Spread spectrum acquisition strategies

Acquisition in most spread spectrum systems is the process of achieving synchronization between the transmitter and receiver PN code generators. Basically with a PN code of length L chips, timing information can be transferred from transmitter to receiver by either transmitting the PN code-driven spreading function and searching for the correct code phase in the receiver, or by transmitting the code phase as an N-bit (where 2N is not less than L) binary number using a fixed spreading function. An alternate approach is to use a combination of these two, i.e., partially resolving the timing uncertainty by transmitting and searching over a short PN code-driven spreading function and then transmitting the remaining timing information as data on the short code spread signal. Acquisition time expressions are developed and compared for these three methods with the objective of identifying the basic mechanisms, limitations and trade-offs.