lesson 2 cellular concept (蜂巢式概念 - 天主教輔仁大學 … · 2016-01-11 · page 1...
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Page 1
Lesson 2Cellular Concept (蜂巢式概念)
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 1 Dr. Sheng-Chou Lin
Lesson 2 Outline
Introduction to cellular Concepts•Cellular structure, Architecture•Why cellular
Introduction to Frequency Planning Concepts & Philosophy•Review: AMPS Spectrum, the Resource•Frequency Reuse Factor N: How to Select, Implications•Ground Rules & Constraints Dictating Frequency Plan
–Hardware constraints–Introduction to Interference constraints
Practical Frequency Planning•Frequency Planning Process Overview•Using real-world tools to judge effectiveness of frequency plan
Sectorization•Rationale: Overview of Capacity and C/I Tradeoffs
Handoff
Page 2
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 2 Dr. Sheng-Chou Lin
Cellular Structure
Geometric Shapes: Square, triangle, Hexagon•without overlap•with equal area•Hexagon: for a given distance (center to farest point) the largest area
Cell Diagrams
o
oo
oo o o o
o
Imaginary Ideal Real
easy to draweasy to consider
free spaceisotropic antennas
The Real World
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 3 Dr. Sheng-Chou Lin
Cell Antenna (3 Ant. Each sector)
Page 3
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 4 Dr. Sheng-Chou Lin
Cell site
Dallas, Texas
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 5 Dr. Sheng-Chou Lin
Cell Site Planning (Dallas Area)
Page 4
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 6 Dr. Sheng-Chou Lin
Dallas MTA Proposed Topology (1999)
Wireless NetworkWireless Network(HLR)(HLR)MSC
BSC
MSC
BSC
BSCBSC
87 BTSs
18 BTSs82 BTSs
86 BTSs
AustinFort Worth
Dallas2Dallas1
BSC
BSC
10 BTSs
15 BTSs
48 BTSs
10 BTSs
35 BTSs 16 BTSs
69 BTSs
83 BTSs
12 BTSs
BSS (Base Station Subsystem)Architecture
•Coding• Access and Duplex
Techniques• Modulation• RF System• Air Interferface
Challenges
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 7 Dr. Sheng-Chou Lin
MSC
BSC
IWF
PSTNPSTN
(Wireline)(Wireline)
WirelineTerminal
LocalPSTN
64 KBPS
CompressedVoice
64 Kbps
BSC
WirelessNetwork
(HLR)
• Wireless is compressed voice at 8 - 13 Kbps.
• But, transport is at 64 Kbps
• An MSC covers 6-12 EO Areas.
• Hence, transport distances are long
Wireless Transport
Page 5
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 8 Dr. Sheng-Chou Lin
Router
IS
MTX
MTX
PSTN
Public Network
DMS-100PBX
DMS MTX
DMS MTX
ICPT1/E1
T1/E1
T1
ICRM
ICRM
ICRM
ICRM
ICRM
ICRM
T1
T1
T1ICP
inter-systemhandofftrunks
Wire Line
Wireless
Cell Sites
DID / IDIDtrunks
T1 T1T1 POTS
linecard
DMS-200DMS-100
BRIPRI ISUP
ISUP
LPP
LPP
Router
Ethernet LAN
Networking &Data Traffic
Service Provider’sData Network
Other Service Provider
Internet ServiceProvider
ISTRU
IS
ISTRU
MTX System Architecture
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 9 Dr. Sheng-Chou Lin
To resolve spectral congestion and user capacity
To provide additional radio capacity radio capacity with noadditional increase in radio
Solution•Large Cells small cells, High power low power•Handoff and interference go up•Frequency Reuse: result in CCI (Cochannel interference)
Frequency Planing•Selecting and allocating channel groups for all of the cellular base stations
(Channel assignment)•To reduce CCI,ADJ (Adjacent Interference)•Different groups of channels for neighboring base stations
Why cellular
Page 6
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 10 Dr. Sheng-Chou Lin
Band-A & Band-B Channels vs.Frequency
A B A' B' RA"
BASE STATION Tx
A B A' B' RA"
MOBILE TxFREQ.(MHz)
CH. #
824 825 835 845 846.5 849 851
991 1 333 666 716 799 1023
869 870 880 890 891.5 894 896
FREQ. (MHz)
ch. # 991 1 333 666 716 799 1023
R = Reserved
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 11 Dr. Sheng-Chou Lin
Cellular Band
BAND-A BAND-B
BAND-AControl Ch.
BAND-BControl Ch.
Ch. No. 1 312 355 666 716 799 991 1023
Extended-B
Extended-A
21 2150 33
83
Band-A Voice Channels: 1 - 312 = 312 ch.667 - 716 = 50 ch.991 - 1023 = 33 ch.
