Signal detection method and device, receiver and computer readable storage medium

Abstract

The invention provides a signal detection method and device for a multiple-input-multiple-output system, a receiver and a computer readable storage medium. The method comprises the following steps: receiving signals from Q transmitting ports by P receiving ports, wherein both P and Q are positive integers; when L is smaller than or equal to the smaller value of P and Q, J receiving ports with smaller receiving signal power in the P receiving ports or K transmitting ports with smaller receiving signal power in the Q transmitting ports are determined, L is the number of space division multiplexing layers of the received signals, J is smaller than or equal to P-L, and K is smaller than or equal to Q-L; determining the power unbalance degree of each receiving port in the J receiving ports or the power unbalance degree of each transmitting port in the K transmitting ports; and performing signal detection processing on the received signal, the signal detection processing including signal ignoring processing. According to the method, the channel estimation matrix in signal detection is simplified, the processing complexity is reduced, and the channel estimation error is reduced or avoided, so that the received signal detection performance is improved.

Description

Technical Field

[0001] This application relates to Multiple Input Multiple Output (MIMO) technology in the field of wireless communication, and in particular, to a signal detection method, apparatus, receiver, and computer-readable storage medium for a multiple input multiple output system. Background Art

[0002] Multiple Input Multiple Output (MIMO) is one of the important technologies for improving system capacity and signal transmission quality in wireless communication systems. The application of MIMO on physical channels is specified in both 3GPP and WIFI protocols. Usually, in the MIMO regulations of 3GPP and WIFI protocols, the transmit powers between different ports of the transmit antennas are equal, that is, the transmit power is balanced, and the corresponding receivers are often designed for the power balance condition.

[0003] However, in an actual wireless communication system, the signal powers of the signals sent from different transmit ports of MIMO when reaching the receiver are often unbalanced, mainly because the wireless fading channels experienced between different transmit ports and different receive antennas in the wireless propagation environment are different, the radio frequency channels of the transmitter or receiver are not ideal, and the signals between some transmit ports and different receive antennas may be physically blocked, etc.

[0004] In the process of forming the transmitter's signal, precoding processing is required, including precoding modes of single transmit port, spatial multiplexing, and transmit diversity. Among them, transmit diversity in 3GPP is based on SFBC of adjacent subcarriers, and transmit diversity in WIFI is based on STBC of adjacent symbols. The receiver needs to adopt corresponding detection methods to process the transmit signal according to this precoding mode. When the power imbalance between different transmit ports corresponding to the receiver and different receive channels reaches a certain degree, continuing to use the conventional receiver detection method designed for the power balance condition will affect the detection performance. Summary of the Invention

[0005] This application provides a signal detection method, apparatus, receiver, and computer-readable storage medium for a multiple input multiple output system.

[0006] On the one hand, an embodiment of this application provides a signal detection method for a multiple input multiple output system, including:

[0007] Receiving signals from Q transmitting ports via P receiving ports, where both P and Q are positive integers; when L is less than or equal to the smaller value of P and Q, determining J receiving ports with relatively small received signal power among the P receiving ports or K transmitting ports with relatively small received signal power among the Q transmitting ports, where L is the spatial multiplexing layer number of the received signals, J ≤ P - L, and K ≤ Q - L; determining the power imbalance of each of the J receiving ports or the power imbalance of each of the K transmitting ports; performing signal detection processing on the received signals, where the signal detection processing includes signal ignoring processing, and the signal ignoring processing includes at least one of the following two: ignoring the signals received via the receiving ports among the J receiving ports with a power imbalance greater than a first preset threshold; ignoring the signals transmitted by the transmitting ports among the K transmitting ports with a power imbalance greater than a second preset threshold and received by the P receiving ports.

[0008] On the other hand, an embodiment of the present application further provides a signal detection device for a multiple-input multiple-output system. In the multiple-input multiple-output system, signals are received from Q transmitting ports via P receiving ports, where both P and Q are positive integers. The signal detection device includes: a power comparison module for determining J receiving ports with relatively small received signal power among the P receiving ports or K transmitting ports with relatively small received signal power among the Q transmitting ports, where L is the spatial multiplexing layer number of the received signals, J ≤ P - L, and K ≤ Q - L; an imbalance degree calculation module for determining the power imbalance of each of the J receiving ports or the power imbalance of each of the K transmitting ports; a signal detection processing module for performing signal detection processing on the received signals, where the signal detection processing includes signal ignoring processing, and the signal ignoring processing includes at least one of the following two: ignoring the signals received via the receiving ports among the J receiving ports with a power imbalance greater than a first preset threshold; ignoring the signals transmitted by the transmitting ports among the K transmitting ports with a power imbalance greater than a second preset threshold and received by the P receiving ports.

[0009] On yet another aspect, the present application further provides a receiver, and the receiver includes a signal detection device for a multiple-input multiple-output system as described above.

[0010] On yet another aspect, an embodiment of the present application further provides a computing device, including a processor and a memory, and a computer program stored on the memory and executable on the processor, where the processor executes the computer program to implement the signal detection method as described above.

[0011] In another aspect, an embodiment of the present application further provides a computer-readable storage medium, including computer-executable instructions, which, when run by one or more processors, execute the signal detection method as described above.

[0012] A signal detection method for a multiple-input multiple-output system provided by an embodiment of the present application compares a power balance parameter with a preset threshold. When the power imbalance of a transmitting port or a receiving port exceeds the preset threshold and there is port redundancy (L is less than or equal to the smaller value of P and Q), the signal of the receiving port or the transmitting port with a power imbalance exceeding the preset threshold is ignored during the reception signal detection, simplifying the channel estimation matrix, reducing the processing complexity, reducing or avoiding the error of channel estimation, and thus improving the performance of the reception signal detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 FIG. is a schematic hardware structure diagram of a receiver for a signal detection method for a multiple-input multiple-output system according to an embodiment of the present application;

[0014] Figure 2 FIG. is a schematic flowchart of a signal detection method for a multiple-input multiple-output system according to an embodiment of the present application;

[0015] Figure 3 FIG. is a schematic flowchart of a signal detection method when the precoding mode is transmit diversity and there is redundancy at the transmitting port according to another embodiment of the present application;

[0016] Figure 4 FIG. is a schematic block diagram of the structure of a signal detection device for a multiple-input multiple-output system provided by an embodiment of the present application;

[0017] Figure 5 FIG. is a signal detection performance diagram of the signal detection method according to an embodiment of the present application when the precoding mode is transmit diversity;

[0018] Figure 6 FIG. is a schematic flowchart of a receiver for processing a received signal according to an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The embodiments of the present invention will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0020] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above drawings are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence.

