Smooth modulation switching

• US 8,379,761 B2
• Filed: 04/13/2009
• Issued: 02/19/2013
• Est. Priority Date: 04/13/2009
• Status: Expired due to Fees

• Current Assignee: Altobridge Limited (Singapore Technologies Engineering Limited)
• Original Assignee: Altobridge Limited (Singapore Technologies Engineering Limited)
• Inventors: Elyasi, Sattar
• Primary Examiner(s): Liu, Shuwang
• Assistant Examiner(s): TAYONG, HELENE E
• Application Number:
  US12/422,560
• Publication Number:
  US 20100260290A1
• Time in Patent Office: 1,408 Days
• Field of Search: 375/302, 375/260, 375/308, 375/297, 375/279, 375/295, 375/296, 375/219, 455/456
• US Class Current: 375/302
• CPC Class Codes: H04L 1/0003 by switching between different modulation schemes
• CPC Class Codes: H04L 1/009 arrangements specific to transmitters

Abstract

A transmitter comprises a channel encoder to encode data bits; a modulator to modulate the encoded data bits, wherein the modulator selects one of a first modulation scheme and a second modulation scheme for each of a plurality of time slots; wherein, for each time slot, the channel encoder: includes a prefix and a suffix at the beginning and end, respectively, of the encoded data bits corresponding to the respective time slot, the prefix and the suffix being selected based on the selected modulation scheme for the respective time slot; and passes the prefix, the encoded data bits, and the suffix to the modulator; wherein, for each time slot, the modulator: modulates the prefix, the encoded data bits, and the suffix received from the channel encoder according to the selected modulation scheme for the respective time slot; and applies a window function to the prefix and the suffix.

Claims

1. A transmitter configured to transmit modulated signals over a communication link, the transmitter comprising:

a channel encoder configured to encode data bits to create encoded data bits;

a modulator configured to modulate the encoded data bits, wherein the modulator selects as a selected modulation scheme one of a first modulation scheme or a second modulation scheme for each respective time slot of a plurality of time slots;

wherein, for each respective time slot, the channel encoder;

includes a prefix and a suffix at a beginning and an end, respectively, of the encoded data bits corresponding to the respective time slot, the prefix and the suffix being selected based on the selected modulation scheme for the respective time slot; and

passes the prefix, the encoded data bits, and the suffix to the modulator;

wherein, for each respective time slot, the modulator;

modulates the prefix, the encoded data bits, and the suffix received from the channel encoder according to the selected modulation scheme for the respective time slot; and

wherein, for consecutive time slots of the plurality of time slots, the modulator;

applies a window function to the prefix and the suffix of the consecutive time slots when the selected modulation scheme differs between the consecutive time slots, the window function being configured to smoothly ramp up the prefix and smoothly ramp down the suffix of the consecutive time slots to minimize discontinuity between the consecutive time slots.

2. The transmitter of claim 1, wherein the first modulation scheme is Gaussian Minimum-Shift Keying (GMSK) and the second modulation scheme is 8-Phase Shift Keying (8 PSK).

3. The transmitter of claim 2, wherein:

the prefix and the suffix corresponding to the first modulation scheme each comprise a constant bit repeated a predefined number of times; and

the prefix and the suffix corresponding to the second modulation scheme each comprise a constant symbol repeated a predefined number of times.

4. The transmitter of claim 1, wherein the window function comprises a Hanning window function.

5. The transmitter of claim 1, wherein the modulator combines the prefix, the encoded data bits, and the suffix for each of the consecutive time slots such that at least a portion of the prefix corresponding to each of the consecutive time slots is transmitted during a guard band prior to each of the consecutive time slots.

6. The transmitter of claim 1, wherein the modulator combines the prefix, the encoded data bits, and the suffix for each of the consecutive time slots such that at least a portion of the prefix corresponding to each of the consecutive time slots is transmitted during a period when power levels on the communication link are at a minimum level.

7. The transmitter of claim 1, wherein:

the communication link comprises a control channel; and

the modulator applies the window function to the prefix and the suffix of the consecutive time slots only when the selected modulation scheme differs between the consecutive time slots.

