HTC to announce updated security program

South Korea HTC

Associated Press (2011-09-21 18:28:50)

Jack Tong, president of HTC North Asia, holds the company's new smartphone Raider 4G during a press conference in Seoul, South Korea, Wednesday, Sept. 21, 2011. The smartphone, which runs on Android 2.3 and featuring the 4.5-inch touch screen, will go on sale in the domestic market from ends of this month. The price hasn't been announced. (AP Photo/Lee Jin-man)

HTC has disclosed the presence of a flaw in some of its smart mobiles which some sources have said makes it easy to access users’ personal data. HTC for its part claims that the flaw will not lead to the loss of any personal data. According to initial investigation, the issue could be the result of a malignant third party program. The company has pledged to develop and distribute a new security program as soon as possible.

AndroidPolice, the science blog, points out that HTC has launched many intelligent mobiles such as Thunderbolt, EVO 3D, EVO 4G and others that all have security flaws that result in disclosure of account numbers, emails, global positioning system(GPS) information and texts of users.

HTC says that they are concerned with the security of consumer data and that investigations by HTC have not shown that disclosure of customers’ data was caused by faulty HTC software. The company is worried data disclosures might be due to malignant third party programs.

HTC has indicated that they are working to develop a patch and will soon announce an updated security program. The company will inform all consumers to download the program and update their mobile device software.

HTC also suggests that customers not download, update and install programs from websites that they do not explicitly trust. Although there have not been any reports of damage to consumers’ rights, the company is taking measures to nip the problem in the bud.

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Mobile phone spec sheets: What do they mean?

Spec sheets for tech devices can sometimes be confusing. Though generally, comparing two mobile phones (or tablets) on a pure spec-for-spec basis is a good rule of thumb to determine a winner (‘this one has a bigger screen, better camera, it must be the better option!’), a list of abbreviations, file formats and numbers doesn’t always give you the full picture.

Avid consumers of mobile phones know, as does anyone who regularly reads tech and gadget blogs, it’s the good old user experience at the end of the day that wins out.

The INQ Cloud Touch and BlackBerry Torch 9810 both received three and a half stars in our reviews. However, if we scored every phone based on their specs alone, the Torch 9810 would win hands down with it’s more powerful processor and better camera.

But ultimately we felt that each phone offered an overall experience of equivalent value when you take into consideration price, ease of use, features and - crucially - who the phones are aimed at.

So, what should we expect from specs?

As soon as a phone or tablet is announced, there’s usually an accompanying list of specs.

GSM 850/900/1800/1900, 512MB, 1.2GHz, 8.1-megapixels, 32GB. All of these figures will be instantly familiar to the average tech fan; if not you can find out with a cursory Googling.

But what do they all really mean?

We’ve put together this short guide to all of what we think are the most important mobile phone specs are and what to consider when weighing up two similarly-specced devices.

Size and weight

Pretty self explanatory this. The dimensions of a smartphone are usually expressed in a Height x Width x Depth format, with measurements for each normally given in millimetres. The weight of a phone is shown in grams and is usually given with the weight of the phone including the battery.

Screen sizes, pixel counts, PPI and screen types

In contrast to a phone’s dimensions, a phone’s screen size is normally expressed in terms of inches. This measurement is derived from a diagonal measurement, e.g. from the top right corner to the bottom left.

So while two phones may have the same stated screen sizes (i.e. 3.5-inches) they might not be exactly the same shape; one may be longer and thinner than another.

Screen size doesn’t give you an idea of how detailed a display is either; this is when the resolution (normally expressed as number of pixels across height x width) and the PPI value (the number of pixels per inch).

The materials and type of technology used in a phone’s screen also have an impact on how well it performs. Different types of display hold up better in certain lighting conditions than others and some are better at reproducing colours and shades.

AMOLED and Super AMOLED screens generally boast superior levels of contrast compared to LCD type screens. Screens with IPS (In Plane Switching) technology can be tweaked to provide stunning levels of detail while providing fantastic viewing angles. Have a look at our recent comparison of these smartphone screens for a better idea.

Operating System / OS: The Operating System is the main program that basically ties everything together, from the phone’s dialler and settings menus to the camera application to the web browser and games like Angry Birds.

For example the OS for Apple’s iPhone and iPad is iOS, the OS for BlackBerry phones is called BlackBerry OS, and Android devices currently run on Android 2.x or Android 3.x depending on if they’re phones or tablets. Windows Phone 7 or Windows Phone is the new mobile OS from Microsoft.

CPU and speeds - 1GHz, 800MHz: The CPU (short for Central Processing Unit) also known as the processor is the part of the phone that responds to your commands; open an app, start the phone’s browser etc.

CPU performance is measured in terms of the frequency at which it powers through processes, measured in Hertz, megahertz (MHz) and gigahertz (GHz). The faster the CPU, the more quickly your phone will be able to respond to your commands.

