Te Awa valley community network
Te Awa is a valley community of 14 households spread over 4.2 km, with no fibre except at the school at the eastern end. The community has NZ$18,000. A 2.4 GHz directional link is cheap and reaches 4 km at about 3 Mbps, but rain fade is common and the valley has two ridges. A 5 GHz link gives about 8 Mbps but needs line of sight and fails through the ridges. A fibre extension quote is NZ$60,000. Four households have remote workers who need 2 Mbps up and down for video calls; the marae needs reliable upload for live-streamed tangi; a farm needs a low-bandwidth sensor link. Relay points would be solar-powered, and winter generation is about 40% of summer. The school is willing to host the backhaul and act as a hub.
1. Recommend a network topology and radio choice. Explain how the ridges, rain fade, and the 2 Mbps video requirement shape your answer.
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The 5 GHz option's 8 Mbps headline rate is misleading in this terrain. At 4.2 km with two ridges, line of sight is not achievable from a single link, so 5 GHz would require at least one relay on a ridge. Each relay adds cost, power demand, and a failure point. The 2.4 GHz link has lower throughput but better diffraction around obstacles and longer reach, which matters more here than peak rate.
A sensible topology is a hub-and-relay tree rooted at the school. The school hosts the fibre backhaul and a 2.4 GHz sector or point-to-point link to a solar relay on the first ridge. That relay serves households on the near side and links to a second relay or directly to the far cluster. The farm's sensor link can use a low-power LPWAN or a cheap 2.4 GHz link at low duty cycle; it should not consume a video-grade share.
The 2 Mbps video requirement is per household, and four remote workers may overlap. If all four stream at once, the access network needs about 8 Mbps aggregate plus overhead. A single 3 Mbps 2.4 GHz link cannot carry that. The design should therefore either schedule video calls (the community can agree on time windows), use two radios on different channels to increase aggregate capacity, or place the video users closest to the relays where modulation is higher. Traffic shaping should prioritise video and marae uploads over bulk downloads.
Rain fade means the design should not run links at their maximum modulation. A 3 Mbps link operated at 1.5–2 Mbps has margin; an 8 Mbps link operated at 8 Mbps will drop in rain. The recommendation is 2.4 GHz for reach and resilience, a relay tree, and capacity management rather than a single high-rate link.
2. The relays are solar-powered with winter generation at 40% of summer. Explain how you would design for power resilience and what failure modes remain.
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Winter generation at 40% means the solar budget must be sized for the worst month, not the annual average. The first step is an energy budget per relay: radio transmit power, router/switch, and any heater or battery management. A relay that draws 6 W continuously needs 144 Wh per day. At 40% winter yield, the panel must produce that in the shortest useful winter day, with derating for cloud, panel angle, and dirt. Battery capacity should cover at least three to five days of autonomy, because a multi-day storm is the realistic failure, not a single cloudy afternoon.
The design should also reduce demand. Radios can run at lower transmit power if relay spacing is shorter; that may mean more relays but lower energy per site. Polling intervals for the farm sensor can be long. Video traffic can be shaped so the network does not carry unnecessary load. A low-power wake-on-demand mode for the relay's second radio can save energy outside peak hours.
Remaining failure modes: a multi-day winter storm exhausting the battery; a relay losing line of sight after vegetation growth; a single relay failure partitioning the far cluster; and the school hub losing fibre or power. Mitigations include a bypass path or a second relay on a different ridge, a documented manual fallback (e.g. a 4G modem at the marae), and monitoring that reports battery voltage and link quality before failure. The community should also define a priority order for load shedding: marae upload and voice first, video second, bulk updates last. Resilience here is as much governance as hardware.
3. Evaluate the equity implications of the NZ$18,000 budget and recommend how the community should decide who gets connected first.
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The budget forces a phased build, and any phasing creates winners and losers. The households furthest from the school are likely to cost the most per connection because they need more relays. A purely cost-per-household rule would connect the near cluster first and leave the remote households, possibly including the marae or the farm, until later. That is efficient but may entrench the disadvantage the project is meant to address.
The community should make the criteria explicit before choosing a build order. Relevant criteria include: essential service (the marae's live-streamed tangi and the farm's sensor link are not just entertainment), existing disadvantage (households with no mobile coverage or with students learning from home), willingness to host a relay or contribute labour, and technical feasibility. A weighted scoring approach, agreed at a community meeting, is more defensible than an ad hoc decision by the project lead.
The farm's low-bandwidth sensor link is cheap and can be connected early even if its video capability waits. The marae should probably be in the first phase because its upload need is culturally significant and it can act as a community access point. The four remote workers have an economic case, but they also have alternatives such as travelling to the school or using mobile data; that should be weighed, not assumed.
The community should also plan for the second phase explicitly, with a date and a funding route, so that “not yet” does not become “never”. Transparency about cost per household and the reasons for the order will matter as much as the technology. Equity is not treating everyone identically; it is justifying differential treatment with stated criteria.