Operational characteristics of the Layer 1 time-division multiple access, which handles airlink management, channel maintenance, and cell transfers, can be difficult to verify prior to full type approval. This discussion is devoted to understanding Layer 1 operation and ensuring spec compliance.
Communication systems rely upon protocols for their very survival.
L1 is primarily responsible for airlink management, encompassing GSM channel acquisition, channel maintenance in a hostile RF environment, and cell transfers when the current channel becomes ineligible for use. The physical channel is defined by frequency as well as by time. This scheme is referred to as TDMA since data is sent in time-limited bursts under strict network control. One of these slots is used for a single mobile handset, leaving the potential for another seven mobile handsets to gain access to the network on the same frequency pair, each using different slot assignments. Figure 1 portrays a typical session whereby the BTS transmits a burst to the mobile handset within one time slot, and then receives from the mobile handset a related burst three time slots later.