http://www.hindawi.comThe latest articles from Hindawi Publishing Corporation© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/149803Orthogonal frequency division multiplexing- (OFDM-) based amplify-and-forward (AF) cooperative communication is an effective way for single-antenna systems to exploit the spatial diversity gains in frequency-selective fading channels, but the receiver usually requires the knowledge of the channel state information to recover the transmitted signals. In this paper, a training-sequences-aided linear minimum mean square error (LMMSE) channel estimation method is proposed for OFDM-based cooperative diversity systems with multiple AF relays over frequency-selective fading channels. The mean square error (MSE) bound on the proposed method is derived and the optimal training scheme with respect to this bound is also given. By exploiting the optimal training scheme, an optimal low-rank LMMSE channel estimator is introduced to reduce the computational complexity of the proposed method via singular value decomposition. Furthermore, the Chu sequence is employed as the training sequence to implement the optimal training scheme with easy realization at the source terminal and reduced computational complexity at the relay terminals. The performance of the proposed low-complexity channel estimation method and the superiority of the derived optimal training scheme are verified through simulation results.Kai Yan, Sheng Ding, Yunzhou Qiu, Yingguan Wang, and Haitao Liu© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/271989Group key exchange (GKE) is one of the basic building blocks in securing group communication. A number of solutions to GKE problem have been proposed, but most of them are not scalable and require a number of rounds linear with the number of group members. We present a method of constructing constant-round and identity-based protocol via secret sharing for GKE within universally composability (UC) framework. The resultant protocol focuses on round efficiency and three rounds of communication are required. The protocol allows the batch verification of messages signed by all other group participants. Moreover, compared with other identity-based protocols, the key generation center (KGC) in our protocol is not always online.Chunjie Cao, Chao Yang, Jianfeng Ma, and Sangjae Moon© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/586878We study the potential benefits of base-station (BS) cooperation for downlink transmission in multicell networks. Based on a modified Wyner-type model with users clustered at the cell-edges, we analyze the dirty-paper-coding (DPC) precoder and several linear precoding schemes, including cophasing, zero-forcing (ZF), and MMSE precoders. For the nonfading scenario with random phases, we obtain analytical performance expressions for each scheme. In particular, we characterize the high signal-to-noise ratio (SNR) performance gap between the DPC and ZF precoders in large networks, which indicates a singularity problem in certain network settings. Moreover, we demonstrate that the MMSE precoder does not completely resolve the singularity problem. However, by incorporating path gain fading, we numerically show that the singularity problem can be eased by linear precoding techniques aided with multiuser selection. By extending our network model to include cell-interior users, we determine the capacity regions of the two classes of users for various cooperative strategies. In addition to an outer bound and a baseline scheme, we also consider several locally cooperative transmission approaches. The resulting capacity regions show the tradeoff between the performance improvement and the requirement for BS cooperation, signal processing complexity, and channel state information at the transmitter (CSIT).Sheng Jing, David N. C. Tse, Joseph B. Soriaga, Jilei Hou, John E. Smee, and Roberto Padovani© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/598401This paper presents a new class of low-density parity-check (LDPC) codes over ℤ2a represented by regular, structured Tanner graphs. These graphs are constructed using Latin squares defined over a multiplicative group of a Galois ring, rather than a finite field. Our approach yields codes for a wide range of code rates and more importantly, codes whose minimum pseudocodeword weights equal their minimum Hamming distances. Simulation studies show that these structured codes, when transmitted using matched signal sets over an additive-white-Gaussian-noise channel, can outperform their random counterparts of similar length and rate.Elisa Mo and Marc A. Armand© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/865393The International Telecommunication Union-Radiocommunication sector (ITU-R) has conducted frequency sharing studies between fixed services (FSs) using a high altitude platform station (HAPS) and fixed-satellite services (FSSs). In particular, ITU-R has investigated the power limitations related to HAPS user terminals (HUTs) to facilitate frequency sharing with space station receivers. To reduce the level of interference from the HUTs that can harm a geostationary earth orbit (GEO) satellite receiver in a space station, previous studies have taken two approaches: frequency sharing using a separated distance (FSSD) and frequency sharing