Cellular Technologies: The Difference Between GSM, CDMA, UMTS, and LTE
- 15 Jan, 2021
Cell phones have improved a lot over the last two decades. When cell phones launched, a phone could make and receive phone calls with bad voice quality, little to no security, and frequent dropped calls. These days, we have excellent voice quality, we can send text messages, browse the web, stream videos, and much more without needing to be connected to WiFi.
This is made possible by a great variety of cellular technology which has evolved over time, and have their roots all across the world. In this article, we'll be breaking down these technologies, which contributed to the evolution of cell phone communication and helped the transition from analog to digital modulation.
Different Cell Phone Technologies
The following technologies have helped mobile communication evolve from the earliest 1G cell phones of the 1980s to the high speed 4G LTE smartphones we enjoy today.
- Advanced Mobile Phone Systems (AMPS)- A cell phone standard used to define the first generation of analog mobile communication.
- Code Division Multiple Access (CDMA)- A method used to manage the users accessing a frequency channel on CDMA-based networks.
- Code Division Multiple Access 2000 (CDMA2000)- A cell phone standard used to define the third generation of CDMA mobile communication.
- Digital Advanced Mobile Phone Systems (DAMPS)- The second-generation successor to AMPS.
- Evolution Data Optimized or Evolution Data Only (EVDO)- A mobile broadband technology used to provide the CDMA2000 network with high-speed internet.
- Evolved High Speed Packet Access (HSPA+)- A mobile broadband technology used to provide the UMTS network with high-speed internet.
- Global System for Mobile Communications (GSM)- A cell phone standard used to define the second generation of mobile communication.
- Long Term Evolution (LTE)- A cell phone standard used to define the fourth generation of mobile communication for GSM and CDMA networks.
- Time Division Multiple Access (TDMA)- A method used to manage the users accessing a frequency channel on TDMA-based networks.
- Universal Mobile Telecommunications System (UMTS)- A cell phone standard used to define the third generation of GSM mobile communication.
Why are Cell Phone Technologies Important?
Cell phones use radio waves to make calls, send text messages, browse the web, and stream videos. These waves travel from your phone to the nearest cell phone tower that’s provided by your mobile operator. The tower then forwards the information to a switching center or control center to connect you to the internet or the user you are trying to reach.
The radio frequencies mobile devices use to transmit information are part of the electromagnetic spectrum, which is allocated by ICASA. It’s important to note that the majority of the spectrum has been allocated for something. For that reason, new cell phone technology, such as GSM, CDMA, UMTS, TDMA, and LTE, are developed to optimise the use of the frequency bands that have been allocated for cellular use.
Even though these technologies are designed to improve network capacity, reduce latency, improve data speeds, and provide us with better signal, they are not perfect. Sometimes we experience slow speeds, dropped calls, and poor signal due to the distance between your phone and the closest cell tower, or building material blocking the signal's path. Fortunately, cell phone signal boosters can help solve those problems. They eliminate dropped calls, improve your signal strength, and improve your data speeds.
What’s the Difference Between AMPS and DAMPS?
AMPS and DAMPS are based on different technologies – AMPS used analog signals and DAMPS used digital modulation. AMPS correspond to the first generation of mobile networks (1G), while DAMPS, the successor to AMPS, was used for the second generation of mobile networks and beyond (2G, 3G, 4G, etc).
What is AMPS?
In 1983, the first cell phone standard, AMPS, was introduced. It used analog signals to transmit information and was only capable of transmitting voice at a maximum speed of 9.6 Kbps. The problem with AMPS was that it wasn’t encrypted (making the signal extremely vulnerable for eavesdropping), voice quality wasn’t good, and users experienced lots of dropped calls.
AMPS used Frequency Division Multiple Access (FDMA) technology to allow multiple people to use the same frequency band when transmitting information. FDMA divides the frequency band into multiple frequency channels, but due to analog signals, each channel could only be used by one person. Analog is a continuous signal that cannot be compressed or manipulated, thus it couldn't be shared with other users.
For example, pretend you are in a payphone room with four phones. The room represents the frequency band, FDMA divides the band and provides four different payphone stations, which represent the frequency channels. Each phone can only be used by one person at a time, meaning the room only has a capacity of four people. If someone enters the room to make a phone call while all of the phones are occupied, they will vanish from the room (i.e. drop the call they are trying to make) because the capacity of the room has been exceeded.
This was identical to the way landlines worked at the time, where no matter how many phones your home had, only one could be used at a time – otherwise, you’d receive a busy signal.
