Broadband RF signal receiving system with low carrier-to-signal ratio based on KK processing

Abstract

The invention provides a broadband RF signal receiving system with a low carrier-to-signal ratio based on KK processing. According to the system, a traditional KK algorithm is improved to meet the requirement for a lower carrier power ratio, and core devices comprise a laser, a polarization controller, a dual-drive Mach-Zehnder modulator, an optical amplifier, a photoelectric detector and the like. Firstly, continuous optical carriers output by a laser are adjusted through a polarization controller, then are injected into a dual-drive Mach-Zehnder modulator and are modulated by radio frequency signals. And the modulated optical signal is finally detected by a photoelectric detector, data sampling is carried out on the output signal, and data extraction is carried out from the sampled data by using a digital filter in a digital signal processing module. And finally, estimating and reconstructing the SSBI interference based on the improved KK algorithm, then completing elimination of the SSBI interference in the signal, and realizing relatively low CSPR. According to the invention, the system performance is improved, the architecture is simplified, the adaptability and expansibility are enhanced, and an efficient solution is provided for the next generation of optical communication and a mobile forward transmission system.

Description

Technical Field

[0001] The present invention relates to the field of optical communication and microwave photon, and in particular to a broadband RF signal receiving system with a low carrier signal ratio based on KK processing. Background Art

[0002] With the continuous expansion of data center scale and the diversification of application requirements, the demand for interconnection bandwidth has shown explosive growth, and the demand for low-latency, high-performance communications has become more urgent. In this context, optical communication technology has become the core support for data center interconnection due to its advantages of high speed and large capacity. Among them, direct detection (DD) systems occupy an important position in optical communication systems due to their simple implementation, low power consumption and low cost. However, DD systems still face some key technical challenges, among which signal-signal beat interference (SSBI) has become the main bottleneck limiting the improvement of system performance. SSBI not only causes signal distortion, but also significantly reduces the system's receiving sensitivity and bit error performance. Efficient interference suppression technology is urgently needed to overcome this obstacle.

[0003] Although a variety of SSBI elimination algorithms have been proposed, they still have significant limitations in practical applications. Although the first-order SSBI elimination algorithm has low computational complexity, its compensation gain is limited, the error performance is difficult to further improve, and the robustness is poor. The second-order SSBI elimination algorithm has improved the receiving performance, but it is easy to have residual SSBI interference, and is sensitive to the carrier power ratio (CSPR), and requires a complex joint optimization process. Although the selected linear filter algorithm provides a higher compensation gain, the significant increase in computational complexity and system delay, as well as the increase in power consumption, limit its large-scale promotion and application. The SSBI estimation and elimination algorithm can almost completely eliminate SSBI, but the sensitivity to the optical signal-to-noise ratio (OSNR) and high computational complexity are still the main problems. In addition, the traditional KK receiver can theoretically completely eliminate SSBI and provide the best performance, but its high implementation cost and additional bandwidth requirements, and the need to meet the minimum phase signal conditions, which requires a large carrier power ratio, are limited in practice.

[0004] In response to the above problems, this study proposed a broadband RF signal receiving system with low carrier signal ratio based on KK processing. By introducing an optimized signal reconstruction algorithm and an improved digital signal processing (DSP) module, the scheme can accurately estimate and effectively eliminate SSBI in the received signal, while significantly reducing the demand for high CSPR. While ensuring system performance, the improved KK receiver design also successfully improved the system's receiving sensitivity and anti-interference ability, and significantly reduced complexity and cost. This scheme not only provides a performance optimization path for existing optical communication systems, but also lays a solid technical foundation for building efficient and low-cost optical communication networks in the future. Summary of the invention

