Claims:1. An improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms, comprising:
a Rx front end module configured with plurality of receivers each configured with a low noise amplifier to amplify and down convert radio frequency signals from an antenna module to intermediate frequency (IF) signals, digitize and pass the IF signals through configurable decimation filters to obtain a digital output signal at an appropriate sample rate;
a FPGA connected to said Rx front end module configured to receive, filter, decimate and estimate and correct phase difference of said digital output signal from said Rx front end module and wherein said FPGA utilizes digital beamforming technique to increase gain of said digital output signal from said Rx front end module to increase the transfer rate of radio frequency signals;
a demodulator connected to said FPGA configured to receive said digital output signal with increased gain from said FPGA to filter and decimate the digital output signal to obtain baseband signals; and
a radio module configured to receive said baseband signals to perform scrambling, differential encoding and RRC filtering on said baseband signals and generate a radio frequency output signal,
whereby said system provides radio frequency output signal with faster data rates, additional gain, and enables voice and data communication in said MSS transmitter (Tx) – receiver (Rx) terminals of airborne platforms.
2. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said improved communication system additionally comprises a remote interface unit that provides interface for said audio device and an ethernet switch and wherein said remote interface unit comprises plurality of processing circuits and a microcontroller.
3. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said improved communication system utilizes digital beamforming technique to achieve higher data rates by utilizing existing satellite resources used for existing 300bps network and provides voice and data communication towards control centre with up to 3828 bps.
4. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said IF signals are filtered in IF filters and high dynamic range ADCs digitize the IF signals.
5. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said system additionally comprises an audio processing unit that converts the audio signals into digital signals and converts processed digital signals to audio signals and thereby provides audio communication across airborne platforms using an audio device.
6. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said plurality of receivers include four receivers each receiver handling two channels that are connected to said FPGA to achieve 8dB gain.
7. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said digital beamforming technique includes steps comprising of phase aligning the signals from 8 channels, down converting the signals to base band, estimating phase change for each channel and applying an equivalent phase correction for each channel.
8. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said digital Beam Former technique is realized in TRE has Solid State SSPA with power output of +46dBm to increase the data rate up to 3828 bps.

9. A method of providing improved communication for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms, comprising:
amplifying and down converting radio frequency signals from an antenna module to obtain intermediate frequency (IF) signals;
digitizing and passing the IF signals through configurable decimation filters to obtain a digital output signal at an appropriate sample rate;
filtering, decimating and estimating and correcting phase difference of said digital output signal;
utilizing digital beamforming technique to increase gain of said digital output signal to increase the transfer rate;
filtering and decimating said digital output signal with increased gain to obtain baseband signals; and
performing scrambling, differential encoding and RRC filtering said baseband signals to generate a radio frequency output signal,
whereby said method aids to provide radio frequency output signal with faster data rates, additional gain, and enables voice and data communication in said MSS transmitter (Tx) – receiver (Rx) terminals of airborne platforms.
, Description:FORM 2
THE PATENT ACT, 1970
(39 of 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)

1. TITLE OF THE INVENTION:
Improved communication system for MSS Transmitter (Tx) – Receiver (Rx) Terminal For Airborne Platform
2. APPLICANT:
Name: AVANTEL LIMITED
Nationality: INDIAN COMPANY
Address: Plot No.68 & 69, Jubilee Encalve Layout, IVth Floor, Madhapur, Serilingampally, Hyderabad-500081, Telangana.

3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in which it is to be performed:

4. DESCRIPTION:
The present specification is an improvement or modification of the invention claimed in the complete specification of the main patent application with application number 2238-CHE-2009.
Field of the invention:
[0001] The present disclosure generally relates to the technical field of wireless signal communication, and in specific relates to an improved Mobile Satellite Services (MSS) transmitter-receiver terminal configured to provide efficient and improved communication such as voice and data communication at higher rates and provide required gain for signals to and from an airborne platform to a ground-based control station also referred as hub stations within the footprint of Satellite.
Background of the invention:
[0002] Terrestrial very high frequency (VHF) or ultra-high frequency (UHF) networks use high power transmitters covering broad services, which enable one-way broadcast of content to user equipment such as televisions and radios. By contrast, wireless telecommunication networks utilize low power transmitters, which cover relatively small areas. Unlike broadcast networks, wireless networks may be adapted to provide two-way interactive services between user equipment such as telephones and computer equipment.