Imagine how much spectrum would be needed to support the cellular demand of today's day and age. To optimize the use of frequency bands, cell phone communication systems started using digital telecommunication technologies.
What is DAMPS?
DAMPS, also known as IS-54 and IS-123, is the 2G digital version of AMPS. Rather than using analog, it used digital modulation. Digital modulation is the process of converting your voice or analog signal into digital code, compressing it which optimizes the use of the frequency channel, and then sending it to the receiver who decodes the information.
Similar to AMPS, DAMPS used FDMA to divide the frequency band into multiple channels. In addition to FDMA, it introduced TDMA technology to increase the number of people that could share one channel. TDMA breaks down the frequency channel into three time slots. Each time slot gives the user a specific amount of time in which they can send or receive information.
Let’s go back to the payphone analogy to elaborate further. In the room (frequency band), there are four phones (channels), rather than one person being at each phone, there are three people (time slots) in line at each phone. The first person in line at each phone can make a call, but they can only send or receive information within the time allowed. Once the time has run out, they have to go to the back of the line and wait for the other two people to use their time slots before they can send or receive information again. Since the transitions between the first person and the other people in line are very short, the receiver wouldn’t notice the time gap.
With the use of digital signals and a combination of FDMA and TDMA, the number of people that could access the network at the same time tripled.
What’s the Difference Between GSM and CDMA?
GSM and CDMA are two forms of radio technologies that cell phone networks use to transmit voice and data. GSM is used by most of the world.
The main difference between CDMA and GSM technologies is how they connect to the network. GSM phones use removable Subscriber Identification Module (SIM) cards to access the network. By contrast, CDMA phones are directly connected to the network. So, if you ever decided to switch phones, GSM devices require you to pop your SIM card into the new phone. On the other hand, CDMA devices require you to get in contact with your cellular service provider to make the change. For that reason, many GSM iPhones, Samsungs, Google Pixels, and LGs, experience compatibility issues when trying to connect them to a CDMA carrier, and vice versa.
Another major difference between both networks is the technologies they use to transmit information. GSM uses a combination of FDMA and TDMA, while CDMA uses spread spectrum technology.
What is GSM?
GSM is a digital telecommunications standard that was developed by the European Telecommunications Standard Institute (ETSI) to define the 2G cellular network. 2G GSM offered voice calls, SMS messaging, and basic data services.
Every network (2G, 3G, and 4G LTE) utilizes cellular frequency bands to send and receive information, which varies by country. 2G GSM used the 850 MHz and 1900 MHz frequency bands in North and South America, and the 900 MHz and 1800 MHz bands in Europe, Asia, Australia, Middle East, and Africa.
To transmit information, GSM uses FDMA and TDMA. FDMA breaks down the radio frequency band into multiple channels and TDMA breaks the channel down into time slots to allow more people to transmit information at the same time.
Unlike DAMPS, the TDMA technology GSM used divided each channel into eight time slots rather than three. The GSM payphone room functions the same as the DAMPS payphone room described above, but rather than each payphone having a line of three people, it can have up to eight. Remember, each person can only send or receive information during the time allowed. After the first person at each line has used up their time, they have to go to the back of the line and wait for the other people to use up their time. Even though the channel can be used by more people, it does not decrease the voice transmission rate, meaning that the receiver won’t notice the time division.
In order to access the network or to enter the payphone room, each handset device is required to use a SIM card. The SIM card holds your mobile subscription identification number, your phone number, and your service subscription details. In addition, the SIM card assigns each voice transmission a time slot and tells the network what services you can access.
The 2G GSM network didn’t provide the most efficient data services – its speeds were about 14.4 Kbps. Enhancements were later made to the network to improve the efficiency of the data. Over time, General Packet Radio Service (GPRS) was introduced, which offered a maximum download speed of 171 Kbps. GPRS was followed by Enhanced Data Rate for GSM Evolution (EDGE), which offered a maximum download speed of 386 Kbps. Since speeds where improving, but weren’t fast enough to be considered 3G, 2G networks that utilize GPRS are also known as 2.5G, and those that use EDGE are known as 2.75G.
What is CDMA?
CDMA was designed by Qualcomm. It was first used by the military during World War ll to prevent the Axis from jamming radio signals. It operates on the 800 MHz and 1900 MHz frequency bands to transmit information.
CDMA uses a channel access method to transmit data. It gives its users full access to the entire spectrum of bands to optimize the use of the available bandwidth. Each channel can support up to 61 users. Let's use the payphone room analogy to elaborate on how CDMA works. This new payphone room is more efficient, it allows way more people to use the same frequency channel simultaneously. In the CDMA payphone room, there are four payphone stations and there can be up to 61 people at each station. The phone stations represent the frequency channels, and the people represent the users of the CDMA network.
