Broadband network for coaxial cable using multi-carrier modulation
View Patent ↗A broadband local area data network uses coaxial cable wiring for interconnection of terminal devices. Orthogonal frequency division multiplexing (OFDM) with bit loading is used to overcome channel impairments and provide a path for terminal devices to transmit to and receive from other terminal devices. Probe messages are sent between devices to characterize the communication channel and determine optimum bit loading. The data network shares the cable spectrum with other services and uses frequency bands not used by other services. Adaptive power control can be used to maintain signal to noise ratio in a communication between terminal devices. Frequency coordination can be used to avoid interference between the LAN communications and other services transmitted on the cable.
1. A network device comprising:
a) a multi-carrier modulator for forming a probe message comprising a preamble, a channel estimation training sequence, and a bit loading training sequence wherein the probe message is formed using orthogonal frequency division multiplexing (OFDM); and
b) a transmitter for transmitting the probe message through the communication channel during an assigned slot in a framing structure that contains multiple slots over coaxial cable.
2. The device of claim 1 , wherein:
a) the preamble is a predetermined sequence of Quadrature Phase Shift Keying (QPSK) encoded data bits;
b) the channel estimation training sequence is a predetermined sequence of QPSK encoded OFDM symbols; and
c) the bit loading training sequence is a predetermined sequence of Binary Phase Shift Keying (BPSK) encoded OFDM symbols.
3. The device of claim 1 , wherein the modulator forms a beacon message and the transmitter broadcasts the beacon message, the beacon message providing a common time reference for synchronization of data network terminals receiving the beacon message.
4. A chip for use in a network device, the chip comprising:
a) a multi-carrier modulator for forming a probe message comprising a preamble, a channel estimation training sequence, and a bit loading training sequence wherein the probe message is formed using orthogonal frequency division multiplexing; and
b) a transmitter for transmitter for transmitting the probe message through the communication channel during an assigned slot in a framing structure that contains multiple slots over coaxial cable.
5. The chip of claim 4 , wherein the chip further comprises a receiver for receiving bit loading information and wherein the multi-carrier modulator uses the bit loading information to modulate future transmissions.
6. A network device comprising:
a) a receiver for receiving probe messages from a sending network device, the probe messages comprising a preamble, a channel estimation training sequence, and a bit loading training sequence, wherein the probe message was formed using OFDM;
b) a demodulator for demodulating the OFDM probe messages;
wherein the network device estimates the channel characteristics based upon the received probe messages.
7. The network device of claim 6 , further including a transmitter, wherein the bit loading training sequence is used to compute a bit loading profile and wherein the transmitter transmits back, to the node from which the bit loading training sequence was sent, bit loading information determined from the bit loading profile.