Transcript What is Wireless Communication

Advanced Wireless Communication
Systems
Administrative
Lectures:
Thursday 17:10-20:00, Bld. 28, Rm. 301
Lecturer:
Nathan Blaunstein, [email protected]
Bld. 37, Rm. 515, int. 77382
Reception:
Sunday 11:00-13:00
Exam:
A and B
Final Grade:
10% - Homework; 90%- Exam
Administrative
Adv. Wireless Comm. Sys.
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Advanced Wireless Comm. Systems
Course Content
Overview of existing wireless networks
Cellular networks: FDMA, TDMA, CDMA
Resource planning in CDMA cellular networks
Multi-carrier principle; FFT and DFT methodology
Multiple access radio channels
OFDM concept
Wireless networking
Architectures of WLAN, WLL, Ad-hoc
Adv. Wireless Comm. Sys.
WiFi and WiMAX networks
Course Program
2
Advanced Wireless Communications
Lecture 1: Overview
Objectives
Refresh basic wireless enabling technologies
Be aware of existing technologies and evolution
Outline
Overview of wireless network key characteristics
Wireless network examples
Major standardization bodies
Wireless network evolution
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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What is Wireless Communication ?
Exchanging information between parties w/o wires

Stationary or mobile parties
Examples
Mobile radio systems (cellular)
Paging systems
Wireless LAN (WLAN)
Ad-Hoc Networks (Peer or self-organized LAN)
Wireless Local Loop (WLL)
WiFi and WiMAX Networks
Cordless phones
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
Geographical Distribution
Limited range & limited mobility PTP

Cordless phones, remote controls, meter reading,
baby monitors, “Bluetooth” devices, PAN

Bluetooth: 10 m; Cordless: few 100cm; others - less
Local area coverage

WLAN in buildings

~ 100 meters

Roaming with IEEE 802.11g & HIPRERLAN standards
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
Geographical Distribution (cont.)
Wide Area

Cellular networks

Coverage: Nation-wide, Global
Satellite

Geostationary Earth Orbit (GEO): ~ 35,900 km

LEO: few 100 km-1500 km (Globalstar, Late “Iridium”)

Popular applications
 Global Positioning System (GPS); Internet Access
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
Geographical Distribution (cont.)
Fixed Radio Access

Wireless Local Loop (WLL)

Bypass of local landline telephone

Broadband Access to Local Exchange: LMDS,
HIPERACCES

“Last mile” but can get up to 15-25 Km

Line Of Site (LOS)
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
Supported Services
Voice
Short Data Messages (SMS)
Low data rate (9.6 Kbps CS, 64/114 Kbps CS & PS)
High and variable data rate (144, 344 Kbps, 2 Mbps)
Web access and browsing (WAP, iMode - Japan)
Directory services (news/travel/sports/finance, etc.)
Loc. depend. services (maps, navigation, nearest café)
Tele-services (meter reading, vending machines)
HI-FI audio
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
Circuit Switching
End-to-end resources are allocated to the two end parties
upon connection setup and are released upon teardown.
During the connection, the circuit is used only by the two
parties for one-way transmission
Packet Switching
No channel resources are reserved for an end-to end
connection
Transmitters get channel resources upon demand, namely
when they need to transmit an information burst (packet)
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
Networking & Topology Aspects
Multiple cells vs. Fixed layout (WLAN, WLL)
Mobile vs. Stationary users
Handoff and admission control protocols
Call and message routing protocols
Channel format
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
(Reverse)
Duplexing Method
(Forward)
Simultaneous bi-directional transmission
In cellular – between subscriber and base station
Commonly separated by time or frequency domains:

Frequency Division Duplexing (FDD) - Constant

Time Division Duplexing (TDD) – Dynamic
Careful frequency separation VS. Time Delay
Rigid VS. flexible allocation
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
Multiple Access (MA) Techniques
Methods of sharing a single transmission resource
among multiple users
Common techniques

Time Division MA (TDMA)

Frequency Division MA (FDMA)

Code Division MA (CDMA)

Frequency Hopped (fast & slow) MA (FHMA)

Space Division Multiple Access (SDMA)

Hybrid
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
Multiple Access Techniques (cont.)
Two main groups, depending on the bandwidth per user
Narrowband systems

