CDMA 120 – cdmaOne and CDMA2000 Concepts and Terminology phần 3 pdf

Section 2: BackgroundCDMA 120 Section 2-29 cdma university Coherent / Non-Coherent Detection RVS FWD O 1 QZ– 2 ABC 3 DEF I N FO SEND END D V Coherent Detection of the Forward Link Cohere

Section 2: Background

CDMA 120 Section 2-29

cdma university Coherent / Non-Coherent Detection

RVS

FWD O

1 QZ– 2 ABC 3 DEF

I N FO SEND END

D V

Coherent Detection of the Forward Link

Coherent detection requires that the carrier signal used in the transmitter and the receiver are

perfectly matched in both frequency and phase In cdmaOne systems, the Forward link detection in the mobile is coherent (Forward link is BTS>>>mobile.)

Non-coherent Detection of the Reverse Link of IS-95

Non-coherent detection refers to the case where the phase information is not available to the

receiver In cdmaOne systems, the Reverse link is a non-coherent link since the phase information

is not available As a result, the detection process at the Base Station becomes non-coherent.

(Reverse link is mobile>>>BTS.)

Note: For CDMA2000 Radio Configuration RC-3 to RC-6, a Pilot is provided on the Reverse link and therefore coherent demodulation can be employed.

CDMA 120 Section 2-30

1 2 3

7 8 0

D V

Signal-to-Noise ratio (SNR)

Signal-to-Noise ratio is used to evaluate the performance of a radio communication system.

It is defined as the decibel of the ratio of signal power to noise power:

N

SP P SNR = 10 log

Section 2: Background

CDMA 120 Section 2-31

0 V

+1 V

(a)

-1 V +1 V

-1 V +1 V

(b)

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Correlation

Correlation is a measure of similarity between any two arbitrary signals It is computed by

multiplying the two signals and then summing (integration) the result over a defined time window For example:

z Figure (a) — the two signals are identical and therefore their correlation is 1 or 100%.

z Figure (b) — the two signals are uncorrelated and therefore knowing one of them does not provide any information on the other.

CDMA 120 Section 2-32

Tx

Digital communication systems use E /N

Figure of Merit in Digital Systems

The primary measure of performance in digital systems is the ratio of bit energy (E b ) to noise

density (N 0 ): E b /N 0 Unlike analog signals that are power signals, digital signals are energy signals.

A useful relationship is obtained by relating E b /N 0 to the signal to noise ratio:

N

E

N N S

b =

0

R

W x P

P N

EN

S

b =

0

Section 2: Background

CDMA 120 Section 2-33

MMT98010132Ac-rev1.emf

Cellular PCS Fixed Wireless

Cellular

Commonly viewed as wireless service to mobile subscribers in the 800 MHz band.

PCS

Wireless service for mobile subscribers in the 1900 MHz band.

Fixed Wireless (Wireless Local Loop)

Wireless service for residential and office subscribers using fixed terminals Fixed wireless

services are provided in either the 800 MHz or 1900 MHz bands.

Cellular Channels

The FCC has allocated spectrum for use by cellular service providers The allocated spectrum is divided into channels that are separated by 30 KHz This is a direct result of the analog

requirement for 30 KHz to support a single subscriber using FM modulation.

Each CDMA channel is approximately 1.25 MHz There is no guard band required between

adjacent CDMA channels However, a guard band is established between a CDMA system and any other system.

Preferred Channels

Each system operator of the cellular band (A, B) has a Primary and a Secondary Channel.

These are 283 and 691 for the A carrier and 384 and 777 for the B carrier.

