System and method for satellite communications using hybrid optical and millimeter wave transceivers

Abstract

A system for satellite communications includes a decision logic module, a payload integrated circuit, an optical transceiver, an optical array, a millimeter wave transceiver, and an antenna array. The decision logic module evaluates channel conditions and selects one of four transmission modes based on a signal quality metric. The payload integrated circuit generates outbound baseband data and receives demodulated data. The optical transceiver is coupled to the decision logic module and transmits and receives optical signals over a free space link using a first or second modulation format. The optical array is responsible for optical signal transmission and reception. The millimeter wave transceiver is coupled to the decision logic module and transmits and receives millimeter wave signals over a free space millimeter wave link using a third or fourth modulation format. The antenna array supports millimeter wave transmission and reception. The first modulation format requires a higher signal-to-noise ratio and provides a higher spectral efficiency than the second modulation format, and the third modulation format requires a higher signal-to-noise ratio and provides a higher data rate than the fourth modulation format.

Description

Technical Field

[0001] This invention relates generally to satellite communications; more specifically, it relates to a system and method for satellite communications scenarios, using a hybrid optical and millimeter-wave (mmWave) transceiver. Background Technology

[0002] Satellite communications play a vital role in the world today, enabling high-speed, low-latency global connectivity and data exchange without the need for physical fiber optic or cable links. Satellite communications are crucial for telecommunications, broadcasting, military operations, weather forecasting, and GPS. Through satellites, real-time communications can be provided to remote areas, filling gaps in digital transmission and offering services such as emergency communications and internet access.

[0003] Figure 1 An exemplary scenario diagram of a hybrid optical and millimeter-wave (mmWave) network architecture for satellite communication data transmission is shown. Satellite communication includes transmission paths between satellites and communication paths between satellites and ground stations. Traditional satellite communication relies on radio frequency wireless communication methods, including millimeter-wave links. However, these technologies face various challenges. First, millimeter-wave communication transmits in an omnidirectional manner, resulting in low overall power efficiency of the communication system. Second, due to narrowband operation and limited signal-to-noise ratio, even with advanced modulation schemes such as 16-QAM or 64-QAM, the data rate of millimeter-wave links is typically kept below 10 Gbps per user. To enable simultaneous communication by multiple users, a phased array architecture is required to provide spatial multiplexing functionality. However, the significant sidelobe effect severely limits the total number of concurrent beams, thus limiting communication capacity. Nevertheless, millimeter-wave technology does have certain advantages. Compared to traditional low-frequency radio frequency links below 6 GHz, it can provide relatively higher data rates. In addition, it can ensure stable data transmission quality during inter-satellite communication in the space atmosphere and withstand the severe weather conditions that may occur when communicating between satellites and ground stations.

[0004] Compared to millimeter-wave links, optical wireless links, using highly collimated lasers, can transmit signals in free space. Furthermore, optical wireless links offer two significant advantages over millimeter-wave links. First, in broadband mode, the operating bandwidth can reach 20 GHz or even higher. Combined with coherent modulation, optical wireless links can achieve rates up to tens of Gbps; for example, using 16-QAM coherent modulation at a 10 GHz bandwidth can achieve a rate of 80 Gbps. Second, due to the high directionality of the collimated laser, optical signals can be transmitted over long distances with significantly reduced loss compared to the omnidirectional transmission of millimeter-wave signals. However, optical wireless links are susceptible to atmospheric scattering and adverse weather conditions, which can drastically affect the optical signal strength or even completely block link transmission.

[0005] Therefore, a hybrid optical and millimeter-wave transceiver system that can dynamically adapt to different atmospheric conditions is also needed to maintain high-speed and reliable satellite communication transmission. Summary of the Invention

[0006] The purpose of this invention is to provide a system and method to address the aforementioned deficiencies and unmet needs in the prior art.

[0007] This invention provides a novel physical layer transceiver implementation scheme aimed at achieving high-speed and reliable satellite communication. This paper focuses on the architecture, operating principle, and implementation details of a hybrid millimeter-wave / optical wireless communication transceiver for satellite-to-satellite and satellite-to-ground station communication. The hybrid transceiver employs decision logic to adaptively activate either optical wireless or millimeter-wave links by evaluating communication channel conditions. Furthermore, the modulation format can be dynamically optimized to ensure sufficient signal-to-noise ratio and reliable communication quality. The solution provided by this invention includes an energy-efficient millimeter-wave phased array transceiver supporting simultaneous multi-beam functionality, and an optical wireless transceiver with an adaptive modulation scheme. Compared to conventional methods, the solution provided by this invention offers higher data rates, enhanced reliability, and higher power consumption and area efficiency.

[0008] According to a first aspect of the invention, a system for satellite communication is proposed, which uses a hybrid optical and millimeter-wave transceiver. The system includes a decision logic module, a payload integrated circuit, an optical transceiver, an optical array, a millimeter-wave transceiver, and an antenna array. The decision logic module is used to evaluate channel conditions and select a transmission mode based on the evaluated channel conditions. The payload integrated circuit is used to generate outgoing baseband data signals and receive demodulated data signals. The optical transceiver is coupled to the decision logic module and the payload integrated circuit and is used to transmit and receive optical signals via a free-space optical wireless link using a first modulation format or a second modulation format. The optical array is optically coupled to the optical transceiver and is used for optical signal transmission and reception. The millimeter-wave transceiver is coupled to the decision logic module and the payload integrated circuit and is used to transmit and receive millimeter-wave signals via a free-space millimeter-wave link using a third modulation format or a fourth modulation format. The antenna array is coupled to the millimeter-wave transceiver and configured for millimeter-wave signal transmission and reception. The decision logic module is also configured to determine channel conditions based on signal quality metrics and select one of four transmission modes: optical transmission using a first modulation format, optical transmission using a second modulation format, millimeter-wave transmission using a third modulation format, and millimeter-wave transmission using a fourth modulation format. The first modulation format requires a higher signal-to-noise ratio and provides higher spectral efficiency than the second modulation format, while the third modulation format requires a higher signal-to-noise ratio and provides a higher data rate than the fourth modulation format.

