Method and apparatus for achieving channel variability in spread spectrum communication systems
View Patent ↗A method and apparatus are disclosed for modulating a communication signal in a code division multiple access (CDMA) environment using orthogonal N by N Hadamard spread spectrum codes Orthogonal spreading codes are used that have lengths that are not a power-of 2 to provide additional channel variability for various multimedia applications and increase the flexibility of the number of channels/bandwidth relationship. The Hadamard codes are multiples of 4 (4n) and demonstrate a good cross-correlation property, making them very useful in the flexible design of code division multiple access (CDMA) systems. A transmitter encodes each of N data streams (N not being a power of 2), to be transmitted using a 4n codeword, N i . The received signal is passed through a filter matched to the characteristics of the appropriate codeword, N i , and PN spreading sequence.
1. A method for receiving spread spectrum signals in a communication system comprising:
decoding said received spread spectrum signal with an orthogonal function sequence to produce a digital signal, wherein the length of said orthogonal function is selected from a group that includes substantially all multiples of four that are not an integral power of two with a range of channels supported by said communication system; and
detecting a data signal in said digital signal.
2. The method according to claim 1 , wherein said orthogonal function sequence is a length of N and is a Hadamard code having a length of 4n, where N equals 4n and n is an integer.
3. The method according to claim 1 , further comprising the step of demodulating said spread signal using a PN sequence.
4. The method according to claim 3 , further comprising the step of synchronizing said PN sequence to an appropriate lag due to channel transmission delay.
5. The method according to claim 1 , further comprising the step of synchronizing said decoding to an appropriate lag due to channel transmission delay.
6. The method according to claim 2 , wherein said decoding step is performed for up to 4n data signals.
7. A receiver for receiving spread spectrum signals in a communication system comprising:
an orthogonal function decoder that combines said received spread spectrum signal with an orthogonal function sequence to produce a digital signal, wherein the length of said orthogonal function is selected from a group that includes substantially all multiples of four that are not an integral power of two within a range of channels supported by said communication system; and
a processor for detecting a data signal in said digital signal.
8. The receiver according to claim 7 , wherein said orthogonal function sequence has a length of N and is a Hadamard code having a length of 4n, where N equals 4n and n is an integer.
9. The receiver according to claim 7 , further comprising a decoder for demodulating said spread signal using a PN sequence.
10. The receiver according to claim 9 , further comprising means for synchronizing said PN sequence to an appropriate lag due to channel transmission delay.
11. The receiver according to claim 7 , further comprising means for synchronizing said orthogonal function decoder to an appropriate lag due to channel transmission delay.
12. The receiver according to claim 7 , wherein said orthogonal function decoder processes up to 4n data signals.