Guard interval .

58
• guard interval https://store.theartofservice.com/the-guard-interval- toolkit.html

Transcript of Guard interval .

Page 1: Guard interval .

• guard interval

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 2: Guard interval .

DVB-T Basics of DVB-T

1 DVB-T is a COFDM transmission technique which includes the use of a Guard Interval

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 3: Guard interval .

DVB-T Basics of DVB-T

1 The length of the Guard Interval can be chosen. It is a trade off between data

rate and SFN capability. The longer the guard interval the larger is the potential SFN area without creating intersymbol

interference (ISI). It is possible to operate SFNs which do not fulfill the guard interval condition if the self-

interference is properly planned and monitored.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 4: Guard interval .

DVB-T Technical description of a DVB-T transmitter

1 to decrease receiver complexity, every OFDM block is extended, copying in front of it its own end (cyclic prefix). The width of such guard interval can be 1/32, 1/16,

1/8, or 1/4 that of the original block length. Cyclic prefix is required to operate single

frequency networks, where there may exist an ineliminable interference coming from

several sites transmitting the same program on the same carrier frequency.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 5: Guard interval .

DVB-T Technical description of a DVB-T transmitter

1 ModulationCoding rateGuard interval

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 6: Guard interval .

DVB-T Technical description of the receiver

1 The property that the guard interval at the end of the symbol is placed

also at the beginning is exploited to find the beginning of a new OFDM

symbol

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 7: Guard interval .

DVB-T Technical description of the receiver

1 Guard interval disposal: the cyclic prefix is removed.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 8: Guard interval .

DVB-T Europe

1 Bulgaria (MPEG-4 AVC, FEC=2/3, guard interval - 1/4, 64 QAM. Official simulcast started in March 2013, full

switch has been done in 30 September 2013.)

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 9: Guard interval .

Digital Video Broadcasting - Transmission

1 Guard Interval Not Applicable 1/4, 19/256, 1/8, 19/128, 1/16, 1/32, 1/128 1/64 or

1/128

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 10: Guard interval .

Multi-carrier code division multiple access - Variants

1 Once frequency domain spreading has taken place and the OFDM

subcarriers have all been allocated values, OFDM modulation then takes place using the IFFT to produce an

OFDM symbol; the OFDM guard interval is then added; and if

transmission is in the downlink direction each of these resulting

symbols are added together prior to transmission.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 11: Guard interval .

IEEE 802.11 - Protocol

1 B1 B2 Assumes short guard interval (SGI) enabled, otherwise reduce each data rate by

10%.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 12: Guard interval .

IEEE 802.11n-2009 - Data rates

1 Data rates up to 600Mbit/s are achieved only with the maximum of four spatial streams using one 40MHz-wide channel. Various modulation schemes and coding rates are defined by the standard and are represented by a Modulation and Coding Scheme (MCS) index value. The table below shows the relationships between

the variables that allow for the maximum data rate. GI (Guard Interval) : Timing between

symbols. http://www.airmagnet.com/assets/whitepaper/W

P-802.11nPrimer.pdfhttps://store.theartofservice.com/the-guard-interval-toolkit.html

Page 13: Guard interval .

IEEE 802.11n-2009 - Wi-Fi Alliance

1 The baseline certification covers both 20MHz and 40MHz wide channels, and up to two spatial streams, for

maximum throughputs of 144.4Mbit/s for 20MHz and 300Mbit/s for 40MHz (with short guard interval)

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 14: Guard interval .

Time division multiple access - 2G systems

1 The mobile phone is not allowed to transmit for its entire time slot, but

there is a guard interval at the end of each time slot

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 15: Guard interval .

IEEE 802.11ac - Mandatory and optional features

1 ** 400 ns Short Guard Interval (SGI)

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 16: Guard interval .

Guard interval

1 In telecommunications, 'guard intervals' are used to ensure that

distinct transmissions do not interfere with one another. These

transmissions may belong to different users (as in Time division multiple access|TDMA) or to the

same user (as in Orthogonal frequency-division multiplexing|

OFDM).https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 17: Guard interval .

