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Wireless Technology and Network Convergence

Wireless Technology and Network Convergence. A Brief History. Wireless communications originated with the demonstration by Tesla in 1893, followed by the invention of wireless telegraph by Marconi in 1896

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Wireless Technology and Network Convergence

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  1. Wireless Technology and Network Convergence

  2. A Brief History • Wireless communications originated with the demonstration by Tesla in 1893, followed by the invention of wireless telegraph by Marconi in 1896 • Advances in wireless communications have led to radio, television, mobile telephones, and communication satellites • Development of wireless networks: LAN, MAN, and WAN • Trend continues: Voice – Data – Broadband • Need to support mobility

  3. Trends • Revenue for wireless communication industry has surpassed that of wired telephony industry • Wireless applications span both local area and wide area for: • voice-oriented services, and • data-oriented services • Global cellular networks are providing very convenient communication infrastructure • Broadband wireless networks are evolving: Wireless LANs are very popular

  4. Licensed and Unlicensed Bands • Licensed: • Cellular/PCS • Expensive (PCS bands in US were sold for around $20B) • Time consuming to deploy new applications rapidly at low costs • Unlicensed: • Industrial, Medical, and Scientific (ISM) Bands • Free, component costs are also low • New applications such as WLAN, Bluetooth are easily developed • With the increase in frequency and data rate, the hardware cost increases, and the ability to penetrate walls also decreases

  5. Duplexing • Duplexing facilitates communications in both directions simultaneously: base station to mobile and mobile to base station • Duplexing is done either using frequency or time domain techniques: • Frequency division duplexing (FDD) • Time division duplexing (TDD) • FDD is suitable for radio communication systems, whereas TDD is more suitable for fixed wireless systems

  6. Multiple Access Techniques • Frequency Division Multiple Access • Time Division Multiple Access • Spread Spectrum Multiple Access • Space Division Multiple Access • Packet Radio

  7. Frequency Division Multiple Access (FDMA) • The frequency spectrum is divided into unique frequency bands or channels • These channels are assigned to users on demand • Multiple users cannot share a channel • Users are assigned a channel as a pair of frequencies (forward and reverse channels) • FDMA requires tight RF filtering to reduce adjacent channel interference

  8. Channel-1 Channel-5 Channel-6 Channel-7 Channel-8 Channel-9 FDMA TIME Channel-2 Channel-3 Channel-4 Channel-5 Channel-6 Channel-7 Channel-8 Channel-9 FREQUENCY

  9. Time Division Multiple Access-TDMA • TDMA systems divides the radio spectrum into time slots, and in each time slot only one use is allowed to either transmit or receive • Transmission for any user is non-continuous • In each TDMA frame, the preamble contains the address and synchronization information • TDMA shares a single carrier frequency with several users • TDMA could allocate varied number of time slots per frame to different users

  10. TDMA FREQUENCY Channel-10 Channel-3 Channel-4 Channel-5 Channel-6 Channel-8 Channel-9 Channel-1 Channel-7 Channel-2 TIME

  11. Spread Spectrum Multiple Access (SSMA) • SSMA uses signals that have a transmission bandwidth several orders of magnitude greater than the minimum required RF bandwidth • SSMA provides immunity to multipath interference and robust multiple access capability • SSMA is bandwidth efficient in multi-user environment • SSMA techniques: • Frequency hopped (FH) multiple access • Direct sequence (DS) multiple access • Also known as code division multiple access (CDMA)

  12. FHMA • Carrier frequencies of individual users are varied in a pseudorandom fashion within a wideband channel • Data of each user is broken into uniform size bursts that are transmitted on different channels at different time instants based on their pseudo-noise (PN) code sequence • In the FH receiver, a locally generated PN code is used to synchronize the receiver’s instantaneous frequency with that of the transmitter • FHMA provides inherent security, and guard against erasures through error control coding and interleaving • Use: Bluetooth and HomeRF

  13. CDMA • The narrowband message signal is multiplied by a very large bandwidth signal called spreading signal • The spreading signal has a pseudo-noise code sequence that has a chip rate which is orders of magnitudes greater than the data rates of the message • All users use the same carrier frequency and can transmit simultaneously • Each use has its own pseudorandom codeword that is orthogonal to the others • The receivers need to know the codeword of the corresponding sender • Power control is used to combat the near-far problem • Near-far problem: • When many mobile users share the same channel, the strongest received mobile signal will capture the demodulator at a base station. Thus a nearby subscriber could overpower the base-station receiver by drowning out the signals of far away subscribers.