Tot. No. of Voice Ch. = 395
Band-A Control Channels: 313 - 333 = 21 Ch
Band-B Voice Channels: 355 - 666 = 312 ch.717 - 799 = 83 ch.
Tot. No. of Voice Ch. = 395
Band-B Control Channels: 334 - 354 = 21 ch.
Page 7
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 12 Dr. Sheng-Chou Lin
• All CDMA RF carriers are 1.25 MHz. Wide can serve ~22 users w/8 kb vocoder (~17 users w/13 kbvocoder)
• The cellular spectrum of one operator is 12.5 MHz. wide. You expect that 10 CDMA carrierswould fit. However, only 9 carriers can be used
– operators must maintain a “token”AMPS presence for several years– “guard bands”are required at the edges of frequency blocks or any frequency boundaries
between CDMA/non-CDMA signals
– no guard bands are required between adjacent CDMA carriers
Possible CDMACenter Freq. Assignments
ChannelNumbers
Forward link (i.e., cell site transmits)Reverse link (i.e., mobile transmits)824MHz
849MHz
869MHz
894MHz
otheruses
A’’ A’’A B A’ B’
1 10 10 1.5 2.5
A B A’ B’
1 10 10 1.5 2.5
991
1023 1
333
334
666
667
716
717
799
991
1023
1 333
334
666
667
716
717
799
~300 kHz.guard bands?possibly required if adjacent-frequency signals are non-CDMA (AMPS, TDMA, ESMR, etc.)
CDMA 800 MHz Cellular Spectrum Usage
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 13 Dr. Sheng-Chou Lin
• A, B, and C licenses can accommodate 11 CDMA RF channels in their 30 MHz of spectrum
• D, E, and F licenses can accommodate 3 CDMA RF channels in their 10 MHz of spectrum
• 260 kHz guard bands are required on the edges of the PCS spectrum to ensure no interference occurswith other applications just outside the spectrum
Guard Bands
Forward link (i.e., cell site transmits)Reverse link (i.e., mobile transmits)1850MHz
B
T
A
B
T
A
B
T
A
B
T
A
B
T
A
B
T
A
Paired Bands
MTA BTAMTABTA MTAMTA
1910MHz
1930MHz
1990MHz
Data Voice
A D B E F C A D B E F C
15 51010 1515151515 555 55
Licensed Licensed
Unlicensed
0
Channel
Numbers 299
300
400
699
700
800
900
1199 0
299
300
400
699
700
800
900
1199
CDMA PCS 1900 MHz Spectrum Usage
Page 8
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 14 Dr. Sheng-Chou Lin
Frequency Reuse (頻率重複使用)
Cluster size N•S = kN, S: Total channels available
for user–k: channels per cell,–N: N cells a cluster
•C = MkN = MS = The total number ofduplex channels.A cluster is replicated M times
•N = 4, 7, 12 typically
Capacity and frequency reuse•Capacity = Channels per cell = (total
channels) / N•Capacity goes up as N decreases,
but CCI goes up
N=7
12
3
4
5 6
7
4
6
1
1
11
1
147 2
7
2
5
47
36
1
2
34
1
1
1
1
1
1
2
2
2
2
2 3
33
3
33
44
424 4
4N=4
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 15 Dr. Sheng-Chou Lin
• Move I cellsalong any chain
• Turn 60 counter-clockwise andmove J cells
Given our propagation model anddesired C/I, we determined D/R inthe last slide.
Now we can establish a channelassignment pattern using thesmallest number of cells which willseparate co-channel cells by atleast D/R. N cells are required.
N is determined from geometry, asshown at left:
Frequency ReuseD/R determines required minimum N
D =distance between twoco-channel transmitters
R = coverage radius where acell is the best server
Example Sketch demonstrates N=7
N = I + I x J + J2 2
N = ( )2 3DR /
D
f1f7
f2
f1
f3J=1
f6
f4
f2
f5
f4 f7
I=2
f1
R R
X+60
X
Page 9
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 16 Dr. Sheng-Chou Lin
N=1: Lethal•awful C/I: every neighbor is cochannel•every neighbor cell is adjacent
channel too!•center 1/3 of each cell OK, rest is lost
in horrible interference
1
11
11
1
1
A Tour of Reuse Factor N
2
3
11
1 1
1
11
2
2 2
22
23
3 3
3
3
3
N = 3 : Better, but still lethal•Cochannel neighbors are now spaced
at D/R of 3.0 - better, but not 18 dB....•Each cell has 6 adjacent channel
neighbors - all the neighbors areadjacent!!