[0009] According to a second aspect of the invention, a method for satellite communication is provided, which uses a hybrid optical and millimeter-wave transceiver. The method includes the following steps: evaluating channel conditions based on signal quality indicators by a decision logic module; selecting one of four transmission modes based on the evaluated channel conditions, including: (a) optical transmission using a first modulation format, (b) optical transmission using a second modulation format, (c) millimeter-wave transmission using a third modulation format, or (d) millimeter-wave transmission using a fourth modulation format; generating an outgoing baseband data signal via a payload integrated circuit and receiving the demodulated data signal; transmitting and receiving optical signals on a free-space optical wireless link using the first or second modulation format via an optical transceiver optically coupled to an optical array; and transmitting and receiving millimeter-wave signals on a free-space millimeter-wave link using the third or fourth modulation format via a millimeter-wave transceiver coupled to an antenna array. The first modulation format requires a higher signal-to-noise ratio and provides higher spectral efficiency than the second modulation format, and the third modulation format requires a higher signal-to-noise ratio and provides a higher data rate than the fourth modulation format.

[0010] Through the above configuration, the technical solution proposed in this invention can achieve the following contributions:

[0011] 1) A transceiver architecture is proposed that enables adaptive switching between optical wireless and millimeter-wave communication under various atmospheric conditions;

[0012] 2) A method is proposed that can select the appropriate communication mode and modulation format based on four different channel scenarios;

[0013] 3) A coherent optical wireless transceiver design is proposed, which supports adaptive switching between modulation formats (especially 16-QAM and PAM-4); and

[0014] 4) A transmitter architecture for a sliding-intermediate frequency (sliding-IF) phased array is proposed, which can use a transadmittance-transimpedance variable gain amplifier to achieve efficient multi-beam synthesis at the intermediate frequency. Attached Figure Description

[0015] The embodiments of the present invention will now be described in more detail with reference to the accompanying drawings, wherein:

[0016] Figure 1 An exemplary scenario diagram of a hybrid optical and millimeter-wave (mmWave) network architecture for satellite communication data transmission is shown;

[0017] Figure 2 A schematic diagram of a satellite communication system using a hybrid optical and millimeter-wave transceiver according to an embodiment of the present invention is shown;

[0018] Figure 3A and Figure 3B The working principle diagram of the hybrid optical / millimeter-wave transceiver is shown, and it is shown how the system according to an embodiment of the present invention can dynamically select the communication link and modulation format based on changing channel conditions;

[0019] Figure 4 A system diagram of an optical wireless transceiver for free-space communication according to an embodiment of the present invention is shown;

[0020] Figure 5A A diagram of a traditional millimeter-wave phased array transmitter architecture is shown.

[0021] Figure 5B An improved millimeter-wave transmitter architecture based on a sliding intermediate frequency design, according to an embodiment of the present invention, is illustrated; and

[0022] Figure 6 A schematic diagram of a satellite communication system using hybrid optics and millimeter-wave transceivers according to an embodiment of the present invention is shown. Detailed Implementation

[0023] In the following description, preferred examples will be used to illustrate systems and methods for satellite communication using hybrid optical and millimeter-wave (mmWave) transceivers. Those skilled in the art will understand that various modifications, including additions and / or substitutions, can be made without departing from the scope and spirit of the invention. Specific details may be omitted to avoid obscuring the invention; however, this disclosure is intended to enable those skilled in the art to practice the teachings herein without extensive experimentation.

[0024] This invention proposes a novel satellite communication method utilizing a hybrid millimeter-wave / optical wireless communication link, thereby achieving high-speed, high-capacity, and reliable satellite communication. One of the key features of this invention is a hybrid millimeter-wave / optical transceiver integrated circuit (IC), which consists of a phased-array millimeter-wave transceiver supporting simultaneous multi-beam functionality, an optical wireless transceiver supporting adaptive switching between orthogonal and pulse amplitude modulation, and decision logic for switching between the millimeter-wave and optical transceivers under different communication channel conditions.

[0025] Specifically, Figure 2 A schematic diagram of a satellite communication system 100 using a hybrid optical and millimeter-wave transceiver according to an embodiment of the present invention is shown. System 100 can be implemented within a satellite or ground station terminal (i.e., terminal 1) and configured to communicate with a remote terminal (i.e., with terminal 2) via free-space propagation using either an optical wireless link or a millimeter-wave link. The selection between the two transmission modes is dynamically determined based on the prevailing atmospheric or environmental channel conditions. The optical wireless link operates by guiding a highly collimated laser beam through free space, thereby enabling high-capacity line-of-sight communication in unobstructed conditions. In contrast, the millimeter-wave link transmits radio frequency signals through the atmosphere, providing more reliable performance in adverse weather or partially obstructed line-of-sight conditions.

[0026] System 100 includes a decision logic module 110, a payload integrated circuit (IC) 112, an optical transceiver 120, an optical array 122, a millimeter-wave transceiver 130, and an antenna array 132. These components are integrated together to form a dynamic adaptive transceiver system for hybrid space-to-ground or inter-satellite communications.

[0027] Decision logic module 110 monitors the channel status of the optical and millimeter-wave links. When system 100 starts up or wakes from sleep mode, decision logic module 110 estimates the availability of the optical wireless channel and enables optical transceiver 120 or millimeter-wave transceiver 130 accordingly. Decision logic module 110 also evaluates the quality of the received signal to determine a suitable modulation format and selects between formats such as 16-QAM, PAM-4, or QPSK based on link quality. Under favorable conditions, the optical link is preferred due to its higher bandwidth, while the millimeter-wave link serves as a backup in adverse weather or signal congestion environments. In some embodiments, decision logic module 110 determines channel conditions based on signal quality metrics and then selects one of four different transmission modes (e.g., one of four different modulation formats). In this regard, signal quality metrics include at least one of the following factors: signal-to-noise ratio (SNR), bit error rate (BER), received signal strength, or channel response waveform.

[0028] Payload IC 112 generates outbound digital data streams, such as telemetry data, control commands, or mission-based payload data, to be transmitted to an external or remote terminal (e.g., terminal 2), and receives demodulated data from an optical transceiver or millimeter-wave transceiver module within terminal 1. The generated data stream can be routed via optical or millimeter-wave communication paths according to the selected link determined by decision logic module 110. Payload IC 112 interfaces with millimeter-wave and optical communication paths by providing baseband signals and receive decoding outputs. Payload IC 112 can also exchange intermediate signals with decision logic module 110, such as millimeter-wave RX signals and ORX signals (optical receive signals), which are used to assist in channel quality assessment and modulation selection.

