MXPA98001459A - Method and system to provide dpsk-psk unified signaling for satellite communications based on c - Google Patents

Abstract

A method and system for multi-user communications in a satellite network based on CDMA. An uplink RF signal containing a coded user message that has been differentially coded by phase and propagated using a Walsh function and a sequence of pseudorandom numbers (PN) for the uplink is received by a satellite receiver. The received uplink RF signal is demodulated by quadrature non-coherently and then agglutinated using the uplink PN sequence and the Walsh function. The differential phase signal containing the coded user message is regenerated on board the satellite by phase comparison and switched to a selected downlink transmitter. The quadrature components of the differential phase signal are then reprogrammed using a Walsh function and a PN sequence for the downlink, followed by quadrature modulation for transmission to a terrestrial receiver. The received downlink RF signal is demodulated by coherently and repropagated quadrature using the Pn sequence and the Walsh function for the downlink. The downlink carrier phase originating from the uplink differential phase is regenerated from the agglutinated quadrature phase band components and, consequently, the coded user message is detected and decoded

Description

METHOD AND SYSTEM TO PROVIDE UNIFIED DPSK-PSK SIGNALING FOR CDMA-BASED SATELLITE COMMUNICATIONS FIELD OF THE INVENTION The present invention relates to the field of telecommunications. More particularly, the present invention relates to a method and system for satellite communications based on CDMA.

