Network Architecture and Radio Resource Management for...

Network Architecture and Radio Resource Managementfor Satellite Digital Multimedia Broadcast System

L. Liang, L. Fan, H. Du, Z. Sun, Barry G. EvansUniversity of SurreyC. Seller, N. ChuberreAlcatel SpaceM. FitchBritish TelecomM. ColeLogica-CMGT. BoivinAlcatel CIT

E. BunoutMotorola Toulouse SAS

ABSTRACT

How to deliver rich multimedia content to mobile usersin a resource-efficient manner is a great challenge to thecommunication society. The Satellite Digital MultimediaBroadcast (SDMB) system has emerged as a promisingsolution on the efficient delivery of the MultimediaBroadcast Multicast Service (MBMS) by implementing asatellite-based broadcast service to complement the 3Gand beyond 3G terrestrial mobile cellular networks.

The SDMB covers large parts of Europe by integratingboth mobile networks and satellite networks. This paperpresents a picture of the SDMB system focusing on Itsinterworking and Radio Resource Management (RRM)

Refereeing of this contribution was handled by M. DeSanctis.

Manuscript received March 9, 2006; revised June 21, 2006.

Released for publication April 27, 2007.

Authoras Current Address:L. Liang, L. Fan, H. Du, Z. Sun and B.G. Evans, CCSR, University of Surrey, Guildford,Surrey, GU2 7XW, UK; C. Sener and N. Chuberre, Alcatel Space, 12 rue de la Baume, 75008,Paris, France; M. Fitch, British Telecommunications, Public limited Company, BT, Exact(831), 81 Newgate Street, London ECIA 7AJ, UK; M. Cole, LogicalCMG UK Limited, 75Hampstead Road, London, NW I ZPL, UK; T. Boivin, Alcatel CIT. 8 rue de la Baume, 75008,Paris, France; and E. Buniout, Motorola Semiconductor SAS, Avenue General Eisenhower,BPI1029, 31023 Toulouse. France.

0885/8985/07/ USA $25.00 Q02007 IEEE

issues and solutions. It first presents an overview of theSDMB system; then the network architecture andinterfaces for the interworking between the SDMB andthe terrestrial network are specified. To support theinterworking on the access layer, we define the SDMBaccess layer that closely follows the Wideband CodeDivision Multiple Access (WCDMA) alr interface in orderto achieve maximum commonality with the TerrestrialUniversal Mobile Telecommunications System(T-UMTS). A proposed radio resource allocationalgorithm on the access layer leads to the optimisation ofradio resources.

INTRODUCTION

The multimedia content delivery to mobile networks canbe both streaming and content downloading. Theone-to-many transmission nature implies that broadcast andmulticast are efficient ways to distribute these contents. Anumber of technologies are under development to distributethose bandwidth-consuming applications in 3G mobilenetworks, which include Multimedia Broadcast & MulticastServices for 3G (MBMS), Digital Video Broadcasting -

Handhelds (DVB-H), as well as terrestrial and satelliteDigital Multimedia Broadcast (DMEB). MBMS [1, 2, 3, 5]were developed in the r~ Generation Partnership Project(3GPP) to provide both multicast and broadcast modes forthe 3G mobile networks to efficiently distribute one-to-manyservices. The SDMB takes advantage of the satellite-inherent

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capability to provide broadcast services over global coverage,to constitute an efficient way to deliver mobile multimediacontents to a potentially unlimited audience.

Using the Universal Mobile Telecommunications System(UMTS) standard, the SDMB system will complementmobile networks with broadcast and multicast capabilities forspectrum-efficient delivery of multimedia services to mobiledevices in both outdoor and indoor environments, withoutintroducing constraints on the user terminal or the consumer.To complement other mobile BroadcastlMulticast solutions,the Mobile Applications & sErvices based on Satellite andTerrestrial inteRwOrking (MAESTRO) integrated project [61is focusing on a satellite broadcast-based architecture toenhance 3G and beyond 3G systems in the delivery of mobilemultimedia broadcast services. The resulting hybridarchitecture makes the most use of satellite and terrestrialtechnologies efficiently. The output of the MAESTROhas been extended to the Digital Video Broadcasting -Handheld plus (DVB-H+). Former partners of theMAESTRO project, i.e., Alcatel Alenia Space, are planningto put the DVB-H+ satellite and terrestrial repeaters in themarket in the next two years.

