WO2018100428A1

WO2018100428A1 - Method and device for signal processing in communication system

Info

Publication number: WO2018100428A1
Application number: PCT/IB2017/001587
Authority: WO
Inventors: Zhe LUO; Tao Tao; Jianguo Liu; Gang Shen; Yan Meng
Original assignee: Alcatel Lucent SAS
Current assignee: Alcatel Lucent SAS
Priority date: 2016-11-29
Filing date: 2017-11-28
Publication date: 2018-06-07
Anticipated expiration: 2019-05-29
Also published as: CN108123903A; CN108123903B

Abstract

The present disclosure relates to a method and device for signal processing in a communication system. The present disclosure uses orthogonal and quasi-orthogonal spreading sequences and spatial channels to discriminate data of a terminal device. Since the spreading sequences utilized by data of the same terminal device are orthogonal, interference from the user itself is eliminated. As spreading sequences utilized by different terminal devices are quasi-orthogonal, interference between users is inhibited through spatial channels. Compared with other non-orthogonal multi-user access scheme, the present disclosure increase the supported overloading factor by combining the orthogonal spreading sequences and spatial channels.

Description

METHOD AND DEVICE FOR SIGNAL PROCESSING IN

COMMUNICATION SYSTEM

FIELD

[0001] The present disclosure generally relates to the field of communication, and more specifically, to a method and device for signal processing in a communication system.

BACKGROUND

[0002] The fifth- generation (5G) mobile communication system needs to support a scenario of massive machine-type-communications (mMTC). In diversified mMTC scenarios, uplink small packets traffic widely exists. Because the grant-free contention based uplink transmission for small packets can reduce signaling overhead and transmission latency, it will play an important role.

[0003] In a conventional mobile communication system, in case that a terminal device in idle state needs to transmit some uplink small packets, the terminal device should connect to a network device (for example, a base station device such as an eNB or a NodeB) before data transmission and obtain the uplink transmission grant. Then, the mobile communication system suffers a high signaling overhead for small packet transmission and a large connection latency. The grant- free contention based uplink transmission can realize one- step uplink transmission. In other words, the terminal device transmits data using contention based uplink transmission, and the base station can recover the data.

[0004] In the contention based uplink transmission, since the network device does not allocate resources for data, data signals for different active terminal devices may collide. Therefore, the form of a signal needs be designed to reduce the collision probability. On the other hand, the transmission capacity for each terminal device and the maximum number of active terminal devices that a system can support simultaneously are important metrics for signal design.

SUMMARY

[0005] According to a first aspect of the present disclosure, there is disclosed a method of signal processing. The method comprises: modulating a signal to be transmitted in a frequency domain; spreading the modulated signal with an orthogonal spreading sequence, the orthogonal spreading sequence being a non-constant amplitude sequence generated randomly; and converting the spread signal from the frequency domain to a time domain.

[0006] According to a second aspect of the present disclosure, there is disclosed a method of signal processing. The method comprises: obtaining information associated with a plurality of terminal devices, the information including orthogonal spreading sequences specific to the terminal devices and channel responses for terminal devices, the orthogonal spreading sequences being non-constant amplitude sequences generated randomly; receiving a signal to be processed; converting the received signal from a time domain to a frequency domain; and de-spreading the converted signal at least in part based on the information.

[0007] According to a third aspect of the present disclosure, there is disclosed a terminal device. The terminal device comprises a controller and a memory including instructions. The instructions, when executed by the controller, cause the terminal device to implement actions, the actions comprising: modulating, in a frequency domain, a signal to be transmitted; spreading the modulated signal with an orthogonal spreading sequence, the orthogonal spreading sequence being a non-constant amplitude sequence generated randomly; and converting the spread signal from the frequency domain to a time domain.

