Wireless LTE and cellular 5 module ppt PDF

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Wireless Cellular and LTE 4G Broadband 17EC81 Dr. Prakash Jadhav B.E, M.Tech., Ph.D, MIEEE, MISTE,

Associate Professor Dept. of Electronics and Communication Engineering Sapthagiri College of Engineering 14/5 Chikkasandra, Hesaragatta main road BENGALURU-560 057

Course Objectives:

Course Outcomes:

This course will enable students to: • Understand the basics of LTE standardization phases and specifications. • Explain the system architecture of LTE and E-UTRAN, the layer of LTE, based on the use of OFDMA and SC-FDMA principles. • Analyze the role of LTE radio interface protocols to set up, reconfigure and release the Radio Bearer, for transferring the EPS bearer. • Analyze the main factors affecting LTE performance including mobile speed and transmission bandwidth.

At the end of the course, students will be able to: • Understand the system architecture and the functional standard specified in LTE 4G. • Analyze the role of LTE radio interface protocols and EPS Data convergence Protocols to set up, reconfigure and release data and voice from users. • Demonstrate the UTRAN and EPS handling processes from set up to release including mobility management for a variety of data call scenarios. • Test and Evaluate the Performance of resource management and packet data processing and transport algorithms.

Module 5

Radio Resource Management and Mobility Management: • PDCP overview • MAC/RLC overview • RRC overview • Mobility Management • Inter-cell Interference Coordination Text Books: Arunabha Ghosh, Jan Zhang, Jefferey Andrews, Riaz Mohammed, ‘Fundamentals of LTE’, Prentice Hall, Communications Engg. and Emerging Technologies. Reference Books: 1. 2. 3.

LTE for UMTS Evolution to LTE-Advanced’ Harri Holma and Antti Toskala, Second Edition - 2011, John Wiley & Sons, Ltd. Print ISBN: 9780470660003. ‘EVOLVED PACKET SYSTEM (EPS) ; THE LTE AND SAE EVOLUTION OF 3G UMTS’ by Pierre Lescuyer and Thierry Lucidarme, 2008, John Wiley & Sons, Ltd. Print ISBN:978-0-470-05976-0. ‘LTE – The UMTS Long Term Evolution ; From Theory to Practice’ by Stefania Sesia, Issam Toufik, and Matthew Baker, 2009 John Wiley & Sons Ltd, ISBN 978-0-470-69716-0.

Data flow services in LTE: • • • •

LTE is an end-to-end packet-switched network, designed for high speed data services. LTE uses “bearer” concept to provide varying QoS requirements as per the applications. EPS bearer is defined between the PDN-GW and UE. Each EPS bearer maps to a specific set of QoS parameters like Data rate, latency, packet error rate etc.

• Applications with very different QoS requirements such as e-mail and voice can be put on separate bearers that will allow the system to simultaneously meet their QoS requirements. • The end-to-end connectivity through the network is made via the bearer service, and the bearer service architecture is shown in Figure 10.1.

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2.

An EPS bearer has to cross multiple interfaces, and across each interface it is mapped to a transport layer bearer. An S5/S8 bearer transports the packets of an EPS bearer between a Serving GW (S-GW) and a PDN-GW. S1 bearer transports the packets of an EPS bearer between an eNode-B and an S-GW. Over the radio interface the bearer is referred to as the radio bearer, which transfers data between a UE and the E-UTRAN. Signaling Radio Bearers (SRBs) carry the Radio Resource Control (RRC) signaling messages. Data Radio Bearers (DRBs) carry the user plane data. Radio bearers are mapped to logical channels through Layer 2 protocols. Broadly, the bearers can divided into two classes: Guaranteed Bit Rate (GBR) bearers: • These bearers define and guarantee a minimum bit rate that will be available to the UE. • Bit rates higher than the minimum bit rate can be allowed if resources are available. • GBR bearers are typically used for applications such as yoke, streaming video, and real-time gaming. Non-GBR bearers: • These bearers do not define or guarantee a minimum bit rate to the UE. • The achieved bit rate depends on the system load, the number of UEs served by the eNode-B, and the scheduling algorithm. • Non-GBR bearers are used for applications such as web browsing, e-mail, FTP, and P2P file sharing.

– EPS Bearer Service Architecture: •

Each bearer is associated with a QoS Class Identifier (QCI), which indicates the priority, packet delay budget, acceptable packet error loss rate and the GBR/non-GBR classification.

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The nine standardized QCI defined in the LTE are shown in Table 10.1.

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One EPS bearer is established when the UE connects to a PDN.

