Performance analysis of a CDMA ALOHA network with channel sensing

It has been shown in [1] that the throughput-delay performance of a CDMA ALOHA network, where each station is assigned a spreading code so that each effectively has its own `virtual channel', and where channel sensing and collision detection are also used, is much better than that of a simple CSMA-CD network. Such a system, however, is difficult to implement. A simpler system that may provide good performance and that is easy to implement is a CDMA ALOHA network with just channel sensing. The channel sensing can be provided by a simple correlator and threshold device. In this paper, the performance of such a network is investigated, and some comparisons are made with those of the simple CSMA-CD network and the CDMA ALOHA network with both channel sensing and collision detection. It is shown that when the CDMA-CS network is stable, its performance is not much worse than that of a CDMA-CS/CD network, and much better than that of a simple single channel CSMA-CD system.published_or_final_versio

Combined Semi-definite Relaxation and Sphere Decoding Method for Multiple Antennas Systems

In this paper, a new detection method which combines the semi-definite programming relaxation (SDR) with the sphere decoding (SD) is proposed for 256-QAM multiple-input multiple-output (MIMO) system. In this method, the SDR algorithms are engaged to obtain a primary result. Then, a hyper-sphere is constructed which is centered at the received signal and has its radius equals to the Euclidean distance between the primary result and the received signal. Finally, the SD searching strategy is employed to determine the final result which satisfies the principle of maximum likelihood. Simulation results show that the proposed method can offer optimum BLER performance as well as lower computational complexity than the conventional SD detectors. © 2011 IEEE.published_or_final_versio

Dual-band monopole antenna with frequency-tunable feature for WiMAX applications

A planar dual-band monopole antenna with a frequency-tunable band is presented. The structure of the antenna radiator has a stem connecting to two branches that are used to generate two frequency bands at around 2.4 and 3.4 GHz for Worldwide Interoperability for Microwave Access (WiMAX) applications. The lower band covers the WiMAX frequency band of 2.3-2.4 GHz, while the higher band is frequency-tunable to the WiMAX frequency bands of 3.3-3.4, 3.4-3.6 and 3.6-3.8 GHz. The frequency tunability is achieved by using the reverse-bias voltage across a varactor that is placed between the stem and one of the radiating branches of the radiator. In this study, the radiating branch responsible for the higher band is selected for tuning. A simple and novel biasing circuit, consisting of two radio frequency (RF) choke resistors and an L-shaped stub, is designed for biasing the varactor. Results show that the higher band can be continuously tuned in frequency, yet keeping the lower band unchanged. The reflection coefficient, radiation pattern, and efficiency of the antenna are studied using computer simulation and measurement. © 2013 IEEE.published_or_final_versio

Performance comparison of single and multi-channel CSMA-CD wireless networks using equilibrium point analysis

Conference theme: Mobile Technology for the Human RaceA fundamental defect of simple CSMA-CD multiple access scheme is that messages meant for different stations can collide in the common channel. In this paper, a multi-channel form of CSMA-CD network, created by CDMA signalling, is analyzed. Its performance is shown to be superior to that of a single channel CSMA-CD network.published_or_final_versio

Planar Monopoles with Different Radiator Shapes for UWB Body-centric Wireless Communications

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Dual-band antenna with compact radiator for 2.4/5.2/5.8 GHz WLAN applications

This paper presents a dual-band planar antenna with a compact radiator for 2.4/5.2/5.8-GHz wireless local area network (WLAN) applications. The antenna consists of an L-shaped and $E$-shaped radiating elements to generate two resonant modes for dual-band operation. The L-element fed directly by a 50-Ω microstrip line is designed to generate a frequency band at around 5.5 GHz to cover the two higher bands of the WLAN system (using the IEEE 802.11a standard). The E-element is coupled-fed through the L-element and designed to generate a frequency band at 2.44 GHz to cover the lower band of the WLAN system (using the 802.11 b/g standards). As a result, the L-and E-elements together are very compact with a total area of only 8× 11.3 mm 2. Parametric study on the key dimensions is investigated using computer simulation. For verification of simulation results, the antenna is fabricated on a 40× 30× 0.8mm3 substrate and measured. The effects of the feeding cable used in the measurement system and the housing and liquid crystal display of wireless devices on the return loss, radiation pattern, gain and efficiency are also investigated by computer simulation and measurement. © 2012 IEEE.published_or_final_versio

