Curso 5_Nuevas Tecnologías en Comunicaciones Móviles Celulares_sesion3

Instituto Nacional de Investigación y Capacitación de Telecomunicaciones

UNIVERSIDAD NACIONAL DE INGENIERÍA

Nuevas Tecnologías en

Comunicaciones Móviles

Celulares

Programa de Ingeniería de Comunicaciones Inalámbricas

Msc. Ing. Henry A. Vásquez



Nuevas Tecnologías en Comunicaciones Móviles Celulares Temario:

Sistemas GSM

– Evolución histórica de GSM

– Conceptos básicos de GSM

– Arquitectura de GSM y principales Interfaces. Interfaz de Aire

– Codificación del canal de voz

– Estructura de los canales de tráfico y de control. Identidades empleadas en GSM

– Ejemplos de Trafico

– Sistemas GPRS

• Principio

• Componentes

• Aplicaciones

Sistemas CDMA – Conceptos básicos de CDMA

– Arquitectura del sistema

– Repaso de ensanchamiento espectral

– Códigos utilizados en CDMA

– Codificación del canal de voz. Control de potencia

– Señalización digital. Handoffs en CDMA

– Tipos de canales en CDMA 1x.

Sistemas de 3G

– Visión General de la Industria

– Desarrollo de la Tercera Generación IMT-2000. Requerimientos

– UMTS. Descripción y funcionamiento . CDMA-2000. UMTS. Descripción y funcionamiento.



Sistemas CDMA • CDMA is a "spread spectrum" technology, allowing many users to occupy

the same time and frequency allocations in a given band/space. CDMA

(Code Division Multiple Access) assigns unique codes to each

communication to differentiate it from others in the same spectrum. In a

world of finite spectrum resources, CDMA enables many more people to

share the airwaves at the same time than do alternative technologies.



CDMA Technology

• The CDMA air interface is used in both 2G and

3G networks. 2G CDMA standards are branded

cdmaOne™ and include IS-95A and IS-95B.

CDMA is the foundation for 3G services: the two

dominant IMT-2000 standards, CDMA2000®

and WCDMA, are based on CDMA.



CDMA Technology - CDMA2000

• CDMA2000® represents a family of IMT-2000 (3G) standards

providing high-quality voice and broadband data services

over wireless networks. CDMA2000 builds on the inherent

advantages of CDMA technologies and introduces other

enhancements, such as Orthogonal Frequency Division

Multiplexing (OFDM), advanced control and signaling

mechanisms, improved interference management

techniques, end-to-end Quality of Service (QoS), and new

antenna techniques such as Multiple Inputs Multiple Outputs

(MIMO) and beamforming to increase data throughput rates

and quality of service, while significantly improving network

capacity and reducing delivery cost.




• Currently, CDMA2000 includes CDMA2000 1X (1X) and

CDMA2000 EV-DO (EV-DO) standards. CDMA2000 1X (IS-2000)

supports circuit-switched voice up to and beyond 35 simultaneous

call per sector and high-speed data of up to 153 kbps in both

directions. It was recognized by the International

Telecommunications Union (ITU) as an IMT-2000 standard in

November 1999. CDMA2000 EV-DO (Evolution-Data Optimized)

introduces new high-speed packet-switched transmission

techniques that are specifically designed and optimized for a data-

centric broadband network that can deliver peak data rates

beyond 3 Mbps in a mobile environment. CDMA2000 EV-DO was

approved as an IMT-2000 standard (cdma2000 High Rate packet

Data Air Interface, IS-856) in 2001.




• Built on the principle of backwards compatibility, the

CDMA2000 evolution path has provided operators

favorable economics and a significant time-to-market

advantage in introducing new value-added services.

• CDMA2000 1X was deployed in 2000, as the first

IMT-2000 standard to be commercially available, and

today, along with EV-DO, it is the leading 3G

technology serving around a half billion users

worldwide. CDMA2000 systems provide a family of

related services including cellular, PCS, WLL and

fixed wireless.



CDMA Technology -Spectrum • CDMA2000 operates in a relatively small amount of spectrum, 1.25 MHz, in most

of the frequency bands designated by the International Telecommunication Union

(ITU) for the IMT-2000 systems. The smaller 1.25 MHz channel size enables

greater spectrum assignment flexibility to (a) incrementally assign channels as the

demand for capacity increases, and (b) to facilitate in-band migration deployments

which require the clearing of spectrum.

