Q: What is the current timetable for the development and ratification of the 802.11n standard?

A: Here's the latest timeline for the IEEE standard development for 11n and how the WFA activites overlay. 

Q: What is the general progress of the 802.11n specification?

A: Following are the major milestones which have occurred in 2006.

1) January  '06 – IEEE TGn membership voted unanimously to confirm the 802.11n draft specification

2) March '06 – IEEE membership voted 87% to confirm the draft to 1.0 status.

3) May – May ‘06 – March ‘07– As expected, the first Letter Ballot of the 1.0 draft specification failed to achieve the required 75% approval to move to the next step toward ratification. There were a tremendous number of comments submitted on the draft The comments were divided among eight ad-hoc teams to streamline the process and by March of 2007, all the comments were addressed and a new draft (2.0) was generated.

4) March '07 – present– The letter ballot to move the 2.0 draft to sponsor ballot achieved more than the 75% threshold (83%) in March ‘07. However, historically, task groups generally aim for better than a 90% approval rating. Furthermore, there were 3000+ new comments submitted. The same ad hoc teams are currently meeting regularly to resolve these new comments. The goal of having a new draft for consideration for the sponsor ballot in September appears to be on schedule

Q: What is the Wi-Fi Alliances’ plan of record for certifying pre-ratified product?

A: The WFA is now certifying pre-ratified 802.11n product based on the Wi-Fi CERTIFIED 802.11n draft 2.0 testing program. The certification process was developed by the industry alliance to help ensure baseline performance and interoperability among end products. To achieve this certification, devices must demonstrate interoperability with reference products selected for the test bed. The Wi-Fi Alliance’s decision to certify end-user products based upon the current 802.11n draft 2.0 specification in advance of the IEEE’s final ratification signals the stability of the draft, creates a significant transition for the industry and enhances consumer confidence in purchasing 802.11n products now. Ratified 11n certification is intended to begin in June of 2007. More details on this plan should become available from the WFA.

Q: Will products coming on the market now be upgradeable to the final standard?

A: While no company can guarantee that products now based on the draft 802.11n d2.0 specification will be compatible or upgradeable with the ratified standard, Atheros believes that there is very high probability that this will be so. For Atheros XSPAN chipsets, the changes to the specification from draft 1.0 to draft 2.0 were modest and achieved through firmware upgrades.

Q: Why does Atheros believe that products based on Atheros XSPAN™ technology will likely be compatible with products based on the final 802.11n standard?

A: The draft is very stable. Reasons to believe in the stability of the 1.0 draft:

• The changes between draft 1.0 and draft 2.0 802.11n specifications were minor and were addressed by firmware upgrades. The comments being addressed for the draft 2.0 802.11n specifications appear to be such that firmware upgrades will enableXSPAN-based products to be compliant.
• A number of companies with high stakes in the standard development have spent the past three to four years developing this specification. It has been given tremendous consideration already.
• It will take a 75% vote of the IEEE membership to make any significant technical change to the spec.
• A number of companies are already shipping product based on the draft 2.0 802.11n specification. This has generated market momentum that favors the ratification of a specification that does not differ greatly from the 2.0 draft.
• Now, draft 2.0-based products are being widely manufactured by enterprise networking equipment vendors as well as retail vendors.

Q: What is Atheros’ involvement in the development of the 802.11n standard?

A: Atheros is very involved in every step of the development of the 802.11n standard and has been so for more than three years now. We drove the development of the Enhanced Wireless Consortium (EWC), the EWC’s specification and adoption of the specification by the IEEE. There are no companies more involved than Atheros in driving and modeling this standard. Our CTO, Bill McFarland, and key members of the technical team attend all key meetings and calls, and vote on every issue. 

Q: How is interoperability with other 802.11n devices assured in the specification?

A: An array of elements is required (that is mandatory in the draft specification) to ensure interoperability. These are:

• A-MPDU Aggregation
• Immediate block ACK transmission
• A-MSDU aggregation
• CCMP/AES/WPA2 encryption/decryption at full speed

Atheros has implemented all of the above in our solutions and are confident that if other silicon providers implement the same elements properly, our solutions will effectively interoperate with theirs.

A: Significant steps must be taken to ensure 802.11n-based products operate effectively with legacy 802.11a, b and g devices and will avoid “stepping on” such legacy devices, especially when 802.11n products shift into the highest throughput mode of 40 MHz channel operation.

In our 802.11n solutions, we have implemented Clear Channel Assessment (CCA). This is a smart technology that allows the 802.11n device to assess the channel on a dynamic basis to determine whether legacy Wi-Fi products are transmitting on a nearby channel. When a legacy transmission is occurring, the 802.11n device “steps down”, allowing for the legacy transmission to occur without performance degradation. When no legacy traffic can be detected, the 802.11n operation resumes.

Atheros has extensive experience in smart radio technologies to leverage the capacity of 40 MHz channel operation while avoiding interference with neighbors. In 2003, our Super A/G technology employed for the first time in WLAN history the 40 MHz channel. In order to create “legacy-friendly” operation, we developed Atheros Adaptive Radio Technology and have successfully used the technology in the three years since its development.

Q: Does the 2.0 draft 802.11n specification call for elements to ensure “neighbor friendly” behavior with legacy 802.11 devices?

A: Yes.  The only significant change made to the draft 1.0 specification was the addition of the “neighbor friendly” behavior for 40MHz operation in the 2.4GHz band. However, just how “friendly” of a neighbor the 40MHz system needs to be is still in a topic of discussion at the IEEE. The current specification in draft 2.0 are these three new requirements: 1. Prior to setting up a 40 MHz access point (AP), the AP is required to scan for legacy traffic in the entire 40MHz spectrum. 2. Prior to each transmission of 40MHz packets, Clear Channel Assessment must be done to ensure that no legacy traffic exists in the entire 40MHz spectrum. 3. Stations associated to a 40MHz AP must assist in scanning for legacy traffic which may have been hidden from the AP.  In short, the IEEE’s specification requires that the 40MHz device does “no harm” to neighboring legacy systems.

