660
`
`IEEE Transactions on Consumer Electronics, Vol. 39, No. 3. AUGUST 1993
`
`POSSIBLE CODING AND MODULATION APPROACHES TO IMPROVE SERVICE
`AVAILABILITY FOR DIGITAL HDTV SATELLITE BROADCASTING AT 22 GHz
`J. Palicot and J. Veillard
`CCETT—“Satellite Broadcasting and Cable Distribution” Department
`BP 59-35512 Cesson Sévigné, France
`
`ABSTRACT :
`
`New coding / modulation approaches are considered to
`improve service availability of digital HDTV satellite
`broadcasting services at 22 GHz. Two possible
`approaches are described which use a concept of
`layered modulation in conjunction with layered picture
`coding and channel coding. By means of this
`technique,
`the service continuity can be extended
`without the needsfor increase the satellite transmitted
`power. the service quality under severe atmospheric
`attenuations beeing reduced from high definition to
`normal definition.
`
`1 - Introduction
`
`The purpose of this paper is to outline possible coding
`and modulation approaches to improve service
`availability requirements for digital HDTV satellite
`broadcasting at the 22 GHz range. The work is being
`undertaken within the framework of the European
`RACE project HDSAT.
`
`The aim is to broadcast to the general public a very
`high quality picture close to that obtained in the studio
`[1], an aim which can be achieved for a bit-rate of
`approximately 45 Mbit/s with coding techniques
`currently under study.
`
`WARC-92 allocated the 21.4 - 22.0 GHz frequency
`band to BSS (HDTV) in Region 1. Due to severe
`atmospheric attenuation levels in this frequency band,
`conventional digital
`techniques exhibiting abrupt
`breakdown failure characteristics may not be able to
`provide the required service availability without a
`penalty on the satellite transmitted power [2].
`
`This paper proposes a hierarchical advanced coding /
`modulation scheme using different bit rates in order to
`extend service availability beyond that offered by
`conventional digital systems using a single bit rate and
`a single modulation scheme.
`
`The advanced approach outlined in this document
`
`achieve a graceful degradation of HDTV service
`during high fades ; this behaviour is very similar to that
`of analogue systems which is well accepted by
`television viewers. Most of the time, e.g. for up to 99%
`of the worst month, the service provides nominal
`HDTV quality, while during heavy rain fades, the
`receiver decodes normal TV picture.
`
`2 - Conceptual hierarchical coding / modulation
`using two different bit-rates
`
`The conceptual coding / modulation approaches are
`built around a frame (see figure 1) consisting of two
`parts:
`
`- Part 1 (R1) : HDTV component with high bit-rate
`signal of duration T1.
`- Part 2 (R2) : Conventional TV component with low
`bit-rate signal of duration T2.
`Frame duration
`
`
`
`High blt rate oomponem
`(R1)
`
`Figure 1 : Time multiplex of high and low
`bit-rate components
`
`The low bit-rate R2 signal is associated with a channel
`coding and modulation which are more robust in
`presence of noise than the channel coding and the
`modulation associated with the high bit-rate signal.
`
`During severe atmospheric attenuations, the receiver
`automatically switches from the HDTV component to
`the conventional TV component. The switching
`criterium can be related to the received power or to the
`bit error ratio of the HDTV component. For a given
`satellite transmitted power, this approach allows to
`extend the service continuity and hence to reduce the
`service outage time.
`
`Manuscript received June 11, 1993
`
`0098 3063/93 $03.00 © 1993 IEEE
`
`TH
`
`'
`
`I
`
`ERICSSON EXHIBIT 1008
`
`

