Wireless and Cellular Communications Marin Thomas IONA COLLEGE Feb/16/2006
Mobile Wireless Devices and Applications
The Difference Between Cellular and PCS Services
Mobile E-Commerce Applications
The Use and Functions of Frequency Bands
The Foundation of the Cellular System Architecture
The Mobile Telephone Switching Office
Wireless Multiplexing Methods
The Design of the Global Wireless Internet
The Elements of the Wireless Access Protocol (WAP)
Secure Wireless Communication
Wireless Application of Satellite Phones and Portable Satellite Terminals
Global Wireless Internet
Wireless Access Service Providers (WASPs) in ASIA, Europe and US support a high-speed connection to the Internet.
Carrier A in the US and Europe connects to its nearest POP and is able to transmit and receive signals using the POPs connection to the Internet
Short message service (SMS), the mobile version of instant message is used to transmit short text messages to and from a mobile phone.
Once a message is sent, it is received by a Short Message Service Center (SMSC).
The SMSC passes the message through the network to the destination mobile device
The SMSC sends a SMS request to the Home Location Register (HLR) to find the roaming customer. The HLR responds to the SMSC with the subscribers status.
The SMSC transfers the message in a Short Message Delivery Point to point format
Wireless Mobile Internet and WAP
It is impractical to deliver all the web content to a phone as it is is to a PC.
For wireless mobile Internet to be efficient, the internet contents such a graphics and hyperlinks needs to be tailored to suite mobile phones capabilities
Wireless Application Protocol (WAP) is an industry standard that allows software developers to create contents suitable for displaying on smart-phone monitors.
Developers write their service according to the WAP specification and it can then be delivered over any mobile network
WAP is driven by the huge wireless mobile market. The number of wireless hand-held devices accessing the internet increases substantially each year compared to wired devices
WAP is an Open no-proprietary device-independent bearer-independent protocol stack
Wireless Standards and Protocols
In 1996 Nokia, Unwired Planet and Ericsson got together to find a way add more value to their services and make WEB more suitable for the limited bandwidth capable devices started the WAP design
350 other companies have joined since then and it became the Open Mobile Alliance
Open Mobile Alliance is continuously working on specifications for the wireless standard to ensure that it evolves properly
WAP: Protocol Elements
Wireless Application Environment (WAE)
Holds the tools that wireless Internet Content developers use
WML: Wireless Markup Language
WLMScript: Lightweight scripting language
The Wireless Session Protocol ( WSP)
determines whether a session between the device and the network will be connection-oriented or connectionless .
If a device needs to talk back and forth with the network during a session, then data is passed both ways between the device and the network; WSP then sends the packet to the Wireless Transaction Protocol layer. (Similar to TCP)
If the session is connectionless, commonly used when information is being broadcast or streamed from the network to the device, then WSP redirects the packet to the Wireless Datagram Protocol layer. (Similar to UDP)
WAP: Protocol Elements
Wireless Transaction Protocol (WTP)
Provides services to accomplish transactions with varying degree of reliability
Acts like a traffic cop, keeping the data flowing in a logical and smooth manner. It also determines how to classify each transaction request:
Wireless Transport Layer (WTLS)
WTLS provides many of the same security features found in the Transport Layer security part of TCP/IP. It checks data integrity, provides encryption and performs client and server authentication.
Wireless Datagram Protocol (WDP)
Works in conjunction with the network carrier layer. WDP makes it easy to adapt WAP to a variety of bearers because all that needs to change is the information maintained at this level.
WAP: Protocol Elements
Also called bearers , these can be any of the existing technologies that wireless providers use.
GPRS (General Packet Radio Service) is the world's most ubiquitous wireless data service, available now with almost every GSM network. GPRS is a connectivity solution based on Internet Protocols that supports a wide range of enterprise and consumer applications.
GPRS customers enjoy advanced, feature-rich data services such as color Internet browsing, e-mail on the move, powerful visual communications such as video streaming, multimedia messages and location-based services.
USSD (Unstructured Supplementary Service Data) is a Global System for Mobile (GSM) communication technology that is used to send text between a mobile phone and an application program in the network. Applications may include prepaid roaming or mobile chatting.
USSD is similar to Short Messaging Service (SMS), but, unlike SMS, USSD transactions occur during the session only. With SMS, messages can be sent to a mobile phone and stored for several days if the phone is not activated or within range.
