5G TDD Inter-Operator Network Synchronization

Already back in 2018 I wrote a post that one new thing about 5G in TDD band n78 will be that network operators need to agree on a common uplink/downlink pattern and in addition synchronize their networks. Recently I was asked to what level of accuracy the networks need to be synchronized so I did a bit of research to find out.

Synchronization actually means two things: In a first step, network operators that use adjacent channels in band n78 have to use the same uplink/downlink pattern as described above. The pattern has to start at the same time across all network operators to prevent transmitting mobiles of one network operator creating interference with downlink transmissions of other network operators. Also, transmissions of one network operator should not overlap with reception slots of another network operator.

So far so good, but with which accuracy do the networks have to be synchronized? ECC Report 296 on “National synchronisation regulatory framework options in 3400-3800 MHz” gives a recommendation of +/- 1.5 microseconds. To set this into perspective: The length of a single symbol in band n78 with a subcarrier spacing of 30 kHz is 33 microseconds. In other words, the networks need to be synchronized to within 10% of a symbol duration.