The Detailed Results
At 4G World in September 2009, Exalt conducted a live demonstration of the
company’s new ExtendAir® 5 GHz point-to-point microwave radio to compare its
performance to that of the latest and best-in-class 802.11n Wi-Fi Ethernet
bridge. The purpose was to evaluate the performance of each system under a
variety of path fading and interference conditions.
Demonstration Set-up
In order to fairly compare the performance of ExtendAir vs. a leading 802.11n
Wi-Fi Ethernet bridge, two identical links were made established via direct
RF cable connections. This was done to provide a controlled RF environment
for the test. Both paths had the exact same level of fixed attenuation, and
variable attenuation was provided to simulate similar path fading conditions.
Both the ExtendAir and 802.11n radios were configured for each test according
to the settings shown in the tables below. In addition, a third 5 GHz radio
was used to introduce an interfering carrier to both paths simultaneously.
Throughput was measured using a layer 2 SmartBits® tester with 1536-byte
sized packets and compared in real-time as tests were performed.
Three separate tests were conducted for each of two unique throughput scenarios:
1) full sustained throughput, which is the maximum throughput that each system
is able to deliver and 2) equivalent sustained throughput of 100 Mbps.
The first test compared resiliency to path fading conditions. The objective
was to determine the amount of fading in dB that the systems could endure before
the target throughput could no longer be maintained. Paths were gradually faded
until a noteworthy degradation in throughput for each system was observed.
The second test compared resiliency to an interfering carrier affecting both
paths on the same channel. The objective was to determine the amount of interference
in dB that the systems could endure before the required throughput could no
longer be maintained.
The third and final test measured link recovery time after completely dropping
both links through fading or interference conditions, and then simultaneously
restoring the link by removing the fade or interference condition.
Connection Diagram
The paths were established according to the following diagram. Each path had
66dB of fixed attenuation and also included 50 dB variable attenuators to
simulate link fading conditions. The interfering carrier was modeled using
an Exalt EX-5i radio with 46 dB of fixed attenuation to each of the two 802.11n
polarizations and the ExtendAir path, plus a 50 dB variable attenuator to
control the level of interference inserted into all paths. For the path fading
tests, this variable attenuator was set at 50 dB, providing a total attenuation
of 96 dB.
Full Throughput Test Radio Configuration
| Radio Configurations |
ExtendAir |
802.11n |
| Channel bandwidth |
33 MHz |
20 MHz (x2) |
| Modulation |
64 QAM |
Not configurable |
| Channel |
5.820 GHz |
5.820 Ghz |
| Polarization |
Single |
Dual |
| Aggregate data rate |
120 Mpbs |
130 Mpbs fixed |
| Aggregate user throughput |
120 Mpbs
(~133 Mbps measured) |
Not configurable
(~104 Mbps measured) |
| System output power |
13 dBm |
13 dBm |
100 Mbps Throughput Test Radio Configuration
| Radio Configurations |
ExtendAir |
802.11n |
| Channel bandwidth |
33 MHz |
20 MHz (x2) |
| Modulation |
16 QAM |
Not configurable |
| Channel |
5.820 GHz |
5.820 Ghz |
| Polarization |
Single |
Dual |
| Data rate |
100 Mpbs |
130 Mpbs fixed |
| User throughput |
100 Mpbs
(~108 Mbps measured) |
Not configurable
(~104 Mbps measured) |
| System output power |
13 dBm |
13 dBm |
Interferer Radio Configuration
| Radio configuration |
Exalt EX-5i |
| Channel Bandwidth |
32 MHz |
| Modulation |
QPSK |
| Channel |
5.820 GHz |
| Polarization |
Single |
| Data rate |
N/A |
| User throughput |
N/A |
| System output power |
+24 dBm |
Path Fade Measurements at Full Sustained Throughput
In this test, the individual paths for the ExtendAir and the 802.11n radios
were faded using the variable attenuators indicated in the diagram above.
The level of attenuation was increased until a noticeable throughput difference
was measured by the SmartBits tester. The attenuation was increased until
the link dropped. With the 802.11n radio, the link behavior was the same
whether a single polarization was attenuated or both polarizations were attenuated
simultaneously. A typical set of results is shown in the graph below.
*link is affected equally with attenuation in either polarization. If a
single polarization goes down the entire link goes down
ExtendAir exhibits 2-3dB better resiliency to path fading conditions than
the 802.11n radio while providing up to 30% more throughput in 20% less spectrum.
The 802.11n radio achieves a peak data rate of 130 Mbps using two cross-polarized
20MHz channels (40MHz total) at 64QAM modulation, yielding net throughut of
104 Mbps. In contrast, ExtendAir requires only a single 32 MHz channel in single
polarization and 64QAM modulation, yielding 133 Mbps of real user throughput.
