WO2012115453A2

WO2012115453A2 - Additional signalling for digital video broadcasting

Info

Publication number: WO2012115453A2
Application number: PCT/KR2012/001366
Authority: WO
Inventors: Ismael Gutierrez; Alain Mourad
Original assignee: Samsung Electronics Co., Ltd.
Priority date: 2011-02-18
Filing date: 2012-02-22
Publication date: 2012-08-30
Also published as: WO2012115453A3; GB201102885D0; KR20120096441A; GB2488168A

Abstract

A method of transmitting data including one or more frames, including a preamble section and a data section is provided. The method includes modulating a signal with a first data sequence of the preamble section to generate a first modulated sequence using a first non-coherent modulation scheme; modulating a second data sequence of the preamble section to generate a second modulated sequence using a second modulation scheme capable of non-coherent detection that provides continuous variation of the second modulated sequence across a length of the first modulated sequence; superimposing the second modulated sequence upon the first modulated sequence to produce a superimposed sequence; and transmitting the superimposed sequence.

Description

ADDITIONAL SIGNALLING FOR DIGITAL VIDEO BROADCASTING

The present invention relates generally to the transmission and reception of synchronization and signalling data, and more particularly, to transmission and reception of synchronization and signalling information in digital video broadcast systems.

A wireless broadcast system, such as a Digital Video Broadcasting (DVB) system, may transmit data in the form of a sequence of frames, wherein each frame includes a preamble section and a data section. A digital video broadcasting system may, for example, operate according to a Terrestrial 2^nd Generation DVB-T2 standard, or, for example, to the following families of standards: Advanced Televisions Systems Committee (ATSC), Integrated Services Digital Broadcasting (ISDB), or Digital multimedia Broadcasting (DMB). The preamble section typically includes control data and the data section typically includes content data. Further information concerning the DVB-T2 standard may be found in the published European Telecommunications Standards Institute (ETSI) standard EN 302 755.

Wireless broadcast systems, and in particular, digital video broadcast systems, are evolving. This has to be balanced with the aim of maximizing compatibility between current and new systems at the levels of services, network infrastructures, and hardware platforms. New developments in signalling technology and hardware mean that the number of signalling modes available increases over time. For example, future standards may be introduced that require additional data to be carried by the preamble section. It would be helpful if new systems co-exist with, and be integrated into, existing systems in the same spectrum. It would also be helpful maximise reuse of available infrastructures and platforms.

However, a preamble of a transmitted signal may need to have a fixed format to enable a synchronization function, rapid initial detection, and the production of standard transmission and reception equipment. There is a need in the art to accommodate future changes in signalling technology, while maintaining backward compatibility with existing hardware.

Therefore, it is an object of the invention to mitigate these problems with the prior art systems.

In accordance with an embodiment of the present invention, a method of transmitting data including one or more frames, including a preamble section and a data section is provided. The method includes modulating a signal with a first data sequence of the preamble section to generate a first modulated sequence using a first non-coherent modulation scheme; modulating a second data sequence of the preamble section to generate a second modulated sequence using a second modulation scheme capable of non-coherent detection that provides continuous variation of the second modulated sequence across a length of the first modulated sequence; superimposing the second modulated sequence upon the first modulated sequence to produce a superimposed sequence; and transmitting the superimposed sequence.

In accordance with another embodiment of the present invention, a method of receiving data comprising one or more frames, including a preamble section and a data section is provided. The method includes receiving a signal comprising a second modulated sequence superimposed on a first modulated sequence; demodulating the signal to extract a first data sequence of the preamble section from the first modulated sequence using a first non-coherent demodulation scheme; removing the superimposition to provide the second modulated sequence; and demodulating the second modulated sequence using a second demodulation scheme to extract a second data sequence of the preamble section, wherein the second demodulation scheme provides non-coherent detection of the second data sequence.

In accordance with another embodiment of the present invention, a transmitter for transmitting data including one or more frames, including a preamble section and a data section is provided. The transmitter includes a modulating unit for modulating a signal with a first data sequence of the preamble section to generate a first modulated sequence using a first non-coherent modulation scheme, and modulating a second data sequence of the preamble section to generate a second modulated sequence using a second modulation scheme capable of non-coherent detection that provides continuous variation of the second modulated sequence across the length of the first modulated sequence; a superimposing unit for superimposing the second modulated sequence upon the first modulated sequence to produce a superimposed sequence; and a transmitting unit for transmitting the superimposed sequence.

In accordance with another embodiment of the present invention, a receiver for receiving data including one or more frames, including a preamble section and a data section is provided. The receiver includes a receiving unit for receiving a signal comprising a second modulated sequence superimposed on a first modulated sequence; a demodulating unit for demodulating the signal to extract a first data sequence of the preamble section from the first modulated sequence, said demodulating using a first non-coherent demodulation scheme; a superimposition removal unit for removing the superimposition to provide the second modulated sequence; and the demodulation unit for demodulating the second modulated sequence using a second demodulation scheme to extract a second data sequence of the preamble section, wherein the second demodulation scheme provides non-coherent detection of the second data sequence.

The above and other aspects, features and advantages of the present invention will be more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a schematic diagram illustrating a frame in an digital video broadcast system;

Figs. 2a to 2d illustrate four tables showing the possible contents of two data fields from an first preamble signalling section of the frame of Fig. 1;

Fig. 3 is a schematic diagram illustrating a receiver system for receiving a first preamble signalling section;

Fig. 4 is a schematic diagram illustrating a receiver system according to an aspect of the invention;

Fig. 5 is a schematic diagram illustrating first and second modulation schemes according to a first embodiment of the invention;

Fig. 6 is a schematic diagram illustrating a receiver system according to a first embodiment of the invention;

Fig. 7 is a schematic diagram illustrating a method of transmitting a signal according to a first embodiment of the invention;

Fig. 8 is a schematic diagram illustrating a receiver system according to a second embodiment of the invention;

Fig. 9 is a schematic diagram illustrating a method of transmitting a signal according to a second embodiment of the invention;

Fig. 10 is a schematic diagram illustrating a method of receiving a signal according to an aspect of the invention;

Fig. 11 illustrates the results of two simulations of a modulation scheme according to a first embodiment of the invention;

Fig. 12 illustrates the results of two simulations of an alternate modulation scheme according to a variation of the first embodiment of the invention;

Fig. 13 illustrates the properties of a symbol transmitted according to the second embodiment of the present invention;

Fig. 14 illustrates the results of two simulations of a modulation scheme according to the second embodiment of the invention;

Fig. 15 illustrates a number of possible modulation patterns; and

Figs. 16a to 16c illustrate example use cases of data fields generated according to the present invention.