[0008] According to a fourth aspect of the present disclosure, there is disclosed a network device. The network device comprises a controller and a memory including instructions. The instructions, when executed by the controller, cause the network device to implement actions, the actions comprising: obtaining information associated with a plurality of terminal devices, the information including orthogonal spreading sequences specific to the terminal devices and channel responses for terminal devices, the orthogonal spreading sequences being non-constant amplitude sequences generated randomly; receiving a signal to be processed; converting the received signal from a time domain to a frequency domain; and de-spreading the converted signal at least in part based on the information. BRIEF DES CRIPTION OF THE DRAWINGS

[0009] Through the following detailed description with reference to the accompanying drawings, the above and other objectives, features, and advantages of example embodiments of the present disclosure will become more apparent. In the example embodiments of the present disclosure, the same reference signs usually represent the same components. [0010] Fig. 1 is a block diagram illustrating an architecture of a communication system according to an embodiment of the present disclosure; [0011] Fig. 2 is a flowchart illustrating a method of signal processing according to the first aspect of an embodiment of the present disclosure;

[0012] Fig. 3 is a flowchart illustrating a method of signal processing according to the second aspect an embodiment of the present disclosure; [0013] Fig. 4 is a block diagram illustrating an apparatus according to the third aspect of an embodiment of the present disclosure;

[0014] Fig. 5 is a block diagram illustrating an apparatus according to the fourth aspect of an embodiment of the present disclosure;

[0015] Fig. 6 is a block diagram illustrating a device according to an embodiment of the present disclosure;

[0016] Fig. 7 is a comparison chart of signal processing performance according to an embodiment of the present disclosure;

DETAILED DESCRIPTION

[0017] Principles and spirits of the present disclosure will now be described with reference to several example embodiments illustrated in the drawings. It should be appreciated that description of these specific embodiments is merely to enable those skilled in the art to better understand and implement the present disclosure, rather than to limit the scope of the present disclosure in any manner.

[0018] The term "network device" used herein refers to other entities or nodes having specific functions in a base station or communication network. The term "base station" as used herein can represent a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), a remote radio unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, or a low power node such as a pico station and a femto station, and the like. In the context of the present disclosure, for the ease of discussion, the terms "network device" and "base station" can be used interchangeably, and an eNB may be mainly taken as an example of the network device.

[0019] The term "terminal device" or "user equipment" (UE) used herein refers to any terminal devices that can perform wireless communication with a base station or with each other. As an example, a terminal device may include a mobile terminal (MT), a subscriber station (SS), a portable subscriber station (PSS), a mobile station (MS), or an access terminal (AT), and the above devices mounted on a vehicle. In the context of the present disclosure, for the ease of discussion, the terms "terminal device" and "user equipment" can be used interchangeably.

[0020] Until now, many non-orthogonal multi-user access (NOMA) schemes have been proposed, such as sparse code multiple access (SCMA) and resource spread multiple access (RSMA). However, these NOMA schemes do not provide detailed methods to support spatial multiplexing by multiple antennae without pre-coding. In the grant- free uplink transmission, due to lack of channel responses, pre-coding is hardly realized. As a matter of fact, it is difficult for some NOMA schemes to support spatial multiplexing without pre-coding. For instance, sparse code multiple access SCMA and pattern division multiple access PDMA schemes are obtained based on the observation of the sum of data of a plurality of terminal devices in each orthogonal resource, namely,

m where y_k denotes the observation for resource k, X_m denotes the data of terminal device m, and h_{m k} denotes the channel response for the terminal device m at resource k. [0021] For the case of multiple receiving antennae, the observation becomes

(Λ,Ι ' - ' ^ )^7" = Κ,Ν^{Χ Τ} = ^HX ( 2 ) where N is an integer which denotes the number of receiving antennae. When spatial multiplexing is utilized, the number of terminal devices is far greater than that of the receiving antennae. Thus, it is difficult to separate a small amount of data for each terminal device. In other words, the matrix H cannot be converted by the receiver into a block diagonal matrix, which implies that the receiver based on the message-passing algorithm (MPA) cannot work efficiently.

[0022] In a 5G mobile communication system, the base station is equipped with a large number of antennae. At the same time, supporting spatial multiplexing will dramatically increase the transmission capacity for each active terminal device and the maximum number of terminal devices that are active simultaneously. However, for the grant-free uplink transmission, pre-coding cannot be realized and thus, spatial multiplexing with pre-coding cannot be supported. Therefore, to support spatial multiplexing in case of pre-coding, dense spreading for data signals is preferred.

[0023] Most of the dense spreading based NOMA schemes use dedicatedly designed short length spreading sequences, such as a Zadoff-Chu (ZC) sequence. It is noted that, due to quasi-synchronization for grant-free transmission, the subcarriers of an OFDM symbol suffer from random linear phase rotation. Therefore, a new spreading sequence should be designed.

