By combining traditional frequency hopping ideas with the concepts of subcarriers and sampling points in OFDM baseband systems, this paper proposes a frequency hopping technology within the baseband called micro frequency hopping. Based on the concept of micro frequency hopping, this paper proposes a micro frequency hopping spread spectrum modulation method based on cyclic frequency shift and cyclic time shift, as well as a micro frequency hopping encryption method based on phase scrambling of baseband signals. Specifically, this paper reveals a linear micro frequency hopping symbol with good auto-correlation and cross-correlation feature in both time domain and frequency domain. Linear micro frequency hopping symbols with different root $R$ have good cross-correlation feature, which can be used in multi-user communication at same time and same frequency. Moreover, there is a linear relationship between the time delay and frequency offset of this linear micro frequency hopping symbol, making it suitable for time delay and frequency offset estimation, also for ranging, and speed measurement. Finally, this paper also verifies the advantages of micro frequency hopping technology through an example of a linear micro frequency hopping spread spectrum multiple access communication system. The author believes that micro frequency hopping technology will be widely used in fields such as the Internet of Things, military communication, satellite communication, satellite positioning, and radar etc.