Method for receiving and transmitting binary data sequences in OTFS-based multi-user SCMA communication system with coordinated multipoint, and receiver and

Abstract

In a method of receiving a binary data sequence from one or more mobile UEs, the binary data sequence is represented by an SCMA signal transmitted over an OTFS communication channel to at least two RRHs of a CoMP radio communication system, the RRHs communicatively connected to a common BBU and serving the one or more mobile UEs from different directions, a continuous time domain signal representing an SCMA signal transmitted from the mobile UE is received at each RRH. After removing a cyclic prefix from a received time domain signal, OTFS demodulation is performed on the received signal, and centralized or decentralized signal detection and recovery is performed on a two-dimensional arrangement of information symbols in the delayed Doppler domain, both of which perform an iterative Gaussian approximation expected propagation process on the information symbols. The detected symbols are de-mapped to recover the binary sequence of transmissions of the respective mobile UEs that have received the signal.

Description

Technical Field

[0001] The present invention relates to a method for transmitting and / or receiving a binary data sequence in a multi-user (MU) sparse code multiple access (SCMA) wireless communication system based on orthogonal time-frequency space (OTFS) with coordinated multi-point (CoMP). The present invention also relates to a transmitter and a receiver implementing the method, and a system comprising one or more such transmitters and receivers, respectively.

[0002] Symbolic representation

[0003] Throughout this specification, boldface symbols represent vectors or matrices, such as x and X. Scalar values ​​are represented in the text by italic lowercase letters, such as x. Superscripts T and H represent the transpose and complex conjugate transpose of a vector or matrix, respectively. Background Art

[0004] The sixth generation (6G) of wireless communications and subsequent technologies are expected to serve an increasing number of high-speed mobile users, such as vehicles, subways, highways, trains, drones, low Earth orbit (LEO) satellites, etc.

[0005] The previous fourth and fifth generation (5G) wireless communications use orthogonal frequency division multiplexing (OFDM) technology, which has high spectral efficiency and high robustness to frequency selective fading channels, and also allows the use of low-complexity equalizers. However, high-speed mobile communications, such as those required for high-speed railways and vehicle-to-everything (V2X) communications, suffer from severe time and frequency dispersion due to speed-dependent Doppler shift or spread and rapidly changing multipath reception. Time and frequency dispersion can cause inter-carrier interference (ICI) and signal fading at the receiver, so this fading is also called doubly selective channel fading. Doubly selective channel fading can seriously impair the performance of OFDM communications.

[0006] As an alternative to OFDM, OTFS modulation has been proposed as a solution to cope with doubly selective fading channels.

[0007] OTFS modulation is a 2D modulation scheme that multiplexes information QAM symbols onto carrier waveforms that correspond to localized impulses in a signal representation known as a Delay-Doppler representation. The OTFS waveforms are distributed in both time and frequency, but they remain approximately orthogonal to each other under typical Delay-Doppler channel impairments. In theory, OTFS combines the reliability and robustness of spread spectrum with the high spectral efficiency and low complexity of narrowband transmission.

[0008] The OTFS waveform is coupled with the wireless channel to directly capture the underlying physics, resulting in a high-resolution delay-Doppler radar image of the constituent reflectors. Thus, the time-frequency selective channel is transformed into an invariant, separable, and orthogonal interaction, where all received symbols experience the same local impairments and all delay-Doppler diversity branches are coherently combined.

[0009] This makes OTFS well suited for wireless communications between transmitters and receivers that are moving at high speed relative to each other, such as receivers or transmitters located on high-speed trains, cars, or even airplanes.

[0010] Figure 1 A block diagram of an exemplary OTFS transmission system is shown. The transmitter 300 includes a first transmitter-side transform unit 306 and a second transmitter-side transform unit 308, which form an OTFS modulator 310 (not shown in the figure). The serial binary data is input to a signal mapper (not shown in the figure), which outputs a two-dimensional sequence x[k, l] of information symbols, wherein the QAM symbols are arranged along the delay period and the Doppler period of the delay-Doppler domain. The information symbol includes a data symbol and a pilot symbol. Depending on the type of the pilot symbol, the guard symbol may surround the pilot symbol. The two-dimensional sequence x[k, l] of the information symbol is input to the first transmitter-side transform unit 306, and an inverse finite symplectic Fourier transform (iSFFT) is performed to generate a matrix X[n, m], which represents the two-dimensional sequence of the information symbol x[k, l] in the time-frequency domain. When the transmitter transmits in the time domain, further transformation is required in the second transmitter-side transform unit 308 to generate a signal s[t] in the time domain, such as a Heisenberg transform. The signal s[t] is then transmitted via antenna 316 on a communication channel.

[0011] In a real environment, the transmitted signal is subjected to double selective fading with Doppler shift when it passes from the transmitter to the receiver through the communication channel. The received signal is a superposition of a direct copy of the transmitted signal and multiple reflected copies, each of which is delayed due to a path delay depending on the length of the signal path delay and is frequency shifted due to the Doppler shift depending on the differential speed between the transmitter, reflector and receiver. Each signal copy is weighted according to its specific path delay and differential speed. Typical Doppler shifts are about 10Hz-1kHz, but larger values ​​may occur in cases of extremely high mobility (such as high-speed trains) and / or high carrier frequencies. Since there are likely to be multiple reflectors and / or moving reflectors in a real environment, the received superimposed signal is scattered over the frequency range, not just frequency shifted, so the signal deformation is also called Doppler shift. In the following description, the real communication channel is also called the actual communication channel.

[0012] exist Figure 1In FIG. 4 , the actual communication channel is represented by undisturbed radio waves emitted by the transmitter antenna 306 and various disordered radio waves coming from different directions and at different distances from each other at the receiver antenna 402. The radio waves may arrive at the receiver's antenna directly or after being reflected one or more times from one or more stationary and / or moving objects, which may introduce Doppler shifts and different delays to the reflected radio waves.

[0013] The receiver 400 picks up the received signal r[t] in the time domain and provides it to the first receiver side transform unit 408, where it is subjected to a Wigner transform to transform the received signal r[t] into a matrix Y[n,m] representing the received signal r[t] in the time-frequency domain. In order to be able to detect the signal in the delay Doppler domain, the matrix Y[n,m] is then provided to the second receiver side transform unit 410, where it is subjected to a finite symplectic Fourier transform (SFFT), which outputs a two-dimensional sequence of information symbols y[k,l] in the delay Doppler domain. The first and second receiver side transform units form an OTFS demodulator 412. The two-dimensional sequence of information symbols y[k,l] is input to a channel estimation and equalization block 414, which performs channel estimation CE and signal detection SD and reconstructs the originally transmitted symbols, and is finally input to a demapper, which outputs the originally transmitted binary data (the demapper is not shown in the figure).

[0014] In vehicular communications, a large number of users move rapidly at different speeds and directions, requiring wireless access and communication, and traditional access schemes such as time division multiple access (TDMA) will soon become overloaded. This scenario is also called massive multiple access. Non-orthogonal multiple access (NOMA) is considered to be a promising solution to achieve high spectral efficiency in traditional overloaded multi-user OFDM and multiple-input multiple-output (MIMO) systems. Existing NOMA methods are mainly divided into power domain NOMA and code domain NOMA. As shown in A. Chatterjee, V. Rangamgari, S. Tiwari, and SSDas in “Nonorthogonal multiple access with orthogonal time-frequency space signal transmission” (IEEE Syst. J., Vol. 15, No. 1, pp. 383-394, March 2021) and Z. Ding, R. Schober, P. Fan, and HV Poor in “OTFS-NOMA: An efficient approach for exploiting heterogenous user mobility profiles” (IEEE Trans. Commun., Vol. 67, No. 11, pp. 7950-7965, November 2019), applying NOMA to OTFS can effectively improve spectrum utilization and support large-scale mobile connections. In OTFS-NOMA, multiple mobile users are allowed to share the same delay-Doppler resource simultaneously and are distinguished by different power levels or by coding (e.g., sparse codewords).

[0015] Specifically, sparse code multiple access (SCMA) is a code-domain NOMA that can provide excellent performance and low receiver complexity, as discussed in “OTFS-SCMA: A code-domain NOMA approach for orthogonal time-frequency space modulation” by K. Deka, A. Thomas, and S. Sharma (IEEE Trans. Commun., Vol. 69, No. 8, pp. 5043-5058, August 2021).

[0016] The SCMA encoder maps log2(M) bits to a K-dimensional codeword of size M selected from a predefined codebook. The K dimensions correspond to K different orthogonal tones, such as OFDMA subcarriers. The K-dimensional codeword is a vector with only N < K non-zero entries. A user cannot transmit data through the subcarriers represented by the other N - K zero entries. In theory, each user can be assigned multiple codebooks, and each codebook can generally be used by multiple users. However, in this specification, it is assumed that each user uses only one SCMA layer.

