MODULATION for MULTIMEDIA TRANSMISSION
with special emphasis on wireless
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• -
Content: SIGNAL MODULATION TECHNIQUES RADIO WAVE PROPAGATION WIRELESS SYSTEMS WIRELESS DATA TRANSPORT SOURCE AND CHANNEL CODING (WHICH WE ARE NOT COVERING)
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SIGNAL MODULATION TECHNIQUES HOW TO OVERLAY BITS OR STREAMS OF BITS ON A SIGNAL TO CARRY THEM?
FOR MULTIMEDIA TRANSMISSION WE NEED TO TRANSFER A LOT OF DATA THUS, WE NEED TO PACK THE DATA EFFICIENTLY ON TRANSMISSION CARRIER (RADIO WAVES, ELECTRIC CURRENT, FOTONS)
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Sinusoidal Waveform
• The signal at frequency around fc: s(t) = Acos(2pfct + q) • To encode the symbol of {0, 1},
– – – – You can encode using the amplitude You can encode using the phase You can encode using the frequency Some combination of amplitude, phase, or frequency.
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Amplitude-Shift Keying (ASK)
CARRIER
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ASK (cont.)
• Signal is
2 Eb s1 t cos( 2pf c t ) Tb s2 t 0 0 t Tb
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Phase-shift Keying (PSK)
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PSK (cont.)
• Signal is
2 Eb s1 t cos( 2pf c t ) Tb 2 Eb s2 t cos( 2pf c t ) Tb 0 t Tb 0 t Tb
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Frequency-shift keying (FSK)
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FSK (cont.)
• Signal is
2 Eb s1 t cos( 2pf1t ) Tb 2 Eb s2 t cos( 2pf 2t ) Tb 0 t Tb 0 t Tb
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HOW TO PUT MORE BITS ON THE CARRIER? 1. BY USING MORE PHASE SHIFTS E.G. 8-PSK
FIGURE 1/V.29 Signal space diagram at 9600 bit/s
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HERE WE USE 8 PHASE VALUES EACH VALUE ENCODES 3 BITS
2. BY USING MORE AMPLITUDE LEVELS AND PHASE SHIFTS – EXAMPLE 16-QAM
(Im) 90°
HERE EACH PHASE/AMPLITUDE D 01000 00101 01010 2 VALUE ENCODES 10010 10101 10011 10100 4 BITS 00000 01111 00010 01101 C 00011
4 11111 11000 180° –4 00111 11001 A –2 01001 10111 01110 11110 00110 –2 10000 10001 10110 11010 2 01011 11101 4 00100 0° (Re)
00001 B 01100 –4 11100 11011 270°
T1702150-93/d03
NOTE – The binary numbers denote Y0n Y1n Y2 n Q3n Q4n . MULTIMEDIA SYSTEMS IREK DEFEE
64-QAM EXAMPLE -COMBINATION OF AMPLITUDE AND PHASE ENCODES SPECIFIC BIT PATTERN
0110000 1100000 0010011 1011101 0110101 1100101 0010001 1011000 90° 8 1111001 1101000 1110001
(Im)
0111000
0101001 D
1000011
0010111 0100001 0010101 6 1011111 1000111 1011011 1000101 0001111 0111100 0001011 0111101 4 1111010 1101100 1110010 1101101 1110011 0010110 0100010 0010100 0100011 0010000 2 C 1011110 1000110 1011010 1000100 1011001 1000000 0001110 0111110 2 0001010 4 0111111 6 0001001 8
(Re)
0001101
0110100
1111011
1100100
0101011
0010010
0101010
1000001
1011100
1000010
0001000 -8 180°
0110111 -6
0001100 -4
0110110 -2
1100111 0011001
1111111
1100110
1111110
1101110
1110110
1101111
1110111
0°
0101111 A
0011010
0101110
1010000
1001001
1010100
1001010
0011110 0100110 0011100 0100111 0011000 -2 1010110 1001110 1010010 1001100 1010001 1001000 0000110 0111010 0000010 0111011 0000001 -4 1111100 1101010 1110100 1101011 1110101 0011111 0100100 0011101 0100101 -6 B 1010111 1001111 1001101 1010011 0000111 0111001 0000011 -8 1111000 1101001 1110000 270° 0100000
T1701310-90
0000000
0110011
0000100
0110010
1100011
1111101
1100010
0101101
0011011
0101100
1010101
1001011
0000101
0110001
1100001
0101000
Note – Binary numbers refer to Y0n , Y1n , Y2n , Q3n , Q4n , Q5n , Q6n . A, B, C, D refer to synchronizing signal elements.