[0003] Wireless networks such as wide-area-networks (WANs) or cellular networks such as global system for mobile communications (GSM) networks and universal mobile telecommunications system (UMTS) networks thereof are not fully covered by network operators especially in geographical areas like India. The wireless network coverage in these areas has limited reception of wireless signals and therefore there is no possibility to make a voice or data call using a mobile phone.

[0004] Use of wireless telephone service is widespread. However, wireless telephone service may be interrupted when wireless base stations providing wireless telephone service become inoperable. In some situations, a wireless service provider may quickly restore wireless telephone service by repairing an inoperable base station. However, in other situations, natural disasters or other events may prevent the wireless service provider from restoring service for an extended period. During these times of service outage, people might not be able to call an emergency operator using a wireless phone. Consequently, this leads to loss of property, severe injury, and/or death.

[0005] Furthermore, communication is central to managing situations in a hostile environment, especially in the context of a military operation or any emergency. Lack of communications and situational awareness paralyzes command and control. Accordingly, there is a need for real-time data that is driving the integration of radio and satellite technology into both commercial and military communication systems.

[0006] Communication over an unreliable public network, however, can provide certain advantages. Public networks such as the Internet, provide an inexpensive and ubiquitous for communication, enabling an entire host of users to communicate directly with each other in a way unmatched by any private network. However, since the communications are public, any party can intercept and read the messages sent, which leads to insecurity. communicated data.

[0007] Today's armed forces are fast, mobile, tightly integrated and closely coordinated, which makes it necessary to quickly and freely communicate across territorial boundaries as well as international boundaries. Existing networks do not provide the required gain and are not feasible for various types of communication. Further, with the advancement in technology, it is crucial to obtain a higher transfer rate of data in communication.

[0008] Therefore, there is a need to provide a network with several ground-based, shipboard, and airborne terminals, which essentially provide communication to and from remote areas, where there is no communication available. This enables seamless communication to/from the mobile platforms within the footprint of the Indian satellite. There is a need to provide an improved Mobile Satellite Services (MSS) transmitter-receiver terminal configured to provide essential communication such as voice and data communication at higher rates and required gain for signals to and from an airborne platform.
Objectives of the invention:
[0009] The primary objective of the invention is to provide an improved Mobile Satellite Services (MSS) transmitter-receiver terminal configured to provide essential communication such as voice and data communication at higher rates and required gain for signals to and from an airborne platform to a ground-based control station.

[00010] Another objective of the invention is to utilize voice and data communication towards the control centre up to 3600 bps in Forward Error Correction coding.

[00011] Another objective of the invention is to utilize voice and data communication towards the control centre up to 3828 bps in Low Density Parity Check Coding.

[00012] The other objective of the invention is to provide an improved Mobile Satellite Services (MSS) transmitter-receiver terminal that utilizes digital beamforming to achieve higher data rates by utilizing the same satellite resources used for the existing 300bps network.

[00013] Yet another objective of the invention is to utilize a low-density parity-check error correction coding to obtain required error performance at a signal to noise ratio while considering an (Eb/N0) of 3 dB.

[00014] Further objective of the invention is to provide an improved Mobile Satellite Services (MSS) transmitter-receiver terminal that provides efficient handling of large parity check matrices in memory-constrained FPGA and efficient handling of log-likelihood processing.
Summary of the invention:
[00015] The present disclosure proposes an enhanced communication system for MSS transmitter (TX) – receiver (RX) terminal for airborne platform. The following presents a simplified summary in order to provide a basic understanding of some aspects of the claimed subject matter. This summary is not an extensive overview. It is not intended to identify key/critical elements or to delineate the scope of the claimed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

[00016] In order to overcome the above deficiencies of the prior art, the present disclosure is to solve the technical problem to provide an enhanced Mobile Satellite Services (MSS) transmitter-receiver terminal configured to provide essential communication such as voice and data communication at higher rates and required gain for signals to and from an airborne platform to a ground-based control station.

[00017] According to an aspect, the invention provides an enhanced communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms. The enhanced communication system comprises a Rx Front-end module, SSPA module and Radio module. The system provides radio frequency output signal with faster data rates, additional gain, and enables voice and data communication in said MSS transmitter (Tx) – receiver (Rx) terminals of airborne platforms. In specific, the enhanced communication system further comprises a remote interface unit that provides an interface for the audio device and an Ethernet switch and wherein the remote interface unit comprises a plurality of processing circuits and a microcontroller.

