Hierarchical modulation

Hierarchical modulation

Hierarchical modulation, also called layered modulation, is one of the signal processing techniques for multiplexing and modulating multiple data streams into one single symbol stream, where base-layer symbols and enhancement-layer symbols are synchronously overplayed to together before transmission.

Hierarchical modulation has been widely proven and included in various standards, such as DVB-T, MediaFLO, UMB (Ultra Mobile Broadband, a new 3.5th generation mobile network standard developed by 3GPP2), and is under study for DVB-H.

Hierarchical modulation is also taken as one of the practical implementation of superposition precoding, which can help achieve the maximum sum rate of broadcast channels. When hierarchical-modulated signals are transmitted, users with good reception and advanced receiver can demodulate multiple layers. For a user with conventional receiver or poor reception condition, it may only demodulate the data stream embedded in the base layer. With hierarchical modulation, a network operator can target users of different types with different services or QoS's.

However, traditional hierarchical modulation suffers from serious inter-layer interference (ILI) so that the achievable rate by low-layer data stream, e.g. the base-layer data stream, is dented by the interference from high-layer signal(s).

For example, for a hierarchically modulated symbol with 16QAM base layer and QPSK enhancement layer, the base-layer throughput loss is up to about 1.5bits/symbol with the total receive signal-to-noise ratio (SNR) at about 23 dB, which is necessary for taking the full potentials of 64-ary QAM. This means, due to ILI, about 1.5/4 = 37.5% loss of the base-layer achievable throughput. Furthermore, due to ILI and the imperfect demodulation of base-layer symbols, the demodulation error rate of higher-layer symbols increases too.

Example

For example, the figure depicts a layering scheme with QPSK base layer, and a 16QAM enhancement layer. The first layer is 2 bits (represented by the green circles). The signal detector only needs to establish which quadrant the signal is in, to recover the value (which is '10', the green circle in the lower right corner). In better signal conditions, the detector can establish the phase and amplitude more precisely, to recover four more bits of data ('1101'). Thus, the base layer carries '10', and the enhancement layer carries '1101'.

ee also

* Link adaptation

External links

* [http://www.broadcastpapers.com/whitepapers/paper_loader.cfm?pid=520 Hierarchical Modulation Explained]
* [http://www.dvb.org/technology/fact_sheets/WP01_DVB-T%20Hierarchical.pdf Hierarchical Modulation under DVB]


Wikimedia Foundation. 2010.

Игры ⚽ Поможем решить контрольную работу

Look at other dictionaries:

  • Metric modulation — In music a metric modulation is a change (modulation) from one time signature/tempo (meter) to another, wherein a note value from the first is made equivalent to a note value in the second, like a pivot. The term was invented to describe the… …   Wikipedia

  • Hierarchy — A hierarchy (Greek: hierarchia (ἱεραρχία), from hierarches, leader of sacred rites ) is an arrangement of items (objects, names, values, categories, etc.) in which the items are represented as being above, below, or at the same level as one… …   Wikipedia

  • Orthogonal frequency-division multiplexing — Passband modulation v · d · e Analog modulation AM · …   Wikipedia

  • Broadcast television systems — There are several broadcast television systems in use in the world today. An analogue television system includes several components: a set of technical parameters for the broadcast signal, a system for encoding color, and possibly a system for… …   Wikipedia

  • Cliff effect — In telecommunications, the (digital) cliff effect or brickwall effect describes the sudden loss of digital signal reception. Unlike analog signals, which gradually fade when signal strength decreases or electromagnetic interference or multipath… …   Wikipedia

  • Digital television transition in the United States — Further information: Digital television transition The DTV (an abbreviation of digital television, also called digital broadcast) transition in the United States was the switchover from analog (the traditional method of transmitting television… …   Wikipedia

  • ATSC Standards — document a digital television format that will have replaced the analog NTSC television system [ [http://home.businesswire.com/portal/site/home/index.jsp?ndmViewId=news view ndmConfigId=1000001 newsId=20071017005469 newsLang=en Major retailer… …   Wikipedia

  • Link adaptation — Link adaptation, or adaptive coding and modulation (ACM), is a term used in wireless communications to denote the matching of the modulation, coding and other signal and protocol parameters to the conditions on the radio link (e.g. the pathloss,… …   Wikipedia

  • Digital terrestrial television — List of digital television broadcast standards DVB standards (Europe) DVB S (satellite) DVB S2 DVB T (terrestrial) DVB T2 DVB C …   Wikipedia

  • QAM (television) — This article is about North American digital television. For other uses of QAM, see quadrature amplitude modulation. QAM stands for quadrature amplitude modulation, the format by which digital cable channels are encoded and transmitted via cable… …   Wikipedia

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”