrum

4.2 Parameters of a Direct Sequence System - bit duration - chip duration - unspread signal bandwidth - spread spectrum signal bandwidth - processing gain - number of chips in one bit - spectrum spreading ratio - signal power - signal bit energy - jammer power Dr. Moshe Ran / Spread Spectrum

4.3 Spectra in the Direct Sequence Spread Spectrum System Dr. Moshe Ran / Spread Spectrum