Consider the following four CDMA code sequences, labeled A,B,C,D: A 1 1 1 1 1 1 1 1 B 1 1 -1 -1 1 1 -1 -1 C 1 -1 1 -1 1 -1 1 -1 D 1 -1 1 1 -1 -1 1 -1 (a) Prove that these four codes cannot be used simultaneously by four devices to communicate upon the same frequencies? (b) Suppose all four codes are in fact used simultaneously by four different devices A,B,C,D (where device x uses code x). Indicate whether any device's transmissions will arrive uncorrupted by the other transmissions.