RAM / Memory: RAM can be confusing, as it’s sometimes listed simply as ‘Memory’ (RAM is short for Random Access Memory). This could possibly lead you to think that Memory refers to internal storage (i.e. where you store your pictures, MP3s, etc) which isn’t the case.

RAM is used to temporarily store app and program information and carries out the ‘physical’ running of processes if you will, things like playing music, running the web browser or loading a game.

Generally speaking, the more RAM a phone has, the more capable it is at carrying out tasks.

MP/Megapixels and camera specification: The megapixel count of a phone’s camera determines how large and roughly how detailed the images it takes will be. A megapixel is a million pixels. A phone with a 12-megapixel camera therefore will take much bigger pictures than a phone with a 3-megapixel camera.

Sure, an 8-megapixel camera means that the phone is capable of taking big images. That’s all. It’s not a totally accurate way to judge camera quality, there are other things, which we’ll go in to in a minute.

Aperture

A specification that we’re increasingly seeing listed in spec lists at the moment is the camera lens aperture, expressed with an ‘f-number’ like f/2.4 or f/2.8.

Generally, the smaller the f-number, the greater amount of light is able to reach the image sensor. Therefore, the camera will the smaller number will be able to perform better in gloomy or poorly-lit conditions without you having to turn the flash on.

The Sony Ericsson Xperia Arc, Xperia Neo and Xperia Ray phones cameras have an aperture of f/2.4, the Nokia N8’s 12-megapixel camera has an aperture of f/2.8 and the HTC Evo 3D has a f/2.2 aperture, but many phones don’t quote the lens aperture in spec sheets.

Most cameraphones will have an auto-setting where the camera will adjust for light accordingly, but others will have a manual control for exposure settings as well.

As well as aperture levels, it’s also worth noting if a phone’s specs mentions anything additional like Sony’s Exmor R sensor, which allows for even greater photo clarity in gloomy locations, combined with the comparatively big apertures of all these phones.

Camera Flash - xenon, LED, dual LED?

Phones with xenon flashes built in are pretty rare these days, generally only seen on Nokia smartphones like the N8.

There are many advantages that xenon flashes have over LED and dual LED. Generally, xenon flashes are better for illuminating shots across a wider range of situations and provide a more powerful burst of light. We’ve seen instances where a xenon flash will properly illuminate an entire area if it’s dark or gloomy where an LED or dual LED flash just doesn’t have the muscle to do this.

Jay Montano over at The Nokia Blog has put together a number of comparison shots which effectively weigh up the advantages of both of these and there’s a similar post demonstrating this over on All About Symbian.

One area where LED and dual LED flashes have an edge over xenon is in terms of video. An LED flash can kick out a continuous stream of light for use when recording video in the dark, something that a xenon flash can’t do. Xenon flashes are also quite big, adding considerable bulk to a handset.

Internal storage and microSD cards: Also, if a smartphone has a powerful camera but only say 8GB of internal storage and no microSD slot to expand the memory, then you’ll have to consider that that 8GB is going to get filled up mighty quick if you’re intent on taking lots of pics.

Internal storage (occasionally referred to as ROM, Read-Only Memory) is where your phone saves things like pictures, apps, music and other files. Internal storage is measured in either MB (Megabytes) or GB (Gigabytes) depending on how much a phone has. 1GB is approximately equivalent to 1000MB.

Music files vary greatly in size depending on the length of the song, their type and their bitrate. Songs ripped in lossless formats like FLAC can be as large as around 30MB for a 3-4 minute song whereas an MP3 of a similar-length song will be around 3-5MB.

Often a spec sheet says you’re getting ‘8GB’ or ‘16GB’ of storage, but in reality you often end up getting fractionally less than that. This is due to space being set aside for firmware, OS upgrades and other things.

In the case of the iPhone 4 for example, some users have reported that 14GB of the supposed 16GB is actually available. This is a common problem with internal memory on all smartphones, something we most recently noticed when we compared the HTC Sensation with the Samsung Galaxy S2.

MicroSD cards: Most phones these days will come with a microSD card slot, which allows you to add more memory by buying an additional microSD memory card.

You can currently get microSD cards of up to 32GB in size. Most phones released over the last couple of years will work with these, making it an easy way to expand storage. 16GB cards are currently available to buy for around £11 to £20 depending on where you look and a 32GB one costs between £33 and £40 at the moment.

Wired connections: micro USB, HDMI and MHL: Most phones these days will have some kind of connection that connects to a mains adapter and to a computer via USB.

Either the phone will have a micro USB connection on it that’ll mean that any micro USB-to-USB wire will work, or a proprietary connection-to-USB cable (that will come supplied in the box), like the iPhone 4.