[0021] The method embodiments provided in the embodiments of the present application can be executed in a receiving end device (or referred to as "receiving end", "receiver", etc.) of a MIMO system. Figure 1 It is a hardware structural block diagram of a receiver for a signal detection method of a multiple-input multiple-output system according to an embodiment of the present application. As Figure 1 shown, the receiver may include one or more ( Figure 1 only one is shown in the figure) processors 102 (the processor 102 may include, but is not limited to, a processing device such as a microprocessor MCU or a programmable logic device FPGA) and a memory 104 for storing data. Among them, the above receiver may further include a transmission device 106 for communication functions and an input / output device 108. Those of ordinary skill in the art can understand that Figure 1 the structure shown in the figure is only schematic and does not limit the structure of the above receiver. For example, the receiver may further include more or fewer components than Figure 1 shown in the figure, or have a different configuration from Figure 1 shown in the figure.

[0022] The memory 104 can be used to store computer programs. For example, software programs and modules of application software, such as the computer program corresponding to the signal detection method in the embodiments of the present invention. The processor 102 executes various functional applications and data processing by running the computer programs stored in the memory 104, that is, implements the above signal detection method. The memory 104 may include a high-speed random access memory, and may also include a non-volatile memory, such as one or more magnetic storage devices, flash memories, or other non-volatile solid-state memories. In some instances, the memory 104 may further include a memory remotely disposed relative to the processor 102, and these remote memories may be connected to the mobile terminal through a network. Examples of the above networks include, but are not limited to, the Internet, an enterprise intranet, a local area network, a mobile communication network, and combinations thereof.

[0023] The transmission device 106 is used to receive or send data via a network. Specific examples of the above network may include a wireless network provided by a communication provider. In one instance, the transmission device 106 includes a network adapter (Network Interface Controller, NIC), which can be connected to other network devices through a base station and thus can communicate with the Internet. In one instance, the transmission device 106 may be a radio frequency (RF) module, which is used to communicate with the Internet wirelessly.

[0024] To solve the problem that when the power balance degree between the transmitting port and the receiving channel exceeds the threshold, continuing to use the conventional receiver detection method will lead to poor detection effect, an embodiment of the present application provides a signal detection method for a multiple-input multiple-output system. When the power imbalance degree between different transmitting ports corresponding to the receiver and different receiving channels reaches a certain level, the signal detection method of the receiver can be adjusted to solve the existing problems and improve the receiver detection performance. This method can be applied to the single-port, spatial multiplexing, and transmit diversity scenarios under 3GPP NR / LTE-A, and can also be applied to similar scenarios in the next-generation wireless communication network. The transmitting end can be a base station (gNB), a relay (Relay), or various gateways (AP). It can also be applied to the transmit diversity scenario in wireless network communication technology, and the transmitting end can be a terminal device (STA). This signal detection method can be executed by the receiving end device.

[0025] Figure 2 The following shows a schematic flowchart of a signal detection method for a multiple-input multiple-output system according to an embodiment of the present application, which may include the following steps S202 to S208:

[0026] Step S202, receive signals from Q transmitting ports via P receiving ports, where both P and Q are positive integers;

[0027] In an embodiment of the present application, the receiving port, that is, the receiving channel, includes components in the receiver for tracking, processing, and measuring signals, and can be composed of radio components, digital circuits, etc. and dedicated software. The transmitting port, that is, the transmitting antenna, includes electronic components with the function of converting radio frequency signal current into spatial electromagnetic waves. The signals received by the receiving port come from the transmitting ports of the transmitting end device.

[0028] Step S204, when L is less than or equal to the smaller value of P and Q, determine J receiving ports with smaller received signal power among the P receiving ports or K transmitting ports with smaller received signal power among the Q transmitting ports, where L is the spatial multiplexing layer number of the received signals, J ≤ P - L, and K ≤ Q - L;

[0029] That L is less than or equal to the smaller value of P and Q means that there are redundant transmitting and / or receiving ports. Therefore, it is feasible to ignore the signals of some transmitting and / or receiving ports.

[0030] In an exemplary embodiment, the received signal power of P receiving ports and Q transmitting ports can be determined in the following manner: for each of the P receiving ports, calculate the total power of the signals received by the receiving port from the Q transmitting ports as the received signal power of the receiving port; for each of the Q transmitting ports, calculate the total power of the signals transmitted by the transmitting port and received at the P receiving ports as the received signal power of the transmitting port.

[0031] In an exemplary embodiment, the reference signal receive power (RSRP) of the received signal can be used as the power of the received signal. In addition, other methods can also be used to determine the received signal power of the receiving ports and transmitting ports, which are not limited herein. For example, the received signal power of the receiving port or transmitting port can be determined according to the maximum power of the received signal.

[0032] In an exemplary embodiment, when the precoding mode of the received signal is single port or spatial multiplexing:

[0033] Determining the J receiving ports with relatively low received signal power among the P receiving ports described in step S204 includes: comparing the received signal powers of the P receiving ports, and sorting the P receiving ports in descending order of received signal power; determining the last J receiving ports in the sorting as the J receiving ports with relatively low received signal power among the P receiving ports;

[0034] Determining the K transmitting ports with relatively low received signal power among the Q transmitting ports described in step S204 includes: comparing the received signal powers of the Q transmitting ports, and sorting the Q transmitting ports in descending order of received signal power; determining the last K transmitting ports in the sorting as the K transmitting ports with relatively low received signal power among the Q transmitting ports.

[0035] In another exemplary embodiment, when the precoding mode of the received signal is transmit diversity, L = 1, where the Q transmitting ports include Q / 2 first - type transmitting ports and Q / 2 second - type transmitting ports. The m - th first - type transmitting port and the m - th second - type transmitting port transmit signals s 2m-2 、 at the (Q·i + 2m - 2) - th sub - carrier respectively and signals s 2m-1 、 at the (Q·i + 2m - 1) - th sub - carrier respectively. Wherein the m - th first - type transmitting port and the m - th second - type transmitting port are regarded as the m - th group of transmitting ports, m = 1, ……, Q / 2, and i is a positive integer, where:

[0036] The determination of the J receiving ports with relatively low received signal power among the P receiving ports described in step S204 includes: comparing the received signal powers of the P receiving ports, and sorting the P receiving ports in descending order of the received signal power; determining the last J receiving ports in the sorting as the J receiving ports with relatively low received signal power among the P receiving ports.