By way of example, embodiments of the invention will now be described in the context of a Digital Video Broadcasting Next Generation Handheld (DVB-NGH) standard, which is based on the 2^nd generation terrestrial DVB-T2 system. However, it will be understood that this is by way of example only and that other embodiments may involve other communication systems in which control data is transmitted and received; embodiments are not limited to the transmission of wireless broadcast signals such as digital video signals. The invention will be described in relation to transmission and reception of a signal; it will be understood that these two operations are complementary and relate to a common inventive concept.

A frame is illustrated in Fig. 1. Each frame 100 typically includes a preamble section 110 and a data section 120, the preamble section and the data section being time-multiplexed. The data section 120 carries data that is arranged in the form of a number of data streams that may be referred to as Physical Layer Pipes (PLP). A physical layer pipe carries, for example, a service such as a video channel provided to a user. Reception of data from the frames, and reception of the data streams, is assisted by signalling, which is typically carried in the preamble of the frame. The signalling may be referred to as physical layer signalling, or Layer 1 (L1) signalling. The signalling may indicate a modulation or coding scheme to be used for decoding data, and it may indicate sections of a data field to be decoded, or the location of a data stream within the data section 120. Although reference to frames is made in the present description, the present invention may also apply to alternate signal structures wherein control data is transmitted and/or received.

The preamble section 110 may include multiple signalling sections. A first preamble signalling section 130, referred to as Preamble 1 (P1) in the DVB-T2 standard, may be used to synchronize the reception of a transmitting data stream, identify the preamble section 110 itself and provide information for initial fast recognition of a broadcast signal. Information 150 regarding transmission and reception parameters may also be provided. A second preamble section 140, referred to as Preamble 2 (P2) in the DVB-T2 standard, provides more detailed pre-signalling 160 and post-signalling 170 parameters for the physical layer.

The first preamble signalling section 130 has four main functions. First, it is used during an initial signal scan for the fast recognition of a broadcast signal, for which just the detection of the first preamble signalling section 130 is enough. The first preamble signalling section 130 has a particular time domain structure that enables synchronization following detection. This means that the first preamble signalling section 130 is necessarily limited in length and complexity. The second purpose of the first preamble signalling section 130 is to identify the preamble itself as a preamble relating to a particular format or standard. The third task is to signal basic transmission parameters that are needed to decode the rest of the preamble, which can help during the initialization process. The fourth purpose of the first preamble signalling section 130 is to enable a receiver to detect and correct frequency and timing synchronization.

The integration of the DVB - Next Generation Handheld (NGH) standard that is designed to deliver mobile TeleVision (TV) services with the DVB-Second Generation Terrestrial (T2) standard that is designed to deliver Standard Definition (SD) and High Definition (HD) fixed TV services, imposes constraints on the signalling structure of a wireless broadcast signal. For example, it may require the use of the same preamble symbol from DVB-T2. This means that the signalling capacity of the preamble symbol (equal to 128 modes) will have to be distributed among both DVB-T2 and integrated DVB-NGH systems. After discounting capacity that cannot be used for technical reasons or that is reserved for future use, there is limited signalling capacity left for the DVB-NGH system; typically this limited capacity is not sufficient to signal all the modes required by DVB-NGH. This raises the problem of signalling capacity shortage, and stresses the need to find an effective way to add extra signalling capacity to accommodate and integrate future extensions and developments.

Embodiments of the present invention are directed towards a modified preamble for a communications signal. The term preamble is used to describe a portion of the signal that has a control function, for example, that allows signal synchronization and/or that carries signalling information. A preamble is typically distinguished from a portion of the signal that carries content data, for example a data section comprising broadcast video data.

In an implementation, the preamble includes a fixed-length pilot symbol located in the beginning of a frame of a signal within each radio-frequency channel. A fixed-length enables the preamble to be used to synchronize reception of the signal. The performance of the preamble is independent of any data carried by the signal. To provide robust detection of the pilot symbol a minimum Signal-to-Noise-Ratio (SNR) of -3dB is required and the Frame Error Rate (FER) is 0.01 for an SNR greater than -4dB. The preamble may further provide protection against interference, such as Inter-Symbol-Interference (ISI) and echoes, tolerate large frequency shifts of up to +/- 500 kHz, provide coarse time and/or frequency synchronization, and have a low Peak-to-Average Power Ratio (PAPR). Any modification of the preamble should, as much as possible, maintain at least one of these properties; i.e., should maintain the synchronization function of the preamble and minimize any degradation in preamble detection. For example, the degradation introduced by any modification may need to be less than a certain tolerable threshold. In the DVB-T2 standard a P1 pilot symbol may comprise a 1K Orthogonal Frequency-Division Multiplexing (OFDM) symbol with two modified guard intervals that have a length of half the primary symbol. The two modified guard intervals include frequency-shifted versions of the main symbol that are correlated in parallel during the detection of the preamble. This produces a particular time domain format that enables the preamble to provide a synchronization function. The frequency power distribution of the main symbol must follow a specific profile to enable detection, i.e., the number of active subcarriers is fixed. This enables the correction of the integer number of frequency offsets to provide coarse frequency synchronization. As well as a synchronization function the pilot symbol of the preamble may carry signalling data. The content of this signalling data is discussed below.

Figs. 2a to 2d illustrate the contents of two data fields that may be carried within a first preamble signalling section 130, as for example illustrated in Fig. 1. A first data field S1 is shown in Fig. 2a. In the DVB-T2 standard, the first data field S1 comprises a 3-bit data sequence that identifies whether the preamble section 110 conforms to the T2 standard. The first data field S1 also identifies whether a second preamble signalling section 140 is transmitted in Single Input Single Output (SISO) format or Multiple Input Single Output (MISO) format. Out of the eight possible bit sequences, only three are used, the rest are reserved for future use. Thus, the first data field S1 can represent one of three different signalling modes in the T2 standard.

Figs. 2b to 2d show the possible contents of a second data field S2 according to the DVB-T2 standard. In this example, the second data field S2 is 4 bits long. Figs. 2c and 2d show the possible contents of these bits when the preamble conforms to the T2 standard: the first three bits signalling a Fast Fourier Transform (FFT) size and a Guard Interval (GI) for the broadcast signal following the preamble section as shown in Fig. 2c, and the last bit indicates whether the preamble sections of a current transmission are of the same type as the current preamble, i.e., not mixed, or are of different types, i.e. mixed, as shown in Fig. 2d. Fig. 2b shows how particular non-T2 bit patterns for the second data field S2 are reserved for Future Extension Frames (FEF) or other future use. Hence, if the signal conforms to the T2-standard, the first data field S2 can represent one of eight different signalling modes. As the mixed bit cannot be freely used, the total number of modes that can be signalled is 64, of which 24 (3 * 8) are defined by the T2 standard.

