Cognitive Radio

1. Introduction
Just imagine if your cellular telephone, personal digital assistant (PDA), laptop, automobiles, and TV were smart as Radar. They will know your daily routine as well as you does. They would have things ready for you as soon as you ask. Similarly if a radio were smart, it could able to learn services available in locally accessible wireless computer networks, and could interact with those networks in their preferred protocols, so you would have no confusion in finding the right wireless network for a video download or a printout. With this it could choose frequencies and wave forms that can avoid interference and minimize the delay that we are facing with the present radio communication system.
Cognitive radio is a form of wireless communication in which a transceiver can intelligently detect which communication channels are in use and which are not in use, and instantly move into the vacant channels while avoiding the occupied ones. This optimizes the use of available radio frequency while minimizing the interference to others.
Cognitive Radio Wireless mesh networks are highly used low cost networks now a day's wireless mesh networks are mostly used in local area networks, wide area networks and metropolitan area networks. Due to their high connectivity, community and neighborhood home networking, enterprise networks and building automation. Mesh connectivity substantially improves network performance like load balancing, fault tolerance, protocol efficiency and throughput. In wireless mesh networks every mesh router act as well as mesh client but every mesh client will not act as mesh router. The unique feature of mesh nodes is they are highly mobile, due to this the nodes keep on changing their network topology. Cognitive Radio networks are an emerging multi hop, wireless networking technology where nodes are able to change their transmission or reception parameters to communicate efficiently without interfacing with licensed users. In a cognitive radio based node, the radio spectrum is dynamically accessed based on instantaneous availability. Secondary unlicensed users dynamically sense the radio spectrum and opportunistically utilize currently idle or underutilized spectrum blocks that are unused by primary users at the moment. The goal is to increase the overall utilization of the radio spectrum, which is a scarce but under-utilized resource as presented by FCC (Federal Communication Commission). The radio spectrum is dynamically sensed and sliced based on current availability and utilization. Therefore, there are no static channels any more in CORNETS and the routing metrics defined over each static channel need to be adapted. Second to handle the dynamic variation in the added dimension of spectrum, routing over CORNETS has to balance between long-term route stability and short-term opportunistic performance. Most existing routing protocol operations over mesh networks do not handle both issues. A new routing solution for CORNETS that addresses both above issues. The design of SAMER seeks to utilize available spectrum blocks by routing data traffic over paths with higher spectrum availability and is more or less a 'least-used spectrum first' routing protocol. It tries to balance between long-term route stability and short-term route performance via building a runtime forwarding route mesh. Once a route mesh that offers a few candidate routers is completed the runtime forwarding path is determined by instantaneous spectrum availability at a local node. This can lead to short term opportunistic performance gain. Our simulations show that SAMER can effectively utilize the available spectrum and achieve high end-to-end throughput. Cognitive radio networks will provide high bandwidth to mobile users through heterogeneous wireless architectures and dynamic spectrum access techniques. Cognitive radio means a radio system whose parameters are changing dynamically according to the external environment.

2. Background and History of Cognitive Radio
There have been many factors that have lead to the development of cognitive radio technology. One of the major drivers has been the steady increase in the requirement for the radio spectrum along with a drive for improved communications and speeds. In turn this has lead to initiatives to make more effective use of the spectrum, often with an associated cost dependent upon the amount of spectrum used. In addition to this there been many instances where greater communications flexibility has been required. Along the way, there have been several significant milestones along the road to develop cognitive radio technology.
The Sophistication possible in a software-defined radio has now reached the level where each radio can conceivably perform beneficial tasks that help the user, help the network, and help minimize special congestion. To support two major applications that arise an SDR's capabilities and make it a cognitive radio.
1. Spectrum management and optimizations.
2. Interface with a wide variety of networks and optimization of network resources.
3. Interface with a human and providing electromagnetic resources to avoid the human in his or her activities.
One of the major scenarios for the steady increase is in the requirement for the radio spectrum along with the drive for improved communication and speed. Intern this has lead to the make more use of the spectrum, with cost dependent upon the amount of spectrum used.
We view software defined radio as a result of an evolutionary process from purely hardware- based equipment to fully software based equipment. The process of this can be roughly described as the following three stages:
1. Hardware Driven Radio
2. Digital Radio
3. Software Defined Radio
2.1 Hardware Driven Radio:
Radio is the wireless transmission of signals through free space by electromagnetic radiation of a frequency significantly below that visible light, in the radio frequency range. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space. Information such as sound , data is carried by changing (modulating) some of the properties of radiated waves, such as their amplitude, frequency, phase or pulse width when the radio waves strike an electrical conductor, the oscillating fields include an alternating current in conductor. The information in the waves can be extracted and transformed back in to its original form at receiver side. The radio communication system sends signals by radio.
2.2 Digital Radio:
In digital radio the analog audio signals are converted in to the digital signals and the signals compressed used the formats as MP2 and transmitted using a digital modulation scheme. The main aim to develop this digital radio is
a. To increase the no. of radio programs in a given spectrum
b. To improve the audio quality
c. To eliminate fading problems in mobile environments
d. To allow additional data casting services
e. To decrease transmission power or no. of transmitters required to cover a region
Digital radio broadcasting standards may provide terrestrial or satellite radio service.
2.3 Software Defined Radio:
A software defined radio is a type of communication transceiver in which all typical functions of communication system like mixing, amplification, modulation/demodulation, and detection are implemented through software. This software is then implemented on reconfigurable hardware which could be used for more than one communication systems. All we need is swapping the software on reconfigurable hardware depending on type of communication system.
The roots of SDR design was laid in the year 1987, when the Air Force Labs(AFRL) funded the development of a programmable modem as a evolutionary step beyond the architecture of the integrated communications, navigation, and the identification architecture(ICNIA). ICNIA was a federated design of multiple radios- that is a collection of many single-purpose radios used as one piece of equipment.