[00018] The Rx front end module is configured with plurality of receivers to amplify and down-convert radio frequency signals from an antenna module to Intermediate Frequency (IF) signals, digitize and pass the IF signals through configurable decimation filters to obtain a digital output signal at an appropriate sample rate. In specific, the plurality of receivers include four receivers each receiver handling two channels that are connected to said FPGA to achieve 8dB gain. The FPGA connected to the Rx front end module is configured to receive, filter, decimate and estimate and correct the phase difference of the digital output signal from the Rx front end modules.

[00019] The FPGA utilizes digital beamforming to increase the gain of the digital output signal from the Rx front end module to increase the transfer rate of radio frequency signals. In specific, the improved communication system utilizes digital beamforming technique to achieve higher data rates by utilizing existing satellite resources used for the existing 300bps network and provides voice and data communication towards the control centre with up to 3828 bps. The digital beamforming technique includes steps comprising of phase aligning the signals from 8 channels, down-converting the signals to baseband, estimating phase difference between each channel and applying an equivalent phase correction for each channel. In specific, the Digital Beam Former technique is realized in TRE has Solid State SSPA with a power output of +46dBm to increase the data rate up to 3828 bps.

[00020] RF Transceivers connected to the FPGA are configured to receive the digital output signals to filter and decimate the digital output signal to obtain baseband signals. The radio module is configured to receive the receiver and transmitter parameters for configuration and monitoring. Data from remote control unit and Client application are processed and framed. Framed data will be submitted to the FPGA to perform scrambling, forward error correction, differential encoding and RRC filtering on the baseband signals and generate a radio frequency output signal. In receiver chain, FPGA performs the demodulation and decoding techniques and transmits the digital data to radio module in synchronous format. The enhanced communication system provides voice and data communication towards the control centre with up to 3828 bps. The system additionally comprises an audio processing unit that converts the audio signals into digital signals and converts processed digital signals to audio signals and thereby provides audio communication across airborne platforms using an audio device.

[00021] According to another aspect, the invention provides a method of providing improved communication for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms. The method includes the steps comprising of amplifying and down-converting radio frequency signals from an antenna module to obtain intermediate frequency (IF) signals. Then, the IF signals are digitized and passed through configurable decimation filters to obtain a digital output signal at an appropriate sample rate.

[00022] Next, the digital output signal is filtered, decimated and the phase difference of the signal between channels is estimated and corrected. Later, the digital beamforming technique is utilized to increase the gain of the digital output signal to thereby increase the transfer rate. Then, the digital output signal with an increased gain is filtered and decimated to obtain baseband signals. Finally, the baseband signals are scrambled, differential encoding and SRRC matched filtering are performed on the baseband signals to generate a radio frequency output signal.

[00023] Further, objects and advantages of the present invention will be apparent from a study of the following portion of the specification, the claims, and the attached drawings.
Detailed description of drawings:
[00024] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, explain the principles of the invention.

[00025] FIG. 1 illustrates an exemplary block diagram of a TRE module of the enhanced communication system for MSS transmitter (TX) – receiver (RX) terminal for airborne platforms in accordance to an exemplary embodiment of the invention.

[00026] FIG. 2 illustrates an exemplary enhanced communication system for MSS transmitter (TX) – receiver (RX) terminal for airborne platform with digital beamformer in accordance to an exemplary embodiment of the invention.

[00027] FIG. 3 illustrates an exemplary flow diagram of a digital beamformer in accordance to an exemplary embodiment of the invention.

[00028] FIG. 4 illustrates an exemplary block diagram of an audio processing unit in accordance to an exemplary embodiment of the invention.

[00029] FIG. 5 illustrates an exemplary method of providing improved communication for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms in accordance to an exemplary embodiment of the invention.
Detailed invention disclosure:
[00030] Various embodiments of the present invention will be described in reference to the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps.

[00031] The present disclosure has been made with a view towards solving the problem with the prior art described above, and it is an object of the present invention to provide an enhanced Mobile Satellite Services (MSS) transmitter-receiver terminal configured to provide essential communication such as voice and data communication at higher rates and required gain for signals to and from an airborne platform to a ground-based control station. The MSS transmitter-receiver (Tx- Rx) Terminals are used for signal communication to send short messages from any stationary or moving platforms to a stationary hub station through MSS transponder of a satellite.

