Long Term Evolution (LTE) wireless networks also known as Enhanced Universal Terrestrial Radio Access Network (E-UTRAN) networks are being standardized by Third Generation Partners Project (3GPP) working groups. For E-UTRAN networks, Orthogonal Frequency Division Multiple Access (OFDMA) is associated with downlink communications and Single-Carrier Frequency Division Multiple Access (SC-FDMA) is associated with uplink communications. User equipments (UEs) of an E-UTRAN network are time and frequency multiplexed on a shared channel such that time and frequency synchronization are required.
The scheduler, in the base-station, has full control of the time and frequency locations of uplink transmissions for all connected user devices, except for UE autonomous transmissions through either the non-synchronized random access channel or the scheduling request channel. To enable proper scheduling and multi-UE management, each UE should be uniquely identified to a base-station. The 3GPP working groups have proposed a 16-bit identifier (ID) for UE's, which represents significant overhead costs for uplink and downlink control signaling in an E-UTRAN network because, in practical implementations, at most a few hundred UE's (compared to 216) will be maintained in uplink synchronization. An uplink synchronized UE can request and have access to uplink transmissions faster than a non-synchronized UE, which first needs to recover synchronization.