using power control (FSPC). In this paper, various performance evaluation results of interference mitigation schemes are presented. The results include performance evaluations using a new interference mitigation approach as well as conventional approaches. An adaptive beamforming scheme (ABS) is introduced as a new scheme for efficient frequency sharing, and the interference mitigation effect on the ABS is examined considering pointing mismatch errors. The results confirm that the application of ABS enables frequency sharing between two systems with a smaller power reduction of HUTs in a cocoverage area compared to this reduction when conventional schemes are utilized. In addition, the analysis results provide the proper amount of modification at the transmitting power level of the HUT required for the suitable frequency sharing.Bon-Jun Ku, Do-Seob Ahn, and Nam Kim© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/675048This paper addresses pre-FFT synchronisation for orthogonal frequency division multiplex (OFDM) under varying multipath conditions. To ensure the most efficient data transmission possible, there should be no constraints on how much of the cyclic prefix (CP) is occupied by intersymbol interference (ISI). Here a solution for timing synchronisation is proposed, that is, robust even when the strongest multipath components are delayed relative to the first arriving paths. In this situation, existing methods perform poorly, whereas the solution proposed uses the derivative of the correlation function and is less sensitive to the channel impulse response. In this paper, synchronisation of a DVB single-frequency network is investigated. A refinement is proposed that uses heuristic rules based on the maxima of the correlation and derivative functions to further reduce the estimate variance. The technique has relevance to broadcast, OFDMA, and WLAN applications, and simulations are presented which compare the method with existing approaches.C. Williams, S. McLaughlin, and M. A. Beach© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/843634There has been renewed interest in decoding Reed-Solomon (RS) codes without using syndromes recently. In this paper, we investigate the complexity of syndromeless decoding, and compare it to that of syndrome-based decoding. Aiming to provide guidelines to practical applications, our complexity analysis focuses on RS codes over characteristic-2 fields, for which some multiplicative FFT techniques are not applicable. Due to moderate block lengths of RS codes in practice, our analysis is complete, without big O notation. In addition to fast implementation using additive FFT techniques, we also consider direct implementation, which is still relevant for RS codes with moderate lengths. For high-rate RS codes, when compared to syndrome-based decoding algorithms, not only syndromeless decoding algorithms require more field operations regardless of implementation, but also decoder architectures based on their direct implementations have higher hardware costs and lower throughput. We also derive tighter bounds on the complexities of fast polynomial multiplications based on Cantor's approach and the fast extended Euclidean algorithm.Ning Chen and Zhiyuan Yan© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/182042We investigate the possibility of multiple high altitude platform (HAP) coverage of a common cell area using a wideband code division multiple access (WCDMA) system. In particular, we study the uplink system performance of the system. The results show that depending on the traffic demand and the type of service used, there is a possibility of deploying 3–6 HAPs covering the same cell area. The results also show the effect of cell radius on performance and the position of the multiple HAP base stations which give the worst performance.T. Hult, D. Grace, and A. Mohammed© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/341726This paper considers a system where one transmitter broadcasts a single common message to two receivers linked by a bidirectional cooperation channel, which is assumed to be orthogonal to the downlink channel. Assuming a simplified setup where, in particular, scalar relaying protocols are used and channel coding is not exploited, we want to provide elements of response to several questions of practical interest. Here are the main underlying issues: (1) the way of recombining the signals at the receivers; (2) the optimal number of cooperation rounds; (3) the way of cooperating (symmetrically or asymmetrically, which receiver should start cooperating in the latter case); and (4) the influence of spectral resources. These issues are considered by studying the performance of the assumed system through analytical results when they are derivable and through simulation results. For the particular choices we made, the results sometimes do not coincide with those available for the discrete counterpart of the studied channel.E. V. Belmega, B. Djeumou, and S. Lasaulce© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/561869This paper presents the impact of synchronization errors on the performance of a downlink multicarrier two-dimensional spreading OFDM-CDMA system. This impact is measured by the degradation of the signal to interference and noise ratio (SINR) obtained after