Exercise 2.1 (Gallager) Consider the electric field in (2.4).
1. It has been derived under the assumption that the motion is in the direction of the line-of-sight from sending antenna to receive antenna. Find the electric field assuming that is the angle between the line-of-sight and the direction of motion of the receiver. Assume that the range of time of interest is small enough so that changes in ((), if;) can be ignored.
2. Explain why, and under what conditions, it is a reasonable approximation to ignore the change in ((), if;) over small intervals of time.