[0017] Figure 2 An example of SCMA coding is shown, with 6-layer codebooks CB1…CB6 (variable nodes) and 4 subcarriers SC1…SC4 (function nodes). Each row represents a dimension, and each column represents a 4-dimensional codeword. In each codebook, the constellation size is 4, meaning there are 4 different codewords to choose from. White entries represent zero elements, and patterned entries represent non-zero elements in the codebook. For example, in codebook 1, the entries in the first row are patterned and the entries in the third row are white, meaning the first dimension is non-zero and the third dimension is zero. In each codebook, there are 2 non-zero dimensions with a patterned lattice. In an AWGN channel, the signal received at the base station is a superposition of codewords selected from the codebooks, indicated by the combined pattern in each subcarrier.

[0018] Codebook design is the most important part of the SCMA encoder. The goal is to design a multi-dimensional lattice constellation with dimensional dependence and constellation power variation while maintaining a large minimum Euclidean distance. Generally speaking, the design of SCMA codes is divided into 3 stages:

[0019] 1) The mapping matrix stage determines the number of layers of interference at each subcarrier, which represents the complexity of detection. Figure 2 The example shown can be regarded as a mapping matrix, meaning that each layer is interfered with by two other layers.

[0020] 2) The constellation point and multi-dimensional mother constellation design stage, in which first a base constellation with a maximized minimum Euclidean distance is designed. Secondly, a unary rotation is performed on the base constellation to control dimensional dependence and power variation, and this unary rotation can be designed to maximize the minimum product distance of the constellation. Thirdly, a complex constellation is constructed by shuffling based on the rotated base constellation; finally, the projection points are minimized using rotation.

[0021] 3) The constellation function operator stage, including several operators such as complex conjugation, phase rotation, and dimension permutation, aiming to design different codebooks for the collision layers.

[0022] Existing NOMA implementations perform poorly in managing radio access for groups of wirelessly connected mobile user equipment (UE) as they pass along multiple remote radio heads (RRHs) connected to a baseband unit (BBU) of a public radio network (PRN).

[0023] Figure 3 An exemplary conventional cellular network providing communications for multiple mobile UEs is shown. Multiple RRHs are connected to a common BBU via bidirectional connections, which can be either wired or wireless. Each RRH exclusively serves all UEs within its radio range, represented by the majority of the ovals emerging from the antennas of the respective RRHs, regardless of their location relative to the RRHs, or whether they are close to or far from the RRHs. Whenever a UE leaves the radio range of one RRH, a handover algorithm is executed in the BBU or a controller further in the system, and the UE is served by another RRH. Uplink connections are shown as solid lines, while downlink connections are shown as dashed lines.

[0024] Attempts have been made to improve service to mobile UEs by dividing the radio coverage area into sectors, where individual RRHs from a co-located set of RRHs provide service to mobile UEs within respective designated sectors. Figure 4 Such a known communication system is depicted in which multiple sets of co-located RRHs are connected to a common BBU via bidirectional connections, which may be wired or wireless. Respective RRHs in a set of co-located RRHs provide communications for mobile UEs within their designated sectors. As the mobile UE moves from one sector to another, an intra-set handover from one RRH in the co-located RRH set to another RRH is performed. The co-located RRH set creates a combined radio range for the set, represented by the mostly oval shapes emerging from the antennas of the respective co-located RRHs. Whenever a UE leaves the radio range of a co-located RRH set, a BBU or a controller further away within the system executes a handover algorithm and the UE is served by another set of co-located RRHs. Uplink connections are shown with solid lines, while downlink connections are shown with dashed lines.

[0025] The known communication system and its operation not only require a lot of resources for inter-RRH or inter-group switching, but also make the utilization rate of system resources extremely low. Summary of the invention

[0026] Therefore, one object of the present invention comprises proposing an improved OTFS access scheme that allows multiple UEs to communicate simultaneously, wherein each UE is simultaneously served by an RRH located in a different spatial direction relative to the user location.

[0027] Obviously, a mobile UE served by multiple RRHs simultaneously will inevitably experience both positive and negative Doppler shifts as it moves away from one RRH and closer to another, or at least will experience different Doppler shifts as it moves relative to the RRHs.

[0028] The present invention solves this problem by combining OTFS-based SCMA (OBSCMA) with coordinated multi-point (CoMP) transmission and reception, which allows exploiting additional diversity from both the Doppler and spatial domains while providing simultaneous communication for multiple mobile users.

[0029] Coordinated multi-point transmission and reception refers to a number of different technologies, which have in common the dynamic coordination of transmission and / or reception of multiple geographically separated sites, with the goal of improving system performance and quality of service for end users. CoMP was originally proposed to improve average spectral efficiency and mitigate inter-cell interference between adjacent cells in traditional cellular networks, and it combines antennas of multiple cells to create an additional spatial dimension. CoMP includes dynamic inter-cell scheduling coordination and multi-site joint transmission / reception, etc. Joint reception means jointly processing signals received at multiple sites to enhance reception performance. Maximum ratio combining and interference suppression combining are examples of schemes that can be used to combine uplink transmissions received at multiple points. Joint transmission means that data is transmitted from a mobile terminal to multiple sites, or jointly transmitted from multiple sites to a mobile terminal in opposite directions, so that not only interference can be reduced, but also received power can be increased. Transmissions to and from sites can also take into account the instantaneous channel conditions of different terminals to improve the received signal strength while reducing interference between different transmissions.

[0030] Figure 5 a) is a schematic diagram showing data processing and message flow along the download direction in a general CoMP system. Figure 5 b) shows a schematic diagram of data processing and message flow in the upload direction in a general CoMP system. Figure 5 In a), data processing in the BBU prepares data to be sent to the UE (represented by a mobile phone icon) via all three RRHs (represented by antenna masts in the figure). The processing may take into account, among other things, the different channel characteristics of the communication link from each RRH to the UE, so that the information sent to each RRH may be slightly different, but carry the same payload. Figure 5 In b), all RRHs transmit their received signals to the BBU for processing.

[0031] The present invention proposes to group multiple users to achieve SCMA, and in order to better utilize the potential performance gain provided by the distributed antenna system of the present invention, CoMP transmission and reception are adopted, which, especially in combination with the distributed antenna system, provides useful diversity and favorable propagation characteristics for mobile communications. Although CoMP was originally proposed to improve average spectral efficiency and mitigate inter-cell interference in traditional cellular networks, the present invention adopts CoMP operation between adjacent RRHs to better utilize diversity.

[0032] The next section discusses the uplink in a CoMP system, where the BBU is connected to multiple RRHs via bidirectional connections, which can be wired or wireless, including electrical or optical links. The RRHs are placed along the paths followed by multiple mobile UEs. Figure 6 An exemplary schematic diagram of this setup is shown in .

[0033] In each transmission time slot, J independent mobile user equipments (UEs) located in the same cell are served by a first RRH in front of them and a second RRH behind them simultaneously.

[0034] The expression "in front of" refers to a direction of any angle within a semicircle extending from the UE as the center, the diameter or base line of the semicircle being perpendicular to the direction of travel of the UE or perpendicular to the straight line between the first and second RRHs, and the arc of the semicircle facing the direction of travel of the UE or the first RRH. The UE moves towards the RRH "in front of" the UE.

[0035] Accordingly, the expression "behind" refers to a direction at any angle within a semicircle extending from the UE as the center, the diameter or base line of the semicircle being perpendicular to the direction of travel of the UE or perpendicular to the straight line between the first and second RRHs, and the arc thereof facing the opposite direction of the direction of travel of the UE or towards the second RRH. The UE is away from the RRH located "behind" the UE.

[0036] Obviously, the communication connection between the UE and the first RRH and the communication connection between the same UE and the second RRH will be subject to different Doppler frequency shifts. One communication connection will be subject to a positive Doppler frequency shift, while the other communication connection will be subject to a negative Doppler frequency shift.

[0037] Although the following assumes a simplified scenario where one RRH is located "in front" of the UE and one RRH is located "behind" the UE, it is obvious that the present invention also covers the generalization that the two RRHs are "located in different directions relative to the UE", because different Doppler frequency shifts will also occur in the generalized scenario.

[0038] In the first step, map the binary data from the UE to the corresponding K-dimensional SCMA codewords. Assume that each UE uses only one SCMA layer, and generally J > K, resulting in an overload factor δ = J / K > 1. Additionally, allocate the SCMA codewords in the delay-Doppler plane and employ OTFS modulation for uplink transmission.

