ls, (see Figures 49.10 and 49.11. To achieve the variable bit multiple access (TDMA) coupled with time division duplex trans- rate capability DECT is able to concatenate individual 32kbit/s mission (TDD) to provide two-way communication on the same timeslots to build up larger capacities. These concatenated timeslots carrier frequency. need not be adjacent or on the same carrier frequency. Potentially the maximum throughput is, therefore, 12 X 32 = 384kbit/s bothway. 49.4.4 Detail radio aspects Handover is another key specified feature of DECT and has been designed to support handovers in 10ms to 15ms. The above applications place a number of requirements on the basic Other radio parameters are given in Table 49.2. design of the radio system. The following are indicative of this process: Each frame consists of 5ms alternate periods of transmission and reception and it is a general requirement that all base and portable 1. Ability to handover between channels on the same base station terminals shall be able to operate on all timeslots. and between channels on different base stations without dis- This technical specification indicates that in cluttered, multi-path, turbance to speech or data. environments outside buildings time dispersion may be a problem. Fix to portable Portable to fix 416.7 N S 364.6 N S Figure 49.11 DECT frame format 49/12 Cordless telecommunications Table 49.2 DECT radio parameters 49.4.6 Frame structure Figure 49.12 (ETSI, 1992b) shows the multiplex burst as it would Parameter Value appear for a normal telephony call and shows also the relationship Frequency band 1880 - 1900MHz between the PHL and MAC layer responsibilities. The 48 bits of the A field support the associated signalling channel requirements (C), Radio channel spacing 1.728MHz the broadcast beacon transmission (Q) and the paging channel (P). Transmitted symbol rate 1.152Mbit/s The remaining 16 bits of the A field is a cyclic redundancy code (CRC) check used to protect the data. R.F. carriers The B field is used to transport the 