Unlike GSM, which provides one phone to be shared amongst a maximum of eight people, CDMA provides a payphone station that is made up of 61 phones. Therefore, every user can make a phone call at the same time and use the entire channel to send and receive information for however long they wish, as opposed to occupying a fraction of the frequency channel with a specific amount of time allocated to each user.
Since multiple people are transmitting information at the same time within the same channel, there needs to be a way to prevent one conversation from colliding or interfering with another. CDMA uses spread spectrum technology to encrypted or encoded each conversation with a randomized unique key to protect voice data and keep it private. The only user that can decode the message is the one who holds the key, which is the receiver.
Because of its efficiency and improved security, many mobile phone standards utilize CDMA as their channel access method, such as IS-95 (also known as CDMAONE), CDMA2000, as well as UMTS.
What’s the Difference Between TDMA and CDMA?
TDMA and CDMA are both channel access technologies. Channel access technologies allow multiple users to share the same frequency band when sending and receiving information. These two standards of digital technology use different algorithms to transmit information between devices.
TDMA is based on the time-division multiplexing (TDM) scheme. To allow multiple users to transmit data through the same channel, TDMA technology divides the signal into different timeslots within the channel. Meaning, every phone call that is being transmitted through the same frequency channel can only send and receive information within their specific time slot.
Using our payphone room analogy, person 1 can use the phone (the channel) to send or receive information within the specific amount of time given to them. After their time is up, they have to go to the back of the line and wait for the others to use up their time slots before person 1 can use the phone again. The data is transmitted in rapid succession, and each transmission uses its own timeslot. As a result, multiple users can share the same frequency channel.
As mentioned earlier, CDMA is based on spread spectrum technology that allows multiple users to use the same frequency channel at the same time, rather than occupying a fraction of the channel. In the payphone room, CDMA provides one payphone station (the channel) that consists of multiple phones.
Unlike TDMA, every person using a CDMA payphone can send and receive information for however long they want – they don’t have to alternate with each other to transmit information. To avoid interference and protect the information, each transmission is encoded with a unique code that corresponds to the source and destination of the signal.
What’s the Difference Between UMTS and CDMA2000?
UMTS and CDMA2000 were used to transition from the 2G network to the 3G network – one was designed to work alongside GSM, while the other works with CDMA. UMTS was developed by the 3rd Generation Partnership Project (3GPP) and CDMA2000 was developed by the 3rd Generation Partnership Project 2 (3GPP2). They are both part of the International Telecommunications Union’s IMT-2000 standard sets, which is a fancy name that represents a family of 3G cellular standards.
What is UMTS?
UMTS is the 3G standard for the GSM network.
UMTS uses Wideband Code Division Multiple Access (W-CDMA) to increased voice capacity and provide faster speeds. The 3G GSM network does not use FDMA or TDMA technology to transmit information like 2G GSM; it uses CDMA technology. The people using the 3G GSM network are no longer given time slots to share a frequency channel.
The UMTS payphone room would look very similar to the CDMA payphone room. Each data transmission would be protected by a unique code that can only be unlocked by the receiver.
Since the GSM technology was very different from what 2G GSM used, new base stations and new frequency allocations were needed to support UMTS technology.
This new standard offered download speeds up to 2 Mbps and upload speeds of 128 Kbps. Later HSPA was integrated into the mobile standard, followed by HSPA+. HSPA increased download speeds up to 14.4 Mbps, while HSPA+ increased download speeds up to 42 Mbps.
What is CDMA2000?
CDMA2000, also known as CDMA2000 1xRTT or IS-2000, is the 3G standard for the CDMA network. It’s based on CDMA technology to allow multiple users to use the same frequency channel at the same time. Each transmission is encrypted with a key that can only be deciphered by the receiver.
Voice and data services use different technologies. Voice uses CDMA2000 1xRTT technology, while data uses CDMA2000 EVDO.
1xRTT (Single Carrier Radio Transmission) was the first type of CDMA2000 technology. Compared to 2G CDMA, CDMA2000 1xRTT doubles the network voice capacity so that more people could talk on the phone at the same time. Under perfect conditions, 1xRTT provided data rates up to 153 Kbps, with real-world data rates averaging between 80 to 100 Kbps. Its successor, 1x Advanced, provided up to four times greater capacity.
