Jin-Seok Han

Interference Mitigation in IEEE 802.15.4 Networks

In this paper, we consider interference mitigation in IEEE 802.15.4 beacon-enabled cluster-tree networks. The proposed scheme first detects the presence of interference by means of packet-error detection and/or channel sensing in a clusterwise manner. In the presence of interference, the coordinator (or cluster head) fast notifies the presence of interference to its end devices by repeatedly transmitting the channel-handoff command. Then, it avoids the interference by the use of temporary channel hopping through predetermined hopping channels. Finally, it selects the best one among the hopping channels, which will be used as the final handoff channel. Simulation results show that the proposed scheme provides marked performance improvement over conventional schemes even in the presence of heavy interference.

Robust transmission of the IEEE 802.15.4 signal in the presence of co-channel interference

IEEE 802.15.4 networks operating in the 2.4 GHz ISM band are seriously affected by co-channel interference from coexisting radio systems such as IEEE 802.11x wireless local area networks. In this paper, we consider the beacon transmission in the presence of co-channel interference in the IEEE 802.15.4 beacon-enabled mode. For reliable transmission of the beacon frame, we propose repeated transmission of the beacon frame depending upon the channel characteristics. The network coordinator and its child nodes estimate the channel characteristics when they experience transmission failure of the beacon frame. The coordinator determines the number of repeated beacon transmissions and the timing gap between the beacon transmissions based on the estimated channel characteristics. Analytic and simulation results show that the proposed scheme can reliably transmit the beacon frame even in the presence of heavy co-channel interference, significantly reducing the network synchronization loss, power consumption as well as transmission delay.

Alleviation of contention collision in IEEE 802.15.4 networks

IEEE 802.15.4 networks employ a medium access control scheme based on carrier sense multiple access with collision avoidance (CSMA/CA). However, CSMA/CA may seriously experience contention collision, suffering from resource wastage in time-varying operation environments. In this paper, we consider the alleviation of contention collision in IEEE 802.15.4 networks by partitioning the transmission period into a number of sub-transmission periods. To this end, the network coordinator and its child devices measure the transmission performance in a distributed manner. When the measured performance is not satisfactory, the coordinator adjusts the number of subtransmission periods considering the operation environment. Each child device uses one of the sub-transmission periods for its signal transmission, effectively reducing the probability of contention collision. Simulation results show that the proposed scheme remarkably reduces packet collision and thus energy consumption in time-varying network environments.

Performance improvement of IEEE 802.15.4 in the presence of co-channel interference

In this paper, we consider performance improvement of IEEE 802.15.4 systems in the presence of co-channel interference from other systems such as wireless local area networks (WLAN). The proposed scheme first detects the presence of interference by means of spectrum sensing or transmission performance testing. When the presence of interference signal is detected, the coordinator changes the carrier frequency for the signal transmission by means of frequency hopping through multiple channels which are predetermined according to the characteristics of interference signal. After signal transmission through these multiple channels for a while, the coordinator selects the best one among the multiple channels and then returns to the original transmission mode through the newly selected channel, efficiently alleviating the interference problem. Finally, the performance of the proposed scheme is verified by computer simulation in the presence of multiple WLANs.1

Distributed Scalable Network Association in Wireless Sensor Networks

Wireless sensor networks (WSNs) need to employ a network association mechanism that can securely allocate a unique address to each node while minimizing energy consumption. However, conventional centralized and broadcasting based network association mechanisms may consume large energy, and distributed network association mechanisms may suffer from addressing failure when applied to large scale WSNs. In this paper, we consider distributed network association with scalability for the construction of a large scale WSN. The proposed mechanism constructs a large scale addressing tree before network initialization. Based on the addressing tree, it allows each router to have its own addressing space which will be used for unique addressing of its child nodes. Then, a novel parent/child selection algorithm can assign routers to be located throughout the whole deployment area. Thus, nodes can join the network in the presence of sufficient neighbor routers and receive a unique address in a distributed manner. Finally, the performance of the proposed scheme is evaluated by computer simulation, showing remarkable performance improvement over conventional schemes when applied to a large scale WSN.

Transmission performance of wireless sensor networks in the presence of co-channel interference

Wireless sensor networks operating in 2.4 GHz ISM band are seriously affected by interference from coexisting radio systems such as IEEE 802.11× wireless local area networks. In this paper, we investigate the transmission performance of wireless sensor networks in the presence of co-channel interference. We first analyze the probability of transmission failure and data throughput associated with transmission schemes in interference environments. The transmission schemes are modeled using a Markov chain taking into account the detection probability of channel sensing detector and the interference channel characteristics. Then, we determine the packet size to maximize the data throughput in the presence of co-channel interference. It is shown that the data throughput and energy consumption are affected by the packet size, data transmission rate, data transmission scheme, detection probability of channel sensing detector, and interference channel characteristics.

Fault-tolerant resource allocation in multi-hop wireless sensor networks

Data gathering is one of the most popular applications in multi-hop wireless sensor networks. Since resources are limited, it is important to efficiently allocate the resource while providing desired performance. In this paper, we consider resource allocation in the uplink of multi-hop wireless networks with the use of data buffers of finite size in the presence of transmission error. We first analyze the probability of buffer occupation of each router and then derive the outage probability associated with buffer overflow and transmission latency. Exploiting the analytic results, we design a resource allocation algorithm that minimally utilizes the resource in multi-hop wireless sensor networks, while guaranteeing desired performance. Finally, the proposed scheme is verified by computer simulation.

Effect of channel sensing on CSMA/CA in IEEE 802.15.4 networks

IEEE 802.15.4 employs a medium access control protocol based on carrier sense multiple access with collision avoidance (CSMA/CA). Channel sensing may have critical impact on the system throughput and energy consumption as well. In this paper, we investigate the effect of channel sensing on the CSMA/CA performance in IEEE 802.15.4 star-topology configured networks. We show that the hidden node ratio (i.e., the probability that any two child nodes cannot hear each other in a star-topology configured network) is highly associated with the target false-alarm probability of the channel sensing detector. We show that the CSMA/CA performance of IEEE 802.15.4 network can significantly be improved by adjusting the hidden node ratio.