What are the key components of a BTS?

A GSM BTS contains: 1) TRX units (Transceiver): each provides one frequency carrier with 8 TDMA timeslots, supporting up to 7 simultaneous voice calls (1 timeslot for control). A sector typically has 1-4 TRX. 2) Power amplifiers: 20-40W per carrier for macro cells. 3) Duplexer/filters: separate TX and RX paths on the same antenna. 4) Antenna system: typically 3 sectors with 120° separation, each with 2 antennas for RX diversity. 5) Control unit: manages timing, A-bis communication, and OAM. 6) Power supply: -48V DC with battery backup for 4-8 hours.

How has the BTS evolved across generations?

2G BTS: simple radio with BSC controlling all intelligence. 20-40W per carrier, rack-mounted indoor equipment. 3G NodeB: adds CDMA processing, Rake receiver, and inner-loop power control. Still controlled by RNC. 4G eNodeB: incorporates BSC/RNC intelligence (scheduling, handover, RRM), connects directly to core via S1. Supports MIMO and OFDM. 5G gNB: CU/DU/RU split architecture, massive MIMO (64-128 antennas), mmWave capability, 200-400 MHz bandwidth. Power: from 20W (2G) to 200+W per band (5G mMIMO). Form factor: from indoor cabinets (2G) to compact outdoor units (5G).

What is the typical RF power output of a BTS?

RF power varies dramatically by generation and cell type. GSM macro BTS: 20-40W per TRX carrier (13-16 dBW). UMTS NodeB: 20-60W per carrier. LTE eNodeB: 40-80W per antenna port, 160-320W total for 4x4 MIMO. 5G gNB (massive MIMO): 200-400W total for 64T64R at sub-6 GHz. 5G mmWave: 2-8W per panel (high gain compensates). Small cells: 0.25-5W. Femtocells: 10-100 mW. The total EIRP (power × antenna gain) determines coverage range: a 5G mMIMO with 200W and 25 dBi beamforming gain produces 63 dBm EIRP.

Mobile Network Infrastructure

Base Transceiver Station (BTS)

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The radio equipment at a cell site that communicates directly with mobile devices over the air interface. In GSM, the BTS handles physical layer functions: modulation, channel coding, RF transmission/reception, and timing advance. Contains one or more TRX units, each supporting 8 TDMA timeslots. Controlled by the BSC via A-bis interface. Evolved into NodeB (3G), eNodeB (4G), and gNB (5G) with increasing on-site intelligence and MIMO capability.

Generation: 2G GSM origin

Power (GSM): 20–40W per carrier

Power (5G mMIMO): 200–400W total

Understanding the BTS

The BTS is the piece of equipment that makes wireless communication possible. It is the physical interface between the wired network infrastructure and the wireless air interface. Every phone call, text message, or data session begins and ends with an RF exchange between the user's device and the BTS. In GSM terminology, "BTS" specifically refers to the 2G radio equipment, but the term is commonly used informally to mean any cell site radio equipment.

A typical macro BTS serves a coverage area of 1 to 35 km radius depending on frequency, terrain, and deployment type. The BTS antenna system is usually sectorized (3 sectors at 120 degrees each), with each sector containing its own set of transceivers, filters, and power amplifiers. Modern deployments include active antenna systems where the radio and antenna are integrated into a single unit mounted on the tower.

BTS RF Specifications

GSM BTS Capacity:
1 TRX = 1 carrier = 8 timeslots
Usable: 7 voice (1 for BCCH/SDCCH)
3 sectors × 4 TRX each = 84 voice channels

Link Budget (macro):
EIRP = P_TX + G_ant − L_cable
Example: 40W (46 dBm) + 18 dBi − 3 dB = 61 dBm
Path loss at 1.8 GHz, 5 km: ~140 dB
Received: 61 − 140 = −79 dBm (above −104 dBm sensitivity)

5G mMIMO EIRP:
200W + 25 dBi beamforming = 78 dBm

Cell Site Evolution

Generation	Equipment	Power/Band	MIMO	Intelligence
2G	BTS	20-40W	1T2R (diversity)	BSC-controlled
3G	NodeB	20-60W	1T2R	RNC-controlled
4G	eNodeB	40-80W/port	4x4 / 8x8	Self-managed
5G	gNB	200-400W	64T64R	CU/DU split

Common Questions

Frequently Asked Questions

Key BTS components?

TRX units (1 carrier, 8 timeslots each), power amplifiers (20 to 40W), duplexer/filters, 3-sector antenna system with RX diversity, control unit, −48V DC power with battery backup (4 to 8 hours).

How has it evolved?

2G BTS: BSC-controlled radio. 3G NodeB: CDMA processing. 4G eNodeB: self-managed + MIMO. 5G gNB: CU/DU split, 64T64R mMIMO, mmWave. Power: 20W to 400W. Form: indoor cabinets to compact outdoor units.

Typical RF power output?

GSM: 20 to 40W/carrier. UMTS: 20 to 60W. LTE 4x4: 160 to 320W total. 5G mMIMO: 200 to 400W. Small cells: 0.25 to 5W. 5G mmWave: 2 to 8W (high gain compensates). EIRP = power × antenna gain.

Related Terms

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Cell Site Equipment

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