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ABSTRACT: Portfolio theory (PT) has been widely used in finance as a tool to aid capital allocation and investment analysis, and to measure economic welfare. Recently, PT has been applied as a spectrum management tool for cognitive radio for QoS management in CR and the pricing of CR access rights. PT is characterized by the analysis of risk and return, concepts that feature widely in wireless communications due to the random nature of traffic and radio channels. Compared with traditional CR resource management techniques (e.g., game theory), where the aim has been the maximization of QoS or another utility measure, the key advantage of PTbased resource management stems from the focus on both the mean utility achieved by a communication system, as well as utility variance. Ignoring QoS (e.g., throughput) variance in communication system design may lead to systems that are unusable by some applications, even though mean QoS remains high. In applications such as pricing-based spectrum management, PT analysis incorporates the variance of investment returns, a key measure of economic welfare, into pricing and trading strategies. In this article we examine the key concepts behind PT, risk and return, as well as their importance in CR and wireless communications. As examples, we analyze the application of PT in solving CR spectrum management problems through QoS management and pricing of spectrum access rights.
IEEE Wireless Communications 09/2011; · 2.58 Impact Factor
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ABSTRACT: Mobile WiMAX's scheduling service is a key factor in Radio Resource Management (RRM) in realizing Quality of Service (QoS). The choice in scheduling algorithm for Mobile WiMAX base stations, albeit outside of the scope of the standard, critically impacts the performance and robustness of Mobile WiMAX networks. This paper provides an in-depth study of four major scheduling algorithms: Round Robin (RR), Max CINR (MC), Fair Throughput (FT) and Proportional Fair (PF). Within the framework of Mobile WiMAX, we also discuss the implementation methodology and tradeoffs associated with these scheduling algorithms. Various Mobile WiMAX scenarios are simulated and analyzed using our Mobile WiMAX ns-2 model for performance throughput efficiency and resource allocation fairness.
Signal Processing and Communication Systems (ICSPCS), 2010 4th International Conference on; 01/2011
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ABSTRACT: Guaranteeing Quality of Service (QoS) in Cognitive Radio (CR) networks is a challenging task due to the random nature of radio channel conditions and primary user traffic. In this paper we analyze the recently proposed mean-variance based QoS and resource management methods, and introduce the concept of mean-variance evaluation of QoS and resource management techniques. Inspired by financial Portfolio Selection theory, mean-variance based resource management techniques for CR networks are statistical approaches and do not require instantaneous knowledge of channel state and Primary User (PU) activity, and enable the option to tradeoff between risk (QoS variance) and reward (QoS mean). Using throughput as a measure of QoS, we present a derivation of the theoretical throughput mean-variance characteristics of a CR-OFDM system employing a mean-variance based QoS management strategy. We conduct an analysis of existing Portfolio Selection based strategies in the mean-variance domain and compare them to the theoretical performance. Finally, we present a further enhancement of the approach by explicitly considering constraints on individual channel power allocation in the mean-variance optimization problem. Simulation results illustrate the effect of our enhancements in improving the risk-reward profile of the mean-variance based QoS management strategy, by moving it closer to the theoretical characteristic.
IEEE Transactions on Wireless Communications 11/2010; · 2.59 Impact Factor
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ABSTRACT: This paper presents a new routing discovery strategy for heterogeneous MANETs. Node heterogeneity is modeled in terms of: types and number of different interfaces, power, and transmission ranges. Our proposed route discovery algorithm is implemented on the top of On-demand Tree-based Routing Protocol (OTRP) and hence it is called OTRP Heterogeneity-Aware (OTRP_HA). OTRP_HA utilizes node heterogeneity and optimizes route discovery to reduce overheads and ensures connectivities between different types of nodes with different interfaces. Each node makes its own decision to participate in the route discovery process according to its location, local density, and available resources. Simulation results show that OTRP_HA outperforms OTRP and AODV and it reduces overheads as a number of nodes and traffic increase, while it also further prolongs the lifetime of battery-powered single-interface nodes when compared to AODV.
Wireless and Mobile Communications (ICWMC), 2010 6th International Conference on; 10/2010
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ABSTRACT: Cognitive Radio (CR) has been recently proposed as a method of alleviating the shortage of radio spectrum, by increasing the efficiency of spectrum use. However, as large portions of spectrum remain under long-term licenses, the economic welfare of the primary license holders must be taken into account, when considering methods of spectrum access that may degrade license holder Quality-of-Service (QoS) and therefore revenue. Several price discovery methods have been proposed to find the fee that license holders should charge for cognitive access to their spectrum. This paper examines the spectrum licenses themselves as an investment class. By performing a reward-to-variability (Sharpe Ratio) analysis of the spectrum license under different levels of CR activity, a floor price for CR access is derived such that the quality of the license holder's spectrum investment from a Sharpe Ratio point of view is not degraded. An example scenario is provided to illustrate this pricing mechanism, and simulation results illustrate its effectiveness in maintaining the quality of the license holder's spectrum investment.
