Welcome to our 2nd article on Cellular Fundamentals.
In this article let's look at the evolution of some of the key technologies.
In 1947 Bell Laboratories introduced the idea of cellular communications with police car technology. Since then, it is undergoing many changes, overcoming many obstacles and reached its current state. It is in 1982 the FCC (Federal Communications Commission) in USA approved the first commercial cellular service called AMPS (Advanced Mobile Phone Service) and allocated frequencies around 824-894MHz. This is called the First Generation (1G) of cellular service. (One point to note here is similar to computers technology where we have many generations of computers; in mobiles also we have generations like 1G, 2G, 2.5G, 3G, 4G etc.,. The later generations have many more features and they are very advanced ones compared to the earlier generations. We will explain these whenever we come across in our articles).
Do you know who made the first mobile phone? Motorola made the first commercially available mobile phone. Martin Cooper, a Motorola employee placed a call to his rival who is head of research at AT&T’s Bell Labs at the time. Sometimes having rivals is very important to do some historical things in life.
As I mentioned, cellular technology underwent many changes and many new technologies came up as the time passes. They have different specifications like channel spacing (means how much bandwidth is allocated for each user), access technology (how multiple users can access the system simultaneously) and they offer different levels of capabilities. Let’s take a look at those in the below table
Though there are many technologies as shown in the table, there are only 3 groups driving these technologies.
- 3GPP (3rd Generation Partnership Project) - which defines the specifications
In this article let's look at the evolution of some of the key technologies.
In 1947 Bell Laboratories introduced the idea of cellular communications with police car technology. Since then, it is undergoing many changes, overcoming many obstacles and reached its current state. It is in 1982 the FCC (Federal Communications Commission) in USA approved the first commercial cellular service called AMPS (Advanced Mobile Phone Service) and allocated frequencies around 824-894MHz. This is called the First Generation (1G) of cellular service. (One point to note here is similar to computers technology where we have many generations of computers; in mobiles also we have generations like 1G, 2G, 2.5G, 3G, 4G etc.,. The later generations have many more features and they are very advanced ones compared to the earlier generations. We will explain these whenever we come across in our articles).
Do you know who made the first mobile phone? Motorola made the first commercially available mobile phone. Martin Cooper, a Motorola employee placed a call to his rival who is head of research at AT&T’s Bell Labs at the time. Sometimes having rivals is very important to do some historical things in life.
As I mentioned, cellular technology underwent many changes and many new technologies came up as the time passes. They have different specifications like channel spacing (means how much bandwidth is allocated for each user), access technology (how multiple users can access the system simultaneously) and they offer different levels of capabilities. Let’s take a look at those in the below table
Though there are many technologies as shown in the table, there are only 3 groups driving these technologies.
- 3GPP (3rd Generation Partnership Project) - which defines the specifications
for GSM technology line,
- 3GPP2 (3rd Generation Partnership Project 2) - which defines the specifications
- 3GPP2 (3rd Generation Partnership Project 2) - which defines the specifications
for CDMA technology line
- IEEE 802 (Institute of Electrical and Electronics Engineers) – A group under
- IEEE 802 (Institute of Electrical and Electronics Engineers) – A group under
IEEE which defines the standards for LAN (Local Area Networks) and MAN
(Metropolitan Area Networks). In current context, this group delivers the
standards for the WiMAX technology.
Now let’s quickly summarize the technology lines so that we can remember them easily.
GSM --> GPRS -->EDGE -->UMTS -->HSDPA -->HSUPA -->LTE
cdmaOne --> CDMA 1x --> CDMA 1x EV-DO -->CDMA 1x EV-DV
wLAN -->WiMAX --> More to come in future
As we saw here, there are many wireless technologies that exist today and many are coming up in future..
Let’s stop our discussion on evolution here.. and start with the CDMA.
CDMA (code division multiple access) itself is not a communication protocol. It is just a multiple access technique. cdmaOne is the brand name of the first cellular communication protocol standard which uses CDMA. The first specification was made as IS-95A (Interim Standard made in the year 1995). A is to indicate that this is the first in that series. This standard supports voice and very low data rates up to 14.4kbps. The next version IS95-B supports voice and data rates up to 115kbps. Please make a note that for any technology, data rates indicated are the peak data rates. In practice, the average data rate is much lower than the data rate indicated.
CDMA 1x system doubles the voice capacity of the cdmaOne system and also supports high-speed data rates. The peak data rate supported is 153kbps. The reason for having 1x in the name is to indicate that this system uses one 1.25MHz channel. There were some works on using CDMA 3x which uses three 1.25 MHz channels to support more users and more data rates. But the invention of other advanced technologies put a full stop to this work. So we are left with 1x only.
