Spatial Diversity In Wireless Communications

Spatial diversity is one of those fundamental technologies used in wireless communications
(cellular networks, Wi-Fi, satellite communications, and broadcasting) that does not get much exposure. The technology is used to combat fading and improve signal quality, enabling reliable communication links, especially in challenging environments characterized by obstacles, interference, or long propagation distances. Let’s take an introductory look. 

Spatial diversity exploits the spatial dimension of wireless channels by deploying multiple antennas at either the transmitter or receiver, or both. By leveraging spatial separation between antennas, spatial diversity techniques minimize the effects of fading, which result from signal attenuation, reflections, and scattering in multipath propagation environments. Through the simultaneous reception of multiple independent copies of a transmitted signal, spatial diversity enhances the likelihood of receiving at least one strong signal, thus improving the overall reliability of communication links.

 

There are three key methods involved - Selection Diversity, Maximal Ratio  Combining (MRC) and Equal Gain Combining (EGC).

 

Selection Diversity: In selection diversity, multiple antennas are strategically placed to receive the same signal, and the antenna with the highest received signal strength is chosen for further processing. This technique is relatively simple to implement and offers improved diversity gain, particularly in scenarios with moderate to severe fading.

 

Maximal Ratio Combining (MRC): MRC combines signals from multiple antennas with different complex weights, determined based on the channel conditions. By weighting each received signal based on its signal-to-noise ratio (SNR) and combining them coherently, MRC maximizes the received signal power, thereby enhancing the overall signal quality and reliability.

 

Equal Gain Combining (EGC): EGC employs a simpler approach by combining signals from multiple antennas with equal weights. While less complex than MRC, EGC provides diversity gain by mitigating the impact of fading through signal averaging.

 

Spatial diversity offers an effective mechanism to combat fading and enhance signal reliability. Through the strategic deployment of multiple antennas and the application of diverse combining techniques, the technology improves data transmission across a wide range of environments and applications.

The Rise Of The HetNet

I’m starting to see the term HetNet used in my reading and even had a student ask me for details this morning. That said – I figured it would make a good blog post.

HetNet is short for Heterogeneous Network and is a term currently being used in the wireless world. Most of us are carrying around smartphones with a number of different antennas built in for access via different network technologies. The neat thing about HetNets is they are able to maintain mobile connectivity (no dropped connections) when switching between different wireless connection technologies. 

The three different connection technologies getting all the HetNet buzz right now are LTE, Carrier WiFi, and enterprise femtocells. LTE is 4G cellular service and Carrier WiFi is just WiFi service provided by a wireless carrier. Femtocells are small cell devices that are connected to an Internet broadband connection. 

So HetNets allow a user device to seamlessly switch from network type to network type– LTE to WiFi to femtocell and vice-versa back and forth without dropping a connection. Pretty neat.

Now, not too long ago, it was believed LTE would be the dominant mobile technology and there would not be a need to alternative type technologies like Carrier WiFi and femotocells. But think about it…… there is only a limited amount of spectrum and bandwidth so providers are looking for ways to lower the number of devices per cell. There are also advantages to having users as close as possible to the different types of base stations. 

As a result, we’re seeing providers like Verizon Wireless and AT&T use HetNets to improve the coverage of their network, increase network capacity to match user demand. enhance the user experience, and lower the cost of delivering mobile broadband services.

Goodbye SMS-Based Text Messaging

ASYMCO put up an interesting piece titled What's up with text messaging? yesterday about texting in Spain. Volume is dropping rapidly with Internet Protocol (IP) based message apps like Whatsapp, Apple's iMessage and Facebook messaging replacing a voice network based text protocol called Short Message Service (SMS). SMS has been around since 1982 and has become a real cash cow for wireless providers. 

Here's more from that ASYMCO post:

• Whatsapp reported that it set a record of 18 billion messages processed over New Year’s Eve. 
• In October Apple announced that iMessage had delivered 300 billion messages during the preceding 12 months.
• Globally SMS traffic is still rising. It’s expected to reach 9.6 trillion in 2012, but at least one analyst forecasts  that SMS’s share of global mobile messaging traffic will fall from 64% in 2011, to 42% in 2016.

I'd also put Skype on the list as a disruptor.

Expect similar results in the United States and other countries. Wireless providers have seen this coming for a while now and (I believe) it's the reason we've seen most implement data caps while, at the same time, encouraging customers to consume more data (translation - go over your data cap) using services like mobile video streaming. 

