Method for separating multiple layers, receiver circuit and wireless communication device

Abstract

A receiver circuit for separating multiple layers multiplexed in an orthogonal frequency division multiplexing (OFDM) signal includes: a descrambling subcircuit configured to descramble multiple signals received on non-adjacent subcarriers of the OFDM signal to generate multiple descrambled signals; an inverse fast Fourier transform subcircuit configured to transform the descrambled signals from the frequency domain to a received signal including multiple samples in the time domain; and a layer separation subcircuit configured to separate the multiple layers multiplexed in the received signal by: defining a first time domain sampling window and a second time domain sampling window according to the size of the inverse fast Fourier transform; extracting one or more first layers from the samples in the first time domain sampling window; and extracting one or more second layers from the samples in the second time domain sampling window. A method for separating multiple layers and a wireless communication device are also provided.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62 / 758,263 filed in the U.S. Patent and Trademark Office on November 9, 2018, and U.S. Non-Provisional Patent Application No. 16 / 239,441 filed in the U.S. Patent and Trademark Office on January 3, 2019, the entire contents of which are incorporated herein by reference. Technical Field

[0003] Various aspects of embodiments of the present application relate to the field of electronic communications. Background Art

[0004] Some forms of electronic communication systems encode digital data on multiple carrier frequencies using a technique known as orthogonal frequency division multiplexing (OFDM), in which multiple closely spaced orthogonal subcarrier signals with overlapping frequency spectra are transmitted to convey the data. In addition, in some forms of electronic communication systems, multiple data streams ("layers") are transmitted in parallel in a configuration sometimes referred to as multiple-in-multiple-out (MIMO). In some cases, the multiple data streams are transmitted using frequency division multiplexing (FDM), in which non-overlapping frequency bands are used to transmit the individual signals.

[0005] In order for the receiver to perform channel estimation for each layer, the demodulation reference signal (DMRS) may include multiple "ports" (one for each layer), where the ports are orthogonal to each other. This orthogonality can be achieved by using frequency division multiplexing (FDM) in which different subcarriers are used in the frequency domain, or by code division multiplexing (CDM) using orthogonal cover codes (OCC) in the time domain (TD-OCC) or orthogonal cover codes (FD-OCC) in the frequency domain.

[0006] For example, such modulation and demodulation techniques may be applied to Long-Term Evolution (LTE). ) and fifth generation (5G) New Radio (NR) and other wireless cellular communication technologies. Summary of the invention

[0007] Aspects of the disclosed embodiments relate to systems and methods for demodulating frequency-division orthogonal cover coded signals.

[0008] According to one embodiment of the present disclosure, a method for separating multiple layers multiplexed using frequency domain orthogonal cover codes (FD-OCC) in an orthogonal frequency division multiplexing (OFDM) signal includes: descrambling multiple signals received on non-adjacent subcarriers of the OFDM signal based on multiplication by corresponding descrambling codes to generate multiple descrambled signals; applying an inverse fast Fourier transform to transform the descrambled signals from the frequency domain to a received signal including multiple samples in the time domain; and separating the layers multiplexed in the received signal in the time domain in the following manner: defining a first time domain sampling window and a second time domain sampling window according to the size of the inverse fast Fourier transform; extracting one or more first layers from the samples in the first time domain sampling window; and extracting one or more second layers from the samples in the second time domain sampling window.

[0009] The first time domain sampling window may correspond to a first half of the samples of the received signal in the time domain, and the second time domain sampling window may correspond to a second half of the samples of the received signal in the time domain.

[0010] The first time domain sampling window may correspond to a first half of the samples of the received signal offset by a leakage parameter in the time domain, and the second time domain sampling window may correspond to a second half of the samples of the received signal offset by the leakage parameter in the time domain.

[0011] The leakage parameter may have an integer value closest to 0.27 times the magnitude of the inverse fast Fourier transform.

[0012] The method may further include applying a fast Fourier transform to the extracted one or more first layers and the extracted one or more second layers to transform the one or more first layers and the one or more second layers from the time domain to the frequency domain.

[0013] The method may also include denoising the extracted one or more first layers and the extracted one or more second layers to generate one or more denoised first layers and one or more denoised second layers.

[0014] The method may further include applying a Fast Fourier Transform to convert the one or more denoised first layers and the one or more denoised second layers from the time domain to the frequency domain.

[0015] According to one embodiment of the present disclosure, a circuit for separating multiple layers multiplexed using frequency domain orthogonal cover codes (FD-OCC) in an orthogonal frequency division multiplexing (OFDM) signal includes: a descrambling circuit, configured to descramble the signal based on multiplying multiple signals received on non-adjacent subcarriers of the OFDM signal by corresponding descrambling codes to generate multiple descrambled signals; an inverse fast Fourier transform circuit, configured to transform the descrambled signal from the frequency domain to a received signal including multiple samples in the time domain; and a layer separation circuit, configured to separate the layers multiplexed in the received signal in the following manner: defining a first time domain sampling window and a second time domain sampling window according to the size of the inverse fast Fourier transform; extracting one or more first layers from the samples in the first time domain sampling window; and extracting one or more second layers from the samples in the second time domain sampling window.

