Although some amount of "guesstimation" is inevitable in most estimation activities, the main risk here is its reliance on the expertise, experience, and, often, the instincts of a single individual.

Agree to use broad estimation ranges rather than single-point estimates and to refine them periodically as the project progresses.

There are many key technologies about the single-user detection, such as synchronization between receiver and transmitter, channel estimation and diversity.