Volume 67, Issue 9-10

This paper presents a novel compact microstrip low-pass filter with wide stop-band and sharp roll-off. The structure consists of a transmission line, loaded with coupled novel Hairpin units. The cut-off frequency of the proposed filter is 2.9 GHz. The measured results show good LPF performance such as sharp roll-off skirt, low insertion-loss, high return-loss in the pass-band and wide upper stop-band of 3.2 to 16.1 GHz with an insertion-loss higher than 20.0 dB. The measured values and the EM-simulation results are in good agreement.

In this paper, a novel design of a circular polarized horn antenna is presented. An anisotropic metamaterial slab with metal periodic structures printed on a substrate is designed and its constitutive parameters and S parameters are analyzed. It shows that the metamaterial is anisotropic and can turn a linearly polarized wave to a circular polarized one. Then a novel horn antenna composed of a conventional rectangular horn antenna and the metamaterial slab is fabricated and measured. The results show that the novel horn antenna radiates a left handed circular polarized wave with an axis ratio below 3 dB at 16 GHz, and its gain and radiation pattern are the same as those of the conventional rectangular horn antenna.

This paper studies the optimal beamforming design for a cognitive relay network in which a secondary network transmits its data using a multi-antenna relay simultaneously with the primary users over the same spectrum. An optimal beamforming approach is proposed to maximize the received signal-to-noise ratio (SNR) of the secondary users, whereas the received interference power at the primary user is kept below a predefined threshold. The maximization of the SNR at the secondary users is derived as an objective function to fumulate a constrained beamforming optimization problem, and the optimization problem can be transformed into a Rayleigh-Ritz ratio problem which is then solved by the generalized singular-value decomposition in a closed form. In response to the practical problem that perfect instantaneous channel state information (CSI) is difficult to be available, we assume that partial CSI is available in the proposed method. Simulation results show that the performance can be further improved by either decreasing the uncertainty in channel coefficients or increasing the number of relay antennas.

This paper focuses on the downlink dual-hop multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay systems that employ the maximal-ratio transmission and receive antenna selection scheme (MRT&RAS) for use in each hop. The system under consideration is equipped with arbitrary N S , N R , and N D antennas at the base station (BS), relay station (RS), and mobile station (MS), respectively. The system performance has been investigated over Nakagami- m fading in presence of independent but not necessarily identically distributed co-channel interferences (CCIs) at both the RS and MS. First, we derive an accurate closed-form approximate expression for the outage probability and a single-integral expression for the average symbol error rate (SER), respectively. Besides, to render direct insights into the combined effect of multiple-antenna and interference on the system performance, the asymptotic expressions for the outage probability and the average SER are also presented. Furthermore, we determine the optimal power allocation (OPA) by using the exact and asymptotic methods, respectively, such that the outage probability is minimized. Finally, numerical results validate the correctness of the derived expressions and show that OPA offers superior performance over uniform power allocation. Our analysis and results provide insights on investigating and optimizing the performance of the downlink MIMO relay transmission in practical interference-limited wireless networks.

Next-generation wireless networks will integrate multiple wireless access technologies and the users will access the network using one of several available radio access technologies. In this paper, we study the spectrum access problem in heterogeneous multipleinput multiple-output (MIMO) networks through a game theoretic approach. The spectrum access problem in the considered system model is defined as joint network selection and discrete power control. We formulate the problem as a noncooperative game where the players are the multi-mode terminals and. The proposed common utility function takes both transmission rate and the power consumption into account. This game is shown to be a potential game which possess at least one pure strategy Nash equilibrium (NE) and the optimal strategy profile which maximizes the total energy efficiency of the heterogeneous MIMO network constitutes a pure strategy NE of our proposed game. Furthermore, we prove that the price of anarchy of the proposed game is equal to 1. In order to achieve the pure strategy NE, we design an iterative spectrum access algorithm. The convergence and the complexity of our designed algorithm is discussed. It is shown that the designed algorithm can achieve optimal performance with low complexity.

Ray tracing is a well-known technique to investigate the multipath propagation in the complex indoor environment. However, it still suffers from the computation time and ray prediction accuracy for the complex indoor environment. Therefore, a new three dimensional (3D) ray tracing based on the Red-Black tree along with object skipping and surface extraction techniques for the complex indoor environment is presented in this paper. The Red-Black tree data structure provides a faster object retrieval mechanism while object skipping technique prevents the unnecessary objects to take part in intersection tests, thus accelerates the ray tracing. Conversely, the surface extraction is a novel technique that makes the tracing of the ray paths easily and accurately, mostly for the complex 3D environment. In addition, the calculation of exact ray paths that reach the receiver after multiple reflections, refractions and/or diffractions is also considered in this paper. The obtained results show that the proposed method provides superior improvement of ray prediction time (75.65% on average) and ray prediction accuracy (27.78% on average) than the existing ray tracing methods.

In this paper we analyze the influence of the connections between users, belonging to the same cell, on the increase of traffic loss. The utilization of Erlang model in this case gives underestimated loss. We calculate some simple examples in the case of GSM. Several numerical examples prove that traffic loss increases with the increase of intra-cell traffic in total traffic and with the increase of the number of channels in the group. The results are confirmed by the computer simulation.

The paper proposes a method to determine the threshold for the iteration stopping criterion based on minimum absolute values of Logarithm Likelihood Ratios (minabsLLR), for turbo codes. The method is based on the simulation of a small number of frames at the signal-to-noise ratio (SNR) wanted for Genie stopper benchmark criterion and the use of a constant, deduced from simulations, which depends on the approximate frame error rate (FER). We used the least squares approximation to provide a formula for the threshold, which depends linearly on SNR. For a representative set of lengths, the coefficients of the previous approximation are also approximated by a linear function, using the least squares method. This approximation depends linearly on interleaver length. By using the proposed method, the number of iterations is reduced up to 3 for small and medium SNRs.

This paper presents a new low-power super source follower (SSF) cell with large output voltage swing and better signal performance. The performance improvement is obtained by replacing one of MOS transistors by two-input floating gate MOS transistor. The bandwidth of the proposed circuit is enhanced by using a resistor in the feedback path of SSF. The basic operating principles of proposed SSF structures are discussed and their lower 3-dB frequency has been derived. An output stage is designed by using proposed SSF structures to verify the performance improvement. The simulations are performed in TSMC 0.18 um CMOS, BSIM3 and Level 49 technology by using Spectre simulator of Cadence.

This work introduces a new low voltage low power superharmonic capacitive coupling quadrature LC oscillator (QLCO) made by coupling two identical cross-connected LC oscillators without tail transistor. In each of the core oscillators, the back-gate nodes of the cross-coupled NMOS pair and PMOS pair, acting as common mode nodes, have been connected directly. Then the core oscillators are coupled together via capacitive coupling of the PMOS common mode node in one of the core oscillators to the NMOS common mode node in the other core oscillator, and vice versa. Only capacitors are used for coupling of the two core oscillators and therefore no extra noise sources are imposed on the circuit. Operation of the proposed QLCO was investigated with simulation using a commercial 0.18 µm RF CMOS technology: it shows a power dissipation of 5.2 mW from a 0.6 V supply voltage. Since the proposed core oscillator has Complementary NMOS and PMOS cross coupled pairs, and capacitive coupling method will not introduce extra phase noise, so this circuit can operate with a low phase noise as low as −126.8 dBc/Hz at 1 MHz offset from center oscillation frequency of 2.4 GHz, as confirmed with simulation.