[0024] The method of the present disclosure considers an uplink transmission scenario, where each terminal device has a single transmission antenna and each network device (such as an eNB) has a large number of receiving antennae. For the case that a terminal device has a plurality of antennae, the terminal device can be considered as a plurality of virtual terminal devices, each of the virtual terminal devices having a single antenna. With orthogonal spreading sequences and spatial multiplexing, methods of the present disclosure can distinguish different data of different terminal devices. In an example scenario, a large number of terminal devices transmit data in the same resource. Namely, there is a high overloading factor. The eNB distinguishes data of different terminal devices with spatial channels. The method of the present disclosure is based on long random orthogonal spreading sequences which can be used to demodulate data of the same terminal device. As the terminal device has a single transmission antenna, data of the same terminal device cannot be distinguished through spatial channels. [0025] Fig. 1 is a block diagram illustrating a communication system 100 according to the embodiments of the present disclosure. The communication system 100 comprises a transmitter 110, a channel 120, and a receiver 130. According to an embodiment of the present disclosure, the transmitter 110 can be a terminal device and the receiver 130 can be a base station device, such as an eNB or a NodeB. [0026] According to an embodiment of the present disclosure, in case that the transmitter 110 transmits data, firstly, a signal to be transmitted is modulated in a frequency domain. Then, the modulated signal is spread with orthogonal spreading sequence which is a randomly generated non-constant amplitude sequences. Then, the spread signal is converted from the frequency domain into a time domain. Correspondingly, in case that the receiver 130 receives data, first of all, information associated with a plurality of terminal devices is obtained. The information includes an orthogonal spreading sequence specific to a terminal device and a channel response for the terminal device. The orthogonal spreading sequence is a randomly generated non-constant amplitude sequence. Then, the signal to be processed is received from channel 120. The received signal is converted from the time domain into the frequency domain. The converted signal is de-spread at least partially based on the information. [0027] Fig. 2 is a flowchart illustrating a method 200 of signal processing by a transmitter 110 in a communication system according to an embodiment of the present disclosure. In some embodiments, the method 200, for instance, can be implemented by the transmitter 110. It shall be appreciated that method 200 may further comprise additional actions and/or omit the shown actions. The scope of the solution described in the present disclosure is not limited in this regard.

[0028] At 210, a signal to be transmitted is modulated in the frequency domain. In some embodiments, the manner of modulation may comprise quadrature phase shift keying (QPSK), quadrature amplitude modulation (QAM), and so on. In some embodiments, QPSK or QAM modulation may comprise serial-to-parallel conversion of the signal to be transmitted and symbol mapping. For example, QAM modulation in the present disclosure may be implemented in various orders, such as 64QAM. However, it should be appreciated that the modulation manner in embodiments of the present disclosure is not limiting. It is possible to utilize various manners of modulation to modulate the signal to be transmitted.

[0029] At 220, the modulated signal is spread with an orthogonal spreading sequence which is a randomly generated non-constant amplitude sequence. In some embodiments, the transmitter 110 can spread the modulated signal in such a manner that a unitary matrix specific to the terminal device can be generated based on a random matrix, and that the unitary matrix can be utilized to spread the modulated signal. It should be appreciated that the unitary matrix is only a form of random orthogonal matrices and in the present disclosure, it is only used for illustrative purpose. In some embodiments, an orthogonal spreading sequence for data symbols of a terminal device can be selected from the unitary matrix. An orthogonal spreading sequence for the data symbol can also be determined directly with data symbols of the terminal device, the orthogonal spreading sequence being in the unitary matrix. [0030] In some embodiments, a baseband signal can be generated through the orthogonal spreading sequence selected in the present disclosure. The baseband signal can be an OFDM symbol. A data signal occupies one or more continuous or non-continuous subcarriers of the OFDM symbol. A plurality of terminal devices can transmit their respective baseband signals within the same time frequency resource or resource region, the time frequency resource being a physical resource block (PRB). As a non-limiting embodiment, the spreading process is illustrated herein. For example, based on a spreading sequence

in the frequency domain, where N denotes the spreading length for OFDM. In some embodiments, a plurality of spread signals should be allocated to orthogonal frequency division multiplexing subcarriers. For the selected spreading sequence [Si > S₂ > S_N ] ₅

