21581 - SCTE Broadband August2022 COMPLETE v1

63 Vol. 44 No. 3 - September 2022 Issue The specific timing limits for each network will depend on the network architecture and the type of applications being supported. Massive MIMO Multiple input multiple output (MIMO) technology can be used to increase the capacity of a radio head and the reliability of the wireless transmission. The most common technique used is spacial diversity which allows radio waves to be transmitted along multiple paths to multiple antennas, increasing the probability that if one path fails the other paths can provide sufficient signal to maintain the connection, hence increasing the reliability. In 4G, two transmit and two receive (2x2) and four transmit and four receive (4x4) configurations are the most prevalent. To increase capacity MIMO’s ability to use spatial multiplexing to transmit different information on these multiple paths, on the same frequency, without interference can be used. In 5G massive MIMO (mMIMO), antenna array sizes in excess of 64x64 are being implemented. 5G RU’s supporting mMIMO have integrated antenna arrays due to the cabling and connector issues that would otherwise arise connecting a separate antenna, and due to the signal losses that would be encountered at FR2 frequencies. This eliminates the co-ax cable used in smaller MIMO configurations. The use of mMIMO also facilities the use of beamforming technology which allows the RU to focus the RF energy of a subset of the MIMO array towards a specific UE. 5G network architecture The architecture of a 5G cell site depends on the architectural split chosen by the mobile network operator (MNO). The 3GPP and eCPRI standards provide multiple options, or splits, of functionality based on the building blocks shown in figure 10. The various functions can then be performed by the CU, DU or RU, depending on the option chosen. Some examples of the most common splits are shown below. technical Figure 9: Beamforming Figure 10: 3GPP and eCPRI functional splits mapped onto CU/DU/RU