Flat Cellular (UMTS) Networks

Traditionally, cellular systems have been built in a hierarchical manner: many specialized cellular access network elements that collectively form a hierarchical cellular system. When 2G and later 3G systems were designed there was a good reason to make system hierarchical: from a cost-perspective it was better to concentrate traffic and to share the cost of processing equipment over a large set of users while keeping the base stations relatively cheap. However, we believe the economic reasons for designing cellular systems in a hierarchical manner have disappeared: in fact, hierarchical architectures hinder future efficient deployments. In this paper, we argue for completely flat cellular wireless systems, which need just one type of specialized network element to provide radio access network (RAN) functionality, supplemented by standard IP-based network elements to form a cellular network. While the reason for building a cellular system in a hierarchical fashion has disappeared, there are other good reasons to make the system architecture flat: (1) as wireless transmission techniques evolve into hybrid ARQ systems, there is less need for a hierarchical cellular system to support spatial diversity; (2) we foresee that future cellular networks are part of the Internet, while hierarchical systems typically use interfaces between network elements that are specific to cellular standards or proprietary. At best such systems use IP as a transport medium, not as a core component; (3) a flat cellular system can be self scaling while a hierarchical system has inherent scaling issues; (4) moving all access technologies to the edge of the network enables ease of converging access technologies into a common packet core; and (5) using an IP common core makes the cellular network part of the Internet

Navigating through a forest of quad trees to spot images in a database

This paper describes how we maintain color and spatial index information on more than 1,000,000 images and how we allow users to browse the spatial color feature space. We break down all our images in color-based quad trees and we store all quad trees in our main-memory database. We allow users to browse the quad trees directly, or they can pre-select images through our color bit vector, which acts as an index accelerator. A Java based textsc{gui is used to navigate through our image indexes

A case for image quering through image spots

We present an image spot query technique as an alternative for content-based image retrieval based on similarity over feature vectors. Image spots are selective parts of a query image designated by users as highly relevant for the desired answer set. Compared to traditional approaches, our technique allows users to search image databases for local (spatial, color and color transition) characteristics rather than global features. When a user query is presented to our search engine, the engine does not impose any (similarity, ranking, cutoff) policy of its own on the answer set; it performs an exact match based on the query terms against the database. Semantic higher concepts such as weighing the relevance of query terms, is left to the user as a task while refining their query to reach the desired answer set. Given the hundreds of feature terms involved in query spots, refinement algorithms are to be encapsulated in separate applications, which act as an intermediary between our search engine and the users

A cache odyssey

This thesis describes the effect of write caching on overall file system performance. It will show through simulations that extensive write caching greatly reduces average file read latency. Extensive write caching reduces the number of disk writes and minimizes disk read/write contention. By taking a closer look at file system write semantics, it will also show that write optimized file systems are not the key issue for UNIX like file systems. Write optimized file systems only reduce disk read/write contention without really solving the cause of disk contention. Simulations using the Sprite traces are used to guide the design of a client and server caching protocol for the Pegasus File Server (PFS). This protocol guarantees data persistency, without writing the data to disk, through replication

Mixed-Media File Systems

This thesis addresses the problem of implementing mixed-media storage systems. In this work a mixed-media file system is defined to be a system that stores both conventional (best-effort) file data and real-time continuous-media data. Continuous-media data is usually bulky, and servers storing and retrieving many streams simultaneously require high throughput and capacity. To design a system that can support such bandwidth requirements, a thorough understanding is required of current I/O technology. An overview is given of commodity hardware that can be used for this purpose and performance experiments are presented that show how to use this hardware efficiently

Band switching for coherent beam forming in full-duplex wireless communication

Bidirectional wireless communication is advantageously achieved by using at least two frequency bands, wherein during a first time period a first one of the frequency bands is used for signal transmission (e.g., downlink) while a second one of the frequency bands is used for signal reception (e.g., uplink), and during a second time period (subsequent to the first time period) the first one of the frequency bands is used for signal reception (e.g., uplink) while the second one of the frequency bands is used for signal transmission (e.g., downlink). By alternating the use of the two frequency bands repeatedly between signal transmission and signal reception throughout the communication, overall communication efficiency is improved and latency times considerably reduced, particularly when implemented in a system having multiple antennas (i.e., antenna arrays) and employing coherent beam forming and antenna diversity

Method of transferring data packets in a communications network

In a method of communication, a first type of data packet is received. The first type of data packet is at least a portion of a second type of data packet. Based on the received first type of data packet, a determination is made as to whether to expect receipt of a subsequent first type of data packet in a given time interval. A status signal is sent if the subsequent first type of data packet is not received in the given time interval as determined in the determining step. In another method of communication, a data packet is received at a physical layer over a circuit switched physical channel. A status of the data packet is determined at the physical layer. A status report is sent to a higher protocol layer based on the determination