EETS 8316 Wireless Networks Fall 2013

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EETS 8316

Wireless Networks

Fall 2013

Dr. Shantanu Kangude

[email protected]

Lecture: Cellular Overview: 3G and 4G

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Third Generation Systems

• High-speed wireless communications to support

multimedia, data, and video in addition to voice

• 3G capabilities:

• voice quality comparable to PSTN

• 144 kbps available to users over large areas

• 384 kbps available to pedestrians over small areas • support for 2.048 Mbps for office use

• symmetrical and asymmetrical data rates

• packet-switched and circuit-switched services • adaptive interface to Internet

• more efficient use of available spectrum • support for variety of mobile equipment

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Driving Forces

• Trend toward universal personal telecommunications • Universal communications access

• GSM cellular telephony with subscriber identity module, is step towards goals

• Personal communications services (PCSs) and personal communication networks (PCNs) also form objectives for third-generation wireless

• Technology is digital using time division multiple access or code-division multiple access

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IMT-2000 Terrestrial Radio

Alternative Interfaces

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CDMA Design Considerations –

Bandwidth and Chip Rate

• Dominant technology for 3G systems is CDMA

– 3 CDMA schemes, share some design issues

• Bandwidth (limit channel to 5 MHz)

– 5 MHz reasonable upper limit on what can be allocated for 3G

– 5 MHz is enough for data rates of 144 and 384 kHz

• Chip rate

– given bandwidth, chip rate depends on desired data rate, need for error control, and bandwidth limitations – chip rate of 3 Mbps or more reasonable

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CDMA Design Considerations –

Multirate

• Provision of multiple fixed-data-rate channels to user

• Different data rates provided on different logical channels • Logical channel traffic can be switched independently

through wireless fixed networks to different destinations • Flexibly support multiple simultaneous applications

• Efficiently use available capacity by only providing the capacity required for each service

• Two methods

– Use TDMA within single CDMA channel – or use multiple CDMA codes

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CDMA Multirate

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UMTS Architecture & Domains

• UTRAN – UMTS Terrestrial Radio Access

Network

– User Equipment (UE) = Mobile

– Node B = Base Station

– Radio Network Controller = RNC like BSC

• Core Network

(Reuse GSM CN)

– Circuit Switched Domain

• MSC, GMSC

– Packet Switched Domain

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GSM and UMTS High level – Original

Src:

http://docstore.mik.ua/univercd/cc/td/doc/product/wireless/moblwrls/cmx/mmg_sg/cmx gsm.htm

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UMTS Release 4

• UTRAN is same as release 99

• Core Network Modified only in the CS

domain

– MSC = 2 entities

• Media Gateway(MGW) for user plane • MSC server for the control plane

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Release 4 Architecture + IMS

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UMTS Release 5

• Core: New platform IMS(

IP Multimedia

Subsystem)

• RAN: HSDPA(

High Speed Downlink

Packet Access

) technology

– allows 14.4 Mbps peak data rate in DL

– data rate achievable by software updates in

nodeB to support new modulations and

coding schemes

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UMTS Release 6

• RAN

– HSUPA allows upto 5.5 Mbps in UL

• Core

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Long Term Evolution (LTE) or 4G

wireless cellular networks from 3GPP

Evolved UMTS Terrestrial Radio

Access Network

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Terms and Definitions

• UE: User Equipment (Mobile)

• eNB: Evolved Node B (Base station)

• S-GW: Serving Gateway (Cellular network edge

router or MTSO)

• E-UTRA/N: Evolved UMTS Terrestrial Radio

Access/Network (Official name of LTE)

• EPS: Evolved Packet System (MTSO network)

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Network Architecture

• S1:

– “Logical Interface” between edge router and eNB

– May involve multiple hops

• X2:

– Control interface between 2 eNBs

– Only exists between eNBs that may need to communicate

• MME (control plane)

– Tracks the location of mobile in the network

• S-GW (user plane)

– Routes packets to appropriate eNB

X2

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Radio Network Functions

• Forwarding of core network control information

– Paging (from network to UE)

– Tracking area update (from UE to network)

– Other IDLE mode mobility/tracking procedures

• Data forwarding in both directions while connected

– Satisfy QoS for flows through scheduling

• Radio resource management

– Manage Radio connection (participation in the radio network)

– Manage mobility during connection

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Core Network Functions

• “Control” Protocol between UE and MME

(MTSO)

– Track the location of UE in idle mode – Track the state (active or idle) of the UE – Page UE to request it to be active

• Data Forwarding in both directions

• QoS control between S-GW (MTSO) and eNB

• Active mode UE mobility (Control information

between MME (MTSO) and eNB)

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Core Network: Tracking Areas and Paging