`

`Palicot and Veillard: Possible Coding and Modulation Approaches to Improve Service Availability for
`Digital HDTV Satellite Broadcasting at 22 GHz
`
`661
`
`Comoluilonal
`on coder
`R I
`
`Comm-l
`encoder
`
`HDTV
`
`1250 lines
`1920 pus
`
`R r
`
`Time
`contpnulon
`K 1
`
`RF
`modulator
`
`Time
`Division
`Multiplexer
`
`Time
`I
`”9'2““
`
`RF
`modulator
`
`I
`
`information
`
`Figure 2 : Conceptual block diagram of a dual bit-rate emission system
`
`Two approaches are described :
`
`Approach A is a "simulcast" system in which the
`conventional TV signal is extracted from the HDTV
`source by applying a process of down-sampling. The
`two signals (HDTV and conventional TV) are
`broadcast simultaneously.
`
`Approach B is an improved variant of approach A,
`obtained by applying a compatible coding scheme.
`
`2-1. AnnmahA
`
`Figure 2 gives a notional conceptual diagram of the
`emission part.
`
`The conventional TV signal is extracted from the
`HDTV source by applying a process of down—
`sampling.
`
`The HDTV branch consists of the following elements :
`
`- A picture encoder which provides the signal with
`the bit rate RHQ
`
`- A channel coder with rate r1 < 1. The bit rate after
`channel coding is R'HQ = RHQ/rl.
`
`- A time compressor with the ratio K1 = K2 / (K2 -
`1). After time compression, we obtain bursts of
`duration T1 and bit rate R]: K1 .R‘HQ.
`
`- An RF modulator (8-PSK) which provides the
`modulated carrier by the bursts with bit rate R1.
`
`The conventional TV branch which processes the
`conventional picture and the associated sound/data
`signals is composed of the following elements :
`
`- The conventional picture encoder (bit rate : RLQ).
`
`- The sound encoder (bit rate Rs).
`
`- The multiplexer between the sound and low quality
`picture. The bit rate at the multiplexer output is :
`RL = RLQ + Rs.
`
`- A channel coder with rate r2 < 1. The bit rate after
`channel coding is :
`R'L = (RLQ + Rs)/r2-
`
`- A time compressor with the ratio K2 which
`provides bursts with the bit rate :
`R2 = R'L . K2 and with the duration T2.
`
`- An RF modulator (QPSK) which provides the
`modulated carrier by the bursts of bit rate R2.
`
`The last element in the chain is the time multiplexer
`which performs the multiplexing between the two
`modulated carriers.
`
`Figure 3 gives a conceptual diagram of the receiving
`part.
`
`

`

`662
`
`IEEE Transactions on Consumer Electronics, Vol. 39, No. 3, AUGUST 1993
`
`
`
`Figure 3 : Conceptual block diagram of a dual bit-rate receiving system
`
`is applied to two RF
`The modulated carrier
`demodulators, one for the low bit rate component, the
`other for the high bit rate component.
`
`After demodulation. high bit rate signal processing is
`as follows :
`
`- time decompression with ratio 1/K1
`— convolutional decoding with rate I]
`- HDTV decoding.
`
`Moreover, it is assumed that 8 BER measurement is
`included in the Viterbi decoder. Low bit rate signal
`processing is as follows :
`
`time decompression with ratio 1/K2
`-
`- Viterbi decoding of the convolutional code with rate
`r2
`
`- demultiplexing of low-quality picture and sounds
`- sound decoding
`- low-quality picture decoding and oversampling to
`provide a 1250 line picture to switcher SW.
`
`When the BER of the high bit rate signal is below a
`predetermined threshold (for example, 104), then the
`low quality picture is applied to the HD monitor. In
`order to avoid frequent switchings between the two
`pictures which may arise due to scintillation
`phenomena, 2 hysteresis system must be provided. For
`example, during an atmospheric attenuation,
`the
`switching HD —) LD is performed for BER = 104,
`but the switching LD —> HD is done for BER = 10-5.
`
`2.2- Approach}:
`
`Approach B is an improved variant of approach A.
`
`Better performance is obtained by applying a
`compatible coding scheme.
`
`Figure 4 gives a conceptual block diagram of approach
`B using a pyramidal coding scheme.
`
`At the transmission side, the HDTV signal is down
`sampled and a compatible 625 lines picture is obtained
`which is applied to encoder 2. The residual component
`(difference between HDTV input and locally decoded
`output of encoder 2) is coded by encoder 1. This
`scheme allows to reduce the transmitted data rate or to
`increase the portion of the data rate allocated to the
`picture component in the multiplex.
`
`At the reception site, upsampling (H : 2/1, V : 2/1) is
`carried out for the output from decoder 2 and the
`resulting information combined with the output from
`decoder l reconstruct the whole HDTV picture.
`
`2.3.W
`
`Two systems are described, one for approach A
`(example 1) and the other for approach B (example 2).
`
`The bit-rates used for the two examples are as follows :
`
`- allocated bit rate for sound and data :
`1 Mbit/s
`
`- allocated bit rate for the compatible picture
`component:
`3.5 Mbit/s (approach A)
`or:8Mbit/s (approach B)
`
`

