Case study: US digital village
The extended range opens up new opportunities to use mmWave spectrum in sparser suburbs and semi-rural areas, which then makes it possible to offload lower frequencies. In such areas, there could be several hundreds of homes per sector. With increasing consumption on both MBB and FWA, the additional capacity that mmWave brings makes such a scenario a sweet spot for combining mmWave and TDD mid band, thereby providing FWA subscribers with high service levels.
In the following simulated scenario, which models the performance achieved in field trials, we illustrate how mmWave extended range can be used to increase capacity and boost user experience. The case is a version of the digital village case study in the Fixed Wireless Access Handbook  that has been adapted to US data consumption patterns.
The original case study includes a stepwise solution and business case analysis showing a return on investment of 22 months. Here, we focus on a comparison of the achievable network capacity, with and without deploying mmWave. The targeted case is a village together with surrounding, more sparsely populated areas where the overall home density is around 150 homes per square kilometer. Current broadband offerings are mainly provided by xDSL or best-effort MBB, but there is no fiber-to-the-home, which makes the area an attractive candidate for FWA.
The existing MBB deployment has as a macro inter-site distance of 3km, and lower FDD bands are used to serve current traffic. Over time, as the MBB traffic grows, it will utilize part of the acquired mid-band spectrum. The excess spectrum can be used for FWA: 100MHz TDD at 3.5GHz and 400MHz in the 28GHz band.
The service targeted by the CSP is FWA with a “fiber-like” experience. This means sold DL data rates of 100-1,000+Mbps without a data cap and with typical DL rates of at least 100Mbps. Combining available spectrum, including lower FDD bands, and mid bands and 28GHz using TDD, the CSP can obtain a combined network deployment catering for both MBB and FWA.
In this analysis, we focus on the mid band and on 28GHz, and we leave out the details on lower bands as well as the performance for the MBB users. However, the suggested approach includes a joint solution for FWA and MBB that also handles the anticipated growth of MBB traffic. Furthermore, as the case is limited by the DL capacity, we leave out the analysis of the UL. To maximize link performance, the case is based on the use of rooftop-placed, high-power CPE that supports mmWave as well as lower bands.
The system is dimensioned to target a minimum DL data rate of 30Mbps for the 5 percent worst located homes, at peak traffic hours, to sustain a fiber-like experience, including multiple HDTV streams per home, also in those worst cases. Regarding data usage, we define a baseline scenario, based on observed current US fixed broadband levels, where the average data consumption per home is expected to be 670GB per month, out of which 90 percent (600GB) is DL traffic [10, 11].
Assuming that 10 percent of the daily traffic occurs during the busiest hour, this corresponds to an average consumption of 2GB per hour at busy hour. We assume an annual growth of 28 percent, partly driven by many homes transitioning from consuming linear TV over satellite or terrestrial broadcast, to using broadband for all media consumption including linear TV and streamed services.
In addition, for comparison we have also defined an all-broadband-media scenario that assumes that all homes have already made this transition. For this case, we assume a consumption rate of 1TB per month per home (900GB per month in the DL) but expect lower annual growth of 10 percent, as the shift to all media consumption over broadband is already completed.
As the capacity needs to grow with an increasing number of customers, as well as with higher average data consumption and speed requirements, it makes sense to gradually increase the capabilities of the network on a needs basis. This means that costs for increased capacity can be taken as late as possible, as opposed to fiber, where a major part of the cost is taken upfront when deploying fiber trunks passing all homes. Furthermore, decisions about capacity enhancements can be made selectively on a sector by sector basis as the numbers of subscribers – and the revenues – increase.
Experienced user data rate
Figure 3 shows the experienced DL user data rate as a function of varying system load for the worst, median and best located homes respectively. The blue curves represent a mid-band-only deployment, while the red ones represent the combined mid-band and mmWave case.