ANC TRE Connection

 

 

*Note: Similar color ports are connected

For this ANC we can connect up to 4 TREs.

Operator dependent Configurations:

·         Connect with coupling and it will also add a loss. With this configuration we can add 2 TREs per one ANC.

 

Longitude and Latitude

Ohhh I should have mention this before. Because this is very important…… without knowing this....

Latitude (parallels) - Horizontal line

This is the angular distance, in degrees, minutes, and seconds of a point north or south of the Equator.

 

 

 

 

Longitude (meridians) - Vertical line

This is the angular distance, in degrees, minutes, and seconds, of a point east or west of the Prime (Greenwich) Meridian.

Distance between Lines

By dividing the circumference of the earth (apprx. 25,000 miles) by 360 degrees, the distance on the earth's surface for each one degree of latitude or longitude is just over 69 miles (111 km). 

You know how to press it but do you know how it works?

Before we move on to the theory behind this, just take a look at these sound clips.

 GOTO clip1: http://www.genave.com/audio/dtmf-page-normal-S00P0501P99.wav                                                                     
GOTO clip2: http://www.genave.com/audio/dtmf-page-slow-CP4D34SS.wav

DTMF- Dual Tone Multi Frequency

Hz	1209	1336	1477
697	1	2	3
770	4	5	6
852	7	8	9
941	*	0	#

Did you ever think of how your response (pressing a particular number) is identified by the receiving side? For an example let’s consider a situation where you are in an Interactive Voice Recording (i.e. calling to customer care).  They asked you to press 1 or 2 or any number to identify your response. Pressing a key will send a sinusoidal tone for each of the two frequencies (i.e. 697 and 1209Hz for “1”). See the image below. The multiple tones are the reason for calling the system multi frequency and it is called as dual tone because of the use of two frequencies. Two frequencies are there to make sure that frequencies generated accidently will not be identified as a press. Columns will have higher frequencies than rows. In normal dialing also we can use DTMF, but only for special purposes (if needed MSC can identify the pressed keys).

Interactive Voice Response (IVR) - is a technology that automates interactions with telephone callers.

Figure 1: DTMF

Pulse dial system was used earlier and it is a slow and older method. For optimum use, push-button phones utilize DTMF signaling, which was also known as touch-tone dialing. 

                                                            Figure 2: Push Button Phone

Now you know the theory, and let’s see how it is implemented

Mark and Space

Mark refers to the duration a DTMF tone is produced (the time which a DTMF digit tone is actually producing sound), and Space refers to the duration of the silence between individual digits.
Notations

• Mark/Space : Pronounced as "Mark and Space”. Refers to the durations of mark and space.

•  40/40: The decoders expect the DTMF tones to exist for at least 40 milliseconds and in silence for 40 milliseconds between each DTMF digit.

References: Some of the images, details and sound clips were taken from the following website. http://www.genave.com

What happened before you made a Call

First of all I would like to ask you a question. How many different modes are there in a mobile phone? Most probably your answer will be two (on/off). But when we look at it technically there are three modes and they are switched off, idle and dedicated mode. When we take a call we can say that our phone is in dedicated mode. If our phone is switched on and not taking any calls we could say it is in idle mode. When we switch on the phone it will immediately goes in to idle mode. Depending on the signal strengths present MS (Mobile Station) will decide to which cell it should camp. There are two important things should happen before setup a call.

                1.       Cell Selection

Immediately after MS switched on Cell Reselection occurs. It refers to the initial registration that a MS will make with a network. C1 is the parameter used for selection. The most favorable cell is indicated by the so called C1 parameter for a MS. MS will search all RF channels and decide which cell to camp using C1 values. A basic equation is given below,

              

                                 C1  = Rx level – Rx level Access min

Rx level: Received signal power for the MS or in other words what signal strength the MS sees the tower at.

Rx level Access min: Minimum access level of the tower. This is a parameter of the antenna of the site.

