Cell Phones • Standards • Cell Phone Technologies • 1G, 2G and 3G • Determining a standard • Wireless Networking
Setting Standards • Three main ways that standards get set in practice: • (I) De-facto standards, i.e., standards set primarily by the market. These standards are often proprietary. • Examples: Microsoft Office and Windows, Java, TCP/IP • Often fast to develop and can be changed readily • But are usually proprietary and may not be “open” • US and cell phones • (II) Voluntary industry agreements, where standards are often jointly developed. These standards are typically open standards, that is, they are not proprietary. Example: bar codes • (III) Standards imposed by National Standards Bodies (NSBs), or agreed upon by regional or international standards development organizations (SDOs). • Examples: meter • Slow to develop • Non-proprietary • Europe and cell phones
Tipping • The economic theory of tipping would suggest that the early adoption of one standard or the decision to formally set one standard in the European Union (EU) could tip the whole world toward that standard. • The adoption of a single standard by a few large firms will likely tip the entire market toward that standard. • In market competition between wireless standards, interconnection may mean that the standard tipping results may apply only if one standard gets far out in front of a competing standard early on before the competing standard has a chance to get established.
Cell Phone Technologies • Cellular system divides a coverage area into small cells. • This allows extensive frequency reuse. • In a typical analog cell-phone system in the United States, the cell-phone carrier receives about 800 frequencies to use across a city. • The carrier chops up the city into cells. Each cell is typically sized at about 10 square miles (26 square kilometers). • Cells are normally thought of as hexagons on a big hexagonal grid
Note 7 cells in pattern From Mukesh Raghuraman 2003
Hexagon grid - Cell Cell base Station Call Handoff Coverage area “Cell” From Mukesh Raghuraman 2003
Movement Between Cells • Ability to change frequency/channel as the unit moves from one cell to another cell. • Enables the concept of frequency reuse. Because cell phones and base stations use low-power transmitters, the same frequencies can be reused in non-adjacent cells. • The ability that made the cellular system possible.
Cell Phone Standards Note wide divergence of standards Not all frequencies/ standards shown From Mukesh Raghuraman 2003
1G - Analog Cell Phone Basics • In US, the analog cell-phone standard called AMPS (Advanced Mobile Phone System) was approved by the FCC and first used in Chicago in 1983. • Each cell has a base station that consists of a tower and a small building containing the radio equipment • A single cell in an analog system uses one-seventh of the available duplex voice channels. That is, each cell (of the seven on a hexagonal grid) is using one-seventh of the available channels so it has a unique set of frequencies and there are no collisions: • A cell-phone carrier typically gets 832 radio frequencies to use in a city. • Each cell phone uses two frequencies per call -- a duplex channel -- so there are typically 395 voice channels per carrier. (The other 42 frequencies are used for control channels) • Therefore, each cell has about 56 voice channels available (395/7). • In other words, in any cell, 56 people can be talking on their cell phone at one time. (Note all of the above is for ANALOG systems) – pretty hopeless for Iowa City!
1G Analog Problems • Cell phones • Limited battery life (typically 8 hours) • Limited range – could have more powerful cell phone mounted in cars • Security • None – easy to listen in • E.g. Squidgy-gate and Camilla-gate (1992) • Very limited number of voice channels
Analog and Digital • Analog – each conversation occupies whole channel. Limits number of open lines in each cell. Frequency Division Multiple Access (FDMA) • Digital – conversation compressed using 0, 1s and sent out in shorter time. Can share each frequency. Time Division Multiple Access (TDMA)
Digital (most of 2G) Analog From The Economist • Analog – each conversation occupies whole channel. Limits number of open lines in each cell. Frequency Division Multiple Access (FDMA) • Digital – uses 0, 1s, compressed and sent out in shorter time. Can share each frequency. Time Division Multiple Access (TDMA)
FDMA • FDMA separates the spectrum into distinct voice channels by splitting it into uniform chunks of bandwidth. • FDMA is used mainly for analog transmission. While it is certainly capable of carrying digital information, FDMA is not considered to be an efficient method for digital transmission. From How Stuff Works
TDMA – 2G • Compression of digital signal allows signal to be sent out in shorter time. • Usually for TDMA, each conversation takes up one third of channel. • Note more frequencies set aside for 2G • Nearly all US and Europe 2G systems use TDMA (exceptions include SprintPCS, CDMA) • Can also include encryption
Another Way to Increase Number of Simultaneous Conversations - CDMA • Code-division Multiple Access (CDMA) • Involves spreading a radio signal out over a range of frequencies. • Each transmission is scrambled using a random “code” • Allows for more simultaneous conversations than other approaches • Handsets stop transmitting when the user isn’t talking – allows more conversations • FDMA is akin to a party at which everybody talks simultaneously, but each pair of speakers converses at a different musical pitch, from booming bass to piping treble. A system in which party-goers took turns to speak at different pitches would be like TDMA. And everybody talking at once, only in different languages (so that other conversations are rendered incomprehensible), would be equivalent to CDMA. (The Economist, 2003)
2G Advantages Over 1G • Cell phones • Increased battery life (significantly more than 8 hours) • Increased range • Security • Possible to encrypt signals • Increased number of voice channels
2G Standard - GSM • Global System for Mobile communications (GSM). • Mandated for use in Europe • In US, companies were allowed to develop and use their own choice of standard for 2G • Result • Europe – single 2G standard GSM • US – multiple standards. Some companies use GSM but on a different frequency from Europe. Standards uses include TDMA, GSM and CDMA
Move to Increase Bandwidth • Increase bandwidth allows for larger amount of data to be received – web browsing, pictures, video, music at increased quality. • How to do this • 2.5G approaches – build on 2G systems • 3G systems – new systems with increased bandwidth over 2.5G systems • Bandwidth • 2G data rates 9.6 Kbps – 14.4 Kbps. • 2.5G data rates 64 – 144 Kbps. • 3G data rates144 Kbps. to 2 Mbps. Live high quality video requires 2Mbps.
