MIMO slotted aloha (MSA) system
View Patent ↗A method including receiving at a synchronizing node a first reference frame from a first reference node at a first time and storing a first time value representing the first time, and calculating a timing estimator by subtracting a minimum time value, representing the distance from the synchronizing node to the first reference node, from the first time value. The method includes receiving at the synchronizing node a second reference frame at a second time and transmitting from the synchronizing node to the first reference node a short timing contention time frame. The method includes receiving at the synchronizing node from the first reference node an arrival time value representing the time at which the first reference node received the short timing contention frame and calculating a time drift from the first arrival time value and the second time value and adjusting the timing estimator based on the time drift.
1. A method comprising:
receiving at a first node a plurality of signals from a plurality of nodes;
determining a plurality of carrier frequency offsets for the plurality of nodes, wherein at least one carrier frequency offset of the plurality of carrier frequency offsets is different than another carrier frequency offset of the plurality of carrier frequency offsets;
determining an average of the plurality of carrier frequency offsets;
adjusting a local oscillator at the first node based on the average of the plurality of carrier frequency offsets; and
transmitting data from the first node to one of the plurality of nodes according to a timing determined by the local oscillator.
2. The method of claim 1 , wherein determining the carrier frequency offset for a node comprises receiving and analyzing one or more preambles.
3. The method of claim 1 , further comprising estimating phase offsets of the plurality of signals.
4. The method of claim 3 , further comprising transmitting from the first node to the plurality of nodes an estimation of the phase offsets of the plurality of nodes.
5. The method of claim 4 , further comprising:
determining an index for each node by analyzing a frequency tone field in the signal received from that node, wherein the index is a randomly-selected complex tone; and
computing channel state information for each of the plurality of nodes.
6. A system comprising:
a first node with an associated transmit frequency and coupled to a plurality of other nodes via a network and comprising:
a local oscillator configured to generate a signal used to establish the transmit frequency; and
a processor configured to:
receive a signal from each of the plurality of other nodes;
determine a carrier frequency offset for each of the plurality of other nodes, wherein at least one carrier frequency offset of the plurality of other nodes is different than another carrier frequency offset of the plurality of other nodes;
determine an average of the plurality of carrier frequency offsets;
adjust the transmit frequency based on the average of the plurality of carrier frequency offsets; and
transmit data to at least one of the plurality of other nodes according to a timing determined by the local oscillator.
7. The system of claim 6 , wherein when the processor determines the carrier frequency offset for a node, the processor receives and analyzes one or more preambles.
8. The system of claim 6 , wherein the processor is further configured to estimate phase offsets of the signals received from each of the plurality of other nodes.
9. The system of claim 8 , wherein the processor is further configured to transmit an estimation of the phase offsets of the plurality of nodes to the plurality of nodes.
10. The system of claim 9 , wherein the processor is further configured to:
determine an index for each node through analysis of a frequency tone field in the signal received from that node, wherein the index is a randomly-selected complex tone; and
compute channel state information for each of the plurality of nodes.