Private:Ahmed Reading Summaries

Will summarize the readings here..

Peer-to-Peer and SVC

• Peer-Driven Video Streaming: Multiple Descriptions versus Layering
• Layered Coding vs. Multiple Descriptions for Video Streaming over Multiple Paths
• Evaluation of the H.264 Scalable Video Coding in Error Prone IP Networks
• Overview of the Scalable Video Coding Extension of the H.264/AVC Standard
• Enabling Adaptive Video Streaming in P2P Systems

Long Term Evolution (LTE)

• Mobile Video Transmission Using Scalable Video Coding
• LTE - An Introduction
• Optimal Transmission Scheduling for Scalable Wireless Video Broadcast with Rateless Erasure Correction Code
• Dynamic Session Control for Scalable Video Coding over IMS
• Scheduling and Resource Allocation for SVC Streaming over OFDM Downlink Systems
• Mobile Broadband: Including WiMAX and LTE
  • Chapter-11: Long Term Evolution of 3GPP
• 3G Evolution HSPA and LTE for Mobile Broadband
  • Chapter-11: MBMS: Multimedia Broadcast Multicast Service
• The UMTS Long Term Evolution: From Theory to Practice
  • Chapter-2: Network Architecture
  • Chapter-14: Broadcast Operation

Acronyms

• 3GPP 3rd Generation Partnership Project
• BM-SC Broadcast Multicast Service Centre
• CN Core Network
• EPC Evolved Packet Core
• EPS Evolved Packet System
• ICI InterCell Interference
• LTE Long Term Evolution
• MBMS Multimedia Broadcast Multicast Service
• MIMO Multiple Input Multiple Output
• OFDMA Orthogonal Frequency Division Multiple Access
• SAE System Architecture Evolution
• SC-FDMA Single Carrier Frequency Division Multiple Access
• TTI Transmission Time Interval
• UE User Equipment
• UTRAN UMTS Terrestrial Radio Access Network

Long Term Evolution of 3GPP

LTE PHY Layer

• Based on OFDMA with cyclic prefix in downlink, and on SC-FDMA with a cyclic prefix in the uplink
• Three duplexing modes are supported: full duplex FDD, half duplex FDD, and TDD
• Two frame structure types:
  • Type-1 shared by both full- and half-duplex FDD
  • Type-2 applicable to TDD
• Type-1 radio frame has a length of 10 ms and contains 20 slots (slot duration is 0.5 ms)
• Two adjacent slots constitute a subframe of length 1 ms
• Supported modulation schemes are: QPSK, 16QAM, 64QAM
• Broadcast channel only uses QPSK
• Maximum information block size = 6144 bits
• CRC-24 used for error detection

[Image Placeholder - Type-1 and Type-2 frames]

OFDMA Downlink

• Scheduler in eNB (base station) allocates resource blocks (which are the smallest elements of resource allocation) to users for predetermined amount of time
• Slots consist of either 6 (for long cyclic prefix) or 7 (for short cyclic prefix) OFDM symbols
• Longer cyclic prefixes are desired to address longer fading
• Number of available subcarriers changes depending on transmission bandwidth (but subcarrier spacing is fixed)

[Image Placeholder - Downlink resource block and slot structure]

Evolved Multicast Broadcast Multimedia Services (eMBMS)

• Is a multimedia service performed either with a single-cell broadcast or multicell mode (aka MBMS Single Frequency Network (MBSFN))
• In an MBSFN area, all eNBs are synchronized to perform sumulcast transmission from multiple cells (each cell transmitting identical waveform)
• There are three types of cells within an MBSFN area: transmitting/receiving, transmitting only, and reserved
• If user is close to a base station, delay of arrival between two cells could be quite large, so the subcarrier spacing is reduced to 7.5 KHz and longer CP is used

LTE MAC Layer

• eNB scheduler controls the time/frequency resources for a given time for uplink and downlink
• Scheduler dynamically allocates resources to UEs at each Transmission Time Interval (TTI)
• Depending on channel conditions, scheduler selects best multiplexing for UE
• Downlink LTE considers the following schemes as a scheduler algorithm:
  • Frequency Selective Scheduling (FSS)
  • Frequency Diverse Scheduling (FDS)
  • Proportional Fair Scheduling (PFS)
• Link adaptation is performed through adaptive modulation and coding

