🗊Презентация Мобильные сотовые сети

Мобильные сотовые сети

Основы сотовой связи There are many types of cellular services; before delving into details, focus on basics (helps navigate the “acronym soup”) Cellular network/telephony is a radio-based technology; radio waves are electromagnetic waves that antennas propagate Most signals are in the 850 MHz, 900 MHz, 1800 MHz, and 1900 MHz frequency bands

Сотовая связь Base stations transmit to and receive from mobiles at the assigned spectrum Multiple base stations use the same spectrum (spectral reuse) The service area of each base station is called a cell Each mobile terminal is typically served by the ‘closest’ base stations Handoff when terminals move

Поколения сотовой связи It is useful to think of cellular Network/telephony in terms of generations: 0G: Briefcase-size mobile radio telephones 1G: Analog cellular telephony 2G: Digital cellular telephony 3G: High-speed digital cellular telephony (including video telephony) 4G: IP-based “anytime, anywhere” voice, data, and multimedia telephony at faster data rates than 3G (to be deployed in 2012–2015)

Развитие сотовой связи

Проблема Множественного Доступа Базовые станции должны обслуживать множество мобильных терминалов одновременно (both downlink and uplink) Все мобильные телефоны в соте нужны для передачи к базовой станции Интерференция между различными отправителями и получателями Поэтому нужна схема множественного доступа

Схемы Множественного Доступа

множественный доступ с разделением каналов по частоте Каждому мобильному назначается отдельный Частотный канал для продолжительности вызова Достаточная защитная полоса требуется для предотвращения интерференции от соседнего канала Как правило, мобильные терминалы имеют одну нисходящую линию связи полосы частот и одну восходящую линию связи полосы частот Разные сотовые сетевые протоколы используют разные частоты

множественный доступ с разделением по времени Время делится на слоты и только один мобильный терминал передает в каждый слот -Как во время лекции, только один может говорить, а другие могут взять слово в свою очередь Каждому пользователю присваивается определенный слот. Нет конкуренции в сотовой сети В отличие от множественного доступа с прослушиванием несущей в WiFi

множественный доступ с кодовым разделением Использование ортогональных кодов для разделения разных трансмиссий Каждый символ бит передается как большее число битов, используя пользовательский код – распространение -Ширина полосы частот, занятой сигналом, намного больше, чем скорость передачи информации Но все Пользователи используют ту же полосу частот совместно

2G(GSM)

GSM Global System for Mobile Communications глобальный цифровой стандарт для мобильной сотовой связи Concurrent development in USA and Europe in the 1980’s The European system was called GSM and deployed in the early 1990’s

GSM услуги Голосe, 3.1 kHz служба коротких сообщений Short Message Service (SMS) 1985 GSM стандарт, который позволяет сообщения не более 160 символов. (incl. spaces) чтобы переть сообщения между телефонами и другими станциями Over 2.4 billion people use it; multi-billion $ industry пакетная радиосвязь общего пользования General Packet Radio Service (GPRS) GSM upgrade that provides IP-based packet data transmission up to 114 kbps Users can “simultaneously” make calls and send data GPRS provides “always on” Internet access and the Multimedia Messaging Service (MMS) whereby users can send rich text, audio, video messages to each other Performance degrades as number of users increase GPRS is an example of 2.5G telephony – 2G service similar to 3G

GSM Каналы Физический канал: каждый таймслот на носителе называется физическим каналом Логический канал: различная информация передается между MS и BTS. Различные типы логических каналов: -канал передачи трафика - каналы управления

GSM Частоты Изначально рассчитаны на диапазон 900 МГц, сейчас также доступен на 800 МГц, 1800 МГц и 1900 МГц диапазонов. Отдельного uplink и downlink частоты Одним из примеров : частотный диапазон каналов 1800 МГц, где несущая радиочастота разделена каждые 200 МГц

GSM Архитектура

Mobile Station (MS) MS is the user’s handset and has two parts Mobile Equipment Radio equipment User interface Processing capability and memory required for various tasks Call signalling Encryption SMS Equipment IMEI number Subscriber Identity Module

