10 Slides to Mobile Wireless

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10 Slides to Mobile Wireless

  1. 1. Mobile Wireless 1G and 2G Systems The Telecom Source 10 Slide Technology Series
  2. 2. Introduction <ul><li>Modern mobile wireless services were introduced in the late 1970’s </li></ul><ul><li>Initial mobile wireless systems were analog and are referred to as first generation systems or 1G </li></ul><ul><li>First generation systems suffered from a number of weaknesses including: low capacity, fraud and weak support for privacy </li></ul><ul><li>Second generation systems were introduced in the early 90’s to address the short-comings of first generation systems </li></ul><ul><li>Second generation systems are digital systems and provide between 3 to 10 times the capacity of 1 st generation systems </li></ul><ul><li>Both 1 st generation and 2 nd generation systems were designed primarily for voice services and are not very suitable for data services </li></ul><ul><li>3 rd generations systems are intended to provide enhanced support for data services and will be discussed in a separate tutorial. </li></ul>
  3. 3. Background <ul><li>Spectrum has been allocated in the 800 MHz, 1800 MHz and 1900 MHz range for 1 st and 2 nd generation mobile wireless communications systems </li></ul><ul><li>Regulatory bodies in each country allocate blocks of spectrum to service providers by a variety of methods such as auction and “ beauty contest ” </li></ul><ul><li>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 </li></ul><ul><li>In many other countries, national licenses are often awarded to service providers as opposed to multiple regional licenses </li></ul><ul><li>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. </li></ul><ul><li>The concept of cells enables higher subscriber capacities due to frequency reuse and lower antenna power requirements </li></ul>
  4. 4. Simple Network Architecture <ul><li>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. </li></ul><ul><li>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. </li></ul><ul><li>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 </li></ul><ul><li>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. </li></ul><ul><li>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. </li></ul>Base Station Controller (BSC) Base Station Controller (BSC) Home Location Register (HLR) BTS BTS BTS BTS BTS BTS BTS Mobile Switching Center (MSC) PSTN
  5. 5. Simplified Operation …Initialization <ul><li>Subscriber turns on handheld </li></ul><ul><li>Handheld scans for a cell with a suitable strong signal and secures a channel for communication with the corresponding MSC </li></ul><ul><li>Handheld sends a registration message to the MSC which includes a unique identifier </li></ul><ul><li>Based on the unique identifier, the MSC is able to identify the subscriber’s home HLR </li></ul><ul><li>The MSC authenticates the subscriber </li></ul><ul><li>The MSC sends a registration message to the home HLR informing the HLR that it [the MSC] now serves the subscriber </li></ul><ul><li>The HLR sends a cancellation message to the previous MSC that served the subscriber </li></ul><ul><li>Handheld is not available to send and receive calls </li></ul>
  6. 6. Simplified Operation … “Hand-Off” <ul><li>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) </li></ul><ul><li>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 </li></ul><ul><li>Generic hand-off process is: </li></ul><ul><ul><ul><li>The signal strength between the handheld and the serving cell is measured </li></ul></ul></ul><ul><ul><ul><li>If the signal strength falls below a predetermined threshold other nearby cells are instructed to measure the signal strength to the handheld </li></ul></ul></ul><ul><ul><ul><li>If the signal strength to another cell is stronger, the cell is instructed to switch the handheld </li></ul></ul></ul><ul><ul><ul><li>The cell allocates a frequency and timeslot for the handheld and the MSC makes the switch </li></ul></ul></ul>Before After
  7. 7. First Generation Systems <ul><li>Numerous 1 st generation mobile systems have been deployed throughout the world. The major ones are still in operation today and are listed below. </li></ul><ul><ul><ul><li>AMPS – Advanced Mobile Service </li></ul></ul></ul><ul><ul><ul><ul><ul><li>Developed by Bell Labs </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>First used commercially in the U.S in 1983 </li></ul></ul></ul></ul></ul><ul><ul><ul><li>NAMPS – Narrowband AMPS </li></ul></ul></ul><ul><ul><ul><ul><ul><li>Developed by Motorola as an interim technology between analog and digital </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Provided 3 times as much capacity as AMPS </li></ul></ul></ul></ul></ul><ul><ul><ul><li>TACS – Total Access Communications System </li></ul></ul></ul><ul><ul><ul><ul><ul><li>Developed by Motorola </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>First used in the U.K in 1985 </li></ul></ul></ul></ul></ul><ul><ul><ul><li>NMT – Nordic Mobile Telephone </li></ul></ul></ul><ul><ul><ul><ul><ul><li>Developed by the Nordic countries and introduced in 1981 </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>NMT450 initially introduced operating in the 450 MHz range </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>NMT900 later developed to accommodate higher capacities </li></ul></ul></ul></ul></ul><ul><ul><ul><li>NTT – Nippon Telegraph and Telephone </li></ul></ul></ul><ul><ul><ul><ul><ul><li>Japanese analog standard </li></ul></ul></ul></ul></ul>