BACKGROUND OF THE INVENTION Code Division Multiple Access (CDMA) is a more effective multiple access platform for terrestrial wireless networks than Division Multiple Access Time (TDMA) or Frequency Division Multiple Access (FDMA) mainly because the CDMA provides a higher frequency reuse efficiency by reusing the same frequency bands in geographically close cells. The higher frequency reuse efficiency provided by the CDMA is also an advantage for satellite communications. However, although most conventional satellite networks are based on either FDMA or TDMA, the recently proposed CDMA satellite networks are largely flexible in nature, REF: 25468 that the processing or commutation of the base band occurs on board the satellite. The operation of the system can be improved in terms of the quality and processing and switching capacity on board the satellite. However, unlike TDMA or FDMA methods, a conventional CDMA method used on board a regenerative satellite requires that different user signals be separated from on-board processing and switching. Uplink demodulation can be used for on-board baseband processing and switching, but coherent demodulation requires a complex equipment implementation, i.e. the adjustment of the carrier phase is required for each individual user signal, the which is restricted on a satellite by the limited available energy. What is needed is a way to provide CDMA communications in a satellite network without requiring coherent demodulation in the uplink reception so that on-board processing and switching of the satellite can be carried out conveniently.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides CDMA transmission of multiple point signals to multiple points across a satellite without requiring coherent demodulation for an uplink receiver in a satellite, and while allowing the processing of the baseband, complete or marginal, and switching on board the satellite. The advantages of the present invention are provided by a method and system that group user message bits (coded) into successive groups in a land based transmitter, then generate a differential phase for each group of message bits plotting each group of message bits over a predetermined PSK constellation. An absolute phase is generated for each group of message bits by arming the differential phase for each group of message bits to the absolute phase for the group of preceding message bits. The signal of the absolute phase is the phase encoded for an uplink RF carrier that forms an uplink RF signal. The RF signal ^ is propagated using an uplink user Walsh function and an uplink beam code sequence, which is transmitted to a satellite that is part of a satellite communication network. The RF signal is received on the satellite and the demodulated non-coherent quadrature signals generate quadrature baseband signals. Next, the quadrature baseband signals are agglutinated using the uplink beam code sequence the uplink user Walsh function. The successive blocks of the agglutinated baseband signals are compared by phase to extract the differential phase signals that carry the user message (encoded). Then, the differential phase signal is switched to a transmitter associated with an appropriate downlink destination path. Two quadrature phase signals of the switched differential phase signal are generated and propagated using the downlink user Walsh function and a downlink beam code sequence, followed by the low pass filtering to form the spectrum of baseband. In this step, propagated quadrature baseband components are printed or edited on the components of the downlink quadrature carrier and transmitted to a ground terminal for which the user attempted the message. The RF signal is received at the ground based receiver, and is coheratively demodulated quadrature into quadrature phase components. The quadrature phase components are propagated using the downlink beam code sequence and the downlink user Walsh function to extract the downlink phase signal. The extracted phase signal is the uplink differential phase signal corrupted by noise and interference in both the uplink and the downlink. The extracted phase signal is used to retrieve the user's message.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention is illustrated by way of example and without limitation in the accompanying figures, in which similar numerical references indicate similar elements and in which: Figure 1 is a block diagram showing the basic functional elements of a uplink transmitter from ground to satellite according to the present invention; Figure 2 is a block diagram showing the basic functional elements of the earth-to-satellite uplink receiver according to the present invention; Figure 3 is a block diagram showing the basic functional elements of a satellite downlink transmitter to ground according to the present invention; and Figure 4 is a block diagram showing the basic functional elements of a satellite downlink receiver to ground according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed primarily to CDMA satellite communication systems and the transmission of CDMA signals from a terrestrial transmission station, through a satellite and back to a terrestrial receiving station without the need for coherent signal demodulation. uplink in the satellite. The present invention facilitates processing and on-board switching of the satellite by providing a simple mechanism for demodulating and separating the individual signals transmitted on an uplink through the same CDMA carrier. The CDMA communication links are effectively improved because the noise and interference that corrupt the uplink signals are not amplified on the satellite, but are suppressed on the satellite. Decoding and recoding of the channel on the satellite can be done to further reduce the BER (Bit Error Percentage) of the uplink. The differential phases of the uplink signals are regenerated by means of a satellite receiver, switched, and sent to the receiver of the appropriate ground station. The detection of downlink transmissions in the ground station is by coherent PSK techniques because the receiver of the ground station can conveniently include the components to adjust the carrier phases of a received signal based on the singularity of the phase of the downlink signal received. In summary, the uplink signaling, on-board processing of the satellite and downlink signaling are each optimized by the present invention. The present invention establishes that a differential PSK technique for CDMA networks is applied to the uplink. An absolute phase carrier for a current (coded) information symbol is determined from the sum of the differential phase corresponding to the current symbol of the absolute phase of the preceding symbol. A conventional PSK signal is then generated by the absolute phase signal and is propagated by a Walsh function that identifies the uplink emitter. Subsequently, the signal is propagated by a sequence of pseudo-random numbers (PN) that identifies a particular satellite beam that covers the uplink emitter. The signal is then amplified in energy for the transmission of the uplink. Uplink reception in a satellite essentially reverses those steps to extract and regenerate a user signal, which is transported in a differential phase form, without channel decoding. No estimate of the carrier phase on the satellite is required for each individual transmitter, and the downward conversion of the frequency to the components of the baseband signal can be performed collectively for all user signals that share the same CDMA carrier. A regenerated differential phase symbol is switched to an appropriate beam transmitter, as indicated by the system, for downlink transmissions to an intended destination. Adjustment or tracking of the phase is easily achieved in a terrestrial receiver, so that downlink transmission is completed by coherent PSK demodulation in the terrestrial receiver. The decoding of the channel is then applied to recover the sender message bits originating from an uplink. Figure 1 is a block diagram showing the basic functional elements of an earth-to-satellite uplink transmitter using differential PSK signaling in a Direct Sequence Code Multiple Address Access Network (DS-CDMA) according to to the present invention. Alternatively, the transmitter of Figure 1 (and the rest of the system shown in Figures 2-4) may be part of a terrestrial wireless network, such as a cellular network or a PCS network. In Figure 1, the information bits forming a user message are encoded, such as by the trellis coder, before plotting the PSK on a ground based transmitter. A bit / symbol interleaver can be employed in a well-known manner either before or after the tracing of the symbols for rigorous or flexible decoding. The encoded information bits are plotted by the MPSK tracer 11 at the signal points in a predetermined PSK constellation in a well-known manner. The resulting phase of each group of coded information bits (ie, of each coded symbols) is treated as a differential phase? Fu (1 (n) .An absolute phase fu (1 (n) for group n of bits of encoded information is derived by adding the differential phase? fu (I (n) for group n in a well-known manner to the value of the absolute phase? fu (n) for the preceding group n-1 by a differential phase encoder 12. The phase and quadrature components of the absolute phase signal are then generated.The phase and quadrature components of the absolute phase signal FU (L) (n) are printed and not edited on the quadrature components of a carrier. RF that has the desired carrier frequency for the uplink by using a standard PSK modulator 13. After PSK modulation, the RF signal propagates in a well-known way at 14 using a Walsh function wu (il ( t) assigned to the user for the uplink by the system a when establishing the call. A sequence of PN bu (t) associated with, eg, a satellite beam for the uplink, is used to further propagate the signal modulated at 15 in a well-known manner to generate a propagated signal su (l1 (t) before of the RF transmission at 16. The RF amplification can be applied to generate a desired transmitted energy before feeding the signal to a transmission antenna Figure 2 is a block diagram showing the basic functional elements of a link receiver upstream using differential PSK signaling in a DS-CDMA network according to the present invention In the on-board uplink receiver, for example, an RF signal received by the satellite ru (t) is converted downwardly to quadrature not coherently to a quadrature baseband signal, and then agglutinated by the PN sequence and the Walsh function used in the transmitter for propagation; in this way the signal of the user's message is extracted from other user signals that share the same CDMA channel. A phase comparator is used to calculate the phase difference between two consecutive docker outputs for on-board switching. The phase difference calculated between two consecutive agglutinators produces the user's message to the bearers. In Figure 2, after the appropriate RF filtering and amplification, a received RF signal is converted downward to a baseband signal by non-coherent quadrature demodulation in 21a and 21b, and low pass filtering in 22a and 22b. A message signal that is intended to be for a particular user is extracted from the demodulated quadrature and phase components by first propagating in a well-known manner using the beam code sequence bu (t) for the user at 23a and 23b, and then agglutinate using the Walsh function of the user u (1) (t) in 24a and 24b and an integration and emptying process in 25a and 25b. For uplink reception, downward conversion and agglutination of the beam code can be performed collectively for all received user signals associated with the same CDMA bearer and the same beam. The quadrature outputs of the integrator 25a and 25b are compared by phase differentially in a well-known manner at 27 using a period delay of the symbol T 26 to produce a differential phase signal containing the desired message information. The resulting differential phase signal is then switched in a well-known manner on board the satellite to be transmitted to an appropriate downlink. After being properly switched, the differential phase symbols regenerated in the satellite receiver (assuming there is no channel decoding) are transmitted to ground destinations to decode the transmitter information. Figure 3 is a block diagram showing the basic functional elements of a satellite downlink transmitter to ground in a CDMA network according to the present invention. The two quadrature phase components of the switched differential phase symbols are divided by the Walsh function d l (t) assigned to the user for the downlink when establishing the call at 31a and 31b. Similar signal components from other calls that are part of the downlink are summed up in a well-known way at 32a and 32b. At 33a and 33b, the signals are propagated using the PN sequence bd (t) for a downlink beam and filtered at 34a and 34b to form the baseband spectrum. The propagated quadrature phase signals are respectively printed or edited on the quadrature components of an RF carrier having a desired carrier frequency for the downlink. The resulting RF signal is transmitted to the destination on the appropriate ground. Although this processing can be carried out individually for each signal of the transmitter, the present invention allows the propagation of the beam code and the quadrature modulation for the downlink transmission to be carried out collectively combining all the signals to be transmitted in the same link beam descending and using the same carrier.

