EP3665883A1 - Apparatuses and methods for generating an apsk signal - Google Patents
Apparatuses and methods for generating an apsk signalInfo
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- EP3665883A1 EP3665883A1 EP17797606.5A EP17797606A EP3665883A1 EP 3665883 A1 EP3665883 A1 EP 3665883A1 EP 17797606 A EP17797606 A EP 17797606A EP 3665883 A1 EP3665883 A1 EP 3665883A1
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- Prior art keywords
- digital signal
- communication apparatus
- constellation
- circle
- signal points
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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
Definitions
- the constellation power is normalized to 1 for simplicity.
- the distance between two adjacent concentric circles is set to D.
- Such constellation is called as (N, K, D)-CPP constellation, as can be seen in figure 2.
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- Engineering & Computer Science (AREA)
- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Digital Transmission Methods That Use Modulated Carrier Waves (AREA)
Abstract
The invention relates to a transmitter communication apparatus (101) for communicating with a receiver communication apparatus (131) via a communication channel. The transmitter communication apparatus (101) comprises: a processing unit (105) configured to generate a stream of modulation symbols and map the modulation symbols to a digital signal constellation for generating a modulated signal, wherein the digital signal constellation comprises a plurality of digital signal points regularly spaced on at least two concentric circles having respective predetermined radii, wherein each circle has the same number of digital signal points and the digital signal points on each circle have the same phase with respect to the digital signal points on the other circles; and a communication interface (103) configured to transmit the modulated signal via the communication channel to the receiver communication apparatus (131). The invention also relates to a corresponding receiver apparatus (131) comprising a processing unit (135) and a communication interface (133) for communicating with the transmitter communication apparatus (101).
Description
DESCRIPTION
APPARATUSES AND METHODS FOR GENERATING AN APSK SIGNAL TECHNICAL FIELD
In general, the present invention relates to the field of wireless communication. More specifically, the present invention relates to a transmitter communication apparatus and a receiver communication apparatus as well as corresponding methods for generating a modulated signal.
BACKGROUND
In single carrier communication systems, physical characteristics— such as amplitude or phase— of a unique frequency tone are modulated to transfer information between a transmitter and a receiver. This is opposed to multi-carrier systems in which multiple frequency tones may be modulated in parallel. Nowadays, the single carrier
communication systems are broadly employed for high-rate point-to-point wireless communication links and for optical fiber communications.
The frequency tone is classically modulated in phase and amplitude— or equivalently in the real and imaginary domain of a complex representation of the phase and amplitude. The number of possible values for a modulation scheme is usually finite so as to make decoding tractable. Hence, as the rate of a communication link for a given bandwidth occupation increases, the number of discrete points in a so-called constellation of phases and amplitudes needs to increase dramatically. Common constellations come from square quadrature amplitude modulations (QAM) which form the vast majority of constellation families used in practical systems, due in particular to their practical labeling properties and decoding simplicity. Figure 8 illustrates a classical constellation used in such systems. The constellation pictured contains 4096 points, wherein each element in this constellation uniquely represents a single log2 4096 = 12 bit sequence.
When high-density constellations are used, for instance, in high-rate point to point wireless communication links, technical problems appear. The square QAM constellations are very sensitive to phase noise, which in contrast to additive white Gaussian noise does not simply add a small error on the received signal but actually rotates it. This rotation
means that points closer to the center of the constellation are much less affected by the phase noise than points farther away from the center. Due to this effect, the density of the constellation points should actually be changed depending on their distance from the center of the constellation— a feature not supported in the design of square QAM constellations.
The peak-to-average power ratio (PAPR) of the QAM constellation greatly increases as the number of points in the constellation grows, which in turns requires the power amplifiers in the transmitter to have a very wide dynamic range in order to accommodate the signals transmitted at both the constellation points closer to the center and the outermost ones. Since high-rate links employing such dense constellations also transmit with extremely high power, the cost of amplifiers supporting both the high power requirement and high dynamic range increases significantly. In practical communication systems, the problem regarding the phase noise in QAM constellations can be avoided or compensated in some limited ways by using better oscillators, up to the point where the phase noise is not the dominant source of errors in the system, or applying more advanced protection of the information bits carried in the outer points of the QAM constellation. Both solutions may be employed concurrently, which is in fact considered by most actors in the related field at the time of application.
For the problem of peak-to-average power ratio (PAPR) under the regulatory constraints of band occupancy, there is no satisfying existing solution in the prior art for single carrier systems and most works fall back into using more expensive power amplifiers with the required dynamic range.
Irregular Amplitude and Phase Shift Keying (APSK) constellations have been used in some applications and standards, especially Digital Video Broadcasting - Satellite - Second Generation (DVB-S2). These solutions typically use Gray labeling to support bit- interleaved coded modulation (BICM) applications, as shown in the patent US7123663 B2. Additionally, their density is not high enough since they are limited to 32 constellation points. The impact of the phase noise is then limited in this case, but so is the throughput that can be achieved by means of this solution. In practice, this also prevents the adoption of more advanced modulation and coding schemes (MCS).
