Blocked Call Vs Dropped Call

A Blocked Call and a Dropped Call are two very common terms used in telecommunications (Cellular Communications) world these days. These two are completely different phenomena, but the impact they create on a customer is the same, annoyance. In this post I am going to discuss what the differences between these two events are, and briefly explain how they can be handled by the mobile service provider.

Blocked Call:

A Blocked Call is an event that can occur only before the call is completed between the called and the calling parties. Completion of the call here implies the connection being complete for either party to exchange talks. Any call you place on a cellular network, the service provider has to find all the resources necessary to connect the call between the two parties. As I mentioned in my previous post about a wireless call, it is not wireless in entirety and it has to access the wire-line network in order to reach the destination cell phone. In case of a long distance call, a service provider should make sure that there is sufficient network capacity all through the intermediate network hops to carry the call from one end to the other.

If there is not sufficient capacity to carry the call through, this results in a blocked call. When you are in a stadium watching a Baseball match or a Cricket match, when you attempt to make a call, you might hear a voice recording saying “the network is currently busy please try after sometime” or the call may just give three beeps and not connect. This is mainly because of insufficient bandwidth availability (Wireless Channels or the Wire-Line Channels) compared to the number of people attempting to access the network. In one of my posts about Why Sprint Nextel has more dropped calls than AT&T and Verizon? I mentioned that Sprint has an advantage of selecting the higher frequency range of (1900 MHz). If Sprint can tackle the dropped calls issue by installing more cell sites to cover the same area as that of its competitors, this automatically provides higher number of wireless channels in the same geographical area thereby reducing the chances of blocked calls. It still has to build the backbone wire-line network to support the calls but for now let us assume that this matter has been taken care. As the customer base keeps increasing in a geographic area, AT&T and Verizon have to eventually invest to tackle the increasing capacity requests from the customers. But Sprint, already has the wireless network to handle increasing capacity which is definitely an advantage but this is not a great situation to be in. Gradual investment as the customer base grows is always a better situation to be in than investing heavily at once expecting the customer base to rise. So this is a catch 22 situation where the decision has to be made by the service provider depending on the traffic analysis and customer growth analysis made over the years.

This is where traffic management comes into picture. A traffic management team makes sure that the network is always ready to handle the calls at any moment of time including the busiest hour of the day. During events like American Idol or on auspicious days like Christmas Day, Mother’s Day, Father’s Day or New Years Day, the network has to be ready to handle the avalanche of calls that can hit the network. Even in events like the baseball matches, the service provider takes necessary actions to provide more wireless channels by process called Cell Sectoring or another process of turning on smaller and more cellular base station towers to cover the same area.

To summarize things, a Blocked Call is something which occurs before the connection is complete between the called party and the calling party. This phenomenon depends on the entire network, the wireless channels on the calling end, the wire-line backbone network, the wireless channels on the destination end.

Dropped Call:

This is an event that can occur only after the call is connected and the exchange of talks has started. This implies that the network has the capacity to handle this call and the resources necessary for the call have already been allocated to the call. In my previous post I mentioned about the various factors that influence and contribute towards dropping of a call. The dropped call is a result of improper R.F. planning or some of the natural phenomena that cellular signals undergo while travelling in the environment surrounding us. Even as the mobile moves from one coverage area to another coverage area, there might be a dead zone resulting in a dropped call. The co-channel interference also can influence a dropped call but this is more evident in GSM network than CDMA network. A blocked call only depends on the wireless part of the network, i.e. the wireless signal power on the calling side and the wireless signal power on the receiving side.

I tried to explain the difference between a Blocked Call and Dropped Call in simple terms and there might be something that you can add to understand the process better. Please add any comments or suggestions on the blog.

Thank you very much for reading the blog.

Sincerely,

Krishna Chaitanya Emani.

Why Sprint Nextel has more dropped calls than its competitors AT&T and Verizon?

Hello all,

Sprint Nextel is a company that has been on a revival for quite some time. The market has been responding positively to the radical steps taken by Sprint to create a niche for itself in the telecom market. The customer service has been improving over the past few months, a positive vibe is being created in the market about the improvements in the customer service and the network reception. Thanks to the new CEO Dan Hesse for re-vamping the company and prioritizing these major issues to be addressed. 

One major issue Sprint Customers always faced is the "Higher Dropped Calls Rate". 

Why does Sprint have more dropped calls than its competitors AT&T and Verizon?

This is the topic of my blog and I will be explaining the reasons for this higher dropped call percentage. 