[0005] In order to meet the conditions of the minimum phase signal, the traditional KK receiver usually needs to rely on a higher CSPR, that is, the carrier power is much higher than the signal power. Although high CSPR can effectively suppress SSBI, it also causes a series of problems. First, high CSPR increases the power demand of the transmitter and aggravates the nonlinear effects in the microwave photonic link, significantly limiting the transmission performance of the system. Secondly, with the increase in power demand, the power consumption and equipment cost of the system also increase, which is particularly unacceptable in large-scale communication systems. On the other hand, although the traditional SSBI attenuation algorithm has weakened the interference to a certain extent, it still has obvious shortcomings. First, the algorithm is highly dependent on higher CSPR, and the accuracy of interference estimation will be significantly reduced under low CSPR conditions. Second, due to the limitations of interference estimation and iterative calculation, residual SSBI is difficult to completely remove, resulting in affected signal quality. Third, the iterative algorithm has high complexity and large delay, which limits its practical application in high-speed optical communication systems. In response to the above problems, the present invention proposes a broadband RF signal receiving system with a low carrier signal ratio based on KK processing. By reconstructing and reducing SSBI in the DSP module, the interference component is first greatly reduced, thereby indirectly improving the CSPR value of the reduced signal. Then, the processed signal is subjected to KK transformation to achieve efficient signal reconstruction under low CSPR conditions.

[0006] In order to achieve the above-mentioned purpose, the present invention establishes a communication link based on a dual-driven Mach-Zehnder modulator, and the devices in the link include a laser source, an arbitrary waveform generator, a dual-driven Mach-Zehnder modulator, a polarization modulator, an optical amplifier, a photodetector, an analog-to-digital conversion module and a digital signal processing module.

[0007] The process of a broadband RF signal receiving system solution with a low carrier signal ratio based on KK processing described in the present invention is as follows:

[0008] Step 1: The continuous optical carrier output by the laser is adjusted by a polarization controller and then input into a dual-drive Mach-Zehnder modulator;

[0009] Step 2: The optical carrier in the modulator is modulated by the input radio frequency (RF) signal;

[0010] Assume that the light field of the carrier is represented by E in (t) = E in exp(jω0t), V π is the half-wave voltage of DDMZM, then the output light field of the upper and lower arms is:

[0011]

[0012] Among them, V DC1is the upper arm bias voltage, V DC2 is the lower arm bias voltage, and the output of the DDMZM after the combination of the two is:

[0013]

[0014] After expanding with Bessel function and retaining the positive and negative first order:

[0015]

[0016] in is the phase shift deviation introduced by the bias voltage of the two arms, β1=jπV DC1 / V π is the modulation index of the upper arm, β2=jπV DC2 / V π is the modulation index of the lower arm. From formula (3), we can see that the optical carrier can be controlled by To attenuate to a certain extent, so as to suppress the optical carrier. The output optical carrier is:

[0017] E in (t)′=E in (t)|J0(β1)-J0(β2)| (4)

[0018] Based on the above theory, the RF signal and LO signal are input into the DDMZM respectively, and the carrier suppressed double-side modulation (CS-DSB) is realized by controlling the bias voltage between the two arms of the DDMZM. ​​Since the optical carrier is suppressed, it can be ignored, and finally the corresponding positive and negative first-order sideband signals are generated respectively:

[0019]

[0020] Step 3: After the modulated optical signal is transmitted, the photodetector receives the signal completely and converts it into an electrical signal in the analog-to-digital conversion module. The expression is:

[0021]

[0022] Where |E LO | 2 is the DC term generated by the self-frequency of the local oscillator carrier, |E s (t) 2 is the signal self-frequency crosstalk SSBI, the third term 2Re{E LO ·E s (t)·exp[j(ω RF -ω LO )]} is the photon down-conversion received signal. Starting from the second row, they are all high-frequency items generated, which can be filtered out by low-speed PD. Therefore, formula (6) can be rewritten as:

[0023]

[0024] Step 4: sampling the converted signal, and processing the sampled data through a digital bandpass filter to extract corresponding information;

[0025] Step 5: Implement effective suppression of SSBI interference in DSP and meet the requirements of reducing CSPR. The specific steps include: Figure 3 As shown in the DSP flow chart, the signal is divided into two branches, upper and lower, after passing through the first node. After the signal is processed by the DSP of the upper branch, the expression is updated to:

[0026]

[0027] Where L(·) is a digital low-pass filter, A=|E LO |, η is the reduction factor. After the signal passes through the second node, its expression is:

[0028]

