Method of modulating a data signal with modulation switching between direct and differential modulation and apparatus for modulation
View Patent ↗A method and apparatus for modulating a data signal for transmission over a channel of a communication system, wherein a direct modulation scheme is applied to a data signal over a given first signal interval. Subsequently, a control measure is determined for switching the modulation scheme for the data signal from the direct modulation scheme to a differential modulation scheme and/or vice versa, which is applied to the data signal over a given second signal interval.
1. A method of modulating a data signal for transmission over a channel of a communication system, the method comprising:
determining whether a direct modulation scheme or a differential modulation scheme is being used;
determining a phase deviation, an amplitude deviation, or both a phase deviation and an amplitude deviation of a received modulation symbol;
judging whether the modulation scheme in use is to be switched or not based on the determined phase deviation, amplitude deviation, or both phase deviation and amplitude deviation; and
switching from the modulation scheme in use to the other modulation scheme, between the direct modulation scheme and the differential modulation scheme, when it is judged that the modulation scheme in use is to be switched.
2. The data signal modulation method according to claim 1 wherein the direct modulation scheme is any one or a combination of PAM, ASK, PSK, and QAM.
3. The data signal modulation method according to claim 1 , wherein the differential modulation scheme is either one or a combination of DPSK and DQAM.
4. The data signal modulation method according to claim 1 wherein the phase deviation, the amplitude deviation, or each of the phase deviation and the amplitude deviation are compared with a corresponding threshold to judge whether the modulation scheme in use is to be switched.
5. The data signal modulation method according to claim 4 , wherein each respective threshold is dynamically determined within the communication system depending on noise, interference, or both noise and interference in a channel.
6. The data signal modulation method according to claim 4 , wherein each respective threshold applied in judging whether to switch from the direct modulation scheme to the differential modulation scheme is different from each respective threshold applied in judging whether to switch from the differential modulation scheme to the direct modulation scheme.
7. The data signal modulation method according to claim 1 , wherein the switching of the modulation scheme includes a hysteresis-like behavior.
8. An apparatus for modulating a data signal for transmission over a channel of a communication system, the apparatus comprising:
a first modulator for applying a direct modulation scheme to the data signal;
a second modulator for applying a differential modulation scheme to the data signal;
a switching unit that switches the modulator to be used between the first modulator and the second modulator; and
a control unit that operates said switching unit based on a phase deviation value, an amplitude deviation value, or both a phase deviation value and an amplitude deviation value of a received modulation symbol.
9. The data signal modulation apparatus according to claim 8 , wherein said control unit comprises a comparator that compares the phase deviation value, the amplitude deviation value, or each of the phase deviation value and the amplitude deviation value with a corresponding threshold.
10. The data signal modulation apparatus according to claim 9 , wherein said control unit comprises a means for storing a lower and an upper threshold for operating said switching unit with a hysteresis-like behavior.