MXPA98001457A - Psk differential signaling in multiple access networks of cod division - Google Patents

Abstract

A method and system for detecting a user signal in a CDMA network. The user message bits (encoded) are grouped into successive groups. A differential phase is generated for each group of message bits by tracing each group of message bits over a predetermined PSK constellation. An absolute phase is generated for each group of message bits based on the differential phase for the group of current message bits and the absolute phase for the group of preceding message bits. The absolute phase signal is the phase encoded to an RF carrier to form an RF signal. The RF signal is broadcast using two code sequences and the broadcast RF signal is transmitted. In the receiver, the RF signal is received and demodulated non-coherently. The demodulated RF signal is agglutinated using the code sequences. The successive blocks of the agglutinated, demodulated RF signal are compared by phase by extracting the differential phase signal containing the user's message (codified).

Description

PSK Differential Signaling in Code Division Multiple Access Networks 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 Code Division Multiple Access (CDMA) communications.

BACKGROUND OF THE INVENTION In the current Code Division Multiple Access (CDMA) systems, both coherent and non-coherent demodulation techniques are used. The coherent demodulation techniques require an accurate carrier phase estimation of a received signal, which in turn needs a pilot signal or a closed phase circuit. Both requirements are not practical, especially for an uplink to a satellite or a base station. The non-coherent orthogonal demodulation techniques require extensive correlation and comparison calculations for symbol detection, resulting in high implementation complexity. Additionally, the non-coherent demodulation techniques provide a REF: 25467 poor performance compared to consistent methods. When the DS-CDMA (Direct Sequence Code Division Multiple Access) signals are coherently demodulated, precise phase tracking of the individual phases is required. When DS-CDMA signals are detected via non-coherent orthogonal demodulation, an operating penalty is paid, which also implies a complex implementation. What is needed is a simple and powerful signaling scheme for CDMA-based communications that reduces the complexity of implementation and improves the operation of the system at the same time.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a method and a system for demodulating signals from multiple points to a point and from a point to multiple points transmitted in a DS-CDMA network without requiring an estimate of the carrier phase. In addition, the present invention provides a simple detection technique for processing demodulated signals and has a better performance than conventional non-coherent techniques.

The advantages of the present invention are provided by a method and a system in which the user message bits (encoded) are grouped into successive groups. A differential phase signal is generated for each group of message bits by plotting each group of message bits on a predetermined PSK constellation. An absolute phase signal is generated for each group of message bits by adding the differential phase in groups of current message bits to the absolute phase signal for the group of preceding message bits. The PSK modulation is invoked with the absolute phase for each group of message bits to form an RF signal. The RF signal is broadcast using two code sequences and then transmitted. In the receiver, the RF signal is demodulated by non-coherent quadrature and agglutinates using the code sequences. Successive blocks of the agglutinated, demodulated RF signal are compared by phase to extract the differential phase containing the user's message (encoded). Finally, the user's message is retrieved.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be illustrated by way of example and without limitation in the accompanying figures in which similar numerical references indicate similar elements, in which: Figure 1 is a block diagram showing the basic functional elements of a transmitter that uses differential PSK signaling in a DS-CDMA network according to the present invention; and Figure 2 is a block diagram showing the basic functional elements of a receiver using differential PSK signaling in a DS-CDMA network according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention simplifies RF demodulation and the subsequent detection process for CDMA communication systems and, consequently, reduces the complexity of implementation and energy requirements that employ critical restrictions on some applications.

