WO2006048090A1 - Method for reducing ambiguity levels of transmitted symbols - Google Patents
Method for reducing ambiguity levels of transmitted symbols Download PDFInfo
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- WO2006048090A1 WO2006048090A1 PCT/EP2005/010602 EP2005010602W WO2006048090A1 WO 2006048090 A1 WO2006048090 A1 WO 2006048090A1 EP 2005010602 W EP2005010602 W EP 2005010602W WO 2006048090 A1 WO2006048090 A1 WO 2006048090A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
- H04L27/183—Multiresolution systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L65/00—Network arrangements, protocols or services for supporting real-time applications in data packet communication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L1/00—Arrangements for detecting or preventing errors in the information received
- H04L1/12—Arrangements for detecting or preventing errors in the information received by using return channel
- H04L1/16—Arrangements for detecting or preventing errors in the information received by using return channel in which the return channel carries supervisory signals, e.g. repetition request signals
- H04L1/18—Automatic repetition systems, e.g. Van Duuren systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/0008—Modulated-carrier systems arrangements for allowing a transmitter or receiver to use more than one type of modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/02—Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/02—Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation
- H04L27/04—Modulator circuits; Transmitter circuits
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/18—Phase-modulated carrier systems, i.e. using phase-shift keying
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2602—Signal structure
- H04L27/261—Details of reference signals
- H04L27/2613—Structure of the reference signals
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L27/345—Modifications of the signal space to allow the transmission of additional information
- H04L27/3455—Modifications of the signal space to allow the transmission of additional information in order to facilitate carrier recovery at the receiver end, e.g. by transmitting a pilot or by using additional signal points to allow the detection of rotations
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L27/3488—Multiresolution systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/003—Arrangements for allocating sub-channels of the transmission path
- H04L5/0048—Allocation of pilot signals, i.e. of signals known to the receiver
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2602—Signal structure
- H04L27/261—Details of reference signals
- H04L27/2613—Structure of the reference signals
- H04L27/26134—Pilot insertion in the transmitter chain, e.g. pilot overlapping with data, insertion in time or frequency domain
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L5/00—Arrangements affording multiple use of the transmission path
- H04L5/0001—Arrangements for dividing the transmission path
- H04L5/0003—Two-dimensional division
- H04L5/0005—Time-frequency
- H04L5/0007—Time-frequency the frequencies being orthogonal, e.g. OFDM(A), DMT
Definitions
- the invention relates to digital communication systems. It is particularly applicable to communication systems where data is transmitted over a time-variant or frequency- variant channel, such as in mobile communication systems or satellite communication. It is particularly applicable to communication systems where data is transmitted over a channel that suffers from noise or interference effects.
- modulated data For transmission over long distances or wireless links, digital data is modulated onto one or more carriers.
- modulation schemes are known in prior art, such as amplitude shift keying (ASK), phase shift keying (PSK) and mixed amplitude and phase modulation like quadrature amplitude modulation, QAM.
- ASK amplitude shift keying
- PSK phase shift keying
- QAM quadrature amplitude modulation
- the modulated signal in terms of for example voltage or field strength, can be expressed by
- a bit sequence, or data word is represented by a symbol which has a complex value A for a certain time interval (symbol duration) , wherein
- mapping represents the momentary phase of the modulated signal.
- a data word consisting of a b-bit bit sequence results in a mapping of 2 b bit sequences to 2 b complex values.
- the probability for errors usually rises with rising data rate, that is with rising number of modulation states and falling symbol duration.
- redundancy can be added to the data, which allows to recognise and to correct erroneous symbols.
- a more economic approach is given by methods which repeat only the transmission of data in which un-correctable errors have occurred, such as hybrid automatic repeat request, HARQ, and incremental redundancy.
- EP 1 293 059 B1 shows a method to rearrange digital modulation symbols in order to improve the mean reliabilities of all bits. This is achievable by changing the mapping rule of bits onto modulation symbols. This patent focuses on the rearrangement for retransmitted data words in an ARQ system.
- WO 2004 036 817 and WO 2004 036 818 describe how to achieve the reliability averaging effect for a system where an original and a repeated data word are transmitted over different diversity branches, or in combination with an ARQ system.
- a major difference between wired communication systems and wireless communication systems is the behaviour of the physical channel over which information is transmitted.
- the wireless or mobile channel is by its very nature variant over time and/or frequency.
- a demodulation of data symbols in a receiver requires an accurate estimation of the channel, usually measured by a channel coefficient, which includes knowledge about the gain, the phase shift, or both properties of the channel.
- a channel coefficient which includes knowledge about the gain, the phase shift, or both properties of the channel.
- pilot symbols are inserted into or between the data symbol stream, which have a predetermined unambiguous amplitude and/or phase value which can be used to determine the channel coefficient. This information is then used for correction measures like adaptive filtering.
- a communication channel may also suffer from noise or interference effects. These effects also influence the transmission of such pilot symbols. Even if the channel does not change its amplitude and phase characteristic, a receiver may make an erroneous estimation of the channel due to noise or interference.
- noise and interference effects just as noise; it will be apparent to those skilled in the art that the statements included hereafter about noise are mutatis mutandis applicable to interference.
- Decision-Feedback Demodulation is an iterative process where a first rough channel estimate (or none at all) is used to demodulate the data symbols. After demodulation, and preferably after decoding, the obtained information is fed back to the channel estimator for an improved estimation resulting from the data symbols. It should be apparent that this process causes not only delay and requires a lot of computations in each iteration step, but it also depends greatly on the quality of the first rough channel estimate due to the feedback loop. Such procedure is known for example from Lutz H.-J.
- This object is achieved by defining a special way of mapping repeated data words onto signal constellation points.
- a rearranged constellation pattern is selected that reduces the number of ambiguities when the original and the repeated data symbols are combined. That is, the number of different results that can be obtained by adding the complex values or vectors in the complex number plane representing the constellation points of a first transmission and of a re-transmission of the same data word is lower than the number of original constellation points or modulation states.
- the number of phase ambiguities is further reduced to one (i.e. phase ambiguity is completely removed) by using only a subset of all modulation states which are possible according to the employed modulation (mapping) scheme for the original and counterpart symbol.
- This subset is chosen such that the complex values (modulation states) representing all modulation symbols comprised in the subset are within one half-plane of the complex plane or within a sub-plane of said half-plane.
- this subset is called “phase ambiguity one subset” or shortly “PAO subset”.
- Reducing amplitude ambiguities and removing phase ambiguities facilitates a better channel estimation, less dependent on or independent of the actual data symbol transmitted.
- the coherent combination of original complex value and counterpart complex value(s) for each one or at least a part of all data words results in a reduced number of phase levels compared to the original constellations;
- the average transmit power of the counterpart constellation(s) is identical to the average transmit power of the original constellation (optional).
- Step b is optional in both cases, as it is not required for the reduction of ambiguity. However it provides the advantage of uniform transmission power on the channel over transmitted and re-transmitted signals.
- the counterpart constellation(s) can be generated and the PAO subset can be selected by the following method: 1. Divide the complex plane into two non-overlapping adjacent sub-planes that each contain half of the constellation points.
- Step 4 is not required if all available modulation states of the modulation scheme are already at least within a half-plane of the complex plane. This is for example the case with pure amplitude modulation like the 8-ASK shown in Figure 1.
- the mentioned mirroring is mathematically exact.
- An approximate mirroring would be sufficient in a real system. Approximate means that the distance between the actual constellation point and the ideal mirrored position is less than half the distance to the closest constellation point representing a different value of the data word. Such approximate mirroring may be beneficially employed in a fixed-point representation of the complex values, where the mathematically exact solution cannot be represented due the reduced accuracy of fixed-point numbers.
- step 4 choose one of the two sub-planes as the PAO subset of symbols to be used for transmission. Again step 4 is not required if all available modulation states of the modulation scheme are already at least within a half-plane of the complex plane.
- constellations that are symmetrical to at least one arbitrary axis in the complex plane preferably a division into two half-planes is done with respect to such a symmetry axis that does not include any signal point.
