Method and apparatus for achieving channel variability in spread spectrum communication systems
A method and apparatus are disclosed for modulating a communication signal in a 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 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 of transmitting spread spectrum signals in a communication system, said method comprising the steps of:
encoding a data signal with an orthogonal function sequence to form a spread 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
adjusting the frequency of said spread signal to a carrier frequency.
2. The method according to claim 1 , further comprising the step of modulating said spread signal by a PN sequence.
3. The method according to claim 1 , 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.
4. The method according to claim 3 , wherein said encoding step is performed for up to 4n data signals.
5. A spread spectrum communication system for transmitting a data signal comprising:
an orthogonal function encoder that combines a data signal with at least an orthogonal function sequence to form a spread 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 spread spectrum communication system; and
means for adjusting the frequency of said spread signal to a carrier frequency.
6. The system according to claim 5 , further comprising an encoder for modulating said spread signal by a PN sequence.
7. The system according to claim 5 , 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.
8. The system according to claim 7 , wherein said encoding step is performed for up to 4n data signals.
9. A method for increasing the channel variability in a communication system comprising:
identifying a number of channels for said communication system; and
selecting an orthogonal function sequence for encoding a data signal, wherein the length of said orthogonal function is the smallest multiple of four that is not less than said number of channels 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.
10. The method according to claim 9 , 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.