Recent academic works have shown that an optimized constellation design based on mutual information in phase noise channels converges towards irregular APSK constellations (see Kayhan et al., IEEE Trans. Wireless Commun., 2014 and Yang et al., IEEE Commun. Lett., 2013). These results confirm the potential of the APSK
constellations, especially when the density increases. However, since they are not built on a predefined structure, the complexity of the decoding operations for such optimized constellations is rather high. They thus serve as benchmarks, and as confirmation of the validity of the intuition, rather than as constructive models. A low-density regular APSK constellation with Gray labeling has also been proposed in Liu et al., IEEE Commun. Lett., 201 1 . This solution exclusively supports Gray mapping and it is thus suitable only for bit-interleaved coded modulation (BICM) approaches. In this context it does not target applications with high data rates, for which multi-level coding approaches are preferred, and does not support advanced modulation and coding schemes (MCS).
Another state-of-the-art solution worth mentioning is the circularly symmetric 64-point constellation as disclosed in the PCT/IB 1995/000893 application, in which a non-scalable structure is proposed for the 64-point constellation and is able to yield higher robustness regarding the phase noise than the quadrature amplitude modulations (QAM), while guaranteeing a high energy efficiency. Additionally, a differential encoder (and decoder) able to preserve the constellation structure is also proposed.
However, the above approaches still have several critical problems: lack of advanced modulation and coding schemes (MCS) as well as lack of support for multi-level coding approaches. Moreover, no reduction on the peak-to-average power ratio (PAPR) is targeted.
In light of the above, there is a need for improved communication apparatuses as well as corresponding methods for generating a modulated signal in an efficient and low-complex manner.
SUMMARY
It is an object of the invention to provide improved communication apparatuses as well as corresponding methods for generating a modulated signal in an efficient and low-complex manner.
The foregoing and other objects are achieved by the subject matter of the independent claims. Further implementation forms are apparent from the dependent claims, the description and the figures.
Generally, the present invention relates to a transmitter communication apparatus and a receiver communication apparatus as well as corresponding methods for generating a modulated signal on the basis of a digital signal constellation. More specifically, embodiments of the invention provide a dense digital signal constellation which can be adapted to high phase noise and still has a low peak-to-average power ratio (PAPR). The constellations built upon the embodiments of the invention are called constant phase polar (CPP) constellations. In such constellations the digital signal points are arranged in concentric circles, wherein an angular distance between two adjacent signal points on any circle is constant. In other words, each circle carries the same number of digital signal points, and the latter are aligned on semi-lines starting from the center.
The embodiments of the invention offer several significant advantages compared to the prior art: first of all, the phase of each point in conventional Amplitude and Phase Shift Keying (APSK) constellations can take any value, which complicates the receiver design since a very large bit width is required at the Analog-to-digital conversion (ADC) and very precise slicing algorithms need to be devised at the receiver. In contrast, according to embodiments of the invention the phase of the digital signal points in the first concentric circle in the constant phase polar (CPP) constellations can constrain the phase of the digital signal points in all the other concentric circles. This simplifies the designs of both the Analog-to-digital conversion (ADC) and the slicer.
Secondly, the embodiments of the invention allow treating the amplitude modulation (AM) and phase modulation (PM) parts separately in order to guarantee that the power amplifier (PA) can always work with a finite number of constant envelope signals, improving its efficiency. Moreover, the embodiments of the invention also reduce the effect of non-
linearity of the amplification even for higher values of low peak-to-average power ratios (PAPR).
Thirdly, the constant phase polar (CPP) constellations according to the embodiments of the invention can be constructed in a fully scalable way. This allows obtaining
constellations whose number of points is any power of 2 without substantial changes in the set-partitioning or slicing. It is worth noting that this is often not the case for -QAM constellations, wherein M is typically chosen as an even power of 2 to simplify detection and equalization procedures. This limitation is not present in the constant phase polar (CPP) constellations by construction. In practice, the embodiments of the invention simplify rate and link adaptation procedures significantly, allowing the adoption of advanced and sophisticated modulation and coding schemes (MCS).
Finally, the constant phase polar (CPP) constellations according to the embodiments allow constructing a set-partitioning of the digital signal points in a straightforward and scalable way to support multi-level coding. This provides high suitability for high data link applications, in which adoption of dense constellations is necessary.
More specifically, according to a first aspect the invention relates to a transmitter communication apparatus for communicating with a receiver communication apparatus via a communication channel. The transmitter communication apparatus comprises: a processing unit configured to generate a stream of modulation symbols and map the modulation symbols to a digital signal constellation for generating a modulated signal, wherein the digital signal constellation comprises a plurality of digital signal points regularly spaced on at least two concentric circles having respective predetermined radii, wherein each circle has the same number of digital signal points and the digital signal points on each circle have the same phase with respect to the digital signal points on the other circles; and a communication interface configured to transmit the modulated signal via the communication channel to the receiver communication apparatus. As used herein, "regularly spaced on at least two concentric circles" means that the angular distance between two neighboring/adjacent digital signal points is constant.
Thus, an improved transmitter communication apparatus is provided, allowing generating a modulated signal in an efficient and low-complex manner.
In a further possible implementation form of the first aspect, the most inner circle has a radius r0 and wherein the distance Δ between the radius of the next larger circle and the radius r0 of the most inner circle is smaller than the radius r0 of the most inner circle.
In a further possible implementation form of the first aspect, the plurality of digital signal points are equally spaced on at least three concentric circles and wherein the distance Δ between respective radii of respective circles is constant.