Many phones these days also come with HDMI ports that allow you to hook your phone up to an HDTV set, for the purposes of watching video recorded on the phone on a bigger screen. Normally, you find an HDMI connection on a phone that’s capable of playing and/or recording video at 720p or 1080p.

If a phone lists ‘MHL’ (Mobile High-Definition Link) in its specs then this means you should be able to stream HD video from the phone even if there’s no HDMI port.

A phone like the HTC Sensation for example, has no HDMI port, but it’s micro USB connection features MHL connectors in it. You’ll have to buy a separate MHL to HDMI cable and adapter to connect your phone to a TV set’s HDMI port. But this means there’s a way to connect your phone to an HDTV screen without there being an HDMI connection on the phone itself.

Wireless Connections; EDGE, GPRS, 3G, HSDPA, Wi-Fi and Bluetooth: EDGE and GPRS generally mean that a phone can access the internet at the slowest possible speeds going on your phone’s network. Your phone will normally display an ‘E’ or ‘G’ icon next to the four bars of signal when you’re connected to either of these.

3G provides a faster and more power-efficient web browsing experience on the go, so much so that it allows you to make video calls (if the phone has a front-facing camera).

HSDPA, sometimes called 3.5G is faster still, and is represented by an ‘H’ or ‘3.5G’ icon on some phones.

HSDPA stands for High Speed Download Packet Access and can support download speeds of up to 14Mbps on your phone, theoretically faster than fixed-line broadband in many instances.

Some phones will also list HSUPA (High Speed Upload Packet Access) speeds as an indicator as to how quickly your phone can upload information (sending emails, uploading pictures to Facebook).

Most phones these days will come with a Wi-Fi antenna built in, which allows you to connect to the internet through a home broadband wireless router or through an open Wi-Fi hotspot in town. The main advantage to doing this is that your web use while you’re connected to Wi-Fi won’t come out of your monthly data plan.

Bluetooth is a short-range wireless technology that allows you to securely “pair” two devices together like a Bluetooth headset or handsfree kit with your phone, and to easily send files like pictures between devices (such as two phones).

GPS and A-GPS: A GPS antenna allows you to locate yourself on navigation programs like Google Maps, Nokia Maps and Bing Maps using satellites that are part of the GPS (Global Positioning System) network.

A-GPS (Assisted GPS) is a term used to describe when a phone uses cellular data from mobile masts to help triangulate your position alongside the GPS, allowing for faster location locking.

Talk Time / Standby Time: A general level of service governed by the phone’s battery and power management techniques, usually measured in hours (for talk time) and days (for standby time; i.e. if the phone it totally inactive).

However, because people use their phones for a number of different things, playing music, playing games, browsing the web, it’s harder to tell just how effective a phone’s battery is.

High-level smartphones which allow you to perform a number of tasks all at once generally don’t have a long lasting battery life; it’s advisable to carry a spare mains charger or USB cable around with you just in case or to charge it every night.

GSM Tri-Band/Quad-Band: Networks in the UK, Europe and (most of) Asia occupy the 900 and 1800 MHz GSM frequency bands of the radio frequency spectrum. Networks in the United States use the 850 and 1900 MHz bands.

Note that this is not to be confused with the MHz of your phone's CPU - if your phone only has a 600MHz chip, that doesn't mean the phone won't work on the 900 - 1800 bands!

Most phones these days are ‘quad band’, meaning that you can use them to make calls virtually anywhere in the world. You’ll often see ‘GSM 850/900/1800/1900’ listed in spec lists - this basically means the phone will be able to make calls wherever there are services supported on these frequencies in the world.

DLNA and AirPlay: DLNA is short for the Digital Living Network Alliance, an affiliation of companies which includes Sony Ericsson, Motorola, Nokia, LG and Samsung.

Devices that are DLNA Certified will work in some capacity with others. The most common use of DLNA in smartphones is the ability to stream audio, photos and video to a DLNA compatible TV set or speaker system.

AirPlay allows for much of the same kind of thing (wireless streaming of audio, video and pictures to compatible devices), but is exclusive to Apple products. With AirPlay you can stream media from your iPhone 4 and iPad 2 to an Apple TV receiver that’s plugged in to an HDTV set.

Conclusion

While this is intended as a brief guide as to what everything means on a spec sheet, there’s more to a list of stats than meets the eye.

At the end of the day, there’s no way of really being able to get a feel for how a phone looks or works until you get some proper hands-on time with one and you need to find the features that suit you, you might not need a Xenon flash and lots of storage.

That said, hopefully this guide gives you a better idea of what to look for in the stats and helps you make an informed choice when you’re in the market for a new phone.

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Smartphone GPS Just Got A Whole Lot Better, And Russian

Sputnik is waiting to boost your GPS reception. The American GPS satellites aren't the only location-finding birds in the sky. Silently and invisibly, the 22 satellites of Russia's GLONASS system partner our GPS, and starting next year smartphones based on Qualcomm chipsets will be able to boost their prowess with GLONASS signals.

