Source coding for interference reduction

• US 7,376,105 B2
• Filed: 09/05/2002
• Issued: 05/20/2008
• Est. Priority Date: 08/21/1998
• Status: Expired due to Fees

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Liu, Chun-Hung, Cem, Erin, Siu, Kai-Yeung, Asada, Haruhiko H.
• Primary Examiner(s): Ngo; Rickey Q.
• Assistant Examiner(s): PATEL, CHANDRAHAS B
• Application Number:
  US10/236,058
• Publication Number:
  US 20030115533A1
• Time in Patent Office: 2,084 Days
• Field of Search: 370/335, 370/342, 370/441, 455/522, 455/574, 455/67.11, 455/67.12, 455/67.13, 455/67.16, 455/68, 455/501, 455/63.1, 455/114.2
• US Class Current: 370/335
• CPC Class Codes: H04J 13/00 Code division multiplex systems for frequency hopping H04B1/713
• CPC Class Codes: H04L 1/0058 Block-coded modulation
• CPC Class Codes: H04L 1/0066 Parallel concatenated codes
• CPC Class Codes: H04L 25/4908 using mBnB codes
• CPC Class Codes: H04L 27/02 Amplitude-modulated carrier systems, e.g. using on-off keying; Single sideband or vestigial sideband modulation H04L27/32 takes precedence
• CPC Class Codes: H04L 27/3411 reducing the peak to average power ratio or the mean power of the constellation; Arrangements for increasing the shape gain of a signal set

Abstract

A method of encoding a transmission signal to reduce multiple access interference at a receiver. A data source signal including a plurality of source symbols is received into a transmitter. The source symbols are encoded using low energy encoding forming encoded codewords. An identifying pattern is applied to the encoded codewords forming a transmission signal. In one embodiment, the identifying pattern is a unique pseudo-random pattern identifying the data source. Once the pattern has been added, multiple transmission signals can be summed together and then modulated onto a carrier wave. The transmission signals are then transmitted on the carrier wave which is at a pre-selected frequency. The low energy encoding format is such that a sequence of signals forming codewords is created. Each sequence of signals is characterized by an energy and normally a high bit consumes energy whereas a low bit requires substantially less energy.

Claims

1. A method of encoding a transmission signal to reduce multiple access interference at a receiver, the method comprising:

receiving a data source signal including a plurality of source symbols into a transmitter;

encoding the source symbols using low energy encoding forming encoded codewords, which includes producing a sequence of signals forming codewords, each sequence of signals characterized by an energy, the codewords having a length, each codeword signifying a specified source symbol on the basis of a mapping between source symbols and codewords mapped such that each symbol of lower probability of occurrence is associated with a codeword of at least equal energy, the length for the codewords based at least on the number of symbols to be coded;

applying an identifying pattern to the encoded codewords forming a transmission signal; and

transmitting the transmission signal on a pre-selected, wireless frequency.

2. The method according to claim 1, wherein the identifying pattern is a unique pseudo-random pattern identifying the data source.

3. A method for encoding according to claim 1, further comprising:

summing multiple transmission signals to form a summed signal.

4. The method according to claim 3, further comprising:

modulating the summed signal on a carrier wave.

5. The method according to claim 1, wherein the transmission signal is a code division multiple access signal.

6. The method according to claim 1 wherein the transmission signal is a direct sequence code division multiple access signal.

7. A method for reducing multiple access interference at a receiver, the method comprising:

receiving at a multiple access receiver a modulated signal having multiple transmitted signals thereon wherein each transmitted signal is encoded using low energy encoding, which includes producing a sequence of signals forming codewords, each sequence of signals characterized by an energy, the codewords having a length, each codeword signifying a specified source symbol on the basis of a mapping between source symbols and codewords mapped such that each symbol of lower probability of occurrence is associated with a codeword of at least equal energy, the length for the codewords based at least on the number of symbols to be coded;

identifying a transmitted signal according to a unique identifying pattern within the signal; and

decoding a transmitted signal using low energy decoding.

8. The method according to claim 7, wherein the unique identifying pattern is a code division multiple access pseudo-random pattern for identifying each data source.

9. A method for determining the capacity of a frequency in a code division multiple access system according to claim 8, further comprising:

receiving a low energy encoding codeword length;

receiving a bit energy to noise ratio for the system;

calculating a maximum number of allowable transmitters based at least upon a low energy encoding codeword length and the system bit energy to noise ratio.

10. The method according to claim 7 further comprising:

informing a control module of the transmitter that assigns transmission frequencies of a number of allowable transmission signals for a given frequency.

11. The method according to claim 10, further comprising:

assigning transmitters to a frequency up to the number of allowable transmissions.

