Friday, February 22, 2013

Legacy Network Architecture

Now We have NGN (Next Generation Network ) Architecture. But before NGN we had Legacy architecture. Following Figure will give an idea about Legacy architecture with all the features/services included. 
Note: SCCP Roaming link will carry only signaling. And through an IDD Carrier we transfer both signaling and voice.

Now this legacy system was replaced by a NGN (MSCs by WCS and MGW).I will talk about it in my next posts......


Generally a SWITCH is a piece of equipment which processes a call or any other subscriber requested activity. Basic function of a SWITCH is Routing and connecting two subscribers. Unlike in Public Switched Telephone Network (PSTN), in cellular networks subscriber can be anywhere in the world. So we need to process the request and route it to a proper destination.

SWITCH is also known as Mobile Switching Centre (MSC) in Mobile Telecommunication Network Architecture. In other words SWITCH Engineering section is responsible for Operation & Maintaining the Core Network (CN). Core network or Network Subsystem (NSS) connects subscribers together in a Cellular Network. These responsibilities differ from company to company. I have listed some general responsibilities of a SWICHING Team:
  •   Operation & Maintenance of SWITCH/MSC/NGN
  •   Operation & Maintenance of SDM/HLR
  •   SWITCH Planning
  •   IDD/ Roaming
  •   Customer Care Complaint
  •   Operation & Maintenance of IP/MPLS network
  •   Quality of Service (QoS), Key Performance Indicator (KPI) & Statistic Reporting
  •   Application Development
 In another company some of the above may be a responsibility of a separate division. But those are listed based on my current experience.

Wednesday, February 6, 2013

Site/Tower Categories

There are few tower/site categories are implemented: Green Field, Roof Top, Mobile Site (COW) and Monopole. Snapshots of those towers are as follows.

In Building Solution (IBS)

 Telecom operators provide IBS to overcome Coverage Issues, Quality Issues and to Increase Capacity. To elaborate this more refer the following Figure: Issues at different heights of a building. Figure shows us a building which consists of over 40 floors.

As mentioned in the figure, at different heights we have different issues. When we provide an IBS we need to clearly identify the issue and then needed to provide a suitable solution for that. There are two types of IBS solutions:
  •         Distributed Antenna System (DAS) – mainly provided solution out of the two

  •          Nano BTS (2G) or Femto Cell (3G)

Distributed Antenna System (DAS)

In a DAS solution we lay a network of antennas as required inside the building using splitters. Used equipment in a DAS solution:

  •     Symmetric (2way, 3 way, 4 way)

  •   Asymmetric (2way tapper)
Using symmetric splitters we can divide a link and get similar output powers from the output (i.e. when the input power= 30 dBm, 27 dBm output at both outputs of a 2 way splitter.). And if we are using an asymmetric splitter we can divide output power asymmetrically (i.e. input power= 30 dBm, output power1= 29 dBm, output power2= 23 dBm).

  •     Omnidirectional Antenna
This kind of antennas can be used to cover a room or a seminar room.

  •         Panel Antenna
Panel antennas can be used cover a place like corridor.



















Design Steps of a DAS

  •         Existing Coverage

We can get to know the existing coverage by doing a Drive Test.

  • Requirement
Based on the results obtained in the drive test we need to identify the issue prevailing in that floor. It may be coverage, quality or capacity issue. Requirement may differ from floor to floor.

  • Antenna Locations

Then we need to plan the antenna types and their locations in each floor. Proposed antenna locations for the Ground floor and for the 1st floor are depicted in the Figure: Proposed Antenna Locations.
  • Antenna Tree (EIRP Table)
We need to calculate the output power of each antenna considering BTS transmit power, splitter losses, jumper losses, connector loses, antenna gain and cable length along the path from BTS to antenna. We have to keep EIRP values of all the antennas in the range of ±2 dBm. Why? To distribute the Rx power of the base evenly, If we want to adjust power of any antenna without effecting other and all of these antennas should be work as a one antenna (because they act as a one antenna covering the building).  To keep these values in the same range we may even use attenuators. But it is not recommended.

 After implementing the planned solution we do another drive test to verify the results. If a building is already covered using a DAS few other service providers can share the resources to provide their services. They only have to provide a BTS and they can use the existing antenna network.
Difficulties in DAS:
    Rent to the building
    High cost
    Installation Difficulty

DAS should be installed when the building construction takes place. Otherwise it is difficult to set up it after the completion of the building construction.

Nano BTS (2G) or Femto Cell (3G)

Now the trend is towards IP based systems. Using a Nano BTS or a Femto cell we can easily solve issues inside a building. This solution is becoming popular in these days. Nano BTS is for 2G and Femto cell is to 3G. No need to do any construction to setup this service. These cells only require internet connectivity.

Nano BTS

It is just plug and play. There is an option called auto configuration which will configure the BTS when it is placed in the desired location. Or we can manually configure it. A Nano BSC can handle up to 100 Nano BTSs at the current licence. They even support power over Ethernet (using a POE adapter) so with minimum number of external connections we can setup a 2G solution. Nano BSC will authenticate its BTSs using their MAC address and IP address.

Femto Cell

For 3G requirement we can use Femto cells. It has a throughput of 7.2 Mbps. And it is functioning in a similar manner to the Nano BTS. Through internet we connect it to the MGW. Using a Femto cell we can provide various services. We can address users that are connected to that Femto Cell separately. Also we can assign a certain user for that cell.