Outline Wireless introduction Wireless cellular (GSM, CDMA, UMTS, WiMAX) Wireless LANs, MAC layer Wireless Ad hoc networks routing: proactive routing, on-demand routing, scalable routing, geo-routing multicast TCP QoS, adaptive voice/video apps Sensor networks

Cellular Wireless Network EvolutionFirst Generation: Analog voiceAMPS: Advance Mobile Phone SystemsResidential cordless phonesFDMASecond Generation: Digital voiceGSM: European Digital Cellular - TDMA IS-54/136: North American - TDMAIS-95: CDMA (Qualcomm)DECT: Digital European Cordless Telephone

Cellular Evolution (cont)Third Generation: Packet datawill combine the functions of: cellular, cordless, wireless LANs, paging etc.will support multimedia services (data, voice, video, image)Requirements384 Kbps for full area coverage2 Mbps for local area coveragevariable bit ratepacket traffic supportflexibility (eg, multiple, multimedia streams on a single connection)

Cellular Evolution (cont)Third Generation: Packet data2.5 GGPRS (for GSM) (General Packet Radio Service )EDGE (for GSM) (Enhanced Data rates for Global Evolution)1xRTT (for CDMA) 3G (W-digital CDMA)IMT-2000/UMTS (International Mobile Telecommunications) (Universal Mobile Transport Service)CDMA 2000, WCDMA, TD-CDMA, TD-SCDMA3+G, 4G systemsOFDM, Software radio, Array antennasWiMAX

Multiple Migration Paths Are Available2G2.5G3G3+G4GPDCGSMTDMA (IS-136)CDMA (IS-95A/B)WCDMAHSPDAOFDMSoftware radioArray antennasGPRSEDGECdma One1XRTT1XEVDO/HDR1 xtreme

cdma2000MC-3XWiMAX

ArchitectureSystem architecturenetworkingaddressingPhysical (PHY) layerradio bandmodulationerror control (FEC/interleaving)frame structuremultiple access (multi-user, up/down)MAC/DLC layerchannel mapping (control/traffic) medium access techniquescall setupstandby behavior

Cellular ConceptGeographical separationCapacity (frequency) reuseBackbone connectivity

1G: AMPS (Advanced Mobile Phone System) ---- FDMAChannels are divided into 4 categories:1. Control (base to mobile) to manage the system2. Paging (base to mobile) to alert mobile users to incoming calls3. Access (bidirectional) for call set up and channel assignment4. Data (bidirectional) for voice, FAX, or data Frequencies are not reused in a group of 7 adjacent cells To add more users, smaller cells can be used In each cell, 57 channels each for A-side carrier and B-side carrier respectively

HandoffHandoff: Transfer of a mobile from one cell to anotherEach base station constantly monitors the received power from each mobileWhen power drops below given threshold, base station asks neighbor station (with stronger received power) to pick up the mobile, on a new channelThe handoff process takes about 300 ms

Organization of Cellular Networks

To register and make a phone callWhen phone is switched on , it scans a preprogrammed list of 21 control channels, to find the most powerful signalIt transmits its ID number on it to the MSC which informs the local HLRadds it to VLR and informs the home MSC which informs the HLRregistration is done every 15 minTo make a call, user transmits dest Ph # on random access channel; MSC will assign a data channelAt the same time MSC pages the destination cell for the other party (idle phone listens on all page ch.)

How does a call get to the mobile ?Suppose (310) 643 - 1111 is roaming in the (408) area code Cell phone registers with the (408) MSC, which adds it to (408) VLR and informs the (310) HLR of the location of the cell phoneA call comes in for (310) 643 1111. Then (310) MSC queries its HLR, and directs the call to the (408) MSCThe (408) MSC forwards the call to the mobile

(Freq DivisionDuplex)

2G: Digital Cellular: IS-54 TDMA SystemSecond generation: digital voice FDMA / TDMASame frequency as AMPS 416 chEach 30 kHz RF channel is used at 48.6 kbps6 TDM slots/RF band (2 slots per user)8 kbps voice coding 16.2 kbps TDM digital channel (3 channels fit in 30kHz)4 cell frequency reuse (not 7)Capacity increase per cell per carrier3 x 416 / 4 = 312 (instead of 57 in AMPS)Additional factor of two with speech activity detection.

