Wireless telecommunication system having improved recognition of modulation type in GPRS

• US 6,717,934 B1
• Filed: 10/22/1999
• Issued: 04/06/2004
• Est. Priority Date: 10/22/1999
• Status: Expired due to Fees

• Current Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Original Assignee: Nokia Corporation
• Inventors: Paatelma, Risto, Kaasila, Pekka
• Primary Examiner(s): Sam, Phirin
• Application Number:
  US09/425,712
• Time in Patent Office: 1,628 Days
• Field of Search: 370/318, 370/321, 370/326, 370/329, 370/336, 370/337, 370/341, 370/345, 370/347, 370/437, 370/442, 370/349, 370/471, 375/269, 375/273, 375/274, 375/279, 375/305, 375/303, 375/329, 375/152, 375/323, 375/324, 375/325, 375/340, 375/343, 375/283, 375/286, 375/287
• US Class Current: 370/347
• CPC Class Codes: H04L 27/0012 arrangements for identifying the type of modulation

Abstract

A method is disclosed for operating a wireless mobile station to receive a time slot sent through a radio channel from a transmitter. In a GPRS embodiment the time slot has a Header portion and a Data portion, wherein the Header portion contains information for specifying whether the Data portion is modulated using 8-PSK modulation or π/4-shifted DQPSK modulation. When modulated using 8-PSK modulation, the Data portion includes a plurality of Pilot symbol sequences at predetermined locations. The method has steps of (a) estimating the quality of the radio channel using symbol sequences found at the predetermined locations, the symbol sequences being assumed to be Pilot symbol sequences; (b) determining a magnitude of a detection error between assumed transmitted Pilot symbol sequences and the detected symbols found at the predetermined locations; (c) calculating a mean of the detection error powers; (d) comparing the calculated mean of the detection error powers with a threshold value; and (e) selecting the modulation type of the Data portion as being one of 8-PSK or π/4-shifted DQPSK based on the result of the step of comparing.

Claims

1. A method for operating a wireless mobile station to receive a time slot sent through a radio channel from a transmitter, the time slot having a first portion and a second portion, said first portion containing information for specifying whether said second portion is modulated using a first modulation type or a second modulation type, wherein when modulated using said second modulation type said second portion comprises at least one predetermined symbol sequence at a predetermined location, comprising steps of:

receiving the time slot;

operating a demodulator for use with the second type of modulation and determining an amount of detected signal energy, assuming the predetermined symbol sequence being located at the predetermined symbol sequence location;

comparing the power of a detection error to a threshold value to derive a modulation type indication; and

based at least in part on the modulation type indication, specifying that said second portion of the received time slot is modulated with the first modulation type or that said second portion is modulated with the second modulation type.

2. A method as in claim 1, wherein the step of operating a demodulator operates a coherent demodulator.

3. A method as in claim 1, wherein the step of operating a demodulator operates an 8-PSK demodulator.

4. A method as in claim 1, wherein the first portion of the time slot containing said information comprises a Coded Data Field Type (CDFT) field.

5. A method as in claim 1, wherein when it is specified that said second portion of the received time slot is modulated with the second modulation type, further comprising a step of operating a coherent detector to detect the second portion of the time slot.

6. A method for operating a wireless mobile station to receive a time slot sent through a radio channel from a transmitter, the time slot having a first portion and a second portion, said first portion containing information for specifying whether said second portion is modulated using a first modulation type or a second modulation type, wherein when modulated using said second modulation type said second portion comprises at least one predetermined symbol sequence at a predetermined location, comprising steps of:

receiving the time slot;

operating a demodulator for use with the second type of modulation and determining an amount of detected signal energy, assuming the predetermined symbol sequence being located at the predetermined symbol sequence location;

comparing the power of a detection error to a threshold value to derive a modulation type indication; and

based at least in part on the modulation type indication, specifying that said second portion of the received time slot is modulated with the first modulation type or that said second portion is modulated with the second modulation type, wherein when it is specified that said second portion of the received time slot is modulated with the second modulation type, further operating a second detector to detect the first portion of the time slot containing the information, and using the detected information for verifying that the second portion of the received time slot is modulated with the second modulation type.