First of all, let me tell you some facts about these three major wireless carriers. 

Verizon uses CDMA (Code Division Multiple Access) technology and operates in the 800 MHzfrequency range. 

AT&T uses TDMA (Time Division Multiple Access) technology and operates in the 800 MHzfrequency range.

Sprint uses CDMA technology and operates in the 1900 MHz frequency range.

Verizon and Sprint use the CDMA technology while AT&T uses the TDMA technology. Each of these technologies have their own advantages and disadvantages, and we are not going into the details of these technologies as they are not responsible for the drop calls, which is the topic of this blog. The next major observation you might have made is in the frequency range in which these carriers operate. Both AT&T and Verizon operate at 800 MHz frequency and Sprint operates at 1900 MHz frequency. Why am I discussing this point? Are you thinking this is the reason for the increased dropped calls on the Sprint Network? If you are thinking that way, you are right on target. Yes the frequency of operation is the major reason for the dropped calls. 

Let me explain in detail why this is a valid reason.

Any wireless signal propagating in the free space follows something called as free space path loss to determine the power of the signal at the receiver.

P_r = P_t G_t G_r ( λ / 4πd )² 

This is the equation which gives the power of the received signal at the receiver, where Pt is the transmitted power. For more detailed explanation please refer to this page.

As you can see the received power at the receiver is directly proportional to the square of the wavelength of the transmitted signal carrier. As frequency is inversely proportional to the wavelength, lower the frequencies => higher the wavelength and therefore, higher received power. You can clearly observe the decrease in the receiving power as the frequency increases in the table given in the following page. So as the frequency of the signal increases the coverage area of the transmitting antenna reduces. This is exactly the problem faced by Sprint. As you can observe the frequency at which Sprint operates (1900 MHz) is higher than the frequency at which both AT&T and Verizon operate (800 MHz) and as the transmission power of a cell tower is restricted by the FCC regulations, the coverage area of Sprint tower would be lesser than the coverage area of AT&T or Verizon tower. So in order to cover the same area, Sprint needs more transmitting antennas at higher operating frequencies than its competitors operating at lower frequencies.

Easiest thing for us to say is, “why doesn’t Sprint install additional antennas to compensate for the higher frequency range and lower coverage area?” Well Sprint did deploy additional towers everywhere throughout the nation and took extra care to make sure the customers have very less to no dropped calls but in spite of the effort, the network is failing to deliver the results as the higher frequencies are more vulnerable to the surroundings than the lower frequencies. Trees around the cell phone might make the signal weak, black paint can make the signal weak, and there are many other factors that can impact the power of the signal. This creates a lot of holes in the network. This is the reason for increased dropped calls when you are travelling from one location to another.

Another phenomenon called diffraction helps the wireless signal to bend around an obstacle’s edge and reach the receiver. Sprint’s higher frequencies fail to impress in this phenomenon too, as the performance of signal undergoing diffraction is better at lower frequencies than at higher frequencies. The signal bends around the edge of the obstacle better at lower frequencies than at higher frequencies.

Penetration is another phenomenon by which the signal reaches the receiver (cell phone) when you are indoors. Even in the phenomenon, Sprint’s higher frequencies perform badly than its competitors. As the signal penetrates through various obstacles it is attenuated (amplitude reduces as it passes through the walls) and as the frequency increases the rate of attenuation increases, thereby making the signal weak indoors. For additional clarification or explanation of the process please refer to the following white paper.

Finally, these are the reasons for Sprint’s higher drop call rate and lack of signal indoors. You might be wondering, why Sprint chose these higher frequencies when there are so many disadvantages associated with the frequency range? Well that’s a valid question and there is a substantial reason for this selection. I would be discussing the reasons and advantages of selecting this higher frequency range in my later blogs.

Currently Sprint is making an intriguing effort to fill the holes in the network and provide spotless network to its customers by using various technologies like using a broadcaster at home to pull the signals and re-broadcast them in the house, using these repeaters in places of reported signal lose etc. Will it be successful in changing the image that the customers currently have? We have to wait and see.

Thanks a lot for reading my blog. Feel free to leave comments on this discussion or also feel free to email me any questions you might have on the following discussions.

References:

1. http://www.crouse-hinds.com/wirelessIO/PDF/White%20Paper/white_paper_frequencies.pdf

2. http://www.dsprelated.com/showarticle/62.php

3. http://www.fcc.gov/pshs/techtopics/techtopics17.html

Sincerely,

Krishna Chaitanya Emani.