Rongsheng Huang

A Fairness-Aware Congestion Control Scheme in Wireless Sensor Networks

The event-driven nature of wireless sensor networks (WSNs) leads to unpredictable network load. As a result, congestion may occur at sensors that receive more data than they can forward, which causes energy waste, throughput reduction, and packet loss. In this paper, we propose a rate-based fairness-aware congestion control (FACC) protocol, which controls congestion and achieves approximately fair bandwidth allocation for different flows. In FACC, we categorize intermediate relaying sensor nodes into near-source nodes and near-sink nodes. Near-source nodes maintain a per-flow state and allocate an approximately fair rate to each passing flow. On the other hand, near-sink nodes do not need to maintain a per-flow state and use a lightweight probabilistic dropping algorithm based on queue occupancy and hit frequency. Our simulation results and analysis show that FACC provides better performance than previous approaches in terms of throughput, packet loss, energy efficiency, and fairness.

A Mobility Management Scheme for Wireless Mesh Networks

Current deployment of the wireless mesh networks (WMN) necessitates mobility management to support mobile clients roaming around the network without service interruption. Though Mobile IP and other previous protocols can be applied to WMNs to gain the micro-mobility as well as macro-mobility support, high signaling cost and long handoff latency problems still degrade the system performance significantly. In this paper we present a new mobility management scheme for WMNs, mesh mobility management (M3). It utilizes some WMNs features and combines the per-host routing and tunneling techniques to reduce the signaling cost as well as to shorten the handoff latency. Our analysis shows that significant benefits can be achieved from this scheme.

SAM-MAC: An efficient channel assignment scheme for multi-channel ad hoc networks

Using multi-channel MAC protocols in mobile ad hoc networks (MANETs) is a promising way to improve the throughput performance. Channel assignment, which directly determines the efficiency of the frequency utilization, is the critical part of multi-channel schemes. Current 802.11-like schemes of multi-channel MAC do not efficiently use the multiple channels due to the overhead caused by channel assignment. Moreover, the control channel saturation problem limits the number of channels of these previous schemes. In this paper, we propose a new scheme called SAM-MAC (Self-Adjustable Multi-channel MAC), which features with one common channel and two half-duplex transceivers for each node. A method called self-adjustment is used to reassign the channels and balance the traffic on different channels. Due to less contention in common channel and smaller channel assignment overhead, this scheme increases the throughput compared with previous approaches. Control channels are free from saturation problem and can furthermore be used for data transmission.

Deterministic Priority Channel Access Scheme for QoS Support in IEEE 802.11e Wireless LANs

The enhanced distributed channel access (EDCA) of IEEE 802.11e has been standardized to support quality of service (QoS) in wireless local area networks (LANs). The EDCA statistically supports the QoS by differentiating the probability of channel access among different priority traffic and does not provide the deterministically prioritized channel access for high-priority traffic, such as voice or real-time video. Therefore, lower priority traffic still affects the performance of higher priority traffic. In this paper, we propose a simple and effective scheme called deterministic priority channel access (DPCA) to improve the QoS performance of the EDCA mechanism. To provide guaranteed channel access to multimedia applications, the proposed scheme uses a busy tone to limit the transmissions of lower priority traffic when higher priority traffic has packets to send. Performance evaluation is conducted using both numerical analysis and simulation and shows that the proposed scheme significantly outperforms the EDCA in terms of throughput, delay, delay jitter, and packet drop ratio under a wide range of contention level.

Cost design for opportunistic multi-hop routing in Cognitive Radio networks

Cognitive radio (CR) is a revolutionary technology with promising applications in military areas since it enables CR users in the field to dynamically access to the vacant licensed frequency bands if no primary users are present. In practice, multi-hop routing in CR networks presents a great challenge due to unreliable traditional links and time varying unlicensed CR links. To improve the performance of multi-hop routing, opportunistic routing (OR) has been proposed and investigated extensively. Instead of using a single next hop, OR forwards a packet to an ordered set of candidate nodes and one node is chosen to relay the packet towards the destination. Most OR protocols prioritize the candidates and make the selection based on the cost defined as expected transmission times (ETX). Actually, ETX, as well as other existing criteria, does not always lead to the best forwarder choice for OR in CR networks since it ignores numerous potential CR links. In this paper, we propose a novel cost criterion for opportunistic multi-hop routing in CR networks, which leverages the unlicensed CR links to prioritize the candidate nodes and optimally selecting the forwarder. Simulation results show that our design efficiently decreases the number of transmissions, and effectively increases the throughput for most node pairs when compared with OR and traditional single-path routing.

