Data transmission system and method

A method of transmitting data packets, where randomness is added to the schedule. Universal broadcast schedules using encoding and randomization techniques are also discussed, together with optimal randomized schedules and an approximation algorithm for finding near-optimal schedules

Optimal Schedules for Asynchronous Transmission of Discrete Packets

In this paper we study the distribution of dynamic data over a broadcast channel to a large number of passive clients. Clients obtain the information by accessing the channel and listening for the next available packet. This scenario, referred to as packet-based or discrete broadcast, has many practical applications such as the distribution of weather and traffic updates to wireless mobile devices, reconfiguration and reprogramming of wireless sensors and downloading dynamic task information in battlefield networks. The optimal broadcast protocols require a high degree of synchronization between the server and the wireless clients. However, in typical wireless settings such degree of synchronization is difficult to achieve due to the inaccuracy of internal clocks. Moreover, in some settings, such as military applications, synchronized transmission is not desirable due to jamming. The lack of synchronization leads to large delays and excessive power consumption. Accordingly, in this work we focus on the design of optimal broadcast schedules that are robust to clock inaccuracy. We present universal schedules for delivery of up-to-date information with minimum waiting time in asynchronous settings

Grammar-based generation of variable-selection heuristics for constraint satisfaction problems

We propose a grammar-based genetic programming framework that generates variable-selection heuristics for solving constraint satisfaction problems. This approach can be considered as a generation hyper-heuristic. A grammar to express heuristics is extracted from successful human-designed variable-selection heuristics. The search is performed on the derivation sequences of this grammar using a strongly typed genetic programming framework. The approach brings two innovations to grammar-based hyper-heuristics in this domain: the incorporation of if-then-else rules to the function set, and the implementation of overloaded functions capable of handling different input dimensionality. Moreover, the heuristic search space is explored using not only evolutionary search, but also two alternative simpler strategies, namely, iterated local search and parallel hill climbing. We tested our approach on synthetic and real-world instances. The newly generated heuristics have an improved performance when compared against human-designed heuristics. Our results suggest that the constrained search space imposed by the proposed grammar is the main factor in the generation of good heuristics. However, to generate more general heuristics, the composition of the training set and the search methodology played an important role. We found that increasing the variability of the training set improved the generality of the evolved heuristics, and the evolutionary search strategy produced slightly better results

The Media Layers of the OSI (Open Systems Interconnection) Reference Model: A Tutorial

The Media Layers of the open systems interconnection (OSI) reference model convert bits to packets. It is a very important aspect of network communication and consists of various networking protocols. At the lowest level the physical layer deals with Media, Signal and Binary Transmission of Bits. Then there is the Data Link layer which deals with media access control (MAC) and logical link control (LLC) Physical Addressing of Frames, for example Ethernet. Finally, there is the Network layer which deals with Path Determination and IP Logical addressing of Packets. This article gives a review of these Media Layers and will contribute to adding knowledge for a networking novice while consolidating concepts for an experienced professional or academic

Optimization Algorithm for Antenna Impedance Matching in Digitally Tunable Network