8. The transmitter of claim 1, wherein the transmitter further comprises a radio frequency (RF) module that up-converts the prefix, the encoded data bits, and the suffix.

9. A communication system comprising:

at least one wireless communication unit to transmit and receive wireless signals to and from at least one mobile device over a communication link; and

a controller coupled to the at least one wireless communication unit to process the wireless signals;

wherein the at least one wireless communication unit comprises;

a receiver to demodulate received signals and to decode received data bits of the demodulated signals; and

a transmitter (a) to encode transmission data bits of a data source to create encoded data bits and (b) to modulate the encoded data bits for transmission to the at least one mobile device;

wherein the transmitter selects as a selected modulation scheme one of a first modulation scheme or a second modulation scheme for each respective time slot of a plurality of time slots;

wherein, for each respective time slot, the transmitter;

includes a prefix and a suffix at a beginning and an end, respectively, of the encoded data bits corresponding to each respective time slot, the prefix and the suffix being selected based on the selected modulation scheme for each respective time slot; and

modulates the prefix, the encoded data bits, and the suffix according to the selected modulation scheme for each respective time slot; and

wherein, for consecutive time slots of the plurality of time slots, the transmitter;

applies a window function to the prefix and the suffix of the consecutive time slots when the selected modulation scheme differs between the consecutive time slots, the window function being configured to smoothly ramp up the prefix and smoothly ramp down the suffix of the consecutive time slots to minimize discontinuity between the consecutive time slots.

10. The communication system of claim 9, wherein the communication system is a Global System for Mobile communications (GSM) network.

11. The communication system of claim 9, wherein the first modulation scheme is Gaussian Minimum-Shift Keying (GMSK) and the second modulation scheme is 8-Phase Shift Keying (8PSK).

12. The communication system of claim 11, wherein:

the prefix and the suffix corresponding to the first modulation scheme each comprise a constant bit repeated a predefined number of times; and

the prefix and the suffix corresponding to the second modulation scheme each comprise a constant symbol repeated a predefined number of times.

13. The communication system of claim 9, wherein the window function is a Hanning window function.

14. The communication system of claim 9, wherein the transmitter transmits the prefix, the encoded data bits, and the suffix for each of the consecutive time slots such that at least a portion of the prefix corresponding to each of the consecutive time slots is transmitted during a guard band prior to each of the consecutive time slots.

15. The communication system of claim 9, wherein the transmitter transmits the prefix, the encoded data bits, and the suffix for each of the consecutive time slots such that at least a portion of the prefix corresponding to each of the consecutive time slots is transmitted during a period when power levels on the communication link are at a minimum level.

16. The communication system of claim 9, wherein:

the communication link comprises a control channel; and

the transmitter applies the window function to the prefix and the suffix of the consecutive time slots only when the selected modulation scheme differs between the consecutive time slots.

17. A method of communicating data in a system utilizing a plurality of time slots, the method comprising:

selecting as a selected modulation scheme one of a first modulation scheme or a second modulation scheme for each respective time slot of the plurality of time slots;

prepending data corresponding to each respective time slot with a prefix based on the selected modulation scheme for each respective time slot;

appending the data corresponding to each respective time slot with a suffix based on the selected modulation scheme for each respective time slot;

modulating the prefix, the data, and the suffix according to the selected modulation scheme for each respective time slot to create a modulated prefix, modulated data, and a modulated suffix for each respective time slot;

applying a window function to the modulated prefix, the modulated data, and the modulated suffix for consecutive time slots of the plurality of time slots when the selected modulation scheme differs between the consecutive time slots, the window function being configured to smoothly ramp up the modulated prefix and smoothly ramp down the modulated suffix of the consecutive time slots to minimize discontinuity between the consecutive time slots; and

after applying the window function, transmitting the modulated prefix, the modulated data, and the modulated suffix of each respective time slot over a communication link such that at least a portion of the modulated prefix of each respective time slot is transmitted when power levels on the communication link are at a minimum level.