Guard interval

1 The purpose of the guard interval is to introduce immunity to propagation

delays, echoes and reflections, to which digital data is normally very

sensitive.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 18: Guard interval .

Guard interval - Use in digital communications systems

1 In COFDM, the beginning of each symbol is preceded by a guard

interval. As long as the echoes fall within this interval, they will not

affect the receiver's ability to safely decode the actual data, as data is only interpreted outside the guard

interval.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 19: Guard interval .

Guard interval - Use in digital communications systems

1 It is a common misconception that each TDMA timeslot begins with a guard interval, however the ITU Technical Specifications (such as

GSM 05.05) clearly define the guard period as being at the end of each timeslot, thus providing protection

against data loss within that timeslot, and protection against interference

to the following timeslothttps://store.theartofservice.com/the-guard-interval-toolkit.html

Page 20: Guard interval .

Guard interval - Use in digital communications systems

1 Longer guard periods allow more distant echoes to be tolerated.

However, longer guard intervals reduce the channel efficiency. For

example, in DVB-T, four guard intervals are available (given as

fractions of a symbol period):

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 21: Guard interval .

Guard interval - Use in digital communications systems

1 Radio waves propagate at the speed of light, per 1000 meter (5 μs/mile).

Ideally, the guard interval is just longer than the delay spread of the

channel.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 22: Guard interval .

Guard interval - 802.11 guard interval

1 The standard symbol guard interval used in 802.11 OFDM is . To increase data rate, 802.11n added optional support for a guard interval. This provides an 11% increase in data

rate.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 23: Guard interval .

Guard interval - 802.11 guard interval

1 To reduce complexity, manufacturers typically only implement a short

guard interval as a final rate adaptation step when the device is

running at its highest data rate.Perahia and Stacey, Next

Generation Wireless LANs, Cambridge University Press, 2008

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 24: Guard interval .

Orthogonal frequency-division multiplexing

1 The low symbol rate makes the use of a guard interval between symbols

affordable, making it possible to eliminate intersymbol interference (ISI) and utilize echoes and time-

spreading (on analogue TV these are visible as Ghosting (television)|

ghosting and blurring, respectively) to achieve a diversity gain, i.e

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 25: Guard interval .

Orthogonal frequency-division multiplexing - Summary of disadvantages

1 * Loss of efficiency caused by cyclic

prefix/guard interval.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 26: Guard interval .

Orthogonal frequency-division multiplexing - Orthogonality

1 To avoid intersymbol interference in multipath fading channels, a guard

interval of length \scriptstyle T_\mathrm is inserted prior to the OFDM

block. During this interval, a cyclic prefix is transmitted such that the

signal in the interval \scriptstyle -T_\mathrm \,\le\, t \,

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 27: Guard interval .

Orthogonal frequency-division multiplexing - History

1 *1971: Weinstein Ebert proposed use of Fast Fourier transform|FFT and

guard intervalS.Weinstein and P. Ebert, Data transmission by

frequency-division multiplexing using the discrete Fourier transform, IEEE

Transactions on Communication

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 28: Guard interval .

Wavelet - Applications of Wavelet Transform

1 Wavelet OFDM can achieve deeper notches than traditional Fast Fourier transform|FFT OFDM, and wavelet

OFDM does not require a guard interval (which usually represents significant overhead in FFT OFDM

systems)

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 29: Guard interval .

Multipath propagation - Multipath propagation in wired media

1 The ITU-T G.hn standard provides a way to create a high-speed (up to 1 Gigabit/s) local area network using existing home wiring (power line

communication|power lines, phone lines and ethernet over coax|coaxial

cables). G.hn uses OFDM with a cyclic prefix to avoid ISI. Because multipath propagation behaves

differently in each kind of wire, G.hn uses different OFDM parameters (OFDM symbol duration, Guard

Interval duration) for each media.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 30: Guard interval .

Digital television

1 * Digital Terrestrial Multimedia Broadcasting (DTMB) adopts time-domain synchronous (TDS) OFDM technology with a pseudo-random signal frame to serve as the guard interval (GI) of the OFDM block and

the training symbol

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 31: Guard interval .