[0039] Without loss of generality, represent the lattice in the delay-Doppler plane as

[0040]

[0041] And the corresponding time-frequency plane is

[0042] Λ = {(mΔf, nT), m = 0, …, M - 1; n = 0, …, N - 1}

[0043] where M and N represent the total number of available subcarriers and the time interval respectively. The choices of T and Δf = 1 / T (Hz) should be greater than the maximum channel delay spread and the maximum Doppler shift respectively. To avoid unnecessary confusion, a simple model is used where each UE and each RRH are equipped with a single transmit antenna and a single receive antenna. It is worth mentioning that the proposed model is also applicable to scenarios involving multiple transmit and receive antennas on the UE and RRH and has the expected performance gain.

[0044] At the transmitter side, in each transmission time slot, every log2Q information bits b from the j-th user j are mapped to a complex K-dimensional sparse codeword c j = [c j,1 , c j,2 , …, c j,K T , which is selected from a user-specific SCMA codebook of size Q where j = {1, 2, …, J}. Assume that only D < K non-zero entries exist in the K-dimensional codeword c j . Now the information symbol of the j-th user can be generated by non-overlappingly allocating the SCMA codeword c j on the delay-Doppler plane Γ.

[0045] Figure 7 shows a schematic diagram of the possible allocation of SCMA codewords in the delay-Doppler domain. The SCMA codewords can be allocated either along the delay axis, as shown in Figure 7 a), or can be allocated along the Doppler axis, as shown in Figure 7 b). For simplicity, here assume that M and N are integer multiples of K, i.e., [M] K = [N] K = 0, where [·]k Represents modulo k operation.

[0046] Then the delayed Doppler symbol Convert to time-frequency domain , for example, by performing an inverse symplectic finite Fourier transform (ISFFT) on each user.

[0047]

[0048] in, and denote the normalized M-point and N-point discrete Fourier transform (DFT) matrices, respectively.

[0049] Next, each time-frequency signal Transform to time domain signal For example, by applying the Heisenberg transformation and emitting a pulse g tx (t),

[0050]

[0051] Where T s =1 / MΔf is the sampling interval.

[0052] A cyclic prefix (CP) is added before the time domain signal generated by each user. After passing through the transmit filter, the signal of each UE is sent out through a dual selective fading channel.

[0053] The channel between the jth user and the uth RRH is characterized as

[0054]

[0055] Among them, PL(d uj ) represents the path loss related to the distance, d uj is the distance between the jth user and the uth RRH, u = {1, 2}. Note that for simplicity, the distance is assumed to remain constant during the OTFS transmission frame. uj Represents a time-varying multipath fading channel with a sampled impulse response

[0056]

[0057] Where L uj and t uj represents the number of multipaths and the timing offset between the jth user and the uth RRH; h uj,i , τ uj,i and v uj,i are the corresponding channel gain, delay and Doppler shift associated with the ith path, respectively.

[0058] The Doppler shift of the i-th path can be further written as

[0059] v uj,i =(k uj,i +β uj,i ) / NT, where the integer k uj,i and real number β uj,i ∈[-0.5,0.5] represents v uj,i The index and fractional part of .

[0060] Maximum channel tap P uj The pulse shaping filters implemented at the transmitter and receiver are typically root-raised cosine (RRC) filters, resulting in P rc (τ) is an equivalent overall raised cosine (RC) roll-off pulse. In addition, it is assumed that the CP is long enough to accommodate the maximum timing offset and maximum channel delay spread of all users. Therefore, there is no inter-frame interference.

[0061] At the receiver, the superposition of UE signals is received. After the time domain signal passes through the receive filter, the CP is removed. The received signal of the jth user from the uth RRH can be expressed as

[0062]

[0063] Then, by receiving the pulse g rx (t) Apply Wigner transform to obtain the time domain signal Transformed into the time-frequency domain,

[0064]

[0065] Finally, the time-frequency signal is transformed by applying the symplectic finite Fourier transform (SFFT) Transforming back to the delay-Doppler domain,

[0066]

[0067] For the convenience of analysis, g tx (t) and g rx (t) uses a rectangular pulse, and the baseband OTFS input-output relationship between the jth user and the uth RRH in the delay-Doppler domain is expressed as

[0068] The input-output relationship developed above can be further vectorized column by column as

[0069]

[0070] in and is a sparse matrix.

[0071] Therefore, the observation result obtained at the uth RRH can be expressed as

[0072]

[0073] in is the complex additive white Gaussian noise (AWGN) at the uth RRH, P j is the transmission power of the jth user.

[0074] Figure 8 1 shows an exemplary schematic block diagram of the uplink system discussed above. The figure shows J transmitters 300, some elements of one transmitter are shown in dashed boxes in the figure. In each transmitter 300, a binary data sequence b j is provided to the SCMA mapper 302, which outputs the corresponding codeword c j , which is allocated in the SCMA codeword allocator 304 to obtain information symbol X in the delay-Doppler domain j . Information symbol X j The signal s is subjected to OTFS modulation in the OTFS modulator 310, and the CP is added to the signal s outputted from the OTFS modulator 310 in the CP adder 312. j After passing through the transmit filter 314, the signal is transmitted to two or more RRHs 400 of the system. The transmission is represented by arrows from each transmit filter 314 to each antenna input 402 of the RRH represented by an adder symbol. At the antenna input 402 of the RRH, in addition to the signal from the transmitter 300, the added noise is received. In each RRH 400, the received superimposed signal and noise pass through a receive filter 404 and the CP is then removed in a CP removal unit 406. The resulting CP-free signal is provided to an OTFS demodulator 408, which demodulates the signal Output to the centralized or decentralized decoder 420. After decoding the signals from two or more RRHs, the obtained decoded signals are provided to the SCMA demapper 422, and the demapped signals are output.

[0075] German patent application 102021126321.1 discloses an exemplary method for transmitting and receiving signals or symbols via OTFS, which application is hereby incorporated herein in its entirety.

[0076] The next section discusses the actual receiver in which the signal for each UE is recovered from the signal received at the RRH. To this end, the equation for the signal received at the RRH is can be rewritten as

[0077]

[0078] in and

[0079] Note that since SCMA codewords are sparse, is a sparse vector. The number of non-zero entries in is only Indicates removal Valid input after the zero in , and Indicates that deletion corresponds to The valid matrix after the zero-indexed columns in . Therefore, The relationship can be simplified to

[0080]

[0081] because Contains from SCMA codeword information, so Every D non-zero elements from the same SCMA codeword in are grouped together. Similarly, The corresponding columns in are grouped together. The signal received at the RRH The equation can now be further rewritten as

[0082]

[0083] in

[0084]

[0085] It is easy to see that the receiving dimension of each RRH is smaller than the number of transmitted SCMA codewords, because J>K. Therefore, the traditional orthogonal multiple access multi-user detection cannot be directly applied to such an overloaded system. To achieve better performance, advanced receiver algorithms are required to recover the signal of each UE.

[0086] In the following, efficient centralized and decentralized detectors for multi-user detection are introduced and their respective advantages and disadvantages are discussed.

[0087] First, a centralized detector is introduced that utilizes the corresponding correlated transmit time slot signals received at multiple RRHs. In the centralized detector, the RRHs will forward the received signals to the BBU for centralized multi-user detection. Note that any time difference between the correlated signals can be compensated or corrected in the BBU. The received signal vector can be expressed as

[0088] y=Hx+ω,

[0089] in and

[0090]

[0091] The direct solution of the above equation is computationally complex because it involves large matrix inversions, and in OTFS communication systems, MN is usually on the order of thousands or even larger. Sparse connected factor graphs can be advantageously used to describe linear models because H is a sparse matrix. The corresponding factor graph includes 2MN observation nodes: y d ,d=1,2,…,2MN, and Variable node x c ,c=1,2,…, If h d,c ≠0 1×D , then the observation node y d With variable node x c There is an edge between them. Let I(d) and θ(c) denote the non-zero components of the dth row and cth column in H (i.e., h d,c ≠0 1×D ), where d = 1, 2, ..., 2MN and Denote the number of non-zero components in the corresponding d-th row and c-th column as |I(d)| and |θ(c)|.

[0092] Several general low-complexity and efficient message passing (MP) algorithms are known for symbol detection in sparse factor graphs. However, the known detection methods may not achieve the required performance for the OTFS-based multi-user SCMACoMP communication system discussed in this paper.

[0093] In the next section, a customized symbol detector is proposed that implements the Gaussian Approximation of Expected Propagation (GAEP). The customized GAEP detector further improves the performance of the previously known expected propagation (EP) symbol detection concept, which already brings better performance than the known MP detector concept with moderate complexity. It is worth noting that the proposed GAEP detector overcomes co-channel user interference and self-interference in the delay-Doppler domain. Co-channel user interference refers to the interference caused by UE signals transmitting on the same channel in a multi-user setting. Self-interference or multipath self-interference refers to the interference caused by multipath transmissions of the same UE.