IS-54 slot and frame structure BASE TO MOBILE

2G: European GSM (Group Special Mobile)Second Generation: Digital voiceFDMA / TDMAFrequency Division duplex (890-915 MHz Up; 935-960 MHz Down)125 frequency carriers, Carrier spacing: 200 Khz8 channels per carrier (Narrowband Time Division)Physical ch 124x8 = 992, reuse factor N = 3 or 4Capacity per cell per carrier: 992/ N = 330 or 248 Speech coder: linear predictive coding (13 Kbps)Modulation: Frequency Shift Keying (Gaussian Minimum Shift Keying)Multilevel, time division frame structureSlow frequency hopping to overcome multipath fading

BCCH: Broadcast Control Channel point-to-multipoint unidirectional control channel broadcasting system information to MS CCCH: Common Control Channelup-link: RACH (Random Access CHannel)down-link: PCH (Paging CHannel) AGCH (Access Grant CHannel) DCCH: Dedicated Control CHannel point-to-point bidirectional control channelSACCH (Slow Associated Control CHannel)FACCH (Fast Associated Control CHannel)SDCCH (Stand Alone Dedicated Control CHannel)GSM Signalling channels

Access techniques for mobile communicationsP - PowerT - TimeF - FrequencyPTPTFPTFFDMA (TACS)TDMA (GSM, DECT)CDMA (UMTS)FATDMA (UMTS)

Spread Spectrum

CDMA (Code Division Multiple Access)unique code assigned to each user; i.e., code set partitioningall users share same frequency, but each user has own chipping sequence (i.e., code) to encode dataNote: chipping rate >> data rate (eg, 64 chips per data bit)encoded signal = (original data bit) X (chipping sequence)decoding: inner-product of encoded signal and chipping sequenceallows multiple users to coexist and transmit simultaneously with minimal interference (if codes are orthogonal)

CDMA Encode/Decode

CDMA: two-sender interference

Orthogonal Variable Spreading Factor

CDMA (Code Division Multiple Access): IS-95 QUALCOMM, San Diego Based on DS spread spectrum

Two frequency bands (1.23 Mhz), one for forward channel (cell-site to subscriber) and one for reverse channel (sub to cell-site)

CDMA allows reuse of same spectrum over all cells. Net capacity improvement: 4 to 6 over digital TDMA (eg. GSM) 20 over analog FM/FDMA (AMPS)

CDMA (contd)One of 64 PS (Pseudo Random) codes assigned to subscriber at call set up time RAKE receiver (to overcome multi path-fading)Pilot tone inserted in forward link for:power controlcoherent referenceSpeech activity detection Voice compression to 8 kbps (16 kbps with FEC)IS-95: 20 wideband channels, BW=1.25 MHz

Third generation services-- vs 2G2M

384K

64K

32K

16K

9.6K

2.4K

1.2Kpoint to pointmultipointbidirectionalunidirectionalmulticastvideoconferenceremote medicalservice videocatalogueshoppingvideoondemandmobileTVinternettelephoneconferencetelephonevoice mailelectronicnewspaperISDNelectronicpublishingFAXdistributionservices(data)mobile radiodistributionservices (voice)pager

Third generation bandwidth assignment -- high frequency 2 GHz, wideband 150 MHzIMT-2000 IMT-20001885202519202010MSS198021102200MSS2170MHzITUIMT-2000IMT-20001880202519002010MSS198021102200MSS2170MHzEUROPEDECTJAPANIMT-2000IMT-2000188520251918.12010MSS1980211022002170MHz1895MSSPHS

UTRAN Architecture(UMTS Terrestrial Radio Access Net)Core NetworkRNCRNCRNSUTRANRNSIubIubIubIubIurIuIuB-nodeB-nodeB-nodeB-node

W-CDMA (Wide Band CDMA)Key featuresImproved capacity and coverage (over second generation); thus, backward compatiblehigh frequency 2 GHz, wideband 150 MHzHigh degree of service flexibility: multiple, parallel services per connection; efficient packet accessOperator flexibility: asynchronous interstation operation; hierarchical cell structures (HCS); adaptive antenna arrays (enabled by uplink pilot symbols); TDD (Time Division Duplex) mode for asymmetric traffic & uncoordinated environments

Radio Interface - protocol architectureRLCRLCLACLACRLCRRCLACMACPhysical LayerL3L2/LACL2/MACL1C-planeU-planeLogicalchannelsTransportchannelsRLC

Layer 1 - up link physical channels(W-CDMA example)DataPilotDedicated PhysicalData Channel Dedicated PhysicalControl ChannelTransmitpower controlTransportformat ind.Slot#1Slot#2Slot#iSlot#15Frame#1Frame#2Frame#iFrame#720.667 ms10 msFeedbackindicatorframesuperframe

Uplink Variable Rate1-rate10 msVariablerate1/2-rate1/4-rate0-rate: DPCCH (Pilot+TPC+RI): DPDCH (Data)R = 1R = 1/2R = 0R = 0R = 1/2

Layer 1 - down link physical channels(W-CDMA example)DataSlot#1Slot#2Slot#iSlot#15Frame#1Frame#2Frame#iFrame#72PilotTPCTFIDPCCHDPDCHframesuperframe0.667 ms10 ms

