GMSK spread modulation

1. A method for transmitting a modulated signal comprising:

obtaining a sequence of data symbols;

obtaining a spread spectrum code comprising a sequence of spread spectrum chips;

generating a sequence of pre-modulation chips by combining the sequence of data symbols with the sequence of spread spectrum chips, wherein for each data symbol of said sequence of data symbols, at least one of the pre-modulation chips is generated by taking into account at least the data symbol and at least one of the spread spectrum chips;

performing Gaussian Minimum Shift Keying (GMSK) modulation using the sequence of pre-modulation chips to produce a spread spectrum GMSK signal; and

transmitting the spread spectrum GMSK signal as said modulated signal,

wherein the spread spectrum GMSK signal is capable of being approximated as a pulse amplitude modulation (PAM) signal.

2. The method of claim 1 wherein the spread spectrum GMSK signal adopts antipodal signaling to represent each data symbol.

3. The method of claim 1 wherein each data symbol corresponds to K spread spectrum chips and K pre-modulation chips, wherein K is a positive integer.

4. The method of claim 1 wherein even ones and odd ones of the sequence of pre-modulation chips separately correspond to in-phase (I) and quadrature (Q) components of the PAM signal.

5. The method of claim 1 wherein the spread spectrum code is a pseudo-noise (PN) code.

6. The method of claim 1 wherein the GMSK modulation adopts a bandwidth-bit duration (BT) product within a range from 0.4 to 0.5.

7. An apparatus for transmitting a modulated signal comprising:

a data processing unit capable of receiving a sequence of data symbols and combining the sequence of data symbols with a spread spectrum code comprising a sequence of spread spectrum chips to produce a sequence of pre-modulation chips, wherein for each data symbol of said sequence of data symbols, at least one of the pre-modulation chips is generated by taking into account at least the data symbol and at least one of the spread spectrum chips; and

a modulator coupled to the data processing unit and configured to perform Gaussian Minimum Shift Keying (GMSK) modulation on the sequence of pre-modulation chips to produce a spread spectrum GMSK signal as said modulated signal to be transmitted, wherein the spread spectrum GMSK signal is capable of being approximated as a pulse amplitude modulation (PAM) signal.

8. The apparatus of claim 7 wherein even ones and odd ones of the sequence of pre-modulation chips separately correspond to in-phase (I) and quadrature (Q) components of the PAM signal.

9. The apparatus of claim 7 wherein the spread spectrum code is a pseudo-noise (PN) code.

10. The apparatus of claim 7 wherein the GMSK modulation adopts a bandwidth-bit duration (BT) product within a range from 0.4 to 0.5.

11. A system for transmitting a modulated signal comprising:

means for obtaining a sequence of data symbols;

means for obtaining a spread spectrum code comprising a sequence of spread spectrum chips;

means for generating a sequence of pre-modulation chips by combining the sequence of data symbols with the sequence of spread spectrum chips, wherein for each data symbol of said sequence of data symbols, at least one of the pre-modulation chips is generated by taking into account at least the data symbol and at least one of the spread spectrum chips;

means for performing Gaussian Minimum Shift Keying (GMSK) modulation using the sequence of pre-modulation chips to produce a spread spectrum GMSK signal; and

means for transmitting the spread spectrum GMSK signal as said modulated signal,

wherein the spread spectrum GMSK signal is capable of being approximated as a pulse amplitude modulation (PAM) signal.