"It's like dual-core location," said Rob Chandhok, president of Qualcomm Internet Services. "You actually have the system able to look at both satellite constellations at one time and leverage them so … you can get a more accurate fix, or a faster fix." According to Qualcomm, adding GLONASS improves GPS accuracy in "deep urban environments" by 50 percent.

Qualcomm announced its GLONASS support in May, spurred in part by a new Russian government requirement that phones sold there include GLONASS or pay additional import taxes. But this is a good thing for Americans and especially Canadians: because the satellites target Russian latitudes, they perform especially well in northern countries.

GLONASS support won't cost extra, and it won't require expensive recoding of GPS software, Chandhok said. It will, however, require GLONASS radios in devices, so it's not just a software upgrade for existing phones.

"The whole point of what we provide in our solution is that the software above [the chipset level] doesn't have to know where the data is coming from," he said.

GLONASS Takes New York

I got to see GLONASS in action, and it's pretty simple. A Qualcomm rep and I took a development phone out onto 28th Street in midtown Manhattan, a tough spot for GPS because of the tall buildings all around. With only GPS turned on, the phone saw two satellites, not enough for a location fix.

In testing dozens of phones, this has been my experience: generally, phones have to rely on inaccurate cell-tower triangulation when they're on side streets in New York City. Sensitive GPS chipsets can find a fix at a corner, where there's a bit more sky. Some phones make me walk several blocks down to a park.

So I was impressed when the Qualcomm guy hit the vodka-fueled-turbo-boost button, and pow: 9 of 22. 14 of 22. Bang. Location locked in. Between GPS and GLONASS there are now 55 satellites to choose from, which makes it much easier to find a fix in a narrow slice of sky.

Commercial GLONASS phones are already out in Russia, and Garmin's new eTrex series of handheld GPS devices already combine GPS and GLONASS in the U.S. The eTrex units aren't phones, though.

The first combined GPS/GLONASS phones will hit the US market "in the coming year," Qualcomm said. The majority of new Qualcomm S2 and S3 processors support GLONASS, which includes the dual-core chips coming out in smartphones like the HTC EVO 3D and T-Mobile MyTouch 4G Slide. Those existing phones won't be able to use GLONASS, though, because the system requires additional radio hardware.

China and the EU are also working on their own GPS satellite constellations, but they won't be ready for a few years. Broadcom and ST-Microelectronics have announced combined GPS/GLONASS support as well.

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Assisted GPS (7 of 7)

Biography

ROD BRYANT is the chief executive officer and chief technology officer of SigNav Pty. Ltd. in Canberra, Australia. Until 1994, Bryant worked at Auspace Ltd. for eight years in a variety of engineering, management, and business development roles associated with satellite engineering. He has a Ph.D. in real-time ultrasonic imaging from the University of Adelaide.

Rod Bryant

Innovation" is a regular column featuring discussions about recent advances in GPS  technology and its applications as well as the fundamentals of GPS positioning. The column is coordinated by RICHARD LANGLEY of the Department of Geodesy and Geomatics Engineering at the University of New Brunswick, who appreciates receiving your comments and topic suggestions. To contact him, see the "Columnists" section of this issue.

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Assisted GPS (6 of 7)

Memory and Hosting Constraints.

In developing the technology, we were required to accommodate a range of memory and hosting constraints. Using the u-Nav chipset, we have implemented an MS-Assisted solution in which the firmware is serially booted into the on-chip static random access memory (SRAM) from the cell baseband chip. This required all of the AGPS firmware to run in 64 Kbytes of program memory and 60 Kbytes of data memory. We also have implemented MS-Based and assisted conventional solutions utilizing external flash memory for the program but internal data memory only.

Utilizing the flexible correlator hardware mentioned earlier, a firmware solution running on a host processor performs all of the subATTO processing to produce code-phase and Doppler measurements or location.

The firmware supports MS-Assisted, MS-Based, and multi-mode operation. It runs on an ARM 9 microprocessor but can easily be ported to others.

It has been uniquely structured to facilitate sharing of the processing resources with foreign, high priority applications as might be found on a cell baseband processor. The firmware adapts gracefully to the loss of processing capacity and loss of signal samples. It is independent of the platform's real-time operating system (RTOS) and can be collapsed into a single task.

Conclusions

GPS operation can be enhanced in its performance through the provision of assistance data wirelessly.

This assistance can be supplied via the user plane or control plane. It can consist of satellite data gathered from remote GPS receivers with direct line of sight to the satellites, coarse receiver position, precise or coarse time, or more specific data derived from these primary elements.