- that respective axis is used; otherwise the symmetry axis will be tilted.
- this method may result in counterpart constellations that are different in shape than the original constellation if the constellation is not point-symmetric to the mirroring point within each sub-plane. This is particularly true if the original constellation represents a PSK or any mixed ASK/PSK modulation apart from QAM. Keeping the shape of the original constellation may have advantages in the implementation of the demodulator (LLR calculator) of the receiver, which will not be discussed in further detail herein.
- step 1 to step 4 of the counterpart constellation generation should then be altered as follows:
- mapping of a word using the original constellation i.e. the mapping of a data word onto a complex value according to the original constellation
- mapping of a data word using a counterpart constellation i.e. the mapping of a data word onto a complex value according to a counterpart constellation, results in the counterpart constellation symbol or simply counterpart symbol.
- the object is achieved by using an identical mapping of pluralities of bits (constituting the data words) to modulation symbols, and using pre-determined bit manipulations on each plurality of bits for the retransmission(s).
- the selection of a PAO subset of the symbols to be used for transmission is done by replacing at least one of the bits within a word (plurality of bits) mapped to a modulation symbol, by a fixed value, e.g. 0 or 1.
- a method for transmitting data in a digital communication system comprises a) selecting a subset of all available modulation states in a pre-determined modulation scheme, to be used for transmission; b) a first transmission step transmitting a first symbol representing a first plurality of bits, the symbol having a first modulation state comprised in said subset; and c) at least one further transmission step (1206) transmitting further symbols representing the first plurality of bits , each of the further symbols having a further modulation state comprised in said subset.
- the addition of complex values associated with said first and said further modulation states yields, for each combination of bit values within the plurality of bits, the same phase of the complex result.
- a computer-readable storage medium has stored thereon program instructions that, when executed in a processor of a transmitter of a digital communication system, cause the transmitter to perform the method according to the first aspect.
- a transmitter for a digital communication system is configured to perform the method of the first aspect.
- a base station for a mobile communication system comprises the transmitter according to the preceding aspect.
- a mobile station for a mobile communication system comprises the transmitter defined in the aspect further above.
- a method for receiving data in a digital communication system comprises a) first and second reception steps receiving a first and a second symbol, both representing a first plurality of bits; b) a likelihood calculation step of calculating likelihood values from the received first and second symbol for at least a subset of the first plurality of bits; and c) a step of setting likelihood values for at least one pre-determined bit out of said first plurality of bits to a value indicating an unknown bit value.
- a computer-readable storage medium has stored thereon program instructions that, when executed in a processor of a receiver of a digital communication system, cause the receiver to perform the method according to perform the method of the preceding aspect.
- a receiver for a digital communication system is configured to perform the method of the aspect further above.
- a base station for a mobile communication system comprises the receiver as defined above.
- a mobile station for a mobile communication system comprises the receiver as defined above.
- Another aspect of the present invention is directed to a transmitter and method for transmitting data in a digital communication system, the method comprising a first transmission step transmitting a first symbol representing a first plurality of bits, the symbol having a first modulation state and at least one further transmission step transmitting further symbols representing the first plurality of bits, each of the further symbols having a further modulation state, wherein a combination of at least one parameter of the first symbol with at least one parameter of one of the further symbols results in a smaller number of different possible resultant parameter states after combination than the number of different parameter states before combination.
- Another aspect of the present invention is directed to a transmitter and method for transmitting data in a digital communication system, the method comprising generating an original symbol by mapping the bits of the original bit sequence using a modulation constellation, generating at least one counter part symbol from the original symbol or from at least one counter part bit sequence generated from the original bit sequence where a combination of the original symbol and the at least one counter part symbol forms a quasi pilot symbol.
- Another aspect of the present invention is directed to a receiver and a method for receiving data in a digital communication system comprising reception of a first and at least one further symbol, obtaining at least one combination of at least one parameter of the first symbol with at least one parameter of the at least one further symbols using the at least one combination to obtain an estimation of a communication channel parameter.
- Fig. 1 gives an overview over various digital modulation mapping constellations
- Fig. 2 illustrates an example of original and repeated data word location for data word no.
- Fig. 3 illustrates an example of original and repeated data word location for data word no.
- Fig. 4 depicts the effect of the described method when applied to QPSK modulation
- Fig. 5 illustrates an alternative example of two mappings for original 8-PSK modulation
- Fig. 6 shows an alternative example of two mappings for original 16-PSK modulation
- Figs. 7 and 8 illustrate two alternatives for improving the reliability of the channel estimation in the case of 8-PSK modulation
- Fig. 9 shows an example of eight mappings for 16-PSK modulation
- Figs. 10 a-c depict examples of results from coherent combining of identical data word values using 2, 4 or 8 different mappings of Fig. 9, respectively;
- Fig. 11 depicts examples of a one-dimensional frame structure for Pilot and Data symbols
- Fig. 12 illustrates steps of a method for data transmission in a digital communication system
- Fig. 13 shows an example of a transmitter chain
- Figs. 14 a-c show an example of combining original and counterpart mapping into a super-mapping for an original 8-PSK modulation.
- Figs. 15 a-c show an example of combining original and counterpart mapping into a super-mapping for an original 16-QAM modulation.
- Fig. 16 shows an example for an original mapping and a counterpart mapping in 16-QAM yielding four different combination result values similar to QPSK modulation states
- Fig. 17 gives an example of an original and a counterpart 4-bit sequence in 16-QAM
- Fig. 18 illustrates steps of a method for improving the reliability in the estimation of transmission channel properties
- Fig. 19 shows steps for determining bits to be replaced by a fixed value and bits to be inverted for re-transmission with PSK
- Fig. 20 illustrates an example for re-transmission with bit inversion with 8-PSK
- Fig. 21 shows steps for determining bits to be replaced by a fixed value and bits to be inverted for re-transmission with ASK
- Fig. 22 illustrates an example for re-transmission with bit inversion with 8-ASK
- Fig. 23 shows steps for determining bits to be replaced by a fixed value and bits to be inverted for re-transmission with mixed ASK/PSK;
- Fig. 24 illustrates an example for re-transmission with bit inversion with 4-ASK/4-PSK
- Fig. 25 depicts the 4-ASK part of the modulation scheme of Fig. 24;
- Fig. 26 depicts the 4-PSK part of the modulation scheme of Fig. 24;
- Fig. 27 shows steps for determining bits to be replaced by a fixed value and bits to be inverted for re-transmission with square QAM
- Fig. 28 illustrates an example for re-transmission with bit inversion with 16-QAM
- Fig. 29 depicts the in-phase part of the modulation scheme of Fig. 28;
- Fig. 30 depicts the quadrature part of the modulation scheme of Fig. 28;
- Figs. 31 to 34 show examples of non-uniform square QAM
- Fig. 35 shows an example of a transmitter chain
- Fig. 36 illustrates an exemplary structure of a base station
- Fig. 37 illustrates an exemplary structure of a mobile station
- Fig. 38 depicts a suboptimum combination and inversion case resulting in a QPSK- equivalent ambiguity situation for an original 4-ASK/4-PSK;
- Fig. 39 depicts a suboptimum combination and inversion case resulting in a QPSK- equivalent ambiguity situation for an original 16-square-QAM
- Fig. 40 illustrates half-planes and half-plane bits in original QPSK according to the present invention
- Fig. 41 illustrates half-planes and half-plane bits in original 8-PSK according to the present invention.
- Fig. 42 shows half-planes and half-plane bits in original 16-QAM according to the present invention.
- Figs. 43 and 44 show examples of half-planes in QPSK and 8-PSK.
- Fig. 45 shows an exemplary receiver structure.
- Figure 46a and 46b show a simplified structure of original and counterpart symbol generation, and their joint interpretation as a Quasi-Pilot.
- Figure 47 illustrates a prior art OFDM frame structure including pilot symbols, shared control symbols, and shared data symbols.
- Figures 48 to 56 illustrate different non-exhaustive possibilities how Quasi-Pilot symbols may be positioned in an OFDM frame.
- Figure 57 shows the process of element-wise multiplication of quasi-pilot components with a spreading code.