We present the SDMB system in terms of the networkarchitecture and the access layer optimization. Its networkarchitecture enables the satellite system to be seamlesslyintegrated with the terrestrial 3G and beyond 3G mobileinfrastructures by extending and adapting the 3"' GenerationPartnership Project (3GPP) standards over a GEOstationary(GEO) satellite network. Its access layer uses a newmultiplexing scheme to achieve high utility of the satellitebandwidth.

The content described herein is presented in four sections.The first of these sections is the SDMB system overview thatgives the coverage and the capacity of the system as well asits business role models; the section entitled SDMB NetworkArchitecture and Interworking presents the SDMB networkarchitectures defining new interfaces and extendingBroadcast Multicast Service Centre (BM-SC) functions; thesection entitled SDMB Access Layer describes the SDMBaccess layer, to which a 2-level multiplexing scheme isproposed. Finally, the Conclusion draws the author'sconclusions for this paper.

SYSTEM OVERVIEW

The SDMB system is illustrated in Figure 1. It can provideanytime, anywhere broadcast services to mobile end users.

Multimedia contents are provided by the content providersand delivered via the high power GEO satellite broadcastcapacity to 3G mobile handset equipments using the 3GPPpush service. The mobile users can interact with the systemusing the terrestrial link provided by the mobile networks.The SDMB system is able to offer umbrella cells with atypical diameter of 700 to 1000 kmn to provide large areacoverage. This gives the advantage to integrate a large

Fig. 1. SDMB Concept Overview to enhanceMBMS delivery on 3G and beyond 3G Systems

number of scattered audiences and significantly reduce theretail service fee.

The system is unidirectional, covering large parts ofEurope with multiple geostationary satellite spot beams. Theoverall system is closely integrated into the architecture of2.5G/3G mobile cellular networks, in a design that aims tomaximize the reuse of technology and infrastructure, andminimize system development cost.

The SDMB service interactivity is achieved at two levels:

" The User Equipments' (UE) local storageenables immediate interactivity and contributesto decrease the access time resulting in anenhanced perceived Quality of Service (QoS);

" The 3G system point-to -point capabilityprovides service interactivity with the distantservice centre, when local interactivity cannotserve the user's requests.

The system infrastructure will typically aim at an averageavailability greater than 95% over the umbrella cell toaddress the 3G handset market. This requires that indoorsatellite coverage must be ensured, which implies large radiomargin, higher than 15 dB, specific reliable transport layersbased on Forward Error Correction (FEC), interleaving anddata carousel techniques, terrestrial repeaters, and selectiveretransmission using the 3G system point-to-point capabilityand/or the satellite direct return link.

Two role models have been identified in the SDMBsystem. The Aggregator Centric Model is centred on the roleof a content provider / aggregator contracting a satelliteoperator to provide broadcast capacity for the Aggregator'scontent to all suitably configured UEs, regardless of MobileNetwork Operator (MNO) affiliation. The MNO CentricModel is much more closely aligned to the MNO's business.Control remains exclusively within the MNO, who candecide whether given traffic should be sent via satellite orterrestrial means. This model is better suited to the option ofbroadcasting data via satellite to selected base stations and,

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MBMS Broadcast Mode

T SDMB Hub ____

repeater

MBMS Multicast Modeover T - UMITS

Fig. 2. Interworking Architecture

for the future when certain mobile handsets might include atransmission-to-satellite capability, is better suited to UMTSprovision in areas of poor terrestrial coverage.

SDMEB NETWORK ARCHITECTUREAND INTERWORKING

Interworking ArchitectureThis section describes the SDMB network architecture and

its interworking between SDMB satellite network and 3Gmobile networks.

Figure 2 illustrates the key functional elements within thenetwork that will be used to support the SDMB service.These elements include:

" SDMB-capable UE: The 3G handset has adual-mode and activates S-DMB features as abackground task in order to allow 3G defaultnetwork operations without requiring additionalWCDMA reception chain.

" SDMB Satellite: The satellite that will supportthe transmission of SDMB services to definedcoverage areas.

" SDMB Terrestrial Repeater: Repeaters may bedeployed to enhance the SDMB signalavailability for UEs in urban areas byretransmitting the satellite signal on the ground.

" SDMB Hub: The Hub controls broadcasttransmission over the SDMB satellite systemtaking media streams as input from theBroadcast Multicast Service Centre (BM-SC).

