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The point is that the output from one relay – or from a number of relays – can be used to control other relays, and the output from these other relays can be used to control yet more relays, and so forth. Thus, by connecting relays together in different ways, it's possible to create all sorts of things, such as the first automatic telephone switching exchange. This little scamp was invented in 1888 by the American undertaker Almon B. Strowger (1839-1902).

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This article originally appeared on EE Times Europe.


It’s all about spectrum Explosive growth in wireless data services is once again transforming an industry well-accustomed to change. The rapid growth in traffic of the 2000s, driven predominantly by voice subscriber additions, is now being followed by an even more dramatic increase in data traffic, as smart phone market penetration accelerates and a flourishing ecosystem of smartphone apps drives explosive growth in the amount of data consumed per subscriber.

To continue to support this growth, spectrum strategy is becoming an ever more crucial factor in determining a wireless operator's success. Spectrum strategy discussions usually center on opening new bands for terrestrial wireless services, but it should be emphasized that the core issue is providing sufficient and pervasive network throughput to keep pace with the acceleration in demand. This is a question not only of adequate spectrum, but also of maximizing spectral efficiency, i.e. to support continued growth in demand for data services, operators must increase spectrum holdings, and also maximize the throughput per unit of available bandwidth per unit of coverage area (the area spectral efficiency, typically measured in kbps/Hz/km2).

3- and 4G wireless data air interfaces have dramatically improved the theoretical spectral efficiency of wireless networks, to the point that LTE can exceed 80% of the Shannon limit in highly-idealized cases. However, even the most elaborate modulation schemes are susceptible to degradation due to interference. As any mobile service subscriber knows, the gap between real world performance and the theoretical ideal is often large. In many cases, this is due to the presence of interference.


Interference can originate from a myriad of sources (Table 1), but the impact to the end user is the same: erratic data throughput that comes nowhere close to the performance levels expected from a channel containing a thermal noise component alone.  In essence, the net spectral efficiency of the channel is degraded by the presence of interference.


Protecting spectral efficiency by managing interference Although radio access technologies have made remarkable advancements in the last decade,  the predominant methods for dealing with interference remain mired in the 1950s:  when an impairment is noted (often the first alert is a customer complaint), a crew is dispatched to identify the interference source by triangulation, and, if possible, make arrangements for it to be switched off.  While it is obviously desirable for interference sources to be eliminated when possible, this process is labor-intensive, slow, and leaves customers exposed to the effects interference while the response team scrambles to identify the issue. For difficult to resolve interference problems, this process can last for months – or indefinitely. Worse yet, less severe interference problems, although common, are often undiagnosed, resulting in a degradation of the aggregate spectral efficiency of the network. Remarkably, interference causing an unloaded noise rise of as little as 3 dB can result in reductions of area spectral efficiency approaching 25%.

Fortunately, advances in adaptive RF digital signal processing (DSP) provide an avenue for implementing a more interference tolerant radio. By monitoring the RF signal for spectral distortions inconsistent with the expected signal, and adapting the channel in real time to compensate for the presence of any detected interference, the effects of impairments can be minimized or eliminated. Figure 1 illustrates the typical integration point for an external RF DSP. As is apparent from the diagram, the RF DSP can be thought of as an augmentation to the radio Rx path itself, that gives the radio the ability to adapt to the instantaneous RF environment. 

About the authorJustin Moon is currently QNX Software Systems’ product manager for the medical market. Since joining the company ten years ago, he has worked on the Custom Engineering Team, specializing in BSP and driver development, and on the Automotive Team. Moon studied computer engineering at St. Lawrence College.

An increase in networked devices in the home, such as tablets, set top boxes (STB), HDTVs, smartphones, and web-enabled media players, has generated a much higher interest in and need for capable home network delivery systems.

Although Wi-Fi networks are still the most dominant form of home networks, the demand for more bandwidth-consuming applications is causing service providers to turn to wired networking solutions that can deliver higher speeds with more reliability than wireless 802.11x standards can. That demand propelled non-Ethernet home networking node shipments past the 40 million units in 2010, says In-Stat.

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