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The latest generation of mobile phones can already be used as game consoles, MP3 players, cameras and personal digital organizers. The next step is the launch of some emerging mobile phone services, such as "Location Services (LBS)" which will provide a series of based on the user's current geographic location. Services, from locating users who make emergency calls, to navigation applications, and providing customized information based on the user's current location.
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The location service was inspired by the PMB2520 single-chip assisted global satellite positioning system (A-GPS) solution developed by Infineon and its US partner Global Locate called "Hammerhead". A-GPS positioning refers to the use of global satellite positioning systems and receiving "auxiliary information" from cellular mobile telephone networks for positioning. A-GPS can accurately position the user in less than one second, with a positioning accuracy of up to several meters. Its high sensitivity means it can work reliably, whether in a building or in a deep suburban canyon.
A-GPS basic principle
Due to the nature of the GPS system, collating data in satellite signals is a complex and time consuming task, but it is unavoidable in autonomous operations. After receiving the auxiliary positioning information directly from the mobile phone mobile network, since it is not necessary to check the data from the satellite signal, the workload of the GPS receiver can be greatly reduced. Depending on the signal strength, this reduces the time to first fix (TTFF) to a few seconds, which in turn can significantly reduce the considerable energy loss required for each positioning, resulting in longer standby and talk time. It is one of the most important features of mobile communication devices.
Even if the A-GPS signal is 1,000 times weaker than the general "open sky" GPS signal, it can still achieve reliable positioning, which means that the A-GPS system is indoors, deep in the canyon or Mobile vehicles can work properly. Even under poor reception conditions with strongly reflected signals, complex algorithms enable the system to achieve precise positioning of signals (intelligent multipath interference suppression techniques).
The system basically has two different modes of operation when using the auxiliary information, namely the mobile device main mode and the mobile device assist mode. In the mobile device main mode, the handset requests additional information from the network and uses the data set for up to several hours. The calculations required for the first and subsequent positioning are performed within the handset. This mode allows for the fastest positioning, but requires the mobile device to have some computing power. In the mobile device assisted mode, the handset requests independent assistance information for each location from the network and sends the GPS data back to the base station for further processing. In this mode, the network needs to perform more work than in the mobile device main mode, so the time required for each positioning is longer, but there is no requirement for the computing power of the mobile device.
The protocol for performing all A-GPS related data exchanges on the mobile phone mobile network can be based on one or two different concepts, namely Control Plane or User Plane. Earlier control plane architectures used dedicated signaling paths for wireless and core networks, which required improvements to existing network infrastructure, which of course was not conducive to network operators. In the user plane (also known as Secure User Plane, SUPL) architecture, mobile communication devices communicate with location servers that use IP links, while existing mobile communication network infrastructure remains unchanged. Data connections can be made over conventional GPRS connections, such as using existing interfaces and protocols in the network. Hammerhead is fully compatible with both concepts.
But Hammerhead does not always rely on receiving auxiliary navigation information from the network alone. Thanks to the high sensitivity integrated low noise amplifier (LNA), the chip can also operate in autonomous operation. However, in this case, it needs to rely entirely on satellite signals for calculations, positioning takes a long time, and indoor reception is limited, which is very common for general GPS devices. To compensate for this shortcoming, a special functional model called "Enhanced Autonomous Mode" has been adopted (which has become a patent of Global Locate). With this mode, A-GPS can use the previously recorded auxiliary navigation data for positioning calculations, which are valid for up to four days. This long-term orbit (LTO) data can be transmitted to the mobile device through any interface, that is, the information does not have to originate from the mobile network, but can be downloaded over the Internet. The technology will play an important role until the mobile network operator completes the construction of the global A-GPS infrastructure.
Single chip integrated RF function and baseband
In the PMB2520 solution, a highly sensitive RF receiver (sensitivity -160dBm) and digital baseband are integrated on a 0.13um CMOS chip. Infineon's RF and system experience, combined with Global Locate's existing A-GPS proprietary technology, provides the foundation for the Hammerhead chip design.
Hammerhead uses "massive parallel association" techniques to receive signals transmitted by satellites on eight parallel channels and compare them to reference codes in more than 32,000 correlators. Compared to the receivers commonly used in vehicle navigation systems, this technology can significantly reduce the initial positioning time and significantly reduce power consumption. Therefore, Hammerhead's first positioning time is only about one second with a sensitivity of -130dBm after cold start. This feature is primarily intended for applications that require only one location and do not require continuous tracking (such as emergency services and tracing).
Due to its large-scale integration, Hammerhead includes external components (SAW filters and some passive components) occupying only 80mm2 of printed circuit board area. Most of the GPS chips on the market currently use a two-chip solution, which often requires a board area of ​​300 mm 2 .
Another aspect that optimizes costs is that the chip is tuned to fit the general handset architecture. Although not a self-contained solution at all, Hammerhead has cleverly used the existing functional units in today's mobile phone designs, such as crystals for high-precision reference clock frequencies (10-40MHz) and real-time clock frequencies (32,768kHz).
The actual location is determined by calculating the raw data of the GPS chip's correlator (time delay difference) in the baseband of the mobile phone. This calculation is based on the software library provided by Global Locate. Compared to a pure DSP-based GPS solution, this solution requires very little computing power, only 3 MIPS, which poses no challenge to the current baseband. This software does not have any real-time requirements or interfere with the phone call flow of the target system. The memory requirements of this software library are not high: no more than 50kb of RAM and no more than 200kb of ROM. The software library can be provided to the target CPU architecture in the form of a binary executable code.
In general, Hammerhead is compatible with many mobile phone baseband solutions for 2.5G and 3G networks, and the digital connection to the main CPU can be done using any of the Hammerhead interface options, which provide a standard UART port. SPI or I2C. The user can configure any of the interfaces to meet the requirements of the target system. The chip requires no more than 9,600 baud for digital interface data rates.
Wide range of applications
Typical applications for A-GPS include searching for "point of interest (POI)" and personal navigation to a predetermined location. POI is a service that provides information about unfamiliar environments and can be used to download information about recent gas stations, recommended restaurants, hotels, and more. Directly related to this, the navigation function is very useful to people, just like the car navigation system, can tell the user how to go to the destination they want to go. It should be noted that in this case, the Pacers need more detailed map information, although this information does not necessarily need to be stored in the phone, it can be sent by the network operator to the user as part of the service if needed. Mobile phone.
People's positioning is another application. Typical uses include "Find Friends" and "Child Tracking" to show the current location of friends and children who need to be supervised. For reasons such as data protection and the nature of the system itself, mechanisms have been added to prevent them from being tracked without their consent. Therefore, information about the location of the individual is never stored unconditionally in the network or server. The system will only respond to queries from the receiver that are explicitly requested by the user to start. However, it is currently technically possible to perform a general positioning without authorization by the user according to the cellular connection situation, and only the network operator can perform such positioning.
Sometimes this technology can even save lives. As part of the enhanced emergency call feature, when the handset makes an emergency call, the caller's current location is automatically transmitted to the emergency control center along with the call. In actual situations, it is often difficult for callers to accurately and reliably report their location. Accurate measurement of the caller's location via A-GPS allows emergency personnel to quickly and accurately determine location and arrive at the site. The United States has enacted laws to enforce this feature called E911 (Enhanced 911) on all mobile phones since 2007, and Japan has passed similar laws. Although Europe does not currently have mandatory regulations in this regard, similar regulations are likely to be introduced.
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