K

k=l, 2, K, the value of subcarrier i is ^ ·¾ , where K denotes the number of

k=\

constellation symbols and x^ denotes modulated signals. In some embodiments, the spreading sequence can be divided into a plurality of portions, and each portion is transmitted on an OFDM symbol. For instance, the spreading sequence [Si , S₂ , S_N can be divided into two portions, namely, [Si ·, S₂ > · · · ·> ^SN/2 ^ ^and [^ΛΓ/2+1 ' ^ΛΓ/2+2 ' · · · ' ^ΛΓ ] , where N is an even number, and the length of the spreading sequence for the OFDM symbol is N/2.

[0031] In some embodiments, to generate a random orthogonal matrix, it is necessary to obtain the identification and/or transmission parameter of the terminal device as a seed. Then, based on the obtained seed, a random matrix is generated using a pseudo-random algorithm. In some embodiments, a unitary matrix is generated by performing singular value decomposition (SVD) to the random matrix.

[0032] In some embodiments, the identification of the terminal device comprises international mobile equipment identity (IMEI). The transmission parameter comprises an orthogonal frequency division multiplexing symbol number or an sub-frame number. In some embodiments, the identification of the terminal device may further comprise a user name. Alternatively, an identifier to identify the terminal device by other parties can also be used as a seed to generate the random matrix. In case that the orthogonal frequency division multiplexing symbol number is employed, as the obtained orthogonal spreading sequence is unique for the symbol, the orthogonal spreading sequence for the number of the symbol can be obtained directly without a selection process.

[0033] In some embodiments, the orthogonal spreading sequence can be a non-constant amplitude sequence. In such an embodiment, the orthogonal spreading sequence differs from a Zadoff-Chu (ZC) sequence which has constant amplitude. In other words, the present disclosure does not require the orthogonal spreading sequence to be a constant amplitude sequence. That is to say, items in the sequence are not required to have a normalized absolute value. Thus, the flexibility of the generated orthogonal spreading sequence can be improved, so as to reduce limitations for system design.

[0034] By performing orthogonal spreading to signals, the signals received at receiver 130 can be distinguished effectively. Collision between different signals of the same terminal device and corresponding signals of different terminal devices can be avoided. It should be appreciated that the orthogonal spreading sequences used between different signals of the same terminal device are orthogonal to each other, and thus, can be distinguished effectively at receiver 130. The spreading sequences utilized between different terminal devices are not necessarily orthogonal. That is, at receiver 130, signals of different terminal devices cannot be distinguished only by spreading sequences, but further by spatial channels. Therefore, the method employed in the present disclosure can also be called semi-orthogonal spreading sequence method.

[0035] At 230, the spread signal is converted from the frequency domain to the time domain. In some embodiments, fast Fourier transform (IFFT) can be utilized to convert the spread signal from the frequency domain to the time domain. As a matter of course, this is non-limiting. Any conversion method from the frequency domain to the time domain currently known or to be developed in the future can be employed in combination with the embodiments of the present disclosure.

[0036] Fig. 3 is a flowchart illustrating a method 300 of signal processing by a receiver in a communication system according to the embodiments of the present disclosure. In some embodiments, method 300, for instance, can be implemented by the receiver 130. It should be appreciated that method 300 may further comprise additional steps not shown and/or omit the shown steps. The scope of the subject matter described herein is not limited in this regard.

[0037] At 310, information associated with a plurality of terminal devices is obtained. In some embodiments, the obtained associated information comprises an orthogonal spreading sequence specific to a terminal device and a channel response for the terminal device. The orthogonal spreading sequence is a non-constant amplitude sequence generated randomly. In some embodiments, obtaining information associated with a plurality of terminal devices comprises detecting a pilot signal for the terminal device and obtaining an orthogonal spreading sequence and a channel response using the pilot signal. For the plurality of terminal devices for which information needs to be obtained, the orthogonal spreading sequence specific for each of the plurality of terminal devices and the channel response for each terminal device should be obtained.

[0038] At 320, the signal to be processed is received. In some embodiments, the signal can be received, for instance, using a plurality of antennae. The received signal can be pre-processed, for example, by making it pass through a filter. By pre-processing the signal, a signal that is more suitable for subsequent processing can be provided. For instance, the amplification of the signal can significantly reduce the demand on sensitivity for subsequent signal processing modules.

