Hierarchical Modulation

1. HIERARCHICAL
MODULATION
Abdulmoneam Ali Belal Essam
Supervised by: Dr. Fadel Digham
10 Feb. 2016 1

2. 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.
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3. 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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4. 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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5. HIERARCHICAL
MODULATION,
A CLOSER
VIEW
• 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.
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6. HIERARCHICAL
MODULATION,
A CLOSER
VIEW
• 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.
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7. HM VS. NON-HM
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8. WHY HM ?
• Hierarchical modulations can help:
• provide different QoS to users with different profiles, e.g. higher throughput for
users with advanced receiver.
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9. 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”).
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10. 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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11. 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.
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12. 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.
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13. 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.
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14. 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 =
𝒅 𝟐
𝒅 𝟏
.
- 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.
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15. 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.
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16. 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.
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17. POWER PENALTY ANALYSIS
• The carrier to noise ratio (CNR) of the hierarchical constellation of Figure (b) is given by:
𝑪𝑵𝑹 =
𝑬 𝒔
𝑵 𝒐
=
𝟐𝒅 𝟏
𝟐
+ 𝟐𝒅 𝟐
𝟐
𝑵 𝒐
• When signals with the hierarchical constellation of Figure (b) are received by the QPSK
receivers, the constellation is treated as QPSK constellation, with power 2 𝑑1
2
.
• To these receivers, the noise consists of two terms, the channel noise 𝑁𝑜, and the scattering
of points in the secondary hierarchy constellation, 2λ2
𝑑1
2
(2 𝑑2
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 =
2 𝒅 𝟏
𝟐
𝑵 𝒐+𝟐λ 𝟐 𝒅 𝟏
𝟐 =
𝑪𝑵𝑹
𝟏+ 𝟏+λ 𝟐 𝑪𝑵𝑹
• MNR is the actual SNR seen by the QPSK receivers in hierarchical systems.
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18. POWER PENALTY ANALYSIS
• The penalty to the QPSK receivers 𝑃 𝑀𝑁𝑅 is the ratio
𝐶𝑁𝑅
𝑀𝑁𝑅
, which is
𝑷 𝑴𝑵𝑹= 𝟏 + 𝟏 + λ 𝟐 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.
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19. 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 19

20. BER PENALTY ANALYSIS
• In the QPSK system, the QPSK constellation is transmitted and the probability of bit
error is : 𝑩𝑬𝑹 𝑄𝑃𝑆𝐾 = 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
𝟐
𝑸
𝟏 − 𝝀
𝟏 + 𝝀 𝟐
𝑪𝑵𝑹 +
𝟏
𝟐
𝑸
𝟏 + 𝝀
𝟏 + 𝝀 𝟐
𝑪𝑵𝑹
• 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.
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21. BER PENALTY ANALYSIS
• This penalty in BER is denoted as 𝑷 𝐵𝐸𝑅, and is defined by the following equation:
𝑸
𝑪𝑵𝑹
𝑷 𝐵𝐸𝑅
=
𝟏
𝟐
𝑸
𝟏 − 𝝀
𝟏 + 𝝀 𝟐
𝑪𝑵𝑹 +
𝟏
𝟐
𝑸
𝟏 + 𝝀
𝟏 + 𝝀 𝟐
𝑪𝑵𝑹
• The BER penalty 𝑷 𝐵𝐸𝑅, 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.
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22. BER PENALTY ANALYSIS
Our Simulations Authors’ Simulations
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23. 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.
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24. 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.
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25. 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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