Open Topics

Vol. 65, n° 7-8, July-August 2010
Content available on SpringerLink

Mutual interference considered power allocationin OFDM-based cognitive networks: the multiple SUs case

Chengshi Zhao* · Mingrui Zou*,** · Kyungsup Kwak*

* Telecommunications Engineering Lab, Graduate School of IT and Telecom., Inha University, 253 YongHyun-Dong, Nam-Gu, Incheon, 402-751, Republic of Korea
** Wireless Network Lab, School of Information and Communication Engineering, Beijing University of Posts and Telecommunications, Beijing, 100876, China

Abstract Power allocation for secondary users (SUs) in cognitive networks is an important issue to ensure the SUs’ quality of service. When the mutual interference between the primary users (PUs) and the SUs is taken into consideration, it is wanted to achieve the conflictfree power allocation while synchronously maximizing the capacity of the secondary network. In this paper, the optimal power allocation problem is considered in orthogonal frequency division multiplexing cognitive networks. The single SU case is primarily formulated as a constrained optimization problem. On this basis, the multiple SUs case is then studied and simulated in detail. During the analysis, themutual interference among the PUs and the SUs is comprehensively formulated as the restrictions on the SU’s transmission power and the optimization problems are finally resolved by iterative water-filling algorithms. Consequently, the proposed power allocation scheme restrains the interference to the primary network, as well as maximizing the capacity of the secondary network. Specifying the multiple-SUs case, simulation results are exhibited in a simplified sce- nario to confirm the efficiency of the proposed waterfilling algorithm, and the influence of the mutual interference on the power allocation and the system capacity is further illustrated.

Keywords Cognitive radio · Power allocation · Water-filling · OFDM

A probabilistic model for sub-carrier allocation in OFDMA systems

Jamal S. Rahhal

Electrical Engineering Department, The University of Jordan, Amman, Jordan

Abstract Orthogonal frequency division multiple-access technique showed a successful utilization of channel features. It implements an orthogonal sub-carrier space to be shared among different users. The management of these sub-carriers in both power and frequency allocation is reflected on the systems performance as better utilization of bandwidth, and hence, better capacity is obtained. Subcarrier allocation is used to avoid deep fading that might occur at some user’s locations but not at other user’s locations. In this paper, we devise an algorithm based on probabilistic model for sub-carrier allocation to avoid deep fading in some user’s signals. By controlling the sub-carrier allocation for each user, we can create a full rank channel for each user and hence, provide maximum capacity for the system. Simulation results showed that using the devised algorithm will avoid deep fading and utilize the bandwidth up to 40% more than localized allocation strategies.

Keywords OFDMA . LTE . LOFDMA . DOFDMA. MIMO . Outage and capacity

Exploiting context, profiles, and policies in dynamic sub-carrier assignment algorithms for efficient radio resource management in OFDMA networks

Aggelos Saatsakis & Kostas Tsagkaris & Panagiotis Demestichas

University of Piraeus, Piraeus, Greece

Abstract Dynamic sub-carrier assignment (DSA) is considered as one of the most important aspects for achieving efficient spectrum utilization in orthogonal frequency division multiple access (OFDMA) based networks. Most of well-known DSA algorithms operate in a best effort manner, where the full set of sub-carriers is used in order to achieve the maximum possible quality of service level per user. However, in a real network environment, there are several management aspects to be considered such as context information (users, services, and radio environment conditions), user profiles, and network operator policies. In the context of OFDMA networks management, DSA algorithms should be extended incorporating such aspects in order to introduce fairness in the assignment of sub-carriers as well as to improve the overall system performance. In this paper, an efficient radio resource management scheme that incorporates a new DSA algorithm which exploits context profiles and policies information is presented. Results showcase the benefits that the proposed approach brings in terms of fairness on sub-carriers assignment and overall system performance.

Keywords Orthogonal frequency division multiple access (OFDMA) . Dynamic sub-carrier assignment (DSA) . Context . Profiles . Policies

Rotated precoder-based OFDM system robust to channel spectral nulls and with reduced PAPR

Xin-Lin Huang* & Gang Wang* & Fei Hu

* Communication Research Center, Harbin Institute of Technology, Harbin 150001, People’s Republic of China
** Department of Electrical and Computer Engineering, The University of Alabama, Tuscaloosa, AL 35487, USA

Abstract Recently, the precoded orthogonal frequency division multiplexing (OFDM) was proposed to show robustness to intersymbol interference channels with spectral nulls. However, due to inserting (M-K) zeros between each two sets of K consecutive information symbols, the average transmitting power of the precoded OFDM system reduces by 10 log10 (M/K) dB compared with the conventional OFDM system. Under the same points, inverse fast Fourier transformation (IFFT), the precoded OFDM system has a higher peak-to-average power ratio (PAPR) compared with the conventional OFDM system. This paper proposes a rotated precoder-based OFDM system robust to channel spectral nulls and with reduced PAPR. The rotated precoder makes the N-point IFFT with N/2 zeros padded. Since half of the information symbols for IFFT are zeros, we have the PAPR reduced by 10 log10 2≈3 dB approximately, compared with the conventional precoded OFDM system. We also show that the proposed OFDM system has the same bit error rate (BER) performance as the conventional precoded OFDM system. Both theoretical performance analysis and simulation results are presented to verify the correctness of our theory analysis.

