Wireless Networks

Wireless Networks

Contents:

1.     Wireless LAN

2.       IEEE 802.11 Standards

3.     Architecture

4.     Services

5.     Mobile Ad hoc Networks

6.       WiFi and WiMAX

7.     Wireless Local Loop

Pre requisite Discussion :

In this chapter we present several wireless local area network (WLAN) technologies. This constitutes a fast-growing market introducing the flexibility of wireless access into office, home, or production environments. WLANs are typically restricted in their diameter to buildings, a campus, single rooms etc. and are operated by individuals, not by large-scale network providers The global goal of WLANs is to replace office cabling, to enable tether less access to the internet and, to introduce a higher flexibility for ad-hoc communication in, e.g., group meetings. The following points illustrate some general advantages and disadvantages of WLANs compared to their wired counterparts.

1.Wireless LAN :

Concepts:

WLAN Some advantage of WLAN (or) Characteristics of WLAN

Flexibility

Within radio coverage, nodes can communicate without further restriction. Radio waves can penetrate walls, senders and receivers can be placed anywhere. Sometimes wiring is difficult if firewalls separate buildings. Penetration of a firewalls is only permitted at certain points to prevent fire from spreading too fast.

Planning

Only wireless ad-hoc networks allow for communication without previous planning any wired network needs wiring plans. As long as devices follow the same standard they can communicate. For wired networks, additional cabling with the right plug and probably interworking units such as switches have to be provided

Design

Wireless networks allow for the design of small, independent devices which can for example be put into a pocket. Cables not only restrict users but also designers of small PDAs, notepads etc. Wireless senders and receivers can be hidden in historic buildings. i.e., current networking technology can be introduced without being visible.

Robustness

Wireless networks can survive disasters e.g., earthquakes or user pulling a plug. If the wireless devices survive people can still communicate. Networks requiring a wired infrastructure will usually break down completely.

Cost

After providing wireless access to the infrastructure via an access point for the first user, adding, additional users to a wireless network will not increase the cost.

Significance:

This helps to know the characteristics and features of using Wireless LAN

2. IEEE 802.11

The three main sections of this chapter present the IEEE standard for WLANs, IEEE 802.11, the European ETSI standard for a high-speed WLAN with QoS support

3. SYSTEM ARCHITECTURE

Wireless networks can exhibit two different basic

Information Based

Ad0-hoc

Infrastructure based:

STA (Station)

Several nodes called stations (STA)

STA are connected to access points (AP) stations (or) terminals with access mechanisms to the wireless medium and radio contact to the AP.

BSS (Basic Service Set)

A Group of stations using the same radio frequency..

The example two BSSs (i.e.) BSS1 and BSS2 - which are connected via a distribution system.

AP (Access Point)

A distribution system connects several BSSs via the AP to form a single network and thereby extends the wireless coverage area.

Distributed System

Interconnection network to form one logical network (ESS :- Extended Service Set) based on several BSS.

Extended service set (ESS) has its own identifier, the ESSID.

The ESSID is the name  of a network and is used to separate different networks. Without knowing the ESSID it should not be possible to participate in the WLAN.

Portal

Bridge to other wired networks.

Significance:

The distribution system connects the wireless networks via the APs with a portal which forms the interworking unit to other LANs.

4. Services

Concept:

Stations can select an AP and associate with it.

The APs support roaming ie. Changing access points

Significance:

The distribution system handles data transfer between the different APs.

APs provide

Synchronization within a BSS

Support power management and

Can control medium access to support time bounded service

5. Mobile Ad hoc Networks Concept:

An ad-hoc network is a local area network (LAN) that is built spontaneously as devices connect. Instead of relying on a base station to coordinate the flow of messages to each node in the network, the individual network nodes forward packets to and from each other. In Latin, ad hoc literally means "for this," meaning "for this special purpose" and also, by extension, improvised or impromptu.

