18-759: Wireless Networks L ecture 17: Cellular Peter Steenkiste - - PDF document

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18-759: Wireless Networks Lecture 17: Cellular

Peter Steenkiste

Peter A. Steenkiste, CMU

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Departments of Computer Science and Electrical and Computer Engineering Spring Semester 2010

http://www.cs.cmu.edu/~prs/wirelessS10/

Outline

Cellular landscape

p

AMPS GSM » HSCSD » GPRS » EDGE CDMA

Peter A. Steenkiste, CMU

2 OFDM

Some slides provided by Rui Aguiar University of Aveiro

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The Cellular Landscape

FDMA 0.15bps/Hz Max.rate 64Kbps TDMA &CDMA 0.30 bps/Hz Max.rate 2 Mbps TDMA CDMA d WCDMA 5-10 bps/Hz

• Max. rate ~

100Mbps/1Gbs

1G Analog 2G Digital Modulation Convolution coding Power Control 2.6G/3G Hierarchical cell structure Turbo-coding 4G Smart antennas? MIMO? Adaptive Systems OFDM Modulation

FDMA TDMA &CDMA TDMA,CDMA and WCDMA p WCDMA

Peter A. Steenkiste, CMU

3 AMPS TACS NMT C-450 PDC GSM HSCSD GPRS IS-54/IS-136 IS-95/IS-95A/IS-95B PHS EDGE Cdma2000 WCDMA/UMTS 3G 1x EV-DO 3G 1X EV-DV

Cellular Standards

2G systems: digital voice

y g

» GSM - FDMA/TDMA, most widely deployed, 200 countries, a billion people » IS-95 - first CDMA-based cellular standard, developed by Qualcomm » IDEN - TDMA, Nextel, merged with Sprint, being phased

• ut for CDMA2000

» IS-136 - uses FDMA/TDMA, North America, Cingular and US Wireless, being phased out for GSM, CDMA2000

Peter A. Steenkiste, CMU

4 US Wireless, being phased out for GSM, CDMA2000 2.5G systems: voice and data channels » GPRS - evolved from GSM, packet-switched, 170 kbps (30-70 in practice) » CDMA2000 1xRTT - evolved from IS-95, 144 kbps

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Cellular Standards

2.75G - almost 3G in speed

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» EDGE - another enhancement of GSM, 384 kbps, 2.75G » Thanks to new modulation scheme (8PSK) – may coexist with GMSK 3G: voice (circuit-switched) and data (packet-

switched)

» UMTS - W-CDMA, successor to GSM networks, 384 kbps - 2 Mbps, European, some Japan, Cingular in U.S.

Peter A. Steenkiste, CMU

5 » CDMA2000 1xEV - CDMA2000 with high data rates - 3.1 Mbps up, 1.8 Mbps down, U.S., Japan, Korean, Canada – Verizon, Sprint 4G: 10 Mbps and up, seamless mobility between

diffferent cellular technologies, mesh, etc.

GSM Evolution

Messages » SMS – Short Message Service » News » USSD – Unstructured Supplementary Service Data Data: » HSCSD – High Speed Circuit-Switched Data » GPRS – General Packet Radio Service » Edge – Enhanced Data Rate for GSM Evolution

Peter A. Steenkiste, CMU

6 » Edge – Enhanced Data Rate for GSM Evolution » UMTS – Universal Mobile Telecommunication System

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HSCSD

Based on fast circuit switching, introduced in phase

2+ (1997) 2+ (1997).

» Non optimum solution for packets (cost/capacity)

Same GSM layers

» Same interoperation function in MSC, » same transport network

Uses multiple time slots per user (max 6)

Peter A. Steenkiste, CMU

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» Changes link level protocol » Bitrates: 19.2 ; 28.8 ; 28.4 ; 48 ; 56 and 64 kb/s. » Asymmetric configurations (n slots on the uplink and m slots on the downlink). » Increases blocking probability of the system

GPRS

General Packet Radio Service Packet-oriented transport service, for data network

connections (Internet)

GPRS features: » Better transmission bit rates(max 150kbps). » Allows burst communications (“immediate”: connections in <1s) » New network applications » New billing mechanisms (user-oriented: by traffic p ex )

Peter A. Steenkiste, CMU

8 » New billing mechanisms (user-oriented: by traffic, p.ex.)

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GPRS principles GPRS principles

Transmission of non-periodic and bursty data (e.g.: mails),

F

t ll k t ( t l ti billi d i t )

Frequent small packets (e.g.: telematic, billing and micro-payments),

» Large but unfrequent packets (e.g.: ftp). Higher bit-rates per TCH (9.05 ; 13.4 ; 15.6 ; 21.4 kb/s),

Higher bit-rates with up to 8 time slots per user, Channel sharing by active terminals, Separate allocation of uplink and downlink channels,

Peter A. Steenkiste, CMU

9 Separate packet transmission network between the

BSC and external packet transmission networks: GSS (based on SGSN and GGSN).

