In this article, we propose a highly reliable transmission strategy based on exploiting channel diversity for Internet of Things (IoT) networks equipped with cognitive radio (CR) capabilities (referred to as CR-IoT networks). Specifically, we investigate the channel-assignment problem with the objective of minimizing the number of assigned channels for each CR transmission subject to link reliability, data rate, and success probability constraints. We use the theory of continuous-time Markov chains to derive mathematical expressions for channel availability and reliability. These expressions are employed in a binary linear program model to formulate the channel assignment optimization problem, which is suboptimally solved using a polynomial-time sequential fixing procedure. Theoretical performance analysis of the proposed channel assignment scheme is derived in terms of a lower bound on the achievable probability of successful packet transmission. Through simulation experiments, we demonstrate significant performance enhancement compared to existing reliability-unaware CR channel assignment algorithms.

Summary Spectrum sharing protocols for cognitive radio networks (CRNs) are often designed based on an exclusive channel occupancy policy. This policy does not allow concurrent cognitive radio (CR) transmissions to take place over the same channel. Unfortunately, this can significantly affect spectrum utilization and network performance. Allowing several secondary users to simultaneously share the same channel naturally improves spectrum utilization and avoids unnecessary blocking of CR transmissions. The key challenge in enabling efficient operation of multichannel CRNs is how to perform efficient power‐controlled media‐access‐control (MAC) protocols. These protocols include both power control and channel assignment. In this paper, we propose a power‐controlled MAC protocol for CRNs based on interference‐channel occupancy model with the objective of maximizing the number of served CR transmissions. It uses a novel power‐controlled channel assignment mechanism that allows several concurrent interference‐limited transmissions to simultaneously proceed over each idle channel in the same neighborhood. We present two variants of the power‐controlled channel assignment mechanism. The first proposed variant is suitable for CRNs with fixed data packet size, whereas the other is suitable for dynamic CRNs with variable packet size. The second variant of our protocol employs a users' scheduling procedure that attempts to fully utilize the available time‐frequency blocks. Simulation results indicate that employing transmission power control along with appropriate channel assignment and users' scheduling in CRNs can significantly improve the spectrum utilization and the overall network performance.

Time-critical, wireless Internet of Things applications have been drawing increasing attention lately. The most characterizing feature of such applications is that a packet has to be delivered within a certain deadline. Not meeting the deadline could result in severe consequences. Jamming attacks utilize the shared nature of the wireless medium to corrupt transmitted packets. Although a corrupted packet could be retransmitted several times until successful delivery, this would add latency and hence could lead to missing the deadline. In this paper, we propose a jamming detection scheme that uses the packet transmission time as a statistic to make detection decisions. The key insight behind our proposed scheme is that, a long transmission/retransmission time for a certain packet indicates an abnormal condition, such as jamming. Therefore, we devise an optimal transmission-time threshold that, when exceeded, a jammer is detected. Unlike most existing detection schemes where, in case of a detection error, retransmission could continue until the deadline is reached, our scheme aims to detect the jammer earlier than the deadline so that the remaining time (until the deadline) could be utilized in retransmitting the packet over a safe channel. The proposed detection scheme is a general framework that can be applied to many situations. After conducting a thorough analysis, we apply the proposed early-stop jamming detection framework to the distributed coordinated function medium access mechanism specified by the 802.11 standard. Our simulation results show significant performance gains achieved by the proposed scheme.

Intra-flow network coding (NC) is an innovative technique that has potential to improve multicast performance in wireless mesh networks (WMNs) by allowing intermediate forwarding nodes (FNs) to use coding and overhearing to reduce the number of required transmissions. However the benefits of the NC technology are limited unless there are protocols to exploit its capabilities. The existing intra-flow NC-based multicast protocols are all based upon the conventional end-to-end transport principle. By such a principle, intermediate FNs are unable to accurately determine the minimum number of coded packets they should transmit in order to ensure successful data delivery to the destinations, and hence redundant packets can be injected into the network, leading to performance degradation. Furthermore, the existing protocols cannot handle the bandwidth heterogeneity of multicast receivers very well. We argue that a receiver-driven hop-by-hop transport approach is more suitable for intra-flow NC and these two techniques can create synergy by enabling cooperation among the FNs. In this paper we propose HopCaster, a novel protocol that incorporates intra-flow NC with hop-by-hop transport to achieve high-throughput reliable multicast and to solve the heterogeneous receiver issue. It completely eliminates the need for estimating the number of coded packets to be transmitted by a FN and avoids transmission of redundant packets, as well as simplifies multicast management and congestion control. Moreover, HopCaster employs a cross-layer rate adaptation mechanism that optimizes radio transmission rate in hop-by-hop multicast by taking into consideration next-hop node population changes. Our evaluations show that HopCaster outperforms the existing NC-based reliable multicast protocol.

In this paper we describe a practical implementation of a distributed video codec deployed on a real visual sensor platform, viz. the MicaZ/Cyclops platform. The codec supports two encoding schemes, one employs Discrete Cosine Transform (DCT) and the other operates on raw pixels. DCT scheme is more costly in terms of computational power consumption, on the other hand it leads to more compression and hence less transmission power consumption. At the same time the DCT scheme may not necessarily achieve minimal overall power consumption (computation and transmission). In this paper we show that the choice of either scheme (DCT or pixel based) depends on the tolerable distortion and power consumption. Results show that for a range of achievable video quality values the DCT scheme demonstrates less overall power consumption. On the other hand for another range of video quality the pixel scheme results in less overall power consumption.