guard interval

DVB-T Basics of DVB-T 1 DVB-T is a COFDM transmission technique which includes the use of a 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.

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.

DVB-T Technical description of a DVB-T transmitter 1 ModulationCoding rateGuard 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

DVB-T Technical description of the receiver 1 Guard interval disposal: the cyclic prefix is removed.

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.)

Digital Video Broadcasting - Transmission 1 Guard IntervalNot Applicable1/4, 19/256, 1/8, 19/128, 1/16, 1/32, 1/1281/64 or 1/128

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.

IEEE Protocol 1 B1 B2 Assumes short guard interval (SGI) enabled, otherwise reduce each data rate by 10%.

IEEE n 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. WP nPrimer.pdf

IEEE n 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)

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

IEEE ac - Mandatory and optional features 1 ** 400 ns Short Guard Interval (SGI)

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).

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.

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.

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 timeslot

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):

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.

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

Guard interval 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,

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

Orthogonal frequency-division multiplexing - Summary of disadvantages 1 * Loss of efficiency caused by cyclic prefix/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 \,

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

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)

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.

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

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).

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.

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

DVB-T - Technical description of the receiver 1 * 'Guard interval disposal:' the cyclic prefix is removed.

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.)

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.

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

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.

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.

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.

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

IEEE n - Data rates 1 If more antennas are used, then n 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

IEEE n - 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)

Fading - Selective fading 1 Inter-symbol interference is avoided by introducing a guard interval between the symbols

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.

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.

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.)

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%).[ 0408B.pdf Presentation given by Dr

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: f

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.

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

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

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).

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)

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

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

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

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