The advancement in wireless communications requires the integration of multiple radios into a single platform to maximize connectivity. In this paper, the design process of reconfigurable antennas is discussed. Reconfigurable antennas are proposed to cover different wireless services that operate over a wide frequency range. They show significant promise in addressing new system requirements. They exhibit the ability to modify their geometries and behavior to adapt to changes in surrounding conditions. Reconfigurable antennas can deliver the same throughput as a multiantenna system. They use dynamically variable and adaptable single-antenna geometry without increasing the real estate required to accommodate multiple antennas. The optimization of reconfigurable antenna design and operation by removing unnecessary redundant switches to alleviate biasing issues and improve the system's performance is discussed. Controlling the antenna reconfiguration by software, using Field Programmable Gate Arrays (FPGAs) or microcontrollers is introduced herein. The use of Neural Networks and its integration with graph models on programmable platforms and its effect on the operation of reconfigurable antennas is presented. Finally, the applications of reconfigurable antennas for cognitive radio, Multiple Input Multiple Output (MIMO) channels, and space applications are highlighted.

Reconfigurable antennas, with the ability to radiate more than one pattern at different frequencies and polarizations, are necessary in modern telecommunication systems. The requirements for increased functionality (e.g., direction finding, beam steering, radar, control, and command) within a confined volume place a greater burden on today's transmitting and receiving systems. Reconfigurable antennas are a solution to this problem. This paper discusses the different reconfigurable components that can be used in an antenna to modify its structure and function. These reconfiguration techniques are either based on the integration of radio-frequency microelectromechanical systems (RF-MEMS), PIN diodes, varactors, photoconductive elements, or on the physical alteration of the antenna radiating structure, or on the use of smart materials such as ferrites and liquid crystals. Various activation mechanisms that can be used in each different reconfigurable implementation to achieve optimum performance are presented and discussed. Several examples of reconfigurable antennas for both terrestrial and space applications are highlighted, such as cognitive radio, multiple-input–multiple-output (MIMO) systems, and satellite communication.

New generation of satellite navigation signals, such as AltBOC (Alternative Binary Offset Keying), CBOC (Composite Binary Offset Keying) and TMBOC (Time Multiplex Binary Offset Keying) bring enhancements in the tracking process, such as more signal power, better multipath mitigation capabilities and more robust navigation. Moreover, one of the most important improvement they bring into the GNSS story is the presence of the two channels: data and pilot. The pilot channel, although dataless, carries the same information about the frequency, carrier and code phase as the data channel.Therefore, the information from both channels can be used to improve the tracking performance. In this context, the main point that is addressed in this paper is the optimization of the data/pilot combining tracking strategies in order to increase tracking stability, accuracy and robustness. Towards this end, non-coherent and coherent data/pilot combining strategies with different weights on each channel are presented, and the outputs from the DLL and PLL tracking loops using different discriminator types are analyzed and discussed. Moreover, an investigation for an optimal trade-off between the minimal tracking error and the best stability is reported with the corresponding results discussed.

The innovative spreading codes used to modulate the new Galileo signals creates new challenges for receiver designers. It is well known in GNSS systems that longer integration times are needed to obtain a better sensitivity. However, the existence of the new tiered code concept that consists of the presence of a secondary code on top of the primary code to modulate the RF signal puts a limitation on the coherent integration time for pilot channels similarly to the effect of data bit ambiguity in data channels. Within this context, this paper tackles this issue by introducing a new algorithm for wiping off the secondary code and increase the coherent integration time. The algorithm is based on the combination of serial and parallel searches. The search for the primary code phase is performed serially within one primary code length, and the secondary code phase is searched in parallel over the entire length of the secondary code. Furthermore, the proposed algorithm improves the Doppler offset estimation and reduces the overall acquisition time.

In this paper, different correlation techniques (narrow correlator, double delta correlator and subcarrier processing) that can be applied to the new Galileo alternate binary offset carrier AltBOC(15,10) modulation are discussed with respect to their functionality, implementation, and multipath mitigation performance. Moreover, effects of the receiver parameters (precorrelation bandwidth, spacing between correlators) on the ranging errors are also presented. The performance of the multipath mitigation concepts is illustrated in 2D and 3D multipath error envelopes assuming multipath scenarios with one and two multipath components and constant signal attenuation factors. The main purpose of this paper is to provide a better understanding of the performance of the AltBOC modulation and the effect of multipath on code and carrier measurements for different multipath environments, and thus help the receiver designers to select the best correlation technique for their particular applications.

GNSS platforms such as the American Global Positioning System (GPS) or the Russian GLONASS system are being continuously updated with new satellites offering new signals, new frequencies and new functionalities. Moreover, new GNSS systems such as the European Union's Galileo system or the Japan's quasi-zenith satellite system (QZSS) are currently being developed and planned to be in function within a couple of years. Taking advantage of these new signals requires the use of a multi-frequency radiofrequency (RF) front-end (FE). In this paper, we highlight the design of such a FE based on a sub-sampling architecture. Indeed, with the technology advances in the integrated circuits (IC) industry, and more particularly the availability of GHz bandwidth analog-to-digital converters (ADC), this is one of the most attractive ways to achieve a multi-frequency FE. While a sub-sampling architecture has already been presented in some other publications, we present a methodology that takes into account the effects of the filters characteristics and out-of-band noise. As a practical example, we apply our methodology to the design of a multi-frequency RF FE for the simultaneousacquisition of the GPS L1C; L2C; L5, and Galileo E1b,c; E5a,bsignals.