ofdm applications

Chapter 8
OFDM Applications

CCU
Wireless Comm. Lab.

Contents
8 OFDM Applications
8.1 DAB
8.2 HDTV
8.3 Wireless LAN Networks
8.3.1 HIPERLAN/2
8.3.2 IEEE 802.11a
8.3.3 IEEE 802.11g
8.4 IEEE 802.16 Broadband Wireless Access System

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8.1 Digital Audio Broadcasting (DAB)

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8.1.1 Introduction to DAB 1/33
Current analog FM radio broadcasting system cannot satisfy
the demands of the future, which are
Excellent sound quality
Large number of stations
Small portable receivers
No quality impairment due to multipath propagation or signal fading

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Current analog FM radio broadcasting systems have reached
the limits of technical improvement.
DAB is a digital technology offering considerable advantages
over today's FM radio.

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Eureka project EU 147: DAB
Launched at 1986
First phase: 4 year plan (1987-1991) of research and development
Participants from Germany, France, Netherlands and United
Kingdom
Second phase (1992-1994, 170 man-years) :completion development of
individual system specifications, development of ASICs, and
considerations of additional services

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Ability to deliver CD-quality stereo sound.
Ease of use of DAB receivers.
Switch between the eight or more stations carried by every
single multiplex.

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No need for drivers to retune as they cross a country.
Wider choice of programs.
Each multiplex is able to carry up to six full-quality stereo
programs.

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Service
Information FIC

Multiplex
Information OFDM Transmitter
Audio
Service Audio Channel Transmission
Encoder Coder Multiplexer
Radio
Frequency
Data
MSC
Service Packet Channel
Multiplexer
Mux Coder

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Audio
Service
OFDM Channel Audio
Tuner
Demodulator Decoder Decoder

Independent
Data
FIC
Service

Packet
Demux

Control Bus Controller
User Interface

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DAB can carry text and images as well as sound.
All but the smallest will be able to display at least two 16-
character lines of text.
Selection by name or programme type.
Enabling broadcasters to transmit programme-associated
data (PAD) such as album title, song lyrics, or contact details.
DAB can be transmitted at lower power than today's FM
and AM services without loss of coverage

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DAB combines two advanced digital technologies to achieve
robust and spectrum-efficient transmission of high-quality
audio and other data.
DAB uses the MPEG Audio Layer II system to achieve a
compression ratio of 7:1 without perceptible loss of quality.
The signal is then encoded at a bit rate of 8-384 kbit/s,
depending on the desired sound quality and the available
bandwidth.

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Signal is individually error protected and labeled prior to
multiplexing. Independent data services are similarly
encoded.
The coded orthogonal frequency division multiplex
(COFDM) technology is used for transmission.
2.3 million bits of the multiplexed signal in time and across
1,536 distinct frequencies within the 1.5 MHz band.

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An conventional FM network must use different frequencies
in each area. In a DAB network, all transmitters operate on a
single frequency.
Such a single frequency network (SFN) makes DAB's use of
the radio spectrum over three times more efficient than
conventional FM.
DAB is designed for terrestrial, cable and for future satellite
broadcasts

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Technical characteristics
Frequency range up to 20 kHz
48 kHz sampling rate; 18-bit resolution
4 audio modes: mono, stereo, dual channel, and joint stereo
Bit rates from 32 kbit/s mono to 384 kbit/s stereophonic programme
Audio frame 24 ms corresponding 1152 PCM audio samples
Digital I/O conform AES/EBU standard
2 kbit/s (bytes of data per frame) for program associated data (PAD)

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Transmission system
Radio signal is normally distorted by
Physical conditions
Multipath propagation
Interference can be avoided by using COFDM
COFDM with error detection and correction provides a digital
transparent channel allowing transmission of a stereo program or any
other data.
Programs are divided into a total of 1536 carrier frequencies
bandwidth 1.5 Mhz.

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8.1.2 DAB System Overview 14/33
Audio, control information, and digital data service are
multiplexed together to form OFDM signal on the air.
The audio is encoded by MPEG audio layer II.
The control information is used to interpret the configuration
of the main service channel (MSC).

