System for testing Nakagami fading channel and verification method thereof

Abstract

A system for testing a Nakagami fading channel and a verification method thereof are provided. The testing system includes a signal generator, a Nakagami fading channel simulator, and a computer. The signal generator is used to output a sine wave signal whose frequency is f and transmit the sine wave signal to the Nakagami fading channel simulator and the computer. The Nakagami fading channel simulator is used to generate a Nakagami fading channel. The computer is used to perform data processing and analysis. In the verification method, time domain fading characteristics, first-order statistics characteristics, and second-order statistics characteristics of the Nakagami fading channel are respectively verified. Verifying the time domain fading characteristics is verifying a waveform fluctuation rate and a fluctuation range on a time domain under different Nakagami fading factors. Verifying the first-order statistics characteristics is mainly verifying amplitude and phase distribution statistics characteristics of the Nakagami fading channel by means of Kolmogorov Smirnov (KS) hypothesis test. Verifying the second-order statistics characteristics is mainly verifying the shape and bandwidth of a power spectrum density function. In the present invention, verification on performance of the Nakagami fading channel simulator or a simulation model has features of accuracy and feasibility.

Claims

1. A system for testing a Nakagami fading channel, comprising: a signal generator; a Nakagami fading channel simulator; and a computer, wherein the signal generator is unidirectionally connected to the Nakagami fading channel simulator and the computer respectively by using SMA cables, and the Nakagami fading channel simulator is unidirectionally connected to the computer by using a general purpose interface bus; the signal generator is configured to output a sine wave signal x whose frequency is f, and the sine wave signal x is transmitted to the Nakagami fading channel simulator and the computer respectively by using the SMA cables; the Nakagami fading channel simulator is configured to generate the Nakagami fading channel during a testing process, and during the testing process, a maximum Doppler frequency shift f.sub.d, loss, a Rician factor K, a phase, and a Nakagami fading factor m are set for the Nakagami fading channel simulator, wherein m is 1 or (K+1).sup.2/(2K+1), one Nakagami fading channel path channel is opened, and the remaining path channels are closed, wherein during the testing process, the Nakagami fading channel simulator is configured to transmit the Nakagami fading channel to the computer through the SMA cables; and the computer is configured to receive the Nakagami fading channel from the Nakagami fading channel simulator through the SMA cables and the computer is configured to analyze the Nakagami fading channel, which is a radio frequency output from the Nakagami fading channel simulator, by obtaining performance indexes of the Nakagami fading channel on a time domain and a frequency domain to verify accuracy of a Nakagami fading channel model, wherein data processing of operation and analysis is performed on a computer, and the method comprises the following steps: Step S1: start a program, perform parameter initialization, and set a sampling frequency and a carrier frequency of a testing system; step S2: verify time domain fading characteristics of the Nakagami fading channel; step S3: verify first-order statistics characteristics of the Nakagami fading channel; step S4: verify second-order statistics characteristics of the Nakagami fading channel; and step S5: end the program, wherein verifying the time domain fading characteristics of the Nakagami fading channel in the step S2 is verifying a waveform fluctuation rate and a fluctuation range on the time domain under different Nakagami fading factors and specifically comprises: obtaining the Nakagami fading channel by means of enveloping of the sine wave signal obtained by e computer, then observing whether an amplitude waveform of the Nakagami fading channel quickly fluctuates on the time domain, wherein a fluctuation range of the amplitude waveform of the Nakagami fading channel is 30 dB to −60 dB; verifying whether the Nakagami fading channel conforms to features of a Rayleigh fading channel when the Nakagami fading factor m is 1; and verifying whether the Nakagami fading channel conforms to features of a Rician fading channel when the Nakagami fading factor m is (K+1).sup.2/(2K+1).