[0016] The first time domain sampling window may correspond to a first half of the samples of the received signal in the time domain, and the second time domain sampling window may correspond to a second half of the samples of the received signal in the time domain.

[0017] The first time domain sampling window may correspond to a first half of the samples of the received signal offset by a leakage parameter in the time domain, and the second time domain sampling window may correspond to a second half of the samples of the received signal offset by the leakage parameter in the time domain.

[0018] The leakage parameter may have an integer value closest to 0.27 times the magnitude of the inverse fast Fourier transform.

[0019] The circuit may further include a fast Fourier transform circuit configured to convert the one or more first layers and the one or more second layers from the time domain to the frequency domain.

[0020] The circuit may also include a denoising circuit configured to denoise the extracted one or more first layers and the extracted one or more second layers to produce one or more denoised first layers and one or more denoised second layers.

[0021] The circuit may further include a fast Fourier transform circuit configured to convert the one or more denoised first layers and the one or more denoised second layers from the time domain to the frequency domain.

[0022] According to one embodiment of the present disclosure, a wireless communication device includes: an antenna; a processor; a memory; a plurality of signal processing circuits coupled to the processor and the memory via a data bus, the signal processing circuit including a receiver, the receiver being configured to receive a plurality of layers multiplexed using a frequency domain orthogonal cover code (FD-OCC) in an orthogonal frequency division multiplexing (OFDM) signal from the antenna, the receiver including: a descrambling circuit configured to descramble the signals based on multiplying a plurality of signals received on non-adjacent subcarriers of the OFDM signal by corresponding descrambling codes to generate a plurality of descrambled signals; an inverse fast Fourier transform circuit, Configured to transform the demodulated signal from the frequency domain to a received signal including multiple samples in the time domain; a layer separation subcircuit, configured to separate the layers multiplexed in the received signal by: defining a first time domain sampling window and a second time domain sampling window according to the size of an inverse fast Fourier transform; extracting one or more first layers from the samples in the first time domain sampling window; and extracting one or more second layers from the samples in the second time domain sampling window, the signal processing circuit being configured to transmit the data streams decoded from the one or more first layers and the one or more second layers to the processor and the memory.

[0023] The first time domain sampling window may correspond to a first half of the samples of the received signal offset by a leakage parameter in the time domain, and the second time domain sampling window may correspond to a second half of the samples of the received signal offset by the leakage parameter in the time domain.

[0024] The leakage parameter may have an integer value closest to 0.27 times the magnitude of the inverse fast Fourier transform.

[0025] The wireless communication device may further include a fast Fourier transform circuit configured to convert the one or more first layers and the one or more second layers from the time domain to the frequency domain.

[0026] The wireless communication device may also include a denoising circuit configured to denoise the extracted one or more first layers and the extracted one or more second layers to generate one or more denoised first layers and one or more denoised second layers.

[0027] The wireless communication device may further include a fast Fourier transform circuit configured to convert the one or more denoised first layers and the one or more denoised second layers from the time domain to the frequency domain. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings, together with the specification, illustrate exemplary embodiments of the present disclosure, and, together with the description, serve to explain the principles of the present disclosure.

[0029] Figure 1 is a diagram of a New Radio (NR) demodulation reference signal (DMRS) configuration type 1 with two layers, N DMRS subcarriers, and a total of 2N subcarriers.

[0030] Figure 2 is a block diagram of a receiver circuit for separating multiple layers of a received signal according to one embodiment of the present disclosure.

[0031] Figure 3 The present invention is a flowchart of a method for separating multiple layers of a signal according to an embodiment of the present disclosure.

[0032] Figure 4A It is a time domain representation of a received signal separated in the time domain according to one embodiment of the present disclosure.

[0033] Figure 4B is a time domain representation of a received signal separated in the time domain using an offset window according to an embodiment of the present disclosure.

[0034] Figure 5 is a graph showing the block error rate (BLER) performance of an embodiment of the present disclosure compared to a comparison receiver and compared to an ideal receiver.

[0035] Figure 6 is a graph showing the mean squared error (MSE) performance of an embodiment of the present disclosure compared to a comparison receiver and compared to an ideal receiver.

[0036] Figure 7 is a block diagram of a wireless communication device according to an embodiment of the present disclosure.