Downlink Variable Rate (DTX based)1-rate1/2-rate1/4-rate0-rate0.625 ms: DPCCH-part (Pilot+TPC+RI): DPDCH-part (Data)

Transport channels (example) Dedicated Channel (DCH): fast change of bit rate (10ms)fast power controlinherent MS addressing

Random Access Channel (RACH) - up link:collisionopen loop power controlexplicit MS addressing

Broadcast Control Channel (BCH) - down link Forward Access Channel (FACH) - down link:slow power controlexplicit MS addressing

Paging Channel (PCH) - down link:use of sleep modes

Multiplexing transport channels ontophysical channels

MS physical layer up-down linkexample of multiplexingmappingphy chphy chDCHDCHDCHCoding and multiplexingUp linkmultiplexingphy chphy chDCHDCHDCHdecoding and demultiplexingphy chphy chphy chphy chCell 1Cell 2Cell 3phy chTFI transmittedon the controlchannelDown link

MAC Services and Functions set-up, release of logical channels data transfer service on logical channels allocation/re-allocation of radio resources measurement report Selection of the transport format Handling of priority within one user/between users Scheduling of control messages (broadcast, paging, notification) Multiplexing/de-multiplexing of higher layers PDUs on/from common or dedicated transport ch. Contention control on the random access channelFunctionsServices

Retransmission Protocol - services and functions Layer 2 connection set-up & release transparent data transfer unacknowledged data transfer acknowledged data transfer connection control segmentation and re-assembly error detection/recovery and in-sequence delivery transfer of user data flow control duplicate detection QoS adaptationFunctionsServicesRCLP PDURCLP PDURCLP PDU160 bit160 bit160 bit10ms10ms32kbit/s16kbit/s

Radio Resource Control (RRC)- functions Broadcast of information provided by the Core Networkrelated to the access segment Set-up, maintenance and release of an RRC connection Set-up, maintenance and release of radio bearers on the user plane Assignment, reconfiguration and release of radio resources for the connection Arbitration of radio resource allocation between cells RRC connection mobility functions Quality of Service control and radio resource allocation among the cells Admission and congestion control Control of the MS measurement reporting

TD-CDMA (TDD-Time Division Duplex)DetectionCoherent, based on midamble

TDD Frame Structuremultiframe =24 frames (240 ms)frame = 15 TS (10 ms)DLULUL->DLcodes023BCCH RACH DL TCH UL TCH 015switching points DL->UL

Packet Data ServiceIn W-CDMA, data pkts can be transmitted in 3 ways:(a) RACH (Random Access Channel): used for small amount of data; no reservations, thus low latency; but, collisions and no power control (on RACH)

Packet Data Service (cont)(b) Request a dedicated channel (like VC setup): MS sends a Res Req msg (on RACH) with traffic specs; network returns a Req All + Cap All (with transport formats) on FACH, if resources are available; Cap_All may be issued separately (later) if the network load is high; MS transmits after receiving the Cap All.

Packet Data Service (cont)(b) Request a dedicated channel (like VC setup):

Packet Data Service (cont)(c) use existing dedicated channel (before it expires): if a DCH was recently used, go ahead and tx the unscheduled pkt on that channel. If timer expired, the MS can still omit the Res Req and issue just the Cap All

Real Time ServicesMS issues Res_Req on RACH (or on DCH if it has one going)Network issues Res All (with TF parameters)MS starts transmission immediately (no wait for Cap_All)Network may later reduce/restore the TF depending on load fluctuations

Congestion ControlCongestion may occur even after careful admission controlWithout cong. control, mobiles tend to increase their tx power, to combat interference, thus aggravating the problemSolutions: (a) lower bit rate of users insensitive to delay (b) perform interfrequency handovers (c) remove connection(s)Congestion control remedies activated by load thresholds

WiMAX - IEEE 802.16a - 3G/4G? Worldwide Interoperability for Microwave Access (WiMAX) is an industry trade organization to promote and certify compatibility and interoperability of broadband wireless access equipments that conform to the IEEE 802.16a specified wireless metropolitan area networks (WMAN)IEEE 802.16a - support WMAN operating at 2-11 GHz that will provide broadband wireless connectivity to fixed, portable and nomadic devicesIt supports WMAN to connect 802.11 hot spots to the Internet providing a wireless alternative to cable and DSL for last mile broadband access

Wireless Access Network (WAN)A WAN provides network access to buildings through exterior antennas communicating with central radio base stations (BSs)The WAN offers an alternative to cabled access networks such as fiber optic links, coaxial systems using cable modems and DSL linksIt serves as an access network bringing broadband service of the Internet access to buildingsUsers inside the building can connect to it with Ethernet or WLANsThe design may allow the extension of the WAN protocols directly to the individual user