• CDMA2000 1X, EV-DO Rel. 0 and Rev. A operate in a paired 2 x 1.25 MHz FDD

channel - compared to other 3G technologies which require a much larger 2 x 5

MHz channel. By using a narrower radio channel, operators benefit from greater

flexibility and improved cost efficiencies in managing their scarce spectrum

resources. EV-DO Rev. B enables operators to aggregate multiple 1.25 MHz

channels, up to 15 channels in 20 MHz of spectrum, to deliver the next-generation

multi-mega-bits-per-second data connectivity and bandwidth intensive applications

more economically.

• Currently, CDMA2000 network infrastructure and user devices are available in

most of the IMT-2000 frequency bands designated by the ITU, including the 450

MHz, 700 MHz, 800 MHz, 1700 MHz, 1900 MHz, AWS and 2100 MHz bands.



CDMA Technology -Spectrum

1Includes IMT-2000 and IMT-Advanced 2Identified at WRC-07 3Includes:

698-862 MHz band in Region 2 (Americas)

790-862 MHz band in Region 1 (Europe, Middle East, Africa, Russia and CIS)

790-960 MHz identified for IMT in Region 3 (Asia-Pacific)



CDMA Technology -Spectrum

In many cases, the frequency assignment is as important as the broadband technology selection.

Using the lower frequency bands is preferable for broadband-intensive network deployments. The propagation

characteristics of the lower (warmer) frequency bands enable RF transmissions to travel greater distances. The increased range

provides larger coverage areas. Fewer cell sites require fewer backhaul connections, which leads to lower costs. The lower

frequency bands also enable better in-building penetration, better mobile performance, less power consumption and higher average

data throughputs in a non-line-of-sight (NLOS) environment.

This is becoming progressively more important as the bandwidth for the backhaul connections must increase to keep up with the

growing demand for mobile broadband services.



CDMA2000 1X

• CDMA2000 1X (IS-2000) is an IMT-2000 (3G) technology, designed to

deliver high-quality voice and high-speed data. It is an efficient wireless

technology for circuit-switched voice communications and it supports packet

data speeds of up to 153.6 kbps in a single 1.25 MHz radio channel.

• CDMA2000 1X was the first 3G (IMT-2000) technology deployed, in October

2000.

• Key features of CDMA2000 1X:

- Voice Capacity: Today, CDMA2000 1X supports 33-40 simultaneous voice

calls per sector in a single 1.25 MHz FDD channel. Using a new codec

(EVRC-B), additional Walsh codes and handset interference cancellation, it

can handle up to 55 simultaneous voice calls. With further receiver

enhancements and minor changes to the radio configuration, 1X Advanced

(1X Rev. E) will quadruple the voice capacity of CDMA2000 1X systems.

- High-Speed Data: Supports bi-directional (up and downlink) peak data rates

up to 153.6 kbps, delivering an average user data throughput of 80-100 kbps

in commercial networks using a 1.25 MHz FDD channel.



CDMA2000 1X

- Spectral Efficiency: Up to 0.180 bit/sec/MHz over a 5 MHz FDD channel.

- Average Latency: 250 msec node-to-node ping, RTT.

- Applications: Supports circuit-switched voice, short messaging service

(SMS), ringtone downloads, multimedia messaging service (MMS), games,

GPS-based location services, music and video downloads.

- Backwards Compatibility: CDMA2000 1X is backwards compatible with 2G

cdmaOne (IS-95A/B) systems and handsets.



CDMA2000 1X Interface The following fundamental CDMA air interface techniques are incorporated into

CDMA2000 1X and backward compatible with cdmaOne:

• Direct Sequence Spread Spectrum Multiple Access: to improve spectral efficiency (system

capacity)

• Orthogonal Code Channelization: for user separation on the downlink (mitigates interference)

• Random Access: to efficiently share radio access resources among all users

• Fast Uplink Power Control: to resolve the near-far field effect (reduce interference)

• Rake Receivers: to resolve and benefit from multipath interference and support soft handoffs

• Soft Handoff: to handoff users between base stations

• Softer Handoff: to handoff users between base station sectors

• Soft Handoff (SHO) Active Set: to provide seamless service with increased spectral efficiency

• Single Frequency Re-use: to increase overall network capacity

• Downlink Slotted Paging: to extend the battery life of mobile devices

• Blind Rate Detection: to enable variable rate decoding without additional overhead

• Downlink Reference Channel: to share a common pilot to increase capacity

• Downlink Channel Structure: to simplify system implementation and efficiency by separating

channels with Walsh codes

• Scrambling: to provide communications privacy

• Speech Regulated Vocoders: to reduce interference and increase system capacity



CDMA2000 1X Interface

Espectro Ensanchado ( Spread Spectrum ) • Sistema en el que se usa mas ancho de banda que el requerido por la tasa efectiva de datos

• Ej. 13 Kbps tomaría 13 kHz de ancho de banda. En un sistema Spread Spectrum tomaría mas de 13 KHz.

