In previous article, the technical challenge/obstacle concerning the coexistence with incumbent services was mentioned. The 3.5GHz band (C-band) identified for 5G network is currently utilized by Malaysia East Asia Satellite (MEASAT) for their operational satellites, of which installation and testing of equipment for a satellite control station is set on Langkawi Island. MEASAT-3, MEASAT-3a, and Africasat-1a will continue to use the C-band spectrum for the upcoming MEASAT-3d satellite, scheduled for launch in the second half of 2021.
The C-band is also used to perform critical commands, telemetry, a range of controls for MEASAT satellites, and to monitor the satellites’ overall health. Control links are transmitted through stations located in Cyberjaya (primary) and Bukit Jalil (back-up). The Cyberjaya and Bukit Jalil control stations also monitor live traffic on the entire C-band payload of the MEASAT satellite fleet to ensure quality of service. Deployment of the 5G Base Station adjacent to the incumbent receiver in the reallocated C-band spectrum will no doubt generate interference in the incumbent’s receiver system.
To date, there are about 2,000 C-band receivers nationwide serving applications such as mobile backhaul, VSAT, video distribution and government links, as illustrated below:
A very typical example of the VSAT application is the very familiar satellite dish deployed at many of the petrol station. Try to observe when you stop-by for petrol filling. VSATs are used to transmit narrowband data (e.g., point-of-sale transactions using credit cards, polling or RFID data, or SCADA), or broadband data (for the provision of satellite Internet access to remote locations, VoIP or video).
How Do We Tackle the Problem?
In order to enable coexistence of the 5G mobile service and FSS in the C-band, mitigating steps should be applied. There are several mitigation techniques proposed where the application of filtering turned out to be the most promising and cost effective solution. The spectrum allocated for FSS is to be given away to accommodate 5G sub-6 deployment in the range of 3.4–3.8GHz depending on local government policies and decision. However in order to enable the coexistence, a guard band between the 5G sub-6 and FSS must be imposed in order to mitigate the channel interference issue. It is almost absurd to replace all FSS satellite stations simply due to the re-adjustment of the spectrum as the cost and impact is too high!
In such a scenario, a retrofitting solution of applying a microwave filter has become a magic solver! Inherently, the FSS satellite system was designed and deployed to cover a broad frequency range. However, the readjustment decision can be solved by the microwave filter. A satellite filter with prescribed frequency response can be installed between the antenna and the LNB of the satellite in order to limit the spectrum for VSAT signal without much impact to the existing ground station.
Retrofit 5G Reject Filter Design
It can be noted that the filter must be designed in order to meet the following requirements:
▪ Low insertion loss
▪ High selectivity
▪ Extremely small guard band applications
▪ Easily installed between the feed and LNB
▪ Rugged shielded case, weight <700g
▪ Size:120mm x 100mm x 70mm (L x W x H)
▪ Power: 100W (max)
As a retrofitted device, the low loss performance plays a critical role in the overall system noise figure performance. The high selectivity specification is to ensure a sufficient suppression on 5G signals within the guard band (band between 5G and FSS spectrum). Due to the outdoor installation and mechanical consideration, the filter must also have low weight and small size for ease of installation.
My next interesting question is, are there any local filter manufacturers which are capable of delivering this solution or similar? I would like to leave this question to the reader. If you find out any, please do share your finding to writer. Thanks!
Originally published at http://filpal.wordpress.com on December 12, 2021.
