Transmitter, communication system and method for transmitting data signals

Abstract

Transmitter for transmitting data signals to at least one communication device via a wired network over a plurality of carriers, wherein the carriers are in frequencies allocated to one or more radio services, each of the radio services being allocated to one or more frequency bands, the transmitter comprising: a symbol generator for creating symbols based on the data signals; a processor for generating copies of the symbols and for determining an allocation of the copies to the plurality of carriers, wherein a first copy and a second copy of each symbol are allocated to carriers which lie in frequency bands which are allocated to different radio services; and a modulator for modulating the copies of the symbols onto the carriers according to the specified allocation.

Description

[0001] The invention relates to a transmitter for transmitting data signals, a communication system for transmitting data signals between a transmitter and a receiver, and a method for transmitting data signals. BACKGROUND

[0002] Powerline modems typically adjust their communication parameters (adaptive modulation) to the channel characteristics to increase throughput and reliability. This adjustment requires channel status information at the transmitter and therefore requires feedback from the receiver to the transmitter.

[0003] In some cases, the sender cannot use channel status information, for example for initial communication (before adapting to the channel characteristics) or for broadcast messages (messages to all stations in the network).

[0004] In these cases, powerline modems typically use a robust communication mode (ROBO mode). For example, the HomePlug standard specifies a ROBO mode where each OFDM (orthogonal frequency-division multiplexing) subcarrier is modulated with the same QAM (quadrature amplitude modulation) constellation (QPSK (quadrature phase-shift keying) in HomePlug). In addition to forward error correction (FEC), a re-code is used, where each encoded bit is repeated two or four times. With these parameters, the communication becomes very robust and is designed to work with virtually all connections within powerline networks.

[0005] To comply with regulations regarding electromagnetic interference (EMI), certain frequencies must be notched. The frequencies that must be notched can vary from country to country. These frequencies are specified by a so-called "tone mask" (frequency mask), which is stored in the powerline modems. To guarantee interoperability, the frequency mask must be the same for all modems (standard broadcast frequency mask (default broadcast tone mask) in the HomePlug standard).

[0006] Frequency masks can vary between countries. Generally, the North American (NA) mask is considered the standard broadcast frequency mask. A frequency mask specifies which carriers are used during data transmission. The frequency mask is known to both the transmitter and receiver. Furthermore, notched frequencies according to other countries' frequency masks can be implemented using amplitude maps. These amplitude maps specify that no power is allocated to the additional frequencies to be notched.

[0007] If the frequency masks for different countries do not match, receiver performance can degrade. For example, the receiver expects information on notched subcarriers. To a certain extent, the lost information can be compensated for by forward error correction and copy coding. Copy coding (also called diversity copying in the HomePlug standard) utilizes frequency diversity (some subcarriers are highly attenuated; some subcarriers exhibit only slight attenuation). However, copy coding does not account for potentially notched subcarriers. Consequently, all copies may be made on the notched subcarriers.

[0008] DE 197 16 011 A1 describes a method and device for transmitting information via power supply lines.

[0009] DE 36 06 354 A1 describes further methods for transmitting data over the lines of a power supply network.

[0010] WO 2012 / 172 361 A1 describes a communication system and procedures for data allocation in a communication system.

[0011] US 2002 / 0188908A1 describes forward error correction with channel matching.

[0012] It is an object of the invention to provide a transmitter, a communication system and a method for transmitting data which offer a higher degree of certainty that the transmitted data will actually be received by a receiver.

[0013] This problem is solved by the subject matter of the independent claims. Further embodiments are specified in the dependent claims. Details of the invention are better clarified by the following description of embodiments in conjunction with the accompanying drawings, whereby features of the different embodiments can be combined with one another, provided they are not mutually exclusive. BRIEF DESCRIPTION OF THE IMAGES Fig. Figure 1 shows a schematic block diagram of a transmitter according to an embodiment of the invention, Fig. Figure 2 shows a schematic block diagram of a system according to an embodiment of the invention, Fig. Figure 3 schematically shows steps of a method according to an embodiment of the invention, Fig. Figure 4 schematically shows an allocation of symbols and their copies according to an embodiment of the invention. Fig. Figure 5 shows the tone masks for North America and for Europe. Fig. Figure 6 schematically shows the attenuation of signals depending on the frequency. Fig. Figure 7a schematically shows a block diagram of a transmitter according to a further embodiment of the invention, Fig. Figure 7b shows a block diagram of a transmitter according to a further embodiment of the invention, Fig. Figure 8 schematically shows the allocation of additional copies to a second subcarrier pair when a multiple-input multiple-output (MIMO) encoding based on Alamouti coding is used. Fig. Figure 9 schematically shows a transmitter according to a further embodiment of the invention, and Fig. Figure 10 schematically shows steps of a method according to a further embodiment of the invention. DETAILED DESCRIPTION

[0014] In Fig. Figure 1 shows a schematic block diagram of a transmitter 100 for transmitting data signals.