GSS: GPRS SubSystem

GPRS Architecture

New entities are defined

SGSN – serving GPRS support node SGS g G S pp GGSN – gateway GPRS support node Interfaces between entities GPRS, GSM, core, e PSTN

Transmission plane

Data packets are transmitted by a tunnel mechanisms

Control plane

GTP: a protocol for tunnel management (create remove etc )

Peter A. Steenkiste, CMU

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GTP: a protocol for tunnel management (create, remove, etc..) GPRS Tunnel Protocol

Radio interface

Changes the logical channels and how they are managed Keeps the concept of “master-slave”

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GPRS Architecture

SGSN

Other GPRS networks BTS BTS MT BSC Gb

SGSN

Gf Gs Gr D EIR Gc Gn GGSN Gi PDN Gp GGSN networks

Peter A. Steenkiste, CMU

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D MSC/VLR HLR

SGSN – serving GPRS support node GGSN – gateway GPRS support node

GPRS introduction in a GSM network

..

... . . .

BTS BTS BSC TRAU MSC/VLR PSTN HLR A Abis IN Plate-form BTS PCU Gb Gs SGSN Gr, Gd, Gf Gn Border GPRS backbone S i WAP SS7 Network Gf EIR Gr MSC/VLR

Peter A. Steenkiste, CMU

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Border Gateway GGSN Inter-operator backbone GPRS backbone Internet PDN Router LAN Service plate-form WAP, WWW, ... Gc

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GSM to GPRS Evolution

BSS Evolution:

• Replace/Upgrade existing elements: BTS, BSC,

Replace/Upgrade existing elements: BTS, BSC, O&M, Network planning, Links (Abis, Ater, …).

• New element: PCU (Packet Controller Unit).

NSS Evolution

• A new core network (GSS) dedicated to GPRS:

IP/ATM based, network packet nodes

Peter A. Steenkiste, CMU

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(SGSN,GGSN), Internet equipment (DNS servers, Firewalls, …).

• Evolution of the network elements: HLR,

MSC/VLR, SS7.

GGSN (Gateway GPRS Support Node) Functions

Gateway:

All th ti t th IP GPRS t k » Allows the connection to other IP or GPRS networks.

Routing:

» IP router which supports dynamic or static routing,

Mobility management:

» Use of routing areas. » Handover management between the BSCs and other SGSNs. All th ti f th k t t d th SGSN

Peter A. Steenkiste, CMU

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» Allows the routing of the packets towards the users SGSNs, according to their mobility.

Sessions management:

» At each session, the SGSN activates a PDP (Packet Data Protocol) context, and allocates an IP address to the MT.

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Security:

» Ciphers the communications towards or from the

GGSN (Gateway GPRS Support Node) Functions

» Ciphers the communications towards or from the mobiles. » Includes firewalls for filtering the packets coming from external IP networks.

Authentication:

» At Attach and inter-SGSN RA updates.

Billing:

Peter A. Steenkiste, CMU

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» Production of the CDRs according to the quantity of information and the session duration (attachment, duration of active PDP context).

SMS:

» Supports the Gd interface for the communications with the SMS-GMSC and the SMS-IWMSC.

MT Registration

There is an explicit registration of the MT in the network: network:

» GPRS attach » GPRS detach – can be started by the MT or by the network » Location packets are periodically sent

HLR (modified!) keeps information on the MT status,

including:

» GPRS state (ready, standby, idle)

Peter A. Steenkiste, CMU

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» GPRS state (ready, standby, idle) » QoS profile (priority 3, delay 4, reliability 5, throughput peak 9 and media 19) » Context PDP (Packet Data Protocol)

– Also stored in GS and in the GGSN and SGSN

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Connection Management

After attach: receive a packet with a PDP identifier

Acts as an address Acts as an address

PDP identifier: per session.