In a further possible implementation form of the first aspect, the processing unit is configured to determine the distance Δ between respective radii of respective circles so as to generate a constellation with unit power on the basis of the following equation:
-ro0V-l)+ (W-l)(4W-2-r0 2 (W+l))
Δ= 3
(W-1)(2W-1) wherein N denotes the total number of concentric circles.
In a further possible implementation form of the first aspect, the processing unit is configured to determine the radius r0 of the most inner circle on the basis of the number of digital signal points per circle and white noise information.
In a further possible implementation form of the first aspect, the processing unit is further configured to map the modulation symbols to the digital signal constellation such that for each modulation symbol a first subset of the modulation symbol identifies the concentric circle the respective digital signal point is located on and a second subset of the modulation symbol identifies the phase or angle of the respective digital signal point.
In a further possible implementation form of the first aspect, each modulation symbol is represented by a bit sequence of m bits with the total number of digital signal points M given by M = 2m and wherein the first subset of a respective modulation symbol comprises the first n bits of a respective bit sequence and the second subset of a respective modulation symbol comprises the last k bits of a respective bit sequence with k = m— n.
In a further possible implementation form of the first aspect, the processing unit is further configured to adapt the digital signal constellation on the basis of information about the
communication channel, in particular the power spectral density of white noise and phase noise.
According to a second aspect the invention relates to a method of operating a transmitter communication apparatus for communicating with a receiver communication apparatus via a communication channel. The method comprises: generating a stream of modulation symbols; mapping the modulation symbols to a digital signal constellation for generating a modulated signal, wherein the digital signal constellation comprises a plurality of digital signal points regularly spaced on at least two concentric circles having respective predetermined radii, wherein each circle has the same number of digital signal points and the digital signal points on each circle have the same phase with respect to the digital signal points on the other circles; and transmitting the modulated signal via the
communication channel to the receiver communication apparatus. Thus, an improved method of operating a transmitter communication apparatus is provided, allowing generating a modulated signal in an efficient and low-complex manner.
According to a third aspect the invention relates to a receiver communication apparatus for communicating with a transmitter communication apparatus via a communication channel. The receiver communication apparatus comprises: a communication interface configured to receive a modulated signal via the communication channel from the transmitter communication apparatus; and a processing unit configured to extract a plurality of modulation symbols from the modulated signal and to demap the plurality of modulation symbols to a digital signal constellation, wherein the digital signal constellation comprises a plurality of digital signal points regularly spaced on at least two concentric circles having respective predetermined radii, wherein each circle has the same number of digital signal points and the digital signal points on each circle have the same phase with respect to the digital signal points on the other circles. Thus, an improved receiver communication apparatus is provided, allowing generating a modulated signal in an efficient and low-complex manner.
In a further possible implementation form of the third aspect, the processing unit is configured to demap the plurality of modulation symbols to the digital signal constellation by demapping for each modulation symbol a first subset of the modulation symbol for identifying the concentric circle the respective digital signal point is located on and a
second subset of the modulation symbol for identifying the phase or angle of the respective digital signal point.
According to a fourth aspect the invention relates to a method of operating a receiver communication apparatus for communicating with a transmitter communication apparatus via a communication channel. The method comprises: receiving a modulated signal via the communication channel from the transmitter communication apparatus; extracting a plurality of modulation symbols from the modulated signal; and demapping the plurality of modulation symbols to a digital signal constellation, wherein the digital signal constellation comprises a plurality of digital signal points regularly spaced on at least two concentric circles having respective predetermined radii, wherein each circle has the same number of digital signal points and the digital signal points on each circle have the same phase with respect to the digital signal points on the other circles. Thus, an improved method of operating a receiver communication apparatus is provided, allowing generating a modulated signal in an efficient and low-complex manner.
According to a fifth aspect the invention relates to a computer program comprising program code for performing the method of the second aspect or the method of the fourth aspect when executed on a computer.
The invention can be implemented in hardware and/or software.
BRIEF DESCRIPTION OF THE DRAWINGS
Further embodiments of the invention will be described with respect to the following figures, wherein:
Figure 1 shows a schematic diagram of a communication network according to an embodiment;
Figure 2 shows a schematic diagram of an exemplary constant phase polar constellation generated by a communication apparatus according to an embodiment; Figure 3 shows a schematic diagram illustrating a procedure for generating a modulated signal according to an embodiment;
Figure 4 shows a schematic diagram of an exemplary multi-level set partitioning and labeling for a constant phase polar constellation generated by a communication apparatus according to an embodiment;
Figure 5 shows a schematic diagram illustrating a comparison of bit error rate between a constant phase polar constellation according to an embodiment and a quadrature amplitude modulation constellation; Figure 6 shows a schematic diagram illustrating a method of operating a transmitter communication apparatus according to an embodiment;
Figure 7 shows a schematic diagram illustrating a method of operating a receiver communication apparatus according to an embodiment; and
Figure 8 shows a state-of-the-art Quadrature Amplitude Modulation constellation.
In the various figures, identical reference signs will be used for identical or at least functionally equivalent features.
DETAILED DESCRIPTION OF EMBODIMENTS
In the following description, reference is made to the accompanying drawings, which form part of the disclosure, and in which are shown, by way of illustration, specific aspects in which the present invention may be placed. It will be appreciated that other aspects may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, as the scope of the present invention is defined by the appended claims.