For example, in a wireless communication system, the present invention greatly facilitates frequency conversion and baseband processing in a base station in a cellular or PCS network, or on board a satellite in a space system, so that less energy is required since the present invention does not require a conventional prediction of the carrier phase for each user signal received in an uplink. In addition, upconversion of a received RF signal to a baseband signal is possible for all user signals transmitted on the same bearer. The corresponding equipment and power reductions are also achieved in a user terminal for a downlink, which is significant, especially for handsets or portable communication devices. In addition, the present invention provides an effective mechanism for separating different uplink signals for on-board processing of a satellite and / or downlink switching. Figure 1 is a block diagram showing the basic functional elements of a transmitter using differential PSK signaling in a DS-CDMA network, for example, as part of a terrestrial wireless network, such as a cellular communications network and a PCS , or from a satellite. The groups of information bits that form a user message of an application are encoded, such as by a trellis encoding, before being plotted at the signal points in a chosen PSK constellation in a well-known manner. A bit / symbol interleaver can be used either before or after the tracing of the symbol for strict or flexible decoding. The encoded information bits are plotted by the MPSK tracer 11 in a differential phase signal? F (1) (n). The resulting phase of each group of coded information bits is treated as a differential phase. An absolute phase f (1) (n) is derived for each signaling interval by giving the differential phase? F (1) (n) for the current signaling interval to the absolute phase value f (1) (nl) for the interval of preceding signaling by a differential phase encoder 12 in a well-known manner. The absolute phase f (1) (n) is printed on a carrier having a desired carrier frequency using a standard PSK modulator 13. After modulation of the carrier phase, the modulated signal is broadcast in a well-known manner at 14 using a Walsh function assigned to the user by the system. Next, a group code sequence associated with, for example, a terrestrial base station or a satellite beam, is used to further diffuse the signal modulated at 15 in a well-known manner prior to 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 receiver using differential PSK signaling in a DS-CDMA network, for example, as part of a terrestrial wireless network, such as a cellular network and a PCS, or a satellite communications network. In the receiver, a received RF signal converted downwardly non-coherently to a baseband signal, and then broadcast by the code sequences corresponding to the code sequences used in the transmitter for broadcast and, therefore, extracting a desired user message signal from other user signals that share the same channel. CDMA. A phase comparator is used which calculates the phase difference between two consecutive agglutinated outputs to detect the user message signal, followed by a channel decoder. In Figure 2, after appropriate RF filtering and amplification, a received RF signal is converted down to a baseband signal by non-coherent quadrature demodulation in 21a and 21b, and low pass filtering in 22a and 22b. A message signal intended to be for a particular user is extracted from the quadrature phase components of the message signal by first aggregating in a well-known manner using the group code for the user at 23, and then agglutinating using the function of Walsh of the user in 24 and an integration and emptying process in 25a and 25b. For the reception of the uplink, the downconversion and the agglutination of the group code can be performed collectively for all user signals received affiliated to a group. The outputs of the integrator 25a and 25b are then compared by differential phase in a well-known way at 27 using a T-delay at 26 to produce a differential phase containing the desired information. When the bit / symbol interleaver is used in the transmitter, the bit / symbol deinterleaver is employed in a well-known manner according to the position of the interleaver. A channel decoder 28, such as a Viterbi decoder that provides flexible or stringent decisions, retrieves the user's message signal. The present invention has been described in relation to the illustrated embodiments, it should be appreciated and understood that modifications can be made without departing from the true spirit and scope of the invention.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following:

Claims (39)

1. A method for generating a user signal in a CDMA network, characterized in that it comprises the steps of: grouping the bits of a user message into groups of successive bits; 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 current group of bits to an absolute phase for a group of bits that precedes the current group of bits; effect the PSK modulation using the absolute phase to form an RF signal; broadcast the RF signal using two code sequences; and transmit the RF signal.

2. The method in accordance with the claim 1, characterized in that the user message bits are encoded.

3. The method according to claim 1, characterized in that the two code sequences include a pseudorandom number sequence associated with a group of users.

4. The method according to claim 1, characterized in that the two code sequences include a Walsh function assigned to a user of a group of users.

5. The method according to claim 1, characterized in that it further comprises the steps of: receiving the RF signal; demodulate by quadrature not coherently the received RF signal; agglutinate the demodulated RF signal using the code sequences; comparing the phases of successive blocks of the agglutinated, demodulated RF signal to extract the differential phase containing the user's message; and retrieve the user's message.

6. The method according to claim 5, characterized in that the user's message bits are encoded.

7. The method according to claim 5, characterized in that the two code sequences include a pseudorandom number sequence associated with a group of users.

8. The method according to claim 5, characterized in that the two code sequences include a Walsh function assigned to a user of a group of users.

9. The method according to claim 5, characterized in that the RF signal is transmitted in a CDMA communication network.

10. The method in accordance with the claim 9, characterized in that the CDMA communication network is a satellite communication network.