despreading and equalization. The contribution of this paper is twofold. First, we use some properties of random matrix and free probability theories to derive a new expression of the SINR. This expression is then independent of the actual value of the spreading codes while still accounting for the orthogonality between codes. This model is validated by means of Monte Carlo simulations. Secondly, the model is exploited to derive the SINR degradation of OFDM-CDMA systems due to synchronization errors which include a timing error, a carrier frequency offset, and a sampling frequency offset. It is also exploited to compare the sensitivities of MC-CDMA and MC-DS-CDMA systems to these errors in a frequency selective channel. This work is carried out for zero-forcing and minimum mean square error equalizers.Youssef Nasser, Mathieu des Noes, Laurent Ros, and Geneviève Jourdain© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/362897Trapping sets are considered the primary factor for degrading the performance of low-density parity-check (LDPC) codes in the error-floor region. The effect of trapping sets on the performance of an LDPC code becomes worse as the code size decreases. One approach to tackle this problem is to minimize trapping sets during LDPC code design. However, while trapping sets can be reduced, their complete elimination is infeasible due to the presence of cycles in the underlying LDPC code bipartite graph. In this work, we introduce a new technique based on trapping sets neutralization to minimize the negative effect of trapping sets under belief propagation (BP) decoding. Simulation results for random, progressive edge growth (PEG) and MacKay LDPC codes demonstrate the effectiveness of the proposed technique. The hardware cost of the proposed technique is also shown to be minimal.Esa Alghonaim, Aiman El-Maleh, and Mohamed Adnan Landolsi© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/896420This paper addresses the problem of optimal channel selection for spectrum-agile low-powered wireless networks in unlicensed bands. The channel selection problem is formulated as a multiarmed bandit problem enabling us to derive the optimal selection rules. The model assumptions about the interfering traffic that motivates this formulation are also validated through 802.11 traffic measurements as an example of a packet switched network. Finally, the performance of the optimal dynamic channel selection is investigated through simulation. The simulation results show that the proposed algorithm consistently tracks the best channel compared to other heuristic schemes.Ali Motamedi and Ahmad Bahai© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/624542We propose a convolutional encoder over the finite ring of integers modulo pk,ℤpk, where p is a prime number and k is any positive integer, to generate a space-time convolutional code (STCC). Under this structure, we prove three properties related to the generator matrix of the convolutional code that can be used to simplify the code search procedure for STCCs over ℤpk. Some STCCs of large diversity order (≥4) designed under the trace criterion for n=2,3, and 4 transmit antennas are presented for various PSK signal constellations.Mario de Noronha-Neto and B. F. Uchôa-Filho© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/658042Turbo product codes (TPCs) are an attractive solution to improve link budgets and reduce systems costs by relaxing the requirements on expensive optical devices in high capacity optical transport systems. In this paper, we investigate the use of Reed-Solomon (RS) turbo product codes for 40 Gbps transmission over optical transport networks and 10 Gbps transmission over passive optical networks. An algorithmic study is first performed in order to design RS TPCs that are compatible with the performance requirements imposed by the two applications. Then, a novel ultrahigh-speed parallel architecture for turbo decoding of product codes is described. A comparison with binary Bose-Chaudhuri-Hocquenghem (BCH) TPCs is performed. The results show that high-rate RS TPCs offer a better complexity/performance tradeoff than BCH TPCs for low-cost Gbps fiber optic communications.Raphaël Le Bidan, Camille Leroux, Christophe Jego, Patrick Adde, and Ramesh Pyndiah© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/604747The problems of redundant RFID reader detection and coverage have instigated researchers to propose different optimization heuristics due to the rapid advance of technologies in large-scale RFID systems. In this paper, we present a layered elimination optimization (LEO) which is an algorithm-independent technique aims to detect maximum amount of redundant readers that could be safely removed or turned off with preserving original RFID network coverage. A significant improvement of the LEO scheme is that amount of “write-to-tag” operations could be largely reduced during the redundant reader identification phase. Moreover, LEO is a distributed approach which does not need to collect global information for centralizing control, leading to no communications or synchronizations among RFID readers. To evaluate the performance of the proposed techniques, we have implemented the LEO technique along with other methods. Both theoretical analysis and experimental results show that