Method and apparatus for bifurcating signal transmission over in-phase and quadrature phase spread spectrum communication channels

Claims

I claim:

1. A modulation system for modulating first and second information signals for transmission in a spread spectrum communication system to first and second system user, said communication system being operative at a predefined nominal data rate, said modulation system comprising:

a PN signal generator for generating in-phase pseudorandom noise (PN.sub.I) and quadrature phase pseudorandom noise (PN.sub.Q) signals of predetermined PN codes;

means for generating a first orthogonal function signal of a predefined length based on said nominal data rate;

a modulation network for combining said PN.sub.I signal with said first information signal and said first orthogonal function signal to provide an I modulation signal, and for combining said PN.sub.Q signal with said second information signal and said first orthogonal function signal to provide a Q modulation signal; and

a transmit modulator for modulating in-phase (I) and quadrature phase (Q) carrier signals of a predefined phase relationship with said I and Q modulation signals for transmission to said first and second system user, respectively.

2. The system of claim 1 wherein said modulation network includes a biphase modulator for modulating said first information signal with said PN.sub.I signal and with a first PN code sequence associated with said first system user, and for biphase modulating said second information signal with said PN.sub.Q signal and with a second PN code sequence different from said first PN code sequence signal.

3. The system of claim 1 wherein said means for generating said first orthogonal function signal includes means for selecting an orthogonal function from a set of orthogonal Walsh functions, and

means for deriving said first orthogonal function signal based on said selected orthogonal function.

4. A modulation system for modulating an information signal of an input data rate, said information signal being transmitted on in-phase (I) and quadrature phase (Q) channels of a spread spectrum communication system using a carrier signal and a replica of said carrier signal in phase quadrature therewith, said I and Q channels being disposed to operate at a predetermined nominal data rate independent of said input data rate, comprising:

a divider circuit for dividing said information signal into first and second portions, and for encoding said first and second portions into first and second encoded signals at said predetermined nominal rate for transmission to one or more intended recipient users over said I and Q channels;

means for generating an orthogonal function signal of a predefined length based upon said nominal data rate;

a PN signal generator for generating in-phase pseudorandom noise (PN.sub.I) and quadrature phase pseudorandom noise (PN.sub.Q) signals of predetermined PN codes;

a modulation network for combining said PN.sub.I signal with said first portion of said information signal and said orthogonal function signal to provide an I modulation signal, and for combining said PN.sub.Q signal with said second portion of said information signal and said orthogonal function signal to provide a Q modulation signal; and

a transmit modulator for modulating said carrier signal and said replica of said carrier signal with said I and Q modulation signals, respectively.

5. The system of claim 4 further including means for adding a timing control signal to said information signal, said timing control signal being indicative of signal propagation delay over said I and Q channels of said communication system.

6. The system of claim 4 wherein said modulation network includes a biphase modulator for modulating said I modulation signal with said PN.sub.I signal, and for biphase modulating said Q modulation signal with said PN.sub.Q signal.

7. A code division multiple access (CDMA) communication system for providing in-phase (I) and quadrature phase (Q) spread spectrum communication channels over which are respectively transmitted a first information signal and it second information signal different from said first information signal, comprising:

a PN generator for generating in-phase pseudorandom noise (PN.sub.I) and quadrature phase pseudorandom noise (PN.sub.Q)signals of predetermined PN codes;

means for generating an orthogonal function signal;

a modulation network for combining said PN.sub.I signal with said first information signal and said orthogonal function signal to provide an I modulation signal, and for combining said PN.sub.Q signal with said second information signal and said orthogonal function signal to provide a Q modulation signal;

a transmit modulator for modulating in-phase (I) and quadrature phase (Q) carrier signals of a predefined phase relationship with said I and Q modulation signals, and for transmitting said I and Q carrier signals over said I and Q communication channels, respectively; and

a receiver for producing an estimate of at least said first information signal in accordance with said I and Q modulated carrier signals received over said I and Q communication channels.

