ITU-R Report: Terrestrial IMT for remote sparsely populated areas providing high data rate coverage
ITU-R WP 5D is progressing a preliminary draft new Report ITU-R M.[IMT TERRESTRIAL BROADBAND REMOTE COVERAGE] which we offer highlights of in this IEEE Techblog post. Co-authors of this draft 5D document are: Huawei Technologies Co. Ltd, Nokia Corporation, Telefon AB – LM Ericsson, Qualcomm Inc. and ZTE Corporation.
This post is an update and replacement of an earlier version, which can be read here. The scope has been broadened to include all types of IMT, not just IMT 2020 (5G).
On a global basis, the total number of mobile subscriptions was around 8 billion in Q3 2019, with 61 million subscriptions added during the quarter, the mobile subscription penetration is at 104 percent. There are 5.9 billion unique mobile subscribers using mobile networks, while 1.8 billion people remain unconnected. In year 2025 it is forecasted to be 2.6 billion 5G subscriptions and 8.6 billion mobile subscriptions globally at a penetration level of about 110 percent.
In 2025 the forecast is for 6.8 billion unique mobile subscribers using mobile networks, while 1.5 billion people remain unconnected, many of whom are below the age of nine.
The prospect of providing mobile and home broadband services for most of the 1.5 billion unconnected people, living in such underserved rural areas, is largely related to techno-economic circumstances.
This Report provides details on scenarios associated with the provisioning of enhanced mobile broadband services to remote sparsely populated and underserved areas with a discussion on enhancements of user and network equipment.
Deploying networks in remote areas is normally more expensive, and at the same time, expected revenues are lower in comparison with deployments in populated areas. A further reason for not being incentivized to deploy new IMT broadband (e.g. IMT-2020/5G) Base Stations (BS) in these areas is the expected number of new BS sites. Therefore, the total economic incentives to deploy traditional networks in sparsely populated areas are consequently narrowed.
 Ericsson Mobility Report, November 2019, mobile broadband includes radio access technologies HSPA (3G), LTE (4G), 5G, CDMA2000 EV-DO, TD-SCDMA and Mobile WiMAX.
The competition model, applying to densely populated areas, is normally not providing rural coverage expansion at a speed that society wish. Connectivity in underserved remote areas is important to national policy makers facing needs of consumers, to service providers for reasons of branding, and to satisfy regulatory conditions in countries.
When expanding coverage in remote areas, it may imply an undesirable local monopoly, suggesting that only one service provider would expand in to such a remote area due to a low consumer base.
Rural coverage might in the future be driven by the need for national security and public safety connectivity, intelligent traffic systems, internet of things, industry automation and end users need for home broadband services as an alternative to fiber connections. In order to fulfill the needs of rural coverage, it is a matter of urgency to identify viable solutions for mobile and home broadband services.
Related ITU-R Recommendations and Reports:
M.819 “International Mobile Telecommunications-2000 (IMT-2000) for developing countries”.
M.1155 “Adaptation of mobile radiocommunication technology to the needs of developing countries”
Solutions that support remote sparsely populated areas providing high data rate coverage:
Possible technical solutions to achieve both extended coverage as well as high capacity in remote areas could be to use dual frequency bands at the same time, one lower band for the uplink (UL) and one higher band for the downlink (DL), in aggregated configurations.
Combining spectrum bands in the mid-band range and the low-band range on an existing grid can provide extended capacity compared to a network only using the low-band range.
An alternative technical solution to provide extended coverage in a remote area using a reduced number of terrestrial BS sites, aiming to bringing cost down, requires careful selection of proper locations and technical characteristics compared to configurations of suburban networks. Realizing such extended network configuration for coverage, several considerations need to be taken into account, both at a BS site and at customer premises. Considerations of accommodating BSs on high towers in sparsely populated areas could be further studied. Such opportunities rest with traditionally high tower used for analogue or digital television with an average inter-site distance (ISD) of the order of 60 km to 80 km designed to provide blanket coverage of national terrestrial television services.
With potential enhancements of base station (BS), user equipment (UE), and customer premises home broadband configurations, it is deemed feasible to deploy a standalone network in the range 3.5 GHz providing high capacity and coverage over tens of kilometers in rural areas. This could potentially be a promising solution for bringing IMT broadband (e.g. IMT-2020/5G) to underserved regions.
Combining spectrum bands in the mid-band range 3.5 GHz and the low-band range, e.g. 600 MHz, 700 MHz or 800 MHz, on an existing grid can provide extended capacity compared to a network only using the low-band range. The reason being that the mid-band range offer access to more spectrum bandwidth, and the low-band range combined, can provide the coverage for cell edge users in a unified manner.
