Selecting the data rate of a wireless network link according to a measure of error vector magnitude

A method of setting a data rate for a node of a wireless network that uses OFDM for communication, the data rate being for sending data to a remote node, the method comprising:

• receiving an OFDM packet from the remote node, a received OFDM packet including a part modulated in a pre-defined way and containing information indicative of the data rate used for at least some of the packet;
• demodulating the part modulated in the pre-defined way to determine the information indicative of the data rate, and further demodulating the at least some of the packet;
• and
• determining a measure of an error vector magnitude (EYM) for the received OFDM packet, the determining using at least the demodulated part that was modulated in the pre-defined way,
• such that the determined measure of the EVM is used to select a data rate for communicating between the node and the remote node.

An apparatus for setting the data rate for a node of a wireless network, the data rate for sending data to a remote node, the apparatus included in the node and comprising:

• means for receiving a packet from the remote node, a received OFDM packet including a part modulated in a pre-defined way and containing information indicative of the data rate used for at least some of the packet;
• means for demodulating, including demodulating the part modulated in the pre-defined way to determine the information indicative of the data rate;
• and
• means for determining a measure of an error vector magnitude (EVM) for the received packet, the means for determining the measure of the EVM coupled to the means for demodulating and using at least the demodulated part that was modulated in the pre-defined way,
• such that the determined measure of the EVM is used to select a data rate for communicating between the node and the remote node.

An apparatus for inclusion in a node of a wireless network, the apparatus comprising:

• a receiver to receive data from a remote node, including an analog-to-digital converter producing samples of packets of data received at the node from the remote node, a packet of data including a part modulated in a pre-defined way and containing information indicative of the data rate used for at least some of the packet;
• a demodulator coupled to the receiver to demodulate samples of the signals received at the receiver to produce demodulated signals, the samples at decision points;
• an error vector magnitude calculator coupled to the receiver and to the demodulator, the error vector magnitude calculator arranged to accept an indication of the rate as a result of the demodulator demodulating the part modulated in a pre-defined way, the error vector magnitude calculator arranged to determine a measure of the signal quality of the decision point samples of the received signal;
• a transmitter to transmit data for transmission to the remote node, the transmitter having a settable data rate, the data rate set according to a data rate signal accepted by the transmitter;
• and
• a data rate setting processor coupled to the error vector magnitude calculator and to the transmitter and producing the data rate signal for the transmitter, the data rate signal set such that the data rate for transmission to a particular node is dependent on the measure of the signal quality produced by the error vector magnitude calculator from signals received from the particular remote node.