For instance, it will be appreciated that a disclosure in connection with a described method may also hold true for a corresponding device or system configured to perform the method and vice versa. For example, if a specific method step is described, a
corresponding device may include a unit to perform the described method step, even if such unit is not explicitly described or illustrated in the figures.
Moreover, in the following detailed description as well as in the claims embodiments with different functional blocks or processing units are described, which are connected with each other or exchange signals. It will be appreciated that the present invention covers embodiments as well, which include additional functional blocks or processing units that are arranged between the functional blocks or processing units of the embodiments described below.
Finally, it is understood that the features of the various exemplary aspects described herein may be combined with each other, unless specifically noted otherwise.
Figure 1 shows a schematic diagram of a communication network 100 comprising a transmitter communication apparatus 101 according to an embodiment and a receiver communication apparatus 131 according to an embodiment, wherein the transmitter communication apparatus 101 and the receiver communication apparatus 131 can communicate with each other via a communication channel.
The transmitter communication apparatus 101 comprises a processing unit 105 and a communication interface 103, wherein the processing unit 105 is configured to generate a stream of modulation symbols and map the modulation symbols to a digital signal constellation for generating a modulated signal and the communication interface 103 is configured to transmit the modulated signal via the communication channel to the receiver communication apparatus 131 .
Similarly, the receiver communication apparatus 131 in figure 1 also comprises a processing unit 135 and a communication interface 133. The communication interface 133 of the receiver communication apparatus 131 is configured to receive the modulated signal via the communication channel from the transmitter communication apparatus 101. After receiving the modulated signal, the processing unit 135 of the receiver
communication apparatus 131 is configured to extract a plurality of modulation symbols from the modulated signal and to demap the plurality of modulation symbols to the digital signal constellation.
The digital signal constellation generated by the transmitter communication apparatus 101 or the receiver communication apparatus 131 above is called constant phase polar (CPP) constellation. The processing unit 105 of the transmitter communication apparatus 101 or the processing unit 135 of the receiver communication apparatus 131 is configured to
adapt the digital signal constellation on the basis of information about the communication channel, in particular white noise and phase noise.
The digital signal constellation, i.e. the constant phase polar (CPP) constellation, comprises a plurality of digital signal points (also referred to as constellation points hereafter) regularly spaced on at least two concentric circles having respective
predetermined radii. The distance between respective radii of respective circles is constant. Furthermore, each concentric circle has the same number of digital signal points and the digital signal points on each circle have the same phase with respect to the digital signal points on the other circles. As used herein, "regularly spaced on at least two concentric circles" means that the angular distance between two neighboring/adjacent digital signal points is constant.
According to a further embodiment, the radius of the most inner circle can be determined on the basis of the number of digital signal points per circle and white noise information, and the distance between the radius of the next larger circle and the radius of the most inner circle is smaller than the radius of the most inner circle. The construction of the constant phase polar (CPP) constellation will be discussed in more details further below. Figure 2 shows a schematic diagram of an exemplary constant phase polar (CPP) constellation 200 generated by a transmitter communication apparatus 101 or a receiver communication apparatus 131 according to an embodiment, wherein the constant phase polar (CPP) constellation 200, by way of example, comprises 4 concentric circles and 64 digital signal points per concentric circle.
According to embodiments of the invention, a constant phase polar (CPP) constellation can comprise N concentric circles and each circle can comprise K digital signal points that share a constant phase in groups of N. Therefore, a total number M of digital signal points ( = N X K) can be obtained for a constant phase polar (CPP) constellation, with M =
2m, V m e M. In the following descriptions, the constellation power is normalized to 1 for simplicity. The distance between two adjacent concentric circles is set to D. Such constellation is called as (N, K, D)-CPP constellation, as can be seen in figure 2.
One of the key features of the constant phase polar (CPP) constellation is that each digital signal point can be identified by a couple of independent parameters, namely its distance from the origin (hereafter also referred to as radius^ and its angular distance from a
reference line, e.g. the x axis on a Cartesian plane (hereafter also referred to as angle These parameters can be assimilated to an amplitude value in amplitude modulation (AM) and a phase value in phase modulation (PM) applications. This feature provides a remarkable robustness to phase noise, since larger rotations of the constellation digital signal points can be accommodated without a significant decrease in terms of bit error rate, which is a significant improvement compared to the conventional quadrature amplitude modulations (QAM).
Additionally, such independence between two parameters is exploited to provide a novel low-complexity mapper and soft demapper and to provide supports for advanced modulation and coding schemes (MCS) and multi-level coding (MLC) approaches. More specifically, a novel systematic labeling is proposed in the embodiments for the digital signal points and a suitable low-complexity log-likelihood ratio (LLR) calculation is formulated, whose complexity does not depend on the constellation size. In this context, an adapted rate design is also disclosed in the embodiments as a necessary component to maximize the performance of the multi-level coding (MLC) approaches.