8. The communication system of claim 7 wherein said receiver further includes a demodulator for demodulating said I and Q modulated carrier signals received over said I and Q communication channels into intermediate received signals using said orthogonal function signal.

9. The communication system of claim 8 wherein said receiver further includes:

means for generating a first despreading signal by replicating said PN.sub.I signal, and

a first correlator for correlating said intermediate received signals using said first despreading signal in order to provide a first set of in-phase (I) and quadrature phase (Q) projection signals.

10. The communication system of claim 7 further including:

a pilot modulation network for combining said orthogonal function signal with a pilot signal in order to provide a modulated pilot signal, and

means for transmitting said modulated pilot signal over a pilot channel.

11. The communication system of claim 10 wherein said receiver further includes:

a demodulator for producing an estimate of said pilot carrier signal by demodulating, using said orthogonal function signal, said modulated pilot signal transmitted over said pilot channel, and

a first phase rotation circuit for generating said estimate of said information signal on the basis of said first set of said I and Q projections and said estimate of said pilot carrier signal.

12. The communication system of claim 11 wherein said receiver further includes:

means for generating a second despreading signal by replicating said PN.sub.Q signal, and

a second correlator for correlating said intermediate received signals using said second despreading signal in order to provide a second set of in-phase (I) and quadrature phase (Q) projection signals.

13. The communication system of claim 12 wherein said receiver further includes a second phase rotation circuit for generating an estimate of said second information signal on the basis of said second set of I and Q projections and said estimate of said transmitted pilot carrier signal.

14. The communication system of claim 11 wherein said receiver further includes means for delaying said first set of I and Q projection signals.

15. A method for transmitting first and second information signals respectively to first and second users in a spread spectrum communication system comprising the steps of:

generating in-phase pseudorandom noise (PN.sub.I) and quadrature phase pseudorandom noise (PN.sub.Q) signals of predetermined PN codes;

generating a first PN code sequence associated with said first user, and a second PN code sequence associated with said second user;

generating an orthogonal function signal of predefined length;

combining said PN.sub.I signal, said first PN code sequence and said orthogonal function signal with said first information signal to provide an I modulation signal, and combining said PN.sub.Q signal, said second PN code sequence and said orthogonal function signal with said second information signal to provide a Q modulation signal; and

modulating in-phase (I) and quadrature phase (Q) carrier signals of a predefined phase relationship with said I and Q modulation signals for transmission to said first and second users, respectively.

16. The method of claim 15 further including the steps of:

biphase modulating said I modulation signal with said PN.sub.I signal, and

biphase modulating said Q modulation signal with said PN.sub.Q signal.

17. The method of claim 16 wherein said step of generating an orthogonal function signal includes the steps of selecting an orthogonal function from a set of orthogonal Walsh functions, and deriving said orthogonal function signal based on said selected orthogonal function.

18. The method of claim 17 further including the step of transmitting said modulated I and Q carrier signals over I and Q communication channels, respectively.

19. A method for modulating an information signal at an input data rate to be transmitted on in-phase (I) and quadrature phase (Q) channels of a spread spectrum communication system using a carrier signal and a replica of said carrier signal in phase quadrature therewith, said I and Q channels being disposed to operate at a predetermined nominal data rate independent of said input data rate, comprising:

dividing said information signal into first and second portions for transmission to one or more intended recipient users over said I and Q channels;

generating an orthogonal function signal of a predefined length independent of said input data rate;

generating in-phase pseudorandom noise (PN.sub.I) and quadrature phase pseudorandom noise (PN.sub.Q) signals of predetermined PN codes;

combining said PN.sub.I signal with said first portion of said information signal and said orthogonal function signal to provide an I modulation signal, and combining said PN.sub.Q signal with said second portion of said information signal and said orthogonal function signal to provide a Q modulation signal; and

modulating said carrier signal and said replica of said carrier signal with said I and Q modulation signals, respectively.

20. The method of claim 19 further including the step of adding a timing control signal to said information signal, said timing control signal being indicative of signal propagation delay over said I and Q channels of said communication system.