Although embodiments of the invention will be described below with relation to two data fields that are carried within a first preamble signalling section, it will be understood that a single data field, or three or more data fields, of any desired length can also be used. These data fields would need to be of a size that could be accommodated by the fixed-length of the preamble. Additionally, it will be understood that the first preamble section could carry a data sequence of a length other than 7 bits depending on the transmission standard that is used, for example standards other than DVB-T2 may use a symbol for synchronization of a different size, which may be followed by further preamble signalling sections. Furthermore, the preamble section need not include multiple signalling sections; the invention can apply to a preamble section with one or multiple signalling sections.

A receiver system for receiving a first preamble signalling section 130 is illustrated in Fig. 3. This receiver system is adapted to provide a discrete signal that is modelled in Equation (1) as:

[Equation (1)]

wherein y is a received broadcast signal, h is a sub-carrier function modelling the channel effects, d ₁₂ is a data sequence generated from data fields S1 and S2, n is a modelled noise term, and i = 1 to N, N beingthe length of the signal. The DVB-NGH/T2 standards use OFDM, or OFDM-based variations, and as such the length of the signal is equal to the number of subcarriers used to transmit the signal. When a 1K FFT size is used with 384 active subcarriers, N = 384. Sub-carriers are then further modulated using the data sequence d ₁₂. Even though OFDM-based systems are preferred, the invention as described below may be used with non-OFDM-based systems.

The receiver system comprises a Fast Fourier Transform (FFT) component 310, a Carrier Distribution Sequence (CDS) Component 320, a Descrambler 330, a Differential-Binary Phase Shift Keying (D-BPSK) Demodulator 340 and a Correlator 350. A wireless broadcast signal P1_A(1…1024) spread across 1024 sub-carriers comprising the first preamble signalling section 130 is received and input into FFT component 310, which is arranged to apply an FFT algorithm to the received signal. In the example, an FFT size of 1K (1024) is used; however, other FFT sizes may alternatively be used depending on the implementation. Following the application of the FFT a frequency-domain signal is input into CDS Component 320. CDS Component 320 uses a carrier distribution table to identify active sub-carriers that carry the first preamble signalling section 130, i.e., it uses a Carrier Distribution Sequence that specifies which subcarriers are used to carry data in order to isolate those subcarriers. In certain embodiments all sub-carriers may be active sub-carriers and so the CDS Component 320 may be omitted. In an example that uses a 1K FFT size, there may be 853 useable sub-carriers of which 384 are used in the DVB-T2 standard, with the remaining sub-carriers being set to zero. The FFT size and any Guard Interval (GI) that is used are signalled in the second data field (S2). Typically, the used carriers occupy a subset of available signal bandwidth. The output of CDS Component 320 comprises a modulated data sequence, in this case of length 384: i.e. y (1…384). In certain embodiments the wireless broadcast signal may be optionally scrambled, in which case the output of CDS Component 320 is passed to Descrambler 330. Descrambler 330 applies a descrambling function to provide an unscrambled modulated data sequence. In one embodiment, scrambling may be applied by bit-by-bit multiplying by a 384-bit scrambling sequence and descrambling applied by an appropriate multiplicative descrambler. As well as the descrambler, additional decryption components may also be optionally provided at this stage. Following descrambling the modulated data sequence is passed to D-BPSK Demodulator 340 which demodulates the modulated data sequence to provide a demodulated data sequence s’, in this example of length 384.

The modulated data sequence is demodulated according to Equation (2):

[Equation (2)]

I.e. a 0 is detected if the magnitude of the change in phase between successive symbols is less than

radians, wherein s₁₂(i) the i-th detected symbol. In other embodiments, alternative demodulators and demodulation schemes may be used; however, it is important that such demodulators and demodulation schemes are capable of non-coherent demodulation; the existing synchronization function of the preamble would not operate successfully if a coherent (de)modulation scheme was used as a synchronized receiver clock would be required. The demodulated data sequence is then input into Correlator 350 wherein the bit values of the two data fields, S1 and S2 are extracted.

An embodiment of the present invention utilizes a superimposed data sequence to increase the capacity of a preamble of a transmitted signal, in this case the first preamble signalling section 130. A third data field S3 of bit length n ₃is used to produce a further modulated data sequence that is superimposed on a modulated data sequence that carries data fields S1 and S2.

According to an embodiment of the present invention, a second modulated data sequence d ₃ is superimposed on a first modulated data sequence d ₁₂according to Equation (3):

[Equation (3)]

The first modulated sequence d₁₂(i) may be produced from a first data sequence by a first modulation scheme; for example, the modulation scheme used to modulate the data sequence that is extracted by the receiver of Fig. 3. In a similar manner, the

second modulated d₃(i) produced from a second data sequence by a second modulation scheme. The term modulation is used to refer to a process by which a first sequence, waveform or signal is transformed into a second sequence, waveform or signal by modification of one or more parameters in accordance with a set rule or function. The first and second data sequences, respectively, carry the two data fields S1 and S2, and the third data field S3. They may include the bit sequences of the fields themselves or suitably prepared bit patterns produced from the bit sequences, as is described in more detail below. Following modulation, superimposition and transmission, a first data sequence may be extracted from a received signal using a first demodulation scheme, for example using a D-BPSK scheme as described with respect to Fig. 3. This may be achieved without altering legacy receiver systems. The second modulated sequence may then also be extracted from the received signal using a second demodulation scheme after the superimposition has been removed.

The properties of the second modulation scheme and the data sequence d₃(i) are chosen such that data fields S1 and S2 can be accurately extracted by the receiver system of Fig. 3 using the first (de)modulation scheme. To fulfill a synchronization function, the first (de)modulation scheme should be non-coherent; i.e. needs to be able to demodulate the first modulated signal without a reference clock signal that is phase synchronized with a carrier waveform. To enable legacy detection of the first and second data fields, the second modulation scheme is selected so as to maintain non-coherent detection of the first modulated sequence. This in turn requires that the second modulation scheme be such to enable demodulation of the second modulated sequence without a synchronized reference clock signal. Successful legacy extraction of data fields S1 and S2 may be achieved by minimizing the changes between adjacent symbols in the data sequence d₁₂(i) produced by the superimposition of data sequence d₃(i). Data sequences with constant amplitude, continuous variation and/or slow variation of phase when compared to data sequence d₁₂(i), for example complex exponential functions, chirp sequences, and Zadoff-Chu functions, may all produce data sequences for d₃(i) that result

in minimum degradation to the first modulated sequence such that S1 and S2 may be successfully detected. The term continuous variation is used to describe the manner in which the second modulated sequence varies across the length of the first modulated sequence; i.e., the second modulated sequence must continue to vary across the length of the first modulated sequence without abrupt changes or discontinuities to avoid degradation.

