Synchronization in wireless communications

The last decade has witnessed an immense increase of wireless communications services in order to keep pace with the ever increasing demand for higher data rates combined with higher mobility. To satisfy this demand for higher data rates, the throughput over the existing transmission media had to be increased. Several techniques were proposed to boost up the data rate: multicarrier systems to combat selective fading, ultra wide band (UWB) communications systems to share the spectrum with other users, MIMO transmissions to increase the capacity of wireless links, iteratively decodable codes (e.g., turbo codes and LDPC codes) to improve the quality of the link, cognitive radios, and so forth

Forward focus: using routing information to improve medium access control in ad hoc networks

Summary Multihop packet forwarding is a vital process in an ad hoc network. All ad hoc networking protocols, but particularly routing and medium access control protocols, must work together in order for the network to be successful. However, current MAC protocols such as IEEE 802.11 do not consider this multihop nature at all. This work develops a modification to 802.11 that focuses on forwarding packets. Routing information is utilized to streamline the sharing of the medium, by allowing forwarding nodes to reuse an already-acquired channel. Using forward focus (FF), nodes are encouraged to participate in the forwarding process and are rewarded for doing so. Simulation-generated performance evaluations reveal that the result is a MAC protocol with improved efficiency and effectiveness

Bayesian compressive sensing framework for spectrum reconstruction in Rayleigh fading channels

Compressive sensing (CS) is a novel digital signal processing technique that has found great interest in many applications including communication theory and wireless communications. In wireless communications, CS is particularly suitable for its application in the area of spectrum sensing for cognitive radios, where the complete spectrum under observation, with many spectral holes, can be modeled as a sparse wide-band signal in the frequency domain. Considering the initial works performed to exploit the benefits of Bayesian CS in spectrum sensing, the fading characteristic of wireless communications has not been considered yet to a great extent, although it is an inherent feature for all sorts of wireless communications and it must be considered for the design of any practically viable wireless system. In this paper, we extend the Bayesian CS framework for the recovery of a sparse signal, whose nonzero coefficients follow a Rayleigh distribution. It is then demonstrated via simulations that mean square error significantly improves when appropriate prior distribution is used for the faded signal coefficients and thus, in turns, the spectrum reconstruction improves. Different parameters of the system model, e.g., sparsity level and number of measurements, are then varied to show the consistency of the results for different cases

Heterogeneous Networking: An Enabling Paradigm for Ubiquitous Wireless Communications

In this paper we explore the principle of heterogeneous wireless networking and discuss the potential avenues towards the realization of the ubiquitous wireless communications. Specifically, we demonstrate that the heterogeneous network architecture, constituted by the fusion of the classic cellular and the ad hoc network topologies, inherits the vital complementary characteristics of both architectures, and thus has the potential of attaining the levels of performance and efficiency required by the future wireless communications

Using Spectrum Auctions to Enhance Competition in Wireless Services

Spectrum auctions are used by governments to assign and price licenses for wireless communications. Effective auction design recognizes the importance of competition, not only in the auction, but in the downstream market for wireless communications. This paper examines several instruments regulators can use to enhance competition and thereby improve market outcomes.

Wireless communications with diffuse waves

Diffuse, multiple-scattered waves can be very efficient for information transfer through disordered media, provided that antenna arrays are used for both transmission and reception of signals. Information capacity C of a communication channel between two identical linear arrays of n equally-spaced antennas, placed in a disordered medium with diffuse scattering, grows linearly with n and can attain considerable values, if antenna spacing a > lambda/2, where lambda is the wavelength. Decrease of a below lambda/2 makes the signals received by different antennas partially correlated, thus introducing redundancy and reducing capacity of the communication system. When the size of antenna arrays is well below lambda/2, the scaling of C with n becomes logarithmic and capacity is low.Comment: RevTEX 4, 3 pages, 2 figure