Use of GSM Logical Channels for CSA

When a mobile/smart phone's power button is pressed the mobile triggers the power up sequence. The mobile station MS is in the radio darkness (ignorant) at this stage about the radio coverage that surrounds it in the geographical area in which it has been switched ON. Once switched on, the mobile device will seek to establish, using the embedded routines in its radio program that will enable it to follow a sequence that brings it out of the radio darkness and into the radio light. It gains knowledge about the radio coverage surrounding it; makes comparison of particular coverage to identify the correct transmission technology for which the mobile device has been designed and manufactured; illuminate its presence to the mobile network in the geogrpahical location where it is dwelling for the purpose of communications; to be radio link-enabled for mobile content communications and radio link-disabled to terminate mobile content communications. 

The diagram below omits 'timing' of events because it is not there to demonstrate the time when each event occurs but it is intended the diagram to offer an at-a-glance visual indication of the sequence of channels involved from power ON to terminating a call.

It is possible that a suggestion could be raised that the above diagram is not entirely realistic because following power and registering with the network what happens if there is an incoming call indicator that is received or immediately following power up and registering with the network an SMS is received? In GSM terms it is possible to select the use of the channels identified above for each of those purposes. So the diagram can be considered for use relating to incoming and/or outgoing communications

For the avoidance of doubt regarding GSM logical channels, it is relevant to mention that under the logical allocation of channels there is a separate and divided appraoch to two logical channel paths, if you will: 'Common Channels (CCH)' and 'Dedicated Channels (DCH)'.

Commons Channels (CCH)
CCH has allocated under it two channel sub-divisions:

Broadcast Channels (BCH) which is divided into a further three sub-channels:

- Frequency Control Channel (FCCH); Synchronisation Channel  (SCH); Broadcast Control Channel (BCCH).

Common Control Channels (CCCH) which is divided into a further three sub-channels:

- Paging Channel (PCH); Random Access Control Channel (RACH);  Access Grant Channel (AGCH)


Dedicated Channel (DCH)
DCH has allocated under it two channel sub-divisions.

Common Channels (CH) which is divided into a further three sub-channels groups:

- Stand-alone Dedicated Control Channel (SDCCH); Slow Associated Control Channel (SACCH) ; Fast Associated Control Channel (FACCH)

Traffic Channels (TCH) which is divided into a further two sub-channels:

- Traffic Channel Full (TCH/F) Rate; Traffic Channel Half (TCH/H) Rate 

As a further point to note two DCH logicals channels are shown in the above diagram that are able to be included (transmitted) either in Common Channels communications and/or Traffic Channel communications.  The SACCH has been highlighted because its content can be communicated included in the SDCCH or TCH transmission.

Question1: Do you know the important content that is transmitted in the SACCH packet and its relevance to informing the MS and Network and to cell site analysis?

Question2:  The other DCH logical channel shared has bot been highlighted. Do you know what that other channel is and the important content it holds in the communications informing the MS and Network and to cell site analysis? To refresh its content can too can be communicated included in the SDCCH or TCH transmission.

The Diagram
The diagram above is divided into FOUR separate MS states:

- Power On
- Idle Mode
- Dedicated Mode
- Idle Mode

Each of these separate elements are paramount to GSM CSA and without their basic existence GSM CSA would not be possible from the mobile device element investigation point of view that forms one of the investigation procedures during CSA.

GSM Mast Installations (Density)

GSM Mast Installations (Density)

.

When planning a cellular radio network there are many aspects to consider. The matter of radio technology and their frequencies (carriers) are but two examples. A relevance to be understood from these examples relate to what services may be obtained and delivered through these carriers? GSM for basic voice and text services and W-CDMA providing high data rates for video, gaming and conferencing etc.
.

