Ruiheng Wu

Sensitivity of cellular wireless network performance to system & propagation parameters at carrier frequencies greater than 2 GHz

In this paper, mathematical analysis supported by computer simulation is used to investigate the impact of both system and propagation loss parameters on the performance of cellular wireless network operating at microwave carrier frequencies greater than 2 GHz, where multiple tier of co-channel interfering cells are considered to be active. The two-slope path loss model and the uplink information capacity of the cellular network is used for the performance analysis. Results show that for carrier frequencies greater than 2 GHz and smaller cell radius multiple tier of co-channel interfering cells become active as compared to carrier frequencies lesser than 2 GHz. The multiple tier of co-channel interfering cells, leads to a decrease in the information capacity of the cellular wireless network. The results also show that the system performance is sensitive to most of the propagation model parameters such as the basic and extra path loss exponent.

CELLULAR SYSTEM INFORMATION CAPACITY CHANGE AT HIGHER FREQUENCIES DUE TO PROPAGATION LOSS AND SYSTEM PARAMETERS

In this paper, mathematical analysis supported by computer simulation is used to study cellular system information capacity change due to propagation loss and system parameters (such as path loss exponent, shadowing and antenna height) at microwave carrier frequencies greater than 2 GHz and smaller cell size radius. An improved co-channel interference model, which includes the second tier co-channel interfering cells is used for the analysis. The system performance is measured in terms of the uplink information capacity of a time-division multiple access (TDMA) based cellular wireless system. The analysis and simulation results show that the second tier co-channel interfering cells become active at higher microwave carrier frequencies and smaller cell size radius. The results show that for both distance-dependent: path loss, shadowing and effective road height the uplink information capacity of the cellular wireless system decreases as carrier frequency increases and cell size radius R decreases. For example at a carrier frequency fc = 15.75 GHz, basic path loss exponent α = 2 and cell size radius R = 100, 500 and 1000m the decrease in information capacity was 20, 5.29 and 2.68%.

Highly linear RF amplifier design: theoretical analysis and experimental study

In this article, a high frequency amplifier design method based on the negative impedance compensation has been demonstrated analytically and experimentally. An effective nonlinear model has been used to simulate the harmonic distortion and intermodulation distortion factors in amplifier design. The simulation and measurement results show that, with this proposed technique, high linearity and high gain accuracy can be achieved. The proposed method is particularly suitable for linearisation of RF/microwave amplifiers with low open–loop gain.

High frequency CMOS amplifier with improved linearity

In this paper, a novel amplifier linearisation technique based on the negative impedance compensation is presented. As demonstrated by using Volterra model, the proposed technique is suitable for linearising amplifiers with low open-loop gain, which is appropriate for RF/microwave applications. A single-chip CMOS amplifier has been designed using the proposed method, and the simulation results show that high gain accuracy (improved by 38%) and high linearity (IMD3 improved by 14 dB, OIP3 improved by 11 dB and adjacent channel power ratio (ACPR) improved by 44% for CDMA signal) can be achieved.

Using the ‘T’ feedback network with the current feedback operational amplifier

Selecting a suitable feedback resistor R F and gain resistor R G is critical to ensure amplifier gain and stability when using current-feedback operational amplifiers (CFOAs). The bandwidth is determined primarily by R F and the gain then set using R G , which also equals the input resistance for the inverting configuration. This presents the applications engineer with very little choice in terms of component selection. In this paper, the feedback resistor R F is replaced by a modified ‘T’ network, resulting in greater design flexibility and improved performance in terms of gain accuracy and bandwidth. The inverting and non-inverting configurations are analysed and the design equations developed for the CFOA with and without the ‘T’ network, which clearly show the performance improvements. These theoretical results are confirmed with SPICE simulations using a commercially available macromodel of an industry standard CFOA.

The Smearing Filter Design Techniques for Data Transmission

Reducing Impulse noise is a very active research area in communication systems. This paper presents a digital smear-desmear technique (SDT) applied to data transmission over band limited channels. A generalized set of filter design criteria based on minimizing the average bit error probability is introduced. The design criteria were applied to a practical digital filter implementing SDT techniques. The SDT is simulated and combined with coded communication systems for high data transmission rate. Simulation results show that the SDT yields a significant improvement in bit error rates for coded systems subject to impulse noise, relative to the systems with no SDT. The technique also completely removes the error floor caused by the impulse noise.

Stability analysis and stabilisation of an amplifier with non-linearity compensation

ABSTRACT The rapid development of wireless communication system has led to pressing need for highly linear amplifier design and implementation as amplifier is one of the most critical devices in transmit and receive chain. In recent years, a number of new and emerging amplifier linearisation techniques using special distortion correction have been receiving more and more attention due to their significant advantages. One of the techniques is the negative impedance compensation. The design results showed that high gain, good linearity and wider bandwidth can be achieved by using the novel compensation method. However, as some kind of feedback can be introduced when applying the negative impedance compensation, the stability of the whole system should be investigated carefully. In this paper, stability analysis and stabilisation have been performed for the amplifier with negative impedance compensation. The simulation results showed that stable circuit behaviour can be achieved by using the capacitive compensation in the negative impedance circuit.

Design of RF amplifier with enhanced performance

In this paper, a RF CMOS amplifier is designed on the basis of a novel negative impedance linearization technique with negative differential resistance (NDR) element. The simulation results show that the designed amplifier can achieve high gain accuracy, good linearity with improved efficiency, revealing that the proposed technique could find wider application in RF/Microwave circuits and systems.

Impact of Sectorization/Vehicular Traffic on Minimum Cell Size for Information Capacity Increase in Cellular Systems

In this paper results of mathematical analysis sup-ported by simulation are used to study the impact of sectorization/vehicular traffic on the theoretical limit for cell size radius reduction in cellular wireless communication systems. Information capacity approach is used for the analysis. Attention is given to the active co-channel interfering cells. Because at carrier frequencies greater than 2 GHz, co-channel interfering cells beyond the first tier becomes dominant as the cell size radius reduces. Results show that for sectorized cellular wireless communication system operating at carrier frequency greater than 2 GHz and having smaller cell size radius in a traffic environment the second tier co-channel interference still becomes active. This causes a decrease in the information capacity of the cellular wireless system. For example for a heavy vehicular traffic environment, at a carrier frequency f C = 15.75 GHz, basic path loss exponent α = 2 and cell radius R = 100, 300 and 500 m for a six sector cellular the decrease in information capacity, because of interference from the second tier was 5.47, 3.36 and 2.78%.

Channel impulse noise minimization using digital smear and desmear filter

The paper describes a digital smear-desmear technique (SDT) based on polyphase sequences with good autocorrelation properties. These sequences are applied to the design of digital smear/desmear filters and combined with Trellis-coded modulation (TCM) codes. The scheme has been investigated for 16-QAM and 64-QAM modulation. The impulse noise is modeled as a sequence of Poisson arriving delta functions with gaussian amplitudes. The impulse noise parameters are computed from experimental data. Results shows that the SDT filter design method yields a significant improvement in bit error rates as when subject to impulse noise, relative to systems with no SDT.