What is the difference between ODU and RRU?

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What is the difference between ODU and RRU?

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The ODU - OutDoor Unit (or RAU - Radio Access Unit) is present in the Microwave system while the RRU is present in the Radio System.

ODU is connected to the satellite dish antenna while RRU - Radio Remote Unit access the antenna of the sector.

ODU is responsible for amplifying power and raising and lowering frequency. And it works at high frequencies, from 6 GHz to 86 GHz.

RRU works on 2G, 3G, 4G, 5G technology, and is responsible for power amplification and modulation, demodulation. It operates on frequencies like 800, 900, 1800, 1900, 2100, 2600 MHz.

Every microwave link is a point-to-point link, and each side of the link has an IDU (In Door Unit) and ODU (Out Door Unit).

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A remote radio head (RRH), also called a remote radio unit (RRU) in wireless networks, is a remote radio transceiver that connects to an operator radio control panel via electrical or wireless interface . When used to describe aircraft radio cockpit radio systems, the control panel is often called the radio head.

Source: Remote radio head - Wikipedia


Microwave ODU ( Outdoor Unit )

The term ODU is used in Split-Mount Microwave systems where an Indoor Unit (IDU) is typically mounted in an indoor location (or weatherproof shelter) connected via a coaxial cable to the ODU which is mounted on a rooftop or tower top location.

Source: https://www.microwave-link.com/microwave/microwave-odu/


The ODU is contains the actual modem that modulates the E1, E3 or STM-1 link onto the IF (Intermediate Frequency)
which is put on the coaxial link towards the ODU.

Conversely, on a different IF, there is the down-link from the ODU towards the demodulator/decoder in the IDU.

In the Mini-Link system, the ODU is commonly called RAU (Radio Access Unit).

ODU for Transport (Microwave) and RRU for Radio (BTS) 2G3G4G or 5G.

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RU: the radio unit

  • handles the digital front end (DFE) and the parts of the PHY layer, as well as the digital beamforming functionality.
  • the key considerations of RU design are size, weight, and power consumption.
  • The purpose of the RU is to convert radio signals sent to and from the antenna to a digital signal that can be transmitted over packet networks.
  • Fronthaul: Connectivity between the RU and DU

In a 5G RAN architecture, the BBU functionality is split into two functional units:

  • a Distributed Unit (DU), responsible for real time L1 and L2 scheduling functions,
  • a Centralized Unit (CU) responsible for non-real time, higher L2 and L3.
  • They are deployed as CNFs on any COTS server.

DU: this is the distributed unit, a logical function (software)

  • that is deployed on a COTS server close to the RU
  • runs the RLC, MAC, and parts of the PHY layer.
  • This logical node includes a subset of the eNB/gNB functions, depending on the functional split option, and its operation is controlled by the CU.
  • Midhaul: Connectivity between the DU and CU

CU: this is the centralized unit (software)

  • runs the RRC and PDCP layers.
  • It is a logical node that includes the gNB functions like transfer of user data, mobility control, RAN sharing (MORAN), positioning, session management etc., with the exception of functions that are allocated exclusively to the DU.
  • The CU controls the operation of several DUs over the midhaul interface
  • The CU’s server and relevant software can be co-located with the DU or hosted in a regional cloud data center.
  • The actual split between DU and RU may be different depending on the specific use-case and implementation ( the O-RAN Alliance definition is Option-7.2 and Small Cell Forum is Option-6)