Cognitive Radio – Three Models for Spectrum Sharing

Continuing in our series on Cognitive Radio, I found a nice summary primer on Cognitive Radio and Software Defined Radio here. The emergence of DSP and higher speed analog-to-digital convertors gives Software Defined Radio techniques an advantage over the traditional demodulator block.

The paper goes on to describe three models for spectrum sharing. They are command and control, exclusive use, and unlicensed use. As for exclusive use, from time to time the US government auctions off spectrum to private companies who can do what they want with the spectrum – similar to property rights. Command and control has been the standard for spectrum usage in the US as bandwidth is licensed to specific users for a specific use case. Finally, the ISM band is an example of unlicensed use in which spectrum is made available on a first-come, first-served basis. There is no guarantee of interference protection.

The paper goes on to discuss how Cognitive Radio techniques must be able to work in all three of these cases. We’ll explore these three methods in the coming weeks.


Best regards,
Hall T.

Cognitive Radio – Spectrum Monitoring is the Key to Practical Applications

The key to developing practical application with Cognitive Radio is a greater awareness of the spectrum and how it’s currently being used. A thorough monitoring of the spectrum over a period of time (say weeks and months) will create a database of date/time/frequency stats that can be used to more reliably predict the future use of the spectrum. In this article paints a picture of a world in which all spectrum users rely on cognitive radio techniques to find and use spectrum without much regard for pre assignment.

Part of the solution is to develop devices and practices that cooperate with each other. In other words all devices on the network should check the spectrum and monitor it so it can share spectrum cooperatively.

Best regards,
Hall T.

Spectral Awareness – How to Implement

Cognitive Radio promotes the concept of using unused spectrum to increase available bandwidth. The basic techniques for finding and managing a portion of spectrum are listed below:

Step 1: Find a frequency. Using Adaptive Frequency techniques, a series of frequencies are scanned.

Step 2: Find an unused time slot in between a periodic user. Typically an Adaptive TDMA technique is used to check the availability of the frequency by monitoring it through several cycles. Only measuring the energy in the channel doesn’t give an accurate reading as noise can appear to be a signal.


Step 3: Use spatial techniques to monitor the spectrum -= The two main techniques are - beam steering and null steering which changes the main lobe of the radiation pattern to focus in a specific area.

Step 4: Use Adaptive bit loading based on Signal to Noise Ratio to insert a signal into the unused spectrum. OFDM techniques can be used that fit the time-frequency/hole.

Step5: Perform interference suppression and multiuser decomposition.

Adaptive Power Control and Ad-Hoc Networks are important for managing the above steps.

Best regards,
Hall T.

Cognitive Radio – The Need it Fills

The need for Cognitive Radio techniques will always be with us as long as we’re short of RF bandwidth. In this article the author propose using licensed bandwidth while it is not currently being used. Game theory techniques can be used to monitor what the other users are doing. Of course, the licensed user gets first priority but if it’s not using the spectrum then others may be able to use it.

The FCC is actively studying Cognitive Radio to make better use of the spectrum and better devices that can adapt to the current conditions. In addition to increasing the spectrum, the FCC hopes to improve interoperability among public service units. Current systems give each public service a dedicated, full-time frequency band. Cognitive radio techniques could let one service use the unused bandwidth of another. It could also be used as a repeater between one public service to another. Cognitive radio could monitor and help translate signals to another public service.

The other advantage is increased reliability in terms of fewer dropped calls, blackout spots, and more. If the communication channel becomes noisy, a cognitive radio-based system could switch the call to a better channel.

Best regards,
Hall T.

Cognitive Radio—the Basics

Cognitive Radio according to Wikipedia is the dynamic modification of the RF signal based on the spectrum, the user behavior, or the state of the network. It’s the logical next step after software defined radio in which the radio usage adjusts to the user and network’s needs. The idea here is that some parts of the spectrum are underutilized. By using cognitive radio techniques, unlicensed users can make use of licensed frequencies that have unused capacity—which is called Licensed Band Cognitive Radio.

There are variations of cognitive radio. The first is called Spectral Sensing Cognitive Radio in which only the radio frequency is monitored. Spectral sensing has been applied to TV channels in order to provide more bandwidth for high definition as well as emergency networks. The technique requires more than just detecting the energy in a channel. It requires a series of nodes to exchange information which is why research is moving towards Cognitive Networking.

The four main functions of Cognitive Radio are

1. Spectrum sensing –finding unused spectrum.
2. Spectrum management – finding the best available spectrum to use based on quality of service criteria.
3. Spectrum mobility –allowing for the shift from one frequency to another
4. Spectrum sharing – scheduling and sharing spectrum in a fair manner


Best regards,
Hall T.

Batteries Use Nanostructure Materials to Generate Power

As the need for portable power explodes due to the increasing number of mobile devices and the shift to alternative energies, battery technology receives substantial research funding and focus. In addition to improving safety, environmental impact, longevity, and power density, so battery makers seek ways to make the battery more malleable so they fit with portable devices and mobile applications.

Nanomaterials provide the structure for batteries. Using carbon nanotubes researchers are able to infuse paper with the ability to make a complete battery with the carbon acting as the electrodes. Medical device researchers are looking to sweat or blood as a potential electrolyte. Thus, by touching the paper, a person makes the paper a complete battery system. Medical researchers see applications in implantable devices in which the carbon nanotubes could be implanted just below the skin so the human body becomes the recharge mechanism for powering a defibrillator for example.

Another nano technique is to use copper nanorods as the active material and attach them to sheets of copper foil. This increases the energy capacity by increasing the surface area of the nanorods.

Application of these technologies can be done with fairly traditional machines. In this example the nanorods are treated like fibers that can be woven into the fabric of a soldier’s uniform and can recharge itself.

Another technology in the research phase is electrowetting which according to Wikipedia uses nanostructured materials to combine the electrolyte material into the electrode space. mPhase proposes to use the technology to power semiconductor based devices through the use of superhydrophobic techniques which combines a liquid electrolyte and active electrode material.

Best regards,
Hall T.

Higher Density Lithium-Ion Batteries for Hybrid Vehicle Use

Lithium ion batteries use cobalt for the positive electrode to achieve higher density. You can see a more detailed diagram here of a typical configuration along with a range of other materials used.

The key challenge is controlling thermal runaway when the separator material fails. That’s when the battery overheats. One solution is to add phosphate or other materials into the battery to help stabilize it.

For the hybrid vehicle application, Lithium-Ion is the current choice with research effort going into increasing the density of the battery so it lasts longer at a lower weight and size. Across the board, vendors are making higher density lithium-ion batteries including Hitachi, and Panasonic, to name a few.

There are other ways of improving Lithium-ion battery capability. In this paper, the authors use nanostructures to coat the cathode to increase the discharge factor of a battery. Another approach uses organic materials for the cathode instead of lithium metal oxides which makes the battery lighter and more environmentally friendly.

Best regards,
Hall T.