Harsh Channel Conditions Research Articles

Comparative Analysis of Transmission Power Level and Packet Size Optimization Strategies for WSNs

Wireless sensor networks (WSNs) are envisioned to be a widely utilized technology in a smart grid (SG). Maximizing the network lifetime (NL) of WSNs in SG deployments is necessary to provide reliability and efficiency of the services offered to the entities involved. Harsh channel conditions in SG environments have a profound impact on the communication channel utilized by WSNs. Therefore, optimizing the transmission power level (TPL) and data packet size (DPS) is of paramount importance for prolonging the WSN NL. In both TPL and DPS optimizations, two general approaches are followed: utilizing a constant TPL and/or DPS or optimizing TPL and/or DPS for each link. However, the joint optimization of the TPL and DPS for each link has not been investigated in the literature. In this study, we present a mixed-integer programming framework, which utilizes a detailed link-layer abstraction to analyze nine TPL and DPS assignment strategies for WSNs employed in SG environments. The results of our analysis reveal that there is a large margin to be exploited in prolonging the WSN NL by an appropriate selection of the strategy to be used in TPL and DPS optimization.

CoFi: Coding-Assisted File Distribution over a Wireless LAN

The wireless channel is volatile in nature, due to various signal attenuation factors including path-loss, shadowing, and multipath fading. Existing media access control (MAC) protocols, such as the widely adopted 802.11 wireless fidelity (Wi-Fi) family, advocate masking harsh channel conditions with persistent retransmission and backoff, in order to provide a packet-level best-effort service. However, the asymmetry of the network environment of client nodes in space is not fully considered in the method, which leads to the decline of the transmission efficiency of the good ones. In this paper, we propose CoFi, a coding-assisted file distribution protocol for 802.11 based wireless local area networks (LANs). CoFi groups data into batches and transmits a random linear combination of packets within each batch, thereby reducing redundant packet and acknowledgement (ACK) retransmissions when the channel is lossy. In addition, CoFi adopts a MAC layer caching scheme that allows clients to store the overheard coded packets and use such cached packets to assist nearby peers. With this measure, it further improves the effective throughput and shortens the buffering delay when running applications such as bulk data transmission and video streaming. Our trace based simulation demonstrates that CoFi can maintain a similar level of packet delay to 802.11, but increases the throughput performance by a significant margin in a lossy wireless LAN. Furthermore, we perform a reverse-engineering on CoFi and 802.11 using a simple analytical framework, proving that they asymptotically approach different fairness measures, thus resulting in a disparate performance.

Link-Layer Coding for GNSS Navigation Messages

In this paper, we face the problem of ensuring reliability of Global Navigation Satellite Systems (GNSSs) in harsh channel conditions, where obstacles and scatter cause long outage events that cannot be counteracted with channel coding only. Our novel approach, stemming from information-theoretic considerations, is based on link-layer coding (LLC). LLC allows us to significantly improve the efficiency in terms of time-to-first-fix with respect to current operational GNSSs, which adopt carousel transmission. First, we investigate the maximum theoretical LLC gain under different Land Mobile Satellite channel conditions. Then, some practical LLC coding schemes, namely, fountain codes and a novel low-density parity-check plus low-rate repetition coding, are proposed and tested in realistic single-satellite and multi-satellite Land Mobile Satellite scenarios, considering the Galileo I/NAV message as study case. Simulation results show that our designed schemes largely improve on carousel transmission and achieve near-optimal performance with limited increase in complexity. Also, back-compatibility of LLC is assessed with respect to present-time GNSS specifications.

A survey on packet size optimization for terrestrial, underwater, underground, and body area sensor networks

SummaryPacket size optimization is a critical issue in wireless sensor networks (WSNs) for improving many performance metrics (eg, network lifetime, delay, throughput, and reliability). In WSNs, longer packets may experience higher loss rates due to harsh channel conditions. On the other hand, shorter packets may suffer from greater overhead. Hence, the optimal packet size must be chosen to enhance various performance metrics of WSNs. To this end, many approaches have been proposed to determine the optimum packet size in WSNs. In the literature, packet size optimization studies focus on a specific application or deployment environment. However, there is no comprehensive and recent survey paper that categorizes these different approaches. To address this need, in this paper, recent studies and techniques on data packet size optimization for terrestrial WSNs, underwater WSNs, wireless underground sensor networks, and body area sensor networks are reviewed to motivate the research community to further investigate this promising research area. The main objective of this paper is to provide a better understanding of different packet size optimization approaches used in different types of sensor networks and applications as well as introduce open research issues and challenges in this area.

