Shawn P. Stapleton’s research while affiliated with Simon Fraser University and other places

A high call-blocking rate is a consequence of an inefficient utilization of system resources, which is often caused by a load imbalance in the network. Load imbalances are common in wireless networks with a large number of cellular users. This paper investigates a load-balancing scheme for mobile networks that optimizes cellular performance with constraints of physical resource limits and users’ quality of service demands. In order to efficiently utilize the system resources, an intelligent distributed antenna system (IDAS) fed by a multibase transceiver station (BTS) has the ability to distribute the system resources over a given geographic area. To enable load balancing among distributed antenna modules, we dynamically allocate the remote antenna modules to the BTSs using an intelligent algorithm. A self-organized network (SON) for an IDAS is formulated as an integer-based linear-constrained optimization problem, which tries to balance the load among the BTSs. An estimation distribution algorithm (EDA) as an evolutionary algorithm is proposed to solve the optimization problem. The computational results of the EDA algorithm demonstrate optimum performance for small-scale networks and near-optimum performance for large-scale networks. The EDA algorithm is faster with marginally less complexity than an exhaustive search algorithm.

A high call blocking rate is a consequence of an inefficient utilization of system resources, which is often caused by a load imbalance in the network. Load imbalances are common in wireless networks with a large number of cellular users. This paper investigates a load-balancing scheme for mobile networks that optimizes cellular performance with constraints of physical resource limits and users quality of service demands. In order to efficiently utilize the system resources, an intelligent distributed antenna system (IDAS) fed by a multi base transceiver station (BTS) has the ability to distribute the system resources over a given geographic area. To enable load balancing among distributed antenna modules we dynamically allocate the remote antenna modules to the BTSs using an intelligent algorithm. A self-optimizing network for an IDAS is formulated as an integer based linear constrained optimization problem, which tries to balance the load among the BTSs. A discrete particle swarm optimization (DPSO) algorithm as an evolutionary algorithm is proposed to solve the optimization problem. The computational results of the DPSO algorithm demonstrate optimum performance for small-scale networks and near-optimum performance for large-scale networks. The DPSO algorithm is faster with marginally less complexity than an exhaustive search algorithm.

Increase in number of mobile users, generates unbalanced load traffic in wireless network. In this study, a load-balancing solution is investigated in order to optimise quality of service. An intelligent distributed antenna system (IDAS) fed by a base transceiver station (BTS) has the ability to distribute the cellular capacity over a given geographic area depending on the time-varying traffic. A virtual cell network is an IDAS with capacity routing capability. To enable load balancing among distributed antenna modules, the authors dynamically allocate the remote antenna modules to the BTS sectors. A self-organised network of virtual cells is formulated as an optimisation problem, which attempts to balance traffic load and minimises the hand-offs as two important cost factors in the network. Two evolutionary algorithms are proposed for optimisation: genetic algorithm and estimation distribution algorithm. Computational results of different traffic scenarios after performing the algorithms, demonstrate that the two algorithms attain excellent key performance indicators for small-scale networks.

The performance of cellular networks is strongly limited by inter-cell interference. In order to reduce this interference, several techniques have been proposed, e.g., the frequency reuse techniques and distributed antenna system (DAS). This paper investigates the combinations of hard frequency reuse (HFR) and soft frequency reuse (SFR) techniques with DAS in a unique cell architecture, which are called DAS-HFR and DAS-SFR, respectively. This paper analytically quantifies the performance of the downlink multi-cell for DAS-HFR and DAS-SFR in terms of the average spectral efficiency. This also shows, the most appropriate frequency reuse technique depends not only on the average achievable data rate inside the cell, but also on the guaranteed achievable data rate (the minimum achievable data rate which is necessary to be obtained regardless of geographic location). The results show that DAS-SFR improves the achievable data rate of cell edges in a multi-cell environment as compared to a DAS-HFR when frequency reuse factor 1 is utilized. The results also show that DAS-SFR significantly increases the system capacity as compared to the DAS-HFR when frequency reuse factor 3 is utilized.

