Speech Coding - Lecture - Mobile Computingr, Lecture notes of Mobile Computing

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Mobile Computing

Cellular Concept

• Base stations (BS): implement space division

multiplex

– Each BS covers a certain transmission area (cell)

– Each BS is allocated a portion of the total number of

channels available

– Cluster: group of nearby BSs that together use all

available channels

• Mobile stations communicate only via the base

station, using FDMA, TDMA, CDMA…

Mobile Station (MS)

• MS consists of following two components

• Mobile Equipment (ME)

• Mobile Subscriber Identity Module (SIM)

• (^) Removable plastic card
• (^) Stores Network Specific Data such as list of carrier

frequencies and current LAI.

• (^) Stores International Mobile Subscriber Identity (IMSI) + ISDN
• (^) Stores Personal Identification Number (PIN) & Authentication

Keys.

• (^) Also stores short messages, charging information, telephone

book etc.

• Allows separation of user mobility from equipment mobility

Base Transceiver Station (BTS)

• One per cell

• Consists of high speed transmitter and receiver

• Function of BTS

– Provides two channels

Signalling and Data Channel

– Performs error protection coding for the radio

channel

Mobile Switching Center (MSC)

• Switching node of a PLMN

• Allocation of radio resource (RR)

– Handover

• Mobility of subscribers

– Location registration of subscriber

• There can be several MSCs in a PLMN

Gateway MSC (GMSC)

• Connects mobile network to a fixed network

– Entry point to a PLMN

• Usually one per PLMN

• Request routing information from the HLR and

routes the connection to the local MSC

AuC/EIR/OSS

• AuC: Authentication Center

– is accessed by HLR to authenticate a user for service

– Contains authentication and encryption keys for subscribers

• EIR: Equipment Identity Register

– allows stolen or fraudulent mobile stations to be identified

• Operation subsystem (OSS):

– Operations and maintenance center (OMC), network

management center (NMC), and administration center

(ADC) work together to monitor, control, maintain, and

manage the network

GSM identifiers

• International mobile subscriber identity (IMSI):

– unique 15 digits assigned by service provider = home

country code + home GSM network code + mobile

subscriber ID + national mobile subscriber ID

• International mobile station equipment identity (IMEI):

– unique 15 digits assigned by equipment manufacturer =

type approval code + final assembly code + serial number +

spare digit

• Temporary mobile subscriber identity (TMSI):

– 32-bit number assigned by VLR to uniquely identify a

mobile station within a VLR’s area

Cell Identifier (CI)

• Within LA, individual cells are uniquely identified

with Cell Identifier (CI).

• It is maximum 2*8 bits

• LAI + CI = Global Cell Identity

Air Interface: MS to BTS

• Uplink/Downlink of 25MHz

– 890 -915 MHz for Up link

– 935 - 960 MHz for Down link

• Combination of frequency division and time division

multiplexing

– FDMA

• (^) 124 channels of 200 kHz

– TDMA

• (^) Burst

• Modulation used

Gaussian Minimum Shift Keying (GMSK)

Air Interface: Logical Channel

• Traffic Channel (TCH)

• Signalling Channel

– Broadcast Channel (BCH)

– Common Control Channel (CCH)

– Dedicated/Associated Control Channel

(DCCH/ACCH)

Sessions: 3 & 4 3. 17 YES NO NO NO YES YES Power On Scan Channels, monitor RF levels Select the channel with highest RF level among the control channels Scan the channel for the FCCH Is FCCH detected? Scan channel for SCH Is SCH detected? Read data from BCCH and determine is it BCCH? Is the current BCCH channel included? Camp on BCCH and start decoding Select the channel with next highest Rf level from the control list. From the channel data update the control channel list

FCCH & SCH

• Frequency Correction Channel
  • (^) send a frequency correction data burst containing all zeros to effect a constant frequency shift of RF carrier
• (^) Repeated broadcast of Frequency Bursts
• (^) Synchronization Channel
  • (^) send TDMA frame number and base station identity code to synchronize MSs
• Repeated broadcast of Synchronization Bursts
• (^) Message format of SCH PLMN color 3 bits BS color 3 bits T1 Superframe index 11 bits T2 multiframe index 11 bits T3 block frame index 3bits BSIC 6 bits" FN 19bits

AGCH & PCH

Access Grant Channel (AGCH)

– BTS to MS

– Assign an SDCCH/TCH to MS

• Paging Channel (PCH)

– BTS to MS

– Page MS