[0039] At 330, the received signal is converted from the time domain to the frequency domain. In some embodiments, fast Fourier transform (IFFT) can be utilized to convert the signal from the time domain to the frequency domain. As a matter of course, this is not limiting and any conversion solution from the frequency domain to the time domain currently known or to be developed in the future can be employed in combination with the embodiments of the present disclosure.

[0040] At 340, the converted signal can be de-spread at least partially based on the obtained information. The input utilized in de-spreading can be seen as a matrix. Each line in the matrix represents a modulated spreading sequence with data information and channel response of the antenna. Each column represents values of a plurality of antennae received on the same subcarrier. For instance, the input matrix can be written as:

Ί,ι '1,2 1,N

M K_m

' 2,1 '2,2 '2,N

' ^ri j∑^Xm,khi,j,m^Sm,j ( 3 ) m—\ k=l

'«,1 'R,2 R,N where R denotes the number of receiving antennae, N denotes the length of spreading sequence, M denotes the number of active terminal devices, h_{i j m} denotes the channel response from the terminal device m to the receiving antenna i at the subcarrier j, ry denotes input matrix element for antenna i at the subcarrier j, K_m denotes the number of constellation symbols for the terminal device m, X_m,k denotes the k^th constellation symbol

^Am,i ' ^Am,2 ' · · · ' ^Λ»_!,Λ? J denotes the spreading sequence for the k^th constellation symbol for the terminal device m.

[0041] The estimated value of a constellation symbol X_{m k} can be calculated as or de-spread as:

The asterisk (*) in equation (4) represents plural conjugation, and (k, m) and (k' , m') are utilized to distinguish different elements represented with the same symbols. The first item (^sm,j )* ^at the rightmost side of the equation (4) has high energy,

because the spreading sequence and the channel response both have high autocorrelation.

The second item at the rightmost side of equation

(4) has low energy because the spreading sequences for the same terminal device are orthogonal. The third item ^at the rightmost

side of equation (4) has low energy, because the spreading sequence and the channel response for different terminal devices both have low autocorrelation.

[0042] In some embodiments, signals are processed using a successive interference cancellation receiver. In each iteration, data of the terminal device with the strongest energy are de-modulated. The de-modulated data may be checked and restored with a forward error correction FEC to improve performance. Then, the signal after FEC coding is output to a next processing device.

[0043] Fig. 4 is a block diagram illustrating an apparatus 400 according to the third aspect of an embodiment of the present disclosure. It should be appreciated that apparatus 400 can be implemented as a terminal device. The apparatus 400 comprises a modulation unit 410, a spreading unit 420, and a frequency-time converting unit 430. The modulation unit 410 is configured to modulate, in a frequency domain, a signal to be transmitted. The spreading unit 420 is configured to spread the modulated signal using an orthogonal spreading sequence. The orthogonal spreading sequence is a non-constant amplitude sequence generated randomly. The frequency-time converting unit 430 is configured to convert the spread signal from the frequency domain to the time domain.

[0044] In some embodiments, the spreading unit 420 may comprise a random orthogonal matrix generating sub-unit and a random orthogonal matrix spreading sub-unit. The random orthogonal matrix generating sub-unit is configured to generate random orthogonal matrices specific to terminal devices based on the random matrix. The random orthogonal matrix spreading sub-unit is configured to spread modulated signals with the random orthogonal matrix. [0045] In some embodiments, the random orthogonal matrix generating sub-unit comprises an obtaining sub-unit and a random orthogonal matrix generating sub-unit. The obtaining sub-unit is configured to obtain identifiers and/or transmission parameter of the terminal device. The random orthogonal matrix generating sub-unit is configured to generate, based on the obtained identifiers and/or transmission parameter of the terminal device, random orthogonal matrices using a pseudo-random algorithm.

[0046] In some embodiments, the identifiers of the terminal device comprise international mobile equipment identity; and the transmission parameter comprises orthogonal frequency division multiplexing symbol number or sub-frame number.

[0047] In some embodiments, the random orthogonal matrix is a unitary matrix; and the random orthogonal matrix generating sub-unit comprises a singular value decomposing sub-unit. The singular value decomposing sub-unit is configured to perform singular value decomposition to the random matrix to generate a unitary matrix.