Subscriber Identity Module A small smart card Encryption codes needed to identify the subscriber Subscriber IMSI number Subscriber’s own information (telephone directory) Third party applications (banking etc.) Can also be used in other systems besides GSM, e.g., some WLAN access points accept SIM based user authentication

Base Station Subsystem подсистема базовых станций Transcoding Rate and Adaptation Unit (TRAU) Выполняет кодирование между 64 кбит / с ИКМ кодирование используется в магистральной сети и 13 Кбит / с используется для кодирования мобильной станции (МС) Base Station Controller (BSC) Контролирует канал (тайм-слот) распределение осуществляемые BTS Управляет хэндоверами в пределах BSS Знает, какие мобильные станции в пределах ячейки и информирует MSC/VLR об этом Base Transceiver System (BTS) Controls several transmitters Each transmitter has 8 time slots, some used for signaling, on a specific frequency

Network and Switching Subsystem подсистема сети и коммутации опорная сеть GSM -телефонная сеть с дополнительными возможностями сотовой сети Mobile Switching Center (MSC) В типичной телефонной станции (сети ISDN Exchange), которая поддерживает мобильную связь Visitor Location Register (VLR) A database, part of the MSC Contains the location of the active Mobile Stations Gateway Mobile Switching Center (GMSC) Links the system to PSTN and other operators Home Location Register (HLR) Contain subscriber information, including authentication information in Authentication Center (AuC) Equipment Identity Register (EIR) International Mobile Station Equipment Identity (IMEI) codes for e.g., blacklisting stolen phones

Home Location Register  домашний регистр местоположения One database per operator Contains all the permanent subscriber information MSISDN (Mobile Subscriber ISDN number) is the telephone number of the subscriber International Mobile Subscriber Identity (IMSI) is a 15 digit code used to identify the subscriber It incorporates a country code and operator code IMSI code is used to link the MSISDN number to the subscriber’s SIM (Subscriber Identity Module) Charging information Services available to the customer Also the subscriber’s present Location Area Code, which refers to the MSC, which can connect to the MS.

Другие системы Operations Support System Система Поддержки Операций The management network for the whole GSM network Usually vendor dependent Very loosely specified in the GSM standards Услуги с добавленной стоимостью -Voice mail Call forwarding Group calls Short Message Service Center Центр Службы Коротких Сообщений -Stores and forwards the SMS messages Like an E-mail server Required to operate the SMS services

Смена Местоположения При перекрытии сот мобильная станция может "видеть" несколько приемопередатчиков (BTSes) МС отслеживает идентификатор для BSC контроля сот Когда мобильная станция приближается в область новойBSC, она просит обновления местоположения Обновления передаются на MSC, заносится в VLR, старая BSC уведомлена и подтверждение передается обратно

Handoff (Handover) When a call is in process, the changes in location need special processing Within a BSS, the BSC, which knows the current radio link configuration (including feedbacks from the MS), prepares an available channel in the new BTS The MS is told to switch over to the new BTS This is called a hard handoff In a soft handoff, the MS is connected to two BTSes simultaneously

Roaming When a MS enters another operators network, it can be allowed to use the services of this operator Operator to operator agreements and contracts Higher billing The MS is identified by the information in the SIM card and the identification request is forwarded to the home operator The home HLR is updated to reflect the MS’s current location

3G, 3.5G and 4G (LTE)

3G Обзор 3G is created by ITU-T and is called IMT-2000

Развитие от 2G

Service Roadmap

GSM развитие к 3G

UMTS Universal Mobile Telecommunications System (UMTS) UMTS is an upgrade from GSM via GPRS or EDGE The standardization work for UMTS is carried out by Third Generation Partnership Project (3GPP) Data rates of UMTS are: 144 kbps for rural 384 kbps for urban outdoor 2048 kbps for indoor and low range outdoor Virtual Home Environment (VHE)

UMTS Frequency Spectrum UMTS Band 1900-2025 MHz and 2110-2200 MHz for 3G transmission  In the US, 1710–1755 MHz and 2110–2155 MHz will be used instead, as the 1900 MHz band was already used.

