A PRESENTATION

ABOUTHIERARCHICAL

MODULATION

Abdulmoneam Ali Belal Essam

10 Feb. 2016

AGENDA

• Hierarchical Modulation (HM), a closer view.

• HM vs. Non-HM.

• Why HM ?

• HM in the real life.

• HM Scheme.

• Hp stream vs. LP stream.

• HM System Parameters.

• Power Penalty Analysis.

• BER Penalty Analysis.

• Research Refinements in hierarchical modulation.

10 Feb. 2016

BEFORE WE START..

• TV technology revolutions: analog color TV, digital TV.

• Digital TV is based on digital data compression and digital data transmission.

• In 1993, The DVB project was founded in Europe as an industry-led consortium of

around 200 broadcasters, manufacturers, network operators, software developers,

regulatory bodies and others committed to designing open interoperable standards

for the global delivery of digital media and broadcast services.

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BEFORE WE START..

• DVB Standards help us to know framing structure, channel coding and modulation for

digital television.

• These DVB standards are the technical basis for implementing digital TV

transmission.

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HIERARCHICAL MODULATION,

A CLOSERVIEW

• 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.

• Such multiple streams are called:

- High priority (HP) stream, Low priority (LP) stream, or

- Basic Information, secondary information, or

- Basic layer, enhancement layer, or

- Coarse information, refinement information.

10 Feb. 2016

HIERARCHICAL MODULATION,

A CLOSERVIEW

• Although hierarchical modulation can be applied to any constellations, we will limit

our discussions to QPSK/16QAM hierarchical modulation.

• The reason is two fold:

- First, most digital satellite systems use QPSK,

- Secondly, the use of a specific hierarchical constellation, QPSK/16QAM in this

case, simplifies the analysis.

10 Feb. 2016

HM VS. NON-HM

10 Feb. 2016

WHY HM ?

• Hierarchical modulations can help:

• provide different QoS to users with different profiles, e.g. higher throughput for

users with advanced receiver.

10 Feb. 2016

WHY HM ?

• provide unequal protection on different contents, e.g., video, audio, text.

• upgrade system to provide better service to new users with advanced receivers

while keeping existing users unchanged (Backward Compatibility, “the upgrade is

transparent to the deployed receivers of the original system”).

10 Feb. 2016

WHY HM ?

• Hierarchical modulation is particularly used to mitigate the cliff effect in digital

television broadcast, particularly mobile TV, by providing a (lower quality) fallback

signal in case of weak signals, allowing graceful degradation instead of complete

signal loss.

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HM IN THE REAL LIFE

Hierarchical modulations are widely used in digital

broadcast system design such as:

• DVB-T.

• Media-FLO (Forward Link Only), a digital broadcast TV

system developed by Qualcomm for mobile television.

• UMB (Ultra Mobile Broadband), a new 3.5th generation

mobile network standard developed by 3GPP2.

• Under study for DVB-H.

10 Feb. 2016

HM SCHEME

• hb

• The basic and secondary information bits

are channel encoded.

• The coded basic information bits are

mapped to the QPSK constellation.

• 𝑑min(𝐻𝑃) = 2𝑑1.

• The basic hierarchical constellation is

next modified according to the coded

secondary information bits.

• The combined constellation is a 16-QAM

constellation with the minimum distance

between two points denoted by 2𝑑2 .

• The two blocks, QPSK Mapper and

Secondary Mapper, in the Figure may be

combined into one.

10 Feb. 2016

HP STREAM VS. LP STREAM

• Specify the quadrant number (1,2,3, or 4).

• Lower code rate (higher protected).

• larger service coverage areas.

• Lower bit rate.

• Specify the symbol’s location within the

quadrant.

• higher code rate (lower protected).

• Smaller service coverage areas.

• Higher bit rate.

10 Feb. 2016

HM SYSTEM PARAMETERS

• Three parameters are required to describe a hierarchical modulation scheme:

- The ratio of the minimum distances in the hierarchical, basic constellations,

called Hierarchy Parameter λ, where λ =𝒅𝟐

𝒅𝟏.

- Code rates for the HP and LP streams.

- Modulation order for the HP and LP streams.

• λ is an important parameter to characterize the system, analysis are provided for it.

10 Feb. 2016

PENALTY ANALYSIS

• The light will be focused on the penalty

analysis performed in the paper shown in

the next figure.

• We will consider for two types of penalties

introduced to the QPSK receivers in the

hierarchical systems,

- Power penalty,

- BER penalty.

10 Feb. 2016

POWER PENALTY ANALYSIS

• When λ is small, the four points in each quadrant of the constellation

form a “cloud”.

• To the originally designed receivers, a cloud represents a point in the

QPSK constellation.

• Therefore, QPSK receivers in the upgraded system will continue to

operate and receive the basic information bits, but at a higher noise

level.

• The additional noise imposes a penalty on the performance of

originally designed receivers.

10 Feb. 2016

POWER PENALTY ANALYSIS

• The carrier to noise ratio (CNR) of the hierarchical constellation of Figure (b) is given by:

𝑪𝑵𝑹 =𝑬𝒔𝑵𝒐

=𝟐𝒅𝟏

𝟐 + 𝟐𝒅𝟐𝟐

𝑵𝒐

• When signals with the hierarchical constellation of Figure (b) are received by the QPSK

receivers, the constellation is treated as QPSK constellation, with power 2𝑑12 .