[0037] [Explanation of Symbols]

[0038] 200: receiver circuit;

[0039] 210: descrambling sub-circuit / descrambling circuit;

[0040] 230: Inverse Fourier transform subcircuit / inverse Fourier transform circuit;

[0041] 250: Layer separation sub-circuit / layer separation circuit;

[0042] 270: Denoising subcircuit / denoising circuit;

[0043] 290: Fourier transform subcircuit / Fourier transform circuit;

[0044] 300: Methods;

[0045] 310, 330, 350, 370, 390: operation;

[0046] 400, 401: layer;

[0047] 410, 411: Leakage;

[0048] 700: wireless communication device;

[0049] 710: Antenna;

[0050] 720: signal processing circuit;

[0051] 730: data bus;

[0052] 740: computing components;

[0053] d k ,d k+2 : Descramble signal;

[0054] h 0 、h 1 : Channel coefficient / frequency domain signal;

[0055] h TD,0 (n), h TD,1 (nN / 2): channel coefficient in the time domain;

[0056] x: extension amount;

[0057] y 0 ,y 2 ,y 2N-2 ,y k ,y k+2 : Subcarrier / received signal. DETAILED DESCRIPTION

[0058] Below, exemplary embodiments will be described in more detail with reference to the accompanying drawings, and in all the drawings, the same reference numerals refer to the same elements. However, the present disclosure may be implemented in various different forms and should not be considered to be limited to the embodiments shown herein. Specifically, these embodiments are provided as examples to make the present disclosure thorough and complete, and to fully convey the various aspects and features of the present disclosure to those skilled in the art. Therefore, processes, elements and technologies that are not necessary for a person of ordinary skill in the art to fully understand the aspects and features of the present disclosure may not be described. Unless otherwise stated, the same reference numerals throughout all the drawings and written descriptions represent the same elements, and therefore they will not be repeated.

[0059] The terms used herein are only used for the purpose of describing specific embodiments and are not intended to limit the present disclosure. Unless the context clearly indicates otherwise, the singular forms "a and an" used herein are intended to also include plural forms. It should also be understood that when the terms "comprises and comprising" and "includes and including" are used in this specification, it is to indicate the existence of the stated features, integers, steps, operations, elements and / or components, but does not exclude the existence or addition of one or more other features, integers, steps, operations, elements, components and / or their groups. The terms "and / or" used herein include any and all combinations of one or more of the related listed items. When expressions such as "at least one of..." are located after a series of elements, it is to modify all elements rather than modifying the individual elements in the series of elements.

[0060] In orthogonal frequency division modulation (OFDM), a data stream is divided into multiple substreams or "layers" with lower data rates, and these individual substreams are transmitted on multiple adjacent subcarriers. When considered in the frequency domain, this can be thought of as transmitting the substreams in parallel. In some cases, frequency domain orthogonal cover codes (FD-OCC) are used to multiplex the data streams on the OFDM subcarriers.

[0061] Signals transmitted on different subcarriers may experience different channels. For example, a signal may experience different degrees of fading (e.g., attenuation) in a frequency-dependent manner (e.g., where the attenuation is not uniform or flat across a frequency band). One form of fading is frequency selective fading, in which a signal partially cancels itself by arriving at a radio receiver via at least two paths ("multipath"), which may be due to reflections (e.g., motion of layers in the ionosphere or, depending on the frequency of the signal, due to physical objects in the environment). A communication channel in which different spectral components of the channel are attenuated to different degrees may be referred to as a frequency selective channel. Other forms of attenuation may include interference from other sources of electromagnetic radiation.

[0062] As described above, the demodulation reference signal (DMRS) includes multiple "ports", one for each layer, where these ports are modulated to be orthogonal to each other through frequency domain multiplexing (FDM), code division multiplexing using orthogonal cover codes in the time domain (TD-OCC) or orthogonal cover codes in the frequency domain (FD-OCC), or a combination thereof.

[0063] The frequency selectivity of the channel may result in at least partial loss of orthogonality between DMRS ports, and may be particularly severe where FD-OCC is applied to non-adjacent subcarriers, such as in DMRS configuration type 1 as specified in the 5G NR technical specification (see, e.g., 3GPP TS 38.211: "Technical Specification Group Radio Access Network; NR; Physical Channels and Modulation (Release 15)," Section 7.4.1.1). In other words, frequency selectivity may make it difficult to recover a data stream propagated by FD-OCC on two non-adjacent subcarriers, because the two parts of the signal may experience different channel conditions, which may result in interference between layers multiplexed between the two non-adjacent subcarriers (inter-layer interference).

[0064] Figure 1 is a schematic diagram of a New Radio (NR) demodulation reference signal (DMRS) configuration type 1 with two layers, N DMRS subcarriers, and a total of 2N subcarriers. For convenience and ease of discussion, Figure 1 Even subcarriers (eg, {y 0 ,y 2 ,…,y 2N-2 However, the odd subcarriers (e.g., {y 1 ,y 3 ,…,y 2N-1}) for processing. Figure 1 In the configuration shown in FIG. , two non-adjacent subcarriers y (eg, subcarrier y k and k+2 ) multiplexes two layers (referred to herein as layer 0 and layer 1). The two layers (layer 0 and layer 1) correspond to two channels, which are represented in the frequency domain by their corresponding channel coefficients h 0 and h 1 indicates (see e.g. Figure 2 ).