2.5G • Uses General Packet Radio Services (GPRS) • GSM and TDMA enhanced to packet based networks – IP based (the available radio resource can be concurrently shared between several users) • GPRS is primarily a simple software upgrade on GSM and TDMA • Relatively easy for the service providers to update their networks • Can simultaneously make telephone calls and transmit data. • Expect to see this generally in place over the next few years [e.g. AT&T moving to GSM with GPRS]
3G • High data rates: • 144 kbits/sec or higher in high mobility (vehicular) traffic • 384 Kbits/sec for pedestrian traffic • 2 Mbits/sec or higher for indoor traffic • Different Standards • WCDMA – Europe and Japan • CDMA2000 from Qualcomm used in USA, Korea • TD-S CDMA China
Setting Standards Europeans set standard for 2G – GSM while US companies were free to develop their own standard Did the imposition of a standard for 2G help the Europeans?
2G – Europe and Setting a Single Standard • Features work across companies – e.g. text messaging • Larger economies of scale in the production of both terminals/handsets and network infrastructure equipment reduce costs and increase availability. • Increase market share for European companies? • Variety of terminal equipment (handsets) tends to be greater. • Larger number of purchasers of service since single standard. By the end of 1993 there were already more than 1 million GSM users in Europe. By contrast, in the U.S., the FCC did not even complete its first auction allocating PCS spectrum until March of 1995. (Could also be partly due to high costs of traditional European phone companies). • Wider coverage area (perhaps)
Text Messaging • Large difference between Europe and US • Ireland around 70 per month, USA 7 per month • Messaging accounts for 20% of revenue for EU cell phone companies. • Why?
Market Impact of European Cell Phone Handset Manufacturers From: The Economist 10/12/2000
SprintPCS National Coverage Dark Green = Digital Coverage Light Green = Analogue Coverage
Benefits From Multiple (Competing) Standards • Types of services tend to differ across technologies. For example, CDMA networks have offered more and better data services than were available on GSM networks. • More technological competition (“highly centralized approach foregoes the benefits of competition in research and development…”) • Greater price competition (at least early on) among competing incompatible standards (perhaps) • Wider coverage area (perhaps)
Setting 3G Standards • Two main standards have been proposed • Wideband CDMA (WCDMA) for Europe and • CDMA2000 for US and other countries • CDMA2000 is a natural migration from CDMA-One (the 2G CDMA standard), • while WCDMA is essentially incompatible with any existing technology.
Will a Single 3G European Standard Help the Europeans • Not clear • 3G does not show real signs of take off. Who will use it? • Will consumers be happy with 2G and 2.5G? • Will WCDMA work as promised? • Will CDMA2000 build a huge lead worldwide? • Will 802.11g, 802.11a, or 802.16 (WiMax) take over?
WiMAX • WiMAX, an acronym that stands for Worldwide Interoperability for Microwave Access, is a certification mark for products that pass conformity and interoperability tests for the IEEE 802.16 standards. Shared data rates up to 70 Mbit/s http://en.wikipedia.org/wiki/Wimax • Aim for line of sight of 30 miles (15 miles non-line of sight). Can cover a metropolitan district. http://en.wikipedia.org/wiki/Wimax • First products expected in 2005. See, for example, http://www.egovmonitor.com/node/691/
Wireless Internet Access • 3G data rates: • 144 kbits/sec or higher in high mobility (vehicular) traffic • 384 Kbits/sec for pedestrian traffic • 2 Mbits/sec or higher for indoor traffic • 802.11g data rate of 20Mbit/sec, 802.11a data rate of about 24Mbit/sec • Usually limited by other parts of the network • Limited range: 300 feet, more with antenna. Office environment, Iowa City? • Voice over IP (VoIP) handsets possible