Meathod and apparatus for encryption of over-the-air communications in a wireless communication system

• US 20060062320A1
• Filed: 08/22/2005
• Published: 03/23/2006
• Est. Priority Date: 09/23/2004
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola Mobility, Inc. (Lenovo Group Ltd.)
• Inventors: Harris, John M., Crocker, Ronald T., Luz, Yuda Y.
• Granted Patent: US 7,804,912 B2
• Time in Patent Office: Days
• US Class Current: 375/269
• CPC Class Codes: H04K 1/006 by varying or inverting the phase, at periodic or random intervals
• CPC Class Codes: H04L 27/2626 Arrangements specific to the transmitter only
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT
• CPC Class Codes: H04L 5/0044 allocation of payload

Abstract

A communication device converts a bit stream to multiple symbols and provides encryption at a physical layer by shifting a phase of each symbol of the multiple symbols to produce multiple encrypted symbols. Each encrypted symbol of the multiple encrypted symbols is modulated with an orthogonal subcarrier to produce at least one modulated subcarrier and the at least one modulated subcarrier is then transmitted via a wireless link. On a receive side, a receiving communication device receives the transmitted, encrypted symbols and provides decryption at a physical layer by shifting a phase of each encrypted symbol in correspondence with the phase used to encrypt the symbol at the transmit side.

Claims

1. A method for encrypting a wireless transmission comprising:

receiving a plurality of symbols;

shifting a phase of each symbol of the plurality of symbols to produce a plurality of phase shifted symbols;

modulating each phase shifted symbol of the plurality of phase shifted symbols with an orthogonal subcarrier to produce at least one modulated subcarrier; and

transmitting the at least one modulated subcarrier via a wireless link.

2. The method of claim 1, wherein the plurality of symbols comprises symbols associated with user data and symbols associated with pilot data, wherein shifting comprises shifting a phase of each symbol that is associated with user data to produce a plurality of phase shifted symbols and not shifting a phase of each symbol that is associated with pilot data to produce a plurality of non-shifted symbols, and wherein modulating comprises modulating each phase shifted symbol of the plurality of phase shifted symbols associated with user data with a first orthogonal subcarrier and modulating each non-shifted symbol of the plurality of non-shifted symbols with a second orthogonal subcarrier.

3. The method of claim 1, wherein modulating comprises spreading each phase shifted symbol of the plurality of phase shifted symbols by at least one spreading code, wherein the at least one modulated subcarrier comprises the plurality of symbols spread by the at least one spreading code and wherein transmitting comprises upconverting the at least one modulated subcarrier from a baseband frequency to a transmit frequency to produce an upconverted signal, amplifying the upconverted signal to produce an amplified signal, and transmitting the amplified signal.

4. The method of claim 1, wherein receiving a plurality of symbols comprises:

receiving a bit stream; and

mapping the bit stream to a constellation of symbols to produce a plurality of symbols.

5. The method of claim 1, wherein the plurality of phase shifted symbols comprises a stream of phase shifted symbols and wherein modulating comprises:

assigning each phase shifted symbol of the plurality of phase shifted symbols to a frequency sub-band of a plurality of frequency sub-bands; and

transforming each phase shifted symbol to a time domain subcarrier associated with the phase shifted symbol'"'"'s frequency sub-band to produce a plurality of modulated time domain subcarriers.

6. The method of claim 5, wherein the plurality of modulated time domain subcarriers are in a parallel form and wherein transmitting comprises:

converting the plurality of modulated subcarriers from a parallel form to a serial form to produce an output signal; and

transmitting the output signal via a wireless link.

7. The method of claim 1, wherein shifting comprises:

assigning each symbol of the plurality of symbols to a frequency sub-band of a plurality of frequency sub-bands to produce a plurality of assigned symbols;

shifting a phase of each assigned symbol of the plurality of assigned symbols to produce a plurality of phase shifted symbols; and

wherein modulating comprises transforming each phase shifted symbol to a time domain subcarrier associated with the phase shifted symbol'"'"'s frequency sub-band to produce a plurality of modulated time domain subcarriers.

8. The method of claim 7, wherein the plurality of modulated time domain subcarriers are in a parallel form and wherein transmitting comprises:

converting the plurality of modulated time domain subcarriers from a parallel form to a serial form to produce an output signal; and

transmitting the output signal via a wireless link.

9. The method of claim 1, wherein shifting a phase comprises shifting a phase of each symbol of the plurality of symbols based on a code word derived from at least one of a session key and a mobile serial number.

