Cellular Networks 101.
Cellular mobile telephone networks deliver service over an area divided up into “cells”; while these cells can be any regular shape, they are most often hexagonal. Each cell is served by its own transmitter and uses different frequencies than the cell sites directly adjacent to prevent interference. This allows for frequencies to be re-used throughout the network, a critical technological factor helped meet demand for mobile telephony. While mobile phone networks not using a cellular system existed on a limited scale prior to cellular networks, they are not discussed for simplification.
Early networks were much more homogenous in both their systems and deployment and largely made up of macrocell sites covering large areas of up to 30+km in rural areas, which limits the amount of times the frequencies can be re-used and thus lowers the capacity of the network. Later networks were much more customized and made up of both macro and microcell sites, which are generally less then 2km, which increase capacity.
In urban areas, a carrier may use different generation technology in the same geographic area and can include even smaller sized cell sites (picocell, femtocell, etc), in additional to public and private Wi-Fi data networks. This provides more capacity, speed, and better coverage but can increase the complexity of network operations. As these modern networks are much more heterogeneous in their makeup, they are sometimes referred to as “HetNets”.
When a person is using their mobile device to make a voice or video call, an uninterrupted connection to the transmitter is very important when moving from one cell to another. This is referred to as a handover or handoff, as one transmitter “hands off” the connection. While this can be an extremely complex engineering operation that can occur at both the network or device level (though more commonly it is the network), there are essentially two types of handoffs.
With a hard handoff, the new cell site is prepared to continue the connection and the mobile device suspends (terminates) the current connection with the old cell site and re-establishes it with the new one. This process is quite short (about 100 milliseconds or 0.1 seconds) but can be noticeable and increases the chance of a “dropped call”, where the new connection is not established. During a soft handoff, the handset receives the connection signal from multiple cell sites at once and determines which is the best signal. This process reduces the risk of dropping the call and can maintain a higher level of connection quality, though can increase network complexity.
Early mobile telephony was designed for voice transmission and based on a circuit-switched system, similar to wireline telephone networks. In circuit-switched networks, a direct connection is established between two parties at the beginning of a call and used exclusively for the duration.
When countries first began building widescale commercial cellular networks in the 1980s, a number of different analog technologies were employed. The limitations of so many national systems included a lack of inter-compatibility and high costs, as carriers were unable to achieve strong economies of scale with first generation (1G) networks. Canada’s Department of Communications first issued its Cellular Mobile Radio Policy and Call for Licence Applications in 1982.
While containing cutting edge connectivity technology, 1G phones were often bulky and visually distinctive. (L) A Motorola DynaTAC 8000X, popularized in the movie Wallstreet. Source: Mike Kuniavsky, CC BY-NC-SA 2.0, Flickr. (M) A Nokia Talkman (Czech version MD59) Nordic Mobile Telephone (NMT) phone. Early 1G phones of all technologies had external batteries and radios. Source: Kryštof Korb, CC BY-SA 3.0, Wikimedia Commons. (R) A Motorola MicroTAC 9800X, the first cellphone that people could carry in a pocket.
While the US eventually deployed a digital version of their 1G technology, the roll-out of second generation (2G) networks in the 1990s saw a movement to digital networks and the emergence of two global standards, the European-developed Global System for Mobile Communications (GSM) and the US-developed CDMA family.
The two standards use differing ways to connect mobile handsets with the network. GSM is based on time division multiple access (TDMA), which allows multiple users to share the same frequency by dividing the signal into different time slots. CDMA uses code division multiple access (CDMA), which allows for several users to share the same frequencies but using an individual coding scheme. More simply, GSM users take turns connecting with the network and CDMA users all transmit at the same time and the system ignores any information not intended for them. It is also important to note, as we will see below, there is a difference between CDMA as a group of standards and an underlying transmission method.
Part of the reason for developing packet-switched systems, based on Internet Protocols, was to facilitate mobile data transmission. While data services were available on circuit-switched systems, having a dedicated connection for an entire session is highly inefficient for the bursty nature of data transmissions such as sending/receiving email or web-browsing. With the growth of the internet and the emergence of the World Wide Web in the 1990s, carriers layered data networks over their voice network coverage. The efficiencies gained from dynamic packet-switched systems also made their way into traditional wireline telephone networks.