Fig. 10 shows a method 1000 of receiving a transmitted signal according to an aspect of the present invention. In step 1010 the detection of a P1 symbol that comprises the first preamble signalling section 130 is attempted. If the detection is unsuccessful, i.e., the P1 symbol is not found, then at step 1020 the detection at step 1010 is repeated. The detection may be repeated a set number of times or for a set time period until a time-out event occurs. If detection is successful, then the method proceeds from step 1020 to step 1030, wherein coarse time and frequency synchronization is performed. This synchronization is deemed to be coarse as further refinement of timing and frequency parameters is performed following detection of data fields S1 and S2 and other possible preamble signalling sections. The coarse time and frequency synchronization then allows the decoding of data fields S1 and S2 at step 1040, as for example described with relation to Fig. 3. At step 1050 an optional check is made as to whether the legacy standards are being used or whether an additional data field S3 is being transmitted. This may be determined by the receiving equipment, i.e., particular equipment is set up to always extract a third data field where present, and/or is set in the bit patterns of S1 reserved for future use. If, for example, legacy equipment is being used, data field S3 is not present and/or the decoding of the third data field S3 is not required then the first and second data fields S1 and S2 are extracted. They may be used to set signalling parameters to allow reception and decoding of a digital video broadcast carried in a data section that follows the preamble section.

If the third data field S3 is being transmitted as well as data fields S1 and S2, then a number of detection steps 1060 are performed. At step 1070 the extracted data fields S1 and S2 are re-encoded to reconstruct the first modulated sequence. In step 1080, an equalisation of the received signal is performed. This may include the removal of the reconstructed first modulated sequence from a superimposed sequence comprising the first and second modulated sequences. At step 1090 the detection of the third data field S3 is performed, which includes the demodulation of the second modulated sequence that results from the equalisation step 1080. Following detection of the third data field S3, all three data fields S1, S2, and S3 are output for use in setting signalling parameters to allow a data stream to be received and decoded.

To receive a signal as generated according to an aspect of the present invention a modified receiver system may be provided. Fig. 4 illustrates a suitable adaptation of the receiver system of Fig. 3. FFT component 410, CDS Component 420, Descrambler 430, Differential-Binary Phase Shift Keying (D-BPSK) Demodulator 440 and Correlator 450 are conserved from the receiver system of Fig. 3. According to an aspect of the invention an additional data field detector (an S3 detector) 460 is provided which receives an output sequence from the CDS Component 420 and the extracted data fields S1 and S2. The S3 detector 460 then extracts the third data field S3 from the CDS Component output sequence using the extracted data fields S1 and S2, for example as set out in step 1090.

The operation of the S3 detector 460 is described in more detail below in relation to two particular embodiments of the present invention.

A first embodiment of the present invention uses hierarchical D-BPSK to provide the second modulation scheme. Fig. 7 illustrates a method of transmitting a wireless broadcast signal according to the first embodiment. It will be understood that following a description of the transmission method, a suitable transmitter including means to perform the processing of steps 710 to 770 may be provided.

Steps

710, 720 and 730 represent a method of producing a first modulated sequence that is compatible with the receiver system of Fig. 3. At step 710 the first and second data fields S1 and S2 are encoded to produce a first and second modulation pattern. These modulation patterns may be required to provide OFDM-based transmission. In the present example, patterns to encode the first data field S1 are based on 8 orthogonal sets of 8 complementary sequences of length 8 (total length of each S1 pattern is 64), while patterns to encode the second data field S2 are based of 16 orthogonal sets of 16 complementary sequences of length 16 (total length of each S2 pattern is 256). These patterns have two main properties. First, the sum of the auto-correlations of all the sequences of the set is equal to a Kronecker delta, multiplied by a KN factor, K being the number of the sequences of each set and N being the length of each sequence. In the case of S1 K=N=8; in the case of S2, K=N=16. Second, each set of sequences is mutually uncorrelated (also called "mates"). Typically, modulation patterns for each bit sequence of S1 and S2 are provided in a look-up table in hexadecimal format, e.g. bit sequence 110 of data field S1 maps onto modulation pattern 2E7B1D4821741247. A look-up table is shown in Fig. 15. The bit sequences CSS_S1 = (CSS_S1,0 … CSS_S1,63) and CSS_S2= (CSS_S2,0 … CSS_S2,255) for given values of S1 and S2 respectively are obtained by taking the corresponding hexadecimal sequence from left to right and from Most Significant Bit (MSB) to Least Significant Bit (LSB), i.e. CSS_S1,0 is the MSB of the first hexadecimal digit and CSS_S1,63 is the LSB of the last digit of the S1 sequence. A first data sequence 715 carrying the first and second data fields is then produced by concatenating two modulation patterns for the first data field S1 with a single modulation pattern for the second data field S2 in the form {CSS_S1, CSS_S2, CSS_S1}. In the present example, this first data sequence has a length of 384. In this regard, the first data sequence carries the first and second data fields.

In step 720 D-BPSK modulation is applied to the first data sequence to produce a first modulated sequence 725. Differential Binary Phase Shift Keying is a known modulation technique wherein the bit patterns of a data sequence are used to change the phase of a carrier waveform. Changes in the phase of the carrier waveform are then used to demodulate a received signal. Constellation diagram 510 of Fig. 5 illustrates the symbol encoding. At step 730 the first data sequence is optionally scrambled to produce a scrambled first modulated sequence 735.

Steps 740 to 760 represent a method of producing a second modulated sequence 765 according to the first embodiment. At step 740 a second data sequence 755 is produced that encodes the n ₃ bits of the third data field S3. In the present example, if n ₃= 3 bits or n ₃= 4 bits the modulation patterns for the first data field S1 (in the case of n ₃= 3) or the second data field S2 (in the case of n ₃= 4) may be re-used to produce a chip sequence of length N_chip less than the length N_fms of the first modulated sequence, i.e. a short sequence. As the length of the chip sequence is less than the length of the first modulated sequence then the chip sequence may be repeated N_rep times over the full length of the first modulated sequence. The chip sequence may also be interleaved as shown in Fig. 7 to produce the second data sequence 755. For example, Equation (4) is as follows:

[Equation (4)]

In a case where n ₃= 4, and N_chip =256, one full chip sequence and one half chip sequence may be concatenated to generate the second data sequence. The repetition and/or the interleaving of the chip sequence across the length of the first modulated sequence ensures that all sequences have maximum diversity and equally affect the detection of the first and second data fields S1 and S2. In other embodiments, sequences other than those provided by the modulation patterns of data fields S1 and S2 may be used, although it is preferred that such sequences maintain good cross-correlation properties, i.e., enable cross-correlation operations on the data. Using the modulation patterns for data fields S1 or S2 does provide an implementation advantage in that existing sequence generation and/or detection modules can be used to provide the same function for the third data field S3. This avoids the need for new hardware and further reduces cost.

In step 750 the second data sequence 755 is modulated using a hierarchical (

) D-BPSK modulation scheme. The constellation diagram 520 for a hierarchical

-D-BPSK modulation scheme is shown in Fig. 5.