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The control information is transmitted over the fast
information channel (FIC), which is made up of fast
information block (FIB).
See the block diagram shown below.

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Conceptual DAB emission block diagram
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8.1.3 DAB Channel Coding 17/33

Channel coding is based on a convolutional code with
constraint length 7.
Punctured convolutional coding allows unequal error
protection (UEP).
Several convolutional coded stream are then combined and
mapped into OFDM symbols.

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−1
The mother code generates from the vector (a ) iI=0 a codeword
+
{( x0,i , x1,i , x2,i , x3,i )}iI=05

x0,i = ai ⊕ ai − 2 ⊕ ai −3 ⊕ ai −5 ⊕ ai −6
x1,i = ai ⊕ ai −1 ⊕ ai − 2 ⊕ ai −3⊕ ai −6
x2,i = ai ⊕ ai −1 ⊕ ai − 4 ⊕ ai −6
x3,i = ai ⊕ ai − 2 ⊕ ai −3 ⊕ ai −5 ⊕ ai −6

for
i = 0,1,2,..., I + 5

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Convolutional encoder

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Puncturing procedure: some predefined coded bits generated
by the mother code are not transmitted.
The first 4I bits are divided into consecutive sub-blocks of 32
bits.
The i-th bit in each sub-block is process according to the
puncturing vector
vPI = (vPI , 0 , vPI ,1 ,..., vPI ,31 )

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For v PI , i = 0 , the corresponding bit shall be taken out of the
sub-block and shall not be transmitted.
For v PI , i = 1 , the corresponding bit shall be retrained in the
sub-block and shall be transmitted.
There are total 24 possible puncturing vectors so the rate of
the punctured convolutional code varies from 8/9 to ¼.

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8.1.4 DAB Modulation 22/33
Transmission frame structure

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Four transmission modes are defined.
Each transmission frame is divided into a sequence of OFDM
symbols.
The first OFDM symbol of the transmission frame shall be
the Null symbol of duration TNULL. The remaining part is
OFDM symbols of duration TS.

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Each OFDM symbol can be expressed as
⎧ j 2π f c t ∞ L K / 2 ⎫
s (t ) = Re ⎨e ∑ ∑ k =∑ / 2 z m ,l , k g k ,l (t − mT F − TNULL − (l − 1)TS )⎬
⎩ m = −∞ l = 0 −K ⎭
with
⎧ 0 for l = 0
g k ,l (t ) = ⎨ j 2πk ( t − ∆ ) / TU
⎩e Rect (t / TS ) for l = 1, 2,..., L

L: Number of OFDM symbols per frame TU: Inverse of the carrier spacing
K: Number of transmitted carriers Δ: Guard interval
TF: Transmission frame duration TS = TU + Δ : Duration of OFDM symbols
TNULL: Null symbol duration Z m,l,k: Complex D-QPSK symbol for carrier k
of OFDM symbol l during transmission frame
fc: Central frequency of the signal
m.
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Definition of the parameters for transmission modes I,II,III, and IV.

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Conceptual block diagram of the generation of the main signal
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Synchronization channel: the first two OFDM symbols
During the time interval [0,TNULL], the main signal s(t) shall
be equal to zero.
The second OFDM symbol is the phase reference symbol
defined by the value of z l,k for l=1:

⎧e jϕ k for − K / 2 ≤ k < 0 and 0 < k ≤ K / 2
z1,k =⎨
⎩ 0 for k = 0

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The values of ϕk shall be obtained from the
following formulae
π
ϕk = ( hi ,k −k ' + n )
2
The values of the parameter hi , j as a function of
indices i and j are specified in the standard

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8.1.5 Channel for DAB OFDM System 29/33
Assume that there are M stations that transmit synchronous
OFDM frame s(t).

s(t ) M
r (t ) = ∑ s (t ) *h j (t )
h1 (t ) j =1

s(t )
receiver
hM (t )

h2 (t )
s(t )

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The signal from the station j propagates to the receiver. The
received signal from the j-th station can be expressed as

rj ( t ) = s ( t ) ∗ h j ( t )
where * denotes the convolution and hj(t) is the channel
impulse response from station j to the receiver.

