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.

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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.

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*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.

d3

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.

d4

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.

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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.

Exalt Introduces ExtendAir G2
Up to 370 Mbps, Lowest Cost Per-Bit

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