[00032] According to an exemplary embodiment of the invention, FIG. 1 refers to an exemplary block diagram 100 of a TRE module of the enhanced communication system for MSS transmitter (TX) – receiver (RX) terminal for airborne platforms. The enhanced communication system 100 comprises a receiver section 115, a FPGA 106, a demodulator 110, and a radio module 112. The system 100 provides radio frequency output signal with faster data rates, additional gain, and enables voice and data communication in said MSS transmitter (Tx) – receiver (Rx) terminals of airborne platforms. In specific, the enhanced communication system 100 further comprises a remote interface unit (RIU) that provides an interface for the audio device and an ethernet switch 111 and wherein the remote interface unit comprises a plurality of processing circuits and a microcontroller.

[00033] The receiver module 115 is configured with plurality of receivers (i.e., RF RXA 102, RF RXB 103, RF RXC 104, RF RXC 105) each configured with a low noise amplifier to amplify and down-convert radio frequency signals from an antenna module to intermediate frequency (IF) signals, digitize and pass the IF signals through configurable decimation filters to obtain a digital output signal at an appropriate sample rate. In specific, the plurality of receivers include four receivers each receiver handling two channels that are connected to said FPGA to achieve 8dB gain.

[00034] The system 100 further comprises eight front end modules 101 (RXIN1, RXIN2, RXIN3, RXIN4 RXIN5, RXIN6, RXIN7, and RXIN8) for each antenna element of the RX antenna array (Antenna unit). In specific, the digital output signal is a 12-bit digit digital output signal. The front end modules 101 together amplify the input signal of -134dBm to the required level of -92dBm. Each Front-end module 101 consists of a cavity Band Pass Filter (BPF), low noise amplifiers (LNAs) and a ceramic BPF. Cavity BPF & ceramic BPFs pass the in-band signals and reject out of RX band frequency signals, cavity BPF has a low insertion of less than 1dB and ceramic BPF is in small size and has an insertion loss of less than 2dB.

[00035] LNAs amplify the received signals with low noise figure for a better signal to noise ratio. The gain of each section is 42dB. RX front-end modules 101 operate on +5V DC supply and draw a maximum total current of 1.35A. The FPGA 106 connected to the receiver module 115 is configured to receive, filter, decimate and estimate and correct phase difference of the digital output signal from the receiver modules 115.

[00036] The FPGA 106 utilizes Digital Beam Forming (DBF) to increase the gain of the digital output signal from the receiver module 115 to increase the transfer rate of radio frequency signals. A gain of 8dB is achieved in the received signal using DBF. In specific, the improved communication system 100 utilizes digital beamforming technique to achieve higher data rates by utilizing existing satellite resources used for the existing 300bps network and provides voice and data communication towards the control centre with up to 3600 bps. This DBF gain increases the C/N of the received signal to support higher data rates of Voice/Data communication link with omnidirectional antennas. DBF is realized with RF Receivers and FPGA sections. RF Receiver integrated circuit (IC) is a high performance, highly integrated radio frequency (RF) Agile Transceiver which consists of inbuilt amplifiers, filters, down converters, AGC circuitry and ADCs. The receiver of the transceiver is used for the design of the beamformer.

[00037] The demodulator 110 chain inside the FPGA 106 is configured to receive the digital output signal from the receiver module 115 to filter, decimate and perform the demodulation and decoding techniques such as Viterbi decoding, differential decoding and descrambling. The digital output signal will be transmitted into synchronous format. The radio module 112 is configured to convert the synchronous data into asynchronous data. Received data from the application in radio module 112 computes the cyclic redundance check and frames the data into HDLC format. Framed data will be forwarded to the FPGA 106 to perform scrambling, differential encoding and SRRC filtering on the baseband signals and generate a radio frequency output signals from Modulator 114. The enhanced communication system 100 provides voice and data communication towards the control centre with up to 3828 bps.