10. The method of claim 9, wherein shifting a phase comprises:

generating a code word based on at least one of a session key and a mobile serial number; and

for each symbol of the plurality of symbols,

generating a sin α and

a cos α

, wherein a is derived from the code word; and

shifting a phase of the symbol based on the sin α and

the cos α

to produce a phase shifted symbol.

11. The method of claim 1, wherein shifting a phase comprises shifting a phase of each symbol of the plurality of symbols based on a code word of a plurality of code words, and wherein the method further comprises:

loading a buffer with a bit sequence based on at least one of a session key and a mobile serial number;

reading a serial sequence out of the buffer;

exclusive or'"'"'ing the serial sequence with a different sequence to produce a code word; and

multiplying the code word by each subcarrier index of a plurality of subcarrier indices to produce the plurality of code words.

12. A method for receiving an encrypted wireless transmission comprising:

receiving at least one modulated subcarrier via a wireless link;

demodulating the at least one modulated subcarrier to produce a plurality of encrypted symbols; and

applying a phase shift to each encrypted symbol of the plurality of encrypted symbols to produce a plurality of decrypted symbols.

13. The method of claim 12, wherein the at least one modulated subcarrier comprises a subcarrier associated with user data and a subcarrier associated with pilot data, wherein demodulating comprises demodulating the subcarrier associated with user data to produce a plurality of encrypted symbols and demodulating the subcarrier associated with pilot data to produce a plurality of non-encrypted symbols, and wherein applying a phase shift comprises applying a phase shift to each encrypted symbol of the plurality of encrypted symbols to produce a plurality of decrypted symbols.

14. The method of claim 12, further comprising mapping each decrypted symbol of the plurality of decrypted symbols to a constellation of symbols to produce a data stream.

15. The method of claim 12, wherein the at least one modulated subcarrier comprises a plurality of modulated subcarriers, wherein the plurality of encrypted symbols comprises a stream of encrypted symbols, and wherein demodulating comprises:

converting the plurality of modulated subcarriers from a serial form to a parallel form to produce a plurality of parallel modulated subcarriers;

demodulating each subcarrier of a plurality of parallel modulated subcarriers by an orthogonal function to produce a plurality of parallel encrypted symbols; and

converting the plurality of parallel encrypted symbols from a parallel form to a serial form to produce a stream of encrypted symbols.

16. A communication device comprising:

a signal processing unit comprising;

a phase shifter that receives a plurality of symbols and applies a phase shift to each symbol of the plurality of symbols to produce a plurality of phase shifted symbols;

an orthogonal modulator that receives the plurality of phase shifted symbols and modulates each phase shifted symbol of the plurality of phase shifted symbols with an orthogonal subcarrier to produce at least one modulated subcarrier; and

a transmitter section coupled to the signal processing unit that transmits the at least one modulated subcarrier via a wireless link.

17. The communication device of claim 16, wherein the plurality of symbols comprises a plurality of symbols associated with user data and a plurality of symbols associated with pilot data, wherein the phase shifter receives the plurality of symbols associated with user data and shifts a phase of each such symbol to produce a plurality of phase shifted symbols, and wherein the orthogonal modulator receives the plurality of phase shifted symbols, receives the plurality of non-shifted symbols associated with pilot data, modulates each phase shifted symbol of the plurality of phase shifted symbols with a first orthogonal subcarrier, and modulates each non-shifted symbol of the plurality of non-shifted symbols with a second orthogonal subcarrier.

18. The communication device of claim 16, wherein the orthogonal modulator comprises at least one spreader, wherein the at least one spreader modulates each phase shifted symbol of the plurality of phase shifted symbols by spreading the phase shifted symbol by at least one spreading code, and wherein the at least one modulated subcarrier comprises the plurality of symbols spread by the at least one spreading code.

19. The communication device of claim 16, wherein the communication device further comprises a symbol mapper that receives a bit stream, maps the bit stream to a constellation of symbols to produce the plurality of symbols, and conveys the plurality of symbols to the phase shifter.

20. The communication device of claim 16, wherein the plurality of phase shifted symbols comprises a stream of phase shifted symbols and wherein the orthogonal modulator comprises:

a serial-to-parallel converter that assigns each phase shifted symbol of the plurality of phase shifted symbols to a frequency sub-band of a plurality of frequency sub bands; and

a transformer that transforms each phase shifted symbol to a time domain subcarrier associated with the symbol'"'"'s frequency sub-band to produce a plurality of modulated time domain subcarriers, wherein the plurality of modulated subcarriers are in a parallel form; and

a parallel-to-serial converter that converts the plurality of modulated subcarriers from a parallel form to a serial form to produce an output signal; and

wherein the transmitter section transmits the at least one modulated subcarrier by transmitting the output signal via the wireless link.