21. The method of claim 20 further including the step of biphase modulating said I modulation signal with said PN.sub.I signal, and the step of biphase modulating said Q modulation signal with said PN.sub.Q signal.

22. In a code division multiple access (CDMA) communication system, a method for providing in-phase (I) and quadrature phase (Q) spread spectrum communication channels over which are transmitted a first information signal and a second information signal different from said first information signal, said method comprising the steps of:

generating in-phase pseudorandom noise (PN.sub.I) and quadrature phase pseudorandom noise (PN.sub.Q) signals of predetermined PN codes;

generating an orthogonal function signal;

combining said PN.sub.I signal with said first information signal and said orthogonal function signal to provide an I modulation signal, and combining said PN.sub.Q signal with said second information signal and said orthogonal function signal to provide a Q modulation signal;

modulating in-phase (I) and quadrature phase (Q) carrier signals of a predefined phase relationship with said I and Q modulation signals;

transmitting said I and Q carrier signals over said I and Q communication channels, respectively; and

producing an estimate of at least said first information signal in accordance with said I and Q modulated carrier signals received over said I and Q communication channels.

23. The method of claim 22 further including the step of demodulating said I and Q modulated carrier signals received over said I and Q communication channels into intermediate received signals using said orthogonal function signal.

24. The method of claim 23 further including the steps of:

generating a first despreading signal by replicating said PN.sub.I signal, and

correlating said intermediate received signals using said first despreading signal in order to provide a first set of in-phase (I) and quadrature phase (Q) projection signals.

25. The method of claim 22 further including the steps of:

combining said orthogonal function signal with a pilot signal in order to provide a modulated pilot signal, and

transmitting said modulated pilot signal over a pilot channel.

26. The method of claim 25 further including the steps of:

demodulating said modulated pilot signal transmitted over said pilot channel,

producing an estimate of said pilot signal transmitted over said pilot channel, and

generating said estimate of said first information signal on the basis of said first set of said I and Q projections and said estimate of said pilot carrier signal.

27. The method of claim 26 further including the steps of:

generating a second despreading signal by replicating said PN.sub.Q signal, and

correlating said intermediate received signals using said second despreading signal in order to provide a second set of in-phase (I) and quadrature phase (Q) projection signals.

28. The method of claim 27 further including the step of generating an estimate of said second information signal on the basis of said second set of I and Q projections and said estimate of said transmitted pilot carrier signal.

29. A modulation system for modulating first and second information signals for transmission in a spread spectrum communication system to first and second system users, said modulation system comprising:

a PN signal generator for generating in-phase pseudorandom noise (PN.sub.I) and quadrature phase pseudorandom noise (PN.sub.Q)signals of predetermined PN codes;

a code sequence generator for generating a first PN code sequence associated with said first system user, and for generating a second PN code sequence associated with said second system user;

an orthogonal function generator for generating a first orthogonal function signal of a predefined length;

a modulation network for combining said PN.sub.I signal, said first PN code sequence and said orthogonal function signal with said first information signal to provide an I modulation signal, and combining said PN.sub.Q signal, said second PN code sequence and said orthogonal function signal with said second information signal to provide a Q modulation signal; and

a transmit modulator for modulating in-phase (I) and quadrature phase (Q) carrier signals of a predefined phase relationship with said I and Q modulation signals for transmission to said first and second system users, respectively.

30. A method for modulating first and second information signals for transmission in a spread spectrum communication system to first and second system users, said method comprising the steps of:

generating in-phase pseudorandom noise (PN.sub.I) and quadrature phase pseudorandom noise (PN.sub.Q) signals of predetermined PN codes;

generating a first PN code sequence associated with said first system user, and generating a second PN code sequence associated with said second system user;

generating a first orthogonal function signal of a predefined length;

combining said PN.sub.I signal, said first PN code sequence and said orthogonal function signal with said first information signal to provide an I modulation signal, and combining said PN.sub.Q signal, said second PN code sequence and said orthogonal function signal with said second information signal to provide a Q modulation signal; and

modulating in-phase (I) and quadrature phase (Q) carrier signals of a predefined phase relationship with said I and Q modulation signals for transmission to said first and second system users, respectively.