12. A method for determining codeword length for a low energy encoded system in order reduce an error probability of receiving an incomplete codeword, the method comprising:

determining a signal to noise ratio for a low energy encoded frequency in a processor;

obtaining a length for binary encoded signal based upon a known number of symbols;

determining a critical length according to the formula

$L_c=\frac{L_b}{1-{\mathrm{\alpha <br><br>}}_1}<br><br>\exp <br><br>\left[\left(1-{\mathrm{\alpha <br><br>}}_1\right)<br><br>{\mathrm{SNR}}_{\mathrm{LE}}\right].$

 

wherein L_c represents the critical length, L_b represents a minimum length for a binary representation of the possible source symbols, α

₁ represents a percentage of high bits for a data source, and SNR represents “

signal to noise ratio”

;

setting the codeword length for low energy encoding to a length that is less than or equal to the critical length; and

outputting the codeword length from the processor.

13. A system for transmitting transmission signals, the system including:

a low energy data source encoder for encoding a data source into codewords using low energy encoding, which includes producing a sequence of signals forming codewords, each sequence of signals characterized by an energy, the codewords having a length, each codeword signifying a specified source symbol on the basis of a mapping between source symbols and codewords mapped such that each symbol of lower probability of occurrence is associated with a codeword of at least equal energy, the length for the codewords based at least on the number of symbols to be coded;

a pseudo-random pattern generator wherein each pseudorandom generator adds a pseudorandom signal to the codewords for the data source forming a transmission signal; and

a modulator for modulating each transmission signal on a carrier frequency.

14. A system according to claim 13, wherein there are a plurality of low energy data source encoders and a plurality of pseudo-random pattern generators each low energy data source encoder and pseudo-random pattern generator pair processing a separate data source creating a separate transmission signal.

15. A system according to claim 14, further comprising:

a summer module for summing the plurality of transmission signals.

16. The system according to claim 13, wherein the transmission signals are code division multiple access signals.

17. A receiver for receiving a code division multiple access signal, the receiver comprising:

a demodulator for removing the carrier frequency from the code division multiple access signal;

a pseudo-random module for separating each low energy encoded signal from the code division multiple access signal, wherein the low energy encoded signal is created by producing a sequence of signals forming codewords, each sequence of signals characterized by an energy, the codewords having a length, each codeword signifying a specified source symbol on the basis of a mapping between source symbols and codewords mapped such that each symbol of lower probability of occurrence is associated with a codeword of at least equal energy, the length for the codewords based at least on the number of symbols to be coded; and

a low energy decoder for decoding each low energy encoded signal.

18. A computer program product for use with a computer processor for encoding a transmission signal to reduce multiple access interference at a receiver, the computer program product comprising a computer readable storage medium having a stored computer executable program code thereon, the computer code comprising:

computer code for receiving a data source signal including a plurality of source symbols;

computer code for encoding the source symbols using low energy encoding forming encoded codewords, which includes computer code for producing a sequence of signals forming codewords, each sequence of signals characterized by an energy, the codewords having a length, each codeword signifying a specified source symbol on the basis of a mapping between source symbols and codewords mapped such that each symbol of lower probability of occurrence is associated with a codeword of at least equal energy, the length for the codewords based at least on the number of symbols to be coded;

computer code for applying pseudo-random pattern to the encoded codewords forming a transmission signal; and

computer code for transmitting the transmission signal on a pre-selected, wireless frequency.

19. The computer program product according to claim 18, further comprising:

computer code for summing multiple transmission signals to form a summed signal.

20. The computer program product according to claim 19, further comprising:

computer code for modulating the summed signal on a carrier wave.

21. A computer program product for use with a computer processor for reducing multiple access interference at a receiver, the computer program product comprising a computer readable storage medium having a stored computer executable program code thereon, the computer code comprising:

computer code for receiving a modulated signal having multiple transmitted signals thereon wherein each transmitted signal is encoded using low energy encoding, the low energy encoding provided by computer code for producing a sequence of signals forming codewords, each sequence of signals characterized by an energy, the codewords having a length, each codeword signifying a specified source symbol on the basis of a mapping between source symbols and codewords mapped such that each symbol of lower probability of occurrence is associated with a codeword of at least equal energy, the length for the codewords based at least on the number of symbols to be coded;

computer code for identifying each transmitted signal according to a unique pseudorandom number within the signal;

computer code for decoding each transmitted signal using low energy decoding; and

computer code for storing the decoded signal in a memory.

22. A computer program product for use with a computer processor for determining codeword length for a low energy encoded system in order to reduce an error probability of receiving an incomplete codeword, the computer program product comprising a computer readable storage medium having a stored computer executable program code thereon, the computer code comprising:

computer code for determining a signal to noise ratio for a low energy encoded frequency;

computer code for obtaining a length for binary encoded signal based upon a known number of symbols;

computer code for determining a critical length according to the formula,

$L_c=\frac{L_b}{1-{\mathrm{\alpha <br><br>}}_1}<br><br>\exp <br><br>\left[\left(1-{\mathrm{\alpha <br><br>}}_1\right)<br><br>{\mathrm{SNR}}_{\mathrm{LE}}\right].$

 

wherein L_c represents the critical length, L_b represents a minimum length for a binary representation of the possible source symbols, α

₁ represents a percentage of high bits for a data source, and SNR represents “

signal to noise ratio”

;

computer code for setting the codeword length for low energy encoding to a length that is less than or equal to the critical length; and

computer code for storing the codeword length to a memory.