802.11e Physical Rates
What are physical rates in IEEE 802.11e?
Physical rates refer to the actual data transmission speeds supported at the PHY layer, inherited from 802.11a/g.
Does 802.11e define new PHY data rates?
No, 802.11e focuses on MAC enhancements and relies on existing PHY layers like 802.11a, b, and g.
What is the range of physical rates supported in 802.11e?
It supports all PHY rates from 802.11a/b/g, ranging from 1 Mbps (DSSS) to 54 Mbps (OFDM).
Does QoS affect physical rate selection in 802.11e?
Indirectly—higher-priority traffic may experience better channel access and maintain higher PHY rates more consistently.
How are physical rates selected in 802.11e networks?
Rate selection is handled by rate adaptation algorithms based on signal quality, not directly by 802.11e.
What modulation schemes are used with 802.11e?
Modulation schemes depend on the PHY—e.g., BPSK, QPSK, 16-QAM, and 64-QAM in OFDM (802.11a/g).
Can 802.11e be used with 802.11n or later PHYs?
Yes, 802.11e QoS concepts were extended into later standards like 802.11n, ac, and ax.
What is the relationship between QoS and physical rates?
QoS prioritizes access to the channel, allowing latency-sensitive traffic to potentially utilize higher PHY rates with fewer retransmissions.
Does 802.11e support dynamic rate shifting?
Yes, stations can dynamically adjust physical rates depending on channel conditions, like in other 802.11 protocols.
Can 802.11e operate at fixed physical rates?
Yes, fixed rate operation is possible but typically discouraged in favor of dynamic adaptation.
Does 802.11e require special PHY hardware?
No, it runs on existing PHY hardware as long as it supports the associated 802.11 standard (a/b/g).
How does EDCA relate to PHY rates?
EDCA affects channel access timing, influencing how effectively higher PHY rates are utilized under congestion.
What is the role of PHY rate in QoS performance?
Higher PHY rates reduce transmission time, minimizing delays and improving performance for QoS-sensitive applications.
Can PHY rates vary during a session?
Yes, physical rates may vary due to rate adaptation algorithms reacting to changing wireless conditions.
Does the Access Category (AC) affect PHY rate selection?
No, AC affects MAC scheduling. PHY rate is still chosen based on link quality and device capabilities.
Is PHY rate visible to upper layers?
Not directly. Upper layers may observe performance changes but don’t control PHY rate selection.
What is the minimum PHY rate in 802.11e?
It depends on the PHY used—for example, 6 Mbps for OFDM (802.11a/g) and 1 Mbps for DSSS (802.11b).
Does 802.11e guarantee minimum PHY throughput?
No, but it enhances delivery prioritization to improve service quality, especially under congestion.
Is physical rate negotiation affected by QoS policies?
Not directly, but prioritized traffic may avoid retransmissions and experience better link conditions, maintaining higher rates.
What happens if the PHY rate drops in a QoS session?
The MAC may increase retransmission attempts, but lower latency classes may still be served first due to prioritization.
Topics in this section,
Modulation |
BW |
Tsc |
FSP=BW/Tsc |
Tdata=1/FSP |
GI=Tdata/4 |
Symbol=Tdata+GI |
1/Symbol |
Bits/Symbol |
Code rate |
Usable sc |
Rate |
|---|---|---|---|---|---|---|---|---|---|---|---|
BPSK |
5 |
64 |
78.125 |
12.8 |
3.2 |
16 |
0.0625 |
1 |
1/2 |
48 |
1.5 |
BPSK |
5 |
64 |
78.125 |
12.8 |
3.2 |
16 |
0.0625 |
1 |
3/4 |
48 |
2.25 |
QPSK |
5 |
64 |
78.125 |
12.8 |
3.2 |
16 |
0.0625 |
2 |
1/2 |
48 |
3 |
QPSK |
5 |
64 |
78.125 |
12.8 |
3.2 |
16 |
0.0625 |
2 |
3/4 |
48 |
4.5 |
16-QAM |
5 |
64 |
78.125 |
12.8 |
3.2 |
16 |
0.0625 |
4 |
1/2 |
48 |
6 |
16-QAM |
5 |
64 |
78.125 |
12.8 |
3.2 |
16 |
0.0625 |
4 |
3/4 |
48 |
9 |
64-QAM |
5 |
64 |
78.125 |
12.8 |
3.2 |
16 |
0.0625 |
6 |
2/3 |
48 |
12 |
64-QAM |
5 |
64 |
78.125 |
12.8 |
3.2 |
16 |
0.0625 |
6 |
3/4 |
48 |
13.5 |
BPSK |
10 |
64 |
156.25 |
6.4 |
1.6 |
8 |
0.125 |
1 |
1/2 |
48 |
3 |
BPSK |
10 |
64 |
156.25 |
6.4 |
1.6 |
8 |
0.125 |
1 |
3/4 |
48 |
4.5 |
QPSK |
10 |
64 |
156.25 |
6.4 |
1.6 |
8 |
0.125 |
2 |
1/2 |
48 |
6 |
QPSK |
10 |
64 |
156.25 |
6.4 |
1.6 |
8 |
0.125 |
2 |
3/4 |
48 |
9 |
16-QAM |
10 |
64 |
156.25 |
6.4 |
1.6 |
8 |
0.125 |
4 |
1/2 |
48 |
12 |
16-QAM |
10 |
64 |
156.25 |
6.4 |
1.6 |
8 |
0.125 |
4 |
3/4 |
48 |
18 |
64-QAM |
10 |
64 |
156.25 |
6.4 |
1.6 |
8 |
0.125 |
6 |
2/3 |
48 |
24 |
64-QAM |
10 |
64 |
156.25 |
6.4 |
1.6 |
8 |
0.125 |
6 |
3/4 |
48 |
27 |
BPSK |
20 |
64 |
312.5 |
3.2 |
0.8 |
4 |
0.25 |
1 |
1/2 |
48 |
6 |
BPSK |
20 |
64 |
312.5 |
3.2 |
0.8 |
4 |
0.25 |
1 |
3/4 |
48 |
9 |
QPSK |
20 |
64 |
312.5 |
3.2 |
0.8 |
4 |
0.25 |
2 |
1/2 |
48 |
12 |
QPSK |
20 |
64 |
312.5 |
3.2 |
0.8 |
4 |
0.25 |
2 |
3/4 |
48 |
18 |
16-QAM |
20 |
64 |
312.5 |
3.2 |
0.8 |
4 |
0.25 |
4 |
1/2 |
48 |
24 |
16-QAM |
20 |
64 |
312.5 |
3.2 |
0.8 |
4 |
0.25 |
4 |
3/4 |
48 |
36 |
64-QAM |
20 |
64 |
312.5 |
3.2 |
0.8 |
4 |
0.25 |
6 |
2/3 |
48 |
48 |
64-QAM |
20 |
64 |
312.5 |
3.2 |
0.8 |
4 |
0.25 |
6 |
3/4 |
48 |
54 |
Reference links