Field Guide · protocol

Also known as: LTE, Long-Term Evolution, 4G LTE, E-UTRA

LTE (Long-Term Evolution) is the 3GPP fourth-generation mobile-broadband standard, built on OFDMA in the downlink and SC-FDMA in the uplink, carrying user data over a grid of resource blocks protected by turbo coding.1 It replaced the circuit-switched core of earlier cellular generations with an all-IP packet architecture, delivering the high-throughput mobile internet that smartphones depend on.

frequency → time (slots / OFDM symbols) → 1 resource block = 12 subcarriers × 1 slot
LTE maps user data onto a time-frequency grid; the smallest schedulable unit is a resource block of 12 subcarriers over one 0.5 ms slot.

Overview

LTE, standardised as E-UTRA (Evolved UMTS Terrestrial Radio Access), was designed for low latency, high peak rates, and flat, IP-based signalling. The radio access network consists of base stations called eNodeBs connected to an Evolved Packet Core (EPC). Unlike the digital land-mobile systems GopherTrunk targets, LTE is a wideband, scheduled, multi-user system: a central scheduler assigns resource blocks to handsets millisecond by millisecond.

Technical characteristics

Property Value
Downlink access OFDMA
Uplink access SC-FDMA (single-carrier FDMA, low PAPR)
Channel bandwidth 1.4, 3, 5, 10, 15, 20 MHz
Subcarrier spacing 15 kHz
Resource block 12 subcarriers × 0.5 ms slot
Modulation QPSK, 16-QAM, 64-QAM (256-QAM in later releases)
Channel coding Turbo code for data; tail-biting convolutional for control
Duplexing FDD and TDD variants
Multi-antenna MIMO up to 4×4 in Release 8

The SC-FDMA uplink is essentially OFDMA with a DFT precoding stage, which lowers the peak-to-average power ratio so handset power amplifiers run more efficiently.

History

3GPP froze LTE in Release 8 (2008), with the first commercial networks launching in 2009–2010.2 Marketed as “4G,” early LTE did not initially meet the ITU IMT-Advanced bar; that gap was closed by LTE-Advanced in Release 10. Successive releases added carrier aggregation, higher-order MIMO, and the machine-type variants that seeded the transition toward 5G NR.

Deployment

LTE became the dominant global mobile-broadband technology of the 2010s and remains widely deployed as the coverage and voice layer beneath 5G. Voice initially fell back to legacy circuit-switched networks until VoLTE carried calls as packets over the LTE bearer itself.

Decoding it with GopherTrunk

GopherTrunk does not decode LTE. LTE is a licensed, scheduled, wideband cellular system whose air interface is out of scope for a land-mobile trunking scanner (P25, DMR, NXDN, TETRA), and its user-plane traffic is encrypted end to end. Recovering LTE requires a 20 MHz-capable front end plus full OFDMA channel estimation, scheduling recovery, and turbo decoding — well beyond GopherTrunk’s narrowband single-carrier decode chain. It is documented here for context on the wider RF landscape a scanner shares the spectrum with.

Sources

  1. LTE (telecommunication) — Wikipedia, for the OFDMA/SC-FDMA air interface, resource-block structure, and all-IP architecture. ↩

  2. LTE — 3GPP, for the Release 8 standardisation timeline and design goals. ↩

See also