WAN ConfigurationThe core components of a WAN system are the subscriber station (SS) and the base station (BS)A BS and one or more SSs can form a cell with a point-to-multipoint (P2MP) structureThe BS controls activity within the cell including access to the medium by SSs, allocations to achieve QoS and admission to the networkMultiple BSs can be configured to form a cellular wireless network. The radius of a cell can be 2-40 km while practical one is around 7-8 km with data rate as 70 Mbps per RF channel at a BSA point-to-point (P2P) or mesh topology also supported by the IEEE 802.16 standard

WMAN (wireless metropolitan area networks)

Protocol Stack

WiMAX: Physical LayerWiMAX can operate in both licensed and unlicensed bandsThe 2.5 and 3.5 GHz licensed bands will be the most common bands for WiMAX applicationsOn 2.4 GHz and 5 GHz non-licensed bands, their usage could be limited due to interference, which can degrade QoS servicesThe minimum channel bandwidth for WiMAX usage is 1.75MHz per channel, while 10 MHz is considered as an optimum

WiMAX: Physical LayerIEEE 802.16a standard featured with 256 OFDM physical layer specification conforms the ETSI HiperMAN standardsOFDM (Orthogonal Frequency Division Multiplexing) Multi-Carrier Modulation

WiMAX: Physical LayerThe transmission time is divided into frames that are divided into slotsIn an FDD system, uplink (SS to BS) and downlink (BS to SS) subframes are time aligned on separate frequency channelsIn a TDD system, each frame is divided into a downlink subframe and an uplink subframeIn both modes, the length of any frame can vary under the control of the BS schedulerIn TDD mode, the length of any uplink and downlink subframe can also vary, allowing asymmetric allocation between uplink and downlink

WiMAX: Physical LayerIEEE 802.16 has specified several physical layers:physical layer for 10-66 GHzphysical layer for 2-11 GHz, which can be further divided into subgroups

WiMAX: MAC Layer FeaturesThe on-air timing is based on consecutive frames that are divided into slotsThe size of frames and the size of slots within the frames can be varied under the control in the BSThe 802.16 MAC provides a connection-oriented service to upper layers of the protocol stackThe QoS parameters for a connection can be varied by the SSs making requests to the BS to change them while a connection is maintainedWhile extensive bandwidth allocation and QoS mechanisms are specified, the details of scheduling and reservation management are left unstandardized

WiMAX: MAC Layer FeaturesMAC protocal data units (MPDUs) are transmitted in time slots. MPDUs are the packets transferred between the MAC and the PHY layerA privacy sublayer performs authentication of network access and connection establishment, key exchange and encryption of MPDUsMAC service data units (MSDUs) are the packets transferred between the top of the MAC and the layer aboveA convergence sublayer at the top of the MAC enables Ethernet, ATM, TDM voice and IP services to be offered over the MAC layer

WiMAX: MAC Layer FeaturesThe MAC is concerned much with performing the mapping from MSDUs to the MPDUsAcross MPDUs, MSDUs can be fragmented. Within MPDUs, MSDUs can be packed (aggregated). Automatic retransmission request (ARQ) is used to request the retransmission of unfragmented MSDUs and fragments of MSDUs

WiMAX: MAC Layer FeaturesEach connection in the uplink is mapped to a scheduling service associated with rules for BS to allocate the uplink capacityThe specification of the rules and the scheduling service for a particular uplink connection is negotiated at setup4 scheduling services defined in the standardUnsolicited grant service (UGS) carries traffic of periodical fixed units of data. The BS grants of the size negotiated at setup regularly and preemptively without an SS request.

WiMAX: MAC Layer FeaturesUsed with UGS, an SS can report status of its transmission queue and request more by the grant management subheaderThe BS can allocate some additional capacity to the SS to allow it recover the normal queue stateThe real-time polling service serves traffic with dynamic nature and offers periodic dedicated request opportunities to meet time requirementsAn SS issues explicit requests and capacity is granted only as the real need. The overhead and latency is more. It is well suited for connections carrying VoIP, streaming video or audio traffic

WiMAX: MAC Layer FeaturesThe non-real-time polling service is similar to the real-time polling service. But connections send bandwidth requests by random access. The served traffic needs to tolerate longer delays and is insensitive to delay jitter suitable for Internet access with a minimum guaranteed rate;A best effort service is defined without throughput and delay guarantees. An SS can send requests for bandwidth by random access or dedicated transmission opportunities if available.

WiMAX: Mesh NetworksThree types of important nodes in Mesh systems:The SSs with direct links to a node are the neighbors of the node. A nodes neighbors are one-hop away from the node.Neighbors of an SS form a neighborhood. `An extended neighborhood contains all the neighbors of the neighborhood.

