Selecting an access point according to a measure of received signal quality

• US 6,940,843 B2
• Filed: 11/03/2003
• Issued: 09/06/2005
• Est. Priority Date: 02/14/2003
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Inventors: de Souza, Ludovico N., Ryan, Philip J., Goodall, David S., Myles, Andrew F.
• Primary Examiner(s): Duong, Frank
• Assistant Examiner(s): MOORE JR, MICHAEL J
• Application Number:
  US10/700,011
• Publication Number:
  US 20040218568A1
• Time in Patent Office: 673 Days
• Field of Search: 370/210, 370/332, 370/338, 370/401
• US Class Current: 370/338
• CPC Class Codes: H04B 17/318 Received signal strength
• CPC Class Codes: H04L 1/0002 by adapting the transmission rate
• CPC Class Codes: H04L 1/0015 characterised by the adaptation strategy
• CPC Class Codes: H04L 1/0026 Transmission of channel quality indication
• CPC Class Codes: H04L 1/206 for modulated signals
• CPC Class Codes: H04L 5/0091 Signaling for the administration of the divided path
• CPC Class Codes: H04W 24/00 Supervisory, monitoring or testing arrangements
• CPC Class Codes: H04W 48/20 Selecting an access point
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]
• CPC Class Codes: H04W 84/18 Self-organising networks, e.g. ad-hoc networks or sensor networks

Abstract

An apparatus for inclusion and a method for operation in a station (STA) of a wireless network. The method includes received data from at least one remote station and determining a measure of the signal quality, e.g., a measure of the EVM from samples of the data received from the remote station(s). If the remote station(s) is/are access point(s), the station selects an access point for association according to criteria that include the measure of the EVM from the remote station. If the received data includes a request management message, the station responds to the request management message with a response management message that include a measure of the EVM of the received data corresponding to the request management message. Thus, the remote station receiving the response management message receives an indication of the quality of the link between the station and the remote station without the receiving remote station necessarily being EVM-capable.

Claims

1. An apparatus for inclusion in a station of a wireless network, the apparatus comprising:

a radio receiver to wirelessly receive data from at least one remote station, said data transmitted by the remote station as at least one packet of data, the receiver including an analog-to-digital converter producing samples of signals received at the station from the remote station;

a demodulator coupled to the radio receiver to demodulate samples of the signals received at the receiver from each station to produce, demodulated signals from each of the remote stations; and

a signal quality calculator coupled to the receiver to determine for each remote station from which data is received a signal quality measure of the-received signal based on the samples of the received data from the remote station,

such that, the receiving station selects one of the remote stations for communication according to a set of at least one criterion, said set including the respective received signal quality measure determined by the signal quality calculator for data from each of the respective remote stations,

wherein the signal quality calculator is an error vector magnitude calculator to determine for each remote station from which data is received a measure of the error vector magnitude of the received data from the remote station, the error vector magnitude based on samples approximately at decision points of the demodulator,

wherein at least some of the stations from which data is received are access points, and wherein the data received from remote stations that are access points are beacons or probe responses, such that one of the criteria for the station to select a remote access point for association is a measure of the error vector magnitude of a beacon or probe response received from the access point, and

wherein the error vector magnitude of a beacon or a probe response received from the access point is used to determine the maximum transmission rate that the link between the station and the remote access points can support, and wherein the determined maximum supported transmission rate is one of the criteria for the station to select a remote access point for association.

2. An apparatus for inclusion in a station of a wireless network, the apparatus comprising:

a radio receiver to wirelessly receive data from at least one remote station, said data transmitted by the remote station as at least one packet of data, the receiver including an analog-to-digital converter producing samples of signals received at the station from the remote station;

a demodulator coupled to the radio receiver to demodulate samples of the signals received at the receiver from each station to produce demodulated signals from each of the remote stations;

a signal quality calculator coupled to the receiver to determine for each remote station from which data is received a signal quality measure of the-received signal based on the samples of the received data from the remote station;

a transmitter to transmit data for transmission to at least one remote station; and

a data rate setting processor coupled to the signal quality 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 remote station is dependent on the measure of the signal quality produced by the signal quality calculator from signals received from the particular remote station,

such that, the receiving station selects one of the remote stations for communication according to a set of at least one criterion, said set including the respective received signal quality measure determined by the signal quality calculator for data from each of the respective remote stations,

wherein in the case that the received data is ascertained to be a probe request, an association request or a reassociation request, a packet for transmission by the transmitter from the station to a particular remote station that sent the request includes a measure of the received signal quality of the request received from the particular remote station,

wherein the measure of signal quality is a measure of the error vector magnitude of the received packet, the error vector magnitude based on samples approximately at decision points of the demodulator, and

wherein the data rate processor includes a memory to store for each remote station from which data was received the measure of error vector magnitude of the last packet received from the remote station, and a running average of the measure of error vector magnitude of a number of packets last received from the remote station.

