4G

CPRI and eCPRI Interfaces for 4G

What Are CPRI and eCPRI?

CPRI, or Common Public Radio Interface, defines key interface specification between REC (Radio Equipment Control) and RE (Radio Equipment) of radio base stations used for cellular wireless networks. It is a protocol of choice for fronthaul communications between towers and base stations (BSs) through several generations of wireless networks. CPRI has efficient and flexible I/Q data interfaces for various standards, such as GSM, WCDMA, LTE, etc.

CPRI: Common Public Radio Interface

CPRI defines key interface specification between REC (Radio Equipment Control) and RE (Radio Equipment) of radio base stations used for cellular wireless networks. CPRI is the short form of Common Public Radio Interface. CPRI is popular standard for transporting baseband I/Q signals to the radio unit in traditional BS (Base Station). CPRI allows efficient and flexible I/Q data interface for various standards e.g. GSM, WCDMA, LTE etc. 

eCPRI: Enhanced Common Public Radio Interface

eCPRI was created and published after CPRI. The eCPRI standard defines specification which connects eREC and eRE via fronthaul transport network. It is used for 5G systems, LTE-Advanced and LTE-Advanced Pro. 

The Purpose of development of CPRI and eCPRI is as follows. 
Radio BSs should offer flexibility during deployment to MNOs( mobile network operators). This is achieved by simplifying BS architecture by dividing radio BS functionality into two modules viz. eREC and eRE. Both parts may be physically separated where in eRE is kept close to RF antenna where as eREC kept at a distant end. Both are connected via a transport network. The eREC contains part of PHY layer functions and upper layer functions of the air interface whereas eRE contains the other part of the PHY layer functions and the analog radio frequency (ARF) functions. The different functions can be located either in the eREC or in the eRE.

CPRI and eCPRI interfaces used for Fronthaul in 4G and 5G Wireless Networks
Interfaces used for Fronthaul in 4G and 5G Wireless Networks

Both CPRI and eCPRI can be used in 5G fronthaul. While, eCPRI is more suitable in 5G fronthaul. Here are the network line rates:

CPRI Line RateLine Bit Rate (Gbps)Line CodingBits/WordTransport Capacity (#WCDMA AxC)Transport Capacity (#20 MHz LTE AxC)
Rate-10.6148B/10B84
Rate-21.22888B/10B1681
Rate-32.45768B/10B32162
Rate-43.07208B/10B40202
Rate-54.91528B/10B64324
Rate-66.14408B/10B80405
Rate-7A8.110064B/66B128648
Rate-79.83048B/10B128648
Rate-810.137664B/66B1608010
Rate-912.165164B/66B1929612
Rate-1024.330264B/66B38419224

This table shows the different transport capacity at different line rates. Since 5G requires tremendous bandwidth expansion, line rate option 10, the newest standard, can meet latest 5G requirements. However, this processing capacity has reached the upper limit of the standard, causing doubt about whether 5G can be used with CPRI for future expansion. .

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