WO2015022170A1

WO2015022170A1 - Transmitting apparatus and method for a mimo broadcast system

Info

Publication number: WO2015022170A1
Application number: PCT/EP2014/066029
Authority: WO
Inventors: Daniel Schneider; Lothar Stadelmeier
Original assignee: Sony Corporation; Sony Deutschland Gmbh
Priority date: 2013-08-15
Filing date: 2014-07-25
Publication date: 2015-02-19

Abstract

A transmitting apparatus for a broadcast system comprises an encoder, a modulator, a MIMO precoder and two transmission antennas. The ΜΓΜΟ precoder is configured to precode said constellation values to obtain two MEVIO encoded signal streams, wherein constellation values are multiplied by a precoding matrix V. For precoding subsequent pairs of constellation values different precoding matrices are applied, wherein subsequently applied precoding matrices are formed by use of different first precoding angles Φ and/or second precoding angles ψ and wherein at least one applied precoding matrix distinguishes from all other applied precoding matrices by having a different first precoding angle Φ and a different second precoding angle ψ.

Description

TRANSMITTING APPARATUS AND METHOD FOR A MIMO BROADCAST SYSTEM

BACKGROUND

Field of the DISCLOSURE

[0001] The present disclosure relates to a transmitting apparatus for a broadcast system and to a corresponding transmission method.

DESCRIPTION OF RELATED ART

[0002] The application of several antennas at the transmitter and the receiver is called MIMO (Multiple Input Multiple Output). MIMO is used in several wireless (LTE, Wifi, terrestrial broadcast, ...) and wired (PLC, DSL, ...) systems and improves the system performance by higher throughput and reliability. Typically, the channel capacity increases with the number of antennas, e.g. the channel capacity might be doubled for a 2x2 MIMO system.

[0003] The only existing broadcast system that deploys MIMO is DVB-NGH as described in "Digital Video Broadcasting (DVB); Next Generation broadcasting system to Handheld, physical layer specification (DVB-NGH)", DVB document A160, November 2012. The precoding in DVB-NGH is defined by a fixed precoding (eSM) described by parameters α, β and Θ and a phase hopping (PH). The phase hopping algorithm changes the phase of the second transmit antenna from one subcarrier to the next with a periodicity of 9. [0004] The "background" description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor(s), to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.

SUMMARY

[0005] It is an object to provide a transmitting apparatus and method having a more optimized precoding and thus providing an improved performance. It is a further object to provide a corresponding computer program for implementing said transmission method and a non-transitory computer-readable recording medium for implementing said transmitting method.

[0006] According to an aspect there is provided a transmitting apparatus for use in a broadcast system, said apparatus comprising:

an encoder configured to encode input data into cell words,

a modulator configured to modulate said cell words into constellation values of a constellation, a MEVIO precoder configured to precode said constellation values to obtain two MIMO encoded signal streams, wherein constellation values to be transmitted on the same carrier by different transmission antennas are multiplied by a precoding matrix V of the form

or of an equivalent form, wherein for precoding subsequent pairs of constellation values different precoding matrices are applied, wherein subsequently applied precoding matrices are formed by use of different first precoding angles Φ and/or second precoding angles Ψ and wherein at least one applied precoding matrix distinguishes from all other applied precoding matrices by having a different first precoding angle Φ and a different second precoding angle ψ, and

two transmission antennas configured to transmit said MEVIO encoded signal streams.

[0007] According to a further aspect there is provided a transmitting apparatus for use in a broadcast system, said apparatus comprising:

an encoder configured to encode input data into cell words,

a modulator configured to modulate said cell words into constellation values of a constellation, a MEVIO precoder configured to precode said constellation values to obtain two MIMO encoded signal streams, wherein constellation values to be transmitted on the same carrier by different transmission antennas are multiplied by a fixed precoding matrix V of the form

or of an equivalent form, wherein the first precoding angle Φ is in the range -π < Φ < π

and the second precoding angle ψ is in the range 0 < ψ < π/2 , and

two transmission antennas configured to transmit said MDVIO encoded signal streams.

[0008] According to still further aspects corresponding method, a computer program comprising program means for causing a computer to carry out the steps of the method disclosed herein, when said computer program is carried out on a computer, as well as a non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method disclosed herein to be performed are provided.

[0009] Preferred embodiments are defined in the dependent claims. It shall be understood that the disclosed apparatus and methods, the disclosed computer program and the disclosed computer- readable recording medium have similar and/or identical preferred embodiments as the claimed transmitting apparatus and as defined in the dependent claims.

[0010] One of the aspects of the disclosure is to provide for a more general precoding hopping. For improved performance, not only the angle is variable, as proposed according to DVB-NGH according to which this angle φ hops from subcarrier to subcarrier, but according to the present disclosure also the angle φ is made variable and not constant as proposed according to DVB-NGH. The optimum precoding hopping set is adopted and optimized, preferably according to the statistics of the considered channel for which no channel information is available since in a broadcast system there is generally no feedback channel from the receiver to the transmitter. The optimization is e.g. done with the help of defined and representative channel models, e.g. as known from DVB-NGH. In preferred embodiments the optimization is complemented with more channel models such as the MGM (Modified Guildford Model) channel model of the DVB MIMO study mission or expected additional channel models of the ATSC3.0 standardization group.

