The ever-growing computation and storage capability of mobile phones have given rise to mobile-centric context recognition systems, which are able to sense and analyze the context of the carrier so as to provide an appropriate level of service. As nonintrusive autonomous sensing and context recognition are desirable characteristics of a personal sensing system; efforts have been made to develop opportunistic sensing techniques on mobile phones. The resulting combination of these approaches has ushered in a new realm of applications, namely opportunistic user context recognition with mobile phones . This article surveys the existing research and approaches towards realization of such systems. In doing so, the typical architecture of a mobile-centric user context recognition system as a sequential process of sensing , preprocessing , and context recognition phases is introduced. The main techniques used for the realization of the respective processes during these phases are described, and their strengths and limitations are highlighted. In addition, lessons learned from previous approaches are presented as motivation for future research. Finally, several open challenges are discussed as possible ways to extend the capabilities of current systems and improve their real-world experience.
This paper proposes a spectrum sharing algorithm to exploit instantaneous spectrum use during the peak hour between two Universal Mobile Telecommunication System (UMTS) operators. The algorithm proposes a modification of the current call admission procedure on UMTS networks in order to accommodate users from the other network. A simulator platform has been developed in order to evaluate the performance of the algorithm. The performance of the instantaneous DSA algorithm is compared with Fixed Spectrum Allocation (FSA) when no spectrum sharing takes place. The paper further investigates the impact of increasing the number of carriers on the achievable spectrum sharing gain. The results show that the spectrum efficiency gains up to 4% can be achieved with three carriers per operator. It also shows that additional call setup delays are introduced by the DSA algorithm.
In this article, empty substrate integrated waveguides (ESIW) technology is applied to design long slot leaky-wave antennas (LWAs). First, a uniform-aperture structure is presented and its limitations on forming the beam are studied. Then, a sinusoidal curve is employed to modify the geometry of guided-wave structure which divides the slot into a number of segments, making a periodic aperture. After that, a method is proposed to regulate the guided waves inside the ESIW. To this end, a modulation function is derived to simultaneously determine the local amplitude and segment length of the physical sinusoidal curve at each individual points on the structure. This results in manipulating the phase constant $(\beta)$ and leakage rate $(\alpha)$ across the aperture which ultimately controls both the tilt angle and sidelobe-level (SLL) of the constructed beam. The slot is placed on the centerline of the broad wall of the ESIW to reduce the cross polarization. The structure is designed to operate at 35 GHz with SLL = −30 dB and a backward tilt angle of $\theta _{m}=-20 ^\circ $ . Finally, the proposed LWA is simulated and a fabricated design is measured. A good agreement is observed between the theoretical, simulated, and measured performance of the antenna.
A new adaptive strategy for a turbo decoder with prior statistical knowledge of extrinsic information is proposed. A test pseudorandom bits block, with distribution patterns of 1s and 0s known by both the transmitter and receiver, is sent to the receiver when the channel status changes and is detected by the receiver. The turbo decoder computes the conditional probability mass functions of the extrinsic information for both arms at each iterative decoding by using the test block. These updated probability mass functions are kept in the turbo decoder to replace the conventional Gaussian assumptions for iterative decoding of an information bits block over AWGN and various fading channels. The simulation results show that the novel iterative turbo decoding has considerable performance gains over conventional ones under the same channel conditions.
The log-normal probability distribution has been commonly used in wireless communications to model the shadowing and, recently, the small-scale fading for indoor ultrawideband (UWB) communications. In this paper, a tight closed-form approximation of the ergodic capacity over log-normal fading channels is derived. This expression can be easily used to evaluate and compare the ergodic capacities of communication systems operating over log-normal fading channels. We also utilize this expression to show that the capacity of a multi-antennas UWB system operating over the IEEE 802.15.3a channel can be improved mainly through receive diversity.