DVB-T - Basics

1 The length of the Guard Interval can be chosen. It is a trade off between

data rate and single-frequency network|SFN capability. The longer the guard interval the larger is the potential SFN area without creating

intersymbol interference (ISI).

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 32: Guard interval .

DVB-T - Technical description of a DVB-T transmitter

1 ; 'Guard interval insertion': to decrease receiver complexity, every OFDM block is

extended, copying in front of it its own end (cyclic prefix). The width of such guard

interval can be 1/32, 1/16, 1/8, or 1/4 that of the original block length. Cyclic prefix is

required to operate single frequency networks, where there may exist an

ineliminable interference coming from several sites transmitting the same program

on the same carrier frequency.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 33: Guard interval .

DVB-T - Technical description of the receiver

1 The property that the guard interval at the end of the symbol is placed

also at the beginning is exploited to find the beginning of a new OFDM

symbol

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 34: Guard interval .

DVB-T - Technical description of the receiver

1 * 'Guard interval disposal:' the cyclic prefix is removed.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 35: Guard interval .

DVB-T - Europe

1 * (MPEG-4 AVC, FEC=2/3, guard interval - 1/4, 64 QAM. Official

simulcast started in March 2013, full switch has been done in 30

September 2013.)

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 36: Guard interval .

SC-FDMA - Transmitter and Receiver Structure of LP-OFDMA/SC-FDMA

1 Just like in OFDM, guard intervals (or called cyclic prefix) with cyclic

repetition are introduced between blocks of symbols in view to

efficiently eliminate time spreading (caused by multi-path propagation)

among the blocks.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 37: Guard interval .

ISDB - Feature

1 * ISDB-T allows to accommodate any combination of HDTV (roughly

8Mbit/s in H.264) and SDTV (roughly 2Mbit/s in H.264) within the given

bitrate determined by the transmission parameters such as

bandwidth, code-rate, guard interval, etc

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 38: Guard interval .

Digital Audio Broadcasting - Modulation

1 The guard interval duration also determines the maximum separation between transmitters that are part of the same single-frequency network (SFN), which is approximately 74km

for TM I.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 39: Guard interval .

Digital Audio Broadcasting - Single-frequency networks

1 Reception difficulties can arise, however, when the relative delay of multipaths exceeds the OFDM guard

interval duration, and there are frequent reports of reception

difficulties due to this issue when there is a lift, such as when there's

high pressure, due to signals travelling farther than usual, and

thus the signals are likely to arrive with a relative delay that is greater

than the OFDM guard interval.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 40: Guard interval .

Digital Terrestrial Multimedia Broadcast - Modulation

1 The DTMB standard uses many advanced technologies to improve their performance, for example, a Pseudorandom number sequence|

pseudo-random noise code (PN) as a guard interval that allows faster synchronization system and a more accurate channel estimation, Low-density

parity-check code|Low-Density Parity Check (LDPC) encoding to protect against mistakes, modulation

Time Domain Synchronization - Orthogonal Frequency Division Multiplexing (TDS-OFDM) which allows the combination of broadcasting in SD, HD

and multimedia services, etc.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 41: Guard interval .

Broadcast relay station - Boosters and distributed transmission

1 digital television stations are technically capable of sharing a channel, however this is more

difficult with the 8VSB modulation and invariable guard interval used in the ATSC standard than with COFDM used in the European and Australian

DVB-T standard

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 42: Guard interval .

IEEE 802.11n - Data rates

1 If more antennas are used, then 802.11n can go up to 288 megabits per second in 20MHz mode with four

antennas, or 600 megabits per second in 40MHz mode with four

antennas and 400 ns guard interval

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 43: Guard interval .

IEEE 802.11n - Wi-Fi Alliance

1 The baseline certification covers both 20MHz and 40MHz wide channels, and up to two spatial streams, for

maximum throughputs of 144.4Mbit/s for 20MHz and 300Mbit/s for 40MHz (with short guard interval)

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 44: Guard interval .