The Ad Hoc Networks is an international and archival journal providing a publication vehicle for complete coverage of all topics of interest to those involved in ad hoc and sensor networking areas. The Ad Hoc Networks considers original, high quality and unpublished contributions

addressing all aspects of ad hoc and sensor networks. Specific areas of interest include, but are not limited to:

·        Mobile and Wireless Ad Hoc Networks

·        Sensor Networks

·        Wireless Local and Personal Area Networks

·        Home Networks

·        Ad Hoc Networks of Autonomous Intelligent Systems

·        Novel Architectures for Ad Hoc and Sensor Networks

·        Self-organizing Network Architectures and Protocols

·        Transport Layer Protocols

·        Routing protocols (unicast, multicast, geocast, etc.)

·        Media Access Control Techniques

·        Error Control Schemes

·        Power-Aware, Low-Power and Energy-Efficient Designs

·        Synchronization and Scheduling Issues

·        Mobility Management

·        Mobility-Tolerant Communication Protocols

·        Location Tracking and Location-based Services

·        Resource and Information Management

·        Security and Fault-Tolerance Issues

·        Hardware and Software Platforms, Systems, and Testbeds

·        Experimental and Prototype Results

·        Quality-of-Service Issues

·        Cross-Layer Interactions

·        Scalability Issues

·        Performance Analysis and Simulation of Protocols

Significance:

It is used for mobile nodes to communicate without any infrastructure.

6. WIFI and WIMAX :

Concepts:

These are used for data transfer and wireless communication such like Bluetooth, but it can connect devices in higher range. WiMAX is similar to the wireless standard known as Wi-Fi, but on a much larger scale and at faster speeds. A nomadic version would keep WiMAX-enabled devices connected over large areas, much like today.s cell phones. We can compare it with Wi-Fi based on the following factors.

Range

Wi-Fi typically provides local network access for around a few hundred feet with speeds of up to 54 Mbps, a single WiMAX antenna is expected to have a range of up to 40 miles with speeds of 70 Mbps or more. As such, WiMAX can bring the underlying Internet connection needed to service localWi-Fi networks.

Scalability

Wi-Fi is intended for LAN applications, users scale from one to tens with one subscriber for each CPE device. Fixed channel sizes (20MHz).

WiMAX is designed to efficiently support from one to hundreds of Consumer premises equipments (CPE)s, with unlimited subscribers behind each CPE. Flexible channel sizes from 1.5MHz to 20MHz.

Bit rate

Wi-Fi works at 2.7 bps/Hz and can peak up to 54 Mbps in 20 MHz channel. WiMAX works at 5 bps/Hz and can peak up to 100 Mbps in a 20 MHz channel.

Quality of Service

Wi-Fi does not guarantee any QoS but WiMax will provide your several level of QoS. As such, WiMAX can bring the underlying Internet connection needed to service local Wi-Fi networks. Wi-Fi does not provide ubiquitous broadband while WiMAX does.

Significance:

Used real time in organizations and used in smart phones.

7. Wireless Local Loop

Concept:

The first step in the receiver involves demodulating the received signal. This is achieved using the same carrier as the transmitter reversing the modulation and results in a signal with approximately the same bandwidth as the original spread spectrum signal. Additional filtering can be applied to generate this signal. While demodulation is well known from ordinary radio receivers, the next steps constitute a real challenge for DSSS receivers, contributing to the complexity of the system. The receiver has to know the original chipping sequence, i.e., the receiver basically generates the same pseudo random sequence as the transmitter. Sequences at the sender and receiver have to be precisely synchronized because the receiver calculates the product of a chip with the incoming signal. This comprises another XOR operation as explained in section 3.5, together with a medium access mechanism that relies on this scheme. During a bit period, which also has to be derived via synchronization, an integrator adds all these products. Calculating the products of chips and signal, and adding the products in an integrator is also called correlation, the device a correlator. Finally, in each bit period a decision unit samples the sums generated by the integrator and decides if this sum represents a binary 1 or a 0. If transmitter and receiver are perfectly synchronized and the signal is not too distorted by noise or multi-path propagation,. On the receiver side, this signal  is XORed bit-wise after demodulation with the same Barker code as chipping sequence.

Applications:

∑     Used to provide data coverage to a small area with high speed with WiMax

∑     Provides an infrastructure for establishing a mobile communication