The wireless network may also perform the location solution, although the benefit of this is debatable. The use of assistance can result in much faster acquisition of weaker signals, and can facilitate navigation solutions that would not otherwise be possible.

The benefit of the time assistance is dependent in a complicated way on its uncertainty. Both the search strategy and the navigation solution have to be adapted to the level of this uncertainty.

CDMA inherently facilitates precise time assistance. GSM networks, however, have to be augmented to provide it and generally will not be.

On the other hand, CDMA cell sizes can be much larger than GSM cell sizes, resulting, in principle, in slower signal acquisition and/or a need for more GPS processing capacity. However, this is not a significant factor in practice.

GSM uses short time slots for transmission and this facilitates interference mitigation via signal blanking. A CDMA handset may employ "antenna switching," but with potentially serious impact on both GPS and voice communication. RF design for concurrent operation is far preferable.

There are some differences between the standards developed for CDMA and GSM but, in general, the assistance supplied and the performance requirements are quite similar. However, the sensitivity required by the standards is well under that required to provide reliable performance under a range of indoor and urban canyon environments.

Hardware-mechanized search engines are useful but typically are not flexible enough to permit the potential of the hardware to be fully realized. subATTO signal processing allows similar performance to be achieved with far less dedicated hardware support, but requires much more general purpose processing capacity. A hybrid of multiple smaller search engines and correlators provide an ideal compromise where such processing capacity is not available.

AGPS solutions require a range of different hardware and software solutions. Our team has experience with hardware employing both correlator fingers and search engines, and with flexible correlator hardware designed to work with a host processor. Our firmware solutions have ranged from MS-Assisted firmware running in 64 KBytes of internal SRAM to taskless, RTOS–independent multi-mode firmware running on a host processor that also supports high priority foreign tasks.

Acknowledgments

The entire engineering team at SigNav contributed to this work through their innovation and tireless dedication. In particular, I wish to thank Eamonn Glennon, who has made major algorithmic contributions. Our colleagues at u-Nav and its partners and customers contributed to our growing collection of insights, as have those of our other partner who cannot yet be named. This article is based on the paper "Lessons Learnt in Assisted GPS" presented at GNSS 2004, the 2004 International Symposium on GNSS/GPS, held in Sydney, Australia, December 6-8, 2004.

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Assisted GPS (5 of 7)

Flexible Design. Figure 2 illustrates an alternative organization designed to address these issues. In this case, the signal processing of each bin is much more sophisticated, and hence the entire search engine no longer lends itself to hardware mechanization. Instead, it is best implemented as a set of correlator channels each with multiple fingers. By using multiple channels together, one or more larger search engines can be built up as needed to span the required code-phase search range.

Figure 2: A two-code-phase subATTO search engine. In addition to the operational blocks described in Figure 1, the ACV (autoconvolution) block constitutes a proprietary algorithm utilizing multiple fast Fourier transform (FFT) bins. The FFT/ACV/squarer process provides improved sensitivity for the same overall integration period compared to the technique of Figure 1.

This arrangement draws on the patented subATTO signal processing technology (see side bar), which facilitates coherent integration over much longer intervals than a bit period. It results in shorter integration periods being used to achieve the same sensitivity. Since this more-flexible architecture also allows all of the hardware resources to be effective all of the time during acquisition, it results in far more cost-effective use of hardware to achieve the required sensitivity and acquisition time.

This approach has been employed using two very different hardware architectures. In the uN8130 baseband processor, a modestly dimensioned hardware search engine is used in tandem with 12 correlator channels comprising four fingers each. The correlators are used for both acquisition and tracking while the search engine performs the more difficult task in acquiring the first satellite and some of the subsequent satellites. Whenever the search engine acquires a signal, it passes it to one of the correlators. This solution has been adapted successfully for both CDMA and GSM operation, with performance well in excess of the standards.

In another example, flexible correlator hardware resources have been incorporated into a chip designed to operate with a host processor. subATTO processing takes place on the host. A search strategy was devised that keeps the hardware working close to its maximum potential throughout the acquisition phase. The resulting performance is well in excess of the standards yet again with minimal hardware costs. This approach demands much more general purpose processing capacity but much less dedicated hardware support.

Figure 3: Core signal-processing scheme. The fast Fourier transform (FFT) block is equivalent to the ensemble of local oscillators, second mixers, and first summers of Figure 2, while the windowing and eliminate data blocks correspond to the ACV (autoconvolution) block in Figure 2. Various estimation algorithms are employed depending on the implementation.

Acquisition Strategies.
We have developed a range of strategies to suit GSM and CDMA standards–based assistance schemes and the hardware architectures previously described. These involve the signal processing schemes described above as well as bit-synchronous signal processing schemes (when bit synchronization is feasible) using both correlators and search engines. We are also working with our chipset partners to optimize their hardware architectures to suit advanced acquisition strategies to improve sensitivity and acquisition time. One example is the use of multiple smaller search engines combined with correlators. This is an ideal compromise when general purpose processing capacity is limited.