The insensitivity to gain and phase mismatches is investigated in a multiband double image rejection transmitter (DIRT). Although a direct in-phase/quadrature (I/Q) modulator architecture is simple, the I/Q gain and phase mismatches directly affect the image rejection ratio (IRR) over the operating frequencies. However, the DIRT has low sensitivity to a small I/Q phase mismatch, while the IRR is predominantly dependent on the IF gain mismatch. Furthermore, there is a region of insensitivity to both gain and phase mismatches in the DIRT. To characterize the mismatch effects of the DIRT, the IRR is theoretically analyzed and simulated at the system level. The proposed DIRT with sliding-IF is implemented on a 0.13-μm CMOS process to prove the insensitivity to the I/Q mismatch effects over 11-15-GHz multiband frequency ranges. For supporting the multiband functionality, frequency dividers-by-4/8/16 are utilized to generate 0.675-, 1.35-, and 2.7-GHz quadrature IF LO signals using 10.8-GHz RF local oscillator (LO) signal. The measurement results show that the in-band image rejection and LO leakage suppression are greater than 48.8 and 43.5 dBc, respectively, over the wideband frequency range. The output referred 1-dB compression point is obtained as high as - 4 dBm with a 1.5-V power supply. A multiband CMOS DIRT operating over Ku -band has not been previously reported.

Gain and phase mismatch effects of a double image rejection transmitter (DIRT) are examined by using error vector magnitude (EVM), image rejection ratio (IRR) and a union bound on the symbol error rate (SER). Although the DIRT has been utilised in many applications, the relationship between EVM and the IRR has not been previously reported. To analyse the relationship between EVM and IRR, the EVM functions are obtained using a complex envelope based matrix model and the IRR functions are approximated to provide insight into the gain and phase mismatch effects. Furthermore, the transmitter architecture has a lower sensitivity on both gain and phase mismatches under a proposed intermediate frequency (IF) gain condition, defined as gain condition-II. The system simulation results show that the IRR greater than 40 dBc can be achieved with 1 dB IF gain mismatch over the phase mismatch variations of 8 to 8 . The SER simulation results are also given for evaluating the system performance.

Unwanted feedback between the donor (receive) and coverage (service) antennas of a relay (repeater) are created by the radio echoes from the local scatters and direct path antenna isolation limitations. These radio echoes create interference not only in the incoming signal from the base station, but also cause instability in the repeater. In this paper, we present an interference cancellation system (ICS) for the multihop WCDMA 3G networks. Various characteristic features of the interference cancellation system are illustrated using the MATLAB simulation results. An isolation gain of 40dB is achieved.

This paper examines the problem of coupling in on-channel repeaters for a WCDMA wireless system. Unwanted feedback between the donor and coverage antennas of a repeater are created by radio echoes from local scatterers; as well as direct path antenna isolation limitations. These radio echoes create interference not only in the incoming signal from the base station, but also cause instability in the repeater. This paper extends the use of an adaptive interference cancellation system (ICS) presented in to WCDMA signaling scheme. Various new characteristic features of the algorithm are illustrated using the MATLAB simulation results.

A design methodology of harmonic output impedance optimization is proposed to achieve high efficient power amplifier. First of all, the effects of harmonic impedances of high frequency and high power device on drain voltage and current are analyzed. The optimum harmonic impedance region for high efficiency improvement are suggested through the analysis of efficiency variations due to the internal impedance and output matching circuit of high frequency and high power device. From the measured results, a GaN harmonic tuned class-F amplifier has achieved 77% drain efficiency at the output power of 20 W. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 779–782, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24164

Maximizing coding efficiency is important in applications where bandpass SigmaDelta modulation is used as a source encoder to synthesize a two-level pulse train in RF class-D amplifiers. A periodic pulse-train model is developed to MIMIC the encoding of a bandpass SigmaDelta modulator for sinusoidal source signals, and it is shown that the coding efficiency of both the model and the modulator vary similarly with changes in carrier oversample ratio. The relationship between coding efficiency and carrier oversample ratio is not monotonic and has significant dips at certain ratios. The predictions of the model are compared with simulation results for a fourth-order bandpass modulator. The results show that coding efficiency is low in a modulator design where the input frequency is one-fourth the sample rate (f_s) and can be increased by as much as 15% by selecting a slightly lower oversample ratio such as (3/10)f_s.