Handover pada GSM Hard handover Soft handover TRAU Tanda2 kecanduan SP Sindrom phantom Bergegas merespon pesan masuk Takut ketinggal informasi shg tdk bisa lepas MS Tidak peduli saat bersosialisasi Mudah cemas krn tdk bawa MS Penurunan kinerja Handover As mobile moves out of range (coverage) of “old” cell Subscriber assigned to “new” RF channel in adjacent cell Controlled by base station controller and MSC “Old” channel now available for “reuse” by another subscriber Handover The process of changing cells during a call is called handover in GSM terminology. The measurements to choose the best target cell are performed by MSs and BTSs. The measurements from the MS and the BTS are processed in the BSC. This evaluation process is called locating. Type of Handover MSC - A • • Controlled by the same BSC Controlled by different BSCs but the same MSC Inter MSC MSC - B Inter BSC Intra BSC BSC BSC BSC SONOFON M • Controlled by different MSCs N BTS BTS SONOFON M SONOFON M N BTS BTS N Hard Handoff vs. Soft Handoff Hard handoff: MS can only converse with one base station at one time; Soft Handoff MS can receive the signals from both stations simultaneously and both stations can receive MS. The network must combine the signals from the two stations in some way. :: Fasilitas soft handoff Neighbor BTS Neighbor BTS Serv BTS CDMA Neighbor BTS Neighbor BTS Serv BTS TDMA(GSM) AOA TDOA Location Information -GSM Service Area Hierarchy The area in which a subscribe r can access the network. GSM Service Area PLMN Service Area (one per operator) MSC/VLR Location Area cell Location Information Hierarchy Location Area Hierarchy HLR VLR MSC1 LA1 VLR MSC2 LA2 HLR: Home Location Register VLR: Visitor Location Register MSC: Mobile Switching Center LA: Location Area TRAU Transcoder Rate Adaptation Unit BTS TRAU TRAU - Transcoder / Rate Adaptation Unit Functions: Conversion of speech from 64 kbit/s on PCM (A-law) to 13/6.5 kbit/s on the GSM radio interface Intermediate rate adoption of data from V.110 frames to the special TRAU frames on the A-bis interface BTS GSM System Architecture HLR/ VLR UM Handset A-bis BTS BSC A MSC SS7 PSTN X.25 OMC (Operation & Maintenance Center) Operation Terminal SIM card Mobile station Radio sub-system Network sub-system Data Terminal PSTN Possible Locations of the TRAU. BTS T R A U BSC BSC BTS T R A U BSC BTS Um MSC A-bis 13Kbit/s speech channel MSC T R A U MSC A-Interface GSM Speech Encoding Bandwidth: 13 kbit/s Encoding algorithm: Regular Pulse Excitation with Long Term Prediction (RPE LTP): Speech is sampled 8000 times per second Each sample is converted into a 13 bit digital value Every 20 ms a 260 bit segment is generated (13 kbit/s) The segment is divided by importance into 182 class 1 bits and 78 class 2 bits For protection, the 182 class 1 bits are mapped into 378 bits The resulting 456 bits (378 + 78) are divided into 8x57 bits The data are transmitted in 4 consecutive TDMA blocks Resulting overall delay is 57.5 msec. BTS Control of TRAU TRAU is controlled by BTS In-band signalling used, if TRAU not at BTS BTS Control functions: Shift between speech and data Shift between full rate and half rate channels Timing of speech frames (BSS - MS) Comfort noise (Discontinuous Transmission) TRAU Signaling TS 0 TS 1 TS 2 TS 31 PCM frame Bit 0 TRAU 2 Mbit/s 16 Synchronization 0000000000000000 32 304 Control bits User data bits 1 C1 - - - - - - - - - - C15 D - Bits 320 user data/control bits 16 kbit/s D/C/T - Bits frame C1 - C4 Frame type: Speech/Idle speech/Data/O&M C5 Channel type: Full rate/half rate C6 - C11 Speech: Time alignment (250/500 us) Data: Intermediate RA (8 or 16 kbit/s) C12 - C15 Speech: Frame indicators (BFI, SID, TAF) C16 C17 - C21 T1 - T4 Speech: Frame indicator (SP) Speech: Spare Speech: Time alignment bits