• Ganancia de proceso: G p= Bw / R Beneficio contra interferencia

• Técnicas Spread Spectrum: Frequency Hopping, Direct Sequence

Espectro Ensanchado: Gp = BW / R

Frequency Hopping

Spread Spectrum: Direct Sequence



Principios de CDMA

• CDMA combina 3 secuencias de ensanchamiento para crear un código único.

• En el receptor las secuencias se utilizan en el orden inverso que en el emisor

• Las 3 secuencias son generadas en ambos extremos y necesariamente no son utilizadas simultaneamente

Secuencias de ensanchamiento



Principios de CDMA

• Walsh Codes: (64 disponibles)

– 64 chips de longitud – dura 1/19200 Seg

– Ortogonales mutuamente

• PN Short codes: Se usa por pares (I + Q)

– Longitud de 215 --- dura 26mS aprox

• Se genera en registro de desplazamiento (15 bits)

• PN Long Code: 1 disponible

– Longitud de 242 --- se repita cada 40 dias

• Se genera en un registro de desplazamiento (42 bits)

Secuencias de ensanchamiento



Principios de CDMA

Funciones Walsh

• En CDMA cada

símbolo es

expandido con los

64 chips de los

código de Walsh

• Luego, por cada

bit de data se

tendrán 64 chips

de salida.



Principios de CDMA

Códigos Offset de Pseudo Ruido (PN Offset) • Son secuencias binarias con características aleatorias.

• Si un mismo código PN es cambiado en el tiempo (time offset), se obtienen dos códigos que son casi

ortogonales.

• Para agregar el offset a un código PN y crear secuencias cuasi ortogonales, se usa un sistema

enmascaramiento. Con diferentes time offsets, se lograrán tener varias secuencias cuasi ortogonales.

Autocorrelación Generación de códigos de pseudo ruído

Seq A: 0010 1011 0011 011

Seq A’: 1011 0011 0110 010

4 chips offset



Principios de CDMA

Códigos Offset de Pseudo Ruido (PN Offset)

• Se usan tres códigos PN en CDMA: 2 Códigos Cortos y 1 Código largo

• La secuencia corta PN sequence posee 32,768 bits, utiliza offset de 64 bits y un total de 512 time offsets,

• La transmisión toma 26.667 ms por cada ciclo. PN offset se utiliza para identificar las celdas y sectores

0

Receptor / Correlador CDMA



Principios de CDMA



Principios de CDMA

Code Channels CDMA: Forward Channels • Existen 64 canales de código, en cada canal CDMA de 1.2288-MHz, de éstos se distinguen 3 canales

principales:

• Canal Piloto: Siempre mantiene el Código de Walsh 0

• Canales de Paging : Walsh Code 1 (W1), puede ser asignado hasta Walsh Code 7 (W7). Asignacion de

canal de tráfico. Busqueda de moviles. SMS

• Canal de Sincronía (Sync Channel): Walsh Code 32 (W32). El resto son canales de tráfico

• La data expandida es ingresada en los canales (I,Q), donde se expanden nuevamente ( Short Sequence PN).

• El Offset del código PN se da de acuerdo al sector transmitido.

Estructura del Enlace Forward PN Offset para identificar sectores y celdas



Principios de CDMA

Forward Channels: Canal Piloto

• Sirve como referencia de sincronismo. No lleva información, simplemente transmite los códigos

PN con su respectivos offset. Es usado por el móvil para identificar las celdas ó sectores y

comparar potencias para el proceso de hand off.

• El canal piloto contiene alrededor del 20% de la potencia de radiación. Se repite cada 26.67

mseg.

• 0

Estructura del Canal Piloto



Principios de CDMA

Forward Channels: Canal Sincronía • Usa Código de Walsh 32. Se compone de una supertrama de 80-ms, dividida en tres tramas de 26.667-ms.

• Transmite la siguiente información:

- System time - System ID - Long-Code State 320 ms into the future,

- Pilot PN de la BTS, - Network ID - System Time, Local Time

• De los 3 canales principales, es el que posee menor potencia.

• El equipo móvil primero sintoniza el canal piloto y luego se engancha al canal de sincronía (W32) para leer la

información de la red y sincronizarse

Estructura del Canal Sync|



Principios de CDMA

Forward Channels: Canal Paging • Similar al DCCH en TDMA. Utiliza W1-W7

• Información de paging, red, códigos PN vecinos, canales vecinos y asignación de móviles a canales de tráfico.