WAP Communication: WEB and Mobile phones
The user turns on the device and opens the minibrowser
The device sends out a radio signal, searching for service
A connection is made with the users service provider
The user selects the desired WEB site
A request is send to a WAP gateway server
The gateway server retrieves the information via HTTP from the WEB site
The gateway server encodes the HTTP data as WML
The WML-encoded data is send to the user’s device
The wireless Internet version of the WEB page selected appears on the user’s mobile phone
What is i-Mode
First introduced in Japan in 1999 by NTT DoCoMo, i-mode is one of the most successful services offering wireless web browsing and e-mail from mobile phones in Japan.
Based on packet-data transmission. Users are charged based on the volume of data transmitted not the duration of time connected to the internet
Unlike WAP, which uses WML as its markup language, I-mode services are built using Ii-mode compatible HTML
Connection to sites, running programs, and transferring e-mails are all done by the I-mode server
Secure Wireless Communication
The key to designing wireless network security is to have a method to keep data confidential and private
The communication between a wireless client and the base station must be secure
Some Techniques for wireless security include the following:
Wireless Transport Layer Security (WTLS)
Provides strong security between a WAP client and the gateway
Encryption technique (SSL) extend security all the way to the application server
WTLS security using RSA algorithms provides encryption of user data
After data passes through the WAP gateway, it is decrypted from WTLS and then encrypted in SSL to present to the application server
SignText provides a digital signature to WAP applications that require the ability to provide persistent proof that someone has authorized a transaction.
The WAP browser displays the exact text to be digitally signed, both the data and the signature are send across the network. When the server receives it, it extracts the signature and validates it against a security database.
It is used mainly for validating the integrity of the data but It doesn't provide confidentiality
WAP Identity Module (WIM)
Used to store and process information needed for user identification and authentication
Encryption keys are processed and stored within the WIM. This technique is used when performing WTLS and application level security function
In a cellular phone, WIM is implemented as a Subscriber Identification Module (SIM), which is a unique number that identifies the device.
WIM is a secure method that enables users to do online transactions
Wireless Public Key Infrastructure (WPKI)
Certification Authorities (CAs) that is responsible for issuing and revoking certificates
Registration Authorities (RAs) that is responsible for binding between public keys and the identities of their holders.
Certificate holders (or subjects), which is machines, software agents or people that have been issued with certificates and can use them to sign digital documents
WPKI defines a PKI Portal. Which is a security-portal converter that translates wireless PKI protocols to and from Internet- protocols through the use of databases and directories to store and distribute certificate and their status.
Server-Assisted Wireless Public Key Infrastructure (SAWPKI)
SAWPKI is a newer version of software solution provided by the E-Business Technology Institute and it functions as follows:
A customer uses the mobile device to establish a secure channel for transacting data and payment instructions.
The cryptographic operations are offloaded to a SAWPKI server on the Internet.
The Customer's mobile device communicates in its normal way just as if it were a full-fledged PKI-enabled computer.
The E-merchants are able to accept transactions in the same way they do from wired PC users over the Internet
Wireless Security Challenges and Limitations
Cellular/PCS devices are vulnerable to interception/detection because the radio link they use is exposed to several miles.
Due to the limited processing power and memory, many encryption algorithms used for PCs cannot be used with cell phones.
Security keys are permanently set before a customer purchases the phone and the customer will not able to change it periodically
There is an inherited security challenge with devices that is always moved
Satellite phone communication is comprised of the Satellite network, the ground network and the satellite phone.
Some features of satellite phone includes Voice, SMS, Called ID, Voice Mail, position location, data transmission and digital facsimile.
Satellite services are offered in all four-ocean regions: Atlantic Ocean East Region (AOR-E), Indian Ocean Region (IOR), Pacific Ocean Region (POR) and Atlantic Ocean West Region (AOR-W).
On the ground is a Land Earth Station (LES), which is basically a land base station that sends radio waves to an from geostationary satellites (GEOs)
Satellite Phones typically have two antennas, a satellite antenna and a cellular antenna for cellular use such as in indoor or near a cellular crevice area.
Some satellite phones need line-of-sight to send and receive signals with geostationary satellites unless the phone is using non-directional antennas.
These phones can cause interference with radio and TV signal when used indoors.
