User Equipment

As in UMTS, the LTE mobile station is called User Equipment (UE). It is constructed using a modular architecture that consists of three main components (see Figure 1):

• Mobile Termination: The MT represents termination of the radio interface. In this entity the RRC signaling is terminated and RRC messages are sent/received.
• Terminal Adapter: The terminal adapter represents the termination of the application-specific service protocols, for example, SIP signaling for VoIP. The terminal adapter might be constructed as an external interface, for example, USB to connect a laptop PC using LTE technology with a mobile network.
• Terminal Equipment: The TE represents termination of the service. Depending on the UE's application capabilities, it may act as the TE or not. For instance, the Apple iPhone with its browser functionalities has full TE capability while a simple USB stick for mobile data transmission has no TE capability at all. In the case of the USB stick, the connected laptop PC is the TE.
  
  

 
Figure 1.: Modular architecture of a UE

1) UE Categories

The UE categories stand for an abstract grouping of common UE radio access capabilities and are defined in 3GPP 36.306.

In particular, the handset-type groups vary in maximum possible throughput (the maximum number of DL-SCH transport blocks bits received within a Time Transmission Interval (TTI)). Assuming a TTI of 1 ms for category 1, the maximum possible throughput is 10 296 bits/1 ms which is approximately 10Mbps of physical layer DL throughput (including the RLC/MAC header information-so the payload throughput will be slightly less).

Category 5 mobiles are the only handsets that support 64 Quadrature Amplitude Modulation (QAM) on the UL as highlighted in Tables 1 and 2. The maximum possible bit rate ranges from 5 Mbps (Cat. 1) to 75 Mbps (Cat. 5).

Table 1: UE categories and DL capabilities (according to 3GPP 36.306). Reproduced with permission from © 3GPP™ 

UE category	Maximum number of DL-SCH transport block bits received within a TTI	Maximum number of bits of a DL-SCH transport block received within a TTI	Approximate maximum bit rate DL (Mbps)
Category 1	10 296	10 296	10
Category 2	51 024	51 024	50
Category 3	102 048	75 376	75
Category 4	150 752	75 376	75
Category 5	302 752	151 376	150

Table 2: UE categories and UL capabilities (according to 3GPP 36.306). Reproduced with permission from © 3GPP™ 

UE category	Maximum number of bits of an UL-SCH transport block transmitted within a TTI	Support for 64QAM in UL	Approximate maximum bit rate UL (Mbps)
Category 1	5 160	No	5
Category 2	25 456	No	25
Category 3	51 024	No	50
Category 4	51 024	No	50
Category 5	75 376	Yes	75