According to an embodiment, a CPP-based signal can be obtained as the composition of K constant envelope phase-modulated signals, thanks to the fact that the digital signal points of the constant phase polar (CPP) constellation share the same radius in groups of K and angle in groups of N. This offers several important advantages as follows: firstly, a very structured but fully scalar constellation can be provided, in which no constraint is imposed on the parameterm = log2 M. Secondly, the power amplifier (PA) is guaranteed to always work with a finite number of constant envelope signals, improving its efficiency. Thirdly, an arbitrary reduction of the peak-to-average power ratio (PAPR) can be allowed by reducing the constant distance between the radii of the concentric circles. Finally, effects of non-linearity of the amplification can be mitigated even for higher values of the peak-to-average power ratios (PAPR). In summary, the embodiments of the invention are characterized by the following innovative steps: first of all, a novel constellation design is provided, allowing an arbitrarily low peak-to-average power ratio (PAPR), arbitrary robustness to phase noise, digital signal points identified by a couple of independent parameters that can be treated separately to guarantee low-complexity mapping and demapping operations, and scalability as well as flexibility in terms of the number of constellation points to support advanced modulation and coding schemes (MCS).
Secondly, a novel low-complexity mapper is provided, wherein the independence of the two aforementioned parameters can be used to provide scalable supports to multi-level coding (MLC) approaches. Also, a novel low-complexity demapper is also provided, wherein the independence of the two aforementioned parameters is used to simplify the log-likelihood ratio (LLR) calculation and to yield low-complexity soft-demapping operation, whose complexity does not depend on the constellation size.
Finally, a novel rate design is disclosed to maximize the performance of multi-level coding (MLC) approaches. In the following, the mapper and demapper of the constant phase polar (CPP) constellation will be described in more details under further reference to figure
Figure 3 shows a schematic diagram illustrating a procedure for generating a modulated signal according to an embodiment, wherein the constant phase polar (CPP) constellation comprises M = 2m digital signal points arranged on N concentric circles, each concentric circle containing K digital signal points which share a constant phase in groups of N, with M = N X K. The constellation power is normalized to 1 for simplicity. Firstly, in a step of constellation construction, a digital signal point P in the constant phase polar (CPP) constellation is written as a complex number in the form P = ■ ej®1 in polar coordinates, where i = 0, ... , N— 1 and I = 0, ... , K— 1. Adjacent digital signal points on a concentric circle are equidistant, giving 0; =— I. Adjacent digital signal points on the same semiline are at distance Δ, giving = r0 + ίΔ. The constellation requires unitary power, which is obtained by leaving the parameter r0 free and defining
-r0(N- 1) + (N- 1) (4W - 2 - r0 2 (N+ 1) )
Δ= V3 . Alternatively, this construction can be seen as a
(W-1)(2W-1) "
quantized rotation of a segment S lying on the x axis of length A(N— 1), with extremities r0 and rN_t. Rotation is performed K - 1 times, with an angle of— . In a next step of encoding 301 according to an embodiment, a total number T of modulation symbols can be encoded and decoded together. This corresponds to transmission of TX M bits. A multi-level code is designed across the modulation symbols to improve the transmission capability. More specifically, a Q error correcting code Ci (T, Di) for 1 < i≤ Q can be used in parallel and each code can output a bit sequence of length T and for each input sequence of length Dt . In brief, these codes can transmit
D =∑=1 information bits by using TX M bits and the overall rate is therefore equal to D/TM. The rate design of those codes, i.e. how to choose their dimensions Dt , will be discussed in more details further below. Every time when a string x comprising D information bits has to be transmitted, these bits can be divided into Q bit strings xlt ... , xQ comprising Dlt ... , DQ bits respectively, and each string xt is then encoded using the relative code C obtaining m codewords c1( ... , cQ of length T. The codewords are re-arranged as rows of a Q x T binary matrix Y. Finally, the T transmitted symbols are selected as the columns of matrix Y.
Furthermore, in a step of a constellation labeling 303 by a mapper according to an embodiment, the labeling can be performed in a radial and angular domain separately. In practice, a total number M = 2m of constellation points (i.e. digital signal points) are mapped into a modulation symbol comprising strings of m bits. Given N = 2n and K = 2k, the m bits corresponding to a constellation point can be divided into two parts, namely the first part of n bits and the second part of k bits, identifying the radius and the angle of the constellation point respectively.
In other words, each modulation symbol is represented by a bit sequence of m bits with the total number of digital signal points M given by M = 2m and the first subset of a respective modulation symbol comprises the first n bits of a respective bit sequence and the second subset of a respective modulation symbol comprises the last k bits of a respective bit sequence with k = m— n. Moreover, the first subset of the modulation symbol identifies the concentric circle the respective digital signal point is located on and a second subset of the modulation symbol identifies the phase or angle of the respective digital signal point.
The constellation labeling is based on the multi-level paradigm, aiming to demap constellation points, i.e. digital signal points, bit by bit sequentially. To achieve this result, the point P = ■ ej®1 is the representation of the string of bit b ... bnbn+1 ... bm, where b ... bn is given by the binary representation of the integer i in n digits and bn+1 ... bm is given by the binary representation of the integer I in k digits.
