Method and system for simulcasting

1. A method for simulcast communication, the method comprising:

modulating a simulcast signal using 8-level modulation;

increasing a time interval spacing between signal pulses of the simulcast signal;

spreading in time the signal pulses of the simulcast signal; and

communicating a stretched modulated simulcast signal formed by increasing the time interval spacing and spreading in time the signal pulses.

2. A method in accordance with claim 1 wherein the modulating comprises modulating the simulcast signal at a bit rate of one of 12 kilobits per second (kbps) and 9.6 kbps.

3. A method in accordance with claim 1 wherein the communicating comprises transmitting the stretched modulated simulcast signal using a Project 25 Time Division Multiple Access (TDMA) standard.

4. A method in accordance with claim 1 wherein the communicating comprises transmitting the stretched modulated simulcast signal using defined channel spaced of one of about 12.5 kilo-Hertz (kHz) apart and 25 kHz apart.

5. A method in accordance with claim 1 further comprising converting an input stream of data to 8-level symbols using three data bits.

6. A method in accordance with claim 5 wherein two most significant bits of the three data bits correspond to two bits of a phase shift level for 4-level mapping.

7. A method in accordance with claim 1 wherein the spreading in time comprises generating signal pulses having a Gaussian curve form.

8. A method in accordance with claim 1 wherein the 8-level modulation comprises one of 8 phase-shift keying (8PSK) modulation and harmonized differential quadrature phase shift keying (H-DQPSK) modulation.

9. A method in accordance with claim 1 wherein the increasing and spreading define a stretched eye pattern opening for the modulated simulcast signal.

10. A method in accordance with claim 1 further comprising encoding the stretched modulated simulcast signal with a protocol code word indicating the 8-level modulation.

11. A method in accordance with claim 10 wherein the encoding comprises using one of an inter-slot signaling channel and a trunking control channel to encode the protocol code.

12. A method in accordance with claim 1 wherein the spreading in time comprises spreading a symbol width of the simulcast signal or increasing a time duration between symbols relative to a time duration of symbols of a 4-level modulation.

13. A method for simulcast communication, the method comprising:

selecting one of a 4-level modulation and an 8-level modulation for modulating a simulcast signal; and

modulating the simulcast signal based on the selected modulation, wherein a bit rate for the simulcast signal is the same for different modulation types; and

selecting said 8-level modulation to include generating a sequence of 8-level pulses, each having a pulse width that is larger than a pulse width of a 4-level pulse generated during said 4-level modulation.

14. A method for simulcast communication, the method comprising:

selecting one of a 4-level modulation and an 8-level modulation for modulating a simulcast signal;

modulating the simulcast signal based on the selected modulation, wherein a bit rate for the simulcast signal is the same for different modulation types;

increasing a spacing between signal pulses of the simulcast signal, and

spreading in time the pulse width of the simulcast signal when using the 8-level modulation.

15. A method in accordance with claim 13 further comprising dynamically switching between the 4-level modulation and the 8-level modulation based on the selected modulation.

16. A method in accordance with claim 13 further comprising using a signal protocol in the modulated simulcast signal to identify the selected modulation.

17. A method in accordance with claim 16 wherein the signal protocol is encoded in one of an inter-slot signaling channel and a trunking control channel.

18. A method in accordance with claim 13 wherein the 4-level modulation comprises one of compatible 4-level Frequency modulation (C4FM), quadrature phase-shift keying (QPSK) modulation and compatible Quadrature Phase Shift Keying (CQPSK) modulation, and wherein the 8-level modulation comprises one of 8 phase-shift keying (8PSK) modulation and harmonized differential quadrature phase shift keying (H-DQPSK) modulation.

19. A method in accordance with claim 13 further comprising communicating at one of a 9.6 kilobits per second (kbps) rate and a 12 kbps rate when using the 8-level modulation.

20. A simulcast communication system comprising:

a transmitter configured to switch between a 4-level modulation mode and an 8-level modulation mode; and

a receiver configured to switch between a 4-level modulation mode and an 8-level modulation mode based on an encoded signal protocol in a simulcast transmission from the transmitter;

wherein said transmitter in said 8-level modulation mode generates a sequence of 8-level pulses, each having a pulse width that is larger than a pulse width of a 4-level pulse generated when said transmitter operates in said 4-level modulation mode.

21. A simulcast communication system comprising:

a transmitter configured to switch between a 4-level modulation mode and an 8-level modulation mode; and

a receiver configured to switch between a 4-level modulation mode and an 8-level modulation mode based on an encoded signal protocol in a simulcast transmission from the transmitter;

wherein the transmitter is further configured to (i) increase a spacing between signal pulses of the simulcast transmission and (ii) spread in time the pulse width of the simulcast transmission when using the 8-level modulation.

22. A simulcast communication system in accordance with claim 21 wherein the transmitter comprises a Gaussian impulse filter configured to perform the stretching.

23. A simulcast communication system in accordance with claim 20 wherein the 4-level modulation comprises one of compatible 4-level Frequency modulation (C4FM), quadrature phase-shift keying (QPSK) modulation and compatible Quadrature Phase Shift Keying (CQPSK) modulation, and wherein the 8-level modulation comprises one of 8 phase-shift keying (8PSK) modulation and harmonized differential quadrature phase shift keying (H-DQPSK) modulation.

24. A simulcast communication system in accordance with claim 20 communicating at a 9.6 kilobits per second (kbps) rate when using the 4-level modulation and at a 12 kbps rate when using the 8-level modulation.

25. A simulcast communication system in accordance with claim 20 wherein the transmitter comprises a first converter configured to convert two bits to a 4-level phase shift in the 4-level modulation mode and a second converter configured to convert three bits to an 8-level phase shift in the 8-level modulation mode.

26. A simulcast communication system in accordance with claim 20 wherein the receiver comprises a first converter configured to convert a 4-level phase shift to two bits in the 4-level modulation mode and a second converter configured to convert an 8-level phase shift to three bits in the 8-level modulation mode.

27. A method for simulcast communication, the method comprising:

generating a sequence of 4-level pulses in which adjacent pulses are spaced apart from each other a duration defined by a first time interval;

generating a sequence of 8-level pulses in which adjacent pulses are spaced apart from each other a duration defined by a second time interval, said second time interval larger than said first time interval; and

increasing a pulse width of each said 8-level pulse by a predetermined amount so that a pulse width of each said 8-level pulse is larger than a pulse width of each said 4-level pulse.