FIGURE 2-1/V.32 bis Signal space diagram and mapping for modulation at 14 400 bit/s per second
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45 41 37 33 29 25 21 17 13 9 5 1 –3 –7
EXAMPLE OF NUMBERS ENCODING BY SPECIFIC BIT PATTERNS
408 396 394 400 414 398 375 349 339 329 326 335 347 359 386 412 371 340 314 290 279 269 265 273 281 302 322 353 390 401 357 318 282 257 236 224 216 212 218 228 247 270 298 337 378 406 350 306 266 234 206 185 173 164 162 170 181 197 220 253 288 327 379 360 310 263 226 193 165 146 133 123 121 125 137 154 179 207 242 289 338 391 384 324 277 229 189 156 131 110 355 294 243 201 160 126 392 330 274 222 177 135 102 380 316 255 203 158 119 367 304 244 194 148 108 362 296 238 186 142 103 365 300 240 190 144 106 372 307 251 199 152 113 84 75 69 73 80 94 98 77 60 50 43 45 52 67 89 79 55 39 28 22 25 33 47 68 95 96 64 41 24 13 9 11 19 34 53 82 87 58 35 17 6 1 3 12 27 46 74 83 54 31 15 4 0 2 10 23 44 70 92 62 37 20 8 5 7 14 29 51 76 100 117 140 172 208 254 299 354 71 48 30 21 16 18 26 40 61 86 90 65 49 38 32 36 42 57 78 112 141 180 221 271 323 387 91 72 63 56 59 66 81 99 118 155 198 248 303 361 101 138 182 230 283 348 415 93 85 88 97 127 171 219 275 336 402 122 163 213 267 328 395 124 166 217 272 331 397 134 174 225 280 341 409
–11 388 320 261 210 167 128
111 147 187 237 291 351 132 168 209 258 315 376
–15 410 343 284 232 183 149 115 –19 –23 –27 –31 –35 –39 –43
369 311 259 214 175 139 116
104 129 157 195 235 285 342 399
403 345 292 249 205 176 150 130 114 107 105 109 120 136 161 191 227 268 319 373 382 332 287 250 215 184 169 153 145 143 151 159 178 202 231 264 308 358 413 377 333 293 260 233 211 200 192 188 196 204 223 245 278 312 352 404 383 346 313 286 262 252 241 239 246 256 276 295 325 363 407 405 370 344 321 309 301 297 305 317 334 356 385 411 389 374 366 364 368 381 393 –43 –39 –35 –31 –27 –23 –19 –15 –11 –7 –3 1 5 9 13 17 21 25 29 33 37 41 45
T1403000-97/d05
Figure 5/V.34 – One-quarter of the points in the superconstellation
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• The more bits we put the better signal to noise must be (small phase and amplitude values are lost in noise) How to put even more bits on a signal?
By using multicarrier modulation – bits are overlayed on many carriers at the same time.
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• ONE USES MANY CHANNELS. EACH CHANNEL IS MODULATED E.G. WITH 8 KBITS/S. WITH MANY CHANNELS OVERALL DATA RATE GROWS • EACH CHANNEL CAN BE INDIVIDUALLY TUNED TO THE TRANSMISSION BANDWIDTH, E.G. SOME CHANNELS CAN BE SKIPPED COMPLETELY.
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• EXAMPLE OF SYSTEM
f
THE NUMBER OF CARRIERS CAN BE VER HIGH IN DIGITAL TELEVISION IT IS ABOUT 8000 EACH CARRIER IS MODULATED IN SOME WAY, E.G. PSK, QAM... THIS SYSTEM IS CALLED OFDM, ORTHOGONAL FREQUENCY DIVISION MULTIPLEX
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• WHERE ARE THESE SIGNAL MODULATION TECHNIQUES APPLIED?
1. PSK, QPSK – GOOD FOR WEAK SIGNALS, APPLIED IN THE GSM SYSTEM, ALSO IN DIGITAL TELEVISION FROM SATELLITES QAM – REQUIRES STRONGER SIGNALS, APPLIED IN DIGITAL CABLE TELEVISION AND IN THE EXTENSION OF GSM CALLED EDGE OFDM – APPLIED IN TERRESTRIAL DIGITAL TELEVISION AND IN NEW WIRELESS LAN’S, VERY EFFICIENT USE OF BANDWIDTH, CAN BE ADJUSTED FOR BAD SIGNAL PROPAGATION
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2.