The overall received signal from all stations can be expressed
as M M
r ( t ) = ∑ rj ( t ) = ∑ s ( t ) ∗ h j ( t )
j =1 j =1
M
= s(t ) ∗ ∑ h j (t )
j =1
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Now we may define the overall channel impulse response as
M
h (t ) = ∑ h j (t )
j =1
The received signal can be expressed as

r (t ) = s(t ) ∗ h (t )

No inter-symbol interference (ISI) if the spreading of h(t) is
less then the guard interval.

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8.1.6 Receiver for DAB OFDM System 32/33
Tuning (frequency) accuracy required is 5%.
Robust frequency tracking is required.
Fast channel and timing tracking to overcome the rapidly
change condition.

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8.1.6 Receiver for DAB OFDM System 33/33

Block diagram of DAB receiver

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8.2 HDTV-Digital Video Broadcasting
(DVB)

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8.2.1 Introduction to DVB 1/34
Audio and video-centric
Very large files transmission.
Quality of service issues.
Guaranteed bandwidth
Jitter
Delay
Large, scalable audience
Broadband downstream, narrowband up
Satellite: DVB-S
Terrestrial: ATSC, DVB-T

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European standard for transmission of digital TV via
satellite, cable or terrestrial
DVB-S (satellite)
QPSK – quadrature phase-shift keying
DVB-T (terrestrial)
COFDM – coded orthogonal frequency division
multiplexing
MPEG-2 compression and transport stream
Support for multiple, encrypted program stream.

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Digital video combines traditional and interactive content and
applications

Traditional Interactive

Film Enhanced DVD
TV Movies/music
Music Interactive games
Books Videophone
Magazines Creating and
Board games sharing documents
Online E-commerce

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8.2.2 DVB System Overview 7/34
MPEG-2 source coding and multiplexing
Outer coding (Reed-Solomon code)
Outer interleaving (convolutional interleaving)
Inner coding (punctured convolutional code)
Inner interleaving
Mapping and modulation (BPSK,QPSK,16-QAM, 64-QAM)
Transmission – orthogonal frequency division multiplexing
(OFDM)

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Operate within existing VHF and UHF spectrum
The system must provide sufficient protection against co-channel
interference (CCI) and adjacent-channel interference (ACI)
OFDM with concatenated error correcting coding is being
specified.
Flexible guard interval is specified
Two mode of operations:
2K mode: suitable for single transmitter operation for small SFN
networks.
8K mode: used both for single transmitter operation and for small and
large SFN networks.

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Multi-level QAM modulation
Different inner code rates (punctured convolutional code)
MPEG stream is separated into
High-priority stream
Low-priority stream
Unequal error protection (UEP)
High-priority stream is high-level protected.
Low-priority stream is low-level protected.

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Functional block diagram of the DVB transmitter

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8.2.3 Channel Coding and Modulation 11/34
Transport multiplex adaptation and randomization
(scrambler)

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The total packet length of the MPEG-2 MUX packet is 188
bytes.
The data of the input MPEG-2 multiplex shall be randomized
with the above circuit.

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Outer coding and outer interleaving
RS (204,188) shortened code from RS (255,239) is adopted.

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Convolutional interleaving
Convolutional byte-wise interleaving with depth I=12

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Inner coding
Convolutional code of rate ½ with 64 states.
Generator polynomial G1=171OCT and G2=133OCT

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Punctured convolutional code

Puncturing pattern and transmitted sequence after parallel-
to-serial conversion for the possible code rate

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Inner interleaving
Bit-wise interleaving followed by symbol interleaving .
Both the bit-wise interleaving and the symbol interleaving processes
are block-based.
Define a mapping (demultiplexing) of the input bits xdi onto
the output bits be,do

In non-hierarchical mode:

xdi = b[ di (mod)v ]( div )( v / 2 ) + 2[ di (mod)(v / 2 )],di ( div ) v

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In non-hierarchical mode:

High-priority input

x'di = bdi (mod) 2,di ( div ) 2
Low-priority input

x' 'di = b[ di (mod)(v − 2 )](div )(( v − 2 ) / 2 ) + 2[ di (mod)((v − 2 ) / 2 )]+ 2,di ( div )( v − 2 )

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Non-hierarchical
modulation mapping

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Hierarchical
modulation mapping

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Bit interleaver
For each bit interleaver, the input bit vector is defined by

B( e) = (be ,0 , be ,1 , be , 2 ,..., be ,125 )
where e ranges from 0 to v-1.