[0065] In addition, for convenience, the following discussion refers to the case of DMRS configuration type 1 in 5G New Radio (NR), where the ratio of subcarriers to DMRS reference signals is 2:1. However, embodiments of the present disclosure may also be applied to other configurations with different ratios between the number of reference signals and the number of carriers. In general, the ratio of subcarriers to reference signals may be Q to 1 (e.g., QN subcarriers and N reference signals). In these cases, separate groups of non-adjacent subcarriers may be processed together. For example, in the case of Q=3, subcarriers {y 0 ,y 3 ,…,y N-3} can be processed together, the subcarriers {y 1 ,y 4,…,y N-2} can be processed together, and the subcarriers {y 2 ,y 5 ,…,y N-1 More specifically, multiple subcarriers may be grouped together, where the mth group of subcarriers {y} m It is defined by:

[0066] {y} m ={y k where k mod Q = m}

[0067] As in Figure 1 As shown in 0 For example, the FD-OCC code is [1,1], which represents the channel coefficient h in the frequency domain corresponding to layer 0 0 Multiplied by a factor of 1, and corresponds to the channel coefficient h in the frequency domain of layer 1 1 is also multiplied by a factor of 1. Therefore, the DMRS sequence r of the zeroth subcarrier is multiplied by the components of the channel coefficients h corresponding to layers 0 and 1. 0 The received signal y at the zeroth subcarrier is generated by the sum of 0 :

[0068] y 0 =h 0,0 r 0 +h 1,0 r 0

[0069] Similarly, for the second subcarrier y 2 For example, the FD-OCC code is [1, -1], which represents the channel coefficient h in the frequency domain corresponding to layer 0 0 Multiplied by a factor of 1, and corresponds to the channel coefficient h in the frequency domain of layer 1 1 Multiply by the coefficient -1. Therefore, the DMRS sequence r of the second subcarrier is multiplied by the components of the channel coefficients h corresponding to layers 0 and 1. 2 The difference between the two generates the received signal y at the second subcarrier. 2 :

[0070] y 2 =h 0,2 r 2 -h 1,2 r 2

[0071] This can be extended to the kth subcarrier and the k+2th subcarrier:

[0072] y k =h 0,k r k +h 1,kr k

[0073] y k+2 =h 0,k+2 r k+2 -h 1,k+2 r k+2

[0074] where r k is the DMRS sequence of the kth subcarrier, and r k+2 is the DMRS sequence of the k+2th subcarrier. (For clarity, in this discussion of the received signal y, additional receiver noise, such as additive white Gaussian noise (AGWN), is omitted. However, one of ordinary skill in the art will understand that the received signal typically includes some noise). For example, the FD-OCC code alternates between [1, 1] and [1, -1]. For the even subcarrier k discussed in this example, the FD-OCC is [1, 1] when k / 2 is even, and the FD-OCC is [1, -1] when k / 2 is odd. (For the odd subcarriers not discussed in detail in this example, the FD-OCC is [1, 1] when (k-1) / 2 is even, and the FD-OCC is [1, -1] when (k-1) / 2 is odd.)

[0075] The received signal y k and k+2 Multiply by the known DMRS sequence r k and r k+2 The complex conjugate of gives the following equation to calculate the descrambled signal d received on the kth subcarrier and the k+2th subcarrier k and k+2 :

[0076] d k =h 0,k +h 1,k

[0077] d k+2 =h 0,k+2 -h 1,k+2

[0078] where d k Right k+2 The + to - in is applied to d k and k+2 This is caused by the different FD-OCC codes ([1,1] vs. [1,-1]).

[0079] The channel coefficients h used to separate the channel coefficients corresponding to layer 0 and layer 1 0 and h 1A comparative technique of involves despreading the received signal in the frequency domain, where the estimated channel coefficients in the frequency domain corresponding to layer 0 are calculated by

[0080]

[0081] (Essentially, by making d k With d k+2 Adding makes 0 The terms are added together and then divided by 2 to remove duplication and make h 1 The term cancels out and restores h 0 ). Similarly, the estimated channel coefficients in the frequency domain corresponding to layer 1 are calculated by

[0082]

[0083] (Essentially, by k Subtract d k+2 So that h 1 The terms are added together and then divided by 2 to remove duplicates and make h 0 The term cancels out and restores h 1 ). Both layers are traditionally placed in the odd subcarrier (k+1) because k+1 is the midpoint between subcarrier k and subcarrier k+2 (the two subcarriers on which FD-OCC spreading is applied).