WiMAX: Mesh Networks

WiMAX: Mesh Networks --centralized scheduling The centralized scheduling is more determined than that in the distributed scheduling modeThe network connections and topology are the same as in the distributed scheduling modeThe request and grant process uses the Mesh Centralized Scheduling (MSH-CSCH) message The BS determines the flow assignments from the resource requests from the SSsThen, the SSs determine the actual schedule from the flow assignments

WiMAX: Mesh Networks -- coordinated distributed scheduling In the coordinated distributed scheduling mode, all the nodes shall coordinate their transmissions in their extended two-hop neighborhoodControl portion of each frame is used to regularly transmit its proposed schedule on a PMP basis to all its neighborsWithin a given channel, all neighbors receive the same scheduleAll stations in a network shall use the same channel to transmit schedule information in a format of specific resource requests and grantsCoordinated distributed scheduling ensures that transmissions are scheduled without a BS

WiMAX: Mesh Networks -- Uncoordinated distributed scheduling Uncoordinated distributed scheduling can be used for fast, ad-hoc setup of schedules on a link-by-link basis, established by directed requests and grants between two nodesData and control traffic are scheduled to avoid collisionsBoth the coordinated and uncoordinated distributed scheduling employ a three-way handshake with MSH-DSCH message:Request is sent to seek availabilities indicating potential slots requested and actual schedule. Grant is sent indicating a subset of the suggested availabilities that fits the request. Grant confirmation is sent back by the requester

WiMAX: Mobility SupportsSimilar to the GSM networks, the standard of IEEE 802.16e introduces Handover schemes to migrate a mobile station from the air-interface of one base station to another to provide mobilityPre-handover process has been designedThe entire Handover process consists of the following five stages:Cell ReselectionHandover Decision and InitiationSynchronization to Target BS downlinkRangingTermination with the Serving BSAnd some special scenarios of Handover process has been defined

Research Issues: QoS ServiceIEEE 802.16d has been designed to support multimedia service with different QoS requirementsThe BS can determine the number of time slots that each SS will be allowed to transmit in an uplink subframeIEEE 802.16d has defined:The framework to support QoS service in the PMP topologyThe signaling mechanism for information exchange between BS and SS such as the connection set-up, BW-request, and UL-MAP The uplink scheduling for UGS service flow IEEE 802.16 has not defined: The uplink scheduling algorithms to implement QoS to rtPS, nrtPS, and BE service flowThe admission control and traffic policing scheme

Research Issues: Mesh NetworksIEEE 802.16d has been designed to support mesh networks in order to extend the coverage of one BS and serve more SSs with limited resourcesThe standard has defined a framework to effectively schedule the traffic among remote SSs, relay SSs, and the BSIEEE 802.16d has defined:The centralized and 2 distributed scheduling mechanisms for information transmission and the Internet access from remote SSsThe management messages to deliver the scheduling informationIEEE 802.16d has not defined: The detailed scheduling algorithms to implement 3 traffic scheduling strategiesThe QoS issue and the scheduling algorithms to ensure the QoS in the mesh networking

Research Issues: Mobility SupportsThe IEEE 802.16e standard has defined the procedures to support mobilityBut the standard has not defined any decision algorithm to decide when to perform a handoverThe challenge of the research on mobility support is how to design quick handover decision algorithms to perform fast handover and ensure the QoS during and after the handoverAnother challenge is to how to combine the mobility support with mesh networking to implement an mobile WiMax mesh networkAnother issue is to establish a comprehensive mobility management system to systematically control the mobility support