Figure 4 is a block diagram showing the basic functional elements of a satellite downlink receiver to ground in a CDMA network according to the present inven. In the downlink receiver, the received RF signal is converted in a downward manner to coherent quadrature to quadrature baseband signals, and is then propagated by the sequence of the PN code and the Walsh function used in the satellite transmitter for propagation, thereby extracting a desired user message signal from other user signals that share the same CDMA channel. A phase comparator is used to calculate the carrier phase of the downlink RF signal for message detection, the downlink carrier phase is the differel phase of the uplink corrupted by noise and interference in both the uplink and the downlink. the downlink. In Figure 4, after appropriate RF filtering and amplification, a received RF signal rd (1, (t) is downconverted to baseband signals by coherent quadrature demodulation at 41a and 41b, and filtering from low pass at 42a and 42b A message signal is extracted which is intended to be for a particular user of the demodulated quadrature phase components by first propagating in a well known manner using the beam code sequence b (t) for the user at 43a and 43b, and then propagating using the Walsh function of the user wd (1) (t) at 44a and 44b and an integration and emptying process at 45a and 45b.The quadrature output of the integrators 45a and 45b are used then for the evaluation of the phase in a well-known way at 46 to produce the downlink carrier phase, which is the uplink differel phase corrupted by noise and interference containing the information of the desired message. When bit / symbol intercalation is used in the terrestrial transmitter, a bit / symbol deinterleaver is used in the terrestrial receiver in a well known manner according to the interleaved position. A channel 47 decoder, such as a Viterbi decoder that provides a rigorous or flexible decision, retrieves the user's message bits. Although the present inven has been described in relation to the illustrated embodiments, it should be appreciated and understood that modifications can be made without departing from the spirit and scope of the inven. It is noted that in relation to this date, the best method known to the applicant to carry out the aforemened inven, is that which is clear from the present description of the inven. Having described the inven as above, property is claimed as contained in the following:

Claims (30)

1. A method for signaling in a satellite communications network based on CDMA, characterized in that it comprises the steps of: receiving an RF signal over an uplink, the RF signal contains a coded user message that has been encoded by phase in a manner differential, and propagated using two code sequences associated with the uplink; demodulate by quadrature non-coherently the RF signal into quadrature baseband components; agglutinate the quadrature baseband components using two code sequences associated with the uplink; comparing consecutive block phases of the agglutinated quadrature baseband components to regenerate the differential phase signal containing the coded user message; switching the regenerated differential phase signal to a selected downlink transmitter; repropaging the quadrature baseband components of the differential phase signal using two code sequences associated with a downlink; and printing or editing the re-paired quadrature baseband components of the differential phase signal on the quadrature components of a downlink carrier to form a downlink RF signal.

2. The method according to claim 1, characterized in that it further comprises the step of transmitting the downlink RF signal.

3. The method according to claim 1, characterized in that the RF signal received on the uplink is received on a satellite and the downlink RF signal is transmitted from a satellite transmitter.

4. The method according to claim 1, characterized in that the two code sequences associated with the uplink include a Walsh function and a sequence of pseudorandom beam numbers for the uplink; and wherein the two code sequences associated with the downlink include a user Walsh function and a sequence of pseudorandom beam numbers for the downlink.

5. The method according to claim 1, characterized in that it further comprises the steps of: grouping the coded user message bits into successive groups in an uplink transmitter; generating a differential phase for each group of message bits by plotting each group of message bits on a predetermined PSK constellation; generating an absolute phase for each group of message bits by adding the differential phase for a group of current message bits to an absolute phase for a group of message bits that precedes the group of current message bits; modulating by phase an uplink carrier using the absolute phase signal to form an RF signal; propagate the RF signal using two code sequences associated with the uplink; and transmit the propagated RF signal over the uplink.

6. The method according to claim 5, characterized in that the uplink RF signal is transmitted from a ground-based transmitter and received in a satellite receiver.

7. The method according to claim 5, characterized in that the two code sequences associated with the uplink include a user Walsh function and a sequence of pseudorandom beam numbers for the uplink.