Fig. 5 illustrates two constellation diagrams, namely 510 and 520, for an D-BPSK, and an hierarchical

-D-BPSK, respectively. In the diagram 510, a constellation symbol stay unchanged if the data bit S₁₂(i) has a “0” value, whereas it rotates π-radian if s₁₂(i) is equal to 1. In diagram 520 however, where

D-BPSK is used, the constellation symbol rotates

radian counterclockwise if the data bit of the super-imposed sequence S₃(i) is equal to “1”, and

/2 radian clockwise if it is equal to “0”. The second data sequence is encoded according to Equation (5):

[Equation (5)]

i.e. a rotation of

radians is provided between consecutive symbols. This produces a second modulated sequence 765. Although this example is described in relation to a modified D-BPSK system, in practice any modulation scheme that enables non-coherent detection can be used, including other PSK schemes (QPSK, 8-PSK, and the like) wherein an additional rotation of

radians from the normal symbol values is provided.

In step 770, the second modulated sequence 765 is superimposed on the first modulated sequence 735 to generate a superimposed sequence d ₁₂₃. In the present example, the first data sequence d₁₂(i) and the second data sequence d₃(i) are multiplied. This is possible since both sequences are complex signals with a magnitude of one, wherein information is carried in the phase of the signal. In other embodiments, depending on the form of the sequences, other superimposition operations could alternatively be used, such as bit-addition, AND operations and the like. In the current example, d ₁₂₃is of length 384 and may be transmitted using known transmission methods.

A receiver system according to the first embodiment of the present invention is shown in Fig. 6. Fig. 6 illustrates, in more detail, components of the S3 detector 460 utilized in the first embodiment. Features not explicitly described are assumed to be conserved from Figs. 3 and 4. In this case signal P1_A(1…1024) may include a received version of transmitted sequence d ₁₂₃.

The S3 detector 460 of Fig. 6 includes an S1, S2 Encoder 660, a hierarchical

-D-BPSK Demodulator 670, an S3 Deinterleaver 680 and an S3 Correlator 690. The S1,S2 Encoder 660 receives the extracted data fields S1 and S2 from the S1, S2 Correlator 650 and reconstructs the first modulated sequence d _12.This reconstructed sequence is then applied to superimposed sequence y(1…384) to remove the superimposition. In the present example, this is achieved by subtracting the first modulated sequence d ₁₂from the superimposed sequence y(1…384). This may be achieved by multiplying the superimposed sequence y(1…384) by a negative version of the reconstructed first modulated sequence d ₁₂.In other embodiments, alternatives to the S1,S2 Encoder 660 and subtractor may be used that remove the superimposition of the first and second modulated sequences.

Following the removal of the superposition the resultant sequence is input into the hierarchical

-D-BPSK Demodulator 670. The resultant sequence represents the second modulated sequence, plus signal noise due to transmission through a communication channel. The hierarchical

-D-BPSK Demodulator 670 demodulates the second modulated sequence assuming the symbol encoding described above with respect to Fig. 7, i.e. assuming a rotation of

radians between the symbols of 0 and 1, wherein each symbol is offset from standard BPSK symbols

/2. In one embodiment,

radians. In other embodiments, that use other modulation schemes to modulate the second data sequence, the Demodulator 670 may be altered accordingly. The result is an estimated second data sequence: s^l’(1_…380) This estimated second data sequence is input into S3 Deinterleaver 680, which removes any interleaving of the second data sequence to leave a series of repeated chip sequences:

where

. These chip sequences are correlated by S3 Correlator 690 to extract the bits of the third data field S3.

Fig. 11 shows simulation results for the reception of signal preambles constructed according to the first embodiment. The graphs show Bit Error Rate (BER) versus Signal to Noise Ratio (in decibels - dB) for data fields S1 and S2 in the existing T2 standard and an adapted NGH standard that incorporates the extra third data field S3 provided by the first embodiment, wherein

radians. References to “old” values in the graphs refer to the data fields S1 and S2 when using the T2 standard, whereas references to “new” values refer to the data fields S1 and S2 when using the embodiments of the present invention. A first graph 1110 shows an Additive Gaussian White Noise (AWGN) noise model and a second graph 1120 shows a TU6-60kmph noise model, wherein TU6 is a Typical Urban Mode 6 channel model with an assumed terminal speed of 60km/h. When n ₃= 3, the capacity of the first preamble signalling section 130 is increased by 43% (10 bits are carried as opposed to 7 bits degradation of data fields S1 and S2. This degradation is slight and enables full detection of the first and second data fields S1 and S2 with existing equipment, i.e. full backward compatibility. When n ₃= 4 the degradation increases by 0.5dB. However, this still allows successful detection of the existing data fields as well as the additional data field S3.

By optimizing the value of

in the hierarchical D-BPSK it is possible to improve performance. In a variation of the first embodiment two values of

are used: a first rotation of

radians for data sequence values relating to the first data field S1 and a second rotation of

₂ radians for

data sequence values relating to the second data field S2. Following from the value for subcarriers relating to the first data field S1 and the use of a second rotation value for subcarriers relating to the second data field S2. For example, Equation (6) is as follows:

[Equation (6)]

The values of the parameter

₁ and

₂may be tuned to align the detection performance of all three data fields. For example, Fig. 12 shows simulation results for the reception of signal preambles constructed according to the present variation, wherein n₃=4,

₁=1.5 radians and

₂=2 radians.

References to “old” values in the graphs refer to the data fields S1 and S2 when using the T2 standard, whereas references to “new” values refer to the data fields S1 and S2 when using the embodiments of the present invention. Again, a first graph 1210 shows an AWGN noise model and a second graph 1220 shows a TU6-60kmph noise model. This results in a 0.5 to 0.7 dB gain as compared to a case where only a single value of

is used. Compared to an existing preamble symbol, the modified preamble according to the present variation of the first embodiment provides an increase in capacity of 57% (11 bits as opposed to 7 bits) with a 1.5dB degradation in data fields S1 and S2. With such an example, the performance gap between all three data fields S1, S2 and S3 is less than 0.25dB.

It is also possible to modify the optimization criteria used to produce tuned values of

and/or

. For example, if one or more of the three fields required different levels of robustness, different tuned values could be accordingly calculated; e.g., a degradation in the detection of data field S2 may be more acceptable than a degradation in the detection of data field S1.

A second embodiment of the present invention will now be described. The second embodiment uses a second modulation scheme wherein a plurality of repeated sequences encodes the third data field S3. The repeated sequences will be referred to as short Continuous Phase Modulated (CPM) sequences. The term short is used to denote that these sequences have a length N_chip less than the length N_fms of the first modulated sequence; typically, N_chipis 16 or 32 whereas in a 1k FFT, DVB-T2 implementation N_fms= 384. The term Continuous Phase Modulated is used to denote a slow yet continuous variance in phase across the length of the second modulated sequence, which is equal in length to the first modulated sequence. A variance in phase is slow if, in the time domain, the time taken for a change in phase of the second modulated sequence is greater than the time taken for a change in phase of the first modulated sequence; with an optimum difference between timings being one that allows detection of data fields S1 and S2 from the first modulated sequence. A variance is continuous if changes in the phase occur without abrupt or discontinuous changes across the whole length of the second modulated sequence, such that when it is superimposed on the first modulated sequence, such changes occur smoothly and continuously across the whole length of the first modulated sequence. This results in short CPM sequences wherein the phase of each sequence varies across the length of the sequence and the difference in phase between two consecutive samples of the short CPM sequence is less than the difference in phase between two consecutive samples of the first modulated sequence. These properties of a second modulated sequence according to the second embodiment prevent degradation to the first modulated sequence such that said sequence can be accurately demodulated to provide data fields S1 and S2.

