## 2 Private and Community 5G Networks
### Overview of the Liverpool 5G Network  
The infrastructure deployed in the Liverpool 5G project is illustrated in Figure 1. In the first phase of the project (from 2018 to 2020), the network topology consisted of 34 nodes and three gateways (POPs) installed in the Kensington area of the city. Each node in the backhaul mesh was collocated with a Wi-Fi AP to provide WLAN connectivity, with some nodes also supporting ZigBee low-power ad hoc networking. The network was designed in such a way that there was a line of sight link along any of the roads between deployed nodes and the connection was based on a mmWave link (IEEE 802.11 ad). The nodes are Blu-Wireless DN-101 LC stations and are attached to street lights or other street furniture at a consistent elevation. The nodes have 90 degree azimuth coverage, one independent beam and a maximum capacity of 5 Gbps (Mac layer). The POP nodes are connected to the gateway through a fiber link, and backhauling is then handled via a local cloud service provider. Furthermore, due to the widely deployed nodes and the high path and penetration loss at 60 GHz, some links may require relays (multi-hop transmissions) to accomplish backhauling, and nodes are clustered around the nearest POP. In the current version of the network (2020-2022), this deployment has been extended to cover a wider area and provide more ubiquitous coverage. Each node is also collocated with a 5G small cell that will run in the N77 band and standalone mode. As such, any user with a compatible handset should receive connectivity within the Kensington area of Liverpool.  
The aim of this deployment is to support a range of social and healthcare applications for the community, from simple health sensor and monitoring services through to VoIP, full HD or 4 K streaming for remote consultations and (potentially) low latency VR tools. As such, the network must be able to meet a challenging set of requirements. Of course, it is very difficult to guarantee a high rate of transmission (or a small latency) in conjunction with highly reliable packet delivery (small packet error rate), due to the random transmission errors caused by the unpredictable behaviour of this type of wireless channel. Specifically, when the link qualities in the network are poor, packets may be retransmitted several times across hops in order to reach their destination. This could result in aggregation and queueing of packets at the core relay nodes, which translates to unreasonably large average end-to-end delay, as well as a low rate of transmission. However, in order to determine the optimal operating point and achievable Quality of Service offered by the network, it is important to analyse the trade-off between the throughput, latency and reliability (PER and PDF) to improve the overall network performance [10]. Finally, average latency, which is defined as the average time from when the packet transmission starts at the source station to when the packet is correctly received by the destination [11], is a particular issue for applications which have strict real-time requirements such as video conferencing or VoIP calls. The next section takes a more detailed look at the characteristics of communications at 60 Ghz to provide a foundation for our analysis work.