* M-SC: The functional entity that controls allaspects of the delivery of SDMB; servicesincluding authentication and authorisation ofsubscribers, the delivery of services over theSDMB network, as well as service billing.

Also in Figure 2 the Content Providers provide themultimedia contents to be delivered over the SDMB system.

The SDMB Satellite Hub (S-HUB) interfaces with the3GGP Multimedia BroadcastlMulticast Service (MBMS)BM-SC which needs to be upgraded to take into account theadditional WCDMA downlink carrier capacity. Moreover, anMBMS-capable 3G network actually opens up the potentialfor the BM-SC to apply policy based routing betweenterrestrial MBMS and satellite SDMB. The policies enablecontents to be broadcasted to UEs either over SDMB; satelliteor via the terrestrial network infrastructure using MBMSBroadcast services. Contents can also be delivered to UEsusing the MBMS Multicast services. For example, arelatively large multimedia service addressing largeaudiences over a scattered area will be routed to the satellitebroadcast network, whereas a football result addressing astadium audience will be delivered using the terrestrialcarrer.

One of the main implications of the introduction ofMBMS Multicast mode over the T-UMTS network is that theBM-SC now manages Join requests at the network level (inaddition to the service level):

" Handling explicit network join and leave (atboth network layer and application layer).

* Authentication and authorisation of the end user(at both network layer and application layer).

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/ --

over GPRS

A-9


Bearer managementprocesses

Hub

DIAMETER / RADIUS

TCP / UDP

IP /I P-Sec

L2

Phy

Gmb*

BM-SC

Fig. 3. Gmb * hearer control signalling plane

Authorisation may optionally be based upon theend user's location.

This is required to ensure the necessary routing path isestablished for the delivery of multicast packets over thenetwork. The BM-SC is now also required to control theactivation of multicast bearer resources within the T-UMTSnetwork.

InterfacesIn SDMB, the Hub is effectively performing the function

of a MBMS-capable Gateway General Packet Radio Service(GPRS) Support Node (GGSN) toward the BM-SC andexternal Public Data Networks. It is noted however that only

SDMBNetwork

Hub BM-SC

DIAMETER / RADIUS

TCP /UDP

IP /I P-Sec

L2

Phy

--- Fully

ContentProvider

iin andfission

Servicennouncemnent

function

To S-HUB

-Gi*-

Fig. 5. BM-SC functional structure

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Fig. 4. G1* User Plane

a subset of the MBMS GGSN functionality is required tosupport SDMB. In particular, the signalling interface Gmband data interface Gi toward the SDMB; Hub only need to beable to support the Broadcast Mode defined in the 3GPPspecifications [2, 4]. Furthermore, the interfaces, particularlyG.~, may need to support functionalities / attributes which arespecific to the SDMB system. For these reasons we refer tothe interfaces as G,,.,*' and G1* respectively, in SDMB. TheGe,t,* interface is principally required to provide the signallingplane interface to control establishment of broadcast bearersover the SDMB system (Hub to UE via satellite or satellite/terrestrial repeater). This includes the means to specifybearer-level QoS requirements and the geographic servicearea.

The ITU-T TSG CN3 work group is currentlyrecommending adoption of the Internet Engineering TaskForce (IETF) Authentication, Authorization, and Accounting(AAA) signalling protocol, Diameter [7], as the basis for theGmnb interface although Remote Authentication Dial In UserService [8] is equally capable of meeting the requirements onthis interface. This is shown in Figure 3 for the SDMB:

Higher layers(peered ith UE)

To GGSN

A-10


liE Uu

Fig. 6. SDMIB a

Q,* user plane interface for Broadcast transmission wasdefined for SDMB. The user plane interface is required tocarry IP traffic from the BM-SC to the satellite Hub fortransmission over the SDMB system. It is assumed that altraffic related to an SDMB service is carried in IP packetswith a distinct multicast-Internet address (i.e., Class Daddress). The use of multicast addressing and, whereapplicable, IETF multicasting procedures on the G,* interfaceshould not be confused with the broadcast nature of theSDMB system: it is assumed that the SDMB Hub has noinformation about the recipients of each SDMB service. G,*is proposed as Figure 4.

