This paper presents a cross-layer approach for enabling high-throughput reliable multicast in multi-hop wireless mesh networks. The building block of our approach is a multicast routing metric, called the expected multicast transmission count (EMTX). EMTX is designed to capture the combined effects of MAC-layer retransmission-based reliability, wireless broadcast advantage, and link quality awareness. The EMTX of single-hop transmission of a multicast packet from a sender is the expected number of multicast transmissions (including retransmissions) required for its next-hop recipients to receive the packet successfully. We formulate the EMTX-based multicast problem with the objective of minimizing the sum of EMTX over all forwarding nodes in the multicast tree, aiming to reduce network bandwidth consumption while ensure high end-to-end packet delivery ratio for the multicast traffic. We provide rigorous mathematical formulations and methods to find near-optimal solutions of the problem computationally efficiently. We present centralized and distributed algorithms, and demonstrate their effectiveness in tackling the EMTX-based multicast problem with a combination of theoretical and numerical results. Simulation experiments show that, in comparison with two baseline approaches, EMTX-based multicast routing reduces the number of hop-by-hop transmissions per packet by up to 40 percent and yet improves the multicast throughput by up to 24 percent.

The IEEE 802.11 MAC protocol performance degrades severely as the number of stations in the collision domain increases in a saturated network. Employing cooperative retransmission at the MAC layer provides a way to work around the performance limitations by exploiting the broadcast nature of wireless communication. This paper presents a new routing metric, termed Expected Cooperative Forwarding Delay (ECFD), with the aim of selecting a minimum end-to-end delay path for multi-hop multi-rate wireless mesh networks. Different from previously proposed cooperative-aware routing metrics such as ORETT, the ECFD metric is based not only on expected cooperative transmission time but accounts for queueing and backoff delays in the path selection process. We describe the design and implementation of ECFD, and conduct extensive simulation experiments in random topologies showing that, under various realistic network traffic patterns, the use of ECFD instead of ORETT and ETT significantly improves both end-to-end delay and throughput.

This paper studies an efficient resource allocation scheme for multicast in OFDMA based wireless networks. Apart from the conventional resource allocation schemes for multicast which allocate exactly the same subcarriers to the users in a multicast group, this paper proposes a more flexible scheme to divide the multicast group members into different subgroups by utilising the diversity of channel coefficient of different users. We first formulate an optimisation problem to maximise the overall transmission rate. Given the NP-hardness of the problem, we design a low-complexity heuristic, Flexible Resource Allocation with Geometric programming (FRAG). FRAG is a two-step heuristic to subdivide the multicast groups and allocate resource to corresponding subgroups. In the first step, we propose a greedy algorithm to subdivide groups and allocate subcarriers given the assumption of even power distribution. Then we use geometric programming (GP) to solve the optimal power allocation problem. Numerical results show that FRAG is able to allocate subcarriers and power efficiently and effectively, and it achieves up to 33% improvement in aggregated throughput.

This paper proposes an opportunistic rate-adaptive expected transmission time (ORETT) metric, which exploits cooperative (relay-aided) retransmissions to achieve high-throughput routing in multi-rate wireless mesh networks. This metric captures the combined effects of MAC-layer cooperative retransmission by neighbor nodes with transmission rate diversity (and rate-dependent link quality). In our approach, a relay node is selected among one-hop neighbors to assist with packet retransmissions and minimize the expected retransmission time. The paper describes the design and implementation of the ORETT routing metric using the DSR routing protocol. Our extensive simulation on the Qualnet platform confirms that multi-rate routing using ORETT significantly reduces the overall transmission time while yielding higher packet delivery ratio compared to single rate unicast or non-cooperative ETT based routing.

We present a cross-layer approach for enabling high-throughput routing in multi-hop wireless networks. This approach builds on a MAC-layer cooperative retransmission mechanism, which is explicitly designed to exploit the benefits of MAC-layer retransmission-based reliability, cooperative communications, and link-quality awareness. Based on this mechanism, we devise a routing metric, called the expected cooperative transmission count (ECTX), to capture the combined effects of MAC-layer cooperative retransmission and per-link estimates of packet delivery ratios. We show that, compared to conventional approaches using the well-known expected transmission count (ETX) metric, our approach has two advantages in principle: 1) with the cooperative retransmission mechanism, one can effectively reduce the expected total number of packet transmissions (including retransmissions) on the same path found by ETX; 2) with the ECTX metric, one may indeed identify a more effective path and further reduce the transmission count. We discuss modifications to IEEE 802.11 MAC to incorporate the cooperative retransmission mechanism, and implement ECTX-based routing using the DSR protocol. Extensive simulations on QualNet demonstrate that ECTX-based routing is significantly more efficient than ETX-based routing, in many instances reducing the transmission count by more than 30% and yet improving the network throughput by up to 80%.