Fading - Selective fading

1 Inter-symbol interference is avoided by introducing a guard interval between the

symbols

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 45: Guard interval .

Multi-carrier spread spectrum - Variants

1 Once frequency domain spreading has taken place and the OFDM

subcarriers have all been allocated values, OFDM modulation then takes

place using the Fast Fourier Transform|IFFT to produce an OFDM symbol; the OFDM guard interval is then added; and if transmission is in the downlink direction each of these resulting symbols are added together

prior to transmission.https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 46: Guard interval .

Single-carrier FDMA - Transmitter and Receiver Structure of LP-OFDMA/SC-FDMA

1 Just like in OFDM, guard intervals (called cyclic prefixes) with cyclic repetition are introduced between

blocks of symbols in view to efficiently eliminate inter-symbol interference from time spreading

(caused by multi-path propagation) among the blocks.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 47: Guard interval .

DVB-T2 - The standard

1 * Guard intervals are 1/128, 1/32, 1/16, 19/256, 1/8, 19/128, and 1/4.

(For 32k mode, the maximum is 1/8.)

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 48: Guard interval .

DVB-T2 - System differences with DVB-T

1 Another example, for an Italian Single-frequency network|SFN DVB-T profile (64-QAM, 8k, coding rate 2/3,

guard interval 1/4) and a DVB-T2 equivalent (256-QAM, 32k, coding

rate 3/5, guard interval 1/16), achieves an increase in bit rate from 19.91Mbit/s to 33.3Mbit/s (+67%).

[http://www.fub.it/public/Morello020408B.pdf Presentation given by Dr

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 49: Guard interval .

DVB-T2 - System differences with DVB-T

1 Recommended maximum bit-rate configurations for 8MHz bandwidth, 32K FFT, guard interval 1/128, pilot

pattern 7:http://tech.ebu.ch/docs/tech/tech33

48.pdf

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 50: Guard interval .

DVB-T2 - Technical details

1 ** Guard interval insertion: a cyclic prefix is inserted before the IDFT symbol, to recover from transmit

channel echoes (multipath). Lengths from 1/128 to 1/4 of the IDFT length

are allowed.

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 51: Guard interval .

Single-frequency network - OFDM and COFDM

1 Since each modulator is very slow, we can afford to insert a guard

interval between the symbols, and thus eliminate the intersymbol

interference|ISI

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 52: Guard interval .

Single-frequency network - DVB-T SFN

1 The guard interval allows for a timing budget, of which several

microseconds may be allocated to time errors of the time-transfer

system used

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 53: Guard interval .

Single-frequency network - Alternative modulations

1 * Single-carrier frequency-domain-equalization (SC-FDE), i.e. single-carrier modulation combined with

guard intervals and fast fourier transform|fft-based frequency

domain equalization, or its multi-user version Single-carrier FDMA (SC-

FDMA).

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 54: Guard interval .

AT command - Hayes' solution

1 In order to avoid licensing Hayes's patent, some manufacturers

implemented the escape sequence without the time guard interval (Time Independent Escape Sequence|TIES)

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 55: Guard interval .

IEEE 802.11a-1999 - Technical description

1 Symbol duration is 4 microseconds, which includes a guard interval of 0.8 microseconds

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 56: Guard interval .

ISDB - Table of terrestrial HDTV transmission systems

1 |COFDM QPSK, 16QAM and 64QAM Hierarchical modulation: multi-

resolution constellation (16QAM and 64 QAM) Guard interval: 1/32, 1/16, 1/8 1/4 of OFDM symbol 2 modes:

2k and 8k FFT

https://store.theartofservice.com/the-guard-interval-toolkit.html

Page 57: Guard interval .

ISDB - Table of terrestrial HDTV transmission systems

1 |BST-COFDM with 13 frequency segments DQPSK, QPSK, 16QAM and

64QAM Hierarchical modulation: choice of three different modulations

on each segment Guard interval: 1/32, 1/16, 1/8 1/4 of OFDM symbol

3 modes: 2k, 4k and 8k FFT

https://store.theartofservice.com/the-guard-interval-toolkit.html