WiMAX

In order to drive the various functions needed to manage connections and mobility, one (or more) slots of the TDMA frame are devoted to carry logical channels for signalling and control purposes. BCCH carries in a point-to-multipoint manner all the system information needed to the mobile terminals roaming in that cell CCCH on the up link carries the random access channel, accessed with contention by all the mobiles roaming in the cell; on the down link, two logical channels are time multiplexed on CCCH, namely: the paging channel, addressing the mobile which is requested by an incoming call the access grant, carrying the acknowledgements to the mobile access. DCCH carries in both up and down links, control channels that are either signalling-dedicated or associated control channels; the former are carrying the call signalling in the phases when the traffic channel has not yet been activated for that call; the latter are active in conjunction with any channel activated (either signalling or traffic channel) and are basically devoted to transport measurement and handover-related information. SDCCH carries the signalling procedure otside the activation of a traffic channel SACCH and FACCH carry the control information associated to traffic (TCH) and signalling channels (SDCCH).The figure summarises the basic concepts driving the possible radio access schemes: FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access) e CDMA (Code Division Multiple Access). For each, the related radio resource usage mechanisms are highlighted in the time, frequency and power domains.In the light of the most recent developments, the most innovative access technique in the field of mobile services is the Code Division Multiple Access (CDMA) technique. In January 1998 ETSI took an important decision about the radio access technique to be used for UMTS:for the asymmetrical portion of the spectrum available for UMTS, a hybrid solution based on a TDMA + narrow band CDMA scheme has been chosenfor the symmetrical portion of the spectrum, a wide band CDMA scheme has been adopted.The former solution is thought mainly for in-door applications, the latter for public/outdoor/high mobility services.The Code Division Multiple Access (CDMA) belongs to the family of spread spectrum techniques. The following figures are recalling just some of the basic concepts on which the CDMA technique is based; this is done just to supply some background information to facilitate the comprehension of the subsequent network considerations. The Orthogonal Variable Spreading Factor Codes ensure the complete ortogonality between the different channels. The use of OVSF codes follows the binary tree scheme of the figure and the choice of the code depends on the bit rate of the connection to be spread.The code sequence has to be repeated bit per bit of the original digital signal, hence the code depth is chosen accordingly. The choice of a given channelisation code inhibits the use of all the derived codes it is subtending in the tree scheme.Being the chip rate constant, the above allocation scheme implies that connections with different bit rates are transmitted with different spreading factors.Third generation mobile services can be grouped according to a bi-dimensional scheme characterising the service bandwidth and its connectivity behaviour.Wherever the de-regulation process has reached an advanced phase (USA, Canada, UK) new service delivery conditions are emerging. For instance, the ability of an operator to be active in both fixed and mobile service context, is strictly dependent on the regulatory constraints adopted in a particular country.These conditions are likely to modify significantly the service grouping and delivery configurations in the near future.The user is interested in being offered an easy way to access services and an easy way to use the relevant features. Possibly, the user requires also that advanced solutions such as single subscription, single number are available together with a simplified process in contacting the Operator/Service Provider.On the other hand, as for the service development process, Operator requirements and economical interests are rapidly changing, mainly due to the growing level of competition. In particular, mobile Operators are more and more concerned with: the reduction of operations costs the reduction of service time to market the capability of developing technology independent services.This is just to say how the pure bit rate (or delay and connectivity) requirements are not enough to identify optimal solutions for mobile systems.A basic issue is then represented by the spectrum requirements for third generation mobile services.The overall bandwidth assigned by WARC 92 to the world regions is shown in the figure. The bandwidth assigned to IMT-2000 systems includes both symmetric and asymmetrical portions.Now, lets consider in a more detailed way the possible architectural choices within the Radio Access Network. For the RAN, a scheme of the kind sketched in the figure, is more or less universally adopted (the depicted architecture is that adopted by ETSI for the UMTS Terrestrial Radio Access Network - UTRAN).UTRAN is composed by several Radio Network Subsystems (RNSs) connected to the Core Network through the Iu interface.The RNSs can be directly interconnected through the Iur interface.Every Radio Network Subsystem is composed of a Radio Network Controller (RNC) and one or more B nodes. These entities are responsible of the radio resource control of the assigned cells;A B-node may contain a single BTS or more than one (typically 3) controlled by a site controller.RNC is responsible for the local handover process and the combining/multicasting functions related to macrodiversity between different B-nodes.The above architecture is adopted as a model of the radio access segment to analyse the main function allocation and architectural problems arising in the definition of third generation mobile systems.The relationship between the mobile and the network is normally seen through the radio interface. It specifies how the information that has to be exchanged between those two entities (both user data and signalling information) has to be organised in a layered framework. Note that the radio interface is not directly specifying the end points of each protocol layer in the network: the allocation of the protocol end-points termination obeys network efficiency and performance criteria that will be discussed.The physical layer implements all the services and functions needed for the transfer of signalling and data information; from a radio resource viewpoint, the basic role of L1 is to map the transport channels to the radio physical channels.The MAC layer offers the transport service to the upper layers, in line with the defined attributes.The Radio Link Control Protocol (RLC) offers services and functions that are ensuring