[0029] Optical transceiver 120 converts electrical signals from payload IC 112 into optical signals via laser modulation and performs the reverse process at the receiving end. Optical transceiver 120 interfaces directly with optical array 122 for transmitting and receiving physical layer signals. The optical transceiver supports coherent modulation schemes, including 16-QAM and PAM-4, and its modulation format can be adjusted according to the signal-to-noise ratio (SNR) and channel availability under the control of decision logic module 110.

[0030] Optical array 122 includes an array of laser diodes (LDs) for transmitting optical signals and an array of photodiodes (PDs) for receiving optical signals. At the transmitting end, the modulated optical signal from optical transceiver 120 is amplified by an erbium-doped fiber amplifier (EDFA) and collimated using a lens to form a narrow directional beam for free-space transmission. At the receiving end, the incident optical signal is first collimated by a lens, then amplified by another erbium-doped fiber amplifier (EDFA), and then converted into an electrical signal by the photodiode array (PD). With erbium-doped fiber amplifiers and lenses used at both ends, long-distance, low-loss optical transmission can be achieved.

[0031] The millimeter-wave transceiver 130 is used to transmit and receive millimeter-wave signals via a phased array architecture and interfaces with the antenna array 132. The millimeter-wave transceiver 130 receives input data from the payload IC 112 and transmits beamforming signals to the antenna array 132 for free-space propagation. The phased array architecture can generate multiple beams simultaneously, thereby enabling spatial multiplexing to support multi-user communication. Power efficiency and modulation efficiency can be further optimized through intermediate-frequency (IF) signal processing.

[0032] Antenna array 132 radiates beamformed millimeter-wave signals into free space and receives them from a remote terminal (e.g., terminal 2). In inter-satellite links, due to stable atmospheric conditions, system 100 primarily employs an optical wireless path. For satellite-to-ground communication, system 100 dynamically switches between optical and millimeter-wave paths based on real-time weather conditions and signal quality to maintain a reliable and high-throughput connection.

[0033] Specifically, in inter-satellite communication scenarios, since free-space conditions in outer space are generally good and unobstructed, optical wireless links can be prioritized to achieve high data rates and large transmission capacity. For satellite-to-ground communication, atmospheric changes become a critical factor, and the system employs a hybrid strategy. In clear weather, optical links can be used to maximize throughput, while in adverse conditions such as cloud cover or precipitation, although data rates may be slightly sacrificed, the system switches to millimeter-wave paths to maintain link continuity.

[0034] Figure 3A and Figure 3B A schematic diagram illustrating the working principle of a hybrid optical / millimeter-wave transceiver is presented, demonstrating how the system, according to an embodiment of the invention, dynamically selects the communication link and modulation format based on changing channel conditions. To clearly demonstrate the behavior patterns under different free-space and atmospheric environments, Figure 3A and Figure 3BThe potential scenarios are categorized into four representative cases, ranging from the most ideal to severely degraded scenarios. Each case highlights the corresponding link selection and modulation strategies employed by the decision-making logic to maintain optimal communication performance.

[0035] In the diagram, "Terminal 1" refers to Figure 2 The system 100 shown can be implemented in a satellite or ground station. Terminal 1 includes an optical transceiver (optical TRX) and a millimeter-wave transceiver (millimeter-wave TRX), as well as support logic for link selection and modulation control. In some embodiments, the optical TRX is configured to convert electrical signals into optical signals for free-space transmission and vice versa (optical signals converted into electrical signals). This configuration may include components such as laser diodes, photodiodes, EDFA amplifiers, and lenses. The optical TRX supports modulation schemes such as 16-QAM and PAM-4, which can be selected based on channel conditions. In some embodiments, the millimeter-wave TRX employs a phased array architecture for beamforming and supports modulation schemes such as 16-QAM and QPSK. The millimeter-wave TRX provides a more reliable alternative when the optical link performance is degraded due to atmospheric interference. Terminal 2 is a remote endpoint, which can be another satellite, a ground station, or an external communication unit. Terminal 2 can use the same transceiver architecture as Terminal 1 or a compatible system, such as an optical ground receiver or a millimeter-wave tracking array.

[0036] Typically, there are four possible channel conditions, and the decision logic module 110 can provide the optimal channel selection based on these conditions.

[0037] like Figure 3A As shown, in Case 1, when channel conditions are favorable—that is, when neither the optical wireless link nor the millimeter-wave link is hindered by atmospheric interference (e.g., inter-satellite or satellite-to-ground communication under good weather conditions)—system 100 can operate in a high-throughput mode. In this case, decision logic module 110 evaluates the channel status and instructs the transceiver system to primarily utilize optical transceiver 120 and optical array 122 for data transmission. Because the optical link has a wide bandwidth and strong directivity in free space, it can support significantly higher data rates. Although millimeter-wave transceiver 130 and antenna array 132 remain enabled, system 100 still prioritizes communication for the optical link. With a good signal-to-noise ratio, decision logic module 110 selects an advanced modulation format (e.g., 16-QAM or higher) to maximize spectral efficiency and throughput.

[0038] like Figure 3AAs shown, in case 2, although the optical wireless link remains available, the received optical power decreases due to the extended communication distance or sparse atmospheric scattering, resulting in a lower signal-to-noise ratio (SNR) at the receiver. Under these conditions, the decision logic module 110 can determine that the existing signal SNR level cannot support the normal transmission of high-order modulation formats such as 16-QAM. Therefore, while system 100 continues to rely on optical transceiver 120 and optical array 122 as the primary communication path, decision logic module 110 instructs the transceiver to downgrade the modulation format to a lower-order modulation format, such as PAM-4 (the hardware implementation of modulation format switching will be discussed later). This downgrading switching scheme based on modulation requirements allows system 100 to maintain long-distance optical communication at medium to high data rates. During this operation, millimeter-wave transceiver 130 and antenna array 132 remain active and available, providing redundant or additional data paths as needed.

[0039] like Figure 3B As shown, in scenario 3, the optical wireless link becomes completely unavailable due to atmospheric obstruction (e.g., thick clouds or severe weather), resulting in a blocked line-of-sight path. In response, the decision logic module 110 can instruct the system 100 to disable the optical transceiver 120 and its associated optical array 122, and switch the communication window to the secondary option, the millimeter-wave transceiver 130 and antenna array 132. Under these adverse conditions, the millimeter-wave link offers higher reliability and still supports 16-QAM or higher modulation formats. Although the achievable data rate may be lower than that of the optical link due to the narrower bandwidth of the millimeter-wave spectrum, this primary / secondary option switching mode ensures continuous and stable communication between terminal 1 and terminal 2.