2. The Nakagami fading channel verification method of the system for testing the Nakagami fading channel according to claim 1, wherein verifying the first-order statistics characteristics of the Nakagami fading channel in the step S3 comprises: separately performing an amplitude and a phase statistical analysis on the obtained Nakagami fading channel, wherein it is known from theories that Rayleigh fading channel amplitude statistics is subject to Rayleigh distribution, and phase statistics is subject to uniform distribution; Rician fading channel amplitude statistics is subject to Rician distribution, and the phase statistics is subject to Gaussian distribution; that feature parameters of probability density functions of Rayleigh distribution, Rician distribution, uniform distribution, and Gaussian distribution are all represented by σ are assumed; in engineering, statistical verification is performed on the Nakagami fading channel based on a Kolmogorov Smirnov hypothesis test, and a verification method is: S31: respectively obtain an amplitude sequence H and a phase sequence θ of the Nakagami fading channel; S32: set a significance level α; S33: obtain a theoretical value of the parameter σ and a corresponding confidence interval Ω by means of least squares estimation; S34: respectively calculate true and theoretical cumulative distribution functions of the amplitude sequence H and the phase sequence θ; and S35: perform random distribution verification by means of Kolmogorov Smimov hypothesis test.

3. The Nakagami fading channel verification method of the system for testing the Nakagami fading channel according to claim 1, wherein verifying the second-order statistics characteristics of the Nakagami fading channel in the step S4 specifically comprises: separately performing autocorrelation and Doppler power spectrum analysis on the obtained Nakagami fading channel, to verify a shape and a bandwidth of a power spectrum density function, wherein when the Nakagami fading factor m is 1, the power spectrum density function is a “standard Rayleigh U-shaped power spectrum” and a spectral bandwidth is 2f.sub.d; when the Nakagami fading factor m is (K+1).sup.2/(2K+1), the power spectrum density function is a “standard Rician U-shaped power spectrum” and carries a line-of-sight signal with a Doppler frequency shift, and the spectral bandwidth is 2f.sub.d.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

(2) FIG. 1 is an instrument connection diagram of a system for testing a Nakagami fading channel according to the present invention.

(3) FIG. 2 is a flowchart of a Nakagami fading channel verification method according to the present invention.

(4) FIG. 3 is a fluctuation diagram of a time domain amplitude of a Nakagami fading channel when m=1 according to the present invention.

(5) FIGS. 4A and 4B are diagrams of first-order statistics characteristics of a Nakagami fading channel when m=1 according to the present invention.

(6) FIGS. 5A and 5B are diagrams of cumulative distribution functions of a Nakagami fading channel when m=1 according to the present invention.

(7) FIGS. 6A and 6B are diagrams of second-order statistics characteristics of a Nakagami fading channel when m=1 according to the present invention.

(8) FIG. 7 is a fluctuation diagram of a time domain amplitude of a Nakagami fading channel when m=(K+1).sup.2/(2K+1) according to the present invention.

(9) FIGS. 8A and 8B diagrams of first-order statistics characteristics of a Nakagami fading channel when m=(K+1).sup.2/(2K+1) according to the present invention.

(10) FIGS. 9A and 9B are diagrams of cumulative distribution functions of a Nakagami fading channel when m=(K+1).sup.2/(2K+1) according to the present invention.

(11) FIGS. 10A and 10B are diagrams of second-order statistics characteristics of a Nakagami fading channel when m=(K+1).sup.2/(2K+1) according to the present invention.

DESCRIPTION OF THE EMBODIMENTS

(12) Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.

(13) The following describes the technical solutions of the present invention in detail with reference to the accompanying drawings and embodiments.

(14) Referring to FIG. 1, a system for testing a Nakagami fading channel in the present invention includes a signal generator U1, a Nakagami fading channel simulator U2, and a computer U3, where the signal generator U1 is unidirectionally connected to the Nakagami fading channel simulator U2 and the computer U3 respectively by using SMA cables, and the Nakagami fading channel simulator U2 is unidirectionally connected to the computer U3 by using a GPIB general purpose interface bus.