BM-SC Functional StructureWith the support of the new defined G,* and G.,,*

interface, the BM-SC can provide new functions in SDMB,such as G,* and G~,* interface support, and path choosingfunction, in addition to the service provisioning and deliveryfunctions as it does in MBMS systems [2]. It consists of a setof sub-functions; as shown in Figure 5:

" Membership Function: the SDMB membershipfunction provides authorization for UEsrequesting to activate an SDMB service in thecommercial scenarios where UE subscribed tomobile operators only or to both mobileoperators and aggregators.

" Session and Transmission Function: The SDMBsession and transmission function is able toschedule SDMB session transmissions.

" Proxy and Transport Function: Proxy andtransport function is a SDMB bearer servicefunction that is for signalling over G,,* interface

* SDMB HUB

cess scheme

between the S-HUBs and the other BM-SCsub-functions, e.g., the BM-SC membershipfunction and the session and transmissionfunctions.

" Service Announcement Function: The BM-SCService Announcement function is able toprovide service announcements for broadcastSDMB user services.

" Security Function: This function gives theBM-SC the ability to authorize and authenticateusers to access the SDMB services.

* Path Choosing Function: Path choosingfunction makes the decision for the BM-SC ifthe content data should be forwarded to thesatellite hub or the GGSN.

To perform the path choosing function, e.g., toterminate the data transferred to satellitenetworks and start transferring them to themobile networks, a new indicator should beadded.

" Satellite/Mobile Indicator is required to indicatethe BM-SC Proxy and Transport function whichpath message should be routed.

SDMEB ACCESS LAYER

Access Layer DefinitionThe SDMB radio access scheme follows closely the

WCDMA air interface in order to achieve maximumcommonality with the T-UMTS. Due to the unidirectional

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LogicalChannels ýDICH DCCII MG** MCCH MSC P

MIAC

Transport DCII DSCH~ FAC1TI PC"

PhysicalChannels DP DCII DPCI PSCI .CPC

AICH AP-AIC SHI

ECSIýCHJ [CDP/CA-ICH

DWCDMA channels releyant to SDMB

Fig. 7. WCDMA channels and relevance to SDMB

ICH

nature of the SDMB system and the point-to-multipointservices, only the subset of WCDMA functionalities requiredfor the support of common I point-to-multipoint channels isrelevant to SDMB. 3GPP specifications have been a startingpoint for the SDMB access scheme definition, andadaptations and modifications have been made to suit thesatellite environment.

The radio network layer within the SDMB access schemeis part of the control plane and is also organised intosub-layers, including the main one: the Radio ResourceControl (RRC) sub-layer. The user and control-plane layersof the SDMB access scheme are summarized in Figure 6.

1) SDMB Access Scheme ChannelsThe functionality of the SDMB radio interface layers is

organized into the concept of channels, each one grouping aspecific set of functions at the user and/or control planes. TheSDMB set of channels, as shown in Figure 7, is a subset ofthe WCDMA set of channels; only the downlink commonchannels are relevant given the unidirectional nature of thesystem and the point-to-multipoint services it provides. TheWCDMA logical channels relevant to SDMB are as follows:

" MBMS point-to-multipoint Traffic Channel(MTCH): it is used for a point-to-multipointdownlink transmission of user plane informationbetween networks and UEs [91.

" MBMS point-to-multipoint Control Channel(MCCH): it is used for a point-to-multipointdownlink transmission of control planeinformation between networks and UEs [9].

* Broadcast Common Control Channel (BCCH):it carries fundamental signalling information in

the SDMB Radio Access Network and itsreception is mandatory for all terminals.

The SDMB-relevant WCDMA transport channels are theForward Access transport CHannel (FACH), which is adownlink transport channel for data transmission, and theBroadcast CHannel (BCH), which is used to broadcastsystem and cell specific information. Their use in SDMBdoes not introduce additional issues.

The WCDMA physical channels relevant to SDMB are asfollows:

" Primary Common Control Physical CHannel(P-CCPCH), which is used to carry the BCHtransport channel.

* Secondary Common Control Physical CHannel(S-CCPCH). which is used to carry the FACH.

" Synchronisation CHannel (SCH), which is adownlink signal used for cell search.

" Common Pilot CHannel (CPICH), which is thephysical channel used to carry the pagingindicators.

" MBMS Notification Indicator Channel (MICH),which is a new MBMS-specific Paging IndicatorCHannel (PICH) used to send the MBMSnotification indicators, thus enabling the UE tobe informed about imminent or on-goingtransfers [9].