Normally MS will receive signals from many cells. For those cells MS will calculate the C1 and find out the maximum value. Then it will camp into that cell. That’s not the end and it will keep gathering information of nearby cells. Normally it will keep tow lists named as Active set and Merge set. In active set we have a primary cell (the cell mobile has already camped at the moment) and another four cells which are having highest signal strengths next to primary cell. And there are several cells in the merge set. If anyone in the merge set gets better than the active set, it will replace the active set cell. This will keep happening. 

                2.       Cell Reselection

Cell reselection is performed as MS traverses through a network in idle mode. MS will keep details of strongest BCCH cells as I mentioned above. As in previous case we have another parameter known as C2 for Reselection. It can be also called as an improved version of C1.

              

                                             C2= C1 + CRO – TO(t)

     

[CRO (Cell Reselection Offset), TO (Temporary Offset)]

The mobile shall regularly search for a better cell according to the cell reselection criteria. If a better cell is found, that cell is selected. But before we select a one we should check for the neighbors. That means for each and every cell we define neighbors. Neighbors are defined using their locations, directions and distances to a particular cell. If it is a neighbor cell we can camp on to it. But if it isn’t MS will not camp into that.

If we want to reduce the number of customers per a cell we can adjust CRO parameter. Or we can say we will give higher priority to a cell by giving a high value to that cell than its neighboring cells. TO is used to avoid unnecessary re-selections. For example consider a person moves along a highway. As he moves along there may be many cells serving him at different points. But there may be one or two major cells which can serve him for a longer distance. In such occasions we prefer him to stay camp in to that major serving cell. To do that we can give a proper timing value for TO. That means MS will not camp into that cell until it stays in that cell for a particular time period. Normally in high ways we go fast and it will avoid unnecessary re-selections and keep camp on to a major cell.

GSM Handover/Handoff

Both Handover and Handoff is used to describe the same process.  There is a process called Cell reselection and I will talk about it later. A particular mobile service provider is given a set of frequencies. Form that few set of frequencies, by doing Frequency Reuse they have to provide the coverage. The total coverage is divided into large number of cells. When the customer moves from one cell to another while taking a call Handover takes place to retain the connection.

This must be carefully considered when you are planning a network. Because this is a measure of the Quality of Service. If we fail to handover properly the call will drop. And when the number of call drops goes high customer may tend to go for another service provider.

There are few ways of categorizing Handover in GSM systems. For GSM only systems there are four categories.

     1. Intra-BTS handover

This occurs within the same BTS when there are some interference takes place. In this case mobile will be locked to the same BTS but the channel allocated to that mobile/time slot will change.

    2. Inter-BTS Intra BSC handover

This type of handover occurs when the mobile moves out of the coverage of one BTS into another BTS and both BTSs are controlled by the same BSC. BSC will take care of the handover by allocating a channel for the user in the second BTS.

  3. Inter-BSC handover

This is a special case of previous one and this time handover occurs between two BSCs. Therefore it has to be controlled by MSC.

  4. Inter-MSC handover

      In this occasion handover occurs between two MSCs.

 

As I mentioned above there are few categories but as far as the mobile is concerned they will look like the same. For GSM systems we use TDMA. Transmitter only transmits in one out of eight time slots and similarly receiver receives in one slot. As a result of this RF module of the mobile may be idling for the remaining six time slots. But it is not the case. During those slots mobile will scans for beacon frequencies which may be more suitable/stronger. When the mobile deals with the BTS it will send the list of radio channels of the beacon frequencies of neighboring BTSs via Broadcast Channel known as BCCH. In addition to this mobile will report back the quality of the existing link with BTS. It is not only the telecommunication network but also the mobile is helping in doing handover. This form of handover is also known as Mobile Assisted Handover (MAHO).

Now with the help of the mobile network has the details regarding the current link quality and the available links or availability of channels nearby cells. Depending on the configurations set or the parameters available, network will decide when to handover and to which cell it should be handed. If network decide to go with the handover it will assign a new time slot to the mobile and also inform the relevant BTSs about the change. Mobile will return during the idling period and will synchronize with the new available parameters and continue the conversation. This can be considered as the perfect scenario. But in practice we may come across few issues.