[0037] The determination of the K transmitting ports with relatively low received signal power among the Q transmitting ports described in step S204 includes:

[0038] For the m-th group of transmitting ports, when the received signal power of the m-th first-type transmitting port is greater than the received signal power of the m-th second-type transmitting port, determining the m-th second-type transmitting port as one of the K transmitting ports;

[0039] For the m-th group of transmitting ports, when the received signal power of the m-th second-type transmitting port is greater than the received signal power of the m-th first-type transmitting port, determining the m-th first-type transmitting port as one of the K transmitting ports.

[0040] Step S206, determining the power imbalance of each of the J receiving ports or the power imbalance of each of the K transmitting ports;

[0041] In an exemplary embodiment, determining the power imbalance of each of the J receiving ports includes: selecting all or part of the receiving ports other than the J receiving ports from the P receiving ports as comparison receiving ports; for each of the J receiving ports, calculating the ratio of the received signal power of this receiving port to the received signal power of each comparison receiving port among the comparison receiving ports, and taking the smallest ratio as the power imbalance of this receiving port;

[0042] Determining the power imbalance of each of the K transmitting ports includes: selecting all or part of the transmitting ports other than the K transmitting ports from the Q transmitting ports as comparison transmitting ports; for each of the K transmitting ports, calculating the ratio of the received signal power of this transmitting port to the received signal power of each comparison transmitting port among the comparison transmitting ports, and taking the smallest ratio as the power imbalance of this transmitting port.

[0043] In an exemplary embodiment, when the precoding transmission mode of the received signal is single-port or spatial multiplexing:

[0044] When determining the power imbalance of each of the J receiving ports, all the receiving ports are selected from the receiving ports other than the J receiving ports among the P receiving ports as comparison receiving ports; when determining the power imbalance of each of the K transmitting ports, all the transmitting ports are selected from the transmitting ports other than the K transmitting ports among the Q transmitting ports as comparison transmitting ports.

[0045] In another exemplary embodiment, when the precoding transmission mode of the received signal is transmit diversity:

[0046] Determining the power imbalance of each of the J receiving ports includes: selecting all the receiving ports from the receiving ports other than the J receiving ports among the P receiving ports as comparison receiving ports;

[0047] Determining the power imbalance of each of the K transmitting ports includes:

[0048] When the m-th second type of transmitting port is determined as one of the K transmitting ports, calculating the ratio of the received signal power of the m-th first type of transmitting port to the received signal power of the m-th second type of transmitting port as the power imbalance of the transmitting port corresponding to the m-th group among the K transmitting ports;

[0049] When the m-th first type of transmitting port is determined as one of the K transmitting ports, calculating the ratio of the received signal power of the m-th second type of transmitting port to the received signal power of the m-th first type of transmitting port as the power imbalance of the transmitting port corresponding to the m-th group among the K transmitting ports,

[0050] where m = 1,..., Q / 2.

[0051] Step S208, performing signal detection processing on the received signal, where the signal detection processing includes signal ignoring processing, and the signal ignoring processing includes at least one of the following two: ignoring the signal received via the receiving port with a power imbalance greater than the first preset threshold among the J receiving ports; ignoring the signal transmitted by the transmitting port with a power imbalance greater than the second preset threshold among the K transmitting ports and received by the P receiving ports.

[0052] It should be noted that the specific implementation manners of signal ignoring mentioned in this application include, but are not limited to, ignoring the signal of the corresponding port, treating it as noise, setting the channel estimation value in the matrix corresponding to the port to zero, or deleting the corresponding port from all ports.

[0053] In the above embodiments, when the power imbalance of the transmitting port or the receiving port exceeds a preset threshold and there is port redundancy (L is less than or equal to the smaller value of P and Q), when performing received signal detection, the signal of the receiving port or the transmitting port whose power imbalance exceeds the preset threshold is ignored, simplifying the channel estimation matrix, reducing the processing complexity, reducing or avoiding the error of channel estimation, and thus improving the performance of received signal detection.

[0054] In an exemplary embodiment, the precoding mode of the received signal is single-port, Q = 1, L = 1. When performing signal detection processing on the received signal, the maximum ratio combining (MRC) algorithm is used. The signal ignoring process is as follows: ignoring the signal received via the receiving port among the J receiving ports whose power imbalance is greater than the first preset threshold; or

[0055] In another exemplary embodiment, the precoding transmission mode of the received signal is spatial multiplexing, L > 1. When performing signal detection processing on the received signal, the minimum mean square error (MMSE) algorithm or the sphere decoding (SD) algorithm is used. The signal ignoring process includes: ignoring the signal received via the receiving port among the J receiving ports whose power imbalance is greater than the first preset threshold; and ignoring the signal transmitted by the transmitting port among the K transmitting ports whose power imbalance is greater than the second preset threshold and received by the P receiving ports.

[0056] In yet another exemplary embodiment, the precoding transmission mode of the received signal is transmit diversity, L = 1. The signal ignoring process includes: ignoring the signal received via the receiving port among the J receiving ports whose power imbalance is greater than the first preset threshold; and ignoring the signal transmitted by the transmitting port among the K transmitting ports whose power imbalance is greater than the second preset threshold and received by the P receiving ports, where:

[0057] For the receiving port among the J receiving ports whose power imbalance is greater than the first preset threshold, when performing the signal detection processing on the received signal, the minimum mean square error (MMSE) algorithm or the sphere decoding (SD) algorithm is used; or

[0058] For the transmitting port among the K transmitting ports whose power imbalance is greater than the second preset threshold, when performing the signal detection processing on the received signal, the maximum ratio combining (MRC) algorithm is used. For example, in one example, for the mth (m = 1,..., Q / 2) group of transmitting ports:

[0059] When the received signal power of the mth first-type transmitting port is greater than the received signal power of the mth second-type transmitting port and the power imbalance of the mth second-type transmitting port is greater than the second preset threshold, the maximum ratio combining (MRC) algorithm is used in the signal detection processing to output As the detection result of performing the signal detection processing on s 2m-2 and s 2m-1 ;

[0060] When the received signal power of the m-th second type of transmit port is greater than the received signal power of the m-th first type of transmit port and the power imbalance of the m-th first type of transmit port is greater than the second preset threshold, the maximum ratio combining (MRC) algorithm is adopted in the signal detection processing, and the output result is expressed as Then, perform symbol transformation processing to obtain As the detection result of performing the signal detection processing on s 2m-2 and s 2m-1 ; where:

[0061]

[0062]

[0063] Wherein, represents multiplying the real part of by -1 to take the inverse, while the imaginary part remains unchanged; represents multiplying the imaginary part of by -1 to take the inverse, while the real part remains unchanged.

