haracter- ised by a number of new features, including the choice of OFDMA. The LTE standards specify an OFDM system with a narrow subcarrier set of 15 kHz bandwidth in the downlink. This allows for smooth transition of a 3G operator to 4G. For example, a W-CDMA system oper- ator which has been allocated a 5 MHz bandwidth as a single carrier to transmit data, will operate an OFDMA system with 300 narrowband subcarriers as shown in Figure 10.30. A CDMA-2000 operator which has a 1.25 MHz bandwidth allocation can use 75 subcarriers of 15 kHz in an OFDMA 4G system. The resource is also allocated on a TDMA basis. An LTE frame is 10 ms, comprising ten 1 ms subframes, which in turn comprises two 0.5 S time slots to facilitate seamless FDD and TDD modes of operation as illustrated in Figure 10.31. Resource allocation algorithm at the base station grants users capacity in multiples of 'resource blocks'. One resource block is defined as a cluster of 12 subcarriers and one 0.5 S time slot, or 7 OFDM symbols, as shown in Figure 10.32 [16]. Some important LTE standard parameters are listed in Table 10.7. A single-carrier FDMA (SC-FDMA) system is used in the uplink. LTE OFDMA also facilitates device operation over a number of different possible band- widths. The LTE standard specifies device operations using a range of bandwidths: 1.25, 5, 10 and 20 MHz. This allows for flexible bandwidth allocation to different operators. The specifi- cation for transmission rates and delay satisfy the requirements listed in Table 10.6. A typical calculation shows the peak throughput for a 5 MHz bandwidth allocation to be equal to 37.8 Mbps as shown in Table 10.8. Terrestrial Broadband Wireless Telecommunications Table 10.6 LTE specification for transmission rates and delay Parameter Minimum requirement set by operators Peak transmission rate (downlink) 100 Mbps Peak transmission rate (uplink) 50 Mbps Downlink peak user throughput 5 b/s/Hz Uplink peak user throughput 2.5 b/s/Hz Spectral efficiency - Downlink 1.6-2.1 b/s/Hz/cell Spectral effici