IEEE 802.22 WRAN (Cognitive Radio)

Brian Pentz, Raymond Chen, Kjell Peterson

 

Introduction

 

Software Defined Radio

 

There is a growing demand in today’s economy for radio-spectrum based communications.  This causes an increasing demand for bandwidth in the finite radio spectrum. 

 

Often, there are spectrum bands that are only used part of the time, and the rest of the time that frequency band is being wasted.  Cognitive radio seeks to fill these wasted spaces with useful communications.

 

The majority of communications devices active today have static carrier frequency and amplitude, defined by hardware.  In such devices, changing these operating parameters means changing the hardware. 

 

Software defined radios can change these operating parameters rapidly, jumping from one frequency to another and varying the output amplitude.  For example, the military uses radios that rapidly change their carrier frequency so that the enemy cannot easily intercept their communications.

 

 

Cognitive (Spectrum Sensing) Radio

 

Cognitive radio is a more domestic application of a software defined radio.  The basic idea of cognitive radio is that it analyzes a portion of the radio frequency spectrum, determines which frequency bands aren’t being used, and broadcasts its data over these unused frequency bands.  This improves the efficiency of standard communications by using unused bandwidth in the radio spectrum.

 

 

 

 


Wireless Broadband Internet in the Television Spectrum

 

 

IEEE 802.22 is a standard that taps into the T.V. spectrum and uses it for wireless broadband internet services.  In this region, wireless broadband internet can be broadcast up to 40km, depending on the terrain.  This is ideal for sparsely populated areas, where it isn’t worth the cost to lay ground cables for internet.

 

 


Frequency Band Allocation

 

The 802.22 standard uses TV broadcasting bands in UHF and VHF.

 

 

 

 

 


The Standard Body

 

IEEE is the standard body.

 

The standard website is…

 

http://www.ieee802.org/22/

 

There is currently no official documentation regarding the Physical Layer.

 

 

 

 

 


System Overview

 

The Basic Block Diagram of a Cognitive Radio System:

·              The PHY (Physical Layer) Block is where Digital Signal Processing is Performed.

·              The MAC (Medium Access Control Layer) Block Determines the Spectrum Available and the Spectrum to be Utilized.

 


The PHY Layer Performs the Signal Generation and Analysis Tasks of the System

 

 

·              PHY Block Diagram : Transmitter

 

 

 

 

·              PHY Block Diagram : Receiver

 


Summary of PHY parameters

Channel Bandwidth

5 MHz

Modulation

QPSK/16-QAM/64-QAM

Coding

Conv./Conv. Turbo

(r = 1/2, 2/3, 3/4)

Duplex Method

Time Division Duplexing (TDD)

FFT Size

512

OFDMA Symbol Time

100.8 µs (11.2 µs guard)

Frame size(s)

5 ms, 10 ms

(49, 98 OFDM symbols, respectively)

Diversity Scheme

Space Time Coding (STC)

+ Beamforming

(for enhanced coverage and range)


Error control coding

 

Turbo Codes

 

Turbo codes are a class of recently-developed high-performance error correction codes finding use in deep space satellite communications and other applications where designers seek to achieve maximal information transfer over a limited-bandwidth communication link in the presence of data-corrupting noise.

 

Simple Viterbi-decoded convolutional codes are now giving way to turbo codes, a new class of iterated short convolutional codes that closely approach the theoretical limits imposed by Shannon's theorem with much less decoding complexity than the Viterbi algorithm on the long convolutional codes that would be required for the same performance. Turbo codes have not yet been concatenated with solid (low complexity) Reed-Solomon error correction codes.

 

Constellations

 

QPSK, 16-QAM, and 64-QAM Constellations are used, depending on location from the Antenna

 

QPSK                                                                          

 

16-QAM   

 

64-QAM

 

 

 

 


IQ Modulation

 

Cognitive Radio Uses QPSK and QAM Modulation.  The Specific I and Q parts for each Modulation Type are Unknown right now.


Pulse Characteristics

 

Ultra short, shape-changing pulse

 

The radio knows what to do, where to go and how to make the operating changes without the user’s awareness and without interfering with other communication equipment.

Cognitive UWB Radio conveys digital binary information over a serial of ultra-short pulse waveforms.

It is capable of dynamically reacting to the spectral environment by seamlessly implementing a unique pulse waveform through the modification of its generation algorithm.

Multi-access Broadcast Technologies

 

·        Cognitive radio uses OFDMA/TDMA.

·        Sub-channels are allocated in the Frequency Domain, and OFDM Symbols allocated in the Time Domain.

 

 

 

Downlink

 

Uplink

 

 

Multi-antenna technology

 

Multi-antenna technology is not used in 802.22.


The Major Players

On-going Standardization

·        Standardizing cognitive radio is still very much on-going.

·        Standardization is expected by 2009.

·        The concept of the ‘cognitive’ radio was originated by Defense Advance Research Products Agency (DARPA) scientist Dr. Joseph Mitola.

·        The SDR Forum, the FCC and industry partners such as General Dynamics, Vanu, Rockwell Collins are major players in this technology.

The SDR Forum

The Software Defined Radio Forum (SDR Forum) is an independent technical council comprising industry scientists, engineers and regulators who are working on the regulatory, technical and operational aspects of software defined radios. Through the Forum’s work and with industry development, software defined radios are making it possible to change waveform properties and applications while operating in the field via the addition or upgrade of software. For SDRs, reprogramming or upgrading a single radio or a radio network takes about as much effort as upgrading a computer’s operating system or program options.

The SDR Forum continues to develop and refine the standards by which upgrades and modifications can be performed so that evolutionary technology can be harmoniously integrated into the radio once it has been sold and installed. The inherent flexibility of software defined radios allows equipment developers, and eventually users, to enhance the operating capabilities of their equipment. As an additional benefit, because software defined radios can allow upgrading, bug fixing and the delivery of additional functionality, the customer receives incremental value on the radio, considerably improving cost-effectiveness.

The U.S. Navy

For its part, the U.S. Navy is likely to be the largest consumer of software defined radios with the military’s Joint Tactical Radio System Initiative (JTRS) radios following closely behind. For the Navy, the software-based Digital Modular Radio (DMR) is replacing a roomful of radios with a single rack of DMRs. The DMR (Figure 1) is a four-channel, full-duplex system that is essentially four radios in one. Currently operating on submarines and surface ships around the world, the DMR (AN/USC-61) is successfully demonstrating the viability of software defined radios on active duty.