[0094] The above is further discussed and eventually developed into the equation at the BBU with two RRHs

[0095] The system model can be represented by a factor graph, where each factor node y d Connect to multiple variable nodes x c, where d = 1, 2, ..., 2MN and Fig. 9 An exemplary factor graph is shown. At factor node y d (represented as boxes) and the corresponding variable node x c The iterative process loop is performed between (represented as circles) until the termination criterion is met. The iteration count is denoted by κ. The input of the iterative process is the OTFS decoded information symbol from the corresponding RRH Corresponding information H about the corresponding channel attributes between the UE and the two RRHs u , prior probability PD(x) and maximum number of iterations n c .

[0096] Initializing the average and variance (in and d∈θ(c)), and after the convergence index δ I After setting κ to zero and the number of iterations κ to 1, the iteration process begins. In this process, the iteration consists of calculating the emitted message on the factor node, and its result is passed to the connected variable node. The corresponding calculation of the emitted message is performed in the variable node, and its result is passed back to the factor node. The transfer of the calculation result is iteratively repeated until the termination criterion is met.

[0097] At each observation node, the received signal y d It can be expressed as

[0098]

[0099] Observation node y u The update message for each iteration is passed to the connected variable node x c ,c∈I(d). The updated and delivered messages are approximated as Gaussian distributions. Therefore, if h d,c [i]≠0, i=1,2,…,D, then the observation node y d The average and variance Send to variable node x c ,in

[0100]

[0101] here, and is the value from variable node x in the (κ-1)th iteration e The received mean and variance vectors. They can be initialized in the first iteration by projecting equally probable symbols onto a Gaussian distribution, as further shown below. σ 2 is the variance of the noise at the receiver input.

[0102] At each variable node x c , the posterior probability is determined based on the information received from the connected factor nodes. The posterior probability at each variable node can be expressed as follows

[0103]

[0104] in Indicates round up operation. is the predefined SCMA codebook for the jth user The set of non-zero elements of j Is from D-dimensional codeword. D (x c = x j ) represents x c = x j If no prior information is observed, the equal probability sign assumption can be used. Then the current posterior probability is projected onto the Gaussian distribution. and set the minimum allowed variance ε, that is, to avoid numerical instabilities. The average of the projections and variance Given by the following formula

[0105]

[0106] According to the Gaussian message combining rule, as described by I. Santos, J. J. Murillo-Fuentes, E. Arias-de Reyna, and P. M. Olmos in “Turbo EP-based equalization: A filter-type implementation” (IEEE Trans. Commun., Vol. 66, No. 9, pp. 4259-4270, September 2018) and S. As described in A.M. Cipriano, C. Poulliat, and M.-L. Boucheret, “Iterative Equalization with Decision Feedback Based on Expectation Propagation” (IEEE Trans. Commun., Vol. 66, No. 10, pp. 4473-4487, October 2018), if h d,c [i]≠0,i=1,2,…,D, then the external distribution can be updated in (6)

[0108]

[0109] Finally, the variable node x c Calculate the average and variance as follows and pass them back to the factor node

[0110]

[0111] Where Δ∈(0,1] is the message attenuation factor used to improve performance and convergence. If the updated variance If negative, the current update is ignored and the value from the previous iteration is used instead.

[0112] In the exemplary process discussed herein, for some small The convergence index Defined as

[0113]

[0114] and represents the indicator function. The convergence indicator is used to determine whether to update the result of the previous iteration. Here, the convergence indicator determines whether P(x c ) is updated to

[0115] if but

[0116] After each iteration the termination criterion is checked. The centralized GAEP detector discussed in this paper is Or reach the maximum number of iterations n c Once the termination criteria are met, Determined as

[0117]

[0118] Finally, SCMA demapping is applied to recover the information bits transmitted by each user.

[0119] It should be noted that although the system description provided before discussing the iterative process refers to a system with two RRHs, it can be easily extended to any other number of RRHs or antennas with the same main points.

[0120] Fig.10An exemplary schematic block diagram of the proposed GAEP detector process is shown. At the factor node, the operations performed include, for example, expected propagation estimates using Gaussian approximation. The operations at the factor node use the information available at the RRH 400, including the intermediate results of the calculations available at each variable node in each iteration. The results of the operations at the factor node are provided to the connected variable nodes. At each variable node, the operations performed include, for example, determining posterior probabilities and message combinations, which use information related to each UE 300, including the intermediate results of the calculations of the factor node when available in each iteration. The results of the operations at the variable node are provided to the factor node after attenuation, which improves the convergence of the process. According to the present invention, the messages updated and transmitted between the factor node and the variable node on the factor graph are approximated as Gaussians, which reduces the computational complexity of using exact messages.

[0121] The centralized GAEP detection process between factor nodes and variable nodes for two RRHs can be briefly summarized as follows:

[0122] enter: H1, H2, PD(x) and n c .

[0123] initialization:

[0124] The number of iterations κ=1.

[0125] Repeat iteratively

[0126] a) Calculate each factor node y d The average value in and variance If h d,c [i]≠0,i=1,2,…,D, then send them back to the connected variable node

[0127] b) At each variable node x c Generate average value and variance If h d,c [i]≠0,i=1,2,…,D, then pass them back to the connected observation nodes

[0128] c) Calculate the convergence index

[0129] d) If Update

[0130] e)κ:=κ+1;

[0131] until Or κ=nc

[0132] Output: P(x).

[0133] Next, we will introduce a decentralized detector that utilizes direct connections between RRHs that are grouped together to serve a specific area. The connections can be wired or wireless, and wired connections include electrical or optical connections. Direct connections between RRHs allow decentralized processing to be implemented in a straightforward manner, thereby enabling collaboration between these RRHs, which requires frequent communication between the RRHs.

[0134] The process structure of the distributed detector is as follows: Fig.11 Here, the first and second RRHs are grouped / composed into a group to serve a limited area. Specifically, the two RRHs apply a GAEP detection process similar to that described above (although independent) to perform symbol detection and iteratively exchange information to further improve performance.

[0135] The external average value is obtained from the second RRH and variance Afterwards, the prior probability of the first RRH is updated to

[0136]

[0137] By applying the GAEP procedure described above a certain number of times n I The first RRH outputs the probability Projection to the posterior Gaussian distribution middle.

[0138] External mean and variance can be calculated as follows and then transmitted to the second RRH,

[0139]

[0140] Similarly, the second RRH first updates the prior probability P D (x c ), and then use the GAEP process (n I Iterations) generate a posterior Gaussian distribution for each symbol. The external mean and variance Finally, it is generated and transmitted back to the first RRH to form an iterative cycle. o After the iteration, each RRH obtains final decision.

[0141] The decentralized detection process of each RRH performing GAEP detection can be briefly summarized as follows:

[0142] enter: H1, H2, n I and n o .

[0143] initialization: and

[0144] Repeat n times in parallel on each RRH o times (i.e., u=1, 2)

[0145] a) Update P D (x);

[0146] b) Using n I The GAEP process of the iterations obtains the output probability P(x u );

[0147] c) Projection to Gaussian distribution middle;

[0148] d) Calculate the external mean and variance

[0149] Exchange the extrinsic mean value between two RRHs and variance

[0150] Repeat until n iterations are completed, then output: P(x u ), u={1,2}.

[0151] From the above discussion, it can be seen that the complexity of the proposed centralized and decentralized detectors is mainly determined by the steps of GAEP. For each main loop iteration of GAEP, the complexity orders of equations (1)-(9) are and For the sake of brevity, express Therefore, the total complexity of the centralized detector and the decentralized detector are and

[0152] In view of the above discussion and according to a first aspect of the present invention, a method for receiving a binary data sequence from one or more mobile UEs is proposed, wherein the binary data sequence is represented by a SCMA signal transmitted to at least two RRHs of a CoMP radio communication system through an OTFS communication channel subjected to double selective fading, in which system at least two RRHs are communicatively connected to a common BBU and provide services to one or more mobile UEs from different directions relative to the corresponding mobile UEs. The method includes receiving a continuous time domain signal representing the SCMA signal transmitted from one or more mobile UEs at each of the at least two RRHs. In a subsequent step, in each of the at least two RRHs, a cyclic prefix is ​​removed from the received time domain signal, and OTFS demodulation is performed on the received continuous time domain signal in each of the at least two RRHs, thereby generating information symbols in the delayed Doppler domain. Then, a corresponding two-dimensional arrangement of information symbols in the delay-Doppler domain from at least two RRHs is provided or and information H about characteristics of corresponding channels between one or more mobile UEs and at least two RRHs u According to the present invention, centralized or decentralized signal detection is performed on the information symbol. The GAEP process is performed in the GAEP process. The detected symbols can then be demapped to recover the transmitted binary sequence of the corresponding mobile UE whose signal has been received.

