Rethink Research has published an interesting article relating the new Wi-Fi voice certification to the outlook for femtocells.

The idea of the article is that voice over Wi-Fi for cell phones is competing with femtocells, and that femtocells may win out. The article distinguishes between business voice and consumer voice, saying that service providers see femtocells as “an important stalking horse for greater control of corporate customers. ” This gives a hint of why femtocells may be unattractive to businesses: many of them would rather not yield this control.

Consumer voice service is controlled by service providers. They have three options in this space: do nothing, deploy femtocells or deploy Wi-Fi. Do nothing is the obvious best choice, since neither of the other options carries a revenue upside. But poor coverage in a home discourages usage and risks cancellations of subscriptions. So in areas of poor coverage something like femtocells or UMA (voice over Wi-Fi) is attractive to service providers. For both technologies the service provider subsidizes the wireless router, but femtocells will remain more expensive than Wi-Fi routers because of their lower sales volumes, so Wi-Fi is more attractive on this count. But UMA requires phones with Wi-Fi, while femtocells will work with any phone in the service provider’s line-up, including legacy ones. So the customers’ experience of femtocells is better - they can choose or keep the phone they want and still get improved coverage at home. This benefit of femtocells clearly outweighs the marginal price advantage of Wi-Fi routers. Femtocells may help subscriber retention in another way: a Wi-Fi router is not tied to any particular cellular service provider, while a femtocell only works with the carrier that supplied it.

The situation in businesses is different. They generally prefer to control their own voice systems, which is why they have PBXs. But a substantial number of business calls are now made on cell phones, even on company premises. These calls don’t go through the PBX, so they are not least-cost-routed and they are not logged or managed by the IT department. Femtocells don’t fix these problems, but Voice over Wi-Fi does. Not service provider Voice over Wi-Fi, like UMA, but SIP-based Voice over Wi-Fi from companies like DiVitas and Agito. What about phone choice though? Won’t corporate customers be stuck with a limited choice of handsets? The answer is yes, only a limited number of phones have Wi-Fi: less than 10% of those sold in 2008. But in the category of enterprise smart phones, like the Nokia Eseries and Blackberries, the attach rate of Wi-Fi will soon be close to 100%.

So femtocells are a good way for service providers to remedy churn caused by poor residential coverage for consumers, but Wi-Fi may be the better option for businesses that want to regain control over their voice traffic.

In news that is huge for VoWi-Fi, the Wi-Fi Alliance announced on June 30th a new certification program, “Voice-Personal.” Eight devices have already been certified under this program, including enterprise access points from Cisco and Meru, a residential access point from Broadcom, and client adapters from Intel and Redpine Signals.

Why is this huge news? Well, as the press release points out, by 2011 annual shipments of cell phones with Wi-Fi will be running at roughly 300 million units. The Wi-Fi in these phones will be used for Internet browsing, for syncing photos and music with PCs, and for cheap or free voice calls.

The certification requirements for Voice-Personal are not aggressive: only four simultaneous voice calls in the presence of data traffic, with a latency of less than 50 milliseconds and a maximum jitter of less than 50 milliseconds. These numbers will produce an acceptable call under most conditions, but a network round-trip delay of 300 ms is generally considered to approach the limit of acceptability, and with a Wi-Fi hop at each end running at the limit of these specifications there would be no room in the latency budget for any additional delays in the voice path. The packet loss requirement, 1% with no burst losses, is a very good number considering that modern voice codecs from companies like GIPS can yield excellent sound quality in the presence of much higher packet loss. This number is hard to achieve in the real world, as phones encounter microwave ovens, move through spots of poor coverage and transition between access points.

Since this certification is termed “Voice-Personal,” four active calls per access point is acceptable; a residence is unlikely to need more than that. Three of the four access points submitted for this certification are enterprise access points. They should be able to handle many more calls, and probably can. The Wi-Fi Alliance is planning a “Voice-Enterprise” certification for 2009.

There are several things that are good about this certification. First, the WFA has seen fit to highlight voice as a primary use for Wi-Fi, and has set a performance baseline. Second, this certification requires some other certifications as well, like WMM power save and WMM QoS. So far in 2008, of 99 residential access points certified only 6 support WMM power save, and of 52 enterprise access points only 13 support WMM power save. One of the biggest criticisms of Wi-Fi in handsets is that it draws too much power. WMM power save yields radical improvements in battery life - better than doubling talk time and increasing standby time by over 30%, according to numbers in the WFA promotional materials.

