System Specifications

From the point of view of “Signals and Systems”, nodes can be described as systems. For example if adhoc networks are used in cellular industry then the mobile phones are the nodes and they can be thought as the systems in which incoming signal is electromagnetic waves and the output signal is voice. ( it can be understood other way round also.) As in the broad sense, adhoc network can be thought as a collection of nodes or terminals so using the above mentioned view we can say that adhoc network is a collection of systems with all the systems invertible.

Like this we can define CDMA as a system which takes a string of bits as input and gives another string of bits as output. The operation this system performs on the input string using another string of bits (called pseudo random sequence) is XOR, which is shown in the figure below.


At the receiving node, the reverse process occurs i.e. the signal is converted into a string of bits and then that string acts as an input to another system(where the inverse operation occurs). The output comes out is another string of bits. In this operation input string is correlated with the same pseudo random sequence, and then the actual string of bits is recovered (the output one in this case) as shown in the figure below.