A method for generating and applying channel spread function in a band-limited system

Abstract

This invention provides a method for generating and applying the channel spread function (CFD) in a band-limited system. The method includes: establishing a mathematical model of the CFD in the band-limited system based on the relationship between the channel transition function (CTU), the CFD, and multipath fading; inputting system parameters of the band-limited system into the mathematical model of the CFD to generate the CFD; the system parameters include the occupied time-frequency resources, channel coherence time, number of multipath paths, and system parameters related to the probability distribution of multipath paths. This invention considers the impact of small-scale fading on the CFD, and the generated CFD is more closely aligned with the actual situation of long-packet wireless communication systems. Compared with the CFD obtained using an equivalent method of the TDL model, the CFD generation method proposed in this invention is more consistent with the characteristics of the measured CFD.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to a method for generating and applying a channel spread function in a band-limited system. Background Technology

[0002] The Channel Spreading Function (CSF) refers to the representation of multipath propagation in the time-delay Doppler domain of a wireless channel. Meanwhile, the representation of multipath propagation in the time-delay domain is called the Channel Impulse Response (CIR), and its representation in the time-frequency domain is called the Channel Transfer Function (CTF). It is worth noting that the CSF and the Channel Impulse Response form a one-dimensional Fourier transform pair (between the time and Doppler domains), while the CSF and the CTF form a two-dimensional Fourier transform pair (between the time and Doppler domains, and between the frequency and time-delay domains).

[0003] The characteristics of the channel spread function (CFD) are instructive for communication system design. For example, when assuming the communication system occupies infinite bandwidth and infinite time, the multipath propagation function of the system exhibits strict sparsity and stability. Regarding sparsity, note that the time delay and Doppler effect of the multipath propagation are determined by the scattering environment; therefore, the Doppler effect and time delay experienced by the multipath are confined to a specific region. Outside this region, there are no multipath representations at the time delay Doppler domain lattice points in the CFD, hence the sparsity of the CFD. Regarding stability, when the communication system has infinite bandwidth and infinite time, all multipaths are separable. The constructive and destructive electromagnetic interference (called small-scale fading) between multipaths is no longer significant; that is, each path is not affected by the interference of other multipaths, hence the stability of the CFD.

[0004] In reality, communication systems with unlimited time and wireless bandwidth do not exist. Therefore, it is very important to generate channel spreading functions that conform to the basic laws of wireless communication for band-limited systems.

[0005] Currently, one existing method for generating the channel spread function of a communication system involves treating the tapped delay link (TDL) channel model of the communication system as an equivalent channel spread function. The drawbacks of this method include: while the TDL model is a simplified channel model suitable for channel characteristic recognition and the design and modeling of short-packet wireless transmission systems, it does not account for channel variations caused by constructive and destructive multipath interference when the data packets transmitted by the communication system are long. Therefore, treating the TDL model as an equivalent channel spread function is not suitable for long-packet wireless transmission systems. Summary of the Invention

[0006] Embodiments of the present invention provide a method for generating and applying channel spread functions in a band-limited system, so as to effectively generate channel spread functions for a band-limited system.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] A method for generating and applying a channel spread function in a band-limited system, comprising:

[0009] Based on the relationship between channel conversion function, channel spread function and multipath fading, a mathematical model of channel spread function in band-limited systems is established.

[0010] Input the system parameters of the band-limited system into the mathematical model of the channel spread function to generate the channel spread function. The system parameters include the time-frequency resources occupied, the channel coherence time, the number of channel multipaths, and the system parameters related to the probability distribution of the channel multipaths.

[0011] The channel spreading function is used to perform link-level channel simulation on the band-limited system.

[0012] Preferably, the mathematical model for establishing the channel spread function in a band-limited system based on the relationship between the channel conversion function, the channel spread function, and multipath fading includes:

[0013] Let the channel spread function in the delay-Doppler domain of the band-limited system be denoted as h(τ,v), where τ∈(0,+∞) represents the time delay and v∈(-∞,+∞) represents the Doppler effect. Suppose that h(τ,v) consists of P0 paths, and each path is numbered p0, p0=1,2,…,P0. Then h(τ,v) is written as:

[0014]

[0015] In equation (1), δ(·) represents the delta function, which has a value only at the point 0. This represents the time delay of the p0th path. This represents the Doppler effect of the p0th path;

[0016] Let the bandwidth of the band-limited system be MΔf, and the occupied time be NT, where M represents the number of subcarrier intervals Δf, and N represents the number of time lengths T, with both N and M being finite values. Assume that the band-limited system satisfies... The maximum Doppler of the channel is less than the subcarrier spacing Δf, and the maximum channel delay is less than the time length T. The band-limited system will perform an observation of h(τ,v) at every time T. Therefore, the channel spread function observed by the band-limited system at time nT can be written as:

[0017]

[0018] In the above formula, p = 1, 2, ..., P represents the index of the tap, τ p and v p Let represent the delay and Doppler of the p-th tap, respectively, and each tap consists of multiple wireless propagation paths;

[0019] The channel spread function corresponding to the band-limited system is:

[0020]

[0021] Where n = 0, 1, ..., N-1 are the slot numbers, m = 0, 1, ..., M-1 are the subcarrier numbers, k = 0, 1, ..., N-1 are the Doppler numbers, and l = 0, 1, ..., M-1 are the delay numbers. Substituting equation (2) into equation (3) yields the expression for the channel spread function observed by the system receiver.

[0022] Preferably, the system parameters of the band-limited system are input into the mathematical model of the channel spread function to generate the channel spread function. The system parameters include the occupied time-frequency resources, channel coherence time, number of channel multipaths, and system parameters related to the probability distribution of channel multipaths, including:

[0023] Suppose that there are Q different channel spreading functions in NT, and each channel spreading function consists of P taps, i.e. Based on the above explanation of formula (2) and small-scale fading, the channel spread function represented by formula (3) can be rewritten as:

[0024]

[0025] According to equation (4), the channel spread function of the band-limited system is generated according to the following processing steps:

[0026] 1. Input the system parameters of the band-limited system: subcarrier spacing Δf, number of subcarriers M, symbol period T, number of symbols N, and channel coherence time. The number of taps P and the maximum delay τ in the channel spread function max Maximum Doppler V max Distribution of tap delay, distribution of tap Doppler, distribution of tap power, and distribution of tap amplitude;

[0027] 2. Generate Q channel spread functions with Q coherent times, based on the distribution of input tap delay, Doppler, power, and amplitude. 1,…,P,q=1,…,Q.

[0028] 3. Substitute the values ​​from the previous two steps into equation (4) to obtain the channel spread function.

[0029] As can be seen from the technical solutions provided by the embodiments of the present invention above, the embodiments of the present invention take into account the impact of small-scale fading of wireless channels, and propose a channel spreading function generation scheme suitable for long-packet or short-packet practical band-limited systems based on the relationship between channel coherence time and data packet length.

[0030] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and will become apparent from the description or may be learned by practice of the invention. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 A flowchart illustrating the generation and application method of a channel spread function in a band-limited system, as provided in an embodiment of the present invention;

[0033] Figure 2 A channel spread function power graph provided in an embodiment of the present invention;

[0034] Figure 3 A power map of a channel spread function generated in a manner equivalent to the TDL model is provided in this embodiment of the invention;

[0035] Figure 4 This invention provides a channel spread function power diagram for a high-speed rail at a measured speed of 371 km / h. Detailed Implementation

[0036] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0037] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements. Furthermore, “connected” or “coupled” as used herein can include wireless connections or couplings. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0038] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0039] To facilitate understanding of the embodiments of the present invention, the following will provide further explanation and description with reference to the accompanying drawings and several specific embodiments. These embodiments do not constitute a limitation on the embodiments of the present invention.

[0040] This invention takes into account the impact of small-scale fading in wireless channels and proposes a channel spreading function generation scheme suitable for practical band-limited systems with long or short packets, based on the relationship between channel coherence time and data packet length.

[0041] This invention provides a method for generating channel spread functions in band-limited systems, offering an alternative solution for channel spread function generation in band-limited systems. The processing flow of this method is as follows: Figure 1 As shown, the processing steps include the following:

[0042] Step S1: Based on the relationship between the channel conversion function, the channel spread function, and multipath fading, establish a mathematical model of the channel spread function in the band-limited system;

[0043] Step S2: Input system parameters such as the time-frequency resources occupied by the system, the channel coherence time, the number of channel multipaths, and the probability distribution related to the channel multipaths into the mathematical model of the established channel spread function to generate the channel spread function.

[0044] Step S3: Use the generated channel spread function to perform link-level channel simulation on the band-limited system to help evaluate the performance of the communication system under time delay and Doppler dispersion channels.

[0045] Specifically, step S1 above includes: First, the channel spread function in the time-delay Doppler domain is denoted as h(τ,v), where τ∈(0,+∞) represents the time delay and v∈(-∞,+∞) represents the Doppler effect. If h(τ,v) consists of P0 paths, and each path is numbered p0, p0 = 1, 2, ..., P0, then h(τ,v) can be written as:

[0046]

[0047] In equation (1), δ(·) represents the delta function, which has a value only at the point 0. This represents the time delay of the p0th path. Let p0 represent the Doppler of the p0th path. It should be noted that when the system bandwidth and time are infinitely large, the system's accuracy in the time delay domain and Doppler domain is infinitely small; considering the complexity of the wireless propagation environment, P0 is a large unknown number.