the LEO is reliable, effective, and efficient. The proposed techniques can provide reliable performance with detecting higher redundancy and has lower algorithm overheads.Ching-Hsien Hsu, Yi-Min Chen, and Heau-Jo Kang© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/473613This paper presents a new approach to decode turbo codes using a nonbinary belief propagation decoder. The proposed approach can be decomposed into two main steps. First, a nonbinary Tanner graph representation of the turbo code is derived by clustering the binary parity-check matrix of the turbo code. Then, a group belief propagation decoder runs several iterations on the obtained nonbinary Tanner graph. We show in particular that it is necessary to add a preprocessing step on the parity-check matrix of the turbo code in order to ensure good topological properties of the Tanner graph and then good iterative decoding performance. Finally, by capitalizing on the diversity which comes from the existence of distinct efficient preprocessings, we propose a new decoding strategy, called decoder diversity, that intends to take benefits from the diversity through collaborative decoding schemes.Charly Poulliat, David Declercq, and Thierry Lestable© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/598080It is increasingly difficult to satisfy growing demands for spectrum with the conventional policy of fixed spectrum allocation. To overcome this problem, flexible/dynamic spectrum sharing methods that can significantly improve spectrum utilization of the spectrum have gained increasing interest recently. This paper presents two dynamic spectrum sharing approaches, a centralized and a decentralized one. The centralized approach is based on hierarchical trading. Each level of hierarchy is composed of “markets” that are associated with a certain spatial area and trading occurrence frequency, whereas area size and trading occurrence frequency depend on the hierarchy level. The decentralized approach is based on game-theory. There, it is assumed that the operators are averse to unequal payoffs and act unselfishly, enabling a stable and sustainable community. Numerical results show that, in the observed scenario, both proposals outperform the reference case of fixed resource allocation significantly in terms of utilized bandwidth. Whereas, negotiation costs for spectrum brokerage appear in the centralized approach, nonnegligible amounts of spectrum are lost in the decentralized approach due to collisions. Thus, a hybrid of centralized and decentralized approach that exploits the benefits of both is also considered.Takefumi Yamada, Dennis Burgkhardt, Ivan Cosovic, and Friedrich K. Jondral© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/639528Session Initiation Protocol (SIP) has been proposed for multimedia services and wide-area connectivity in smart home environments (SHEs). An important issue for SIP deployment in SHEs is network address translator (NAT) traversing. SIP and Real-time Transport Protocol (RTP) packets are delivered between an SHE (i.e., private IP network) and Internet (i.e., a public IP network) through an NAT function of a home gateway, and the NAT translates the IP/transport layer address and port number but leaves the application layer content unchanged. This results in inconsistency between the IP addresses/port numbers in the IP/transport layers and those in the SIP layer. To resolve this issue, we describe six solutions including static route, UPnP, STUN, ICE, ALG, and SBC. Then we compare these solutions in terms of smart home appliance (SHA) modification, scope of NATs supported, multilayer NAT traversal, ease of configuration, security issue, and time complexities.Whai-En Chen, Ya-Lin Huang, and Han-Chieh Chao© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/652325This paper considers an enhancement to multicell processing for the uplink of a cellular system, whereby the mobile stations are allowed to exchange messages on orthogonal channels of fixed capacity (conferencing). Both conferencing among mobile stations in different cells and in the same cell (inter- and intracell conferencing, resp.) are studied. For both cases, it is shown that a rate-splitting transmission strategy, where part of the message is exchanged on the conferencing channels and then transmitted cooperatively to the base stations, is capacity achieving for sufficiently large conferencing capacity. In case of intercell conferencing, this strategy performs convolutional pre-equalization of the signal encoding the common messages in the spatial domain, where the number of taps of the finite-impulse response equalizer depends on the number of conferencing rounds. Analysis in the low signal-to-noise ratio regime and numerical results validate the advantages of conferencing as a complementary technology to multicell processing.O. Simeone, O. Somekh, G. Kramer, H. V. Poor, and S. Shamai (Shitz)© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/318704Cores of cooperative games are ubiquitous in information theory and arise most frequently in the characterization of fundamental limits in various scenarios involving multiple users. Examples include classical settings in network information theory such as Slepian-Wolf source coding and multiple access channels, classical settings in statistics