UMTS Architecture

UMTS Network Architecture UMTS network architecture consists of three domains Core Network (CN): Provide switching, routing and transit for user traffic UMTS Terrestrial Radio Access Network (UTRAN): Provides the air interface access method for user equipment. User Equipment (UE): Terminals work as air interface counterpart for base stations. The various identities are: IMSI, TMSI, P-TMSI, TLLI, MSISDN, IMEI, IMEISV

UTRAN Wide band CDMA technology is selected for UTRAN air interface WCDMA TD-SCDMA Base stations are referred to as Node-B and control equipment for Node-B is called as Radio Network Controller (RNC). Functions of Node-B are Air Interface Tx/Rx Modulation/Demodulation Functions of RNC are: Radio Resource Control Channel Allocation Power Control Settings Handover Control Ciphering Segmentation and reassembly

3.5G (HSPA) High Speed Packet Access (HSPA) is an amalgamation of two mobile telephony protocols, High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), that extends and improves the performance of existing WCDMA protocols 3.5G introduces many new features that will enhance the UMTS technology in future. 1xEV-DV already supports most of the features that will be provided in 3.5G. These include: - Adaptive Modulation and Coding - Fast Scheduling - Backward compatibility with 3G - Enhanced Air Interface

4G (LTE) LTE stands for Long Term Evolution Next Generation mobile broadband technology Promises data transfer rates of 100 Mbps Based on UMTS 3G technology Optimized for All-IP traffic

Advantages of LTE

Comparison of LTE Speed

Major LTE Radio Technogies Uses Orthogonal Frequency Division Multiplexing (OFDM) for downlink Uses Single Carrier Frequency Division Multiple Access (SC-FDMA) for uplink Uses Multi-input Multi-output(MIMO) for enhanced throughput Reduced power consumption Higher RF power amplifier efficiency (less battery power used by handsets)

LTE Architecture

LTE vs UMTS Functional changes compared to the current UMTS architecture

Case Study Mobility: A Double-Edged Sword for HSPA Networks

Context

Context When you are NOT mobile, you use

Context

Context Millions of passengers per day!

Context

Outline Measurement Methodology General Impact of Mobility Mobility Impact on Bandwidth Sharing Mobility Impact in Transitional Region Conclusion

Measurement Routes

Measurement Route

Measurement Setup Two Servers: Lab & Data Center Three types of evaluations: download only; upload only; simultaneous download & upload.

General Impact of Mobility A large spread of HSDPA bit rates and signal quality

Context Common View: Mobility is irrelevant, if not detrimental, to the fairness in HSPA bandwidth sharing among users

Bandwidth Sharing among Users Mobility actually improves the fairness of bandwidth sharing among users

Bandwidth Sharing among Users UE can hardly keep its dominancy under rapid change of radio environment. Mobile nodes may see better signal quality at new locations Cell to cell based scheduling algorithm prevent unfairness from propagating

Context Common View: Mobility affects all flows equally. And TCP flows suffer more than UDP ones

Bandwidth Sharing among Traffic Flows TCP flows see better performance during mobility

Bandwidth Sharing among Traffic Flows TCP traffic is much constrained and adaptive to the channel condition, while UDP traffic keeps pumping almost the same amount of data regardless of the channel condition

Context Common View: Handoffs are triggered in the transitional region between cells and always result in a better wireless connection

Mobility Impact in Transitional Regions throughput often drops sharply, and sometimes, as high as 90% during handoff period.

Mobility Impact in Transitional Regions Ec/Io of the new base stations are statistically better than the original base stations by 10dBm. But almost 30% of all the handoffs do not end up with a better base stations

Conclusion Mobility is a double edged sword Degrades HSPA services, e.g. throughput Improves fairness in bandwidth allocation among users and traffic flows Communication characteristics in HSPA transitional regions are very complicated

Acknowledgement Part of the slides are adapted from the slides of Posco Tso, Harish Vishwanath, Erran Li and Justino Lorenco, Saro Velrajan and TCL India