[00038] According to another exemplary embodiment of the invention, the MSS transmitter (TX) – receiver (RX) terminal for airborne platforms comprises an antenna unit for communication. The antenna unit comprises a receiver (Rx) antenna array, transmitter (Tx) antenna and a GPS Antenna. Rx antenna array is realized with patch type and designed for the frequency band of 2500 - 2520 MHz and is fabricated on RT 5880, 2.2 dielectric to get more gain in Rx frequency band for the better efficiency. This design gives 5dB min at bore sight and 3dB beam width of 90° in both x and y planes. The antenna is designed in a rectangular shape with the feed point arranged on a diagonal of the rectangular and offset at the left side to obtain LHCP polarization. Individual Rx antennas are designed to meet the specifications and arranged in the array to meet the high gain and high beam width with the DBF algorithm implemented in the FPGA.

[00039] The TX antenna is realized with a rectangular patch designed for the frequency band of 2670 - 2690 MHz. This is fabricated on RT 5880, 2.2 dielectric to get more gain in TX frequency band for the better efficiency and gives 5dB min at boresight and 3dB beamwidth of 90° in both x and y planes. The antenna is designed as a rectangular shape with the feed point arranged on diagonal of the rectangular and offset at the left side to obtain LHCP polarization.

[00040] The GPS antenna is realized with a patch type designed for a frequency of 1575 MHz. This is fabricated on FR-4, 4.4 dielectric to get more gain in GPS frequency for the better efficiency gives 3dB min at boresight and 3dB beamwidth of 90° in both x and y planes. The antenna is designed in a square shape with the feed point arranged to get the RHCP polarization.

[00041] According to an exemplary embodiment of the invention, FIG. 2 refers to an exemplary enhanced communication system 200 for MSS transmitter (TX) – receiver (RX) terminal for airborne platform with a digital beamformer. The MSS terminal for communication enables communication from the mobile Tx terminal where the data is transmitted in S-band to the Satellite 202, which in turn, sends this data in C-Band to the ground-based hub station 204. The mobile platform 203 has a built-in GPS receiver working in L-band frequency. Location information (Coordinates) of the mobile platform 203 is received from the GPS Satellites and the same is stored in the memory, and retransmitted in S-band to Satellite 202.

[00042] The satellite 202 transmits the same to the ground-based hub station 204 in C-band. This data enables the user to continuously monitor the location of the mobile platform 203, in addition to receiving the short message from the mobile platform 203, communication from the hub station 204 to the mobile platform 203, a high sensitivity receiver in the S-band is used to receive the data from the satellite 202. In this case, a message from the ground-based hub station 204 is first sent to the satellite 202 in C- band, which in turn, sends the message in S-band to the mobile platform 203.

[00043] According to an exemplary embodiment of the invention, FIG. 3 refers to an exemplary flow diagram 300 of a digital beamformer. The digital beamforming technique includes steps comprising of down converting the signals from 8 channels to base band, estimating phase difference between different channels and applying an equivalent phase correction for each channel to align the phase. The digital beamforming technique is applied to all 8 channels for phase estimation and correction. The phase difference is estimated with respect to a reference signal. The corrected signals are then combined and fed to the demodulator connected to the FPGA. In specific, the Digital Beam Former technique is realized in TRE has Solid State SSPA with a power output of +46dBm to increase the data rate up to 3828 bps.

[00044] According to another exemplary embodiment of the invention, the demodulator takes the signal in digital IF from the DBF algorithm and brings it down to the baseband through the mixer operation. Direct Digital Synthesizer generates the required sine and cosine values to the mixer. Then, multi-stage decimation filters are used to filter and decimate the signal sampling frequency. Decimation filter output goes to IQ complex mixer. The complex mixer corrects the frequency offset. The frequency offset is measured and corrected in 2 stages. FFT processing is first used to estimate the coarse offset which is then corrected. A Digital PLL is then used to track and correct the uncompensated fine frequency and phase offsets. Then matched filter performs the "Square root raised cosine" matched filtering operation.

[00045] The output of matched filter goes to the demodulator signal presence check and also to the symbol tracker. The demodulator signal check module generates a signal indicating whether the input signal is present or not. The symbol tracker generates a 1x sampling rate (symbol rate) by choosing the right sampling instants of the matched filter output. Then Phase and Frequency tracker implements a Digital Phase Locked Loop (DPLL) by calculating the phase error and correcting the phase and frequency. A significant improvement is in the ability to estimate and correct frequency offsets and obtain accurate symbol timing at very low EbN0 of 3dB.