such as robust hypothesis testing, and new settings at the intersection of networking and statistics such as distributed estimation problems for sensor networks. Cooperative game theory allows one to understand aspects of all these problems from a fresh and unifying perspective that treats users as players in a game, sometimes leading to new insights. At the heart of these analyses are fundamental dualities that have been long studied in the context of cooperative games; for information theoretic purposes, these are dualities between information inequalities on the one hand and properties of rate, capacity, or other resource allocation regions on the other.Mokshay Madiman© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/580761This paper addresses the displacement of a base station with optimization approach. A genetic algorithm is used as optimization approach. A new representation that describes base station placement, transmitted power with real numbers, and new genetic operators is proposed and introduced. In addition, this new representation can describe the number of base stations. For the positioning of the base station, both coverage and economy efficiency factors were considered. Using the weighted objective function, it is possible to specify the location of the base station, the cell coverage, and its economy efficiency. The economy efficiency indicates a reduction in the number of base stations for cost effectiveness. To test the proposed algorithm, the proposed algorithm was applied to homogeneous traffic environment. Following this, the proposed algorithm was applied to an inhomogeneous traffic density environment in order to test it in actual conditions. The simulation results show that the algorithm enables the finding of a near optimal solution of base station placement, and it determines the efficient number of base stations. Moreover, it can offer a proper solution by adjusting the weighted objective function.Yong Seouk Choi, Kyung Soo Kim, and Nam Kim© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/754021The MacWilliams identity, which relates the weight distribution of a code to the weight distribution of its dual code, is useful in determining the weight distribution of codes. In this paper, we derive the MacWilliams identity for linear codes with the rank metric, and our identity has a different form than that by Delsarte. Using our MacWilliams identity, we also derive related identities for rank metric codes. These identities parallel the binomial and power moment identities derived for codes with the Hamming metric.Maximilien Gadouleau and Zhiyuan Yan© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/902592In recent years, the wireless mobile markets are witnessing an unprecedented growth. High-quality video service will be greatly needed as one of the hottest wireless multimedia services in the future generation wireless networks. In this paper, a novel content-based distortion control scheme is proposed to provide higher quality of the wireless video services. Our scheme adopts rate-distortion optimization techniques in state-of-the-art video coding standard H.264/AVC. In order to improve the subjective video quality in the process of encode, we create three visual distortion sensitivity models to minimize the perceptual distortion. We arrange more bits to visual distortion sensitive macroblocks during rate-distortion optimization process. The perceptual distortion in these regions is thus efficiently controlled with a relatively higher rate. Meanwhile, rate balance is achieved by allotting fewer bits to macroblocks that are perceptually less sensitive to distortion. Experiments results show that the subjective qualities of encoded video are improved without compromising PSNR.Chang Sun, Hong-Jun Wang, Seoksoo Kim, Young-Sil Kim, Seung-youn Lee, and Xin-Bo Yu© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/521834Relay-based transmission can over the benefits in terms of coverage extension as well as throughput improvement if compared to conventional direct transmission. In a relay enhanced cellular (REC) network, where multiple mobile terminals act as relaying nodes (RNs), multiuser diversity gain can be exploited. We propose an efficient relaying scheme, referred to as Broadcast Reserved Opportunity Assisted Diversity (BROAD) for the REC networks. Unlike the conventional Induced Multiuser Diversity Relaying (IMDR) scheme, our scheme acquires channel quality information (CQI) in which the destined node (DN) sends pilots on a reserved radio resource. The BROAD scheme can significantly decrease the signaling overhead among the mobile RNs while achieving the same multiuser diversity as the conventional IMDR scheme. In addition, an alternative version of the BROAD scheme, named as A-BROAD scheme, is proposed also, in which the candidate RN(s) feed back partial or full CQI to the base station (BS) for further scheduling purpose. The A-BROAD scheme achieves a higher throughput than the BROAD scheme at the cost of extra signalling overhead. The theoretical analysis given in this paper demonstrates the feasibility of the schemes in terms of their multiuser diversity gains in a REC network.Xia Chen, Honglin Hu, Shengyao Jin, and Hsiao-Hwa Chen© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/480293The