Q: What is the 3x3 MIMO design architecture that Atheros has launched with XSPAN products and what is its significance for 802.11n?

A: Single-band (2.4GHz) products based on Atheros’ 802.11n technologies should deliver a maximum of 300 Mbps physical data rates, providing end users with 150 to 180 Mbps real-world throughput levels. Atheros’ initial solutions transmit two data streams; it is expected that subsequent technologies will employ up to 4 streams, enabling even greater throughput levels up to 600 Mbps.  Dual-band, dual-concurrent (2.4 & 5GHz) solutions based on Atheros’ XSPAN technology enable PHY-layer throughput rates up to 600Mbps. (More information on the dual-band, dual-concurrent solutions are discussed below.)

Users should expect significantly higher rate over range with Atheros’ technology versus other companies’ 802.11n offerings. This is because Atheros solutions support the transmission of 2 data streams with 3 transmit and 3 receive chains (or 3Tx/3Rx). This is the 3x3 design architecture that has been discussed.

In solutions where the radio chains outnumber the data chains, greater reliability is achieved in the data transmission; more data reaches the endpoint in a more readable manner. This increased reliability (roughly 50% increase in the reliability of the transmission in 3x3-based solutions) results in roughly 50% greater throughput at range versus more typical 802.11n solutions employing more standard 2Tx/2Rx designs).

This unique, 3Tx/3Rx MIMO design architecture employed by Atheros is called Signal-Sustain Technology™ . It very effectively sustains the 802.11n radio signal, and the corresponding connection.

Figure 1: This 4000 square foot house shows the throughput at range differential that can be achieved through Atheros Signal-Sustain Technology, our 3x3 design architecture versus standard 2x2 MIMO designs.

Atheros recommends that customers implement the 3Tx/3Rx solution on access points/routers to maximize throughput at range. While customers can also implement 3Tx/3Rx on the client side, Atheros recommends for extremely power-sensitive clients, the 2Tx/3Rx design. This design enables optimization of throughput at range while inhibiting the power consumption so critical in portable devices. The throughput-at-range benefits of the 2x3 clients are also significant as shown in the chart below.  (Note, in the 2x3 design, the uplink employs 2Tx while the downlink has the advantage of 3Rx.  This means that no compromise occurs on the downlink function more critical to performance.)

Figure 2: Depicts throughput at range of 2x3 vs. that of 2x2 and 802.11g.

Q: What type of performance should users expect in mixed mode environments?

Scenario One : The access point is based on 802.11n, the client is 802.11g. 

The access point will communicate with the client in 802.11g mode, and the devices will deliver 802.11g performance.


Figure 3: 802.11g client on 802.11n network.

Scenario Two : The access point is based on 802.11n and there are one or more 802.11n clients, and one or more 802.11g clients. 

The access point will communicate in 802.11n to the 802.11n clients; the access point will speak 802.11g to the 802.11g clients. The devices should deliver the performance expected from 802.11n and 802.11g, respectively.

Figure 4: 802.11n and 802.11g clients operating on an 802.11n network.

Scenario Three: The router/access point is 802.11a or 802.11g and it is connected to an 802.11n client. 

The negotiation of protocols will be completely seamless. The 802.11n client will communicate in either legacy 802.11a or 802.11g mode to the legacy AP.


Figure 5: 802.11n client on an 802.11g net.

Q: What is the difference between Signal-Sustain Technology and “antenna configuration” that is offered by some of your competitors?

A; Signal-Sustain Technology (SST) dramatically increases link robustness and throughput by simultaneously transmitting across three spatially-diverse signal paths, and incorporating information from three receivers simultaneously within the signal processing at the receive end. Such robustness cannot be achieved by simply switching a smaller number of simultaneous transmitters between additional antennas as is the case with “antenna configuration”. In fact, in the process of switching among antennas, overhead is increased and end-user throughput is diminished.

In order to achieve SST and the increased reliability attained with the approach, three separate radio transmit and receive paths are required. Atheros efficiently delivers this 3x3 MIMO scheme with its triple radio chip design. This, the worlds only triple radio chipset, delivers optimal radio performance while containing BOM costs.

Q: What are some of the applications that will benefit from all this extra bandwidth that this new 11n technology has to offer?

A: “Triple play” is a term used to describe broadband access simultaneously supporting voice, data, and multimedia (especially video). Until now, Wireless LAN systems were only capable of optimally supporting voice and data. With the advent of high definition (HD) video, the bandwidth requirements for streaming multimedia content have been pushed to 20+Mbps. If multiple streams of HD video are desired, 40-60Mbps is now the minimum performance threshold. The new generation 11n products are capable of supporting 150Mbps actual throughput and can readily support triple play in the home.

Q: What about congestion from a neighbor’s WLAN system?

A: The 2.4GHz band contains only 3 non-overlapping 20MHz channels. With the proliferation of Wi-Fi, more and more people are now “time sharing” the same spectrum and no single user can sustain the full bandwidth capacity of his or her network. For future triple play applications in the home, we recommend dual-band, dual-concurrent solutions. These designs introduce the use of the 5GHz band where up to 24 non-overlapping channels can be found. For bandwidth-hungry and latency sensitive applications such as video, the 5GHz band will support ample traffic and usage scenarios while the 2.4GHz band can readily support the traditional data applications as well as voice.