Energy Harvesting Cognitive Radio Networking for IoT-enabled Smart Grid

The Internet of Things (IoT) provides connectivity to the objects that monitor and sense the environment to integrate physical world with digital world. If IoT is enabled in the Smart Grid (SG), it can benefit from advantages of the IoT such as interoperability, connectivity, etc. By combining the IoT with energy harvesting (EH) and cognitive radio (CR) techniques, the problems of SG, such as harsh channel conditions and limited battery power, may be resolved. Hence, incorporation of EH and CR reveals a new networking paradigm for IoT-enabled SG. To this end, we first introduce CR usage in the IoT-enabled SG, and explain the advantages and challenges of CRs. Furthermore, we propose EH approaches for the resource constraint of wireless devices in the IoT-enabled SG. Operation and node architecture of energy harvesting cognitive radios (EH-CR), and network architecture of the IoT-enabled SG are described to explain details of our networking paradigm. Open issues and future research directions are discussed to enable this new paradigm.

A 274µW clock synchronized wireless body area network IC with super-regenerative RSSI for biomedical ad-hoc network system.

A clock synchronized multi-node wireless body area network (WBAN) transceiver IC with super-regenerative RSSI is proposed for biomedical ad-hoc network system. The ad-hoc network makes stable communication even in the harsh human body channel condition (<;-50 dB attenuation) with low-power consumption. The proposed system consists of two types of IC - a hub and node IC. The hub IC broadcasts the 240 MHz clock signal to the whole node ICs and gather the measured data through body channel communication (BCC). In the node IC, it has 2 key building blocks; 1) Injection locking clock synchronization receiver, and 2) Super-regenerative RSSI (SR-RSSI) and OOK receiver. As a result, the 240 MHz clock is exactly synchronized in the node IC with 90 μW power consumption. And a channel-condition-adapted ad-hoc network is constructed based on the SR-RSSI data. SR-RSSI consumes 184 μW concurrent achieving OOK receiver functionality for the ad-hoc network. The proposed WBAN IC is fabricated in 0.18 μm CMOS technology.

FBMC System: An Insight into Doubly Dispersive Channel Impact

It has been claimed that filter bank multicarrier (FBMC) systems suffer from negligible performance loss caused by moderate dispersive channels in the absence of guard time protection between symbols. However, a theoretical and systematic explanation/analysis for the statement is missing in the literature to date. In this paper, based on one-tap minimum mean square error (MMSE) and zero-forcing (ZF) channel equalizations, the impact of doubly dispersive channel on the performance of FBMC systems is analyzed in terms of mean square error of received symbols. Based on this analytical framework, we prove that the circular convolution property between symbols and the corresponding channel coefficients in the frequency domain holds loosely with a set of inaccuracies. To facilitate analysis, we first model the FBMC system in a vector/matrix form and derive the estimated symbols as a sum of desired signal, noise, intersymbol interference (ISI), intercarrier interference (ICI), interblock interference (IBI), and estimation bias in the MMSE equalizer. Those terms are derived one-by-one and expressed as a function of channel parameters. The numerical results reveal that under harsh channel conditions, e.g., with large Doppler spread or channel delay spread, the FBMC system performance may be severely deteriorated and error floor will occur.

Multiple description transform coded transmission over OFDM broadcast channels

We consider image transmission using multiple description transform coding (MDTC) over orthogonal frequency division multiplexed (OFDM) wireless broadcast channels, where the system may not have any feedback on channel gains. We investigate the redundancy allocation in MDTC–OFDM system, physical layer frequency diversity, and decoding strategies to maximize the quality of reconstruction. Via mathematical analysis, supported by MATLAB simulations, we show that, error resilience of the descriptions can be increased by suitable assignment of coding redundancy in the transform modules at the source, which can be further optimized if the channel characteristics are known at the transmitter. Additionally, the relative performance of the MDTC–OFDM system is studied with respect to a competitive approach, called forward error correction based multiple description coding (MDC) over OFDM, where we show that, for the same redundancy assignment, the MDTC based system performs better under harsh channel conditions.

