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5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006

5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 . Index. Introduction on HSDPASatellite HSDPA (S-HSDPA)Scheduling schemes for S-HSDPAExamined scenario and simulation resultsSatellite MBMS (S-MBMS)Concluding remarks. . S-HSDPA: scheduling for high-bit-rate point-to-point downlink transmissions.

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5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006

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    1. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 HSDPA and MBMS Transmissions via S-UMTS

    2. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Index Introduction on HSDPA Satellite HSDPA (S-HSDPA) Scheduling schemes for S-HSDPA Examined scenario and simulation results Satellite MBMS (S-MBMS) Concluding remarks

    3. S-HSDPA: scheduling for high-bit-rate point-to-point downlink transmissions

    4. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 HSDPA HSDPA is the already standardized evolution of WCDMA for UMTS (from 3GPP TR 25.855 Release 5). HSDPA can permit downlink transmissions at peak bit-rate values even greater than 10 Mbit/s. HSDPA does not use power control but employs new techniques: Adaptive Modulation and Coding (AMC), Fast Physical Layer Hybrid ARQ (F-L1 HARQ), fast packet scheduling and fast cell selection. 3GPP specifications define several Modulation and Coding Schemes (MCS) modes for HSDPA, which represent predefined combinations of modulation (QPSK and 16QAM) and coding rates (1/6, …, 1). The appropriate MCS is selected according to a channel measure made by the User Equipment (UE) and sent to the Base Station (i.e., Node B).

    5. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Radio access network architecture

    6. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 WCDMA transport channels Transport channels constitute the interface by which the Medium Access Control (MAC) communicates with the Physical Layer (L1). Transport Block: A Transport Block is the basic data unit exchanged between L1 and the MAC. Transmission Time Interval (TTI): This is the inter-arrival time of a transport block to be delivered to the physical layer. In HSDPA TTI = 2 ms. TTI is also the interval according to which resources are allocated; it is hence the basis for HSPDA scheduling. There are different MCS combinations for delivering data that are known as Transport Format and Resource Combination (TFRC).

    7. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 HSDPA resource management In the Node B, the scheduler governs the distribution of the radio resources available in the cell among the UEs. The scheduler selects which UE will be served in the next TTI and, supported by the link adaptation functionality, the TFRC and number of assigned codes. 16 codes are available per TTI (one of them is used for signaling). The scheduler at the Node-B tracks the radio channel quality in the downlink direction by considering the received power level by UEs. The UE regularly sends a Channel Quality Indicator (CQI) on the uplink High Speed-Dedicated Physical Control Channel (HS-DPCCH); CQI is an indicator of the TFRC and multi-code number currently supported by the UE.

    8. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 CQI table, an example There are different CQI tables for distinct UE categories. A CQI value is the specification of a TB size (including number of HS-DSCH physical codes, modulation type and coding rate) for which the UE would be able to receive with a Frame Error Rate (FER)<10% after first transmission. The RNC commands the UE to report the CQI with a certain periodicity according to the set {2, 4, 8, 10, 20, 40, 80, 160} ms.

    9. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Terrestrial versus satellite HSDPA Terrestrial HSDPA ? fast adaptation Shorter distance between UE and scheduling entity AMC based on up-to-date channel state information Satellite HSDPA ? slower adaptation Higher distances and propagation delays AMC based on old channel measurements Scheduler location in the terrestrial gateway (bent-pipe satellite) or on board (regenerating satellite with on board processing).

    10. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Selected scenario for satellite HSDPA GEO satellite Multi-spot-beam antenna Bent-pipe Terrestrial gateway as Node B & RNC. Round-trip propagation delay of 560 ms. To maintain as long as possible in the satellite scenario the same characteristics of the terrestrial case: TTI = 2 ms (for a finer scheduling resolution) and CQI update interval to be selected in the available set. Direct return link for the S-HSDPA case for channel measurements. IP-based traffic flows have to be sent via S-HSDPA to mobile users.

    11. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Traffic model for Web traffic sources Web downloading traffic (interactive class) is generated according to a two-state ON-OFF model (UMTS 30.03). The resulting arrival process of datagrams is 2-MMPP.

    12. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Traffic model for video sources Video sources (real-time, conversational class) generate traffic according to a fluid flow traffic model with bit-rate modulated by a discrete-time Markov chain. A video source can be obtained as the superposition of M = 10 ON-OFF minisources (a minisource in the ON state produces a constant bit-rate equal to A).

    13. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Traffic model for video sources (cont’d) Each mini-source produces in ON a constant bit-rate A [bit/s]: We have assumed: m/s = 16. One IP-video packet is generated each 20 ms (video frame). A video packet must be transmitted within a deadline (Tdeadline = 150 ms), otherwise it is dropped. A is a variable parameter

    14. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Scheduling algorithms The classical scheduling algorithms are: Maximum SIR (opportunistic) scheduler: Unfair Efficient (well exploits channel conditions) Round Robin (RR) scheduler: Fair (resources are assigned also to users with bad channel conditions) Inefficient due to packet losses (channel information is not used).