`

`
`
`Patient and Veillard: Possible Coding and Modulation Approaches to Improve Service Availability for
`Digital HDTV Satellite Broadcasting at 22 GHz
`
`663
`
`
`
`Figure 4 : Conceptual block diagram of approach B using a pyramidal coding scheme
`
`- allocated bit rate for the 1-D picture component :
`45 Mbit/s (approach A)
`or : 36 Mbit/s (approach B)
`
`The modulations associated with the two systems are
`as follows :
`
`- High bit rate component
`modulation with rate 2/3.
`
`:
`
`trellis-coded 8-PSK
`
`- Low bit rate component : QPSK modulation.
`
`The channel coding associated with the low bit rate
`component must be very robust in presence of noise.
`At present, the best channel coding scheme which can
`be associated with a QPSK modulation is a new class
`of convolutional codes called "turbocodes" whose
`performances in terms of Bit Error Ratio (BER) is
`close to the Shannon Limit [3]. The ”turbo-code”
`encoder is built from a parallel concatenation of two
`recursive systematic convolutional codes and the
`associated decoder is made of P identical pipeline
`decoders using a feedback decoding rule.
`
`The main parameters of the two examples are given in
`Table 1.
`
`The symbol-rate is thus 27 Mbaud in all cases, which is
`compatible with satellite broadcasting in a 36 MHz
`channel. This bandwidth is currently used by a large
`number of satellites providing DTH reception (e.g., the
`european Eutelsat or the French Telecom-Z satellites).
`
`3 - Theoretical assessment of system performance
`
`It is assumed that the picture decoders include a
`powerful error-correction code (e.g. a (255, 239) Reed-
`Solomon Code) with a suiTable interleaving scheme.
`
`This being so, the following assumptions have been
`taken into account :
`
`- HD picture quality is provided up to a BER = 10'4
`for the HDTV component (the BER refers to the
`output from the Viterbi decoder and can still
`provide nominal picture quality after Reed—
`Solomon decoding).
`
`-
`
`Service continuity is provided up to a BER = 2.10"3
`for the low bit rate component.
`
`- The turbo-decoder applied to the low bit rate
`component uses 3 iterations.
`
`In these conditions, the theoretical performance of
`examples 1 and 2 is as follows:
`
`- C/N in 36 MHz corresponding to the limit
`of HD picture quality (BER = 104) : 7.5 dB
`
`- C/N in 36 MHz corresponding to the service
`interruption
`(BER = 2.10‘3) for the low bit rate component : 0
`dB
`
`Figure 5 shows the failure characteristic of the
`hierarchical system outlined above compared to a
`conventional system which uses a single bit rate with
`the following parameters :
`
`- Bit-rate after HDTV coding : 45 Mbit/s
`- Modulation : TOM-8 PSK with rate 2/3.
`
`It can be seen that the described hierarchical system
`offers an advantage of 5.7 dB in terms of service
`continuity compared to the conventional system.
`
`a] 7,, T
`
`,,
`
`

`

`664
`
`IEEE Transactions on Consumer Electronics, Vol. 39, No. 3, AUGUST 1993
`
`Table 1 : Main parameters of the two examples
`
`a) Low bit rate component :
`
`- Modulation
`- Bit rate before channel coding (R1)
`- Channel coding
`
`- Bit rate after channel coding (R1)
`- Time compression ratio (K2)
`- Transmitted bit rate after time compression (R2)
`
`- Transmitted bit rate ratio (M = Rl/RZ)
`
`b) High bit rate component :
`
`- Modulation
`- Bit rate before channel coding (RHD)
`- Channel coding
`
`- Bit-rate after channel coding (R'HD)
`- Time compression ratio (K1)
`- Transmitted bit rate after time compression (R1)
`
`HDTV
`
`quality
`Conventional
`
` 31:1“:
`
`TV
`Service
`interruption
`
`C/N (dB)in 36MHZ
`1 : Conventional system (single bit mm)
`2 : Hierarchical system
`
`Figure 5 : Picture quality versus C/N
`
`— Antenna efficiency : 70%.
`- LNB noise figure 2 1.7 dB. It seems that this value
`could be obtained with existing mass-production
`assembly techniques [4].
`
`4-2.WWW
`
`At 22 GHz, the following results have been obtained in
`Paris (satellite at 19°W, elevation 30 degrees) :
`
`- Attenuation : A = 5.2 dB for 99% of the worst
`month.
`
`.
`.
`_
`- xix-anon . A — 11.2 dB for 99.9% of the worst
`
`Atmospheric attenuation increases the receiver noise
`temperature in accordance with the following
`equation :
`
`4 - Example of link budget calculation
`
`T = aTC + (1 - a)T() + (F - l)To
`
`4J-Wmm
`
`where Tc=sky temperature (Tc=90°K):
`
`The following parameters have been considered for
`Direct-to—Home receiver equipment at 22 GHz :
`
`F
`a
`T0
`
`=receiver misc 5
`= 10-A/10
`= 290°K
`
`
`
`