[0048] Let the bandwidth of a practical band-limited system be MΔf, and the time occupied be NT, where M represents the number of subcarrier intervals Δf, and N represents the number of time lengths T, with both N and M being finite values. Furthermore, assume the system satisfies... The maximum Doppler of the channel is less than the subcarrier spacing Δf, and the maximum channel delay is less than the time length T. Since the actual number of multipath paths P0 is unknown, when modeling the channel, P taps with higher energy are usually considered, where P << P0. In cellular band-limited systems, P < 10 usually holds true. Meanwhile, the system will observe h(τ,v) once at every time T. Therefore, the channel spread function observed by the system at time nT can be written as:

[0049]

[0050] In the above formula, p = 1, 2, ..., P represents the index of the tap, τ p and v p Let h and represent the time delay and Doppler effect of the p-th tap, respectively. Furthermore, in a band-limited system, each tap consists of multiple wireless propagation paths. Due to the effects of constructive and destructive multipath interference, i.e., small-scale fading, h... nT (τ,v) is a time-varying function.

[0051] For a system with bandwidth MΔf and time NT, under the assumption of ideal transmit and receive waveforms, its corresponding channel spread function is:

[0052]

[0053] Where n = 0, 1, ..., N-1 are the slot numbers, m = 0, 1, ..., M-1 are the subcarrier numbers, k = 0, 1, ..., N-1 are the Doppler numbers, and l = 0, 1, ..., M-1 are the delay numbers. Substituting equation (2) into equation (3) yields the expression for the channel spread function observed at the system receiver. Thus, the mathematical modeling of the channel spread function for the band-limited system is complete.

[0054] II. The process of generating the channel spreading function in step 2 is illustrated below.

[0055] Note that when N-1≥n>n′≥0, h in equation (2) nT (τ,v) and h n′T There is a correlation between (τ, v). According to the basic theory of wireless communication, when At this time, the effect of small-scale fading in the channel can be considered constant, that is, h nT (τ,v) and h n′T (τ,v) are essentially equal. Here Indicates the coherence time of the channel.

[0056] For ease of explanation, assume that there are Q different channel spread functions within NT, and each consists of P taps, i.e. For example Therefore, based on formula (2) and the above explanation of small-scale fading, formula (3) can be rewritten as:

[0057]

[0058] Based on equation (4), we can generate the channel spreading function. Specifically, this involves the following steps:

[0059] 1. Input parameters: subcarrier spacing Δf, number of subcarriers M, symbol period T, number of symbols N, channel coherence time The number of taps P in the channel spread function, and the maximum delay τ max Maximum Doppler V max Distribution of tap delay (e.g., uniform distribution), distribution of tap Doppler (e.g., uniform distribution), distribution of tap power (e.g., exponential distribution), distribution of tap amplitude (e.g., Rayleigh distribution).

[0060] 2. Generate Q channel spread functions with Q coherent times. Specifically, based on the distribution of input tap delay, Doppler, power, and amplitude, generate... p = 1, ..., P, q = 1, ..., Q.

[0061] 3. Substitute the values ​​from the previous two steps into equation (4) to obtain the channel spread function.

[0062] like Figure 2 As shown, based on steps S1-S2 given in this embodiment of the invention, we can obtain M = 256, N = 256, Δf = 15kHz, T = 66.7μs. The channel spread function power diagram is shown below. Where P = 7, and the maximum time delay τ... max =6.67μs, maximum Doppler V max =100Hz, tap delay follows a uniform distribution, tap Doppler follows a uniform distribution, tap power follows an exponential distribution, and tap amplitude follows a Rayleigh distribution.

[0063] like Figure 3 The figure shows the power graph of the channel spread function generated using an equivalent method of the TDL model. Figure 4 This is a power diagram of the channel spread function under the measured channel speed of a high-speed train at 371 km / h, which is compared in this invention. It can be found that the channel spread function generation method proposed in this invention is more consistent with the characteristics of the measured channel spread function than the channel spread function obtained by using the TDL model equivalent method.

[0064] In summary, the embodiments of the present invention take into account the impact of small-scale fading on the channel spreading function, and the channel spreading function generated therefrom is more in line with the actual situation of long packet wireless communication systems.

[0065] like Figure 2 As shown, based on steps S1-S2 given in the embodiments of the present invention, M = can be obtained.