Germane and relevant to obtaining radio services are the radio access technologies needed for that - Masts and Antennas. In radio engineering terms, antennas provide the physical technology to access the services obtained in the radio coverage by use of transmitters and receivers, commonly referred to by the acronym TRXs. The Masts provide the physical location for the siting of the TRXs. An important aspect of Mast installations is knowing the potential customer numbers that will use the services obtained from them. The calculation used for the number of customers and the number of calls that can be handled by one Mast's TRXs is calculated using the Erlang formulae - the number of calls and time length of each call in an hour.
.

Generally, though, to understand how Erlang can be used to determine the number of Masts and TRXs for an area let's just say there are 50,000 potential customers for a particular area. Let us also say to retain quality of service three sectors with 2 or 4 TRXs per sector, s222 or s444 respectively, are required. Let's also indicate that it is known that:

.

=======

.
1 TRX = 3 erlang, 2 TRXs = 5 erlang, 3 TRXs = 15 erlang, 4 TRXs = 20 erlang
.

The relevant TRXs selected for this Mast installation scenario are 2 TRXs and 4 TRXs.
.

Let:
.

50,000 x 0.02 erlang, where 0.02 erlang is used per customer = **1000 erlang
.

Each sector of an s444 may carry up to 20 erlang x 3 sectors = **60 erlang
.

**1000/**60 = 16.7
.

Therefore:
.

16.7 (17) Mast installations would be needed where a configuration of TRXs s444
.

or where
.

33.4 (35) Mast installations would be needed where a configuration of TRX s222
.

================

.

Remember the above is intended only to be illustrative so that it can be used to draw inferences about Masts installations and potential user numbers based upon the density of Masts in an area. An inference, such as, why a Mast further away than Masts sited closer to where a mobile station (MS) may be located routed the text message to the MS?

.

There are a large number of issues to be considered but let us take iwo important issues to be considered are:

.

- Point-to-Area predictions for terrestrial services 30 MHz to 3000 MHz

- Point-to-Point short message service (SMS)

.

In relation to point-to-area it could be the height of buildings surrounding the MS may be a cause for a distant Mast routing a point-to-point SMS text message. Alternatively, it may be the routing of the point-to-point SMS text message from a distant Mast occurred because the MS, in the idle mode, was surrounded by Masts that were at call traffic capacity. Alternatively it could be because of a combination of both buildings and call traffic capacity.

.

Knowing matters like these are very useful when dealing cell site analysis and a reason why they are incorporated into the Core Skills Knowledge of the TrewMTE training courses:

.

GSM Cell Site Analysis Training Course

-------------------------------------------------------

.

Course One: GSM Core Skills Knowledge Course (CSA Part 1)

3-days training

.
Course Two: GSM Cell Site Analysis Course (CSA Part 2)

3-days training
.

Course Three: GSM Cell Site Analysis Course (CSA Part 3)

3-days training
.

3G Cell Site Analysis Training Course

----------------------------------------------------

Course One: 3G Core Skills Knowledge Course (CSA Part 1)

4-days training

.
Course Two: 3G Cell Site Analysis Course (CSA Part 2)

3-days training

.
Course Three: 3G Cell Site Analysis Course (CSA Part 3)

3-days training

.

SIM Card Training

-------------------------
GSM SIM Card Training Course

3-days training

.
USIM/UICC Card Training

------------------------------------

3G USIM/UICC Training Course

3-days training

.
GSM/3G Handset Examination Training

------------------------------------------------------

GSM/3G Mobile Telephone Training Course

4-days training

------------------------------------------------------
MTEB Mobile Telephone Evidence Diplomas (MTEdipl).

GSM MS List of States for the cell selection process

GSM MS List of States for the cell selection process

The GSM mobile station (MS) enters various states when switched on, but in the idle mode. Three such states are PLMN selection, cell selection and location registration that GSM standards described as a "set of states". The overall state of the mobile is thus a "composite of the states of the three processes". As TS 100 930 makes mention "In some cases, an event which causes a change of state in one process may trigger a change of state in another process, e.g., camping on a cell in a new registration area triggers an LR request." Below are those states relevant for MS cell selection but for a more detailed description of the behaviour of these states read GSM05.08.

