21581 - SCTE Broadband August2022 COMPLETE v1

61 Vol. 44 No. 3 - September 2022 Issue technical Comparison of 4G and 5G cell sites 4G cell sites 4G remote radio heads (RRHs) are typically mounted at the top of cell towers or on building rooftops. The ability to cover a large geographic area using radio frequencies in the sub-3GHz spectrum was ideal for these installations. A single sector would consist of an RRH connected through a small form- factor pluggable (SFP) device to a single CPRI link using an optical cable between the RRH and another SFP in the BBU. A short, co-axial jumper cable connects the RF output ports on the RRH to the antenna. A single cell site might cover a range of about 10km. The split of theRRHandBBU functions allowed high loss coaxial cable running up the towers to be eliminated, reducing amplifier power requirements, which in turn led to smaller HVAC and back-up power requirements. However, the lack of contiguous spectrum around 4G frequency bands limits the amount of bandwidth that can be offered to the end user. 5G cell sites In 5G two frequency ranges are offered, FR1 (450-7125MHz) and FR2 (24250-52600MHz). The FR1 frequencies offer channel bandwidths of up to 100MHz depending on the operator’s spectrum holding while FR2 frequencies—referred to as millimetre wave (mmWave)—are in a less crowded area of the frequency spectrum and allow channel bandwidths of up to 400MHz. The higher the channel bandwidth, the greater the potential throughput of the cell. However, the higher the frequency the shorter the distance the RF signal will travel. So 5G cells using mmWave will see a densification in the number of cell sites required to cover the same geographic area. This densification is also required to support the higher capacity for the number of connected devices offered by 5G. RUs using mmWave are typically mounted on street lamps, utility poles or the sides of buildings. This is due to the relatively short distances that mmWave can support. A single site might cover a range of only a few hundred feet. In many 5G RU’s the antenna will be integrated into the RU (see figure 7). This is due to massive MIMO and the mmWave frequencies that form part of 5G. Timing and synchronisation The network densification in 5G and the positioning of 5G small cells in urban areas also creates new challenges in network timing and synchronisation. LTE Advanced and 5G already place more stringent timing demands on the fronthaul network for technologies such as co-ordinated multipoint (CoMP), emergency location services (e.g., E911) and the use of time division duplexing (TDD) in RF transmission and reception. Figure 6: Typical 4G RRH Figure 7: Typical 5G RU