Week1 IntroductiontoDigitalCommunications EE4601 Communication Systems Week1...

download Week1 IntroductiontoDigitalCommunications EE4601 Communication Systems Week1 IntroductiontoDigitalCommunications

of 22

  • date post

    05-Aug-2020
  • Category

    Documents

  • view

    0
  • download

    0

Embed Size (px)

Transcript of Week1 IntroductiontoDigitalCommunications EE4601 Communication Systems Week1...

  • EE4601 Communication Systems

    Week 1

    Introduction to Digital Communications Channel Capacity

    0 c©2011, Georgia Institute of Technology (lect1 1)

  • Contact Information

    • Office: Centergy 5138

    • Phone: 404 894 2923

    • Fax: 404 894 7883

    • Email: stuber@ece.gatech.edu (the best way to contact me)

    • Web: http://www.ece.gatech.edu/users/stuber/4601

    • Office Hours: TBA

    0 c©2011, Georgia Institute of Technology (lect1 2)

  • Introduction

    Digital communications is the exchange of information using a finite set of signal waveforms. This is in contrast to analog communication (e.g., AM/FM radio) which do not use a finite set of signals.

    Why use digital communications:

    • Natural choice for digital sources, e.g., computer communications.

    • Source encoding or data compression techniques can reduce the required

    transmission bandwidth with a controlled amount of message distortion.

    • Digital signals are more robust to channel impairments than analog signals.

    – noise, co-channel and adjacent channel interference, multipath-fading.

    – surface defects in recording media such as optical and magnetic disks.

    • Higher bandwidth efficiency than analog signals.

    • Encryption and multiplexing is easier.

    • Benefit from well known digital signal processing techniques.

    0 c©2011, Georgia Institute of Technology (lect1 3)

  • Protocol Stack (cdma2000 EV-DO) Overview 3GPP2 C.S0024 Ver 4.0

    Air Link Management

    Protocol

    Overhead Messages Protocol

    Packet Consolidation

    Protocol

    Initialization State Protocol

    Idle State Protocol

    Connected State Protocol

    Route Update Protocol

    Session Management

    Protocol

    Session Configuration

    Protocol

    Stream Protocol

    Signaling Link

    Protocol

    Radio Link Protocol

    Signaling Network Protocol

    Control Channel MAC

    Protocol

    Access Channel MAC Protocol

    Reverse Traffic Channel MAC

    Protocol

    Forward Traffic Channel MAC

    Protocol

    Connection Layer

    Session Layer

    Stream Layer

    Application Layer

    MAC Layer

    Security Layer

    Physical Layer

    Security Protocol

    Authentication Protocol

    Encryption Protocol

    Default Packet Application

    Default Signaling Application

    Location Update Protocol

    Address Management

    Protocol

    Key Exchange Protocol

    Physical Layer Protocol

    Flow Control Protocol

    1

    Figure 1.6.6-1. Default Protocols 2

    3

    • This course concentrates on the Physical Layer or PHY Layer.

    0 c©2011, Georgia Institute of Technology (lect1 4)

  • Cellular Radio Chipset

    P r o d u c t B r i e f

    A p p l i c a t i o n E x a m p l e Q u a d - B a n d E G P R S S o l u t i o n

    Power Bus Peripherals

    I2C Interface

    Power Bus Baseband

    I2C

    AC-Adaptor

    Charger

    Pre-Charge

    VBB2

    VRTC

    VBB1

    VMemory

    VBB USB

    VBB Analog

    VBB I/O Hi

    VUSB Host

    SM-POWER (PMB 6811)

    Control

    BB (LR)/Mem/Copro Step down 600 mA

    On-chip Reference

    VBT BB

    VRF3 (BT)

    VRF Main

    VRF VCXO

    Amp VDD

    LED Driver

    Motor Driver

    M

    NiMH/LiIon Battery

    Power Bus Bluetooth

    Power Bus RF

    S-GOLD2 (PMB 8876)

