Wireless communication has experienced tremendous growth in the last decade. High data rate wireless communication is becoming increasingly important to mobile users in corporate and public networks in the indoor environment. Although voice and low data rate services were the first applications of cellular networks, the focus in recent years has shifted to very high-bandwidth delivery, which is a key driver for system and network design. While wireless local area (WLAN) access is important for data applications, mobile users still expect reliable GSM and 3G coverage for their voice service and seamless transition as they move indoors from an outdoor environment. Research shows that 75% of all mobile calls originate inside buildings at work, home or public places. This has in turn led to consumer awareness and expectation of ubiquitous coverage, and the ability to use their wireless devices anywhere.
Relying on the penetration of the GSM and 3G radio signals from the outside for providing in-building coverage is neither practical nor reliable in many buildings, and additional indoor antenna units (AUs) must be installed. Different building shapes and materials such as steel and metalized glass, cause in-building penetration of radio frequency (RF) signals to weaken resulting in reduced data rates and even complete loss of signal. This will become even more apparent over the next few years with the introduction of new 4G technologies which require considerably higher signal integrity and radio frequency than their voice counterpart. Also, with the trend to increasing data rates on wireless networks and a rapidly increasing number of users who want un-tethered access pose new challenges to system integrators and network designers. This results in significant challenges for the wired infrastructure that is required to connect the numerous antennas units.
Wireless over fibre (WoF) systems which also known as Radio over Fibre (RoF) systems have attracted much interest for broadband wireless access, offering a simplified overall system design due to the aggregation of RF signal generation and network management at a central location. Distributing broadband wireless signals over optical fibre has a number of advantages compared with traditional copper cabling. The wide bandwidth of optical fibre further allows different services such as Gigabit Ethernet, IEEE802.11a/g, GSM and 3G to share the same infrastructure, making the wireless-over-fibre approach a truly multi-operator and multiservice technology.
WLANs have had a profound impact on our perception of communication. First of all, the vast majority of users now believe in the new notion of “always on” communication. We are now living in the era of ubiquitous connectivity or “communication anytime, anywhere, and with anything”. Secondly, the concept of broadband communication has caught on very well. As fibre penetrates closer to the end-user environment (Fibre to the Home/Curb/X, FTTH/C/X), wired transmission speeds will continue to rise. Transmission speeds such at 100 Mbps (Fast Ethernet) are now beginning to reach homes. The demand to have this broadband capacity also wirelessly has put pressure on wireless communication systems to increase both their transmission capacity, as well as their coverage.
Figure 1: PRESENT COMMUNICATION SYSTEMS
In general there is a trade off between coverage and capacity. Figure 1 shows the relationship between some of the various standards (present) in terms of mobility (coverage), and capacity. For instance, the cell size of Wireless Personal Area Networks (WPANs) is typically a few metres (picocell), while their transmission rates may reach several tens of Mbps. On the other hand 2G (e.g. GSM), and 3G (e.g. Universal Mobile Telecommunication System (UMTS) and the International Mobile Telecommunications (IMT2000)) systems have cells that extend several kilometres, but have data rates limited to less than 2 Mbps. Therefore, as mobile communication systems seek to increase capacity, and wireless data systems seek to increase coverage, they will both move towards convergence. A case in point is the IEEE 802.16, otherwise known as WiMAX, which appears to lend weight to the notion of convergence, as shown in Figure 1 WiMAX seeks to provide high-bit rate mobile services using frequencies between 2-11 GHz. In addition, WiMAX also aims to provide Fixed Wireless Access (FWA) at bit-rates in the excess of 100 Mbps and at higher frequencies between 10 – 66 GHz. Via: coreelectronics.info/category/coreelectronics