[0064] In this embodiment, the precoding mode of the received signal is transmit diversity. When performing signal detection processing on the received signal, the signal transmitted by the transmit port that meets the preset conditions and received by the receive port is detected using an improved MRC detection method, that is, the detection result of the MRC algorithm is used as the final detection result after symbol transformation. This improved MRC algorithm has a lower processing complexity than the conventional MMSE, and reduces or eliminates the influence of channel estimation errors, achieving better detection performance than the MMSE detection method.

[0065] In addition, in an embodiment where the precoding transmission mode is transmit diversity, for the receive ports among the J receive ports with a power imbalance less than or equal to the first preset threshold or the transmit ports among the K transmit ports with a power imbalance less than or equal to the second preset threshold, when performing the signal detection processing on the received signal, the minimum mean square error (MMSE) algorithm or the sphere decoding (SD) algorithm is adopted.

[0066] The embodiment of the present application also provides a signal detection device for a multiple input multiple output system, and this device is used to implement the above-mentioned method embodiments. As used hereinafter, the term "module" can be any combination of software, hardware, and / or firmware that implements a predetermined function.

[0067] Figure 4It is a schematic block diagram of a signal detection device for a multiple-input multiple-output system according to an embodiment of the present application. In this multiple-input multiple-output system, signals from Q transmitting ports are received via P receiving ports, where both P and Q are positive integers. As Figure 4 shown, the signal detection device 40 includes:

[0068] A power comparison module 410, configured to determine J receiving ports with relatively small received signal power among the P receiving ports or K transmitting ports with relatively small received signal power among the Q transmitting ports, where L is the spatial multiplexing layer number of the received signal, J ≤ P - L, and K ≤ Q - L;

[0069] An imbalance calculation module 420, configured to determine the power imbalance of each of the J receiving ports or the power imbalance of each of the K transmitting ports;

[0070] A signal detection processing module 430, configured to perform signal detection processing on the received signals. The signal detection processing includes signal ignoring processing, and the signal ignoring processing includes at least one of the following two: ignoring the signals received via the receiving ports among the J receiving ports with a power imbalance greater than a first preset threshold; ignoring the signals transmitted by the transmitting ports among the K transmitting ports with a power imbalance greater than a second preset threshold and received by the P receiving ports.

[0071] It should be noted that the above-mentioned various modules can be implemented by software, hardware, firmware, or any combination thereof. For example, they can be implemented in the following ways, but not limited thereto: all the above-mentioned modules are located in the same processor; or the above-mentioned various modules are respectively located in different processors in any combination form.

[0072] In the above signal detection device embodiment, the specific processing details of each module correspond exactly to the above-mentioned signal detection method embodiments, and will not be elaborated here.

[0073] An embodiment of the present application further provides a receiver, which includes the signal detection device in the above device embodiment.

[0074] As Figure 6 shown, in an exemplary embodiment, the working process of the receiver includes: OFDM demodulation, demapping, channel estimation, MIMO detection, and demodulation and decoding, where the embodiments of the present application relate to the MIMO detection link.

[0075] An embodiment of the present application further provides a computing device, including a processor and a memory, and a computer program stored on the memory and executable on the processor. The processor executes the processing steps in any one of the above method embodiments.

[0076] In particular, the above computing device may further include a transmission device and an input / output device, wherein the transmission device is connected to the above processor, and the input / output device is connected to the above processor.

[0077] An embodiment of the present application further provides a computer-readable storage medium, including computer-executable instructions, which, when run by one or more processors, execute any of the above signal detection method embodiments.

[0078] The above computer-readable storage medium may include, but is not limited to: various instantaneous or non-instantaneous storage media such as USB flash drives, read-only memories (ROM), random access memories (RAM), external hard drives, magnetic disks, or optical discs that can store computer programs.

[0079] For specific examples in this embodiment, reference may be made to the examples described in the above embodiments and exemplary embodiments, and details will not be repeated here.

[0080] Obviously, those skilled in the art should understand that the above modules or steps of the present application can be implemented in a general-purpose or special-purpose computing device. They can be concentrated on a single computing device or distributed over a network composed of multiple computing devices. In one embodiment, they can be implemented with program codes executable by the computing device, so that they can be stored in a storage device and executed by the computing device. In some cases, the steps shown or described may be executed in a different order than here. In other embodiments, they can be separately fabricated into individual integrated circuit modules, or multiple modules or steps among them can be fabricated into a single integrated circuit module for implementation. Thus, the present application is not limited to any specific combination of hardware, software, or firmware.

[0081] To enable those skilled in the art to better understand the technical solution of the present application, the following will be described in conjunction with specific scenario embodiments.

[0082] Scenario Embodiment 1

[0083] Assume that the transmit antenna port numbers of a multiple-input multiple-output system are q (q = 0, 1,..., Q), where Q is the number of transmit antenna ports, i.e., the number of transmit ports; the receive antenna port numbers are p (p = 0, 1,..., P), where P is the number of receive antennas, i.e., the number of receive ports. According to the 3GPP protocol, the received signal can be expressed as:

[0084] Y = HWS + N (1)

[0085] Wherein, Channel response matrix Precoding matrix Transmitted symbol Noise L is the number of spatial multiplexing layers. For the precoding transmission modes of single port and transmit diversity of the signal, L is 1 in both cases.

[0086] In the embodiments of the present application, the prerequisite for the MIMO system to perform signal detection processing is that L ≤ min(P, Q), where min(.) represents taking the smaller value of the two.