[0011] The apparatus and methods according to the present disclosure are provided for application in a broadcast system. They can be applied in multi-carrier broadcast systems, according to which the angles angle ψ and φ may generally change from subcarrier to subcarrier in the frequency domain, as well as in single-carrier broadcast systems, according to which the angles ψ and φ may generally change from symbol to symbol in the time domain. In general, according to the present disclosure at least one of the angles φ and φ may change from carrier to carrier, i.e. the precoding matrix V may be different from carrier to carrier, which holds both for a multi-carrier or a single-carrier broadcast system.

[0012] It has also been found according to the present disclosure that an improved performance can be obtained with a transmitting apparatus and method, which use a fixed precoding matrix, in which both angles φ and φ have been optimized.

[0013] The foregoing paragraphs have been provided by way of general introduction, and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

Fig. 1 shows a schematic diagram of two simplified embodiments of a broadcast system, in which the transmitting apparatus according to the present disclosure can be used, Fig. 2 shows a schematic diagram of parts of a 2x2 ΜΓΜΟ broadcast system and the MIMO channel, Fig. 3 shows a schematic diagram of the high-level physical layer of a transmission apparatus,

Fig. 4 shows a schematic diagram of a bit interleaved coding and modulation unit,

Fig. 5 shows a schematic diagram of a general MIMO precoding device,

Fig. 6 shows a schematic diagram of a precoding device as proposed in DVB-NGH, Fig. 7 shows a diagram illustrating phase hopping as performed according to DVB-NGH, Fig. 8 shows a diagram illustrating angle hopping as performed according to a first embodiment of the present disclosure,

Fig. 9 shows a diagram illustrating angle hopping as performed according to a second embodiment of the present disclosure,

Fig. 10 shows a schematic simplified diagram of a transmitting apparatus according to the present disclosure,

Fig. 11 shows a flow chart of a transmitting method according to the present disclosure, and Fig. 12 shows a diagram illustrating the performance of various embodiments of the present disclosure versus known systems.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0015] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, Fig. 1 shows a schematic diagram of two simplified embodiments of a broadcast system, in which the disclosure can be used. Fig. 1 particularly explains two MIMO applications in a broadcast scenario.

[0016] Fig. 1A shows an example of a co-located scenario where the transmitter 10 (depicted as broadcast tower) has two transmission antennas 11, 12 (one is vertical polarized, indicated by arrow 11a; the other is horizontal polarized, indicated by arrow 12a) and the receiver 20 (depicted as laptop) has two receiving antennas 21, 22 (schematically indicated). This is the scenario of cross-polar MEVIO as often used in terrestrial broadcast. Fig. IB shows an example for distributed MIMO with two transmitters 10, 15 each having one transmission antenna 11, 16. The transmitters 10, 15 are synchronized to span a distributed MEVIO system. Herein, both kinds of embodiments of transmitters (i.e. a single transmitter having two transmission antennas or two transmitters each having a single antenna) shall generally be understood as transmitting apparatus in the sense of the present disclosure.

[0017] One way to increase the throughput by MIMO is spatial multiplexing (SM) where parallel and independent data streams are transmitted via the different transmission antennas. Fig. 2 shows a basic 2x2 MIMO broadcast system 1 with the channel 2 (described by the channel matrix H) between transmitter 10 and receiver 20. The solid arrows 3, 4 illustrate the co-channels while the dashed arrows 5, 6 show the cross-channels which result in interference between the two data streams at the receiver 20. The task of the MEVIO detection at the receiver 20 is to recover the transmitted spatial streams. There are different decoding algorithms, e.g. maximum likelihood (ML) algorithm, which is generally optimal. There are also less complex algorithms with non-optimum performance, e.g. linear algorithms like zero-forcing (ZF) or minimum mean sqaure error (MMSE) algorithm.

[0018] Fig. 3 shows a schematic diagram of the high-level physical layer of a transmitter 40 according to the above cited DVB-NGH standard. The transmission apparatus according to the present disclosure may generally have the same or a similar layout. The transmitter 40 comprises an input processing unit 41 for processing input streams (e.g. a TS or GSE stream), a bit interleaved coding and modulation unit 42 for bit interleaved coding and modulation, a frame building unit 43 for frame building, an OFDM generation unit 44 for OFDM generation and two transmission antennas 45, 46 for transmitting the two OFDM streams.

[0019] Fig. 4 shows a schematic diagram of a bit interleaved coding and modulation unit 42 according to the above cited DVB-NGH standard. The transmission apparatus according to the present disclosure may generally comprise such a bit interleaved coding and modulation unit having the same or a similar layout. The bit interleaved coding and modulation unit 42 comprises a FEC (Forward Error Correction) encoding unit 51 , e.g. comprising a combined LDPC/BCH encoder, a bit interleaver 52, a mapping unit 53 for mapping cells to constellations, a MIMO precoder 54, a cell interleaver 55, and a time interleaver 56, e.g. for inter-frame convolutional and intra-frame block interleaving.

