 available for data transmission, 26 are used for then into superframes and hyperframes as shown in Figure 47.10. a training sequence which allows the receiver to estimate the radio The TCH and the associated ACCH uses the 26 frame structure, propagation characteristics and to set up a dispersion equaliser, 6 whilst the BCCH and CCCH use the 51 frame structure. The bits as tail bits, and two stealing flags. These physical channels SDCCH may occupy one physical channel, providing 8 SDCCH, or therefore provide a data throughput of 114 bits every 4.615m or may share a physical channel with the BCCH/CCCH. Typical ar- 24.7kbit/s. rangements for allocating the 8 physical channels could be: The bursts modulate one of the RF carriers using Gaussian Mini- mum Shift Keying (GMSK) modulation with a BT index of 0.3. The 1. 7 channels TCH and SACCH + 1 channel allocation of the carrier can be such that frequency hopping is BCCH/CCCH/SDCCH achieved, i.e consecutive bursts of a physical channel will be carried 2. 6 channels TCH and SACCH + 1 channel BCCH/CCCH+ 1 by differing RF carriers. This "hopping" is performed every TDMA channel SDCCH. frame, or every 4.615ms and provides extra protection against channel fading and co-channel interference. Each cell must have at least one physical channel assigned to the A number of logical channels can be carried by the physical BCCH/CCCH, where there are 2 or more carriers per cell, the channels described above. These are summarised in Table 47.4. non-BCCH carriers may have all 8 channels allocated to TCH. There are two categories of traffic channels; speech, whether full rate using 22.8kbit/s or half rate using 11.4kbit/s, and data, provid- 47.5.3 Speech coding and channel coding ing a variety of data rates. There are four basic categories of control channels, known as the broadcast control channel (BCCH), the The speech coder is a regular pulse excited linear predictive coder common control channel (CCCH), the standalone dedicated control (RPE-LPC) with long term prediction. This provi