A method of operating a distributed MIMO system, wherein the distributed MIMO system is configured to serve one or more wireless communication devices (u 1,..., u N) and comprises: a plurality of access points (A 1,..., A K), each comprising a time circuit configured to keep track of a local time of the access point (A 1,..., A K); and wherein the method comprises performing an intra-group synchronization procedure for a group (G 1) of at least three access points (A 1 -A 3), which do not have access to a central time reference, said intra-group synchronization procedure comprising: for each access point (A i) in the group (Gi): transmitting (T;), from that access point (A i), a synchronization signal; obtaining (O i) a transmission time indicator indicating a transmission time of that synchronization signal in the local time of that access point (A i); receiving (R im, R in), by each of the other access points (A m, A n) in the group, the synchronization signal; and obtaining (O im, O in) reception time indicators indicating reception times, in the local times of the other access points (A m, A n), when the synchronization signal was received by the other access points (A m, A n) in the group; and obtaining, based on the obtained transmission time indicators and reception time indicators, timing adjustment parameters for counteracting time differences between the local times of the access points (A 1 -A 3) in the group (Gi); wherein the method further comprises phase-coherently transmitting a signal to a wireless communication device (u k) served by the distributed MIMO system. a plurality of access points (A 1,..., A K), each comprising a time circuit configured to keep track of a local time of the access point (A 1,..., A K); and wherein the method comprises performing an intra-group synchronization procedure for a group (G 1) of at least three access points (A 1 -A 3), which do not have access to a central time reference, said intra-group synchronization procedure comprising: for each access point (A i) in the group (Gi): transmitting (T;), from that access point (A i), a synchronization signal; obtaining (O i) a transmission time indicator indicating a transmission time of that synchronization signal in the local time of that access point (A i); receiving (R im, R in), by each of the other access points (A m, A n) in the group, the synchronization signal; and obtaining (O im, O in) reception time indicators indicating reception times, in the local times of the other access points (A m, A n), when the synchronization signal was received by the other access points (A m, A n) in the group; and obtaining, based on the obtained transmission time indicators and reception time indicators, timing adjustment parameters for counteracting time differences between the local times of the access points (A 1 -A 3) in the group (Gi); wherein the method further comprises phase-coherently transmitting a signal to a wireless communication device (u k) served by the distributed MIMO system. for each access point (A i) in the group (Gi): transmitting (T;), from that access point (A i), a synchronization signal; obtaining (O i) a transmission time indicator indicating a transmission time of that synchronization signal in the local time of that access point (A i); receiving (R im, R in), by each of the other access points (A m, A n) in the group, the synchronization signal; and obtaining (O im, O in) reception time indicators indicating reception times, in the local times of the other access points (A m, A n), when the synchronization signal was received by the other access points (A m, A n) in the group; and transmitting (T;), from that access point (A i), a synchronization signal; obtaining (O i) a transmission time indicator indicating a transmission time of that synchronization signal in the local time of that access point (A i); receiving (R im, R in), by each of the other access points (A m, A n) in the group, the synchronization signal; and obtaining (O im, O in) reception time indicators indicating reception times, in the local times of the other access points (A m, A n), when the synchronization signal was received by the other access points (A m, A n) in the group; obtaining, based on the obtained transmission time indicators and reception time indicators, timing adjustment parameters for counteracting time differences between the local times of the access points (A 1 -A 3) in the group (Gi);