Clustering in Vehicular Ad Hoc Networks using Affinity Propagation

The need for an effective clustering algorithm for Vehicular Ad Hoc Networks (VANETs) is motivated by the recent research in cluster-based MAC and routing schemes. VANETs are highly dynamic and have harsh channel conditions, thus a suitable clustering algorithm must be robust to channel error and must consider node mobility during cluster formation. This work presents a novel, mobility-based clustering scheme for Vehicular Ad hoc Networks, which forms clusters using the Affinity Propagation algorithm in a distributed manner. This proposed algorithm considers node mobility during cluster formation and produces clusters with high stability. Cluster performance was measured in terms of average clusterhead duration, average cluster member duration, average rate of clusterhead change, and average number of clusters. The proposed algorithm is also robust to channel error and exhibits reasonable overhead. Simulation results confirm the superior performance, when compared to other mobility-based clustering techniques.

Exploiting Cooperative Relay for High Performance Communications in MIMO Ad Hoc Networks

With the popularity of wireless devices and the increase of computing and storage resources, there are increasing interests in supporting mobile computing techniques. Particularly, ad hoc networks can potentially connect different wireless devices to enable more powerful wireless applications and mobile computing capabilities. To meet the ever increasing communication need, it is important to improve the network throughput while guaranteeing transmission reliability. Multiple-input-multiple-output (MIMO) technology can provide significantly higher data rate in ad hoc networks where nodes are equipped with multiantenna arrays. Although MIMO technique itself can support diversity transmission when channel condition degrades, the use of diversity transmission often compromises the multiplexing gain and is also not enough to deal with extremely weak channel. Instead, in this work, we exploit the use of cooperative relay transmission (which is often used in a single antenna environment to improve reliability) in a MIMO-based ad hoc network to cope with harsh channel condition. We design both centralized and distributed scheduling algorithms to support adaptive use of cooperative relay transmission when the direct transmission cannot be successfully performed. Our algorithm effectively exploits the cooperative multiplexing gain and cooperative diversity gain to achieve higher data rate and higher reliability under various channel conditions. Our scheduling scheme can efficiently invoke relay transmission without introducing significant signaling overhead as conventional relay schemes, and seamlessly integrate relay transmission with multiplexed MIMO transmission. We also design a MAC protocol to implement the distributed algorithm. Our performance results demonstrate that the use of cooperative relay in a MIMO framework could bring in a significant throughput improvement in all the scenarios studied, with the variation of node density, link failure ratio, packet arrival rate, and retransmission threshold.

A Conflict Avoidance Scheme for WiMedia Wireless Home Networks

We propose an efficient resource reservation scheme for UWB (Ultrawideband) WPAN (Wireless Personal Area Network) with D-MAC (Distributed Medium Access Control). Since the WiMedia D-MAC supporting DRP (Distributed Reservation Protocol) scheme causes lots of conflicts due to failure of beacon detection in wireless channel environment, overall performances of the WiMedia D-MAC can be deteriorated. Therefore, we propose Relay DRP protocol, which makes a relay path to avoid DRP conflicts or harsh channel conditions through cooperative relay transmission scheme and is compliant with the current WiMedia D-MAC protocol. Simulation results demonstrate performance improvements of the proposed method for throughput and energy consumption.

Relay-Aided Amplify-and-Forward Powerline Communications

Powerline communications (PLC) is a favorable technique for many smart grid applications. By transmitting information over the existing powerline infrastructure, PLC has the benefit of low deployment cost. However, due to low transmit power, limited bandwidth, and harsh channel conditions, reliable long-distance and high-capacity PLC is challenging. Relay-aided (RA-) PLC is promising in addressing these issues. In this paper, we investigate the performance of the amplify-and-forward (AF) RA-PLC system from an information-theoretic perspective. The capacity of AF-based RA-PLC is analyzed for frequency-selective PLC channels. The capacity bounds are derived, and the optimal power allocation between the transmitting nodes and the optimal power distribution over the signal frequency band are obtained. The capacity benefits and features of AF-based RA-PLC are evaluated with two prevalent powerline channel models. Based on the signal attenuation model, the capacity of AF-based RA-PLC is compared with direct-link (DL-)PLC, and the effect of relay location is revealed. In addition, based on the transmission line (TL) model, the effects of branch density and load impedance on the capacity of AF-based RA-PLC are evaluated.