The interleaved output vector

A( e) = ( ae ,0 , ae ,1 , ae , 2 ,..., ae ,125 )
is defined by
ae ,w = be ,H e ( w )

where He(w) is a permutation function which is different for each
interleaver.
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Symbol interleaver
Map v bit words onto the 1512 (2K mode) or 6048 (8K mode) active
carriers per OFDM symbol.
To spread consecutive poor channels into random-like fading.
Symbol interleaver address generation schemes are employed for the
symbol interleaver.

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Signal constellations and mapping
OFDM transmission
All data carries in one OFDM frame are modulated using either QPSK,
16-QAM, 64QAM, non-uniform 16-QAM or non-uniform 64-QAM.
The non-uniform signal constellation provides unequal error
protection (UEP).

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The QPSK, 16-QAM and 64-QAM mapping and the
corresponding bit patterns

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The non-uniform 16-QAM and 64-QAM mappings

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OFDM frame structure
Each frame has duration TF
Consists of 68 OFDM symbols
Four frames constitute one super-frame
Each OFDM symbol contains K=6817 (8K mode) or K=1705 (2K mode)
carriers
The duration of each OFDM symbol is TS =TU+Δ where Δ is the
guard interval and TU is the useful part.
The symbols in an OFDM frame are numbered from 0 to 67
Scattered pilot cells (carrier)
Continual pilot carriers
TPS carriers

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The pilot can be used for frame synchronization, frequency
synchronization, time synchronization, channel estimation,
transmission mode identification.
The carriers are indexed by k ∈ [ K min ; K max ] , where Kmin=0
and Kmax=1704 or 6816.
Numerical values for the OFDM parameters for the 8K and
2K modes for the 8Mhz channels.

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The emitted signal is described by the following expression:
⎧ j 2 πf c t ∞ 67 K max ⎫
s ( t ) = Re ⎨ e ∑0 ∑ k =∑ c m ,l , k × ψ m ,l , k ( t ) ⎬
⎩ m = l =0 K min ⎭
⎧ j 2 π Tk ' ( t − ∆ − l ×Ts − 68 × m ×Ts )
⎪ ( l + 68 × m ) × TS ≤ t ≤ ( l + 68 × m + 1) × TS
ψ m ,l , k ( t ) = ⎨ e
U

⎪
⎩ 0 else
k: carrier number
l: OFDM symbol number fc: central frequency of the RF signal

m: frame number k’: k’=k-(Kmax - Kmin)/2

K: number of transmitted carriers cm,l,k: complex symbol for carrier k of
data symbol number l in frame number
TS: symbol duration m
TU: inverse of the carrier spacing
Δ: Guard interval

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Duration of symbol part for the guard intervals for 8Mhz
channel

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Reference signal
Various cells within the OFDM frame are modulated with reference
information whose transmitted values is known to the receiver
The value of the pilot information is derived from a pseudo random
binary sequence (PRBS)
Two kinds of pilots: scattered pilot and continual pilot

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Location of scattered pilot cells
Pilot is modulated according to
Re{cm ,l ,k } = 4 / 3 × 2(1 / 2 − wk )
Im{cm ,l ,k } = 0

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Location of continual pilot carriers
Pilot is modulated according to
Re{cm ,l ,k } = 4 / 3 × 2(1 / 2 − wk )
Im{cm ,l ,k } = 0

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Transmission parameter signaling (TPS)
The TPS carriers are used for the purpose of signaling parameters
related to the transmission scheme.
The TPS is transmitted in parallel on 17 TPS carriers for 2K mode
and on 68 carriers for the 8K mode.