the correctness of the data transfer (ARQ functions) and performs the data segmenting/re-assembling features. This protocol could in principle be embedded in the MAC protocol.The presence of a Layer 2/LAC (Link Access Control) level is still under discussion in ETSI. Its role could consist in supplying retransmission features mainly in relation to handover and macrodiversity requirements, whenever they cannot be supplied by the RLC Protocol. The option of having a second ARQ layer depends on the archirectural solutions that will be adopted for the handover and macrodiversity resolution.Layer 3 contains, at least in the radio access segment on the C-Plane, services and functions related to the control of the radio resources.Layer 1 services refer typically to the transport role; a transport channel is specified by the way (e.g. bit rate and delays) adopted to transport the data offered by the upper layers; this role is played by making use of physical channels, directly defined on the physical structure of the radio interface.The example represents the up link physical channels under discussion in ETSI for the W-CDMA scheme.On the up link, two type of physical channels are identified, namely dedicated physical channels and common channels.The dedicated channels are: the Dedicated Physical Data Channel (DPDCH) used to carry the data (user or control data) generated by the MAC and upper layers the Dedicated Physical Control Channel (DPCCH) used to carry control information generated at Layer 1; specifically: pilot symbols for the channel estimate; transmission power control information and the transport format indicator (the latter specifies the configuration of encoding, interleaving, bit rate and physical channel mapping applied to the transport channels); in addition, DPCCH carries the feedback information channel, controlling the transmission diversity of the base station.A single common channel is defined on the up link, namely the physical random access channel (PRACH), offering the early access capabilities to the MSs. The PRACH is based on a Slotted Aloha concept; the access slots are defined on the depicted frame structure and the broadcast channel reports the needed information about the PRACH that can be accessed in that particular cell.Both DPDCH and DPCCH obey the frame structure depicted in figure; the frame is a 10 ms frame, split in 15 slots, each one lasting 0.667 ms, corresponding to a power-control period. The number of bits inserted in each slot depends on the spreading factor adopted in that particular instant. Different connections can then use different rates and the rate of a connection can be changed along the connection itself. The Dedicated Channel has to be maintained in any case, due to the information it is carrying.The change of bit rate may also imply the modification of the mapping between transport and physical channels, whose configuration is controlled through the Transport Format Indicator.The basic chip rate for the ETSI proposal is 4.096 Mchips/s. Additional chip rates are specified for the FDD mode, namely 8.192 Mchips/s and 16.384 Mchips/s. These are for further evolution of the radio access towards services requiring a transmission capacity greater than 2Mbit/s. Also for the down link, dedicated and common physical channels are foreseen. In the dedicated channels, data information generated at Layer 2 or above, are time-multiplexed with the control information generated at Layer 1 (pilot, power control and transport format indication).The frame structure is the same as for the up link.Whenever the total bit rate of a connection exceeds the maximum allowed bit rate for a single DPCH, a multi-code transmission is adopted, employing more than one DPCH for that connection; if a single spreading factor is used for each DPCH, the Layer 1 control information is associated to one only of the physical channels: the other does not transmit in the corresponding slot period.The common physical channels defined on the down link are: the primary Common Control Physical Channel used to carry the Broadcast Channel (BCH) the secondary Common Control Physical Channels, used to carry the Forward Access Channel (FACH) and the Paging Channel (PCH); FACH is used to transmit mobile specific control information and short packets.Both primary and secondary common channels obey the frame structure described for the dedicated channels; the only difference is that for the Common Channels, the single slot includes only two data fields, containing the pilot and the data information respectively; both primary and secondary control channels adopts a fixed bit rate, which is defined at system level for the former and at a cell level for the latter (the cell BCCH informs the roaming mobiles about the secondary channel bit rate). A primary and a secondary synchronisation channels are defined on the down link and transmitted with specific codes synchronously with each BCH slot; the former is unique for all the system, the latter identifies the scrambling code associated to the specific station.On the down link, Data and Control channels are time multiplexed. With the same spreading factor, variable bit rate within the same Physical Channel is managed through a discontinuous transmission mechanism, as depicted in the figure.High bit rate connections require, as seen, multi-code transmission using more than one Physical Channel.The figure lists the transport channels that are mapped onto the physical channels previously introduced; the main characteristics of each transport channel are summarised in the figure.Each transport channel is associated to a transport format (represented by the transport format indicator); the transport format belongs to a set of possible transport formats that can be associated to that transport channel.At Layer 1, the Dedicated Transport Channel, in general undergoes some processing before being mapped to physical channels and transmitted (after spreading); the basic process steps are shown in the figure.Several transport channels can be multiplexed before being mapped to one or more physical channels. Channel coding is performed in general per each transport channel independently; several options are available for the coding algorithm (convolutional, Reed-Solomon, turbo coding) that can possibly be use in conjunction. Different transport channels can possibly be interleaved.The static rate matching is performed at a slow pace, typically when a transport channel is added or removed from the pool of jointly transmitted transport channels. This process is done in order to fulfil the transmission quality requirements of each transport channel, by maintaining at the same time a uniform bit energy per each channel. Another role of the static rate matching is to adjust the (coded) channel bit rate in accordance with the available bit rate of the dedicated physical channels.The dynamic rate matching