System and method of uncorrelated code hopping in a communications system
View Patent ↗A system and method are used to provide uncorrelated code hopping in a communications system. A multi-bit linear shift register receives data and clocks the data fifteen times. A word assembler receives the shifted data and outputs a fifteen bit word. A mixer mixes the fifteen bit word with an numerical value of active codes to generate a mixed signal. A divider divides the mixed signal to produce a divided signal. A truncator truncates the divided signal to its seven most significant bits to produce a pseudo random hop number. A code matrix shifter circularly shifts the active codes in a code matrix based on the pseudo random hop number to produce a circularly shifted code. A transmitter transmits the circularly shifted code matrix.
1. A system, comprising:
a multi-bit linear shift register that receives data, the data being clocked multiple times;
a word assembler that receives the shifted data and outputs a fifteen bit word;
a mixer that mixes the fifteen bit word with a numerical value of active codes to generate a mixed signal;
a divider that divides the mixed signal to produce a divided signal;
a truncator that truncates the divided signal to its seven most significant bits to produce a pseudo random hop number;
a code matrix shifter that circularly shifts the active codes in a code matrix based on the pseudo random hop number to produce a circularly shifted code; and
a transmitter that transmits the circularly shifted code.
2. The system of claim 1 , wherein the multi-bit linear shift register is configured to be clocked fifteen times to shift the data fifteen bits.
3. The system of claim 1 , further comprising:
a node in a synchronous code-division multiple access communications system that comprises the multi-bit linear shift register, the word assembler, the mixer, the divider, the truncator, the code matrix, and the transmitter.
4. The system of claim 1 , wherein the word assembler is configured to form each word as y15:1=[s7:1, s15:8], such that s7:1 are seven most significant bits and s15:8 are eight least significant bits of the shifted data.
5. The system of claim 1 , wherein the code matrix shifter is configured shift the active codes according to:
f(k,i)=active_code_list[modulo(2*Na-128-hop_number(k)+i, Na)],
wherein:
the code matrix elements ci,j are the elements of the code matrix,
k indicates a spreading interval,
i indicates a row in the code matrix,
Na is the numerical value of active codes,
active_code_list is a list of the active codes, in increasing order, with each element in a range 0 to 127,
u is a list of unused codes in the code matrix, in increasing order, with each element in a range 0 to 127,
hop_number is the pseudo random hop number, and
128-Na≦i≦127.
6. The system of claim 1 , wherein the transmitter is configured to mix a symbol or a quadrature amplitude modulated symbol with respective rows of the code matrix before transmitting the code matrix.
7. The system of claim 1 , wherein the multi-bit linear shift register is configured to hop by a power of 2 number of clock cycles in a binary hopping scheme.
8. The system of claim 1 , wherein the multi-bit linear shift register is configured to be clocked one time to shift the data fifteen bits.
9. The system of claim 8 , further comprising a feedback path across each cell of the fifteen-bit linear shift register.
10. A method, comprising:
clocking a shift register multiple times;
assembling a word based on the shifted data;
mixing the word with a numerical value of active codes to generate a mixed signal;
dividing the mixed signal to produce a divided signal;
truncating the divided signal to its seven most significant bits to produce a pseudo random hop number;
circularly shifting the active codes in a code matrix based on the pseudo random hop number to produce a circularly shifted code; and
transmitting the circularly shifted code.
11. The method of claim 10 , wherein the shifting step occurs over fifteen clock cycles.
12. The method of claim 10 , wherein the shifting step occurs over one clock cycle.
13. The method of claim 10 , wherein each word is formed as y15:1=[s7:1, s15:9], such that s7:1 are seven most significant bits and s15:9 are eight least significant bits of the shifted data.
14. The method of claim 10 , wherein the circularly shifting of the active codes occurs according to:
f(k,i)=active_code_list[modulo(2*Na-129-hop_number(k)+i, Na)],
wherein:
the code matrix elements ci,j are the elements of the code matrix,
k indicates a spreading interval,
i indicates a row in the code matrix,
Na is the numerical value of active codes,
active_code_list is a list of the active codes, in increasing order, with each element in a range 0 to 127,
u is a list of unused codes in the code matrix, in increasing order, with each element in a range 0 to 127,
hop_number is the pseudo random hop number, and
129-Na≦i≦127.
15. The method of claim 10 , wherein before the transmitting step a symbol or quadrature amplitude modulated symbol is mixed with respective rows of the circularly shifted code matrix.
16. The method of claim 10 , wherein the shifting step comprises a binary hopping scheme.