[00046] PLL output goes to the spectral inversion module and then to the Viterbi and LDPC decoders. Soft input Viterbi/LDPC decoders correct the bit errors and improve the BER performance. Output from Viterbi/LDPC decoders goes to differential decoder, it removes 180 degrees phase ambiguity. The descrambler is the final block to implement the inverse operation of the scrambling block in the modulator.
[00047] According to another exemplary embodiment of the invention, LDPC is robust against burst errors, each input bit is used for generation of multiple parity bits and each parity bit is generated from multiple input bits. Because of this, any loss of input/parity bits due to masking or shadowing (due to rotating blades of helicopter) can be recovered from the unshadow/unmasked input/party bits. LDPC works up to 3dB SNR for the required BER of 10-6. Because of superior performance of LDPC in terms of EB/N0 and efficient error correction mechanism, this is proposed even on helicopters under rotor shadowing effect.

[00048] According to another exemplary embodiment of the invention, the FPGA receives the baseband data from the radio module in synchronous mode and performs the various operations on it, such as 1/2 FEC decoding, LDPC decoding, descrambling, Differential Encoding/Decoding and SRRC filtering. The processed data is fed to a transceiver through DAC. Sampling frequency to DAC is decided based on the configured data rate of operation. The transceiver generates the RF output at a configured frequency and its output will be fed to SSPA for further amplification. In specific, the radio module is utilized as a radio controller to configure and monitor the radio module. The FPGA performs DBF and other modulator functionalities.

[00049] The system includes an additional baseband section. The baseband section is utilized to configure and monitor the radio module parameters. It communicates with MMI/remote interface unit (RIU) through an Ethernet interface. It configures the RF receiver through SPI interface when configuration command is received from MMI/RIU. It configures the FPGA through UART and GPIO interfaces. It receives GPS data from a GPS receiver transmitted by the GPS satellite through the UART interface. It transmits and receives baseband data bit by bit with respect to clock to/from the FPGA through the synchronous interface.

[00050] The Remote Interface Unit (RIU) provides audio communication to the MSS TRE M-II remotely through the MSS Tx-Rx Client. RIU is communicated with the TX-RX client and MSS TRE through an Ethernet switch. An audio device such as a headset is provided at RIU for the user audio interface. Audio exchange port is provided at RIU for ICS. RIU mainly consists of Microcontroller, audio processing circuits. RIU is provided with an isolated Ethernet interface port to interface crypto device for voice applications. RIU operates on a + 28V DC power supply. RIU is designed to meet the compliance of environmental specs MIL-STD-810G, EMI/EMC specs MIL-STD-461E and Electrical power characteristics MIL-STD-704A.

[00051] According to an exemplary embodiment of the invention, FIG. 4 refers to an exemplary block diagram 400 of an audio processing unit. The audio processing unit comprises a baseband section 403, a vocoder section 402, an audio transceiver 401, and a DC-DC converter 404. Baseband section 403 consists of microcontrollers to interface to the MSS TRE through the Ethernet interface. Radio module interfaced to Voice processor through UART for Voice communication.

[00052] It receives data from TRE, processes the voice packets and sends it to the Voice processor. Similarly, the radio module receives the data from the Voice processor, processes and sends it to MSS TRE. The second microcontroller is an interface to the external crypto device through an Ethernet interface. Two microcontrollers are interfaced through TTL interfaces. The baseband 403 section provides audio on Headset and exchange interfaces. This section generates Dial tone and incoming call alert during voice calls.

[00053] The audio transceiver 401 comprises an audio receiver and an audio transmitter. The audio receiver consists of Audio switches, amplifiers, a Volume controller, audio transformer and differential line drivers. It receives audio Rx signal from Voice processing and Sidetone signal from Audio transmitter. These two signals are combined using Op-amps through the audio switch, the switch selects either enabling or disabling sidetone.

[00054] The controller handles Vocoder section 402 through a dedicated serial port interface for Voice. It receives the data from the serial interface and performs the necessary processing and framing on the received data. It sends or receives packets to/from the satellite through DBF Terminal. The controller has an Ethernet interface that is used to take voice frames to/from the terminal and performs necessary processing.

[00055] The audio transmitter comprises a MIC Amplifier, a differential receiver, an AGC amplifier, a Headset/Exchange selection switch, and programmable gain amplifier sections. It receives audio signals from Headset or exchange and selects one of the audio signal based on user selection. Headset MIC signals are amplified in the MIC amplifier. The incoming exchange differential audio signals are converted to single-ended signals in the differential receiver and amplified in an audio AGC amplifier. The output of the switch is connected to a programmable gain amplifier where transmitted audio levels are controlled with user input. The output of the programmable amplifier is connected to the final output.