You might be wondering why we thought of CDMA, when the GSM is already in place. The reason is to provide more data rates to users. As we saw in the table, GSM is based on TDMA and it uses a 200 KHz channel that is divided in to 8 time slices giving each user a bandwidth of 25 KHz. This bandwidth is not sufficient for many data applications. This made the technologists across world to look for an alternative technology that provides support for higher capacity and high data rate applications. Hence, we got the CDMA.
Another question that may come into your mind may be why 1.25MHz?
The answer is simple. The initial communication standard AMPS used 25MHz band. In which 12.5 MHz for Uplink and 12.5 MHz for Downlink. When CDMA was developing Qualcomm (Note: Qualcomm is the pioneer who developed CDMA and holds many patents in this technology) claimed 10% increase in capacity and spectrum usage when compared to AMPS. So they started developing on 1.25MHz.
Get yourself familiar with some jargon:
Forward Channel – Is the channel from the BTS to the mobile phone. As the BTS controls and governs the communication, it broadcast the information and guides the mobile for proper communication. That’s why this channel is called Forward Channel (In GSM this is called Downlink as the mobile is receiving information from the BTS on this channel)
Reverse Channel – Is the channel from mobile phone to the BTS. Mobile always responds to the control information from BTS and it obeys whatever BTS says. So the channel from mobile to BTS is called as Reverse channel. (In GSM this is called Uplink as mobile sends information on this channel)
In our next article, let’s discuss about the different codes and channels used in CDMA and their significance.
Now let’s quickly summarize the technology lines so that we can remember them easily.
GSM --> GPRS -->EDGE -->UMTS -->HSDPA -->HSUPA -->LTE
cdmaOne --> CDMA 1x --> CDMA 1x EV-DO -->CDMA 1x EV-DV
wLAN -->WiMAX --> More to come in future
As we saw here, there are many wireless technologies that exist today and many are coming up in future..
Let’s stop our discussion on evolution here.. and start with the CDMA.
CDMA (code division multiple access) itself is not a communication protocol. It is just a multiple access technique. cdmaOne is the brand name of the first cellular communication protocol standard which uses CDMA. The first specification was made as IS-95A (Interim Standard made in the year 1995). A is to indicate that this is the first in that series. This standard supports voice and very low data rates up to 14.4kbps. The next version IS95-B supports voice and data rates up to 115kbps. Please make a note that for any technology, data rates indicated are the peak data rates. In practice, the average data rate is much lower than the data rate indicated.
CDMA 1x system doubles the voice capacity of the cdmaOne system and also supports high-speed data rates. The peak data rate supported is 153kbps. The reason for having 1x in the name is to indicate that this system uses one 1.25MHz channel. There were some works on using CDMA 3x which uses three 1.25 MHz channels to support more users and more data rates. But the invention of other advanced technologies put a full stop to this work. So we are left with 1x only.
You might be wondering why we thought of CDMA, when the GSM is already in place. The reason is to provide more data rates to users. As we saw in the table, GSM is based on TDMA and it uses a 200 KHz channel that is divided in to 8 time slices giving each user a bandwidth of 25 KHz. This bandwidth is not sufficient for many data applications. This made the technologists across world to look for an alternative technology that provides support for higher capacity and high data rate applications. Hence, we got the CDMA.
Another question that may come into your mind may be why 1.25MHz?
The answer is simple. The initial communication standard AMPS used 25MHz band. In which 12.5 MHz for Uplink and 12.5 MHz for Downlink. When CDMA was developing Qualcomm (Note: Qualcomm is the pioneer who developed CDMA and holds many patents in this technology) claimed 10% increase in capacity and spectrum usage when compared to AMPS. So they started developing on 1.25MHz.
Get yourself familiar with some jargon:
Forward Channel – Is the channel from the BTS to the mobile phone. As the BTS controls and governs the communication, it broadcast the information and guides the mobile for proper communication. That’s why this channel is called Forward Channel (In GSM this is called Downlink as the mobile is receiving information from the BTS on this channel)
Reverse Channel – Is the channel from mobile phone to the BTS. Mobile always responds to the control information from BTS and it obeys whatever BTS says. So the channel from mobile to BTS is called as Reverse channel. (In GSM this is called Uplink as mobile sends information on this channel)
In our next article, let’s discuss about the different codes and channels used in CDMA and their significance.