[0040] like Figure 3B As shown, in scenario 4, channel conditions become extremely harsh, with both the optical wireless link and the millimeter-wave link experiencing severe performance degradation due to dense atmospheric interference. In this situation, decision logic module 110 determines that optical transceiver 120 and optical array 122 are unusable, and communication must rely entirely on millimeter-wave transceiver 130 and antenna array 132. However, the received millimeter-wave signal strength is significantly weakened, resulting in a low signal-to-noise ratio (SNR), meaning it cannot support high-level modulation formats such as 16-QAM. To maintain connectivity, decision logic module 110 can select a lower-level modulation scheme, such as QPSK, which has higher noise tolerance. Furthermore, system 100 can reduce the bandwidth of the millimeter-wave link to suppress noise; although this adjustment leads to a lower data rate, it can still effectively improve the SNR. This configuration allows system 100 to maintain basic communication even under the most severe free-space conditions.

[0041] The following descriptions illustrate the operating principles of the optical wireless transceivers and millimeter-wave transceivers, respectively. These transceivers correspond to the communication modules within System 100 and are responsible for modulating, transmitting, receiving, and demodulating data on free-space optical channels and millimeter-wave channels.

[0042] Figure 4 A system diagram of an optical wireless transceiver for free-space communication according to an embodiment of the present invention is shown. The optical transceiver 200 (i.e., the optical wireless transceiver) includes a coherent optical wireless transmitter 210 and an optical wireless receiver 220. On the transmitter side, four Mach-Zehnder modulators (MZMs) and two MZM-based optical phase shifters can be controlled using electrical drivers to achieve coherent 16-QAM modulation.

[0043] Taking branches MZM1 and MZM2 as an example, when there is no signal input, the optical signals output by MZM1 and MZM2 are in phase. When an additional π phase shift is applied after MZM1, the optical signals of the two branches become out of phase, resulting in destructive interference, and the output signal is zero.

[0044] When the differential electric drivers I-DRVP and I-DRVN provide differential drive signals to MZM1 and MZM2 respectively, the phase shift of the two branches will deviate by 180°. A stronger drive signal will make the phase of the two optical signals closer to being in phase, thus increasing the power of the total output optical signal after superposition. In this way, the electrical signal can be modulated onto the amplitude of the optical signal.

[0045] The superimposed optical signals from MZM1, MZM2, MZM3, and MZM4 will undergo phase shifts of θ1 and θ2, respectively. If θ1 - θ2 equals π / 2 (i.e., θ1 - θ2 = π / 2), the final output signal after merging the four branch signals will be an N-QAM modulated signal, such as 16-QAM. Conversely, if θ1 equals θ2 (i.e., θ1 = θ2), the final output signal will be a PAM-N signal, such as PAM-4.

[0046] Based on this principle Figure 2 The decision logic module described herein can support switching between different modulation schemes by controlling phase shifts θ1 and θ2. Variable phase shift control can be achieved through thermal management. It is certain that the 16-QAM modulation scheme can provide a higher data rate, while the PAM-4 modulation scheme, although providing a relatively lower data rate, has a higher tolerance for signal-to-noise ratio.

[0047] At the receiving end, the optical signal is collimated by a lens and amplified by an EDFA, then combined with the local optical signal by an optical mixer. The output of the optical mixer is received by two pairs of balanced photodiodes to recover the I and Q electrical signals, respectively. The analog electrical signal is then processed by a variable gain amplifier (VGA), digitized by a high-speed ADC, and finally deserialized and equalized in the digital signal processing unit.

[0048] For this purpose, the optical wireless transmitter 210 can be configured to at least: convert in-phase and quadrature baseband data signals into differential analog signals using a digital-to-analog converter and a drive amplifier; modulate the laser output using multiple Mach-Zehnder modulators, which can be used to generate QAM or PAM optical signals; and amplify and collimate the modulated optical signal using an erbium-doped fiber amplifier and a lens to facilitate free-space transmission. The optical wireless receiver 220 can be configured to at least: receive and amplify the collimated free-space optical signal; coherently mix the received signal with a local oscillator using an optical mixer; detect in-phase and quadrature components using two pairs of balanced photodiodes; amplify the electrical output using a transimpedance amplifier and a variable gain amplifier; and digitize and process the signal using an analog-to-digital converter and a digital signal processor.

[0049] More specifically, such as Figure 4 The configuration shown starts with a pair of digital baseband data signals (labeled Data1 and Data2), forming a coherent transmit and receive link. These two data streams are first converted to analog signals by two independent digital-to-analog converters (DACs), each DAC corresponding to the in-phase (I) and quadrature (Q) components of the signal. The DAC output of the I channel can be fed to two differential drivers (I-DRVP and I-DRVN), while the DAC output of the Q channel can be fed to two corresponding drivers (Q-DRVP and Q-DRVN). These differential driver pairs provide high-speed analog signals to control a set of four Mach-Zehnder modulators (MZM1-MZM4), which can be arranged in a nested structure to perform dual-polarization modulation.

[0050] MZM1 and MZM2 can form an I-path modulation branch, while MZM3 and MZM4 can form a Q-path branch. Each MZM modulates the optical carrier signal from the laser source based on the analog electrical signal received from the driver. The modulation output phase shifts of the MZMs are θ1 and θ2, respectively, and are thermally adjusted by an integrated thermal control circuit. The values ​​of θ1 and θ2 determine the modulation format, specifically: when θ1 - θ2 is approximately equal to π / 2, the resulting modulation format is quadrature amplitude modulation (QAM), such as 16-QAM; while when θ1 = θ2, a pulse amplitude modulation (PAM) format is formed, such as PAM-4.

[0051] The composite optical signal, after amplitude modulation and phase modulation, can be amplified by an erbium-doped fiber amplifier (EDFA) to enhance transmission power, and then collimated by a lens so that it can be propagated to a remote terminal in free space.

[0052] Next, at the receiving end, the incident light signal is first collimated and amplified by a combination of a second lens and an EDFA, and then coherently mixed with the local oscillator laser signal using an optical mixer. This mixing process generates four output optical paths corresponding to the I and Q signal branches. These signals are guided to two pairs of balanced photodiodes (PDs), which convert the optical field into differential currents. Each pair of photodiodes specifically supplies either the I or Q component. The electrical outputs of the photodiodes can then be passed through transimpedance amplifiers (TIAs) and variable gain amplifiers (VGAs) to provide a stable analog signal with adjustable amplitude.