7. A method for operating a wireless mobile station to receive a time slot sent through a radio channel from a transmitter, the time slot having a first portion and a second portion, said first portion containing information for specifying whether said second portion is modulated using a first modulation type or a second modulation type, wherein when modulated using said second modulation type said second portion comprises at least one predetermined symbol sequence at a predetermined location, comprising steps of:

receiving the time slot;

operating a demodulator for use with the second type of modulation and determining an amount of detected signal energy, assuming the predetermined symbol sequence being located at the predetermined symbol sequence location;

comparing the power of a detection error to a threshold value to derive a modulation type indication; and

based at least in part on the modulation type indication, specifying that said second portion of the received time slot is modulated with the first modulation type or that said second portion is modulated with the second modulation type;

wherein specifying further comprises operating a second detector to detect the first portion of the time slot containing the information to derive a further modulation type indication, combining the modulation type indication and the further modulation type indication and, based on the combined modulation type indications, specifying that said second portion of the received time slot is modulated with the first modulation type or that said second portion is modulated with the second modulation type.

8. A method for operating a wireless mobile station to receive a time slot sent through a radio channel from a transmitter, the time slot having a first portion and a second portion, said first portion containing information for specifying whether said second portion is modulated using a first modulation type or a second modulation type, wherein when modulated using said second modulation type said second portion comprises at least one predetermined symbol sequence at a predetermined location, comprising steps of:

receiving the time slot;

operating a demodulator for use with the second type of modulation and determining an amount of detected signal energy, assuming the predetermined symbol sequence being located at the predetermined symbol sequence location;

comparing the power of a detection error to a threshold value to derive a modulation type indication; and

based at least in part on the modulation type indication, specific that said second portion of the received time slot is modulated with the first modulation type or that said second portion is modulated with the second modulation type, wherein when it is specified that said second portion of the received time slot is modulated with the second modulation type, further operating a second detector to detect the first portion of the time slot containing the information, and using the detected information to verify that the second portion of the received time slot is modulated with the second modulation type.

9. A method for operating a wireless mobile station to receive a time slot sent through a radio channel from a transmitter, the time slot having a first portion and a second portion, said first portion containing information for specifying whether said second portion is modulated using a first modulation type or a second modulation type, wherein when modulated using said second modulation type said second portion comprises a predetermined symbol sequence at a predetermined location, comprising steps of:

receiving the time slot;

operating a first detector using first modulation type detection to detect the first portion of the time slot containing the information to derive a first modulation type indication;

operating a second detector using second modulation type detection to detect the predetermined symbol sequence at the predetermined location to derive a second modulation type indication; and

based on both the first modulation type indication and the second modulation type indication, specifying that said second portion of the received time slot is modulated with the first modulation type or that said second portion is modulated with the second modulation type.

10. A method for operating a wireless mobile station to receive a time slot sent through a radio channel from a transmitter, the time slot having a first portion and a second portion, said first portion containing information for specifying whether said second portion is modulated using a first modulation type or a second modulation type, wherein when modulated using said second modulation type said second portion comprises a predetermined symbol sequence at a predetermined location, comprising steps of:

receiving the time slot;

operating a first detector using first modulation type detection to detect the first portion of the time slot containing the information to derive a first modulation type indication;

operating a second detector using second modulation type detection to detect the predetermined symbol sequence at the predetermined location to derive a second modulation type indication; and

based on a combination of the first modulation type indication and the second modulation type indication, specifying that said second portion of the received time slot is modulated with the first modulation type or that said second portion is modulated with the second modulation type.