[0048] In some embodiments, the apparatus 400 further comprises a resource distributing unit. The resource distributing unit is configured to transmit a plurality of modulated signals of the terminal device on the same physical resources.

[0049] In some embodiments, the apparatus 400 further comprises a segmenting unit configured to segment the orthogonal spreading sequence into at least one part. Each portion in at least one part is transmitted on an orthogonal frequency division multiplexing symbol.

[0050] In some embodiments, the apparatus 400 further comprises a distributing unit. The distributing unit is configured to distribute the spread signal to the orthogonal frequency division multiplexing subcarriers.

[0051] Fig. 5 is a block diagram illustrating an apparatus 500 according to the fourth aspect of an embodiment of the present disclosure. It can be appreciated that the apparatus 500 can be implemented as a network device. The apparatus 500 comprises an information obtaining unit 510, a receiving unit 520, a time-frequency converting unit 530, and a de-spreading unit 540. The information obtaining unit 510 is configured to obtain information associated with the terminal device. The information including an orthogonal spreading sequence specific to a terminal device and a channel response for the terminal device. The orthogonal spreading sequence is a randomly generated non-constant amplitude sequence. The receiving unit 520 is configured to receive a signal to be processed. The time-frequency converting unit 530 is configured to convert the received signal from the time domain to the frequency domain. The de-spreading unit 540 is configured to de-spread the converted signal at least partially based on the orthogonal spreading sequence. In some embodiments, the orthogonal spreading sequence of the de- spreading unit 540 for de- spreading the signal is a non-constant amplitude sequence. [0052] In some embodiments, the information obtaining unit 510 further comprises a pilot detection sub-unit and a pilot processing sub-unit. The pilot detection sub-unit is configured to detect pilot signals for the terminal device. The pilot processing sub-unit is configured to obtain, using a pilot signal, an orthogonal spreading sequence and a channel response.

[0053] In some embodiments, the apparatus 500 further comprises a successive interference cancellation receiver configured to process the converted signal.

[0054] For the sake of clarity, some optional modules of apparatus 400 and apparatus 500 are not shown in Fig. 4 and Fig. 5. However, it is to be understood that various features as described with reference to Figs. 1-5 are likewise applicable to apparatus 400 and apparatus 500. Besides, various units in apparatus 400 and apparatus 500 may be hardware modules or software modules. For example, in some embodiments, the apparatus 400 and apparatus 500 may be partially or completely implemented using software and/or firmware, for example, implemented as a computer program product embodied on a computer readable medium. Alternatively or additionally, the apparatus 400 and apparatus 500 may be partially or completely implemented based on hardware, for example, an integrated circuit (IC) chip, an application specific integrated circuit (ASIC), a system on chip (SOC), a field programmable gate array (FPGA), and so on. The scope of the present invention is not limited in this aspect.

[0055] Fig. 6 is a schematic block diagram of an example device 600 suitable for implementing embodiments of the present disclosure. The device 600 can be used to implement the network device and/or to implement the terminal device. As shown in the figure, the device 600 comprises a controller 610 which controls the operations and functions of device 600. For example, in some embodiments, the controller 610 can implement various operations by means of instructions 630 stored in a memory 620 coupled thereto. The memory 620 can be any proper type adapted to the local technical environment and be implemented with any proper data storage technology, including but not limited to, a semiconductor-based storage device, a magnetic storage device and system and an optical storage device and a system. Though Fig. 6 only illustrates one memory unit, multiple physically different memory units may exist in device 600.

[0056] The controller 610 may be any proper type adapted to the local technical environment, comprising, but not limited to, one or more of a general computer, a dedicated computer, a micro-controller, a digital signal controller (DSP) and one or more of a controller-based multi-core controller architecture. The device 600 may also comprise a plurality of controllers 610. The controller 610 may be coupled with a transceiver 640 which can achieve reception and transmission of information by means of one or more antennae 650 and/or other components.

