MIMO for handset Wi-Fi

I mentioned earlier that the Wi-Fi Alliance requires MIMO for 802.11n certification except for phones, which can be certified with a single stream. This waiver was for several reasons, including power, size and the difficulty of getting two spatially separated antennas into a handset. Atheros and Marvell appear to have overcome those difficulties; both have announced 2×2 Wi-Fi chips for handsets. Presumably TI and Broadcom will not be far behind.

The Atheros chip is called the AR6004. According to Rethink Wireless,

The AR6004 can use both the 2.4GHz and the 5GHz bands and is capable of real world speeds as high as 170Mbps. Yet the firm claims its chip consumes only 15% more power than the current AR6003, which delivers only 85Mbps. It will be available in sample quantities by the end of this quarter and in commercial quantities in the first quarter of next year.

The AR6004 appears to be designed for robust performance. It incorporates all the optional features of 802.11n intended to improve rate at range. Atheros brands this suite of features “Signal Sustain Technology.” The AR6004 is also designed to reduce the total solution footprint, by including on-chip power amplifiers and low-noise amplifiers. Historically on-chip CMOS power amplifiers have performed worse than external PAs using GaAs, but Atheros claims to have overcome this deficiency, prosaically branding its solution “Efficient Power Amplifier.”

The 88W8797 from Marvell uses external PAs and LNAs, but saves space a different way, by integrating Bluetooth and FM onto the chip. The data sheet on this chip doesn’t mention as many of the 802.11n robustness features as the Atheros one does, so it is unclear whether the chip supports LDPC, for example.

Both chips claim a maximum 300 Mbps data rate. Atheros translates this to an effective throughput of 170 Mbps.

Of course, these chips will be useful in devices other than handsets. They are perfect for tablets, where there is plenty of room for two antennas at the right separation.

Sharing Wi-Fi Update

Back in February 2009 I wrote about how Atheros’ new chip made it possible for a phone to act as a Wi-Fi hotspot. A couple of months later, David Pogue wrote in the New York Times about a standalone device to do the same thing, the Novatel MiFi 2200. The MiFi is a Wi-Fi access point with a direct connection to the Internet over a cellular data channel. So you can have “a personal Wi-Fi bubble, a private hot spot, that follows you everywhere you go.”

The type of technology that Atheros announced at the beginning of 2009 was put on a standards track at the end of 2009; the “Wi-Fi Direct” standard was launched in October 2010. So far about 25 products have been certified. Two phones have already been announced with Wi-Fi Direct built-in: the Samsung Galaxy S and the LG Optimus Black.

Everybody has a cell phone, so if a cell phone can act as a MiFi, why do you need a MiFi? It’s another by-product of the dysfunctional billing model of the mobile network operators. If they simply bit the bullet and charged à la carte by the gigabyte, they would be happy to encourage you to use as many devices as possible through your phone.

WiFi Direct may force a change in the way that network operators bill. It is such a compelling benefit to consumers, and so trivial to implement for the phone makers, that the mobile network operators may not be able to hold it back.

So if this capability proliferates into all cell phones, we will be able to use Wi-Fi-only tablets and laptops wherever we are. This seems to be bad news for Novatel’s MiFi and for cellular modems in laptops. Which leads to another twist: Qualcomm’s Gobi is by far the leading cellular modem for laptops, and Qualcomm just announced that it is acquiring Atheros.

First 802.11n handset spotted in the wild – what took so long?

The fall 2009 crop of ultimate smartphones looks more penultimate to me, with its lack of 11n. But a handset with 802.11n has come in under the wire for 2009. Not officially, but actually. Slashgear reports a hack that kicks the Wi-Fi chip in the HTC HD2 phone into 11n mode. And the first ultimate smartphone of 2010, the HTC Google Nexus One is also rumored to support 802.11n.

These are the drops before the deluge. Questions to chip suppliers have elicited mild surprise that there are still no Wi-Fi Alliance certifications for handsets with 802.11n. All the flagship chips from all the handset Wi-Fi chipmakers are 802.11n. Broadcom is already shipping volumes of its BCM4329 11n combo chip to Apple for the iTouch (and I would guess the new Apple tablet), though the 3GS still sports the older BCM4325.

Some fear that 802.11n is a relative power hog, and will flatten your battery. For example, a GSMArena report on the HD2 hack says:

There are several good reasons why Wi-Fi 802.11n hasn’t made its way into mobile phones hardware just yet. Increased power consumption is just not worth it if the speed will be limited by other factors such as under-powered CPU or slow-memory…

But is it true that 802.11n increases power consumption at a system level? In some cases it may be: the Slashgear report linked above says: “some users have reported significant increases in battery consumption when the higher-speed wireless is switched on.”

