WCDMA Radio Interface Physical Layer

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WCDMA Air Interface Physical Layer

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WCDMA Radio Interface Physical Layer

www.huawei.com

Copyright 2008 Huawei Technologies Co., Ltd. All rights reserved.

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WCDMA Air Interface Physical Layer

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ForewordThe physical layer offers data transport services to higher layers. The physical layer is expected to perform the following functions in order to provide the data transport service, for example: spreading, modulation and demodulation, despreading, Inner-loop power control and etc.

Copyright 2008 Huawei Technologies Co., Ltd. All rights reserved.

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WCDMA Air Interface Physical Layer

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ObjectivesUpon completion of this course, you will be able to:Outline radio interface protocol Architecture Describe structure and functions of different physical channels Describe UMTS physical layer procedures

Copyright 2008 Huawei Technologies Co., Ltd. All rights reserved.

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WCDMA Air Interface Physical Layer

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Contents1. Physical Layer Overview 2. Physical Channels 3. Physical Layer Procedure

Copyright 2008 Huawei Technologies Co., Ltd. All rights reserved.

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WCDMA Air Interface Physical Layer

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Contents1. Physical Layer Overview 2. Physical Channels 3. Physical Layer Procedure

Copyright 2008 Huawei Technologies Co., Ltd. All rights reserved.

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WCDMA Air Interface Physical Layer

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UTRAN Network StructureCNIu-CS RNS Iur RNC RNC Iub NodeB Iub NodeB Iub NodeB Core Network CS PS Iu-PS Iu-CS RNS CS PS Iu-PS

UTRANIub NodeB

Uu

UECopyright 2008 Huawei Technologies Co., Ltd. All rights reserved. Page5

UTRAN: UMTS Terrestrial Radio Access Network. The UTRAN consists of a set of Radio Network Subsystems connected to the Core Network through the Iu interface. A RNS consists of a Radio Network Controller and one or more NodeBs. A NodeB is connected to the RNC through the Iub interface. Inside the UTRAN, the RNCs of the RNS can be interconnected together through the Iur. Iu(s) and Iur are logical interfaces. Iur can be conveyed over direct physical connection between RNCs or virtual networks using any suitable transport network.

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WCDMA Air Interface Physical Layer

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Uu Interface Protocol StructureGC Nt DC

Duplication avoidanceGC C-plane signaling Nt DC U-plane information control UuS boundary

control

control

RRCcontrol control

L3radio bearer PDCP PDCP BMC RLC

L2/PDCP L2/BMC L2/RLClogical channel

RLC

RLC

RLC

RLC RLC RLC

RLC

MAC PHYCopyright 2008 Huawei Technologies Co., Ltd. All rights reserved. Page6

L2/MACtransport channel

L1

The layer 1 supports all functions required for the transmission of bit streams on the physical medium. It is also in charge of measurements function consisting in indicating to higher layers, for example, Frame Error Rate (FER), Signal to Interference Ratio (SIR), interference power, transmit power, It is basically composed of a layer 1 management entity, a transport channel entity, and a physical channel entity. The layer 2 protocol is responsible for providing functions such as mapping, ciphering, retransmission and segmentation. It is made of four sub-layers: MAC (Medium Access Control), RLC (Radio Link Control), PDCP (Packet Data Convergence Protocol) and BMC (Broadcast/Multicast Control). The layer 3 is split into 2 parts: the access stratum and the non access stratum. The access stratum part is made of RRC (Radio Resource Control) entity and duplication avoidance entity. duplication avoidance terminates in the CN but is part of the Access Stratum. The higher layer signalling such as Mobility Management (MM) and Call Control (CC) is assumed to belong to the non-access stratum, and therefore not in the scope of 3GPP TSG RAN. In the C-plane, the interface between 'Duplication avoidance' and higher L3 sublayers (CC, MM) is defined by the General Control (GC), Notification (Nt) and Dedicated Control (DC) SAPs. Not shown on the figure are connections between RRC and all the other protocol layers (RLC, MAC, PDCP, BMC and L1), which provide local inter-layer control services. The protocol layers are located in the UE and the peer entities are in the NodeB or the RNC.