  14. CDMA Features • Many users of CDMA share the same frequency – either TDD or FDD may be used • CDMA has soft capacity limit – system performance is inversely proportional to the number of users • Multipath fading is reduced because of the signal spread • Channel data rates are very high • Prone to self-jamming and near-far problem • Self-jamming: when the spreading sequences of different users are not exactly orthogonal • Near-far problem occurs at a CDMA receiver if an undesired user has a high detected power compared to the desired user

  15. Space Division Multiple Access (SDMA) • SDMA controls the radiated energy for each user and serves different users by using spot beam antennas • Different areas covered by antenna beam may be served by same or different frequencies • Reverse links present difficulty: • Transmitted power from each subscriber must be controlled to prevent any single user from driving up the interference level • Transmit power is limited by battery consumption at the subscriber unit

  16. Packet Radio • In Packet Radio (PR) access techniques, many subscribers attempt to access a single channel in an uncoordinated manner • Collisions from simultaneous transmissions from multiple transmitters are detected at the base station receiver, in which case an ACK or NACK signal is broadcasted by the base station to alert the user • PR subscribers use a contention technique to transmit on a common channel

  17. Carrier Sense Multiple Access Protocols (CSMA) • In CSMA protocols, each terminal on the network is able to monitor the status of the channel before transmitting information • Variations: • 1-persistent CSMA • non-persistent CSMA • p-persistent CSMA • CSMA/CD

  18. Convergence of Public Network • Carriers now use converged technology primarily in core, backbone portion of their networks to carry customer traffic more efficiently • Although carriers increasingly add IP equipment when they replace their voice switches, the majority of voice traffic is still carried in circuit switched networks • A circuit is a physical path for the transmission of voice, image or data.

  19. ITU defines circuit switching as : “The switching of circuits for the exclusive use of the connection for the duration of a call” • When a person or modem dials a call, the network sets up a path between the caller and the dialed party • Circuit switching is an example of a connection-oriented system • The path is maintained exclusively for the duration of the call and not shared • This causes wasteful utilization of network capacity

  20. Circuit-Switching

  21. Other Switching Technique-Message Switching • Message switching transfers arbitrary sized messages from a source to a destination using one or more message switches • Each switch stores the complete message before forwarding it • Normally messages are stored for only a short time, but they may be stored for days in some cases

  22. A message being sent using one intermediate message switch.

  23. The telex network is an example of a message switched network • Since the messages are stored in each message switch, message switching is suitable for the transfer of electronic mail and is used to send email to isolated parts of the world using connections provided by modems over the telephone network • Since there is no direct connection between the sender and the recipient, it is not possible to use message switching to login to a remote computer

  24. Rationale for Convergence • The Internet Protocol (IP) does not have this limitation • The Internet is a connection-less packet-switched network. • Packets from other sources fill pauses in one conversation • Eg. when a call is on hold, network capacity is used for other traffic • Moreover, technical advances have improved the quality of voice and video carried on packet networks • In addition, costs for routers, hard drives and fiber optics have decreased • The capability to deploy and maintain a single network for voice, data and video

  25. As VoIP protocols become increasingly standardised, custom interfaces between switches and applications will increasingly become unnecessary

  26. VoIP Networks • Cable TV, wireless mobile and traditional local exchange carriers use common IP core and edge IP network components when they upgrade their networks to IP • Components include: • Softswitches • Media gateways • Media servers • Application servers

  27. Softswitches • Process calls (issue commands on setting up and ending calls) • Communicate with billing systems • Acts as an overall network control point

  28. Media Gateways • Switch calls and translate protocols between different networks and between public network trunks such as T-1 and T-3 trunks and IP networks

  29. Media Servers • Generate touch-tone • Play announcements • Generate voice over IP packets from voice mail application • Convert voice mail messages to digital IP packet and vice versa • Record voice mail messages • Generate ring tones, busy signals, dial tone

  30. Application Servers • Contain complex applications • Eg. • unified messaging (capability to receive voice mail, e-mail, and fax messages on personal computers) • Large audio conferencing systems

  31. Peer-to-Peer Services • P2P services operate in a decentralised mode without softswitches to control signaling and communication • Napster, Gnutella, KaZaA – enable sharing of free music over the Internet • Skype introduced P2P architecture for VoIP without central servers

  32. Calling 911-VoIP vs Circuit switched • The Wireless Communication and Public Safety Act (1999) establishes 911 as the emergency number throughout the US. • The first emergency number was 999 used in London • The act mandated all carriers to connect 911 call to appropriate local emergency dispatch centre • It also mandated FCC to develop a plan for wireless providers to transition to enhanced 911 (E911) • Under E911, the agent who answer 911 calls is able to receive the callers’ phone number and location

  33. Mobile Services • Competition between mobile network operators, and the desire for more robust networks have led to the implementation of third generation digital networks by major mobile operators

  34. Evolution from 1G, 2G, 2.5G to 3G • The 1st G of cellular service used analog equipment in the early 1980s • The 1st service in US is AMPS • The 2nd G started in 1990s when carriers upgrade their analog to digital networks to gain more capacity • These include GSM, CDMA, TDMA and iDEN (Motorola)

  35. 2.5 G • Provides transition to WCDMA • Most GSM operators implemented GPRS and EDGE before WCDMA for the following reasons: • WCDMA equipment was not stable until 2004 • Small, lightweight 3G handset were not widely available prior to 2004 • Installing GPRS and EDGE delayed the large expenses to upgrade to WCDMA • Handset for GPRS and EDGE were readily available • GPRS and EDGE operate on the same frequencies as GSM