is performed on the up link, after multiplexing, to adapt the instantaneous bit rate of the multiplexed transport channels to the bit rate of the dedicated physical channel(s); on the down link, DTX is used to cope with bit rate misalignments; both static and dynamic rate matching use unequal repetition techniques.The transport channel multiplexing is performed on a time-division basis, within a radio frame.Inter frame interleaving is performed within a single transport channel over more than one frame for those services that require this kind of mechanism; intra frame interleaving is performed on a single frame and can apply to multiplexed transport channels.The multiplexing technique is applied to Dedicated Channels only, all the common channels (RACH, BCH, PCH and FACH) are independently coded (on both the up and down link) and each is mapped on a single physical channel.The configuration of coding and multiplexing of the transport channel(s) is given by the Transport Format Indicator which identifies the instant (10ms) configuration within a set of pre-defined transport configurations; it was already said that this indicator is carried on both the up and down link over the Dedicated Physical Control Channel (DPCCH)The differences between up and down link are due to the soft handover mechanism; moreover, on the receiving side, the down link Dedicated Physical Channel, Data and Control part are time multiplexed, as already stated.The effect of macrodiversity on the receiving side is shown in the figure; the equivalent physical channels (carrying the same information bits through different cells) are combined in the MS receiver; also TPC and TFI can be combined in the MS if they bear exactly the same information through different cells. In the example, on the MS receiving side, all the three cells involved in the active set use the same TFI, hence, in this case, it could be combined in the MS.It may happen that different services of the same call are using differently the macrodiversity mechanism, for instance, along the same call, it may happen that for one connection a macrodiversity state is active while for another connection no macrodiversity is allowed (for radio transmission reasons); in this case, the TFIs of the various cells are in general different from each other and may not be combined.The MAC layer manages the mapping of the logical channels to the transport channels by controlling the mapping/multiplexing mechanisms previously introduced.The transport format is chosen within the set of available transport formats.Priorities are handled by choosing the appropriate transport formats; for instance, data with high priority can use an high bit rate format; the same solution can be adopted for data which have accumulated a high delay in the upper layer queues.On the down link, still the transport formats can be used to fulfil different priority requirements arising between different users.Most of the functions listed in the figure may require an exchange of signalling information between MAC layers belonging to MS and the relevant end point in the access network.Contention control is related to the collision event that may arise on the random access channel (the contention is detected by Layer 1 and possibly resolved by Layer 3).The layer 2 functions residing above the MAC layer, take the role of controlling the data transfer of any connection; to do so they supply error correction, retransmission, combining and multi-casting when needed.These roles can be split for the U-plane between the Link Access Control (if present) and the Radio Link Control (RLC) functions.RLC controls the transfer of user data; in sequence delivery; segmentation and re-assembly mechanisms; Automatic Repeat Request (ARQ) functions. Through the above mechanisms, RLC supports upper layers with: acknowledged mode operation (ARQ and variable bit rate) unacknowledged mode operation (variable bit rate) transparent mode operation (no RLC service)An example of segmentation function is reported in the figure; in this case the RCL service allows to transmit with different rates, RCL data PDUs, according to the need of the traffic source; the bit rate can be changed every frame period (10 ms).If present, the LAC implements all the functions tied to the connection control and the Layer 2 algorithms: establishment and release of LAC connections; ARQ; flow control; segmentation, re-assembly.The above services are used to supply assured, unassured and transparent transport services to layer 3 PDUs. The basic requirements for the Radio Resource control refer to: the need for broadcasting messages to the MSs in a given area (general control provided on the General Control SAP) the need for notifying paging messages and other mobile-specific information within a given area (notification control provided on the Notification SAP) the need for setting-up and releasing connections (point-to point or multiparty connections provided on the Dedicated Control SAP); for each control it must guarantee: the correct transfer of messages along the connection the correct management of priorities between signalling and non-signalling messages (e.g. short messages) sharing the same control channels.The RRC connection is a signalling connection between the MS and the Radio Access Network.The control of radio bearers includes the execution of the admission control algorithms and may include the setting-up of the radio parameters for Layers 1 and 2; this choice heavily conditions the splitting edge between radio dependent and independent functions that will be discussed in the following.The control of radio resources for the connection is tied to the allocation/de-allocation of resources also along the same connection.The RRC mobility functions refer also to handover and macrodiversity.The TD-CDMA logical channel structure is similar to that adopted for the W-CDMA case. Traffic channel and control channels are envisaged: traffic channel, used to transfer user data or layer 3 signalling data control channels, further divided in common control and dedicated channels Common Control Channels BCCH Broadcast Channel (DL) SCH Synchronisation Channel (DL) FACHForward Access Channel (DL) PACHPaging Channel (DL) RACHRandom Access Channel (UL) Dedicated Channel DCCHDedicated Control Channel-ACCH and SDCCH (DL&UL) DTCHDedicated Traffic Control (DL&UL)The ETSI proposal for the TD-CDMA access scheme is based on: 15 slots per frame; 10 ms frame duration (the same as for the FDD case) 24 frames per multiframe; 240 ms multiframes switching points between up and down sessions to adapt to the varying UL/DL asymmetric traffic 16 orthogonal codes (Walsh) are available for each time slot.The code management within a given time slot can assign one or more orthogonal codes to a given transport channel. Multicode/multislot arrangements are then used to cope with high bit rate services.************