If you want to know more about SMS and IP based texting I've got an earlier posted titled Why Are My iPhone Text Messages Sometimes Blue and Sometimes Green? linked here.

Why Are My iPhone Text Messages Sometimes Blue and Sometimes Green?

Lately I've been getting this question a lot. Here's what's up.

Green messages on your iPhone use a voice text protocol called Short Message Service (SMS). SMS was developed way back in 1982 and designed to run on voice networks using a separate channel used for signaling. Technically SMS was easy to implement and, with the popularity of mobile phones, it became very popular really fast. Messages are limited in length 160 characters and as a result many of us have learned to abbreviate words using text-speak shorthand.

iMessage is different. It's Internet Protocol (IP) based and does not require a voice connection. You can use IP based text services like iMessage on cellular data networks along with WiFi networks and your computer.

Now here's the big advantage - you don't need a text message plan to send and receive iMessage based texts. You do need some kind of text message plan to send and receive SMS (green) messages.

When are messages green? Here's a few common scenarios:

1. You or your friend have not updated your iPhone to iOS5
2. You or your friend are not registered with Apple iMessage. 
3. You or your friend are in a place where there is no cellular data signal but there is a voice network signal.
4. You send a message to someone not on the same network as you and only one of you has an iPhone. For example, you've got an AT&T account and your friend has a Verizon Wireless account. If you both have iPhones and both have data connections iMessage will work cross-carrier. 
5. You're on the same network but one of you has iMessage turned off. To turn iMessage on and off on your iPhone use Settings -> Messages -> iMessage On/Off

Is SMS sticking around? Not for long with "free" services like iMessage and this is rapidly becoming a problem for the providers. SMS has been a huge cash cow for wireless providers earning an estimated $114.6 billion in 2010.

Some Sweet Bandwidth - Update Your AT&T 4S iPhone

Back from vacation today and my wife did a software upgrade to iOS 5.1 on her AT&T Wireless service iPhone 4S. Sure enough her indicator now reads "4G" (upper left hand corner) and she's getting some pretty nice bandwidth. Here's a screen shot after running the speedtest.net app.

As a comparison, here's the same test run on my AT&T 3GS iphone.

I'm also updated to iOS 5.1 but no "4G" for me on my older phone.

Is it really "4G" on her phone? Well - no. It's running a 3G service called HSPA+ (sort of 3G on steroids - up to 56 Mbit/s downstream and 22 Mbit/s upstream) which AT&T is using to get over the bandwidth hump until LTE rolls out. I've written about 4G services fairly extensively - follow this link to read my older posts.

Regardless, that's some sweet bandwidth. If you've got an iPhone 4GS running on the AT&T network, be sure you're up to date on upgrades. As for me and my almost 3 year old 3GS - I'm stuck in the "3G" world until I upgrade my phone. The 3GS does not have a HSPA+ radio in it.

How can you check which iOS version you are running on your iPhone? On your phone select "Settings", "General" and then "Software Update". You should see a screen like the screen shot from my 3GS below. 

If you are not up to date follow the instructions on the Apple website. 

Wireless Spectrum Auctions - Is There a Better Way?

I've been reading a lot lately about the possibility of voluntary spectrum auctions in the US. These voluntary auctions would be a little different than what's been done in the past. In previous auctions, all revenue gained has gone directly to the Treasury Department. The proposed voluntary auctions would allow the current owner of a piece of spectrum to keep a portion of the revenue from the sale. For the FCC to hold voluntary auctions, Congress would need to change current spectrum auction regulations.

Why is spectrum so critical now? There is is only so much capacity any communications channel can transmit and, with devices becoming more and more complex, bandwidths must keep rapidly rising.  To give some perspective on growth, Network Solutions predicts a growth of 30 times current usage in the next 5 years. Broadbandbreakfast.com breaks it down like this - a Motorola Razor (introduced in the fourth quarter of 2004) on the average uses about 8 megabytes (MB) of data per month. Compare that to a typical smartphone (like an iPhone) that uses approximately 900 MB a month and an average tablet (like an iPad) that uses 2 gigabytes per month. You can see where this is going....

Is there a more efficient way to sell existing spectrum? Perhaps. George Mason Law School Professor Thomas Hazlett has been questioning the FCC incentive auction plan for a while now. Back in December 2010, Hazlett was a panelist at a Telecommunications and Media Forum sponsored by the International Institute of Communications in Washington, D.C., At that time he recommended the FCC take a look at spectrum overlay licenses and allow parties to negotiate private agreements, rather than allowing the government to act as a middleman.