  8. 8. Second Generation Systems <ul><li>2 nd generation systems were introduced to address the shortcomings of 1 st generation systems. The major 2G systems are listed below. </li></ul><ul><ul><ul><li>TDMA (IS-136) – Time Division Multiple Access </li></ul></ul></ul><ul><ul><ul><ul><ul><li>Adopted by the Telecommunications Industry Association in 1992 </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>The move to TDMA IS-136 was via IS-54 </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>First used commercially in 1993 </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Deployed in the 800 MHz and 1900 MHz bands </li></ul></ul></ul></ul></ul><ul><ul><ul><li>GSM – Global System for Mobile Communications </li></ul></ul></ul><ul><ul><ul><ul><ul><li>European digital standard </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Currently the most widely adopted mobile wireless standard worldwide </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Enables international roaming </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Deployed in the 900 MHz, 1800 MHz and 1900 MHz bands </li></ul></ul></ul></ul></ul><ul><ul><ul><li>CDMA (IS-95) – Code Division Multiple Access </li></ul></ul></ul><ul><ul><ul><ul><ul><li>Developed by Qualcomm </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>First used commercially in 1996 </li></ul></ul></ul></ul></ul><ul><ul><ul><ul><ul><li>Deployed primarily in the 800 MHz band </li></ul></ul></ul></ul></ul>
  9. 9. TDMA (IS-136) <ul><li>TMDA systems use the concept of time division multiplexing which enables multiple users to share the same radio channel </li></ul><ul><li>The radio spectrum is divided into 30 KHz channels </li></ul><ul><li>Separate radio channels exists for sending (uplink) and receiving (downlink) information </li></ul><ul><li>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 </li></ul><ul><li>Each 30 KHz channel is divided into 6 timeslots </li></ul><ul><li>Each user is assigned 2 timeslot s on an uplink channel for sending and 2 timeslot on a downlink channel for receiving. Therefore 3 subscribers can use a channel simultaneously </li></ul>      UNLINK user1 user2 user3 user4 user5 user6 user7 user8 user9 user1 user2 user3 user4 user5 user6 user7 user8 user9 Radio channel 1 Radio channel 2 Radio channel 3 Radio channel 1 Radio channel 2 Radio channel 3 user1 user2 user3 user4 user5 user6 user7 user8 user9 user1 user2 user3 user4 user5 user6 user7 user8 user9 DOWNLINK
  10. 10. GSM <ul><li>Like TDMA, GSM uses the concept of time division multiplexing </li></ul><ul><li>The radio spectrum is divided into 200 KHz channels </li></ul><ul><li>Separate radio channels exists for sending and receiving information </li></ul><ul><li>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 </li></ul><ul><li>Each 20 0 KHz channel is divided into 8 timeslots </li></ul><ul><li>At any point in time 1 timeslot must be allocated for control channel purposes. Therefore u p to 7 subscribers can use a channel simultaneously. </li></ul><ul><li>Each user is assigned 1 timeslot on an uplink channel for sending and 1 timeslot on a downlink channel for receiving </li></ul>      UNLINK user1 user2 user3 user9 user… user… user17 user… user… user1 user2 user3 user9 user… user… user17 user… user… Radio channel 1 Radio channel 2 Radio channel 3 Radio channel 1 Radio channel 2 Radio channel 3 user4 user5 user6 user4 user… user… user… user… user… user4 user5 user6 user… user… user… User… user… user… DOWNLINK user7 user8 user… user16 user… user24 user7 user8 user… user16 user… user24
  11. 11. CDMA (IS-95) <ul><li>CDMA, unlike TDMA and GSM, does not use the concept of time division multiplexing </li></ul><ul><li>CDMA is based on direct sequence spread spectrum technology </li></ul><ul><li>The spectrum is divided into 1.23 MHz channels. More than 1 channel can be assigned to a cell </li></ul><ul><li>Separate radio channels exists for sending and receiving information </li></ul><ul><li>A given radio channel can be reused in every cell (including adjacent cells) </li></ul><ul><li>All users share the same frequency at the same time </li></ul><ul><li>Each user signal is modulated (using XOR operation) with a unique pseudo-random high bit rate code sequence (PN – pseudo noise sequence) </li></ul><ul><li>At the receiver, knowledge of the code sequence used for a given signal enables the signal to be extracted (using XOR). The other signals appear to the receiver as noise </li></ul>1 1 0 Original Signal Transmitter PN 1 0 0 1 0 0 0 0 1 1 1 1 Coded Signal 0 1 1 0 0 0 1 1 1 1 0 0 Receiver PN 1 0 0 1 0 0 0 0 1 1 1 1 1 1 0 Decoded Signal
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