[0020] The performance of SM MIMO systems can be improved by linear precoding at the transmitter. For multi-carrier systems the precoding is applied for each subcarrier separately. Fig. 4 shows a possible location of the MIMO precoding at the transmitter. The precoding is preferably applied on the level of QAM symbols. After mapping to complex QAM symbols in the mapping unit 53 a serial-to- parallel converter (S/P; not shown) splits the single data stream into the two transmit streams before applying the precoding in the MIMO precoding unit 54. In a next step each MIMO stream is modulated, e.g. by OFDM in the OFDM generation unit 44 (as shown Fig. 3).

[0021] The linear precoding can be described by a matrix F. The optimum precoding matrix depends on the channel. Thus, channel state information (CSI) is generally required at the transmitter in order to apply the optimum precoding for the current channel conditions. For bidirectional communication systems the required CSI may be transmitted from the receiver to the transmitter. For broadcast systems this is impossible since there is generally no feedback path from the receivers to the transmitter. Even if there would be a return channel from the many receivers to the transmitter, it would be impossible for the transmitter to optimize the precoding for all receivers simultanously.

[0022] From MFMO theory it is known that the optimum precoding matrix F can be factored into two parts:

F = VP (1)

where V is a unitary matrix (i.e. V"¹ = V*) which is derived from the channel matrix H via a singular value decomposition (SVD). P is a diagonal matrix which describes the power allocation (PA) between the spatial streams, e.g. for 2x2 MIMO with two spatial streams:

(2)

L 0 -*fl a. where s is the power of the first stream and the power of the second stream fulfils the condition that the total power is equal to 1.

[0023] The unitary property of V implies that the total power is preserved by this precoding. The unitary property also leads to a special representation: For two streams, the complex 2x2 matrix V is described by two angles ψ and φ. One representation is:

C OS-ψ ΞΗΐψ 1 0 ^' cos-ψ είηψ

(3)

■0 [- ίΌΤϊψ CO Sl ϊ where the range of ip and φ to represent all possible beamforming matrices is 0≤ ip≤ - and — φ≤ π. There might by many other definitions of V, e.g.

The different definitions are equivalent and can be converted into each other. In the following the definition according to (3) is used.

[0024] Fig. 5 illustrates a schematic block diagram illustrating an embodiment of a precoding unit 54a employing a general precoding scheme as represented the above equations (1), (2) and (3). The precoding unit 54a comprises a power allocation unit 61 representing the power allocation matrix P (equation (2)), a coding unit 62 representing the unitary matrix V (equation (3)) including a first coding element 63 and a second coding element 64 (phase hopping unit), and preferably a power imbalance unit 65.

[0025] The precoding applied according to DVB-NGH is defined as follows: A fixed precoding (eSM - enhanced spatial multiplexing) described by the parameters a, β and 9, and a phase hopping (PH). The PH algorithm changes the phase of the second transmit antenna from one subcarrier to the next with a periodicity of 9.

[0026] Fig. 6 illustrates a schematic block diagram illustrating an embodiment of a precoding unit 54b employing a precoding scheme as used by DVB-NGH. It comprises an eSM unit 71 including a power allocation unit 72 (which corresponds to the power allocation unit 61 and represents the power allocation matrix P), a coding unit 73 (which corresponds to the coding unit 63) and a power imbalance unit 74 (which corresponds to the power imbalance unit 65). The precoding unit 54b further comprises a phase hopping unit 75.

[0027] The fixed precoding can be presented by:

with i = 0, ..., (N_cellls/2)-l.

The power allocation unit 72 can be represented by:

The coding unit 73 can be represented by:

cosf? sinfl

si e -COS0.

The power imbalance unit 74 can be represented by.

r o 4ϊ ⁰=β

The phase hopping can be represented by:

x₂ ^' _M (Tx 2) = x_2M (Tx 2) * e^r^ or

[0028] The parameters as used in DVB-NGH are summarized in Table 1 for different QAM constellations on the two spatial streams, β describes a deliberate power imbalance between the two transmission antennas (the reason is compatibility between MIMO and SISO). The default value is β = 0.5, i.e. equal power on the two transmission antennas.

Table 1

[0029] The parameters of eSM unit 71 and the phase hopping unit 75 can be related to the general MIMO theory (as explained above with reference to Fig. 5) as follows: a describes the power allocation between the two spatial streams, i.e. the matrix P. <? of eSM and the phase hopping angle correspond to ψ and φ, respectively. If the antenna power imbalance β is neglected, the DVB-NGH parameters and the general precoding are related to the parameters of (2) and (3) as follows: power allocation: H is the same; unitary precoding: ψ = <p_Pi1— π ψ = d.

[0030] The precoding might be illustrated in the precoding domain, where the two angles ψ and φ span a 2D area. Fig. 7 shows the eSM+PH parameters, i.e. 9 hopping angles hl- h9, in this angle domain, ψ is fixed, while φ ,hops' from subcarrier to subcarrier.

