Electronic Communications Act, 2005 (Act No. 36 of 2005)ICASARadio Frequency Spectrum Assignment Plan for the Frequency Band 2500 to 2690 MHz (IMT2600)AppendicesAppendix E : Network synchronization for the frequency band 2500 to 2600 MHz |
The Radio Frequency Spectrum Assignment Plan for the frequency band 2500 to 2690 MHz. The frequency band 2500-2690MHz provides a total bandwidth of 190 MHz for the IMT service. South Africa has decided to implement International Mobile Telecommunications (IMT) Time Division Duplex (TDD) in the Final Radio Frequency Migration Plan 2019 published in Government Gazette 42829 (Notice 600 of 2019) and to increase the usable bandwidth of IMT2600.
The frequency band 2500 to 2690 is to be assigned to more than one licensee. In order to ensure that more than one licensee is able to operate their networks in TDD mode, in the same geographic area, in a coordinated manner, it is important that these networks are synchronised in order to avoid interference.
In order to avoid interreference where there is co-existence of TDD Networks and to avoid all Base Stations to Base Station as well as User Equipment to User Equipment interferences it is important to synchronise the base stations so that transmit and receive roughly at the same time. This to say that operation is synchronised in such a way that there is no simultaneous uplink and downlink occurring between any pairs of cells which may interfere with each other in the same band.
In order to avoid interference between TDD networks operating in adjacent frequency carriers, the radio transmissions of adjacent TDD networks shall be synchronised with the uplink and downlink frames aligned in time. Such synchronisation of networks is very important due to the fact that this is the best way to avoid interference between networks and ensure efficient use of spectrum resources by avoiding inter-operator guard bands and additional base stations filtering.
Network synchronisation has been successfully implemented in IMT Advance TDD networks ensuring efficient use of the spectrum resource by avoiding the need for guard bands between licensee’s assignments. Similarly, interlicensee’s synchronisation and time alignment of uplink and downlink transmissions (slot and frame synchronisation) are also necessary for efficient deployment of IMT2020 New Radio networks in unpaired band assignments. This RFSAP therefore, is aimed at facilitating synchronised operation among IMT Advance and IMT2020 networks operating in adjacent frequency blocks to make the best use of the valuable spectrum resource.
The Authority recommends to licensees that two (2) transmission frame structures for IMT-Advance and IMT2020 macro-cell networks operating in unpaired New Radio Frequency Bands, taking into account technology advances and system design requirements:
| 1. | Scenario 1: IMT2020 only, no legacy IMT Advance TDD networks: 2.5ms periodicity frame structure (DDDSU) for high system capacity and efficiency (Figure 1), and 2.5ms dual periodicity frame structure (DDDSU+DDSUU) for prioritisation of UL transmission (Figure 2). |
| 2. | Scenario 2: IMT2020 co-existence with IMT Advance TDD network: 5ms periodicity frame structure compatible with LTE TDD network (DDDDDDDSUU) (Figure 3). However, this is accompanied with twice the latency of Scenario 1. |
Figure 1: 2.5ms periodicity frame structure
Figure 2: 2.5ms dual periodicity frame structure
Figure 3: 5ms periodicity frame structure
In South Africa, there are legacy IMT Advance TDD networks in the frequency band IMT2600 as illustrated in the Scenario 2. The Authority therefore recommends that licences, in designing their network consider a 5ms periodicity frame structure for IMT2020 network (DDDDDDDSUU,8:2), and 5ms periodicity frame structure for IMT Advance network (DSUDD,3:1).
Licensees are encouraged to agree on the preferred synchronisation method. The Authority will step in, order to mediate in the case where there is no consensus amongst licensee.