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Assisted GPS (4 of 7)

Furthermore, it inevitably degrades the front-end noise figure of the GPS receiver, thereby offsetting performance gains relative to alternative approaches.

CDMA Mode Switching.
In the case of a CDMA handset, the main alternative is to switch modes between GPS and the handset. The two subsystems cooperate so the receiver "listens" only during timeslots when the handset is not permitted to transmit.

For example, during the 16-second response period, the transmitter may only be able to transmit for a fraction of the time in bursts of a few hundred milliseconds. While this process allows roaming to continue, it may well represent an unacceptable limitation on speech communication during that period. Meanwhile, the imposition of antenna switching constraints on GPS signal processing also is significant as integration periods must be sized to fit within these constraints.

GSM Signal Blanking.
For GSM, the problem is less extreme because the technology uses timeslots of only a few milliseconds in width. Signal blanking can be used during these slots, thereby efficiently avoiding the need for cooperation between the software of the two subsystems.

Nevertheless, the blanking itself eats into the GPS integration periods, thereby degrading sensitivity and/or increasing typical acquisition times.

Receiver Architectures

In tailoring a GPS receiver for embedded AGPS applications, several factors need to be considered including correlator design, memory requirements, and microprocessor control issues.

AGPS receivers need to acquire weak signals quickly. To meet the demands of the market and exceed the demands of the AGPS standards, more-sophisticated baseband hardware is needed than was required of conventional GPS receivers of only a few years ago. Essentially, this means many more correlator taps or "fingers." How those fingers are organized and the type of signal processing employed are critical factors.

Limited Coherent Integration. 
Figure 1 illustrates a common search engine architecture. This design performs multiple rounds of coherent integration for each of the n fingers per frequency bin, and integrates the results non-coherently. The architecture lends itself to efficient hardware mechanization through reuse of the arithmetic elements. Chips have been produced using this design to incorporate multiple bins and 20,000 fingers or more. Other designs, such as u-Nav Microelectronics' uN8130 baseband chip (with which the author is very familiar), combines a 2,048 finger × four-bin search engine with 12 four-finger correlators.

Figure 1: A two-bin hardware search engine. The first set of mixers mix the final local oscillator signals with the incoming signal to downconvert the selected satellite signal to near baseband. The first set of summing blocks perform coherent integration on the downconverted, despread signal. The squaring blocks compute the magnitudes of the complex integrals resulting from the coherent integrations. The second set of summing blocks perform non-coherent integration on the squarer outputs. A shift register produces multiply delayed versions of the locally generated pseudorandom noise code.

The first limitation of this hardware search engine is the coherent integration period is limited to much less than a navigation message bit. If not, the probability of bit transitions occurring within integration periods will be high, and excessive random losses will result. The effect of this limitation is to ensure the squaring losses prior to the non-coherent integration are relatively large. The end result is relatively long overall integration periods are required to achieve the desired sensitivity.

The second limitation of this approach is that, when it is possible to constrain the search to a small range of code phases, the rest of the fingers are effectively wasted. When precise time assistance is available this means most of the potential of the search engine hardware is wasted all of the time. When only coarse time assistance is available, it means the full potential of the hardware is being utilized for acquiring the first satellite signal — but, again, most of its capacity is wasted when acquiring subsequent satellite signals.

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Assisted GPS (3 of 7)

Time Slots.

Another technical difference relates to the fact that GSM uses short time slots, so each handset communicates in frequent short bursts. CDMA handsets, on the other hand, communicate using much longer bursts. This impacts on the forms of cell-phone interference mitigation techniques that can be employed by AGPS solutions in the two cases as will be discussed in a later section.

Cell Sizes.

A third technical difference relates to the fact that the GSM technology has a limitation on its cell sizes of around 35 kilometers in radius. CDMA cell sizes, on the other hand, are only limited by transmission power and relevant standards (such as CDMA code-phase search ranges). Hence, they can be much larger. If the coarse location assistance is derived from the cell location, its uncertainty can be much larger in a CDMA system than in a GSM system. In practice, however, this is not a significant factor because the most-demanding AGPS environments tend to be in inner-cities where cell sizes can be limited to a few kilometers in radius.

AGPS Standards

Both the CDMA and the GSM communities have developed standards for control plane AGPS messaging (TIA/EIA/IS-801-1, 3GPP2 C.S0022-0-1, 3GPP TS 25.331) and for minimum operational performance of AGPS handsets (TIA 916, 3GPP2 C.P9004-0, 3GPP TS 25.171 V6.0.0). There is considerable similarity between the assistance fields included in the two protocols. The minimum performance standards are measured in both cases using five separate statistical tests.