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The TPS carriers convey information on:
a) Modulation of the QAM constellation pattern
b) Hierarchy information
c) Guard interval
d) Inner code rate
e) 2K or 8K transmission mode
f) Frame number in a super-frame
g) Cell identification.

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8.3 Wireless LAN Networks

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8.3.1 Introduction to Wireless LAN Networks
1/36
IEEE 802.11 - The first international standard for WLAN,
1997.
Infrared (IR) baseband PHY (1Mbps, 2Mbps)
Frequency hopping spread spectrum (FHSS) radio in 2.4GHz band
(1Mbps, 2Mbps)
Direct sequence spread spectrum (DSSS) radio in the 2.4GHz band
(1Mbps, 2Mbps)
IEEE 802.11a, 1999
5GHz band
Orthogonal frequency division multiplexing (OFDM)
6Mbps to 54Mbps

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2/36
IEEE 802.11g
(802.11b + 80211a) operating at 2.4GHz band
ERP-DSS/CCK: IEEE 802.11b-1999
ERP-OFDM: IEEE 802.11a-1999
PBCC (optional)
CCK-OFDM (optional)

IEEE 802.11h/D2.2, September 2002
Radar detection in 5GHz band
Regulatory (ETSI EN 301 893 v.1.2.1)
Power control

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3/36
Typical wireless system

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8.3.2 Indoor Environment 4/36
Delay spread - refection of RF signal from wall, furniture, etc.
Path loss
Interference - microwave oven, Bluetooth, cordless phone, etc.
Statistic channel model for WLAN

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Typical indoor
environment

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Delay spread

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Typical measurement results I - 1 m away from the
transmitter

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Typical measurement results II - 10m, 8m, and 13.5m away
from the transmitter

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Computer model for indoor channels

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Ray tracing simulation result

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8.3.3 Statistic Channel Model for WLAN 11/36
This channel model was agreed to be a baseline model for
comparison of modulation methods.
Simple mathematical description and in the possibility to vary
the RMS delay spread.
The channel is assumed static throughout the packet and
generated independently for each packet.

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The received signal
K
rn = ∑ xn −k hk + wn
*

k =0
where wn is the additive white Gaussian noise, xn is the
transmitted signal and hk is the baseband complex impulse
response
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8.3.3 Statistic Channel Model for WLAN13/36
Channel impulse response

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Typical multipath delay spread

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8.3.3 Statistic Channel Model for WLAN15/36
Path loss

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8.3.4 802.11a WLAN Standard 16/36
OFDM system with punctured convolutional code.
52 carriers with 4 pilot tones.
Date rate from 6Mbps to 54Mbps

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8.3.4 802.11a WLAN Standard 17/36

Rate dependent parameters

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8.3.4 802.11a WLAN Standard 18/36
Timing related parameters

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8.3.4 802.11a WLAN Standard 19/36
Transmitter of 802.11a

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8.3.4 802.11a WLAN Standard 20/36
All the subframes of the signal are constructed as an inverse
Fourier transform of a set of coefficients, Ck , with Ck defined
as data, pilots, or training symbols.
N ST / 2
rSUBFRAME (t ) = wTSUBFRAME (t ) ∑C
k = − N ST /2
k exp( j 2πk∆ f )(t −T GUARD)

where wT (t ) is a time window function defined by

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8.3.4 802.11a WLAN Standard 21/36
Cyclic extension and window function (a) single reception and
(b) two receptions

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8.3.4 802.11a WLAN Standard 22/36
Implemented by IFFT

frequency- time-domain
domain input output

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8.3.4 802.11a WLAN Standard 23/36
OFDM packet structure

A short OFDM training symbol consists of 12 subcarriers, which
are modulated by the elements of the sequence S, given by

The short training signal shall be generated according to
N ST / 2
rSHORT (t ) = wTSHORT (t ) ∑S
k = − N ST
k
/2
exp( j 2πk∆ f )
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8.3.4 802.11a WLAN Standard 24/36
A long OFDM training symbol consists of 53 subcarriers
given by

The long training signal shall be generated according to

Signal field - modulation with 6Mbps

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8.3.4 802.11a WLAN Standard 25/36
Data field includes
Service field - scrambler initialization
PSDU - carry the data to be transmitted.
Tail bit field - 6 bits of zero to return the convolutional encoder to zero
state.
Pad bits (PAD) - zero bits.
DATA scrambler and descrambler
Scrambler and descrambler use the same module.