In this work, we explore different methods to tune the antenna impedance in mobile devices. Mismatch from antenna impedance can cause undesirable effects such as spurious emissions, channel leakages, increased noise floor, degraded receiver sensitivity and so on. With the advancement in technology, digitally tunable reactive components are now available. Thus, a feedback system with tunable circuitry and the aperture tuning method where the component is directly embedded in the antenna design are some of the popular choices of solution. The ‘look-up table’ method is currently widely adopted in wireless industry. The hardware component chain (RF chain) contains the set-up to measure Γ_in(ratio of reflected signal to transmitted signal in dB) and a circuit to be tuned according to the values found in the look-up table. The look-up table is a pre-defined calibration chart provided by the manufacturer. It is saved in the memory of the device for permanent use during its lifespan. In this thesis, in the effort to eliminate the process of creating this look-up table and also to free up large space of memory, we approach an analytical solution to predict the exact values of the component in the tunable circuit – hence, making the procedure a one-time measurement, so called the open-loop configuration. In Chapter 3, a thorough mathematical analysis has been developed to integrate the Q factors of each component into a sample pi-circuit. In such setup, the system is expected to calculate ZL (or the antenna, load) with measured Γ_in and then compute the three capacitance values that yield the best transducer gain by conjugate matching method. However, due to many non-ideal characteristics of the components, calibrating the setup and incorporating the calibration data into analytical solution becomes very challenging. Therefore, the closed-loop configuration is more useful. It collects the empirical data of Γ_in, apply the optimization algorithm and then tune the circuitry in feedback manner, until the lowest desired Γ_in is reached. (Note that there is no difference between the closed and open loop configuration in the physical set-up. ) The purpose of this thesis is to develop the optimization algorithm used in closed-loop configuration. It involves three degrees of freedom using three Digitally Tunable Capacitors (DTCs). Accordingly, the challenge of this research points to inventing a 3D-unconstrained optimization technique that is simple enough to be implemented in a microprocessor without employing complex equation-solving libraries. In Chapter 4, the Hill-Climbing algorithm is investigated to see if it provides a suitable approach for finding the global minimum Γ_in in the 3D space gradient defined by 3 variables or DTCs. The Hill Climbing method, however, will limit its solution to finding only the local minimum within the gradient. This means that the location of the solution will change with the resolution of the gradient and the search step-size. Therefore,it is expected that Hill Climbing algorithm yields different solutions depending on the increment size and the starting location of the search. Chapter 5 develops a new algorithm that is based on Grid Searching. The main idea is to grasp the picture of the entire gradient of 3D space and zoom-in closer to the global point by iteration. The challenge lies in defining the boundary of zoom-in region without leaking the global point and leaving it behind. Also, the scanning of the reduced region in each iteration must not be too rigorous – meaning requiring too many data points. All different pi-network will have its limited coverage region on Smith Chart, of which the load impedance can be matched with. Therefore, selecting the reactive component with the suitable range of capacitance is also an important step, in order to fully utilize the work of this thesis. Apart from that, the algorithm does not require any information about the antenna, frequency of operation nor the configuration of the DTCs. Overcoming these challenges will guarantee the device to have the best optimized state of impedance match, at a specific frequency. Given that the algorithm is a 3D optimization technique, the work of this research does not only apply to tuning a pi-tuner. The three DTCs can be also integrated in the aperture tuning system. Thesis Supervisor: Professor Safieddin Safavi-Naeini.

Antenna tuning for WCDMA RF front end

Modern mobile handsets or so called Smart-phones are not just capable of communicating over a wide range of radio frequencies and of supporting various wireless technologies. They also include a range of peripheral devices like camera, keyboard, larger display, ash-light etc. The provision to support such a large feature set in a limited size, constraints the designers of RF front ends to make compromises in the design and placement of the antenna which deteriorates its performance. The surroundings of the antenna especially when it comes in contact with human body, adds to the degradation in its performance. The main reason for the degraded performance is the mismatch of impedance between the antenna and the radio transceiver which causes part of the transmitted power to be reflected back. The loss of power reduces the power amplifier efficiency and leads to shorter battery life. Moreover the reflected power increases the noise floor of the receiver and reduces its sensitivity. Hence the over performance of the radio module in terms of Total Radiated Power and Total Isotropic Sensitivity, gets substantially degraded in the face of these losses. This thesis attempts to solve the issue of impedance mismatch in RF front-ends by introducing an adaptive antenna tuning system between the radio module and the antenna. Using tunable reactive components and by intelligently controlling them through a tuning algorithm, this system is able to compensate the impedance mismatch to a large extent. The improvement in the output power and the reduction in the Return Loss observed in the measurements carried out for WCDMA, as part of this thesis work, confirm this. However, the antenna tuner introduces an insertion loss and hence degrades the performance in perfect match conditions. The overall conclusion is that the adaptive antenna tuner system improves the performance much more than it degrades it. Hence it is an attractive solution to be included in mobile terminals on a commercial scale