Designing Wireless Communication Systems

Challenges & Solutions of Designing Wireless Communication Systems

There are numerous challenges involved in designing wireless communication systems. As numerous wireless devices increase the need for strong wireless communications, solutions are being created for the problems that arise with wireless systems.

Multipath Propagation

As explained by this Cisco article, multipath propagation creates significant issues in a wireless system. It causes signals to be delayed as they encounter various obstacles en route to its access point. In an office or home setting, signals may bounce off objects such as walls, desks, and ceilings. Segments of a signal may arrive to their destination later. The delay caused by multipath propagation can confuse receivers and intersymbol interference occurs. The greater the delay, the more likely errors in bit packets will result. Multipath propagation has the ability to corrupt data and nullify signals.

Spectrum

With all usable spectrum being allocated and the demand for broadband growing larger, modern wireless design is being faced with the problem of utilizing existing bands more efficiently.

The problem is exasperated by the history of the wireless spectrum. Since the 1920s, a section of wireless spectrum could be purchased and owned by those with a license. Licensing slows down the process of reallocating spectrum for wider usage and makes it difficult to keep up with growing demands. The reallocation process also goes against the desired use for spectrum to be used for several different radio systems rather than being fragmented and sectioned off.

Designing Wireless Communication Systems

Synchronization

Propagation time is one the factors that makes synchronization difficult. Regardless, successful wireless systems must be synchronized. Sychronization relies on signal exchange between nodes. These nodes generate timestamps which are sent to another node to complete the process of synchronization. Sensor networks require synchronization to achieve complex tasks such as data fusion.

When solving the problem of synchronization, many factors must be considered.

Cost and Size: Sensor nodes in devices must be like the devices they are used in – small and relatively inexpensive. Cost and size must always be considered when sensor nodes are used.

Scalability: A synchronization scheme should scale with an increasing number of nodes since sensor nodes must be in a considerable number in a sensor network.

Immediacy: Many sensor networks require triggering events to be report to the appropriate node immediately. This is the case with emergency or security systems. Therefore, delays in such systems can be disastrous and protocol designers cannot rely on excessive processing.

Synchronization also is a vital part of many scheduling algorithms that are used to conserve energy such as power savings. Existing synchronization systems are unsuitable for most wireless devices. GPS is too complex, expensive, unreliable in certain conditions and are often too large to fit into the constraints of many communication systems.

Solutions

For the problems listed above, various solutions have been proposed.

Synchronization: A potential system for a synchronization scheme for a wireless sensor network is the proposed Reference Broadcast Synchronization (RBS) system. The RBS system is different from the traditional system. Instead of the sender being synchronized with the receiver, two receivers are synchronized with each other and nodes send reference beacons to one another. In contrast to time stamps, reference points are used to compare clocks. Since a single broadcast propagates to every receiver simultaneously errors are supposedly minimized. Although this system was previously applied in broadcast, the RBS system would be one of the first times it was utilized for sensor networks systems.

Spectrum

Because of the issues regarding spectrum usage, there have been numerous proposed changes to the way the spectrum is used. For starters, the use of the band 3.5 GHz is being considered. Use of this band could increase reusability of channels in certain area. Because military radar is known to use this band, more ideas have been proposed to avoid interference. These new ideas are being used to develop “smart” radios that have software that can detect unused radio channels. These same radios could have the ability to operate on a much wider range of frequencies and be able to communicate with secured databases that will ward them away from military or other protected radio systems.

In addition to the use of smart radios, the FCC wants to clear up more bandwidth for wireless use. This was seen in recent years as the 700 MHz band was freed as TV made the transition from analog to digital. TV broadcasters collectively agreed to auction off spectrum in the 600 MHz band. Although this process will likely take years, it is apart of the prime spectrum desired for wireless.

Multipath Propagation

A solution to the issue of multipath propagation is diversity, which is the use of two antennas for each radio with the hope of increasing the chances that a better signal is received by either antenna. Diversity antennas are separated from the radio ensuring that multipath propagation is less likely to affect the other antenna. The receiving antenna receives a composite signal that is closer to the original.


Sources

http://www.ciscopress.com/articles/article.asp?p=2351131&seqNum=3

http://newsroom.cisco.com/feature-content?type=webcontent&articleId=983185

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