EVDO focuses on implementing high-speed data rates for the CDMA network. This technology increased data rates up to 2.4 Mbps, and with later revisions, it increased to 3.1 Mbps. Keep in mind that EVDO only addresses data, not voice. To work, it needed a specific frequency channel, which was separated from the voice network. As a result, voice and data cannot be used simultaneously.
What’s the Difference Between WCDMA and CDMA?
The WCDMA network (also known as UMTS) is based on CDMA technology and is one of the most popular air interfaces use in mobile devices. Just like CDMA systems, WCDMA uses a coding scheme to send and receive information.
The main difference between WCDMA and CDMA is that they are designed to work with different networks. WCDMA is a 3G technology designed to work alongside the 3G GSM network. CDMA, on the other hand, is a 2G technology that is a direct competitor to GSM.
Additionally, WCDMA’s frequency bands are much wider than those used by CDMA – hence the name Wideband CDMA. WCDMA uses frequency bands that are 5MHz wide, while CDMA uses bands that are 1.25MHz wide. The wider bands support more data capacity and allow more users to transmit information simultaneously.
What’s the Difference Between EVDO, HSPA, and HSPA+?
EVDO, HSPA, and HSPA+ are mobile broadband technologies. Meaning, these technologies make accessing the internet through your phone possible. 3G CDMA networks utilize EVDO, while 3G GSM networks use HSPA and HSPA+. The differences between EVDO and HSPA are how they work and the speeds they can achieve.
What is EVDO?
EVDO is the mobile broadband technology used by the 3G CDMA network. Basically, EVDO enables carriers that utilize the 3G CDMA network to provide their mobile devices with high-speed internet access.
EVDO separates voice services from data services to maximize data transfer and provide high-speed internet access. In other words, voice and data operate on different frequency channels. As a result, voice and data cannot be used simultaneously. Meaning, that you won't be able to access the internet or any data tools while you are talking on the phone.
When EVDO was adopted, under perfect conditions, it could achieve download speeds up to 2.4 Mbps and upload speeds of 153 Kbps. Most users would experience download speeds of 400-700 Kbps. Revisions were later made to improve data rates. With Revision A (Rev. A), EVDO’s download speeds improved to 3.1 Mbps, and upload speeds improved to 1.8 Mbps. Revision B (Rev. B) drastically enhanced the data speeds; it provided maximum download speeds of 14.7 Mbps and maximum upload speeds of 5.4 Mbps.
What is HSPA and HSPA+?
HSPA is the mobile broadband technology used by the 3G UMTS network. HSPA is composed of two different protocols: High Speed Downlink Packet Access (HSDPA) and High-Speed Uplink Packet Access (HSUPA). These technologies enhanced the original 3G data rates of 2 Mbps downlink and 128 Kbps uplink, to 14.4 Mbps downlink and 5.8 Mbps uplink.
In 2008, HSPA+, an improved version of HSPA, was introduced. It enhanced the 3G UMTS network even more. With HSPA+ data rates could reach up to 42 Mbps downlink and 11.5 Mbps uplink. Since HSPA+ couldn’t quite hit 4G speeds, it’s also known as 3.5G.
Unlike EVDO, HSPA and HSPA+ are able to transmit voice and data simultaneously.
Difference Between GSM, UMTS, CDMA, CDMA2000, and LTE
GSM/UMTS, CDMA/CDMA200, and LTE are mobile standards that were developed to work with different networks. GSM and CDMA were used to move into the 2G network, while UMTS and CDMA2000 were used to transition into the 3G network. LTE, on the other hand, migrates CDMA/CDMA2000 and GSM/UMTS into the 4G network.
Since LTE pushes CDMA/CDMA2000 and GSM/UMTS networks into the next generation, it’s seen as the first step into streamlining the network. It was designed to increase the capacity, speed, and throughput of the mobile network.
LTE allows us to make phone calls, send text messages, browse the web, stream high-quality videos, and play games. To fulfill all of these demands with low latency and high speeds, LTE uses different technologies to transmit information from a cell site to a mobile device (known as downlink), and to transmit information from a mobile device to a cell site (known as uplink). It utilizes Orthogonal Frequency Division Multiple Access (OFDMA) for the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) for the uplink. These technologies improved the channel compacity to allow more people to send and receive information at fast speeds.
Due to the technologies it uses, the LTE network offers a maximum download speed of 300 Mbps and a maximum upload speed of 75Mbps. Enhancements were later made to the 4G LTE standard and speed improved. LTE Advanced offered download speeds up to 1Gbps and LTE Advanced Pro supported download speeds up to 3 Gbps.
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