[00056] Further, the audio processing unit comprises a voice processor. The voice processor receives the analog signal from the audio transmitter as codec input and converts the audio signals into digital format, the digital audio signal is sent to Vocoder section 402. In Vocoder section 402, the audio data is compressed and is transmitted to Baseband section 403. Similarly, the voice processor receives audio data from Baseband section 403, decompresses it, and transmits it to codec. The codec converts the received data from Vocoder section 402 to analog signal and it is sent to the audio receiver.

[00057] According to another exemplary embodiment of the invention, FIG. 5 refers to a method of providing improved communication for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms. The method includes the steps comprising of amplifying and down-converting radio frequency signals from an antenna module to obtain intermediate frequency (IF) signals at step 501. Then at step 502, the IF signals are digitized and passed through configurable decimation filters to obtain a digital output signal at an appropriate sample rate.

[00058] Next at step 503, the digital output signal is filtered, decimated and the phase difference of the signal is estimated and corrected. Later, the digital beamforming technique is utilized to increase the gain of the digital output signal to thereby increase the transfer rate at step 504. Then at step 505, the digital output signal with an increased gain is filtered and decimated to obtain baseband signals. Finally, the baseband signals are scrambled, differential encoding and RRC filtering are performed on the baseband signals to generate a radio frequency output signal at step 506.

[00059] According to another exemplary embodiment of the invention, Forward Error Correction coding and decoding are done in Digital Communications to obtain an improvement in the required signal to noise ratio for meeting a specified error performance. Convolution encoding (at half rate) and Viterbi decoding have been employed for a long time.

[00060] Low-Density Parity Check (LDPC) is the error correction coding technique. In LDPC, a block of parity bits (say 972 bits) is generated from a block of input data bits (say 972 bits) using a parity check matrix (which has been adapted from one of the wireless standards). A large parity check matrix is used but it is sparsely populated (i.e., Low Density). The characteristic feature is that each input bit is used in multiple parity bits and each parity bit is derived from multiple input bits.

[00061] LDPC error correction is an iterative technique with about 5 to 50 iterations. The received multi-bit data (from ADC) are used as the inputs for the first iteration where the (apriori) likelihood of each input bit being 0 and 1 is obtained based on the sample value. Each iteration modifies the likelihood by combining the likelihood of multiple bits. The output of each subsequent iteration uses the modified likelihoods of the previous iteration as input. The iteration ends when the output bits satisfy the parity check matrix conditions or when the maximum specified iteration is reached.

[00062] Since the input and parity bits are spread throughout the packet, LDPC works well even if some part of the packet is shadowed or masked as in the case of reception in a helicopter with masking caused by blade rotation. In Conventional FEC, however, the redundancy added by FEC convolutional encoder is more “local “ and it is difficult to correct the errors if such errors extend over a block.

[00063] Half rate (972 input bits with 972 parity bits) LDPC Encoder and Decoder are implemented in the FPGA. The implementation also includes carrier acquisition, Frame synchronisation and Symbol Timing recovery in each packet. Another key aspect of implementation is the efficient handling of such large parity check matrices in memory-constrained FPGA and the efficient handling of log-likelihoods. The required error performance is obtained at a signal to noise ratio (EBN0) of 3 dB.

[00064] Numerous advantages of the present disclosure may be apparent from the discussion above. In accordance with the present disclosure, an improved Mobile Satellite Services (MSS) transmitter-receiver terminal is disclosed that is configured to provide essential communication such as voice and data communication at higher rates and required gain for signals to and from an airborne platform to a ground-based control station. The proposed system utilizes voice and data communication towards the control centre up to 3828 bps.

[00065] The present disclosure provides an improved Mobile Satellite Services (MSS) transmitter-receiver terminal that utilizes digital beamforming to achieve higher data rates by utilizing the same satellite resources used for the existing 300bps network. The system utilizes a low-density parity-check to obtain the required error performance at a signal to noise ratio (Eb/N0) of 3 dB. The proposed system aids to provide improved and efficient handling of large parity check matrices in memory-constrained FPGA and efficient handling of log-likelihood processing.

