Say hello to Cognitive Radio technology! The future of wireless!


Delivery of web content and video over next-generation wireless networks will require large amounts of bandwidth. The existing wireless spectrum in most countries, however, has already been fully allocated. Optimizing the use of this spectrum is therefore necessary to allow further development of wireless services.

One promising approach is called ’cognitive radio’, whereby a primary, licensed user and an unlicensed, secondary user share a wireless spectrum. However, adoption of this method has been hindered by the inability to avoid signal interference, which must be kept low. Now, Rui Zhang and Ying-Chang Liang, from the A*STAR Institute for InfoComm Research in Singapore and Feifei Gao, currently of Jacobs University in Germany, have proposed a practical and efficient scheme to determine and avoid interference on channels shared by multiple users1.

The team had previously proposed an approach for minimizing interference called ‘cognitive beamforming’. Under this scheme, a secondary radio uses multiple antennas—each transmitting at different powers—to modify its transmission parameters in a manner that avoids interference. However, this proposal required perfect and complete information about the primary radio and its channels to avoid interference, which made the scheme significantly less practical.

Under Zhang and co-workers’ new proposal, this stringent requirement is avoided because the secondary radio can ‘learn’ about the primary radio by periodically sampling its transmissions. The secondary radio can then numerically construct an ’effective interference channel’ that allows it to estimate the interference its transmissions would cause, and to alter them to minimize interference. The new proposal also allows for simultaneous primary and secondary transmissions at the same frequency, in contrast to other cognitive radio schemes.

Zhang and his co-workers also showed that a trade-off exists between the time the secondary radio spends learning to reducing the interference it causes, and the time it spends actually transmitting data. They calculated the optimum time spent at each activity, so as to maximize the secondary radio’s transmission speed.

The proposed scheme can be extended to multiple primary radio receivers and channels, and, while it has not yet been implemented, is potentially relevant to any wireless system that requires supporting two radio networks on a single frequency, according to Zhang. More generally, it “breaks the fundamental gridlock inherent to the conventional operation mode of cognitive radios,” says Zhang, “and the general cognitive beamforming approach on which it is based has already motivated considerable follow-up research.”

The future of Wireless Communications


am a telecom professional with a special interest towards wireless communications. While this is not a technical blog, I could not help writing something related to this field. So the following are a few trends which according to me, could define the direction of the wireless world in the next few years –

Long Term Evolution (LTE) – LTE is a term used for next generation wireless broadband technology, also referred to as 4G. It is seen as an evolution of the current GSM and WCDMA networks. Salient features of the standards based on LTE would include increased download and upload rates, use of MIMO (Multiple Input and Multiple Output) as antenna technology, OFDM (Orthogonal Frequency Division Multiplexing) as the modulation technique, improved spectral efficiency and quality of service, better integration with existing standards, embedded security and an all ‘IP’ network. LTE is still in testing stages and is expected to be launched widely by 2011-2012. It is has been endorsed by many big wireless operators and product manufacturers of the world.

WiMAX – Worldwide Interoperability for Microwave Access is the name give to the IEEE 802.16 standard. It would be used to provide last mile mobile broadband as well as backhaul or network access applications. It could be an alternative to wired broadband like cable and DSL and has been projected to provide 10s of Mbits/sec of speed to a stationary or mobile client many kilometers away. WiMax services have already been launched in many parts of the world. WiMax is especially considered a viable solution for developing countries to provide coverage in the rural areas. One of the biggest debates in the wireless industry is which technology will be more widely adopted 5 years from now – WiMax or LTE?

Femtocells – Femtocell is a small base station or an access point for providing cellular service in a residential or office environment where signal penetration is weak and limited. They connect to the service provider’s core network through an existing wired broadband connection. Femtocells are considered a good solution for subscribers who live in remote areas where the service providers’ coverage is limited and thus they can help in providing coverage and quality of service as good as the wireline phones. They are not standard specific and can be used with GSM, CDMA, 3G etc. Femtocells are now being deployed in various parts of US and Europe.

Adhoc Networks – Mobile Ad Hoc Networks (MANETs) can operate without any infrastructure and possess self-organizing capabilities. The mobile nodes communicate among themselves using multihop radio relaying, without the packets passing through a central access point or a base station.  The commercial deployment of adhoc networks is still a few years away, but they are being used in defense services, emergency operations, sensor networks and hybrid wireless networks. Ad hoc networks are one of the most widely researched area within wireless communications.

Location based services – Location based services on cellphones have gained importance in the past few years especially in emergency situations. Many different GPS techniques have been used for determining the geographic location of a caller or the phone, but the nearest accuracy possible with current technology is about 100 meters. While tracking people through their cellphones may raise privacy concerns, a precise location determination can be very helpful in times of crisis or a calamity. In the US, E911 services are available, though many companies are working on increasing the precision and accuracy of such services.

Cognitive and Software defined radios – The efficiency of a wireless network to some extent depends on the radios it is using. Cognitive radios are designed to understand their environment and location and modify their own parameters like frequency, power, modulation in such a way so as to utilize the unused spectrum dynamically in order to maximize spectral efficiency and minimize interference. Software defined radios are the ones in which the otherwise hardware components like amplifiers, receivers, modulators etc. are implemented using a software. Thus they can used to run on different radio protocols just by modifying the software. A lot of academic research has been done on these two radio technologies and they are expected to be deployed soon commercially.

Spectral Efficiency – Achieving a higher spectral efficiency is one of the primary goals for any radio technology. Simply defined, it is the amount of useful information that can be communicated across a fixed bandwidth network. It is generally measured in Bits/second/Hertz. Minimizing interference and increasing throughput are the best ways to increase the spectral efficiency. With each new technology, the spectral efficiency generally goes up. With the spectrum becoming more and more crowded, a better spectral efficiency is in the interests of both providers and handset manufacturers on one side and the consumer on the other.

Internet and Mobility – Internet has become an integral and inseparable part of both personal and professional life for many of us. People want to be connected anywhere, anytime even on the move in land, air or sea. 3G cellular services have made this possible on mobile phones. Mobile WiMax claims to provide data rates of more than 1 Mbps when moving at speeds upto 100 km/hr. Airlines across the world are preparing to provide Wifi services in the sky. Important factors to be considered here are the connection continuity and the actual date rate.

Mobile content – As the voice market matures, the content on the mobile handset let it be data, video or advertisements has become a major source of revenue for those involved in the wireless business. From the consumer’s perspective, the availability of all the information at one place is very convenient and they are willing to shell extra money for that. Mobile social networking and mobile banking are also gaining popularity among users. With these, requirements for privacy and security are being discussed and accordingly solutions are being developed.

Open Access – The ability to use the mobile phone on any network and for any application has been gaining voice among the consumers. While globally, most service providers keep their network open, there are still some networks which are locked and the user does not enjoy the ability to utilize the network for his own applications. Recognizing this demand and to keep up with competition, most service providers have planned to open their networks in the future. Also, companies are designing open source mobile platforms, whose code can be modified and developed to suit certain applications. This has the potential to give birth to new services.