This reality appears to contradict the opinion of one of the most knowledgeable engineers in the Wi-Fi industry, Bill McFarland, CTO at Atheros, who says:

The important metric here is the energy-per-bit transferred, which is the average power consumption divided by the average data rate. This energy can be measured in nanojoules (nJ) per bit transferred, and is the metric to determine how long a battery will last while doing tasks such as VoIP, video transmissions, or file transfers.

For example, Table 1 shows that for 802.11g the data rate is 22 Mbps and the corresponding receive power-consumption average is around 140 mW. While actively receiving, the energy consumed in receiving each bit is about 6.4 nJ. On the transmit side, the energy is about 20.4 nJ per bit.

Looking at these same cases for 802.11n, the data rate has gone up by almost a factor of 10, while power consumption has gone up by only a factor of 5, or in the transmit case, not even a factor of 3.

Thus, the energy efficiency in terms of nJ per bit is greater for 802.11n.

Here is his table that illustrates that point:
Effect of Data Rate on Power Consumption

Source: Wireless Net DesignLine 06/03/2008

The discrepancy between this theoretical superiority of 802.11n’s power efficiency, and the complaints from the field may be explained several ways. For example, the power efficiency may actually be better and the reports wrong. Or there may be some error in the particular implementation of 802.11n in the HD2 – a problem that led HTC to disable it for the initial shipments.

Either way, 2010 will be the year for 802.11n in handsets. I expect all dual-mode handset announcements in the latter part of the year to have 802.11n.

As to why it took so long, I don’t think it did, really. The chips only started shipping this year, and there is a manufacturing lag between chip and phone. I suppose a phone could have started shipping around the same time as the latest iTouch, which was September. But 3 months is not an egregious lag.

Bluetooth 3.0 arrives

The Bluetooth 3.0 specification has finally been ratified.

The main new feature is the Alternate MAC/PHY (AMP), that lets Bluetooth piggyback on Wi-Fi for high speed data transfers. The way it works is that applications write to the traditional Bluetooth Profile APIs, and connections are negotiated using the traditional Bluetooth radio. But then for high-speed data transfers the system switches to a direct peer-to-peer Wi-Fi session. This enables things like bulk syncing of photos from your phone to your PC, or streaming uncompressed CD stereo audio to wireless loudspeakers.

I wrote about Bluetooth AMP before, wondering why it retained a dependency on Bluetooth radio. The answer is that in idle, listening mode waiting for activity, Bluetooth is more power efficient than Wi-Fi, while Wi-Fi is more power efficient for bulk data transfers. This makes Bluetooth’s other next big thing, LE (formerly Wibree), an interesting complement to AMP: for power efficiency Bluetooth devices will reside in two modes, very low power idle mode (LE), and Wi-Fi mode when transferring data.

The Bluetooth 3.0 specification talks about 802.11 rather than 11g or 11n, since 802.11n is not yet ratified, but some of the companies involved will be supporting draft 802.11n anyway.

From an industry point of view there are several interesting aspects to this announcement, among them:

  • Atheros’ ascendence. Atheros, a leader in Wi-Fi, only recently got into the Bluetooth market, and currently only plays in the PC Bluetooth market. It dabbled in headset Bluetooth and got out, and has not yet announced Bluetooth for handsets. So Atheros is a minor player in Bluetooth, eclipsed by CSR and Broadcom, and several others. But Kevin Hayes of Atheros was the technical editor for the 802.11 Protocol Adaptation Layer of the Bluetooth 3.0 specification, and Atheros supplied the video and the demo of AMP at the 3.0 announcement event.
  • Potential movement of Wi-Fi into feature phones. Handset makers slice the market into four main segments: ultra low cost phones, basic phones, feature phones and smart phones. Wi-Fi is now pretty much ubiquitous in new smartphones, but effectively absent in all other types of cell phone. But feature phones have music and cameras which generate exactly the data that Bluetooth 3.0 was designed to sync with PCs, so Bluetooth 3.0 provides a motivation to handset manufacturers to add Wi-Fi to their feature phones. This will vastly boost the Wi-Fi attach rate in 2010 and beyond.
  • Another nail in the coffin of UWB (Ultra Wide-Band). In its original conception, AMP was to use WiMedia’s flavor of UWB. Later Wi-Fi was added to the mix, and now UWB is absent from the spec. UWB has so far failed to meet its performance expectations, and rather than fix it the WiMedia Alliance threw in the towel in March 2009. I suppose it is possible that the few companies still toiling away on fixing UWB will eventually overcome its performance woes, and that it will get adopted into the Bluetooth specification.