31. A dual-mode modulation system for, during operation in a first mode, modulating first and second information signals for transmission in a spread spectrum communication system to first and second system users and for modulating, during operation in a second mode, a third information signal of an input data rate, said third information signal being transmitted on in-phase (I) and quadrature phase (Q) channels of the spread spectrum communication system using a carrier signal and a replica of said carrier signal in phase quadrature therewith, said dual-mode modulation system comprising:

a divider circuit for dividing, during operation in said second mode, said third information signal into first and second portions for transmission to one or more intended recipient users over said I and Q channels;

a PN signal generator for generating in-phase pseudorandom noise (PN.sub.I) and quadrature phase pseudorandom noise (PN.sub.Q) signals of predetermined PN codes;

an orthogonal function signal generator for generating a first orthogonal function signal of a predefined length based on a nominal data rate of said communication system;

a modulation network for combining said PN.sub.I signal with said first information signal and said first orthogonal function signal to provide an I modulation signal during operation in said first mode and for combining said PN.sub.I signal with said third information signal and said first orthogonal function signal to provide said I modulation signal during operation in said second mode, and for combining said PN.sub.Q signal with said second information signal and said first orthogonal function signal to provide a Q modulation signal during operation in said first mode and for combining said PN.sub.Q signal with said third information signal and said first orthogonal function signal to provide said Q modulation signal during operation in said second mode; and

a transmit modulator for modulating in-phase (I) and quadrature phase (Q) carrier signals of a predefined phase relationship with said I and Q modulation signals for transmission over said I and Q communication channels, respectively.

32. A method for modulating first and second information signals for transmission in a spread spectrum communication system to first and second system users during operation of said system in a first mode, and for modulating a third information signal of an input data rate, said third information signal being transmitted on in-phase (I) and quadrature phase (Q) channels of the spread spectrum communication system during operation in a second mode using a carrier signal and a replica of said carrier signal in phase quadrature therewith, said method comprising the steps of:

dividing, during operation in said second mode, said third information signal into first and second portions for transmission to one or more intended recipient users over said I and Q channels;

generating in-phase pseudorandom noise (PN.sub.I) and quadrature phase pseudorandom noise (PN.sub.Q) signals of predetermined PN codes;

generating a first orthogonal function signal of a predefined length based on a nominal data rate of said communication system;

combining said PN.sub.I signal with said first information signal and said first orthogonal function signal to provide an I modulation signal during operation in said first mode and for combining said PN.sub.I signal with said third information signal and said first orthogonal function signal to provide said I modulation signal during operation in said second mode, and for combining said PN.sub.Q signal with said second information signal and said first orthogonal function signal to provide a Q modulation signal during operation in said first mode and for combining said PN.sub.Q signal with said third information signal and said first orthogonal function signal to provide said Q modulation signal during operation in said second mode; and

modulating in-phase (I) and quadrature phase (Q) carrier signals of a predefined phase relationship with said I and Q modulation signals for transmission over said I and Q communication channels, respectively.

33. In a code division multiple access (CDMA) communication system for providing in-phase (I) and quadrature phase (Q) spread spectrum communication channels over which are respectively transmitted different first and second information signals using I and Q modulated carrier signals, a receiver for producing an estimate of at least said first information signal in accordance with said I and Q modulated carrier signals received over said I and Q communication channels.

34. The receiver of claim 33 further including a demodulator for demodulating said I and Q modulated carrier signals received over said I and Q communication channels into intermediate received signals using said orthogonal function signal.

35. The receiver of claim 34 further including:

a PN.sub.I signal generator for generating a first despreading signal by replicating said PN.sub.I signal, and

a first correlator for correlating said intermediate received signals using said first despreading signal in order to provide a first set of in-phase (I) and quadrature phase (Q) projection signals.