11. A method for operating a wireless mobile station to receive a time slot sent through a radio channel from a transmitter, the time slot having a first portion and a second portion, said first portion containing information for specifying whether said second portion is modulated using a first modulation type or a second modulation type, wherein when modulated using said second modulation type said second portion comprises a predetermined symbol sequence at a predetermined location, comprising steps of:

receiving the time slot;

operating a first detector using first modulation type detection to detect the first portion of the time slot containing the information to derive a first modulation type indication;

operating a second detector using second modulation type detection to detect the predetermined symbol sequence at the predetermined location to derive a second modulation type indication; and

based on a more reliable one of the first modulation type indication or the second modulation type indication, specifying that said second portion of the received time slot is modulated with the first modulation type or that said second portion is modulated with the second modulation type.

12. A method for operating a wireless mobile station to receive a time slot sent through a radio channel from a transmitter, the time slot having a first portion and a second portion, said first portion containing information for specifying whether said second portion is modulated using a first modulation type or a second modulation type, wherein when modulated using said second modulation type said second portion comprises a predetermined symbol sequence at a predetermined location, comprising steps of:

receiving the time slot;

operating a first detector using first modulation type detection to detect the first portion of the time slot containing the information to derive a first modulation type indication;

operating a second detector using second modulation type detection to detect the predetermined symbol sequence at the predetermined location to derive a second modulation type indication; and

if either one of the modulation type indications is deemed to be unreliable, using the other modulation type indication as well for specifying that said second portion of the received time slot is modulated with the first modulation type or that said second portion is modulated with the second modulation type.

13. A receiver unit for use in a digital wireless communication system, comprising:

a receiver for receiving a time slot sent through a radio channel from a transmitter, the time slot having a first portion and a second portion, said first portion containing information for specifying whether said second portion is modulated using a first modulation type or a second modulation type, wherein when modulated using said second modulation type said second portion comprises a predetermined symbol sequence at a predetermined location;

a first detector using first modulation type detection for detecting the first portion of the time slot containing the information to derive a first modulation type indication;

a second detector using second modulation type detection for detecting an assumed predetermined symbol sequence at the predetermined location to derive a second modulation type indication; and

a processor, responsive to at least one of the first modulation type indication and the second modulation type indication, for specifying that said second portion of the received time slot is modulated with the first modulation type or that said second portion is modulated with the second modulation type.

14. A receiver unit as in claim 13, wherein the predetermined symbol sequence is coherently modulated.

15. A receiver unit as in claim 13, wherein the predetermined symbol sequence is modulated with 8-PSK modulation.

16. A receiver unit as in claim 13, wherein the first portion of the time slot containing said information is modulated with π

/4-shifted DQPSK modulation.

17. A receiver unit as in claim 13, wherein the first portion of the time slot containing said information comprises a CDFT field.

18. A receiver unit as in claim 13, and further comprising a combiner for combining the first modulation type indication and the second modulation type indication, and wherein said processor, based on the combined modulation type indications, specifies that said second portion of the received time slot is modulated with the first modulation type or that said second portion is modulated with the second modulation type.

19. A receiver unit as in claim 13, wherein said receiver unit is located within a mobile station.

20. A method for operating a wireless mobile station to receive a time slot sent through a radio channel from a transmitter, the time slot having a Header portion and a Data portion, wherein the Header portion contains information for specifying whether the Data portion is modulated using 8-PSK modulation or π

/4-shifted DQPSK modulation, wherein when modulated using 8-PSK modulation the Data portion comprises a plurality of Pilot symbol sequences at predetermined locations, comprising steps of;

estimating the quality of the radio channel using symbol sequences found at the predetermined locations, the symbol sequences being assumed to be Pilot symbol sequences;

determining a magnitude of a detection error between assumed transmitted Pilot symbol sequences and the detected symbols found at the predetermined locations;

calculating a mean of the detection error powers;

comparing the calculated mean of the detection error powers with a threshold value; and

selecting the modulation type of the Data portion as being one of 8-PSK or π

/4-shifted DQPSK based on the result of the step of comparing.

21. A method as in claim 20, and further comprising a step of varying a magnitude of the threshold value as a function of at least one characteristic of the radio channel.

22. A method as in claim 20, and further comprising a step of varying a magnitude of the threshold value as a function of the power of the radio channel noise, as determined from a predetermined symbol sequence that comprises part of the Header portion.