Spectrum is subdivided into many narrowband channels

One or more channels are exclusively assigned to a user

FDMA, TDMA
Wideband systems

Each transmission channel spans a wide spectrum

Many transmitters simultaneously access the channel

CDMA, FHMA
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Multiple Access Techniques (cont.)
code
code
code
Channel
Lectures 1 & 2:
Overview
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Multiple Access Techniques (cont.)
Channels
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Multiple Access Techniques (cont.)
Frequency Hopping: FHMA
code
Lectures 1 & 2:
Overview
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Example: Frequency Hopping in GSM
slot 3 user
Total allocated spectrum is ~ 70 MHz
Lectures 1 & 2:
Overview
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Multiple Access Techniques (cont.)
Space Division: SDMA
Spot bean antennas
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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FDMA Basic Principles
An up-down link pair is solely allocated per user on demand
The pair carries a single phone circuit – whether used or not
Channel bandwidth is usually 25-30 kHz
Symbol time relatively long
Cont. transmission
low ISI
less bits are needed for e.g., sync.
Concurrent up-down transmission
Mobiles need duplexers
RF filters to lower adjacent channel interference
Many channels share Base’s antenna resulting in harmonies
generation at near max power efficiency

adjacent channel interference
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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TDMA Basic Principles
N time slots are grouped into a frame

User is allocated corresponding slots in repeating frames
Addr. + sync
* Adapted from Rappaport: “Wireless Communication”
User transmission is not continuous

Lower battery consumption

“Mobile assisted handoff” by listening on other slots
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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TDMA Basic Principles (cont.)
Up and down links are duplexed either by FDD or TDD

With FDD, delay is induced between up & down link slots

Thus, no need for duplexers
Transmission rate are high compared with FDM

Requires equalizers to reduce ISI
Guard bits are required to gradually suppress signal

Otherwise, xmitted spectrum expends
interference
Synchronization is crucial
Flexible bandwidth allocation for various services and
asymmetric up & down traffic
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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CDMA Basic Principles
1) Coding with pseudorandom noise
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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CDMA Basic Principles (cont.)
2) Spreading the coded signal
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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CDMA Basic Principles (cont.)
3) Decoding and de-spreading
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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CDMA Basic Principles (cont.)
Self jamming due to imperfect code orthogonality
Soft handoff done by the Mobile Switching Center (MSC)
Multipath fading is dominant due to signal spread
The “near-far” problem makes power control crucial
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Mobile Network Generations
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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2G, 3G and in Between
2G Technologies
GSM
Digital AMPS (IS-54)
 TDMA/FDMA
 TDMA/FDMA
 200 kHz per channel
 30 kHz per channel
 8 slots per frame
 3 slots per frame
CDMAone (IS-95)
Japan PDC
 CDMA
 TDMA/FDMA
 1.25 MHz channels
 25 kHz per channel
 64 voice channel/carrier
 3 slots per frame
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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2G, 3G and in Between
2G - Inefficient Internet Access
Use Circuit rather Packet switched channels
Not efficient for bursty and asymmetric traffic
Limited to speech coder rates for a single channel
Standard
Data rate
GSM
Plain: 9.6 kbps
HSCSD: 9.6/14.4 kbps per 1 slot
57.6 kbps
115.2 kbps
Lectures 1 & 2:
Overview
CDMA (IS-95A)
14.4 kbps
IS-136 (IS-54)
9.6 kbps
PDC
9.6 kbps
Adv. Wireless Comm. Sys.
per 4 slots
per 8 slots
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2G, 3G and in Between
I-mode: Web Support for 2G (cont.)
Internet micro-browser
Runs in PDC cellular network in Japan
Uses 9.6 kbps channel (Packet or Circuit Switching)
Provides games, colored graphics, directory services
Used by over than 25 million subscribers
More than 40,000 non-official sites
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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GSM/GPRS Terminology
BTS (Base Transmitter/Receiver Station)

Operates a set of radio channels
BSC (Base Station Controller)

Controls up to 1000 BTS + power control and handover
MSC (Mobile Switching Center)

Connects mobiles to fixed telephone and data networks
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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GSM/GPRS Terminology (cont.)
HLR (Home Location Register)

Data base connected to MSC and SGSN with subscriber
information such as location, service access and
authentication data
VLR (Visitor Location Register)

Contains subscribers visiting from other SGSN areas
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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GPRS Operation
SGSN (Serving GPRS Support Node)

Deliver packets to station within its area

Queries HLR to get subscriber profile

Detects new stations in a given service area

Registers new subscribers in the service area
GGSN (Gateway GPRS Support Node)
 An
interface to external IP networks

