# Millimetre-Wave Backhaul for 5G Networks: Challenges and Solutions
## 6 Case Study and Performance Evaluation  
We evaluate the performance of a simulated 60-GHz mm-wave backhaul network using the proposed framework, with the same network distribution as given in Section 3, _i.e._, five SBSs are uniformly distributed in a 100 m \(\times\) 100 m area. Fibre links, mm-wave links and two blockages are all considered to approach a realistic scenario. Two available RF chains are assumed at each SBS. Besides free space channel attenuation, other loss caused by rain attenuation, oxygen absorption and RF components in the mm-wave system is also considered in our simulation. We choose the capacity optimization to work out a routing scheme and then perform the STDMA scheduling using the heuristic method. We assume that the data demands arrive in units of packets based on the Poisson model [25] and is possible to be generated between any two SBSs. The total simulation time is 10\({}^{6}\) time slots, each of which lasts 10 us, and there are a small amount of required data initially. The MAC control overhead is assumed as two time slots in each frame. When a required datum has not been scheduled within 5000 time slots, it is discarded automatically. Detailed channel settings are listed in Figure 5a. Figure 5b-d illustrate the performance of the throughput, delay and packet loss rate, respectively, achieved by the five schemes, where HBF, BF, HDP and FDP refer to hybrid beamforming, analogue  
Figure 5: (**a**) Channel parameter settings and (**b–d**) the performance of the throughput, delay and packet loss rate of five schemes, respectively (HBF, BF, HDP and FDP refer to hybrid beamforming, analogue beamforming, half-duplex and full-duplex, respectively, while non-STDMA is the scheme that does not adopt spatial reuse at all). beamforming, half-duplex and full-duplex, respectively, while non-STDMA is the scheme that does not adopt spatial reuse at all. The \(x\)-axis is the normalized traffic load. For example, a traffic load of two represents that the coming traffic requires a sum rate at every SBS in the backhaul system to be twice as the average capacity of a single link. From Figure 5, we can observe that the performance of five schemes falls into three categories: (I) the proposed STDMA scheme supporting both new physical layer techniques (HBF and FDP); (II) two STDMA schemes adopting one new physical layer technique (HBF and HDP and BF and FDP); (III) two conventional schemes without new physical layer techniques or even without spatial reuse (BF and HDP and non-STDMA). As shown in Figure 5b, the throughput of the proposed scheme grows rapidly with the increase of traffic load and keeps the highest among all schemes, which is more than twice that achieved by all other schemes at a heavy traffic load of four. The throughput of the schemes in Category II starts dropping at a traffic load of three, and the improvement brought by full duplex is slightly more obvious than that brought by hybrid beamforming, which supports two RF chains at each SBS. Undoubtedly, without the supports of new physical layer techniques or even without spatial reuse, the schemes in Category III achieve the least backhaul network throughput gain. In Figure 5c, the growing speeds of the average delay of schemes in Category II and Category III slow down at traffic loads of 2.5 and 1.5, respectively. We conduct further explorations of the delay performance at higher traffic loads and find that the delay of the proposed scheme increases slowly when the traffic load is five. The convergence point of each scheme shows that when the traffic load exceeds a certain level, the spatial reuse capability of the scheme could hardly handle the quickly emerging large amount of required flows, and the network simply discards more packets without adding much delay. Since the upper bound of delay is 50 ms, the schemes in Category III already approach the upper bound at light traffic loads, while the other three schemes converge to a delay, which is only half of the upper bound.