They are:

·         Old and new BTSs synchronized: As I mentioned above mobile is provided with all the required details. For fine adjustment of synchronization mobile may optionally send four access bursts even though the synchronization is already good. They are shorter than the standard bursts. Because of that they will not overlap with other bursts.

·         Time offset between synchronized old and new BTS: if there exist a time offset between the old and new BTSs, mobile will be informed about the offset. So mobile station can make the adjustment and then the handover takes place as a standard synchronized handover.

·         Non-synchronized handover: For this to happen mobile will transmit 64 access bursts on the new channel. That will help the BTS to determine and adjust the timing of the mobile. After it has done mobile can access the new BTS and it will enable the mobile to re-establish the connection through new BTS with correct timing. 

As time passes new technologies arises. Earlier we talked about how the handover takes place within GSM/2G network. But later we see 3G, HSPA and LTE. So we may encounter a situation where we want to handover from GSM to any other or vice-versa. It is known as Inter-system/inter-RAT handover.

·         UMTS / WCDMA to GSM handover

We can divide this further into two.

o   Blind handover: This form of handover occurs when the BTS hands off the mobile by just passing it the details of the new cell to the mobile without linking to it and setting the timing, other parameters of the mobile for the new cell. In this mode, the network selects what it believes to be the optimum GSM based station. The mobile first locates the BCCH of the new cell, gains timing synchronization and then carries out non-synchronized inter-cell handover.

o   Compressed mode handover:   The mobile uses the gaps of transmission that occur to analyze the reception of local GSM base stations using the neighbor list to select suitable candidate base stations. Having selected a suitable base station the handover takes place, again without any time synchronization having occurred.

·         Handover from GSM to UMTS / WCDMA:   This form of handover is supported within GSM and a "neighbor list" was established to enable this occur easily. As we know the GSM/2G network is normally more extensive than the 3G network, this type of handover does not normally occur. If a mobile go away from a coverage area, then it will have to quickly find a new base station to stay in touch. The handover from GSM to UMTS occurs to provide an improvement in performance and can normally take place only when the conditions are right. The neighbor list will inform the mobile when this may happen.

2.5G(GPRS)

In 2.5G there are 3 main subsystems. They are NSS (Network Switching Subsystem), BSS (Base Station Subsystem), GSS (Group Switch Selector). Actually BSS consist of BTS, BSC and TC with their relevant interfaces. MSC and A (interface) will form NSS. And for 2.5G GGSN (Gateway GPRS Support Node), SGSN (Serving GPRS Support Node), PCU (Packet Control Unit) will form GSS. GSS is linked to BSS and NSS as follows (Through BSC).

Transceiver (TRX)

PDCH can be static or dynamic. When we configure a BTS we can define Min_PDCH, Max_PDCH depending on the customer base. Voice will get the highest priority. If the voice traffic keep increasing we can reduce the number of P channels until it reaches Min_PDCH. Then more subscribers will be able to make calls and data speeds will be reduced at that moment.

On the other hand if the demand for data is getting higher and higher P slots will get up to a maximum of defined Max_PDCH.

Getting Started

My first experience was at a NOC (Network Operating Center). Before going into details of that I would like to give a brief on 2G and 3G. 

What is GSM?

First let’s look at what it stands for, Global System for Mobile Communications: originally from Groupe Spécial Mobile. Key elements of the GSM network are as follows.

 

GSM is used to describe technologies for Second Generation (2G) digital cellular networks. First Generation (1G) is an analog cellular network. In 2G standard originally described a digital, circuit switched network optimized for full duplex voice telephony. It was further developed for packet data transfer via GPRS (General Packet Radio Services). EDGE (Enhanced Data rates for GSM Evolution) gives more increase in data transfer. Later 3G was introduced.