Multi-antenna systems incorporating smart antenna techniques present numerous advantages compared to their single antenna counterparts including increased capacity and range, by exploring spatial diversity. The current status and novel research directions in the framework of such array systems are presented. Furthermore, the application of nonlinear antenna arrays in the design of novel RF/microwave front-ends, that present compact, low cost and energy efficient solutions for smart antenna array applications is demonstrated. In this manner, the advantages of such systems in terms of their application within next generation networks are highlighted both from the point of view of digital signal processing techniques, as well as alternative analog radio front-end architectures.
Research efforts on next generation wireless communication networks focus on the integration of coexisting heterogeneous types of networks, while providing an increasing number of applications and services, which, in turn, require a high quality of service (QoS). On the other hand, there is an increasing demand for energy efficiency and low cost solutions.
Multi-antenna systems offer higher speed and range compared to single antenna systems, by exploring spatial diversity. Smart antenna techniques applied in multiple antenna systems have a significant impact on the efficient use of the spectrum, the minimization of the cost of establishing new wireless networks, the enhancement of the quality of service, and the realisation of re-configurable, robust and transparent operation across multi-technology wireless networks.
This chapter provides an overview on novel research directions in the framework of such antenna arrays. First, the capability of increasing the capacity of traditional mobile communication links by placing multiple antennas at the receiver and at the transmitter (MIMO systems) is demonstrated. Second, multi-antenna architectures are presented, analyzing the various advantages, disadvantages, as well as challenges that have to be addressed by implementing the transmitter and receiver functions in the digital domain versus the analog domain. The use of digital signal processing techniques applied in beam-forming and adaptive beam-forming methodologies is then presented. Finally, an introduction to nonlinear antenna arrays is provided, followed by a demonstration of their potential application as novel analog front-ends with beam-forming capabilities within the framework of smart antenna arrays.
Key Terms in this Chapter
Retro-Directive Array: A retro-directive array is capable of re-transmitting an interrogating signal back to its source without requiring a priori knowledge of its direction of arrival (DoA) or any signal processing.
Channel Capacity: Amount of bits per second that can be transmitted in a reliable way by a communications channel.
Channel State Information: Knowledge about the communication channel matrix, which relates the transmitted and the received signals.
Active Integrated Antenna: An active integrated antenna (AIA) consists of a passive radiating element and an active circuit, integrated in the same substrate.
Beamforming: Beamforming with antenna arrays is a technique that consists of several antennas whose outputs are controlled in phase and gain, i.e., multiplied by complex weights, in order to achieve a gain pattern that can be manipulated electronically.
Spatial Diversity: Redundancy introduced in the system, generated by sampling the spatial domain using different antennas
Coupled Oscillator Array: A nonlinear dynamical system formed by an array of oscillators coupled through a coupling network.
Phased Array: An array of antennas in which the relative phases of the radiated signals are controlled in order to steer the main lobe of the radiation pattern towards a desired direction and minimize radiation towards undesired directions.
Self-Oscillating Mixer: A circuit that has the functionality of both a mixer and an oscillator. Usually, one first designs an oscillator and subsequently optimizes it to provide mixer conversion gain.
Multiple-Input Multiple-Output (MIMO) System: A system in which there are multiple antennas available simultaneously at the transmitter and the receiver.