• El canal de paging se divide en 2,048 slots, de 80 ms. Ciclo total de 163.84 seconds.

• Sleep mode se establece para slots específicos. Cada móvil escucha un slot distinto

• Un canal paging puede manejar hasta 32 canales de tráfico.

• Antes del Código de Walsh, la data es expandida con un código de secuencia larga. La máscara de este

código está basada en el número del canal de paging y el offset PN del sector correspondiente. Es un nivel

de seguridad adicional

Estructura del Canal Paging



Principios de CDMA

Forward Channels: Canal Tráfico • Transmiten voz, datos y señalización durante una llamada. Se utiliza un long code con una máscara basada

en el ESN de cada usuario. Walsh Code puede ser asignado en cualquiera de los 55 códigos restantes

• Envío de mensajes como: Autenticación, mensajes de alerta, handoff y medidas de seguridad (cambios en el

long code)

• Se incluye el subcanal de control de potencia. Consiste de un bit por cada 125 mseg insertado en la data,

para que el móvil pueda detectarlo y aumentar o disminuir su potencia en pasos de 1 dB.

Estructura del Canal Tráfico



Principios de CDMA

Forward Channels: Sincronización

• El móvil encuentra un canal piloto y se sincroniza con la secuencia PN ( 26.67 ms).

• El móvil lee el canal de sincronía ( 26.67 ms por trama) y queda sincronizado a la red. Monitorea el canal de

paging y obtienen los parámetros del sistema.

• Si se da una llamada, el móvil se mueve hacia un canal de Walsh adecuado (canal de tráfico activo)

• La recepción posee un Rake Receiver. Este combina coherentemente los multitrayectos para crear una señal

de banda base mas robusta. Luego la señal es procesada: descrambled, deinterleaved, y decodificada con

Viterbi.

• El Receptor (The Rake receiver) es una única parte del Sistema CDMA que permite buscar señales

multitrayecto fuertes, de otras estaciones base y deslizar las señales en el tiempo para encontrar su código.

• Una vez encontrado, el receptor puede demodular la señal, combinarla coherentemente para crear un

receptor mejorado que pueda manejar handoffs sin rupturas.

• La mayoría de móviles poseen tres elementos de recepción (fingers). Las estaciones base poseen cuatro

fingers




Simplified block diagram of the RAKE receiver



Principios de CDMA

CDMA: Control de Potencia • La estación móvil emite ráfagas de señal, para ahorro de batería y disminuir el ruido en la red

• La potencia de transmisión se va decrementando 3 dB de acuerdo a la degradación del data rate

• La señal es enviada por ráfagas (bursted) en Grupos de Control (Power Control Groups - PCGs) de 1.25-ms,

luego existen 16 PCGs en cada trama de 20-ms

• El móvil envía un mensaje llamado access probe (en el canal de acceso), y espera una respuesta en el canal

paging. Si no recibe respuesta espera un tiempo y luego incrementa su potencia e intenta nuevamente. Los

parámetros de incrementos, tiempo e intentos son dados por la red

Power Control Groups



Principios de CDMA

Control de Potencia: Forward

• La RB continuamente reduce la potencia de los usuarios en el Forward link

• Cuando el Móvil detecta errores en el forward link solicita mayor energía

• La BTS incrementa la potencia de ese usuario y luego comienza a

disminuirla progresivamente de nuevo.



Principios de CDMA

Control de Potencia: Reverse

• Lazo Abierto: Móvil ajusta la potencia basado en la potencia de la señal recibida de la celda

• Lazo Cerrado: la celda indica +- 1dB @ 800Hz basado en mediciones de potencia en la celda

• Lazo Externo: La controladora detecta gran cantidad de errores (FER) y setea el punto mínimo de potencia



Principios de CDMA

CDMA: Hand Off

• Soft handoffs: El móvil realiza un nuevo enlace con otra estación

base antes de cortar la comunicación con la anterior. El móvil

constantemente busca PN offsets como posibles candidatos. El

móvil puede solicitarlo

• Softer handoff: Involucra dos sectores de la misma BTS.

• Hard handoff: Involucra una completa desconexión de la celda

original antes de pasar a otra celda.

• Idle Handoffs: Durante el estado IDLE, el móvil opera soft, softer,

and hard handoffs según lo requiera.