[0084] The channel coefficients in the frequency domain may be obtained by applying an inverse Fourier transform (e.g., an inverse fast Fourier transform (IFFT)) to the channel coefficients in the frequency domain. The estimated channel coefficients of computation layer 0 in the time domain are

[0085]

[0086] where N is half of the 2N subcarriers (since this expression only considers even-numbered subcarriers) and where N also specifies the size of the inverse Fourier transform. The above expression calculates the estimated channel coefficients of layer 1 in the time domain In the general case of QN subcarriers and N reference signals, the step size (e.g., h 0,2k ) will become the step size Qk (for example, h 0,Qk ).

[0087] The estimated channel coefficients in the frequency domain for layer 0 and layer 1 are and In the above expression, the term:

[0088]

[0089] and

[0090]

[0091] represents the cross-layer interference caused by frequency domain despreading, which is i,k ≠h i,k+2 These cross-layer interference terms appear in the calculated channel coefficients in the time domain corresponding to layer 0 As interference from layer 1:

[0092]

[0093] and similar terms will appear in the calculated channel coefficients in the time domain corresponding to layer 1 , thus indicating cross-layer interference from layer 0.

[0094] As described above, this cross-layer interference may be caused by k and k+2 ) is caused by the frequency selective channel that is more likely to occur in the case of

[0095] Various aspects of embodiments of the present disclosure relate to separating two layers multiplexed by frequency domain orthogonal cover codes (FD-OCC) in the time domain. This can be contrasted with performing layer separation in the frequency domain as described above. This approach improves the preservation of orthogonality of the signals in the presence of frequency selective channels and improves the block error rate (BLER) of the estimated received signal, especially for large subcarrier spacing (e.g., 30 kilohertz (kHz)).

[0096] Figure 2 is a block diagram of a receiver circuit for separating a received signal according to an embodiment of the present disclosure. Figure 2 As shown in , a receiver circuit 200 (or a layer separation receiver circuit) according to one embodiment includes a descrambling subcircuit 210, an inverse Fourier transform subcircuit 230 (e.g., an inverse fast Fourier transform subcircuit), a layer separation subcircuit 250, a denoising subcircuit 270, and a Fourier transform subcircuit 290 (e.g., a fast Fourier transform subcircuit). The components of the receiver circuit 200 may be referred to herein as circuits or subcircuits.

[0097] Figure 3 is a flow chart of a method for separating signals by the receiver circuit 200 according to an embodiment of the present disclosure. Figure 4Ais a time domain representation of a received signal separated in the time domain according to an embodiment of the present disclosure. For convenience, Figure 2 and Figure 3 Only pairs are shown as y k and k+2 In the case of even subcarriers (e.g., k is an even subcarrier) of the OFDM signal, the even subcarriers of the OFDM signal can be demodulated to receive layer 0 and layer 1. However, one of ordinary skill in the art will appreciate that in the present example of 5G NR DMRS configuration type 1, the odd subcarriers of the OFDM signal can be demodulated simultaneously to receive additional layers on the odd subcarrier y. Similarly, in the case of a modulation configuration with different ratios of subcarriers to reference signals (e.g., QN subcarriers and N reference signals), each group of subcarriers can be processed independently.

[0098] As in Figure 2 and Figure 3 As shown in k and k+2 is supplied to the descrambling circuit 210 of the receiver circuit 200 to descramble the signal in operation 310 of the method 300. As described above, the received signal y k and k+2 Can have the following forms:

[0099] y k =h 0,k r k +h 1,k r k

[0100] y k+2 =h 0,k+2 r k+2 -h 1,k+2 r k+2

[0101] The reference sequence r k and r k+2 Scramble. As mentioned above, y k For k+2 The + to - in the equation is applied to y k and k+2 For the kth subcarrier and the k+2th subcarrier, the received signal y k and k+2 Multiply by the known reference sequence r k and r k+2 The complex conjugate of to obtain the descrambled signal d k and k+2 ,For example:

[0102] d k =h 0,k+h 1,k

[0103] d k+2 =h 0,k+2 -h 1,k+2

[0104] In operation 330, the inverse Fourier transform circuit (eg, inverse fast Fourier transform (IFFT) circuit) 230 transforms the descrambled signal d k and k+2 Transform from frequency domain to time domain.

[0105] Mathematically, an inverse Fourier transform of size N is applied to the received signal without despreading to calculate the channel coefficients of the received signal in the time domain

[0106]

[0107] So as to replace d k =h 0,k +h 1,k The above definition of and separating the terms where k is even versus where k is odd to account for the different FD-OCCs ([1,1] versus [1,-1]):

[0108]

[0109] Collect the channel coefficients h corresponding to layer 0 0 The term and the channel coefficient h corresponding to layer 1 1 item:

[0110]

[0111] Notice The above expression can be rewritten as:

[0112]

[0113] is equivalent to:

[0114]

[0115] Therefore, as can be seen in the above equation, the signal corresponding to the layer 0 channel h TD，0 Part of The first half of the sample corresponds to the layer 1 channel h TD,1 The portion of is offset by N / 2 samples (e.g., appears in the second half of the N samples). In other words, the layers multiplexed by FD-OCC appear as two offset versions of the channel impulse response (CIR), as shown as Figure 4A400 and 401.

