Wireless Communications: Is it Entirely Wireless?

Hello all,

The topic of this blog might be slightly confusing for people who are not familiar with the wireless communications and cellular communications. When you call a technology wireless communications, why should there be a question if it is really wireless? With little over and year experience in the wireless industry, I thought of sharing the knowledge that I gained during this experience.

When you make a call from your mobile phone to any other mobile phone in the same area, how do you think the call is connected? The simplest answer one can give is to say that the call goes from my mobile to the destination mobile and the call is completed. But what actually happens in between the mobile phones is a mystery to many people. Let me give a description of what actually happens when you call someone from your mobile phone. Before going to the details of the call flow, let me discuss few of the very terms used in mobile communications.

Base Station: A base station is a wireless receiver installed by the wireless service provider, which receives signals from various mobile devices in a pre-defined geographic area and processes them to complete the call.

Base Station Controller (BSC): A Base Station Controller coupled with the base station make a Base Station Subsystem. Number of base stations are connected to a base station controller which connects the calls to the Mobile Switching Center (MSC) which is described next.

Mobile Switching Center (MSC): This is more intelligent than the Base Station Controller and has far more responsibilities than the BSC. This is like the Switch used in the old telephone systems, which connect the calls between originating and destination telephones.

When you make a call from your mobile phone, the call goes to the local Base Station which is responsible for the calls in your geographic area. Then the call is sent to the BSC and then handed over to the MSC through a wire-line connection made between the Base Station and the BSC and then from the BSC to the MSC. A single MSC has many Base Stations Controllers connected to it and each MSC maintains a register of all the mobile users under each and every Base Station. When the call reaches the MSC, it checks for the location of the destination mobile phone number and transfers the call to the destination Base Station again on a wire-line connection. Then the call is handed off to the destination mobile phone over a wireless channel.

This is a simple case where the call is between two mobile phones belonging to the same Mobile Switching Center (MSC). Even in such a simple case, it is pretty clear that a wireless to wireless or a mobile to mobile call is not wireless in entirety. It is wireless only from our mobile phones to the closest Base Station and then goes a really strong wire-line network built by the mobile service providers. In a more complex case where the call has to travel longer distances, or has to jump from one MSC to another, it is still wireless only from the mobile to the base station and then it traverses the wire-line network over longer distances built between MSC. I will discuss about the various call flows later in my blog taking one scenario at a time.

Please let me know if you have any questions about the explanation I have given in the following blog.

Thanks,
Krishna C. Emani