Method and apparatus for estimating link quality

1. A method for determining a metric for link quality between a first node and a remote node of a wireless network, said nodes communicating using a handshake protocol in which said first node expects to receive an acknowledgement (ACK) of receipt of a data packet from said remote node, said method comprising the steps of:

providing a measure for any combination of:

a) noise-related losses (pn) between said first and remote nodes,

b) collision induced losses (pc) between said first and remote nodes,

c) hidden-node losses (ph) between said first and remote nodes,

d) a slot being erroneously detected as busy when a successful transmission could have been made (pexp) between said first and remote nodes, and

e) a probability of successful reception of a packet when a collision occurs (pplc) between said first and remote nodes,

at least one of said combined measures being based on a number (A) of acknowledgements received from said remote node vis-à-vis a number (T) of packets transmitted to said remote node; and

using said measure to determine said link quality metric between said first node and said remote node;

wherein said nodes communicate using an IEEE 802.11 protocol and providing said measure comprises:

measuring a collision induced loss probability pc as pc=1−(T 1 ·A 0 )/(T 0 ·A 1 ), where said first node contends and transmits data packets T 0 times and of these A 0 are successful because an ACK is received by said first node; and

where the first node transmits T 1 data packets after a Priority Interframe Spacing (PIFS) interval, which is shorter than a Distributed Inter-Frame Space (DIFS) interval, and of these A 1 are successful because an ACK is received by said first node.

2. A method as claimed in claim 1 wherein said nodes communicate using either a two-way or a four-way handshake protocol.

3. A method as claimed in claim 1 further comprising the step of:

selecting a channel for communication between said first and remote nodes based on the link quality metric.

4. A method as claimed in claim 1 further comprising the step of:

adjusting carrier sensitivity based on the link quality metric including de-sensitizing carrier sensitivity to improve quality.

5. A method as claimed in claim 1 comprising:

adjusting carrier sensitivity based on said measure of collision induced losses and said measure of a slot being erroneously detected as busy when a successful transmission could have been made between said first and remote nodes.

6. A method as claimed in claim 1 further comprising:

adjusting transmit power at said first node based on the link quality metric including reducing power to improve quality.

7. A method as claimed in claim 6 comprising:

adjusting transmit power based on said measure of collision induced losses and said probability of successful reception of a packet when a collision occurs between said first and remote nodes.

8. A method as claimed in claim 1 comprising:

determining a respective link quality metric for each remote node with which said first node communicates across said wireless network.

9. A method for determining a metric for link quality between a first node and a remote node of a wireless network, said nodes communicating using a handshake protocol in which said first node expects to receive an acknowledgement (ACK) of receipt of a data packet from said remote node, said method comprising the steps of:

providing a measure for any combination of:

a) noise-related losses (pn) between said first and remote nodes,

b) collision induced losses (pc) between said first and remote nodes,

c) hidden-node losses (ph) between said first and remote nodes,

d) a slot being erroneously detected as busy when a successful transmission could have been made (pexp) between said first and remote nodes, and

e) a probability of successful reception of a packet when a collision occurs (pplc) between said first and remote nodes,

at least one of said combined measures being based on a number (A) of acknowledgements received from said remote node vis-à-vis a number (T) of packets transmitted to said remote node; and

using said measure to determine said link quality metric between said first node and said remote node;

wherein providing said measure comprises determining a noise-related loss probability pn as pn=1−A S /T S , where said first node transmits T S second and subsequent data packets and of these A S are successful because an ACK is received by said first node.