– static: allocated by the MT home networks – Dinamic: allocated by the GGSN

PDP profile:

Type PDP identifier

Peter A. Steenkiste, CMU

17 de t e Requested QoS correspondent GGSN address

PDP context activation

MT SGSN GGSN

Activate PDP Context Request Security Functions Create PDP Context Request PDP type,PDP Address QoS Requested,Access Point,… PDP type,PDP Address Q S N ti t d A P i t

Peter A. Steenkiste, CMU

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Activate PDP Context Accept Create PDP Context Response QoS Negotiated,Access Point,… PDP type,QoS Negotiated,… PDP type,PDP Address QoS Negotiated,…

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Time Slot

GPRS Radio Interface

1 2 4 3 5 6 7 1 2 3 4 1 2 4 3 5 6 7 1 2 3 4 1 2 4 3 5 6 7 1 2 3 4 1 2 4 3 5 6 7 1 2 3 4

Uplink

F1 F2 F3 F4 F1

Carrier frequency

Peter A. Steenkiste, CMU

19 Downlink

User1 Voice User2 Voice User3 GPRS User4 GPRS User5 GPRS

F2 F3 F4

frequency

GPRS: logical channels

Group Channel Function Direction p

Packet data Traffic channel PDTCH

Data Traffic MS BSS

Packet broadcast control channel PBCCH

Broadcast Control MS BSS

Packet common Control Channel PRACH PAGCH

Random Access Access Grant MS BSS MS BSS

Peter A. Steenkiste, CMU

20 Control Channel (PCCCH) PPCH PNCH Paging Notification MS BSS MS BSS Packet Dedicated Control Channels PACCH PTCCH Associated Control Timing Advance Control MS BSS MS BSS

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Data Transfer (Uplink)

MT BSS

PRACH or RACH PAGCH or AGCH

T

PACCH PACCH

Packet Immediate assignment Packet resource Request Packet resource assignment F T i i Packet channel Request

Peter A. Steenkiste, CMU

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Transmission

PDTCH PACCH PDTCH PACCH

Frame Transmission Negative Acknowledgement Retransmission of blocks in error Acknowledgement

Data Transmission (downlink)

Packet paging request

MT BSS

PRACH or RACH PAGCH or AGCH

Paging Packet channel Request

PACCH PACCH or PAGCH

Packet Immediate assignment Packet paging response Packet resource assignment

PPCH or PCH

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Transmission

PDTCH PACCH PDTCH PACCH

Negative Acknowledgement Retransmission of blocks in error Frame Transmission Acknowledgement

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Enhanced Data rates for GSM Evolution (EDGE)

Objective:

Increase the data bitrates (GPRS EGPRS) Increase the data bitrates (GPRS EGPRS).

Bitrates:

• 473 kb/s for the terminals of 100 km/h maximum.
• 80-130 kb/s on average.
• 144 kb/s for the terminals of 250 km/h maximum.

Means:

Peter A. Steenkiste, CMU

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• 1- New modulation (8-PSK).
• 2- Link adaptation

New

mobiles, upgrade/replacement

• f

TRXs and capacity enhancement (Abis, …).

EDGE

Enhanced Data Rates for GSM Evolution Enhanced Data Rates for GSM Evolution » Announced as low-cost 3G (marketing…) » 2.5G evolution to GSM » Improved GPRS structure, but retaining basic structure » Improved data rates (144kbps a 470kbps) » Improved spectrum efficiency (2-6x)

Peter A. Steenkiste, CMU

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» EDGE supports GMSK & (new) 8-PSK » Requires lots of changes in transceiver design!

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Goals of 3G?

Greater system capacity both in terms of

users and bandwidth users and bandwidth

Good support for mobility at high data rates

at high speeds

cdma2000 (Qualcomm) vs. W-CDMA » W-CDMA is the air interface for Universal Mobile Telecommunication system (UMTS), successor of GSM

Peter A. Steenkiste, CMU

25 – Uses two 5MHz bands for up and down link – UMTS sometimes also uses single band (TDD) » cdma2000 is successor of Qualcomm’s cdma – Uses two 1.25 MHz bands for up and down link – Adds 64 orthogonal channels relative to IS95 – Evolution Data Optimized (EV-DO) adds TDMA

Code Division Multiple Access (CDMA)

CDMA uses codes to convert between analog

g voice signals and digital signals.

It then uses codes to divide voice and control

data into data streams called “channels”

Peter A. Steenkiste, CMU

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CDMA Signal Generation

Analog to digital conversion (Pulse Code

g g ( Modulation)

Vocoding Encoding and Interleaving Channelization Conversion of the digital signal to a RF signal

(modulation)

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(modulation)

Variable Rate Vocoder

Human speech is full of pauses (thinking,

iti t h b k t ) waiting to hear back, etc.)