The five tests are of sensitivity, nominal accuracy, dynamic range, multipath scenario, and moving scenario with periodic update. The nominal accuracy tests are for static accuracy under typical signal strength conditions rather than weak signal conditions and with no multipath present. Performance in the presence of multipath is tested separately, as are the performances under weak signal conditions and under typical land-based dynamic conditions. 

One difference between the two performance standards is the handset must respond within 16 seconds in the CDMA case but has 20 seconds to respond in the GSM case. In both cases the required sensitivity is –147 dBm, and the horizontal positioning accuracy, although defined differently, is similarly around 30 meters.

Another difference is the GSM standard allows for either precise or coarse time assistance. When only coarse time assistance is provided, the sensitivity test is conducted with one satellite at –142 dBm. This is a recognition there is a performance penalty for not providing precise time assistance.

The other main difference is that, in the case of MS-Assisted (UE-Assisted) operation, the CDMA standard calls for the absolute code-phase accuracy to be tested, whereas the GSM standard calls for the location to be computed in accordance with a defined algorithm and for the accuracy of the result to be tested. This is more significant than it seems because the code-phase test is of absolute code-phase accuracy rather than relative code-phase accuracy. To pass this test, the time assistance must be used to determine the measurement instant with nanosecond precision.

The reason for this requirement is the location server can combine GPS and CDMA measurements in performing a hybrid fix only if the absolute GPS code-phase measurements are known for a precise time (according to the CDMA handset's local clock).

These standards have emerged from complex techno-political negotiations between network operators, handset manufacturers, technology providers, and semiconductor manufacturers. They represent negotiated compromises between these various groups rather than a true consensus as to real-world requirements. In particular, the author considers the sensitivity requirement to be lacking in stringency. For reliable positioning under most indoor conditions, sensitivity of at least –150 dBm is essential and better than –153 dBm is desirable. Sensitivity of better than –185dBm is ideal.

Cell-Phone Interference

One of the technical problems facing the GPS cell-phone developer is the interference to GPS reception from the very strong cellular transmissions of the handset. This is an even more serious issue given that the GPS front-end and antenna performance typically is compromised as a result of the severe physical constraints on the design. It is further exacerbated by the need for extreme sensitivity.

The ideal solution to this problem is to provide sufficient filtering in the GPS RF path to permit concurrent operation of the receiver and handset transmitter. However, the significant benefits that flow from such an approach come at a cost. In particular, the more complex RF design results in additions to the bill of materials that add cost and space.

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MS/UE Assisted.

In principle, the receiver can be simplified if some of the computation, such as the navigation solution, is performed by the network. This form of operation is referred to as mobile station–assisted (MS-Assisted) or user equipment–assisted (UE-Assisted) in contrast to solutions performed in the user's equipment: MS-Based or UE-Based.

The advantage in terms of simplifying the handset is questionable given the computational capacity of modern cell-phone and GPS chipsets. Furthermore, if the location information is required in the handset, this advantage is offset by the need to communicate back and forth. Nevertheless, such architectures are commonplace.

The network has coarse information about the location of a receiver embedded in a cell phone. If it supplies this to the receiver, along with its uncertainty, the receiver then can use this to determine which satellites to search for, restrict its search ranges, and initialize its navigation solution. The uncertainty typically is supplied in the form of either the size and orientation of the semi-major and semi-minor axes of an ellipsoid of uncertainty, or the horizontal radius and vertical height of a cylinder of uncertainty.

Time Assistance.

The network also can supply time and its uncertainty. This may be supplied precisely using hardware in the handset, or much more coarsely over the air from a server. If it is sufficiently precise (for example, to within a few microseconds), it can be used to restrict the search range for the absolute code phases of the satellite signals. If it is less precise (for example, only to within many microseconds to a few seconds), it can be used to restrict the search range for the relative code phases of the satellite signals once an initial signal has been acquired.

If the time assistance is fairly precise (to a few milliseconds or better), the handset position errors resulting from the uncertainty in the satellite positions corresponding to the time uncertainty will be small enough (a few meters) to be tolerated in most cases.

However, if it is coarser than this, the navigation solution also will have to solve for the time error. Note that the receiver may only have code-phase measurements rather than full pseudorange measurements as used in a normal receiver — requiring a procedure to resolve the one-millisecond code-phase ambiguities and a special algorithm to solve for the time error.

Additional Assistance.

Alternatively to supplying position, time, and satellite-derived data, the network can derive and provide other assistance including approximate code phases at a certain instant in time, with the corresponding uncertainties, as well as the Doppler offsets with their uncertainties.

Assistance can be supplied in the "user plane" or in the "control plane."

In the latter case, assistance is supplied via communication over the signaling channels from a server integrated into the network infrastructure. The standards discussed in a later section relate to this form of assistance.

