Lecture 02 EEE 441: Wireless And Mobile Communications BRAC University

Several PCS systems High-tier Systems  GSM: Global System for Mobile Communications The most common mobile telephony system  IS-136 USA digital cellular mobile telephony system TDMA based multiple access  IS-95 CDMA based multiple access

Several PCS systems (cont’d)‏ Low-tier systems  Residential, business and public cordless access applications and systems Cordless Telephone 2 (CT2) :  EU standard, FDMA Digital Enhanced Cordless Telephone (DECT)‏  EU standard, TDMA Personal Access Communication Systems (PACS)‏  US standard, TDMA/FDMA Personal Handyphone System (PHS)‏  Japan standard, TDMA

Several PCS systems (cont’d)‏ Wideband wireless systems  For Internet access and multimedia transfer CDMA2000 W-CDMA 3G

Several PCS systems (cont’d)‏ Other PCS Systems  Special data systems CDPD: Cellular Digital Packet Data Advanced Radio Data Information System (ARDIS)‏  Paging Systems  Mobile Satellite Systems  ISM band systems: Bluetooth, Wi-Fi, etc.

Example Wireless System 1: Cordless Telephones

Cordless Telephones Cordless Phone Base unit PSTN Telephone Network

Cordless Telephones (cont’d)‏ Characterized by:  low mobility (in terms of range and speed)‏  low power consumption  full-duplex wireless voice communication  low cost equipment  no handoffs between base units First appeared as analog devices Digital devices appeared later with:  CT2 and DECT standards in Europe  PACS in the US  PHS in Japan

Cordless Telephones (cont’d)‏ Some features:  32 Kb/s adaptive differential pulse code modulation (ADPCM) digital speech encoding  Tx power < 10 mW  Low-complexity radio signal processing  No forward error correction (FEC)  Simple Frequency Shift Modulation (FSK)‏  Time Division Duplexing (TDD)‏

Example Wireless System 2: Cellular Telephones

Cellular Telephones Characterized by  High-speed mobility  Wide range  Full-duplex wireless voice communication  Handoff and roaming support  Integrated with PSTN  High transmission power capable handset (~2W)‏

Wireless System Definitions  Mobile Station  A station in the cellular radio service intended for use while in motion at unspecified locations.  Base Transciever Station (BTS)  A fixed station in a mobile radio system used for radio communication with the mobile stations. Base Stations are located at the center or edge of a coverage region. They consists of radio channels and transmitter and receiver antennas mounted on top of a tower.

Wireless System Definitions (Cont’d)‏  Mobile Switching Center (MSC)  Switching center which coordinates the routing of calls in a large service area. In a cellular radio system, the MSC connects the cellular base stations and the mobiles to the PSTN (telephone network). It is also called the Mobile Telephone Switching Office (MTSO).  Subscriber  A user who pays subscription charges for using a mobile communication system.  Transceiver  A device capable of simultaneously transmitting and receiving radio signals.

 Control Channel  Radio channel used for transmission of call setup, call request, call initiation and other beacon and control purposes.  Forward Channel  Radio channel used for transmission of information from the base station to the mobile.  Reverse Channel  Radio channel used for transmission of information from the mobile to the base station. Wireless System Definitions (Cont’d)‏

 Simplex System  Allows one-way communication only.  Half Duplex System  Allows two-way communication by using the same radio channel for both transmission and reception. At any given time, the user can either transmit or receive information, but cannot do both.  Example?  Full Duplex System  Allows simultaneous two-way communication.  Example? Wireless System Definitions (Cont’d)‏

 Handoff  The process of transferring a mobile station from one channel or base station to another.  Roamer  A mobile station which operates in a service area other than that from which the service has been subscribed.  Page  A brief message which is broadcast over the entire service area, usually in simulcast fashion by many base stations at the same time. Wireless System Definitions (Cont’d)‏

Cellular Telephony: Architecture

FVC RVC FCC RCC Base Station Forward Voice Channel Reverse Voice Channel Forward Control Channel Reverse Control Channel

Functions of Cellular System High capacity is achieved by:  limiting the coverage of each base station transmitter to a small geographical area called a cell  reusing the same radio channels in another cell located some distance away (frequency reuse)‏

Mobile Switching Center (MSC)‏ MSC performs handoff to allow call to proceed uninterrupted when user moves from one cell to another. Typical MSC handles 100,000 cellular users and 5,000 simultaneous conversations at a time.

Setting up call made TO mobile user... (Ref: Rappaport, Fig. 1.6)

Call-Setup Sequence Step 1: Incoming telephone call to number is received at MSC. Step 2: MSC dispatches the request to all base stations in the cellular system. Step 3: The base stations broadcast the Mobile Identification Number (MIN), which is the subscriber’s telephone number, as a paging message over the FCC throughout the cellular system.

Step 4: Target mobile receives paging message sent by the base station in its cell, and responds by identifying itself over the RCC. Step 5: The base station relays the ack sent by the mobile to the MSC and informs MSC that handshake has been performed. Step 6: The MSC instructs the base station to move the call to an available FVC/RVC pair. Call-Setup Sequence (Cont’d)‏

Step 7: The base station signals the mobile to change frequencies to the FVC/RVC pair instructed by the MSC. At the point another data message (alert) is transmitted over the FVC to instruct the mobile to ring. __________________________________________ Now the call is in progress. The MSC adjusts the transmitted power of the mobile to maintain call quality, and performs handoffs when necessary. Call-Setup Sequence (Cont’d)‏

Incoming Telephone Call to Mobile X 3, 7 PSTNPSTN Mobile X Mobile Switching Center 2, Step 1 Base Stations (Ref: Rappaport, Fig. 1.6) Call-Setup Sequence: Summary‏

Setting up call made BY mobile user... (Ref: Rappaport, Fig. 1.7)

Call-Setup Sequence Step 1: When a mobile originates a call, it sends its telephone number (MIN), electronic serial number (ESN), and telephone number of called party to the base station. It also transmits a station class mark (SCM) which indicates what the maximum power level is for the particular user. Step 2: The cell base station receives data, forwards it to MSC. Step 3: The MSC validates the request, makes connection to the called party through the PSTN, and instructs the base station and mobile user to move to an unused FVC/RVC pair to allow the conversation to begin.

Telephone Call Placed by Mobile X PSTNPSTN Mobile Switching Center (Ref: Rappaport, Fig. 1.6) Call-Setup Sequence: Summary‏

Roaming All cellular systems provide a service called roaming. This allows subscribers to operate in areas other than its home area. Periodically, the MSC issues a global command over each FCC in the system, asking for all mobiles which are previously unregistered to report their MIN and ESN over the RCC. If a particular mobile user has roaming authorization for billing purposes, MSC registers the subscriber as a valid roamer.

Notices Reading:  Rappaport, Ch 1  Rappaport, Figs Quiz 1  Next class  On material from Lectures HW 1  Due next class