[0057] When the device 600 actions as the terminal device, the controller 610 and the transceiver 640 can operate in cooperation to implement the method 200 described above with reference to Fig. 2. When the device 600 actions as a network device, the controller 610 and the transceiver 640 can operate cooperatively to implement the method 300 described above with reference to Fig. 3. All the features described above with reference to Figs. 2 and 3 are applicable to device 600, which will not be repeated here. [0058] Fig. 7 is a comparison chart of signal processing performance according to an embodiment of the present disclosure. According to an embodiment, assuming that the terminal device transmits 24 bits in an OFDM symbol through QPSK modulation, and the spreading sequence length N=72, the QPSK modulation can generate 12 constellation symbols. There are two approaches for generating a spreading sequence. The first method is the "random" method according to the present disclosure. A vector from the unitary matrix is selected as the spreading sequence for the terminal device m; and the unitary matrix can be obtained through singular value decomposition. The second method is based on "ZC" sequence whose length is 71. The non-stop cyclic shifts are used as spreading sequences for the terminal device; and different roots are used to generate semi- orthogonal spreading sequences. The modulated spreading sequences are mapped into six successive physical resource blocks, where one resource block has 6x12 sub-carriers. For the traditional uplink transmission, six terminal devices can utilize these resources for operation.

[0059] Fig. 7 illustrates an error bit rate BER in case that no forward error correction FEC is performed. In Fig. 7, a specially designed ZC-based spreading sequence is compared with the orthogonal spreading sequence proposed in the present disclosure, where different numbers of receiving antennae and different overloading factors are used. In simulation, the signal-to-noise ratio SNR for each spreading sequence ranges from -5dB to 5dB; and the maximum time difference between receiving signals of different terminal devices is 66.7μ8. It is noted that each terminal device has a single antenna and each eNB has a plurality of receiving antennae. In the figure, the number of receiving antennae is used as a value of the lateral axis. As can be seen from the simulation result in Fig. 7, the signal waveform of the orthogonal spreading sequence of the present disclosure can support greater overloading factors with the assistance of massive receiving antennae, for instance, can reach 1600%. The overloading factors of NOMA scheme without using spatial multiplexing normally can reach 150%-400%. Besides, the spreading sequence generated randomly has better performance than ZC spreading sequence designed dedicatedly. [0060] Some embodiments of the present disclosure employ spreading sequences and spatial channels to discriminate data of the terminal device. Compared with the NOMA scheme, the combination of spreading sequences and spatial channels can increase the supported overloading factors significantly. The spreading sequences in the present disclosure are a vector of the unitary matrix generated randomly. The spreading sequences are plural and have non-uniform absolute values. Because sub-carriers of OFDM symbols are affected by random linear phase rotation, the orthogonality of short spreading sequences designed dedicatedly will be affected accordingly. Besides, because the number of potential spreading sequences is large enough to produce spreading sequences generated randomly, the collision probability of spreading sequences will decline correspondingly As the spreading sequences utilized by different terminal devices are non-orthogonal, the interference between users is inhibited through spatial channels. The spreading sequences employed by data of the same terminal device are orthogonal, so as to reduce interference from the user itself. A plurality of terminal devices can transmit data of different sizes to the eNB.

[0061] In the depiction of the embodiments of the present disclosure, the term "includes" and its variants are to be read as open-ended terms that mean "includes, but is not limited to." The term "based on" is to be read as "based at least in part on." The term "an example embodiment" or "the example embodiment" is to be read as "at least one example embodiment."

[0062] It will be noted that embodiments of the present disclosure can be implemented in software, hardware, or a combination thereof. The hardware part can be implemented by a special logic; the software part can be stored in a memory and executed by a suitable instruction execution system such as a microprocessor or special purpose hardware. Ordinary skilled in the art may understand that the above device and method may be implemented with computer executable instructions and/or in processor-controlled code, for example, such code is provided on such as a programmable memory or a data bearer such as an optical or electronic signal bearer.

[0063] Further, although operations of the present methods are described in a particular order in the drawings, it does not require or imply that these operations are necessarily performed according to this particular sequence, or a desired outcome can only be achieved by performing all shown operations. On the contrary, the execution order for the steps as depicted in the flowcharts may be varied. Alternatively, or in addition, some steps may be omitted, a plurality of steps may be merged into one step, and/or a step may be divided into a plurality of steps for execution. It should also be noted that the features and functions of the above described two or more units may be embodied in one means. In turn, the features and functions of the above described one means may be further embodied in more units.

[0064] Although the present disclosure has been described with reference to various embodiments, it should be understood that the present disclosure is not limited to the disclosed embodiments. The present disclosure is intended to cover various modifications and equivalent arrangements included in the spirit and scope of the appended claims.

