CMC ICT3207 Call Flow

Associate Professor

Dept. of Electrical and Electronic Engineering

University of Dhaka

Dr.

Mohammad

J

unaebur

R

ashid (

JR

)

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ICT3207: Cellular and Mobile Communication (3.0 Cr)

Course Teacher

Bangladesh University of Professionals

Lecture 19

Communication management (CM)

• The CM layer provides telecommunications services such as speech, fax, and data to users via RR and MM layers (Fig. 15.13).

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Lecture 19

Communication management (CM)

- _{Call control: CC manages the most circuit-oriented services (speech, circuit data) through}

the MSC/VLR, GMSC, IWF, and HLR.

• CC functions set up calls (mobile-originating or base-originating), maintain calls, and release calls. To establish calls, the MS number has to be assigned.

• Mobile station roaming number (MSRN) is the routing number, another number which can be a GSM subscriber or third party international mobile subscriber identity (IMSI) and

Lecture 19

Communication management (CM)

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Lecture 19

Communication management (CM)

• In this case, on the request of a base station, the signal strength of a specified radio carrier is measured in one time frame, and, on request, the measurements are forwarded to the base

station to assist in the handover process. This is called MAHO.

• The MSC uses two sets of information to decide whether a handover should be initiated and which BTS is the candidate BTS for the handover.

• The two sets are:

(1) the signal strengths of the MS, as received at the neighboring BTSs and

(2) the signal strengths of neighboring BTSs received at the MS. The latter information is

from MAHO.

-_{Handover: The GSM handover algorithm is not specified as a standard. It is a feature of}

mobile assistance handover (MAHO) and is carried out within the unit.

Lecture 19

Communication management (CM)

- Supplementary services management (SSM)

CC provides supplementary services such as call waiting, call forwarding, and automatic answering. SSM is a point-to-point management service. An SSM service center (SSM-SC)

may connect to several GSM networks. SSM consists of two functions: 1. Mobile terminating short message and

2. Mobile originating short message

- Short message services

• CC provides point-to-point short message services (SMS-PP). GSM is connected to the short message service center.

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Lecture 19

Network management (NM)

• An NM center oversees the following administration tasks: 1. Subscriber management—subscription administration

2. Billing and accounting 3. Maintenance

a. Minimizing failures

b. Monitoring operations and indicating by alarm improper operation situations

4. Subscriber administration tasks provide the selected approval code for ME (mobile

equipment) within the IMEI number. The code totals 15 digits and consists of type approval code (TAC) + final assembly code (FAC) + serial number which stores in EIR.

5. In the GSM telecommunication management network (TMN), all operation and

maintenance machines compose a network which is linked to all traffic handling machines. The GSM Q3 is a network management protocol for operation systems functions and traffic

Lecture 19

Overview of GSM

• GSM's strength: GSM is the first to apply the TDMA scheme developed for mobile radio systems. It has several distinguishing features:

1. Roaming in all countries 2. Connection to ISDN

5. Frequency hopping

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Lecture 19

Frequency Management

• The function of frequency management is to divide the total number of available channels into subsets which can be assigned to each cell either in a fixed fashion or dynamically.

• Frequency management refers to designating set-up channels and voice channels (done by the FCC), numbering the channels (done by the FCC), and grouping the voice channels into

subsets (done by each system according to its preference).

• Channel assignment refers to the allocation of specific channels to cell sites and mobile units. A fixed channel set consisting of one or more subsets is assigned to a cell site on a long-term basis.

• During a call, a particular channel is assigned to a mobile unit on a short term basis. For a short-term assignment, one channel assignment per call is handled by the mobile telephone switching office (MTSO).

• Ideally channel assignment should be based on causing the least interference in the system. However, most cellular systems cannot perform this way.

Lecture 19

Frequency Management

• Lets assume, the total number of channels operating in a system is 666. Therefore we describe the 666 channel numbering first.

• A channel consists of two frequency channel bandwidths, one in the low band and one in the high band.

• Two frequencies in channel 1 are 825.030 MHz (mobile transmit) and 870.030 MHz (cell-site transmit). The two frequencies in channel 666 are 844.98 MHz (mobile transmit) and 889.98 MHz (cell-site transmit).

• The 666 channels are divided into two groups: block A system and block B system.

• Each block has 333 channels (Fig. 8.1). The voice channels are assigned as follows: Channels 1-312 (312 voice channels) block A;

Channels 355-666 (312 voice channels) block B

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Lecture 19

Lecture 19

Frequency Management

• These 42 set-up channels are assigned in the middle of all the assigned channels to facilitate scanning of those channels by frequency synthesizers (Fig. 8.1).

• In the new additional spectrum allocation of 10 MHz (Fig. 8.2), an additional 166 channels are assigned.

• Since a 1 MHz is assigned below 825 MHz (or 870 MHz), in the future, additional channels will be numbered up to 849 MHz (or 894 MHz) and will then circle back. The last channel number is 1023 (=210). There are no channels between channels 799 and 991.

4 MHz: 845-849 MHz 1 MHz: 824-825 MHz

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Lecture 19

Frequency Management

• The number of voice channels for each system is 312. We can group these into any number of subsets.

• Since there are 21 set-up channels for each system, it is logical to group the 312 channels into 21 subsets.

• Each subset then consists of 16 channels. In each set, the closest adjacent channel is 21 channels away (Fig. 8.1).

• The 16 channels in each subset can be mounted on a frame and connected to a channel combiner. Wide separation between adjacent channels is required for meeting the requirement of minimum isolation.

Lecture 19

Frequency Management

• In a seven cell frequency-reuse cell system each cell contains three subsets, iA + iB + iC, where i is an integer from 1 to 7.

• If we consider, for instance in 1A → 15 channels, in 1B → 15 channels and in 1C → 15 channels, then the total number of voice channels in a cell is about 45.

• The minimum separation between three subsets is 7 channels.

• If six subsets are equipped in an omnicell site, the minimum separation between two adjacent channels can be only three (21/6 > 3) physical channel bandwidths.

For example,

1A + lB + 1C + 4A + 4B + 4C

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Lecture 19

Frequency-spectrum utilization

• Since the radio-frequency spectrum is finite in mobile radio systems, the most significant challenge is to use the radio-frequency spectrum as efficiently as possible.

• Geographic location is an important factor in the application of the frequency-reuse concept in mobile cellular technology to increase spectrum efficiency.

• Frequency management involving the assignment of proper channels in different cells can increase spectrum efficiency.

• The techniques for increasing frequency spectrum can be classified as

1. Increasing the number of radio channels using narrow banding, spread spectrum, or time division

2. Improving spatial frequency-spectrum reuse

Lecture 19

Frequency-spectrum utilization

5. Reducing the load of invalid calls

a. Off-air call setup - reducing the load of set-up channels b. Voice storage service for No-Answer calls

c. Call forwarding

d. Reducing the customers' Keep-Dialing cases e. Call waiting for Busy-Call situations