4. Alternative Telecommunication Technologies
4.7 Configurations of Alternative Telecommunication Technologies in
4.7.1 Introduction
A technical investigation was undertaken to investigate and devise possible practical and implementable designs for wide-area telecommunication solutions for the areas in and surrounding the existing and planned locations of telescopes. The detailed report is included in Appendix 4.
The investigation involved:
■ detailed geographical mapping of locations (and occupancy) of farms;
■ cataloguing existing services (before and after application of regulations) and the basic RFI footprints of these services;
■ investigation of technology options (backhaul, links, etc.), specifications and potential for RFI impact through in-situ measurements;
■ understanding the planned fibre optic network of SARAO to establish the potential for shared resources and infrastructure;
■ identification of geographical sites and positions for localised telecommunications provisioning through in-situ observations, and determining suitable hardware;
■ investigation of the choice of suitable frequencies for different areas; and
■ a final analysis of possible RFI impact of the technology system solution proposed.
Given the user requirements as laid on in Section 4.4, the following overarching requirements guided the investigation:
1. Convenient and affordable data access at the places of residence and immediate surrounds, for farm owners and workers.
2. Mobile phone coverage wherever possible.
3. Personal wide-area voice communications for emergency and safety.
The area of consideration is approximately bordered by Fraserburg, Carnarvon, Williston, Brandvlei, Vanwyksvlei and some distance up to Kenhardt further north (Figure 4).
4.7.2 Findings
The proposed technology solutions may essentially be separated into two categories:
1. Data and packet-based voice communications 2. Safety and emergency (mobile) communications
Figure 4: Approximate geographical area of the 2-D investigation into a wide-area telecommunication solution.
1. Data and voice communications
Data: It is unlikely that a single technology-based network will meet the requirements.
Therefore, a network containing a mix of technologies will need to be considered. A network facilitating ease of access and affordable data connection, over the largest possible area, is a priority. A solution enabling seamless connectivity for data packet-based transmission systems
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such as Whatsapp, Skype and Zoom), as well as to and from the outside PSTN and mobile networks, is ideal. Unfortunately, while a network complying with the above is deemed feasible from a purely technical point of view, it will be expensive (more than R100 M).
Unless data access is obtained via one of the mobile networks, general data access will have to be provided via some form of fixed link mechanism, either radio or cable- based.
Due to the general topography of the area, the low density of users (if towns are excluded) and the large distances involved, the options are limited. The proposed network solution, as illustrated in Figure 5, would be the most practical. The various components of such a configuration will be dealt with in the ensuing paragraphs.
The bulk of the proposed solution is radio frequency-based which, at the least cost, would utilise ISM (e.g. WiFi) but which would not be feasible throughout the entire area due to RFI impact and telescope (existing and planned) locations. Terrain permitting, for ISM band Figure 5: General data network concept.
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downlinks, 25 - 30 km from a telescope would be considered as a safe distance. In the event of RFI spillage, antennae choice needs to be carefully considered to mitigate for any impact. All areas where RFI impact must be negated (e.g. close proximity to a telescope) licensed band transmission in a frequency band above that of the SKA operational and scientific domain should be implemented.
If radio frequency
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based, service to users should be in the form of downlinks from strategically chosen high sites. During the investigation, potential high areas had been determined topographically and checked for performance, however, these would need to be individually surveyed to confirm feasibility. The choice of generic antenna type at the high sites will be important not only in terms of performance but also in the containment of RFI. The preferred type of antenna for the ISM band links is the horn type.An extended backhaul link network will be required to interconnect the positions of the high sites. It should be possible to utilise some of SARAO’s planned infrastructure, particularly their fibre optic network for backhaul communications. The present network does not make provision for additional services, but the infrastructure at terminating nodes could be shared to a certain extent. The investigation of this study assumes that additional fibre optic links will be required in addition to the infrastructure planned for telescope use. Users placed close to the fibre optic network could be connected by terrestrial overhead all-dielectric self-supporting (ADSS) lines. These are also the positions with the highest impact in terms of RFI due to proximity to existing and planned telescopes. A total of 101 such connections is envisaged at this stage, but might have to be revised after the necessary surveys.
The network described above will be functional from a technical point of view and should be capable of delivering the standard of service as expected and required. It will, unfortunately, be a costly solution due to the low density of users.
With the restrictions on wide area, terrestrial radio frequency-based services in the area, a VSAT (satellite) based service appears to offer a logical alternative. The VSAT terminal would act as a replacement for the subscriber unit in the alternative with microwave/fibre optic cable backhaul. It is also a very simple type of installation. Any active electronic equipment could act as a source of RFI. It is known that such problems were found during the initial testing of the VSAT terminal equipment bought by SARAO for distribution to the community as internet replacement. It is, therefore, essential that any new VSAT equipment be thoroughly tested for compliance before rollout. A testing campaign to this effect is currently underway.
Voice: The implementation of Picocell LTE base stations could be considered in selected positions but with due care. Due to the current non-existence of the conventional telephone network, there is preference to cover as much of the area as possible. It is, however, incompatible with the SKA scientific purpose, except for in limited locations.
The use of mobile phones at user locations for WiFi applications and LTE, should not be problematic. GSM operation, however, could be a threat within approximately 4 km from a telescope. This is clearly terrain-related.
The proposed network’s possible RFI impact was extensively investigated as best possible and deemed compliant on theoretical grounds.
2. Safety and emergency (mobile) communications
A network providing wide-area emergency and safety-related voice communications is a high priority to the community and considered essential. A system based on Very High Frequency (VHF) Low Band DMR type repeaters, mobile- and handheld radios was investigated. Coverage studies indicate very good coverage over the area of interest, using 12 repeater sites. Such an implementation should potentially be affordable, cost- effective and well suited to satisfy this requirement. The solution will also fit in with the network envisaged by SARAO themselves for internal use.
4.7.3 Incorporation of Future Technologies
The nature and extent of future technologies are inherently speculative. However, two possibilities are worth mentioning:
1. Pervasive satellite-linked personal communications
These have the attraction of offering almost universal access with low latency, such as Starlink or the rumoured Amazon equivalent. To date, voice services via satellite have been expensive. Starlink is intended as a fixed-/semi-fixed point data service and not a replacement for mobile phone type usage. This might change over time but will require a different mobile device as connection will not be possible via a WiFi connection on a mobile device due to permitted power levels and achievable signal strengths. Published costs at this point are still relatively high.
2. 5G
5G in its current South African format will not be permissible in the KCAAA due to the local spectral occupation, which falls in the SKA frequency band of interest. The higher region 5G spectrum (i.e. above 20 GHz) could be a future option but will require many small cells to cover a significant area. It is primarily a technology intended for densely populated environments, and practical application over a large area such as the greater SKA domain would be challenging. The distances involved are too large to ensure area coverage at that frequency.