• Tracking Area

– A subset of eNBs represented as a single unit – Multiple overlapping tracking areas possible – Multiple hierarchical tracking areas possible

• Benefits of tracking areas

– Lower resolution of tracking of Idle UEs by MME

– less frequent tracking updates in MME as UE moves in IDLE

• Paging

– Request by “core network” to join the “radio network”

– Performed over a tracking area when traffic pending for a UE – All cells in a tracking area PAGE a UE

• Importance of tracking areas and paging

– Critical for the UE and the core to maintain correct tracking area – Paging reliability is important

– UE joins a radio network after receiving a valid page

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RRC Connection and Radio Network

Radio Resource Control (RRC):

Manages radio network participation of UEs

Two states:

– RRC_IDLE (UE is not part of the radio network)

• No UE state in the eNB

• UE may perform tracking area updates for core network (mobility) • UE may receive PAGE from the core network

– RRC_CONNECTED (UE becomes part of radio network)

• UE state exists in the eNB

– Data flows with their characteristics – Any measurement or capability reports

• A UE address called C-RNTI (Cell-Radio Network Temporary ID) • UE may be scheduled in the UL and DL

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Core network states and RRC

states

Power-Up

LTE_DETACHED

RRC: NULL

RRC Context in network: - Does not exist

Allocated UE-Id(s): - IMSI

UE position:

- Not known by network

Mobility

- PLMN/Cell selection

DL/UL activity: - None

LTE_ACTIVE

RRC: RRC_CONNECTED

RRC Context in network:

- Includes all information necessary for communication

- ID unique in Tracking Area (TA-ID) - ID unique in cell (C-RNTI)

- 1 or more IP addresses

UE position:

- Known by network at cell level

Mobility: - Handover

DL/UL activity:

- UE may be configured with DRX/DTX periods

LTE_IDLE

RRC: RRC_IDLE

Context in network:

- Includes information to enable fast transition to LTE_ACTIVE (e.g. security key information)

- ID unique in Tracking Area (TA-ID) - 1 or more IP addresses

UE position:

- Known by network at Tracking Area (TA) level

Mobility:

- Cell reselection

DL activity:

- UE is configured with DRX period

Perform “Registration”

- Allocate C-RNTI, TA-ID, IP addr - Perform Authentication

- Establish security relation

Change of PLMN/deregistration

- Deallocate C-RNTI, TA-ID, IP address New traffic

- Allocate C-RNTI Inactivity

- Release C-RNTI - Allocate DRX for PCH

Timeout of periodic TA-update - Deallocate TA-ID, IP address

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FDD Frames and Sub-Frames

• Frame

– System level quantum of repetition – 10 ms

• Sub-frame

– Smallest quantum for scheduling in time-domain – Comprises of 2 slots (significance for PHY only) – 1 ms

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FDD DL Frame Composition

10 Sub-frames per frame One

Resource Block (RB) = 12

sub-carriers

L1-L2 Control Channel: Maximum 3 out of 14 symbols

OFDM frequency carriers

Time

1 sub-frame = 14 OFDM symbols

OFDM symbols are MIN

quantum of time in OFDM

systems for any data carriage

Resource Block = Minimum Quantum for Scheduling in DL or UL

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Overhead in DL frames

• Broadcast System information interspersed

in the DL (e.g. Network name etc.)

• L1-L2 Control channel: Allocation of

transmission grants

– For DL transmissions (like DL-MAP in WiMax)

– For UL transmissions (like UL-MAP in WiMax)

• Unicast control PDUs to UEs

• Random Access (as Ranging in WiMax)

Responses

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FDD UL Frame Composition

10 Sub-frames per frame

1 Resource Block (RB) = 12 sub-carriers Control

channel on the edges

Data in UL-SCH Random Access Channel (RACH) Slot for Ranging

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UL Overhead

• Control Channel on the edges for HARQ

ACK-NACKs , Scheduling Requests etc.

• RACH channel or Ranging Slots as in

WiMax

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Random Access/Ranging

• Used by a UE in UL when

– No dedicated resources for TX available – No UL synchronization

• Utilizes

– Preamble transmission in eNB configured RACH slots – eNB responds with the Timing Advance value

A RACH access is the only way the possible

existence of UE’s transmission is not

“pre-known” to the eNB; All other transmissions are

pre-scheduled by the eNB

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Handover (Handoff)

• Mobility of the UE => The UE-eNB association changes • Idle mode mobility (cell-reselection)

– Camping (ready to connect) on best cells desired – Tracking area updates to core network if any change – No urgency as no calls/flows on going

• Connected mode mobility (Handover)

– Current eNB manages the transition based on measurement reports from UE

– Preparations as in RRC connection establishment required at target eNB before UE can transition