[0087] In this embodiment, the reference signal receive power (RSRP) is used as a parameter to measure the power imbalance, and the RSRP pq represents the reference signal power from transmit port q to receive port p. In the actual implementation process, the power imbalance reference factor that can be adopted can also be the maximum power value of the receive port or the transmit port, etc.

[0088] In the embodiments of this scenario, assume Q = 4, P = 4, L = 2. Here, L > 1, indicating that the precoding transmission mode of the signal is the spatial multiplexing mode, and the received signal can be expressed as:

[0089]

[0090] When performing signal detection in the receiver to carry out MIMO detection, the Minimum Mean Squared Error (MMSE) algorithm or the Sphere Decoding (SD) detection can be used. This embodiment adopts the MMSE detection method, and its detection formula is as follows:

[0091]

[0092] Where represents the soft decision value of signal detection on signal S, that is, the Log-Likelihood Ratio (LLR) output, H e = HW, the superscript "′" represents the conjugate transpose, and the superscript "-1" represents the inverse operation.

[0093] For the transmit ports, Q > L and there is a port redundancy of (Q - L) = 2 at the transmitting end, that is, at most 2 transmit ports may be deleted due to too low power in subsequent processing. In this embodiment, deleting the transmit port, treating the transmit signal corresponding to the transmit port as noise, or ignoring the transmit signal all mean deleting the corresponding transmit port, that is, this port no longer participates in the subsequent MIMO detection processing.

[0094] The sum of the RSRP corresponding to each transmit port q to all receive ports is counted as

[0095] U q = (|RSRP 0q | + |RSRP 1q | +... + |RSRP Pq |) and sorted from largest to smallest. Here, it is assumed that U0 and U1 are relatively small values among the 4 transmit ports. The power imbalance is calculated using the following expression:

[0096]

[0097]

[0098] When it satisfies TH is the first preset threshold. For example, if both transmit ports 0 and 1 satisfy the condition, the signals of transmit ports 0 and 1 in formula (2) will be much smaller than the noise, then the channel estimation error corresponding to transmit ports 0 and 1 will be very large, and the performance of the MMSE detection processing in formula (3) will decline subsequently. The corresponding transmit ports can be deleted in the subsequent processing, and formula (2) for MIMO detection processing can be simplified to:

[0099]

[0100] It is equivalent to simplifying H in formula (3) e and avoiding introducing a large channel estimation error to ensure the signal detection performance.

[0101] Similarly, assuming that for the receive ports, P > L and the port has a redundancy of (P - L) = 2, that is, at most 2 receive ports may be deleted in the subsequent processing due to the too small received signal power. The sum of the RSRP of all transmit ports corresponding to each receive port p is counted as V p = (|RSRP p0 | + |RSRP p1 | +... + |RSRP pQ |), and sorted from largest to smallest. Let V0 and V1 be the smaller values among the 4 receive ports. The power imbalance is calculated using the following expression:

[0102]

[0103]

[0104] When it satisfies TH is the second preset threshold. For example, if both receive ports 0 and 1 satisfy this condition, the two receive ports can be deleted in the subsequent processing, and formula (2) for entering MIMO detection processing is transformed into:

[0105]

[0106] corresponding to H in formula (3) e is simplified and the channel estimation error is avoided to ensure the signal detection performance.

[0107] Considering the number of transmit ports and receive ports comprehensively, as long as L < P or L < Q, there is redundancy in all ports. When the power imbalance of the transmit port exceeds the first preset threshold or the power imbalance of the receive port exceeds the second preset threshold, the signal of the corresponding channel of this port will be ignored, or in other words, this port will be deleted.

[0108] Scenario Embodiment 2

[0109] Assume that the transmit port numbers of a multiple-input multiple-output system are q (q = 0, 1,..., Q), where Q is the number of transmit ports; the receive port numbers are p (p = 0, 1,..., P), where P is the number of receive ports. According to the 3GPP protocol, the received signal is still expressed by the above formula (1):

[0110] Y = HWS + N (1)

[0111] where channel response matrix precoding matrix transmitted symbol noise L is the number of spatial multiplexing layers. For the cases of single-port and transmit diversity in the precoding transmission mode of the signal, L is 1. The prerequisite for a MIMO system to perform detection is L ≤ min(P, Q), where min(.) represents taking the smaller value of the two.

[0112] Assume that the reference signal received power RSRP is used as a parameter to measure the power imbalance of the port, and use RSRP pq as the reference signal power from transmit port q to receive port p.

[0113] In this scenario embodiment, assume that the precoding transmission mode of the received signal is single-port, Q = 1 and L = 1. If L < P, there is only the case where the receive port is deleted when the corresponding power imbalance of the receive port exceeds the preset threshold.

[0114] Assume that the number of receive ports is 4, P > L and the port has a redundancy of (P - L) = 3, that is, at most 3 receive ports may be deleted in subsequent processing due to the too small received signal power. The sum of the RSRP of all transmit ports corresponding to each receive port p is denoted as V p = |RSRP p0|, and sort them from largest to smallest. Let V0 and V1 be the smaller values among the 4 receiving ports. The power imbalance is calculated using the same expressions as the above formulas (6a) and (6b):

[0115]

[0116]

[0117] When TH is the second preset threshold. For example, if both port 0 and port 1 meet the conditions, the receiving port can be deleted in subsequent processing. The formula (2) for MIMO detection processing can be transformed into:

[0118]

[0119] It is equivalent to using H in formula (3) e to obtain a simplified form and avoid channel estimation errors to ensure signal detection performance.

[0120] Scenario Embodiment Three

[0121] Assume that in a multiple-input multiple-output (MIMO) system, the transmitting port numbers are q (q = 0, 1,..., Q), where Q is the number of transmitting ports; the receiving port numbers are p (p = 0, 1,..., P), where P is the number of receiving ports. According to the 3GPP protocol, the received signal is still expressed as formula (1):

[0122] Y = HWS + N (1)

[0123] where the channel response matrix the precoding matrix the transmitted symbol the noise L is the number of spatial multiplexing layers. For the precoding transmission modes of single-port and transmit diversity for signals, L is 1. The prerequisite for MIMO system detection is L ≤ min(P, Q), where min(.) represents taking the smaller value of the two.

[0124] Assume that the power imbalance of the ports is measured using the reference signal received power (RSRP) as a parameter, and pq RSRP is the reference signal power from transmitting port q to receiving port p.