New Frontiers in Dynamic Spectrum, 2010 IEEE Symposium on; 05/2010
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ABSTRACT: This paper presents heterogeneity ratio (HR) as a new routing metric for heterogeneous MANETs. This metric is the ratio of number of powerful nodes to hop count that is used to select the best path to destination. Node heterogeneity is modeled in terms of: types and number of different interfaces, power, and transmission ranges. Our proposed routing metric is based on developing route discovery algorithm that is implemented on the top of on-demand tree-based routing protocol (OTRP)[2] to accommodate nodes heterogeneity. Simulation results show that using HR with OTRP heterogeneity aware outperforms other metrics like minimal hop count and maximal number of powerful nodes.
Communications, 2009. APCC 2009. 15th Asia-Pacific Conference on; 11/2009
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ABSTRACT: As block coding and intelligent receiver combining in multi-antenna systems moves from the theorectical into the physical domain, it is necessary to apply robust analysis to the problems encountered with the development of real radio systems that are often overlooked during theoretical development of methods and processes. One such problem is the lack of synchronization between the transmitter and receiver sampling clocks. This text attempts to analyze the significance of poorly correcting for differences in the transmit and receive sample clocks by simulating the BER of an Alamouti space-time coded system under a variety of sample rates and clock offsets. The results can be used to estimate the impact on link quality by a given sampler's estimation error using the empirical model given.
Signal Processing and Communication Systems, 2009. ICSPCS 2009. 3rd International Conference on; 10/2009
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ABSTRACT: In most existing channel decision mechanisms for cognitive radio (CR), it is assumed that instantaneous channel state information (CSI) and primary user (PU) activity information is available. However, in many CR network applications, frequent channel sensing and estimation could introduce excessive overhead and reduce system throughput. Channel sensing by secondary users (SUs) may also not be completely reliable, and sensing error could result in reduced PU and SU quality of service (QoS). In this paper we examine the recently proposed use of historical CSI, combined with portfolio theory based optimization to arrive at joint channel decision and power allocation strategy for CR-OFDM. By also considering historical PU occupancy statistics, we extend this method to enable provision of a soft guarantee for both PU and SU traffic QoS. Simulation results show the effectiveness of the improved method in increasing the SU throughput and reducing PU interference, especially under conditions where the PU occupancy and signal to noise and interference ratio (SNIR) is positively correlated.
Signal Processing and Communication Systems, 2009. ICSPCS 2009. 3rd International Conference on; 10/2009
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ABSTRACT: The paper presents a new scheme of concatenated codes, referred to as serially concatenated turbo (SCT) codes. The code is constructed as the serial combinations of two turbo codes, i.e. turbo recursive systematic convolutional (RSC) codes and turbo Bose Ray Chaudhuri Hocquenghem (BCH) codes, linked by a pseudo-random interleaver. In comparison with the conventional turbo RSC codes, SCT codes have higher minimum distance values. Based on conducted simulations, it is found that SCT codes outperform turbo RSC codes at the waterfall and error floor regions, while they require reasonable number of iterations at their iterative decoding structure to achieve good performance.
Wireless Communications, Networking and Mobile Computing, 2009. WiCom '09. 5th International Conference on; 10/2009
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ABSTRACT: This paper presents a customizable framework for employing Cognitive Radio in Intermittently Connected Wireless Networks, which aims to maximize transmission opportunities that arise when fully connected network partitions are formed. Various layer 3 routing and information dissemination protocols would benefit from increased opportunity utility. We propose to use Cognitive Radio to permit multiple flows to occur in close proximity while minimizing spectrum wastage. We provide an example implementation of the proposed MAC framework which could increase the MAC throughput of networks exhibiting intermittent connectivity and network partition.
Personal, Indoor and Mobile Radio Communications, 2009 IEEE 20th International Symposium on; 10/2009
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ABSTRACT: Performance evaluations of multi-hop ad hoc network routing protocols have been primarily conducted through analytic and simulation-based studies, which frequently fail to accurately predict real-world performance and behaviour. One reason for this is the challenge in developing low cost, representative test beds with the degree of flexibility and mobility required. We have developed a portable wireless ad hoc node (PWAN) device which establishes multi-hop routes using the OLSR routing protocol. The PWAN's performance has been investigated using two test bed configurations to evaluate its capacity under conditions of high node density in a short-range, multi-hop environment. Our results illustrate that such networks are capable of providing high quality connections when traffic density is low. However, the network link quality deteriorates dramatically as the traffic level increases, and the network topology becomes unstable until the traffic level is reduced.
