Expression for evaluating performance of BPSK with MRC in Nakagami fading

A strikingly simple and fast to compute expression is derived for the performance of binary phase shift keying (BPSK) with maximal ratio combining (MRC) diversity in a Nakagami (1960) fading channel. The expression is valid for all Nakagami-m parameters. Furthermore, no concession is made as far as the accuracy of the results is concerned.     

Outdoor ventilation performance of various configurations of a layout of two adjacent buildings under isothermal conditions

This paper explores the pedestrian-level wind environment around two buildings of unequal heights for the effects of ratio of height of upwind building to that of downwind building, referred to as buildings height ratio, spacing distance between the buildings, and direction of ambient wind, on the outdoor air ventilation. The objective is to propose appropriate spacing distances for various configurations of this type of buildings layout in a suburban area of Kuala Lumpur, which would enable harnessing the full ventilation potential of the local wind conditions. A three-dimensional numerical technique employing computational fluid dynamics simulation of continuity and Reynolds-Averaged Navier-Stokes equations was used to study the turbulent flow field around the full-scale sizes of the buildings. Results indicate the influence of spacing distance between buildings, relative heights of the buildings and direction of ambient wind on outdoor ventilation. Results also show that 3-D turbulent flow processes such as lateral and secondary flows play significant roles in defining the wind flow pattern and ventilation availability. The perpendicular wind direction presents remarkable adverse effects compared to the inclined direction, while a higher upwind building height which would ordinarily be expected to proportionally obstruct wind flow could be of advantage, at low values of building height ratios, in enhancing outdoor ventilation. The findings established the need to give consideration to climatic factors such as wind flow and direction in planning urban cities, as it affects buildings to be situated in close proximity, especially when there is height difference.     

Decision feedback equalisation of coded I-Q QPSK in mobile radioenvironments

The bit error rate (BER) performance of equalised I-Q quadrature phase-shift keying (QPSK) is evaluated for wideband cellular systems. Decision feedback equalisation with the square-root Kalman updating algorithm is employed for I-Q coded systems. A gain of about 6 dB is achieved in favour of the I-Q scheme compared with the conventional Gray-mapped QPSK at a BER of 10^-3     

Hybrid macro/microdiversity techniques in the reverse-link wireless communication networks

We investigate microdiversity-augmented macrodiversity techniques in wireless communication networks. The setup consists of K widely separated access ports each carrying N antennas. The conventional selection macrodiversity (Scheme I) and two proposed methods (Scheme II and Scheme III) for port selection are investigated and their performance are compared. Scheme II utilizes the advancement in distributed antennas and radio-on-fiber technologies whereas Scheme III utilizes these technologies in a way similar to the soft handover of CDMA systems. After the port selection, the microdiversity uses n strongest signals (n les N) of the selected port for diversity combining if practical constraints preclude the use of all N signals. Analytical performance expressions for the probability of error and outage probability for Scheme I are developed. Simulations are used to investigate Scheme II and Scheme III and it is observed that these latter schemes exhibit performance superiority over the conventional macrodiversity selection method. The power savings obtained using the proposed architecture and new selection schemes could be used either for coverage extension or to increase capacity in wireless networks     

Cooperative relaying in multi-antenna fixed relay networks

Space, cost, and signal processing constraints, among others, often preclude the use of multiple antennas at wireless terminals. This paper investigates distributed decode-and-forward fixed relays (infrastructure-based relaying) which are engaged in cooperation in a two-hop wireless network as a means of removing the burden of multiple antennas on wireless terminals. In contrast to mobile terminals, the deployment of a small number of antennas on infrastructure-based fixed relays is feasible, thus, the paper examines the impact of multiple antennas on the performance of the distributed cooperative fixed relays. Threshold-based maximal ratio combining (MRC) and threshold-based selection combining (SC) of these multiple antenna signals are studied and analyzed. It is found that the end-to-end (E2E) error performance of a network which has few relays with many antennas is not significantly worse than that which has many relays each with a fewer antennas. Obviously, the former network has a tremendous deployment cost advantage over the latter. It is also observed that the E2E error performance of a network in which the multiple antennas at relays are configured in SC fashion is not significantly worse than that in which MRC is used. For implementation, SC presents a significantly lower complexity and cost than a full-blown MRC. The analysis in this paper uses the versatile Nakagami fading channels in contrast to the Rayleigh model used in most previous works     

Response to the comments on the paper “Outdoor ventilation performance of various configurations of a layout of two adjacent buildings under isothermal conditions”

This paper is a response to the paper “Comments on the paper ‘Outdoor ventilation performance of various configurations of a layout of two adjacent buildings under isothermal conditions’ (by Ayo et al. (2015), Building Simulation, 8: 81–98)”.     

Practical capacity calculation for time-hopping ultra-wide band multiple-access communications

In this letter the practical capacity, known as the cutoff rate, of time-hopping (TH) ultra-wide band (UWB) communication system is evaluated for multiple-access channels. The cutoff rate can be used for determining various system tradeoffs. For instance, it is shown in this letter that if synchronization problems would preclude high spreading factors, a suitable number of hops can be used instead to achieve the same performance. Moreover, it is demonstrated that the cutoff rate evaluated here can be a fast way of gaining insights into the multiuser capacity of TH-PPM UWB systems.     

Multiaxial fatigue of extruded ZK60 magnesium alloy

Multiaxial monotonic and cyclic behaviors of ZK60‐T5 magnesium extrusion are investigated. Strain‐controlled tests were performed at standard laboratory condition with fully reversed straining. Twinning‐detwinning deformation plays an important role in the cyclic axial behavior for tests that were performed under strain amplitudes higher than 0.4%. However, the hysteresis loop for the 0.4% was found symmetric and no sign of twinning‐detwinning deformation was observed. On the contrary, the cyclic shear behavior was found to be similar to conventional alloys and no significant asymmetric or twinning‐detwinning deformations were observed. The multiaxial fatigue tests suggest that multiaxiality and nonproportionality are not detrimental to fatigue life. Three multiaxial fatigue damage models were used: Smith‐Watson‐Topper, Fatemi‐Socie, and Jahed‐Varvani. While Fatemi‐Socie and Jahed‐Varvani models show comparable estimation, Smith‐Watson‐Topper overestimates shear and nonproportional lives.