[0153] Simulations show that similar n is needed c and n o n I Therefore, the proposed centralized and decentralized detectors have comparable computational complexity and are both able to effectively recover the signal of each individual user.

[0154] However, centralized detectors may face high communication overhead when transmitting information between RRHs and BBUs, especially when each RRH has a large number of antennas. The amount of complex-valued data transmitted from each RRH to the BBU includes MNN u Receive and 3N u L u Channel state information (CSI), where N u represents the number of antennas of the u-th RRH, and Then, the BBU will The detected complex-valued data is broadcast to each RRH. Therefore, the total complex-valued data transmitted between RRH and BBU in the centralized detector is For decentralized detectors, each RRH performs local computation in parallel, collaborates with each other, and exchanges limited consensus information. The information exchanged only includes the Average and variance, so that the overall transmission between each RRH Such a small amount of data exchange can not only alleviate the high requirements for interconnection bandwidth between distributed RRHs, but also avoid a large amount of data transmission between RRHs and BBUs in centralized detectors.

[0155] In addition, the BBU is generally located far away from the RRH, requiring high computing power to solve the large-dimensional problem of multi-user detection. Therefore, centralized detectors may exhibit higher latency in communication, which has a negative impact on user experience. However, in a decentralized detector, the calculation can be performed in a decentralized and parallel manner between two adjacent RRHs, which greatly reduces the latency in the communication system.

[0156] Table 1 shows the comparison of the performance of centralized detectors and decentralized detectors:

[0157]

[0158] In the next section, the OBSCMA system with CoMP discussed above for the uplink scenario is extended to the downlink scenario, ie, from two or more RRHs to one or more mobile UEs. Fig.12 An exemplary block diagram is shown in FIG. 3. In the SCMA mapper 302 of the BBU, various binary data streams b to be transmitted to the corresponding UE are mapped to the SCMA mapper 302 of the BBU. J Each of these maps to the SCMA signal c J and obtains each transmission signal X by SCMA codeword allocation performed in the SCMA codeword allocator of the BBU J The superimposed input delayed Doppler signal X is given by

[0159]

[0160] in Contains the delayed Doppler symbol of the jth user. The BBU provides the superimposed signal X to each RRH 400, of which only one RRH 400 is exemplarily circled in the box marked "400", where OTFS modulation is applied to the superimposed signal X in the OTFS modulator 310, and CP is added to the generated time domain signal in the CP adder 312. After passing through the transmit filter 314, each RRH 400 broadcasts the resulting time domain signal to the mobile users.

[0161] At each mobile UE 300, antenna 402 receives the transmitted signals from all RRHs 400 and the inevitable noise, represented by the adder symbol. In the corresponding mobile UE 300, after the signal is output from the receive filter 404, the CP is removed in the CP removal unit 406. Next, OTFS demodulation is applied in the OTFS demodulator 412 to recover the signal in the delay-Doppler domain, where the input-output relationship can be expressed as

[0162]

[0163] in, is the observation signal of the jth user, is the vectorized variable of X, is the complex AWGN of the jth user, P u represents the transmit power of the u-th RRH.

[0164] The above expression can be rewritten as

[0165]

[0166] in

[0167] After removing redundant zeros and grouping each D non-zero elements of the same SCMA codeword into After that, the above relationship can be simplified to

[0168] y j =H j x+ω j

[0169] in and

[0170] Since the input-output relationship has similar characteristics to the uplink system in the case of the centralized detector discussed previously, in the detector 420, exactly the same process can be used to detect and recover the signal from the jth user, and the decoded signal is available at the output of the SCMA demapper 422. It should be noted that the roles of the RRH and the UE are different with respect to Figure 8 Therefore, some components of the UE use Figure 8 The reference numerals used for the RRHs in the specification and vice versa are used for the RRHs in the specification.

[0171] According to a second aspect of the present invention, a method for receiving a binary data sequence represented by SCMA is proposed, wherein the binary data sequence is transmitted from two or more RRHs of a CoMP radio communication system to one or more mobile UEs through an OTFS communication channel subjected to double selective fading, in which system at least two RRHs are communicatively connected to a common BBU and provide services to one or more mobile UEs from different directions. The method comprises, at each of the one or more UEs, receiving signals from at least two RRHs from an antenna of the UE in the time domain. After removing a cyclic prefix from the received time domain signal, performing OTFS demodulation on the received continuous time domain signal, thereby generating information symbols in the delay Doppler domain. The information symbols in the delay-Doppler domain from at least two RRHs and the information H about the properties of the corresponding channels between the UE and the at least two first RRHs u After signal detection and recovery, its output is demapped to recover the binary sequence transmitted for the mobile UE. According to the present invention, signal detection and recovery includes initializing and executing an iterative loop, which performs iterative expected propagation with a Gaussian approximation process on signals from at least two RRHs serving the mobile UE from different directions. The process is repeated until the termination criterion is met, at which time the detected signal is output to the demapping step.

[0172] According to a third aspect of the present invention, a method is proposed for transmitting a binary data sequence in a corresponding transmission time slot from a common BBU and at least two RRHs connected to the common BBU via a CoMP radio system at the same time, wherein the binary data sequence is sent to two or more UEs via an OTFS communication channel subjected to double selective fading. In this system, at least two RRHs are communicatively connected to a common BBU and provide services to two or more mobile UEs from different directions. The method includes receiving binary sequences of two or more UEs at the BBU. In a signal mapper of the BBU, each binary data sequence to be transmitted to the corresponding UE is mapped into a K-dimensional SCMA codeword, which is arranged on a delay Doppler plane. At the BBU, the SCMA codewords are combined into a common or shared transmission frame, which is transmitted from the BBU to at least two RRHs. Each RRH performs OTFS modulation on the common / shared transmission frame, adds a cyclic prefix (CP) to the generated time domain signal, and transmits the resulting continuous time domain signal to two or more UEs through a communication channel.

[0173] In the next section, simulations are used to evaluate the performance of the proposed method for uplink and downlink communications. In the simulations, the carrier frequency is centered at 4 GHz and the subcarrier spacing Δf = 15 kHz. The roll-off factor of the RRC filter is set to 0.4 for both the transmitter and the receiver. Unless otherwise specified, delay-Doppler planes with M = 64 and N = 16 are considered. It is also assumed that J = 6 users simultaneously share K = 4 orthogonal resources and D = 2 non-zero entries are found in each codeword. The design of the user-specific codebook is in accordance with the proposal proposed in K. Xiao, B. Xia, Z. Chen, B. Xiao, D. Chen and S. Ma in "Codebook Design and Advanced Decoding for Capacity-Based Sparse Code Multiple Access Systems" (IEEE Transactions on Wireless Communications, Vol. 17, No. 6, pp. 3834-3849, June 2018), with size Q = 4 and the same transmit power is assumed.

[0174] In the simulation, the following Figure 6 The scenario shown, where the mobile users are evenly and independently distributed in the cells. The RRHs are located along the highway, separated by d h =1000m. The vertical distance between RRH and the highway line d p = 150m, the width of the road is d w =50m. The distance-dependent path loss propagation model is PL(d)[dB]=142.1+37.6log 10 (d), as proposed by M. Tao, E. Chen, H. Zhou and W. Yu in “Content-centric sparse multicast beamforming for cached cloud RAN” (IEEE Transactions on Wireless Communications, Vol. 15, No. 9, pp. 6118-6131, September 2016), where d is the distance in kilometers. The noise power spectral density of each receiver is set to -174 dBm / Hz. A typical urban channel model with exponential power delay distribution is adopted, as discussed in M. Failli in “Digital Land Mobile Radio Communications” (COST 207, European Communities, Luxembourg, 1989). The speed of the jth mobile user is set to λj = 300 km / h, resulting in a maximum Doppler shift ν j,max =111Hz, The Doppler shift of the i-th delay of the channel between the j-th user and the u-th RRH is generated using Jakes’ formula as described in P. Raviteja, K. T. Phan, and Y. Hong, “Embedded Pilot-Aided Channel Estimation for OTFS in Delay-Doppler Channels,” IEEE Transactions on Vehicular Technology, Vol. 68, No. 5, pp. 4906-4917, May 2019, and in P. Raviteja, K. T. Phan, Y. Hong, and E. Viterbo, “Interference Cancellation and Iterative Detection for Orthogonal Time-Frequency-Space Modulation,” IEEE Transactions on Wireless Communications, Vol. 17, No. 10, pp. 6501-6515, October 2018, i.e., ν uj,i =v j,max cos(ρ uj,i ), where if the jth user is moving away from the uth RRH, then ρ uj,i Evenly distributed in If the jth user is moving towards the uth RRH, then ρ uj,i Evenly distributed in superior.

