Error code performance evaluation method for parallel relay UWOC system
By adopting two-hop structure and EGC technology in the parallel relay UWOC system, combined with the generalized Gamma distributed ocean turbulence model, the problem of existing systems failing to effectively evaluate the bit error performance is solved, and rapid bit error rate evaluation and performance improvement in turbulent environments are achieved.
Patent Information
- Application Number
- CN202311132679.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-09-04
- Publication Date
- 2025-03-04
AI Technical Summary
Existing parallel relay UWOC systems do not involve bit error performance evaluation, resulting in a lack of effective method for bit error rate evaluation in turbulent fading environments.
The two-hop parallel relay UWOC system is used, combined with the generalized Gamma distributed marine turbulence statistical model and Equal Gain Combining (EGC) technology, the system's average bit error rate theoretical closed expression is derived.
In an environment that considers complex factors such as FFIR hidden path loss and multipath effect, the theoretical bit error rate performance of parallel relay UWOC systems is quickly calculated, and theoretical guidance is provided on the upper-level network planning of relay UWOC systems.
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Figure CN119561660A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to a parallel relay underwater wireless optical communication (UWOC) system, and an error performance evaluation strategy when the UWOC system works in a turbulent fading environment, belonging to the technical field of wireless optical communication, especially underwater wireless optical communication. Background Art
[0002] In recent years, with the increasing attention paid by mankind to marine rights and interests, and the large-scale development of marine resources, the demand for underwater multimedia communications has become particularly urgent. Compared with traditional hydroacoustic and radio frequency communications, UWOC has the advantages of lower link delay and implementation cost, extremely high transmission bandwidth, and better safety performance, so UWOC has gradually become the mainstream technology for realizing high-speed and reliable underwater information transmission. However, the absorption, scattering and turbulence effects that are prevalent in the marine environment greatly limit the communication range of the UWOC system. As far as traditional point-to-point (P2P) transmission technology is concerned, even UWOC based on laser light sources is only suitable for short-range communication, generally less than 100m. UWOC communication based on relay-assisted technology is one of the technical means that can effectively overcome this defect. Its basic idea is to set up appropriate relay nodes and divide the total communication distance into multiple shorter or parallel links, thereby reducing the adverse effects of damage factors in the link.
[0003] Existing research results show that the introduction of relay nodes can effectively improve the signal-to-noise ratio of the link and thus reduce the bit error rate of the system. The so-called "bit error rate" is defined as the proportion of information bits with transmission errors in the total received information block. It is one of the important indicators to measure the transmission performance of a communication system. Generally speaking, the main purpose of serial relay is to achieve long-distance communication, while parallel relay is mainly to avoid obstacles on the direct transmission link between two points, or to further improve the overall communication quality of the system by introducing parallel links and diversity reception on the basis of the original P2P communication. In view of the fact that there are many performance studies on serial relay UWOC systems at this stage, and there are very few studies on parallel relay UWOC, especially on bit error performance, therefore, the use of appropriate parallel relay transmission technology to improve the performance of communication indicators such as bit error rate of UWOC systems, and obtain the corresponding fast bit error performance accurate evaluation method, can obviously provide convenience for the theoretical performance research and practical system design of UWOC systems. Summary of the invention
[0004] Purpose of the invention: In view of the defect or deficiency that the existing parallel relay UWOC system is limited to the analysis of performance indicators such as system outage probability, but does not involve the evaluation of system error performance, the present invention proposes a parallel relay UWOC system that works in a generalized Gamma distribution (GGD) ocean turbulence statistical model, adopts two hops and equal gain combining (EGC) technology at the receiving end, and effectively evaluates the average error performance of the system, in order to provide a solution in terms of the theoretical rapid measurement method of the error performance of the parallel relay UWOC system.