Maintains routing information

Does network subscription and screening
 Address
Lectures 1 & 2:
Overview
mapping
Adv. Wireless Comm. Sys.
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2G, 3G and in Between
Enhanced Data rate for GSM Evolution (EDGE)
Requires new h/w & s/w at GSM and IS-136 base stations
New 8-PSK modulation coexisting with GSM’s GMSK
Supports 9 selectable air interfaces

Multiple Coding Schemes (CS)

Various error control protection levels
Data rates depends on the selected CS

14.4, 28.8, 32 and 43.2 kbps per time slot

Up to 8 x 43.2 = 345.6 kbps for a frame

Vendors claim for only 150 kbps
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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2G, 3G and in Between
IS-95B for 2.5 CDMA
Subscriber can acquire several channels (4? out of 64)
Total claimed data rate 64 kbps
Circuit and Packet switched access
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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3G Wireless Networks (IMT-2000)
Main Camps
3Gpp – 3G Partnership Project for Wide CDMA (W-CDMA)
3Gpp2 – 3G partnership Project for CDMA 2000
Major Requirements
Global coverage and mobility for 144 - 384 kbps
Limited coverage and mobility for 2 Mbps
High spectral efficiency Circuit
Flexible for new services
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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3G Key Characteristics
Standard
Operation Mode
Dplx. Features
CDMA 2000
Multi-carrier DSCDMA Nx1.2288
Mcps,
N=1,3,6,9,12
FDD
TDD
- Compatibility with IS-95A/B
- Channel (carrier) bandwidth 1.25 MHz
- 1X (carrier) supports 144 kbps or 128
voice calls
- Multi-carrier will support 2.4 Mbps
W-CDMA
(UMTS)
Variable DSCDMA
with Nx0.960
Mcps,
N=4,8,16
FDD
TDD
- Compatibility with GSM, IS-136,
PDC and 2.5G TDMA technologies
- Network structure of GSM
- Up to 2.048 Mbps on downlink for
stationary user
- Min of 5GHz per radio channel
- 100-350 voice calls/channel
- 10 ms frame with 16 slots
- New base stations
* Adapted from Rappaport: “Wireless Communication”
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Mobile Data Evolution
GPRS
~ 150 kbps
IS-95B
64 kbps
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
Modulation Techniques
Encoding message source into a transmittable form
The receiver needs to recover the message
Common techniques:
 Amplitude
Modulation (AM) – Analog

Frequency Modulation (FM) – Analog

On-Off Keying (OOK) – Digital

Binary Phase Shift Keying (BPSK) – Digital

Quadrature Phase Shift Modulation (QPSK) – Digital
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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AM Example
Only carrier amplitude varies according message signal
Carrier frequency is much higher than max signal frequency
The term
Lectures 1 & 2:
Overview
should be positive
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FM Example
The instantaneous frequency of the FM signal varies about
the
, proportionally to the message signal
More resistant to noise compared with AM
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Binary Digital Modulation
When the message data is “0”, the transmitted signal is:
When the message data is “1”, the transmitted signal is:
is the bit period
Modulation techniques differ by the choice
Advantages over analog modulation:

Better noise immunity

Easier to multiplex multimedia information forms

Support source coding, error correction, etc.
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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General Digital Modulation
Performed on a sequence of symbols (pulses) with “m”
states, each comprising “n” bits, hence
n  log 2 m
Techniques differ by the symbol states and size
One modulation performance measure is:

Spectral (bandwidth) efficiency
bps/Hz

Shannon’s upper bound:
log 2 ( 1  S N )
 S N is the Signal to Noise ratio
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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General Digital Modulation (cont.)
Another modulation performance measure is:

Power (energy) efficiency
Eb N 0
The ratio between Signal Energy/bit to Noise PSD
Usually we need to tradeoff between spectral and power
efficiencies, e.g.,

Error control coding – Lowers spectral efficiency

M-ary coding – Decreases
Eb
An important factor for mobile radio is Interference Immunity
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Pulse Shaping
A symbol pulse transmitted through a band-limited channel
smears in time causing Inter Symbol Interference (ISI)
May lead to detection errors in the receiver
Increasing the channel bandwidth is not a solution
Pulse shaping is used to reduce ISI while maintaining a
limited bandwidth of a modulated signal