George Ou of ZDNet reports that the 802.1X authentication techniques used on some Wi-Fi handsets may be vulnerable. The problem is that these handsets may not validate the certificate from the authentication server. This design choice speeds up roaming, but means that the handset could disclose user login credentials to a sophisticated, determined attacker. Ou suggests using WPA-PSK with a long password instead of 802.1X with these handsets.

Vocera’s documentation, which Ou references, has more depth on the performance trade-offs of various Wi-Fi security options.

Redpine Signals has announced that it is sampling a low power 802.11n chip suitable for cell phones. A reference design was certified in January, making it the first handset-grade 802.11n chip to market.

One of the major benefits of 802.11n is MIMO, so you might think that since a handset is unlikely to have multiple antennas, 802.11n isn’t going to help much. Actually, it will make an enormous difference in reliability and range, and consequently throughput. I wrote before about the array of improvements incorporated in 11n. The one of greatest interest in this context is Space-Time Block Coding (STBC).

The WFA website shows 90 Access Points (APs) certified for 802.11n, but STBC is optional in 11n, not mandatory, and not all the AP chipsets support it. The main makers of AP chipsets are Atheros, Broadcom and Marvell. None of these have mentioned STBC until recently. But now Broadcom says it is in the BCM4322, which is set to ship in the first quarter of 2008, and Marvell says it is in the TopDog 11n-450, which is scheduled to ship in 2Q 2008.

This Techworld article has a good discussion of the current state of enterprise 11n access points, noting that multi-radio APs are currently too power-hungry to be powered over Ethernet (PoE).

In May 2007 I showed a chart of dual-mode phone certifications by time. Certifications have continued to grow since then, as the updated graph below shows. These numbers are pretty raw, for example six certifications in November 2006 were for variations on a Motorola phone first certified in October. If you go back and look at the previous chart you will also notice discrepancies in the number of certifications for any particular month. These are presumably because of revisions at the WFA website.

From 2006 to 2007 smartphone certifications were essentially flat, going from 33 to 36, while feature phone certifications went from 11 to 21. These add up to 44 dual mode phone certifications in 2006 and 57 in 2007.

The coming crop of smartphones are data friendly, third-party software friendly phones with Wi-Fi. But there’s more! The processing power of the ARM application processors used in phones lags that of mobile PC CPUs by about 7 years, so this year’s phones will have roughly the computing power of a 2001 laptop.

These changes come together to make phones chip away at the uses of notebook PCs. Many people who used PCs only for email now use Blackberries instead. Many phones are good substitutes for personal organizer software on PCs. The iPhone can credibly substitute for a PC for web browsing.

These trends motivated Instat to say last November:

Smartphone use will grow mostly from use as a laptop replacement

According to Gartner, the year-on-year notebook sales growth numbers for notebook PCs from 2004 to 2007 remained healthy: 36%, 28%, 22%. The crossover in unit volume came in 2006, when smartphones and notebooks both shipped roughly 80 million units worldwide. That 22% unit growth in notebook sales from 2006 to 2007 represented a jump to over 100 million units shipped. Compare this to a 70% jump in smartphone unit shipments in the same period, to over 130 million.

I have previously written about OpenMoko. It seems now that it was the drop before the deluge. Google’s Android appears to have gained good traction with Sprint and T-Mobile joining the Open Handset Alliance, with Dell rumored (update) to be planning an Android-based phone, and with Verizon expressing lukewarm support. Nokia has for some time sponsored open source handset software through Maemo.org, but this week it upped the ante with its acquisition of TrollTech. Trolltech is responsible for Qtopia, a semi-open source platform used in Linux-based phones. That makes four credible Linux-based mobile phone software platforms. Update: Make that five - the LiMo Foundation is a consortium of carriers (including NTT DoCoMo and Vodafone), phone makers (including Samsung, Motorola and LG) and others “dedicated to creating the first truly open, hardware-independent, Linux-based operating system for mobile devices.”

