DESC:FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
Title: METHOD OF DIGITALLY MODULATED BASEBAND DATA PROTECTION IN MF-TDMA RETURN CHANNEL SATELLITE COMMUNICATION

APPLICANT DETAILS:
(a) NAME: Bharat Electronics Limited
(b) NATIONALITY: Indian
(c) ADDRESS: Outer Ring Road, Nagavara, Bangalore - 560045 Karnataka, India

PREAMBLE TO THE DESCRIPTION:
The following specification (particularly) describes the nature of the invention (and the manner in which it is to be performed):

METHOD OF DIGITALLY MODULATED BASEBAND DATA PROTECTION IN MF-TDMA RETURN CHANNEL SATELLITE COMMUNICATION

FIELD OF INVENTION:
The present disclosure relates in general to field of satellite communications, and more particularly, relates to technique and method of digitally modulated baseband data protection in Multi-Frequency Time-Division Multiple Access (MF-TDMA) return channel satellite communication.

BACKGROUND OF THE INVENTION:
The following background discussion includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication expressly or implicitly
In recent times, there has been a significant development in satellite communications systems. Various channelization, frequency hopping techniques and various methods for baseband data protection and bandwidth conservation are known in the existing systems.
US8077652B discloses MF-TDMA frequency hopping. Systems, methods, and devices are described for scheduling and mapping upstream communications in a satellite communications system. The disclosure includes various channelization and frequency hopping techniques. A gateway is described to perform novel allocation of time slots on upstream frequency channels to allow frequency hopping. A subscriber terminal may perform frequency hopping according to the allocation, and the range may be limited to the transition range of a digitally controlled oscillator unit at the Subscriber terminal. A gateway is described to allocate time slots on different upstream frequency channels in a prioritized manner. Subscriber terminals may receive the allocation, and then control the assignment of their upstream traffic to the time slots. In this method, frequency hopping where transmit and receive frequencies are changing in each transmit frame of time slot is disclosed. Further, there is a complex operation for baseband data protection.
US7,359,457B2 discloses transmission apparatus, reception apparatus and digital radio communication method. A transmission apparatus includes a frame configuration determiner that determines a modulation system from among a plurality of modulation systems on a communication situation. A first symbol generator modulates a digital transmission signal according to the modulation system determined by the frame configuration determiner and generates a first symbol, the first symbol comprising a first quadrature baseband signal. A second symbol generator modulates the digital transmission signal according to a predetermined modulation system and generates a second symbol, the second symbol comprising a second quadrature baseband signal. In this method, modulation is changing with modulating data frame.
US005673291A discloses simultaneous demodulation and decoding of a digitally modulated radio signal using known symbols. System and methods according to the present invention provide a combination of demodulation and decoding, termed decodulation herein. By using knowledge of known symbols, decoding known symbols first, and then using the information obtained by decoding known symbols to decode unknown symbols, improved performance can be achieved. This technique can also be used to alleviate the conventional 3dB loss suffered system using differentially coding and modulation as compared to coherent detection system. In this method, decoding is done with known pattern (i.e. data-aided) in sync word. But the sync word is not changing with time.
Therefore, there is a need for techniques and methods for addressing the above-mentioned problems related to baseband data protection in satellite communication, in addition to providing other technical advantages.