[0116] Thus, in some embodiments, in operation 350, the layer separation circuit 250 separates the two layers (layer 0, channel h) by cutting or slicing the signal in the time domain according to two windows (a “first window” and a “second window”). 0 and layer 1 channel h 1 , or more formally, the channel coefficients h corresponding to layer 0 0 and the channel coefficient h corresponding to layer 1 1 ), so that each window contains one of the CIRs ("cutting" two complete CIRs into two parts), as in Figure 4A In FIG. 1 , the first N / 2 data points are indicated by a thick dashed line and a thin dashed line for representing two parts corresponding to two layers. More formally speaking, the first N / 2 data points can be regarded as corresponding to the channel coefficients of layer 0 in the time domain (e.g., the data points of the first window ), and the last N / 2 data points can be regarded as corresponding to the channel coefficients of layer 1 in the time domain (e.g., the data points of the second window ).

[0117] Simply cutting the received signal into two parts at N / 2 as described above may result in the portion of the signal corresponding to the leakage from the IFFT operation being omitted from the signal. Figure 4A Layer 0 leakage 410 around n=120 is shown, and layer 1 leakage 411 around n=60 to the left of the "cut" at n=70.

[0118] Therefore, in some embodiments of the present disclosure, in operation 350 , the layer separation circuit 250 shifts the window earlier in time to include the “leakages” 410 and 411 . Figure 4B is a time domain representation of a received signal separated in the time domain using an offset window according to an embodiment of the present disclosure.

[0119] In more detail, in some such embodiments, the samples are extracted from layers that pass through even indexes (counting from 0, e.g., h 0 )(Wrap around end of ):

[0120] and [Nx,N-1]

[0121] And extract the layers through odd indexes (e.g., h 1 ):

[0122] and

[0123] Or in other words, extract samples from layers through odd indices in the following interval:

[0124]

[0125] The offset amount or offset size is set based on various conditions specific to the channel.In some embodiments, the extension amount x is set to x=round(0.27N), where a "round" function rounds its given argument to the nearest integer.

[0126] In some embodiments, the denoising circuit 270 denoises the separated signal in the time domain in operation 370. In some embodiments, the denoising is performed by a per-tap minimum mean square error (MMSE) filter that assigns a weight to each tap of the estimated channel impulse response, wherein each weight is assigned based on the relative signal and noise power of its corresponding tap. Figure 2 A plurality of denoising circuits 270 arranged in parallel are shown, but this is a conceptual representation, and the embodiments of the present disclosure are not limited thereto. In some embodiments, a plurality of parallel signal streams may be processed by the same denoising circuit 270. For example, the separated signals in the time domain may be denoised sequentially by a single denoising circuit 270, denoising one separated signal at a time.

[0127] Then, in operation 390, the channel coefficient h in the time domain may be TD,0 (n) and h TD,1 (n) Provided to a Fourier transform circuit (eg, a fast Fourier transform circuit or an FFT circuit) 290 to transform the time domain signal into a frequency domain signal h 0 and h 1 Then the frequency domain signal h 0 and h 1 is subjected to further processing (e.g., to separate multiple data streams multiplexed within the signal). Figure 2 A plurality of parallel-arranged Fourier transform circuits 290 are shown, but this is a conceptual representation, and the embodiments of the present disclosure are not limited thereto. In some embodiments, a plurality of parallel signal streams may be transformed by the same Fourier transform circuit 290. For example, separate signals in the time domain may be sequentially transformed by a single Fourier transform circuit 290, with one separate signal being transformed at a time.

[0128] Figure 5 is a graph showing the block error rate (BLER) performance of an embodiment of the present disclosure compared to a comparison receiver and compared to an ideal receiver. Figure 6is a graph showing the mean square error (MSE) performance of an embodiment of the present disclosure compared to a comparative receiver and compared to an ideal receiver. In more detail, Figure 5 and Figure 6 The simulation results for the case of 30kHz subcarrier spacing, Rank 2 (2 layers or data streams transmitted in parallel), and 100MHz bandwidth under the modulation and coding scheme (MCS) 19 of 5R NG and the channel profile of "Extended Vehicular A, 30kHz Doppler frequency" (EVA 30) are shown.