This work introduces MultiSphere, a method to massively parallelize the tree search of large sphere decoders in a nearly-independent manner, without compromising their maximum-likelihood performance, and by keeping the overall processing complexity at the levels of highly-optimized sequential sphere decoders. MultiSphere employs a novel sphere decoder tree partitioning which can adjust to the transmission channel with a small latency overhead. It also utilizes a new method to distribute nodes to parallel sphere decoders and a new tree traversal and enumeration strategy which minimize redundant computations despite the nearly-independent parallel processing of the subtrees. For an 8 × 8 MIMO spatially multiplexed system with 16-QAM modulation and 32 processing elements MultiSphere can achieve a latency reduction of more than an order of magnitude, approaching the processing latency of linear detection methods, while its overall complexity can be even smaller than the complexity of well-known sequential sphere decoders. For 8 × 8 MIMO systems, MultiSphere's sphere decoder tree partitioning method can achieve the processing latency of other partitioning schemes by using half of the processing elements. In addition, it is shown that for a multi-carrier system with 64 subcarriers, when performing sequential detection across subcarriers and using MultiSphere with 8 processing elements to parallelize detection, a smaller processing latency is achieved than when parallelizing the detection process by using a single processing element per subcarrier (64 in total).
We propose an enhanced user position assisted soft handover algorithm for wideband CDMA based UTRA system. The proposed algorithm is based on the UTRA soft handover algorithm and the user's position information. The estimated user position and projected motion play an assisting role when the network decides to add/remove a base station to/from the user's active set. The positioning error and positioning delay are modelled. The performance of the proposed algorithm has been compared with that of the UTRA algorithm, by carrying out simulations in UTRA vehicular environment, for various user mobility and propagation conditions. The system performance is evaluated in terms of the system resource efficiency, i.e. mean active set number and active set update rate, and the quality of service, i.e. call outage and blocking probability. The results are presented through graphs and discussed.
In conventional hybrid beamforming approaches, the number of radio-frequency (RF) chains is the bottleneck on the achievable spatial multiplexing gain. Recent studies have overcome this limitation by increasing the update-rate of the RF beamformer. This paper presents a framework to design and evaluate such approaches, which we refer to as agile RF beamforming, from theoretical and practical points of view. In this context, we consider the impact of the number of RF-chains, phase shifters' speed, and resolution to design agile RF beamformers. Our analysis and simulations indicate that even an RF-chain-free transmitter, which its beamformer has no RF-chains, can provide a promising performance compared with fully-digital systems and significantly outperform the conventional hybrid beamformers. Then, we show that the phase shifter's limited switching speed can result in signal aliasing, in-band distortion, and out-of-band emissions. We introduce performance metrics and approaches to measure such effects and compare the performance of the proposed agile beamformers using the Gram-Schmidt orthogonalization process. Although this paper aims to present a generic framework for deploying agile RF beamformers, it also presents extensive performance evaluations in communication systems in terms of adjacent channel leakage ratio, sum-rate, power efficiency, error vector magnitude, and bit-error rates.
Although Geostationary-Equatorial-Orbit (GEO) satellites have achieved significant success in conducting space missions, they cannot meet the 5G latency requirements due to the far distance from the earth surface. Therefore, Low-Earth-Orbit (LEO) satellites arise as a potential solution for the latency problem. Nevertheless, integrating the 5G terrestrial networks with LEO satellites puts an increased burden on the satellites' limited budget, which stems from their miniature sizes, restricted weights, and the small available surface for solar harvesting in the presence of additional required equipment. This paper aims to design the Electrical Power System (EPS) for 5G LEO satellites and investigate altitudes that meet the latency and capacity requirements of 5G applications. In this regard, accurate solar irradiance determination for the nadir-orientation scenario, Multi-Junction (MJ) solar cells modeling, backup batteries type and number, and designing highly-efficient converters are addressed. Accordingly, the power budgeting of the 5G LEO satellite can be achieved based on defining the maximum generated power and determining the satellite's subsystem power requirements for 5G missions. In the sequel, the measured and simulated values of the electrical V-I characteristics of an MJ solar panel are compared to validate the model by using a Clyde Space solar panel that reaches a maximum power generation of approximately 1 W at ( I MPP =0.426 A, V MPP =2.35 V). Moreover, a synchronous boost converter circuit is designed based on commercial off-the-shelf elements.
This paper proposes a novel carrier frequency offset (CFO) estimation method for generalized MC-CDMA systems in unknown frequency-selective channels utilizing hidden pilots. It is established that CFO is identifiable in the frequency-domain by employing cyclic statistics (CS) and linear regression (LR) algorithms. We show that the CS-based estimator is capable of mitigating the normalized CFO (NCFO) to a small error value. Then, the LR-based estimator can be employed to offer more accurate estimation by removing the residual quantization error after the CS-based estimator
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