Handoff for wireless networks with mobile relay stations

Wireless Relay networks have become very important technologies in the future wireless systems. Current research works mostly focus on scenarios where relay stations are either stationary or mobile with uniform velocity. However, in many applications, relay stations are mobile with irregular patterns. In particular, when mobile relay stations (MRSs) are deployed to complement the cellular systems, many issues such as handoff should be carefully investigated. In this paper, we focus on the handoff problem and propose a new handoff decision algorithm based on the relative velocities of user equipment (UE) to the serving access point (AP) and the target AP. We have show that the proposed handoff algorithm can significantly improve the handoff successful rate when the mobile relay station changes its moving patterns.

Improving throughput by tuning carrier sensing in 802.11 wireless networks

In this paper, we study the impacts of physical carrier sensing and channel rate on the throughput of 802.11 wireless networks with chain topology. Firstly, we show that by adopting different carrier sensing thresholds for the RTS and CTS transmissions, the blocking problem caused by exposed terminals can be greatly alleviated. In 802.11 wireless networks with this modification, the spatial reuse ratio under certain channel rates can be increased to 13, which is the highest value to our best knowledge. Secondly, in multi-rate networks, we demonstrate that 13 is still the best value of spatial reuse ratio in terms of maximizing the achievable data rate under certain conditions. Thirdly, this paper proposes a new method to address the intra-flow contention by decreasing the carrier sensing threshold of the source node. This method requires less response time than that of the traditional method which adjusts the backoff window size. Finally, extensive simulations are implemented in NS2 and the results show that our scheme significantly improves the throughput of 802.11 wireless networks with chain topology.

Enhancing Handoff Performance by Introducing Ad Hoc Mode into Cellular Networks

As all-IP feature becomes dominant in the next generation networks (NGNs), ad hoc mode is gaining more attention as an appealing addition to cellular networks. Consequently, multi-hop handoffs become inevitable, which bring challenging issues to network designers. Handoff dropping (HOD) rate and the bandwidth reservation for the required HOD rate are two important metrics to evaluate the handoff performance of a cellular system. By introducing ad hoc mode into cellular systems, we can either achieve lower HOD rate or reserve less bandwidth for the same required HOD rate. In this paper, we incorporate traffic information from neighboring BSs and propose an algorithm to find the minimum bandwidth reservation for each BS. Since its performance greatly depends on the access probability to the adjacent cells, we further propose to utilize the embedded ad hoc networks to gather the traffic load information of neighboring cells. With such information, handoff calls can effectively select the best paths to the proper BSs. It has been demonstrated that our scheme can significantly improve the system performance.

SAM-MAC: an efficient channel assignment scheme for multi-channel ad hoc networks

Using multi-channel MAC protocols in mobile ad hoc networks (MANETs) is a promising way to improve the through-put performance. Channel assignment, which directly determines the efficiency of the frequency utilization, is the critical part of multi-channel schemes. Current 802.11-like schemes of multi-channel MAC do not efficiently use the multiple channels due to the overhead caused by channel assignment. Moreover, the control channel saturation problem limits the number of channels of these previous schemes. In this paper, we propose a new scheme called SAM-MAC (Self-Adjustable Multi-channel MAC), which features with one common channel and two half-duplex transceivers for each node. A method called self-adjustment is used to reassign the channels and balance the traffic on different channels. Due to less contention in common channel and smaller channel assignment overhead, this scheme increases the throughput compared with previous approaches. Control channels are free from saturation problem and can furthermore be used for data transmission.

Resolving RACH Congestion for High Speed Moving Group in Wireless Networks

When many cellular users take high capacity transit (HCT), a group of mobile terminals (MTs) may have to initiate handoffs and location updates more or less at the same time, which will cause congestion on the random access control channel (RACH), leading to many handoff and location update failures. To overcome this problem, we propose a new scheme, called GHA/RALU (Group Handoff Avoidance/Rate Adjusted Location Update Scheme), to deal with this group mobility issue. The idea is first to delay the normal location update (NLU) requests until the group handoff requests are completed and then spread the NLU requests within a calculated time interval based on the available bandwidth of the RACH. Our analysis shows that the proposed scheme significantly improves the success probability of the group handoffs and NLUs, saves the RACH resource, and accelerates the handoff initiated by the moving-in-together MTs.