[0053] The generated I and Q analog signals are digitized by high-speed analog-to-digital converters (ADCs) to produce digital samples, which are then further processed by a digital signal processor (DSP). The DSP performs signal equalization, clock and carrier recovery, demodulation, and data reconstruction, ultimately generating recovered digital data corresponding to the original Data 1 and Data 2 signals.

[0054] Therefore, based on the given operating mechanism, the optical wireless transceiver can implement the operating mechanism through the optical transceiver 120 and the optical array 122, and achieve [the desired operation]. Figure 2 Within the system architecture 100 shown, the optical transceiver 120 employs... Figure 4The coherent modulation architecture shown includes a Mach-Zehnder modulator and an optical phase shifter, configured to selectively generate 16-QAM or PAM-4 optical signals depending on channel conditions. The modulation format can be selected by a decision logic module 110, which dynamically adjusts the relative phase shifts θ1 and θ2 based on the estimated signal-to-noise ratio. The phase shift control can be achieved through thermal tuning or a similar mechanism integrated into the modulator array.

[0055] The optical array 122 integrated within system 100 can provide Figure 4 The illustrated optical signal path provides the physical interface. At the transmitting end, the optical array includes a laser diode source for directing... Figure 4 The coherent optical transmitter shown provides an optical carrier with a continuous wave. The optical carrier is then modulated by four Mach-Zehnder modulators (MZM1-MZM4) under the control of a differential electric driver, thereby forming I and Q signal branches. Subsequently, the modulated optical output can be boosted to a power level by an integrated erbium-doped fiber amplifier (EDFA) and then collimated by a lens for free-space propagation.

[0056] At the receiving end, the input optical signal is first collimated and amplified, and then mixed with the local oscillator optical signal through an optical mixer, such as... Figure 4 As shown. The output of the mixed operation is then connected to a balanced photodiode, which generates differential electrical signals corresponding to the I and Q components. These signals are then passed through a variable gain amplifier and digitized by a high-speed ADC, thereby achieving signal recovery and demodulation processing in the digital signal processing chain. All signal routing between the optical array 122 and the modulation / demodulation components within the optical transceiver 120 can follow... Figure 4 The coherent optical architecture shown.

[0057] The payload IC 112 provides baseband digital data to the optical transceiver 120 for modulation and receives the recovered I and Q signals after photoelectric detection and analog-to-digital conversion at the receiving end. Simultaneously, the decision logic module 110 continuously monitors the link status, including received signal power and error performance, and selects the optimal modulation format to maintain data throughput and communication reliability.

[0058] Therefore, the optical communication path in system 100 supports adaptive, high-speed, and directional-focused free-space transmission. The configuration allows system 100 to re-modulate the modulation format, thus responding to damage caused by changing atmospheric or distance conditions without requiring hardware replacement or physical intervention.

[0059] Figure 5A The diagram shows the architecture of a traditional millimeter-wave phased array transmitter, where the number of millimeter-wave elements is proportional to the square of the number of beams, resulting in significant signal distribution loss. Figure 5BAn improved millimeter-wave transmitter architecture based on a sliding intermediate frequency design according to an embodiment of the present invention is shown. This architecture can reduce signal loss and achieve efficient multi-beam synthesis with fewer millimeter-wave units.

[0060] One of the key requirements for millimeter-wave transceivers is the ability to support simultaneous multi-beam functionality, enabling the transmission of data to multiple users at the same time. Figure 5A The circuitry for a conventional millimeter-wave phased array transmitter is shown, which can simultaneously provide four beams using four antennas. To achieve this, data from the four beams must be processed by a total of 16 phase shifters and variable gain amplifiers operating at millimeter-wave frequencies. These 16 phase shifters and variable gain amplifiers effectively form a 4×4 matrix, processing the four input data streams and synthesizing four output millimeter-wave signals, which are then fed into a power amplifier for transmission through the antennas.

[0061] The main drawback of this architecture is that the number of millimeter-wave units is proportional to the square of the number of beams (N). 2 It is directly proportional to the power loss. In addition, due to the inherent characteristics of millimeter wave frequencies, there will be significant power loss in the power combining and power decomposition paths of the signal distribution.

[0062] This invention employs a sliding intermediate frequency (IF) architecture, which supports efficient multi-beam synthesis at the IF frequency, where the IF frequency is 1 / M of the radio frequency (RF frequency), and M is typically 5. For example... Figure 5B As shown, the four data streams from the four beams are upconverted to millimeter-wave frequencies through a two-step frequency upconversion process. In the first step, the input data is mixed with an intermediate frequency local oscillator (IFLO) to generate an intermediate frequency signal. Phase shift and gain control functions are applied to the IFLO and IF signals, respectively. The IFLO signal is typically generated by dividing the radio frequency local oscillator (RFLO) signal by 4. Therefore, by implementing phase shift and gain control in the intermediate frequency path, extremely high efficiency in terms of power consumption and area can be achieved.

[0063] Furthermore, the transadmittance-transimpedance (TAS-TIS) architecture can be used for intermediate frequency (IF) variable gain control. The input signal is first converted to a current-domain signal, and variable gain amplification is achieved in the process. Then, a second-stage transimpedance amplifier converts the gain-controlled current-domain signal back to the voltage domain. Notably, multi-beamforming can be performed in the current domain at the transadmittance output. Since the current-domain signal is not limited by a voltage source, high linearity multi-beamforming can be achieved. Moreover, because the IF frequency is much lower than the millimeter-wave frequency, the power efficiency of multi-beamforming can also be significantly improved.

[0064] The synthesized multi-beam signal is then fed into N millimeter-wave elements, where it undergoes a second-step frequency up-conversion before being transmitted to the power amplifier and antenna. Based on the technical solution provided in this invention, its number of millimeter-wave components compared to N in traditional architectures... 2 Unlike the direct proportionality, in the architecture of the given technical solution, the number of components is only proportional to N. Therefore, the overall power and area efficiency can be greatly improved.

[0065] The above configuration can be implemented as follows: Figure 5B The millimeter-wave transceiver 230 is described above. The millimeter-wave transceiver 230 employs the sliding intermediate frequency (IF) architecture discussed earlier and is configured to perform beamforming and gain control at the IF level. Each data stream first passes through a first-stage mixer and is mixed with the IF local oscillator signal to generate an IF signal, which is then up-converted to the millimeter-wave frequency using a second-stage mixer driven by the RF local oscillator.