11. The method according to claim 9, characterized in that the CDMA communication network is a cellular network.

12. The method according to claim 9, characterized in that the CDMA communication network is a PCS network.

13. A method for detecting a user signal in a CDMA network, characterized in that it comprises the steps of: receiving a CDMA signal modulated by PSK, the received signal contains a user message that has been grouped into blocks of bits, each block of bits is differentially encoded by phase and diffused using two code sequences; demodulate by quadrature not coherently the received signal; agglutinate the demodulated signal using the code sequences; comparing the phases of successive blocks of the agglutinated or joined signal, demodulated, to extract the differential phase that contains the message of the user; and retrieve the user's message.

14. The method according to claim 13, characterized in that the user's message bits are encoded.

15. The method according to claim 13, characterized in that the two code sequences include a pseudorandom number sequence associated with a group of users.

16. The method according to claim 13, characterized in that the two code sequences include a Walsh function assigned to a user of a group of users.

17. The method according to claim 13, characterized in that the RF signal is received in a CDMA communication network.

18. The method in accordance with the claim 17, characterized in that the CDMA communication network is a satellite communications network.

19. The method according to claim 17, characterized in that the CDMA communication network is a cellular network.

20. The method according to claim 17, characterized in that the CDMA communication network is a PCS network.

21. A CDMA communication system, characterized in that it comprises: a PSK plotter for tracing groups of user message bits in differential phases according to a predetermined PSK constellation; a differential phase encoder for generating a current absolute phase for each group of message bits based on a sum of the differential phase for a current group and an absolute phase for a group of message bits that precedes the current group of bits of message; a PSK modulator for modulating by phase an RF carrier with the current absolute phase to form an RF signal; and a diffusion spectrum diffuser for spreading the RF signal using two code sequences.

22. The CDMA communication system according to claim 21, characterized in that the user message bits are encoded.

23. The CDMA communication system according to claim 21, characterized in that the two sequence codes include a pseudorandom number sequence associated with a group of users.

24. The CDMA communication system according to claim 21, characterized in that the two code sequences include a Walsh function assigned to a user of a group of users.

25. The CDMA communication system according to claim 21, characterized in that it further comprises a transmitter for transmitting the RF signal over a CDMA communication network.

26. The CDMA communication system according to claim 25, characterized in that it further comprises a receiver for receiving the RF signal; a non-coherent quadrature demodulator to demodulate the received RF signal; a diffusion spectrum agglutinator for agglutinating or pooling the demodulated RF signal using the code sequences; a differential phase comparator for generating a differential phase for each group of bits of the user message, the differential phase is a difference between an absolute phase for a current group of bits and an absolute phase for a group of bits that precedes the group of current bits; and a decoder for decoding each group of user message bits based on a corresponding differential phase.

27. The CDMA communication system according to claim 26, characterized in that the user message bits are encoded.

28. The CDMA communication system according to claim 26, characterized in that the two code sequences include a pseudorandom number sequence associated with a group of users.

29. The CDMA communication system according to claim 26, characterized in that the two code sequences include a Walsh function assigned to a user of a group of users.

30. The CDMA communication system according to claim 26, characterized in that the CDMA communication network is a satellite communications network.

31. The CDMA communication system according to claim 26, characterized in that the CDMA communication network is a cellular network.

32. The CDMA communication system according to claim 26, characterized in that the CDMA communication network is a PCS network.

33. A CDMA communications system, characterized in that it comprises: a receiver for receiving an RF signal over a CDMA communication network, the RF signal is a CDMA signal modulated by PSK containing a user message that has been grouped into blocks of bits , each block of bits is differentially coded by phase and diffused using two code sequences; a non-coherent quadrature demodulator to demodulate the received RF signal; a diffusion spectrum agglutinator for binding the demodulated RF signal using the code sequences; a differential phase comparator for generating a differential phase for each block of bits of the user message, the differential phase is a difference between an absolute phase for a current block of bits and an absolute phase for a block of bits preceding the block of bits. current bits; and a decoder for decoding each group of user message bits based on a corresponding differential phase.

34. The CDMA communication system according to claim 33, characterized in that the bits of the user message are encoded.

35. The CDMA communication system according to claim 33, characterized in that the two code sequences include a pseudorandom number sequence associated with a group of users.

36. The CDMA communication system according to claim 33, characterized in that the two code sequences include a Walsh function assigned to a user of a group of users.

37. The CDMA communication system according to claim 33, characterized in that the CDMA communication network is a satellite communication network.

38. The CDMA communication system according to claim 33, characterized in that the CDMA communication network is a cellular network.

39. The CDMA communication system according to claim 33, characterized in that the CDMA communication network is a PCS network.