Last updated on November 24th, 2023 at 08:31 am
The modern consumer grade device using dual GPS frequency in contrast with older single frequency ( L1 ) approaches is called the L5 GPS. For many years, the consumer devices have relied upon the single frequency GPs receivers primarily known as the L1 frequency, to calculate the location. Whereas, there is a significant shift in newer gadgets which embraces the dual frequency GPS which improves efficiency and decreases error.
GPS Signal’s Journey
Global Positioning System ( GPS ) is a constellation of satellites orbiting the Earth in a Medium Earth Orbit which was developed by the United States Military. Even though it was developed for the military, the GPS was opened to the public for commercial purposes. Now, GPS has become an integral part of modern life, from turn to turn navigation to food delivery, everything relies on the GPS systems. However, the cornerstone of GPS is that the L1 frequency has its limitations.
The L1 ( 1575.42 MHz ) frequency has played an important role in shaping the modern world, but it is not without its limitations. This frequency is at 1575.42 MHz and it is more susceptible to multipath errors, which occurs when the GPS signal gets reflected by the buildings, terrains or any other obstacles before it reaches the receiver. As the GPS system relies on measuring the time taken to receive which is then converted to distance, this reflected signal leads to discrepancies causing error in distance calculation leading to less accurate measurements.
To address all these limitations, the US government initiated a modern GPS program. As a part of this effort, 3 new GPS signals are introduced for civilian purposes. L2 ( 1227.6 MHz ) , L5 ( 1176.45 MHz )and L1C ( 1575 MHz ). Where L1C is still in development and lacks navigation data, L2 and L5 signals have made significant advances in improving the GPS accuracy.
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L1 vs L2 vs L5 GPS Comparison
| GPS Signal | L1 GPS | L2 GPS | L5 GPS |
|---|---|---|---|
| Frequency | 1575.42 MHz | 1227.60 MHz | 1176.45 MHz |
| Modulation | Coherent BPSK | Coherent BPSK | Composite BOC (10,5) |
| Bandwidth | ~2 MHz | ~2 MHz | ~24 MHz |
| Navigation | Navigation Message (50 bps, BPSK) | P Code (10.23 M chips/s, BPSK) | Navigation Message (BPSK) |
| Codes | C/A Code (1.023 M chips/s, BPSK) | L2C Code (1.023 M chips/s, varying modulation) | L5 Signal (10.23 M chips/s, Composite BOC) |
| P Code (10.23 M chips/s, BPSK) | Encrypted M Code | L1C Signal (various waveforms) | |
| Transmit | Transmit Power: Varies | Transmit Power: Varies | Transmit Power: Varies |
| Data Rate | Data Rate: 50 bps | Data Rate: N/A | Data Rate: N/A |
| Chip Rate | Chip Rate: Varies | Chip Rate: Varies | Chip Rate: Varies |
| Channels | Tracking Channels: Multiple | Tracking Channels: Multiple | Tracking Channels: Multiple |
| Antenna | Antenna: Circularly polarized | Antenna: Circularly polarized | Antenna: Circularly polarized |
| Accuracy | Positional Accuracy: ~5 meters (L1 C/A), | Positional Accuracy: ~5 meters (P Code), | Positional Accuracy: ~1 meter (L5) |
| ~0.3 meters (P Code) | ~5 meters (L2C), Encrypted M Code | ||
| Positional Accuracy: ~1 meter (L2P) |
Technical Specification of L1 GPS (Coarse/Acquisition Code)
- Frequency: 1575.42 MHz
- Modulation: Coherent Binary Phase-Shift Keying (BPSK)
- Bandwidth: Approximately 2 MHz
- Signal Structure:
- Navigation Message: 50 bits per second, BPSK modulation
- Coarse Acquisition (C/A) Code:
- Code Rate: 1.023 million chips per second
- Modulation: BPSK
- Code Length: 1023 chips per period
- Precise (P) Code:
- Code Rate: 10.23 million chips per second
- Modulation: BPSK
- Code Length: 10230 chips per period
- Encrypted Military (M) Code:
- Code Rate: 10.23 million chips per second
- Modulation: BPSK
- Code Length: 10230 chips per period
Technical Specification of L2 GPS (Precision Code and P(Y)-code)
- Frequency: 1227.60 MHz
