s 23040 Ts 21952 Ts 24144 Ts inverse of sampling frequency, i.e., Ts=1 1/(15000 X 2048) [107]. The length of the radio frame, subframe, and slot can alternatively be expressed in the number of time samples which are integer values. Both 5 ms and 10 ms switching-point periodicity are supported. The first subframe in all configurations and the sixth subframe in configuration with 5 ms switching-point periodicity consist of DwPTS, GP, and UpPTS. The sixth subframe in configuration with 10 ms switching-point periodicity consists of DwPTS only. All other subframes consist of two equally sized slots. For TDD systems, the GP is reserved for downlink to uplink transition. Other subframes/fields are assigned for either downlink or uplink transmission, as shown in Table 9-18. The uplink and downlink transmissions are separated in the time domain. Table 9-18 Various Permissible Uplink/Downlink Configurations in Frame Structure Type 2 where "S" Denotes the Special Subframe [107] Subframe Number Switching-Point Configuration Periodicity 10 ms 10 ms 10 ms 10 ms 9.15 3GPP LTE physical layer protocols 9.15.3 Physical Resource Blocks The smallest time-frequency resource unit used for downlink/uplink transmission is called a resource element, defined as one sub-carrier over one OFDM/SC-FDMA symbol [107,116]. For both TDD and FDD duplex schemes, as well as in both downlink and uplink, a group of 12 sub- carriers contiguous in frequency over one slot in time form a Resource Block (RB), as shown in Figure 9-67 (corresponding to one slot in the time-domain and 180 kHz in the frequency-domain). Transmissions are allocated in units of resource blocks. One downlink/uplink slot using the normal CP length contains seven symbols. There are 6, 15, 25, 50, 75, and 100 resource blocks corre- sponding to 1.4, 3, 5, 10, 15, and 20 MHz channel bandwidths, respectively [107]. Note that the One Slot N symb OFDM/SC-FDMA Symbols k = NRBN RB -1 Resource block N symb X N SC RB resource elements Resource element (k,l) Frequency l = Nsymb FIGURE 9-67 Str