Where is a navigation chip in my iPhone?
There are three subsystems in Global Navigation Satellite Systems (GNSS): a satellite constellation, a control segment and user equipment.
A navigation receiver is a part of the user equipment, it is something that:
- is placed on a user side,
- receives satellites’ signals,
- calculates and provides to the user with a PVT (position, velocity, time) solution.
But where are the boundaries of the navigation receiver? Should it have a case and buttons? Is a power supply adaptor a required part of the receiver? If I calculate PVT into my matlab script, is it enough to name this script “navigation receiver”?
What is an average, typical, regular navigation receiver in 2022?
European Union Agency for the Space Programme estimated a whole amount of mounted GNSS receivers at 6.5 billion units. The vast majority is associated with smartphones, wearables, tourism and health devices, which contribute about 6.0 billion of the amount. Two smartphone oriented companies, Qualcomm and Broadcom, had about 40% of the market revenue in 2017. So, we should take a look at smartphones if we want to figure out the typical navigation receiver.
Let’s open iPhones of several generations and discover how they realize GNSS positioning.
iPhone 3G and 3GS
The iPhone 3G became the first iPhone with the GPS positioning feature. It was issued in 2008 and had been produced for two years. The phone was based on a 32-bit Samsung processor and contained plenty of specialized chips. We should pay attention to a separated Infineon PMB 2525 Hammer-head II GPS chip. The chip has 3.59 x 3.75 mm dimensions and is built with a 130 nm technology. There is an RF front-end and a baseband module into the single chip, so a developer needs to add an antenna, a SAW filter, power supply, and the main processor interface to use navigation.
There are a lot of other Infineon telecommunication chips in the device. I guess it is a reason why we can see PMP2525 instead of alternative chips like SiRF.
Infineon PMP 2525 supports an A-GPS technology. The technology supplies the chip by mobile-network time and GPS satellites ephemeris. As a result, the receiver can obtain a PVT solution faster. Time to the first fix — TTFF — is the base characteristic for navigation receivers. It can be described as the time interval duration between the receiver power-on and PVT provided to an user. It is claimed by Infenion the PMP with A-GPS support can achieve 1 second TTFF. The interval is increased to 30 seconds without the support. The characteristics are typical even for modern navigation chips.
Tracking sensitivity is another important characteristic. It is a possibility to work under harsh reception conditions and weak signals. PMP 2525 can track signals with power of minus 160 dBm (power value divided by 1 mWt and described in dB). In other words, the signal’s power can be about 100 zeptowatts (100 x 10–21). High sensitivity is in high demand for smartphones due to very inappropriate antennas that are used in the phones. The GPS antenna of iPhone 3G is unified with WiFi and BT and has quite modest properties.
Apple iPhone 3GS continues to use PMP2525 chip, but the chip was relocated to another side of the main board.
iPhone 4 and 4S
Apple iPhone 4 was issued in 2010 and it had become a completely new phone. It had a big touch screen, high-performance processors, new cameras, new network standards, improved autonomy, and, as a result, increased battery capacity. But the increased battery needs additional space, so engineers decreased the main board’s size. The board looks completely different. It is longer and narrower. There is high-density component assembly on both sides of the board. Antennas, including a GNSS one, are integrated into the phone case.
If you lack space, you cannot use a lot of specialized chips. You need to use integrated solutions, so iPhone 4 has a lot of systems-on-chip. The main one is a new Apple A4 which is the first SoC of the A-series. There are an ARM application processor, a graphic processor, and even SDRAM crystals.
Apple iPhone 4 had two versions: CDMA and GSM, but the versions have different GPS receivers too!
The GSM version had a specialized Broadcom BCM4750 navigation chip:
The BCM4750 structure is similar to PMP2525. It contains an analog L1 GPS front-end and a digital baseband module in a single 90 nm chip. The baseband module has a processor, 24 correlation channels, and a fast signal acquisition engine. Broadcom claimed a progressive A-GPS support and sensitivity of about 162 dBm.
But the main marketing point was the chip’s energy efficiency. In the tracking mode, the power consumption can be decreased to 13 mWt. Power efficiency is an essential requirement for mobile applications, and the 13 mWt is a great result! It was achieved by periodically suspending the chip. The phone had a LiPo-battery with 3.7 voltage and 1420 mAh capacity. So, theoretically, the receiver can work for about 100 hours powered by the battery. Just theoretically :)
The iPhone 4 CDMA version used Qualcomm MDM6600 to process navigation signals. But the primary role of the MDM6600 in the phone is to be a telecommunication modem. It’s a fusion of a multichannel analog transceiver HJ11-VF535–200 and a multisystem digital baseband processor HJ11-VJ130 in a single module. The transceiver’s channels are used to work with 2G, 3G, and CDMA mobile network signals, and just one of them is used to deliver a GPS L1 link to an intermediate frequency. Then GPS L1C/A signals are processed by digital modules of the baseband processor. The solution was named by Qualcomm as IZat gpsOneGen 8.