Today's SDR is a general purpose device in which the same radio tuner and processors are used to implement many wave forms at many frequencies. Modern SDR also implements necessary cryptography, error correction coding as forward error correction coding, and source coding of video, voice, or data in software's as well. This type has many advantages as
a. More versatile
b. Cost effective
c. Upgraded with new software's foe new wave forms
d. New applications after sale, delivery, and installation.
2.3.1 Basic SDR
An SDR is a radio in which the properties of carrier frequency. Signal bandwidth, modulation, and network access are defined by software.SDR implements the forward error correction coding and source coding of voice, video, or data in software as well in cognitive radio networks.
Cognitive radio is one of the new long term developments taking place and radio receiver and radio communications technology. After the software defined radio which is slowly becoming more of a reality, cognitive radio (CR) and cognitive radio technology will be the next major step forward enabling more effective radio communications systems to be developed. The idea for cognitive radio has come out of the need to utilize the radio spectrum more efficiently, and to be able to maintain the most efficient form of communication for the prevailing conditions. By using the levels of processing that are available to develop a radio that is able to look at the spectrum, detect which frequencies are clear, and then implement the best form of communication for the required conditions. In this way cognitive radio technology is able to select the frequency band, the type of modulation, and power levels most suited to the requirements, prevailing conditions and the geographic regulatory requirements.
The actual definition of software defined radio from the SDR forum is 'radio in which some or the entire physical layer functions are software defined'. Several manufacturers have also found it convenient to be able to revise the software in fielded equipment without having to perform a recall, thus saving huge costs of maintenance and logistics. A new features and services can be added to the radio and expanding the market for the product.
2.3.2. Hardware Architecture of an SDR:
Hardware and Software domains of software defined radio. The span of information covered is necessarily broad. It focuses on some aspects of hardware and software that is analysis has some subtle differences.
In general Hardware is analyzed in terms of its capabilities. Cognitive radio assumes that there is an underlying system hardware and software infrastructure that is capable of supporting the flexibility demanded by the cognitive algorithm. In general, it is possible to provide significant flexibility with the radio domain. This means that context is important. This context is most readily visible in the application programming interface, but is also apparent in the strict timing requirements inherent to radio systems, and the development and debugging complexities associated with radio design. The underlying the hardware structure for system provides the maximum bounds for performance
The basic SDR hardware architecture must include the radio front end, modem, cryptographic security and application function. In addition to these for some radios we also include support for network devices connected to either the plain text side or the modem side for the radio, allowing the radio to provide network services and to be controlled by the Ethernet. Software radios will provide control for external radio frequency (RF) analog functions as antenna management, power amplifiers. The architectures that are designed for SDR must allow the RF external features to be added if or when required for a particular installation or customer requirement.
2.3.3 Software Architecture of an SDR:
The objective of the software architecture in an SDR is to place waveforms and applications onto a software-based radio platform in a standardized way. These waveforms and applications are installed, used, and replaced by other applications as required to achieve the user's objectives. To make the waveform and application interfaces standardized, it is necessary to make the hardware platform present a set of highly standardized interfaces. This way, vendors can develop their waveforms independent of the knowledge of the underlying hardware. Similarly hardware developers can develop a radio with standardized interfaces which can be variety of waveforms from standardized libraries. This way the waveform development proceeds by assuming a standardized set of interfaces for the radio hardware, and the radio hardware translates commands and status messages crossing those interfaces to the unique underlying hardware through a set of common drivers.
Software is subject to difference in structure that are similar to those difference seen in hardware domain. Software designed to support base band signal processing generally does not follow philosophy or architecture this is used for developing application level software. Underlying these differences is the need to accomplish a variety of quite different goals.
2.3.4 Design Philosophies and Patterns:
Software design has been largely formalized in to a variety of design philosophies. There are mainly four design philosophies are used for programming software defined radio.
1. Linear Programming
2. Object- Oriented Programming
3. Component Based Programming
4. Aspect Oriented Programming
Linear Programming:
Linear Programming is a methodology in which the developer follows a linear thought process for the development of the code. The process follows a logical flow. As this process follows a logical flow this type of programming is dominated by conditional flow control and loops. C is the most popular Linear Programming today, with assembly development reserved for a few brave souls who required truly high speed without the overhead incurred by a compiler.
Object Oriented Programming:
OOP is a striking shift from Linear Programming. Linear Programming has data structures. It also contains variables that contain an arbitrary composition of native types such as float or integer. Object Oriented Programming extends the data structure concept to describe a wole object. Object is a collection of member variables and functions that can operate on those member variables. The difference inherit in OOP have dramatic implications for the development of software. There are several languages that support Object oriented programming languages. The two important languages are Java and C++. There are several other languages today that are OOP languages.
Component-Based Programming:
It is a suitable extension of the OOP. In thus language the concept of an object is constrained, instead of allowing any arbitrary structure for the object. Under CBP the basic unit is a component. The component comprises one or more classes and is completely defined by its interfaces and its functionality. The primary component of CBP is to create stand-alone component that can be easily interchanged between implementation. CBP is a coding style, and there are no mainstream languages that are designed explicitly for CBP. If any one of the components fails, it needs to take appropriate action to prevent further mal functions.
Aspect-Oriented Programming:
AOP allows for the creation of relationships between different classes. The relationships are arbitrary but they can be used to encapsulate the housekeeping code that is needed to create compatibility between two classes. The relationship class encompasses an aspect of class thus context can be provided through the use of aspects. AOP acquires the creation of new language constructs that can associate an aspect to a particular class. There are several languages as Aspect j, Aspect C++, and Aspect #, among others.
2.3.5 Cognitive Radio: The Technologies Required
Reliable cellular technology is now in widespread use, and new applications are driving in industry. Where these applications go next is a paramount importance for product developers. CR is the name adopted to refer to new technologies believed to enable some of next major wireless applications. Processing resources and other critical enabling technologies for wireless applications now are available.
2.3.6 Radio Flexibility and Capability:
More than 40 different types of military radios are currently in operation. These radios have diverse characteristics: therefore a large number of examples can be drawn from the pool of military radios. The first radios deployed in large number were single purpose solution. They were capable of one type of communication (analog voice). Analog voice communication is not particularly efficient for communicating information. The fixed point solutions have been replaced with higher data rate and voice capable radios with varying degrees of software integration. This design change has enabled interoperability, upgradability and portability. Basing CR on an SDR platform is not a requirement, but it is practical approach because SDR flexibility allows developers to modify existing systems with little or no new hardware development, as well as to add cognitive capabilities.