Satellite phones will allow people to make and receive calls anyplace on Earth by routing telephone signals through a complex sequence that takes just milliseconds.
1 - A user turns on satellite phone, which signals the nearest satellite that it wants to make a call.
2 - The user dials the phone and the signal is picked up by the satellite, which beams the call to other satellites in the network. It travels from satellite to satellite until it gets close to its destination.
3 - If the call is going to a regular land-based telephone, the last satellite beams it to a ground station on Earth, which transfers to a ground station.
4 - The ground station routes the call over existing land-based telephone lines to its final destination - the phone being called.
5 - If the call is intended for another satellite phone, the final satellite beams it directly to the recipient's handset. -- If the call is intended for a cellular phone, the satellite beams it to the nearest cellular antenna on Earth, which then transmits it to its destination.
Logging Information such as call duration, service used and service area used is reported to the service provider for billing
Portable Satellite Terminals
Portable Satellite Terminals are powerful communication devices.
It provides communication from anywhere in the world
Uses geostationary satellites for high-quality long-distance geographic coverage
Military and government secure voice, fax, data and video communications.
Broadcast-quality live audio or store-and-forward video transmission.
Remote LAN connection to corporate VPN.
Mobile office: Voice, data, video and Internet access for remote technical personnel.
Part of a complete portable Telemedicine System.
High-speed file transfer for high resolution digital images, video clips or data.
Satellite Systems Geostationary Satellite (GEO) Medium-earth orbiting Satellite (MEO) Low-earth orbiting Satellite (LEO) Satellite Advantage Disadvantage LEO
Propagation delay is smaller (10~15 msec)
Low transmission power required
Low price for equipment and crevice
Low coverage area
Ate least 6 LEOs needed for covering a single region
High system complexity due to handovers and tracking
Relatively longer propagation delay (~40 msec)
Bigger footprint than LEOs
Cheaper than GEOs
Footprint is less than GEO
Multiple MEOs are needed to cover a region
High system complexity due to handovers and tracking
Satellite is stationary relative to the earth, so no frequency changes due to the relative motion of the satellite and antennas on earth
Linking with the satellite by its earth station is easy
One satellite can cover almost a fourth of the earth. Three satellites can cover most of the inhabited portions of the earth
Low system complexity
Signal can weaken after traveling > 35,000 km
Polar regions and the far northern and southern hemispheres are poorly served
Noticeable propagation delay due to distance (~125 msec)
High transmission power is required
You Say GEO, I Say LEO, O My, OH MEO
Wireless PAN and LAN
Network Coverage Area
Wireless Transmission Technology
Infrared Transmission Technology
Wireless LAN Primer
Network Coverage Area
Electromagnetic (EM) Radiation
A natural phenomenon that allows information to be carried from transmitter to a receiver via a medium such as the air or fiber optic cable
EM Radiation Includes gamma radiation, X-rays, ultraviolet, infrared, radar and radio waves. Radio waves are used for telecommunications
Wireless devices produce electromagnetic waves of different frequencies that travel through space
spectrum is the term that describes a set of radio waves that can be used to transmit information
Frequency is the number of times that a wave's peak passes a fixed point in a specific period of time. Frequency is the measurement of the number of times that a repeated event occurs per unit time. It is also defined as the rate of change of phase of a sinusoidal waveform. Frequency is a specific location on the electromagnetic spectrum
Frequency vs. Bandwidth
Bandwidth is the range between two frequencies. Bandwidth is measured in Hertz. A cellular operator may transmit signals between 824-849 MHz, for a total bandwidth of 25 MHz. Bandwidth also refers to data rates when communicating over certain media or devices. According to the Shannon-Hartley theorem, the data rate of reliable communication is directly proportional to the frequency range of the signal used for the communication. In this context, the word bandwidth can refer to either the data rate or the frequency range of the communication system (or both). In radio communications, for example, bandwidth is the range of frequencies occupied by a modulated carrier wave, whereas in optics it is the width of an individual spectral line or the entire spectral range.
