First Generation (1G) Mobile Systems
1G of mobile wireless communication were based on the analog transmission system for speech services [21]. 1G was first introduced in 1979 by Nippon Telephone and Telegraph (NTT) in Tokyo, Japan as a significant leap in mobile communication, especially in terms of capacity and mobility. Two years later, the cellular epoch reached Europe. In the United States, the Advanced
Mobile Phone System (AMPS) was launched in 1982. The system was allocated a 40MHz bandwidth within the 800-900MHz frequency range by the Federal Communications Commission (FCC). AMPS offered 832 channels, with a data rate of 10Kbps. Although omnidirectional antennas were used in the earlier AMPS implementation, it was realised that using directional antennas would yield better frequency reuse. Directional antennas yield better frequency reuse since a BS can have many sectors using various directional antennas at different frequencies. Total Access Communication System (TACS) was deployed in the United Kingdom in 1983. 1G cellular system had very low data rates of 2.4Kbps and were analogue based allowing only voice calls. The drawbacks of 1G telephony were [22]:
Poor voice quality as analogue signals are easily affected by interference.
Poor battery life.
There was no security of data as analog signals did not allow advanced encryption methods. Hence, anybody could listen to the conversation easily by simple techniques.
Limited capacity and poor handoff reliability.
Second Generation (2G) Mobile Systems (Digital)
In the end of 1980s, the Second Generation (2G) mobile systems were announced, and were launched on the Global System for Mobile Communications (GSM) standard which used audio quality digital modulation to provide voice and limited data services [21]. Compared to 1G systems, 2G systems used digital multiple access technology, such as Time Division
Multiple Access (TDMA) and Code Division Multiple Access (CDMA). Three primary advantages of 2G networks over 1G were that voice conversations were digitally encrypted; 2G systems were significantly more efficient on the spectrum over their predecessors; and data services for mobiles were introduced in 2G like Short Messaging Service (SMS), fax and paging. In the late 1990s, 2.5G was introduced which used the General Packet Radio Service (GPRS) standard with improved data rates of 64-144Kbps [23]. 2.5G was developed in between its predecessor, 2G, and its successor, third generation (3G). Later on, Enhanced Data Rates for GSM Evolution (EDGE), also dubbed 2.75G, was launched as a mobile technology that allows improved data transmission rates as a backward-compatible extension of GSM.
Third Generation (3G) Mobile Systems
3G is the 3rd generation of mobile telecommunications. 3G systems support services that provide an information transfer rate of at least 2Mbps. It uses wide band wireless network with which clarity is increased and therefore satisfying the International Mobile Telecommunications-2000 (IMT-2000) specifications by the International Telecommunication Union (ITU). Universal Mobile Telecommunications System (UMTS) is a European 3G standard developed by 3GPP. CDMA2000 is the American 3G standard developed by 3GPP2 in 2001. 3G finds applications in wireless voice telephony, mobile internet access, fixed wireless internet access, video calls and mobile television. Later 3G releases provide mobile broadband access of several Mbps to smartphones and mobile modems in laptop computers.
Fourth Generation (4G) Mobile Systems
4G is the successor of 3G and it aims to provide mobile broadband internet access. Some of its possible applications include amended mobile web access, Internet Protocol (IP) technology gaming services, high definition mobile television, three dimension (3D) television, video conferencing and cloud computing. Two 4G candidate systems are commercially deployed: the Mobile Worldwide Interoperability for Microwave Access (WiMAX) standard and Long Term Evolution (LTE) standard [21]. LTE uses Orthogonal Frequency Division Multiplexing (OFDM) and OFDM access, which divides a channel usually 5, 10 or 20MHz wide into smaller sub channels or subcarriers each 15 KHz wide. Each is modulated with part of the data with one of several modulation schemes like Quadrature Amplitude Modulation (QAM), 16QAM and 64QAM. LTE also defines MIMO operation that uses several transmitter- receiver-antennas. The data stream is divided between the antennas to boost speed and to make the link more reliable. Using OFDM and MIMO let LTE achieve data rates of up to 100 Mbps downstream and 50 Mbps upstream under the best conditions. LTE Advanced (LTE-A) is an improvement of LTE and is the candidate for IMT-Advanced standard formally submitted by the 3GPP organisation to ITU in the fall 2009. The target of 3GPP LTE-A is to reach and surpass the ITU requirements. The peak downlink data rate for LTE- A is 1Gbps and peak uplink data rate is 500Mbps. 4G traffic exceeded 3G traffic for the first time in 2015 according to [9]. The Institute of Electrical and Electronics Engineers (IEEE) 802.16m (WiMAX) is under development, with the objective to fulfil the IMT-Advanced criteria of 1Gbps for stationary reception and 100Mbps for mobile reception.
Fifth Generation (5G) Mobile Systems
5G denotes the next major phase of mobile telecommunications standards beyond the 4G/IMT-Advanced standards [24]. At present, standardisation activities are being carried out in this area. It is expected that the 5G mobile system will be an all-IP based model for wireless and mobile networks interoperability. Below is a summary list of 5G requirements [25] from various 5G bodies such as 5G Infrastructure Associate (5G IA), 5G Forum, 5G Mobile Communication Promotion Forum (5GMF) and 5G Infrastructure Public Private Partnership (5G-PPP).
1. Higher system capacity: The target is set to achieve a 1000-fold system capacity per km2.
2. High data rates: 5G should target to provide multi-Gbps transmission rates up to 20Gbps along with more uniform Quality of user Experience (QoE) compared to 4G.
3. Supports massive connectivity: 5G should support up to 10-100 times more connected devices which can be up to 100 billion devices.
4. Zero latency: 5G has to provide not only higher data rate, but also a negligible user plane latency of less than 1ms over the RAN, a large leap from LTE’s 5ms.
5. Higher energy efficiency: 5G target to save energy in both the RAN and the terminals with up 90% reduction in network energy consumption and also up to 10 years battery life for low power machine type device. 6. Mobility: Target maximum speed of up to 500km/h.
8. Network flexibility: Multi RAT system, Network Function virtualisation (NFV) and Software Defined Networks (SDN).
9. Flexible Spectrum: Efficient integration of existing cellular bands and new spectrum bands over a wide range of frequency bands from the current frequency bands below 6GHz to above 6GHz (30GHz-300GHz) mmW bands incorporating carrier aggregation, operation in unlicensed spectrum bands and cognitive radio.
10. High density networks: Advanced small cells and Self-Organizing Networks (SON).
The NGMNA feels that 5G should be rolled out by 2020 to meet business and consumer demands [26]. In addition to providing simply faster speeds, it is predicted that 5G networks also will need to meet new use cases, such as [27]:
1. Enhanced mobile broadband (eMBB): Virtual and augmented reality, 3D video, holographic presence.
2. Massive machine type communication (mMTC) for IoT devices: e- health, millions of sensors connected, smart home.
3. Ultra-reliable and low latency communications (uRLLC): remote surgery, vehicle to everything communication, self-driving cars, drone delivery, smart manufacturing.