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8.3.4 802.11a WLAN Standard 26/36
DATA field should be coded with a convolutional encoder of coding
rate R = 1/2, 2/3, 3/4.
The rate 2/3 and 3/4 code is generated by puncturing the rate 1/2
convolutional code with generator polynomial g0=1338 and g1 = 1718.

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8.3.4 802.11a WLAN Standard 27/36
Puncturing procedure for rate 3/4 code

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8.3.4 802.11a WLAN Standard 28/36
Puncturing procedure for rate 2/3 code

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8.3.4 802.11a WLAN Standard 29/36
Data interleaving
All encoded data bits shall be interleaved by a block interleaver with
block size corresponding to the number of bits in a single OFDM
symbol.
The interleaver is defined by a two-step permutation.
The coded bits are interleaved in the transmitter and deinterleaved in
the receiver.
The purpose of the interleaver is to prevent long burst of errors.

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8.3.4 802.11a WLAN Standard 30/36
Subcarrier modulation mapping
BPSK, QPSK, 16-QAM, or 64-QAM is employed depending on the
rate required.
The interleaved date is grouped into 1, 2, 4, or 6 bits and mapped to
BPSK, QPSK, 16-QAM, or 64-QAM constellation points.

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8.3.4 802.11a WLAN Standard 31/36
Signal constellations - BPSK, QPSK, and 16-QAM

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8.3.4 802.11a WLAN Standard 32/36
• Signal constellations - 64-QAM

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8.3.4 802.11a WLAN Standard 33/36
OFDM modulation
The stream of complex number is divided into groups of 48
complex number.
We may write the complex number dk,n which corresponds
to subcarrier k of OFDM symbol n.

An OFDM symbol is defined as Data carriers

Pilot carriers
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8.3.4 802.11a WLAN Standard 34/36
Where M(k) maps from subcarrier number 0 to 47 into
frequency index

The contribution of the pilot subcarriers for the nth OFDM
symbol is produced by Fourier transform sequence P, given
by

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8.3.4 802.11a WLAN Standard 35/36
The polarity of the pilot subcarriers is controlled by the
sequence

Subcarrier frequency allocation

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8.3.4 802.11a WLAN Standard 36/36
802.11a transmitter and receiver structure

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8.4 IEEE 802.16
Broadband Wireless Access System

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Wireless Comm. Lab.
109

8.4.1 Introduction to IEEE 802.16 1/25
BWAS is the broadband wireless technology used to deliver
voice, data, Internet, and video service in the 25-GHz and
higher spectrum.

CCU
Wireless Comm. Lab.
110

BWAS scenario

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Wireless Comm. Lab.
111

IEEE 802.16 wireless MAN background
Target: FBWA (fixed broadband wireless access)
Fast local connection to network
Project development since 1998

CCU
Wireless Comm. Lab.
112

Point-to-multipoint wireless MAN: (not a LAN)
Base station (BS) connected to public networks
BS serves subscriber station (SSs)
SS typically serves a building
Provide SS with access to public network.
Compared to Wireless LAN
Multimedia QoS not only contention-based
Many more users
Much higher data rates
Much longer distances

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Wireless Comm. Lab.
113

Properties of 802.16
Broad BW: up to 134 Mbps in 28 MHz wide channel (10-
66 GHz)
Support simultaneous multiple services with full QoS
IPv4, IPv6, ATM, Ethernet, etc.
BW on demand (per frame)
MAC designed for efficient spectrum use
Comprehensive, modern and extensible security
Support multiple frequency allocation from 2-66 GHz
OFDM & OFDMA for NLOS applications

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Wireless Comm. Lab.
114

TDD & FDD
Link adaptation: adaptive modulation & coding
Per subscriber, per burst, per up-/down- link
Point-to-multipoint topology, with mesh extensions
Support for adaptive antennas and space-time coding
Extensions to mobility