C1 Normal Cell Selection ‑ This is the process of initial cell selection, searching all RF channels.
.
C2 Stored List Cell Selection ‑ This is the process of initial cell selection where BCCH carrier information (e.g. a BA list) for the selected PLMN is stored in the MS.
.
C3 Camped Normally ‑ This is where the MS is camped on a cell of the selected PLMN and may be able to make and receive calls. (Whether or not the MS can make and receive calls depends on the state within the location registration process). The MS monitors received level and the system information and checks whether cell reselection is needed.
.
C4 Normal Cell Reselection ‑ This is where the MS has determined that cell reselection is needed and an attempt is being made to reselect a new cell.
.
C5 Choose Cell ‑ This is where the MS has returned to idle mode from "connected mode" and is choosing a suitable cell to camp on.
.
C6 Any Cell Selection ‑ This is where the MS is unable to camp normally on any cell of the selected PLMN, or cannot obtain service because of certain responses to a location registration (LR) attempt. It is searching for a cell of any PLMN to camp on (so that emergency calls can be made).
.
C7 Camped on any Cell ‑ This is where the MS has camped on a cell irrespective of its PLMN identity, so that emergency calls can be made.
.
C8 Any Cell Reselection ‑ This is where the MS is attempting to reselect a cell, irrespective of PLMN identity.
.
C9 Choose Any Cell ‑ This is where the MS is returning to idle mode, after having entered "connected mode" from the "camped on any cell" state to make an emergency call. It is attempting to find an acceptable cell to camp on.

GSM Mast Installations (Density)

GSM Mast Installations (Density)

.

When planning a cellular radio network there are many aspects to consider. The matter of radio technology and their frequencies (carriers) are but two examples. A relevance to be understood from these examples relate to what services may be obtained and delivered through these carriers? GSM for basic voice and text services and W-CDMA providing high data rates for video, gaming and conferencing etc.
.

Germane and relevant to obtaining radio services are the radio access technologies needed for that - Masts and Antennas. In radio engineering terms, antennas provide the physical technology to access the services obtained in the radio coverage by use of transmitters and receivers, commonly referred to by the acronym TRXs. The Masts provide the physical location for the siting of the TRXs. An important aspect of Mast installations is knowing the potential customer numbers that will use the services obtained from them. The calculation used for the number of customers and the number of calls that can be handled by one Mast's TRXs is calculated using the Erlang formulae - the number of calls and time length of each call in an hour.
.

Generally, though, to understand how Erlang can be used to determine the number of Masts and TRXs for an area let's just say there are 50,000 potential customers for a particular area. Let us also say to retain quality of service three sectors with 2 or 4 TRXs per sector, s222 or s444 respectively, are required. Let's also indicate that it is known that:

.

=======

.
1 TRX = 3 erlang, 2 TRXs = 5 erlang, 3 TRXs = 15 erlang, 4 TRXs = 20 erlang
.

The relevant TRXs selected for this Mast installation scenario are 2 TRXs and 4 TRXs.
.

Let:
.

50,000 x 0.02 erlang, where 0.02 erlang is used per customer = **1000 erlang
.

Each sector of an s444 may carry up to 20 erlang x 3 sectors = **60 erlang
.

**1000/**60 = 16.7
.

Therefore:
.

16.7 (17) Mast installations would be needed where a configuration of TRXs s444
.

or where
.

33.4 (35) Mast installations would be needed where a configuration of TRX s222
.

================

.

Remember the above is intended only to be illustrative so that it can be used to draw inferences about Masts installations and potential user numbers based upon the density of Masts in an area. An inference, such as, why a Mast further away than Masts sited closer to where a mobile station (MS) may be located routed the text message to the MS?

.

