What is the GPS L2 Band?

The GPS L2 band has a center frequency of 1227.60 MHz and a bandwidth of 11 MHz. The frequency range of the GPS L2 Band is 1221.1 to 1233.1 MHz. The GPS L2 band has a lower operating frequency than the GPS L1 band (which has a center frequency of 1575.42 MHz) and thus travels better though obstacles like clouds, trees and buildings.

The GPS L2 band was originally developed for military use. However, over time, it started to be used for civilian applications as well. An updated L2 signal, called the L2C signal, was developed specifically for civilian applications. This then enabled the development of dual-frequency GNSS receivers that used both L1 and L2 signals to provide better accuracy.

Scientifically, L2 aids in ionospheric monitoring, space weather studies, and time transfer applications, ensuring accurate synchronization for network time protocols and diverse scientific research. Additionally, it plays a role in enhancing location services for search and rescue operations.

GPS L2 Band Signals

The GPS L2 Band uses four different types of signals for navigation and ranging: L2 civil moderate (L2 CM) code, the L2 civil long (L2 CL) code, P (Y) code, and the M-code.

L2 CM Code: The L2 CM code is transmitted by the GPS Block IIR-M, IIF, III, and other subsequent block satellites. It is used as a ranging signal to communicate satellite-to-user distance information to the GPS satellites. The L2 CM code is time-multiplexed i.e. it is transmitted over a unique time slot to avoid interference and signal strength degradation. The use of time multiplexing enables this signal to transmit a relatively large amount of information as it utilizes the full bandwidth at any given time. It uses a sequence, a linear pattern of random binary numbers generated after every fixed time period.

L2 CL Code: The L2 CL signal is also time-multiplexed. It is generated by the GPS Block IIR-M, II-F, III, and other block satellites. Similar to the L2 CM code, L2 CL is also used as a ranging code, but with a different code length (relatively longer than the L2 CM code). It also uses a random binary number sequence for coding the original data, like the L2 CM code. Furthermore, it is possible to include any additional navigation-related data to be conveyed to the satellite along with both L2 CL and L2 CM codes, which the ground station determines.

P (Y) Code: The P code is a precision signal and is reserved specifically for security and mission-critical applications such as military and defense. The term “Y” is a special code that may also be used when anti-spoofing capabilities are required to further enhance the degree of security.

M-Code: M-code is a signal that is used in the L1 band to improve security and anti-jamming capabilities of military navigation using GPS. M-code signals can be delivered to specific areas from GPS Block III satellite systems. It uses special modulation techniques to ensure selective jamming of the commercial C/A (coarse/acquisition) code (a different type of code transmitted in the GPS L1 band) and continues receiving the desired M-code signals from the military receivers. In general, the M-code signal offers relatively better performance and flexibility compared to the P (Y) code. The table given below details the properties and parameters of the above codes for the L2 band.

Click here to read about all GPS frequency bands.