We propose a routing metric for enabling high-throughput reliable multicast in multi-rate wireless mesh networks. This new multicast routing metric, called expected multicast transmission time (EMTT), captures the combined effects of 1) MAC-layer retransmission-based reliability, 2) transmission rate diversity, 3) wireless broadcast advantage, and 4) link quality awareness. The EMTT of one-hop transmission of a multicast packet minimizes the amount of expected transmission time (including that required for retransmissions). This is achieved by allowing the sender to adapt its bit-rate for each ongoing transmission/retransmission, optimized exclusively for its next-hop receivers that have not yet received the multicast packet. We model the rate adaptation process as a Markov decision process (MDP) and derive an efficient procedure for computing EMTT from the theory of MDP. We present receiver-initiated algorithms and describe protocol implementation for the EMTT-based multicast routing problem. Numerical results are presented to demonstrate the accuracy of the proposed algorithms against optimal solutions to the multicast routing problem. Simulation experiments confirm that, in comparison with single-rate multicast, multi-rate multicast using the EMTT metric effectively reduces the overall multicast transmission time while yielding higher packet delivery ratio and lower end-to-end latency.

This paper studies probabilistically reliable multicast in wireless mesh networks (WMNs), utilizing MAC layer re-transmission and wireless broadcast advantage to improve both the multicast throughput and the delivery rate. We first present a new multicast routing metric which we call the expected multicast transmissions (EMT). EMT captures the effect of link packet delivery ratio, MAC layer retransmission and wireless broadcast advantage at the same time. The EMT of a MAC layer multicast transmission is the expected number of data transmissions (including retransmissions) required for a packet to reach all the recipients. The EMT of a multicast tree is the sum over the EMT of each forwarding node. Then, we propose a probabilistically reliable on-demand (PROD) multicast protocol with the objective of minimizing the EMT of the multicast tree. Simulation results show that, in comparison with existing approaches, PROD reduces the end-to-end packet loss ratio by up to 30% and improves the multicast throughput by up to 25%. In addition, it reduces the number of transmissions per packet by up to 40% and thus significantly reduces the network overhead of the multicast session.

In this paper, we proposed a probabilistically reliable multicast routing (PRMR) which uses link packet delivery rate as the link-quality-based metric to find paths from source to destinations. In order to increase the reliability of the multicast session, we use a pair of disjoint paths to connect the source to each destination. We reduce the total number of forwarding nodes by exploiting the wireless broadcast advantage. Our experiment results show that PRMR can increase the average reliability by up to 25% and the node with the lowest reliability by up to 50% in comparison with ODMRP.

To support reliable multicast routing in wireless mesh networks, it is important to protect multicast sessions against link or node failures. The issue of protecting multicast sessions in wireless mesh networks is a new problem to the best of our knowledge. In this paper, we propose a resilient forwarding mesh approach for protecting a multicast session in wireless mesh networks. Utilizing the wireless broadcast advantage, a resilient forwarding mesh effectively establishes two node disjoint paths for each source-destination pair. This allows a multicast session to be immune from any single link or intermediate node failure. We introduce four heuristic algorithms to obtain approximate solutions that seek to minimize the number of required broadcast transmissions. We evaluate the performance of these heuristic algorithms against the optimal resilient forwarding mesh (ORFM) obtained by solving an integer linear programming (ILP) formulation of the problem. Experimental results demonstrate that one of these heuristic algorithms, which we call the minimal disjoint mesh algorithm (MDM), performs sufficiently close to ORFM. Besides, we find that the resilient forwarding mesh approach provides efficient 1+ 1 protection (Pioro and Medhi, 2004) to the multicast session without incurring much additional overhead on a single minimal cost multicast tree