In 802.11 wireless LANs, partial packets are often received which usually contain only a few errors. According to the current 802.11 standard, such packets have to be retransmitted. Much effort has been invested recently in repairing such packets without retransmitting the entire packet, e.g., by using error correction (EC) code or retransmitting only the corrupted blocks. In this paper, we study the software partial packet recovery and propose a comprehensive scheme called UNITE with the following key features. First, UNITE supports both the EC-based and block-based methods, because they are suited for different scenarios and can complement each other to achieve higher performance. Second, UNITE employ AMPS, an error estimator designed by us, which is capable of estimating the error condition in each individual partial packet and providing key information for repairing the packet. Third, UNITE selects the repair method for each packet to optimize the link performance under configurable system resource constraint, such as CPU or power. We implement UNITE on the Madwifi open-source driver. Our experiments show that UNITE outperforms other recovery schemes while not over-consuming the system resources.

Opportunistic Routing (OR) has been proven effective for wireless mesh networks. However, the existing OR protocols cannot meet all the requirements for high-speed, multi-rate wireless mesh networks, including: running on commodity Wi-Fi interface, supporting TCP, low complexity, supporting multiple link layer data rates, and exploiting partial packets. In this paper, we propose Practical Opportunistic Routing (POR), a new OR protocol that meets all above requirements. The key features of POR include: packet forwarding based on a per-packet feedback mechanism, block-based partial packet recovery, multi-hop link rate adaptation, and a novel path cost calculation which enables good path selection by considering the ability of nodes to select appropriate data rates to match the channel conditions. We implement POR within the Click modular router and our experiments in a 16-node wireless testbed confirm that POR achieves significantly better performance than the compared protocols for both UDP and TCP traffic.

In this paper, we study the One-Sender-Multiple-Receiver (OSMR) transmission technique, which allows one sender to send to multiple receivers simultaneously by utilizing multiple antennas at the sender. To study the physical-layer characteristics of OSMR, we implement a prototype OSMR transmitter/receiver with GNU software defined radio and conduct experiments in a university building. Our results are positive and show that wireless channels allow OSMR for a significant percentage of the time. Motivated by our physical-layer study, we propose extensions to the 802.11 MAC protocol to support OSMR transmission, which is backward-compatible with existing 802.11 devices. We also note that the access point (AP) needs a packet scheduling algorithm to efficiently exploit OSMR. We show that the scheduling problem without considering the packet transmission overhead can be formalized as a linear programming problem, but the scheduling problem considering the overhead is NP-hard. We then propose a practical scheduler based on a two-phase algorithm that can also handle channel fluctuations. We test the proposed protocol and algorithm with simulations driven by traffic traces collected from wireless LANs and channel-state traces collected from our experiments, and the results show that OSMR significantly improves the downlink performance.

In this paper, we propose Coded Relay (Crelay) for multi-hop wireless networks. Crelay exploits both the partial packets and the overhearing capabilities of wireless nodes, and uses an error correction code in packet forwarding. When a node overhears a partial packet from an upstream node, it estimates the number of errors in the packet and informs the upstream node. The upstream node calculates the number of parity bytes required to correct the errors and can usually send only a small amount parity bytes instead of sending the complete packet, hence improving the network efficiency. We propose a novel protocol for packet forwarding with partial packets and overhearing, which forwards individual packets and will work seamlessly with upper layers. We also propose a practical algorithm for finding the packet forwarding path. We implement Crelay within the Click modular router and our experiments show that it can significantly improve the performance of wireless networks.

Opportunistic routing improves the performance of multi-hop wireless networks by exploiting the overhearing opportunities. However, without special hardware support, the current opportunistic routing protocols cannot exploit partial packets, i.e., packets with errors but still containing much useful information. In this paper, we present pMORE, a software-only opportunistic routing protocol capable of exploiting partial packets. pMORE performs random network coding at the granularity of blocks and uses block checksum test to efficiently locate correct information in a partial packet and avoid the risk of propagating errors. We design an algorithm to assemble packets with partial packets to add maximum fresh information while maintaining a low overhead. The experiment results from a 12-node indoor wireless testbed show that pMORE achieves higher throughput than MORE with a median throughput gain of 1.34×.

In wireless LANs, partial packets are often received which usually contain only a few errors. According to the current 802.11 standard, such packets have to be retransmitted. Much effort has been invested recently in repairing such packets without retransmitting the entire packet, e.g., by using error correction (EC) code or retransmitting only the corrupted blocks. In this paper, we revisit this problem, and propose Unite, a framework for more efficient partial packet recovery. Unite is motivated by two key observations. First, the two repair methods, i.e., the EC-based and block-based, are not mutually exclusive and can be combined to achieve higher performance. Second, the recently introduced error estimators can be utilized to determine the optimal repair method depending on the condition of each partial packet. The combined method should achieve better performance than each individual method; in addition, it should remain low in complexity because the EC-based and block-based method are both simple in nature. Unite uses AMPS, a recently proposed estimator, for error estimation. We implement Unite on the Madwifi open source driver, and our experiments show that Unite outperforms other recovery schemes.

In this paper, we study the One-Sender-Multiple-Receiver (OSMR) transmission technique, which allows one sender to send to multiple receivers simultaneously by utilizing multiple antennas at the sender. We implemented a prototype OSMR transmitter/receiver with GNU Software Defined Radio, and conducted experiments in a university building to study the physical layer characteristics of OSMR. Our results are positive and show that wireless channels allow OSMR for a significant percentage of the time. Motivated by our physical layer study, we propose extensions to the 802.11 MAC protocol to support OSMR transmission, which is backward compatible with existing 802.11 devices. We also note that the AP needs a packet scheduling algorithm to efficiently exploit OSMR. We show that the scheduling problem without considering the packet transmission overhead can be formalized as a Linear Programming problem, but the scheduling problem considering the overhead is NP-hard. We then propose a greedy algorithm to schedule OSMR transmissions. We tested the proposed protocol and algorithm with simulations driven by traffic traces collected from wireless LANs and channel state traces collected from our experiments, and the results show that OSMR significantly improves the downlink performance.