21. The communication device of claim 16, further comprising a code word generator coupled to the phase shifter that generates a plurality of code words based on at least one of a session key and a mobile serial number and wherein the phase shifter shifts a phase of each symbol of the plurality of symbols based on a code word of the plurality of code words.

22. The communication device of claim 21, wherein the code word generator comprises:

a buffer that stores a bit sequence based on at least one of the session key and the mobile serial number;

an Exclusive OR function that receives a serial sequence based on the bit sequence stored in the buffer and exclusive OR'"'"'s the serial sequence with a different sequence to produce a code word; and

a multiplier that multiplies the code word by each subcarrier index of a plurality of subcarrier indices to produce a plurality of code words.

23. The communication device of claim 21, wherein the phase shifter comprises:

a sine and cosine function generator that, for each symbol of the plurality of symbols, generates a sin α and

a cos α

, wherein a is derived from a code word of the plurality of code words; and

a quadrature encryptor coupled to the sine and cosine function generator that, for each symbol of the plurality of symbols, shifts a phase of the symbol of the plurality of symbols based on the sin α and

the cos α

generated with respect to that symbol to produce a phase shifted symbol.

24. A communication device comprising:

a receiver section that receives a modulated carrier via a wireless link and downconverts the modulated carrier to produce a downconverted signal;

a signal processing unit coupled to the receiver section and comprising;

an orthogonal demodulator that receives the downconverted signal and demodulates the downconverted signal to produce a stream of encrypted symbols; and

a phase shifter that receives the stream of encrypted symbols and applies a phase shift to each symbol of the stream of encrypted symbols to produce a plurality of decrypted symbols.

25. The communication device of claim 24, wherein the modulated carrier comprises encrypted symbols associated with user data and non-encrypted symbols associated with pilot data, wherein the orthogonal demodulator demodulates the downconverted signal to produce a plurality of encrypted symbols and a plurality of non-encrypted symbols, and wherein the phase shifter applies a phase shift to each encrypted symbol of the plurality of encrypted symbols to produce a plurality of decrypted symbols.

26. The communication device of claim 24, wherein the downconverted signal comprises a plurality of spread symbols and wherein the orthogonal demodulator comprises at least one despreader that demodulates each symbol of the plurality of spread symbols by despreading the symbol by at least one spreading code.

27. The communication device of claim 24, wherein the signal processing unit further comprises an inverse symbol mapper that receives each symbol of the plurality of decrypted symbols and, for each decrypted symbol, recovers a plurality of bits corresponding to the decrypted symbol.

28. The communication device of claim 24, wherein the orthogonal modulator comprises:

a serial-to-parallel converter that assigns the downconverted signal to a plurality of time domain subcarriers; and

an inverse transformer that transforms each time domain subcarrier of the plurality of time domain subcarriers to a frequency domain subcarrier to produce a plurality of encrypted symbols, wherein the plurality of encrypted symbols are in a parallel form; and

a parallel-to-serial converter that converts the plurality of encrypted symbols from a parallel form to a serial form to produce a stream of encrypted symbols.

29. The communication device of claim 24, further comprising a code word generator coupled to the phase shifter that generates a plurality of code words based on at least one of a session key and a mobile serial number and wherein the phase shifter shifts a phase of each encrypted symbol of the plurality of encrypted symbols based on a code word of the plurality of code words to produce the stream of decrypted symbols.

30. The communication device of claim 29, wherein the code word generator comprises:

a buffer that stores a bit sequence based on at least one of the session key and the mobile serial number;

an Exclusive OR function that receives a serial sequence based on the bit sequence stored in the buffer and exclusive OR'"'"'s the serial sequence with a different sequence to produce a code word; and

a multiplier that multiplies the code word by each subcarrier index of a plurality of subcarrier indices to produce a plurality of code words.

31. The communication device of claim 29, wherein the phase shifter comprises:

a sine and cosine function generator that, for each symbol of the plurality of symbols, generates a sin α and

a cos α

, wherein α

is derived from a code word of the plurality of code words; and

a quadrature encryptor coupled to the sine and cosine function generator that, for each encrypted symbol of the plurality of encrypted symbols, shifts a phase of the symbol based on the sin α and

the cos α

generated with respect to that symbol to produce a decrypted symbol.