Base Station Analysis: From Macro Base Stations to SDR Base Stations
A base station, a critical component of public mobile communication networks, is a type of radio station. It operates within a specific radio coverage area and facilitates information transmission between mobile phone terminals and the mobile switching center. In simple terms, a base station is a transceiver station for wireless signals.
(1) Macro Base Stations
First, let’s examine macro base stations. These are the primary wireless signal transmission stations used by communication operators. They offer extensive coverage, typically up to 35 kilometers, making them particularly suitable for suburban areas with dispersed communication traffic. Macro base stations operate at higher power levels and provide omnidirectional coverage to ensure stable signals.
Additionally, there are micro base stations and pico base stations. Micro base stations are mainly deployed in urban areas, offering shorter coverage distances of about 1 - 2 kilometers and employing directional coverage technology. Pico base stations, on the other hand, are used for filling coverage gaps in urban hotspots, with very low transmission power and a coverage range of 500 meters or less.
Next, let’s discuss another type of base station - the distributed base station. This design separates the signal transmission and reception functions into multiple independent devices distributed across a certain area, collectively forming a complete base station system. This architecture offers greater flexibility and scalability, allowing better adaptation to diverse regional and scenario-specific requirements. Moreover, by decentralizing signal processing and transmission, distributed base stations reduce the power requirements of individual devices, further minimizing electromagnetic radiation impacts.
As a modern solution for network coverage, distributed base stations separate the radio frequency (RF) unit from the traditional macro base station’s baseband unit (BBU), connecting them via fiber optics. In this setup, the BBU is co-located with the core network and wireless control equipment in a central equipment room, while the remote radio unit (RRU) is deployed at planned sites and connected to the BBU through fiber optics. This approach not only reduces construction and maintenance costs but also significantly improves the efficiency of network deployment.
(2) SDR Base Stations and Repeaters
Software-Defined Radio (SDR) is an innovative wireless communication technology that can also be considered a unique design methodology or philosophy. It transcends the limitations of traditional dedicated hardware by defining wireless communication protocols through software. Currently, SDR hardware platforms primarily adopt one of three architectures: SDR based on General-Purpose Processors (GPP), non-GPP structures using Field-Programmable Gate Arrays (FPGA), or hybrid SDR architectures combining GPP with FPGA/SDP. Among these, GPP-based SDR architectures are particularly notable for their efficiency and flexibility.
SDR base stations, designed and developed based on the SDR concept, stand out for their programmable and redefinable RF units. This capability enables intelligent spectrum allocation and support for multiple network modes, allowing a single device to accommodate various network technologies. For example, the same equipment can simultaneously support both GSM and LTE networks.
Repeaters: These are wireless signal relay products whose core components include antennas, RF duplexers, low-noise amplifiers, mixers, electrically adjustable attenuators, filters, and power amplifiers, forming uplink and downlink amplification chains. Their working principle involves capturing the downlink signal from a base station via the donor antenna, amplifying it with a low-noise amplifier while suppressing noise to improve the signal-to-noise ratio. The signal is then down-converted to an intermediate frequency, filtered, power-amplified, and finally transmitted to mobile stations via the retransmission antenna. Similarly, the repeater receives uplink signals from mobile stations, processes them in the reverse direction, and enables two-way communication between the base station and mobile devices. Key performance indicators for repeaters include intelligence level (e.g., remote monitoring capability), low IP3 value (mandated to be below -36 dBm by radio committees), low noise figure, overall stability, and quality technical support.
Repeaters (RP repeaters) are not only devices that connect network lines but are also commonly used for bidirectional forwarding of physical signals between two network nodes. As the simplest type of networking device, repeaters operate at the physical layer, relaying, replicating, adjusting, and amplifying signals to effectively extend network reach. To address signal attenuation during transmission, repeaters play a vital role by connecting physical lines and amplifying weakened signals to ensure data integrity.
Furthermore, repeaters are widely used in wireless communications, such as mobile signal repeaters and amplifiers. These devices capture base station signals in the downlink, amplify and filter them, and then retransmit the signals to the coverage area. In the uplink, they receive and process signals from mobile devices and transmit them to the corresponding base station. Repeaters offer an effective solution for extending network coverage without increasing the number of base stations, thanks to their low cost, simple structure, and ease of installation.
(3) Fiber Optic Repeaters: These devices convert received signals into optical signals for transmission via fiber optics, then reconvert the optical signals back into electrical signals for retransmission.
(4) Frequency-Shift Repeaters: This type of repeater upconverts the received signal frequency to a microwave signal for transmission. After transmission, it downconverts the signal back to its original frequency, amplifies it, and retransmits it.
(5) Indoor Repeaters: These are simple devices designed differently from outdoor repeaters. The structure of mobile communication repeaters varies depending on their specific type.
