Saturday, May 7, 2011

Wireless LAN


Wireless LAN

Wireless local area networks (LAN) are playing a major role in the information technology revolution. They are finding their way into a wide variety of markets including financial sectors, corporations, health care, and education. For example, wireless devices are used in New York Stock Exchange for trade reporting. Employees in a company can initiate a wireless video conference instantaneously without having to go through the tedious procedure of connecting the communicating devices using wires. Indeed, according to a research study by Frost and Sullivan, the wireless LAN market is set to reach $697.7 million in 2003.

One of the factors that could have had an adverse impact on the market for wireless devices, is the interoperability issue between products developed by different vendors. However, the IEEE has developed the 802.11 standard, compliance with which should alleviate this issue. Other factors that will impact the long-term success of wireless LAN largely depends on improving the technology, reducing installation costs, and predicting the market and customer needs. While initial costs to install a wireless LAN infrastructure may be greater than its wired counter-part, in the long-term, benefits due to the wireless network can be significantly higher when the users are constantly mobile.

Wireless LAN Classifications

Wireless LAN can be broadly classified into two categories: ad hoc wireless LAN and wireless LAN with infrastructure. In ad hoc networks, several wireless nodes join together to establish a peer-to-peer communication as shown in Figure 1. They typically require no administration. Networked nodes share their resources without a central server. In wireless LAN with infrastructure, there is a high-speed wired or wireless backbone. Wireless nodes access the wired backbone through access points (see Figure 2). These access points allow the wireless nodes to share the available network resources efficiently.

Ad hoc wireless LAN

Figure 1: Ad hoc wireless LAN.

Wireless Critical Challenges

Since wireless devices need to be small and wireless networks are bandwidth limited, some of the key challenges in wireless networks are:
  • data rate enhancements;
  • minimizing size and cost;
  • low power networking;
  • user security.
Enhancing Data Rate

Wireless LAN with infrastructure

Figure 2: Wireless LAN with infrastructure.

Improving the current data rates to support future high speed applications is essential, especially, if multimedia service are to be provided. Data rate is a function of various factors such as the data compression algorithm, interference mitigation through error-resilient coding, power control, and the data transfer protocol. Therefore, it is imperative that manufacturers implement a well thought out design that considers these factors in order to achieve higher data rates.

Data compression plays a major role when multimedia applications such as video conferencing is to be supported by a wireless network. Currently, compression standards such as MPEG-4 produce compression ratios of the order of 75 to 100. The challenge now is to improve these data compression algorithms to produce high quality audio and video even at these compression rates. Unfortunately, highly compressed multimedia data is more sensitive to network errors and interference and this necessitates the use of algorithms to protect sensitive data from being corrupted. Efficient error control algorithms with low overhead must be explored. Another way to enhance the data rates would be to employ intelligent data transfer protocols that adapt to the time-varying network and traffic characteristics.

Low Power Design

The size and battery power limitation of wireless mobile devices place a limit on the range and throughput that can be supported by a wireless LAN. Bottlenecks in the wired portion of a LAN also affect the throughput.

The complexity and hence the power consumption of wireless devices vary significantly depending on the kind of spread spectrum technology being used to implement the wireless LAN. Normally, direct sequence spread spectrum (DSSS) based implementations require large and power-hungry hardware compared to frequency hopped spread spectrum (FHSS). They tend to consume about two to three times the power of an equivalent FHSS system. But, the complex circuitry provides better error recovery capability to DSSS systems compared to FHSS. FHSS is generally less tolerant to multipath and other interference. In fact, there is a constant debate going on both in academia and the wireless industry regarding the pros and cons of DSSS versus FHSS. It is the right time for researchers and developers to approach these issues in wireless LAN technologies together and from a global perspective. This may also enable different vendors to develop wireless LAN technologies that can co-exist and operate together.

Security in wireless networking

Security is a big concern in wireless networking, especially in m-commerce and e-commerce applications. Mobility of users increases the security concerns in a wireless network. Current wireless networks employ authentication and data encryption techniques on the air interface to provide security to its users. The IEEE 801.11 standard describes wired equivalent privacy (WEP) that defines a method to authenticate users and encrypt data between the PC card and the wireless LAN access point. In large enterprises, an IP network level security solution could ensure that the corporate network and proprietary data are safe. Virtual private network (VPN) is an option to make access to fixed access networks reliable. Since hackers are getting smarter, it is imperative that wireless security features must be updated constantly.

In conclusion, wireless LAN technologies still have a long way to go. Both fundamental and practical problems still persist in this area. Therefore, it may be crucial to develop innovative and commercially viable solutions to some of the key issues and challenges discussed in this article to ensure the success of emerging wireless applications.

R. Chandramouli
Email: rchandr1@stevens-tech.edu
Web: www.ece.stevens-tech.edu/~mouli

K.P. Subbalakshmi
Email: ksubbala@stevens-tech.edu
Web: www.ece.stevens-tech.edu/~suba




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