Generally, at a BS site, the antenna height and the radio frequency (RF) output power have a profound impact on the coverage and capacity performance. Effective performance solutions are also represented by a high level of antenna sectorization, high antenna beamforming gain, and the use of MIMO antennas, as well as the use of carrier-aggregation. Furthermore, additional spectrum bands and bandwidth, and usage of redundant signaling protocol will improve performance. As the UL performance is the limiting factor, enhancing the UE transmission performance is key to enable extended coverage. For a home broadband deployment in a “wireless fiber” configuration using an outdoor directional antenna mounted line-of-sight to the BS antenna site extend the coverage range significantly by avoiding building penetration losses.
Underserved sparsely populated areas are every so often characterized by limited internet access and basic mobile service provide by a 2G network designed for voice connectivity. Therefore, one of the key aspects providing coverage in a remote area, aiming to bringing cost down, is possible to use such existing 2G network grid by means of conventional spectrum bands in 600 MHz, 700 MHz, 800 MHz, 850 MHz or 900 MHz for UL connectivity in combination with the band 3.5 GHz for the DL system installed in a high tower used for analogue or digital terrestrial television with an average ISD of the order of 60 km to 80 km designed to provide blanket coverage of national terrestrial television services.
It is assumed that a conventional 2G or 4G antenna arrangement is used for the UL system. For the IMT-2020/5G 3.5 GHz DL system, an antenna array is assumed to have 64 dual-polarized antenna elements installed in a television towers at a height of about 250 m. The considered ISD is regarded to be representative for a conventional 2G network grid. The maximum supported coupling loss for 2G is approximately 137 – 144 dB to support acceptable control channel signaling, and here assuming a maximum of 140 dB coupling loss is needed for basic coverage. The propagation losses are similar for IMT-Advanced/4G at 600 MHz, 700 MHz, 800 MHz, 850 MHz and at 900 MHz, here searching for an ISD that results in 140 dB coupling loss at the cell-edge for 4G at 800 MHz. From experience it is estimated that at 140 dB coupling loss occurs at an ISD of about 4 km. In terms of IMT-2020/5G, a beamformed coupling loss of approximately 143 dB should be supported.
The DL and UL user throughput can be estimated in a deployment scenario using the parameters above. For DL, over 20 times capacity gain can be achieved by utilizing an additional IMT-2020/5G connectivity link in the band 3.5 GHz compared to an IMT-Advanced/4G connectivity link only in the band 800 MHz. This is in recognition of the wider bandwidth of the band 3.5 GHz together with the advanced BS antenna array deployed. For users located at the cell edge, data rates of over 100 Mbit/s can be reached in the DL direction using conventional 5G UE terminals.
Due to the limited UE transmit power of 23 dBm together with the propagation conditions in the band 3.5 GHz, a standalone network has limited possibilities to provide adequate coverage in the UL direction for users located at the cell edge.
Adding the new band 3.5 GHz for mobile and home broadband connectivity, networks can clearly deliver on the promise to increase on the coverage requirements for IMT-2020/5G services, but only adequately in the DL direction. For such a communication circumstances, a IMT-2000/2G or IMT-Advanced/4G grid is indispensable to combine to provide adequate UL coverage.
Analyzing configurations for an IMT broadband network operating only in the band 3.5 GHz:
For the circumstances in underserved remote areas the DL capacity performance can be significantly improved by using the band 3.5 GHz whilst the UL coverage is representing the bottleneck in attempts of satisfying needs for coverage. With potential upgrades of BS and consumer premises UE configurations, the feasibility of providing improved remote area coverage is considered by using only the band 3.5 GHz.
Addressing firstly the UL coverage issue for a standalone network using only the band 3.5 GHz, a potential network upgrade can include increased BS antenna height. Obviously, increased RF power only would not resolve the issues involved. In addition, improved configuration, such as usage of high gain directional UE antenna deployed at the consumer premises for home broadband systems may need to be incorporated into the network design for improved remote coverage and for the reciprocity between DL and UL performance.
This assumption for IMT-2020/5G macro sites is considering the use of television towers at a height of about 250 m, applying ISDs of the order of 60 km to 80 km which is considered to reflect realistic distances for current terrestrial television networks.
In addition, a conventional RF power of 23 dBm is considered for UE at the consumer premises using home broadband services configured for rooftop installation using a high-gain antenna of 20 dBi at about 10 m height can reach 5 Mbit/s at cell edge at reasonably low traffic loads for the UL, and 120 Mbit/s for DL.
With omni-directional UE antennas, the ISD will need to be reduced to 40 km to achieve similar performance at cell edge.
Annex 1. List of acronyms and abbreviations:
|MIMO||Multiple Input Multiple Output|
ITU-R Proposal: Report on IMT-2020 for remote sparsely populated areas providing high data rate coverage