Cooperative Distributed MAC Design for Cross-layer Link Adaptation of UWB WPAN Devices

In this paper, we propose an efficient resource reservation scheme using cross-layer link adaptation for Ultra Wide Band Wireless Personal Area Network with Distributed Medium Access Control (D-MAC). Since the WiMedia D-MAC supporting Distributed Reservation Protocol (DRP) scheme causes lots of conflicts due to failure of beacon detection in wireless channel environment, overall performances of the WiMedia D-MAC can be deteriorated. Therefore, we propose Relay DRP protocol with Relay Node Selection criterion, which makes a relay path to avoid DRP conflicts or harsh channel conditions through cross-layer link adaptation of cooperative relay transmission scheme and is compliant with the current WiMedia D-MAC protocol. Simulation results demonstrate performance improvements of the proposed method for throughput and energy consumption.

A Novel Data-Aided Channel Estimation With Reduced Complexity for TDS-OFDM Systems

In contrast to the classical cyclic prefix (CP)-OFDM, the time domain synchronous (TDS)-OFDM employs a known pseudo noise (PN) sequence as guard interval (GI). Conventional channel estimation methods for TDS-OFDM are based on the exploitation of the PN sequence and consequently suffer from intersymbol interference (ISI). This paper proposes a novel dataaided channel estimation method which combines the channel estimates obtained from the PN sequence and, most importantly, additional channel estimates extracted from OFDM data symbols. Data-aided channel estimation is carried out using the rebuilt OFDM data symbols as virtual training sequences. In contrast to the classical turbo channel estimation, interleaving and decoding functions are not included in the feedback loop when rebuilding OFDM data symbols thereby reducing the complexity. Several improved techniques are proposed to refine the data-aided channel estimates, namely one-dimensional (1-D)/two-dimensional (2-D) moving average and Wiener filtering. Finally, the MMSE criteria is used to obtain the best combination results and an iterative process is proposed to progressively refine the estimation. Both MSE and BER simulations using specifications of the DTMB system are carried out to prove the effectiveness of the proposed algorithm even in very harsh channel conditions such as in the single frequency network (SFN) case.

A Multi-Dimensional Code-Division-Multiplexed OFDMA Modem Using Cyclic Rotated Orthogonal Complete Complementary Codes

In this paper we present a novel multiple access scheme based on a combination of multi-carrier OFDMA techniques and a multi-dimensional spread spectrum modem that makes use of rotated mutually orthogonal complete complementary codes. A multi-dimensional code-division multiple access (MD-CDMA) modem with recent designs of perfectly orthogonal complete complementary codes, produces an innovative modulation technique, which is further improved upon by exploiting the rotational properties of the spreading codes to increase the throughput and spectral efficiency. The system is extended by making use of multiple carrier frequencies as in orthogonal frequency-division multiple access (OFDMA), providing additional benefits such as diversity by being able to spread the data in frequency and/or in time. The proposed modem offers multiple access interference (MAI)-free operation due to the perfect autocorrelation and zero cross-correlation properties of the spreading codes. The uniquely proposed modulation technique together with the integration of rotated complete complementary codes, produces a system with better spectral efficiency compared to a theoretical non-spread system, with high data throughput rates, better noise tolerances in harsh channel conditions and an increased user capacity. Various other benefits such as low complex channel estimation and synchronisation, rate adaption, and resistance to the near-far problem can be attributed to the system.

Exploiting Fading Dynamics along with AMC for Energy-Efficient Transmission over Fading Channels

The basic adaptive modulation and coding (AMC) in its lowest mode blindly transmits the frames without payload during outages, which wastes energy. In this letter, we propose to exploit fading dynamics (FD) along with AMC to achieve a higher energy efficiency. In the proposed FD-AMC approach, the frame transmission is suspended judiciously during the outages, thereby saving energy, particularly in harsh channel conditions.

