Ultra wideband networks system and method capable of switching to high-speed mode or low-speed mode

An ultra wideband network transmitter and receiver, and a method capable of switching to a high-speed mode or a low-speed mode are provided. The transmitter includes a multi-band orthogonal frequency division multiplexing (MB-OFDM) modem; a direct sequence code division multiple access (DS-CDMA) modem; a mode switch which switches to the MB-OFDM modem or the DS-CDMA modem according to a mode control signal; a phase lock loop (PLL) which locks a frequency used for MB-OFDM type modulation or the DS-CDMA type modulation; and a central processing unit (CPU) controls the PLL and mode switch. The receiver includes an MB-OFDM modem; an DS-CDMA modem; an automatic gain controller; an analog-to-digital converter; an PLL; a mode switch; and an CPU. The method includes receiving a command to transmit data; and switching to an MB-OFDM modem to select to a high-speed operation mode.