5G Transport: The Impact of Millimeter Wave and Sub-6 Radios

Part two in a blog series about how Fujitsu is bringing the 5G vision to life

As communications service providers (CSPs) prepare to deploy 5G, a number of factors will need to be considered as they plan their radio access network (RAN) architecture. An important aspect of this planning is an understanding of the 5G radio interface (NR) specifications and spectrum options.

Both millimeter wave (mmWave) and sub-6 GHz radio architectures have a fronthaul, midhaul and backhaul in terms of transport. However, the differences in the coverage aspects of these two radio types will define the network topology.

The high frequencies of mmWave radios result in reduced coverage of a given area, requiring a more dense deployment outside of traditional cell towers. The mmWave radios will be deployed in a small cell type of configuration, since a large number are required to cover a given area.  In urban areas, the dense deployment of mmWave radios will most likely be on street lamps, and the side or top of buildings. Sub-6 radios, however, enable coverage configurations similar to 4G LTE radios. Therefore, Sub-6 radio topology could be similar to a C-RAN LTE fronthaul, in which dark fiber is used where available, and some form of multiplexing such as WDM or packet multiplexing is used where fiber is lacking.

Initially, the mmWave radios will be best-suited for high throughput applications such as fixed wireless access (FWA), while sub-6 radios will be best used for mobility.  In the long term, both radio types will be used for both use cases.

Since sub-6 radio coverage dynamics are similar to LTE, many CSPs will consider deploying sub-6 much like 4G LTE in a C-RAN to realize DU pooling efficiencies and offer higher performance using cell site aggregation.

Alternatives to a centralized pool of DUs, whether mmWave or Sub-6 radio, is an integrated DU and RU which eliminates the fronthaul transport and discrete fiber connections between the two.  This alternative expedites service delivery while reducing capital and operational expense, but also eliminates pooling and cell site aggregation capabilities.  Cell sites with integrated DUs will have midhaul, or what the IEEE refers to as fronthaul-II, in this section of the RAN transport.

Based on the various deployment options for mmWave and Sub-6 radios, either WDM based transport or a newer packet based transport using Time Sensitive Ethernet (TSN) will be used to pass 5G eCPRI/xRAN channels, as well as legacy 4G CPRI channels, from the cell site to a central aggregation point when an abundance of dedicated dark fiber is not available.

This blog is the second in a series about our vision for 5G transport. See part one here.

About Joe Mocerino

As Principal Solutions Architect, Joe engages wireless and wireline operators and partners in the mobile xHaul ecosystem. His mobile transport expertise includes fronthaul, backhaul, CPRI, TSN, packet, OTN, and SONET technologies. Joe has designed, developed, and deployed wireless and wireline transport solutions that maximize capacity and coverage for high-value automated operation. A fan of music and fitness, Joe enjoys playing guitar in his home recording studio and cycling.