[0005] Technical solution: A two-hop parallel relay UWOC system error performance evaluation scheme, including the following steps
[0006] Considering the channel environment with complex fading factors such as GGD ocean turbulence, fading free impulse response (FFIR) implicit path loss and multipath effect, a two-hop parallel relay UWOC system with EGC merging technology at the receiving end is considered. Firstly, the theoretical expression of the bit error rate from the first hop source node S to each relay node i, 1≤i≤N (N is the number of relay nodes) in the two-hop parallel relay UWOC system is derived respectively: And the theoretical closed-form expression P of the bit error rate from the second-hop relay node i to the target node D after EGC combined reception be2 ; Then, according to the above two bit error rates and the number of relay nodes N, the theoretical closed-form expression of the end-to-end (e2e) average bit error rate of the final two-hop parallel relay UWOC system is obtained:
[0007] As a preferred solution, for the case where the transmission distance from relay node i to target node D, i.e., N+1 node, is approximately equal, the theoretical calculation formula for the end-to-end (e2e) average bit error rate of the two-hop parallel relay UWOC system changes with the number of relay nodes N is: It can be expressed as
[0008]
[0009] In the above formula, N is the number of parallel relay nodes, represents the average received bit error rate from the source node S to the i-th relay node in the first hop, P be2 It represents the average received bit error rate after EGC combination from each relay node i to the target node D, i.e., node N+1 in the second hop.
[0010] As a preferred solution, the average received bit error rate from the source node S to the i-th relay node is The calculation formula is as follows:
[0011]
[0012] In the above formula, a i and c i represents the shape parameter of the GGD fading distribution experienced by the source node S to the i-th relay node, b i is the scale parameter. represents the gamma function, Indicates the advanced transcendental foxH function. in is the matched filtering received signal of the detection current waveform signal required on the corresponding path, that is, the path from the source node S to the i-th relay node, R is the responsivity of the photodetector R = ηq / hf, η, q, h, f are the photodetector quantum efficiency, electron charge, Planck constant and light frequency in water respectively; the integrand It represents the pulse shaping signal P(t) passing through the FFIR channel The received signal waveform after P(t) indicates the amplitude value is 2P b The gate function signal has a value range of [0, T b ], T b is the symbol width, P b is the average power of the source transmitted symbols, is the FFIR from the source node S to the i-th relay node, * represents the convolution operation; is the standard deviation of the Gaussian integrated noise component.
[0013] As a preferred solution, the average received bit error rate P after EGC combination from the relay node i to the target node D is be2 The calculation formula is as follows:
[0014]
[0015] In the formula, Φ=μ1 2 / (μ2-μ1 2 ), ψ=μ1 / (μ2-μ1 2 ), where μ1 and μ2 are the first-order and second-order origin moments of the equivalent fading coefficient h, respectively. The variables in this formula Here a i , c i and b iThey represent the shape parameter and scale parameter of the GGD fading distribution experienced by the i-th relay node to the target node D. Without loss of generality, they are similar to the GGD turbulent fading distribution parameter a between the source node S and the relay node i. i , c i and b i are exactly the same; the equivalent fading coefficient h satisfies in represents the GGD turbulence attenuation coefficient experienced by the link from the source node S to the i-th relay node in the first hop, or from the i-th relay node to the target node D in the second hop, GG(·) represents Subject to parameter a i , b i , c i GGD distribution; is the matched filtering signal of the detection current waveform signal required for the link between the i-th parallel relay node and the target node D, i.e., node N+1, represents the received signal waveform after the pulse shaping function P(t) passes through the corresponding link FFIR, where It is the FFIR from relay node i to target node N+1; function d n (x, y) = Γ(x+n / y) / Γ(x).
[0016] As a preferred solution, the end-to-end (e2e) average bit error rate calculation formula of the two-hop parallel relay UWOC system assumes that the average receiving bit error rates from the source node S to the i-th relay node are approximately equal, that is, Under the condition, it can be further simplified into the general formula:
[0017]
[0018] The first term on the right side of the above equation Defined as 0 when N=1.
[0019] As a preferred solution, the foxH function description form of the GGD ocean turbulence fading probability density function (Probability Density Function, PDF) is as follows:
[0020]
[0021] Where b i is the scale parameter, a i and c i is the shape parameter, represents a random variable that follows a GGD distribution.
[0022] As a preferred solution, the non-fading channel impulse response FFIR data can be obtained by simulating the motion of photons using a computer Monte Carlo method under given system transceiver parameters, such as ocean water quality, transmission distance, receiver aperture, emission light source wavelength, etc.
