The Enhanced Position Location Reporting System (EPLRS) is a secure, jam resistant, computer controlled communications network that distributes near real-time tactical information, generally integrated into radio sets, and coordinated by a Network Control Station. It is primarily used for data distribution, and position location and reporting. It enhances command and control of tactical units by providing commanders with the location of friendly units. It was first fielded by the US Army in 1987..

Basically the term "position location" is a tautology or a pleonasm, using two terms for one entity.

EPLRS is a Time Division Multiple Access

Time division multiple access

Time division multiple access is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This...

 System that uses a frequency hopping, spread spectrum waveform

Waveform

Waveform means the shape and form of a signal such as a wave moving in a physical medium or an abstract representation.In many cases the medium in which the wave is being propagated does not permit a direct visual image of the form. In these cases, the term 'waveform' refers to the shape of a graph...

 in the UHF band. It incorporates the Thornton family of COMSEC devices, and has the capability for Over the Air Rekeying (OTAR). EPLRS uses the Army Data Distribution System version of the X.25

X.25

X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...

 CCITT and MIL-STD-1553B protocols to interface with Army Tactical Command and Control System (ATCCS).

Situation Awareness Data Link (SADL), installed on USAF F-16 and A-10 fighters, coordinates with EPLRS for ground support missions.

Network Control Station

Each network is controlled by a Network Control Station (NCS), AN/TSQ-158. These have gone through several iterations.

Third Gen

Downsized version to fit in HMMWV, first fielded in 1991. Dimensions: 8.5'x7'x6', 4000lbs

• 1 AN/UYK-44
  AN/UYK-44
  The AN/UYK-44 is the standard 16-bit computer of the U.S. Navy used in surface ship, submarine, and ground C4I platforms....
  
  (V) Enhanced Processor (EP) computer

Fourth Gen

The AN/TSQ-158(V)4 is produced by Raytheon

Raytheon

Raytheon Company is a major American defense contractor and industrial corporation with core manufacturing concentrations in weapons and military and commercial electronics. It was previously involved in corporate and special-mission aircraft until early 2007...

. Housed in a HMMWV replacing the AN/UYK-44 computer with a toughbook laptop computer. Data is displayed through the FBCB2

FBCB2

Force XXI Battle Command Brigade and Below is a Linux based communication platform designed for commanders to track friendly and hostile forces on the battlefield. It increases a vehicle commander's situational awareness of the battlefield by gathering information near real-time based on vehicle...

platform.