Fig. 9 illustrates a method of transmitting a wireless broadcast signal according to the second embodiment. It will be understood that following a description of the transmission method, a suitable transmitter including means to perform the processing of steps 910 to 960 may be provided. Steps 910 to 930 correspond substantially to steps 710 to 730 of Fig. 7, as such a first data sequence 915 is generated from data fields S1 and S2, modulated at step 920 using D-BPSK to generate a first modulated sequence 925, and optionally scrambled at step 930 to produce a scrambled first modulated sequence 935, which is equivalent to sequence 735.

The second embodiment differs from the first embodiment in the manner of the second modulation scheme, i.e., the manner in which the second modulated sequence is produced. In Fig. 9, k short sequences, S3_k gernerated

based on a function which provides sequences with constant amplitude, slow variation of phase and/or a smooth transition between adjacent short sequences. Preferably the function meets all three requirements. Examples of functions are tones, chirps, complex exponential functions or Zadoff-Chu functions. Tones include data sequences wherein information is carried in the phase of the sequence and chirps include data sequences wherein information is carried in the frequency of the sequence. For example, a tone sequence may be generated according to Equation (7):

[Equation (7)]

and a chirp sequence may be generated according to Equation (8) :

[Equation (8)]

wherein l denotes the l-th component of sequence S3_k

and

_kis a phase modifier for the k-th sequence. Fig. 13 illustrates the real and imaginary components of an chirp sequence. The chirp sequence is repeated three times across 100 samples and from the real and imaginary plots (1310, 1320 and 1330) it can be seen how the frequency of the chirp waveform increases towards the end of each sequence (i.e., is “swept”).

In one variation of the second embodiment a set of tones or chirps superimposed onto the part of the first modulated sequence carrying the first data field (S1) is different from a set of tones or chirps superimposed onto the part of the first modulated sequence carrying the second data field (S2). As with the use of two

of values in the variation of the first embodiment, the use of different tones or chirps for sequence portions corresponding to the different first and second data fields S1 and S2 allows optimization based on the particular characteristics of the S1 and S2 portions of the first modulated sequence. It also enables a more selective degradation of the detection of the first and second data fields, for example, degradation to the detection of the first data field S1 may be preferred over degradation to the detection of the second data field S2 (and vice versa).

A smooth transition between adjacent short sequences is achieved by appropriately tuning the sequences so that all sequences start and finish with similar phases, i.e., the phase difference between the end of a sequence and the start of an adjacent sequence is less than a predetermined threshold; the threshold being selected so that data fields S1 and S2 can still be successfully detected. As a slow modification of phase between samples is required to prevent degradation to the existing data fields, the use of sequences in which information is carried in the phase or frequency is somewhat counterintuitive. However, it has been found that such sequences can be successfully used.

Each short sequence S3_krepeated Nrep times across the length of the first modulated sequence, which in the present case corresponds to the full spectrum of active subcarriers of the preamble. This is illustrated in the second modulated sequence 955, N_rep=N_fms/(K x N_chip) and K=n₃/n₄, K=n₃/n₄n3 and n4 are two bit size parameters. The repetition has two main functions. First, it enables the noise term introduced by the communication channel to components of each sequence to be filtered, effectively reducing the noise level by a factor equal to 1+Nrep. Second, the repetition ensures that all components experience similar fading effects within the communication channel, so that no channel estimation is required and the third data field S3 can be detected non-coherently. Assuming the communication channel is reasonably flat across the subcarriers carrying the short sequence, the good cross-correlation properties of the short sequences are preserved, i.e., the ability to produce accurate cross-correlation results is maintained. The short sequences S3_k may also further be interleaved across the second modulated sequence 955.

In one variation of the second embodiment different repetition patterns may be used. For example, a standard repetition pattern may simply repeat the components of the chip sequences in order, for example: [d₀ … d_N-1] [d₀ … d_N-1] [d₀ … d_N-1] [d₀ … d_N-1]. A modified pattern may then reverse the components in alternate repetitions, for example: [d₀ … d_N-1] [d_N-1 … d₀] [d₀ … d_N-1] [d_N-1 … d₀]. The modified pattern may be used to average out any constant shift that would remain in the equivalent channel of adjacent components d_i and d_i+1.

Once a second modulated sequence 955 is generated, it is superimposed on the first modulated sequence 735 at step 960 in a similar manner to step 770 of Fig. 7 to produce a superimposed sequence d ₁₂₃,which may be transmitted using known transmission methods.

Fig. 8 illustrates a receiver system according to the second embodiment of the present invention. Regarding Fig. 6, Fig. 8 illustrates, in more detail, the components of the S3 detector 460. Features not explicitly described are assumed to be conserved from Figs. 3 and 4. In this case signal P1_A(1…1024) may include a received version of transmitted sequence d ₁₂₃, for example that produced by step 960 above.

The S3 detector 460 of Fig. 8 includes an S1, S2 Encoder 860, a Phase Detector 870, an Averaging Component 880 and an Estimator 890. The S1,S2 Encoder 860 has substantially the same function as S1,S2 Encoder 660, i.e., to reconstruct the first modulated sequence from data fields S1 and S2 so as to remove the superimposition of the first and second modulated sequences. Again, a subtractor may be used to subtract a reconstructed sequence from a received superimposed sequence y(1…384). Thus, the input to the Phase Detector 870 comprises a received second modulated sequence, plus any noise introduced by the communication channel as shown in Equation (9):

[Equation (9)]

The operation of the Phase Detector 870, Averaging Component 880 and Estimator 890 will now be described in relation to two examples: a first using tones and a second using chirps. The tones and chirps may be constructed according to the models presented above.

In the Phase Detector 870 the phase difference between successive samples of the second modulated sequence is measured in order to estimate the phase modifier term

^r _k as repeated across each set of short sequences. Assuming that noise terms are filtered out, the received second modulated signal is shown in Equation (10):

[Equation (10)]

wherein for tone sequences the phase difference

_r(l) of l-th component being of repetition r is estimated according to Equation (11):

[Equation (11)]

where l =0…N _chip-2;

and for chirp sequences the phase difference

_r(l) of an l-th component is estimated according to Equation (12):

[Equation (12)]

where l =0…N _chip-2.