    15. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Proportional fairness scheduler Proportional Fair (PF) strategy serves the user with largest Relative Channel Quality Indicator (RCQI): Ri(t) is the instantaneous data rate experienced by the i-th user if it is served by the packet scheduler, li(t) is the average user throughput (on a suitable sliding time window). Ri(t) can be calculated as the throughput that the UE can support in the next TTI (TB size/TTI depending on the CQI). PF provides a good trade-off between the users that have better channel conditions and those that up to now have received less resources. PF combines fairness and opportunistic aspects.

    16. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Earliest Deadline First (EDF) IP packets are served according to their urgency: each packet has a deadline to be transmitted. The EDF scheduling index is built as follows (for the i-th user): A modified priority index for Web IP-packets is considered to saturate to 0.9 when these packets are close (or exceed) their virtual deadline (P-EDF scheduling technique):

    17. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Simplified channel model A GOOD-BAD channel model has been considered to characterize the SIR fluctuations for each user. Sojourn times in GOOD and BAD states are exponentially distributed. The mean sojourn times in the GOOD and BAD states, Tgood and Tbad, depend on both the UE speed and the environment. We have considered a fixed Tgood value of 6 s and a fixed Tbad value of 2 s.

    18. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Simplified channel model (cont’d) Due to the high Round-Trip propagation Delay (RTD) of about 560 ms (GEO bent-pipe case), when there is a channel state change, the UE receives a packet with an adequate TFRC for the channel after RTD. The propagation delay can cause a misalignment between the adopted TFRC level and the channel condition at the receiver. In general, we can consider 4 cases for the FER: Transmission in GOOD and reception in BAD: FER = 1 Transmission in GOOD and reception in GOOD: FER ? 0 Transmission in BAD and reception in BAD: FER ? 0 Transmission in BAD and reception in GOOD: FER = 0

    19. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Transmission modes for the ON-OFF channel Selected transmission CQI levels: BAD state: QPSK with 1/3 coding rate, 5 codes/TTI, 3319 bits in the transport block corresponding to a capacity of 3319 bits/0.002 s ? 1.6 Mbit/s allocated on a TTI basis. GOOD state: 16QAM with 1/3 coding rate, 10 codes/TTI, 14411 bits in the transport block corresponding to a capacity of 14411 bits/0.002 s ? 7.2 Mbit/s allocated on a TTI basis.

    20. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Management of IP packets produced by sources IP packets of (maximum) 1500 bytes are used for Web and video traffic. MAC queues are filled with IP packets and a pointer controls the part of the IP packet that has been already transmitted. Parts of different IP packets are allowed to be present in the same transport block. The transport block size varies for different CQI levels We assume that data from only one UE is scheduled in one TTI, i.e., multi-code operation refers to the allocation of one or more codes to one UE.

    21. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Numerical assumptions for simulations

    22. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Simulation results

    23. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Simulation results (cont’d)

    24. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Simulation results (cont’d)

    25. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Simulation results (cont’d)

    26. S-MBMS: scheduling for point-to-multipoint transmissions

    27. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Proposed S-MBMS architecture GEO bent-pipe satellite No return link via satellite Integrated terrestrial-satellite architecture: forward link via satellite; return link via a terrestrial 3G segment Dual mode 3G mobile terminal with WCDMA air interface Downlink scheduling without knowledge of the channel to the mobile user.

    28. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Concluding remarks and future work Satellite communications have a potential market in providing downlink high-bit-rate services and in supporting multimedia services on broad areas of the earth. A fundamental task is to extend the terrestrial HSDPA and MBMS standards to the satellite scenario to allow 3G mobile users to access both segments (hybrid networks). We have focused on HSDPA and MBMS provision via a GEO bent-pipe satellite, defining suitable network architectures and radio resource management techniques. Simulation results for S-HSDPA show that the extension of HSDPA to the satellite scenario is feasible provided that channel adaptation and traffic class prioritization is adequately introduced. A future investigation is needed according to the following aspects: To introduce traffic class prioritization in the PF scheme; To adopt a more realistic channel model (intra- and extra-cell interference) for an appropriate CQI selection; To schedule more UEs per TTI.

    29. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Thank you! giannetti12@unisi.it

    30. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 AMC in terrestrial HSDPA

    31. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 From MAC (transport blocks) to PHY in HSDPA

    32. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 Scheduling for S-MBMS The packet scheduler in the satellite (unidirectional) MBMS case has to decide on resource allocations without knowledge of the state of individual channels: channel state dependent scheduling is not possible due to the multipoint nature of the downlink channel. MBMS scheduler tasks on a TTI basis: Time-multiplexing of flows with different QoS requirements into fixed physical channels, in a way that can satisfy these requirements. Adjusting the transmit power of the physical channel carrying the data flows on the basis of the required reception quality of the service (target BLER) under the constraint that the total available power for all the physical channels within a beam is fixed. Scheduler implementation: (i) prioritization of different service requests; (ii) resource allocation on a TTI basis, taking into account transmit power, available codes, requested rate.

    33. 5th MCM of COST 290 Action, Delft, The Netherlands, February 9-10, 2006 S-MBMS channel mapping and protocol stack Each MBMS service is mapped one-to-one onto an MBMS point-to-multipoint Traffic CHannel (MTCH) logical channel MTCHs are mapped onto the Forward Access Channel (FACH) transport channel. One or more FACH(s) can be conveyed (physical level) by the Secondary Common Control Physical CHannel (S-CCPCHs).

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