36. In a code division multiple access (CDMA) communication system for providing in-phase (I) and quadrature phase (Q) spread spectrum communication channels over which are respectively transmitted different first and second information signals using I and Q modulated carrier signals, a method of receiving information transmitted over said I and Q communication channels comprising the step of producing an estimate of at least said first information signal in accordance with said I and Q modulated carrier signals received over said I and Q communication channels.

37. The method of claim 36 further including the step of demodulating said I and Q modulated carrier signals received over said I and Q communication channels into intermediate received signals using said orthogonal function signal.

38. The method of claim 37 further including the steps of:

generating a first despreading signal by replicating said PN.sub.I signal, and

correlating said intermediate received signals using said first despreading signal in order to provide a first set of in-phase (I) and quadrature phase (Q) projection signals.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to communication systems utilizing spread spectrum signals, and, more particularly, to a novel and improved method and apparatus for communicating information in a spread spectrum communication system.

II. Description of the Related Art

Communication systems have been developed to allow transmission of information signals from a source location to a physically distinct user destination. Both analog and digital methods have been used to transmit such information signals over communication channels linking the source and user locations. Digital methods tend to afford several advantages relative to analog techniques, including, for example, improved immunity to channel noise and interference, increased capacity, and improved security of communication through the use of encryption.

In transmitting an information signal from a source location over a communication channel, the information signal is first converted into a form suitable for efficient transmission over the channel. Conversion, or modulation, of the information signal involves varying a parameter of a carrier wave on the basis of the information signal in such a way that the spectrum of the resulting modulated carrier is confined within the channel bandwidth. At the user location the original message signal is replicated from a version of the modulated carrier received subsequent to propagation over the channel. Such replication is generally achieved by using an inverse of the modulation process employed by the source transmitter.

Modulation also facilitates multiplexing, i.e., the simultaneous transmission of several signals over a common channel. Multiplexed communication systems will generally include a plurality of remote subscriber units requiring intermittent service of relatively short duration rather than continuous access to the communication channel. Systems designed to enable communication over brief periods of time with a set of subscriber units have been termed multiple access communication systems.

A particular type of multiple access communication system is known as a spread spectrum system. In spread spectrum systems, the modulation technique utilized results in a spreading of the transmitted signal over a wide frequency band within the communication channel. One type of multiple access spread spectrum system is a code division multiple access (CDMA) modulation system. Other multiple access communication system techniques, such as time division multiple access (TDMA), frequency division multiple access (FDMA) and AM modulation schemes such as amplitude companded single sideband are known in the art. However, the spread spectrum modulation technique of CDMA has significant advantages over these modulation techniques for multiple access communication systems. The use of CDMA techniques in a multiple access communication system is disclosed in U.S. Pat. No. 4,901,307, issued Feb. 13, 1990, entitled "SPREAD SPECTRUM MULTIPLE ACCESS COMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS", assigned to the assignee of the present invention.

In the above-referenced U.S. Pat. No. 4,901,307, a multiple access technique is disclosed where a large number of mobile telephone system users each having a transceiver communicate through satellite repeaters or terrestrial base stations using CDMA spread spectrum communication signals. In using CDMA communications, the frequency spectrum can be reused multiple times thus permitting an increase in system user capacity. The use of CDMA results in a much higher spectral efficiency than can be achieved using other multiple access techniques.

More particularly, communication in a CDMA system between a pair of locations is achieved by spreading each transmitted signal over the channel bandwidth by using a unique user spreading code. Specific transmitted signals are extracted from the communication channel by despreading the composite signal energy in the communication channel with the user spreading code associated with the transmitted signal to be extracted.