[0175] Assume that the receiver knows all CSI. After a lot of experiments, we select Δ=0.3、ε=10 -8 , and n c = 20, which shows a satisfactory compromise between convergence speed and accuracy. The simulation results are the average of 1000 independent Monte Carlo experiments.

[0176] First, the impact of SCMA codeword allocation on receiver performance is studied. Fig.13 The average bit error rate (ABER) performance of the proposed OBSCMA and CoMP uplink systems under different SCMA codeword allocations is shown. Without loss of generality, a centralized GAEP detector is applied and the SCMA codewords are allocated along the delay axis, as Figure 7 (a), also called delay distribution, or distribution along the Doppler axis, as shown in Figure 7 (b) is also called Doppler distribution.

[0177] In order to highlight the superiority of the proposed GAEP algorithm, Fig.13The baseline performance of the conventional MP algorithm as proposed in HBMishra, P. Singh, AKPrasad, and R.Budhiraja, “OTFS Channel Estimation and Data Detection Design with Superimposed Pilots” (IEEE Transactions on Wireless Communications, 2021) and in P.Raviteja, KTPhan, Y.Hong, and E.Viterbo, “Interference Cancellation and Iterative Detection for Orthogonal Time-Frequency-Space Modulation” (IEEE Transactions on Wireless Communications, Vol. 17, No. 10, pp. 6501-6515, October 2018) is also provided. It can be observed that in the considered OBSCMA with CoMP uplink, the proposed GAEP algorithm outperforms the MP algorithm. It is also noted that the SCMA codeword allocation has little impact on the receiver performance. In the remaining simulations, unless otherwise stated, the SCMA codewords will be allocated along the delay axis.

[0178] Fig.14 The ABER performance of the proposed scheme is compared with Figure 4 The RRH solution shown in the figure is Figure 3 The ABER performances of the conventional cellular network schemes shown (denoted as Scheme I and Scheme II, respectively) are compared. Fig.14 The performance of the conventional OFDM-SCMA counterpart is also shown as a benchmark for different schemes. Note that the proposed GAEP algorithm can be directly generalized to the OFDM-SCMA scenario, so the details are omitted here for brevity. The results show that all receivers benefit from higher transmit power and the proposed OBSCMA can achieve better performance than its OFDM-SCMA counterpart in each scheme. The proposed OBSCMA with CoMP system significantly outperforms all other schemes due to the exploitation of channel diversity.

[0179] It is also noted that as the transmit power increases, the ABER performance of Scheme I and Scheme II cross each other in each OBSCMA and OFDM-SCMA scenario. This is because Scheme II has good propagation gain but limited spatial diversity gain.

[0180] Fig.15 The ABER performance of the proposed centralized and decentralized OBSCMA detectors with CoMP in the uplink of the system is shown. The results clearly show that after a sufficient number of iterations, the ABER performance of the decentralized detector will gradually approach the ABER performance of the centralized detector. To ensure the convergence of the decentralized detector, a larger number of iterations n is used. I Requires relatively small n o value, and vice versa, that is, a smaller number of iterations n I Need a larger n oTherefore, the proposed decentralized detector can strike a balance between the local processing efficiency of each RRH and the communication overhead between RRHs.

[0181] exist Fig.16 The ABER performance of centralized and decentralized detectors at different user mobile speeds was tested in . As the mobile user speed increases, the ABER performance gradually improves and reaches saturation after the speed exceeds 600km / h. This is because OTFS modulation can resolve more different paths in the Doppler domain with the help of higher user speeds. Therefore, better performance becomes possible. It is again noted that when the number of iterations is sufficient, the ABER performance of the decentralized detector is close to that of the centralized detector, while when the number of iterations is insufficient for different speeds, the ABER performance of the decentralized detector decreases slightly.

[0182] Fig.17 It is further shown that the centralized and decentralized detectors (n I =3,n o =5). Obviously, due to the higher resolution of the OTFS delay-Doppler grid, the ABER performance of both centralized and decentralized detectors improves with increasing M and N. This brings diversity benefits because the receiver can resolve more signal paths in the channel.

[0183] Finally, in Fig.18 The ABER performance of the proposed OBSCMA with CoMP system is tested for downlink scenario in

[14] . In order to highlight the advantages of the proposed scheme, the performance of the conventional OFDM-SCMA counterpart is provided as a benchmark. Fig.18 The performance of a special scenario, although unrealistic, is also shown, assuming that the signals transmitted by the RRHs before and after the user experience positive or negative Doppler shifts at the same time to illustrate the advantage of the proposed scheme. It is obvious that the proposed OBSCMA with CoMP system performs significantly better than its OFDM-SCMA counterpart in downlink transmission. Comparing only the special scenario, the proposed OBSCMA with CoMP system can exploit more diversity from signals experiencing positive and negative Doppler shifts, thereby achieving better performance.

[0184] The various elements of the transmitter and receiver presented herein may be implemented in hardware, software modules or a combination thereof (ie hardware controlled and / or parameterized by software).

[0185] The receiving and transmitting methods respectively proposed in this article can be represented by computer program instructions. When executed by a microprocessor, the computer program instructions respectively cause the computer and / or control hardware components of the receiver or transmitter of the OTFS-based multi-user SCMA communication system with CoMP as proposed above to execute the methods as proposed above.

[0186] The computer program instructions may be retrievably stored or transmitted on a computer readable medium or data carrier. The medium or data carrier may be physically embodied, for example in the form of a hard disk, a solid state disk, a flash memory device, etc. However, the medium or data carrier may also include a modulated electromagnetic, electrical or optical signal, which is received by the computer with the aid of a corresponding receiver and transmitted to the computer's memory and stored therein.

[0187] The proposed OBSCMA communication within the CoMP framework can naturally exploit diversity from the delay domain, Doppler domain, and spatial domain, resulting in better performance and effective support for large-scale mobile connections, especially in large-scale mobile connections. OBSCMA with CoMP systems further allows efficient processing in the receiver.

[0188] The proposed detection and recovery procedures for the GAEP-based centralized and decentralized detectors for uplink scenarios exploit the underlying channel diversity received from RRHs connected to the same BBU. The centralized GAEP procedure can be used in downlink scenarios without major modifications, where each UE receives superimposed signals from two or more RRHs. The OBSCMA communication within the proposed CoMP framework and the proposed detectors demonstrate superior effectiveness in both uplink and downlink communications, improving massive mobile connectivity and enabling high-speed and ultra-reliable communications for a variety of emerging mobile applications, including online gaming, high-speed railway systems, and vehicle-to-everything (V2X).

[0189] In certain embodiments of the system, decoding exploits the beneficial properties of mobile edge computing, particularly reduced communication latency and reduced risk of communication interface congestion.

[0190] Although the present invention has been described above assuming that each RRH has one antenna, the use of a multi-antenna system can provide additional diversity, multiplexing, and antenna gain compared to a traditional single-antenna system, and the present invention can be easily extended to such a multi-antenna system without departing from the scope of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0191] Hereinafter, exemplary embodiments of the present invention will be described in more detail with reference to the accompanying drawings. In the accompanying drawings,

[0192] Figure 1 shows a block diagram of a general OTFS transmission system,

[0193] Figure 2 A schematic example of SMA encoding is shown.

[0194] Figure 3 An exemplary conventional cellular network providing communications for a plurality of mobile UEs is shown.

[0195] Figure 4 A known communication system is shown, in which multiple sets of RRHs are connected to a common BBU via bidirectional connections.

[0196] Figure 5 A schematic diagram showing message flows and data processing in upload and download directions in a general CoMP system,

[0197] Figure 6 An exemplary schematic diagram of a CoMP system adopted by the present invention is shown.

[0198] Figure 7 Schematic diagram showing a possible allocation of SCMA codewords in the delay-Doppler domain,

[0199] Figure 8 shows an exemplary schematic block diagram of an uplink system discussed herein,

[0200] Fig. 9 An exemplary factor graph showing a centralized detection process,

[0201] Fig.10 An exemplary block diagram of the proposed centralized GAEP detector process is shown.

[0202] Fig.11 shows a schematic process structure of a decentralized detector process,

[0203] Fig.12 shows an exemplary block diagram of a downlink system discussed herein,

[0204] Fig.13 The average bit error rate (ABER) performance of the proposed OBSCMA with CoMP uplink system is shown for different SCMA codeword allocations.

[0205] Fig.14 The proposed scheme and Figure 4 The RRH co-location solution shown in the figure and Figure 3 ABER performance comparison of traditional cellular network solutions shown.

[0206] Fig.15 The ABER performance of the proposed centralized and decentralized detectors for OBSCMA with CoMP in the system uplink is shown.

[0207] Fig.16 The ABER performance of centralized and decentralized detectors at different user moving speeds is shown.