There are a large number of issues to be considered but let us take it two important issues to be considered are:

.

- Point-to-Area predictions for terrestrial services 30 MHz to 3000 MHz

- Point-to-Point short message service (SMS)

.

In relation to point-to-area it could be the height of buildings surrounding the MS may be a cause for a distant Mast routing a point-to-point SMS text message. Alternatively, it may be the routing of the point-to-point SMS text message from a distant Mast occurred because the MS, in the idle mode, was surrounded by Masts that were at call traffic capacity. Alternatively it could be because of a combination of both buildings and call traffic capacity.

.

Knowing matters like these are very useful when dealing cell site analysis and a reason why they are incorporated into the Core Skills Knowledge of the TrewMTE training courses:

.

GSM Cell Site Analysis Training Course

-------------------------------------------------------

.

Course One: GSM Core Skills Knowledge Course (CSA Part 1)

3-days training

.
Course Two: GSM Cell Site Analysis Course (CSA Part 2)

3-days training
.

Course Three: GSM Cell Site Analysis Course (CSA Part 3)

3-days training
.

3G Cell Site Analysis Training Course

----------------------------------------------------

Course One: 3G Core Skills Knowledge Course (CSA Part 1)

4-days training

.
Course Two: 3G Cell Site Analysis Course (CSA Part 2)

3-days training

.
Course Three: 3G Cell Site Analysis Course (CSA Part 3)

3-days training

.

SIM Card Training

-------------------------
GSM SIM Card Training Course

3-days training

.
USIM/UICC Card Training

------------------------------------

3G USIM/UICC Training Course

3-days training

.
GSM/3G Handset Examination Training

------------------------------------------------------

GSM/3G Mobile Telephone Training Course

4-days training

.
All courses now have credits towards the MTEB Mobile Telephone Evidence Diploma (MTEdip).

GSM MS List of States for the cell selection process

GSM MS List of States for the cell selection process

The GSM mobile station (MS) enters various states when switched on, but in the idle mode. Three such states are PLMN selection, cell selection and location registration that GSM standards described as a "set of states". The overall state of the mobile is thus a "composite of the states of the three processes". As TS 100 930 makes mention "In some cases, an event which causes a change of state in one process may trigger a change of state in another process, e.g., camping on a cell in a new registration area triggers an LR request." Below are those states relevant for MS cell selection but for a more detailed description of the behaviour of these states read GSM05.08.

C1 Normal Cell Selection ‑ This is the process of initial cell selection, searching all RF channels.
.
C2 Stored List Cell Selection ‑ This is the process of initial cell selection where BCCH carrier information (e.g. a BA list) for the selected PLMN is stored in the MS.
.
C3 Camped Normally ‑ This is where the MS is camped on a cell of the selected PLMN and may be able to make and receive calls. (Whether or not the MS can make and receive calls depends on the state within the location registration process). The MS monitors received level and the system information and checks whether cell reselection is needed.
.
C4 Normal Cell Reselection ‑ This is where the MS has determined that cell reselection is needed and an attempt is being made to reselect a new cell.
.
C5 Choose Cell ‑ This is where the MS has returned to idle mode from "connected mode" and is choosing a suitable cell to camp on.
.
C6 Any Cell Selection ‑ This is where the MS is unable to camp normally on any cell of the selected PLMN, or cannot obtain service because of certain responses to a location registration (LR) attempt. It is searching for a cell of any PLMN to camp on (so that emergency calls can be made).
.
C7 Camped on any Cell ‑ This is where the MS has camped on a cell irrespective of its PLMN identity, so that emergency calls can be made.
.
C8 Any Cell Reselection ‑ This is where the MS is attempting to reselect a cell, irrespective of PLMN identity.
.
C9 Choose Any Cell ‑ This is where the MS is returning to idle mode, after having entered "connected mode" from the "camped on any cell" state to make an emergency call. It is attempting to find an acceptable cell to camp on.