CCU
Wireless Comm. Lab.
115

802.16 bit rate and channel size

Channel Symbol QPSK 16- 64-
Width Rate Bit rate QAM QAM
(MHz) (Msym/ (Mbps) Bit rate Bit rate
20 s)
16 32 (Mbps)
64 (Mbps)
96

25 20 40 80 120

28 22.4 44.8 89.6 134.4

CCU
Wireless Comm. Lab.
116

802.16 link adaptation scenario

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Wireless Comm. Lab.
117

8.4.2 Introduction to Physical Layer of 802.16
9/25
Physical layer of 802.16
OFDM (WMAN-OFDM air interface):
256-FFT W/ TDMA (TDD/FDD)
OFDMA (WMAN-OFDMA air interface) :
2048-FFT W/ OFDMA (TDD/FDD)
Single-Carrier (WMAN-SCa air interface):
TDMA (TDD/FDD)
BPSK, QPSK, 4/16/64/256-QAM

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Wireless Comm. Lab.
118

10/25
OFDM time-domain symbol description
Useful symbol time Tb
Cyclic prefix Tg
Symbol time Ts = Tb + Ts

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Wireless Comm. Lab.
119

11/25
OFDM frequency domain
Data carriers
Pilot carriers
Null carriers

CCU
Wireless Comm. Lab.
120

12/25
The Transmitted signal at the antenna

⎧ j 2πf ct N used / 2 j 2πk∆f ( t −Tg ) ⎫
s (t ) = Re⎨e ∑ /ck e ⎬
⎩ k = − N used 2 ⎭

CCU
Wireless Comm. Lab.
121

13/25
Four types of forward error correction (FEC)
Code Type 1: Reed-Solomon code only
Code Type 2: Reed-Solomon code + block convolutional code
Code Type 3: Reed-Solomon + parity check
Code Type 4: Block turbo code

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Wireless Comm. Lab.
122

14/25
OFDM carrier allocations

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Wireless Comm. Lab.
123

15/25
Transmit diversity – space time coding

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Wireless Comm. Lab.
124

16/25
STC encoding
Transmits 2 complex symbols s0 and s1, using the MISO
channel (2 Tx, one Rx) twice with channel vector values h0 (for
antenna 0) and h1 (for antenna 1).
First channel use : antenna 0 transmits s0 , antenna 1
transmit s1
*
Second channel use: antenna 0 transmit s0 , antenna 1
transmit − s1 *

The receiver get the benefit of the 2nd order diversity

CCU
Wireless Comm. Lab.
125

17/25
STC usage with OFDM

CCU
Wireless Comm. Lab.
126

18/25
Concatenated Reed-Solomon / convolutional code (RS-CC)
•RS code is derived from (255,239) RS code that can
correct up to 8 symbol errors.
•The RS encoded block is then encoded by a
convolutional code of rate ½ with generator polynomial

•Convolutional encoder

CCU
Wireless Comm. Lab.
127

19/25
Concatenated Reed-Solomon / convolutional code (RS-CC)
RS code is derived from (255,239) RS code that can correct up
to 8 symbol errors.
The RS encoded block is then encoded by a convolutional
code of rate ½ with generator polynomial


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Wireless Comm. Lab.
128

20/25
Puncturing pattern

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Wireless Comm. Lab.
129

21/25
Channel coding and modulation

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Wireless Comm. Lab.
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22/25
Block turbo codes
Based on the product of two component codes.
Binary extended Hamming code or parity check code

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Wireless Comm. Lab.
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23/25
The component codes are used in a two dimensional
matrix form
kx information bits are encoded into nx bits by using (nx,kx)
block code.
After encoding the rows, the columns are encoded using a
(ny,ky) block code, where the check bits of the first code are
also encoded.

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Wireless Comm. Lab.
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24/25
Convolutional turbo code
Circular recursive systematic convolutional
The turbo code encoder

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Wireless Comm. Lab.
133

25/25
Convolutional turbo code channel coding and modulation

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Wireless Comm. Lab.
134

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