[0129] As in Figure 5 As shown in , embodiments of the present disclosure (curve labeled “Time Domain Separation”) exhibit significantly lower block error rates (BLERs) than comparative techniques (curve labeled “Frequency Domain Despreading”) for a wide range of signal to noise ratio (SNR) values ​​(e.g., SNR greater than 22 decibels (dB)), and exhibit performance close to ideal performance (curve labeled “Ideal Channel Estimation”). As shown in Figure 6 As shown in , embodiments of the present disclosure (line labeled “time domain separation”) exhibit significantly smaller mean square error (MSE) over the entire range of SNR values ​​(e.g., from 18 dB to 40 dB) than comparative techniques (line labeled “frequency domain despreading”).

[0130] Figure 7 is a block diagram of a wireless communication device according to one embodiment of the present disclosure. For example, the wireless communication device may be a user equipment (UE), such as a mobile phone (e.g., a cell phone), a tablet computer, a notebook computer, a mobile hotspot, and similar devices equipped with a cellular radio. The wireless communication device may also be a node in a wireless communication network (e.g., a cellular base station or a base transceiver station). In some embodiments of the present disclosure, the wireless communication device may be used in conjunction with other forms of wireless communication (e.g., a wireless local area network (e.g., a network based on Wi-Fi or IEEE 802.11 standards)).

[0131] like Figure 7 As shown, in some embodiments, the wireless communication device 700 includes one or more antennas 710, which are configured to send and receive electromagnetic signals. The received electromagnetic signals may be supplied to one or more signal processing circuits 720. These signal processing circuits 720 may include Figure 2The receiving circuit 200 shown. The signal processing circuit 720 may also include, for example, a filter bank (e.g., a low-pass, high-pass, and / or band-pass filter), an amplifier (e.g., for amplifying a received signal and / or for amplifying a generated signal for transmission), an analog-to-digital converter (ADC), a digital-to-analog converter (DAC), and / or the like. The signal processing circuit 720 may be configured to send a digital signal (e.g., a data bit stream) to a computing component 740 on a data bus 730 and receive a digital signal (e.g., a data bit stream) from the computing component 740. For example, the computing component 740 may include a random access memory (e.g., a dynamic random access memory (DRAM)), a persistent memory (e.g., a flash memory), a microprocessor, an input / output controller, and / or the like. In some embodiments including user devices such as mobile phones, tablet computers, etc., the wireless communication device 700 may include one or more user interface devices, such as a touch-sensitive display panel, a speaker, a microphone, and a camera. In some embodiments, such as embodiments in which wireless communication device 700 is a node in a wireless communication network, wireless communication device 700 may include additional networking hardware, such as an Ethernet adapter and / or a wireless LAN adapter (e.g., for Wi-Fi or similar purposes).

[0132] In various embodiments of the present disclosure, the signal processing circuit 720, the receiver circuit 200, and the subcircuits of the receiver circuit 200 may include one or more different implementations of analog, digital, and mixed signal components. In some embodiments of the present disclosure, one or more circuits are implemented using application specific integrated circuits (ASICs) such as digital signal processors (DSPs). In some embodiments, various subcircuits are implemented using field programmable gate arrays (FPGAs). In some embodiments, some aspects such as inverse Fourier transform subcircuits or inverse fast Fourier transform subcircuits may be implemented using a dedicated core (e.g., a digital signal processing core) within an FPGA. In some embodiments, one or more subcircuits are implemented in a computer code executed by a processor (e.g., in the case of "software defined radio"). The receiver may also be implemented as a component or subcircuit of a system on a chip (SoC).

[0133] Thus, embodiments of the present disclosure provide systems and methods that more reliably separate layers encoded in an OFDM signal than comparable techniques.Some embodiments of the present disclosure relate to techniques for separating layers in the time domain.

[0134] While the present disclosure has been described in conjunction with certain exemplary embodiments, it should be understood that the present disclosure is not limited to the disclosed embodiments, but on the contrary is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims and their equivalents.

Claims

1. A method for separating multiple layers of an orthogonal frequency division multiplexed signal multiplexed using frequency domain orthogonal cover codes, the method comprising: descrambling a plurality of signals received on non-adjacent subcarriers of the OFDM signal based on multiplication by corresponding descrambling codes to generate a plurality of descrambled signals; applying an inverse fast Fourier transform to transform the plurality of descrambled signals from the frequency domain to a received signal comprising a plurality of samples in the time domain; The plurality of layers multiplexed in the received signal are separated in the time domain to: extracting one or more first layers from the sample; as well as extracting one or more second layers from the sample; and Defining a first time domain sampling window and a second time domain sampling window according to the size of the inverse fast Fourier transform, wherein the first time domain sampling window corresponds to the first half of the samples of the received signal in the time domain, The second time domain sampling window corresponds to the second half of the samples of the received signal in the time domain.

2. The method according to claim 1, wherein the first time domain sampling window corresponds to the first half of the samples of the received signal shifted by a leakage parameter in the time domain, The second time domain sampling window corresponds to the second half of the samples of the received signal shifted by the leakage parameter in the time domain. 3 . The method of claim 2 , wherein the leakage parameter has an integer value closest to 0.27 times the magnitude of the inverse fast Fourier transform.

