Nikolaos I. Miridakis

A Survey on the Successive Interference Cancellation Performance for Single-Antenna and Multiple-Antenna OFDM Systems

Interference plays a crucial role for performance degradation in communication networks nowadays. An appealing approach to interference avoidance is the Interference Cancellation (IC) methodology. Particularly, the Successive IC (SIC) method represents the most effective IC-based reception technique in terms of Bit-Error-Rate (BER) performance and, thus, yielding to the overall system robustness. Moreover, SIC in conjunction with Orthogonal Frequency Division Multiplexing (OFDM), in the context of SIC-OFDM, is shown to approach the Shannon capacity when single-antenna infrastructures are applied while this capacity limit can be further extended with the aid of multiple antennas. Recently, SIC-based reception has studied for Orthogonal Frequency and Code Division Multiplexing or (spread-OFDM systems), namely OFCDM. Such systems provide extremely high error resilience and robustness, especially in multi-user environments. In this paper, we present a comprehensive survey on the performance of SIC for single- and multiple-antenna OFDM and spread OFDM (OFCDM) systems. Thereby, we focus on all the possible OFDM formats that have been developed so far. We study the performance of SIC by examining closely two major aspects, namely the BER performance and the computational complexity of the reception process, thus striving for the provision and optimization of SIC. Our main objective is to point out the state-of-the-art on research activity for SIC-OF(C)DM systems, applied on a variety of well-known network implementations, such as cellular, ad hoc and infrastructure-based platforms. Furthermore, we introduce a Performance-Complexity Tradeoff (PCT) in order to indicate the contribution of the approaches studied in this paper. Finally, we provide analytical performance comparison tables regarding to the surveyed techniques with respect to the PCT level.

Multiuser Relaying over Mixed RF/FSO Links

A multiuser dual-hop relaying system over mixed radio frequency/free-space optical (RF/FSO) links is investigated. Specifically, the system consists of m single-antenna sources, a relay node equipped with n≥ m receive antennas and a single photo-aperture transmitter, and one destination equipped with a single photo-detector. RF links are used for the simultaneous data transmission from multiple sources to the relay. The relay operates under the decode-and-forward protocol and utilizes the popular V-BLAST technique by successively decoding each users transmitted stream. Two common norm-based orderings are adopted, i.e., the streams are decoded in an ascending or a descending order. After V-BLAST, the relay retransmits the decoded information to the destination via a point-to-point FSO link in m consecutive timeslots. Analytical expressions for the end-to-end outage probability and average symbol error probability of each user are derived, while closed-form asymptotic expressions are also presented. Capitalizing on the derived results, some engineering insights are manifested, such as the coding and diversity gain of each user, the impact of the pointing error displacement on the FSO link and the V-BLAST ordering effectiveness at the relay.

Dual-Hop Communication Over a Satellite Relay and Shadowed Rician Channels

A dual-hop amplify-and-forward (AF) relaying scheme over shadowed Rician fading channels is investigated. Specifically, the source and destination nodes are equipped with N and M antennas, respectively, whereas the relay is equipped with a single antenna. Communication via satellite relaying represents a direct application of the considered infrastructure. To this end, we study the scenario when the source and the destination are terrestrial nodes, whereas the end-to-end communication is established through an intermediate AF relay node, which is a satellite. To fully exploit the spatial diversity provided by multiple antennas, maximum ratio transmission and maximum ratio combining are implemented at the source and the destination, respectively. First, a new closed-form expression for the probability density function (pdf) of the sum of independent and identically distributed (i.i.d.) squared shadowed Rician random variables is derived by assuming integer distribution parameters. Capitalizing on the latter pdf, new closed-form results for the cumulative distribution function (cdf) and the moment function of the end-to-end signal-to-noise ratio (SNR) are obtained. Particularly, the proposed unified analysis includes the channel-state-information (CSI)-assisted and the fixed-gain AF relaying protocols. New expressions for important performance measures, namely, the outage probability, the average symbol error probability (ASEP), and the ergodic capacity of the end-to-end SNR, are presented for both AF schemes. Moreover, some useful engineering insights are manifested, such as simplified asymptotic outage performance results, the diversity order, and the impact on the number of antennas at the source and the destination.

Power control schemes in wireless sensor networks for homecare e-health applications

Power control is an important research topic for ad-hoc Wireless Sensor Networks (WSNs). In todays sophisticated and competitive wireless environment, the control of the energy consumption in a WSN for homecare e-health makes it possible to guarantee basic levels of system performance, such as connectivity, throughput, delay, QoS and survivability in the presence of both mobility-immobility and a large number of sensor nodes. Recent advances in sensor fabrication technology, low-power digital and analogue electronics, and low-power wireless communication systems have made it possible to develop low-cost, robust and survivable WSNs to support activities such as assisted living and ambient intelligence (Aml). A large variety of approaches for intelligent energy-efficient schemes have been simulated over different performance metrics. In this paper, various decision support schemes are proposed evaluating the selection of different network infrastructures in terms of routing optimization and signal strength selection.