2) SDMB Radio Link Layer DefinitionThe SDMB radio access layer protocols comprising the

Radio Resource Control (RRC), the Packet Data

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Fig. 8. MBMS Notification, RB Setup, and Data Transfer procedures

Convergence Protocol (PDCP), the Radio Link Control(RLC), and the Medium Access Control (MAC) sub-layersimplement a subset of those functionalities defined inT-UMTS. The RRC is responsible for the broadcast ofinformation related to the non-access stratum layers andaccess stratum layers; the establishment, reconfiguration andrelease of radio bearers; and the initial spot beam selection,but does not implement any of the functions related to RRCconnection given that there is no direct satellite return linkwithin the baseline architecture. For the system informationbroadcast, the RRC includes specific parameterconfigurations required for the SDMB system. The PDCPprovides header compression and decompression of IP datastreams. Similar to MBMS, the Unidirectional mode(U-mode) of the RObust Header Compression (ROHC)protocol is the only operation mode supported in SDMBsince the packets are sent only in one direction from theSDMB Radio Access Network (RAN) to the UE, and there isno return path from the decompressor (located at the UE) tothe compressor (located at the SDMB RAN). As for the RLC,only the transparent mode (for BCCH) and unacknowledgedmode (for the three newly defined MBMS logical channels -MCCH, MSCH, and MTCH) are applicable, which includessupport for the added RLC unacknowledged modefunctionality defined for MBMS such as out of sequenceService Data Unit (SDU) delivery. All of the newly-definedfunctionalities associated with MAC for MBMS such asbuffering, and the addition and reading of MBMS-ID are alsosupported in SDMB.

Given the unique nature of the SDMB system and thatonly the MBMS broadcast mode is supported, only a subsetof those MBMS UMTS Terrestrial Radio Access Network(UTRAN) procedures described in [9] is pertinent to SDMB.

Figure 8 shows three main procedures for the delivery ofthe MBMS services within SDMB radio access network -

notification, radio bearer establishment, and data transfertriggered by the session-start procedure of BM-SC.

Radio Resource Management SchemesRadio resources in satellite networks such as bandwidth,

transmit power and codes are generally limited due to thephysical and regulatory restrictions as well as theinterference-limited nature of CDMA networks. In order tosupport high user densities in CDMA networks, whilemaintaining high quality in the wireless links, radio resourcemanagement is essential. In order to maxim-ize the overallSDMB system capacity, a Radio Resource Allocation (RRA)has been proposed. The performance of the proposed RRAhas been evaluated via simulation studies and compared withexisting schemes. The obtained results will be used asrecommendations for the optimum SDMB systemconfiguration and algorithm selection at the access layer.

The RRA is responsible for estimating of the requirednumber of logical / transport / physical channels, andmapping them together with the actual Transport FormatCombination Set (TFCS) for each physical channel [101.Previous research on the channel mapping has used aconventional single-stage bin-packing algorithm [11 ], whichassumes that the MBMS MTCH are mapped one-to-one ontothe Forward Access CHannel (FACH) transport channels,which are subsequently multiplexed onto the SecondaryCommon Control Physical CHannel (S-CCPCH). This typeof channel mapping which considers only a single-level ofmultiplexing at the physical layer is shown in Figure 9A. Theproblem with this simple one-to-one mapping at the transportchannel is that there exists residual capacity on the transportchannel which is not utilized when the bit rate of the logicalchannel does not exactly match the corresponding bit rate ofthe transport channel, i.e., the MTCH rate is less than theFACH rate.

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Logical channel

Transport channel

Physical channel

Logical channel

Transportzhannel

Physical channel

(11)

0))

Fig. 9. Channel mapping options considering:Fig. 9A. Transport channel multiplexing

Fig. 9B. Logical and transport channel multiplexing

In order to resolve the resource utilisation inefficiencyexperienced in single-level channel multiplexing scheme, anoptimised two-level channel multiplexing approach has beenproposed [12]. This algorithm performs channel multiplexingat both transport and physical channels. At the first level ofmultiplexing, multiple logical channels are mapped onto asingle transport channel (logical channel multiplexing);whereas the mapping of several transport channels onto aphysical channel (transport channel multiplexing) is regardedas the second level of multiplexing as shown in Figure 9B.The introduction of MBMS-ID field and the Target ChannelType Field (TCTF) in newly standardized MAC-in headermakes logical channel multiplexing become a feasiblesolution in designing efficient RRA multiplexing schemes.Aiming at achieving the highest possible degree of utilisingthe residual capacity on transport and physical channels, atwo-stage bin-packing with optimum estimation algorithmhas been proposed to extend the research in [12]. It must alsobe noted that it is generally assumed that only services withsimilar characteristics and QoS requirements are multiplexedtogether to the same transport channel.