According to an embodiment, an exemplary multi-level set partitioning and labeling for a constant phase polar (CPP) constellation is shown in figure 4, wherein labeling a constellation point can be decomposed into a radial domain 401 and an angular domain
402 in which the radius and the angle of the constellation point can be identified respectively. By way of illustration, a digital signal point P = r3 ■ ej®6 corresponds to the string 0110110 in figure 4. In a next step of noise modeling, a basic discrete point-to-point transmission model affected by both white noise and phase noise is considered. In fact, if the symbol P = ■ ej®1 is transmitted, the symbol Q = r■ eje = ■ ej(-6l+ev) +∑ is received, wherein z is the channel noise. The white noise component is distributed according to a bivariate
Gaussian distribution, z~Norm2 (0,∑), with covariance matrix∑ = ^ °2^, wherein S = is the signal-to-noise ratio (SNR) of the system. A phase noise creates a circular shift of the transmitted symbol, without changing its magnitude. The phase noise angle θρ follows von Mises distribution, 0P~VM(O, κρ). The dispersion parameter κρ is analogous to the reciprocal of the variance, more precisely var(#p) = 1 - = wherein It is the modified Bessel function of order i.
Under some conditions, it is possible to separate the overall noise into a radial component and an angular component, so that the radial and angular component of the received symbol can be decoded separately through the equivalent channels r = + rz and Θ = Qx + θζ.
Given the nature of the channel noise, rz only depends on the white noise and is distributed according to the Gaussian distribution rz~Norm (0, σ ). The formulation of the angular component distribution is more complex, since it is affected by both the white and the phase noise. However, it is possible to approximate it with a Gaussian distribution as
0z~Norm(O, <) with variance =
As can be seen, depends on the radius of the circle. Hence, the radial domain has to be decoded first and the result is used to decode the angular domain. In the following, a technique to calculate the log-likelihood ratios (LLRs) used by the multi-level decoder will be described in more details.
In further steps of demapping 305 and decoding 307, it is possible to separate the decoding in the radial and angular domains in view of the multi-level coding construction. Moreover, since the two domains share the same labeling structure and are affected by a noise equivalent to white noise, it is possible to use the same demapper for these two domains. In the following, an algorithm able to calculate the log-likelihood ratios (LLRs) of the bits of a single received symbol over either the radial or the angular domain will be described first, followed by the use of this algorithm in the constant phase polar (CPP) constellation.
The calculation of the log-likelihood ratio (LLR) of a received symbol in the form y = x + z will be discussed in the following, wherein the transmitted symbol is a non-negative integer with binary expansion ... cr (i.e. x =∑£=1 cfc2fe_1 and x e {0,1,2, ... , 2r_1)) and z is the white noise, with z~Norm(Q, o2). According to the multi-level coding paradigm, the log-likelihood ratios (LLRs) are calculated bit-by-bit in a sequential order on the basis of the received signal and the previously decoded bits. Given xt =∑k l = 1 ck2k~1, yt = v~ ^1 and Oi = - ^ according to the model, the log-likelihood ratio (LLR) of bit q can be calculated as
This calculation would require the sum over a large amount of points. On the other hand, the log-likelihood ratio (LLR) can be expressed in terms of wrapped normal distribution as
where ility density function of the
wrapped normal distribution.
The calculation of the log-likelihood ratios (LLRs) depends generally on the number of constellation points. Using certain properties of the constellation and mathematical approximations, the log-likelihood ratio (LLR) calculation can be independent on the number of constellation points using wrapped normal distributions for LLRs approximation.
Accordingly, an additional simplification can be performed by approximating the wrapped normal distribution with a von Mises distribution: let κ be the concentration parameter of the von Mises distribution used to approximate such wrapped normal distribution, and /„(·) be the modified Bessel function of first kind of order n, then the simplified low- complexity log-likelihood ratio (LLR) of the bit i can be computed as:
LLffj = 2 (σ;) cos(y^), wherein (t) = A 1 and A 1 is the inverse of l(t) =
The auxiliary function can be computed offline and tabulated to speed up the calculation. It is worth noting that the result above shows that the complexity of the demapper does not increase with the number of the constellation points, when the demapper is operated in soft-decoding mode. Once the T symbols are received, demapping begins. The first n bits, belonging to the radial domain, are initially decoded. For every symbol, the LL^ is calculated using as input y =— r ^- and σ = ^: these correspond to the LLRs of the first row of Y, and consequently can be used in the decoder of the code C . The result of the decoding is the string x . This string is then re-encoded through the code C to obtain the codeword c , which will be used to calculate y2 and σ2. This procedure of calculating the LLRs using previously decoded bit, decoding of a row and cancellation of the decoded bit for next level is repeated until all the bits of the radial domain are decoded. The decoding of the angular domain proceeds in a similar way, however using a different value of σ for every symbol, calculated on the basis of the radius of the ring calculated in the first part of the demapping. At the end of the process, T constellation points are obtained.
Finally, in order to design the rates of the M error correcting codes Ci (T, D ) used, the capacity of the equivalent binary symmetric channel (BSC) is calculated. A binary symmetric channel (BSC) is completely defined by its error probability p, and has capacity Cap = 1 + p log2 p + (1 - p) log2 (l - p). For every level of the radial domain, the error probability p; can be calculated as
Pi = 2 /Ϊ ^Ν (θί \ 0, πσί άθί Ξ 2
with θί = πγι and ; = A 1 For the angular domain, the capacity of a level is
calculated as the average of the capacities of all the circles of the level.