3. An apparatus for inclusion in a station of a wireless network, the apparatus comprising:

a radio receiver to wirelessly receive data from at least one remote station, said data transmitted by the remote station as at least one packet of data, the receiver including an analog-to-digital converter producing samples of signals received at the station from the remote station;

a demodulator coupled to the radio receiver to demodulate samples of the signals received at the receiver from each station to produce demodulated signals from each of the remote stations; and

a signal quality calculator coupled to the receiver to determine for each remote station from which data is received a signal quality measure of the-received signal based on the samples of the received data from the remote station,

such that, the receiving station selects one of the remote stations for communication according to a set of at least one criterion, said set including the respective received signal quality measure determined by the signal quality calculator for data from each of the respective remote stations.

wherein the signal quality calculator is an error vector magnitude calculator to determine for each remote station from which data is received a measure of the error vector magnitude of the received data from the remote station, the error vector magnitude based on samples approximately at decision points of the demodulator, and

wherein the determining of the measure of the error vector magnitude of the received packet includes determining a result of a function of the average of the squared Euclidian distance on the I,Q plane between decision-point samples of the signal received and the nearest ideal constellation points to the decision points samples.

4. An apparatus for inclusion in a station of a wireless network, the apparatus comprising:

a radio receiver to wirelessly receive data from at least one remote station, said data transmitted by the remote station as at least one packet of data, the receiver including an analog-to-digital converter producing samples of signals received at the station from the remote station;

a demodulator coupled to the radio receiver to demodulate samples of the signals received at the receiver from each station to produce demodulated signals from each of the remote stations; and

a signal quality calculator coupled to the receiver to determine for each remote station from which data is received a signal quality measure of the-received signal based on the samples of the received data from the remote station.

such that, the receiving station selects one of the remote stations for communication according to a set of at least one criterion, said set including the respective received signal quality measure determined by the signal quality calculator for data from each of the respective remote stations.

wherein the signal quality calculator is an error vector magnitude calculator to determine for each remote station from which data is received a measure of the error vector magnitude of the received data from the remote station, the error vector magnitude based on samples approximately at decision points of the demodulator, and

wherein the error vector magnitude calculator is coupled to the demodulator and wherein determining of the measure of the error vector magnitude of the received packet includes determining a result of a function of the average of the squared Euclidian distance on the I,Q plane between decision-point samples of the signal received and the correct ideal constellation points for the signal as determined by demodulating the signal.

5. A method in a station of a wireless network, the method comprising:

wirelessly receiving data from at least one remote station, said data transmitted by the remote station as at least one packet of data;

sampling the received data corresponding to the received packet to form data samples;

demodulating the data samples;

determining a measure of signal quality from the samples of the received data; and

selecting one of the remote stations for communication according to a set of least one criteria including the respective determined received signal quality measure for data from each of the remote stations,

wherein the determining of the measure of signal quality includes determining a measure of the error vector magnitude of the received data from received samples approximately at the decision points for demodulating the data, and

wherein the determining of the measure of the error vector magnitude of the received packet includes determining the average of the squared Euclidian distance on the I,Q plane between decision-point samples of the signal received and the nearest ideal constellation points to the decision point samples.

6. A method in a station of a wireless network, the method comprising:

wirelessly receiving data from at least one remote station, said data transmitted by the remote station as at least one packet of data;

sampling the received data corresponding to the received packet to form data samples;

demodulating the data samples;

determining a measure of signal quality from the samples of the received data; and

selecting one of the remote stations for communication according to a set of least one criteria including the respective determined received signal quality measure for data from each of the remote stations,

wherein the determining of the measure of signal quality includes determining a measure of the error vector magnitude of the received data from received samples approximately at the decision points for demodulating the data, and

wherein the determining of the measure of the error vector magnitude of the received packet includes determining the average of the squared Euclidian distance on the I,Q plane between decision-point samples of the signal received and the correct ideal constellation points for the signal as determined by demodulating the signal.