8. The method in accordance with the claim 1, characterized in that in addition to the steps of: receiving the downlink RF signal, the link RF signal contains the user message that has been regenerated, repropagating and printing on the quadrature components the downlink RF signal; coherently demodulating the downlink RF signal into quadrature baseband components; agglutinate the quadrature baseband components using the two code sequences associated with the downlink; evaluating a downlink carrier phase of the agglutinated quadrature baseband components; and retrieve the user's message.

9. The method according to claim 8, characterized in that the downlink RF signal is transmitted from a satellite transmitter and received in a ground-based receiver.

10. The method according to claim 8, characterized in that the two code sequences associated with the downlink include a user Walsh function and a sequence of pseudorandom beam numbers for the downlink.

11. A method for signaling in a satellite network based on CDMA, characterized in that it comprises the steps of: grouping the encoded user message bits into successive groups in an uplink transmitter; generating a differential phase for each group of message bits by plotting each group of message bits on a predetermined PSK constellation; generating an absolute phase for each group of message bits by adding the differential phase for a group of current message bits to an absolute phase for a group of message bits that precedes the group of current message bits; modulating per phase an uplink carrier using the current absolute phase to form an RF signal; propagate the RF signal using two code sequences associated with the uplink; and transmit the propagated RF signal over the uplink.

12. The method according to claim 11, characterized in that the uplink FR signal is transmitted from a ground-based transmitter and received at a satellite receiver.

13. The method according to claim 11, characterized in that the two code sequences associated with the uplink include a user Walsh function and a sequence of pseudorandom beam numbers for the uplink.

14. A method for signaling in a satellite network based on CDMA, characterized in that it comprises the steps of: receiving a downlink RF signal, the downlink RF signal containing a user message that has been regenerated, repropagating and printing on the quadrature components of the downlink RF signal; coherently demodulating the downlink RF signal in quadrature baseband components; agglutinate quadrature baseband components using two code sequences associated with the downlink; evaluating a downlink carrier phase of the agglutinated quadrature baseband components; and retrieve the user's message.

15. The method in accordance with the claim 14, characterized in that the downlink RF signal is transmitted from a satellite transmitter and received in a ground based receiver.

16. The method in accordance with the claim 14, characterized in that the two code sequences associated with the downlink include a user Walsh function and a sequence of pseudorandom beam numbers for the downlink.

17. A satellite communication system based on CDMA, characterized in that it comprises: an RF receiver for receiving an RF signal on an uplink, the RF signal contains a coded user message that has been differentially coded by phase, and propagated using two code sequences associated with the uplink; a non-coherent quadrature modulator for quadrature non-coherently demodulating the RF signal into quadrature baseband components; a spread spectrum agglutinator for agglutinating the quadrature baseband components using two code sequences associated with the uplink; a phase comparator for comparing consecutive blocks of phases of the agglutinated quadrature baseband components and regenerating the differential phase signal of the coded user message; a switch for switching the regenerated differential phase signal to a selected downlink transmitter; a propagation spectrum propagator for repropagating the quadrature baseband components of the differential phase signal using two code sequences associated with a downlink; and a quadrature modulator for modulating a downlink carrier using the quadrature baseband components repropagated from the differential phase signal to form a downlink RF signal.

18. The CDMA-based satellite communications system according to claim 17, characterized in that it further comprises a satellite transmitter for transmitting the downlink RF signal to a ground-based receiver.

19. The CDMA-based satellite communications system according to claim 17, characterized in that the CDMA-based communication system is a satellite tranceptor.

20. The CDMA-based satellite communications system according to claim 17, characterized in that it further comprises: a PSK plotter for tracing the user message bits encoded in differential phases, the coded user message bits are grouped into blocks of message bits before being plotted by phase differentially; a differential phase encoder for generating a current absolute phase for each block of message bits by adding the differential phase for a current block of message bits to an absolute phase for a block of message bits preceding the current block of message bits; a PSK modulator for phase modulating an uplink carrier using the current absolute phase to form an RF signal; a propagation spectrum propagator for propagating the RF signal using the two code sequences associated with the uplink; and a transmitter for transmitting the RF signal propagated over the uplink.

