Presentation on theme: "Cellular Telephony Characterized by High mobility provision Wide-range Handoff and roaming support Integrated with sophisticated public switched telephone."— Presentation transcript:
Cellular Telephony Characterized by High mobility provision Wide-range Handoff and roaming support Integrated with sophisticated public switched telephone network (PSTN) High transmit power requires at the handsets (~2W)
Power falloff actually helps A common misconception is that since received power is proportional 1/ra, capacity is badly hurt as the pathloss exponent a increases. Wrong! Smaller cells when range is short give more bandwidth reuse!
Cellular Networks First Generation Analog Systems Analog Modulation, mostly FM AMPS Voice Traffic FDMA/FDD multiple access Second Generation (2G) Digital Systems Digital Modulation Voice Traffic TDMA/FDD and CDMA/FDD multiple access 2.5G Digital Systems Voice + Low-data rate Third Generation Digital Voice + High-data rate Multimedia Transmission
Frequency Bands/Channels The information from sender to receiver is carried over a well defined frequency band. A channel Each channel has a fixed frequency bandwidth (in KHz) and Capacity (bit-rate) Different frequency bands (channels) can be used to transmit information in parallel and independently.
Simplex Communication Normally, on a channel, a station can transmit only in one way. This is called simplex transmission To enable two-way communication (called full-duplex communication) We can use Frequency Division Multiplexing We can use Time Division Multiplexing
Duplex Communication FDD FDD Frequency Division Duplex Forward channel and reverse channel use different frequency bands
Duplex Communication TDD TDD Time division Duplex A singe frequency channel is used. The channel is divided into time slots. Mobile station and base station transmits on the time slots alternately
What is Mobility Initially Internet and Telephone Networks is designed assuming the user terminals are static No change of location during a call/connection A user terminals accesses the network always from a fixed location Mobility and portability Portability means changing point of attachment to the network offline Mobility means changing point of attachment to the network online
Degrees of Mobility Walking Users Low speed Small roaming area Usually uses high-bandwidth/low-latency access Vehicles High speeds Large roaming area Usually uses low-bandwidth/high-latency access Uses sophisticated terminal equipment (cell phones)
Cellular Standards 0G : Early Mobile Telephone Systems One high-power transmitter was used to cover a large area-- -approx. 50km. Located at a very high spot The mobiles were simultaneously connected using different Frequency channels Capacity of such systems was very limited
1G 1G is first-generation wireless telephone technology that are analog- based and were introduced in the 1980s. Nordic Mobile Telephone, used in Nordic countries, Switzerland, Netherlands, Eastern Europe and Russia. AMPS (Advanced Mobile Phone System) used in the United States and Australia TACS (Total Access Communications System) in the United Kingdom In Japan there were multiple systems. Three standards, TZ-801, TZ- 802, and TZ-803 were developed by NTT, while a competing system operated by DDI used the JTACS (Japan Total Access Communications System) standard.
2G 2G is second-generation wireless telephone technology that are digital-based and were introduced in the G technologies can be divided into TDMA-based and CDMA- based standards GSM (TDMA-based), originally from Europe but used worldwide (Time Division Multiple Access) iDEN (TDMA-based), proprietary network used by Nextel in the United States IS-136 (D-AMPS), (TDMA-based, commonly referred as simply TDMA in the US) IS-95 (cdmaOne), (CDMA-based, commonly referred as simply CDMA used in the US and parts of Asia PDC (TDMA-based), used exclusively in Japan 2G services are frequently referred as Personal Communications Service, or PCS, in the United States
2G and Data 2G is developed for voice communications Can send data over 2G channels by using modem Provides data rates in the order of ~9.6 Kbps Increased data rates are required for internet applications This requires evolution towards new systems: 2.5 G
2.5 G 2.5G is between 2G and 3G cellular wireless technologies used to describe 2G-systems that provide packet switching in addition to circuit switching 2.5G provides some of the benefits of 3G (e.g. it is packet-switched) and can use some of the existing 2G infrastructure in GSM and CDMA networks. Mobile systems such as GSM with its General Packet Radio Service (GPRS) & its evolution called Enhanced Data Rate for Global Evolution (EDGE), are covering full range of mobility from fixed to high speed train mobility The GSM/GPRS/EDGE is supporting low mobile data rates only and is, currently, dominating the world in 2G systems
2.5G GSM Basic GSM could only provide 9.6 Kbps High Speed Circuit Switched Data (HSCSD) allows multiple slots to be assigned for data connection. Problem : usage of scarce radio resource, since it is circuit switched allocates timeslots even when nothing is being transmitted. Advantage : Good for real-time applications. General Packet Radio Services (GPRS) allows up to 115 Kbps. It is Packet Switched Enhanced Data rate for GSM Evolution (EDGE) now known as Enhanced data rates for Global Evolution increase data rates by 3-fold.