Keywords Spectral nulls . Bit error rate (BER) .Peak-to-average power ratio (PAPR) . Rotated precoder . Inverse fast Fourier transformation (IFFT) .Precoded OFDM

Experimental investigation of mobile radio propagation at 1.8 GHz over macrocellular dense urban regions of Delhi

M. V. S. N. Prasad* K. Ratnamala**

*National Physical Laboratory,
**National Geophysical Research Institute

Abstract The design of future-generation mobile communication systems depends critically on the suitability of path loss prediction methods and their suitability to various regions. To investigate the radio channel behavior, experimental measurements in the 1.8 GHz band were conducted in the dense urban regions of New Delhi for six GSM base stations. Path loss exponents and break point distances have been deduced, and observed results have been compared with various prediction methods, and their standard deviations have been presented. Measured regression line exhibited lowest standard deviations followed by rooftop propagation method compared with Cost 231 Hata and Cost 231 Walfisch–Ikegami (WI) prediction methods. Variation of observed results has been explained in terms of vertical and horizontal propagation mechanisms which is the novelty of this paper.

Keywords Dense urban . Path loss modeling . Measurements . 1.8 GHz band . Prediction methods

Mobile-to-mobile fading channels in amplify-and-forward relay systems under line-of-sight conditions: statistical modeling and analysis

Batool Talha · Matthias Pätzold

University of Agder, Grimstad, Norway

Abstract This paper deals with the modeling and analysis of narrowband mobile-to-mobile (M2M) fading channels for amplify-and-forward relay links under line-of-sight (LOS) conditions. It is assumed that a LOS component exists in the direct link between the source mobile station (SMS) and the destinationmobile station (DMS), as well as in the links via the mobile relay (MR). The proposed channel model is referred to as themultiple-LOS second-order scattering (MLSS) channel model. The MLSS channel model is derived from a second-order scattering process, where the received signal is modeled in the complex baseband as the sum of a single and a double scattered component. Analytical expressions are derived for the mean value, variance, probability density function (PDF), cumulative distribution function (CDF), level-crossing rate (LCR), and average duration of fades (ADF) of the received envelope of MLSS channels. The PDF of the channel phase is also investigated. It is observed that the LOS components and the relay gain have a significant influence on the statistics of MLSS channels. It is also shown that MLSS channels include various other channel models as special cases, e.g., double Rayleigh channels, double Rice channels, single-LOS doublescattering (SLDS) channels, non-line-of-sight (NLOS) second-order scattering (NLSS) channels, and single- LOS second-order scattering (SLSS) channels. The correctness of all analytical results is confirmed by simulations using a high performance channel simulator. Our novel MLSS channel model is of significant importance for the system level performance evaluation of M2M communication systems in different M2M propagation scenarios. Furthermore, our studies pertaining to the fading behavior of MLSS channels are useful for the design and development of relay-based cooperative wireless networks.

Keywords Amplify-and-forward relay systems · Mobile-to-mobile fading channels · Double Rayleigh process · Double Rice process · Probability density function · Level-crossing rate · Average duration of fades

A trajectory-aware handoff algorithm based on GPS information

Thazin Ei & Furong Wang

Department of Electronics and Information Engineering, Huazhong University of Science and Technology, Wuhan, China

Abstract In this paper, we propose a trajectory-aware handoff algorithm based on position, velocity, signaling delay, and receive signal strength (RSS) of mobile terminal (MT). In order to provide seamless service in modern heterogeneous networks, handoff of the MT should be initiated with correct timing. In our algorithm, velocity of MT is divided into two parts as radial velocity and tangential velocity. For more precise handoff initiation, tangential velocity of MT is neglected, and only radial velocity of MT is considered in handoff decision making. Moreover, before handoff decision, least square line method is applied to RSS of MT to avoid unnecessary back-and-forth handoffs (ping-pong handoffs) between different services. A simulation is provided to compare the proposed algorithm with other various handoff methods, and the results prove this algorithm to have outperformed others.