In addition to the above techniques shared with cdmaOne, CDMA2000 1X

incorporates the following evolutionary air interface techniques that are

crucial to enhancing the performance of the standard:

• Variable Length Orthogonal Codes: to support variable data rates

• Uplink Complex Spreading: to increase data rates and network capacity

• Fast Downlink Power Control: to reduce transmit power usage and increase

capacity

• Data Rate Configurable Channels: to support applications that use a variety of

data rates

• Dual-Event Downlink Paging: to further extend the battery life of mobile devices

• Uplink Channel Structure: to multiplex control and data channels

• Reserve Mode Random Access: to access the network more efficiently

• Parallel Turbo Codes: to improve capacity through more efficient forward error

correction

• Coherent Uplink Detection: to improve data rates and coverage

• Continuous Uplink Operation: to increase transmission range and capacity,

while reducing interference to hearing aids and other devices.



CDMA2000 1X Advanced

1X Advanced includes a collection of enhancements that can theoretically increase voice capacity

by up to 100 Erlangs, or a factor of four over legacy CDMA2000 1X networks. To put this into

perspective, this industry-leading voice technology can support more than 80 times the number of

calls than older analog networks. 1X Advanced allows an operator to tradeoff this capacity

improvement to increase network coverage by up to seventy percent or triple 1X data network

capacity.



CDMA2000 Evolution • CDMA2000 offers operators a robust, long-term evolution path that delivers the performance and economics to meet the rapidly

evolving needs of the mobile market place over the long-term. The CDMA2000 evolution path is built on the principle of

backward and forward compatibility, in-band migration, and support of heterogeneous networks.

• CDMA2000 offers some of the highest voice capacity and data rates, and lowest latencies among the leading wide area network

technologies available today to deliver high-quality voice and broadband multimedia data services. Most of the technology

enhancements are enabled through software upgrades.



CDMA2000 Evolution • CDMA2000 technologies will continue to interoperate and coexist with wider-bandwidth OFDM-based

technologies such as 802.11n for wireless local area network (WLAN) connectivity and LTE.

CDMA2000 will offer global roaming, ubiquitous high-performance mobile broadband and voice services with a defined evolution

path, while OFDMA solutions will augment CDMA2000 capacity by leveraging wider-bandwidths and MIMO antennas in densely

populated hot-zones where the demand for broadband connectivity is extremely high.



CDMA Technology – CDMA450

• CDMA450 represents a family of CDMA2000 technologies

that operate across the 410-470 MHz band.1 It is the only 3G

(IMT-2000) solution that is commercially available for

deployment in this frequency band.

• CDMA450 systems support all CDMA2000 standards

developed by 3GPP2 and published by the TIA as TIA-EIA-

IS-CDMA2000 (CDMA-MC) including: CDMA2000 1X, 1xEV-

DO Release 0, Revision A, and future enhancements to

these technologies. These technologies are capable of

delivering voice, Internet access, multicasting and broadband

data services in both rural and urban settings using fixed,

limited mobility and full mobility networks.




• A significant competitive advantage of CDMA450 is that it

can provide advanced telecommunication services over wide

areas economically due to the enhanced propagation

characteristics enabled by the low frequency band. By

combining the expanded range of the 450 MHz frequency

band with the benefits of CDMA2000’s industry-leading

spectral efficiency, superior voice capacity, greater

broadband data speeds, lower latency and quality of services

(QoS) features, CDMA450 presents a powerful value

proposition for operators and customers alike.




• Leading infrastructure vendors are playing an active role in

deploying CDMA450 services worldwide. There is a broad

range of commercially available CDMA450 devices that

includes fixed wireless phones, desktop modems, machine-

to-machine modules, ultra low-cost handsets and USB

thumb-drive modems. Multi-band (CDMA450/CDMA800) and

multi-mode (CDMA450/GSM900) WorldModeTM devices

allow customers to enjoy the benefits of broader international

roaming services.




• Due to its superior performance and economics, there is significant

momentum behind the deployment of CDMA450 across Africa, Asia,

Europe and Latin America. It is rapidly becoming the technology of

choice for providing universal access to services that will help increase

social and economic prosperity. Millions of people are using the

technology in densely populated urban areas as well as sparsely-

populated rural areas to communicate, connect to the Internet and benefit

from innovative data solutions.

• With the identification of the 450 MHz band for IMT by the International

Telecommunication Union (ITU) at the 2007 World Radiocommunication

Conference (WRC-07), regulators in many countries are in the process of

allocating the band for 3G broadband services, creating new

opportunities for CDMA450.

1. The 450 MHz band includes sub-bands in the frequency ranges of 410-430 MHz, 450-470

MHz and 470-490 MHz.



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Curso 5_Nuevas Tecnologías en Comunicaciones Móviles Celulares_sesion3

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