CDMA 2000 CDMA2000 is a hybrid 2.5G / 3G technology of mobile cellular standards that use narrow band CDMA to send voice and data. CDMA2000 standards are approved radio interfaces for the ITU's IMT-2000 standard and a direct successor to 2GCDMA, IS-95 (cdmaOne) CDMA2000 1xRTT CDMA2000 EV-DO, and CDMA2000 EV-DV CDMA2000 is considered a 2.5G technology in 1xRTT and a 3G technology in EVDO and is standardized by 3GPP2
CDMA 2000 The designation "1x", meaning "1 times Radio Transmission Technology", indicates the same RF bandwidth as IS-95: a duplex pair of 1.25 MHz radio channels "Evolution, Data Only" or "Evolution, Data Optimized". The official name, defined by the Telecommunication Industry Association, is "CDMA2000,
2.5 Technology Evolution of TDMA Systems For 2.5G GSM - High-Speed Circuit-Switched Data (HSCSD), is an enhancement to GSM mobile phone system with data rates up to 38.4 kbit/s. For GSM and IS General Packet Radio Service (GPRS) is a packet oriented Mobile Data Service available to users of GSM & IS-136 with data rates from 56 up to 114 kbit/s. For 2.5G GSM and IS Enhanced Data rates for GSM Evolution (EDGE), is a technology that allows increased data transmission rates of up to 384 Kbps Evolution of CDMA Systems IS-95B Up to 64 Kbps
International Mobile Telecommunications(IMT-2000) IMT-2000 is the global standard for third generation (3G) wireless communications as defined by the International Telecommunication Union. In Oct 2007, ITU took a decision of global importance to include WiMAX-derived technology in the framework of the IMT-2000 set of standards Allowing deployment of a range of voice, data, and multimedia services to both stationary and mobile devices. Opens the door to mobile Internet, catering to demand in both urban and rural markets
International Mobile Telecommunications(IMT-2000) The system envisages a platform for distributing converged fixed, mobile, voice, data, Internet and multimedia services. One of its key visions is to provide seamless global roaming, enabling users to move across borders while using the same number and handset. It is expected that IMT-2000 will provide higher transmission rates: a minimum speed of 2 Mbit/s for stationary or walking users, 348 kbit/s in a moving vehicle. Second-generation systems only provide speeds ranging from 9.6 kbit/s to 28.8 kbit/s
3G 3G is the third generation of mobile phone standards and technology based on ITU standards under IMT G technologies enable network operators to offer users a wider range of more advanced services while achieving greater network capacity through improved spectral efficiency. Services include wide-area wireless voice telephony and broadband wireless data, all in a mobile environment. Typically, they provide service at 5-10 Mb per second.
3g Systems Evolution of Systems CDMA system evolved to CDMA2000 CDMA2000-1xRTT: upto 307 Kbps CDMA2000-1xEVDO: upto 2.4 Mbps CDMA2000-1xEVDV: 144 Kbps data rate GSM and IS-136 evolved to W-CDMA (Wideband CDMA) (also called UMTS) Up to Mbps data-rates Future systems 8Mbps Expected to be fully deployed by New spectrum is allocated for these technologies
Upgrades paths for 2G Technologies
Basics Early mobile telephony systems were not cellular. Coverage over a large area was provided by a high powered transmitter mounted on a tall tower. Frequency reuse was not employed. That resulted in very low capacity The cellular concept arose from the need to restructure the radio telephone system with the increase in demand. The increase in demand could not be satisfied just by additional spectrum allocations Cellular Concept: replace large transmitters with many smaller transmitters. Neighboring base stations (BS) are assigned different sets of channels. Capacity can be increased by additional partitions
Basics Cell – a geographical area covered by a BS Frequency Reuse – the frequency channels allocation scheme For convenience, the cells are shown with a hex pattern. A hex pattern is the simplest pattern that can tessellate an area In practice, cells are not hexagonal and BS are not exactly in the center of the cell