Satelitt kommunikasjon Kapittel 13 Tord I. R.

Overview ● Satellite overview + Iridium ● Digital Video Broadcasting ● Forward link (MPEG-2 Transport stream) ● Return link (Channel Access) ● QoS

References ● Ganz A. Et al., Multimedia Wireless Networks ● ETSI EN v1.3.1 ● ETSI TR v1.2.1 ● The DVB transport stream ● Iridium tutorial

Orbits ● GEO Geosyncronous Earth Orbit (36000 km) Thuyara, Inmarsat. ● MEO Middle Earth Orbit (10000 km) ICO ● LEO Low Earth Orbit (ca km) Large: Iridium, Globalstar Small: Orbcomm, Teledesic. ● Propagation delay (one way) 2.6 – 167 ms. ● Ku band (10-17 GHz) ● Ka band (18-31 GHz)

Iridium ● 66 satellites, 700 km orbit, costs $62 mill. 700 kg. Each sattellite covers 4350 km diameter with 48 beams. ● 12 gateways located around the world. ● Phone to satellite 1616 – MHz, 2.4 kbps. ● Satellite to satellite/gateway 23GHz, 19GHz downlik, 29GHz uplink. ● Iridium follows the GSM architecture.

Digital Video Broadcasting (DVB) ● Multimedia Wireless Networks focuses only on DVB. ● ETSI EN ● ETSI TR ● Dish size: 0.6 to 1.2m. ● Up link (Return link) 150kbps-380kbps-2Mbps. ● Down link (Forward link) 38Mbps.

DVB Return channel system

NCC-Satellite-RCST – NCC – Network core controll – RCST – Return Channel Satellite Terminal

Forward link / Broadcast channel ● MPEG-2 Transport Stream ● Several transport streams are multiplexed on MPEG-2 TS – DVB data piping – DVB data streaming – DVB multiprotocol encapsulation – DVB data carousel – DVB object carousel

Return Link ● All RCST transmissions are controlled by the NCC. ● The NCC broadcasts a Terninal Burst Time Plan (TBTP) for each superframe, indicating when each RCST can send data. The RCST are identified by channel id. ● The TBTP is based on demand and QoS requirements. ● A time slot is identified with superframe id, superframe counter, frame number and timeslot number. ● Data are sent with fixed- or dynamic-slot MF-TDMA

MF-TDMA

QoS ● All transmissions are controlled by the NCC ● Capacity requests are categorized into 5 categories: – Continuous rate assignment (CRA) Fixed min. Bandw. (constant bit rate applications). – Rate-based dynamic capacity (RBDC) dynamic per superframe. (variable bit rate applications). – Volume-based dynamic capacity (VBDC) cumulateive requests (variable bit rate, delay tolerant applications). – Absolute volume-based dynamic capacity (AVBDC) none-cumulative VBDC. – Free Capacity Assignment (FCA) (best effort)

QoS ● Signaling method for capacity requests: – Satellite access control (SAC) field. A SYNC contains an optional SAC field. – Data unit labeling method (DULM). Piggybacked on the assigned periods of TRF traffic. – Mini-slot method. Logged-on units that use less than the full traffic slots. – Contention-based mini slot method. Accessed mini- slot on a contention basis, uses slotted aloha for back off.