There are four steps for the 2-stage bin-packing channelmultiplexing. The first step is to estimate the number of therequired MTCHs for each stream service that is the numberof servers that will guarantee the target blocking probability.The second step is to estimate the intermediate-bins (FACHs)required, which will be used in the next step of 2-levelchannel multiplexing. Optimum estimation algorithm isapplied at this step, which compares the set of requiredMTCHs' bit rates and the set of available FACHs' bit rates tofind the best fit to achieve both minimum FACH residualcapacity and minimum number of required FACHs. This stepfinishes the first stage of channel multiplexing (logical

channel multiplexing) and leads to the maximum utilisationon both FACHs and S-CCPCHs. Best-Fit bin-packingalgorithm [11], where the FACH is assigned to a feasible bin(S-CCPCHs, if any) having the smallest residual capacity, ischosen as the mapping algorithm in the second stage ofchannel multiplexing (transport channel multiplexing) in thatit achieves the best performance under certain bin-packingmapping conditions.

In order to evaluate the performance of 2-level channelmultiplexing, simulation has been carried out for a widerange of different traffic mixes and physical channelcapacities, as highlighted below:

" Traffic mix of x% streaming service and (I1-x)%download service: 80% - 20%; 50% - 50%;20% -80%

" S-CCPCH configurations: 3 x 384 kbps;2 x384 kbps; 1 x 384 kbps; 3x 128kbps;1 x 384kbps +3 x 128 kbps

The traffic mixes herein refer to the capacity allocated to(reserved for) each type of services (streaming, download)assuming implicitly a fixed boundary for the capacity.

Typical scenarios illustrated in this article:

" Scenario 1: 3 S-CCPCHs of 384 kbps each, withtraffic mix of 80% for streaming and 20% fordownload;

" Scenario 2: 3 S-CCPCHs of 384 kbps each, withtraffic mix of 50% for streaming and 50% fordownload.

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V ',aý


MTCHs 256 LŽ1 3

FACHs 256 l~ 256 ~256 [7

S-CCPCHs 3Z84

W: Streaming IM Download R Streaming + Download

Fig. 10. Channel mapping structure utilizing 2-stagebin-packing algorithm combination for Scenario 1

1400

120

o1000

800

600

g400

*~200

0

Scenario I Scenario 2

Hk --

Single-level1 I ~Single-levelN Streamning FAClh 0 Domiload FACHs 0 Residual caliwity of FAC~h

Fig. 11. Comparison of FACHs capacity utilisation between single-leveland 2-level channel multiplexing under different traffic mixes

The overall channel mapping configuration for Scenario 1is illustrated in Figure 10. After the mapping for thestreaming services (MTCHs) has been performed, there is noresidual capacity on streaming FACHs, whilst there areresidual capacities on S-CCPCHs, which are assigned todownload FACHs for carrying download services. Forinstance, the 128 kbps residual capacity on S-CCPCH 3 isallocated to one download FACH 6, which in turn is assignedequally in capacity to 2 MTCHs of 64 kbps each, so as toaccommodate two download applications.

The simulation results show that the proposed 2-levelchannel multiplexing achieves higher utilisation on FACHsthan single-level multiplexing by assigning more MTCHsinto them. As seen from Figure 11, there is a fairly largeamount of residual capacity, which could not be furtherutilized and appears as a pure waste of capacity onFACHs/S-CCPCHs, remaining in FACHs in single-levelmultiplexing for both scenarios. Numerically, these residualFACH capacities for Scenario I and 2 are: 704 kbps and 640kbps, respectively, which correspond to 61.1% and 55.6% oftotal FACH capacities. However, by applying 2-levelmultiplexing, these residual capacities are further fullyutilised and zero residual FACHs capacities have beenachieved for both Scenarios. As seen from Figure 12, theproposed 2-level multiplexing also increased the transmissioncapacity over limited physical channel capacity. By usingsingle-level multiplexing, the total MTCH transmissioncapacity (streaming and download) is 448 kbps and 480 kbps

for Scenario 1 and 2, respectively. However, when theproposed 2-level multiplexing is applied, the total MTCHtransmission capacity over the same lower layerFACHs/S-CCPCHs is significantly increased to 1152 kbpsand 1088 kbps, respectively, which in effect leads to betterradio resource utilisation.