In particular spread spectrum communication systems it has been desired to allow various types of user channels (e.g., voice, facsimile, or high-speed data) to operate at different data rates. These systems have typically been designed to have channels operative at a nominal data rate, and also to have reduced data rate traffic channels for providing more traffic data capacity. However, increasing traffic capacity by using reduced data rate channels lengthens the time required for data transmission, and typically requires utilization of relatively complex data coders and decoders. Moreover, in certain spread spectrum communication systems there is also a need for increased data rate traffic channels allowing for transmission at data at rates higher than the nominal rate.

Accordingly, it is an object of the present invention to provide a CDMA spread spectrum communication system in which traffic channel capacity may be increased in the absence of a corresponding reduction in data rate. It is a further object of the invention to provide such a CDMA system in which communication channels are available for data transmission at higher than the nominal system rate.

SUMMARY OF THE INVENTION

The implementation of CDMA techniques in spread spectrum communication systems using orthogonal PN code sequences reduces mutual interference between users, thereby allowing higher capacity and better performance. The present invention provides an improved system and method for communicating information over in-phase (I) and quadrature phase (Q) communication channels in a CDMA spread spectrum communication system.

In an exemplary embodiment, first and second information signals are respectively transmitted over the I and Q communication channels using direct sequence spread spectrum communication signals. In-phase pseudorandom noise (PN.sub.I) and quadrature phase pseudorandom noise (PN.sub.Q) signals of predetermined PN codes are used for spreading the first and second information signals, respectively. In particular, the PN.sub.I signal is combined with the first information signal and an orthogonal function signal to provide an I-channel modulation signal. Similarly, the PN.sub.Q signal is combined with the second information signal and the orthogonal function signal to provide a Q-channel modulation signal. The I-channel and Q-channel modulation signals are used for modulating in-phase (I) and quadrature phase (Q) carrier signals for transmission to a receiver via the I and Q communication channels, respectively.

In the exemplary embodiment the receiver is operative to produce an estimate of at least the first information signal on the basis of the I-channel and Q-channel modulated carrier signals received over the I and Q communication channels. The received I-channel and Q-channel modulated carrier signals are demodulated into intermediate received signals using the orthogonal function signal. In particular, the intermediate received signals are decorrelated using a despreading PN.sub.I signal in order to provide a first set of in-phase (I) and quadrature phase (Q) projection signals. A phase rotator operates to provide an estimate of the first information signal based on the first set of I and Q projection signals and a received pilot signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention will become more apparent from the detailed description set forth below when taken in conjunction with the drawings in which like reference characters identify correspondingly throughout and wherein:

FIG. 1 shows a block diagram of a conventional spread spectrum transmitter;

FIG. 2 shows a block diagram of a preferred embodiment of a spread spectrum transmitter disposed to transmit I-channel and Q-channel information signals in accordance with the invention;

FIG. 3 provides a more detailed representation of the modulation and spreading network included within a preferred embodiment of the spread spectrum transmitter;

FIG. 4 depicts a pilot generation network for providing I and Q channel pilot sequences;

FIG. 5 shows an exemplary implementation of an RF transmitter incorporated within a preferred embodiment of the invention;

FIG. 6 is a block diagram of an exemplary diversity receiver disposed to receive the RF signal energy transmitted over the I and Q communication channels;

FIG. 7 is a block diagram of a receiver finger selected to process signal energy received over a selected transmission path; and

FIG. 8 provides a more detailed representation of the selected receiver finger illustrated in FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, there is shown a spread spectrum transmitter such as is described in U.S. Pat. No. 5,103,459, issued Apr. 7, 1992, entitled "SYSTEM AND METHOD FOR GENERATING SIGNAL WAVEFORMS IN A CDMA CELLULAR TELEPHONE SYSTEM", which is assigned to the assignee of the present invention, and which is herein incorporated by reference. In the transmitter of FIG. 1, data bits 100 consisting of, for example, voice converted to data by a vocoder, are supplied to an encoder 102 where the bits are convolutional encoded with code symbol repetition in accordance with the input data rate. When the data bit rate is less than the bit processing rate of the encoder 102, code symbol repetition dictates that encoder 102 repeat the input data bits 100 in order to create a repetitive data stream at a bit rate which matches the operative rate of encoder 102. The encoded data is then provided to interleaver 104 where it is block interleaved. The interleaved symbol data is output from interleaver 104 at an exemplary rate of 19.2 ksps to an input of exclusive-OR gate 106.

