One of the most challenging and interesting recent trends is integration of computing equipment and devices by using wireless communication technologies. Resulting networks, known as wireless computing systems, enhance functionality of computing equipment by freeing communication from location constraints of wired computing systems.
Types of Wireless Computing Systems
Wireless computing systems are classified broadly into two categories:
1. Fixed wireless systems – These wireless computing systems support little or no mobility of their computing equipment. For example, a LAN can be set up using wireless technology to get rid of hassles of cables. The LAN will work as a conventional wired LAN except for the difference that it does not need any cabling and the communication bandwidth may be much lower.
2. Mobile wireless systems – These wireless computing systems support mobility of computing equipment used to access resources of wireless network. In turn, these systems support mobility of users and allow mobile users to access information from anywhere and at anytime. Resulting computing environment is often called mobile computing or nomadic computing. It no longer requires a user to maintain a fixed position in network, and enables almost unrestricted user mobility. Computing equipment used commonly in mobile wireless systems include smart phones, personal digital assistants (PDAs), and pagers with Internet access.
Issues in Wireless Computing Systems
Wireless computing systems communicate by modulating radio waves or pulsing infrared light. Wireless communication is linked to the wired network infrastructure by stationary transceivers. The area covered by an individual transceiver’s signal is known as a cell. Cell sizes very widely. For instance, an infrared transceiver can cover a small meeting room, a cellular (mobile) phone transceiver has a range of a few miles, and a satellite beam can cover an area more than 400 miles in diameter.
Successful use of wireless computing systems faces several challenges. The important ones among them are:
1. Lower bandwidths – The channel capacity typically available in wireless networks is much lower than that available in wired networks due to limited spectrum availability, power restrictions, and noise levels.
2. Variable bandwidths – The limited bandwidth of a mobile wireless system is also variable depending on location. Channel reuse, therefore, must be an integral part of the system in order to provide service to as many potential subscribers as possible.
3. Higher error rates – Noise and Interference have more impact on wireless computing systems than on wired computing systems. This, in turn, increases communication latency resulting from retransmissions, retransmissions time-out delays, and error-correction protocol processing.
4. Increased security concerns – Security is a greater concern in wireless systems than in wired systems since information may be traveling in free space (with the exception of infrared LANs). Moreover, a stronger level of authentication is needed in a mobile environment where network nodes can potentially join or leave a network dynamically.
5. Dynamically changing network – The topology of a mobile wireless network changes dynamically due to movements of mobile nodes, resulting in dynamic connections and disconnections of nodes. Moreover, the number of mobile nodes in a network cell varies dynamically, and large concentrations of mobile users, say, at conventions and public events, may overload network capacity.
6. Lost or degraded connections – Mobility in a mobile wireless system can cause wireless connections to be lost or degraded. While communicating and moving simultaneously, users may travel beyond the coverage of network transceivers or enter area of high interference.
7. Support for routing and location management functions – Mobile wireless systems also need to provide support for routing functions (to maintain communication with mobility) and location management functions (to keep track of locations of mobile nodes).
8. Limited power – Mobile nodes are battery operated and hence have limited power available. As a result, the power required for transmitting and receiving must be minimized in mobile wireless systems.
Wireless computing systems have several interesting and important applications such as:
- Mobile e-commerce applications, popularly known as m-commerce applications.
- Web surfing using wireless devices.
- Access to corporate data by sales people and other frequent travelers while they are traveling.
- Mobile video-on-demand applications.
- Location-sensitive services such as programs that help finding nearby movie theaters or restaurants in an unfamiliar location.
Over the years, several wireless technologies have been introduced. Out of these, some of the most popular ones are described below.
1. 2G and 3G Technologies
The early mobile phones used first-generation technology that was analog, circuit-based, narrowband, and suitable only for voice communications. Then came the second-generation wireless-networking technology (popularly known as 2G technology) that was digital, circuit-base, and narrowband but suitable for voice and limited data communications.
Currently, we have the third-generation wireless-networking technology (popularly known as 3G technology) that is suitable for voice and advanced data applications, including online multimedia and mobile e-commerce.
2. Wireless LANs
Wireless Local Area Networks (WLANs) are like traditional LANs having a wireless interface to enable wireless communication among the equipment that are part of the LAN. A wireless LAN may be further connected to a more extensive fixed network such as LAN, WAN, the Internet, etc. The primary component of a wireless LAN is the wireless interface card that has an antenna.
This interface card can be connected to the mobile unit as well as to the fixed network. Wireless LANs have limited range and are designed to be used only in local environments such as a building, hallway, park, or office complex. The main advantage is the flexibility and mobility supported by a wireless LAN; bandwidth considerations are secondary, IEEE 802.11 is a popular WLAN standard. Wi-Fi is the embedded technology of WLAN based on the IEEE 802.11 standard.
It was originally developed to be used for mobile computing devices (such as laptops) in LANs. However, it is now increasingly used for many other services, including Internet and VoIP phone access, gaming, and basic connectivity of consumer electronics products such as televisions, digital cameras, and DVD players.
WiMAX stands for Worldwide Interoperability for Microwave Access. It is a technology based on the IEEE 802.16 standard that aims at WMANs (Wireless Metropolitan-Area Networks). Hence, WiMAX aims to provide wireless data communication over long distances in different ways, including point-to-point link and full mobile cellular type access.
WiMAX has proved to be a very useful technology for providing wireless broadband access in those areas where we do not have a good copper network or cable TV network (often referred to as last mile connectivity). WiMAX has the added advantage of interoperability and economies of scale due to international standardization. WiMAX currently operates in the frequency band of 3.3 to 3.4 GHz.
4. Wireless Local Loops (WLLs)
Wireless Local Loops (WLLs) technology supports fixed wireless systems. WLLs provide several MHz of bandwidth that can be used of high-speed Internet access and data transfer in addition to the basic telephone service. These loops allow long-distance carriers to bypass the existing wired local loops owned by local telephone carriers (which may result in the saving of tremendous access charges).
Due to this reason many long-distance companies in advanced countries (like the U.S.) are looking to build their WLLs to avoid paying access charges. Moreover, in developing nations where laying thousands of miles of copper cable is impractical, WLLs can be used to provide telephone and low-speed data transfer services.
5. Radio-router Technology
Radio-router Technology is an emerging wireless technology designed to make links in an IP network mobile. It uses a radio-transmission framework for packet-based, broadband, IP wireless communications.
A radio-router network can be built on top of an existing IP infrastructure, rather than from the ground up like a 3G network. Since IP network technology is already well developed and inexpensive, radio-router systems are relatively easy, quick, and economical to implement.
6. Multihop Wireless Networks
In most wireless network environments, radio channel is used to connect mobile equipment to a base station in a single hop. The base station itself is connected to a wired infrastructure.
Consider an environment where there is no wired infrastructure yet connectivity must be maintained among users who can move around arbitrarily and can at times not be in direct transmission range of each other. Multihop wireless networks, also known as instant infrastructure systems, provide wireless communications capability is such environments.
7. Wireless Application Protocol (WAP)
We saw in the discussion above that many different wireless access technologies exist that are not interoperable. Designing and building networks and applications for each technology would certainly be a very difficult job for developers.
With the proliferation of the Internet and wireless communications devices, Internet access using mobile devices has become important for anywhere, anytime information access capability. However, redesigning of all web sites to support downloading of information by mobile users is certainly not feasible.
To address these issues, researchers started working towards the development of a technology that could allow development of applications that are independent of the underlying wireless access technology and that could also enable access of information from existing web sites using mobile devices. The result of this was wireless application protocol (WAP).