[0031] One idea of the present disclosure is a more general precoding hopping (also called angle hopping herein). For improved performance, not only the angle is variabel and hops from subcarrier to subcarrier but also the angle ψ. The optimum precoding hopping set is adopted and optimzed to the statistics of the considered channel. The optimization has been done, according to an embodiment, with the help of defined and representative channel models from DVB-NGH. In other embodiments the optimization is done with more channel models such as the MGM (Modified Guildford Model) channel model of the DVB MIMO study mission or expected additional channel models of the ATSC3.0 standardization group.

[0032] The precoding hopping changes the precoding matrix from carrier to carrier, i.e. from subcarrier to subcarrier in a multi-carrier system and from symbol to symbol in a single-carrier system. The precoding hopping is preferably repeated periodically. An embodiment for the proposed precoding will be explained in the following.

[0033] Let ip( .) and (ί) (i = 0, ... , N— 1) be the angles of the set of N precoding matrices V(i). The full precoding matrix is derived from the angles according to equation (3). The precoding of the iith subcarrier is given by (periodic repetition of the precoding across the subcarriers/frequency):

V(n ) = VfmodOi V)), n = 0., ... , K - 1 (5)

where K is the number of subcarriers and mod() is the modulo operator.

[0034] Fig. 8 shows an example of the proposed hopping angles j 1 -j 8 in the precoding domain for a set of eight precoding matrices, compared to the known hopping hangles hl-h9.

[0035] In the optimization process of the hopping parameters it turned out that a symmetry constraint can be applied on the set of precoding matrices. Fig. 9 shows an example of a set of four precoding matrices where the circles kl , k2 represent the first two precoding angles and the circles k3, k4 show the third and fourth precoding angles. The second half of entries can be derived from the first half via the following symmetry rule:

• ψ mirrored at π/4 = -—

• ψ mirrored at 0: <p_m—— ψ

Using this symmetry constraint, the second half of the set of precoding angles is given as (based on ψ(,ί ) and φ(ί) for i = 0, ... . ^ - 1):

for i = - N - l.

[0036] The total transmit power is distributed to the MEMO streams by the power allocation (PA). The power allocation is defined by the PA coefficients coefficients ct^ (m = Ι, ,., , Μ where M is the nu streams. The total power is constraint to 1 :

For two MIMO streams, the power allocation matrix is then given by equation (2). For two MIMO streams, a stream imbalance between the first and second stream can be defined as:

R =— = - z 1 -

[0037] A simplified layout of a transmitting apparatus 100 according to the present disclosure is depicted in Fig. 10. According to said embodiment the transmitting apparatus 100 comprises an encoder 1 10 configured to encode input data into cell words, a modulator 120 configured to modulate said cell words into constellation values of a constellation, a MIMO precoder 130 configured to precode said constellation values to obtain two MIMO encoded and two transmission antennas 140, 141 configured to transmit said MEMO encoded signal streams. The encoder 110 and the modulator 120 may be implemented by a BICM modulator 42 as e.g. shown in Figs. 3 and 4, and the M O precoder 130 generally has the same layout as a MMO precoder 54a or 54b as shown in Figs. 5 and 6. [0038] In an embodiment the MMO precoder 130 is configured such that constellation values, in particular pairs of constellation values, to be transmitted on the same carrier by different transmission antennas are multiplied by a precoding matrix V of the form

cos-ψ skap or of an equivalent form, e.g. as indicated above in equations (3) and (4). For precoding subsequent pairs of constellation values to be transmitted on the same carrier (i.e. sub-carrier in a multi-carrier broadcast system, e.g. using OFDM, or the single carrier in a single-carrier broadcast system) by different transmission antennas different precoding matrices (i.e. having different precoding angles) are applied, wherein subsequently applied precoding matrices are formed by use of different first precoding angles Φ and/or second precoding angles ψ and wherein at least one applied precoding matrix distinguishes from all other applied precoding matrices by having a different first precoding angle Φ and a different second precoding angle ψ. In other words, at a time two constellation values (one from each MEMO encoded data stream), which are to be transmitted on the same carrier, but by different transmission antennas, form a pair of constellation values, which are precoded by one MIMO precoding matrix. The next pair of constellation values to be transmitted on the next carrier is then precoded by the next MIMO precoding matrix. If e.g. four different MIMO precoding matrices are provided every fourth pair of constellation values is then precoded by use of the same MIMO precoding matrix.

[0039] Thus, as explained above with reference to Figs. 8 and 9, the second precoding angle ψ is not fix, but is variable like the first precoding angle Φ. Thus, in the most general case, for at least one precoding matrix the second precoding angle ψ deviates from the value that is provided for all other precoding matrices. In more realistic cases that second precoding angle ψ will be varied from precoding matrix to precoding matrix, just like the first precoding angle Φ and as exemplarily shown in Fig. 8.