• To these receivers, the noise consists of two terms, the channel noise 𝑁𝑜, and the scattering

of points in the secondary hierarchy constellation, 2λ2𝑑12 (2𝑑2

2).

• The modulation noise ratio (MNR) is introduced to be the ratio of the power of QPSK

constellation to the combined noise power, and it is given by:

𝑴𝑵𝑹 =2𝒅𝟏𝟐

𝑵𝒐+𝟐λ𝟐𝒅𝟏𝟐=

𝑪𝑵𝑹

𝟏+ 𝟏+λ𝟐 𝑪𝑵𝑹

• MNR is the actual SNR seen by the QPSK receivers in hierarchical systems.

10 Feb. 2016

POWER PENALTY ANALYSIS

• The penalty to the QPSK receivers 𝑃𝑀𝑁𝑅 is the ratio 𝐶𝑁𝑅

𝑀𝑁𝑅, which is

𝑷𝑴𝑵𝑹= 𝟏 + 𝟏 + λ𝟐 𝑪𝑵𝑹

• The penalty, a function of both λ and CNR, is a measure of how much the QPSK

receivers suffer due to the addition of the secondary information, it represents the

additional carrier power that is needed in the hierarchical system so that the QPSK

receivers can see the same cleanness of the constellation as in the QPSK system

• The larger the penalty is, the worse these receivers will perform in the hierarchical

system.

10 Feb. 2016

POWER PENALTY ANALYSIS

Our Simulations Authors’ Simulations

For λ = 0.1 , when the transmission power in the hierarchical

system has a 7dB CNR, the QPSK receivers effectively get a

QPSK constellation with equivalence of CNR = 6.75dB,

because the penalty is 0.25dB.10 Feb. 2016

BER PENALTY ANALYSIS

• In the QPSK system, the QPSK constellation is transmitted and the probability of bit

error is : 𝑩𝑬𝑹𝑄𝑃𝑆𝐾 = 𝑸 𝑪𝑵𝑹

• The probability of raw bit error (without error correction coding) made by the QPSK

receivers in the hierarchical system is given by (performed by Vitthaladevuni et al. ),

𝑩𝑬𝑹 =𝟏

𝟐𝑸

𝟏 − 𝝀

𝟏 + 𝝀𝟐𝑪𝑵𝑹 +

𝟏

𝟐𝑸

𝟏 + 𝝀

𝟏 + 𝝀𝟐𝑪𝑵𝑹

• A comparison of the last two equations reveals that, for a given CNR, the addition of

the secondary information bits in the hierarchical system causes the QPSK receivers

to have a larger BER, and hence introduces a penalty to these receivers.

10 Feb. 2016

BER PENALTY ANALYSIS

• This penalty in BER is denoted as 𝑷𝐵𝐸𝑅, and is defined by the following equation:

𝑸𝑪𝑵𝑹

𝑷𝐵𝐸𝑅=𝟏

𝟐𝑸

𝟏 − 𝝀

𝟏 + 𝝀𝟐𝑪𝑵𝑹 +

𝟏

𝟐𝑸

𝟏 + 𝝀

𝟏 + 𝝀𝟐𝑪𝑵𝑹

• The BER penalty 𝑷𝐵𝐸𝑅, also a function of 𝝀 and CNR, represents the additional carrier

power that is needed in the hierarchical system so that the QPSK receivers can have

the same BER as in QPSK system without the secondary information.

10 Feb. 2016

BER PENALTY ANALYSIS

Our Simulations Authors’ Simulations

10 Feb. 2016

RESEARCH REFINEMENTS IN HIERARCHICAL MODULATION

• The Rotated constellation, one of

the main innovations in the DVB-T2

standard.

• It is an optional feature to improve

performance in frequency selective

channels.

• Angle of Rotation is a big challenge in

such a refinement.

10 Feb. 2016

RESEARCH REFINEMENTS IN HIERARCHICAL MODULATION

• concatenated coding strategy : mixing the two streams in order to make the

encoding of the LP stream dependent on the well protected HP stream.

• Improve the LP decoding performance while keeping the HP decoding

performance unchanged.

10 Feb. 2016

REFERENCES

• Hong Jiang and Paul Wilford, “A Hierarchical Modulation for Upgrading Digital Broadcast

Systems”, IEEE Transactions on Broadcasting, vol. 51, no. 2, 2005, pp. 223-229.

• Alexander Schertz and Chris Weck, “Hierarchical modulation - The transmission of two independent

DVBT multiplexes on a single frequency”, EBU Technical Review, April 2003.

• Shu Wang, Soonyil Kwon and Sukwoo Lee, LG Electronics Mobile Research, USA“On Enhancing

Hierarchical Modulations”, CONFERENCE PAPER , JANUARY 2008.

• “Hierarchical modulation”, Wikipedia.

• DVB Fact Sheet - May 2014.

• Hugo Meric, Jerome Lacan, Fabrice Arnal, Guy Lesthievent and Marie-Laure Boucheret, “Combining

Adaptive Coding and Modulation with Hierarchical Modulation in Satcom Systems”, IEEE

TRANSACTIONS ON BROADCASTING, DECEMBER 2011.

• Seyed Mohammad Sajad Sadough and Pierre Duhamel, “On the Interaction Between Channel

Coding and Hierarchical Modulation”, an IEEE ICC 2009 proceedings candidate.

• Ladislav Polak, Tomas Kratochvil, “Performance of the Rotated Constellation in DVB-T2”, ICDT 2012.

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