- Figure 58 shows the process of quasi-pilot-wise multiplication of quasi-pilot symbols with a spreading code.
- Figure 59 illustrates the process of element-wise spreading of quasi-pilot components with a spreading code.
- Figure 60 illustrates the process of quasi-pilot-wise spreading of a quasi-pilot symbol with a spreading code.
- Figure 61 shows the process of an element-wise constant phase shift of quasi-pilot components.
- Figure 62 is an example of QPSK showing original and counterpart constellations when the power combination and phase combination should result each in one level.
- Figure 63 is an example of 8-PSK showing original and counterpart constellations when the power combination and phase combination should result each in one level.
- Figure 64 is an example of 16-QAM showing original and counterpart constellations when the power combination and phase combination should result each in one level.
- Figure 65 illustrates the usage of different modulation schemes depending on whether
- Figure 66 illustrates the usage of the same modulation schemes for original symbols, counterpart symbols, and simple data symbols.
- Figure 67 is a flowchart diagram about the method to obtain one or more counterpart constellation(s) from an original constellation when power combination is considered.
- Figure 68 is a flowchart diagram about the method to obtain one or more counterpart constellation(s) from an original constellation when amplitude combination is considered.
- Figure 69 is a flowchart diagram about the method to obtain one or more counterpart constellation(s) from an original constellation when phase combination is considered.
- Figure 70 is an example of 4-ASK/4-PSK showing original and counterpart constellations when the amplitude combination and phase combination should result each in one level.
- Figure 2 shows an example of a transmission using the 16-QAM modulation scheme.
- Table 1 such a data modulation symbol carries four bits. In the method described herein, these four bits are transmitted twice:
- the complex plane is divided along imaginary axis 203 into two non-overlapping adjacent sub-planes 204 and 205.
- the imaginary axis is a symmetry axis.
- Diagonal line 206 might also be used, but it is advantageous to select a parting line for both sub-planes, on which no constellation points are located.
- symmetry axes for both sub-planes are determined.
- the real axis 207 is a symmetry axis for both sub-planes.
- the position of a constellation point in the counterpart constellation has to be mirrored with respect to a point 208, 209 on the symmetry axis, that is the real axis 207, from the original constellation point.
- all constellation points belonging to sub-plane 204 have to be mirrored with respect to point 208, while all constellation points belonging to sub-plane 205 have to be mirrored with respect to point 209.
- this mirroring point 208, 209 should be equal to the average of all complex values in the respective sub-plane.
- the modulation states or constellation points of the original mapping and the counterpart constellation are highlighted.
- one of the sub-planes 204 and 205 is chosen as PAO subset to be used for the transmission. If sub-plane 204 is chosen, only constellation points (modulation states) 9-16 are used for both transmission and retransmission. Conversely, if sub-plane 205 is chosen as PAO subset, only constellation points 1-8 are used for both transmission and retransmission.
- Figures 43 and 44 show examples of possible divisions of the complex plane into non- overlapping adjacent sub-planes (here half planes).
- Modulation states on one of the sub- planes 4301 or 4302, 4303 or 4304, 4401 or 4402, 4403 or 4404, 4405 or 4406, 4407 or 4408 could be chosen as the subset of modulation states to be used for the transmissions.
- Half planes 4305 or 4306 are not recommended, as there are modulation states on the line dividing the sub-planes.
- PAO subset contains only some of the constellation points available in the original modulation scheme
- data to be transmitted has to be adapted to the reduced channel capacity. Assuming that the PAO subset contains exactly half of the constellation points available in the original modulation scheme, this can for example be done by
- a higher order modulation scheme may be used, for example 32- QAM instead of 16-QAM.
- Figure 3 shows a first 301 and a further mapping 302 for 64-QAM.
- the complex plane is divided into two non-overlapping adjacent sub-planes along the imaginary axis 303.
- each constellation point is mirrored from its original position in the first constellation with regard to the average complex value 304, 305 in the same sub-plane, respectively according to the sub-plane to that a constellation point belongs.
- Either the right or the left half-plane is selected to be used for transmission, i.e. the PAO subset either comprises constellation points 1 to 32 or constellation points 33 to 64.
- the PAO subset either comprises constellation points 1 to 32 or constellation points 33 to 64.
- the complex plane is divided along imaginary axis 403 into two non-overlapping adjacent sub-planes 404 and 405.
- the constellation points are mirrored with regard to average values 406 and 407, respectively.
- the word number "1" is represented in the first mapping by vector 408 and in the second mapping by vector 409.
- average carrier amplitude is defined to be 1
- each vector has a length of 1.
- Coherent combining of the symbols is equivalent to the addition of both vectors which yields a real number 410 of V2.
- Fig. 4 b-d show the coherent combining for word numbers "2", "3" and "4" respectively.
- the original (first) mapping follows the 8-PSK scheme.
- the complex plane is divided along imaginary axis 503 into non-overlapping adjacent sub-planes 504 and 505.
- each constellation point is mirrored with regard to average complex value 506 or 507, respectively.
- the constellation point for the word number "1" is mirrored with respect to point 507 to position 508.
- the counterpart (second) mapping 502 results in a mixed ASK/PSK constellation.
- sub-plane 504 points 5-8
- sub-plane 505 points 1-4
- Figure 6 shows a similar situation for the case that the original (first) mapping is a 16- PSK scheme. If the ambiguity is to be removed, then the counterpart (second) mapping is quite irregular.
- the complex plane of original constellation (first mapping) 701 is divided into two non-overlapping adjacent sub-planes 706 and 707 by imaginary axis 705.
- the mappings of a given data word onto a constellation point are permuted such that the same word is assigned exactly once to each position (constellation point) in its sub-plane within all mappings 701-704. Consequently, coherent combining of all four transmissions of the same word results in the same value, independent of the word value.
- word number "1" is represented by vector 708 in the first mapping 701 , by vector 709 in second mapping 702, by vector 710 in the third mapping 703 and by vector 711 in mapping 704.
- the result 712 is the real value of roughly 2.6131 for all word values assigned to the right half-plane, as for all word values the same vectors are added, just in different order.
- the real value of roughly -2.6131 is the result 713 for all values assigned to the left half-plane. Consequently ambiguity can be completely removed by using four mappings of words onto constellation points and choosing either only modulation states 1-4 or only modulation states 5-8 to be used for the transmissions.
- the complex plane is divided along imaginary axis 803 into non-overlapping adjacent sub-planes 804 and 805.
- the position is mirrored with regard to the real axis 806, which is a symmetry axis for both sub-planes.
- the combination of first (original) transmission and repeated transmission of word number "1" is the sum of vectors 807 and 808, which yields the real value of roughly 0.7654 at point 812. The same would hold true for word number "4".
- the result is roughly 1.8478 at point 811.
- Figure 9 shows 8 different mappings for 16-PSK. If only first and second mapping are combined, 4 results are possible on either half of the real axis, as shown in Fig. 10a (four amplitude levels). When the first four mappings are combined, two results occur for each possible PAO subset, as shown in Fig. 10b (two amplitude levels). Only when all 8 mappings are combined, ambiguity is completely removed when reducing the set of used constellation points to those on the right or those on the left half-plane.
- Data frame 1101 contains data transmitted according to prior art, in this case with constellation rearrangement.
- data frame 1102 contains only data transmitted according to the method presented herein.
- Data frame 1103 contains data transmitted according to both methods.
- Data word 1104, transmitted using a first (original) mapping, is repeated as data word 1105 according to a second mapping as described in detail above. The same applies to data word 1106, which is re-transmitted as data word 1107.
- the amount and position of ReRe data symbols may be additionally signalled in a Control Channel explicitly or by means of a predefined parameter from the transmitter to the receiver, to provide the receiver with knowledge which part of the data frame follows which repetition strategy.
- an original symbol and its counterpart symbol(s) are transmitted in adjacent places within a time frame, since the benefit of repetition rearrangement depends on channel conditions that are as equal as possible for original and counterpart symbols.
- the original and counterpart symbol can be transmitted on adjacent subcarriers, in adjacent time slots, or both. The latter possibility is particularly applicable when there are several counterpart symbols to be transmitted with the same original symbol, for example three counterpart symbols for 8-PSK.