[0066] Furthermore, the millimeter-wave transceiver 230 may include a transadmittance amplifier for converting the intermediate frequency signal into a current-domain signal, and a transimpedance amplifier for converting the current-domain signal back into the voltage domain. By employing a current-domain output, multi-beamforming can be performed at the output of the transadmittance amplifier, resulting in improved linearity and power efficiency due to the lower operating frequency.

[0067] Based on the above working mechanism, the sliding intermediate frequency millimeter-wave transmitter architecture can be implemented by a millimeter-wave transceiver 130 and an antenna array 132, and applied to... Figure 2 Within the architecture of the system 100 shown, the millimeter-wave transceiver 130 also includes, for example, Figure 5B The illustrated IF domain signal processing chain uses transadmittance (TAS) and transimpedance (TIS) stages to perform beamforming and gain control in the IF domain. The four input data streams mentioned are provided by the payload IC 112, which first converts them to IF signals using an IF local oscillator derived from an RF oscillator. Low-loss, high-linearity multi-beamforming is achieved by applying gain operations and phase adjustments specific to each beam in the current domain.

[0068] The synthesized intermediate frequency (IF) signals from each beam are then up-converted in a second stage and transmitted to the antenna array 132 via a power amplifier. Since beamforming is performed at the IF end, and the number of millimeter-wave links increases linearly with the number of beams (i.e., N, where N is a positive integer), system 100 achieves higher power efficiency and lower circuit complexity. The decision logic module 110 can also configure the modulation format for each millimeter-wave beam based on link quality, thereby maintaining reliable multi-user communication in dynamically changing channel environments.

[0069] Figure 6A schematic diagram of a satellite communication system 300 using a hybrid optical and millimeter-wave transceiver according to an embodiment of the present invention is shown. The configuration of system 300 is similar to that of the aforementioned system 100, but it further includes an environmental conditions module 340.

[0070] The environmental conditions module 340 is used to assess atmospheric or channel conditions, especially in cases of uncertain or fluctuating operating conditions, when communication is initiated between terminal 1 and terminal 2. Before selecting a transmission mode, terminal 1 can send a probe signal according to the four communication scenarios (Scenario 1 to Scenario 4) and wait for a response signal from terminal 2. The environmental conditions module 340 can analyze the received response signal to infer the most suitable transmission scheme. In one example, the decision analysis of the application may involve a direct waveform inspection of the returned signal.

[0071] In some embodiments, the environmental conditions module 340 employs a correlation-based method to identify a suitable data transmission scheme based on the characteristics of the received response signal. To facilitate this correlation analysis, standard training patterns can be stored in the on-chip memory of the system 300 to assist in environmental assessment. The stored training patterns can be sent before continuous communication begins or inserted as a prefix into each communication data packet during continuous communication. Upon receiving the sent training pattern, the environmental conditions module 340 performs correlation verification between the received pattern and the pre-stored pattern (e.g., by comparing the received signal characteristics with pre-loaded reference values). Based on the detected correlation level, channel conditions can be determined, and a suitable communication scheme can then be selected accordingly.

[0072] In some embodiments, the environmental conditions module 340 includes a machine learning (ML) model or an artificial intelligence (AI) model for classifying the returned signal from terminal 2 in order to select an appropriate transmission scheme. The ML or AI model can be trained using supervised or semi-supervised learning techniques on a dataset containing labeled signal patterns corresponding to different environmental conditions and channel scenarios. Each training sample can include a time-domain or frequency-domain representation of the returned signal and label it with the optimal transmission mode (e.g., optical modulation features of 16-QAM, optical modulation features of PAM-4, millimeter-wave features of 16-QAM, or millimeter-wave features of QPSK).

[0073] In one example, training data can consist of short-duration signal captures, such as received waveforms between 10 and 100 microseconds, sampled at high resolution (e.g., hundreds of megasamples per second). These time-domain signals can optionally be transformed to the frequency domain using a fast Fourier transform (FFT) operation to extract their classification-related spectral features, noise bands, and harmonic characteristics. Depending on the model architecture, either the original representation or the transformed representation can be used as input features.

[0074] In some embodiments, the AI ​​model may also include a convolutional neural network (CNN), a recurrent neural network (RNN), a transformer model, or other architectures capable of pattern recognition of signal data. During inference, the environmental conditions module 340 may receive a response signal from the terminal 2, extract a predefined time period, perform necessary preprocessing (e.g., normalization or domain transformation), and then input the processed signal into the model.

[0075] ML or AI models can output classification labels or confidence vectors, indicating estimated channel conditions or optimal matching in a predefined transmission scenario. The output from the model can guide the decision logic module 310 to select the optimal transceiver path and modulation scheme before active data transmission. The proposed AI-assisted method enables system 300 to predict atmospheric effects, scattering, or link attenuation before relying entirely on real-time signal-to-noise ratio feedback.

[0076] By leveraging AI to provide interpretation instructions for signal pattern recognition, the environmental conditions module 340 enhances the reliability and adaptability of the hybrid communication system in fuzzy or time-varying free-space environments. In this way, the pre-communication inference mechanism provides an additional decision-making layer beyond real-time signal-to-noise ratio monitoring, enabling the system 300 to proactively determine the most suitable link configuration before active data exchange begins.

[0077] In both systems 100 and 300, the decision logic module 110 is configured to dynamically switch between the aforementioned four transmission scenarios (e.g., between 16-QAM optical modulation, PAM-4 optical modulation, 16-QAM millimeter-wave modulation, and QPSK millimeter-wave modulation). As used herein, the term "dynamic" refers to the system's ability to switch from one transmission mode to another in real time based on changing channel or environmental conditions. For example, a system (e.g., system 100 or 300) might initially operate in scenario 1 (high SNR optical link), but the decision logic might switch to scenario 2 (PAM-4 optical signal) upon detecting increased atmospheric scattering or a decrease in received optical power. If conditions worsen further, such as during dense fog or heavy rain, the system might switch to scenario 3 or 4, depending on the availability and quality of the millimeter-wave link. Conversely, if channel conditions improve (e.g., adverse atmospheric conditions clear or satellite repositioning), the system can recover from an inefficient mode to an efficient mode.

