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This paper considers the suitability of a range of multi-input-multi-output (MIMO) orthogonal frequency-division multiplexing architectures for use in urban hotspots. A ray-tracing propagation model is used to produce realistic MIMO channel data. This information is used to determine the expected throughput and area coverage for various physical (PHY) layer schemes. Site-specific throughput predictions are generated in a city-center environment. Link adaptation (LA) is shown to play a key role in the choice of space-time algorithm, the use of adaptive modulation and coding, and the number of antennas employed at both ends of the radio link. No single PHY layer scheme is suitable to cover the entire coverage area. Results demonstrate the need for MIMO LA under a wide range of channel conditions. For the area under test, 2% of covered locations selected a spatial multiplexing (SM) scheme, 50% selected a space-time block coding (STBC) scheme, and 48 % selected a hybrid SM/STBC scheme. With suitable power control and LA, for the scenario under consideration, high peak capacities and good geographic coverage were achieved. Index Terms--Link adaptation (LA), orthogonal frequency-division multiplexing (OFDM), power control, propagation, space-time block codes (STBCs), spatial multiplexing (SM).

For multihop and ad hoc networks, a conventional 1-D channel model cannot capture the spatial correlation of the shadowing processes. This paper investigates the joint spatial correlation property of the shadowing process for peer-to-peer (P2P) radio links in urban environments. When a fixed base station is assumed, statistical analysis reveals that the shadowing process is mainly a result of spatial displacement at the mobile station (MS). Furthermore, the joint correlation property of the MS-MS channel shows that MS displacements at each end of the P2P link have an independent and equal effect on the correlation coefficient. A sum-of-sinusoids simulation model is proposed to generate the joint correlation shadowing process for urban P2P radio channels. The performance of the proposed channel simulator is analyzed in terms of the autocorrelation and joint correlation function of the simulated shadowing process. Simulations illustrate that the proposed model is able to output deterministic shadowing with a normal distribution (in decibels) and the desired correlation properties. It is thus suitable for use in system-level simulations, such as the evaluation of routing and radio resource management algorithms in ad hoc or mesh networks. Index Terms--Ad hoc, channel model, multihop, shadowing, spatial correlation, urban.

In this paper, an advanced site-specific image-based ray-tracing model is developed that enables multielement outdoor propagation analysis to be performed in dense urban environments. Sophisticated optimization techniques, such as preprocessing the environment database using object partitioning, visibility determination, diffraction image tree precalculation, and parallel processing are used to improve run-time efficiency. Wideband and multiple.input--multiple-output (MIMO) site-specific predictions (including derived parameters such as theoretic capacity and eigenstructure) are compared with outdoor site-specific measurements at 1.92 GHz. Results show strong levels of agreement, with a mean path-loss error of 2 dB and a mean normalized-capacity error of 1.5 b/s/Hz. Physical-layer packet-error rate (PER) results are generated and compared for a range of MIMO-orthogonal frequency-division-multiplexing (OFDM) schemes using measured and predicted multielement channel data. A mean [E.sub.b]/ [N.sub.o] error (compared to PER results from measured channel data) of 4 and 1 dB is observed for spatial-multiplexing and spacetime block-code schemes, respectively. Results indicate that the ray-tracing model successfully predicts key channel parameters (including MIMO channel structure) and thus enable the accurate prediction of PER and service coverage for emerging MIMO-OFDM networks such as 802.11n and 802.16e. Index Terms--Multiple-input-multiple-output (MIMO), propagation, ray tracing, scattering.

The Mosque of Ibn ḥūlūn was the third congregational Mosque built in the Muslim capital of Egypt. The first, originally built by 'Amr, the conqueror of the country, in a.h. 21 (a.d. 642), was re-built and extended by many governors in succession, and still remains—a monument of great historical, if of slight artistic interest. The second, known as Gāmi' al 'Askar, or the Camp Mosque, was built in a.h. 169 (a.d. ), in the military suburb which had grown up since a.h. 133 to the N.E. of the original capital. This Mosque was increased in size in a.h. 211 (a.d. ) and is heard of as late as a.h. 517 (a.d. 112¾); but all traces of it have been lost for many centuries, nor have any details come down to us with regard to its plan and architecture. [ABSTRACT FROM PUBLISHER]

The traveller in Egypt who wishes to visit the Mosque of Amr may now leave Cairo either by train or carriage, and step out in the immediate neighbourhood. But he who prefers the most picturesque and interesting route will either ride or walk, and taking the street which runs parallel to the Khalīg, or Canal of Cairo, will pass out of the town by the gate of Sayyida Zeinab. Following the road past the picturesque little Mosque of Zein al Ābidin, he will pass under the Aqueduct, and proceed along the track which leads him through a country of mounds and dust-heaps past the Mosque of Abu-s-Suūd to the N. front of the building which he seeks (see Plan I.). Here let him ascend the mound which lies outside the huts by which the facade of the Mosque is shut in, and, facing towards them, take a general view of the scene. To his left he looks over a dusty space of comparatively low-lying ground, to the Aqueduct under which he passed twenty minutes ago; on his left front the citadel of Cairo stands out in the distance beyond a large expanse of high dust-mounds. Straight before him is the Mosque, but he can see little of it excepting the higher part of the two minarets, the mass of huts shutting out the view of the low walls; but behind the Mosque, at some two miles' distance, the limestone cliffs of Mukattam gleam in the sunshine: while further to the right the eye rests on a dusty height crowned by disused windmills. [ABSTRACT FROM PUBLISHER]

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Competing Interests: Conflicts of interest The authors declare no conflicts of interest.

Competing Interests: Conflicts of interest The authors declare no conflicts of interest.

Competing Interests: Conflicts of interest The authors declare they have no conflicts of interest.