- the first counterpart symbol can be transmitted in an adjacent time slot in the same subcarrier as the original symbol; the second counterpart symbol can be transmitted in the same time slot in an adjacent subcarrier to the original symbol; the third counterpart symbol can be transmitted in an adjacent subcarrier in an adjacent time slot to the original symbol.
- mapping constellations that result in combined signal points that come to lie on the right axis in the graphs, usually representing the real part axis in the complex signal plane. It should be apparent to those skilled in the art that other mappings can be defined that reach a reduced number of ambiguities without resulting in combined signal points on the real axis. For example, it is very easy to define QAM mappings that result in signal points on the imaginary axis. Likewise it is easily possible to define mappings for PSK that result in points on a straight line inclined at a certain angle to the real axis. Which of such mappings is chosen can be an implementational choice of the system designer, and has no direct influence on the technical concept as far as this invention is concerned.
- a control word is pre-pended to each data word.
- the control word assumes a specific value for each transmission, e.g. "1" for the first transmission of a data word, "2" for the second transmission of the same data word, and so on.
- the super-mapping maps the different values of concatenated control word and data word to modulation states or super-constellation points. Thus, different mappings from data word values to modulation states are obtained for different values of the control word. If the super-mapping is arranged in an appropriate way, the different mappings from data word values to modulation states may exhibit the properties described above.
- Figure 14a shows an original constellation for the example 8-PSK
- Figure 14b shows the related counterpart constellation.
- constellation point 1401 represents symbol "1" in a first transmission
- constellation point 1402 represent the same symbol in a second transmission or re-transmission.
- Figure 15a shows an original constellation for the example 16-QAM
- Figure 15b shows the related counterpart constellation. It may be noted that the difference to the constellations shown in Figure 2 is limited to different labels of the constellation points, following the same reason as described above for Figures 14a-c. From the constellations in Figures 15a and 15b the super-constellation in Figure 15c is obtained by including the constellation points from both constellations, prepending a leading "0" or "1" to the label to signify whether this constellation point was generated using the original or the counterpart mapping respectively. Since the positions of constellation points are identical, and the original and counterpart constellations vary only in the labelling, in Figure 15c each constellation point has to represent two labels.
- constellation point 1501 represents value “1” in a first transmission and value "4" in a second transmission or re-transmission. Consequently, it represents the values "01" and “14" in the super-constellation.
- point 1502 represents "4" in the first transmission and "1” in the second transmission. In the super constellation of figure 15c it represents the values "04" and "11".
- Figure 12 shows a flow chart for a method which may be used to reduce the ambiguities in data symbols in a digital communication system.
- the method consists of a mapping generation step 1201, a transmission step 1205 and one or more re-transmission steps 1206.
- a first mapping is generated in step 1202.
- This mapping may be generated at random, according to a specified algorithm or by simply reading it from a table stored in the transmitter employing this method. This table may further be received from another entity like a base station or a mobile station for which the transmission is designated.
- an appropriate PAO subset of all modulation states is selected to be used for the transmissions, following the rules given above. This step may alternatively be carried out after step 1204.
- a further step 1203 then generates a second mapping according to one of the algorithms given above.
- Step 1204 queries whether more mappings should be generated. In this case the loop returns to step 1203. If not, the method proceeds with step 1209.
- the generated mappings may be stored in the table for later use.
- the generation step 1201 is not necessarily required for each transmission session or even for each transmitted data word. Furthermore, it is also possible to store all used mappings during production of the transmitter, for example with the firmware download, or to receive all mappings from another entity and to store them in the table in the memory.
- step 1209 data to be transmitted is adapted to the reduced transmission capacity, for example by rearranging bits to a higher number of words or by puncturing bits.
- step 1205 a symbol is transmitted according to the first mapping representing a data word.
- the same data word is transmitted again as a re-transmit symbol in step 1206 according to a second mapping generated in step 1203.
- Step 1207 queries whether more mappings exist according to which the data word should be transmitted. If this is the case, the method goes back to repeat steps 1206 and 1207. If no further mapping exists, the method ends the transmission of this data word. Although all transmissions of the same data word should advantageously be sent in close temporal proximity, other data words might be transmitted in between.
- a transmitter 1300 is illustrated which can be used to transmit data according to the method described above.
- an information bit stream to be transmitted is encoded in encoder 1301.
- the encoded bit stream is interleaved in random bit interleaver 1302.
- S/P unit 1303 groups of bits are combined to data words.
- data words are repeated for re-transmission. The repetition factor and the ratio of data words to be repeated is depending on the particular version of the method.
- the generated words are sent to mapper 1305.
- Mapper 1305 may work according to different modes.
- mapping control unit 1306 which selects the mapping mode to be applied to the words. If the third mode is selected, mapper 1305 receives mapping information from mapping control unit 1306 which may comprise a memory 1307 for storing a table containing mapping information. Mapping control unit 1306 is further configured to select in the third mapping mode the second and further mappings (i.e.
- mappings may be calculated at run time according to the rules given above. Alternatively they may be read out from the table in memory 1307 where they have previously been stored according to a communication system design.
- mapping modes as described above may be used alternatively, according to information provided by the network or by the receiving unit. Further they may be used alternately within a single frame according to a pre-defined pattern like with frame 1103 shown in Fig. 11. Information about such a pattern, as well as information about the mappings used may be sent to the receiving unit via control data transmitter 1308 and transmission channel 1312. Further, repetition control unit 1309 controls the repetition factor of repeater 1304 according to the requirements of mapping control unit 1306. For example, in the third mapping mode repetition control unit 1309 receives information from mapping control unit 1306 about the number of repetitions required for the selected mapping.
- pilot data is added and frames are combined in Pilot/Data frame creation unit 1310 before the information is modulated onto a carrier in modulator 1311.
- the modulated signal is sent to a receiving entity via channel 1312.
- transmitter 1300 may comprise further units like IF stage, mixers, power amplifier or antenna. From a signal flow point of view, such units might also be seen comprised in channel 1312, as they all may add noise to the signal or exert phase shift or attenuation on the signal.
- Units 1301 to 1311 may be implemented in dedicated hardware or in a digital signal processor. In this case the processor performs the method described herein by executing instructions read from a computer-readable storage medium like read-only memory, electrically erasable read-only memory or flash memory. These instructions may further be stored on other computer-readable media like magnetic disc, optical disc or magnetic tape to be downloaded into a device before it is brought to use. Also mixed hardware and software embodiments are possible.
- the present invention may be implemented using one mapping of words (pluralities of bits) to modulation states together with additional bit manipulation steps.
- a required bit manipulation step is the replacement of at least one bit by a fixed value to select a sub- plane according to the methods outlined above.
- the applied mapping is a Gray mapping, closest neighbours always differ in the value of only one bit. For example modulation state 1701 is assigned to the bit sequence "0000".
- the four closest neighbours 1702-1705 are assigned to bit sequences "0001", "0010", "0100” and "1000".
- Each sequence of four bits is associated with a further bit sequence which is obtained by bit inversion as explained below. Additionally, in both original and counterpart bit sequence, at least one of the bits, which has to be appropriately chosen, is replaced by a fixed value, e.g. 0 or 1. As a result of combining the first symbol resulting from the first bit sequence with the further symbol resulting from the further bit sequence, phase ambiguity is removed and one of two possible vector sum results 1706 or 1707 is obtained, depending on the fixed value of the replaced bit(s). Due to the effect of the reduction of the phase ambiguity to one, these one or more bits that carry said fixed value are referred to as PAO bit(s).
- the flow chart of Fig. 18 illustrates the steps necessary for removing phase ambiguity in transmission channel estimation.
- a first sequence or plurality of bits is received.
- step 1802 one or more bit(s) within the received plurality of bits is replaced by a fixed value. This corresponds to the selection of the PAO subset of modulation states to be used for the transmissions, which is described herein above.