Bandwidth vs. Capacity
Bandwidth for a particular service is fixed, but the number of calls and the rate of data transmission is not. Channel capacity, is the amount of discrete information bits that can be reliably transmitted over a channel. In other words, the channel capacity of a given channel is the maximum information transport rate (in bit/s) that can be achieved with zero error probability. Theoretically, the channel capacity purely refers to the transport of actual information bits in a given transmitted bit stream, regardless of the possibly added redundancy by the channel encoder
The wavelength is the distance between repeating units of a wave pattern
Wireless devices transmit using either Radio frequency waves or Infrared waves
Radio frequency (RF) signals have frequencies in the range of 1 to 20 GHz
RF signals are transmitted using either Narrowband or Spread spectrum technology
Narrowband uses microwave frequencies for transmission. Has very limited use in LANs due to interference with different networks. Requires FCC licensing
Spread Spectrum can employ Frequency Hopping or Direct Sequence.
Spread Spectrum requires a bandwidth that is several times the original bandwidth
In FHSS, the sender sends on one carrier frequency for a short period of time, then hops to another frequency for the same period of time and so on, after N hopping, the cycle is repeated.
Spreading prevents an intruder from getting information.
The sender and receiver agree on the sequence of the allocated bands
In DSSS, each bit to be send by the sender is replaced by a sequence of bits called chip code.
To avoid buffering, the time needed to send one original bit should be the same as the time needed to send one chip code.
Infrared (IR) is also a transmission method used in wireless LANs. It has wavelengths between 800 and 900nm.
IR is considered more secure because it can’t propagate through opaque objects such as walls
More immune to interference such as radio transmission and microwave ovens
IR systems use very high frequencies, just below visible light in the electromagnetic spectrum, to carry data. Like light, IR cannot penetrate opaque objects; it is either directed (line-of-sight) or diffuse technology.
Inexpensive directed systems provide very limited range (3 ft) and typically are used for personal area networks but occasionally are used in specific wireless LAN applications.
Diffuse (or reflective) IR wireless LAN systems do not require line-of-sight, but cells are limited to individual rooms.
ISM Frequency BAND
In 1985, FCC modified the radio spectrum regulations for unlicensed devices. The modification authorized wireless LANs to operate in Industrial, Scientific and Medical (ISM) bands.
The use of these bands doesn't require a license if the equipment operates under 1 W of power
The 902 MHz band and the 5.725 GHz band are available only in the US; the 2.4 GHz band is available globally
Bluetooth (WPAN) Primer
Transmits data over low-power radio waves. Avoids interference with other devices by sending week signals (about 1 milliwatt). Telephones can transmit up to 3 watt signals
Doesn’t require line-of-sight between communicating devices
Facilitate fast and secure wireless communications
Handle voice/data communication for spontaneous (ad-hoc) networks
Embedded Logic or add-on adapter
Transmits up to 32 ft max due to low power usage
2.45GHz frequency band (ISM)
Data transfer rate: 1 to 2Mb/s
Unique 48-bit address for each device
Uses Master/Slave relationship in one-to-one or one-to-many configuration
Master determines the timing of hopping intervals and channels used
Uses frequency-hopping spread spectrum radio
Piconets: A collection of bluetooth devices connected together in an ad-hoc fashion.
Between 2-8 devices per piconet
One device in the piconet acts as the master the rest are slaves.
A device can be slave at different Piconets but can only be a master at one Piconet
A device can be a master and a slave at the same time
Connect piconets together to form scatternets
Bluetooth: Connection Modes
A Bluetooth device in the Connection state can be in any of the four following modes: Active, Hold, Sniff and Park mode.
Active Mode: In the active mode, the Bluetooth unit actively participates on the channel. The master schedules the transmission based on traffic demands to and from the different slaves. In addition, it supports regular transmissions to keep slaves synchronized to the channel. Active slaves listen in the master-to-slave slots for packets. If an active slave is not addressed, it may sleep until the next new master transmission.
Sniff Mode: Devices synchronized to a piconet can enter power-saving modes in which device activity is lowered. In the SNIFF mode, a slave device listens to the piconet at reduced rate, thus reducing its duty cycle. The SNIFF interval is programmable and depends on the application. It has the highest duty cycle (least power efficient) of all 3 power saving modes.
Hold Mode : Devices synchronized to a piconet can enter power-saving modes in which device activity is lowered. The master unit can put slave units into HOLD mode, where only an internal timer is running. Slave units can also demand to be put into HOLD mode. Data transfer restarts instantly when units transition out of HOLD mode. It has an intermediate duty cycle (medium power efficient) of the 3 power saving modes.
