The ultimate goal of humanity in today’s society is the possibility of the exchange of any imaginable data at any given time, form any place. This goal may only be made possible by means of wireless network technology.
Over the years, mobile communications have caused an improvement in terms of humanity’s communication networks through the provision of a vital capability, otherwise known as mobility. Before mobile communication systems were introduced, the only possible means of communication were established to and from fixed locations (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004).
However, people aim to communicate with each other, and not with places. Mobile communication systems have become an important infrastructure in today’s civilization. Mobile communication systems have now just began to develop from merely offering the usual fax and voice communication services to providing information superhighway services which can exchange a mixture of voice, text, and images. Wireless technology is the core of mobile communication systems.
Voice conversation has been a major service for quite sometime now as far as fixed networks are concerned. However, the advent of the information superhighway communication services has been changing the world at a very rapid pace (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). It is evident that the information superhighway services have spread throughout the world at a much faster rate than other services. Through the information superhighway, user can easily browse sites found at the World Wide Web in order to retrieve different of data counting as well images. Users may also benefit from online shopping and/or other buy and sell services at cyberspace. Moreover, they can just about instantaneously trade electronic mail messages as a substitute to conventional postal services process. Aligned with the subject of the rising popularity of communication via the information superhighway in fixed networks, the kinds of services delivered through mobile communication have changed their focus from exclusively voice conversation to accessing the information superhighway and electronic mail correspondence (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004).
Today, it seems that a mobile phone is more than just a tool for voice conversation. Mobile phone is now serves as an instrument for communication which facilitates different kinds of electronic communications for both business and private use. The 2G systems allow access to only text information due to the low speed of data transfer rates as well as to the relatively small displays generated by portable phones (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). However, third generation or 3G systems are deployed with much better representation compared to the 2G systems (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004).
The 2G systems are designed based on the well-known cellular concept (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). Multiple base stations are distributed uniformly as much as possible over a wide geographical area to communicate with users. All the wireless channels in the available frequency bandwidth are grouped and each base station is assigned a different channel group. In this way, a wide geographical area can be covered utilizing a limited frequency bandwidth. To enable as many mobile users as possible to communicate with the same base stations, wireless multiple access techniques must be adopted. Several multiple access techniques exist. The type that is used depends on the type of traffic. If there is continuous traffic requiring a very short transmission delay, for instance, voice conversation, demand-assign based multiple access is applied, in which the channels are divided in a static fashion and each user is allowed one or more channels by a base station during its communication, irrespective of whether or not transmitted data is generated. The demand-assign based multiple access consists of Time Division Multiple Access, otherwise known as TDMA, and there is also the Frequency Division Multiple Access, otherwise known as FDMA, and Code Division Multiple Access or CDMA. Channels are configured using the available bandwidth either in frequency, time, or code space. In CDMA, unlike in TDMA and FDMA, all the base stations use the same frequency bandwidth and all users divide up to a similar frequency bandwidth and time (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). However, different spreading code sequences are employed to segregate one user from the other.
Alternatively, if data generation is random and has a high peak-to-average rate ratio, random multiple access is employed, wherein several users share a single communication channel and they transmit their packets in a random or partially coordinated way. Any random multiple access technique can be combined with any demand-assign based multiple access technique. The moment a portable phone enters an active state, it requests a channel from a base station. The base station assigns one of multiple channels based either on CDMA, FDMA, or TDMA (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). The assigned channel is shared by a group of active portable phones. The portable phone stays in the group until it leaves the active state. The channel assignment acts as admission control so that the channel does not become overloaded. During the active state, portable phones in the same group access a base station based on a random multiple access technique. This type of wireless access will be important for the fourth generation or 4G systems which provide advanced information superhighway access services to mobile users (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004).
The first generation or 1G mobile communications systems were installed around 1980. These systems employed analog FM wireless access using narrowband FDMA of which the channel spacing ranges from 25 to 30 kHz (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). On the other hand, in 2G systems which were deployed in the 1990’s, TDMA with the channel spacing of about 25 to 200 kHz were generally employed. Afterwards, a wireless access technique based on narrowband direct sequence CDMA was developed. It channel spacing is 1250 kHz, which is much wider compared to other 2G systems.
As earlier pointed out, major services offered by the present 2G systems are advancing from voice conversation to multimedia communications over the information superhighway. On the other hand, the 1G as well as 2G systems were generally designed in such a way that they may be best utilized for basic services such as facsimile, voice, and low-speed voice-band data. It is expected that the coming 3G systems can provide advanced services with much higher transfer rates and much better representation.
There are three strong grounds for the development of 3G systems. First is multimedia. Second is higher capacity and third is global standard. In 2G systems, the data transfer rate is only around 9.6 kilobytes per second, which is far too slow for retrieving rich information comprising text and images (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). A significant wide data rate range will be in demand, for instance, for as low as 8 kilobytes per second to a couple of megabits per second (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). Next, to be able to manage the quick and still ongoing development of mobile communications, the problem concerning link capacity should likewise be considered. Finally, setting up a universal standard is turning out to be ever more vital in the 21st century, when people travelling around the globe for either leisure and business purposes are growing in number because given that 2G system standards are, comparatively, regional in standard.
Data transfer rates of up to 2Mbps and the same quality as fixed networks are the targets (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). For the transfer of image information of 1 Mbyte, 14 minutes is necessary at a 9.6 kbps user rate in 2G systems, but the transmission time will be significantly shortened with an Mbps transfer rate (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004).
The future of wireless network technology rests in the 4G systems. The main goal is offering mobile users broadband multimedia services. In the not so distant future, it will be in full force in fixed networks established on the next generation technology of the information superhighway. The data exchanged over the information superhighway will become all the more rich. Generally, the data may possibly hold high quality moving and still images.