Remarkably, GNSS was combined with mobile telecommunication instead of local communications like WiFi or Bluetooth. The reason is a synergy of navigation and mobile network. Any navigation receiver can work better with precise time and ephemeris aiding. The data can be provided by the mobile network via A-GPS technology. So, it is much easier to combine and debug the technology in a single module than establish links via an application processor. Users noticed improvements in navigation in comparison with previous phone versions: the first fix was faster and the GNSS navigation worked better in harsh conditions.
Another interesting change in the 4th iPhone is an STMicroelectronics L3G4200D 3-axes gyro. Combining the gyro and accelerometer measurements, it was possible to realize pedestrian dead reckoning (PDR) and navigate indoors.
Apple iPhone 4S was issued in 2011. And it supported GLONASS! There was a lot of buzz in Russian newspapers about that. The improvement in navigation is a consequence of the replacement of MDM6600 by Qualcomm MDM6610. The phone did not use the GLONASS system all the time, it was enabled in cases of weak GPS signals or a low number of visible GPS satellites.
As we can see, the fusion of GNSS and telecommunication functions in a single chip became mainstream. Since the iPhone 4 model, we cannot isolate a special GNSS chip: repair it, calculate the cost, calculate power consumption, and so on. The GNSS receiver disappeared as a separated object.
iPhone 5, 5S, 5C
Apple iPhone 5 was issued in 2012. Navigation signals were processed by a new Qualcomm MDM9615 chip (gpsOneGen 8A). In contrast to MDM6610 it is just a digital baseband processor, analogue processing was taken out to Qualcomm RTR8600.
The RTR chip is a multichannel RF-transceiver produced by 65-nm technology. It has 10 receiving channels, two of them are used for GNSS L1 baseband processing, the others are used for mobile networking.
iPhones 5S and 5C use a Qualcomm WTR1605L RF transceiver instead of the RTR one. The chip size was decreased twice, the channel number was increased. As a result, the phones began to support Beidou navigation signals.
Apple iPhone 5S has a new A7 application processor SoC. It’s the first 64-bit iPhone SoC. From a navigation point of view, it is interesting because of its M5 co-processor. It processes gyroscope and accelerometer data.
iPhone 6 to iPhone 11
In the next several models, transceivers and baseband processors have become better, but the approach is the same.
Apple iPhone 6 was issued in 2014. The baseband processor was replaced by Qualcomm MDM9625M (IZat gpsOneGen 8B). WTR1605L was moved to another side of the logic board.
The phone used an InvenSense MPU-6700 chip as a multi-axes gyro and accelerometer. There was an additional Bosch Sensortec BMA280 accelerometer. It has lower sensitivity, but consumes a third (130 uA).
Apple iPhone 7 was issued in 2016. It has two versions, due to patent disputes between Apple and Qualcomm. The first one used an Intel PMB9943 (aka Intel XMM7360) baseband processor paired with two Intel PMB5750s RF transceivers (placed on another side of the board). It was the beginning of an Intel era. These chips were used for GNSS also.
Apple iPhone 8 and X also have several versions: Qualcomm one and Intel one. But in the 2018 models XR and XS, Intel replaced Qualcomm completely. Intel PMB9955 (XMM7560) is used and it supports all GNSS systems: GPS, GLONASS, Galileo and Beidou.
Apple iPhone 11 was issued in the autumn of 2019. And it had a ultra wideband (UWB) chip and antenna! The UWB can be used for indoor positioning, it is very promising technology.
iPhone 11 has an Intel X927YD2Q (XMM7660) baseband processor, paired with an Intel 5765 P10 A15 08B13 H1925 RF transceiver. They are used for GNSS navigation and 2G, 3G, 4G mobile networking.
iPhone 12, 13: 5G is coming
iPhones 12 and 13 are a new turn for the series because of three circumstances:
- Intel sold the majority of its smartphone modem business to Apple. Apple got about 17,000 patents and 2200 new workers. Development of new chips, including GNSS, is continuing in Californian Apple departments.
- Xiaomi and several other brands had issued phones with dual-band GNSS support by the time. There are wideband navigation signals in the L5/E5/B2 band. The wideband signals have dramatically better accuracy under multipath conditions, so the navigation receiver can achieve better results in urban areas.
- The 5G networks became a reality, so a phone needed any 5G support to be considered as a flagman.
As a result, in iPhone 12 and 13 Qualcomm chips are used again.
The twelfth model contains the Qualcomm Snapdragon X55M SoC and Qualcomm SDR865 RF transceiver. The phone has two GNSS antennas and supports L1 and L5 navigation signals.
The iPhone 13 has an interesting double layer board. The Snapdragon chip was updated to X60M. It is implemented by a 5 nm technology instead of the 7 nm of the previous model, so it is more energy efficient. The transceiver is changed by a SDR868 one.
Conclusion
So, how does a regular navigation receiver look in 2022? It has dissolved in telecommunication chips. The chips are developed by a few big companies.
Luckily, for me as a navigation engineer, we have a lot of applications for “abnormal” receivers: geodesy and aviation, trackers and synchronization, driverless cars and car sharing. A lot of work!