    D A

    A

    A D

    D

    I2S / DAII2S SSC

    TEAKLite®

    GPTU IR-Memory

    GSM Cipher Unit

    RF Control

    Speech and Channel

    Decoding Equalizer

    D A

    A D

    Speech and Channel

    Encoding

    8 PSK/GMSK Modulator

    D A

    A D

    SRAM

    MOVE Copro

    DMAC ICUKeypad

    USB FS OTG

    Fast IrDA

    MMC/SD IF

    CAPCOM

    GPTU

    RTC

    I2C

    JTAG

    AUX ADC

    SCCU

    FCDP

    EBU

    GSM Timer

    GEA-1/2/3 CGUAFC

    GPIOs

    ARM®926 EJ-SUSIM

    USARTsSSCUSIF Camera

    IF Display

    IF

    Multimedia IC IF

    FLASH/SDRAM

    SMARTi DC+ (PMB 6258) GSM 900/1800

    GSM 850/1900

    Atomatic Offset

    Compensation

    Control Logic

    SAM Fast PLL

    850

    900

    1800

    1900

    Rx/Tx

    Multi Mode PA

    850 900

    1800 1900

    I

    Q

    CLK

    DAT

    ENA

    AFC

    RF Control

    26 MHz

    Car Kit

    Earpiece

    Ringer

    Headset

    M U

    X

    0* #

    321

    8

    54

    7

    SDC

    MMC

    6

    9

    • This course concentrates on the digital baseband; baseband modulation/demodulation.

    0 c©2011, Georgia Institute of Technology (lect1 5)

  • Course Objectives

    1. Brief review of probability and introduction to random processes.

    • message waveforms, transmission media or waveform channels, noise and interference are all random processes.

    2. Mathematical modelling and characterization of physical communication

    channels, signals and noise.

    3. Design of digital waveforms and associated receiver structures for recovering channel-corrupted digital signals.

    • emphasis will be on waveform design, receiver processing, and perfor-

    mance analysis for “additive white Gaussian noise (AWGN) channels.”

    • mathematical foundations are essential for effective physical layer mod-

    elling, waveform design, receiver design, etc.

    • communication signal processing is a key element of this course. Our

    focus will be on the “digital baseband” and not the “analog RF.”

    0 c©2011, Georgia Institute of Technology (lect1 6)

  • Basic digital communication system

    source

    sink

    source encoder

    source decoder

    channel encoder

    channel decoder

    digital modulator

    demodulator digital

    waveform channel

    0 c©2011, Georgia Institute of Technology (lect1 7)

  • Some Types of Waveform Channels

    • wireline channels, e.g., twisted copper pair, coaxial cable, power line

    • fiber optic channels (not considered in this course)

    • wireless (radio) channels

    – line-of-sight (satellite, land microwave radio)

    – non-line-of-sight (cellular, wireless LAN)

    • underwater acoustic channels (submarine communication)

    • storage channels, e.g., optical and magnetic disks.

    – communication from the present to the future.

    0 c©2011, Georgia Institute of Technology (lect1 8)

  • Mathematical Channel Models

    Additive White Gaussian Noise Channel (AWGN):

    S (f)n N /2o

    -W 0 W

    + s(t)

    n(t)

    r(t) = s(t) + n(t)

    Receiver thermal noise can be modeled as spectrally flat or “white.”

    Thermal noise power in bandwith W is

    No 2

    · 2 ·W = NoW Watts

    At any time instant t0, the noise waveform n(t0) is a Gaussian random variable with zero mean and variance NoW .

    For a given channel input s(t0), the channel output r(t0) is also a Gaussian random variable with mean s(t0) and variance NoW .

    0 c©2011, Georgia Institute of Technology (lect1 9)

  • Mathematical Channel Models

    Linear Filter Channel:

    c(t) s(t)

    n(t)

    + *r(t) = s(t) c(t) + n(t)

    An ideal channel has impulse response c(t) = αδ(t− t0) and, therefore,

    r(t) = αs(t− to) + n(t)

    An ideal channel only attenuates and delays a signal, but otherwise leaves it undistorted. The channel transfer function is

    C(f) = F [c(t)] = αe−j2πfto, |f | < B

    where B is the system bandwidth.

    • The magnitude response |C(f)| = α is flat in frequency f .

    • The phase response 6 C(f) = −2πfto is linear in frequency f .

    0 c©2011, Georgia Institute of Technology (lect1 10)

  • Mathematical Channel Models

    Two-Ray Multi-path Channel:

    Suppose r(t) = αs(t) + βs(t− τ).

    Since r(t) = s(t) ∗ c(t), we have c(t) = αδ(t) + βδ(t− τ).

    Hence C(f) = α + βe−j2πfτ .

    Using |C(f)|2 = C(f)C∗(f), we can obtain

    |C(f)| = √

    α2 + β2 + 2αβ cos(2πfτ)

    Using the Euler identity, ejθ = cos(θ) + j sin(θ), we have

    6 (C(f) = −Tan−1 β sin(2πfτ)

    α+ β cos(2πfτ)

    0 c©2011, Georgia Institute of Technology (lect1 11)

  • Mathematical Channel Models

    Two-Ray Multi-path Channel:

    Suppose α = β = 1. Then

    |C(f)| = √

    2 + 2 cos(2πfτ)

    6 C(f) = −Tan−1 sin(2πfτ)

    1 + cos(2πfτ)

    0 0.5 1 1.5