OBJECTIVES OF THE INVENTION:
The primary object of the present invention is to overcome the problem stated in the prior art.
Another object of the present invention provides a method of digitally modulated baseband data protection in Multi-Frequency Time-Division Multiple Access (MF-TDMA) return channel satellite communication.
SUMMARY OF THE INVENTION:
The present invention provides a method of digitally modulated baseband data protection in MF-TDMA return channel satellite communication comprising:
a) an interactive satellite network consists of multiple terminals connected to a centralized hub under an MF-TDMA system, where each node is transmitting under an allocated time frame in the time-Frequency plane, where each frame is constructed using Bandwidth Time Units (BTU) as the basic building block;
b) a multi-channel receiver includes multiple receiver chains of RF, IF and ADC paths;
wherein N number of terminals in a one MF-TDMA channel, where each terminal bandwidth and time slot in which the terminals send their respective baseband data frame to form a super-frame.
In an embodiment, PDU packets 1 are read from return link encaptulation (RLE) encoder to form FEC encoder frame 2 frame which is sufficient for formation of one bandwidth-time-unit(BTU).
In an embodiment, a clock buffer 3 generates synchronous clocks for the complete one terminal system. Transmit enable (Tx enable) 6 open the window for transmit frame in its assigned time slot from supper frame, where the frame timer 4 generate clock pulse for gold code 5, where in each time slot, the gold code generates a new code for sync word.
In an embodiment, the TDMA frame 7 consist of preamble, Sync word, terminal transmiter ID(Tx-ID), Payload and End-of-frame(EoF) symbols. Sync word is the K symbols of generated by Gold code and it is changing in every time slot of transmit frame.
In an embodiment, the digital to analog converter (DAC) 9 provides clock for digital modulator which is generating RF signal.
In an embodiment, the RF channelizer block 11 segregates the received return channels, where RF channelizer segregate M return channels of MF-TDMA satellite network, where each channel is down converted using complex multiplier 12 by using frequency synthesizer 13 to baseband IQ signal.
In an embodiment, the demodulator block demodulates the baseband data and correlates with data-aided technique by using known sync word which is provided by 13 sync word generator.
In an embodiment, the watch-dog timer 19 have the timing record of frame duration and frame repetition in each supper frame timing, where an initial sync word is known for remote transmitter and HUB receiver, where as soon as end-of-frame(EoF) 16 is detected, it generates the pulse for new sync word generation which is using the Gold codes, where in any case, EoF detection is failed, then watch-dog timer will provide the pulse for new SWG word.
In an embodiment, the initial sync word 22 is set for data-aided correlation, where if initial sync word is not detected, then the receiver remains in waiting state, whereas soon as sync word is detected, the data boundary is detected.