- a bit separates the set of modulation symbols in such a way that for a first fixed value of said bit the remaining 50% of the modulation symbols can be represented by a first half-plane of the complex plane, and for a second fixed value of said bit the remaining 50% of the modulation symbols can be represented by a second half-plane of the complex plane, and the first and second half-plane are non-overlapping and adjacent and the boundary between the first and second half-plane contains the complex origin 0+jO, then this bit is referred to as a "half-plane bit". Examples for QPSK, 8-PSK and 16- QAM are shown in Figures 40 to 42, respectively.
- half-plane bit 4001, 4101 and 4201 selects vertically separated half-planes 4002, 4102, 4202 or 4003, 4103, 4203 depending on its fixed value.
- half-plane bit 4004, 4104 and 4204 selects vertically separated half-planes 4005, 4105, 4205 or 4006, 4106, 4206 depending on its fixed value.
- step 1803 the first plurality of bits is mapped to a modulation state according to a pre ⁇ defined Gray mapping of bit sequences to modulation states.
- step 1804 the first bit sequence is transmitted by modulating a carrier according to the modulation state assigned to the bit sequence in the Gray mapping.
- a sub-set of bits comprised in the bit sequence is determined for inversion in step 1805.
- Determining step 1805 may for example be carried out by executing a determining algorithm, by receiving data from a peer entity or by just reading data from a memory.
- step 1806 a further plurality of bits is obtained by taking the first plurality of bits from step 1801 and inverting those bits according to one of the inversion rules determined in step 1805.
- This further bit sequence is mapped onto a modulation state in step 1807 according to the same Gray mapping used in step 1803.
- step 1802 the bit replaced by a fixed value in step 1802 is selected such that the modulation state to which the further plurality of bits is mapped in step 1807 is also comprised within the PAO subset of modulation states selected with the bit operation in step 1802.
- step 1808 the first sequence is re-transmitted by transmitting the further sequence obtained in step 1806, that is by modulating the carrier according to the modulation state obtained in step 1807.
- Step 1809 queries whether there are further re-transmissions of the same first bit sequence to be done. If this is the case, the method returns to box 1805. If not, the method ends and the transmission and re-transmissions of the first bit sequence are done.
- one inversion rule is chosen to obtain a further bit sequence.
- This inversion rule can be expressed as a sub-set of bits which have to be inverted.
- a half-plane bit that is chosen to be used for phase ambiguity reduction to one i.e. according to above definition a PAO bit
- n be the number of bits mapped onto one PSK symbol (step 1901 ). From the n bits, choose n-1 bits for inversion candidates (step 1902). Inversion Rule(s): Determine the bits to be inverted by obtaining all possible combinations using 1 to all n-1 bits of the chosen n-1 bits (step 1903). Obtain the n-1 counterpart bit sequences from the original bit sequences by inverting the bit(s) from the above found combinations.
- One half-plane bit which is not chosen for inversion is the PAO bit, i.e. the half- plane bit to be replaced by a fixed value (step 1904).
- Inversion rules Invert only the 1st, only the 3rd, or both the 1st+3rd bit.
- Half-plane bits are the first and the second bit
- the second bit is selected as the PAO bit and therefore replaced by a fixed value 0 or 1.
- Modulation state 2001 is assigned to bit sequence "000".
- bit sequences "100", “001” and “101” are obtained, to which modulation states 2002-2004 are assigned.
- the symbols are combined by adding the vectors 2005-2008 representing the complex values of the carrier for these modulation states.
- the result is point 2009 for the fixed PAO bit value of 0, and point 2010 for the fixed PAO bit value of 1. Therefore the result can only have one amplitude value and one phase value.
- n be the number of bits mapped onto one ASK symbol (step 2101).
- the 8-ASK-modulation with the mapping of Fig. 22 is regarded.
- bars 2201, 2202 and 2203 indicate where bit 1 , 2 and 3, respectively, has a value of "1".
- the bit order assumed is b- ⁇ b 2 b 3 .
- Modulation state 2204 is assigned to bit sequence "011". according to the inversion rule above, the counterpart sequence, "001", is obtained by inverting the second bit. To the counterpart sequence "001", modulation state 2205 is assigned. The symbols are combined by adding vectors 2206 and 2207 representing the complex values of modulation states 2204 and 2205. By calculating the combination result of all first bit sequences with their counterpart sequence, it becomes apparent that the result is always point 2208. Therefore in this case there is no ambiguity left in the determination of the transmission channel properties.
- a PSK half-plane bit which has not been selected for inversion in the mentioned PSK part is selected as PAO bit for being replaced by a fixed value (step 2304).
- star-QAM of Fig. 24 is regarded.
- PSK part (see Figure 26) o
- the second bit 2402 is chosen for inversion.
- Inversion rule Invert the 2nd PSK bit 2402.
- Original bit sequences in Gray Coding 00, 01 , 11 , 10
- Counterpart sequences inverting 2nd bit 2402 01, 00, 10, 11
- ASK/PSK inversion rule bits o 1 st bit of ASK part 2403 is 3rd bit of ASK/PSK part o 2nd bit of PSK 2402 part is 2nd bit of ASK/PSK part Half-plane bits in the PSK part are the first and the second PSK bit 1st bit 2401 of PSK part is chosen as PAO bit to be replaced by a fixed value 0 or 1 , since the second PSK bit has been chosen for inversion.
- Modulation state 2405 is assigned to bit sequence "0010".
- the PSK sub-sequence is "00" and the ASK sub-sequence is "10".
- a special way of mixed ASK/PSK modulation is the combination of two orthogonal Gray Coded m-ASK / 2-PSK modulations.
- This mixed constellation is sometimes also called "square QAM", in the following simply sq-QAM.
- sq-QAM square QAM
- the bit to be inverted is the bit that has the same bit value for the exactly m/2 symbols with the smallest transmit power of the m-ASK part (step 2702). This is technically equivalent to the m symbols of the m-ASK/2-PSK with the smallest transmit power.
- the bit to be inverted is the bit that carries the 2-PSK part information (step 2703).
- step 2705 Select the bit carrying the PSK information of AP1 (i.e. the half-plane bit) to be the PAO bit, i.e. replaced by a fixed value (step 2705).
- the same inversion bit may be alternatively identified as the bit that carries the same bit value for the exactly m/2 symbols with the highest transmit powers of the m-ASK part.
- the in-phase component could be chosen to be either AP1 or AP2 with the quadrature component being the respective other one. This does not make a difference to the effect of ambiguity reduction. In one case the combination results have real values, in the other case they have imaginary values. It may further be noted that in the case of any square-QAM the selected half-plane bit from AP1 as PAO bit is also a half-plane bit of the square QAM; specifically it may be a half-plane bit 4201 or 4204 that represents the in-phase or co-phase half-plane 4202, 4203, 4205, or 4206, depending on its value, as can be seen in Figure 42.
- AP1 and AP2 Two components orthogonal to each other but not parallel to any of the real and imaginary axes could be chosen to be AP1 and AP2, respectively.
- AP1 is defined as the 2-ASK/2-PSK in Figure 29
- AP2 is defined as the 2-ASK/2-PSK in Figure 30.
- the bit that carries the PSK information is the 1st ASK/PSK bit 2802, which is equal to zero for a phase of 90 degrees against the real axis and equal to 1 for a phase of 270 degrees against the real axis (see Figure 30).
- o Inversion rule AP2 Invert the 1 st ASK/PSK bit 2802.
- the first bit as PAO bit is set to the fixed value "1".
- Modulation state 2805 is assigned to bit sequence "1011".
- the counterpart "1101” is obtained by inverting the second and third bit and is associated with modulation state 2806.
- Combination of both symbols is accomplished by adding the vectors 2807 and 2808 representing the respective complex values of the modulation states.
- the result is point 2809.
- the inversion rules are obtained by executing the algorithms described in the present invention.
- the inversion rules are determined for each modulation scheme used in the communication system or device and are stored in a memory or look-up table for quickly obtaining the inversion rules.
- the inversion rules are coded into a hardware or software module, where step 1805 is equivalent to controlling which of those hardware or software modules is chosen during transmission.
- the target is an optimum reduction of ambiguity levels by combining complex values of the first and further pluralities of bits mapped onto modulation states.