3.
The OFDM modulation
• Applications: Digital Terrestrial Television: 8 000 carriers Digital Mobile Television 4 and 8 000 carriers Wireless LAN (802.11a/g): 52 carriers Ultra Wide Band: many carriers in many bands NEW 4th generation mobile system called LTE (Long Term Evolution)
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Ultra Wide Band Network
• Ultra Wide Band is wireless network of very short range but with very high data transfer rate (600 Mb/s to 1000 Mb/s and more) This network can eliminate MONITOR cable. Then mobile device can drive the monitor directly.
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Imagine this
Mobile devices are more and more capable (processors, memory, hard discs), resembling PC from few years ago
UWB Ultra Wide Band
Mobile device has wireless links to keyboard and display Bluetooth
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UWB opportunity
• If Ultra Wide Band system becomes popular and monitors/TV’s will get it, and if mobile devices will have it, then they interface directly.
There will be no need for PC anymore!(?)
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UWB is Multi-band OFDM
• Central Idea #1:
– Divide the spectrum into bands that are 528 MHz wide.
Band Group #1 Band #1 Band #2 Band #3 Band Group #2 Band #4 Band #5 Band #6 Band #7 Band Group #3 Band #8 Band #9 Band #10 Band Group #4 Band #11 Band #12 Band Group #5 Band #13 Band #14
3432 MHz
3960 MHz
4488 MHz
5016 MHz
5544 MHz
6072 MHz
6600 MHz
7128 MHz
7656 MHz
8184 MHz
8712 MHz
9240 MHz
9768 MHz
10296 MHz
f
• Advantages:
– Transmitter and receiver process smaller bandwidth signals. – Instantaneous processing BW = 528 MHz.
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Exploiting the Band Plan
• Exploit range of band group’s to separate applications:
Band Group #1 Band #2 Band Group #2 Band #5 Band #1 Band #3 Band #4 Band #6
3432 MHz
3960 MHz
4488 MHz
5016 MHz
5544 MHz
6072 MHz
f
Longer Range Apps Use BG #1 and #2
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Exploiting the Band Plan
• Exploit range of band group’s to separate applications:
Band Group #3 Band #8 Band Group #4 Band #11 Band #7 Band #9 Band #10 Band #12 3432 MHz 3960 MHz 4488 MHz 5016 MHz 5544 MHz 6072 MHz 6600 MHz 7128 MHz 7656 MHz 8184 MHz 8712 MHz 9240 MHz 9768 MHz 10296 MHz
f
`
Shorter Range Apps Use BG #3 and #4
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Overview of Multi-band OFDM
• Central Idea #2:
– Interleave OFDM symbols across all bands.
3168 Band # 1 3696 Band # 2 4224 Band # 3 4752 Time
• Advantages:
Freq (MHz)
– Exploits frequency diversity. – Provide robustness against multi-path / interference. – Same transmit power as if the entire band is used.
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IMPORTANT EXAMPLE
• EDGE – ENHANCED DATA RATE FOR GSM EXPANSION TECHNIQUE FOR INCREASING THE BIT RATE OF GSM SYSTEM BY USING 8-PSK. IT IS ADOPTED FOR DATA TRANSFER BUT REQUIRES MAJOR HARDWARE UPGRADES IN THE SYSTEM
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Application – GSM system
GPRS
Rate 9.05kb/s 13.4kb/s 15.6kb/s 21.4kb/s Code 0.5 0.66 0.75 1.0 Rate CS1 CS2 CS3 GMSK (1 bit/s/symbol)CS4
EDGE - Key Aspects
• A new modulation Scheme - 8PSK
EDGE
Rate
8.8 kb/s 11.2 kb/s 14.8 kb/s 17.6 kb/s
Code
0.53 0.66 0.80 1.00
Rate MCS1 MCS2 MCS3 GMSK (1 bit/s/symbol) MCS4
• 200 KHz Channel spacing - unchanged
• Symbol rate unchanged - 270k symbol/s BUT - 3 bits/symbol
EDGE = GMSK + PSK
Rate 22.4 kb/s 29.6 kb/s 44.8 kb/s 59.2 kb/s Code Rate 0.37 0.49 0.76 1.00
MCS5 MCS6 MCS7 MCS8
8-PSK (3 bit/s/symbol)
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•
CDMA – CODE DIVISION MULTIPLE ACCESS
MODULATION WHICH ENABLES THE USE OF SAME RADIO BAND BY MANY USERS AT THE SAME TIME. IT IS DIFFERENT FROM PREVIOUS MODULATION SCHEMES WHERE ONLY ONE USER CAN USE THE BAND AT SAME TIME CDMA IS A ”MAGIC” SYSTEM
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• WHAT IS CDMA? CODE DIVISION MULTIPLE ACCESS - 1. METHOD: FREQUENCY HOPPING TRANSMITTER SENDS DATA IN SHORT BURSTS CHANGING FREQUENCIES QUICKLY IN A CODED FASHION
1 5 8 7 6 ......