DETAILED DESCRIPTION OF DRAWINGS:
To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of their scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings in which:
Fig. 1: illustrates a schematic diagram of Multi-Frequency Time-Division Multiple Access (MF-TDMA) based interactive satellite network.
Fig. 2: illustrates a block diagram representation of MF-TDMA terminal transmitter.
Fig. 3: illustrates a block diagram representation of MF-TDMA HUB receiver.
Fig. 4: illustrates a schematic diagram of RF channelizer segregated spectrums.
Fig. 5: illustrates a schematic a flow diagram of HUB Receiver MF-TDMA for one received terminal.
DETAILED DESCRIPTION:
For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.
It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.
The terms “comprises”, “comprising”, “includes”, or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a setup, device or method that comprises a list of components or steps does not include only those components or steps but may include other components or steps not expressly listed or inherent to such setup or device or method. In other words, one or more elements in a system or apparatus proceeded by “comprises... a” does not, without more constraints, preclude the existence of other elements or additional elements in the system or method.
An Interactive Satellite Network consists of multiple terminals connected to a centralized Hub under an MF-TDMA system. Each node is transmitting under an allocated time frame in the Time-Frequency plane. Each frame is constructed using Bandwidth Time Units (BTU) as the basic building block. So a multi-channel receiver should be facilitated at the Hub.
A traditional Multi channel receiver System includes multiple receiver chains of RF, IF and ADC paths. Cost and performance can be achieved using DSP based processing of baseband. Availability of wide band ADCs and high density FPGAs open a gate for the multi-channel receiver design with reduced hardware complexity thereby making the system design cost more effective.
The present invention relates to a terminal baseband data protection with most cost effective implementation for MF-TDMA interactive satellite network using different sync word in each MF-TDMA return channel BTU.
The present invention discloses the unique concept of remote terminals return channel baseband data protection in MF-TDMA satellite network. Due to hopping in sync word, the intended receiver module only can detection the correlation pattern which will determine the baseband data boundary and collect the baseband data in correct format. The unintended receiver module won’t detect the sync words which leads to wrong format of data collection due to unknown correlation pattern for data boundary detection. Further, the FEC decoder block acts as a encryptor block.
Various embodiments of the present disclosure are further described with reference to FIG. 1 to FIG. 5.
FIG. 1 illustrates a schematic diagram of Multi-Frequency Time-Division Multiple Access (MF-TDMA) based interactive satellite network, in accordance with an embodiment of the present disclosure. FIG. 1 details the MF-TDMA satellite network with NCC at the Hub and N number of terminals which interactively communicating back to the hub. The network is based on the MF-TDMA technology in which the hub allocates the frequencies to terminal.
FIG. 2 illustrates a block diagram representation of MF-TDMA terminal transmitter, in accordance with an embodiment of the present disclosure This block diagram is made for one terminal. There will N number of terminals in a one MF-TDMA channel. Each terminal bandwidth and time slot in which the terminals send their respective baseband data frame to form a super-frame. The PDU packets 1 are read from return link encaptulation(RLE) encoder to form FEC encoder frame 2 frame which is sufficient for formation of one bandwidth-time-unit(BTU). Clock buffer 3 generates synchronous clocks for the complete one terminal system. Transmit enable(Tx enable) 6 open the window for transmit frame in its assigned time slot from supper frame. The frame timer 4 generate clock pulse for gold code 5. In each time slot, the Gold code will generate a new code for sync word. The TDMA frame 7 consist of preamble, Sync word, terminal transmiter ID(Tx-ID), Payload and End-of-frame(EoF) symbols. Sync word is the K symbols of generated by Gold code and it is changing in every time slot of transmit frame. The transmitter enable 6 pulse will be remained high during modulator 8 digitally modulating the transmitting frame. Digital to analog converter(DAC) 9 provides clock for digital modulator which is generating RF signal.
FIG. 3 illustrates a block diagram representation of MF-TDMA HUB receiver, in accordance with an embodiment of the present disclosure. This is a receiver block placed at satellite HUB which received the return RF channel 10 with RF front end.
FIG. 4 illustrates a schematic diagram of RF channelizer segregated spectrums, in accordance with an embodiment of the present disclosure. The RF channelizer block 11 segregates the received return channels as per figure 4. RF channelizer segregate M return channels of MF-TDMA satellite network. The each channel is down convert using complex multiplier 12 by using frequency synthesizer 13 to baseband IQ signal. The demodulator block demodulate the baseband data and correlate with data-aided technique by using known sync word which is provided by 13 sync word generator(SWG. The sync word correlator provides the frame boundary for 15 deframer block. The baseband data is starong in respective 18 transmitter ID(T-ID) buffer. The T-ID 20 provides ready signal to 21 FEC decoder block as soon as write the complete data of FEC encoded frame of transmitter.
fsym = Symbol clock frequency
ffec = FEC decoder clock frequency
ffec = M*N* fsym
The watch-dog timer 19 have the timing record of frame duration and frame repetition in each supper frame timing. The initial sync word is known for remote transmitter and HUB receiver. As soon as end-of-frame(EoF) 16 is detected, it generates the pulse for new sync word generation which is using the Gold codes. In any case, EoF detection is failed, then watch-dog timer will provide the pulse for new SWG word.
FIG. 5 illustrates a flow diagram of HUB Receiver MF-TDMA for one received terminal, in accordance with an embodiment of the present disclosure. As shown in FIG. 5, initial sync word 22 is set for data-aided correlation. If initial sync word is not detected, then the receiver remains in waiting state. As soon as sync word is detected, the data boundary is detected. The baseband data is store in respective T-ID 24 buffers. The watch-dog time set its frame timing and after detecting the EoF, the new sync word is generated by using Gold code. In next frame cycle, if sync word 27 for correlation is not detected then it will check for X times based on slot repetition in supper frame of per second. After completion of X times, if not detected then it will be in waiting state. Otherwise proceed for saving data in respective T-ID buffer 29 and FEC decoder 30. After decoding the decoded data is accepted by RLE decoder.
The baseband data protection of return channel MF-TDMA of the present invention comprise of the following features:
a) Gold code generator
b) Sync word hopping
c) Double baseband data protection
a) In the present invention, gold code generator is generating gold codes which are known for transmitting terminal and receiver hub module. The Gold codes are generated dynamically which are synchronous with satellite hub receiver module.
b) In sync word hopping of the present invention, sync word is replaced by Gold codes in each of terminal transmit frame. Only intended receiver terminal can synchronize with remote transmitting terminal. The sync word hopping is based on supper frame repeating per second. If supper frame is repeating X time per second, then Gold code will repeat after generating X numbers of code.
c) In double baseband data protection, the intended hub receiver module only can detect the correlation word for baseband data boundary adjustment. For unintended receiver module baseband data frame won’t be detected. The receiver module will store wrong baseband data. At the same time the FEC decoder acts as encryptor which will decode the wrong data.
NOVEL ASPECTS OF THE PRESENT INVENTION
1. The baseband data frame is protected by changing sync symbols synchronically in each transmitted MF-TDMA frame. Intended receiver terminal can only synchronize the baseband data frame and can find the data frame boundary.
2. The sync symbols are generated using Gold code for data-aided receiver correlation. Intended receiver terminal correlate with received frame and find out the data boundary. For unintended receiver terminal, the FEC decoder acts as an encryptor of FEC decoded data frame.
3. Unlike frequency hopping where huge bandwidth is consumed, here only single carrier frequency is shared by multiple terminals. So, Satellite communication bandwidth is conserved in this technique. Due to data-aided correlation method, another 3dB receiver sensitivity will also increase.
Unlike conventional systems and methods, sync word is hopping in each transmit and receive frame of time slot and a simplex operation for baseband data protection is employed in the present invention.
Unlike conventional systems and methods, modulation is not changing in the present invention. Only sync word is changing with transmit frame of its time slot.
Unlike conventional systems and methods, decoding is done with known pattern(i.e. data-aided) in sync word. But the sync word is changing in each of the transmit time slot.
The foregoing description of the invention has been set merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the substance of the invention may occur to person skilled in the art, the invention should be construed to include everything within the scope of the invention.
,CLAIMS:We Claim:

1. A method of digitally modulated baseband data protection in MF-TDMA return channel satellite communication comprising:
a) an interactive satellite network consists of multiple terminals connected to a centralized hub under an MF-TDMA system, where each node is transmitting under an allocated time frame in the time-Frequency plane, where each frame is constructed using Bandwidth Time Units (BTU) as the basic building block;
b) a multi-channel receiver includes multiple receiver chains of RF, IF and ADC paths;
wherein N number of terminals in a one MF-TDMA channel, where each terminal bandwidth and time slot in which the terminals send their respective baseband data frame to form a super-frame.
2. The method of digitally modulated baseband data protection in MF-TDMA return channel satellite communication as claimed in claim 1, wherein a PDU packets 1 are read from return link encaptulation (RLE) encoder to form FEC encoder frame 2 frame which is sufficient for formation of one bandwidth-time-unit(BTU).
3. The method of digitally modulated baseband data protection in MF-TDMA return channel satellite communication as claimed in claim 1, wherein a clock buffer 3 generates synchronous clocks for the complete one terminal system. Transmit enable (Tx enable) 6 open the window for transmit frame in its assigned time slot from supper frame, where the frame timer 4 generate clock pulse for gold code 5, where in each time slot, the gold code generates a new code for sync word.
4. The method of digitally modulated baseband data protection in MF-TDMA return channel satellite communication as claimed in claim 1, wherein the TDMA frame 7 consist of preamble, Sync word, terminal transmiter ID(Tx-ID), Payload and End-of-frame(EoF) symbols. Sync word is the K symbols of generated by Gold code and it is changing in every time slot of transmit frame.

5. The method of digitally modulated baseband data protection in MF-TDMA return channel satellite communication as claimed in claim 1, wherein a digital to analog converter (DAC) 9 provides clock for digital modulator which is generating RF signal.
6. The method of digitally modulated baseband data protection in MF-TDMA return channel satellite communication as claimed in claim 1, wherein a RF channelizer block 11 segregates the received return channels, where RF channelizer segregate M return channels of MF-TDMA satellite network, where each channel is down converted using complex multiplier 12 by using frequency synthesizer 13 to baseband IQ signal.
7. The method of digitally modulated baseband data protection in MF-TDMA return channel satellite communication as claimed in claim 1, wherein a demodulator block demodulates the baseband data and correlates with data-aided technique by using known sync word which is provided by 13 sync word generator.
8. The method of digitally modulated baseband data protection in MF-TDMA return channel satellite communication as claimed in claim 1, wherein the watch-dog timer 19 have the timing record of frame duration and frame repetition in each supper frame timing, where an initial sync word is known for remote transmitter and HUB receiver, where as soon as end-of-frame(EoF) 16 is detected, it generates the pulse for new sync word generation which is using the Gold codes, where in any case, EoF detection is failed, then watch-dog timer will provide the pulse for new SWG word.
9. The method of digitally modulated baseband data protection in MF-TDMA return channel satellite communication as claimed in claim 1, wherein initial sync word 22 is set for data-aided correlation, where If initial sync word is not detected, then the receiver remains in waiting state, whereas soon as sync word is detected, the data boundary is detected.