Shared Broadcast Channel Research Articles

Drizzle: Cooperative Symbol-Level Network Coding in Multichannel Wireless Networks

Errors are inherently present in unreliable wireless channels. The primary challenge in designing error-control protocols in the medium-access control (MAC) or physical layer is to effectively maximize achievable throughput in wireless networks, even when unpredictable and time-varying errors exist. Network coding has successfully been applied to improve throughput in IEEE 802.11-based wireless networks with a shared broadcast channel. In state-of-the-art physical-layer designs in multichannel wireless networks [such as IEEE 802.16 Worldwide Interoperability for Microwave Access (WiMAX)], however, the convenience of a shared wireless broadcast channel to perform opportunistic listening no longer exists, and hybrid automatic repeat request (HARQ) is the predominant error-control protocol in the physical layer, rather than plain automatic repeat request in IEEE 802.11 MAC. Would network coding be well employed in multichannel wireless networks and able to bring further improvements over HARQ? This paper proposes Drizzle, which is a new solution to maximizing throughput with the presence of errors, which takes advantage of network coding at the symbol level in multichannel wireless networks. By operating at the symbol level and using soft-decision values, we show that Drizzle is able to exploit both time and cooperative diversity in realistic multichannel wireless networks, to adapt to time-varying and bursty channel errors, and to efficiently collect as many correct symbols as possible at the receiver.

Adaptive initialization algorithm for ad hoc radio networks with carrier sensing

We propose an algorithm for coordinating access to a shared broadcast channel in an ad hoc network of unknown size n . We reduce the runtime necessary to self-organize access to the channel over the previous algorithm of Cai, Lu and Wang. The runtime of that algorithm is O ( n ) . The goal of our work is to improve the constant factor in this estimation. Apart from the experimental evidence of algorithm quality, we provide a rigorous probabilistic analysis of its behavior.

A distributed laxity-based priority scheduling scheme for time-sensitive traffic in mobile ad hoc networks

Characteristics of Mobile Ad hoc Networks such as shared broadcast channel, bandwidth and battery power limitations, highly dynamic topology, and location dependent errors, make provisioning of quality of service (QoS) in such networks very difficult. The Medium Access Control (MAC) layer plays a very important role as far as QoS is concerned. The MAC layer is responsible for selecting the next packet to be transmitted and the timing of its transmission. We have proposed a new MAC layer protocol that includes a laxity-based priority scheduling scheme and an associated back-off scheme, for supporting time-sensitive traffic. In the proposed scheduling scheme, we select the next packet to be transmitted, based on its priority value which takes into consideration the uniform laxity budget of the packet, the current packet delivery ratio of the flow to which the packet belongs, and the packet delivery ratio desired by the user. The back-off mechanism devised by us grants a node access to the channel, based on the rank of its highest priority packet in comparison to other such packets queued at nodes in the neighborhood of the current node. We have studied the performance of our protocol that combines a packet scheduling scheme and a channel access scheme through simulation experiments, and the simulation results show that our protocol exhibits a significant improvement in packet delivery ratio under bounded end-to-end delay requirements, compared to the existing 802.11 DCF and the Distributed Priority Scheduling scheme proposed recently in [ACM Wireless Networks Journal 8 (5) (2002) 455–466; Proceedings of ACM MOBICOM '01, July 2001, pp. 200–209].

Performance study of SRMA multiple access protocols

In this paper we are concerned with packet broadcast networks in which users communicate with the central station. The key problem is multiple access of a shared broadcast channel. The performance of a family of SRMA (split-channel reservation multiple access) protocols for multiple access proposed by Tobagi and Kleinrock (1976) is studied. We analyse the performance of SRMA-RM (request message) and modified SRMA-RAM (request answer message) protocols in terms of the throughput and the average packet delay. Bounds on the throughput are also established for both protocols.

Performance of Double-Tier Access-Control Schemes Using a Polling Backbone for Metropolitan and Interconnected Communication Networks

We consider a double-tier communication network architecture for metropolitan area and packet radio networks for controlling the access of network terminals into a single shared broadcast channel. Terminals are organized into local groups in accordance with their geographical proximity or other criteria. Each local group can be associated with a primary station. The latter can serve as an unbuffered repeater for terminal transmissions unto the multiple-access channel. A polling policy is used by the primary stations to gain access into the shared communications backbone. Once a primary station is provided access into the channel, it initiates a local access control procedure. Message delay performance results and bounds are obtained for general reservation local-access procedures. In particular, we analyze and present performance results for a polling/tree-random-access procedure which can be effectively used for many packet radio and cellular digital radio networks, as well as for a polling/positionalpriority scheme for CATV and fiber-optic based networks.

Dynamic Behavior of a CSMA-CD System with a Finite Population of Buffered Users

In packet broadcast networks with buffered users, queues of packets at the users interfere with each other through a shared broadcast channel. Therefore, it is difficult to analyze the performance of such Systems by classical queueing theory. This paper provides an approximate performance analysis of a slotted nonpersistent CSMA-CD system with a finite number of users, each having a buffer of finite capacity. We develop an approximate Markovian model of the system with a multidimensional state vector. To analyze the model, We utilize an approximate analytical technique called equilibrium point analysis (EPA). Then, the throughput and average packet delay characteristics are obtained and the system stability behavior is demonstrated. An approximate expression is also derived for the probability distribution of the number of packets in a buffer. Numerical results from both analysis and simulation are given to illustrate the accuracy of those analytic results. Using the analytic results, we examine the effect of the collision detection capability on the system performance. Furthermore, we consider how to select both the rescheduling probability and the buffer size that guarantee the system stability, keep the probability of buffer overflow sufficiently small, and at the same time minimize the average packet delay.

Virtual Time CSMA: Why Two Clocks Are Better than One

A new carrier sense multiple access (CSMA) algorithm, called virtual time CSMA, is described and analyzed. This algorithm uses a novel approach to granting access to the shared broadcast channel based on variable-rate clocks. Unlike other CSMA algorithms, the operation of virtual time CSMA reduces to the ideal case in the zero propagation time limit: a work-conserving, first-come first-served M/G/1 queueing system. The algorithm does not appear to be difficult to implement, but offers better throughput-delay performance than existing CSMA algorithms. A simple closed form technique for estimating the mean message delay is presented. This technique is of independent interest because of its applicability to certain sliding window tree conflict resolution algorithms. Extensive numerical results for the algorithm are presented, including comparisons with simulation and with other CSMA algorithms.

Packet Broadcast Networks—A Performance Analysis of the R-ALOHA Protocol

In packet broadcast networks, users are interconnected via a broadcast channel. The key problem is multiple access of the shared broadcast channel. The performance of the R-ALOHA protocol for multiple access is studied in this paper. Two user models with Poisson message arrivals are analyzed; each message consists of a group of packets with a general probability distribution for group size. In the first model, each user handles one message at a time. In the second model, each user has infinite buffering capacity for queueing. Analytic models are developed for characterizing message delay and channel utilization. Bounds on channel throughput are established for two slightly different protocols. Numerical results from both analysis and simulation are presented to illustrate the accuracy of the analytic models as well as performance characteristics of the R-ALOHA protocol.