`

`
`
`Palicot and Veillard: Possible Coding and Modulation Approaches to Improve Service Availability for
`Digital HDTV Satellite Broadcasting at 22 GHz
`
`665
`
`Table 2 : CIN reduction due to atmospheric attenuation
`
`Atmospheric
`attenuation (dB)
`
`Receiver noise tem-
`perature increase
`(dB)
`
`A C/N (dB)
`
`system
`
`Conventional
`
`C1earskyC/Nin361tfi1ztoguarantee
`HD picture quality for 99% of the worst month
`
`ClearskyC/Nin36MHz toguaranteeservice
`availability for 99.9% of the worst month
`
`With a receiver noise figure F = 1.7 dB, the C/N
`reduction due to atmospheric attenuation is given in the
`Table 2.
`
`4.3.mm
`
`The clear sky C/N requirement has to be defined in
`order to satisfy the most stringent condition almost
`these two constraints :
`
`- HD picture quality guaranteed for 99% of the worst
`month
`- Service availability guaranteed for 99.9% of the
`worst month.
`
`These C/N requirements are given in Table 3 below for
`the hierarchical and conventional systems.
`
`A technical margin of 2 dB has been included for both
`systems.
`
`It can be seen that the hierarchical system meets both
`requirements with approximately the same C/N.
`
`The following assumptions are made for the purposes
`of link budget calculations (clear sky) :
`
`Satellite EIRP
`-
`- Free space loss
`- Gaseous absorption
`- Pointing margin
`- Up-link C/N
`
`: 56 dBW
`: 210.8 dB
`: 1.4 dB
`: 0.5 dB
`: 30 dB
`
`Other contributions such as ageing are not taken into
`account in these calculations.
`
`With the above hypothesis, the antenna sizes (D)
`required for DTH reception are as follows :
`
`- Conventional system : D = 150 cm
`- Hierarchical system : D = 80cm
`
`It is evident that on the basis of the above parameters,
`only the hierarchical system will provide 99.9%
`service availability with a reasonable antenna size.
`
`'T'l
`
`