[00066] It will readily be apparent that numerous modifications and alterations can be made to the processes described in the foregoing examples without departing from the principles underlying the invention, and all such modifications and alterations are intended to be embraced by this application.

 
5. CLAIMS:
We Claim:
1. An improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms, comprising:
a Rx front end module configured with plurality of receivers each configured with a low noise amplifier to amplify and down convert radio frequency signals from an antenna module to intermediate frequency (IF) signals, digitize and pass the IF signals through configurable decimation filters to obtain a digital output signal at an appropriate sample rate;
a FPGA connected to said Rx front end module configured to receive, filter, decimate and estimate and correct phase difference of said digital output signal from said Rx front end module and wherein said FPGA utilizes digital beamforming technique to increase gain of said digital output signal from said Rx front end module to increase the transfer rate of radio frequency signals;
a demodulator connected to said FPGA configured to receive said digital output signal with increased gain from said FPGA to filter and decimate the digital output signal to obtain baseband signals; and
a radio module configured to receive said baseband signals to perform scrambling, differential encoding and RRC filtering on said baseband signals and generate a radio frequency output signal,
whereby said system provides radio frequency output signal with faster data rates, additional gain, and enables voice and data communication in said MSS transmitter (Tx) – receiver (Rx) terminals of airborne platforms.
2. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said improved communication system additionally comprises a remote interface unit that provides interface for said audio device and an ethernet switch and wherein said remote interface unit comprises plurality of processing circuits and a microcontroller.
3. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said improved communication system utilizes digital beamforming technique to achieve higher data rates by utilizing existing satellite resources used for existing 300bps network and provides voice and data communication towards control centre with up to 3828 bps.
4. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said IF signals are filtered in IF filters and high dynamic range ADCs digitize the IF signals.
5. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said system additionally comprises an audio processing unit that converts the audio signals into digital signals and converts processed digital signals to audio signals and thereby provides audio communication across airborne platforms using an audio device.
6. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said plurality of receivers include four receivers each receiver handling two channels that are connected to said FPGA to achieve 8dB gain.
7. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said digital beamforming technique includes steps comprising of phase aligning the signals from 8 channels, down converting the signals to base band, estimating phase change for each channel and applying an equivalent phase correction for each channel.
8. The improved communication system for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms as claimed in claim 1, wherein said digital Beam Former technique is realized in TRE has Solid State SSPA with power output of +46dBm to increase the data rate up to 3828 bps.

9. A method of providing improved communication for MSS transmitter (Tx) – receiver (Rx) terminal for airborne platforms, comprising:
amplifying and down converting radio frequency signals from an antenna module to obtain intermediate frequency (IF) signals;
digitizing and passing the IF signals through configurable decimation filters to obtain a digital output signal at an appropriate sample rate;
filtering, decimating and estimating and correcting phase difference of said digital output signal;
utilizing digital beamforming technique to increase gain of said digital output signal to increase the transfer rate;
filtering and decimating said digital output signal with increased gain to obtain baseband signals; and
performing scrambling, differential encoding and RRC filtering said baseband signals to generate a radio frequency output signal,
whereby said method aids to provide radio frequency output signal with faster data rates, additional gain, and enables voice and data communication in said MSS transmitter (Tx) – receiver (Rx) terminals of airborne platforms.
6. DATE AND SIGNATURE:
Dated this 29th day of July, 2021

7. ABSTRACT:
Title: Improved communication system for MSS Transmitter (Tx) – Receiver (Rx) Terminal for Airborne Platform
The present disclosure proposes an improved Mobile Satellite Services (MSS) transmitter-receiver terminal is disclosed that is configured to provide essential communication such as voice and data communication at higher rates and required gain for signals to and from an airborne platform to a ground-based control station. The enhanced communication system 100 comprises a receiver module 115, a FPGA 106, a demodulator 110, and a modulator 114 a radio module 112. System 400 comprises a baseband control card 403, a vocoder card 402 and an Audio Tx and Rx 401. The proposed system provides voice and data communication towards the control centre up to 3828bps. The present disclosure provides an improved Mobile Satellite Services (MSS) transmitter-receiver terminal that utilizes digital beamforming to achieve higher data rates by utilizing the same satellite resources used for the existing 300bps network. The proposed system aids to provide improved and efficient handling of large parity check matrices in memory-constrained FPGA and efficient handling of log-likelihood.