- Modulation: Coherent Binary Phase-Shift Keying (BPSK)
- Bandwidth: Approximately 2 MHz
- Signal Structure:
- Precise (P) Code:
- Code Rate: 10.23 million chips per second
- Modulation: BPSK
- Code Length: 10230 chips per period
- Civilian (L2C) Code:
- Code Rate: 1.023 million chips per second (varies based on the type of modulation used, such as BPSK or QPSK)
- Modulation: Varies (e.g., BPSK, QPSK)
- Code Length: 1023 chips per period
- Encrypted Military (M) Code:
- Code Rate: 10.23 million chips per second
- Modulation: BPSK
- Code Length: 10230 chips per period
- Precise (P) Code:
Technical Specification of L5 GPS
- Frequency: 1176.45 MHz
- Modulation: Composite Binary Offset Carrier (BOC)
- Bandwidth: Approximately 24 MHz
- Signal Structure:
- Navigation Message:
- Modulation: BPSK
- L5 Signal (L5):
- Composite BOC (10,5) modulation
- Code Rate: 10.23 million chips per second
- Code Length: 10230 chips per period
- L1C Signal:
- Compatibility signal for interoperability with other GNSS systems
- Modulation: Various waveforms including BPSK, QPSK, and others
- Navigation Message:
The Power of L5 GPS
Among the new signals that came out, L5 stands out as the beacon of advanced navigation. While both L2 and L5 signals exhibit greater power and bandwidth than the L1, it’s the L5 frequency that is exceptionally good. One of the main features is its resistance to interference and multipath errors. Unlike L2 that enhances the L1 accuracy when used together, L5 can be used independently.
Introduced on supported satellites in 2014, L5 signals has been broadcasted by 17 GPS satellites as of June 2022. For optimal usefulness, a signal broadcasted by less than 18-24 satellites is considered limited availability. This means that there needs to be further more satellites put into orbit, in order to use L5 at its full potential. The current Goal is to launch 24 L5 capable satellites into orbit by 2027.
Why L5 Matters
L5 frequency’s significance lies in its role as the most advanced GPS signal available for civilian use. While this was initially developed for high performance applications such as the aircraft navigation, its usage has been extended to everyday consumer devices. Manufacturers have started including L5 in smartphones, fitness tracker, in car navigation systems and smartwatches to offer higher GPS accuracy.
The True use of the L5 signal lies in its radio frequency. Operating at 1176.45 MHz, L5 occupies a frequency exclusively reserved for aircraft navigation across the globe. The inherent exclusivity of this frequency protects the L5 frequency from other radio wave interferences, such as the TV broadcast, radars and ground based navigation aids. This interference free frequency is important for ensuring accurate and reliable navigation.
The above feature of L5 data makes the devices employ advanced techniques to determine signals with little to no errors which can be used in pinpointing location with more accuracy. This capability of L5 is really useful in areas where the GPS signal received is very compromised.
Furthermore, the increased strength of L5 signals translates to improved coverage in dense urban places. The indoor reception of GPS and the quick location locking made possible only with the help of L5’s lower frequency.
L5’s Influence Beyond GPS
While GPS is used in synonymous with navigation, it is worth acknowledging that GPS is just one of the several Global Satellite Navigation Systems ( GNSS ). L5’s reach extends beyond just the GPS system. Other GNSS systems such as the BeiDou of China, Galileo of Europe and IRNSS of India are transmitting their signals in L5 frequency. Even the GLONASS of Russia is planning to launch satellites with L5 capability by 2025.
Multi-GNSS receivers that has the capability to receive signals from various satellite constellations, can use the L5 frequency for greater location accuracy. These receivers provides improved accuracy by using data from multiple GNSS systems.