What does this mean? Here's piece of an article from The Journal of Economic Perspective (Volume 22, Number 1—Winter 2008) written by Hazlett.

Consider a television broadcasting service. Video transmitted over-the-air can cheaply deliver valuable content to households, but that simultaneously makes it difficult for another video signal to be transmitted on the same channel to standard TV sets in the area. The U.S. analog standard adopted by the FCC in 1941 delivers one program in a 6 MHz band. The same frequency space can, using digital formats, deliver five to ten pictures of similar clarity or, alternatively, one or two programs in high-definition. Alternatively, a single 6 MHz channel allocated TV band spectrum could economically be used to supply, say, broadband service connecting computer users to the Internet. The wireless broadband option is effectively eliminated, however, under the digital TV standard adopted in the United States, where TV stations (to retain their licenses) must transmit high- powered video broadcasts across the entire 6 MHz band.

Since transmission rules are fixed by law, a TV broadcaster will tend to emit too much power and to underutilize spectrum-saving techniques. Were the broadcaster to enjoy frequency ownership, on the contrary, it would profit by investing in improved receivers (allowing, say, both an over-the-air TV signal and two-way Internet access in the same band) or substituting TV signal delivery by cable and satellite.

The Hazlett Plan sure makes a lot of sense to me.

AT&T and Verizon Wireless Upgrade Rollout Plans

FierceWireless had a good short post yesterday titled AT&T to launch LTE by mid-2011 that detailed Fourth Generation (4G) Long Term Evolution (LTE) plans for AT&T and Verizon Wireless. The AT&T details come from a presentation by AT&T Operations CEO John Stankey at the Bank of America Merrill Lynch 2010 Media, Communications & Entertainment Conference. Here’s some highlights from the post:

AT&T 3G

• Is readying a nationwide HSPA+ (this is 3G technology) upgrade for this year, which AT&T executives have said will allow the carrier to deliver real-world download speeds of 7 Mbps. In the meantime, the carrier continues to upgrade backhaul to cell sites it has upgraded to HSPA 7.2 technology.
• Network upgrade efforts have been hampered by continuing parts shortages from key vendors. Stankey said company is currently dealing with $300 million worth of backlogged network equipment.
• By Oct. 1, will have added 600 additional radio carriers in San Francisco, which has been a trouble spot for the company.

AT&T 4G (LTE)

• Currently conducting LTE trials in Baltimore and Dallas and is is spending $700 million in capital expenditures on LTE this year.
• Stankey said AT&T is working on a different kind of implementation for LTE than other carriers, and needs to carry forward its UMTS services (3G) to ensure that voice and data services can work simultaneously on both UMTS and LTE.

Verizon Wireless 4G (LTE)

• Intends to launch 25-30 commercial LTE markets in the fourth quarter of this year, covering 100 million POPs. Verizon has said it plans to double the number of its LTE markets 15 months after its initial launch this year.

Check out the FierceWireless post for details and to see key slides from Stankey’s presentation.

AT&T 2G Network Services Changing?

Timothy Butler has an interesting post over at Open for Business (OFB) titled Fewer Bars in More Places: AT&T Network Upgrades Degrade Service for 2G Phones. Here's a couple of quotes from Butler:

In an act affecting owners of 2G cell phones on AT&T Mobility’s network, including the highly visible, and originally highly expensive first generation iPhone, Open for Business has learned that AT&T has been quietly sacrificing 2G signal strength in an effort to speed up the build out of its next generation 3G network. The first generation iPhone was trumpeted by the company as recently as seven months ago; many 2G phones continue to be sold by the Dallas-based company today.

According to Butler, until recently AT&T has primarily relied on the 850 MHz frequency band that offers better indoor reception for their 2G EDGE service. He says AT&T technicians confirmed to OFB that transmitters for the 2G signal used by the original iPhone and most other handsets, including most AT&T offered BlackBerry and RAZR models, have been shifted to the weaker 1900 MHz band in some areas.

