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 shift register receives data. The shift register is clocked to shift the data. A scaler performs a scaling operation on the data with a numerical value of active codes. A truncator truncates the scaled data 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.
1. A system, comprising:
a receiver configured to receive circularly shifted code, the circularly shift code being generated by:
a shift register configured to receive data, the shift register being clocked to shift the data,
a scaler configured to scale the shifted data with a numerical value of active codes,
a truncator configured to:
truncate the scaled data to its seven most significant bits, and
produce a pseudo random hop number, and
a code matrix shifter configured to circularly shift rows of active codes in a code matrix based on the pseudo random hop number.
2. The system of claim 1 , wherein the shift register is configured to be clocked n times to shift the data n times, and wherein n is a number of bits in the shift register.
3. The system of claim 1 , wherein the shift register is configured to be clocked one time to shift the data one time.
4. The system of claim 1 , further comprising a feedback path to a first cell of the shift register, wherein the feedback path starts after a last two cells of the shift register.
5. The system of claim 1 , further comprising:
a node in a synchronous code-division multiple access communications system that comprises the shift register, the scaler, the truncator, and the code matrix shifter.
6. The system of claim 1 , wherein the code matrix shifter is configured to shift the active codes according to:
f ( k,i )=active_code_list[modulo(2* Na− 128−hop_number( k )+ i, Na )],
wherein:
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.
7. The system of claim 1 , wherein the 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 , further comprising a feedback path across each cell of the shift register.
9. The system of claim 8 , wherein the shift register is configured to be clocked one time to shift the data n times, and wherein n is a number of bits in the shift register.
10. The system of claim 1 , wherein the scaler comprises:
a word assembler configured to:
receive the shifted data, and
output a word;
a mixer configured to:
mix the word with the numerical value of active codes, and
generate a mixed signal; and
a divider configured to:
divide the mixed signal, and
produce a divided signal.
11. The system of claim 10 , wherein the word assembler is configured to form each word as y15:1=[s7:1, s15:8], such that s7:1 are the seven most significant bits, s15:8 are the eight least significant bits of the shifted data, and y15 is the most significant bit.
12. A method, comprising:
receiving circularly shifted code generated by:
shifting data using a shift register,
scaling the shifted data using a numerical value of active codes,
truncating the scaled data to seven most significant bits to produce a pseudo random hop number, and
circularly shifting rows of active codes in a code matrix based on the pseudo random hop number.
13. The method of claim 12 , wherein:
the circular shifting occurs over n clock cycles, and
n is a number of bits in the shift register.
14. The method of claim 12 , wherein the shifting occurs over one clock cycle.
15. The method of claim 12 , wherein the circularly shifting of the active codes occurs according to:
f ( k,i )=active_code_list[modulo(2* Na− 128−hop_number( k )+ i,Na )],
wherein:
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.
16. The method of claim 12 , wherein the shifting comprises a binary hopping scheme.
17. The method of claim 12 , wherein the scaling further comprises:
assembling a word based on the shifted data;
mixing the word with a numerical value of active codes to generate a mixed signal; and
dividing the mixed signal to produce a divided signal.
18. The method of claim 17 , wherein each of the words is formed 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.