[0023] Beneficial effects:
[0024] Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects: the method provided by the present invention for evaluating the average bit error rate of a parallel relay UWOC system using two-hop and receiving end EGC merging technology can quickly calculate the theoretical bit error rate performance of the proposed parallel relay UWOC system in a complex communication environment that takes into account comprehensive factors such as FFIR hidden path loss and multipath effect, and GGD ocean turbulence fading, thereby providing theoretical guidance for the upper-layer network planning research of the relay UWOC system. BRIEF DESCRIPTION OF THE DRAWINGS
[0025] Figure 1 This is a schematic diagram of the implementation structure of a two-hop parallel relay UWOC system. In the figure, S represents the source node, D represents the target node, and R i represents the i-th (1≤i≤N) relay node, N is the number of relay nodes; h (0，i) (t) is the FFIR from the source node S to the i-th relay node, h (i，N+1) (t) is the FFIR from the i-th relay node to the target node D.
[0026] Figure 2 This is a block diagram of the principle implementation of the average bit error performance evaluation scheme of the two-hop parallel relay UWOC system proposed in the present invention.
[0027] Figure 3 It is a two-hop parallel relay UWOC system with a total length of 40 meters in the near-shore coastal water quality. When different numbers of relay nodes N are used, the theoretical calculated value and Monte Carlo simulation value of the system average bit error rate change with the node transmission power. Comparison curve chart. DETAILED DESCRIPTION
[0028] The present invention will be further described below in conjunction with specific embodiments, and it should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. After reading the present invention, those skilled in the art will be able to modify various equivalent forms of the present invention within the scope defined by the appended claims of the present application.
[0029] The present invention is a method for rapid performance evaluation of the average bit error rate of a two-hop parallel relay UWOC system under GGD ocean turbulence fading, FFIR hidden path loss and multipath transmission environments. The specific implementation method and application examples are described as follows:
[0030] Step 1: Model the received signal model that has experienced composite fading factors such as GGD ocean turbulence, FFIR hidden path loss and multipath effect, where the PDF expression of the GGD random variable is converted into a higher transcendental foxH function form, and based on this, the theoretical closed-form expression of the average bit error rate from the first hop source node S to each relay node i in the above composite fading two-hop parallel relay UWOC system is derived.
[0031] Step 2: Based on the fact that the sum of N independent and differently distributed GGD random variables still obeys the GGD distribution, the PDF mathematical expression of the second-hop equivalent fading channel coefficient is obtained according to the EGC merging technology, thereby calculating the theoretical closed-form expression P of the average bit error rate of the receiving end after EGC merging from relay node i to target node D be2 ;
[0032] Step 3: Based on the bit error rates at two locations and P be2 , and the number of relay nodes N are used to obtain the theoretical closed-form expression of the final end-to-end (e2e) average bit error rate, which is also the final bit error performance of the two-hop parallel relay UWOC system.
[0033] The GGD model is used to describe Figure 1 The ocean turbulence effect caused by the temperature and salinity gradient on the i-th transmission link in . After converting its PDF into foxH function form, it has the following mathematical expression
[0034]
[0035] In the formula, is the GGD turbulence attenuation coefficient experienced by the link from the source node S to the i-th relay node in the first hop, or from the i-th relay node to the target node D in the second hop, b i is the scale parameter of the corresponding link PDF, a i and c i is the shape parameter, represents the gamma function, For advanced transcendent foxH functions.
[0036] Assuming that the transmitted information adopts a simple On-Off Keying (OOK) modulation method, the original data sequence transmitted by the transmitter can be expressed as
[0037]
[0038] Where, T b is the symbol width of the OOK symbol, b k∈{0, 1} is the OOK transmission symbol of the kth time slot; P(t) = 2P b M(t) is the amplitude value of 2P b The pulse shaping waveform, where P b is the average transmission power of the OOK symbol, M(t) is the power of the b ] is a unit pulse shaping function with values within ]. Therefore, the time domain received signal received at the i-th relay node can be expressed as:
[0039]
[0040] In the above formula, is the time domain waveform of the impulse response of the composite fading channel corresponding to the i-th hop path, where is the FFIR corresponding to the i-th hop, is the turbulence attenuation coefficient corresponding to the i-th jump; * represents the convolution operator; n(t) is an additive white Gaussian noise process, where the mean value of the noise at each time sampling point is 0 and the variance is σ 2 =4KTB / R L , where K, T, B, R L represent the Boltzmann constant, Kelvin temperature, filter bandwidth and the load resistance value of the system respectively.