[0066] 256, N=256, Δf=15kHz, T=66.7μs, The channel spread function power diagram is shown below. Where P = 7, and the maximum time delay τ... max =6.67μs, maximum Doppler V max =100Hz, tap delay follows a uniform distribution, tap Doppler follows a uniform distribution, tap power follows an exponential distribution, and tap amplitude follows a Rayleigh distribution. For example... Figure 3 The figure shows the power graph of the channel spread function generated using an equivalent method of the TDL model. Figure 4 This is a power diagram of the channel spread function under the measured channel conditions at 371 km / h for high-speed rail, which is the subject of this invention.

[0067] III. Evaluating Communication System Performance Based on the Generated Channel Spread Function

[0068] Note that the channel spread function generated based on steps S1-S2 is a channel characterization method for a communication system with bandwidth MΔf and time period NT. To perform link-level simulation of this communication system under a specific channel environment, the system bandwidth MΔf, occupancy time NT, and system coherence time can be determined first. Number of channel taps P, maximum channel delay τ max Channel maximum Doppler v max The inputs, such as tap and Doppler distribution, are fed into steps S1-S2 to generate the channel spread function corresponding to the channel environment. The generated channel spread function is then substituted into the system's time-delay Doppler domain input-output relationship. Finally, system performance is evaluated, including metrics such as channel estimation accuracy, bit error rate, and channel capacity. Because this channel spread function generation method considers multiple metrics related to channel time and frequency dispersion, it can provide a more accurate channel reference for communication system evaluation.

[0069] It can be observed that the channel spread function generation method proposed in this invention is more consistent with the characteristics of the measured channel spread function compared with the channel spread function obtained by using the TDL model equivalent method.

[0070] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of one embodiment, and the modules or processes shown in the drawings are not necessarily essential for implementing the present invention.

[0071] As can be seen from the above description of the embodiments, those skilled in the art can clearly understand that the present invention can be implemented by means of software plus necessary general-purpose hardware platforms. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in various embodiments or some parts of the embodiments of the present invention.

[0072] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for apparatus or system embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. The apparatus and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0073] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for generating and applying a channel spread function in a band-limited system, characterized in that, include: Based on the relationship between channel conversion function, channel spread function and multipath fading, a mathematical model of channel spread function in band-limited systems is established. Input the system parameters of the band-limited system into the mathematical model of the channel spread function to generate the channel spread function. The system parameters include the time-frequency resources occupied, the channel coherence time, the number of channel multipaths, and the system parameters related to the probability distribution of the channel multipaths. The band-limited system is simulated at the link level using the channel spreading function. The mathematical model for the channel spread function in a band-limited system, based on the relationship between the channel conversion function, the channel spread function, and multipath fading, includes: The channel spread function in the time-delay Doppler domain of the band-limited system is denoted as... , Indicates time delay. Let Doppler be an example, and let... Depend on It consists of several paths, and the sequence number of each path is... , ,but writing: (1) In equation (1), This refers to the delta function, which only has a value at 0. Indicates the first The delay of each path, Indicates the first Doppler of a single path; The bandwidth of the band-limited system is set to The time occupied is , Indicates subcarrier spacing The number, Indicates the length of time The number, and and All values ​​are finite, and the band-limited system is assumed to satisfy... The maximum Doppler of the channel is less than the subcarrier spacing. The maximum channel delay is less than the time length. The band-limited system at each time All will be If one observation is conducted, then in The channel spread function observed by the band-limited system at time t is written as: (2) In the above formula Indicator representing the tap. and They represent the first The delay and Doppler of each tap, each tap consisting of multiple wireless propagation paths; The channel spread function corresponding to the band-limited system is: (3) in, The slot number is the time slot number. The subcarrier number. The serial number is for Doppler. Let be the sequence number of the time delay. Substituting equation (2) into equation (3) yields the expression for the channel spread function observed by the system receiver.

2. The method according to claim 1, characterized in that, The system parameters of the band-limited system are input into the mathematical model of the channel spread function to generate the channel spread function. These system parameters include the occupied time-frequency resources, channel coherence time, number of channel multipaths, and system parameters related to the probability distribution of channel multipaths. Assumption Inside There are 10 different channel spread functions, and each channel spread function is composed of 10 different channel spread functions. It consists of taps, namely Based on the above explanation of formula (2) and small-scale fading, the channel spread function represented by formula (3) can be rewritten as: (4) According to equation (4), the channel spread function of the band-limited system is generated according to the following processing steps: Input the system parameters of the band-limited system: subcarrier spacing Number of subcarriers Symbol period Number of symbols Channel coherence time Number of taps in the channel spread function Maximum delay Maximum Doppler Distribution of tap delay, distribution of tap Doppler, distribution of tap power, and distribution of tap amplitude; generate A coherent time A channel spread function is generated based on the distribution of input tap delay, Doppler, power, and amplitude. , , , Substituting the values ​​from the previous two steps into equation (4), we obtain the channel spread function. .

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