Signal Processing and Communication Systems, 2008. ICSPCS 2008. 2nd International Conference on; 01/2009
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ABSTRACT: With significant research being conducted in Ultra Wideband communications to increase error performance, this paper proposes a combination of user multiplexing and data encoding to achieve a BER improvement. Through the use of non-binary turbo coding, data is modulated to form a time hopping code which is applied to a time-reversed UWB system. Comparative results with conventional binary coding are given, showing the possibility for BER improvements in systems with a low number of users. Slight performance degradations for a large number of users exist. The effects of a user applying turbo coding on other users not applying forward error correction is also studied.
Wireless Communications and Networking Conference, 2008. WCNC 2008. IEEE; 05/2008
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ABSTRACT: A 12-b 300 MSPS Current-Steering DAC with 0.13 um CMOS technology is presented. In order to reduce the chip area, a laminated-step layout technique is proposed. Based on this technique, the occupied DAC core size is only 0.26 mm<sup>2</sup> even in 12-b resolution. Further, a current auto-averaging technique, an output impedance enhancement circuit, and the novel latched switching cell logic are discussed to keep the desired 12- b DAC performance. The measured results are within plusmn1 LSB for DNL. The measured SFDR is 70 dB under Nyquist output frequency with 50 mW power dissipation at 3.3 V power supply.
Circuit Theory and Design, 2007. ECCTD 2007. 18th European Conference on; 09/2007
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ABSTRACT: A simple algorithm for the weight calculation of turbo codes with convolutional interleavers is presented. For codes with short interleaver lengths, the weight distributions are computed using conventionally proposed methods and then utilised together with the interleaver properties to determine the weight specifications for the code with a longer desired length. Based on the calculated weights, a new upper bound for the code is computed. It agrees with simulation results of the code performance in the error-floor region
IET Communications 03/2007; · 0.83 Impact Factor
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ABSTRACT: In this paper, some issues governing the block-wise performance of convolutional interleavers used in turbo codes are presented. Two different constructions of convolutional interleaver differing by the position of stuff bits in the interleaved data block are considered here. The performance assessment is based on the contribution of each weight to the overall code performance. For the given turbo code and each utilized interleaver, weight contribution is computed to finalize the code behavior in different signal to noise ratios. Simulations have been performed to verify the conducted analysis
Communications, 2005 Asia-Pacific Conference on; 11/2005
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ABSTRACT: This paper considers application of a convolutional interleaver and the issue of influence of the space parameter in the turbo code performance. Similarly to previously considered convolutional interleavers, the new interleavers are designed as block interleavers and their performance in different code structures is compared with the interleaver having higher periods and space value of 1. In each comparison, the number of inserted stuff bits at the end of each data block is considered to be of similar order. Finally, suitable modification to the new interleavers is proposed improving performance for the codes with lower number of stuff bits
Communications Theory Workshop, 2005. Proceedings. 6th Australian; 03/2005
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Mobile Future, 2004 and the Symposium on Trends in Communications. SympoTIC '04. Joint IST Workshop on; 11/2004
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ABSTRACT: This work presents an algorithm for computation of the free distance parameter of turbo codes with a convolutional interleaver implemented to act as a block interleaver. Based on the properties of the interleaver and the algorithm applied, we can also determine the other low weights of turbo codes and this is useful in determining the performance of the error floor of turbo codes. For different turbo code structures, the relevant parameters have been computed. The error rate simulations confirm the algorithm results.
Personal, Indoor and Mobile Radio Communications, 2004. PIMRC 2004. 15th IEEE International Symposium on; 10/2004
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ABSTRACT: Previous work has shown that the performance of a space time spreading (STS) system using Walsh codes with two transmit antennas at the base station (BS) is degraded in the presence of mutual interference from adjacent sectors in the same cell. We use modified Walsh-Hadamard sequences exhibiting improved cross-correlation performance, which potentially mitigates the effects of MAI (multiple access interference). The presented study also looks at variation of sets of different modified Walsh-Hadamard codes being used by the adjacent interferer, with a hundred randomly selected pairings being chosen, as well as the case where one set of alternate codes is used. It is shown using simulation that significant improvement of the order of 0.5-2 dB is possible using these sequences instead of the standard Walsh code previously proposed.
Spread Spectrum Techniques and Applications, 2004 IEEE Eighth International Symposium on; 10/2004
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ABSTRACT: The combination of space-time codes and a closed loop transmission diversity technique is currently receiving a lot of attention since it allows one to improve the performance of wireless communications channels. This paper proposes a simple closed loop transmission diversity technique to improve further the performance of the channels through proposing a structure of feedback information in order to reduce the time required for processing the feedback information at the transmitter. Calculations and simulations show that our technique performs especially well when it is combined with the Alamouti code.
Signal Processing and Its Applications, 2003. Proceedings. Seventh International Symposium on; 08/2003