Performance Analysis of the Ordered V-BLAST Approach over Nakagami-m Fading Channels

The performance of the V-BLAST approach, which utilizes successive interference cancellation (SIC) with optimal ordering, over independent Nakagami-m fading channels is studied. Systems with two transmit and n receive antennas are employed whereas the potential erroneous decision of SIC is also considered. In particular, tight closed-form bound expressions are derived in terms of the average symbol error rate (ASER) and the outage probability, in case of binary and rectangular \mathcal{M}-ary constellation alphabets. The mathematical analysis is accompanied with selected performance evaluation and numerical results, which demonstrate the usefulness of the proposed approach.

A Novel Power-Efficient Middleware Scheme for Sensor Grid Applications

Sensor grid deployments integrate wireless sensor networks (WSNs) and Grid Computing (GC) into a merged platform. A middleware architecture is a prerequisite for sensor grids in order to bridge the two heterogeneous technologies and efficiently support aggregated grid services available to a large number of grid users. On the other hand, the energy conservation of the participating sensor nodes is an essential factor for QoS provisioning, thereby extending WSNs survivability and providing diversity to potential grid services. For the best of our knowledge, power awareness for middleware architectures for sensor grids has never been studied in the literature so far. The rationale of our work employs a scheduler which provides QoS to the grid users from an energy awareness perspective by interacting with an appropriate resource manager. Our simulations show the effectiveness of the proposed scheme whereas a proxy-based middleware for sensor grids has been adapted.

Green Cognitive Relaying: Opportunistically Switching Between Data Transmission and Energy Harvesting

Energy efficiency has become an encouragement, and more than this, a requisite for the design of the next-generation wireless communication standards. In this paper, a dual-hop cognitive (secondary) relaying system is considered, incorporating multiple amplify-and-forward relays, a rather cost-effective solution. First, the secondary relays sense the wireless channel, scanning for a primary network activity, and then convey their reports to a secondary base station (SBS). Afterward, the SBS, based on these reports and its own estimation, decides cooperatively the presence of primary transmission or not. In the former scenario, all the secondary nodes start to harvest energy from the transmission of primary nodes. In the latter scenario, the system initiates secondary communication via a best relay selection policy. Performance evaluation of this system is thoroughly investigated, by assuming realistic channel conditions, i.e., non-identical link distances, Rayleigh fading, and outdated channel estimation. The detection and outage probabilities as well as the average harvested energy are derived as new closed-form expressions. In addition, an energy-efficiency optimization problem is analytically formulated and solved, while a necessary condition in terms of power consumption minimization for each secondary node is presented. From a green communication standpoint, it turns out that energy harvesting greatly enhances the resources of secondary nodes, especially when primary activity is densely present.

Performance analysis of V-BLAST reception under multiuser decode-and-forward cooperation

The performance of a dual-hop system is studied and evaluated, where m single-antenna source nodes communicate with a destination equipped with n ≥ m antennas via m single-antenna relays. The decode-and-forward protocol is implemented at the relays whereas the classical ordered V-BLAST scheme is performed at the destination. The analysis involves spatially independent non-identically distributed Rayleigh channel fading channels, reflecting on distinct average received powers among the different source and/or relay nodes with the destination, suitable for practical applications. The identically distributed scenario is also included as a special case. Novel union closed-form system bound expressions are derived in terms of the outage probability and the average symbol error probability. These bounds correspond to the cases of both the perfect and the imperfect channel state information at the relay and the destination nodes. The numerical results, accompanied with the equivalent simulation ones, reveal the accuracy of the proposed approach.

On the Ergodic Capacity of Underlay Cognitive Dual-Hop AF Relayed Systems Under Non-Identical Generalized-

The ergodic capacity of underlay cognitive (secondary) dual-hop relaying systems is analytically investigated. Specifically, the amplify-and-forward transmission protocol is considered, while the received signals undergo multipath fading and shadowing with non-identical statistics. To efficiently describe this composite type of fading, the well-known generalized-K fading model is used. New analytical expressions and quite accurate closed-form approximations regarding the ergodic capacity of the end-to-end communication are obtained, in terms of finite sum series of the Meijers-G function. The analytical results are verified with the aid of computer simulations, while useful insights are revealed.

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The authors propose a new reception scheme based on the successive interference cancellation (SIC) approach by jointly performing zero forcing (ZF) and minimum mean squared error (MMSE) according to a defined threshold. A complexity analysis is provided although upper and lower complexity bounds are also derived. A detailed performance evaluation is presented, which explicitly indicates the usefulness of the proposed switching method across the conventional ZF-SIC and MMSE-SIC in terms of computational savings and/or error resilience. An alternative switching threshold which is based on the ergodic capacity is also presented, in case of capacity-driven applications.