[0041] Without considering interference cancellation and only using matched filtering, and each node works in the "decode-forward" mode, the integrated current output by the receiver at node i in the 0th time slot can be expressed as:
[0042]
[0043] Where b0 is the OOK transmission symbol of the 0th time slot to be detected, L 0，i is the channel memory length between the source node and the i-th relay node; is the integrated noise of the receiver, which has a mean of 0 and a variance of A matched filtering receiving signal for a desired detection current waveform signal; is the inter-symbol crosstalk caused by channel time dispersion, where R = ηq / hf is the responsivity of the photodetector, η, q, h, f are the photodetector quantum efficiency, electron charge, Planck constant and light frequency in water, respectively; It represents the received waveform of the pulse shaped signal after passing through the corresponding path FFIR, where: is the FFIR from the source node to the i-th relay node.
[0044] Assuming channel state information It is known at the relay node that each T b Integrated current in seconds and the optimal decision threshold For comparison, the final conditional bit error rate related to the channel state information can be written as
[0045]
[0046] In the above formula, P(1) and P(0) are the probabilities of the source node sending 1 or 000K symbols, respectively. Generally, P(1) = P(0) = 1 / 2. The function Q(·) is defined as make The above formula can be further simplified as:
[0047] In this way, the average bit error rate of the P2P link between the source node S and the i-th relay node can be calculated by the following formula:
[0048]
[0049] According to formula (1) The relevant operation properties of the foxH function in the PDF expression of , the average bit error rate expression at the first hop i-th parallel relay node can be obtained as
[0050]
[0051] Next, we calculate the bit error rate at the second hop target node. It is not difficult to see that the target node N+1 is in the 0th time interval, and the integrated current signal after EGC merging can be expressed as
[0052]
[0053] In the above formula, is the turbulent channel fading coefficient between the i-th parallel relay node and the target node N+1, and its statistical characteristics are completely equal to the turbulent fading coefficient between the source node and the i-th relay node; L i，N+1 is the channel memory length between the ith parallel relay node and the target node; is the integrated noise of the receiver at the target node, with a mean of 0 and a variance of A matched filtering receiving signal for a desired detection current waveform signal; is the inter-symbol interference caused by channel time dispersion, Indicates amplitude is 2P b The pulse shaping function of the received signal time domain waveform after passing through the corresponding link FFIR, where is the FFIR from relay node i to target node N+1.
[0054] because Right now Subject to parameter a i , b i , c i The GGD distribution of the system is shown in Table 8. From the symbol description in the following paragraphs, once the system parameters are determined, is a constant, then That is, the original GGD turbulent fading random variable The constant product term h l Still satisfies the GGD distribution. Let Useful signal weighting term obtained by EGC merging technology The PDF of the equivalent fading coefficient h in can be approximated as
[0055]
[0056] In the formula Where μ1 and μ2 are the first-order and second-order origin moments of the equivalent attenuation coefficient h. Define the function but The variables
[0057] Assume that the channel state information is known to the receiver at the second hop target node D, and convert the integrated current Its optimal decision threshold For comparison, the final conditional bit error rate related to the channel state information can be written as
[0058]
[0059] make The above formula can be further simplified as:
[0060] According to the relevant operation properties of the foxH function, the average bit error rate of the receiving end after EGC merging from each relay node i to the target node D, that is, node N+1 in the second hop is:
[0061]
[0062] Assuming that the transmission distance from the i-th relay node to the target node N+1 is considered to be approximately equal, the total average bit error rate of the two-hop parallel relay UWOC system after EGC merging can be expressed as follows:
[0063]
[0064] Where N is the number of parallel relay nodes, It is expressed as the average received bit error rate from the source node S to the i-th relay node in the first hop, calculated by formula (7); P be2represents the average received bit error rate after EGC merging from each relay node i to the target node N+1 in the second hop, calculated by formula (11).