In the system of FIG. 1 the interleaved data symbols are scrambled to provide greater security in transmissions over the channel. Scrambling of the voice channel signals may be accomplished by pseudonoise (PN) coding the interleaved data with a PN code specific to an intended recipient subscriber unit. Such PN scrambling may be provided by the PN generator 108 using a suitable PN sequence or encryption scheme. The PN generator 108 will typically include a long PN generator for producing a unique PN code at a fixed rate of 1.2288 MHz. This PN code is then passed through a decimator, with the resulting 9.2 MHz scrambling sequence being supplied to the other input of exclusive-OR gate 106 in accordance with subscriber unit identification information provided thereto. The output of exclusive-OR gate 106 is then provided to one input of exclusive-OR gate 110.

Again referring to FIG. 1, the other input of exclusive-OR gate 110 is connected to a Walsh code generator 112. Walsh generator 112 generates a signal corresponding to the Walsh sequence assigned to the data channel over which information is being transmitted. The Walsh code provided by generator 112 is selected from a set of 64 Walsh codes of length 64. The 64 orthogonal codes correspond to Walsh codes from a 64 by 64 Hadamard matrix wherein a Walsh code is a single row or column of the matrix. The scrambled symbol data and Walsh code are exclusive-OR'ed by exclusive-OR gate 110 with the result provided as an input to both of the exclusive-OR gates 114 and 116.

Exclusive-OR gate 114 also receives a PN.sub.I signal from PN.sub.I generator 118, while the other input of exclusive-OR gate 116 receives a PN.sub.Q signal from PN.sub.Q generator 118. The PN.sub.I and PN.sub.Q signals are pseudorandom noise sequences typically corresponding to a particular area, i.e., cell, covered by the CDMA system and relate respectively to in-phase (I) and quadrature phase (Q) communication channels. The PN.sub.I and PN.sub.Q signals are respectively exclusive-OR'ed with the output of exclusive-OR gate 110 so as to further spread the user data prior to transmission. The resulting I-channel code spread sequence 122 and Q-channel code spread sequence 126 are used to bi-phase modulate a quadrature pair of sinusoids. The modulated sinusoids are summed, bandpass filtered, shifted to an RF frequency, and again filtered and amplified prior to being radiated via an antenna to complete transmission over the communication channel. Further details on the use of a pilot signal and multiple modulators is described in the above U.S. Pat. No. 5,103,459.

It is observed that in the transmission system of FIG. 1 the same information, i.e., the channel data 100, is conveyed over the communication channel at the nominal channel data rate by the I-channel code spread sequence 122 and the Q-channel code spread sequence 126. As is described hereinafter, the present invention provides a technique for transmitting a pair of distinct information signals at the nominal rate using the PN.sub.I code and the PN.sub.Q code, respectively. When distinct information signals are separately transmitted by each pair of I and Q communication channels, the number of channels within the spread spectrum system capable of operating at the nominal system data rate is effectively doubled. Alternatively, a given CDMA communication channel may be bifurcated into independent in-phase (I) and quadrature phase (Q) channels. This allows, for example, a single information signal to be transmitted at twice the nominal rate by dividing the signal between the I and Q channels. In a similar fashion to that which is disclosed in U.S. Pat. No. 5,103, 459, a pilot signal may be combined with the multiple channel modulated data for transmission.