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WCDMA Air Interface Physical Layer

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Many functions are managed by the RRC layer. Here is the list of the most important: Establishment, re-establishment, maintenance and release of an RRC connection between the UE and UTRAN: it includes an optional cell re-selection, an admission control, and a layer 2 signaling link establishment. When a RNC is in charge of a specific connection towards a UE, it acts as the Serving RNC. Establishment, reconfiguration and release of Radio Bearers: a number of Radio Bearers can be established for a UE at the same time. These bearers are configured depending on the requested QoS. The RNC is also in charge of ensuring that the requested QoS can be met. Assignment, reconfiguration and release of radio resources for the RRC connection: it handles the assignment of radio resources (e.g. codes, shared channels). RRC communicates with the UE to indicate new resources allocation when handovers are managed. Paging/Notification: it broadcasts paging information from network to UEs. Broadcasting of information provided by the non-access stratum (Core Network) or access Stratum. This corresponds to system information regularly repeated. UE measurement reporting and control of the reporting: RRC indicates what to measure, when and how to report. Outer loop power control: controls setting of the target values. Control of ciphering: provides procedures for setting of ciphering. The RRC layer is defined in the 25.331 specification from 3GPP.

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WCDMA Air Interface Physical Layer

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The RLCs main function is the transfer of data from either the user or the control plane over the Radio interface. Two different transfer modes are used: transparent and nontransparent. In non-transparent mode, 2 sub-modes are used: acknowledged or unacknowledged. RLC provides services to upper layers: data transfer (transparent, acknowledged and unacknowledged modes). QoS setting: the retransmission protocol (for AM only) shall be configurable by layer 3 to provide different QoS. notification of unrecoverable errors: RLC notifies the upper layers of errors that cannot be resolved by RLC. The RLC functions are: mapping between higher layer PDUs and logical channels. ciphering: prevents unauthorized acquisition of data; performed in RLC layer for non-transparent RLC mode. segmentation/reassembly: this function performs segmentation/reassembly of variable-length higher layer PDUs into/from smaller RLC Payload Units. The RLC size is adjustable to the actual set of transport formats (decided when service is established). Concatenation and padding may also be used. error correction: done by retransmission (acknowledged data transfer mode only). flow control: allows the RLC receiver to control the rate at which the peer RLC transmitting entity may send information.

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WCDMA Air Interface Physical Layer

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MAC services include: Data transfer: service providing unacknowledged transfer of MAC SDUs between peer MAC entities. Reallocation of radio resources and MAC parameters: reconfiguration of MAC functions such as change of identity of UE. Requested by the RRC layer. Reporting of measurements: local measurements such as traffic volume and quality indication are reported to the RRC layer. The functions accomplished by the MAC sub-layer are listed above. Heres a quick explanation for some of them: Priority handling between the data flows of one UE: since UMTS is multimedia, a user may activate several services at the same time, having possibly different profiles (priority, QoS parameters...). Priority handling consists in setting the right transport format for a high bit rate service and for a low bit rate service. Priority handling between UEs: use for efficient spectrum resources utilization for bursty transfers on common and shared channels. Ciphering: to prevent unauthorized acquisition of data. Performed in the MAC layer for transparent RLC mode. Access Service Class (ACS) selection for RACH transmission: the RACH resources are divided between different ACSs in order to provide different priorities on a random access procedure.

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WCDMA Air Interface Physical Layer

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PDCP UMTS supports several network layer protocols providing protocol transparency for the users of the service. Using these protocols (and new ones) shall be possible without any changes to UTRAN protocols. In order to perform this requirement, the PDCP layer has been introduced. Then, functions related to transfer of packets from higher layers shall be carried out in a transparent way by the UTRAN network entities. PDCP shall also be responsible for implementing different kinds of optimization methods. The currently known methods are standard