- a channel estimation for this is generally inferior compared to a situation of a single resultant complex value, it may be beneficial from a demodulated LLR value point of view for the data bits transmitted in the pluralities of bits, or from the point of view of reducing the loss of transmission capacity.
- bit bi is determined as the bit to be inverted in the inversion rule.
- the number of half-plane bits that have to be used as PAO bits with a fixed value depends on the number of phase levels that the inversion rules alone can achieve. If the result achieved by the inversion rules comprises two phase levels, then setting one half-plane bit as PAO bit is sufficient. If the result achieved by the inversion rules comprises four phase levels, then setting two half- plane bits as PAO bits is required. Generally for removal of phase ambiguity the number of required PAO bits is the dual logarithm (logarithm to the base 2) of the number of phase levels that results from the used inversion rules. It may be noted that the fixed bit value of a first PAO bit and the fixed bit value of a second PAO bit may be chosen independently. Of course the more PAO bits are used, the higher the loss of transmission capacity.
- the above strategies for reducing the amplitude or phase levels for ASK and PSK are also applicable to a mixed ASK/PSK.
- the 4-ASK part is modified to reduce the number of amplitude levels from four to one by inverting the first ASK bit.
- the 4-PSK part is not modified, such that altogether the only inversion rule is the inversion of 4-ASK/4-PSK bit number three, being equivalent to 4-ASK bit number one.
- the combination results in one amplitude and four phase levels, equivalent to a QPSK.
- vector 3801 represents the constellation point for the bit sequence "0010".
- the first ASK bit is the third bit in the sequence. Therefore the inversion rule determines to invert the third bit, which yields bit sequence "0000" represented by vector 3802.
- the combination of both transmissions yields value 3803.
- Other possible combination results for different values of the bit sequence are 3804, 3805 and 3806.
- both the first and the second bit have to be set to fixed values. Depending on the combination of these fixed values, one single of the combination results 3803, 3804, 3805 and 3806 is obtained.
- a suboptimum reduction of ambiguity levels can be achieved if either of the AP1 or AP2 inversion rules are modified.
- the AP1 inversion rule is equivalent to reducing ambiguities for an m-ASK part
- the AP2 inversion rule is equivalent to reducing ambiguities for a 2-PSK part.
- the reduction for the m-ASK part of AP1 should follow the extended algorithm as outlined above for reducing n amplitude levels of ASK to 2 k amplitude levels.
- the AP2 inversion rule for reducing the 2-PSK part should be replaced by the inversion rule for reducing the m-ASK part of AP2 to 2 k as outlined in the extended algorithm above. It should be mentioned that of course the value of k for AP1 can be different from the value of k for AP2. For the required number of PAO bits to remove phase ambiguity complete, see the explanation further above. In the example of Figure 39 it is shown that a combination of one amplitude level and four phase levels is achieved by
- both half-plane bits b1 and b2 of the 16- QAM have to be set to fixed values.
- bit sequence "0010” is represented by vector 3901.
- AP1 inversion rule determines the third bit b 3 of the bit sequence as bit to be inverted (being the second bit of bi and bs).
- AP2 inversion rule determines the fourth bit b 4 to be inverted (being the second bit of b 2 and b 4 ).
- the resulting bit sequence for the second transmission is "0001", represented in the complex plane of modulation states by vector 3902.
- the combination of both modulation states achieved by addition of vectors 3901 and 3902, yields complex point 3903.
- bit sequence "0011” represented by vector 3904 the bit sequence for the second transmission is "0000" represented by vector 3905.
- the combination of both values again yields complex value 3903.
- the original constellation may be different from what is shown in the examples. However the procedure as outlined above can still be used as long as the mapping of bit sequences is compliant to the Gray coding/mapping strategy.
- bit sequences in a frame have to use the approach as disclosed in the present invention. This also applies to the bit manipulation implementation.
- a transmitter 3500 is illustrated, which can be used to transmit data according to the method described above.
- a bit stream to be transmitted is encoded in encoder 3501.
- the encoded bit stream is interleaved in random bit interleaver 3502.
- S/P unit 3503 groups of bits are combined into bit sequences (pluralities of bits) which are later represented by one transmitted symbol.
- symbols are repeated for re-transmission. The repetition factor and the ratio of symbols to be repeated is depending on the particular version of the method.
- Inversion bit determining unit 3506 which may comprise a memory 3507 for storing a table containing bit inversion information, determines particular bits of repeated bit sequences to be inverted in the selective bit inverter 3508, depending on the modulation scheme as described above. The bits may be determined for inversion based on information received from a peer entity, by carrying out respective algorithms or by reading stored information from a memory. Inversion bit determining unit 3506 may further comprise sub-units (3509-3512) carrying out sub- steps of the methods for determining the sub-set(s) of bits for inversion and sub-steps of the methods for determining the sub-set(s) of bit(s) for replacement as PAO bit(s) as described above.
- Bit inverter unit 3508 may further comprise a bit replacement unit to replace PAO bit(s) by a selected fixed value.
- Transmitter 3500 may further comprise a control data transmitter 3513 transmitting information about repetition of bit sequences and about inverted bits via the same or another transmission channel.
- Mapper 3514 maps symbols, representing one bit sequence each, to modulation states using a mapping which is invariant at least between transmission of a symbol and re ⁇ transmission of the same symbol with a part of the bits inverted, like described above.
- pilot data is added and frames are combined in Pilot/Data frame creation unit 3515 before the information is modulated onto a carrier in modulator 3516.
- the modulated signal is sent to a receiving entity via channel 3517.
- transmitter 3500 may comprise further units like IF stage, mixers, power amplifier or antenna. From a signal flow point of view, such units might also be seen comprised in channel 3517, as they all may add noise to the signal or exert phase shift or attenuation on the signal.
- Units 3501 to 3516 may be implemented in dedicated hardware or in a digital signal processor. In this case the processor performs the method described herein by executing instructions read from a computer-readable storage medium like read-only memory, electrically erasable read-only memory or flash memory. These instructions may further be stored on other computer-readable media like magnetic disc, optical disc or magnetic tape to be downloaded into a device before it is brought to use. Also mixed hardware and software implementations are possible.
- the described techniques reduce the data transmission capability (capacity) of the transmission channel. Therefore the receiver has to know how to treat the received original and counterpart data. This knowledge may for example be obtained by signalling from the transmitter to the receiver.
- Preferably some pre-determined patterns are defined for a communication system, which define the location and method to which part of the data and in which fashion the described method is applied. Then it is sufficient to signal a simple parameter that points to or represents one of these pre-defined patterns, from which the receiver can reconstruct the particular method and fashion employed by the transmitter.
- the methods outlined above may for example mean that one or more of the bits transmitted is replaced or punctured. In other words, the original value of such bit(s) is lost to the receiver. Since the receiver, by way of the method described in the preceding paragraph, may have knowledge about which of the bits are affected in such a way, it is able to adapt its output to this situation.
- the receiver should set the information for such affected bits to a value that signifies "unknown". For example if the receiver (demodulator) uses LLR information as the output, an LLR value representing "unknown" is 0. If it uses bit probabilities, the respective probability value is 0.5. If hard decision is used, i.e.
- the receiver may randomly generate a bit value since it has no information at all on which it could base the decision for the value of said replaced or punctured bit.
- a bit that is replaced or punctured in the transmitter is part of a bit sequence after FEC encoding, i.e. adding of redundancy.
- the replacement or puncturing of a bit merely removes a part of the redundancy, but does not automatically introduce a loss of bit information or bit error.
- the remaining transmitted redundancy may still be able to compensate for such loss of redundancy such that after FEC decoding no bit or block error results.
- Fig. 45 shows an exemplary structure of a receiver which could be used to receive data transmitted by transmitter 1300 or 3500.
- Control data receiver 4510 may receive respective information from the transmitter. The received data may directly specify the replaced bits, or it may specify a pre-defined scheme stored for example in table 4511 , from which this information may be derived. Unit 4512 uses this information to control unit 4508 accordingly.
- unit 4507 may be controlled to skip calculation of meaningless LLR values in order to reduce its calculation requirements.