[0015] The transmitter 100 includes a symbol generator 102 for generating symbols based on the data signals. For example, the symbol generator can be implemented as a quadrature amplitude modulator (QAM), with the symbols being generated according to BPSK (binary phase-shift keying), QPSK (quadrature phase-shift keying), 2-QAM, 4-QAM, 8-QAM, 16-QAM, 64-QAM, 256-QAM, or corresponding other modulation schemes.

[0016] The transmitter 100 further comprises a processor 104 for generating copies of the symbols and for determining an allocation of the copies to a plurality of carriers, wherein a first copy and a second copy of each symbol are allocated to carriers located in frequency bands assigned to different radio services. That is, the first copy of a symbol is allocated to a carrier located in a frequency band assigned to one radio service, while the second copy of the same symbol is allocated to a carrier located in a frequency band assigned to a different radio service. The same applies to the copies of the other symbols.

[0017] The term "copy of a symbol" also includes the original of a symbol. For example, if an original and a copy of the original are allocated to the carriers, then two copies of the symbol carrying the same information are allocated. "Generating copies of a symbol" can also include providing the original symbol and at least one additional copy of the symbol. Current implementation schemes for robust communication schemes (ROBO mode) use 2, 4, or 5 copies; however, more copies are possible.

[0018] The 104 processor can also be referred to as a "diversity copier".

[0019] Furthermore, the transmitter 100 includes a modulator 106 for modulating the copies of the symbols onto carriers according to the specified allocation. The modulator 106 can be implemented as an OFDM modulator, which modulates the symbols onto a set of subcarriers.

[0020] The carriers are then transmitted via a wired network 108, which is schematically represented in Fig. Figure 1 shows the wired network. For example, it could be a powerline network or a DSL (digital subscriber line) network. The transmitter could be a powerline modem or a DSL modem.

[0021] In the wired network 108, the carriers are located on frequencies which are assigned to radio services, wherein the frequency range of all radio services is preferably allocated within the entire HF (high frequency) and VHF (very high frequency) range by allocating one or more frequency bands of the frequency range to each radio service.

[0022] With this approach, carriers for transmitting identical information are allocated in such a way that frequencies assigned to a particular radio service are never used by more than one carrier. For example, the "RADIO ASTRONOMY" service allocates the following frequency bands: 13360 to 13410 kHz, 25550 to 25670 kHz, 37.5 to 38.25 MHz, and 70.45 to 74.8 MHz. If the powerline communication modem or transmitter is operated near a radio astronomy station, all these frequencies can be excluded from transmission (for example, via an amplitude map stored in the transmitter or an internal measurement unit in the transmitter designed to identify external interference). A receiver specified, for example, by the HomePlug standard, does not detect frequency exclusions in the radio astronomy bands (the coding follows the broadcast frequency mask).If the carriers are assigned in such a way that at most one frequency carrier out of several carriers carrying identical information lies in the radio astronomy bands, the system guarantees that the other carriers will be received by the second powerline communication modem.

[0023] Other examples of radio services are - aeronautical mobile (or) service (of route services)), - aeronautical radio navigation, fixed service - land mobile service, - maritime mobile service, - maritime radio navigation service, - meteorological aids service, - mobile radio service, - astronomy service, - radiolocation service, - Radio navigation service, - Standard frequency and a time service, - industrial, scientific and medical (ISM) services, - RFID services, - EAS (electronic article surveillance / electronic article surveillance service), - meteorological-satellite service, - mobile satellite service (mobile-satellite service), - Space Operation Service - Space Research Service - or other services.

[0024] According to ITU (International Telecommunication Union) radio regulations, each radio service can have more than one frequency allocation. To select the optimal frequency for radio transmissions, multiple allocations can be reserved for a single radio service.

[0025] The frequencies allocated to a specific radio service should not be assigned more than once to powerline frequency carriers transmitting identical information. The frequency bands for radio services can be found, for example, in ERC Report 25, the European table of frequency allocations and uses in the frequency range from 9 kHz to 3000 GHz, or in the ITU Radio Regulations.