Even with 2G networks becoming robust, radios, electronics, and battery were decreasing in size. Later 2G feature phones would boast a range of design aesthetics (L) An Ericsson T28 cellphone. Ericsson is primarily known as a telecom equipment manufacturer and got out of the handset business in 2012. Source: Holger Ellgaard, CC BY-SA 3.0, Wikimedia Commons. (M) A Nokia 5110 in a common ‘candy bar’ form factor (the first cellphone of one of this site’s researchers). Source: Soltys0, CC BY-SA 2.5, Wikimedia Commons. (R) A Motorola RAZR V3i, one of the thinnest feature phones of its time. First released in 2005.
Just because 2G networks were slower than today’s, does not mean the phones weren’t “smart”. (L) A Nokia N-95, which featured a 2-way slider to access multimedia buttons (closed) and a numeric keypad (open). Source: Asmin18, CC BY-SA 3.0, Wikimedia Commons. (M) A BlackBerry 7230, circa 2003. This phone had 16 MB storage, 1 MB RAM, and BlackBerry’s famous full-QWERTY keypad. Source: Stephen Foskett, CC BY-SA 3.0, Wikimedia Commons. (R) An HTC Dream, also known as the T-Mobile G1. This was the first Android phone. Source: Michael Oryl, CC BY-SA 2.0, Flickr.
The CDMA family evolved from the original 2G IS-95 (cdmaOne) system to the third generation (3G) IS-2000 (CDMA2000). GSM used a number of packet-switched technologies moving from early (2G) General Packet Radio Service (GPRS) and Enhanced Data Rates for GSM Evolution (EDGE) systems towards their 3G Universal Mobile Telecommunications System (UMTS) system. The first 3G technology for the GSM standards used Wideband Code Division Multiple Access (WCDMA) transmission technology, a different radio access standard from 2G GSM but which used the same core network technology. Thus, starting with 3G networks, GSM and CDMA networks use variations of CDMA transmission standards.
While the CDMA family has some advantages over GSM, including enhanced security and ability to use 2G base stations for 3G networks, UMTS offered greater spectral efficiency and bandwidth to network operators and GSM became the more commonly deployed globally technology. The GSM 3G standard has continued to be enhanced into a number of variations of High Speed Packet Access (HSPA) systems. Some of the more advanced versions that provide faster data rates, such as HSPA+ and Dual Cell HSPA, have been referred to as 3G+, 3.5G, etc to show their evolution.
3G networks, with increased capacity and speed for data-transmissions helped make smartphones mainstream. (L) While the original iPhone was 2G and Symbian, BlackBerry, Palm, and Windows Mobile had apps previously, the iPhone 3G was the first smartphone for many people and increased the cultural cache of smartphones, especially in North America. The iPhone 3G, 3GS, 4, and 4S are all 3G phones. Source: Matthieu Riegler, CC-BY, Wikimedia Commons. (M) A Nokia 6500 Slide, a feature phone with 3G connectivity. Source: David Sykes, CC BY-NC-ND 2.0, Flickr.(R) An LG Optimus 7, running the Windows Phone 7 operating system (OS). Microsoft has been making software for mobile devices, including cellphones, for over a decade using various iterations of their OS. Source: LG전자, CC-BY, Flickr.
Two fourth generation wireless technologies are being deployed around the world: WiMax and Long Term Evolution (LTE). WiMax is a standard that developed out of the IEEE 802.16 standard. While WiMax launched earlier, LTE (3GPP Release 8) is the natural successor to the GSM and CDMA families and has become the de facto 4G standard. (For further information on standards bodies, see Spectrum Regulation & Legislation.)
It is important to note that while LTE has been approved to be called a 4G technology, it does not meet the speed standard set by the ITU. Its next iteration, LTE Advanced (3GPP Release 10), is expected be a true 4G standard. The ITU-R requirements for 4G standards, the International Mobile Telecommunications Advanced (IMT-Advanced) specification, has a peak speed requirement of 100 Mbit/s for high mobility situations (such as in cars or on transit) and 1 Gbit/s for low mobility situations (such as walking or stationary people).
While more advanced network technologies will be important to users that demand higher speeds and increased data throughput, emerging uses of cellular data networks may have other priorities. Machine-to-Machine (M2M) connections are expected to be a growing use of data networks and an important part of creating “smart” cities and economies; an example of a wireless M2M application in Canada is Smart Meters. With M2M communications, coverage, reliability and availability are more important than bandwidth and may provide incentive to maintain older but more robust and wider-coverage networks.
For further reading on network technologies, see: