Lesson 2 Cellular Concept (蜂巢式概念 - 天主教輔仁大學 … · 2016-01-11 · Page 1 Lesson 2 Cellular Concept (蜂巢式概念) Mobile Radio Communication Seminar Lesson

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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



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



Cell Antenna (3 Ant. Each sector)

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Cell site

Dallas, Texas



Cell Site Planning (Dallas Area)

Page 4



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



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

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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



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

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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



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.

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• 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



• 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

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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



• 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

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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!!



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

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• 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



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



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

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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



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?

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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



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

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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



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

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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.



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



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



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

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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



Lesson 2 Complete

Documents

Lesson 2 Cellular Concept (蜂巢式概念 - 天主教輔仁大學 … · 2016-01-11 · Page 1 Lesson 2 Cellular Concept (蜂巢式概念) Mobile Radio Communication Seminar Lesson