Docstoc

Mobile Wireless

Document Sample
Mobile Wireless Powered By Docstoc
					                                 Mobile Wireless
                                    1G and 2G Systems

                                    The Telecom Source
                                10 Slide Technology Series



Telecom Source Consulting Inc.
www.thetelecomsource.com | 905-854-5400
Introduction
   Modern mobile wireless services were introduced in the late 1970’s

   Initial mobile wireless systems were analog and are referred to as first
   generation systems or 1G

   First generation systems suffered from a number of weaknesses
   including: low capacity, fraud and weak support for privacy

   Second generation systems were introduced in the early 90’s to address
   the short-comings of first generation systems

   Second generation systems are digital systems and provide between 3
   to 10 times the capacity of 1st generation systems

   Both 1st generation and 2nd generation systems were designed primarily
   for voice services and are not very suitable for data services

   3rd generations systems are intended to provide enhanced support for
   data services and will be discussed in a separate tutorial.
Background
   Spectrum has been allocated in the 800 MHz, 1800 MHz and 1900 MHz range
   for 1st and 2nd generation mobile wireless communications systems

   Regulatory bodies in each country allocate blocks of spectrum to service
   providers by a variety of methods such as auction and “beauty contest”

   In the U.S., for example, spectrum blocks have been allocated by geographic
   area via the auction method. Competition was introduced by awarding multiple
   licenses per geographic area. Some service providers acquired licenses in
   multiple geographic area to create national networks

   In many other countries, national licenses are often awarded to service
   providers as opposed to multiple regional licenses

   Mobile wireless communications systems tend to be referred to as cellular
   systems because of the practice of dividing the network coverage area into a
   large number of smaller contiguous coverage areas called cells.

   The concept of cells enables higher subscriber capacities due to frequency
   reuse and lower antenna power requirements
Basic Network Architecture
                                                                                Home
                                                                               Location                                     PSTN
                                                  BTS                          Register
                                                                                (HLR)
                                     BTS

                       BTS                        BTS                       Base Station
                                                                             Controller
                                     BTS                                       (BSC)                         Mobile Switching
                                                                                                                 Center
                       BTS                                                                                        (MSC)
                                                                            Base Station
                                     BTS                                     Controller
                                                                               (BSC)


Cell – the coverage area is divided into a number of smaller geographic areas called cells. Cells can vary in size from less than 100 meters to
tens of kilometers. Each cell site contains a base transceiver station.

BTS – the base transceiver station contains a transceiver (transmitter/receiver) for communication with subscriber handhelds that are within the
cell. The base station is also connected to a base station controller.

BSC – the base station controller contains the logic to control each of the base stations including functions such as handoff from one base
station to another as subscribers move from cell to cell

MSC – the mobile switching center manages the setup and tear down of calls. The MSC is connected to the PSTN to enable completion of
calls to other networks and wireline telephones.

HLR – the home location register stores subscriber information and keep track of a subscriber’s location as the subscriber moves around the
network. The MSC interacts with the HLR.
Simplified Operation - Initialization
 1.   Subscriber turns on handheld

 2.   Handheld scans for a cell with a suitable strong signal and secures a channel
      for communication with the corresponding MSC

 3.   Handheld sends a registration message to the MSC which includes a unique
      identifier

 4.   Based on the unique identifier, the MSC is able to identify the subscriber’s
      home HLR

 5.   The MSC authenticates the subscriber

 6.   The MSC sends a registration message to the home HLR informing the HLR
      that it [the MSC] now serves the subscriber

 7.   The HLR sends a cancellation message to the previous MSC that served the
      subscriber

 8.   Handheld is now available to send and receive calls
Simplified Operation – “Handoff”
   Hand-off refer to the function of maintaining a call as a
   subscriber moves from cell to cell within a network (and
   hence, the call is transferred from cell to cell)                    Before


   Hand-off can occur between cells controlled by the
   same BSC, between cells controlled by different BSCs,
   between cells controlled by different MSCs, or even
   between cells in different networks

   Generic hand-off process is:
        1.    The signal strength between the handheld and the          After
              serving cell is measured
        2.    If the signal strength falls below a predetermined
              threshold other nearby cells are instructed to
              measure the signal strength to the handheld
        3.    If the signal strength to another cell is stronger, the
              cell is instructed to switch the handheld
        4.    The cell allocates a frequency and timeslot for the
              handheld and the MSC makes the switch
First Generation Systems
Numerous 1st generation mobile systems have been deployed throughout the world. The
major ones are still in operation today and are listed below.