AnalogChannelCount

CDMAChannelNumber

TransmitterFrequencyAssignment (MHz)Mobile Base

991 824.040 869.040///////// 22

333 834.990 879.990

334 835.020 880.020///////// 22

355 835.650 880.650

356 835.680 880.680B

644 844.320 889.320

645 844.350 889.350///////// 22

666 844.980 889.980

667 845.010 890.010///////// 22

716 846.480 891.480

717 846.510 891.510///////// 22

799 848.970 893.970

MMT98010133Ag.emf

Section 2: Background

CDMA 120 Section 2-35

Reverse CDMA Channel

1.25 MHz

MMT98010109Ag.emf

CDMA Channels in the Cellular Band

In the cellular band, a CDMA channel is a pair of frequencies 45 MHz apart In this example,

channel 758 consists of a Reverse CDMA Channel centered at 847.74 MHz and a Forward CDMA Channel centered at 892.74 MHz.

CDMA 120 Section 2-36

cdma university The Cellular CDMA Channel (continued)

Each block has preferred channels to reduce subscriber access time These preferred

channels are spaced every 1.25 MHz (25 channels) beginning with Channel 25 (Channels

25, 50, 75, 100, 125 and so on) Channels that occur on the border between blocks,

however, are not preferred channels (e.g., Channel 300).

Transmit Frequency Band (MHz)

Block Designator

Val id CDMA

Fr equency

A ssignments

CDMA Cha nnel Number

Personal Sta tion

Base Sta tion

A(15 M Hz)

Not Val idValidCond Val id

0–2425–275276–299

1850.000–

1851.2001851.250–

1863.7501863.800–

1864.950

1930.000–

1931.2001931.250–

1943.7501943.800–

1944.950D

(5 MHz)

Cond Val idValidCond Val id

300–324325–375376–399

1865.000–

1866.2001866.250–

1868.7501868.800–

1869.950

1945.000–

1946.2001946.250–

1948.7501948.800–

1949.950B

(15 M Hz)

Cond Val idValidCond Val id

400–424425–675676–699

1870.000–

1871.2001871.250–

1883.7501883.800–

1884.950

1950.000–

1951.2001951.250–

1963.7501963.800–

1964.950E

(5 MHz)

Cond Val idValidCond Val id

700–724725–775776–799

1885.000–

1886.2001886.250–

1888.7501888.800–

1889.950

1965.000–

1966.2001966.250–

1968.7501968.800–

1969.950F

(5 MHz)

Cond Val idValidCond Val id

800–824825–875876–899

1890.000–

1891.2001891.250–

1893.7501893.800–

1894.950

1970.000–

1971.2001971.250–

1973.7501973.800–

1974.950C

(15 M Hz)

Cond Val idValidNot Val id

900–924925–11751176–1199

1895.000–

1896.2001896.250–

1908.7501908.800–

1909.950

1975.000–

1976.2001976.250–

1988.7501988.800–

1989.950

CDMA 120 Section 2-38

Reverse CDMA Channel

Forward CDMA Channel

1.25 MHz

MMT98010111Ag.emf

CDMA Channels in the PCS Band

In the PCS band, a CDMA Channel is a pair of frequencies separated by 80 MHz In this example, CDMA Channel 25 has a Reverse CDMA Channel centered at 1851.25 MHz and a Forward

CDMA Channel centered at 1931.25 MHz.

Section 2: Background

CDMA 120 Section 2-39

cdma university The PCS CDMA Channel (continued)

Notes

The US PCS band is based on 50 KHz channels Thus, a 1.25 MHz CDMA channel is 25 channels (25 x 50 KHz = 1.25 MHz) wide, excluding any required guardband.

CDMA 120 Section 2-40

cdma university Fixed Wireless (Wireless Local Loop)

MMT98010692Ac.emf

Fixed Wireless (Wireless Local Loop, WLL)

A cdmaOne system can provide an efficient, cost-effective alternative to the traditional wireline local loop A CDMA-based interface can be used to support only fixed wireless subscribers or a mix of fixed wireless and high mobility subscribers.