[0026] If, for example, Norway decides that frequencies for maritime radio services in coastal regions should be excluded from powerline communication, only the modem's amplitude map is programmed to implement the notch filters. The diversity copier according to this invention ensures that redundantly transmitted information is allocated to an individual radio service allocation as infrequently as possible. Since it is highly unlikely that all of the allocated frequencies are notched when they "belong" to different radio services, it is ensured that all information is received reliably.

[0027] Powerline communication modems operating in a single location can be affected by a single application. For example, a powerline communication modem operating in a store or warehouse can be disrupted by electronic article surveillance (EAS) services operating in the same building. Powerline communication modems operating near an airport can be disrupted by aeronautical services. This interference can reduce the signal-to-noise ratio (SNR) of powerline communication transmissions in all frequency bands allocated to aeronautical services. If redundantly transmitted information is copied no more than once onto frequencies allocated to a single radio service, only one of the copies could be affected by that single radio service. In this context, a radio service corresponds to aeronautical services.The frequencies used for aeronautical services can be used for multiple individual radio transmissions between aircraft and the airport, or vice versa. The aeronautical services are located at 2.85–3.025 MHz, 3.4–3.5 MHz, 4.65–4.7 MHz, 5.48–5.68 MHz, 6.525–6.685 MHz, 8.815–8.965 MHz, 10.005–10.1 MHz, 11.275–11.4 MHz, 13.26–13.36 MHz, 17.9–17.97 MHz, and 21.924–22.00 MHz.

[0028] For example, RFID and EAS services are allocated at 3.15 to 3.4 MHz (EAS), 7.4 to 8.8 MHz (EAS), 10.2 to 11 MHz (EAS), 13 to 13.2 MHz (RFID) and 13.9 to 14.1 MHz (RFID).

[0029] In Fig. Figure 2 shows a schematic block diagram of a system 200 for transmitting data between a transmitter 100 and a receiver 201 via the wired network 108. The receiver 201 comprises a demodulation unit 206, a further processor 204, and a data signal generator 202. The signals received via the wired network 108 are demodulated by the demodulation unit 206 and further processed in the processor 204 so that the copied symbols from the individual carriers can be combined. For example, maximum ratio combining (MRC) can be used.The allocation scheme of copies of the plurality of carriers is, for example, stored as an allocation table in a memory unit 210 on the transmitter side 100 and in another memory unit 208 on the receiver side 201, so that the respective processors 104, 204 both have knowledge of the same allocation scheme in order to enable the allocation of copies of the symbols to the carriers in the same way as the combination of copies on the receiver side 201.

[0030] In Fig. Figure 3 shows a schematic flowchart of a method according to an embodiment of the invention. In step S300, symbols are generated based on data signals. Copies of the symbols are generated in step S302.

[0031] An allocation of copies to the multitude of carriers is determined in step S304, whereby the copies of each symbol are allocated to carriers which lie in frequency bands which are allocated to different radio services.

[0032] In step 306, the copies of the symbols are modulated onto the carriers according to the specific allocation from step S304.

[0033] In Fig. Figure 4 shows an example of the allocation of copies to OFDM subcarriers (represented by arrows) according to the described rules. The example uses two copies of each QAM symbol. The first QAM symbol, c1, is allocated to the first and last subcarriers (correspondingly for the second symbol). The third symbol, c3, falls within the aeronautical band, and its copy should not be allocated to the same or any other aeronautical band. Likewise, the other copies should not fall within the same band. For example, one copy of the fifth symbol, c5, and one copy of the fourth symbol, c4, are each allocated to a frequency in the maritime band, whereas the other copy of the respective fourth symbol, c4, or fifth symbol, c5, is allocated to a different carrier that is not part of the maritime band.

[0034] Fig. Figure 5 shows the standard broadcast frequency mask of the HomePlug standard, the NA (North America) mask. This frequency mask is available to both the transmitter and receiver. In Europe, additional frequencies must be excluded (see EU mask in Figure 5). Fig. 5) The EU mask is an example of a radio service. The encoding at the transmitter must comply with the broadcast frequency mask (NA mask). The transmitter should also not apply power to the subcarriers that must be additionally omitted (e.g., as specified by the EU mask). This is specified by an amplitude map. Consequently, frequency carriers transmitting identical information should not be allocated in such a way that frequencies omitted by the EU mask (FprEN 50561-1) and not listed in the North American mask are never used by more than one carrier. The HomePlug specification excludes frequencies listed in its North American frequency mask.