4. The method according to claim 1 further includes applying a fast Fourier transform to the extracted one or more first layers and the extracted one or more second layers to transform the one or more first layers and the one or more second layers from the time domain to the frequency domain. 5 . The method according to claim 1 , further comprising denoising the extracted one or more first layers and the extracted one or more second layers to generate one or more denoised first layers and one or more denoised second layers.

6. The method according to claim 5, further comprising: A Fast Fourier Transform is applied to convert the one or more denoised first layers and the one or more denoised second layers from the time domain to the frequency domain.

7. A receiver circuit for separating multiple layers of an orthogonal frequency division multiplexed signal multiplexed using frequency domain orthogonal cover codes, the receiver circuit comprising: a descrambling subcircuit configured to descramble the plurality of signals received on non-adjacent subcarriers of the OFDM signal based on multiplying the plurality of signals by corresponding descrambling codes to generate a plurality of descrambled signals; an inverse fast Fourier transform subcircuit configured to transform the plurality of descrambled signals from the frequency domain to a received signal comprising a plurality of samples in the time domain; as well as a layer separation subcircuit configured to separate the plurality of layers multiplexed in the received signal in the time domain to: extracting one or more first layers from the sample; and extracting one or more second layers from the sample, wherein the layer separation subcircuit is further configured to define a first time domain sampling window and a second time domain sampling window according to the size of the inverse fast Fourier transform, wherein the first time domain sampling window corresponds to the first half of the samples of the received signal in the time domain, The second time domain sampling window corresponds to the second half of the samples of the received signal in the time domain.

8. The receiver circuit according to claim 7, wherein the first time domain sampling window corresponds to the first half of the samples of the received signal shifted by a leakage parameter in the time domain, The second time domain sampling window corresponds to the second half of the samples of the received signal shifted by the leakage parameter in the time domain.

9. The receiver circuit of claim 8, wherein the leakage parameter has an integer value that is closest to 0.27 times the magnitude of an inverse fast Fourier transform.

10. The receiver circuit of claim 7, further comprising a fast Fourier transform subcircuit configured to convert the one or more first layers and the one or more second layers from the time domain to the frequency domain.

11. The receiver circuit according to claim 7 further includes a denoising subcircuit, which is configured to denoise the one or more extracted first layers and the one or more extracted second layers to produce one or more denoised first layers and one or more denoised second layers.

12. The receiver circuit of claim 11, further comprising a fast Fourier transform subcircuit configured to convert the one or more denoised first layers and the one or more denoised second layers from the time domain to the frequency domain.

13. A wireless communication device, comprising: antenna; processor; Memory; A plurality of signal processing circuits are coupled to the processor and the memory via a data bus, wherein the signal processing circuits include a receiver circuit, wherein the receiver circuit is configured to receive a plurality of layers multiplexed by frequency domain orthogonal cover codes in an orthogonal frequency division multiplexed signal from the antenna, and the receiver circuit includes: a descrambling subcircuit configured to descramble the plurality of signals received on non-adjacent subcarriers of the OFDM signal based on multiplying the plurality of signals by corresponding descrambling codes to generate a plurality of descrambled signals; an inverse fast Fourier transform subcircuit configured to transform the plurality of descrambled signals from the frequency domain to a received signal comprising a plurality of samples in the time domain; a layer separation subcircuit configured to separate the plurality of layers multiplexed in the received signal in the time domain to: extracting one or more first layers from the sample; and extracting one or more second layers from the sample, The signal processing circuit is configured to transmit a data stream decoded from the one or more first layers and the one or more second layers to the processor and the memory, wherein the layer separation subcircuit is further configured to define a first time domain sampling window and a second time domain sampling window according to the size of the inverse fast Fourier transform, wherein the first time domain sampling window corresponds to the first half of the samples of the received signal shifted by a leakage parameter in the time domain, The second time domain sampling window corresponds to the second half of the samples of the received signal shifted by the leakage parameter in the time domain. 14 . The wireless communication device of claim 13 , wherein the leakage parameter has an integer value that is closest to 0.27 times the magnitude of an inverse fast Fourier transform.

15. The wireless communication device of claim 13, further comprising a fast Fourier transform subcircuit configured to convert the one or more first layers and the one or more second layers from the time domain to the frequency domain.

16. The wireless communication device according to claim 13 further includes a denoising subcircuit, which is configured to denoise the one or more extracted first layers and the one or more extracted second layers to produce one or more denoised first layers and one or more denoised second layers.

17. The wireless communication device of claim 16, further comprising a fast Fourier transform subcircuit configured to convert the one or more denoised first layers and the one or more denoised second layers from the time domain to the frequency domain.

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