[0065] Assume that the average received bit error rate from the source node S to the i-th relay node is approximately the same (that is, each link has approximately the same transmission distance and turbulent fading parameters), that is Then the above formula (12) can be summarized into the general form:
[0066]
[0067] The first term on the right side of the above equation Defined as 0 when N=1.
[0068] Example of application of the error performance evaluation method of the parallel relay UWOC system in the numerical simulation of the ocean aggregate fading channel environment:
[0069] Next, we compare the average bit error rate theoretical performance evaluation method of the two-hop parallel relay UWOC system proposed in this invention with the Monte Carlo numerical simulation method under a composite fading channel model that integrates factors such as offshore coastal water quality FFIR hidden path loss and multipath effect, as well as GGD ocean turbulence, to verify the feasibility and effectiveness of the proposed bit error rate performance evaluation method.
[0070] The core simulation parameters are assumed as follows: The coastal water quality is selected, and its absorption and scattering coefficients are (0.179, 0.219) m -1 ; The total distance of the end-to-end link of the two-hop parallel relay UWOC system is Z = 40m; The transceiver is located in the deep sea; Turbulence scintillation index The wavelength of the light source at the transmitting end is 532nm, and the beam waist radius is W r =3mm, half divergence angle Blue-green laser; receiver half divergence angle θ div =40°, receiver aperture radius r a =0.2m; system load resistance R L =100Ω, transmission rate R b =1Gbps.
[0071] Figure 3The theoretical expression of the end-to-end average bit error rate of the two-hop parallel relay UWOC system after EGC merging is given under different numbers of parallel relay nodes N (i.e., formula (13)), and the comparison curve between the theoretical calculation results and the Monte Carlo numerical simulation results with the change of node transmission power. From the simulation results shown in the figure, it can be seen that under the water quality of the near-shore coast, when the total transmission distance is fixed at 40m, as the number of parallel relay nodes N increases, the average bit error rate of the two-hop parallel relay UWOC system will decrease rapidly compared with the traditional end-to-end direct transmission scheme without relay connection; in comparison, the traditional direct transmission scheme is still as high as 10 even when the transmission power reaches 30dBm. -1 Above, the system basically cannot work. On the contrary, after the introduction of parallel relay nodes, the system bit error performance is greatly improved, and as the number of relay nodes N increases, the system bit error performance is better. This shows that the UWOC system using parallel relay auxiliary technology can effectively reduce the impact of adverse factors such as path loss and turbulent fading on signal transmission, thereby increasing the effective communication distance. In addition, it can be seen from the simulation curve results shown in the figure that the proposed two-hop parallel relay UWOC system, which is based on the use of foxH function to approximate the PDF of the equivalent fading coefficient h after merging, and then obtains the numerical calculation results of the theoretical approximate calculation formula of the system average bit error rate, and the average bit error rate accurate value obtained by simulating the system working process using the Monte Carlo method basically has the same change trend and bit error rate performance, and the error between the two is small. All of these show that the theoretical average bit error rate evaluation method of the proposed two-hop parallel relay UWOC system is effective and feasible.
[0072] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.
Claims
1. A two-hop parallel relay underwater wireless optical communication (UWOC) system error performance evaluation scheme, characterized by: The following steps are included Considering the channel environment with complex fading factors such as generalized gamma distribution (GGD) ocean turbulence, fading free impulse response (FFIR) implicit path loss and multipath effect, a two-hop parallel relay UWOC system with equal gain combining (EGC) technology at the receiving end is considered. Firstly, the theoretical expression of the bit error rate from the first hop source node S to each relay node i, 1≤i≤N (N is the number of relay nodes) in the two-hop parallel relay UWOC system is derived respectively. And the theoretical closed-form expression P of the bit error rate from the second-hop relay node i to the target node D after EGC combined reception be2 ; Then, according to the bit error rates at the above two locations and the number of relay nodes N, the theoretical closed-form expression of the end-to-end (e2e) average bit error rate of the final two-hop parallel relay UWOC system is obtained:
2. According to claim 1, a two-hop parallel relay UWOC system error performance evaluation scheme is characterized in that: For the case where the transmission distance from relay node i to target node D, i.e., node N+1, is approximately equal, the theoretical calculation formula for the end-to-end (e2e) average bit error rate of the two-hop parallel relay UWOC system changes with the number of relay nodes N is: It can be expressed as In the above formula, N is the number of parallel relay nodes, represents the average received bit error rate from the source node S to the i-th relay node in the first hop, P be2 It represents the average received bit error rate after EGC combination from each relay node i to the target node D, i.e., node N+1 in the second hop.