[0035] The frequencies listed in the North American frequency mask are primarily the US HAM (amateur radio) bands, as well as some guard frequencies adjacent to each band allocation. A HomePlug modem sold in Europe can additionally protect all radio services specified in FprEN 50561-1. This includes more frequencies than just the US HAM bands. Additional frequencies, such as broadcast frequencies, must be dynamically or permanently excluded. The diversity copier of the HomePlug receiving modem does not recognize these additional frequency exclusions (there is only one HomePlug standard worldwide). According to the invention, the additional frequencies to be protected by FprEN 50561-1 (compared to the North American frequency mask) are to be allocated only once with redundant information for powerline transmissions.The FprEN 50561-1 standard protects the following additional radio applications: aeronautical mobile services (route services), civil aircraft, civil band radio (CB radio) and radio broadcasting.

[0036] In Fig. Figure 6 shows the signal-to-noise ratio (SNR) versus frequency as a median value from many channel realizations. As shown from Fig. As can be seen in Figure 6, the higher the frequency, the higher the attenuation. Furthermore, the noise is typically higher for lower frequencies and decreases for higher frequencies. To address these issues, frequency diversity is achieved by distributing the information across carriers located at two or more individual frequencies. According to embodiments of the invention, the frequency selection is performed according to the following principles (where n is the frequency carrier index and N is the total number of subcarriers): allocating the carrier with the lowest frequency (n = 1) and the carrier with the highest frequency (n = N), then allocating the carrier with the second lowest (n = 2) and the second highest frequency (n = N-1), continuing with a carrier with the third lowest frequency, and so on. This ensures that the strongest and lowest subcarriers are assigned according to the decreasing signal-to-noise ratio of Fig. 6 can be combined.

[0037] Another alternative is to allocate the lowest frequency carrier (n = 1) and its subcarrier n = N / 2, then the second lowest (n = 2) and its subcarrier n = N / 2+1, continuing with the third lowest, and so on. This reflects the fact that noise decreases at higher frequencies and attenuation increases at higher frequencies. Furthermore, nested patterns can also be used.

[0038] Fig. Figure 7a schematically shows a transmitter with forward error correction (FEC) 702, QAM mapping 704, and OFDM modulation 706, wherein the diversity copier 708 is located between the QAM mapping 704 and the OFDM modulator 706. The diversity copier 708 assigns copies of the QAM symbols to the OFDM subcarriers. In this embodiment, the copy allocation operates at the QAM symbol level.

[0039] According to Fig. 7b. Copy allocation can also be performed at a bit level (before QAM mapping). If copy encoding is performed at the bit level, the receiver must be adjusted accordingly, for example, in addition to the log-likelihood radio (LLR) of the QAM demapping.

[0040] The encoding can be extended to systems with multiple input and output variables (MIMO, multiple-input multiple-output), as schematically shown in Fig. 8 shown. Fig. Figure 8 shows four subcarriers (1, 2, K+1, K+2, and a system with two transmit ports and one receive port). Alamouti coding is applied to two adjacent subcarriers, resulting in the information being split between the two carriers. The two symbols c1 and c2 are transmitted on the first subcarrier from their respective transmit ports 1 and 2. On the second subcarrier, the conjugate complexes of the two symbols are transmitted, i.e., -c2* and c1*, from their respective transmit ports 1 and 2. i (k) denote the channel coefficients from transmit port i (i=1,2) to receive port k of subcarrier k. Additionally, the copies are assigned to another subcarrier pair (subcarrier K and K+1 in the Fig. 8) allocated to provide frequency diversity. The allocation of the other frequency pair should follow the principles introduced above. Alternatively, Alamouti encoding can be performed in the time domain. Instead of transmitting the additional copies on a different frequency pair, the copy can be distributed in the time domain. The encoding can be combined in any possible way (e.g., Alamouti encoding in the time domain, additional copies in the frequency domain). Other MIMO schemes can also be used.

[0041] According to one embodiment of the invention, the copies of the symbols can be allocated in the time domain instead of, or in addition to, their allocation to a plurality of carriers. Powerline communication modems often suffer from synchronous noise (for example, synchronous with the 50 Hz line frequency). The encoding of the redundant information (i.e., the different copies of the same symbol) can be implemented such that some copies are not affected by this synchronous noise. The noise characteristics of other devices located in the powerline communication network can also be taken into account.

[0042] This is in Fig. 9 is described in more detail. According to a further embodiment, a transmitter 900 comprises a processor 902 and is connected to a wired network 904. The processor 902 is configured to generate copies of data signals and to determine an allocation of the copies to a plurality of time intervals, wherein the copies of each data signal are allocated to time intervals with different noise characteristics on the wired network 904.

[0043] In Fig. Figure 10 shows a schematic flowchart for a process according to a further embodiment.