Cellularguru.net has a good frequency FAQ that describes the difference between the 850 and 1900 MHz bands:

What is the difference between the 850 and 1900 bands? They are the two
different wireless bands available to North America. 850 was the original cellular band, and it was split into two, the "A" band and the "B" band. The "B" band was for the wireline phone company and the "A" band was for a non-wireline provider. The 850 band has been around for 15+ years, and the systems are very well built out. The FCC mandated that a certain amount of land be covered by a signal. The 1900 band was placed in operation several years after 850. The 1900 band is also known as PCS, and the two terms are used interchangeably, which can be confusing when trying to follow a conversation. There are 6 bands A through F, and some of those can be split into others. The requirements for the 1900 were not as strict as 850. Only a certain percentage of the population needed coverage (67% IIRC). Than means building the urban areas pretty much met the entire FCC buildout requirement for a given area. From what I can gather, there rules have been relaxed even further.

Which is "better"? Here's more from Cellularguru.net:

Which is better, 850 or 1900? In general, you are going to get more performance out of 850 than you are going to get out of 1900 for several reasons.

1. As mentioned earlier, back when the 850 licenses were issued, they had to cover a certain amount of land cover. This required deploying their system throughout many rural areas (not ALL though). 1900 licenses only need to cover up to 67% of the population, and in many cases they don't even have to meet that.

2. The higher the frequency, the shorter the usable range. You need approximately twice as many 1900 MHz towers to cover a given area than 850 MHz towers. Most 1900 MHz towers are in urban and suburban areas. A properly built 1900 system will work as well as a properly built 850 system, but it will likely cost more to deploy and operate.

Sometimes 1900 will work better in a city because 1900 MHz signals tend to work better in the middle of the city with large buildings as the shorter wavelength allows the signal to go around corners easier. Also, due to network loading, 850 towers have to be "turned down" in urban areas so as to not overload, so the playing field is leveled. 3. Leaving the technical details aside, it seems that 850 MHz signals penetrate most modern buildings better than 1900 MHz signals. There are many factors involved such as the material of the walls, the proximity of the local cell towers and various other factors. The fact that 850 MHz carriers have been in operation longer and have optimized their coverage is an important factor to consider. If there is a window nearby, chances are that either system will work, assuming that there is some sort of signal available at the window! The bottom line is this: when you try out a service, make sure you bring your phone to all the areas you'll be using to make sure it works where you need it.

Here's more from the Butler piece:

OFB was able to confirm this situation for itself using multiple devices in St. Louis, MO, and also obtained information on similar cases across the country. Reports suggested the problem started to appear as AT&T ramped up its 3G network in preparation for the iPhone 3G in early 2008. Each AT&T technician OFB talked to concerning this problem offered the same solution: that the customer should purchase new, 3G-enabled equipment at the customer’s own expense.

I'm still one of those first generation $400 iPhone users so Butler's accusation concerns me. His piece goes on:

AT&T’s executive director of analyst relations, Mark Siegel, “categorically” denied to OFB that AT&T was advising customers to dump 2G equipment such as the iPhone for 3G versions. In a follow-up message, Siegel added that the company was not requiring anyone to switch to 3G equipment. Although that is technically true, customers in affected areas are all but required to upgrade due to the dramatic signal strength drop over the last few months.

Where's Apple on this? Butler writes OFB also attempted to reach Apple for comment, but had not received a response from the company by press time.

Is WiMAX Dead?

International telecom advisors Analysys Mason, headquartered in London with offices in over 80 countries, released an interesting report last week on worldwide wireless opportunities for revenue growth. The report predicts cellular technologies will take the largest revenue share between now and 2015. Globally, the study predicts 2.1 billion wireless broadband customers will generate USD784 billion in service revenue by 2015.

Here's some detail from the report:

The revenue increase of about 2400% will be underpinned by continued developments in wireless technologies, improvements in devices and more flexible pricing options.

Because W-CDMA to HSPA to HSPA+ is the natural evolution path for GSM operators, the number of HSPA and HSPA+ customers worldwide will increase from 61 million at the end of 2008 to 1.1 billion at the end of 2015.

Cellular technologies will dominate wireless broadband services, with twenty times as many users as WiMAX by the end of 2015.

LTE will take off relatively slowly, but its customer base will reach 440 million by 2015, with associated revenue of USD194 billion.

WiMAX will be squeezed from developed markets by fixed and cellular broadband services and by 2015 will serve just 98 million customers worldwide, of which 92% will be in developing regions.

The report continues:

WiMAX will fail to achieve a significant share of the rapidly developing wireless broadband market, contributing only 2% of global revenue. “By 2015, there will be twenty times as many customers for cellular broadband services as for WiMAX,” according to Dr Alastair Brydon, co-author of the report, “The vast majority of MNOs will not break ranks to WiMAX, but will upgrade to LTE, resulting in over four times more LTE users by the end of 2015.”