[0040] In the following Table 2 exemplary optimized precoding parameters (angles ψ and Φ) are given for unitary precoding hopping for different kinds of modulation, said table including a set of four precoding matrices. In said table N bpcu describes the number of bits per MIMO subcarrier. For instance, for 16-QAM modulation on the first stream (i.e. 4 bits) and QPSK modulation on the second stream (i.e. 2 bits), in total 6 bits are transmitted. Further, it holds in the subsequent tables that Φ = π and Φ = -π are actually the same due to the 2π periodicity of Φ.

Table 2

[0041] In the following Tables 3.1 and 3.2 exemplary optimized precoding parameters (angles ψ and Φ) are given for unitary precoding hopping for different kinds of modulation, said tables including a set of two precoding matrices. Unitary precoding V

N_bpcu modulation Index i

0 1

— TC

16-QAM 3^π

6

QPSK 1 π , , 1

--ψ(0) =-π -φ(0) = π

2 θ

0 1

—π

16-QAM

8

16-QAM 1 π . , 1

-φ(0) = π

0 1

—π

64-QAM Ι^π

10

16-QAM 1 τΐ , . 1

--ψ(Ο) = -π -φ(0) = π

2 Ο

0 1

—π

64-QAM 3^π

12

64-QAM 1 π . . 1

-φ(0) = π

0 1

—π

256-QAM

14

64-QAM 1 ττ .. , 1

--φ(θ) = -π -φ(β) = π 2 ο

Table 3.1

Unitary precoding V

N_bpcu modulation Index ΐ

0 1

π

16-QAM

6

QPSK 1 π . . 3

-φ(0) = -π

0 1

π

16-QAM

8

16-QAM 1 π . . 3

— - ψ Co; =— π -φ(0) = -π 0 1

π

64-QAM

10

16-QAM 1 π .. , 3

--ψ(.ο)=-_π -φ(0) = -π

0 1

π

64-QAM

12

64-QAM 1 π , . 3

--ψ(0)=-π -0(0) = -π

0 1

π

256-QAM

14

64-QAM 1 π 3

- (0) = -π

Table 3.2

[0042] In the following Table 4 the, in a preferred embodiment, additionally performed power allocation is indicated, which is preferably applied in combination with the unitary precoding using precoding matrices as given above in Table 2 or 3.

Table 4

[0043] In another embodiment the M O precoder 130 is configured such that the constellation values are xed precoding matrix V of the form

or of an equivalent form, wherein the first precoding angle Φ is in the range -π < Φ < π and the second precoding angle Ψ is in the range 0 < ψ < π/2. Thus, the precoding is simplified compared to the previously explained preconding since a constant and fixed precoding is preferably applied for all subcarriers according to this embodiment.

In the following Tables 5 and 6 exemplary optimized precoding parameters (angles ψ and Φ) are given for unitary precoding and optionally used power allocation for different kinds of modula- tion, said tables including a single precoding matrix per N_bpcu.

Table 5

Table 6 [0044] Preferably, in this embodiment the MIMO precoder is configured to apply a precoding matrix V using a value for the second precoding angle ψ which is different from 0°, 15°, 22°, 25°, arctan((V2 + 4)/ (Λ/2 + 2)). Also in this embodiment both angles ψ and φ are jointly optimized and not only the angle φ as in DVB-NGH. Table 5 includes values for the most common channel conditions, while Table 6 is optimized for special channel conditions, where is unequal to π/4.

[0045] Multiple tables may be defined (optimized for different channel conditions), where the broadcaster may chose depending on the expected channel conditions and channel statistics.

[0046] Fig. 11 shows a flow chart of a transmitting method 200 according to the present disclosure. The method generally comprises the steps of encoding (S10) input data into cell words, modulating (S20) said cell words into constellation values of a constellation, precoding (S30) said constellation values to obtain two MIMO encoded signal streams, and transmitting (S40) said MEVIO encoded signal streams.

[0047] In one embodiment, in the step S30 of precoding constellation values to be transmitted er by different transmission antennas are multiplied by a precoding matrix V of the form

or of an equivalent form, wherein for precoding subsequent pairs of constellation values different precoding matrices are applied, wherein subsequently applied precoding matrices are formed by use of different first precoding angles Φ and/or second precoding angles ψ and wherein at least one applied precoding matrix distinguishes from all other applied precoding matrices by having a different first precoding angle Φ and a different second precoding angle ψ.

[0048] In another embodiment in the step S30 of precoding constellation values to obtain two

MIMO encoded signal streams, wherein the constellation values to be transmitted on the same carrier by different transmission antennas are multiplied by a fixed precoding matrix V of the form

Γ cQs-ψ sirap or of an equivalent form, wherein the first precoding angle Φ is in the range -π < Φ < π

and the second precoding angle Ψ is in the range 0 < ψ < π/2.

[0049] Fig. 12 shows a diagram illustrating the performance of various embodiments of the present disclosure versus known systems. In particular, the mutual information over SNR is shown for conventional systems according to DVB-NGH (curve a) and according to spatial multiplexing without precoding (curve b) and for proposed systems without symmetry (curves c to g) and with symmetry (curves h to 1) for different numbers of precoding matrices. As shown, a system using two precoding matrices without symmetry (curve c) provides the best result and approx. 0.3dB gain compared to the conventional system according to DVB-NGH (curve a).