In the former case, the assistance is supplied from a user server (typically Web-based), using standard communications channels such as Short Messaging Service (SMS) and General Packet Radio Service (GPRS) over Global System for Mobile Communications (GSM) networks, or Single Carrier Radio Transmission Technology (1xRTT) over code division multiple access (CDMA) networks.

CDMA vs. GSM

There are technical differences between GSM and CDMA cellular technologies that impact AGPS implementation in these networks. Equally importantly, the two communities have evolved different AGPS standards discussed in the next section.

Precise Timing.

The first technical difference relates to the fact that precise timing is fundamental to CDMA operation. The handset synchronizes to the communications code very precisely (that is, well below the microsecond level). Using hardware (for example, a pulse and message), precise network time can be transferred to the GPS receiver subsystem. Of course, this time will contain an error equal to the communication latency between the network and the handset, but it is more than adequate as precise time assistance for the AGPS purposes described in the previous section.

GSM does not use spread spectrum codes, and hence this form of precise time assistance is not intrinsically available in a GSM network. To deliver precise time assistance (with uncertainties of 5 or 10 microseconds), GSM networks have to be augmented. Not surprisingly, few network operators are keen to roll out additional infrastructure for this purpose, and GSM deployment of AGPS typically is required to operate with coarse time assistance.

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Using Cellular Telephone Networks for GPS Anywhere

The first two articles to appear in the innovation column in GPS World more than 15 years ago were entitled "GPS: A Multipurpose System" and "The Limitations of GPS." In the first article, GPS was trumpeted as a revolutionary positioning and navigation technique that could be used in all sorts of unexpected ways. This premise has stood the test of time with new uses for GPS still being discovered. The second article reminded readers that GPS may not be a panacea for all of our positioning needs — that there are some situations in which GPS fails us. In particular, it was noted that GPS signals are "blocked" by buildings, making indoor use of GPS impossible. But what was impossible 15 years ago is possible today.

New designs have greatly improved the sensitivity of GPS receivers so they can make code-phase measurements even on the severely attenuated signals inside buildings. And if the signal is too weak for the receiver to extract the satellite navigation message itself, the necessary data can be sent to the receiver using a cellular telephone network, which also can supply timing information to help the GPS receiver acquire signals more quickly. In this month's column, we will investigate how this so-called "assisted GPS" works and why we can now say that GPS works (virtually) anywhere. — R.B.L.

The integration of GPS into cellular telephones enables a potentially vast array of new applications ranging from consumer gimmicks through efficiency multipliers for enterprises to lifesaving safety and security applications. In the United States, the Enhanced-911 regulations have been and remain a major catalyst for this deployment. In Europe, the commercial potential of location-based services (LBS) is driving it. Regardless of the drivers, the technology convergence is happening with an ever-increasing momentum.

These new applications and the cell-phone environment itself, however, pose significant challenges for the GPS community. They demand GPS solutions that can be implemented in tiny spaces at extremely low cost in extremely high volumes, operate reliably in a much broader range of environments than was hitherto considered possible, acquire signals in seconds under extreme conditions and, for some applications, do so without the aid of stored orbital data.

These problems and the availability of cellular communications itself spawned the concept of assisted GPS (AGPS) in which the network assists the GPS receiver to perform its various functions. This article reports on AGPS developments leveraging cellular telephone networks to help acquire and deliver accurate GPS fixes from anywhere, anytime.

System Considerations

In developing a user system for AGPS, several factors must be considered, including the type of assistance to be provided by the network, the type of cell-phone network and the corresponding AGPS standards, and environmental factors such as radio frequency (RF) compatibility between the GPS module and the host platform.

Benefits of Assistance.
There are many types of assistance that can be provided by the network to the GPS receiver. The receiver could be a fully functional receiver capable of selecting satellites, acquiring signals, achieving time synchronization, extracting data, performing measurements, and computing its own navigation solution. Nevertheless, its acquisition speed can be enhanced through the provision of assistance.

Furthermore, it can avoid spending time to extract all of the required data from the satellite signals if most of this is supplied by the network.

Signal Levels.
More importantly, the range of signal levels at which the receiver can operate can be greatly increased if the receiver is relieved of the requirement to extract the 50 bits-per-second navigation data stream that is modulated onto the signals. This data cannot be extracted in a timely manner (or at all in many cases) if the received signal power is below about –172 dBW (–142 dBm) but code-phase measurements can still be made for much weaker signals than this. Since the navigation data is not location specific, it can be supplied by a remote receiver that has a clear line of sight to the same satellites.

The data supplied by the network in this way can include ephemeris coefficients, almanac coefficients, satellite health data, satellite clock error coefficients, atmospheric error coefficients, and so on. Additionally, excerpts from the data sequence can be supplied to facilitate coherent integration over periods much longer than a navigation data bit interval.

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