time
EACH USER HAS DIFFERENT CODE E
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THERE MIGHT BE SOME COLLISIONS BUT THIS IS NOT CRITICAL
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• THERE ARE TWO TYPES OF FREQENCY HOPPING: FAST: MULTIPLE HOPS PER BIT SLOW: MULTIPLE BITS PER HOP IN THE GSM SYSTEM, SLOW HOPPING IS IMPLEMENTED, IN THE BLUETOOTH SYSTEM MUCH FASTER BUT BIT RATE IS FASTER TOO.
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MANY USERS USE THE SAME BAND BUT WITH DIFFERENT HOPPING SEQUENCE. SOMETIMES HOPS COLLIDE BUT LOSS IS ELIMINATED BY ERROR PROTECTION FREQUENCY HOPPING ALLOWS TO 1. ENSURE IMMUNITY AGAINST DISTORTIONS 2. REUSE THE SPECTRUM BY MANY USERS 3. ENHANCE SECURITY, IT IS HARD TO INTERCEPT TRANSMISSION
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2. METHOD: DSSS – DIRECT SEQUENCE SPREAD SPECTRUM HERE EACH SIGNAL SYMBOL IS MULTIPLIED BY A SEQUENCE pi(t) which is different for each user i and has the following properties
n-1
Spi(t)pj(t) =
t=0
1 for i=j 0 otherwise
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• THE SEQUENCE IS SELECTED IN SUCH A WAY THAT ITS SPECTRUM RESEMBLES WHITE NOISE, THAT IS, IT IS ALMOST FLAT IN WIDE BAND • ASSUME THAT ALL USERS SEND THEIR SIGNALS IN THE WIDE BAND, THE SIGNALS ADD UP, THIS LOOKS LIKE INCREASED NOISE LEVEL IN THE CHANNEL
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• IF THE USER i RECEIVES THE SIGNAL AND MULTIPLIES IT BY THE pi(t), ITS OWN SIGNAL WILL MULTIPLY AND SUM TO 1 AND OTHER SIGNALS TO ZERO. • SUCH SYSTEM CAPACITY IS LIMITED BY PERFORMANCE, USAGE IS LIMITED BY NOISE
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COMPARISON OD BOTH METHODS DSSS SIGNAL SPECTRUM IS FLAT
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• PROCESSING GAIN FOR CDMA
G = BSPREAD/B BSPREAD - CODE RATE (CODE SEQUENCE BIT RATE)
B – SIGNAL RATE
G=10-100 TYPICALLY
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• PRINCIPLE OF SIGNAL CORRELATION DETECTION IS VERY ROBUST • ANOTHER ADVANTAGE IS THAT NEIGHBOURING TRANSMITTERS CAN USE THE SAME BAND HANDOVER BETWEEN BASE STATIONS CAN BE ”SOFT”, WE WILL EXPLAIN THIS LATER
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CDMA HAS HIGH RESISTANCE TO INTERFERENCE
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RADIO WAVES
RADIO WAVES ARE LIMITED RESOURCE WHICH HAS TO BE USED EFFICIENTLY RADIO WAVES PROPAGATE IN SPACE IN A WAY DEPENDING OF FREQUENCY HIGH FREQUENCY RADIO WAVES PROPAGATE WITHIN HORIZON AND ARE ATTENUATED ACCORDING TO THE FORMULA L=C + log(d) L is loss in dB, C is constant, d is distance
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RADIO WAVES - PROPAGATE IN STRUCTURES AND BUILDINGS (C CONSTANT) -ARE REFLECTED FROM OBJECTS -HAVE INTERFERENCE LIKE WAVES THUS, RADIO SYSTEMS HAVE TO BE DESIGNED CAREFULLY TAKING INTO ACCOUNT PHYSICAL DISTRIBUTION OF RADIO WAVES
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THERE ARE SEVERAL METHODS FOR EFFICIENT MANAGEMENT OF RADIO TRANSMISSION: - FDM, FREQUENCY DIVISION MULTIPLEX TRANSMITTERS USE DIFFERENT FREQUENCY BANDS (example: television, radio) -TDM, TIME DIVISION MULTIPLEX, TRNSMITTERS ARE USED AT DIFFERENT TIMES -SDM, SPATIAL DIVISION MULTIPLEX, TRNSMITTERS OPERATE IN SEPARATED AREAS (mobile phones) -CDM, CODE DIVISION MULTIPLEX, TRANSMITTERS OPERATE WITH DIFFERENT ACCESS CODES WHICH MINIMIZE INTERFERENCE (mobile phones) If we have transmitters and receivers we can talk about Access to the reception and systems are called CDMA, FDMA,...