But a phone doesn’t have to be open-source to be an open application platform, and this category is just as vigorous, but better established. Nokia’s Symbian phones have always been open to an extent - there are over 2 million developers registered in Nokia’s developer organization, Forum Nokia. Then we have Microsoft. Microsoft claims that sales of Windows Mobile phones are set to double year-on-year, to 20 million units. Windows Mobile provides a sufficiently open application environment that applications like Skype run on it. The iPhone is not yet officially an open application environment, but there is still a healthy slate of applications from third parties for those with the stomach to take the unofficial route. This is scheduled to change in February when the open-ness goes official with the release of Apple’s SDK for the iPhone. So that’s three major open application environments for smart phones.

2008 is also the year that Wi-Fi phones will come into their own. The dam broke with the iPhone. Wi-Fi on the iPhone raises the bar for all the other smart phones, making Wi-Fi a baseline checklist item for the next generation of smart phones. Previously mobile network operators were fearful that Wi-Fi in a phone would divert traffic from their data networks. This fear led, for example, to AT&T’s removal of Wi-Fi from their version of the Nokia E61. But there is now new evidence. At last week’s IT Expo East I heard an unsubstantiated report that 60% of wireless data usage in December was by 2% of the phones: iPhones. If this is even partly true, it would demonstrate that a web-friendly phone will drive traffic on the cellular data network even when it has Wi-Fi.

QoS metrics are important, and several companies have products that measure packet loss, jitter, latency and so on. But you can have perfect QoS, and your VoIP system can still be defective for all sorts of reasons.

I spoke with Gurmeet Lamba, VP of Engineering, at Clarus Systems at the Internet Telephony Expo this week. He said that even if a VoIP system is perfectly configured on installation, it can decay over time to the point of unusability. Routers go down and are brought up again with minor misconfigurations; moves, adds and changes accumulate bad settings and policy violations.

VoIP systems are rarely configured perfectly even on installation. For example, IP phones have built-in switches so you can plug your PC into your desk phone. Those ports are unlocked by default. But some phones are installed in public areas like lobbies. It’s easy for installers to forget to lock those ports, so anybody sitting in the lobby can plug their laptop into the LAN. There are numerous common errors of this kind. Clarus has an interesting product that actively and passively tests for them; it monitors policy compliance and triggers alarms on policy violations.

Clarus uses CTI to do active testing of your VoIP system, looking for badly configured devices and network bottlenecks. Currently it works only on Cisco voice networks, but Clarus plans to support other manufacturers.

Clarus started out focusing on automated testing of latency, jitter and packet loss for IP phone systems. It went on to add help desk support with remote control of handsets, and the ability to roll back phone settings to known good configurations.

The next step was to add “Business Information,” certifying deployment configurations, and helping to manage ongoing operations with change management and vulnerability reports. Clarus’ most recent announcement added passive monitoring based on a policy-based rules engine.

Clarus claims to have tested over 350 thousand endpoints to date. It has partners that offer network monitoring services.

802.11n incorporates all earlier amendments to 802.11, including the MAC enhancements in 802.11e for QoS and power savings.

The design goal of the 802.11n amendment is “HT” for High Throughput. The throughput it claims is high indeed: up to 600 Mbps in raw bit-rate. Let’s start with the maximum throughput of 802.11g (54 Mbps), and see what techniques 802.11n applies to boost it to 600 Mbps:

1. More subcarriers: 802.11g has 48 OFDM data subcarriers. 802.11n increases this number to 52, thereby boosting throughput from 54Mbps to 58.5 Mbps.

2. FEC: 802.11g has a maximum FEC (Forward Error Correction) coding rate of 3/4. 802.11n squeezes some redundancy out of this with a 5/6 coding rate, boosting the link rate from 58.5 Mbps to 65 Mbps.

3. Guard Interval: 802.11a has Guard Interval between transmissions of 800ns. 802.11n has an option to reduce this to 400ns, which boosts the throughput from 65 Mbps to 72.2 Mbps.

4. MIMO: thanks to the magical effect of spatial multiplexing, provided there are sufficient multi-path reflections, the throughput of a system goes up linearly with each extra antenna at both ends. Two antennas at each end double the throughput, three antennas at each end triple it, and four quadruple it. The maximum number of antennas in the receive and transmit arrays specified by 802.11n is four. This allows four simultaneous 72.2 Mbps streams, yielding a total throughput of 288.9 Mbps.