[0029] in α=1-η, B is a constant used to adjust the DC component of the signal, 2ηRe[E s (t)*e(t)] and η|e(t) 2 is the interference term generated by the secondary beat frequency, and its power is very small and can be ignored. It can be seen from the above formula that after the signal is processed by the first layer of DSP, the SSBI interference of the signal is attenuated to α|E s (t) 2 , then we can adjust the constant B to Afterwards, the signal expression is updated to:

[0030]

[0031] According to formula (4), we can derive the CSPP expression of the signal at this time as:

[0032]

[0033] From formula (11), we can see that the CSPR is reduced by 1 / α. Generally speaking, when α is less than 1 and close to 0, the CSPR of the original signal will be amplified. Removing most of the SSBI is equivalent to reconstructing a low CSPR signal to form a high CSPR signal. Finally, the signal is processed by KK to achieve down-conversion reception. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1A flowchart of a broadband RF signal receiving system with a low carrier signal ratio based on KK processing according to the present invention;

[0035] Figure 2 A schematic diagram of an optical link of a broadband RF signal receiving system with a low carrier signal ratio based on KK processing proposed by the present invention;

[0036] Figure 3 To improve the KK algorithm flow chart; DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings:

[0038] Figure 1 This is a flow chart of a broadband RF signal receiving system with a low carrier signal ratio based on KK processing according to the present invention, which specifically includes the following steps:

[0039] Step 1: Figure 2 As shown, the continuous optical carrier output by the laser is adjusted by the polarization controller and then input into the dual-drive Mach-Zehnder modulator;

[0040] Step 2: The optical carrier in the modulator is modulated by the input RF signal;

[0041] Assume that the light field of the carrier is represented by E in (t) = E in exp(jω0t), V π is the half-wave voltage of DDMZM, then the output light field of the upper and lower arms is:

[0042]

[0043] Among them, V DC1 is the upper arm bias voltage, V DC2 is the lower arm bias voltage, and the output of the DDMZM after the combination of the two is:

[0044]

[0045] Expand the above formula using Bessel function and retain the positive and negative first order:

[0046]

[0047] in is the phase shift deviation introduced by the bias voltage of the two arms, β1=jπV DC1 / V π is the modulation index of the upper arm, β2=jπV DC2 / V π is the modulation index of the lower arm. From formula (3), we can see that the optical carrier can be controlled by To attenuate to a certain extent, so as to suppress the optical carrier. The output optical carrier is:

[0048] E in (t)′=E in (t)|J0(β1)-J0(β2)| (15)

[0049] Based on the above theory, the RF signal and LO signal are input into the DDMZM respectively, and the carrier suppressed double-side modulation (CS-DSB) is realized by controlling the bias voltage between the two arms of the DDMZM. ​​Since the optical carrier is suppressed, it can be ignored, and finally the corresponding positive and negative first-order sideband signals are generated respectively:

[0050]

[0051] Step 3: After the modulated optical signal is transmitted, the photodetector receives the signal completely and converts it into an electrical signal in the analog-to-digital conversion module. The expression is:

[0052]

[0053] Where |E LO | 2 is the DC term generated by the self-frequency of the local oscillator carrier, |E s (t) 2 is the signal self-frequency crosstalk SSBI, the third term 2Re{E LO ·E s (t)·exp[j(ω RF -ω LO )]} is the photon down-conversion received signal. Starting from the second row, they are all high-frequency items generated, which can be filtered out by low-speed PD. Therefore, formula (6) can be rewritten as:

[0054]

[0055] Step 4: sampling the converted signal, and processing the sampled data through a digital bandpass filter to extract corresponding information;

[0056] Step 5: DSP process Figure 3 As shown, the signal is split into two branches, upper and lower, after passing through the first node. After the signal is processed by the DSP of the upper branch, the expression is updated to:

[0057]

[0058] Where L(·) is a digital low-pass filter, A=|E LO |, η is the reduction factor. After the signal passes through the second node, its expression is:

[0059]

[0060] in α=1-η, B is a constant used to adjust the DC component of the signal, 2ηRe[E s (t)*e(t)] and η|e(t) 2 is the interference term generated by the secondary beat frequency, and its power is very small and can be ignored. It can be seen from the above formula that after the signal is processed by the first layer of DSP, the SSBI interference of the signal is attenuated to α|E s (t) 2 , then we can adjust the constant B to Afterwards, the signal expression is updated to:

[0061]

[0062] According to formula (4), we can derive the CSPP expression of the signal at this time as:

[0063]

[0064] From formula (11), we can see that the CSPR is reduced by 1 / α. Generally speaking, when α is less than 1 and close to 0, the CSPR of the original signal will be amplified. Removing most of the SSBI is equivalent to reconstructing a low CSPR signal to form a high CSPR signal. Finally, the signal is processed by KK to achieve down-conversion reception.