It looks like WiMAX may not fit predicted migration paths according to Analysys Mason. You can get details from the report here.

The FCC 700 MHz Auction Results Podcast

Mike Q and I recorded "The FCC 700 MHz Auction Results" podcast today. Below are the show notes. You can listen directly by turning up your speakers and clicking here. If you have iTunes installed you can get this one, listen to others, and subscribe to our podcasts by following this link.

If you don't have iTunes and want to listen to other podcasts and read shownotes using your web browser, turn up your speakers and click here.

Shownotes:

Intro: On March 18, FCC Auction 73 bidding round 261 ended and, after 38 days and $19.592 billion in bids (almost double the $10 billion the FCC had hoped for), the FCC closed out the auction. In this podcast we review and discuss the auction results.

Mike: Gordon, can you give us an overview of the auction results?
Sure Mike - this comes from the FCC auction website linked up in the shownotes.

Rounds: 261 (started on 1/24 and ended on 3/18)

Bidding Days: 38

Qualified Bidders: 214

Winning Bidders: 101 Bidders won 1090 Licenses

Auction 73 concluded with 1090 provisionally winning bids covering 1091 licenses and totaling $19,592,420,000, as shown in the Integrated Spectrum Auction System. The provisionally winning bids for the A, B, C, and E Block licenses exceeded the aggregate reserve prices for those blocks. The provisionally winning bid for the D Block license, however, did not meet the applicable reserve price and thus did not become a winning bid. Accordingly, Auction 73 raised a total of $19,120,378,000 in winning bids and $18,957,582,150 in net winning bids (reflecting bidders' claimed bidding credit eligibility), as shown above.

Mike: Before we get into the auction results, can you give us an overview of the different spectrum blocks? I know we've done this before but - how about a quick refresher?
Sure Mike - this comes from a blog I wrote back on January 14.

Back in 2005 Congress passed a law that requires all U.S. TV stations to convert to all digital broadcasts and give up analog spectrum in the 700 MHz frequency band. This law will free up 62 MHz of spectrum in the 700 MHz band and effectively eliminate channels between 52 and 69. This conversion, which has a deadline of February 18, 2009, has freed up spectrum that is being split up by the FCC into five blocks:

• A-Block - 12 MHz, split up into 176 smaller economic areas
  
• B-Block - 12 MHz, split up into 734 cellular market areas
  
• C-Block - 22 MHz, up into 12 regional licenses
  
• D-Block - 10MHz, combined with approximately 10MHz allocated for public safety, a single national license.
  
• E-Block - 6 MHz, split up into 176 smaller economic areas

So in summary, each spectrum block in the 700 MHz auction, except for the national public safely D-Block, has been assigned an area designation by the FCC.
All FCC areas, along with names, county lists, maps and map info data can be found on the Commission's website linked here.

Mike: How about a quick review of the D-Block again?
Sure Mike, this also comes from that January 14 blog:

The D-Block lately has been most interesting to watch. Early on it appeared Frontline Wireless would be one of the biggest bidders for D-Block spectrum - the company was setup for D-Block and had worked closely with the FCC on putting together specifications for the spectrum. Frontline built a formidable team including Vice Chairman Reed Hundt, who served as Chairman of the FCC between 1993 and 1997. The business plan, the organization, the technology seemed to all be in place........ On January 12 the company placed the following statement on their website:

Frontline Wireless is closed for business at this time. We have no further comment.

Another company, Cyren Call also looked like they were planning to bid on the D-Block Auction but did not.

What happen? Rumor has it Frontline could not attract enough funders - it seemed like a good investment - or at least you may think so up front. Many are now asking if the FCC's approach to solving the public safety inter-operability problem is in trouble.

Mike: OK, how about the results?
Here's a summary from the Wall Street Journal:

Verizon and AT&T accounted for 80% of the nearly $20 billion AT&T agreed to pay $6.6 billion for 227 spectrum licenses in markets covering much of the country. Verizon Wireless, a joint venture of Verizon Communications Inc. and Vodafone Group PLC, won 109 licenses for $9.4 billion.

Dish Network Corp., which bid for spectrum through Frontier Wireless LLC, did acquire a significant footprint, winning 168 licenses throughout the country for $712 million. Satellite-TV providers are looking for a way into the high-speed Internet business to better compete with cable and phone companies. But Credit Suisse analyst Chris Larsen said in a research note that the particular segment of spectrum Dish acquired would make it difficult for the company to offer interactive wireless broadband service. He said the company could use the spectrum to broadcast data or for on-demand video.