[0208] Fig.17 The results show that the centralized and decentralized detectors (n I =3,n o =5).

[0209] Fig.18 The ABER performance of the proposed method and conventional OFDM-SCMA communication is compared in two cases.

[0210] Fig.19 shows a schematic flow chart of a method according to a first aspect of the present invention,

[0211] Fig. 20 1 and 2 show exemplary flow charts of centralized signal detection and decentralized signal detection, respectively.

[0212] Fig.21 shows an exemplary flow chart of a method according to the second aspect of the present invention,

[0213] Fig. 22 shows an exemplary flow chart of a method according to a third aspect of the present invention,

[0214] Fig.23 An exemplary block diagram of a UE according to the present invention is shown.

[0215] Fig.24 shows an exemplary block diagram of an RRH according to the present invention, and

[0216] Fig.25 An exemplary block diagram of a BBU according to the present invention is shown.

[0217] Throughout the drawings, the same or similar elements may be represented by the same reference numbers. DETAILED DESCRIPTION

[0218] Figures 1 to 18 This has been discussed before and will not be repeated here.

[0219] Fig.19An exemplary flow chart of a method 100 for receiving a binary data sequence from one or more mobile UEs 300 according to a first aspect of the present invention is shown. In step 110, a continuous time domain signal representing a SCMA signal transmitted from one or more mobile UEs 300 is received at each of two or more RRHs 400. Next, in step 120, a cyclic prefix is ​​removed from the time domain signal received from each of at least two RRHs 400, and in step 130, each of the two or more RRHs performs OTFS demodulation on the received continuous time domain signal, thereby generating a two-dimensional arrangement corresponding to information symbols in the delay Doppler domain. In step 140, each of the two or more RRHs provides a corresponding two-dimensional arrangement of information symbols in the delay Doppler domain or subjects it to centralized or decentralized signal detection. The detection signal output from the signal detection is provided to a demapping stage (step 160) for recovering the transmitted binary sequence of the corresponding mobile UE 300 of the received signal.

[0220] Note that the boxes with dashed outlines and dashed arrows connecting the boxes in the figure indicate optional parallel execution of decentralized signal detection steps.

[0221] Fig. 20 a) and b) show exemplary flow charts of centralized signal detection and decentralized signal detection, respectively. Fig. 20 The centralized signal detection shown in a) starts with receiving a corresponding two-dimensional arrangement of information symbols in the delay-Doppler domain from at least two RRHs 400 and information about the properties of the corresponding channels between the UE and at least two first RRHs 400 in the common BBU (step 142). Next, in step 144, the information from the at least two RRHs 400 is mapped onto a factor graph having factor nodes and variable nodes, and an iterative loop is initialized and executed in step 150. The iteration includes performing iterative expectation propagation with a Gaussian approximation process on signals from at least two RRHs 400 serving one or more mobile UEs 300 from different directions (step 152). In step 156, it is checked whether the termination criteria are met. If not, that is, the "no" branch of step 156, the iteration is repeated. Otherwise, it is the "yes" branch of step 156, and in step 158, the detected signal is output to the demapping step (not shown in the figure).

[0222] Fig. 20b) The decentralized signal detection shown starts with initialization and execution of an iterative loop (step 150). The iteration includes executing step 152, in each of at least two RRHs 400 serving one or more mobile UEs 300 from different directions, iteratively performing the expected propagation and Gaussian approximation process on the signal received in the corresponding RRH 400. At the end of each iteration, in step 154, the RRHs 400 exchange the corresponding intermediate results and check in step 156 whether the termination criteria are met. If not, that is, the "no" branch of step 156, the iteration is repeated. Otherwise, it is the "yes" branch of step 156, and in step 158, the detected signal is output to the demapping step (not shown in the figure).

[0223] Fig.21 An exemplary flow chart of a method 200 for receiving a binary data sequence according to a second aspect of the present invention, the binary data sequence being represented by a SCMA signal transmitted from two or more RRHs 400 of a CoMP radio communication system to one or more mobile UEs 300 through an OTFS communication channel subject to double selective fading, is shown. In step 202, in the time domain, a superposition of signals from at least two RRHs 400 is received at an antenna 402 of a UE 300. In step 204, a cyclic prefix is ​​removed from the received time domain signal. In step 206, OTFS demodulation is performed on the received continuous time domain signal, thereby generating a corresponding two-dimensional arrangement of information symbols in the delay-Doppler domain, and in step 208, signal detection is performed on the information symbols using attribute information about the corresponding channels between the UE 300 and at least two first RRHs 400. Signal detection is an iterative process, and in step 210, the detected symbols from at least two RRHs 400 are mapped to a factor graph having factor nodes and variable nodes, after which an iterative loop is initialized in step 212. The iterations include iterative expectation propagation with a Gaussian approximation process in step 214. At the end of each iteration, in step 216, it is checked whether the termination criteria are met. If not, i.e., the "no" branch of step 216, the iterations are repeated. Otherwise, the "yes" branch of step 216, in step 218, the detected signal is output to a demapping step 220 to retrieve the transmitted signal.

[0224] Fig. 22A method 500 is shown for simultaneously transmitting a binary data sequence from a common BBU and in corresponding transmission time slots in a CoMP radio system via at least two RRHs 400 connected to the common BBU, the binary data sequence being sent to two or more UEs 300 through an OTFS communication channel subject to double selective fading according to a third aspect of the present invention. In step 502, binary sequences of two or more UEs 300 are received at the BBU. In step 504, each binary data sequence to be transmitted to the corresponding UE 300 is mapped into a K-dimensional SCMA codeword, and in step 506, the SCMA codewords are combined into a common or shared transmission frame. In step 508, the common or shared transmission frame is transmitted from the BBU to at least two RRHs 400. Each RRH performs OTFS modulation on the common or shared transmission frame in step 510, and adds a cyclic prefix to the generated time domain signal in step 512. In step 514, each RRH 400 transmits the generated continuous time domain signal to two or more UEs 300 through a communication channel.

[0225] Fig.23 An exemplary block diagram of a UE 300 according to yet another aspect of the invention is shown. One or more antennas 316, 402 and associated transmit and / or receive circuits 302-314, 404-422, one or more microprocessors 450, a volatile memory 452 and a non-volatile memory 454 are communicatively connected via one or more signal or data lines or buses 458. The non-volatile memory 454 stores computer program instructions which, when executed by the one or more microprocessors 450, configure the UE 300 to perform the method according to the second aspect of the invention.

[0226] Fig.24 An exemplary block diagram of an RRH 400 according to a further aspect of the invention is shown. One or more antennas 316, 402 and associated transmit and / or receive circuits 302-314, 404-422, one or more microprocessors 450, a volatile memory 452 and a non-volatile memory 454, and one or more interfaces 456 enabling communication with a BBU and / or a further RRH are communicatively connected via one or more signal or data lines or buses 458. The non-volatile memory 454 stores computer program instructions which, when executed by the one or more microprocessors 450, configure the RRH 400 to perform the RRH-side steps of the method according to the first and / or third aspects of the invention.

[0227] Fig.25An exemplary block diagram of a BBU according to yet another aspect of the present invention is shown. One or more microprocessors 450, a volatile memory 452 and a non-volatile memory 454 and one or more interfaces 456 for enabling communication with two or more RRHs 400 are communicatively connected via one or more signal or data lines or buses 458. The non-volatile memory 454 stores computer program instructions that, when executed by the one or more microprocessors 450, configure the BBU to perform the BBU-side steps of the method according to the first and / or third aspects of the present invention.

[0228] Definitions and Reference Number List (Part of the Specification)

[0229] ABER Average Bit Error Rate

[0230] AWGN Additive White Gaussian Noise

[0231] Δf Subcarrier spacing

[0232] DFT Discrete Fourier Transform

[0233] iSFFT Inverse Finite Symplectic Fourier Transform

[0234] M Delay box quantity

[0235] MSE Mean Square Error

[0236] MP Messaging

[0237] N is the number of Doppler frequency bins

[0238] OFDM Orthogonal Frequency Division Multiplexing

[0239] OTFS Orthogonal Time-Frequency Space

[0240] SFFT Finite Symplectic Fourier Transform

[0241] SNR Signal to Noise Ratio

[0242] 100 Methods

[0243] 110 Receiving signal

[0244] 120 Remove CP

[0245] 130 OTFS demodulation

[0246] 140 signal detection

[0247] 142 Receiving information symbols and channel characteristics in public BBU

[0248] 144 Mapping

[0249] 150 Initialize & execute iteration loop

[0250] 152Iterative Expectation Propagation Using Gaussian Approximation

[0251] 154 Exchange intermediate results

[0252] 156Does the termination criteria meet?