[0065] In summary, this study proposes a low carrier signal ratio broadband RF signal receiving system based on KK processing to address the limitations of traditional SSBI elimination algorithms in terms of complexity, cost, and performance. By optimizing the signal reconstruction algorithm and digital signal processing module, this solution significantly reduces the CSPR requirement while effectively eliminating SSBI interference and improving the system's receiving sensitivity and anti-interference ability.

Claims

1. A broadband RF signal receiving system with low carrier signal ratio based on KK processing, characterized in that: The following steps are involved: Step 1: The continuous optical carrier signal emitted by the laser is adjusted by the polarization controller and then injected into the dual-drive Mach-Zehnder modulator; Step 2: The optical carrier is modulated with the input radio frequency signal in the modulator to complete the modulation process of the optical signal; Step 3: The modulated optical signal is received by a photodetector and converted into an electrical signal by an analog-to-digital conversion module; Step 4: sampling the converted electrical signal, and extracting distortion information from the sampled signal through a digital bandpass filter; Step 5: Optimize the system design in the digital signal processor (DSP), reduce the carrier-to-carrier power ratio (CSPR) requirement, achieve effective suppression of SSBI interference, and ensure the stability and efficient operation of the system.

2. According to claim 1, a broadband RF signal receiving system solution with low carrier signal ratio based on KK processing is characterized in that: In step five, the DSP module is designed as a two-way signal processing architecture. The lower branch signal remains in its original state without additional processing, while the upper branch signal estimates and reconstructs the self-beating frequency interference (SSBI) in the signal. Subsequently, the two signals are delayed and compensated, and the first step of DSP processing is completed by subtracting the SSBI interference reconstructed by the upper branch from the lower branch signal to remove some interference items. Finally, by superimposing a DC signal of sufficient strength, it is ensured that the minimum phase condition of KK processing is met, and the phase information of the signal is restored by the KK algorithm.

3. According to the scheme of a broadband RF signal receiving system with low carrier signal ratio based on KK processing as described in claim 2, it is characterized in that: The transmitted RF signal is loaded into the optical signal through a dual-drive Mach-Zehnder modulator (DDMZM), and then the power is compensated by EDFA. Finally, the optical signal is processed by a low-speed PD, and the obtained signal expression is: Where |E LO | 2 is the DC term generated by the self-frequency of the local oscillator carrier, |E s (t) 2 is the signal self-frequency crosstalk SSBI, the third term 2Re{E LO ·E s (t)·exp[j(ω RF -ω LO )]} is the photon down-conversion received signal. Starting from the second row, they are all high-frequency items generated, which can be filtered out by low-speed PD. Therefore, formula (1) can be rewritten as: Where L(·) is a digital low-pass filter, A=|E LO |, η is the reduction factor. After the signal passes through the second node, its expression is: in α=1-η, B is a constant used to adjust the DC component of the signal, 2ηRe[E s (t)*e(t)] and η|e(t) 2 is the interference term generated by the secondary beat frequency, and its power is very small and can be ignored. It can be seen from the above formula that after the signal is processed by the first layer of DSP, the SSBI interference of the signal is attenuated to αE s (t) 2 , then we can adjust the constant B to Afterwards, the signal expression is updated to: According to formula (5), we can derive the CSPP expression of the signal at this time as: From formula (6), we can see that the CSPR is reduced by 1 / α. Generally speaking, when α is less than 1 and close to 0, the CSPR of the original signal will be amplified. Removing most of the SSBI is equivalent to reconstructing a low CSPR signal to form a high CSPR signal. Finally, the signal is processed by KK to achieve down-conversion reception.

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