- Transmitter 1300 or 3500 and/ or receiver 4500 may be part of a base station 3600 as shown in figure 36.
- a base station may further comprise data processing units 3601 and 3602, a core network interface 3603 and a corresponding receiver 3604 which may be constructed as shown in Figure 45.
- a counterpart to base station 3600 might be a mobile station 3700 as shown in Fig. 37.
- a mobile station may further comprise antenna 3701 , antenna switch 3702, data processing unit 3703 and controller 3704.
- Mobile station 3700 might be a mobile phone or a module to be integrated into a portable computer, PDA, vehicle, vending machine or the like.
- a mobile phone may further comprise mixed signal unit 3705 and a user interface comprising keyboard 3706, display 3707, speaker 3708 and microphone 3709.
- a method and a transmitter according to the above described embodiment may completely remove ambiguity in the combination result of retransmitted ⁇ symbols. This may advantageously improve the reliability of the channel estimation in a digital communication system.
- a better channel estimation has the advantage of reduced error rates and may provide connection with wireless communication systems in areas of weak coverage, fast fading conditions and other adverse circumstances.
- the general and detailed description have shown how data symbols can be used for purposes of e.g. channel estimation. This process is shown in a simplified way again in Figure 46a and 46b, assuming that the phase ambiguity is reduced to one by fixing a certain bit; this bit is denoted as "pilot bit" in the figures.
- the pilot bit is multiplexed together with the data bits to generate the original sequence, which is ultimately used to generate the original symbol and the at least one counterpart symbol.
- the pilot bit is multiplexed together with the data bits to generate the original sequence, which is ultimately used to generate the original symbol and the at least one counterpart symbol.
- what kind of data may actually be preferably transmitted on such symbols. This is outlined as most applicable for a mobile radio system scenario; however the same considerations can be applied mutatis mutandis to fixed line or other types of communication systems.
- Original Symbol A symbol that is generated from an original bit sequence as illustrated in Figure 46.
- Counterpart Symbol(s) At least one symbol that is generated from an original symbol, or from at least one counterpart sequence to an original bit sequence, as illustrated in
- Quasi-Pilot Symbol The combination of an original symbol and the corresponding counterpart symbol(s).
- Pilot Symbol A single symbol that can be used as a reference symbol for channel estimation.
- Simple Data Symbol A single symbol conveying data bits to one or more receivers.
- Simple Control Symbol A single symbol conveying information that is required or helpful for successful system operation.
- a simple data symbol may convey any kind of data. This may include control data or signalling data, as well as data pertaining to a user or service application such as voice data, video data, software data etc.
- Simple control symbols on the physical layer are generally used for signalling purposes. For signalling purposes a lot of information needs to be transmitted between the network and the terminals. This information includes signalling messages generated above the physical layer, as well as the required physical layer control channels needed for system operation but not necessarily visible for higher layer functionality. This kind of information is usually transmitted as simple control symbols. The following channels are explained for their use in relation to the UMTS network. Other networks may use different names, however regardless of the name there will exist some data that fulfils the same or similar functionalities as those described here. Therefore the description should be understood as to be not restricting only to a UMTS system or the given names of channels.
- a synchronisation channel is needed for the cell search.
- frame and slot synchronisation is obtained, as well as information on the group the cell belongs to.
- a broadcast channel is used to transmit information specific to the network or for a given cell.
- the most typical data needed in every network is the available random access codes and access slots in the cell, or the types of transmit diversity methods used with other channels for that cell.
- this channel is needed for transmission with relatively high reliability in order to reach all the users within the intended coverage area.
- a forward access channel carries control information to terminals known to locate in the given cell, for example after a random access message has been received by the base station. It may also be used to transport packet data to a terminal.
- a paging channel carries data relevant for the paging procedure, that is when the network wants to initiate communication with the terminal.
- a simple example is a speech call to a terminal; the network transmits the paging message to the terminal in those cells belonging to the location area that the terminal is expected to be in.
- a random access channel is intended to be used to carry control information from the terminal to the network. It is typically used for signalling purposes, to register the terminal after power-on to the network, or to perform location update after moving from one location to another, or to initiate a call. For proper system operation the random access channel must be heard from the whole desired cell coverage area, which requires a relatively high reliability of the transmitted data.
- An acquisition indicator channel is used to indicate from the base station the reception of the random access channel signature sequence. Therefore it needs to be heard by all terminals in the cell, which requires a relatively high reliability of the transmitted data. This channel commonly is not visible to higher layers.
- a paging indicator channel operates together with a paging channel to provide terminals with efficient sleep mode operation. Consequently this channel has to be heard by all terminals in the cell, which requires a relatively high reliability of the transmitted data.
- a shared control channel carries necessary physical layer control information to enable reception/demodulation/decoding of data on a shared data channel, and to perform possible physical layer combining of the data sent on a shared data channel in case of retransmission or an erroneous data packet
- a dedicated physical control channel may furthermore carry necessary control information containing feedback signals, such as ARQ acknowledgements (both positive ACK and negative NAK), as well as link quality information (such as a channel quality indicator CQI).
- ARQ acknowledgements both positive ACK and negative NAK
- link quality information such as a channel quality indicator CQI
- Modulation scheme used for data transmission e.g. BPSK, QPSK, 8-PSK, 16- QAM, 64-QAM, etc.
- First transmission / retransmission indicator indicating whether a receiver should combine the actual received data with previously received data, or whether buffers should be flushed and filled only with new data
- Orthogonalization may for example be achieved by spreading or multiplication with orthogonal sequences, e.g. OVSF sequences that result from a Walsh-Hadamard matrix.
- orthogonal sequences e.g. OVSF sequences that result from a Walsh-Hadamard matrix.
- a possibility to reduce the correlation is scrambling or multiplication with non-orthogonal sequences such as pseudo-noise sequences, e.g. Gold sequences.
- Orthogonalization or correlation reduction techniques may also be applied to the present invention. This can be accomplished by applying the symbol-based orthogonalization or correlation reduction techniques jointly to the Quasi-Pilot Symbol, or by applying these techniques individually to each of the original and counterpart quasi-pilot symbol(s). This is shown for the multiplication with a spreading code in Figures 57-58.
- bit-based orthogonalization or correlation reduction techniques are applied to the original and counterpart sequence(s) identically, or individually to each of the original and counterpart bit sequence(s).
- the quasi-pilot components may also be spread by bandwidth expansion. Again this spreading may be done based on the constituent components individually, or jointly based on the quasi-pilot symbol.
- Figures 59-60 show an example of bandwidth spreading with a spreading code.
- Figure 47 shows a simple case where the ratio of pilot symbols to shared control symbols is one, i.e. the number of such symbols per frame is identical. Therefore it is easy to combine each one pilot symbol with each one control symbol to one quasi-pilot symbol. However in a system it is possible that the said ratio is not equal to one.
- One solution is that just as many quasi-pilot symbols are constructed as there are both pilot and control symbols. For example if there are n pilot symbols and m control symbols, then min(n,m) quasi-pilot symbols may be generated, and additionally either n-m pilot symbols or m-n control symbols are transmitted as simple symbols according to prior art schemes.
- the transmission using quasi-pilots requires a modulation scheme that conveys at least two bits per symbol, it may occur that the data that pertains to the same transport channel (e.g. shared control channel) cannot be completely mapped onto quasi-pilot symbols. Generally the excess data may be transmitted using a modulation scheme that is independent from the quasi-pilot modulation scheme, as shown in Figure 65. From a uniform design point of view however it may be preferable to transmit such a transport channel using a single modulation scheme. In such a case it may be preferable to either reduce the number of symbols, or optionally to repeat some of the non-quasi-pilot symbols to fill out the available bandwidth, as shown in Figure 66.
- control or signalling data within the first time slot(s) of a frame.
- shared data channels or other channels which transmit user data at least partially in a time-multiplexed fashion it may be preferable from a timing point of view to transmit a control channel well in advance to the corresponding data channel to which the control data pertains, in order to allow a receiver time to process the control data and take the required actions for proper reception of the data information.
- This is particularly applicable for shared control and data channels.