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 17 Dr. Sheng-Chou Lin
Frequency ReuseImplications of N
N is the number of cells in thefrequency reuse pattern.
N is a very important factor, since itdetermines:
Capacity of A CellChannels per cell =
(total channels) / N•As N goes up, capacity becomes
progressively worse Interference
•As N goes up, interferencebecomes progressively better
Channelsper Cell* D/R
395198132997966564944
1.7322.4493.0003.4643.8734.2434.5834.8995.196
40 5.47736 5.745
N
123456789
101112 33 6.000
*Assuming use of 395 voice channelsincluding expanded spectrum
Page 10
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 18 Dr. Sheng-Chou Lin
• nEach wireless technology (AMPS,NAMPS, D-AMPS, GSM, CDMA) uses aspecific modulation type with its ownunique signal characteristics
• nThe total traffic capacity of a wirelesssystem is determined largely by radiosignal characteristics and RF design
• nRF signal vulnerability to Interferencedictates how much interference canbe tolerated, and therefore how farapart same-frequency cells must bespaced
• nFor a specific S/N level, the SignalBandwidth determines how many RFsignals willit?in the operatorlicensed spectrum
AMPS , D-AMPS , N-AMPS
CDMA
30 30 10 kHz
200 kHz
1250 kHz
1 3 1 Users
8 Users
22 Users1
1
11
1
11
11
1
11
1
1
12
34
4
32
56
17
Typical Frequency Reuse N=7
Typical Frequency Reuse N=4
Typical Frequency Reuse N=1
Vulnerability:C/I 17 dB
Vulnerability:C/I 12-14 dB
Vulnerability:E b/No 6 dB
GSM
17 dB = 101.7
50
14 dB = 101.4
25
12 dB = 101.216
Spectrum (頻譜) Usage and System Capacity (容量)Signal Bandwidth, Vulnerability, and Frequency Reuse
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 19 Dr. Sheng-Chou Lin
Sectorization
Advantages•Cell radius unchanged•CCI D/R , cluster size N , frequency
reuse , capacity •Omni-directional antenna Directional
antenna•Three 120o sectors, six 60o sectors•For N=7 and 120o sectors, number of CCI
decreases from 6 to 2. C/I = 24.2dB.•C/I =18 dB < (sectoring CCI, N=7). = N
12 (omni), Increase in capacity 12/7•Downtilting the sector antenna to reduce
CCI Disadvantages
•Number of antenna •Trunking efficiency , channels 3
groups•Handoffs , not a major concerns since it
occurs within the same cell withoutintervention from MSC
Page 11
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 20 Dr. Sheng-Chou Lin
Comparison of Typical CoverageUsing Omni and Sector Antennas
-95 dBm
-113 dBm
Miles0 5 10 15 20 25
Coverage ComparisonUsing Sector and Omni Antennas
• ERP = 100w• Ant. Ht. 150 ft.• DB-833 vs Omni Whip
The figure shows computed coveragein miles for•an omnidirectional collinear vertical
antenna and•a panel antenna typically used for sector
applications•Computation used Okumura-Hata formula
from Lesson 3 -95 dbm is typical design limit for edge
of a cell -113 dbm is interfering contour which
would deliver 18 dB C/I at a distant celledge (-95 dbm)
Notice how substantially bothcoverage and interference aresuppressed off the back of the sectorantenna
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 21 Dr. Sheng-Chou Lin
Rationale for Sectorization
Sectorization is a tool for moretightly controlling frequencyutilization in a cellular system
We saw that if the number ofchannels remains constant,sectorization actually reduces thecapacity of a cell
So, why would anyone want tosectorize?•In hope of being able to reduce N•To substantially improve C/I, even if N
is not changed•To gain flexibility to control traffic
distribution and reduce interference attroublesome boundaries where largecells and small cells meet
45
1515
15
35.61erlangs
27.03erlangs
N=7 Omni
N=4Sector?
Page 12
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 22 Dr. Sheng-Chou Lin
Sectorization Improves Reuse Density In a system where N=7 omni works well,
N=4 120 sector may be feasible•possible 55% increase in capacity
Problems and additional considerations:•increased system complexity•handoffs & handovers very critical to achieving
acceptable performance•possibility of specific local propagation
conditions unsuitable for sectorization•cost of sectorization
N=7 Omni Plan
N=4 120ºSector Plan
-95 dBm-113 dBm
C/I = 18 dB
N=7Omni
N=4 120ºSector
Voice Channels
Total voice channels 312( ignoring expanded spectrum )
45/cell 26/sector78/cell
Capacity, Erlangs 35.6 18.4/sector55.2/cell
N=7/N=4Comparison
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 23 Dr. Sheng-Chou Lin
Handoff (交遞)
Mobile automaticallytransfers the call to anew channel of the newchannel base station.