FIG. 2 shows a block diagram of a preferred embodiment of a spread spectrum transmitter 150 disposed to transmit distinct I-channel 154 and Q-channel 156 information signals in accordance with the invention. For purposes of ease in illustration only a single channel pair is illustrated. It should be understood that in the transmission scheme the transmitter may included numerous copies of the circuit as disclosed in FIG. 2 for other user channels, in addition to a pilot channel. As is described below, the I-channel and Q-channel information signals are provided over I and Q communication channels utilizing RF carrier signals of the same frequency transmitted in phase quadrature. In an exemplary implementation one-half of a total number of system users receive information exclusively over the I-channel, while the remaining users receive information exclusively over the Q-channel. Alternatively, in a high data rate implementation each user receives an I-channel and a Q-channel information signal modulated by an identical Walsh code. In this way one-half of the data comprising a single information signal may be transmitted over each of the I and Q channels, thereby allowing for data transmission at twice the nominal rate.

In particular applications the information signals 154 and 156 may consist of, for example, voice converted to a stream of data bits by a vocoder or other digital data. Information signals 154 and 156 may be individual user channel signals (e.g. User A data and User B data) or a single high rate data channel signal that is demultiplexed by demultiplexer 152 into the two data streams. The data streams are then respectively supplied to a pair of encoding and interleaving networks 160 and 164. The networks 160 and 164 convolutional encode the information signals 154 and 156, and interleave with code symbol repetition in accordance with the input data rate. In the absence of code symbol repetition the networks 160 and 164 operate at a nominal rate of, for example, 9.6 kbit/s. When the input data bit rates (e.g., 4.8 kbit/s) of the information signals are lower than this nominal rate, the bits comprising the information signals 154 and 156 are repeated in order to create a repetitive data stream at a rate identical to the nominal symbol rate (e.g. 9.6 kbit/s). The encoded data is then interleaved and output from the networks 160 and 164 as encoded and interleaved symbol streams a.sub.n and b.sub.n.

The streams of symbols a.sub.n and b.sub.n, respectively corresponding to convolutional encoded and interleaved versions of the sampled I-channel 154 and Q-channel 156 information signals, are supplied to a modulation and spreading network 170. The network 170 operates to modulate the symbol streams a.sub.n and b.sub.n with a signal supplied by a Walsh generator 174. In the preferred embodiment, the signal provided by Walsh generator 174 consists of a Walsh code sequence assigned to the particular pair of I and Q communication channels over which the a.sub.n and b.sub.n symbol streams are transmitted. For an exemplary data rate of 9.6 kbit/s, the Walsh sequence provided by generator 174 will typically be selected from a set of 64 orthogonal Walsh codes of length 64.

In the preferred embodiment the chip rate of the Walsh sequences is chosen to be 1.2288 MHz. In this regard it is desirable that the chip rate be exactly divisible by the baseband data rates to be used in the system. It is also desirable for the divisor to be a power of two. Assuming at least one user channel operating at a nominal baseband data rate of 9600 bits per second results in an exemplary Walsh chip rate of 1.2288 MHz, i.e., 128.times.9600.

As is indicated by FIG. 2 the modulation and spreading network 170 is further provided with PN.sub.I and PN.sub.Q spreading signals by PN.sub.I and PN.sub.Q sequence generators 178 and 180. The PN.sub.I sequence is related to the I communication channel and is used within the network 170 to spread the a.sub.n symbol stream into an I-channel code spread sequence S.sub.I. Similarly the PN.sub.Q sequence is utilized by the network 170 to spread the b.sub.n symbol stream prior to transmission as a Q-channel code spread sequence S.sub.Q over the Q communication channel. The resultant I-channel and Q-channel code spread sequences S.sub.I and S.sub.Q are used to bi-phase modulate a quadrature pair of sinusoids generated within an RF transmitter 182. In RF transmitter 182 the modulated sinusoids will generally be summed, bandpass filtered, shifted from a basesband frequency to IF frequency to an RF frequency, and amplified at various frequency stages prior to being radiated via an antenna 184 to complete transmission over the I and Q communication channels.

Assuming the transmitter 150 to be the i.sup.th of N such transmitters, where i=1, . . . N, the I-channel and Q-channel spread sequences S.sub.I (i) and S.sub.Q (i) produced thereby may be represented as:

S.sub.I (i)=a.sub.n (i)W.sub.i PN.sub.I