3. A two-hop parallel relay UWOC system error performance evaluation scheme according to claim 2, characterized in that: The average received bit error rate from the source node S to the i-th relay node The calculation formula is as follows: In the above formula, a i and c i represents the shape parameter of the GGD fading distribution experienced by the source node S to the i-th relay node, b i is the scale parameter. represents the gamma function, Indicates the advanced transcendental foxH function. in is the matched filtering received signal of the detection current waveform signal required on the corresponding path, that is, the path from the source node S to the i-th relay node, R is the responsivity of the photodetector R = ηq / hf, η, q, h, f are the photodetector quantum efficiency, electron charge, Planck constant and light frequency in water respectively; the integrand It represents the pulse shaping signal P(t) passing through the FFIR channel The received signal waveform after P(t) indicates the amplitude value is 2P b The gate function signal has a value range of [0, T b ], T b is the symbol width, P b is the average power of the source transmitted symbols, is the FFIR from the source node S to the i-th relay node, * represents the convolution operation; is the standard deviation of the Gaussian integrated noise component.
4. According to claim 2, a two-hop parallel relay UWOC system error performance evaluation scheme is characterized in that: The average received bit error rate P after EGC combination from the relay node i to the target node D be2 The calculation formula is as follows: In the formula, Φ=μ1 2 / (μ2-μ1 2 ), ψ=μ1 / (μ2-μ1 2 ), where μ1 and μ2 are the first-order and second-order origin moments of the equivalent fading coefficient h, respectively. The variables in this formula Here a i , c i and b i They represent the shape parameter and scale parameter of the GGD fading distribution experienced by the i-th relay node to the target node D. Without loss of generality, they are similar to the GGD turbulent fading distribution parameter a between the source node S and the relay node i. i , c i and b i are exactly the same; the equivalent fading coefficient h satisfies in represents the GGD turbulence attenuation coefficient experienced by the link from the source node S to the i-th relay node in the first hop, or from the i-th relay node to the target node D in the second hop, GG(·) represents Subject to parameter a i , b i , c i GGD distribution; is the matched filtering signal of the detection current waveform signal required for the link between the i-th parallel relay node and the target node D, i.e., node N+1, represents the received signal waveform after the pulse shaping function P(t) passes through the corresponding link FFIR, where It is the FFIR from relay node i to target node N+1; function d n (x, y) = Γ(x+n / y) / Γ(x).
5. According to claim 2, a two-hop parallel relay UWOC system error performance evaluation scheme is characterized in that: The end-to-end (e2e) average bit error rate calculation formula of the two-hop parallel relay UWOC system assumes that the average receiving bit error rates from the source node S to the i-th relay node are approximately equal, that is, Under the condition, it can be further simplified into the general formula: The first term on the right side of the above equation Defined as 0 when N=1.
6. A two-hop parallel relay UWOC system error performance evaluation scheme according to claim 1, characterized in that: The foxH function description form of the GGD ocean turbulence fading probability density function (Probability Density Function, PDF) is as follows: Where b i is the scale parameter, a i and c i is the shape parameter, represents a random variable that follows a GGD distribution.
7. A two-hop parallel relay UWOC system error performance evaluation scheme according to claim 1, characterized in that: The non-fading channel impulse response FFIR data can be obtained by simulating the motion of photons using a computer Monte Carlo method under given system transceiver parameters, such as ocean water quality, transmission distance, receiver aperture, wavelength of the transmitting light source, etc.