Dispersed Cooperative Wireless and Nanoscale Networks
Due to the inherent broadcast nature of the radio channel wireless communication systems generate mutual interference. The traditional design paradigm for wireless communication systems is coexistence, where the amount of interference between different systems is controlled by fixed or slowly adaptive radio resource allocation. A recent development is cognitive radio, which tries to dynamically reuse spectral resources on a shorter time scale, while maintaining an acceptable level of interference. Cognitive radio in that respect may be considered a fast avoidance technique.
Cooperative wireless does the contrary. Here the co-located wireless systems are considered as a wireless entity of heterogeneous nodes rather than a collection of interfering systems. Such interference is not considered as disturbance but rather as signal, which may improve the communication of all nodes in range. This paradigm shift is comparable to the recent drastical change in the perception of multipath propagation. Once considered a major impairment that leads to signal degradation due to fading and frequency selectivity, it is now known to be the key enabler to MIMO wireless (spatial multiplexing).
While coexistence is based on a system level perspective, cooperative wireless puts forward the notion of heterogeneous wireless node. Most wireless nodes comprise typical analog and digital signal processing blocks such as frequency synthesis, down-conversion, filters, etc. In the long term we anticipate another major paradigm shift, as the systems become more dense and node separation is no longer much larger than the wavelength: the functionality of a classical wireless node may be dispersed into spatially separate subnodes, which communicate with each other through the wireless medium (including near field coupling effects). The capabilities of this community of subnodes depend on their (random) aggregation and we have to design signaling and protocols in such a way, that evolutionary growth of collective capabilities is enabled. A important application area of these scheme are Nanoscale Networks.
In a sense the paradigm shift from wireless nodes to dispersed wireless is reminiscent of the lumped element versus distributed element paradigm in circuit design. In dispersed wireless networks the cooperation paradigm is extended to the hardware and propagation level. An illustrative example could be a cloud of subnodes, which interacts nonlinearly with an impinging electromagnetic field and in this way performs processing similar to a neural network.