Google had indicated interest in a nationwide package of licenses before the auction, but it bid just high enough to trigger rules that will force winners of one segment of spectrum, known as the C-block, to allow any mobile devices and applications on their networks. Verizon won the lion's share of spectrum in this segment. Google had pushed for the regulation since its efforts to sell some mobile services had been stymied by major carriers, which traditionally have strictly limited the kinds of devices that consumers could use on their networks. Even before the auction had wrapped up, Google scored a victory as Verizon voluntarily agreed to open its network to devices it doesn't sell through its own retail network. Verizon released details of its new policy on Wednesday.

Mike: Were there any licenses that dod not get any bids?
There were 1,099 licenses auctioned and only eight did not receive any bids:

A-Block:

Lubbock, Texas
Wheeling, W.Va.

B-Block:

Bismarck, N.D.
Fargo, N.D.
Grand Forks, N.D.
Lee, Va.
Yancey, N.C.
Clarendon, S.C.

Mike: So, what will happen to these?
These licenses will need to be re-auctioned by the FCC. I'm guessing they were over priced, the FCC will end up dropping the re-auction minimum bid and they will end up going quickly.

Mike: What's going to happen with D-Block?
The Public Safety D-Block did not meet the minimum bid and the FCC will have to decide what to do. It looks like the FCC could go one of two directions for the re-auction - drop the price or change the requirements.

From the start, the public safety D-Block auction was seen as one of the biggest auction challenges...... I've expressed my opinion on the D-Block in the past........ the FCC still has some major work ahead before they can close this one out.

This comes from InfoWorld:

On Thursday, the FCC voted to de-link the so-called D block from the rest of the auction results. The D block was a 10MHz block that was to be paired with another 10MHz controlled by public safety agencies, and the winning bidder would have been required to build a nationwide voice and data network to serve both public safety and commercial needs. But the FCC failed to receive its $1.33 billion minimum bid for the D block, with the lone $472 million bid coming from Qualcomm.

The FCC has no plans to immediately reauction the D block, a spokeswoman said. Instead, the agency "will consider its options for how to license this spectrum in the future," the FCC said in a news release.

Mike: So, it looks like the big carriers won?
For the most part, yes. Kevin Martin had an interesting quote in an EFluxMedia piece though:

"A bidder other than a nationwide incumbent won a license in every market," FCC chairman Kevin Martin said hinting that it’s possible for a "wireless third-pipe" competitor to emerge in every market across the U.S. This would increase the competition and the first one to benefit from it will be the consumer.

Things still could get interesting!

Analog Cellular Technology "Sunsetted" Today

Today both AT&T and Verizon shut off their analog networks based on an FCC decision way back in 2002 tto "analog sunset" Advanced Mobile Phone System (AMPS) networks. AMPS, first generation cellular technology developed in the early 1980's, requires separate frequency channels for each phone conversation and is extremely bandwidth hungry.

Both Verizon and AT&T gave up front notification and worked with analog customers for years to get them switched over (almost all were years ago) so the shut down will have negligible effect. There may still be a few AMPS networks out there in this country after today - shutdown is optional and some small rural carriers may have not shut down today. Eventually they all will.

You may have read around the first of the year about General Motor's OnStar systems and how the OnStar network was converting to CDMA based communications on January 1, 2008. Here's a quote from InfoWorld on the InStar conversaion:

Some users of wireless roadside assistance have also been left behind in the transition......... The automaker didn't wait for the Feb. 18 deadline but instead shut down its analog service on Jan. 1. In a statement on the transition last year, GM said about 90 percent of its subscribers' cars had CDMA or could be converted to use it. Others would lose their OnStar service. The wholly owned subsidiary of GM said last October it had about 5 million subscribers.

Residential and business alarm systems have been preparing for the shut down for a while also. Here's more from the InfoWorld piece:

....... AMPS isn't only used for cell phones. Many alarm companies use the system to alert police or fire departments to emergencies at homes or businesses. About three years ago, the Alarm Industry Communications Committee (AICC) industry group took a survey which revealed that just under 1 million of the approximately 30 million monitored home and business alarm systems used an analog cellular network, said AICC chairman Louis Fiore. About 850,000 of them used the system only as a backup in case the phone line was cut, he said.

In the end, faster and more efficient digital systems took over with AMPS becoming too expensive to support and maintain.