Keywords Handoff algorithms . Position information . Velocity information . Handoff decision

Transparent resource sharing framework for internet services on handheld devices

Wouter Haerick · TimWauters · Chris Develder · Filip De Turck · Bart Dhoedt

Ghent University-IBBT, Gaston Crommenlaan 8 bus 208, 9050 Ghent, Belgium

Abstract Handheld devices have limited processing power and a short battery lifetime. As a result, computationally intensive applications cannot run appropriately or cause the device to run out of battery too early. Additionally, Internet-based service providers targeting these mobile devices lack information to estimate the remaining battery autonomy and have no view on the availability of idle resources in the neighborhood of the handheld device. These battery-related issues create an opportunity for Internet providers to broaden their role and start managing energy aspects of batterydriven mobile devices inside the home. In this paper, we propose an energy-aware resource-sharing framework that enables Internet access providers to delegate (a part of) a client application from a handheld device to idle resources in the LAN, in a transparent way for the end-user. The key component is the resource sharing service, hosted on the LAN gateway, which can be remotely queried and managed by the Internet access provider. The service includes a battery model to predict the remaining battery lifetime. We describe the concept of resource-sharing-as-a-service that allows users of handheld devices to subscribe to the resource sharing service. In a proof-of-concept, we evaluate the delay to offload a client application to an idle computer and study the impact on battery autonomy as a function of the CPU cycles that can be offloaded.

Keywords Resource sharing · Battery autonomy prediction · Internet services · Handheld devices

Fair data collection in wireless sensor networks: analysis and protocol

Md. Abdul Hamid* · Muhammad Mahbub Alam** · Md. Shariful Islam** · Choong Seon Hong** · Sungwon Lee**

* Department of Information and Communications Engineering, Hankuk University of Foreign Studies, 89 Wangsan-ri, Mohyeon myon, Cheon-gu, Yongin-si, Kyongki-do, 449-791, South Korea
** Department of Computer Engineering, School of Electronics and Information, Kyung Hee University, 1 Seocheon, Giheung, Yongin, Gyeonggi 446-701, South Korea

Abstract In general, wireless sensor networks (WSNs) consist of many sensors which transmit data to a central node, called the sink, possibly over multiple hops. This many-to-one data routing paradigm leads to nonuniform traffic distribution for the different sensors (e.g., nodes closer to the sink transfer more traffic than those farther away). In this paper, we perform an analysis of the fairness issue by presenting a tree-based WSN and derive the throughput, delay, and energy distribution for each sensor under the fairness constraint. Based on the analysis, we design our fair data collection protocol in which each node decides its media access and packet forwarding strategies in a distributed manner. Finally, we demonstrate the effectiveness of our solution through simulations. The results for the proposed protocol show the accuracy of the analysis and show that the protocol ensures the fair delivery of packets and reduces end-to-end delay. Based on the analysis, we also quantitatively determine the energy required for each of the nodes and show that a nonuniform energy distribution can maximize the network lifetime for the WSN scenario under study.

Keywords Wireless sensor networks · Fair data collection · Source-to-sink delay · Network energy distribution · Analysis and protocol design

Less Impact Better Service (LIBS) A service paradigm for Internet telephony

Lefteris Mamatas* · Vassilis Tsaoussidis**

*University College London, Torrington Place, London WC1E 7JE, UK
**Democritus University of Thrace, Vas. Sofias 12, 67100 Xanthi, Greece

Abstract We discuss a new packet service paradigm, called “Less Impact Better Service” (LIBS). In simple terms, LIBS primarily schedules packets based on the delay they cause and cancels service differentiation policies when the cumulative delay due to prioritization becomes significant for non-prioritized packets. Based on LIBS, we evaluate different service policies that prioritize small packets using different service boundaries and we show that, by and large, LIBS satisfies better a number of applications with diverse demands in delay and throughput. We emphasize on Voice over IP applications, which are delay-sensitive but also utilize small packets and rates. Among other traditional performance measures, we also measure fairness in the context of LIBS, that is, we address the question whether the delay experienced per flow is proportional to the delay caused by that flow. We obtained very promising simulation results.

Keywords Service differentiation · QoS · VoIP

Responsive pricing modeled with Stackelberg game for next-generation networks

Vesna Radonjić & Vladanka Aćimović-Raspopović

Telecommunication Networks Department,The Faculty of Transport and Traffic Engineering, University of Belgrade, Vojvode Stepe 305, 11000 Belgrade, Serbia

Abstract In this paper, we study the problem of resource allocation between users in next-generation networks. The starting assumption is that the service provider tries to come up with convincing offers of service level to subscribers, based on demand responsive pricing scheme, while trying to maximize its profit. We developed two algorithms with different usage-based pricing strategies. Both algorithms solve pricing optimization problem using Stackelberg game with service provider acting as a leader and users behaving as followers. We developed the bandwidth management server to perform automatic optimal bandwidth allocation to each user’s session and maximize its expected utility while maximizing the overall service provider’s revenue. For both algorithms, we also performed the procedure for optimization of the capacity offered to users.  

Keywords Next-generation networks . Responsive pricing . Stackelberg game . Bandwidth managementserver . Quality of service . Service level agreement