[0125] In this scenario embodiment, assume that the precoding transmission mode of the received signal is transmit diversity, L = 1. For the receiving ports, if L < P, there is a case where the receiving ports with power imbalance exceeding the preset threshold are deleted. At this time, the signal detection process performed on the receiving ports is the same as that in the case where the precoding transmission mode of the received signal in Scenario Embodiment Two is single-port, and will not be elaborated here.

[0126] For the transmit port, there are two cases where the number of transmit ports is 2 and 4 according to the 3GPP protocol:

[0127] When the number of transmit ports is 2, as Figure 3 shown, the two transmit ports include a first - type transmit port (transmit port 0) and a second - type transmit port (transmit port 1). When the received signal power of transmit port 0 is greater than that of transmit port 1, the power imbalance of this group of ports is calculated as the ratio of the sum of the RSRP of transmit port 0 to the sum of the RSRP of transmit port 1. When the calculated power imbalance is greater than the preset threshold, perform MRC signal detection on this group of transmit ports and output the corresponding LLR result; when the calculated power imbalance is less than the preset threshold, perform MMSE signal detection on this group of transmit ports and output the corresponding LLR result; when the received signal power of transmit port 0 is less than that of transmit port 1, the power imbalance of this group of ports is calculated as the ratio of the sum of the RSRP of transmit port 1 to the sum of the RSRP of transmit port 0. When the calculated power imbalance is greater than the preset threshold, perform MRC signal detection on this group of transmit ports, perform a sign transformation on the calculation result, and output the final LLR result; when the calculated power imbalance is less than the preset threshold, perform MMSE signal detection on this group of transmit ports and output the LLR result.

[0128] Transmit ports 0 and 1 send s0 on the 2i - th sub - carrier, Transmit ports 0 and 1 send s1 on the (2i + 1)-th sub - carrier, The received signal is expressed as (for the WIFI protocol, it refers to two adjacent symbols):

[0129]

[0130] where the received signals of receive port p (p = 0, 1) on the 2i - th and (2i + 1)-th sub - carriers are y p (2i), y p (2i + 1), the channel estimation values from transmit port q (q = 0, 1) to receive port p (p = 0, 1) on the 2i - th and (2i + 1)-th sub - carriers are h pq (2i), h pq (2i + 1), the noises of receive port p (p = 0, 1) on the 2i - th and (2i + 1)-th sub - carriers are n p (2i), n p (2i + 1), and the superscript * represents conjugate. Then the conventional method for transmit diversity processing in the receiver is the MMSE detection method:

[0131]

[0132] wherein represents the LLR output for signal detection of S. The superscript 'denotes conjugate transpose, and the superscript -1 denotes inverse operation.

[0133] When the transmission powers of the transmit ports are unbalanced, if the received signal power of transmit port 0 is greater than that of transmit port 1, the unbalance degree is:

[0134]

[0135] When TH is a preset threshold value, and the MMSE detection in formula (10) is still adopted; when In formula (9), the signal of transmit port 1 is much smaller than the noise, so the channel estimation error corresponding to transmit port 1 is very large, and adopting the MMSE detection in formula (10) will cause performance degradation. At this time, if the channel estimation value related to transmit port 1 is set to 0, then the representation of the received signal can be changed to:

[0136]

[0137] That is, it is reduced to a single-port transmission signal of only transmit port 0, and the received signal of the 2i-th subcarrier can be expressed as:

[0138]

[0139] The received signal of the (2i + 1)-th subcarrier can be expressed as:

[0140]

[0141] Then, adopting a simpler Maximal Ratio Combining (MRC), regarding the signal of transmit port 1 as noise, will instead improve the performance, that is, the detection method is as follows:

[0142]

[0143]

[0144] wherein are the LLR results for signal detection of s0 and s1 respectively, and these results are output in sequence.

[0145] Similarly, if the received signal power of transmit port 0 is less than or equal to the power of transmit port 1, the unbalance degree is:

[0146]

[0147] The channel estimation value corresponding to the transmit port 0 is 0, and the received signal can become:

[0148]

[0149] That is, it is reduced to a single-port transmit signal with only transmit port 1. The received signal of the 2i-th subcarrier can be expressed as:

[0150]

[0151] The received signal of the 2i + 1-th subcarrier can be expressed as:

[0152]

[0153] Then, first use MRC combining, regarding the signal of transmit port 0 as noise, the detection method can be expressed as:

[0154]

[0155]

[0156] Then perform symbol transformation on the result:

[0157]

[0158]

[0159] Where are the LLR outputs for signal detection of s0 and s1 respectively. The operation of formula (18a) is equivalent to multiplying the real part of by -1 to take the inverse, while the imaginary part remains unchanged; the operation of formula (19b) is equivalent to multiplying the imaginary part of by -1 to take the inverse, while the real part remains unchanged; in this embodiment, formula (14), formula (18) and formula (19) are collectively referred to as the improved MRC detection method.

[0160] When the number of transmit ports is 4, number the ports as port 0, port 1, port 2, port 3. Divide port 0 and 2 into the first group, and port 1 and 3 into the second group. Perform the Figure 3 processing flow on each group of ports respectively, and output the LLR results of the corresponding groups respectively.

[0161] Assume that the number of receive ports is 2. According to the 3GPP protocol, transmit port 0 and 2 send s0 on the 4i-th subcarrier, Transmit port 0 and 2 send s1 on the (4i + 1)-th subcarrier, Transmit port 1 and 3 send s2 on the 4i + 2-th subcarrier, Transmit port 1 and 3 send s3 on the (4i + 3)-th subcarrier, The received signal is expressed as:

[0162]

[0163] Take transmit ports 0 and 2 as a group, and transmit ports 1 and 3 as another group. The processing within each group is similar to the method when the number of transmit ports is 2. The conventional method is to perform the MMSE detection of formula (10).

[0164] Taking the group of transmit ports 0 and 2 as an example, if the power of transmit port 0 is greater than the power of transmit port 2, the imbalance parameter is:

[0165]

[0166] When TH is a preset threshold, and the MMSE detection of formula (10) is still used; when A simpler MRC combining is adopted, regarding the signal of transmit port 2 as noise, and the detection method is as follows:

[0167]

[0168]

[0169] Where are the LLR outputs of s0 and s1 respectively.

