Cooperative Retransmissions Through Collisions

Interference in wireless networks is one of the key capacity-limiting factors. Recently developed interference-embracing techniques show promising performance on turning collisions into useful transmissions. However, the interference-embracing techniques are hard to apply in practical applications due to their strict requirements. In this paper, we consider utilising the interference-embracing techniques in a common scenario of two interfering sender-receiver pairs. By employing opportunistic listening and analog network coding (ANC), we show that compared to traditional ARQ retransmission, a higher retransmission throughput can be achieved by allowing two interfering senders to cooperatively retransmit selected lost packets at the same time. This simultaneous retransmission is facilitated by a simple handshaking procedure without introducing additional overhead. Simulation results demonstrate the superior performance of the proposed cooperative retransmission.Comment: IEEE ICC 2011, Kyoto, Japan. 5 pages, 5 figures, 2 tables. Analog Network Coding, Retransmission, Access Point, WLAN, interference, collision, capacity, packet los

Co-channel digital signal separation : application and practice

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2008.Includes bibliographical references (leaves 84-86).This thesis studies the theory and application of co-channel digital signal separation techniques. We set up a test-bed with the GNU Software Defined Radio (SDR) platform where we implement and experiment with single-antenna signal separation algorithms. We mainly investigate linearly-modulated digital signals. To do this, we design a multiple RFID card reader capable of decoding multiple commodity ID cards simultaneously. These passive RFID cards transmit DBPSK waveforms once activated. A signal separation function at the receiver delivers great convenience to the users without increasing the complexity and cost of the cards. Second, we derive the optimal criteria for deciding the start of an RFID frame. We show that the commonly utilized correlation rule is suboptimal and that a correction term needs to be considered to achieve the best detection performance. Several rules for frame synchronization are proposed and analyzed numerically using Monte Carlo simulation. These signal separation techniques present an opportunity to improve the capacity of wireless systems and combat interference. This thesis documents design issues in the physical and application layers, thereby demonstrating the great flexibility and strength of the GNU SDR system.by Dawei Shen.S.M

Co-channel DBPSK source separation

Thesis (S.M.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2007.Includes bibliographical references (leaves 51-53).This thesis presents a Differential Binary Phase Shift Key (DBPSK) source separation system implemented with the GNU Software Defined Radio (SDR) platform and interfaced with the existing MIT community Radio Frequency Identification (RFID) system. Source separation, well studied in the theoretical signal processing setting, presents an opportunity to achieve higher throughput in a practical SDR deployment. While much research has centered around the design of complex multi-input-multi-output (MIMO) and code division multiple access (CDMA) systems, single antenna source separation presents a simple alternative that is suitable in settings such as RFID where sources are naturally synchronized. Motivated by the analysis of physical channel properties with GNU SDR, this thesis documents the complete design process from the physical layer to the application layer and presents a realization of a co-channel DBPSK source separating technique. The result is an intelligent RFID source-separating reader that is capable of decoding multiple "dumb" cards.by Grace R. Woo.S.M

Embracing Wireless Interference: Analog Network Coding

Traditionally, interference is considered harmful.Wireless networks strive to avoid scheduling multiple transmissions at the same time in order to prevent interference. This paper adopts the opposite approach; it encourages strategically picked senders to interfere. Instead of forwarding packets,routers forward the interfering signals. The destination leverages network-level information to cancel the interference and recover the signal destined to it. The result is analog network coding because it codes signals not bits. So, what if wireless routers forward signals instead of packets? Theoretically, we prove that such an approach doubles the capacity of the canonical relay network. Surprisingly, it is also practical. We implement our design using softwareradios and show that it achieves significantly higher throughput than both traditional wireless routing and prior work on wireless network coding