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THESE ACCESS SYSTEMS CAN BE USED IN ALL KIND OF COMBINATIONS, TDMA/FDMA/SDMA ETC.
SYSTEMS CAN BE DESIGNED FOR OPTIMAL USE OF RADIO WAVES WITH THOSE ACCESS SYSTEMS:
1. SDMA – IS A BASIS FOR CELLULAR SYSTEMS, FREQUENCIES CAN BE REUSED IN SEPARATED CELLS
THERE IS A TRANSMITTER IN THE CENTER OF EACH CELL
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• THE COST OF THIS IS THAT ONE NEEDS TO IMPLEMENT HANDOVER WHEN MOVING BETWEEN THE CELLS AND ALSO TRACK THE LOCATION USERS • WITHIN THE CELLS TDMA/FDMA, CDMA CAN BE REUSED IN DIFFERENT COMBINATIONS EXAMPLE: THE GSM SYSTEM: OPERATES IN TWO BANDS 900 AND 1800 MHz, WIDTH 25 AND 75 MHz, WIDTH OF ONE CHANNEL – 200 kHz FDMA CHANNEL DIVIDED INTO 8 time slots - TDMA WHY? IT SAVES THE NUMBER OF TRANSMITTERS
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- IN ADDITION THE GSM SYSTEM HAS ALSO A KIND OF CDMA – FREQUENCY HOPPING: FREQUENCY BAND CAN BE CHANGED FROM TIME SLOT TO TIME SLOT ACCORDING TO SPECIFIC PATTERN. THIS LEADS TO STATISTICALLY BETTER USE.
-HOW MANY USERS CAN BE SUPPORTED? IF ONE BASE STATION TAKES 5 MHz IT CAN SUPPORT 200 USERS (175). MINIMUM CELL SIZE IS 100-500M(?). SO WE CAN GET HIGH DENSITY OF USERS/km2
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RADIO NETWORK SERVICES:
- BROADCAST, SINGLE TRANSMITTER, MULTIPLE RECEIVERS - PASSIVE - COMMUNICATIVE – 1-1 RADIOTELEPHONE - CELLULAR, CELL TRANSMMITTERS, MANY (MOBILE) USERS - ACTIVE - WIDE AREA – BIG COVERAGE - SMALL AREA, WIRELESS LAN -AD HOC NETWORKS, NO FIXED CELL TRANSMITTERS TERMINALS CAN SERVE AS CELL TRANSMITTERS TOO, EXAMPLE PERSONAL WIRELESS LAN BLUETOOTH
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•
WHAT MIGHT BE THE RADIO SYSTEM AND WIRELESS NETWORK REQUIREMENTS FOR MULTIMEDIA? 1. SUFFICIENT BANDWIDTH HUNDREDS kb/s to FEW MEGABITS PER SECOND 2. STREAMING WITH BANDWIDTH RESERVATION 3. FAST INTERACTIVITY (CONNECTIONLESS SERVICE)
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4. RELIABLE CONNECTIONS WITH NO DATA LOSS, ESPECIALLY IMPORTANT WITH MOBILE USERS IT CAN BE QUITE DIFFICULT WITH STREAMS OF SEVERAL HUNDRED KILOBITS PER SECOND
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