System frames 220 and 230 are offset with respect to each other. A cell transmitting system frame 220 and a cell transmitting system frame 230 may be seen as a cluster of cells, divided into a first subset comprising the cell transmitting system frame 220 and a second subset comprising the cell transmitting system frame 230. System frame 220 comprises uplink access opportunities 222 and 224, separated from each other by 20 ms, and system frame 230 comprises uplink access opportunities 232 and 234, separated from each other by 20 ms. Due to the offset between system frame 220 and system frame 230, the cluster of cells that transmit system frame 220 and system frame 230 collectively provides uplink access opportunities every 10 ms, since uplink access opportunity 232 occurs 10 ms after uplink access opportunity 222. Similarly, 10 ms separates uplink access opportunity 224 from uplink access opportunity 232, and uplink access opportunity 234 from uplink access opportunity 224. Thus the cluster of cells transmitting system frame 220 and system frame 230 collectively provides an access opportunity pattern consistent with a lower-latency access requirement than that provided by system frame 210.