[0253] 158 output detection signal

[0254] 160 SCMA demapping

[0255] 200 Methods

[0256] 202 Receive superimposed signal

[0257] 204 Remove CP

[0258] 206 OTFS demodulation

[0259] 208 Signal Detection

[0260] 210 Mapping

[0261] 212 Initialize & execute iterative loop

[0262] 214Iterative Expectation Propagation Using Gaussian Approximation

[0263] 216Does the termination criteria meet?

[0264] 218 output detection signal

[0265] 220 SCMA demapping

[0266] 300 transmitters / UE

[0267] 302 SCMA Mapper

[0268] 304SCMA codeword distributor

[0269] 306 first transmitting side conversion unit

[0270] 308 second transmitting side conversion unit

[0271] 310 OTFS modulator

[0272] 312 CP Adder

[0273] 314 Transmitter Filter

[0274] 316 Antenna

[0275] 400 receivers / RRH

[0276] 402 Antenna

[0277] 404 Receive Filter

[0278] 406 CP Removal Unit

[0279] 408 first receiver side conversion unit

[0280] 410 Second receiver side conversion unit

[0281] 412 OTFS Demodulator

[0282] 414Channel estimation and equalization module

[0283] 420 detector / decoder

[0284] 422SCMA Demapper

[0285] 450 microprocessor

[0286] 452 Volatile Memory

[0287] 454 Non-volatile memory

[0288] 456 interface

[0289] 458 signal / data line / bus

[0290] 500 Methods

[0291] 502 Accepted

[0292] 504 Mapping

[0293] 506 Merge

[0294] 508 Launch

[0295] 510OTFS modulation

[0296] 512Add CP

[0297] 514 launch

Claims

1. A method (100) for receiving a binary data sequence from one or more mobile user equipment (UE) (300), the binary data sequence being represented by a sparse code multiple access (SCMA) signal, the sparse code multiple access (SCMA) signal being transmitted over an orthogonal time-frequency space modulation (OTFS) communication channel subject to double selective fading to at least two remote radio heads (RRHs) (400) of a coordinated multi-point (CoMP) radio communication system, wherein the at least two RRHs (400) are communicatively connected to a common baseband unit (BBU) and serve the one or more mobile UEs (300) from different directions relative to the respective mobile UEs (300), the method (100) comprising: - receiving (110) at each of the at least two RRHs (400) a continuous time domain signal representing a SCMA signal transmitted from the one or more mobile UEs (300), - in each of the at least two RRHs (400), removing (120) a cyclic prefix from the received time domain signal, - In each of the at least two RRHs (400), performing (130) OTFS demodulation on the received continuous time domain signal to obtain information symbols The corresponding two-dimensional arrangement in the delay-Doppler domain, - Corresponding information symbols in the delay-Doppler domain from the at least two RRHs (400) and information (H) on characteristics of corresponding channels between the UE and the at least two first RRHs (400). u ) is provided to or subjected to centralized or decentralized signal detection (140-1, 140-2), and - outputting the detected symbols to a demapping stage (160) in order to recover the transmitted binary sequence of the corresponding mobile UE (300) whose signal has been received, The centralized and decentralized signal detection (140-1, 140-2) both detect the information symbol Perform an iterative Gaussian approximation expectation propagation process.

2. The method (100) according to claim 1, wherein: The centralized signal detection (140-1) includes: - receiving (142) information symbols in the delay-Doppler domain from the at least two RRHs (400) and information (H) on properties of corresponding channels between the UE and at least two first RRHs (400) in the common BBU. u ), - mapping (144) the information from the at least two RRHs (400) onto a factor graph having factor nodes and variable nodes, - initializing (150) and executing an iterative loop that performs (152) iterative expectation propagation using a Gaussian approximation process on signals from at least two RRHs (400) serving the one or more mobile UEs (300) from different directions, - repeating (156) said iteration until a termination criterion is met, and - Outputting (158) the detected signal to a demapping step (160).

3. The method (100) according to claim 1, wherein: The decentralized signal detection (140-2) includes, at each of the at least two RRHs (400) that are communicatively connected to each other: - initializing (150) and executing an iterative loop that performs (152) iterative expectation propagation using a Gaussian approximation process on the signals of each RRH (400), - exchanging (154) intermediate results with the at least one other RRH (400) at the end of each iteration, - repeating (156) said iteration until a termination criterion is met, and - Outputting (158) the detected signal to a demapping step (160).

4. The method (100) according to claim 3, wherein: Outputting (158) the detected signal to the demapping step (160) includes transmitting the detected signal to a common BBU.

5. A method (200) for receiving a binary data sequence represented by a SCMA signal transmitted from two or more RRHs (400) of a CoMP radio communication system to one or more mobile UEs (300) through an OTFS communication channel subject to double selective fading, wherein the at least two RRHs (400) are communicatively connected to a common BBU and serve the one or more mobile UEs (300) from different directions, the method (100) comprising: At each of the one or more UEs (300): - receiving (202) a superposition of signals from at least two RRHs (400) at an antenna (402) of the UE (300) in the time domain, - removing (204) a cyclic prefix from the received time domain signal, - performing (206) OTFS demodulation on the received continuous time domain signal, thereby generating information symbols in the delay Doppler domain The corresponding two-dimensional arrangement of - information symbols in the delay-Doppler domain from the at least two RRHs (400) and information (H) on characteristics of corresponding channels between the UE (300) and the at least two first RRHs (400). u ) performs signal detection (208), and - demapping (220) the detected symbols to recover the binary sequence transmitted for the mobile UE (300), The signal detection and recovery (208) includes: - mapping (210) the detected symbols from the at least two RRHs (400) onto a factor graph having factor nodes and variable nodes, - initializing (212) and executing an iterative loop that performs (214) iterative expectation propagation using a Gaussian approximation process on signals from at least two RRHs serving the mobile UE (300) from different directions, - repeating (216) said iteration until a termination criterion is met, and - Outputting (218) the detected signal to a demapping step (220).

6. A method (500) for simultaneously transmitting a binary data sequence in corresponding transmission time slots from a common BBU via at least two RRHs (400) of a CoMP radio system, wherein the binary data sequence is sent to two or more UEs (300) through an OTFS communication channel subject to double selective fading, wherein the at least two RRHs (400) are communicatively connected to the common BBU and serve the one or more mobile UEs (300) from different directions, the method comprising: - receiving (502) at the BBU the binary sequences of the two or more UEs (300), - in a signal mapper of the BBU, mapping (504) each binary data sequence to be transmitted to the corresponding UE (300) into a K-dimensional SCMA codeword, the K-dimensional SCMA codeword being arranged on a delay-Doppler plane, - combining (506) the SCMA codewords into a common or shared transmission frame at the BBU, - transmitting (508) the common or shared transmission frame from the BBU to the at least two RRHs (400), - in each of the at least two RRHs (400), performing OTFS modulation (510) on the common or shared transmission frame, - in each of the at least two RRHs (512), adding (512) a cyclic prefix (CP) to the generated time domain signal, and - transmitting (514) the resulting continuous time domain signal from each of the at least two RRHs (400) to the two or more UEs (300) over the communication channel.

7. A UE (300) or RRH (400), comprising the following structures, respectively, communicatively connected via one or more signal or data lines or buses (458): one or more antennas (316, 402) and associated transmit and / or receive circuits (302-314, 404-422), one or more microprocessors (450), volatile memory (452) and non-volatile memory (454), wherein: The non-volatile memory (454) stores computer program instructions which, when executed by the microprocessor (450), configure the UE (300) to perform the method of claim 5, or respectively configure the RRH (400) to perform the method of claim 1 and / or claim 3, and / or configure the RRH (400) to perform the RRH-side steps of the method of claim 6.

8. A BBU comprising the following structures, which are communicatively connected via one or more signal or data lines or buses (458): one or more antennas (316, 402) and associated transmit and / or receive circuits (302-314, 404-422), one or more microprocessors (450), volatile memory (452), and non-volatile memory (454), wherein: The non-volatile memory (454) stores computer program instructions which, when executed by the microprocessor (450), configure the UE (300) to perform the BBU-side steps of the method of claim 6.

9. A wireless communication system comprising two or more RRHs (400) according to the first alternative of claim 7, the RRHs (400) being communicatively connected to a common BBU.

10. A computer program product comprising computer program instructions which, when executed by a microprocessor, cause a computer and / or a control hardware block, module or component of a UE (300) according to claim 7 to perform the method of claim 5, or cause a computer and / or a control hardware block, module or component of an RRH (400) according to claim 7 to perform the method of claim 1 and / or claim 3, or cause a computer and / or a control hardware block, module or component of a BBU associated with two or more RRHs (400) to perform the steps described in claim 2.

11. A computer readable medium or data carrier on which the computer program product according to claim 10 is retrievably transmitted or stored.

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