21. The satellite communication system based on CDMA according to claim 20, characterized in that the RF signal for the uplink is transmitted by a ground-based transmitter.

22. The CDMA-based satellite communication system according to claim 20, characterized in that the two code sequences associated with the uplink include a user Walsh function and a sequence of pseudorandom beam numbers for the uplink, and in where the two code sequences associated with the downlink include a user Walsh function and a sequence of pseudo-random beam numbers for the downlink.

23. The CDMA-based satellite communications system according to claim 17, characterized in that it further comprises: a downlink receiver for receiving the downlink RF signal; a coherent quadrature demodulator for consistently quadrature demodulating the downlink RF signal into quadrature baseband components; a spread spectrum agglutinator for agglutinating the quadrature baseband components using two code sequences associated with the downlink; a phase comparator for evaluating a downlink carrier phase of the agglutinated quadrature baseband components; and a channel decoder for detecting and decoding the coded user's message.

24. The satellite communication system based on CDMA according to claim 23, characterized in that the downlink RF signal is received by a receiver based on ground.

25. A satellite communication system based on CDMA, characterized in that it comprises: a PSK plotter for tracing the user message bits encoded in differential phases, the encoded user message bits are grouped into blocks of message bits before being plotted by differentially phase; a differential phase encoder for generating a current absolute phase for each block of message bits by adding the differential phase for a current block of message bits to an absolute phase for a block of message bits preceding the current block of message bits; a PSK modulator for modulating by phase an uplink carrier using the current absolute phase to form an RF signal; a propagation spectrum propagator for propagating the RF signal using two code sequences associated with the uplink; and a transmitter for transmitting the RF signal propagated over the uplink.

26. The satellite communication system based on CDMA according to claim 25, characterized in that the RF signal for the uplink is transmitted by a ground-based transmitter.

27. The CDMA-based satellite communications system according to claim 25, characterized in that the two code sequences associated with the uplink include a user Walsh function and a sequence of pseudorandom beam numbers for the uplink.

28. The satellite communication system based on CDMA, characterized in that it comprises: a downlink receiver for receiving a downlink RF signal; a coherent quadrature demodulator for consistently quadrature demodulating the downlink RF signal into quadrature baseband components; a spread spectrum agglutinator for agglutinating the quadrature baseband components using two code sequences associated with the downlink; a phase comparator for evaluating a downlink carrier phase of the agglutinated quadrature baseband components; and a channel decoder for detecting and decoding the coded user's message.

29. The CDMA-based satellite communications system according to claim 28, characterized in that the downlink RF signal is received by a receiver based on ground.

30. The CDMA-based satellite communications system according to claim 28, characterized in that the two code sequences associated with the downlink include a user Walsh function and a sequence of pseudorandom beam numbers for the downlink. SUMMARY OF THE INVENTION A method and system for multi-user communications in a satellite network based on CDMA. An uplink RF signal containing a coded user message that has been differentially coded by phase and propagated using a Walsh function and a sequence of pseudorandom numbers (PN) for the uplink is received by a satellite receiver. The received uplink RF signal is demodulated by quadrature non-coherently and then agglutinated using the uplink PN sequence and the Walsh function. The differential phase signal containing the coded user message is regenerated on board the satellite by phase comparison and switched to a selected downlink transmitter. The quadrature components of the differential phase signal are then reprogrammed using a Walsh function and a PN sequence for the downlink, followed by quadrature modulation for transmission to a terrestrial receiver. The received downlink RF signal is demodulated by coherent and repropagated quadrature using the PN sequence and the Walsh function for the downlink. The downlink carrier phase originating from the uplink differential phase is regenerated from the agglutinated quadrature baseband components and, consequently, the coded user message is detected and decoded.