LTE Radio Interface Architecture

• Data to be transmitted in the downlink enters the processing chain in the form of IP packets on one of the SAE bearers
• IP packets are passed through multiple protocol entities:
  • Packet Data Convergence Protocol (PDCP) performs IP header compression, to reduce the number of bits to transmit over the radio interface, based on Robust Header Compression (ROHC) in addition to ciphering and integrity protection of the transmitted data
  • Radio Link Control (RLC) is responsible for segmentation/concatenation, retransmission handling, and in-sequence delivery to higher layers
    • offers services to the PDCP in the form of radio bearers
  • Medium Access Control (MAC) handles hybrid-ARQ retransmissions and uplink and downlink scheduling at the eNodeB
    • offers services to the RLC in the form of logical channels
  • Physical Layer (PHY) handles coding/decoding, modulation/demodulation, multi-antenna mapping, and other typical physical layer functions
    • offers services to the MAC layer in the form of transport channels

RLC

• Depending on the scheduler decision, a certain amount of data is selected for transmission from the RLC SDU buffer and the SDUs are segmented/concatenated to create the RLC PDU. Thus, for LTE the RLC PDU size varies dynamically
• In each RLC PDU, a header is included, containing, among other things, a sequence number used for in-sequence delivery and by the retransmission mechanism
• A retransmission protocol operates between the RLC entities in the receiver and transmitter. By monitoring the sequence numbers of the incoming PDUs, the receiving RLC can identify missing PDUs
• Although the RLC is capable of handling transmission errors due to noise, unpredictable channel variations, etc., error-free delivery is in most cases handled by the MAC-based hybrid-ARQ protocol

MAC

• A logical channel is defined by the type of information it carries and is generally classified as:
  • a control channel, used for transmission of control and configuration information necessary for operating an LTE system
  • a traffic channel, used for the user data
• A transport channel is defined by how and with what characteristics the information is transmitted over the radio interface
• Data on a transport channel is organized into transport blocks. In each Transmission Time Interval (TTI), at most one transport block of a certain size is transmitted over the radio interface to/from a mobile terminal in absence of spatial multiplexing
• Associated with each transport block is a Transport Format (TF), specifying how the transport block is to be transmitted over the radio interface (it includes information such as transport-block size, the modulation scheme, and the antenna mapping)
• By varying the transport format, the MAC layer can realize different data rates. Rate control is therefore also known as transport-format selection

Mobile Video Transmission Using Scalable Video Coding

• MBMS extends existing 3GPP architecture by introducing:
  • MBMS Bearer Service delivers IP multicast datagrams to multiple receivers using minimum radio and network resources and provides an efficient and scalable means to distribute multimedia content to mobile phones
  • MBMS User Services
    • streaming services - a continuous data flow of audio and/or video is delivered to the user's handset
    • download services - data for the file is delivered in a scheduled transmission timeslot
• The p-t-m MBMS Bearer Service does neither allow control, mode adaptation, nor retransmitting lost radio packets (thus, QoS provided for transport of multimedia applications is in general not sufficiently high to support a significant portion of the users for either download or streaming applications)
• Consequently, 3GPP included an application layer FEC based on Raptor codes for MBMS
• MBMS User Services may be distributed over p-t-p links if decided to be more efficient

MBMS

• Introduced for WCDMA (UMTS) in Release 6
• Supports multicast/broadcast services in a cellular system
• Same content is transmitted to multiple users located in a specific area (MBMS service area) in a unidirectional fashion
• The Broadcast Multicast Service Center (BM-SC) node is responsible for authorization and authentication of content provider, charging, and overall data flow through Core Network (CN)
• In case of multicast, a request to join the session has to be sent to become member of the corresponding MBMS service group
• In contrast to previous releases of Universal Terrestrial Radio Access Network (UTRAN), in MBMS a data stream intended for multiple users is not split until necessary (in UTRAN, one stream per user existed both within CN and RAN)
• MBMS services are power limited and maximize the diversity without relying on feedback from users
• Two techniques are used to provide diversity:
  • Macro-diversity: combining transmission from multiple cells
    • Soft combining: combines the soft bits received from the different radio links prior to (Turbo) coding
    • Selection combining: decoding the signal received from each cell individually, and for each TTI selects one (if any) of the correctly decoded data blocks for further processing by higher layers
  • Time-diversity: against fast fading through a long Transmission Time Interval (TTI) and application-level coding
    • because broadcast cannot rely on feedback, MBMS uses application-level forward error-correcting coding, namely Systematic Raptor codes