10. A method for determining a metric for link quality between a first node and a remote node of a wireless network, said nodes communicating using a handshake protocol in which said first node expects to receive an acknowledgement (ACK) of receipt of a data packet from said remote node, said method comprising the steps of:

providing a measure for any combination of:

a) noise-related losses (pn) between said first and remote nodes,

b) collision induced losses (pc) between said first and remote nodes,

c) hidden-node losses (ph) between said first and remote nodes,

d) a slot being erroneously detected as busy when a successful transmission could have been made (pexp) between said first and remote nodes, and

e) a probability of successful reception of a packet when a collision occurs (pplc) between said first and remote nodes,

at least one of said combined measures being based on a number (A) of acknowledgements received from said remote node vis-à-vis a number (T) of packets transmitted to said remote node; and

using said measure to determine said link quality metric between said first node and said remote node;

wherein said nodes communicate using an IEEE 802.11 protocol and providing said measure comprises:

determining a hidden-node loss probability ph as ph=1−(A 1 ·T S )/(A S ·T 1 ), where the first node transmits T 1 data packets after a Priority Interframe Spacing (PIFS) interval, which is shorter than a Distributed Inter-Frame Space (DIFS) interval, and of these A 1 are successful because an ACK is received by said first node; and

where said first node transmits T S second and subsequent data packets and of these A S are successful because an ACK is received by said first node.

11. A method for determining a metric for link quality between a first node and a remote node of a wireless network, said nodes communicating using a handshake protocol in which said first node expects to receive an acknowledgement (ACK) of receipt of a data packet from said remote node, said method comprising the steps of:

providing a measure for any combination of:

a) noise-related losses (pn) between said first and remote nodes,

b) collision induced losses (pc) between said first and remote nodes,

c) hidden-node losses (ph) between said first and remote nodes,

d) a slot being erroneously detected as busy when a successful transmission could have been made (pexp) between said first and remote nodes, and

e) a probability of successful reception of a packet when a collision occurs (pplc) between said first and remote nodes,

at least one of said combined measures being based on a number (A) of acknowledgements received from said remote node vis-à-vis a number (T) of packets transmitted to said remote node; and

using said measure to determine said link quality metric between said first node and said remote node;

wherein said nodes communicate using an IEEE 802.11 protocol and providing said measure comprises:

estimating a probability pexp that a slot is erroneously detected as busy when in fact a successful transmission could have been made; and

estimating said probability pplc of successful reception of a packet when a collision occurs, as pexp+pplc=(T 1 ·A 0 )/(T 0 ·A 1 )−I/R where there are R MAC slots in which said first node does not transmit and that I of these are idle, where said first node contends and transmits data packets T 0 times and of these A 0 are successful because an ACK is received by said first node;

where the first node transmits T 1 data packets after a Priority Interframe Spacing (PIFS) interval, which is shorter than a Distributed Inter-Frame Space (DIFS) interval, and of these A 1 are successful because an ACK is received by said first node.

12. A first node of a wireless network comprising:

a driver operable in the first node of the wireless network for determining a metric for link quality between the first node and a remote node of the wireless network, said nodes communicating using a handshake protocol in which said first node expects to receive an acknowledgement (ACK) of receipt of a data packet from said remote node, said driver being arranged to:

provide a measure for any combination of:

a) noise-related losses (pn) between said first and remote nodes,

b) collision induced losses (pc) between said first and remote nodes,

c) hidden-node losses (ph) between said first and remote nodes,

d) a slot being erroneously detected as busy when a successful transmission could have been made (pexp) between said first and remote nodes, and

e) a probability of successful reception of a packet when a collision occurs (pplc) between said first and remote nodes,

at least one of said combined measures being based on a number (A) of acknowledgements received from said remote node vis-à-vis a number (T) of packets transmitted to said remote node; and

use said measure to determine said link quality metric between said first node and said remote node;

wherein said nodes communicate using an IEEE 802.11 protocol and, in order to provide said measure, said driver being further arranged to:

measure a collision induced loss probability pc as pc=1−(T 1 ·A 0 )/(T 0 ·A 1 ), where said first node contends and transmits data packets T 0 times and of these A 0 are successful because an ACK is received by said first node; and

where the first node transmits T 1 data packets after a Priority Interframe Spacing (PIFS) interval, which is shorter than a Distributed Inter-Frame Space (DIFS) interval, and of these A 1 are successful because an ACK is received by said first node.