CDMA vocoder varies compression of the

voice signal into one of four data rates, based

• n the user’s speech activity

The four rates are: Full, 1/2, 1/4, 1/8 Full rate when the person talks very fast

Peter A. Steenkiste, CMU

28 1/8 when the person is silent or nearly so CDMA systems can use either a 8 Kbps or a

13 Kbps vocoder

» Extended Variable Rate Coding (EVRC) vocoder produces the quality of the 13 Kbps vocoding, with a 8 Kbps rate

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Encoding and Interleaving

Builds redundancy into the signal to recover

y g information loss

Encoding relies on convolutional encoding Simplified scheme is the repetition code:

every bit is repeated three times

The encoded bits are called symbols The decoder at the receiver uses a majority

Peter A. Steenkiste, CMU

29 The decoder at the receiver uses a majority

logic rule

Combat burst errors

(built in BTS and phones)

Interleaving

Reduce the effect of burst errors and recover

lost bits

Symbols are said to be interleaved or

scrambled in a pattern that the receiver knows

De-interleaving at the receiver unscrambles

the bits, spreading any burst errors that occur d i t i i

Peter A. Steenkiste, CMU

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during transmission

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Channelization

The encoded voice is further encoded to

separate it from other encoded voice data

The encoded symbols are spread over the

entire bandwidth of the CDMA channel

The receiver knows the code and uses it to

recover the data

Peter A. Steenkiste, CMU

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Code channels in CDMA

Code channel is a stream of data designated

g for a specific use of person

This channel may be voice data or overhead

control data

Channels are separated by codes The forward and reverse links use different

types of channels

Peter A. Steenkiste, CMU

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yp

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Two types of codes

BTS to mobile

» Walsh codes » Nearly “orthogonal” codes » Unique enough that the voice data can only be recovered by a receiver applying the same Walsh code

Mobile to BTS

P d d N i (NS) d

Peter A. Steenkiste, CMU

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» Pseudorandom Noise (NS) codes » Appears to be random but is not » 4.4 trillion combinations of code for CDMA » Less computationally intensive » (assigned during setup, hardwired set of codes for discovery)

At the receiver…

RF to digital signal

g g

Despreading of the signal De-interleaving and decoding Voice decompression Digital to Analog voice recovery

Peter A. Steenkiste, CMU

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Forward Link Channels

Pilot » The BTS constantly transmits here. » The mobile uses this channel to acquire the system. » Mobile uses the pilot signal to monitor and adjust its power Sync » The BTS constantly transmits here. The mobile uses this channel for time synchronization – system time and

Peter A. Steenkiste, CMU

35 identification number of the cell site. The mobile ignores the sync channel after it is synchronized.

Forward Link Channels

Paging

g g

» CDMA uses up to seven paging channels » It transmits overhead information such as commands and pages to mobiles » Traffic channel assignment during call set-up » Mobile ignores paging channel after a traffic channel is established Traffic

Peter A. Steenkiste, CMU

36 » CDMA uses 55-61 forward traffic channels to send both voice and overhead control data during a call » When the call is completed, the mobile tunes back into the paging channel

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Reverse Link Channels

Access » Register with the network » Originate calls » Respond to pages and commands » Transmit overhead messages Traffic » Only used when there is a call Transmits voice data to the BTS

Peter A. Steenkiste, CMU

37 » Transmits voice data to the BTS » Transmits the overhead control information during the call

Call processing stages

Initialization » Acquires the system via the Pilot code channel » Synchronizes with the system via the Sync code channel Idle mode » Mobile and base station communicate over the access and paging code channels » The mobile obtains overhead information via the paging code channel

Peter A. Steenkiste, CMU

38 Access mode » Call origination » Use of access and paging channels for call set up until a traffic channel has been established

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Call Overhead Messaging

Uses “Dim and Burst” or “Blank and Burst”

signaling, which replaces part of the voice traffic with system messages

Strong data recovery schemes prevent the

user from detecting this

Peter A. Steenkiste, CMU

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cdma2000 vs W-CDMA

cdma2000 W-CDMA Chip Rate 3.6864 Mbps 4.096 Mbps Downlink Pilot for Channel Estimation CDM common pilot TDM dedicated Pilot

Peter A. Steenkiste, CMU

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Antenna Beamforming

• Aux. Pilot

TDM dedicated Pilot BS Synchronization Synchronous Asynchronous

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cdma2000/W-CDMA similarities

Coherent forward link (FL) and reverse link (RL)

( ) ( )

Fast power control in FL and RL Variable length orthogonal Walsh sequences for

FL channelization

Complex QPSK spreading on FL and RL Identical Polynomials for Convolutional Codes

P ll l t b d f hi h d t t

Peter A. Steenkiste, CMU

41 Parallel turbo codes for higher data rates

cdma2000/W-CDMA similarities

Variable spreading factors for higher data

p g g rates

Mobile assisted inter-frequency hard handoff

procedures

Variable rate operation with blind rate

estimation for simple services (voice)

Continuous reverse link operation

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p

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What is Next?

OFDM WiMAX Long Term Evolution Cellular Landscape

Peter A. Steenkiste, CMU

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References

http://www.youtube.com/watch?v=EDDEsX7v

p y aII

http://www.youtube.com/watch?v=bur9hq_ab

• g

Peter A. Steenkiste, CMU

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