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Default Bearer: EPS bearer is established throughout the lifetime of the PDN connection to provide the UE with always-on IP connectivity to that PDN.

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Dedicated bearer: Any additional EPS bearer established to the same PDN.

LTE Protocol Architecture: • The protocol architecture in LTE between the UE and the core network is divided: – User plane protocol stack – Control plane protocol stack

1. User plane protocol stack: User plane protocol stack as shown in Figure 10.2 – The user plane is responsible for transporting IP packets carrying application-specific data from the PDN-GW to the UE. – This is done by encapsulating the IP packets in an Evolved Packet Core (EPC)-specific protocol and tunneling them from the PDN-GW to the eNode-B using the GPRS Tunneling Protocol (GTP). – From the eNode-B the packets are transported to the UE using the Packet Data Convergence Protocol (PDCP).

2. Control plane protocol stack: Control plane protocol stack as shown in Figure 10.3 • The control plane is used for transporting signaling between the Mobility Management Entity (MME) and the UE. • The type of signaling handled over the control plane is typically related to bearer management, QoS management, and mobility management including functions such as handover and paging. • In LTE, Layer 2 of the protocol stack is split into the following sublayers: – Medium Access Control (MAC) – Radio Link Control (RLC) and – PDCP.

• The layer 2 structure for the downlink: It is depicted in Figure 10.4.

• Radio bearers are mapped to logical channels through PDCP and RLC sublayers.

• The Service Access Point (SAP) between the physical layer and the MAC sublayer provides the transport channels that are used by the physical layer to provide services to the MAC. • The SAP between the MAC sublayer and the RLC sublayer provides the logical channels that are used by the MAC layer to provide services to the RLC. • One RLC and PDCP entity per radio bearer in the UE and eNode-B.

• MAC layer multiplexes the data and control information from all the radio bearers at the UE and eNode-B. i.e., MAC layer multiplexes several logical channels on the same transport channel.

– Packet Data Convergence Protocol (PDCP) Overview: • A PDCP entity is associated either with the control plane or user plane depends on which radio bearer it is carrying data for, Each radio bearer is associated with one PDCP entity. • Each PDCP entity is associated with one or two RLC entities depending on the radio bearer characteristic (uni-directional or bi-directional) and the RLC mode. • PDCP is used only for radio bearers mapped on DCCH and DTCH types of logical channels. • The main services and functions of the PDCP sublayer for the user plane and control plane as shown in Figure 10.5 are as follows.

Functions of PDCP sublayer for the user plane: – Header compression and decompression of IP data flows with the Robust Header Compression (ROHC) protocol. – Ciphering and deciphering of user plane data. – In-sequence delivery and reordering of upper-layer PDUs at handover – Buffering and forwarding of upper-layer PDUs from the serving eNode-B to the target eNode-B during handover – Timer-based discarding of SDUs in the uplink

Functions of PDCP sublayer for the control plane: – Ciphering and deciphering of control plane data. – Integrity protection and integrity verification of control plane data – Transfer of control plane data

The PDCP PDUs can be divided into two categories: – The PDCP data PDU: It is used in both the control and user plane to transport higher layer packets. It is used to convey either user plane data containing a compressed /uncompressed IP packet or control plane data containing one RRC message and a Message Authentication Code for Integrity (MAC-I) field for integrity protection. – The PDCP control PDU: It is used only within the user plane to convey a PDCP status report during handover and feedback information for header compression. It carries peer- to-peer signaling b/w the PDCP entities at two ends. It doesn’t carry higher layer SDU. • The constructions of the PDCP data PDU formats from the PDCP SDU for the user plane and the control plane are shown in Figure 10.6.

• The various types of PDCP PDU carried on the user and control plane are shown in Table 10.2. • There are three different types of PDCP data PDUs, distinguished by the length of the Sequence Number (SN).

• The PDCP SN is used to provide robustness against packet loss and to guarantee sequential delivery at the receiver. • The PDCP data PDU with the long SN is used for the Un-acknowledge Mode (UM) and Acknowledged Mode (AM) and the PDCP data PDU with the short SN is used for the Transparent Mode (TM). • Besides the SN field and the ciphered data, the PDCP data PDU for the user plane contains a `D/C' field that is to distinguish data and control PDUs. • This is required since the PDCP data PDU can carry both user plane and control plane data.

PDCP performs Header compression, Integrity and Ciphering »

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– Header Compression: ROHC framework defined by IETF provides Header Compression in LTE. The protocols at different layers network (IP), transport (TCP, UDP), Application (RTP) bring significant amount of header overhead. Efficient header compression scheme is needed for VoIP services. The ROHC framework contains “profiles” (Header Compression Algorithms). Each profile specifies particular network layer, transport layer or upper layer. The supported profiles in 3GPP Release 8 are listed in Table 10.3.