Compact MIMO antenna for portable devices in UWB applications

A compact multiple-input-multiple-output (MIMO) antenna with a small size of 26× 40mm2 is proposed for portable ultrawideband (UWB) applications. The antenna consists of two planar-monopole (PM) antenna elements with microstrip-fed printed on one side of the substrate and placed perpendicularly to each other to achieve good isolation. To enhance isolation and increase impedance bandwidth, two long protruding ground stubs are added to the ground plane on the other side and a short ground strip is used to connect the ground planes of the two PMs together to form a common ground. Simulation and measurement are used to study the antenna performance in terms of reflection coefficients at the two input ports, coupling between the two input ports, radiation pattern, realized peak gain, efficiency and envelope correlation coefficient for pattern diversity. Results show that the MIMO antenna has an impedance bandwidth of larger than 3.1-10.6 GHz, low mutual coupling of less than-15 dB, and a low envelope correlation coefficient of less than 0.2 across the frequency band, making it a good candidate for portable UWB applications. © 2013 IEEE.published_or_final_versio

A Novel Method for Designing M-Band Linear-Phase Perfrect-Reconstruction filter Banks

This paper studies the design of M-channel perfect-reconstruction (PR) linear-phase (LP) filter banks (FBs) with M=2k using a tree-structured FB. It is based on a observation of Fliege(1995) that the length of the analysis filters is decreased by a factor of two when the depth of the tree is increased by one, while its transition bandwidth is increased by the same factor. A lattice-based 2-channel LP FB is chosen because the frequency responses of the lowpass and highpass analysis (synthesis) filters can be designed to be closely symmetric to the other around π/2. By properly selecting the filter length, transition bandwidth. and stopband attenuation of the 2-channel PR LP FBs at each level of the tree structure, it is possible to design uniform PR LP FB with excellent frequency characteristic and much lower system delay.published_or_final_versio

Design of chipless UWB RFID system using A CPW multi-resonator

In this paper, the design of a novel chipless ultra-wideband radio-frequency identification (UWB RFID) system is proposed. The system employs printable uniplanar chipless tags and a pair of high-gain reader antennas. The chipless tag is composed of two UWB monopole antennas, connected by a coplanar waveguide (CPW). The tag's ID is represented by a spectral signature in the UWB frequency range, and is created by a multi-resonator embedded on the coplanar waveguide. The detection of the tag's ID is based on using only the amplitude of the spectral signature, which significantly simplifies the complexity of detection. The reader employs two separate Vivaldi antennas-one for transmitting a vertically polarized signal, and the other for receiving a horizontally polarized signal-to reduce the mutual coupling between the uplink and downlink signals. Further reduction of mutual coupling is achieved by using a copper plate at the reader to separate the uplink and downlink signals. These two proposed methods together reduced the mutual coupling by 20 dB. The chipless RFID tag with eight coplanar waveguide resonators in a group and the reader antennas were designed using computer simulation, and fabricated on Rogers substrates for measurement. The results of studies in an anechoic chamber showed that the proposed UWB RFID system could achieve a reading range of larger than 30 cm, at least three times longer than the maximum distance of a similar system reported by others. This indicated that the proposed system has great potential for short-range item tracking at low cost. © 1990-2011 IEEE.published_or_final_versio

Comparison of Semidefinite Relaxation Detectors for High-Order Modulation MIMO Systems

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