This problem was eliminated in IS-136, due to the extra capacity and flexibility of digital control channels. The VSELP vocoder digitizes the voice and outputs an 8 kbit/s data stream that represents the voice. Speech is sampled in 20 msec time increments (blocks) that create 160-bit/speech blocks. Digital Control Channels (DCCH) can be accessed only by IS-136 mobile stations and have the same functionality as their analog counterparts. 6. Experimental studies of the radiation levels of antennas BTS. Each channel is divided into six time slots. Burst Format Preamble Burst Payload TDMA Burst Guard Time Preamble Burst Payload TDMA Burst Guard Time ORBIT CONTROL • problem: constellation earth station - satellite is not constant!! Therefore, remote mobile stations should transmit their packets before mobile stations in close proximity to base stations. As in the case of the radio interface, the transmission of information in the time division of channels is carried out as part of a TDMA frame (in the Air-IF frame of the traffic channel). For example, 156 symbols x 2 = 324 bits in each time slot (frame) as opposed to 148 symbols x 1 =148 bits in the GSM frame. TDMA Burst Structure 31. If it finds no secondary channel, the unit attempts to access the system as an analog station. 2.33, and the temporal envelope mask for signals emitted in the AV interval of a full TDMA frame is shown in Fig. The minimum unit being frame (or TDMA frame) is made of 8 time slots. It is based very strongly on the European GSM system. These antennas are called directive antennas and are identified by their degree of directionality. 9.3. 7.1. MOBILE STATIONS 4.1. 0000002686 00000 n 0000003059 00000 n If an antenna is focused to serve one-third of its possible 360  range, it is called a 120  directional antenna. 10.5. Fig . The temporal envelope mask for the NB, FB, DB, and SB signals of the full TDMA frame is shown in Fig. Principles of mobile network organization. TDMA Burst Amplitude Time 3 symbols 3 symbols 156 symbols 3 symbols 1 symbol = 2 bits 32. The Forward Digital Control Channel (FDCCH) is not limited to the 21 fixed frequencies and limited paging capacity of analog control channels. If the decoding process indicates that it is not a valid speech slot, the receiver will attempt to decode it as a FACCH message. TDMA power classes include: Class 1 4 W max, 6 mw min, 1.333W average Class 2 1.6 W max, 6 mw min, .533W average Class 3 0.6 W max, 6 mw min, .2W average (reduces minimum cell radius for microcellular systems) Class 4 Dual-mode MSs transmit in bursts, so their average output power is properly measured during the burst period. Additionally, the path-balancing concept is “alive-and-well” in TDMA. There are two types of cells in a TDMA network: Omnidirectional cells Sectored cells An omnidirectional cell uses an antenna that radiates in all directions, and single or multiple channel sets can be assigned to the cell. In the process of comparison, the parameter RXQUAL, adopted for assessing the quality of communication, is calculated. Differential Quadrature Phase Shift Keying (DQPSK) modulation, coupled with a 33% transmit duty cycle for full-rate TDMA, causes a typical measurement of about 30% of peak burst power. Z��|t��h�-�@Qyجo���k7h����s�\�v]4-�8X���̙3�1j��T�^���`U���STOW�Oo�}�w�T�F�BE�l����mT��2�]��w�F�li�$m&�{��͏��7��d��8��n��‿� A signal coming from a tower to a handset might come from any one of several directions. The “slow-channel” uses a few dedicated bits within each time slot and does not affect speech quality. 0000000776 00000 n For help you can check writing expert. 44. Network Management System Tasks. Nb the number of bursts. 30. Different forms of the envelopes of the emitted signals correspond to different durations of the AB interval (88 bits) with respect to other specified intervals of the full TDMA frame (148 bits). Some of these areas are considered sub-channels. SFH operation mode assigned by MSC switching center, 2.8. 3.1. (For more information on GSM, refer to the GWEC module AI- GSM .). 2.6. 65. If it cannot find digital capability, it assumes that it has found an older AMPS-only control channel. xref Goals and objectives of design. I have been using it since last year. These sub-channels should not be confused with RF channels. 7.11. 3.4. The TDMA concept permits reuse of the existing cellular plan. Distribution of network management functions. The SACCH is a continuous data stream of signaling sent beside speech data. Since, according to the GSM standard, an informational message is transmitted over the radio channel with a speed of 270.833 kbit / s, the time interval of a TDMA frame contains 270833Х577Х10-6 = = 156.25 bits. Once it locates the strongest channel it will attempt to register with that network using “overhead” messages. BASE STATIONS General. General provisions. In other words, some of the existing 30 kHz wide channels that were used for FM must be retired from FM service and used for new TDMA service. Digital Verification Color Code (DVCC) is the digital equivalent to the analog SAT tone. This is the first packet transmitted by the mobile station, and the signal transit time has not yet been measured. TDMA offers high performance with respect to capacity, courage and mobility.TDMA mainly transmit data in a buffer-and-burst method and the transmission of any user is non- continuous. Thus, all time slots NB, FB, SB, DB and AB have the same frame length of 156.25 bits. There are 162 symbols per time slot and the symbol period is 41.16 msec. %PDF-1.4 %���� 51. There are no guard and ramp symbols as the forward channel is not bursted, but present continuously. The principle of forming slow jumps in the SFH frequency is that the message transmitted in the time interval of the TDMA577 μs frame allocated to the MS subscriber is transmitted (or received) in each subsequent frame at the new fixed frequency (Fig. Features of propagation of radio waves used in the GSM standard (decimeter waves (900 MHz, 1800 MHz, 1900 MHz)), 23. TDMA uses a vocoder to model the tone and noise generation of the human throat, and the acoustic filtering of the mouth and tongue, by breaking the speech up into long-term short-term vector sum blocks. Theoretically, TDMA should be able to work in an environment where the signal to interference (S/I) requirements are not as stringent as AMPS. There are some disadvantages of TDMA. 3) The time synchronization interval SB is designed to synchronize the time of the base and mobile stations. One way of getting around this interference is to put a time limit on the system. All cellular architectures, whether microcell- or macrocell-based, have a unique set of propagation problems. 3.7. Future improvements in vocoder technology will likely lead to only one time slot being needed for each phone. Shared Control Feedback (SCF) flags are part of this access channel and provide information to control channel access by multiple mobiles. Pi/4 is used because the design of a QPSK modulator is more complex. 5) AV access interval provides the access permission of the MSk mobile station of the new base station. If you wish to opt out, please close your SlideShare account. If you continue browsing the site, you agree to the use of cookies on this website. Frame structure and signal shaping in GSM standard (with TDMA) As a result of these transformations, each sample of the level of the original analog speech signal is represented as an encrypted (encoded) message consisting of 114 bits, which in turn consists of two independent ED information packets (EncriptedData — encoded, encrypted data) 57 bits each (Fig. Thus, the NB time slot contains 156.25 bits with a duration of one bit equal to 577 / 156.25 = 3.69 μs. 0000001178 00000 n Therefore, three conversations can share the same frequency as a result of the concept of “time division”. used for GSM standard, 24. In 1989, the CTIA chose TDMA as the technology of choice for existing 800 MHz cellular markets and for 1.9 GHz markets. In fact: - NBTDMA is a traffic channel slot; - FBTDMA is the frequency correction packet slot; - SBTDMA is a synchronization packet slot; - DBFDMA is the idle packet slot; - AV TDMA is an access packet slot. 55. In IS-54, speech quality is degraded non-linearly as more speech frames are replaced.

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