- An example for a conventional solution is given in Figure 47 for an OFDM system.
- An OFDM frame consists of several time slots, in this case 7 "OFDM Symbols", and of several carrier frequencies, here 8 "subcarriers".
- the pilot and shared control symbols are frequency-multiplexed inside the first OFDM symbol; both together are time- multiplexed with the shared data symbols.
- FIG. 48 A corresponding solution according to the present invention is shown in Figure 48.
- This Figure shows a time-multiplexing of quasi-pilot symbols with shared data symbols.
- the quasi-pilot symbols contain the multiplexing of pilot bits and shared control bits according to Figure 46. Since in this case a quasi-pilot symbol, i.e. an original and counterpart symbol carry shared control information, one quasi-pilot symbol can be used for channel estimation, and each of the constituent (original and counterpart) symbols carries the shared control information.
- pilot and control information are multiplexed ultimately onto modulation symbols, this can be interpreted as a "modulation multiplexing" or “modulation division multiplexing" (MDM) of pilot and control information onto the same symbol.
- MDM modulation division multiplexing
- the multiplexing of original and counterpart symbols is according to Figure 48 in frequency-domain, therefore it is called “frequency counterpart multiplexing" (FCM).
- FCM frequency counterpart multiplexing
- Figure 50 and Figure 51 show a similar approach however here the quasi-pilot and shared data symbols are frequency-multiplexed.
- parameters or components of these symbols are for example the real part, imaginary part, power, amplitude, phase, or terms or quantities derived from one or more of these.
- the target of improving the channel estimation capability is achieved by reducing the number of possible amplitude levels, achieved by reducing the number of different combined values obtainable for all data word values, by adding for each data word value amplitude values associated with said data word value according to a first and at least one further mappings, to a lower number than the number of amplitude levels within said first mapping.
- the target of improving the channel estimation capability is achieved by reducing the number of possible power levels, achieved by reducing the number of different combined values obtainable for all data word values, by adding for each data word value power values associated with said data word value according to a first and at least one further mappings, to a lower number than the number of different power levels within said first mapping.
- the target of improving the channel estimation capability is achieved by reducing the number of possible phase levels, achieved by reducing the number of different combined values obtainable for all data word values, by adding for each data word value phase values associated with said data word value according to a first and at least one further mappings, to a lower number than the number of different phase levels within said first mapping.
- Figures 62-64 show exemplary solutions for QPSK, 8-PSK, and 16-QAM respectively.lt should be noted that in this and in the following sections the terms "original constellation”, "counterpart constellation” are used to describe the behaviour on the symbol level, and are therefore not restricting the applicability to just one of the approaches for the generation of a Quasi-Pilot according to Figure 46.
- the unique target power level after combination is set to 2.0. Then it is defined that the symbols should have a target phase level after combination of 0. This leads in the last step to the following for the counterpart constellation:
- the actual estimation of a channel coefficient h in such a case may preferably employ the following strategy.
- the power levels of a symbol from an original and counterpart constellation is denoted by p 0 and p c respectively, and likewise the amplitude levels by a 0 and a c , and the phase levels by ⁇ 0 and ⁇ c .
- the amplitude level combination is also preferable in those cases, as the ASK prefers amplitude level combination to power level combination due to just a single required counterpart constellation.
- the unique target amplitude level after combination is set to 8/sqrt(21). Then we define the target phase level after combination of 0. This leads in the last step to the following for the counterpart constellation:
- the effect to arrive at the counterpart constellation may again be either achieved by modifying the mapping rule between bit sequence to modulation state, or by modifying the original bit sequence into a counterpart sequence prior to mapping said counterpart sequence to a modulation state according to the mapping rule that is used also for the original bit sequence mapping. It may be noted that in the case of power or amplitude or phase combining a single counterpart constellation can be constructed that is always sufficient to achieve the goal of power/amplitude/phase level reduction, provided that the counterpart constellation does not have to have the same layout in the complex plane as the original constellation; such a different layout can for example be seen comparing the right-hand and left-hand constellations in Figure 6.
- the described possibilities of using the quasi-pilot for data transmission are applicable regardless of the method how the reduction of ambiguity levels for the quasi-pilot is achieved. Therefore it is also preferable to transmit for example a shared control channel using a quasi-pilot like in Figures 48-56 in case that the quasi-pilot has been generated using e.g. the power- and phase-combination method.
- a quasi-pilot like in Figures 48-56 in case that the quasi-pilot has been generated using e.g. the power- and phase-combination method.
Abstract
Description
Claims
Priority Applications (6)
Application Number | Priority Date | Filing Date | Title |
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US11/718,500 US7965793B2 (en) | 2004-11-03 | 2005-09-30 | Method for reducing ambiguity levels of transmitted symbols |
BRPI0516876-7A BRPI0516876A (en) | 2004-11-03 | 2005-09-30 | method for transmitting data in a digital communication system, computer readable storage media, transmitter for a digital communication system, base station for a mobile communication system, method for receiving data in a digital communication system, receiver for a digital communication system, base station for a digital communication system, mobile station for a digital communication system |
MX2007005387A MX2007005387A (en) | 2004-11-03 | 2005-09-30 | Method for reducing ambiguity levels of transmitted symbols. |
JP2007539480A JP4722135B2 (en) | 2004-11-03 | 2005-09-30 | Method for transmitting data in a digital communication system |
EP05796388.6A EP1807960B1 (en) | 2004-11-03 | 2005-09-30 | Method for reducing ambiguity levels of transmitted symbols |
US13/103,220 US8422589B2 (en) | 2004-11-03 | 2011-05-09 | Method and apparatus for transmitting data in a digital communication system, and computer-readable storage medium relating thereto |
Applications Claiming Priority (10)
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EP04026071.3 | 2004-11-03 | ||
EP04026071A EP1655877A1 (en) | 2004-11-03 | 2004-11-03 | Method and transmitter structure reducing ambiguity by repetition rearrangement in the bit domain |
EP04026082.0 | 2004-11-03 | ||
EP04026082A EP1655878A1 (en) | 2004-11-03 | 2004-11-03 | Method and transmitter structure reducing ambiguity by repetition rearrangement in the symbol domain |
PCT/EP2005/007929 WO2006048060A1 (en) | 2004-11-03 | 2005-07-20 | Method and transmitter structure reducing ambiguity by repetition rearrangement in the symbol domain |
PCT/EP2005/007928 WO2006048059A1 (en) | 2004-11-03 | 2005-07-20 | Method and transmitter structure reducing ambiguity by repetition rearrangement in the bit domain |
EPPCT/EP2005/007928 | 2005-07-20 | ||
EPPCT/EP2005/007929 | 2005-07-20 | ||
PCT/EP2005/008081 WO2006048061A1 (en) | 2004-11-03 | 2005-07-25 | Method and transmitter structure removing phase ambiguity by repetition rearrangement |
EPPCT/EP2005/008081 | 2005-07-25 |
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US11/718,500 A-371-Of-International US7965793B2 (en) | 2004-11-03 | 2005-09-30 | Method for reducing ambiguity levels of transmitted symbols |
US13/103,220 Continuation US8422589B2 (en) | 2004-11-03 | 2011-05-09 | Method and apparatus for transmitting data in a digital communication system, and computer-readable storage medium relating thereto |
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WO2006048090A1 true WO2006048090A1 (en) | 2006-05-11 |
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EP (1) | EP1807960B1 (en) |
KR (1) | KR20070090900A (en) |
BR (1) | BRPI0516876A (en) |
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WO2009017152A1 (en) * | 2007-07-30 | 2009-02-05 | Kyocera Corporation | Ofdm transmitting apparatus, ofdm receiving apparatus, and interleaving method |
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- 2005-09-30 BR BRPI0516876-7A patent/BRPI0516876A/en not_active Application Discontinuation
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- 2005-09-30 WO PCT/EP2005/010602 patent/WO2006048090A1/en active Application Filing
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BRPI0516876A (en) | 2008-09-23 |
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MX2007005387A (en) | 2007-08-14 |
EP1807960B1 (en) | 2013-11-06 |
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