Federal Communications Commission (FCC) adapted the definition for software defined radios as a 'Communication device whose attributes and capabilities are developed and/or implemented in software'. The common characteristics of software capable radios are fixed modulation capabilities, relatively small number of frequencies, limited data rate and data rate capabilities and finally the ability to handle data under software control. Some of the examples of software capable radios are
1. SINCGARS ( Single-Channel Ground and Airborne radio System)
2. PLRS (Position Location reporting System)
3. AN/WSC-3
4. AN/ARC-164 Have Quick II
5. AN/ARC-220
6. AN/VRC-99
7. LST-SE
8. AN/PRC-6725 or Leprechaun
9. MBTIR ( Multiband Intra/Inter team Radio)
10. CSEL(Combat Survivor/Evader Locator)
11. MIDS ( Multi function Information Distribution System)
2.3.7 Examples of SDR:
Other products related to SDR include GNU Radio and Vans any wave base station.
GNU Radio: it is a free software toolkit that is available on internet. It allows anyone to build a narrowband SDR. Using a Linux based computer a Radio Frequency (RF) front end and an Analog to Digital Converter (ADC), one can build a software defined receiver. By adding a Digital to Analog Convertor (DAC) and possibly a power amplifier one can build a software defined transmitter.
Vans any wave Base Station: it is a software defined system that uses commercial off-the shelf (COTS) hardware and proprietary software to build a wireless cellular infrastructure. The goal is simultaneous support for multiple standards, reduced operating expenses, scalability and future proofing (cost-effective migration).

Source: Essay UK - http://doghouse.net/free-essays/information-technology/cognitive-radio.php


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