Section 2: Background

CDMA 120 Section 2-41

SECTION REVIEW

105AC_00

• cdmaOne and its Key Standards

• Primary Multiple Access Techniques

• CDMA Network Architecture

• Digital Spread Spectrum Signal Modulation Steps

z Define the term cdmaOne.

z List the key standards that govern the operation of cdmaOne systems.

z Define the primary Multiple Access techniques employed today: FDMA, TDMA, and

CDMA.

z Describe the architecture of a CDMA network.

z List the fundamental processing steps in the modulation of a digital spread spectrum signal.

z Define the term “Fast Fading.”

z Describe the allocations of cellular and PCS spectrum in the United States.

z Describe the applications of cdmaOne systems.

Comments/Notes

Section 3: Codes in cdmaOne

CDMA 120 Section 3-1

CDMA 120 Section 3-2

SECTION INTRODUCTION

106AC_00.emf

• Basics of Spreading Codes

• Orthogonal Sequences (Walsh Codes)

• Pseudorandom Noise (PN) Sequences

Basics of Spreading Codes

cdmaOne systems use two types of code sequences:

z Orthogonal sequences (Walsh codes).

z Pseudorandom noise (PN) sequences.

This section examines the basic properties of both codes.

Note: The CDMA2000 Overview section will introduce a new type of code, the Quasi-orthogonal

code.

Section 3: Codes in cdmaOne

CDMA 120 Section 3-3

cdma university Section Introduction (continued)

SECTION INTRODUCTION

106AC_00.emf

• Basics of Spreading Codes

• Orthogonal Sequences (Walsh Codes)

• Pseudorandom Noise (PN) Sequences

Section Learning Objectives

After completing this section, you will be familiar with the basic properties of both orthogonal and

PN codes and will be able to:

z List the two types of code sequences used in cdmaOne systems.

z List and describe the properties of orthogonal and PN codes.

z Describe how these two code sequences are generated.

z Describe the process of time shifting the PN code sequence (Masking).

z Describe the process of spreading and despreading using these two codes.

z Describe the properties of the PN short and long codes.

CDMA 120 Section 3-4

A

A 0 0 1 1

0 1 0 1

0 0 0 1MMT98010155Ag.emf

A 0 0 1 1

0 1 0 1

0 1 1 0MMT98010156Ag.emf

AND Function

The “AND Function” figure depicts a two-input AND gate and its corresponding truth table.

A and B denote the inputs to the gate, while Y denotes its output The AND operation (or function)

is simply defined by the equation:

The AND gate outputs a logic “1” only when both inputs A and B are logic “1” as well The output

of the AND gate is zero if any of its inputs assumes the logic “0” state Understanding AND gate operation will prove useful in the discussion that follows.

XOR Operation

The “XOR Function” figure depicts a two-input XOR gate and its corresponding truth table.

A and B denote the inputs, while Y denotes its output The XOR operation (or function) is simply defined by the equation:

The XOR gate produces a one when the two inputs are at opposite levels When the total number of ones at the inputs is odd, the result of XORing them is “1” Understanding XOR operation is

B A

Y = •

B A B A B A

Y = ⊕ = • + •

Section 3: Codes in cdmaOne

CDMA 120 Section 3-5

Orthogonal functions have ZERO CORRELATION Two binary sequences are orthogonal if the process of "XORing"

them results in an equal number

of 1's and 0's:

EXAMPLE:

0000 0101 0101

CDMA 120 Section 3-6

cdma university Generation of Orthogonal Codes

• Repeat – Right – Below

Creating Orthogonal Functions

Orthogonal codes are easily generated by starting with a seed of 0, repeating the 0 horizontally and vertically, and then complementing the 0 diagonally This process is continued with the newly- generated block until the desired codes with the proper length are generated.

Sequences created in this way are referred to as Walsh codes.

Section 3: Codes in cdmaOne

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263

CDMA 120 Section 3-8

In orthogonal spreading, each encoded symbol is XORed with all 64 chips of the Walsh code For example, in the figure a symbol of value “1” is orthogonally spread with Walsh code 59, thus

yielding a 64-chip representation of the symbol.