Handoff threshold isslightly stronger than aparticular signal(minimum signal foracceptable voicequality)
Mobile SwitchingCenter (MSC)
Local TelephoneExchange
Call Starts
Cell-1
t 2
Call Ends
Cell-2
t 1
t 3
Cell-3
Hand-off Required atBoundary Crossings
Page 13
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 24 Dr. Sheng-Chou Lin
For Call Continuation
•to avoid dropping call as mobileleaves coverage range of theserving cell
To Avoid Interference
•maintain desired C/I ratio
•avoid giving, receivinginterference in other cells
For Operational Reasons
•For Load Balancing,Maintenance on VCH, etc.
Basic Cellular Call Processing:Why Handoff
AB
CD
Distance, km
A B
RSSI,dBm
-120
-50
C DSites
C/I
RSSI
Drop
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 25 Dr. Sheng-Chou Lin
Hand-off Mechanism
Base Station RF Antenna
Adjacent Cell
Adjacent Cell
Adjacent Cell
Adjacent Cell
Adjacent Cell
Adjacent Cell
1. Base Station continiously measure RSSI [C/I]2. Based on this measurements deceide the Handoff request.3. Once Handoff request is identified, asks adjacent cells to measure the
RSSI on that mobile and send the measurements.4. Identifies the candidate cell for Handoff5. Starts Handoff
Page 14
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 26 Dr. Sheng-Chou Lin
CDMA vs. AMPS/TDMA Handoffs Soft handoff: unique handoff capability provided by CDMA, since
•spread spectrum shares the same channel in every cell.• Its ability to select between the instantaneous received signals from a variety of BS
AMPS/TDMA Handoffs Break-before-make AMPS takes approximately 200 ms TDMA takes between 400-600 ms Can diminish call quality Increased chance of dropped calls
CDMA Handoffs Make-before-break Directed by the mobile not the base
station Undetectable by user Improves call quality
CellSiteA
HANDOFF
CellSite
B
MAKE
AMPSTDMA
BREAK
CellSite
A
CellSite
B
CellSite
A
CellSiteB
CDMA
Soft handoff can only be used between CDMAchannels having identical frequency assignments.
Soft handoff provides diversity of Forward and ReverseTraffic Channel paths on the boundaries between basestations.
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 27 Dr. Sheng-Chou Lin
Soft handoff
Soft Handoff :
Eliminates “Ping-Pong”effect and chances of dropped calls
CellSite
A
CellSite
BMTX
BSC
PSTN
the mobile station starts communications with a target basestation without interrupting communications with the currentserving base station.
Can involve up to three cells simultaneously and use all signals Mobilestation compares frames from each cell, and uses the best one
Page 15
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 28 Dr. Sheng-Chou Lin
Channel AssignmentIn channel assignment, we dole out
the channels to the cells, muchlike a dealer in a card game dealsout cards from the deck until everyplayer has a set.
A channel set is a collection ofchannels which could be assignedat one cell
Channels in a channel set normallyare N channels apart, where N isthe reuse factor
Channels in a set must meetcombiner minimum frequencyspacing requirements
Notice that Sets 1 and 3(i.e., 1 and N) are adjacent
frequencies
If N=3, for example:
1 2 3 4 5 6 7 8 9 10 12Channels
Freq.
Channel Set 1 1, 4, 7, 10, . . .Channel Set 2 2, 5, 8, 11, . . .Channel Set 3 3, 6, 9, 12, . . .
12
3
2
31 1
1
2
3
32
N=3
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 29 Dr. Sheng-Chou Lin
Frequency Planning for N=7
B-BAND N=7 CHANNEL SETSChannel Set 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21Designations H1 I1 J1 K1 L1 M1 N1 H2 I2 J2 K2 L2 M2 N2 H3 I3 J3 K3 L3 M3 N3
Control Ch. 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354
Voice 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375Channels 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396
397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666
Expanded 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732Spectrum 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753
754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795796 797 798 799
Set Channel Count Summary 416Control 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
Normal B 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 14 14 14B' 4 4 4 4 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4
Total Voice 19 19 19 19 18 19 19 19 19 19 19 19 19 19 19 19 19 19 18 18 18
Page 16
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 30 Dr. Sheng-Chou Lin
Wireless Comm. Definitions
Base Station (BS) Control Channel Forward Channel Full Duplex System Half Duplex System Handoff Mobile Station (MS) Mobile Switch Center (MSC) Page Reverse Channel Roamer Simplex System Subscriber Transceiver
Mobile Radio Communication Seminar
Lesson 2 - Cellular Concept 31 Dr. Sheng-Chou Lin
Lesson 2 Complete
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