[0050] Thus, in summary, a general precoding where the precoding is divided into a unitary precoding and a power allocation, where the unitary precoding is described by two angles for 2x2 MIMO and where the unitary precoding generally hops from subcarrier to subcarrier (for a multi-carrier broadcast system) or from symbol to symbol (in a single-carrier broadcast system). The precoding hopping matrices are preferably taken from a given set and are repeated periodically. Preferably, the set of precoding matrices deploys a symmetry property. In another embodiment the unitary precoding is fix for all subcarriers for a given set of QAM constellations per ΜΓΜΟ stream. The power allocation is preferably fixed for a given set of QAM constellations per ΜΓΜΟ stream. The disclosed apparatus and method improves the MIMO precoding for broadcast applications and therefore improves the overal system performance (higher throughput, lower SNR requirements).

[0051] The foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. As will be understood by those skilled in the art, the present disclosure may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present disclosure is intended to be illustrative, but not limiting of the scope of the disclosure, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, defines, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.

[0052] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0053] In so far as embodiments of the disclosure have been described as being implemented, at least in part, by software-controlled data processing apparatus, it will be appreciated that a non- transitory machine-readable medium carrying such software, such as an optical disk, a magnetic disk, semiconductor memory or the like, is also considered to represent an embodiment of the present disclosure. Further, such a software may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0054] The elements of the disclosed devices, apparatus and systems may be implemented by corresponding hardware and/or software elements, for instance appropriated circuits. A circuit is a structural assemblage of electronic components including conventional circuit elements, integrated circuits including application specific integrated circuits, standard integrated circuits, application specific standard products, and field programmable gate arrays. Further a circuit includes central processing units, graphics processing units, and microprocessors which are programmed or configured according to software code. A circuit does not include pure software, although a circuit includes the above-described hardware executing software.

[0055] It follows a list of further embodiments of the disclosed subject matter:

1. A transmitting apparatus for a broadcast system, said transmitting apparatus comprising:

an encoder (110) configured to encode input data into cell words,

a modulator (120) configured to modulate said cell words into constellation values of a constellation,

a MEVIO precoder (130) configured to precode said constellation values to obtain two ΜΓΜΟ encoded signal streams, wherein constellation values to be transmitted on the same carrier by different transmission antennas are multiplied by a precoding matrix V of the form

two transmission antennas (140, 141) configured to transmit said MIMO encoded signal streams.

2. The transmitting apparatus according to any preceding embodiment,

wherein the MIMO precoder (130) is configured to precode said constellation values by applying precoding matrices for precoding subsequent pairs of constellation values formed by use of different first precoding angles Φ and different second precoding angles ψ.

3. The transmitting apparatus according to any preceding embodiment,

wherein the MIMO precoder (130) is configured to apply a number N of precoding matrices for precoding N pairs of constellation values and to periodically re-use the same N precoding matrices for precoding subsequent N pairs of constellation values, in particular an even number N, the second half of said N precoding matrices being symmetrical to the first half of said N precoding matrices.

4. The transmitting apparatus according to embodiment 3,

wherein the first precoding angle Φ(ΐ) of the second half is obtained by 0·) =— * ^■— -j^" , and

wherein the second precoding angle ψ(ί) of the second half is obtained by ψ(ύ = 7 - ^ - 7),

H , Nft

for t = - 1.

5. The transmitting apparatus according to any preceding embodiment,

wherein the MEVIO precoder (130) is configured to precode said constellation values by additionally multiplying constellation values to be transmitted on the same carrier by different transmission antennas, before multiplying them by the precoding matrix V, by a power allocation matrix P of the form J* = with a being a power coefficient with 0 < a < 1.

0 I

6. The transmitting apparatus according to any preceding embodiment,

wherein the MIMO precoder (130) is configured to apply different precoding matrices depending on the encoding applied by the encoder and/or the modulation applied by the modulator.

7. The transmitting apparatus according to embodiment 3,

wherein the MEVIO precoder (130) is configured to apply precoding matrices V using values for the first precoding angle Φ and the second precoding angle ψ selected from one of the following tables according to the number N and according to the modulation applied by the modulator:

Unitary precoding

or

Unitary precoding V

N bpcu modulation Index t

0 1

— TC

16-QAM

6

QPSK 1 π , . 1

-~ψ( ) =-π -<£(θ) = π 2 ΰ

0 1

— π

16-QAM

8

16-QAM 1 π , , 1

--ψ(Ο) =-π - (0) =π

2 6

0 1

— π

64-QAM

10

16-QAM 1 . . 1

-ψ(β) = ^η

2 <3

0 1

—π

64-QAM 3^π

12

64-QAM 1 π , . 1

--Ψ(Ο) =-π - (0) = π

2 6

0 1

— π

256-QAM

14

64-QAM 1 π , , 1

--ψ(θ) =-^η - (θ) = π 2 ο or

8. The transmitting apparatus as according to embodiment 5,

wherein the MIMO precoder (130) is configured to apply power allocation matrices P using values for the power coefficient selected from the following table according to the number N of precoding matrices for precoding N pairs of constellation values and according to the modulation applied by the modulator:

64-QAM

256-QAM 0.5288

14

64-QAM

9. A transmitting apparatus for a broadcast system, said transmitting apparatus comprising:

an encoder (110) configured to encode input data into cell words,

a modulator (130) configured to modulate said cell words into constellation values of a constellation,

a MIMO precoder (130) configured to precode said constellation values to obtain two MIMO encoded signal streams, wherein the constellation values are multiplied by a fixed precoding matrix V of the form

and the second precoding angle Ψ is in the range 0 < ψ < π/2, and

10. The transmitting apparatus according to embodiment 9,

wherein the MEMO precoder (130) is configured to apply a precoding matrix V using values for the first precoding angle Φ and the second precoding angle ψ according to one of the following tables:

or Unitary precoding V

NJbpcu modulation Φ

16-QAM π

6 π

Ξ

QPSK

16-QAM π

8 κ

Ξ

16-QAM

64-QAM π

10 π

5

16-QAM

64-QAM π

12 π

S

64-QAM

256-QAM π

14 κ

Ξ

64-QAM

11. The transmitting apparatus according to embodiment 10,

wherein the MIMO precoder (130) is configured to precode said constellation values by additionally multiplying constellation values to be transmitted on the same carrier by different transmission antennas, before multiplying them by the precoding matrix V, by a power allocation matrix P of the form P = with a being a power coefficient with 0 < a < 1 , and

0 T^iz wherein the MDVIO precoder (130) is configured to apply a power allocation matrix P using values for the power coefficient selected from one of the following tables according to the number N of precoding matrices for precoding N pairs of constellation values and according to the modulation applied by the modulator:

Power Precoding matrix F

allocation P

N_bpcu modulation a. F = VP

16-QAM 0.S326 0.4007

0.6788 0.Ξ826 -0.4007.

QPSK

16-QAM 0,5211 0,4780

8 0.5431 0.S211 -0.4780

16-QAM

64-QAM 0,5279 0,4705 ^'

10 0.5573 0.Ξ279 -0.470S.

16-QAM

or

12. The transmitting apparatus according to preceding embodiment 10,

wherein the MEVIO precoder (130) is configured to apply a precoding matrix V using a value for the second precoding angle ψ which is different from 0°, 15°, 22°, 25°, arctan((J^" 2 + 4)/ (V2 + 2)).

13. A transmission method for a broadcast system, said transmission method comprising:

encoding input data into cell words,

modulating said cell words into constellation values of a constellation,

precoding said constellation values to obtain two MIMO encoded signal streams, wherein constellation values to be transmitted on the same carrier by different transmission antennas are multiplied by a form

transmitting said Μ ΜΟ encoded signal streams.

14. A transmission method for a broadcast system, said transmission method comprising:

encoding input data into cell words,

modulating said cell words into constellation values of a constellation,

precoding said constellation values to obtain two MIMO encoded signal streams, wherein the constellation values to be transmitted on the same carrier by different transmission antennas are multiplied precoding matrix V of the form

and the second precoding angle Ψ is in the range 0 < ψ < π/2, and

transmitting said MIMO encoded signal streams.

15. A computer program comprising program code means for causing a computer to perform the steps of said method according to embodiment 13 or 14 when said computer program is carried out on a computer.

Claims

an encoder configured to encode input data into cell words,

a modulator configured to modulate said cell words into constellation values of a constellation, a MIMO precoder configured to precode said constellation values to obtain two MIMO encoded signal streams, wherein constellation values to be transmitted on the same carrier by different transmission antennas are multiplied by a precoding matrix V of the form

two transmission antennas configured to transmit said MIMO encoded signal streams.

2. The transmitting apparatus as claimed in claim 1 ,

wherein the MIMO precoder is configured to precode said constellation values by applying precoding matrices for precoding subsequent pairs of constellation values formed by use of different first precoding angles Φ and different second precoding angles ψ.

3. The transmitting apparatus as claimed in claim 1 ,

wherein the MIMO precoder is configured to apply a number N of precoding matrices for precoding N pairs of constellation values and to periodically re-use the same N precoding matrices for precoding subsequent N pairs of constellation values.

4. The transmitting apparatus as claimed in claim 3,

wherein the number N is an even number and wherein the second half of said N precoding matrices is symmetrical to the first half of said N precoding matrices.

5. The transmitting apparatus as claimed in claim 4,

wherein the first precoding angle Φ(ΐ) of the second halfis obtained by ψCO = -<p (i - ^~), and

wherein the second precoding angle ψ(ί) of the second half is obtained by for i = ., N - 1.