Nyquist sampling techniques

Gaussian pulse shaping – specially effective for MSK
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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On-Off_Keying (OOK) - ASK Example
One form of OOK: Amplitude Shift Keying (ASK)
Keying (switching) the carrier sinusoid on if the input bit is “1”
and off if “0”.
Message input
Transmitted
waveform
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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OOK - FSK Example
Another OOK forms: Frequency Shift Keying (FSK)
Keying (switching) the carrier sinusoid frequency into
if the input bit is “1” and into
if “0”.
As FM where the modulating signal is binary
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Minimum Shift Keying - MSK
FSK with minimum frequency spacing that generates
orthogonal FSK signals ( i.e.,
)
Spectrally efficient and attractive for mobile radio
When passing the modulating data waveform through a
Gaussian pulse-shaping filter we get GMSK modulation
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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BPSK Example
Transmitting the carrier sinusoid with
a phase of
and with phase
if the input bit is “1”:
if “0”:
As FM where the modulating signal
is binary
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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QPSK Example
Special case of M-ary Phase Shift Keying (MPSK)
Each bit pair “00”, “01”, “10”, “11” form a symbol transmitted
during a symbol period, each shifted by
Geometric
Representation
Of energy and
phase
Phase
Energy
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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QAM Example
Quadrature Amplitude Modulation
With MPSK signals have the same energy
With QAM they may different energies
A combination of digital AM and PM
Geometric
Representation
Of energy and
phase
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Coherent and Differentiated Detection
Differentiated detection don’t require a coherent reference
signal at the Receiver
Makes Receiver easy and cheap to build
Differential encoding convert a binary sequence
differential sequence
{d k }
{mk }
into a
by the operation
dk  mk  dk 1
Power efficiency is inferior compared with coherent detection
When used, we get a D-modulation, e.g., DPSK
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
Frequency Band
International pacts to prevent mutual interference
Wireless services separation
Radio propagation properties
Total transmission capacity
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
Frequency Band - Examples
Special Each bit pair “00”, “01”, “10”, “11” form a symbol
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Network Characteristics
Channel Bandwidth
Link separation
Transmission capacity
Lectures 1 & 2:
Overview
Standard
Bandwidth
AMPS
30 kHz
GSM
200 kHz
IS-95
1.25 MHz
PHS
300 kHz
DECT
1.728 MHz
3G CDMA2000
1.25/5/10/20 MHz
3G IMT-2000
WCDM
1.25/3.75/7.5/
11.25/15 MHz
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Major Mobile Standards Characteristics
Current Standards in North America
Standard
Type
Year
AMPS
Cellular
CDPD
MA
Spectrum
Modul.
Bandwidth
1983 FDMA
824-894 MHz
FM
30 kHz
Cellular
1993 FH
824-894 MHz
GMSK
30 kHz
IS-95
Cellular
PCS
1993 CDMA
824-894 MHz
1.8-2.0 GHz
QPSK
BPSK
1.25 MHz
GSM 1900
PCS
1994 TDMA
1.85-1.99 GHz
GMSK
200 kHz
MIRS
SMR
PCS
1994 TDMA
Several
16-QAM
25 kHz
FLEX
Paging
1993 Simplex
Several
4-FSK
15 kHz
PACS
Cordless
PCS
1994
1.85-1.99 GHz
DQPSK
300 kHz
* Adapted from Rappaport: “Wireless Communication”
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Major Mobile Standards Characteristics
Current Standards in Europe
Standard
Type
Year
ERMES
Paging
GSM
MA
Spectrum
Modul.
Bandwidth
1993 FDMA
Several
4-FSK
25 kHz
Cellular
PCS
1990 TDMA
890-960 MHz
GMSK
200 kHz
CT2
Cordless
1989 FDMA
864-868 MHz
GMSK
100 kHz
DECT
Cordless
1993 TDMA
1.88-1.9 GHz
GFSK
1.728 MHz
DCS-1800
Cordless
PCS
1993 TDMA
1.71-1.88 GHz
GMSK
200 kHz
* Adapted from Rappaport: “Wireless Communication”
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Major Mobile Standards Characteristics
Current Standards in Japan
Standard
Type
Year
NTT
Paging
PDC
M-A
Spectrum
Modul.
Bandwidth
1979 FDMA
280 MHz
FSK
12.5 kHz
Cellular
1993 TDMA
810-1501 MHz
DQPSK 25 kHz
NTT
Cellular
1979 FDMA
400/800 MHz
FM
PHS
Cordless
1993 TDMA
1.895-1.907 GHz
DQPSK 300 kHz
25 kHz
* Adapted from Rappaport: “Wireless Communication”
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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Wireless Technologies - Summery
Lectures 1 & 2:
Overview
Adv. Wireless Comm. Sys.
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