  36. 3G • Transition from 2G CDMA TO 3G CDMA2000 is less costly and complex than transition from GSM networks to WCDMA • The major incentive for upgarding is the increased voice capacity as well as the desire for a network capable of handling advanced application • Because it is easier to implement, CDMA2000 has more subscribers compared to WCDMA

  37. CDMA2000 1X (voice and data) • Provides “always on” data rates • Doubles the voice capacity • SK Telecom, the largest carrier in South Korea implements the 1st release of CDMA2000 in October 2000 • Only requires new cards in the base transceiver system and software in the mobile switching centre • Routers, billing, authentication and authorisation systems, and connection to IP networks are necessary for data services

  38. CDMA2000 1xEV-DO (data optimised- high data rate) • Network providers already have the 1st stage CDMA2000 can upgrade to higher data speeds by adding software and channel cards to their base stations for high data rate • HDR service is a data-only enhancement with higher downlink speeds • No capacity is gained for voice traffic

  39. WCDMA

  40. MobileFi • 802.20: IP Mobile Broadband Wireless Access • In 2002, the IEEE stated its intention to provide mobility in vehicles such as trains traveling up to 150mph or 250kmph, and to support higher data rates and more users than currently available • Flarion uses a form of orthogonal FDM (OFDM) in equipment called FLASH-OFDM. • Flash is short for Fast, Low-latency Access with Seamless Handoff • FLASH-OFDM spreads signals over a wider frequencies and at faster rate than OFDM

  41. Flarion service includes handoffs between Wi-Fi and FLASH-OFDM networks so that users use Wi-Fi when it is availabale and Flarion when it is not • Flarion supports VoIP and able to prioritise traffic • It is not expected to be available until 2008 • T-Mobile, Vodafone and TIME dotCOM (in Malaysia) are conducting trials of Flarion equipment

  42. Wi-Fi, Wireless broadband, Sensor Networks and PANs • Wi-Fi IEEE 802.11 • Wireless broadband - WiMax • Zigbee and IEEE 802.15 • PANs

  43. Evolution of Wireless LAN • Early experiences (1970-72): IBM, HP, Motorola • Abandoned due to limited performance and unavailability of frequency bands • Early challenges: • Complexity and cost • Bandwidth • Coverage • Interference • Frequency administration • Emergence of unlicensed bands • Release of Industrial, Scientific and Medical (ISM) bands in 1985 • Applications: military, home and enterprise networks, mobile networks, teetherless access

  44. Wi-Fi is based on 802.11 technology • It is originally intended tio provide wireless computing for staffs within businesses and commercial organisations • However, residential customers adopted Wi-Fi faster than enterprises because of its simplicity, fewer concerns about security and the benefit of avoiding the expenses for cabling • Its advantage is low equipment cost and easier installation • Benefits were also immediately noticed for healthcare, education, retailing and warehousing

  45. IEEE 802.11 • Standardization group formed in 1990, first standards completed in 1997 • IEEE 802.11 is the first WLAN standard; only one to secure a market • 802.11a: PHY layer supports 11Mbps using CKK (complementary code keying) technology • 802.11b: PHY layer supports 54 Mbps using OFDM • Uses CSMA/CA for contention data • Supports both infrastructure as well as ad hoc modes

  46. IEEE 802.11 Protocol Architecture Logical link control Contention-free service Contention service Point coordination function (PCF) MAC layer Distributed coordination function (DCF) 2.4-Ghz frequency-hopping spread spectrum 1Mbps 2Mbps 2.4-Ghz direct sequence spread spectrum 1Mbps 2Mbps Infrared 1Mbps 2Mbps 5-Ghz orthogonal FDM 6, 9. 12. 18, 24, 36, 48, 54 Mbps 2.4-Ghz direct sequence spread spectrum 5.5 Mbps 11 Mbps IEEE 802.11 IEEE 802.11a IEEE 802.11b

  47. 802.11a – higher speeds, smaller coverage, more channels • Wi-Fi is also sold to hotspot operators particularly hotel, convention centres, cafes, airports • Hotspots offer higher-speed Internet access than most cellular network’s data offering and cost less to build than cellular base station • 802.11 wireless standards are based on Ethernet protocols • 802.11a is the only 802.11 standard that operates at 5 GHz • The use of 5 GHz band avoids interference from microwave ovens, Bluetooth equipments and cordless phones that operate at 2.4 GHz • Disadvantage is the signal fade faster

  48. 802.11b • When they were first available, 802.11 equipments were equipped with only 802.11b chips • Now most use b and g which are designed to interoperate • Because home broadband connections are slower than 802.11 networks, no advantage is gained

  49. 802.11g • Support higher data rates than 802.11b • Use 2.4 gHz bands • The higher speeds and capacity of g and a are required to support voice over IP on WLANs

  50. 802.11n • Backward compatibility with a, b and g • Improve coverage by overcoming a certain amount of interference • Increase speeds and supports more users per access point

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