Integrity and Ciphering: – The security-related functions in PDCP include integrity protection and ciphering. – A PDCP PDU counter, denoted by the parameter COUNT, is maintained and used as an input to the security algorithm. – The format of COUNT is shown in Figure 10.7, which has a length of 32 bits and consists of two parts: the Hyper Frame Number (HFN) and the PDCP SN. – The SN is used for reordering and duplicate detection of RLC packets at the receive end. – If the key does not match the MAC-I field, then the PDCP PDU does not pass the integrity check, and the PDCP PDU will be discarded. – The ciphering function includes both ciphering and deciphering. – It is performed on both control plane data and user plane data.

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For the control plane, the data unit that is ciphered is the data part of the PDCP PDU and the MAC-I; for the user plane, the data unit that is ciphered is the data part of the PDCP PDU.

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Neither integrity nor ciphering is applicable to PDCP control PDUs.

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The ciphering function is activated by upper layers, which also configures the ciphering algorithm and the ciphering key to be used.

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The ciphering is done by an XOR operation of the data unit with the ciphering stream.

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The ciphering stream is generated by the ciphering algorithm based on ciphering keys, the radio bearer identity, the value of COUNT, the direction of the transmission, and the length of the key stream.

–MAC/RLC Overview: • Functions of MAC Layer: – – – – –

It performs multiplexing and demultiplexing of logical channels on to the transport channel. At eNode-B, it performs multiplexing and prioritizing various UEs serving by the eNode-B. At UE, it performs multiplexing and prioritizing various radio bearers associated with the UE. It provides services to the RLC layer through logical channels. It takes services from PHY layer through transport channels.

• Functions of RLC Layer: – It performs segmentation and concatenation on PDCP PDUs based on size mentioned by the MAC layer. – Reorders RLC PDUs if they receive out of order due to H-ARQ process in the MAC layer. – RLC supports ARQ mechanism.

Data Transfer Modes of RLC: RLC entity can be operated in three different modes: – Transparent Mode (TM) – Unacknowledged Mode (UM) – Acknowledged Mode (AM)

• The Transparent Mode (TM): Following are feature of TM mode – The TM mode is the simplest mode – The TM mode is not used for user plane data transmission – RLC entity doesn’t add any RLC header to the PDU. – No data segmentation or concatenation. – No retransmissions. – Order of delivery is not guaranteed. Ex., RRC broadcast messages, paging messages uses TM.

• The Unacknowledged Mode (UM): – – – – – – –

Order of delivery is guaranteed. DTCH logical channels operate in this mode. UM RLC entity performs data segmentation or concatenation RLC SDUs. No retransmissions of the lost PDU. Ex., delay-sensitive, error-tolerant real-time applications like VoIP Relevant RLC headers are included in the UM Data PDU. At the Rx, UM RLC entity performs duplicate detection and reordering

• The Acknowledged Mode (AM): – The AM mode is the most complex one, which requests retransmission of missing PDUs in addition to the UM mode functionalities.

– It is mainly used by error-sensitive and delay-tolerant applications. – An AM RLC entity can be configured to deliver/receive RLC PDUs through DCCH and DTCH. – An AM RLC entity delivers/receives the AM Data (AMD) PDU and the STATUS PDU indicating the ACK/NAK information of the RLC PDUs. – When the AM RLC entity needs to retransmit a portion of an AMD PDU, which results from the ARQ process and segmentation, the transmitted PDU is called the AMD PDU segment. – The operation of the AM RLC entity is similar to that of the UM RLC entity, except that it supports retransmission of RLC data PDUs. – The receiving AM RLC entity can send a STATUS PDU to inform the transmitting RLC entity about the AMD PDUs that are received successfully and that are detected to be lost.

Purpose of MAC and RLC Layers

• The main services and functions of the RLC sublayer include – Transfer/receive PDUs from upper layers. – Error detection using ARQ (only in AM mode) – Concatenation, segmentation and reassembly of RLC SDUs (only in UM and AM data transfer) – In-sequence delivery of upper-layer PDUs (only in UM and AM data transfer) – Duplication detection (only in UM and AM data transfer) – RLC SDU discard (only in UM and AM data transfer) – RLC re-establishment.