13. A first node of a wireless network comprising:

a driver operable in the first node of the wireless network for determining a metric for link quality between the first node and a remote node of the wireless network, said nodes communicating using a handshake protocol in which said first node expects to receive an acknowledgement (ACK) of receipt of a data packet from said remote node, said driver being arranged to:

provide a measure for any combination of:

a) noise-related losses (pn) between said first and remote nodes,

b) collision induced losses (pc) between said first and remote nodes,

c) hidden-node losses (ph) between said first and remote nodes,

d) a slot being erroneously detected as busy when a successful transmission could have been made (pexp) between said first and remote nodes, and

e) a probability of successful reception of a packet when a collision occurs (pplc) between said first and remote nodes,

at least one of said combined measures being based on a number (A) of acknowledgements received from said remote node vis-à-vis a number (T) of packets transmitted to said remote node; and

use said measure to determine said link quality metric between said first node and said remote node;

wherein, in order to provide said measure, said driver is further arranged to determine a noise-related loss probability pn as pn=1−A S /T S , where said first node transmits T S second and subsequent data packets and of these A S are successful because an ACK is received by said first node.

14. A first node of a wireless network comprising:

a driver operable in the first node of the wireless network for determining a metric for link quality between the first node and a remote node of the wireless network, said nodes communicating using a handshake protocol in which said first node expects to receive an acknowledgement (ACK) of receipt of a data packet from said remote node, said driver being arranged to:

provide a measure for any combination of:

a) noise-related losses (pn) between said first and remote nodes,

b) collision induced losses (pc) between said first and remote nodes,

c) hidden-node losses (ph) between said first and remote nodes,

d) a slot being erroneously detected as busy when a successful transmission could have been made (pexp) between said first and remote nodes, and

e) a probability of successful reception of a packet when a collision occurs (pplc) between said first and remote nodes,

at least one of said combined measures being based on a number (A) of acknowledgements received from said remote node vis-à-vis a number (T) of packets transmitted to said remote node; and

use said measure to determine said link quality metric between said first node and said remote node;

wherein said nodes communicate using an IEEE 802.11 protocol and, in order to provide said measure, said driver being further arranged to:

determine a hidden-node loss probability ph as ph=1−(A 1 ·T S )/(A S ·T 1 ), where the first node transmits T 1 data packets after a Priority Interframe Spacing (PIFS) interval, which is shorter than a Distributed Inter-Frame Space (DIFS) interval, and of these A 1 are successful because an ACK is received by said first node; and

where said first node transmits T S second and subsequent data packets and of these A S are successful because an ACK is received by said first node.

15. A first node of a wireless network comprising:

a driver operable in the first node of the wireless network for determining a metric for link quality between the first node and a remote node of the wireless network, said nodes communicating using a handshake protocol in which said first node expects to receive an acknowledgement (ACK) of receipt of a data packet from said remote node, said driver being arranged to:

provide a measure for any combination of:

a) noise-related losses (pn) between said first and remote nodes,

b) collision induced losses (pc) between said first and remote nodes,

c) hidden-node losses (ph) between said first and remote nodes,

d) a slot being erroneously detected as busy when a successful transmission could have been made (pexp) between said first and remote nodes, and

e) a probability of successful reception of a packet when a collision occurs (pplc) between said first and remote nodes,

at least one of said combined measures being based on a number (A) of acknowledgements received from said remote node vis-à-vis a number (T) of packets transmitted to said remote node; and

use said measure to determine said link quality metric between said first node and said remote node;

wherein said nodes communicate using an IEEE 802.11 protocol and, in order to provide said measure, said driver being further arranged to:

estimate a probability pexp that a slot is erroneously detected as busy when in fact a successful transmission could have been made; and

estimate said probability pplc of successful reception of a packet when a collision occurs, as pexp+pplc=(T 1 ·A 0 )/(T 0 ·A 1 )−I/R where there are R MAC slots in which said first node does not transmit and that/of these are idle, where said first node contends and transmits data packets T 0 times and of these A 0 are successful because an ACK is received by said first node;

where the first node transmits T 1 data packets after a Priority Interframe Spacing (PIFS) interval, which is shorter than a Distributed Inter-Frame Space (DIFS) interval, and of these A 1 are successful because an ACK is received by said first node.