CONCLUSIONS

The innovative SDMB concept proposed in theMAESTRO project can provide wide coverage and cheapservice for multimedia content broadcasting to complement3G and beyond 3G mobile networks. It's fully compatiblewith IP and designed based on the 3GPP MBMS standards,which allow us to easily integrate SDMB with the terrestrialmobile networks.

The proposed SDMB network architecture providesflexibility to enable operators to gradually adopt powerfulfunctions to distribute media to their subscribers with fullcompatibility with MBMS systems. The enhanced BM-SCand new interface between the BM-SC and the satellite HUBmakes it feasible to support both SDMB satellite broadcastand MBMS mobile one-to-multipoint delivery to adaptdifferent network situations and subscriber distributions.

The access layer is defined for SDMB that follows closelythe WCDMA4 air interface in order to achieve highcommonality with the T-UMTS. To resolve the resourceutilisation inefficiency experienced in single-level channel

IEEE A&E SYSTEMS MAGAZINE, JULY 2007 INSERT A1

Twio-IevelT"o-leve

A-15


-- U Streaming M'IHs*Download MIEHs

-Scenario 1

Scenario 2

0 200 400 600 g00 1000 1200 1400

111lantmlsalon capacity of streaming and download MTCH9(kbps)

Fig. 12. Comparison of total M[TCHs transmission capacity between single-leveland 2-level channel multiplexing under different traffic mixes

multiplexing scheme of the RRA, an optimised two-levelchannel multiplexing approach has been proposed. Thesimulation showed that this scheme achieved the maximumutilisation on FACHs by assigning more M[TCHs into themand increased the transmission capacity over limited physicalchannel capacity comparing to the conventional single levelmultiplexing.

ACKNOWLEDGEMENT

This work was performed within the framework of theproject MAESTRO IST-2003-507023, which is funded bythe European Commission (EC). The authors express theirgratitude to EC for providing the funding, and all theMAESTRO partners for their valuable discussions.

REFERENCES

[I] Multimedia Broadcast/ Multicast Service; Stage 1,3GPP TS 22.146 v6.2.0, September 2004.

[2] Multimedia Broadcast / Multicast Service; Architecture andfumctional description, (Release 6),

3GPP TS 23.246 v6.8.0, October, 2005.

[3] MBMS CNlI procedure description (Release 6),3GPP TR 29.846 1.00 (2003-10).

[4] Interworking between the Public Land Mobile Network (PLMN)supporting packet based services and Packet Data Networks (PDN),

(Release 6), 3GPP TS 29.061 V6.6.0, October, 2005

[5] Introduction of the MBMB in the Radio Access Network(Stage 2, Release 6),

3GPP TS 25.346 V2.4.0 (2003-11).

[6] MAESTRO website:http://ist-maestro.dyndns.orgtMAESTRO/index.htrn.

[7] P. Calhoun, J. Loughney, E. Guttman, Gl. Zorn and J. Arkko,Diameter Base Protocol,

IETF RFC 3588, September 2003.

[8] C. Rigney, S. Willens, A. Rubens and W. Simpson,Remote Authentication Dial In User Service,

=ET RFC 2865, June 2000.

[9] 3GPP TS 25.346 V6.3.0:Introduction of the Multimedia Broadcast/Multicast Service(MBMS) in the Radio Access Network; Stage 2 (Release 6),

December 2004.

[10] 3GPP, Technical Specification TS 25.301 V6.2.0,Radio Interface Protocol Architecture,

March 2005.

[11] S.Martelo and P.Toth,Knapsack problems: Algorithms and computer implementations,

John Wiley & Sons Ltd., 1990.

[12] H. Du, L. Fan and B.G. Evans,Two-level Channel Multiplexing: A Novel Radio ResourceAllocation Strategy for Satellite Digital MultimediaBroadcast System,

ICC 2006, Istanbul, Turkey, I1I- 15 June 2006.

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