[0170] If the received signal power of transmit port 0 is less than or equal to the received signal power of transmit port 2, the imbalance parameter:

[0171]

[0172] When TH is a preset threshold, and the MMSE detection of formula (10) is still used; when Then first adopt MRC combining, regarding the signal of transmit port 0 as noise, that is, the detection method is as follows:

[0173]

[0174]

[0175] Then perform the symbol transformation:

[0176]

[0177]

[0178] Where are the LLR outputs of s0 and s1 respectively. The processing of transmit ports 1 and 3 can be obtained by analogy. LLR output

[0179] In the embodiments of the present application, the detection performance of LTE-A transmit diversity under 3GPP with an imbalance of 10 dB and 15 dB is tested. Referring to Figure 5 , when the imbalance is 10 dB, the performance of MMSE detection is better than that of the improved MRC detection method; when the imbalance is 15 dB, the performance of the improved MRC detection is better than that of MMSE detection. Assuming that the imbalance steps from 10 dB to 15 dB at an interval of 1 dB, the signal-to-noise ratio (dB) required for the receiver system in this embodiment to reach 90% throughput is tabulated in Table 1. It can be seen that the threshold TH = 12 dB is taken as the demarcation point for the performance of MMSE detection and the improved MRC detection method.

[0180] Imbalance degree (dB) 10 11 12 13 14 15 Conventional MMSE 1.7 1.9 2.1 2.2 2.3 2.4 The method of this application 2.3 2.2 2.1 2.0 1.9 1.8

[0181] Table 1

[0182] In summary, a signal detection method, device, receiver, and computer-readable storage medium for a multiple-input multiple-output system provided by the present application solve the problem that when the power imbalance between different transmit ports and different receive ports corresponding to the receiver reaches a certain level, continuously using the conventional receiver detection method designed for power balance conditions will affect the detection performance, enabling the performance to reach a potentially better level while reducing the processing complexity. Among them, the signal detection method mainly considers three factors: the precoding transmission mode of the signal received by the receive port from the transmit port, the power imbalance of the receive port, and the power imbalance of the transmit port; port deletion or signal ignoring processing is performed on the corresponding receive port or transmit port through the above three factors.

[0183] The above are only the preferred embodiments of the present application and are not used to limit the present invention. For those skilled in the art, various changes and modifications can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the principle of the present application shall be included within the protection scope of the present application.

Claims

1. A signal detection method for a multiple-input multiple-output system, characterized in that Including: Receiving signals from Q transmitting ports via P receiving ports, where both P and Q are positive integers; When L is less than or equal to the smaller value of P and Q, determining J receiving ports with relatively low received signal power among the P receiving ports or K transmitting ports with relatively low received signal power among the Q transmitting ports, where L is the spatial multiplexing layer number of the received signals, J ≤ P - L, and K ≤ Q - L; Determining the power imbalance degree of each of the J receiving ports or the power imbalance degree of each of the K transmitting ports; Performing signal detection processing on the received signals, where the signal detection processing includes signal ignoring processing, and the signal ignoring processing includes at least one of the following two: Ignoring the signals received via the receiving ports among the J receiving ports with a power imbalance degree greater than a first preset threshold; Ignoring the signals transmitted by the transmitting ports among the K transmitting ports with a power imbalance degree greater than a second preset threshold and received by the P receiving ports.

2. The signal detection method according to claim 1, wherein: The precoding mode of the received signals is single-port, Q = 1, L = 1. When performing the signal detection processing on the received signals, the maximum ratio combining (MRC) algorithm is used, and the signal ignoring processing is: ignoring the signals received via the receiving ports among the J receiving ports with a power imbalance degree greater than a first preset threshold; or The precoding transmission mode of the received signals is spatial multiplexing, L > 1. When performing the signal detection processing on the received signals, the minimum mean square error (MMSE) algorithm or the sphere decoding (SD) algorithm is used, and the signal ignoring processing includes: ignoring the signals received via the receiving ports among the J receiving ports with a power imbalance degree greater than a first preset threshold; and ignoring the signals transmitted by the transmitting ports among the K transmitting ports with a power imbalance degree greater than a second preset threshold and received by the P receiving ports.

3. The signal detection method according to claim 1, wherein The precoding transmission mode of the received signals is transmit diversity, L = 1. The signal ignoring processing includes: ignoring the signals received via the receiving ports among the J receiving ports with a power imbalance degree greater than a first preset threshold; and ignoring the signals transmitted by the transmitting ports among the K transmitting ports with a power imbalance degree greater than a second preset threshold and received by the P receiving ports, where: For the receiving ports among the J receiving ports with a power imbalance degree greater than a first preset threshold, when performing the signal detection processing on the received signals, the minimum mean square error (MMSE) algorithm or the sphere decoding (SD) algorithm is used; or For the transmitting ports among the K transmitting ports with a power imbalance degree greater than a second preset threshold, when performing the signal detection processing on the received signals, the maximum ratio combining (MRC) algorithm is used.

4. The signal detection method according to claim 1, wherein The precoding transmission mode of the received signal is transmit diversity, L = 1. The Q transmit ports include Q / 2 first-type transmit ports and Q / 2 second-type transmit ports. The m-th first-type transmit port and the m-th second-type transmit port respectively transmit signals s on the (Q·i + 2m - 2)-th subcarrier 2m-2 and respectively transmit signals s on the (Q·i + 2m - 1)-th subcarrier 2m-1 and where the m-th first-type transmit port and the m-th second-type transmit port are regarded as the m-th group of transmit ports, m = 1, ……, Q / 2, i is a positive integer. Among them, determining the K transmit ports with relatively small received signal power among the Q transmit ports includes: For the mth group of transmitting ports, when the received signal power of the mth first-type transmitting port is greater than the received signal power of the mth second-type transmitting port, determining the mth second-type transmitting port as one of the K transmitting ports; For the m-th group of transmission ports, when the received signal power of the m-th second-type transmission port is greater than the received signal power of the m-th first-type transmission port, the m-th first-type transmission port is determined as one of the K transmission ports.