This 2-3 dB advantage results in improved availability, slightly longer distances
and/or reduced antenna size.
Interference Measurements at Full Sustained Throughput
In this test, an interfering signal was introduced on the same channel and
summed to both paths simultaneously. The interfering signal was gradually
increased by reducing the level of attenuation in the interfering signal
path. The level of interference was increased until a noticeable throughput
difference was measured by the SmartBits tester. The amount of attenuation
reduction (equivalent to the power of the interfering signal) was recorded.
The interfering signal was increased until the link dropped completely and
corresponding measurements were made. Note: with the 802.11n radio, the link
behavior was the same whether either or both polarizations were subjected
to interference.
As with the path fade tests, ExtendAir exhibits 3-4dB better resiliency to
interference than 802.11n. The result of this difference was readily observable:
by the time the interference started affecting ExtendAir, the 802.11n link
had already dropped. Because 802.11n and other Wi-Fi systems cannot reliably
sustain a link at full throughput under these conditions, Wi-Fi systems must
utilize adaptive modulation in an attempt to maintain a connection at the expense
of lower throughput.
Link Recovery Time at Full Sustained Throughput
Both the ExtendAir and 802.11n links were individually subjected
to severe path fading and interference conditions in order to cause the links
to drop. In each case, when the impairment was removed the ExtendAir link
recovered in less than two seconds while the 802.11n link recovered only
after seven seconds. This indicates that under identical path impairment conditions,
ExtendAir is not only more resilent than 802.11n, but it also recovers faster
when affected by path fading or interference.
Path Fade Measurements at 100 Mbps Throughput
In this test, the configuration of the ExtendAir radio was modified to provide
approximately the same throughput as the 802.11n radio. By simply changing
the radio’s modulation from 64QAM to 16QAM, ExtendAir delivered 108 Mbps
as measured by the SmartBits tester. As with the previous path fade test,
the paths were gradually faded until a measureable throughput impact was
observed.
For a sustained throughput of approximately 100 Mbps, ExtendAir exhibited
9dB better resiliency to path fading conditions than 802.11n. This is due to
ExtendAir’s ability to deliver the required throughput at 16QAM modulation
instead of 802.11n’s required 64QAM. This performance advantage means that
ExtendAir can achieve more than twice the distance as 802.11n or that antenna
size can be reduced from a 6 ft. (1.8m) diameter to a 2 ft. (60cm) diameter,
yielding significant cost savings. For a given link distance at 100 Mbps sustained
throughput, ExtendAir provides nearly ten times the transmission resiliency
in faded path conditions than the best 802.11n radio.
Interference Measurements at Equivalent Sustained Throughput
The same interference test was performed for the 100Mbps throughput comparison
with ExtendAir configured for 108 Mbps, comparable to the maximum of 104
Mbps provided by the 802.11n radio. Once again, the interfering signal was
injected by gradually reducing the attenuation in the interfering signal
path.
In this configuration, ExtendAir also exhibited 9 dB better interference rejection
than did the 802.11n radio. Furthermore, before the ExtendAir link was even
affected by the interfering signal, the 802.11n link had dropped. This demonstrates
that at the 100 Mbps throughput level, ExtendAir delivers nearly ten times
higher interference rejection than the best 802.11n radio on the market. Simply
put, ExtendAir can provide fast and reliable connections where Wi-Fi and OFDM
radios can’t.
Link Recovery Time at 100Mbps Throughput
As with the previous link recovery test, the ExtendAir
link recovered in less than two seconds while the 802.11n link recovered
after approximately seven seconds. This link recovery behavior is clearly consistent
regardless of the throughput or the type of link impairment experienced
by both systems.
Conclusions
Exalt demonstrated that ExtendAir can deliver guaranteed performance and throughput
under severe link fading and interference conditions, significantly outperforming
the leading 802.11n OFDM Wi-Fi Ethernet bridge in both the path fading and
interference rejection tests. The results indicate that at full throughput,
ExtendAir can provide an additional link fade margin of 2-3 dB while providing
approximately 4dB additional interference rejection. At the same 100Mbps
throughput, ExtendAir provided 9dB better fade margin and interference rejection
than the 802.11n system.
These performance advantages translate directly into higher availability,
longer paths, significantly lower antenna sizes, and lower costs.
ExtendAir also delivers significantly higher maximum throughput than is possible
with the latest 802.11n Wi-Fi technology.
Finally, ExtendAir delivers the performance detailed above at about the same
price of an 802.11n link.