To illustrate the advantages according to the embodiments of the present invention, a performance evaluation of the constant phase polar (CPP) constellation is carried out and shown in figure 5, wherein figure 5 shows a schematic diagram illustrating a comparison of bit error rates (BER) between the constant phase polar (CPP) constellation and the conventional quadrature amplitude modulation (QAM) constellation as a function of a signal-to-noise ratio (SNR).
The bit error rates (BER) of the constant phase polar (CPP) constellation are calculated with respect to the signal-to-noise ratio (SNR) in both coded and uncoded cases under strong phase noise, which are denoted by dashed lines and solid lines in figure 5 respectively. The result of the conventional quadrature amplitude modulation (QAM) constellation is denoted by the plain solid line.
As can be seen at first glance, the constant phase polar (CPP) constellation outperforms the quadrature amplitude modulation (QAM) constellation even without the multi-level coding, as indicated by the solid lines. This is due to the fact that the quadrature amplitude modulation (QAM) constellation is not built to handle strong phase noise.
As for the results based on the multi-level coding, the bit error rate of the constant phase polar (CPP) constellation, as indicated by the dashed line, plunges sharply as a function of the signal-to-noise ratio (SNR). This validates the great advantages of the rate design and the mapper/demapper as presented above as well as shows their significant gains in performance in comparison with the uncoded cases.
Figure 6 shows a flow diagram illustrating a corresponding method 600 for operating the transmitter communication apparatus 101 . The method 600 comprises the steps of:
generating 601 a stream of modulation symbols; mapping 603 the modulation symbols to a digital signal constellation for generating a modulated signal, wherein the digital signal constellation comprises a plurality of digital signal points regularly spaced on at least two concentric circles having respective predetermined radii, wherein each circle has the same number of digital signal points and the digital signal points on each circle have the same phase with respect to the digital signal points on the other circles; and transmitting
605 the modulated signal via the communication channel to the receiver communication apparatus 131 .
Figure 7 shows a flow diagram illustrating a corresponding method 700 for operating the receiver communication apparatus 131. The method 700 comprises the steps of: receiving 701 a modulated signal via the communication channel from the transmitter
communication apparatus 101 ; extracting 703 a plurality of modulation symbols from the modulated signal; and demapping 705 the plurality of modulation symbols to a digital signal constellation, wherein the digital signal constellation comprises a plurality of digital signal points regularly spaced on at least two concentric circles having respective predetermined radii, wherein each circle has the same number of digital signal points and the digital signal points on each circle have the same phase with respect to the digital signal points on the other circles. While a particular feature or aspect of the disclosure may have been disclosed with respect to only one of several implementations or embodiments, such feature or aspect may be combined with one or more other features or aspects of the other implementations or embodiments as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms "include", "have", "with", or other variants thereof are used in either the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term "comprise". Also, the terms "exemplary", "for example" and "e.g." are merely meant as an example, rather than the best or optimal. The terms "coupled" and "connected", along with derivatives may have been used. It should be understood that these terms may have been used to indicate that two elements cooperate or interact with each other regardless whether they are in direct physical or electrical contact, or they are not in direct contact with each other.
Although specific aspects have been illustrated and described herein, it will be
appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific aspects shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific aspects discussed herein.
Although the elements in the following claims are recited in a particular sequence with corresponding labeling, unless the claim recitations otherwise imply a particular sequence
for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.
Many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. Of course, those skilled in the art readily recognize that there are numerous applications of the invention beyond those described herein. While the present invention has been described with reference to one or more particular embodiments, those skilled in the art recognize that many changes may be made thereto without departing from the scope of the present invention. It is therefore to be understood that within the scope of the appended claims and their equivalents, the invention may be practiced otherwise than as specifically described herein.
Claims
1 . A transmitter communication apparatus (101 ) for communicating with a
communication apparatus (131 ) via a communication channel, the transmitter
communication apparatus (101 ) comprising: a processing unit (105) configured to generate a stream of modulation symbols and map the modulation symbols to a digital signal constellation for generating a modulated signal, wherein the digital signal constellation comprises a plurality of digital signal points regularly spaced on at least two concentric circles having respective predetermined radii, wherein each circle has the same number of digital signal points and the digital signal points on each circle have the same phase with respect to the digital signal points on the other circles; and a communication interface (103) configured to transmit the modulated signal via the communication channel to the receiver communication apparatus (131 ).
2. The transmitter communication apparatus (101 ) of claim 1 , wherein the most inner circle has a radius r0 and wherein the distance Δ between the radius of the next larger circle and the radius r0 of the most inner circle is smaller than the radius r0 of the most inner circle.
3. The transmitter communication apparatus (101 ) of claim 2, wherein the plurality of digital signal points are equally spaced on at least three concentric circles and wherein the distance Δ between respective radii of respective circles is constant.
4. The transmitter communication apparatus (101 ) of claim 2, wherein the processing unit (105) is configured to determine the distance Δ between respective radii of respective circles on the basis of the following equation:
-ro0V-l)+ (W-l)(4W-2-r0 2 (W+l))
Δ= 3
(W-1)(2W-1) wherein N denotes the total number of concentric circles.
5. The transmitter communication apparatus (101 ) according to any one of claims 2 to 4, wherein the processing unit (105) is configured to determine the radius r0 of the most inner circle and the number of digital signal points per circle on the basis of information about the communication channel, phase noise density and white noise density.