• Services and functions of MAC sublayer: – Mapping between logical channels and transport channels – Multiplexing/ Demultiplexing of MAC SDUs belonging to one or more logical channels from the same transport block – Scheduling for uplink and downlink transmission

– Error correction through H-ARQ – Priority handling between logical channels of one UE or between UEs by means of dynamic scheduling. – Transport format selection, i e, selection of MCS for link adaption. – Padding if the MAC PDU is not fully filled with data.

PDU Headers and Formats RLC PDU formats • RLC PDUs can be categorized into RLC data PDUs and RLC control PDUs.

• The formats of different RLC Data PIDUs are shown in Figure 10.8

– Framing Info (FI) field: The FI field indicates whether a RLC SDU is segmented at the beginning and/or at the end of the Data field. – Length Indicator (LI) field: The LI field indicates the length in bytes of the corresponding Data field element present in the UMD or AMD-PDU – Extension bit (E) field: The E field indicates whether a Data field follows or a set of E field and LI field follows. – SN: field: The SN field indicates the sequence number of the corresponding UMD or AMD PDU. – It consists of 10 bits for AMD PDU, AMD PDU segments and STATUS PDUs and 5 bits or 10 bits for UMD PDU.

• For AMD PDU and AMD PDU segments, additional fields are available: – Data/Control (D/C) field: The D/C field indicates whether the RLC PDU is an RLC Data PDU or an RLC Control PDU. – Re-segmentation Flag (RF) field: The RF field indicates whether the RLC PDU is an AMD PDU or an AMD PDU segment. – Polling bit (P) field: The P field indicates whether the transmitting side of an AM RLC entity requests a STATUS report from its peer AM RLC entity.

• Additionally, the RLC header of an AMD PDU segment contains special fields including: – Segment Offset (SO) field: The SO field indicates the position of the AMD PDU segment in bytes within the original AMD PDU. – Last Segment Flag (LSF) field: The LSF field indicates whether the last byte of the AMD PDU segment corresponds to the last byte of an AMD PDU. (A) The format of the STATUS PDU is shown in Figure 10.9, which consists of the following fields:

– Control PDU Type (CPT) field: The CPT field indicates the type of the RLC control PDU, and in Release 8 the STATUS PDU is the only defined control PDU. – Acknowledgment SN (ACK_SN) field: The ACKSN field indicates the SN of the next not received RLC Data PDU, which is not reported as missing in the STATUS PDU. – Extension bit 1 (E1) field: The El field indicates whether a set of NACK_SN, El, and E2 follows. – Extension bit 2 (E2) field: The E2 field indicates whether a set of SO start and SO end follows. – Negative Acknowledgment SN (NACK_SN) field: The NACK_SN field indicates the SN of the AMD PDU (or portions of it) that has been detected as lost at the receiving side of the AM RLC entity. – SO start (SO start) field and SO end (SO end) field: These two fields together indicate the portion of the AMD PDU with SN = NACK_SN that has been detected as lost at the receiving side of the AM RLC entity

(B) MAC PDU Formats: MAC layer receives data from RLC as MAC SDUs and passes the MAC PDUs to PHY layer. – The MAC PDU contains TWO fields: MAC PDU header & MAC payload

• MAC Payload: It contains zero or more MAC SDUs, zero or more MAC control elements, and optional padding. • MAC PDU header: It consists of one or more MAC PDU subheaders.

• The format of a typical MAC subheader is shown in Figure 10.11, which contains five different fields as explained in the following:

1. R: It is reserved field and set to ‘0’ always. 2. E: It is an extension field to indicate the presence of more fields in the MAC header. 1. If E=1, set of R/R/E/LCID fields follows 2. If E=0, either MAC SDU, a MAC control element, or Padding follows. 3. LCID: Logical Channel ID: It indicates the logical channel instance of the corresponding MAC SDU or the type of the corresponding MAC control element, or padding. 4. F: It indicates the size of the Length field. 1. F=0, size of MAC SDU or MAC control element < 128 bytes. 5. L: It indicates the length of the corresponding MAC PDU or MAC control element in Bytes.

(C) The MAC PDU for random access response It has a different format, as shown in Figure 10.12.

• MAC header consists of one or more MAC PDU subheaders. Subheader contains payload information. • Payload contains one or more MAC Random Access Responses (MAC RAR) and optional padding.

• ARQ Procedures: LTE applies two-layer retransmission scheme. 1. H-ARQ Protocol: • It is a low latency and low overhead feedback protocol in MAC layer. • It is responsible for handling transmission errors by retransmissions based on H-ARQ processes. • H-ARQ is the use of conventional ARQ along with an Error Correction technique called “Soft Combining”. ‘ • Soft Combining' data packets that...