5. 40 MHz channels: all previous versions of 802.11 have a channel bandwidth of 20MHz. 802.11n has an optional mode (controversial and not usable in many circumstances) where the channel bandwidth is 40 MHz. While the channel bandwidth is doubled, the number of data subcarriers is slightly more than doubled, going from 52 to 108. This yields a total channel throughput of 150 Mbps. So again combining four channels with MIMO, we get 600 Mbps.

Lower MAC overhead
But raw throughput is not a very informative number.

The 11a/g link rate is 56 Mbps, but the higher layer throughput is only 26 Mbps; the MAC overhead is 54%! In 11n when the link rate is 65 Mbps, the higher layer throughput is about 50 Mbps; the MAC overhead is down to 25%.

Bear mind that these numbers are the absolute top speed you can get out of the system. 802.11n has numerous modulation schemes to fall back to when the conditions are less than perfect, which is most of the time.

But to minimize these fall-backs, 11n contains additional improvements to make the effective throughput as high as possible under all circumstances. These improvements are described in the following paragraphs.

Fast MCS feedback - rate selection.
Existing equipment finds it hard to track rapid changes in the channel. Say you walk through the shadow of a pole in the building. The rate may go from 50 to 6 to 50 mbps in one step. It’s hard for conventional systems to track this, because they adapt based on transmit errors. With delay sensitive data like voice you have to be very conservative, so adapting up is much slower than down. 11n adds explicit per-packet feedback, recommending the transmission speed for the next packet. This is called Fast MCS (Modulation and Coding Scheme) Feedback.

LDPC (Low Density Partity Check) coding
LDPC is a super duper Forward Error Correction mechanism. Although it is almost 50 years old, it is the most effective error correcting code developed to date; it nears the theoretical limit of efficiency. It was little used until recently because of its high compute requirement. An interesting by-product of its antiquity is that it is relatively free of patent issues.

Transmit beam-forming
The term beam-forming conjures up images of a laser-like beam of radio waves pointing exactly at the client device, but it doesn’t really work like that. If you look at a fine-resolution map of signal intensity in a room covered by a Wi-Fi access point, it looks like the surface of a pond disturbed by a gust of wind – it is a patchwork of bumps and dips in signal intensity, some as small as a few cubic inches in volume. Transmit beam-forming adjusts the phase and transmit power at the various antennas to move one of the maxima of signal intensity to where the client device is.

STBC
In a phone the chances are that there will only be one Wi-Fi antenna, so there will be only one spatial channel. Even so, the MIMO technique of STBC (Space-Time Block Coding) enables the handset to take advantage of the multiple antennas on the Access Point to improve range, both rate-at-range and limiting range.

Incidentally, to receive 802.11n certification by the Wi-Fi Alliance, all devices must have two or more antennas except handsets which can optionally have a single antenna. Several considerations went into allowing this concession to handsets, mainly size and power constraints. STBC is particularly useful to handsets. It yields the robustness of MIMO without a second radio, which saves all the power the second radio would burn. This power saving is compounded with another: because of the greater rate-at-range the radio is on for less time while transmitting a given quantity of data. STBC is optional in 802.11n, though it should always be implemented for systems that support 802.11n handsets.

Hardware assistance
Many of these features impose a considerable compute load. LDPC and STBC fall into this category. This is an issue for handsets, since computation costs battery life. Fortunately these features are amenable to hardware implementation. With dedicated hardware the computation happens rapidly and with little cost in power.

I sat down with my iPhone and my MacBook, turned on the iPhone and tapped on the screen where it said “Activate iPhone.” The screen went black. Not a good sign.
Then I remembered that the iPhone needs to be plugged in to the PC physically to activate it. This is weird, because one of the things I like best about my MacBook is the way I can just put my Mororola Razr on the desk near it and download photos without any fuss.
So I plugged in the iPhone to the USB and fired up iTunes to do the activation.
Some of the questions were intrusive. It forced me to enter my social security number, also a credit card number for iTunes. I would have preferred to wait until I was ready to buy something from iTunes before giving it credit card info.
The minimum billing I could find was $59.99 a month plus a $36 activation fee for an obligatory 2 years.
This is a $1,536 commitment; add in the $600 for the phone and this toy costs over $2,000.
iTunes showed me my new phone number, and the phone screen said:
“Waiting for AT&T activation. This may take some time.”
This sounded ominous, but within a minute the phone said it was activated.
I made a phone call. Sounded OK.