6. The transmitter communication apparatus (101 ) of any one of the preceding claims, wherein the processing unit (105) is further configured to map the modulation symbols to the digital signal constellation such that for each modulation symbol a first subset of the modulation symbol identifies the concentric circle the respective digital signal point is located on and a second subset of the modulation symbol identifies the phase or angle of the respective digital signal point.
7. The transmitter communication apparatus (101 ) of claim 6, wherein each modulation symbol is represented by a bit sequence of m bits with the total number of digital signal points M given by M = 2m and wherein the first subset of a respective modulation symbol comprises the first n bits of a respective bit sequence and the second subset of a respective modulation symbol comprises the last k bits of a respective bit sequence with k = m— n.
8. The transmitter communication apparatus (101 ) of any one of the preceding claims, wherein the processing unit (105) is further configured to adapt the digital signal constellation on the basis of information about the communication channel.
9. A method (600) of operating a transmitter communication apparatus (101 ) for communicating with a receiver communication apparatus (131 ) via a communication channel, the method (600) comprising: generating (601 ) a stream of modulation symbols; mapping (603) the modulation symbols to a digital signal constellation for generating a modulated signal, wherein the digital signal constellation comprises a plurality of digital signal points regularly spaced on at least two concentric circles having respective predetermined radii, wherein each circle has the same number of digital signal points and the digital signal points on each circle have the same phase with respect to the digital signal points on the other circles; and
transmitting (605) the modulated signal via the communication channel to the receiver communication apparatus (131 ).
10. A receiver communication apparatus (131 ) for communicating with a transmitter communication apparatus (101 ) via a communication channel, the receiver
communication apparatus (131 ) comprising: a communication interface (133) configured to receive a modulated signal via the communication channel from the transmitter communication apparatus (101 ); and a processing unit (135) configured to extract a plurality of modulation symbols from the modulated signal and to demap the plurality of modulation symbols to a digital signal constellation, wherein the digital signal constellation comprises a plurality of digital signal points regularly spaced on at least two concentric circles having respective predetermined radii, wherein each circle has the same number of digital signal points and the digital signal points on each circle have the same phase with respect to the digital signal points on the other circles.
1 1 . The receiver communication apparatus (131 ) of claim 10, wherein the processing unit (135) is configured to demap the plurality of modulation symbols to the digital signal constellation by demapping for each modulation symbol a first subset of the modulation symbol for identifying the concentric circle the respective digital signal point is located on and a second subset of the modulation symbol for identifying the phase [or angle] of the respective digital signal point.
12. A method (700) of operating a receiver communication apparatus (131 ) for communicating with a transmitter communication apparatus (101 ) via a communication channel, the method (700) comprising: receiving (701 ) a modulated signal via the communication channel from the transmitter communication apparatus (101 ); extracting (703) a plurality of modulation symbols from the modulated signal; and demapping (705) the plurality of modulation symbols to a digital signal constellation, wherein the digital signal constellation comprises a plurality of digital signal points
regularly spaced on at least two concentric circles having respective predetermined radii, wherein each circle has the same number of digital signal points and the digital signal points on each circle have the same phase with respect to the digital signal points on the other circles.
13. A computer program product comprising a program code for performing the method (600) of claim 9 or the method (700) of claim 12, when executed on a computer or a processor.
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| PCT/EP2017/078449 WO2019091544A1 (en) | 2017-11-07 | 2017-11-07 | Apparatuses and methods for generating an apsk signal |
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| FR3109044A1 (en) * | 2020-04-07 | 2021-10-08 | Orange | Telecommunication method with polar constellations and corresponding devices |
| FR3116169A1 (en) * | 2020-11-10 | 2022-05-13 | Orange | Telecommunication method with repeating symbol binary coding and corresponding devices |
| CN115442194A (en) * | 2021-06-02 | 2022-12-06 | 中兴通讯股份有限公司 | Data transmission method, communication node and computer readable storage medium |
| US20230318900A1 (en) * | 2022-03-29 | 2023-10-05 | Qualcomm Incorporated | Adaptation of amplitude and phase shift keying (apsk) modulation |
| CN115333905B (en) * | 2022-10-12 | 2023-01-03 | 南通中泓网络科技有限公司 | Signal modulation mode identification method |
| CN116527120B (en) * | 2023-06-30 | 2023-11-14 | 北京融为科技有限公司 | Signal mapping method and device based on satellite communication |
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| US7123663B2 (en) | 2002-06-04 | 2006-10-17 | Agence Spatiale Europeenne | Coded digital modulation method for communication system |
| CN102752261B (en) * | 2011-04-20 | 2015-06-17 | 清华大学 | Constellation mapping method based on absolute phase shift keying (APSK) constellation map, coded modulation method and system |
| CN103095641B (en) * | 2011-11-04 | 2016-04-20 | 北京数字电视国家工程实验室有限公司 | A kind of APSK constellation maps and de-mapping method |
| CN102710581B (en) * | 2012-05-07 | 2014-09-03 | 清华大学 | Soft solution mapping method |
| TR201815713T4 (en) * | 2013-02-14 | 2018-11-21 | Newtec Cy | Modulation with an apsk tool satellite with a single ring with dots in uneven intervals. |
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