18. The method of claim 17, wherein:

transmitting the modulated prefix, the modulated data, and the modulated suffix of each respective time slot comprises transmitting the modulated prefix, the modulated data, and the modulated suffix of each respective time slot during a guard band prior to the each respective time slot.

19. The method of claim 17, wherein:

applying the window function to the modulated prefix, the modulated data, and the modulated suffix for the consecutive time slots comprises applying a Hanning window function to the modulated prefix, the modulated data, and the modulated suffix.

20. The method of claim 17, wherein:

the prefix and the suffix corresponding to the first modulation scheme each comprise a constant bit repeated a predefined number of times; and

the prefix and the suffix corresponding to the second modulation scheme each comprise a constant symbol repeated a predefined number of times.

21. The method of claim 17, wherein:

selecting as the selected modulation scheme one of the first modulation scheme or the second modulation scheme comprises selecting as the selected modulation scheme one of a Gaussian Minimum-Shift Keying (GMSK) or a 8-Phase Shift Keying (8-PSK) for each respective time slot of the plurality of time slots, the first modulation scheme comprising the Gaussian Minimum-Shift Keying (GMSK) and the second modulation scheme comprising the 8-Phase Shift Keying (8-PSK).

22. A method of communicating data in a system utilizing a plurality of time slots, the method being implemented via execution of computer instructions configured to run at one or more processors and configured to be stored at one or more non-transitory memory elements, the method comprising:

executing one or more first computer instructions configured to select as a selected modulation scheme one of a first modulation scheme or a second modulation scheme for each respective time slot of the plurality of time slots;

executing one or more second computer instructions configured to prepend data corresponding to each respective time slot with a prefix based on the selected modulation scheme for each respective time slot;

executing one or more third computer instructions configured to append the data corresponding to each respective time slot with a suffix based on the selected modulation scheme for each respective time slot;

executing one or more fourth computer instructions configured to modulate the prefix, the data, and the suffix according to the selected modulation scheme for each respective time slot to create a modulated prefix, modulated data, and a modulated suffix for each respective time slot;

executing one or more fifth computer instructions configured to apply a window function to the modulated prefix, the modulated data, and the modulated suffix for consecutive time slots of the plurality of time slots when the selected modulation scheme differs between the consecutive time slots each time slot, the window function being configured to smoothly ramp up the modulated prefix and smoothly ramp down the modulated suffix of the consecutive time slots to minimize discontinuity between the consecutive time slots; and

after executing the one or more fifth computer instructions, executing one or more sixth computer instructions configured to transmitting the modulated prefix, the modulated data, and the modulated suffix of each respective time slot over a communication link for each respective time slot such that at least a portion of the modulated prefix of each respective time slot is transmitted during a period when power levels on the communication link are at a minimum level;

wherein;

the computer instructions comprise the one or more first, second, third, fourth, fifth, and sixth computer instructions.

23. The method of claim 22, wherein:

executing the one or more sixth computer instructions configured to transmit the modulated prefix, the modulated data, and the modulated suffix of each respective time slot comprises transmitting the modulated prefix, the modulated data, and the modulated suffix of each respective time slot when power levels on the communication link are at a minimum level.

24. The method of claim 22, wherein:

executing the one or more fifth computer instructions configured to apply the window function to the modulated prefix, the modulated data, and the modulated suffix for the consecutive time slots comprises applying a Hanning window function to the modulated prefix, the modulated data, and the modulated suffix.

25. The method of claim 22, wherein:

the prefix and the suffix corresponding to the first modulation scheme each comprise a constant bit repeated a predefined number of times; and

the prefix and the suffix corresponding to the second modulation scheme each comprise a constant symbol repeated a predefined number of times.

26. The method of claim 22, wherein:

executing the one or more first computer instructions configured to select as the selected modulation scheme one of the first modulation scheme or the second modulation scheme comprises selecting as the selected modulation scheme one of a Gaussian Minimum-Shift Keying (GMSK) or a 8-Phase Shift Keying (8-PSK) for each respective time slot of the plurality of time slots, the first modulation scheme comprising the Gaussian Minimum-Shift Keying (GMSK) and the second modulation scheme comprising the 8-Phase Shift Keying (8-PSK).