6. The transmitting apparatus as claimed in claim 1,

wherein the MIMO precoder is configured to precode said constellation values by additionally multiplying constellation values to be transmitted on the same carrier by different transmission antennas, before multiplying them by the precoding matrix V, by a power allocation matrix P of the form F with a being a power coefficient with 0 < a < 1.

0 T

7. The transmitting apparatus as claimed in claim 1,

wherein the MIMO precoder is configured to apply different precoding matrices depending on the encoding applied by the encoder and/or the modulation applied by the modulator.

8. The transmitting apparatus as claimed in claim 3,

wherein the ΜΓΜΟ precoder is configured to apply precoding matrices V using values for the first precoding angle Φ and the second precoding angle ψ selected from one of the following tables according to the number N and according to the modulation applied by the modulator:

or

0 1

-it

64-QAM 3*

12

64-QAM 1 π , . 1

--0(0) =-π -0(0) = π

Δ 0

0 1

— π

256-QAM

14

64-QAM 1 π , 1

ψ(₀) =-_π -φ(0) = π

2 ο or

Unitary precoding V

N_bpcu modulation Index i ( Φίί)

0 1

π

16-QAM

6

QPSK 1

-Ψ(0) =^π -0(0) = -π

0 1

π

16-QAM

8

16-QAM 1 π . . 3

-φ(θ") = -π 2-^{ψ (Ο) =}Ϊ0^π

0 1

π

64-QAM

10

16-QAM 1 -0(0) = -

0 1

π

64-QAM

12

64-QAM 1 π , . 3

_Ξ-ψ(ο)=-_π -0(0) = -ΤΓ

0 1

π

256-QAM

14

64-QAM 1 7Γ. , , 3

^-ψ(0) =-π -0(0) = -π

9. The transmitting apparatus as claimed in claim 6, wherein the MIMO precoder is configured to apply power allocation matrices P using values for the power coefficient selected from the following table according to the number N of precoding matrices for precoding N pairs of constellation values and according to the modulation applied by the modulator:

10. A transmitting apparatus for a broadcast system, said transmitting apparatus comprising:

an encoder configured to encode input data into cell words,

a modulator configured to modulate said cell words into constellation values of a constellation, a MIMO precoder configured to precode said constellation values to obtain two MEMO encoded signal streams, wherein the constellation values to be transmitted on the same carrier by different transmission antennas are multiplied by a fixed precoding matrix V of the form

i . or of an equivalent form, wherein the first precoding angle Φ is in the range -π < Φ < π

and the second precoding angle Ψ is in the range 0 < ψ < π/2, and

11. The transmitting apparatus as claimed in claim 10,

wherein the MIMO precoder is configured to apply a precoding matrix V using values for the first precoding angle Φ and the second precoding angle ψ according to one of the following tables:

16-QAM π

8 π

4

16-QAM

64-QAM π

10 π

4

16-QAM

64-QAM it

12 π

4

64-QAM

256-QAM π

14 κ

4

64-QAM or

12. The transmitting apparatus as claimed in claim 11 ,

wherein the ΜΓΜΟ precoder is configured to precode said constellation values by additionally multiplying constellation values to be transmitted on the same carrier by different transmission antennas, before multiplying them by the precoding matrix V, by a power allocation matrix P of the form

P = [ ff o with a being a power coefficient with 0 < a < 1, and wherein the MIMO precoder is configured to apply a power allocation matrix P using values for the power coefficient selected from one of the following tables according to the number N of precoding matrices for precoding N pairs of constellation values and according to the modulation applied by the modulator:

or

13. The transmitting apparatus as claimed in claim 11 ,

wherein the MIMO precoder is configured to apply a precoding matrix V using a value for the second precoding angle ψ which is different from 0°, 15°, 22°, 25°, arctan((J^" 2 + 4)/ (V2 + 2)).

14. A transmission method for a broadcast system, said transmission method comprising: encoding input data into cell words,

modulating said cell words into constellation values of a constellation,

precoding said constellation values to obtain two MIMO encoded signal streams, wherein constellation values to be transmitted on the same carrier by different transmission antennas are multiplied by a precoding matrix V of the form

cosi^ simp

V = or of an equivalent form, wherein for precoding subsequent pairs of constellation values different precoding matrices are applied, wherein subsequently applied precoding matrices are formed by use of different first precoding angles Φ and/or second precoding angles ψ and wherein at least one applied precoding matrix distinguishes from all other applied precoding matrices by having a different first precoding angle Φ and a different second precoding angle ψ, and

transmitting said MIMO encoded signal streams.

15. A transmission method for a broadcast system, said transmission method comprising:

encoding input data into cell words,

modulating said cell words into constellation values of a constellation,

precoding said constellation values to obtain two MIMO encoded signal streams, wherein constellation values to be transmitted on the same carrier by different transmission antennas are multiplied by a fixed precoding matrix V of the form

cos¾l> sira/>

V = or of an equivalent form, wherein the first precoding angle Φ is in the range -π < Φ < π

and the second precoding angle Ψ is in the range 0 < ψ < π/2, and

transmitting said MEVIO encoded signal streams.

16. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to claim 14 or 15 to be performed.