The paper deals with the evolution of GSM networks from the simple circuit switched networks to the contemporary third generation of mobile communications which is based on packet switching. Throughout the paper, the third generation of mobile communication is denoted by 3G, as it is denoted in the technical field.
The main contents of this article give an overview of how mobile technology has evolved over time and as it has been witnessed in many technologies, the successor generation has some improvements on the problems noted in the predecessor. This is witnessed by interoperability in 3G which was a major problem in the 2G of the mobile networks. In some scenarios, WLAN is taking the better part of applicability as compared to cellular networks (Johan, 2002).
Evolution of cellular communication
Reviewing a bit of history, cellular communication has developed in the past mainly due to voice services. This has been offered by most telephone networks but the mobile cellular networks have given it even more flexibility. In the year 2002, the use of cellular phones surpassed the one billion users mark and by this time, it accounts for more than 66% of the total telephone and communications services. The most applied means is the Global systems for Mobile Communications (GSM) which appears to be even absorbing TDMA use into it. This can be attributed to the widespread nature of GSM networks which gives it better connectivity. Coming with the 2G and 3G networks is the aspect of data transmission. This is what has led to adoption of packet switched networks in cellular communication. It has also led to development of protocols from GSM, GPRS, and EDGE to CDMA which forms the basis of 3G networks (Daniel, 2000).
Actual implementation or use of cellular communication began in the 1980s with each country deploying its own networks. This brought about the element of control across borders and regions. The main types of networks were wired since wireless technology was almost solely confined to broadcast and satellite services. This formed the first generation of cellular communications which was rapidly replaced by 2G communications in the 90s.
The second generation began taking root in cellular communications in 1990s. However, most of the requirements of the communication links had not changed (remained voice calls) hence the technological shift was slow. Boarders started opening up to communication links giving rise to a large network of networks. 2Gs coexist in 4 different forms namely GSM, CDMA1, TDMA and PDC.
It was formed and implemented by 1992 but actual handsets to use the network were released in 1993. This shift was mainly witnessed in European countries which had founded GSM but were also available in Australia and South Africa. By 2002, there were over 470 GSM operators with more than 646 million users in over 122 countries in the world.
The system allows 8 users to share a 200 kHz radio channel by assigning unique time slots to the users. All over the world, GSM networks use 900/1800 MHZ frequencies except for North America where they use 1900 MHZ band. In the near future, it is anticipated that new frequency bands of 450 and 850 MHz will be used.
- Services offered by GSM
- Short messaging with characters less than 160
- Data transfer by use of circuit-switched data (CDC) with a data rate of up to 14.4 kbps
The speed limitations in data transfer are mostly addressed in high speed CDC and GSM packet radio service which has a speed of up to 57.6kbps for HSCDC and more than 100kbps for GPRS (Johan, 2002)
The major features of GPRS that makes it better for data transfer and being a predecessor of most 3G networks include:
- Always on
- High speeds in data access.
- Improved usage of radio resources.
- Separate allocation of uplink and downlink channels.
- Simultaneous data and voice transfer.
Having relied heavily on GPRS deployment, technology took another turn in 2001 from concentrating on voice transfer to data transfer. This led to rapid evolution in this sector that saw many technologies improve data transfer.
Enhanced data rate transfer for global evolution (EDGE) was implemented as an improvement to GPRS. This technology introduced a modulation technique that tripled the bandwidth of the channel doing the same to the data capacity. EDGE forms a core technology towards the evolution of 3G technologies (Johan, 2002)
This technology emerged from the use of spread spectrum which was being employed in military communications. This technique was approved in the year 1995 but remained insignificant until 2000 when it gained over 20 million users globally. It forms a very strong background to the contemporary 3G CDMA technology widely used in mobile internet access devices.
In this mode of cellular networks, up to 64 users can use a 1.25 MHz channel. This is made possible by decoders and multiplexers that allow for data separation according to attached pseudo-random codes.
The other two technologies are not of great significance since TDMA dealt with analog cellular signals and of late has shifted into GSM. PDC on the other hand may be viewed as part of CDMA hence these two elements of 2G created the foundation to 3G (Johan, 2002).
The main factors than can be referred to as the main facilitating factors to the evolution of 3G include: need for higher bit rates, new frequencies and the need for more capacity. There are two proposed systems for 3G which are recognized by International Telecommunications Union.
- UMTS. This system comprises of 2 different but related modes:
- CDMA direct spread. Also called wide band CDMA or frequency division duplex (FDD).
- CDMA –TDD time division duplex mode of CDMA
- CDMA 2000. This is a multicarrier form of CDMA which evolved from CDMA one. (Daniel, 2000)
Universal Mobile Telecommunications System carried out the transition from 2G to 3G in a series of releases which can be summarized as:
- Release ’99 or release 3. This was the first release with the following features.
- Bearer services.
- Voice calls services which were compatible with GSM.
- Circuit switched data rates of up to 64 kbps
- Packet switched data rates of up to 384 kbps.
- Release 4
- Edge radio
- Multimedia messaging.
- Improved location services.
- Release 5
- IP multimedia subsystems (IMS)
- IP version 6
- Improvements on release 4
- Release 6.
- WLAN integration.
- Multimedia multicast and broadcast.
- Improvements on IMS
- HSUPA (Daniel, 2000)
However, CDMA 2000, which is compatible with UMTS, evolved on its own from PDC in Japan and currently 3G technologies are employed almost in all sectors of telecommunications in Japan.
3G has also undergone radical evolutions mainly in the architecture of the networks. For example, there has been a shift from UTRAN to embrace of IP based architecture. This has greatly enabled the integration of 3G technologies in the internet hence allowing them to operate as extensions of the internet. These technologies have the ability to be internetworked with other networks. For examples, WLANs employ wireless broadcasting to provide network access services to many machines with an ability to connect to a wireless network (Daniel, 2000). The commonly used frequencies are:
- 2.4 GHZ unlicensed band. This band is also known as IEEE 802.11b. This connection achieves a practical top speed of 5.5 Mbps but theoretically aspired to achieve up to 11 Mbps. However, home RF and Bluetooth technologies have invaded the band for short distance interconnections. WLAN has reacted by shifting to 5GHz unlicensed band to avoid interference by the Bluetooth.
- 5GHZ unlicensed band. This band is also IEEE 802.11a which is an evolution from IEEE 802.11b. It can achieve maximum speed of 30Mbps with a theoretical top speed of 54Mbps. This is implemented as ETSI HIPER LAN for increased speed, data security and reduced interference.
- Cellular layer. This is mainly for full network coverage, voice call services and medium level data transfer rates.
- Hot spot layer. This is the layer that offers little mobility with high data rates. This is the category of WLANS.
- Personal network layer. This is mainly used for short range interconnectivity. Data rates are medium and this is mainly exhibited while interconnecting devices like laptops, PDAs and phones using Bluetooth. (Johan, 2002)
Johan V. 2002, Mobile Network Evolution: a revolution on the move. IEEE communications magazine
Daniel C. 2000. 3G Wireless Networks in the journal Evolution of communications technology, IEEE consortium