(15) The signal generator U1 is used to output a sine wave signal x whose frequency is f and that has an appropriate power. In this embodiment, the signal generator U1 uses an Agilent 33511B 2 channel 20 MHz function signal generator. During a testing process, the signal generator U1 outputs a sine wave signal x with frequency f is 10 MHz and power level is −10 dB, and the sine wave signal x is transmitted to the Nakagami fading channel simulator U2 and the computer U3 respectively by using the SMA cables (data cable).

(16) The Nakagami fading channel simulator U2 is used to generate a Nakagami fading channel y. In this embodiment, the Nakagami fading channel simulator U2 uses a Keysight Technologies FS8 channel simulator. During a testing process, a fading mode of the simulator is set as the Nakagami fading channel of which a maximum Doppler frequency shift f.sub.d is 500 Hz, loss is 0 dB, a Rician factor K is 10, a phase is 90°, and a Nakagami fading factor m is 1 or (K+1).sup.2/(2K+1), that is, 5.76, one Nakagami fading channel path channel is opened, and the remaining path channels are closed. When m is 1, it is verified whether the Nakagami fading channel conforms to features of a Rayleigh fading channel. When m is 5.76, it is verified whether the Nakagami fading channel conforms to features of a Rician fading channel. A specific calculation process of impact of the value of m on Nakagami fading channel distribution is mastered by a person skilled in the art and is not described in detail herein.

(17) The computer U3 is used to operate and analyze the Nakagami fading channel y output in a radio frequency manner from the Nakagami fading channel simulator U2, to obtain performance indexes of the Nakagami fading channel on a time domain and a frequency domain, to verify accuracy of the channel model. Without loss of generality, the computer U3 uses a PC terminal.

(18) Referring to FIG. 2, during implementation of the Nakagami fading channel verification method of the present invention, processes of data processing related to operation and analysis are mainly performed on a terminal of the computer U3. A process thereof includes: S1: start; S2: verify time domain fading characteristics of the Nakagami fading channel; step S3: verify first-order statistics characteristics of the Nakagami fading channel; step S4: verify second-order statistics characteristics of the Nakagami fading channel; and step S5: end.

(19) The verifying time domain fading characteristics of the Nakagami fading channel in step S2 specifically includes the following steps:

(20) Because the amplitude of the high-frequency sine wave signal x obtained by the computer U3 stably fluctuates within a time period, a Nakagami fading channel h may be obtained by means of enveloping of the high-frequency signal y obtained by the computer U3, and then it is observed whether an amplitude waveform of the Nakagami fading channel h quickly fluctuates on the time domain, where a fluctuation range of the amplitude waveform (a fast fading signal) of the Nakagami fading channel h is 30 dB to −60 dB. When the Nakagami fading factor m is 1, the time domain fading characteristics thereof are shown in FIG. 3. When the Nakagami fading factor m is 5.76, the time domain fading characteristics thereof are shown in FIG. 7. A specific calculation process of the fluctuation range of the fast fading signal is mastered by a person skilled in the art and is not described in detail herein.

(21) The verifying first-order statistics characteristics of the Nakagami fading channel in step S3 includes: separately performing amplitude and phase statistical analysis on the obtained Nakagami fading channel h, where it is known from theories that Rayleigh fading channel amplitude statistics is subject to Rayleigh distribution, and phase statistics is subject to uniform distribution; Rician fading channel amplitude statistics is subject to Rician distribution, and the phase statistics is subject to Gaussian distribution; that feature parameters of probability density functions of Rayleigh distribution, Rician distribution, uniform distribution, and Gaussian distribution are all represented by a are assumed; in engineering, statistical verification may be performed on the Nakagami fading channel h based on a Kolmogorov Smirnov hypothesis test theory. Without loss of generality, a verification method thereof is: first, respectively obtaining an amplitude sequence H and a phase sequence θ of the Nakagami fading channel h; then setting a significance level α, which may be usually set to 0.01; then obtaining a theoretical value of the parameter a and a corresponding confidence interval Ω by means of least squares estimation; then respectively calculating actual and theoretical cumulative distribution functions of the amplitude sequence H and the phase sequence θ; and at last, performing random distribution verification by means of Kolmogorov Smimov (KS) hypothesis test. When the Nakagami fading factor m is 1, the first-order statistics characteristics thereof are shown in FIGS. 4A and 4B and FIGS. 5A and 5B, and a verification result shows that an amplitude is subject to Rayleigh distribution, and phase statistics is subject uniform distribution. When the Nakagami fading factor m is 5.76, the time domain fading characteristics thereof are shown in FIGS. 8A and 8B and FIGS. 9A and 9B, and the verification result shows that the amplitude is subject to Rician distribution, and the phase statistics is subject to Gaussian distribution. The verification results are both consistent with theoretical analysis. A true test simulation result is shown in Table 1. Specific implementation of the KS hypothesis test method is mastered by a person skilled in the art and is not described in detail herein.

(22) Table 1 Distribution verification result of first-order statistics characteristics of a Nakagami fading channel of the present invention

(23) TABLE-US-00001 True Threshold Type of value of rejecting distribution test the to which Value Verification Significance Theoretical Confidence statistical original statistics is of m type level α parameter σ interval Ω amount hypothesis subject m = 1 Amplitude 0.01 0.7150 [0.7097, 0.0055 0.0094 Rayleigh sequence 0.7203] distribution Phase 0.01 −3.1411; 3.1415 [−3.142, 0.0093 0.0094 Uniform sequence 3.1411]; distribution [3.1415, 3.1425] m = 5.76 Amplitude 0.01   0.9002; 0.3178 [0.8950, 0.0084 0.0094 Rician sequence 0.9053]; distribution [0.3142, 0.3215] Phase 0.01 −0.0017; 0.3969 [−0.007, 0.0087 0.0094 Gaussian sequence 0.0042]; distribution [0.3928, 0.4011]

(24) The verifying second-order statistics characteristics of the Nakagami fading channel in step S4 specifically includes: separately performing autocorrelation and Doppler power spectrum analysis on the obtained Nakagami fading channel h. In engineering, the shape and bandwidth of a power spectrum density function may be verified. In theory, when the Nakagami fading factor m is 1, the power spectrum density function is a “standard Rayleigh U-shaped power spectrum” and a spectral bandwidth is approximately 2f.sub.d; when the Nakagami fading factor m is (K+1).sup.2/(2K+1), the power spectrum density function is a “standard Rician U-shaped power spectrum” and carries a line-of-sight (LOS) signal with a Doppler frequency shift, and the spectral bandwidth is approximately 2f.sub.d.

(25) In this embodiment, when m is 1, the second-order statistics characteristics thereof are shown in FIGS. 6A and 6B, and a verification result shows that the power spectrum density function is a “standard Rayleigh U-shaped power spectrum” and a spectral bandwidth is approximately 1000 Hz and is equal to 2f.sub.d (a theoretical value). When the Nakagami fading factor m is (K+1).sup.2/(2K+1), that is, 5.76, the second-order statistics characteristics thereof are shown in FIGS. 10A and 10B, and the verification result shows that the power spectrum density function is a “standard Rician U-shaped power spectrum” and carries a line-of-sight (LOS) signal with a Doppler frequency shift 0 Hz, and the spectral bandwidth is approximately 1000 Hz and is equal to 2f.sub.d (a theoretical value).

(26) The Nakagami fading channel verification method of the present invention can implement verification of performance of the Nakagami fading channel simulator or a simulation model, has features of good stability and accuracy, and is applicable to a scenario in which a radio channel needs to be modeled and simulated, and performance of a channel simulator needs to be verified.

(27) A person skilled in the art can perform various modifications and transformations on the present invention. If these modifications and transformations are within the scope of claims of the present invention and equivalent technologies, these modifications and transformations are also within the protection scope of the present invention.

(28) Content that is not described in detail in the specification is the prior art well known to a person skilled in the art.

(29) It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention c over modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.