5. The signal detection method according to claim 4, wherein: For the m-th group of transmission ports, when the received signal power of the m-th first-type transmission port is greater than the received signal power of the m-th second-type transmission port and the power imbalance of the m-th second-type transmission port is greater than the second preset threshold, the maximum ratio combining (MRC) algorithm is adopted in the signal detection processing to output For the m-th group of transmission ports, when the received signal power of the m-th second-type transmission port is greater than the received signal power of the m-th first-type transmission port and the power imbalance of the m-th first-type transmission port is greater than the second preset threshold, the maximum ratio combining (MRC) algorithm is adopted in the signal detection process to output The signal detection process further includes: Pair Perform symbol transformation processing to obtain Wherein: Among them, respectively represent the detection results of performing the signal detection processing for s 2m-2 , s 2m-1 . means multiplying the real part of by -1 to take the inverse, while keeping the imaginary part unchanged; means multiplying the imaginary part of by -1 to take the inverse, while keeping the real part unchanged.

6. The signal detection method according to claim 1, wherein The precoding mode of the received signal is single-port or spatial division multiplexing, where: Determining the J receiving ports with relatively small received signal power among the P receiving ports includes: Comparing the received signal powers of the P receiving ports, and sorting the P receiving ports in descending order of received signal power; Determining the last J receiving ports in the sorting as the J receiving ports with relatively small received signal power among the P receiving ports; Determining the K transmitting ports with relatively small received signal power among the Q transmitting ports includes: Comparing the received signal powers of the Q transmitting ports, and sorting the Q transmitting ports in descending order of received signal power; Determining the last K transmitting ports in the sorting as the K transmitting ports with relatively small received signal power among the Q transmitting ports.

7. The signal detection method according to claim 1, characterized in that The precoding mode of the received signal is transmit diversity, where: Determining the J receiving ports with relatively small received signal power among the P receiving ports includes: Comparing the received signal powers of the P receiving ports, and sorting the P receiving ports in descending order of received signal power; Determining the last J receiving ports in the sorting as the J receiving ports with relatively small received signal power among the P receiving ports.

8. The signal detection method according to claim 1, wherein The received signal powers of the P receiving ports and the Q transmitting ports are determined in the following manner: For each of the P receiving ports, calculating the total power of the signals received by this receiving port from the Q transmitting ports as the received signal power of this receiving port; For each of the Q transmitting ports, calculating the total power of the signals transmitted by this transmitting port and received at the P receiving ports as the received signal power of this transmitting port.

9. The signal detection method according to claim 1, wherein: Determining the power imbalance degree of each of the J receiving ports includes: Selecting all or part of the receiving ports other than the J receiving ports from the P receiving ports as comparison receiving ports; For each of the J receiving ports, calculating the ratio of the received signal power of this receiving port to the received signal power of each comparison receiving port among the comparison receiving ports, and taking the smallest ratio as the power imbalance degree of this receiving port; Determining the power imbalance degree of each of the K transmitting ports includes: Selecting all or part of the transmitting ports other than the K transmitting ports from the Q transmitting ports as comparison transmitting ports; For each of the K transmit ports, calculate the ratio of the received signal power of this transmit port to the received signal power of each of the comparison transmit ports among the comparison transmit ports, and use the smallest ratio as the power imbalance degree of this transmit port.

10. The signal detection method according to claim 9, characterized in that, When the precoding transmission mode of the received signal is single port or spatial division multiplexing: The selecting all or part of the receive ports other than the J receive ports from the P receive ports as comparison receive ports includes: Selecting all the receive ports other than the J receive ports from the P receive ports as comparison receive ports; The selecting all or part of the transmit ports other than the K transmit ports from the Q transmit ports as comparison transmit ports includes: Selecting all the transmit ports other than the K transmit ports from the Q transmit ports as comparison transmit ports.

11. The signal detection method according to claim 9, wherein When the precoding transmission mode of the received signal is transmit diversity: The selecting all or part of the receive ports other than the J receive ports from the P receive ports as comparison receive ports includes: Selecting all the receive ports other than the J receive ports from the P receive ports as comparison receive ports.

12. The signal detection method according to claim 4, characterized in that, Determining the power imbalance degree of each of the K transmit ports includes: When the m-th second type of transmit port is determined as one of the K transmit ports, calculate the ratio of the received signal power of the m-th first type of transmit port to the received signal power of the m-th second type of transmit port, and use it as the power imbalance degree of the transmit port corresponding to the m-th group among the K transmit ports; When the m-th first type of transmit port is determined as one of the K transmit ports, calculate the ratio of the received signal power of the m-th second type of transmit port to the received signal power of the m-th first type of transmit port, and use it as the power imbalance degree of the transmit port corresponding to the m-th group among the K transmit ports, where m = 1,..., Q / 2.

13. The signal detection method according to claim 4, characterized in that When the precoding transmission mode of the received signal is transmit diversity, the value of Q is 2 or 4.

14. The signal detection method according to claim 3, characterized in that: For the receive ports among the J receive ports with a power imbalance degree less than or equal to a first preset threshold or the transmit ports among the K transmit ports with a power imbalance degree less than or equal to a second preset threshold, when performing the signal detection processing on the received signal, use the minimum mean square error MMSE algorithm or the sphere decoding SD algorithm.

15. A signal detection device for a multiple-input multiple-output system, in which signals from Q transmitting ports are received via P receiving ports in the multiple-input multiple-output system, where, Both P and Q are positive integers, and the signal detection device is characterized in that it includes: A power comparison module, configured to determine J receive ports with relatively small received signal power among the P receive ports or K transmit ports with relatively small received signal power among the Q transmit ports, where L is the number of spatial division multiplexing layers of the received signal, J ≤ P - L, and K ≤ Q - L; An imbalance calculation module, configured to determine the power imbalance of each of the J receiving ports or the power imbalance of each of the K transmitting ports; A signal detection and processing module, configured to perform signal detection and processing on the received signals. Among them, when performing signal detection and processing on the received signals, the signal detection and processing includes signal ignoring processing, and the signal ignoring processing includes at least one of the following two: Ignoring the signals received via the receiving ports among the J receiving ports with a power imbalance greater than a first preset threshold; Ignoring the signals transmitted by the transmitting ports among the K transmitting ports with a power imbalance greater than a second preset threshold and received by the P receiving ports.

16. A receiver, characterized in that, The receiver includes the signal detection device according to claim 15.

17. A computing device, comprising a processor and a memory, and a computer program stored on the memory and executable on the processor, characterized in that , when the processor executes the computer program, the signal detection method described in any one of claims 1 to 14 is implemented.

18. A computer-readable storage medium, including computer-executable instructions, which when run by one or more processors, execute the signal detection method described in any one of claims 1-14.

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