17.4 In a code division multiple access network, N stations are simultaneously communi- cating using one channel. A sending station places data on the common channel by multiplying the data with its code. A station can receive data froma sending station if it knows the latter's code. a. What multiplication technique do the stations use for encoding or decoding? b. Prove that the receiving station can get the data sent by the sender if it multiplies the entire data with the sender's code and then divides the result by N.