           AMPS – Advanced Mobile Service
                     Developed by Bell Labs
                     First used commercially in the U.S in 1983


           NAMPS – Narrowband AMPS
                     Developed by Motorola as an interim technology between analog and digital
                     Provided 3 times as much capacity as AMPS


           TACS – Total Access Communications System
                     Developed by Motorola
                     First used in the U.K in 1985


           NMT – Nordic Mobile Telephone
                     Developed by the Nordic countries and introduced in 1981
                     NMT450 initially introduced operating in the 450 MHz range
                     NMT900 later developed to accommodate higher capacities


           NTT – Nippon Telegraph and Telephone
                     Japanese analog standard
Second Generation Systems
2nd generation systems were introduced to address the shortcomings of 1st
generation systems. The major 2G systems are listed below.

           TDMA (IS-136) – Time Division Multiple Access
                   Adopted by the Telecommunications Industry Association in 1992
                   The move to TDMA IS-136 was via IS-54
                   First used commercially in 1993
                   Deployed in the 800 MHz and 1900 MHz bands

           GSM – Global System for Mobile Communications
                   European digital standard
                   Currently the most widely adopted mobile wireless standard worldwide
                   Enables international roaming
                   Deployed in the 900 MHz, 1800 MHz and 1900 MHz bands

           CDMA (IS-95) – Code Division Multiple Access
                   Developed by Qualcomm
                   First used commercially in 1996
                   Deployed primarily in the 800 MHz band
TDMA (IS-136)
  TMDA systems use the concept of time division multiplexing which enables multiple users to share the same
  radio channel

  The radio spectrum is divided into 30 KHz channels

  Separate radio channels exists for sending (uplink) and receiving (downlink) information

  A number of 30 KHz channels are assigned to each cell. The same frequencies are reused in other cells far
  enough away for avoid interference

  Each 30 KHz channel is divided into 6 timeslots

  Each user is assigned 2 timeslots on an uplink channel for sending and 2 timeslot on a downlink channel for
  receiving. Therefore 3 subscribers can use a channel simultaneously

               Radio channel 1   user1   user2   user3   user1   user2   user3
               Radio channel 2   user4   user5   user6   user4   user5   user6       UNLINK
               Radio channel 3   user7   user8   user9   user7   user8   user9




              Radio channel 1    user1   user2   user3   user1   user2   user3
              Radio channel 2    user4   user5   user6   user4   user5   user6       DOWNLINK
              Radio channel 3    user7   user8   user9   user7   user8   user9
GSM
 Like TDMA, GSM uses the concept of time division multiplexing
 The radio spectrum is divided into 200 KHz channels
 Separate radio channels exists for sending and receiving information
 A number of 200 KHz channels are assigned to each cell. The same frequencies are reused in other cells far
 enough away for avoid interference
 Each 200 KHz channel is divided into 8 timeslots
 At any point in time 1 timeslot must be allocated for control channel purposes. Therefore up to 7 subscribers
 can use a channel simultaneously.
 Each user is assigned 1 timeslot on an uplink channel for sending and 1 timeslot on a downlink channel for
 receiving

      Radio channel 1   user1   user2   user3   user4   user5   user6   user7   user8
      Radio channel 2   user9   user… user…     user4   user… user…     user…   user16        UNLINK
      Radio channel 3   user17 user… user…      user… user… user…       user…   user24




      Radio channel 1   user1   user2   user3   user4   user5   user6   user7   user8
      Radio channel 2   user9   user… user…     user… user… user…       user…   user16        DOWNLINK
      Radio channel 3   user17 user… user…      User… user… user…       user…   user24
CDMA (IS-95)
  CDMA, unlike TDMA and GSM, does not use the concept of
  time division multiplexing
                                                                 Original Signal
  CDMA is based on direct sequence spread spectrum                    1                1
  technology                                                                       0

  The spectrum is divided into 1.23 MHz channels. More than 1    Transmitter PN
  channel can be assigned to a cell                               1 0 0 1 0 1 0 1 1 0 1 0

  Separate radio channels exists for sending and receiving
  information                                                    Coded Signal
                                                                  0 1 1 0 0 1 0 1 0 1 0 1
  A given radio channel can be reused in every cell (including
  adjacent cells)
                                                                 Receiver PN
  All users share the same frequency at the same time
                                                                  1 0 0 1 0 1 0 1 1 0 1 0
  Each user signal is modulated (using XOR operation) with a
  unique pseudo-random high bit rate code sequence (PN –
  pseudo noise sequence)                                         Decoded Signal
                                                                     1                 1
  At the receiver, knowledge of the code sequence used for a                       0
  given signal enables the signal to be extracted (using XOR).
  The other signals appear to the receiver as noise
Telecom Source Consulting Inc.

        www.thetelecomsource.com

        info@thetelecomsource.com

				
DOCUMENT INFO
Shared By:
Stats:
views:57
posted:3/9/2011
language:English
pages:12
Description: Mobile exchange center - MSC is whole GSM network core, its control all BSC business, provide exchange function and and other functions in the system of connection, MSC can provide direct or through mobile gateway GMSC provide and the public switched telephone network (PSTN), integrated services digital network (ISDN), public data networks (PDN) for fixed network interface functions, to mobile users and mobile users, mobile users and fixed network users connected with each other.