What is the GPS L5 Band?

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Mar 20, 2024

The GPS L5 band has a center frequency of 1176.45 MHz and a bandwidth of 12.5 MHz. The broadcast of GPS signals in the L5 band has been reserved specifically for aviation safety services and mission-critical applications. Due to their critical nature, the signals transmitted in this band have relatively higher powers compared to signals in the GPS L1 and L2 bands. The lower frequency range of the L5 GPS band gives signals transmitted at these frequencies better propagation and penetrating properties over those sent in via L1/L2 bands, thereby enhancing the quality of reception.

Before December 2005, the basic GPS capability included the standard positioning service (SPS) on the L1 band and the precise positioning service (PPS) on both L1 and L2. Although these two bands offered good signal reception quality, the US government proposed a modernization plan to further improve the quality of service (QoS), and thus added the L5 band. However, since the GPS L5 signals incorporate advanced GNSS capabilities such as including multiple types of information (timing, synchronization, ranging, etc.), the constellations needed to be upgraded to support the new signal types. Therefore, it is expected that GPS L5 signals will eventually be supported by GPS satellites and receivers as they are continuously improved. Hence, the GPS L5 band will be useful not only for aviation purposes but also for other applications such as surveyors, advanced tracking in defense, and other mission-critical applications.

The GPS L5 signal consists of two different carrier frequencies which are in-phase and Quadrature, and these two signals are out of phase by 90˚. Each of them is modulated using the BPSK modulation scheme by a separate binary sequence. The in-phase signal consists of navigation, ranging, and synchronization data while the Quadrature signal contains only the synchronization data. Furthermore, the two signals use pseudo-random number (PRN) codes so that they are unique to each other and therefore, do not interfere when transmitted and received in the same L5 band. In general, every GPS system includes a PRN generator that generates different codes by selectively delaying one signal with respect to others in the time domain, which results in multiple unique satellite codes. These codes are then allocated to individual mobile users. 

The two carrier frequencies carry data using an in-phase signal and a pilot using Quadrature signal. A pilot signal is a signal that is used to provide reference (for timing synchronization, continuity, etc.) for other signals that are yet to be transmitted for primary communication purposes. Both the carrier signals have a time duration of 1 ms and deliver a chip rate of 10.23 Mbps during communication. 

The table below provides the important parameters used to generate GPS L5 signals in the bands. 

GNSS Technology

GPS

GPS

GPS Signaling Technique

L5 In-Phase

L5 Quadrature

Center Frequency

1176.45 MHz

1176.45 MHz

Channel Access Technique

CDMA

CDMA

Frequency Band

L5

L5

Modulation Scheme

BPSK

BPSK

Types of Signals Used

Data

Pilot

Data Rate

50 bps (bits per second)

-

Received Power (dBm)

-127.9

-127.9

Click here to learn more about all GPS frequency bands.

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