`

`666
`
`IEEE Transactions on Consumer Electronics, Vol. 39, No. 3, AUGUST 1993
`
`There are two modes of operation depending on the
`C/N ratio :
`
`-
`
`In normal conditions, the two phase comparators
`(QPSK and 8-PSK) are used sequentially during the
`frame.
`
`- At very low C/N, the 8-PSK comparator cannot be
`used because cycle slippings occur. The QPSK
`phase comparator is then used in a TDMA mode.
`For this purpose, a carrier recovery preamble is
`added at the beginning of each frame, so that the
`carrier can be recovered before each QPSK burst
`demodulation.
`
`6 - Conclusion
`
`The new coding/modulation approach described in this
`paper is an example of how service continuity could
`be increased by using a concept of layered modulation
`in conjunction with layered picture coding and layered
`channel coding. Other variants of this approach are
`currently under investigation. It can already be
`deduced, however, that by means of this technique,
`service continuity could be extended to, or even
`exceed, 99.9% of the worst month without the need for
`increasing the satellite transmit power, the service
`quality under severe attenuation conditions being
`reduced from high definition to normal television.
`Nominal high-quality sound service is preserved even
`during severe fades and the sound fails after the failure
`of picture.
`
`The concepts outlined in this paper are being
`experimentally verified in the CCE'I'T's laboratories
`and an initial prototype modem will be available by the
`end of 1993.
`
`References
`
`[l]
`
`[2]
`
`[3]
`
`C. Dosch, "Direct Satellite Broadcasting of
`Digital HDTV in the 20 GHz Frequency Range",
`EBU Review, Technical N° 244, December
`1990.
`C. Dosch, "New Broadcasting Modulation
`Techniques - An Overview“, IEE Week end
`Seminar
`"Broadcasting of Tomorrow".
`Cambridge. 4-6 Sept. 1992.
`C. Berrou, A. Glavieux, "Near Shannon Limit
`Error Correcting Coding and Decoding : Turbo-
`Codes", ICC 93, 23-26 May, Geneva
`\
`[4] CD. Howson. C. Guo, G. Haquet and M.
`Fujimoto "A 22 GHz band low»cost, low-noise
`down converter for DBS", IEEE Trans. on
`Consumer Electronics, Vol 38, N° 3, August
`1992.
`
`5 - Implementation problems for the modem
`
`The hierarchical modem can be implemented with only
`one RF modulator/demodulator. At the emission side,
`the carrier is modulated in phase and quadraurre by the
`baseband signals [(0 and 00) as shown in the
`following
`equation :
`
`y(t) = I(t) cos toot + Q(t) sin (not
`
`If tpk is the phase state at t = KTs where Ts is the
`symbol period, then I(KTs) and Q(KTs) are given by
`the equations :
`
`1(KTs) = cos tpk
`Q(KTs) = Sin ‘Pk
`
`with:
`
`(pK:k1t/N+1I:/2N;K=0l0N-l
`N = 2 for QPSK modulation
`N = 4 for 8-PSK modulation.
`
`the modulated carrier at
`the reception side,
`At
`frequency to is multiplied by the in-phase and
`quadrature components of a sinusoidal signal delivered
`by a VCO at the same frequency. Phase and frequency
`control is obtained with a decision feedback Costas
`loop carrier recovery circuit which uses the l and Q
`demodulated baseband signals to supply an error
`voltage 8 applied to the VCO.
`
`As the symbol rate is the same for both modulations,
`the symbol clock can be recovered by zero crossing
`detection of signals I(t) and Q(t).
`
`For carrier recovery, the error voltage 8K supplied by
`the phase comparator is given by the equation :
`
`8x = KQK —QKiK where:
`
`lk = I(KTs)
`Qk = Q(KTs)
`
`- for QPSK demodulation :
`
`a I
`
`K = sgnI,
`
`QK = sgan
`
`— for 8—PSK demodulation :
`
`f‘=[J—‘—‘—‘7J—J—LS"(1 +9 )3: "(I —Q )+sgnll]sin7l/8
`
`Q.=[S ”(I +Q )-25 ”(I —Q )+Sgan]SiIlfi/8
`
`
`
`
`
`m I
`
`

`

`
`
`Palicot and Veillard: Possible Coding and Modulation Approaches to Improve Service Availability for
`Digital HDTV Satellite Broadcasting at 22 GHz
`
`667
`
`BIOGRAPHIES :
`
`Jacques VEILLARD was born in
`Rennes, France in 1945. He is
`graduated from Ecole Supérieure
`d'Electronique de l'Ouest (ESEO) and
`has a degree of Doctor in Electronics
`from the University of Rennes. From
`1973 to 1988, he was involved in
`studies of analog and digital
`modulation techniques for satellite
`broadcastingJ—leisnowattheheadof
`the department DCS where he has in
`charge the introduction of new TV
`systems
`in satellite and cable
`networks. He is also involved within
`European projects Eureka 95 and
`HDSAT and in various international
`bodies (EBU).
`
`Jacques PALICOT was born in Laval,
`France in 1957. He received the
`Doctor degree in Electronics from the
`University of Rennes. In 1984, he
`joined the Centre Commun d'Etudes
`de Telediffusion et Telecom-
`munications (CCE’I‘I‘). Since 1988,
`he
`is
`involved in studies of
`
`equalization techniques applied to
`digital transmissions and new TV
`systems (MAC and HDMAC). He
`participates in various international
`bodies EBU, CCIR and within
`european projects Eureka 95 and
`HDSAT.
`
`
`
`fifiT—l—H
`
`
`ff T
`
`