Analysis of a deterministic power level selection algorithm with small and large power steps for Aloha networks under saturation

Standard power control techniques are not deployable in Aloha networks due to lack of central controlling entity and/or inefficiency of such algorithms in large networks with bursty traffic. To handle this problem in practice, simple transmission power selection algorithms are used for ranging and/or combating harsh channel conditions. In such algorithms, the transmission power is steadily increased by an amount called power step, until the packet is successfully transmitted. Noting that ranging is the major concern of this approach, small power steps are ideal for its operation. However, as we will show in this paper, using small power steps with this algorithm causes a throughput collapse in large networks, when capture effect is considered in the analysis. In the asymptotic case, the throughput of this algorithm will be less than the throughput of the Binary Exponential Backoff (BEB) scheme which only uses a single power level. To show these results, we will present an asymptotic analysis of this algorithm with small power steps in an ideal communication channel where BEB is used as the retransmission scheme. In order to strengthen the results, we will prove the existence of better choices for power steps by extending the analysis for large power steps and we will show that properly chosen large power steps guarantee higher throughputs and require approximately the same average powers as small power steps. Our analysis and simulation results show that small power steps should be avoided with the mentioned power selection algorithm except probably for ranging and once the ranging process is complete, larger power steps should be used to exploit the capture effect.

Enabling Distributed Medium Access Control for Impulse-Based Ultrawideband Radios

Impulse-based ultrawideband (I-UWB) is an attractive radio technology for large ad hoc and sensor networks due to its robustness to multipath effects, subcentimeter ranging ability, simple hardware, and low radiated power. Large distributed networks, such as ad hoc and sensor networks, often implement distributed medium access control (MAC) protocols based on carrier sense multiple access (CSMA). In CSMA, narrowband systems check for medium activity before transmitting by checking for in-band energy around a carrier frequency. I-UWB systems lack a carrier, and the narrow pulses, low radiated power, harsh channel conditions, and strict Federal Communications Commission power limits present challenges in detecting medium activity. We propose a pulse sensor for I-UWB systems that overcomes the challenges of quickly, reliably, and efficiently identifying medium activity. The pulse sensor enables distributed MAC protocols for I-UWB radios that are analogous to CSMA for narrowband radios. Simulations show that the proposed pulse sensor architecture is practical for I-UWB radios

Channel estimation for 5.9 GHz dedicated short-range communications receiver in wireless access vehicular environments

A channel estimation scheme for the design of a 5.9 GHz dedicated short-range communications receiver for the purpose of vehicle-to-vehicle and vehicle-to-roadside communications is proposed. The receiver is based on the popular wireless local area network standard IEEE 802.11a, but with extended symbol duration. On the basis of analyses and simulations, the proposed receiver has superior design characteristics for the harsh channel conditions of wireless access vehicular environments. The performance of the proposed scheme is tested under varying velocity, signal-to-noise ratios, transmission modes, packet lengths and channel properties. The proposed design improves the overall packet error rate performance, enabling the system to achieve higher data rates and larger packet lengths at high relative velocities. Simulation results show slight improvements in the quadrature phase-shift keying transmission, whereas there is substantial improvement in the cases of 16- and 64-ary quadrature amplitude modulations compared to conventional design.

Forward-link capacity in smart antenna base stations with dynamic slot allocation

We consider a base station, which communicates to a set of portable stations using a smart antenna operating in multibeam, packet-switched, space division multiple access (SDMA) mode. We assume that the system operates using time division duplexing (TDD) and focus on the problem of access to the stations by the base station in the forward-link direction. A polling protocol is used which permits efficient access in this type of system. The operation of the protocol is unique in that it permits dynamic slot allocation and accommodates variations in channel time coherence. In the protocol, dynamic slot assignment is integrated into the forward-link beam scheduling. This allows us to explore the value of dynamic station slot assignment when constructing the SDMA/TDMA frames. The results show the improvements in capacity, which are possible in such systems and give insight into the degradation in protocol performance that occurs when channel coherence times decrease. We find that very large improvements in capacity are possible using dynamic slot allocation, especially under harsh channel conditions. We also investigate various base station queueing issues in this type of system. It is shown that care must be taken in how buffering is performed so that blocking effects do not unnecessarily degrade the forward-link capacity.