[0044] In step S1000, copies of data signals are created.

[0045] In step S1002, an allocation of copies to the majority of time intervals is determined, whereby the copies of each data signal are allocated to time intervals with different noise characteristics on the wired network 904.

[0046] By allocating the copies to time intervals with different noise characteristics, it is possible to avoid two copies of a symbol being allocated to time intervals in which sources of interference are present, e.g., in the peaks of an alternating current in a power grid.

[0047] The allocation of symbols or data signals according to the embodiments of the invention offers new robust (ROBO) modes with improved bit rate and robustness compared to known ROBO modes. A more intelligent allocation of copies is proposed, taking into account regulatory concerns regarding electromagnetic interference and powerline channel characteristics.

Claims

[1] Transmitter for transmitting data signals to at least one communication device via a wired network over a plurality of carriers, wherein the carriers are in frequencies allocated to one or more radio services, each of the radio services being allocated to one or more frequency bands, the transmitter comprising: a symbol generator for creating symbols based on the data signals; a processor for generating copies of the symbols and for determining an allocation of the copies to the plurality of carriers, wherein a first copy and a second copy of each symbol are allocated to carriers which lie in frequency bands which are allocated to different radio services; and a modulator for modulating the copies of the symbols onto the carriers according to the specified allocation. [2] Transmitter according to claim 1, wherein one or more of the radio services comprise cut-out frequencies of a frequency mask according to the European standard FprEN50561-1. [3] Transmitter according to claim 1 or 2, wherein one of the radio services comprises at least one of the following: aeronautical mobile radio service, aeronautical radio navigation (fixed / stationary service), land radio service, maritime radio service, marine radio navigation service, meteorological support service, mobile radio service, astronomy service, radio location service, radio navigation service, standard frequency and time service, industrial, scientific and medical (ISM) service, RFID service, electronic article surveillance service, meteorological satellite service, mobile satellite service, space operations service, space research service or other services. [4] Transmitter according to any one of claims 1 to 3, wherein the copies of each symbol are further allocated to the carriers according to a predetermined algorithm, wherein the predetermined algorithm optimizes the allocation to the carriers such that copies of a bit or symbol in an available frequency range have a high frequency spacing. [5] Transmitter according to any one of claims 1 to 3, wherein the copies of each symbol are further allocated to the carriers according to a predetermined algorithm, wherein the predetermined algorithm optimizes the allocation to the carriers such that all copies of different symbols have the same frequency spacing. [6] Transmitter according to any one of claims 1 to 5, further comprising an encoder with multiple inputs and multiple outputs, wherein the encoder is configured to encode the symbols on adjacent subcarriers of the plurality of carriers, wherein the processor is further configured to generate copies of the encoded data signals and to determine an allocation of the copies of the encoded data signals to the plurality of carriers, wherein the copies of each encoded data signal are allocated to adjacent subcarriers which lie in frequency bands that are allocated to different radio services. [7] Transmitter according to any one of claims 1 to 6, further comprising a storage unit for storing an allocation table, wherein the processor is configured to determine the allocation based on the allocation table. [8] Transmitter according to one of claims 1 to 7, wherein the processor is further configured to generate one or more copies of the data signals and to determine an allocation of the copies to a plurality of time intervals, wherein the copies of each data signal are allocated to time intervals with different noise characteristics on the wired network. [9] Transmitter according to any one of claims 1 to 8, wherein one or more of the copies are generated only for a robust communication mode (ROBO mode). [10] Transmitter according to any one of claims 1 to 9, wherein the carriers are located in a frequency range for communication, and wherein one or more radio services are distributed in the frequency range for communication. [11] Transmitter according to claim 10, wherein the one or more radio services are distributed in the frequency range for communication by allocating each of the frequencies of the frequency range to at least one of the one or more radio services, or by allocating each of a part of the frequencies of the frequency range to at least one of the one or more radio services. [12] Communication system for transmitting data between a sender and a receiver over a wired network, the system comprising: a transmitter according to any one of claims 1 to 11; and a receiver with a combination unit, wherein the combination unit is designed to determine the data signal based on received copies of the symbols. [13] Method for transmitting data signals to at least one communication device via a wired network over a plurality of carriers, wherein the carriers are in frequencies already allocated to one or more radio services, each of the radio services being allocated to one or more frequency bands, comprising the method: Generating symbols based on the data signals; Creating copies of the symbols; Determining an allocation of copies to the plurality of carriers, wherein the copies of each symbol are allocated to carriers which lie in frequency bands which are allocated to different radio services; and Modulating the copies of the symbols onto the carriers according to the specified allocation.

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