Catálogo de publicaciones - libros

To exploit multi-rate capability as well as improve performance in wireless networks, many relaying mechanisms are proposed on IEEE 802.11 media access control (MAC) layer. However, no effort has been invested to exploit the multi-rate capability for power saving mechanism in MAC. In this paper, we propose a Power Efficient Relaying MAC Protocol, called PERP, to achieve both performance improvement and power saving by leveraging the multi-rate capability. In proposed relaying scheme, if a node can support low rate node’s packet at higher rate and has sufficient power, after voluntarily helping data transmission at higher rate, all nodes go into sleep mode as quickly as possible to reduce power consumption. Simulation results show that the PERP improves throughput by 30~50% as well as reduces power consumption and transmission delay by 10~55% than the legacy mechanism.

Wireless Multimedia Broadcastings have been being promising applications. Recently, the multimedia multicastings have started to be embedded into the legacy wireless networks. To provide high quality multimedia with multicast, wireless multicast ARQ (Automatic Repeat reQuest) scheme is required. In multicast ARQ, multiple receivers may return feedback control packets, such as ACK (Acknowledgement) or NAK (Negative ACK), simultaneously to the transmitter. In this paper, we show that the multiple feedback control packets can be successfully decoded in transmitter without additional hardware cost. Based on the proposition, we described a conceptual flow of wireless multicast algorithm, and then proposed multimedia multicast protocol on Multiband-OFDM Wireless Personal Area Network (MB-OFDM WPAN) specifications. In simulation, we showed that the proposed mechanism reduces the power consumption and achieves improved performance.

Multi-path strategy is one of the favorable choices to transmit data efficiently and flexibly in sensor networks. Due to various applications, it is hard to devise a generic WSN routing strategy to meet all requirements of various applications and environments at the same time. Therefore, a novel routing strategy should provide flexible schemes which adjusts forwarding schemes dynamically according to the different requirements. In this paper, we proposed an adaptive multi-path routing algorithm (AMPRA), which could provide convenient client-interface for flexible switching between various routing strategies. Through studying the local minimum phenomenon , a new method Clockwise-Rule is proposed to overcome the local minimum phenomenon . Based on the Clockwise-Rule , AMPRA provides flexible transmission schemes. Simulations show that AMPRA can significantly improve the performance of networks.

In clustered ad hoc networks, it is often required that a clusterhead, a leader of cluster, send a message to all its neighbor clusterheads. One simple approach is to use a flooding scheme in which every bridge node receiving a message simply relays it only if it receives the message for the first time. However, the flooding tends to degrade network efficiency severely because many bridges relay the message unnecessarily, causing neighbor clusterheads to receive multiple copies of the same message along different paths. A distributed self-pruning algorithm proposed in this paper attacks this problem.

In wireless communications, chaotic communications have been a field of interest due to its low complexity in hardware implementation and low power consumption in chaotic signal generation. Among the modulation schemes using the chaotic signal, Differential Chaos Shift Keying (DCSK) is a robust noncoherent technique. Multiple-input multiple-output (MIMO) system is a technology that uses multiple transmit and/or multiple receive antennas in order to improve the system performance in wireless systems. In our paper, we have proposed a new scheme of MIMO-DCSK which utilizes the benefits of MIMO system into the chaotic communication system by transmitting and receiving DCSK modulated signals through multiple antennas. Our analysis and simulation results show how the chaotic communications in the new MIMO-DCSK benefits over the single input single output (SISO) system and the BER performance of DCSK in additive white Gaussian noise (AWGN) channels using Alamouti space-time code and the maximum likelihood decoding is analyzed.

In this paper we present extended age dependent backoff protocol (EADB), an extension of the age dependent backoff (ADB) proposed to alleviate the delay and jitter of real-time packets. The proposed retransmission scheme considers not only the persistence factors but also the contention window (CW) to reduce collision rate. The persistence factor (PF) is based on the ages of the real-time packets in the transmission queue and the lifetimes of real-time packets. Moreover, we also consider the collision rate that stations experience to adjust the CW. The proposed scheme is able to prevent the degradation the performance of the network caused by setting the CW as the minimum value after successful transmission. Simulation results indicate that the EADB provides the delay, jitter, and drop rate better than ADB.

Leader election is an extensively studied problem in Ad hoc networks. In our study, an extended idea of leader election algorithms for energy saving on arbitrary changing topological environment is derived. Our focus is to reduce the number of leader election processes, to make it more energy efficient. The proposed algorithm shows that each node maintains a list of candidates to minimize the total number of leader elections. Simulation results show that the leader election algorithm using candidates has less leader elections process and generates less message than those of the existing leader election algorithms.

We measured a performance of data transmission between a desktop PC and a PDA in an infrastructure network based on IEEE 802.11x wireless LAN. Assuming that a PDA is mainly used for downloading data from its stationary server, i.e., a desktop PC, a PC and a PDA acts as a fast sender and a slow receiver, respectively, due to substantial differences in their computational capabilities. With data transmission between these heterogeneous terminals a transmission time during downstream is slower than that during upstream by 20% at maximum. To mitigate this, we present two distinct approaches. First, by increasing the size of a receive buffer for a PDA the congestion window size of TCP becomes more stable. Thus, an approximate 32% increase in throughput can be obtained by increasing its size from 512 bytes to 32768 bytes. Second, a pre-determined delay between packets to be transmitted at the sender should be given. By assigning the inter-packet delay of 5 ms during downstream achieves a best performance which improves by 7% compared to that without such a delay. Besides, such a delay reduces the number of erroneous packets remarkably.

We propose a novel route optimization protocol for intra-NEMO communication using a hierarchical and distributed caching scheme. The proposed scheme employs the routing cache of each nested MRs to optimize a route to be taken for traffic between MNNs within nested mobile network. For this goal, it supports an efficient cache design and adaptive mechanism for managing cache. By using tree based routing, it has greater data efficiency with less packet overheads, and improves the latency of the data traffic using an optimal route. To support seamless mobility, we propose a solution that reduces the mass signaling for all nested mobile networks when the nested MR handoff frequently occurs. The proposed scheme has approximately 29% of performance improvements in comparison with previous schemes.

WSNs (Wireless Sensor Network) can employ a burst technique known as 802.11e TXOP (Transmission Opportunity) operation to send sensor data backlogged during the sleep period [1] and FEC (Forward Error Correction) techniques to resist against their high BER (Bit Error Rate) [2]. This paper extends the 802.11e evaluation model [3], [4] to accurately calculate the performance of two TXOP schemes such as BI (Basic Immediate ACK) and BB (Basic Block ACK) with FEC codes. The generalized model accounts for the effect of propagation errors negligible in wireless LANs, the impact of HOB (Head-Of-Block) collision, and the effect of adopting FEC codes. This paper evaluates this extended model over real WSN channels abstracted by Gilbert model. The numerical calculations over real WSN traces confirm that the inclusion of HOB collisions causes the throughput difference of BB by up-to 194% comparing to [3]. They also predicts a trade-off between the performance improvement and the overhead of FEC codes over WSN channels.