Park Mode: In the PARK mode, a device is still synchronized to the piconet but does not participate in the traffic. Parked devices have given up their MAC or active member address and occasional listen to the traffic of the master to re-synchronize and check on broadcast messages. It has the lowest duty cycle (power efficiency) of all 3 power saving modes.
Each piconet in the scatternet will have a unique hopping sequence
The more piconets in a small location, the greater chance of collisions
It Is possible that one or more piconets in a scatternet will be using the same channel at the same time, which will result in collisions.
Collision will be handled by retransmission
Wireless LAN Primer 802.11 legacy The original version of the standard IEEE 802.11 released in 1997 specifies two raw data rates of 1 and 2 megabits per second (Mbit/s) to be transmitted via infrared (IR) signals or in the Industrial Scientific Medical frequency band at 2.4 GHz. IR remains a part of the standard but has no actual implementations. The original standard also defines Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) as the media access method. A weakness of this original specification was that it offered so many choices that interoperability was sometimes challenging to realize. It is really more of a "meta-specification" than a rigid specification, allowing individual product vendors the flexibility to differentiate their products. Legacy 802.11 was rapidly supplemented (and popularized) by 802.11b. 802.11b The 802.11b amendment to the original standard was ratified in 1999. 802.11b has a maximum raw data rate of 11 Mbit/s and uses the same CSMA/CA media access method defined in the original standard. 802.11b standard uses Complementary code keying (CCK) as its modulation technique, which is a variation on CDMA. Hence, chipsets and products were easily upgraded to support the 802.11b enhancements. operates in 2.4 GHz band 802.11b is usually used in a point-to-multipoint configuration, wherein an access point communicates via an omni-directional antenna with one or more clients that are located in a coverage area around the access point. Typical indoor range is 30 m at 11 Mbit/s and 90 m at 1 Mbit/s. 802.11b cards can operate at 11 Mbit/s, but will scale back to 5.5, then 2, then 1 Mbit/s (a.k.a Adaptive Rate Selection), if signal quality becomes an issue.
Wireless LAN Primer
The 802.11a amendment to the original standard was ratified in 1999. The 802.11a standard uses the same core protocol as the original standard, operates in 5 GHz band, with a maximum raw data rate of 54 Mbit/s.
The data rate is reduced to 48, 36, 24, 18, 12, 9 then 6 Mbit/s if required. 802.11a has 12 non-overlapping channels, 8 dedicated to indoor and 4 to point to point.
It is not interoperable with 802.11b, except if using equipment that implements both standards.
Since the 2.4 GHz band is heavily used, using the 5 GHz band gives 802.11a the advantage of less interference. However, this high carrier frequency also brings disadvantages. It restricts the use of 802.11a to almost line of sight, necessitating the use of more access points; it also means that 802.11a cannot penetrate as far as 802.11b since it is absorbed more readily, other things (such as power) being equal.
802.11a was not widely adopted overall because 802.11b was already widely adopted
Wireless LAN Primer
In June 2003, a third modulation standard was ratified: 802.11g. This flavour works in the 2.4 GHz band (like 802.11b) but operates at a maximum raw data rate of 54 Mbit/s.
802.11g hardware will work with 802.11b hardware. In older networks, however, the presence of an 802.11b participant significantly reduces the speed of an 802.11g network. The modulation scheme used in 802.11g is orthogonal frequency-division multiplexing (OFDM) for the data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbit/sit can achieve higher data rates because of its similarities to 802.11a.
Most of the dual-band 802.11a/b products became dual-band/tri-mode, supporting a, b, and g in a single mobile adaptor card or access point. Despite its major acceptance, 802.11g suffers from the same interference as 802.11b in the already crowded 2.4 GHz range.
Devices operating in this range include microwave ovens, Bluetooth devices, and cordless telephones.
Wireless LAN Future
In January 2004 IEEE announced that it had formed a new 802.11 Task Group (TGn) to develop a new amendment to the 802.11 standard for local-area wireless networks.
The real data throughput is estimated to reach a theoretical 540 Mbit/s (which may require an even higher raw data rate at the physical layer), and should be up to 40 times faster than 802.11b, and near 10 times faster than 802.11a or 802.11g.
It is projected that 802.11n will also offer a better operating distance than current networks.