Systems and methods for providing adaptive pulse position modulated code division multiple access for ultra-wideband communication links

• US 20040057501A1
• Filed: 09/23/2002
• Published: 03/25/2004
• Est. Priority Date: 09/23/2002
• Status: Active Grant

• Current Assignee: Meta Platforms, Inc. (f/k/a Facebook, Inc.)
• Original Assignee: Lucent Technologies, Inc. (Nokia Corporation)
• Inventors: Calin, Doru, Balachandran, Krishna, Ji, Tingfang, Kang, Joseph H.
• Granted Patent: US 7,187,715 B2
• Time in Patent Office: Days
• US Class Current: 375/146
• CPC Class Codes: H04B 1/7176 Data mapping, e.g. modulation
• CPC Class Codes: H04B 2001/6908 using time hopping
• CPC Class Codes: H04L 25/4902 Pulse width modulation; Pulse position modulation

Abstract

An adaptive pulse position modulated CDMA scheme for use in UWB communications systems is disclosed. A stream of input bits is encoded with spreading code sequence. The spreading code sequence consists of a number of code elements that may have one of two values. Each bit is encoded into a symbol consisting of a predefined number of chips, which are transmitted during a symbol period. Next, at least one code element is associated with each chip in the symbol. Then, an encoded pulse is generated in each chip. Each encoded pulse has a value determined by multiplying the data bit with the code value associated with the particular chip. The encoded pulse is then pulse position modulated by shifting the position of the pulse to a first position or a second position within the chip depending upon the encoded value of the pulse.

Claims

8. A transmitter for transmitting a pulse position modulated spread spectrum signal in a communications system, comprising:

a spreading code sequence generator for generating at least one spreading code sequence, each spreading code sequence comprising a plurality of elements having either a first value or a second value;

a spread spectrum encoder, operable for;

receiving a stream of input data bits;

receiving at least one spreading code sequence from the spreading code generator; and

encoding each bit of the stream of input data bits into a symbol, having a finite symbol period, and comprising a plurality of chips, wherein each chip comprises a chip period;

associating at least one code element with each chip in the symbol; and

generating an encoded pulse in each chip of the symbol, wherein the encoded pulse has a value equal to the product of the bit and the code value associated with the particular chip;

a pulse position modulator operable for modulating each pulse by shifting the position of the pulse within each chip based on the encoded value of the pulse; and

an antenna for transmitting the pulse position modulated signal over an ultra-wideband communications channel.

9. The transmitter of claim 8, wherein the spreading code sequence comprises an orthogonal code sequence.

10. The transmitter of claim 8, wherein the spreading code sequence comprises a pseudorandom code sequence.

11. The transmitter of claim 8, wherein modulating the position of the encoded pulse within each chip, comprises:

placing the pulse at a first position within the chip if the encoded value associated with the pulse is a first value; and

placing the pulse at a second position within the chip if the encoded value associated with the pulse is a second value

12. The transmitter of claim 11, wherein the first position and second position within each chip is separated by a predefined time shift.

13. The transmitter of claim 12, wherein the predetermined time shift is equal to one-half of the chip period.

14. The transmitter of claim 8, wherein each chip comprises a chip period that is greater than a delay spread associated with an Ultra-wideband (UWB) communications system.

15. A receiver for receiving a pulse position spread spectrum signal in an ultra-wideband (UWB) communications system, the pulse position modulated spread spectrum signal comprising a plurality of symbols, each symbol representing one data bit and consisting of a plurality of chips, each chip having a chip period and each chip containing an encoded pulse, comprising:

an ultra-wideband antenna operable for receiving the pulse position modulated spread spectrum signal;

a demodulator operable to demodulate the pulse position modulated spread spectrum signal by detecting the position of the encoded pulse within each chip period to determine a value associated with the encoded pulse; and

a spread spectrum decoder operable for;

receiving at least one spreading code sequence; and

decoding each symbol by combining the appropriate code value of the spreading code sequence with the value of encoded pulse in each chip of the symbol to extract the data bit.

16. The receiver of claim 15, wherein the spreading code sequence comprises an orthogonal code sequence.

17. The receiver of claim 15, wherein the spreading code sequence comprises a pseudorandom code sequence.

18. The receiver of claim 15, wherein detecting the position of the encoded pulse within each chip period to determine a value associated with the encoded pulse comprises determining a multi-level value of the likelihood that the pulse is located in either a first position or a second position within each chip period.

19. The receiver of claim 15, wherein detecting the position of the pulse within each chip to retrieve the spread spectrum signal, comprises determining whether the pulse is located at a first position or a second position within each chip period.

20. The receiver of claim 18, wherein the first position and second position are separated by a predetermined time shift equal to one-half of the chip period.

21. The receiver of claim 19, wherein the first position and second position are separated by a predetermined time shift equal to one-half of the chip period.

22. The method of claim 15, wherein each chip comprises a chip period that is greater than a delay spread associated with the ultra wideband (UWB) communications system.

23. A method of receiving a pulse position modulated spread spectrum signal, the pulse position modulated spread spectrum signal comprising a plurality of symbols, each symbol representing one data bit and consisting of a plurality of chips, each chip having a chip period and each chip containing an encoded pulse, comprising:

receiving the pulse position modulated spread spectrum signal;

demodulating the pulse position modulated spread spectrum signal by detecting the position of the encoded pulse within each chip period to determine a value associated with the encoded pulse; and

receiving at least one spreading code sequence; and

decoding each symbol by combining the appropriate code value of the spreading code sequence with the value of encoded pulse in each chip of the symbol to extract the data bit.

1. A method of modulating a communications signal within an ultra-wideband communications system, comprising:

receiving a plurality of bits in an input data stream;

receiving at least one spreading code sequence comprises of a plurality of elements having either a first value or a second value;

encoding each bit of the stream of input data bits into a symbol having a finite symbol period, and comprising a plurality of chips, wherein each chip comprises a chip period;

associating at least one code element with each chip in the symbol;

generating an encoded pulse in each chip of the symbol, wherein the encoded pulse has a value equal to the product of the bit and the code value associated with the particular chip; and

modulating the position of the encoded pulse within each chip depending upon the encoded value associated with the pulse.

2. The method of claim 1, wherein the spreading code sequence comprises an orthogonal code sequence.

3. The method of claim 1, wherein the spreading code sequence comprises a pseudorandom code sequence.

4. The method of claim 3, wherein modulating the position of the encoded pulse within each chip, comprises:

placing the pulse at a first position within the chip if the encoded value associated with the pulse is a first value; and

placing the pulse at a second position within the chip if the encoded value associated with the pulse is a second value.

5. The method of claim 4, wherein the first position and second position within each chip is separated by a predefined time shift.

6. The method of claim 5, wherein the predetermined time shift is equal to one-half of the chip period.

7. The method of claim 1, wherein each chip comprises a chip period that is greater than a delay spread associated with an Ultra wideband (UWB) communications system.

24. The method of claim 23, wherein detecting the position of the pulse within each chip to determine a value associated with the encoded pulse, comprises determining a multi-level value of the likelihood that the pulse is located in either a first position or a second position within each chip period.

25. The method of claim 23, wherein the first position and second position are separated by a predetermined time shift equal to one-half of the chip period.

26. The method of claim 24, wherein the first position and second position are separated by a predetermined time shift equal to one-half of the chip period.

24-1. The method of claim 23, wherein detecting the position of the encoded pulse within each chip period to determine a value associated with the encoded pulse, comprises determining whether the pulse is located at a first position or a second position within each chip period.