The 3G systems have a much higher data transfer capability and it is able to manage the Transmission Control Protocol and Internet Protocol or TCP/IP traffic more efficiently than any other 2G system (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). However, the 3G core networks will slowly evolve from 2G by taking advantage of their legacy and therefore, the 3G core networks may not be fully optimized to the TCP/IP packet traffic. Therefore, it is the 4G system core network that must be fully optimized to TCP/IP traffic. Data transfer rates of 3G systems may not be sufficiently high to handle a variety of information comprising rich images. Completely different wireless and network architectures from 2G and 3G systems are thus, necessary (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004).
The wireless part will become closer to a wireless LAN, but with wide area mobility management as in the 2G and 3G systems. Mobile communication systems require many call control functions and a distributed database, and quick and stable connections between them are necessary. They will be embedded in the TCP/IP based core networks based on a virtual leased line concept (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). Voice traffic can be transferred as TCP/IP packets, for instance, voice over IP, but how to guarantee the QoS and reduce latency is a major technical problem. This may be much easier to realize if TCP/IP over asynchronous transfer mode or ATM networks are used (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004).
In consideration of the wireless part, wireless Internet access will be the core: TCP/IP packet over the air, broadband random multiple access and significant asymmetric traffic between forward and reverse links (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). An efficient wireless random multiple access technique must be developed. Probably, there will be demand for peak throughput of more than 2 Mbps in a vehicular environment and more than 10-20 Mbps in stationary-to-pedestrian environments on the forward links (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). Due to asymmetric traffic between the forward and reverse links, wireless access networks must be completely redesigned from the 3G systems.
There are other means to offer multimedia services to mobile users with the help of wireless technologies. One of which is through wireless LAN (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). The other approach is by mean of wireless ATM. It is highly probable that cellular core network architectures will migrate to packet/cell-based architectures and will converge with wireless LAN or wireless ATM architectures in the 4G era or inter-technology mobility management will be introduced among cellular, wireless LAN and wireless ATM networks. As one may expect, TCP/IP traffic will dominate over the circuit switched type traffic in the near future, for instance, voice, and therefore, TCP/IP-based core networks are highly desirable for 4G services. There are also many development activities to accommodate TCP/IP traffic over ATM networks. One advantage of the ATM network is that it can transfer efficiently different types of traffic, for instance, the delay sensitive voice traffic and best effort type TCP/IP traffic, while guaranteeing their respective QoS requirements (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004).
In the 4G systems, the frequency bands will most likely rest higher than 5 GHz (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). In this case, the wireless channel links will not only be especially power-limited, but interference-limited as well (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). This suggests that a nano-cell or pico-cell structure should be employed and there is no doubt that an adaptive antenna array will play an important part in bringing to an end this power setback.
The provision of nationwide coverage is almost impossible for 4G systems. High multimedia traffic areas are the only ones that may possibly be covered (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). These suggest that 4G systems may need to be designed apart from the cellular concept that relies on the statistical properties of propagation channels.
The question remains to be on which concept should the design of the 4G systems be based? One solution may be an ad hoc wireless network. Base stations are installed where they are needed and are added or deleted; they are connected to each other in a self-configuring way to transfer TCP/IP traffic(Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004) . This is similar to the present Internet architecture in fixed networks (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004).
One of the potential candidates is a hybrid random multiple access technique using CDMA or that what is referred to as orthogonal frequency division multiplex or OFDM (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). This is due to the fact that both CDMA and OFDM offer a good measure of robustness against multipath fading at the same time as they guarantee flexibility in the multi-rate and high-speed services provided (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004).
Several wireless devices are employed for communication purposes. Nowadays, these can be distinguished generally as cellular, fixed wireless, LANs, personal area networks (PANs), and ad hoc devices (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). There is also the somewhat associated category which is broadcasting. There is no assurance that this classification will still apply or be of value in the years to come. Nonetheless, it offers a relevant approach to study the present condition.
Wireless networks are multiuser systems in which data is transferred via radio waves (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). Modern wireless networks have evolved over the years. The 1G system is based on analog technology. It is designed to provide voice telephony services. The 2G system is based on digital technology. It is designed to provide better spectral efficiency, more robust communication, voice privacy, and authentication capabilities. The 2.5G system is based on 2G systems. It is designed to provide the 2G systems with a better data rate capability. Lastly, the 3G system is designed to provide multimedia services in their entirety (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004).
Mobile communication systems nowadays are considered to be a significant infrastructure. These days, they are about to evolve into wireless multimedia communication systems that can flexibly provide various types of information technology services to mobile users. In almost every decade, novel generation system emerges. Wireless access techniques developed from 1G to 2G, and to 3G so that digital technology can be fully utilized to enhance quality and frequency efficiency. The 4G systems will surface by the year 2010 (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). Its core network will be TCP/IP-based (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). For the reason that the projected frequency bands are higher than several GHz and that the data throughput over the air is also going beyond several Mbps, wireless links are severely power-limited (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). A hybrid random multiple access technique employing OFDM and CDMA may be a prospective technique (Aggelou, 2004; Basagni, Conti, Giordano, & Stojmenovic, 2004). Adopting the familiar and longtime applied cellular concept might not be a good idea. Employing wireless ad hoc networks that permit flexible set up of base stations might perhaps prove to be a more sound solution. In addition, receive functions can be separated from the base station and can be geographically distributed to cause reduction in the transmit power of portable phones.
As a final point, the 21st century will be a wireless multimedia society, wherein a combination of mobile communications, together with the information superhighway will play key roles. Before the realization of this society, very difficult and interesting challenges await and dare the human mind.