[0078] To maintain communication continuity during such transitions, the payload IC may include a data alignment buffer or synchronization unit. Components employed (e.g., data alignment buffers or synchronization units) are used to temporarily store outgoing and incoming data during mode switching intervals, ensuring that the data stream remains logically continuous from the perspective of higher-layer protocols or remote terminals before and after the switch. The data alignment buffer or synchronization unit can operate as a first-in-first-out (FIFO) queue, a dual-port memory, or any structure capable of coordinating the switching between different modulation formats and physical layer paths, thereby preventing data loss or duplication at switching boundaries. In some embodiments, the data alignment buffer or synchronization unit may also be configured to copy or replay the most recently transmitted data after a transmission mode switch. This allows the receiver to compensate for transient packet loss that may occur during the switching window, particularly if the previous communication mode has degraded due to atmospheric fading or link interruption. The retransmitted data window may be determined based on a preset time threshold or data count metric (e.g., the most recent N packets or M milliseconds of data) and may also include metadata so that the receiver can identify and eliminate duplicate data if necessary.

[0079] In this specification, the term "transmission mode" refers to a specific combination of the type of communication link (e.g., optical or millimeter-wave signal) and the modulation format (e.g., high-level or low-level). The system described herein can dynamically select from four different transmission modes in response to changing atmospheric or channel conditions. Further characteristics / definitions of these four transmission modes are as follows:

[0080] 16-QAM optical modulation: This is a high-level / high-order modulation mode implemented on a coherent optical wireless link. This mode achieves high spectral efficiency, typically around 4 bits per hertz (bps / Hz), and requires a relatively high signal-to-noise ratio, typically above 15 dB, for reliable demodulation. This mode is suitable for free-space conditions with minimal atmospheric interference and may be geared towards short to medium line-of-sight ranges.

[0081] PAM-4 optical modulation: This is a low-complexity modulation format that uses four-level pulse amplitude modulation on the optical link. This mode can provide a moderate data rate at a relatively low signal-to-noise ratio threshold (typically around 12-14 dB) while maintaining higher receiver sensitivity than 16-QAM. This mode has advantages in long-distance or partially degraded optical conditions.

[0082] 16-QAM millimeter-wave modulation: This is a high-throughput RF mode that uses phased array beamforming on millimeter-wave channels. Under good RF propagation conditions, this mode provides approximately 4 bits per hertz (bps / Hz) of performance, but is more susceptible to atmospheric fading than QPSK. This mode supports a communication range of 1-2 kilometers and requires a signal-to-noise ratio higher than 15 dB.

[0083] QPSK millimeter-wave modulation: This is a reliable backup mode using quadrature phase shift keying on millimeter-wave links. This modulation mode requires a low signal-to-noise ratio, typically around 8-10 dB, and can still maintain stable communication even under dense atmospheric interference. This mode has lower spectral efficiency, approximately 2 bits per hertz (bps / Hz), but provides greater transmission range and noise immunity.

[0084] In this disclosure, 16-QAM is referred to as a high-order / high-level modulation format, while PAM-4 and QPSK are referred to as low-order / low-level modulation formats. These classifications are based on trade-offs between data rate, noise margin, and transmission range. The choice among the provided modes can be determined by the system's decision logic based on real-time or predictive channel evaluation.

[0085] As described above, this invention provides a novel transceiver architecture for satellite communications to facilitate communication transmission between satellites and between satellites and ground stations. The provided architecture employs a hybrid optical wireless and millimeter-wave transceiver, capable of switching between the two communication methods based on free-space channel conditions, while also providing an adaptive modulation scheme. By dynamically selecting appropriate communication methods and modulation formats, the system can support high-speed, reliable communication across various atmospheric environments. To achieve these capabilities, this paper details the implementation methods of the optical transceiver and the millimeter-wave transceiver, with a focus on the adaptive modulation scheme of the optical transceiver and the energy-efficient synchronous multi-beam millimeter-wave phased array transmitter. Compared to conventional methods, the technical solution proposed in this invention offers higher data rates, enhanced reliability, and higher power and area efficiency.

[0086] The functional units and modules of the apparatus and methods according to the embodiments disclosed herein can be implemented using computing devices, computer processors, or electronic circuits, including but not limited to application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), microcontrollers, and other programmable logic devices configured or programmed according to the teachings of this disclosure. Those skilled in the art of software or electronics can readily write computer instructions or software code that execute in computing devices, computer processors, or programmable logic devices based on the teachings of this disclosure.

[0087] All or part of the methods according to the embodiments can be performed in one or more computing devices, including server computers, personal computers, laptops, and mobile computing devices (such as smartphones and tablets).

[0088] Embodiments may include computer storage media, transient and non-transient memory devices storing computer instructions or software code, which can be used to program or configure computing devices, computer processors, or electronic circuits to perform any of the processes of this invention. Storage media, transient and non-transient memory devices may include, but are not limited to, floppy disks, optical disks, Blu-ray discs, DVDs, CD-ROMs, magneto-optical disks, ROMs, RAMs, flash memory devices, or any type of medium or device suitable for storing instructions, code, and / or data.

[0089] Each functional unit and module according to the various embodiments can also be implemented in a distributed computing environment and / or cloud computing environment, wherein all or part of the machine instructions are executed in a distributed manner by one or more processing devices interconnected by a communication network, such as an intranet, a wide area network (WAN), a local area network (LAN), the Internet, and other forms of data transmission media.

[0090] The above description of the present invention is provided for illustrative purposes. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations will be apparent to those skilled in the art.

[0091] These embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling those skilled in the art to understand the various embodiments of the invention and the various modifications suitable for the intended particular use.

Claims

1. A system for satellite communication, using a hybrid optical and millimeter-wave (mmWave) transceiver, characterized in that, The system includes: The decision logic module is used to evaluate channel conditions and select a transmission mode based on the evaluated channel conditions. The payload integrated circuit is used to generate outgoing baseband data signals and receive demodulated data signals. An optical transceiver is coupled to the decision logic module and the payload integrated circuit, and is used to transmit and receive optical signals via a free-space optical wireless link, wherein the optical signals are formed using a first modulation format or a second modulation format. An optical array, optically coupled to the optical transceiver, is used to provide optical signal transmission and optical signal reception; A millimeter-wave transceiver, coupled to the decision logic module and the payload integrated circuit, is used to transmit and receive millimeter-wave signals via a free-space millimeter-wave link, wherein the millimeter-wave signals are formed using a third or fourth modulation format; and An antenna array, coupled to the millimeter-wave transceiver, is used to provide millimeter-wave signal transmission and millimeter-wave signal reception; The decision logic module is further configured to determine the channel conditions based on signal quality indicators and select one of four transmission modes, including optical transmission using the first modulation format, optical transmission using the second modulation format, millimeter-wave transmission using the third modulation format, and millimeter-wave transmission using the fourth modulation format. The first modulation format requires a higher signal-to-noise ratio and provides higher spectral efficiency than the second modulation format, and the third modulation format requires a higher signal-to-noise ratio and provides higher data rate than the fourth modulation format.