Claims

I/We Claim:

1. A method of signal processing, comprising:

modulating, in a frequency domain, a signal to be transmitted;

spreading the modulated signal with an orthogonal spreading sequence, the orthogonal spreading sequence being a non-constant amplitude sequence generated randomly; and

converting the spread signal from the frequency domain to a time domain.

2. The method according to Claim 1, wherein spreading the modulated signal comprises:

generating a random orthogonal matrix specific to a terminal device; and

obtaining the orthogonal spreading sequence with the random orthogonal matrix.

3. The method according to Claim 2, wherein generating the random orthogonal matrix specific to the terminal device comprises:

obtaining an identification and/or a transmission parameter of the terminal device; and generating, based on the obtained identification and/or transmission parameter of the terminal device, the random orthogonal matrix using a pseudo-random algorithm.

4. The method according to Claim 3, wherein the identification of the terminal device includes an international mobile equipment identity, and the transmission parameter includes an orthogonal frequency division multiplexing symbol number or a subframe number.

5. The method according to Claim 2, wherein the random orthogonal matrix is a unitary matrix, the unitary matrix being generated by performing singular value decomposition on a random matrix.

6. The method according to Claim 1, further comprising:

transmitting a plurality of modulated signals of the terminal device on the same physical resource.

7. The method according to Claim 1, wherein the orthogonal spreading sequence is partitioned into at least one segment, and each of the at least one segment is transmitted in an orthogonal frequency division multiplexing symbol.

8. The method according to Claim 1, further comprising:

distributing the spread signal into orthogonal frequency division multiplexing sub-carriers.

9. A method of signal processing, comprising:

obtaining information associated with a plurality of terminal devices, the information including orthogonal spreading sequences specific to the terminal devices and channel responses for the terminal devices, the orthogonal spreading sequences being non-constant amplitude sequences generated randomly;

receiving a signal to be processed;

converting the received signal from a time domain to a frequency domain; and de-spreading the converted signal at least in part based on the information.

10. The method according to Claim 9, wherein obtaining the information associated with the plurality of terminal devices comprises:

detecting pilot signals for the terminal devices; and

obtaining, using the pilot signal, the orthogonal spreading sequences and the channel responses.

11. The method according to Claim 9, further comprising:

processing the signal with a successive interference cancellation receiver.

12. A terminal device, comprising:

a controller;

a memory including instructions which, when executed by the controller, causing the terminal device to perform actions, the actions comprising:

modulating, in a frequency domain, a signal to be transmitted;

converting the spread signal from the frequency domain to the time domain.

13. The terminal device according to Claim 12, wherein the actions further comprise: generating a random orthogonal matrix specific to a terminal device; and obtaining the orthogonal spreading sequence using the random orthogonal matrix.

14. The terminal device according to Claim 13, wherein the actions further comprise: obtaining an identification and/or a transmission parameter of the terminal device; and generating, based on the obtained identification and/or transmission parameter of the terminal device, the random orthogonal matrix using a pseudo-random algorithm.

15. The terminal device according to Claim 14, wherein the identification of the terminal device includes an international mobile equipment identity, and the transmission parameter includes an orthogonal frequency division multiplexing symbol number or a subframe number.

16. The terminal device according to Claim 13, wherein the random orthogonal matrix is a unitary matrix, the unitary matrix being generated by performing singular value decomposition on a random matrix.

17. The terminal device according to Claim 12, wherein the actions further comprise: transmitting a plurality of modulated signals of the terminal device on the same physical resource.

18. The terminal device according to Claim 12, wherein the orthogonal spreading sequence is partitioned into at least one segment, and each of the at least one part is transmitted in an orthogonal frequency division multiplexing symbol.

19. The terminal device according to Claim 12, wherein the actions further comprise: distributing the spread signal onto orthogonal frequency division multiplexing sub-carriers.

20. A network device, comprising:

a controller;

a memory comprising instructions which, when executed by the controller, causing the network device to perform actions, the actions comprising:

receiving a signal to be processed;

21. The network device according to Claim 20, wherein the actions further comprise: detecting pilot signals for the terminal devices; and

22. The network device according to Claim 20, wherein the actions further comprise: processing the signal with a successive interference cancellation receiver.