The phase difference estimates

_r(l) are then used to estimate the phase modifier term

_k ^r This is achieved using Equation (13) for tone sequences:

[Equation (13)]

and the following calculation for chirp sequences using Equation (14):

[Equation (14)]

The output of Phase Detector 870 thus comprises a number of phase modifier estimates

_k ^r. These estimates are then averaged over the repetitions (r) of each sequence S3_K by Averaging Component 880. This may be achieved for tone sequences using Equation (15):

[Equation (15)]

and for chirp sequences using Equation (16):

[Equation (16)]

The averaging over each set of repeated sequences performed by the Averaging Component 880 filters, i.e. removes, the noise n(i) introduced by the communication channel. The output of the Averaging Component 880 includes a number of phase modifier estimates for each set of short sequences,

_k (1 … n ₃). These are input into the Estimator 890 which extracts the corresponding bit values of the third data field, i.e. S3(1 … n ₃). In one embodiment Estimator 890 comprises a maximum likelihood (ML) estimator wherein

a transmitted

^r _k field is estimated by computing the distance to all possible transmitted values, as shown in Equation (17):

[Equation (17)]

This process is repeated for all values of k from 1 to N _rep, obtaining n ₄ bits on each repetition until all n ₃bits are extracted.

The choice of function to produce the repeated short sequences depends on each implementation. Comparing the averaging expressions for tone and chirp sequences it is apparent that chirp sequences offer better noise filtering as the denominator N_rep(N_chip-1)² calculation is larger than the denominator N_rep(N_chip-2) the tone calculation. However, a chirp function may introduce a high frequency component at the end of each chirp sequence that may introduce a larger degradation to the detection of data fields S1 and S2 than tone sequences.

Fig. 14 shows simulation results for the reception of signal preambles constructed according to the second embodiment. The graphs show Bit Error Rate (BER) for each data field S1, S2, S3 and Frame Error Rate (FER) for a P1 symbol versus Signal to Noise Ratio (in decibels - dB) for the existing T2 standard (solid line plots) and an adapted NGH standard (dashed line plots) that incorporates the extra third data field S3 provided by the second embodiment, the short sequences being based on a chirp function and n ₃= 4. Frame Error Rate is used for the P1 symbol as in the present example there is one P1 symbol per frame and a check is made to see if the complete P1 symbol has been received correctly. A first graph 1410 shows an AWGN noise model and a second graph 1420 shows a TU6-60kmph noise model. In the illustrated simulations, the degradation in detection of the first and second data fields S1 and S2 is around 1.5dB when n ₃= 3 and less than 2dB when n ₃= 4.

Figs. 16a, 16b and 16c show use of the new third data field S3 in the DVB-NGH standard. These uses are provided as examples only and should not be seen as limiting. The Figs. show possible bit patterns for data fields S1, S2 and S3, wherein S3 is of length (n ₃)4 bits, 3 bits and 2 bits respectively. Fig. 16a illustrates a case where n ₃ = 4 bits. Building on the bit patterns for data fields S1 and S2 shown in Figs. 2a to 2d, an S1 bit pattern of 10x indicates that the DVB-NGH standard is being used. The least significant bit of data field S1 then indicates SISO/MISO as for the T2 standard. Bit 1 of field 1 of data field S2 indicates the NGH profile (NGH Prof.) being used (for example T2 Mobile, NGH, and the like) and the last two bits of field 1 indicate FFT parameters. The “mixed” bit of data field S2, i.e. field 2, is signalled as shown in Fig. 2d. The first bit of the new third data field then indicates the waveform used, for example, OFDM, Single Carrier (SC)-OFDM and the like. The last three bits of the third data field S3 then fully signal the guard interval (GI) such that Cyclic Prefix (CP) correction is not required. In Fig. 16b, where n ₃ = 3 bits, a bit pattern of 011 may be used for the first data field S1 and the SISO/MISO parameter may be signalled by the first bit of the third data field S3. The second bit then indicates the waveform, as described above. And finally, the third bit of the third data field S3 may provide a hint for the guard interval which is fully resolved with subsequently transmitted information; for example, the hint may prime the reception apparatus for a particular subset of intervals. Fig. 16c shows a n ₃ = 2 case, wherein the SISO/MISO parameters are signalled by the third bit of the first data field S1 and the third data field S3 provides a waveform indication and guard interval hint.

The above embodiments are to be understood as illustrative examples of the invention. Further embodiments of the invention are envisioned. For example, the invention may be adapted to be used with different forms of data signals that use different transmission and reception standards. The invention may be applied to alternative data included in a transmitted signal, wherein limitations in the signal format mean that further signal capacity is required, for example, relating to alternate forms of control data. The examples described above demonstrate that superimposing a new sequence on an existing sequence generates extra capacity while providing a tolerable degradation to the detection performance of the existing sequence. Certain described examples provide an increase in capacity of over fifty-percent, while only introducing a degradation of around 1.5dB.

Advantages of the invention will be apparent to those in the art from the description. In particular, the present invention increases capacity while maintaining full backward compatibility. Both embodiments can be simply implemented as part of next generation NGH or T2-mobile receivers without complex and expensive components. The detection of the first and second data fields S1 and S2 uses existing system components and at least the first embodiment allows the re-use of those components to detect the third data field S3. The described solution also adds capacity without affecting the timing and/or frequency synchronization properties of a preamble symbol. The Peak-to-Average Power Ratio (PAPR) of the preamble section is substantially maintained, for example in some embodiment a degradation of only around 0.5dB is introduced.

The method of transmitting and/or receiving data according to the present invention may be implemented using dedicated circuits or appropriately programmed components. Additionally, embodiments of the invention can also be implemented through computer readable code/instructions in/on a medium, e.g., a computer readable medium, to control at least one processing element. The medium can correspond to any medium/media permitting the storage and/or transmission of the computer readable code. The computer readable code can be recorded/transferred on a medium in a variety of ways, with examples of the medium including recording media, such as magnetic storage media (e.g., ROM, floppy disks, hard disks, etc.) and optical recording media (e.g., CD-ROMs, or DVDs), and transmission media such as Internet transmission media. Furthermore, the media may also be a distributed network, so that the computer readable code is stored/transferred and executed in a distributed fashion.

Embodiments of the invention are described in terms of functional block components and various processing steps. Such functional blocks may be realized by any number of hardware and/or software components configured to perform the specified functions. For example, an embodiment of the invention may employ various integrated circuit components, e.g., memory elements, processing elements, logic elements, look-up tables, and the like, which may carry out a variety of functions under the control of one or more microprocessors or other control devices. Similarly, where the elements of an embodiment of the invention are implemented using software programming or software elements the invention may be implemented with any programming or scripting language such as C, C++, Java, assembler, or the like, with the various algorithms being implemented with any combination of data structures, objects, processes, routines or other programming elements. Furthermore, an embodiment of the invention could employ any number of conventional techniques for electronics configuration, signal processing and/or control, data processing and the like.