2. The system according to claim 1, wherein the first modulation format is 16-QAM, the second modulation format is PAM-4, the third modulation format is 16-QAM, and the fourth modulation format is QPSK.

3. The system according to claim 1, wherein the signal quality indicators include at least one of signal-to-noise ratio, bit error rate, received signal strength, or channel response waveform.

4. The system of claim 1, wherein the optical transceiver comprises a plurality of Mach-Zehnder modulators and is used to switch between the first modulation format and the second modulation format by adjusting the phase difference between the two optical branches, wherein quadrature amplitude modulation (QAM) is implemented when the phase difference is π / 2, and pulse amplitude modulation (PAM) is implemented when the phase difference is zero.

5. The system of claim 1, wherein the millimeter-wave transceiver comprises a sliding-intermediate frequency (sliding-IF) architecture, the sliding-intermediate frequency architecture being used to perform beamforming and gain control at the intermediate frequency level.

6. The system according to claim 1, wherein the optical transceiver comprises: Optical wireless transmitter, which is used for: The in-phase and quadrature baseband data signals are converted into differential analog signals through a digital-to-analog converter and a driver amplifier. as well as Multiple Mach-Zehnder modulators are used to generate quadrature amplitude modulation (QAM) or pulse amplitude modulation (PAM) optical signals to modulate the laser output; as well as Optical wireless receiver, which is used for: Receive and amplify collimated free-space light signals; The received optical signal is coherently mixed with the local oscillator using an optical mixer; Detect in-phase and quadrature components; The electrical output is amplified using a transimpedance amplifier and a variable gain amplifier; as well as The amplified electrical output is digitized and processed using an analog-to-digital converter and a digital signal processor.

7. The system according to claim 1, wherein the millimeter-wave transceiver is used to upconvert each data stream through a two-stage frequency conversion process, and the millimeter-wave transceiver further comprises: The first-stage mixer is used to mix the data stream with the intermediate frequency local oscillator signal to generate an intermediate frequency signal; as well as The second-stage mixer is used to up-convert the intermediate frequency signal using the radio frequency local oscillator signal to generate a millimeter-wave frequency.

8. The system according to claim 1, wherein the millimeter-wave transceiver further comprises: A transadmittance amplifier is used to convert an input signal into a current-domain signal. as well as A transimpedance amplifier is used to convert the current domain signal back to the voltage domain signal, and the transimpedance amplifier performs multi-beam synthesis in the current domain at the output of the transadmittance amplifier.

9. The system according to claim 1, wherein the millimeter-wave transceiver comprises N millimeter-wave units to support N synchronous beams, such that the number of millimeter-wave units is linearly related to the number of beams, where N is a positive integer.

10. The system according to claim 1, further comprising: An environmental conditions module is used to send a probe signal to a remote terminal, receive a response signal, and determine channel conditions by analyzing the waveform data of the response signal. The environmental conditions module includes a machine learning model trained on labeled waveform data, which is used to classify transmission conditions and indicate one of the four transmission modes to the decision logic module.

11. A method for satellite communication, using a hybrid optical and millimeter-wave (mmWave) transceiver, characterized in that, The method includes: The decision logic module evaluates channel conditions based on signal quality indicators; Based on the evaluated channel conditions, one of four transmission modes is selected, including: (a) Optical transmission using the first modulation format; (b) Optical transmission using a second modulation format; (c) Millimeter-wave transmission using a third modulation format; or (d) Millimeter-wave transmission using the fourth modulation format; The payload integrated circuit generates the outgoing baseband data signal and receives the demodulated data signal. Optical transceivers optically coupled to an optical array transmit and receive optical signals on a free-space optical wireless link using either the first or the second modulation format. Millimeter-wave signals are transmitted and received on a free-space millimeter-wave link using the third modulation format or the fourth modulation format via a millimeter-wave transceiver coupled to an antenna array. The first modulation format requires a higher signal-to-noise ratio and provides higher spectral efficiency than the second modulation format, and the third modulation format requires a higher signal-to-noise ratio and provides higher data rate than the fourth modulation format.

12. The method according to claim 11, wherein the first modulation format is 16-QAM, the second modulation format is PAM-4, the third modulation format is 16-QAM, and the fourth modulation format is QPSK.

13. The method according to claim 11, wherein the signal quality indicator includes at least one of signal-to-noise ratio, bit error rate, received signal strength, or channel response waveform.

14. The method of claim 11, further comprising: The phase difference between the two optical branches in the Mach-Zehnder modulator architecture of the optical transceiver is adjusted, wherein quadrature amplitude modulation (QAM) is achieved when the phase difference is π / 2, and pulse amplitude modulation (PAM) is achieved when the phase difference is zero.

15. The method of claim 11, further comprising: Beamforming and gain control are performed at the intermediate frequency level of millimeter-wave transceivers using a sliding-intermediate frequency (sliding-IF) architecture.

16. The method of claim 11, further comprising: The millimeter-wave transceiver upconverts each data stream through a two-level frequency conversion process, including: The data stream is mixed with the intermediate frequency local oscillator signal to generate an intermediate frequency signal; and The intermediate frequency signal is mixed with the radio frequency local oscillator signal to generate a millimeter wave signal.

17. The method of claim 11, further comprising: The input signal is converted into a current domain signal using the transadmittance amplifier in the millimeter-wave transceiver. Multibeam synthesis is performed at the output of the transadmittance amplifier and in the current domain. as well as A transimpedance amplifier is used to convert the current domain signal back to the voltage domain signal.

18. The method of claim 11, further comprising: A change in channel conditions is detected to switch from the first transmission mode to the second transmission mode, wherein the first transmission mode is selected from one of (a)-(d), and the second transmission mode is selected from the remaining transmission modes that are different from the first transmission mode.

19. The method of claim 18, further comprising: Detect subsequent changes in the channel conditions; as well as Initiating a second conversion, wherein the second conversion includes: (i) If the original conditions have been restored, then restore to the first transmission mode; or (ii) If the channel conditions deteriorate or change further, switch to the third transmission mode.

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