Abstract
The cellular industry is evolving at a very fast pace. In fact, cellular networks have experienced significant changes over the last few years. In order to keep up with this constant evolution, planning tools must also adapt in order to reflect the particularities and architecture of each generation. In this chapter, we will first present the characteristics and the architecture of the four main generations of cellular networks (1G, 2G, 3G and 4G). We will then expose different planning problems related to each generation followed by a short description of different solutions that have been proposed in the literature.
TopFirst Generation Cellular Networks
The first generation of cellular networks appeared in the early 80’s. This generation was analog and only used for voice communications. The transmission speed was very limited and the size of the devices was huge compared to what we have today. The following are the main 1G standards.
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Advance Mobile Phone System (AMPS)
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Total Access Communication System (TACS)
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Nordic Mobile Telephone (NMT)
It is important to note that these three standards were not compatible with each other. In fact, mobile users were not able to roam between two different networks thus providing a very limited mobility. A few years later, a second generation was born. That’s really with the advent of this generation that the interest started to appear for cellular networks.
TopSecond Generation Cellular Networks
The advent of 2G networks was a huge milestone since they were digital and capable of carrying voice and data traffic at a maximum speed of 9.6 kbps. Several 2G standards were developed.
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Global System for Mobile Communications (GSM)
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Interim Standard-95 (IS-95)
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Interim Standard-136 (IS-136)
However, the GSM standard was, and still is, the most popular system worldwide. As we can see in Figure 1, GSM networks are composed of two main parts: a Base Station Subsystem (BSS) and a Network Switching Subsystem (NSS). On one side, the BSS is composed of Base Transceiver Stations (BTS) and Base Station Controllers (BSC). The BTS are used to transmit/receive information to/from the mobile users via the air interface. The BSC are mainly used to manage the radio resources and handovers. On the other side, the NSS is composed of Mobile Switching Centers (MSC), often called switches, which are responsible for the switching functions and Gateway MSC (GMSC) to ultimately give access to the Public Switched Telephone Network (PSTN). Finally, different databases such as the Home Location Register (HLR) and the Visitor Location Register (VLR) are also used in order to keep the information related to the subscribers.
Network planners really started to worry about cellular network planning when 2G network were introduced. Different problems such as the coverage, frequency assignment and cells to switches assignment will be exposed in the following sub-sections.
Key Terms in this Chapter
Vertical Handover: Handover happening between two different access networks. For example, an active mobile user could be moving from a UMTS cell to a Wi-Fi hot spot.
3G: Third generation of cellular networks. The goals for this third generation were to reach speed of up to 2 Mbps, provide a worldwide compatibility (global mobility) and be backward compatible. The main 3G standard is UMTS (Universal Mobile Telecommunications System).
1G: First generation of cellular networks. This analog system appeared in the early 80’s and was mainly used for voice communications. AMPS, TACS and NMT are three different 1G standards.
Handover: When a mobile user with an active call is moving from one cell to another cell (crossing the boundary), the automatic process in which the communication is transferred from the first base station to the second base station is called handover. Simple and complex handovers are possible. In a simple handover, both cells are linked to the same switch (MSC) while in a complex handover, both cells are connected to different switches. Obviously, complex handovers are much more costly in term of resources utilisation since several updates are required.
4G: Fourth generation of cellular networks. This is the future generation of cellular networks. The requirements for this new generation are not set in stone yet. However, the main goal is to integrate different access networks around a common IP (Internet Protocol) core network.
2G: Second generation of cellular networks. They appeared in the early 90’s and they were numeric (instead of analog as in 1G networks). Voice and data can now be transmitted at a maximum speed of 9.6 kbps. The main 2G standard is GSM (Global System for Mobile Communications).
Network Reliability: Capacity of the network to offer the same services even during a failure. Single failures (node or link) are usually considered since they account for the vast majority of failures.
Horizontal Handover: Handover happening between two cells of the same network. A user moving from a UMTS cell to another UMTS cell is an example of horizontal handover.
Network Planning: The goal of network planning is to interconnect different equipments in order to share resources among several users. When planning a network, we want to achieve a given objective. For example, the network planner may want to minimize the cost, minimize the delay, maximize the throughput, etc.