For the sake of brevity, conventional electronics, control systems, software development and other functional aspects of the systems (and components of the individual operating components of the systems) may not be described in detail. Furthermore, the connecting lines, or connectors shown in the various figures presented are intended to represent functional relationships and/or physical or logical couplings between the various elements. It should be noted that many alternative or additional functional relationships, physical connections or logical connections may be present in a practical device.

It is to be understood that any feature described in relation to any one embodiment may be used alone, or in combination with other features described, and may also be used in combination with one or more features of any other of the embodiments, or any combination of any other of the embodiments.

While the present invention has been shown and described with reference to certain embodiments and drawings of the portable terminal, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims and their equivalents.

Claims

A method of transmitting data including one or more frames, including a preamble section and a data section, the method comprising:modulating a signal with a first data sequence of the preamble section to generate a first modulated sequence using a first non-coherent modulation scheme; modulating a second data sequence of the preamble section to generate a second modulated sequence using a second modulation scheme capable of non-coherent detection that provides continuous variation of the second modulated sequence across a length of the first modulated sequence; superimposing the second modulated sequence upon the first modulated sequence to produce a superimposed sequence; and transmitting the superimposed sequence.
A method of receiving data comprising one or more frames, including a preamble section and a data section, the method comprising:receiving a signal comprising a second modulated sequence superimposed on a first modulated sequence;demodulating the signal to extract a first data sequence of the preamble section from the first modulated sequence using a first non-coherent demodulation scheme; removing the superimposition to provide the second modulated sequence; anddemodulating the second modulated sequence using a second demodulation scheme to extract a second data sequence of the preamble section,wherein the second demodulation scheme provides non-coherent detection of the second data sequence.
A transmitter for transmitting data including one or more frames, including a preamble section and a data section, the transmitter comprising:a modulating unit for modulating a signal with a first data sequence of the preamble section to generate a first modulated sequence using a first non-coherent modulation scheme, and modulating a second data sequence of the preamble section to generate a second modulated sequence using a second modulation scheme capable of non-coherent detection that provides continuous variation of the second modulated sequence across the length of the first modulated sequence; a superimposing unit for superimposing the second modulated sequence upon the first modulated sequence to produce a superimposed sequence; and a transmitting unit for transmitting the superimposed sequence.
A receiver for receiving data including one or more frames, including a preamble section and a data section, the receiver comprising:a receiving unit for receiving a signal comprising a second modulated sequence superimposed on a first modulated sequence;a demodulating unit for demodulating the signal to extract a first data sequence of the preamble section from the first modulated sequence, said demodulating using a first non-coherent demodulation scheme; a superimposition removal unit for removing the superimposition to provide the second modulated sequence; andthe demodulation unit for demodulating the second modulated sequence using a second demodulation scheme to extract a second data sequence of the preamble section,wherein the second demodulation scheme provides non-coherent detection of the second data sequence.
The method of claim 1 or the transmitter of claim 3, wherein the second modulation scheme comprises the generation of a plurality of short sequences carrying a third field (S3) that are repeated across the length of the first modulated sequence to form the second modulated sequence.
The method of claim 1, the method of claim 2, the transmitter of claim 3 or the receiver of claim 4, wherein the signal comprises a plurality of sub-carriers transmitting a superimposed sequence.
The method or the receiver of claim 6, wherein the first data sequence carries a first field (S1) and a second field (S2), the first field being demodulated from a first set of sub-carriers and the second field being demodulated from a second set of sub-carriers.
The method or the receiver of claim 7, wherein the second demodulation scheme comprises hierarchical differential phase shift keying (
-DPSK).
The method or the receiver of claim 8, wherein the second demodulation scheme assumes a rotation of up to
radiansbetween consecutive symbols of the second data sequence.
The method or the receiver of claim 9, wherein the differential phase shift keying comprises differential binary phase shift keying (D-BPSK) and wherein
is less than π/2 radians.
The method or the receiver of claim 8, wherein a first rotation of
₁radiansis assumed between consecutive symbols of the first field (S1) and a second rotation of
₂radiansis assumed between consecutive symbols of the second field (S2).
The method or the receiver of claim 7, wherein the second data sequence carries a third field (S3) in a chip sequence_,the chip sequence being repeated and/or interleaved across the second data sequence.
The method or the receiver of claim 12, wherein the chip sequences carrying the third field (S3) are derived from a set of sequences that are used to generate the first data sequence carrying the first and second fields (S1, S2).
The method of claim 2 or the receiver of claim 4, wherein the second modulated sequence comprises a plurality of short sequences carrying a third field (S3) that are repeated across the length of the first modulated sequence.
The method or the transmitter of claim 5, the method or the receiver of claim 14, wherein each short sequence is of a length N_chip that is less than the length of the first modulated sequence N_fms.
The method or the transmitter of claim 5, the method or the receiver of claim 14, wherein a phase of each short sequence varies across the length of the short sequence, the difference in phase between two consecutive samples of the short sequence being less than the difference in phase between two consecutive samples of the first modulated sequence.
The method or the transmitter of claim 5, the method or the receiver of claim 14, wherein the short sequences are at least one of repeated and interleaved, across the second modulated sequence.
The method or the transmitter of claim 5, the method or the receiver of claim 14, wherein the plurality of short sequences comprise at least one of:tones, wherein part of the third field (S3) is carried in a phase value of the short sequence; and chirps, wherein part of the third field (S3) is carried in a frequency sweep of the short sequence.
The method or the transmitter of claim 5, the method or the receiver of claim 14, wherein each short sequence is tuned such that a phase difference between an end of one short sequence and a beginning of an adjacent short sequence is less that a predetermined threshold.
The method or the transmitter or the receiver of claim 17, wherein the second modulated sequence comprises a set of tones superimposed onto a part of the first modulated sequence carrying the first field (S1) that are different from a set of tones superimposed onto a part of the first modulated sequence carrying the second field (S2).
The method or the transmitter or the receiver of claim 17, wherein the second modulated sequence comprises a set of chirps superimposed onto a part of the first modulated sequence carrying the first field (S1) that are different from a set of chirps superimposed onto a part of the first modulated sequence carrying the second field (S2).
The receiver of claim 17, wherein the receiver further comprises:a phase difference determining unit for determining a phase difference between consecutive samples of the second modulated sequence to produce a plurality of phase estimates;an averaging unit for averaging the phase estimates to determine an average phase estimate for each sequence,; and using the average phase estimate to extract phase or frequency sweep values representing encoded data.
The receiver of claim 4, wherein the receiver further comprises:a reconstructing unit for reconstructing the first modulated sequence from the extracted first data sequence; anda subtracting unit for subtracting the reconstructed first modulated sequence from the signal to provide the second modulated sequence, to remove the superposition.