H.264 video encoding technology, which has emerged as one of the most promising compression standards, offers many new delivery-aware features such as data partitioning. Efficient transmission of H.264 video over any communication medium requires a great deal of coordination between different communication network layers. This paper considers the increasingly popular and widespread 802.11 Wireless Local Area Networks (WLANs) and studies different schemes for the delivery of the baseline and extended profiles of H.264 video over such networks. While the baseline profile produces data similar to conventional video technologies, the extended profile offers a partitioning feature that divides video data into three sets with different levels of importance. This allows for the use of service differentiation provided in the WLAN. This paper examines the video transmission performance of the existing contention-based solutions for 802.11e, and compares it to our proposed scheduled access mechanism. It is demonstrated that the scheduled access scheme outperforms contention-based prioritized services of the 802.11e standard. For partitioned video, it is shown that the overhead of partitioning is too high, and better results are achieved if some partitions are aggregated. The effect of link adaptation and multirate operation of the physical layer (PHY) is also investigated in this paper.Yaser Pourmohammadi Fallah, Panos Nasiopoulos, and Hussein Alnuweiri© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/195948A method is proposed to identify the existence of line-of-sight (LOS) for time-varying, frequency selective radio channels. The proposed method considers the second-order statistical characteristics of underlying process in the channel taps. Identification is established by comparing the autocorrelation coefficients of the first tap with those of any other tap when the other tap reaches its coherence time. Numerical results and related discussions are presented considering several practical scenarios.Serhan Yarkan and Hüseyin Arslan© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/543290The aim of this paper is to present the results of a measurement campaign focused on the evaluation of penetration loss into buildings in an urban area as a function of the elevation angle. An empirical model to predict penetration loss into buildings is developed based on measured data obtained using a remote-controlled airship. The impact on penetration loss of different buildings and user positions within the buildings is presented. The measured data are evaluated as a function of the elevation angle. The measurement campaign was carried out at 2.0 GHz and 3.5 GHz carrier frequencies, representing the frequency band for high altitude platform third-generation mobile systems and, potentially, next generation mobile systems, mobile WiMAX, for example, the new penetration loss model can be used for system performance simulations and coverage planning.Jaroslav Holis and Pavel Pechac© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/732418An efficient scheduling scheme is proposed to increase the available capacity of VoIP services over evolved UTRA uplink. On top of the advantages of persistent scheduling, the proposed scheme adaptively share the resources of two VoIP users to get early-termination gain of dynamic scheduler. Through system-level simulations, the performance of the proposed algorithm is evaluated in terms of the capacity enhancement of VoIP services. Comparisons with the original persistent scheduling and the HSUPA scheduler reveal that the proposed scheme increases the capacity of VoIP services up to 20%.Yong-Seok Kim© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/734216The atmosphere and rainfall significantly limit the performance of millimeter wave links and this has to be taken into account, particularly, during planning of high altitude platform (HAP) networks. This paper presents results from the measurement and simulation of these phenomena. A simulation tool from our previous analyses of terrestrial point-to-multipoint systems has been modified for HAP systems. Based on a rainfall radar database and gas attenuation characteristics as measured by a Fabry-Perot resonator, the performance of a simple link, two-branch diversity links, and more complicated HAP scenarios are discussed.S. Zvanovec, P. Piksa, M. Mazanek, and P. Pechac© 2008, Hindawi Publishing Corporation. All rights reserved.http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/864031In a free-space optical communication system employing fiber-optic components, the phasefront distortions induced by atmospheric turbulence limit the efficiency with which the laser beam is coupled into a single-mode fiber. We analyze different link scenarios including a geostationary (GEO) satellite, a high-altitude platform (HAP), and an optical ground station (OGS). Single-mode coupled optically preamplified receivers allow for efficient suppression of background noise and highly sensitive detection. While GEO-to-OGS communication suffers from atmospheric turbulence, we demonstrate that GEO-to-HAP communication allows for close to diffraction-limited performance when applying tip-tilt correction.Franz Fidler and Oswald Wallner© 2008, Hindawi Publishing Corporation. All rights reserved.