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DTUS065 rev A.7 – June 27, 2014
Since the 2.4 GHz band is often saturated, using the relatively unused 5 GHz
band gives 802.11a provides a significant advantage. However, this high
carrier frequency also brings a slight disadvantage: The effective overall
range of 802.11a is slightly less than that of 802.11b/g; 802.11a signals
cannot penetrate as far as those for 802.11b because they are absorbed more
easily by walls and other solid objects in their path.
V.3.4
802.11n
802.11n can operate on either the 2.4 GHz or 5 GHz band. According to the
chosen one, the above notes about range and band saturation also apply.
802.11n also allows using a channel width of either 20 MHz or 40 MHz to
double bandwidth. “HT20” refers to the standard single channel operation;
“HT40” refers to the extended double channel operation.
802.11n hardware may allow transmission of more than one data stream (so-
called “spatial streams”) simultaneously. In order for the streams not to
interfere with each other, the radio signal must bounce on obstacles in
various directions, or the antennas must be polarized. Both cases result in
lower range due to power losses, but faster transmission.
The number of spatial streams must not be confused for the number of
antennas. Furthermore antennas can be dedicated to emission or reception
only. Hence an 802.11n radio specification must include three numbers:
number of transmitters, number of receivers, and number of spatial streams.
In order to automatically adapt to radio conditions, the 802.11n uses various
transmission parameters: number of streams, modulation, channel width and
so on. The resulting transmission format is named Modulation and Coding
Scheme (MCS). WLn products handle 1 to 3 streams depending on the
model. Here are the physical bit rates achievable with one and two streams:
Maximum bit rate (Mbps)
1 stream
2 streams
Channel
width
20
MHz
40
MHz
Channel
width
20
MHz
40
MHz
MCS 0
7.2
15
MCS 8
14.4
30
MCS 1
14.4
30
MCS 9
28.9
60
MCS 2
21.7
45
MCS 10
43.3
90
MCS 3
28.9
60
MCS 11
57.8
120
MCS 4
43.3
90
MCS 12
86.7
180
MCS 5
57.8
120
MCS 13
115.6
240
MCS 6
65.0
135
MCS 14
130.0
270
MCS 7
72.2
150
MCS 15
144.4
300
Note 1
: When the peer station cannot handle short guard intervals, the bit rate is reduced
by about 10%. Guard interval is an 802.11n feature allowing shortening some idle times
during transmission.
Note 2
: As can be inferred from the above table, the bit rate is proportional to the
number of streams. A 3 streams radio can transfer up to 450 Mbps.
Note 3
: Actual bitrate and throughput depend on the distance between stations, antennas
quality and radio conditions
For detailed information and relationship about MCS, bit rates,
maximum transmit power and receiver sensitivity, refer to either the
CDROM or the quick start guide appropriate for each product.
