Network forensics

Network forensics is a sub-branch of digital forensics relating to the monitoring and analysis of computer network traffic for the purposes of information gathering, legal evidence, or intrusion detection. Unlike other areas of digital forensics, network investigations deal with volatile and dynamic information, making network forensics often a pro-active investigation.

Network forensics generally has two uses:

The first, relating to security, involves monitoring a network for anomalous traffic and identifying intrusions. An attacker might be able to erase all log files on a compromised host; network-based evidence might therefore be the only evidence available for forensic analysis. 

The second form of Network forensics relates to law enforcement. In this case analysis of captured network traffic can include tasks such as reassembling transferred files, searching for keywords and parsing human communication such as emails or chat sessions. 

Two systems are commonly used to collect network data:

"Catch-it-as-you-can" - This is where all packets passing through certain traffic point are captured and written to large storage with analysis being done subsequently in batch mode. 

"Stop, look and listen" - This is where each packet is analyzed by a faster processor in a rudimentary way in memory and only certain information saved for future analysis.

Types

Ethernet – Applying forensic methods on the Ethernet layer is done by eavesdropping bit streams with tools called monitoring tools or sniffers. The most common tool on this layer is Wireshark (formerly known as Ethereal). It collects all data on this layer and allows the user to filter for different events. With these tools, websites, email attachments and more that have been transmitted over the network can be reconstructed. An advantage of collecting this data is that it is directly connected to a host. If, for example, the IP address or the MAC address of a host at a certain time is known, all data for or from this IP or MAC address can be filtered.

 TCP/IP – For the correct routing of packets through the network (e.g., the Internet), every intermediate router must have a routing table which is the best source of information if investigating a digital crime. To do this, it is necessary to reverse the sending route of the attacker, follow the packets, and find where the computer the packet came from (i.e., the source of the attacker).

Another source of evidence on this layer is authentication logs. They show which account and which user was associated with an activity and may reveal who was the attacker or at least sets limits to the people who come into consideration of being the attacker.

The Internet – The internet can be a rich source of digital evidence including web browsing, email, newsgroup, synchronous chat and peer-to-peer traffic.

Wireless forensics is a sub-discipline of network forensics. The main goal of wireless forensics is to provide the methodology and tools required to collect and analyze (wireless) network traffic that can be presented as valid digital evidence in a court of law. The evidence collected can correspond to plain data or, with the broad usage of Voice-over-IP (VoIP) technologies, especially over wireless, can include voice conversations.

 

Second Screen or Multi Screen

Second screen, sometimes also referred to as "companion device" (or "companion apps" when referring to a software applications), is a term that refers to an additional electronic device (e.g. tablet, smartphone) that allows a television audience to interact with the content they are consuming, such as TV shows, movies, music, or video games. Extra data is displayed on a portable device synchronized with the content being viewed on television.

Several studies show a clear tendency of the consumer to use a device while watching television. They show high use of tablet or smartphone when watching television, and indicate a high percentage of comments or posts on social networks being about the content that's being watched.

Based on these studies, many companies both in content production and advertising have adapted their delivery content to the lifestyle of the consumer in order to get maximum attention and thus profits. Applications are becoming a natural extension of television programming, both live and on demand.

Applications

Many applications in the "second screen" are designed to give the consumer another way of interactivity. They also give the media companies another way to sell advertising content. Some examples:

·         Transmission of the Master's Golf Tournament, application for the iPhone (rating information and publicity)
·         TV programs broadcast live tweets and comment.
·         Synchronization of audiovisual content via web advertising.
·         Applications that extend the content information.
·         Shows that add on their websites, content devoted exclusively to the second screen.
·         Applications that synchronize the content being viewed to the portable device.
·         Video game console playing with extra data, such as a map or strategy data that synchronize with the content being viewed to the portable device.
·         TV discovery application with recommendation, EPG (live content), personalization.

Sports Broadcasting

Sports broadcasters, to stem the flight of the TV audience away from watching the main screen (new name for the television) to the second screen, are offering alternative and enhanced content to the main program. The idea is to present content related to the main program, such as unseen moments, alternative information, soundtrack, and characters. New technologies allow the viewer to see different camera angles while watching the game.

            

iBurst

Burst (or HC-SDMA, High Capacity Spatial Division Multiple Access) is a wireless broadband technology which optimizes the use of its bandwidth with the help of smart antennas.

Description

HC-SDMA was announced as considered by ISO TC204 WG16 for the continuous communications standards architecture, known as Communications, Air-interface, Long and Medium range (CALM), which ISO is developing for intelligent transport systems (ITS). ITS may include applications for public safety, network congestion management during traffic incidents, automatic toll booths, and more.

The HC-SDMA interface provides wide-area broadband wireless data-connectivity for fixed, portable and mobile computing devices and appliances. The protocol is designed to be implemented with smart antenna array techniques (called MIMO for multiple-input multiple-output) to substantially improve the radio frequency (RF) coverage, capacity and performance for the system.

Technology

The HC-SDMA interface operates on a similar premise as cellular phones, with hand-offs between HC-SDMA cells repeatedly providing the user with a seamless wireless Internet access even when moving at the speed of a car or train.

The protocol:

·         specifies base station and client device RF characteristics, including output power levels, transmit frequencies and timing error, pulse shaping, in-band and out-of band spurious emissions, receiver sensitivity and selectivity;

·         defines associated frame structures for the various burst types including standard uplink and downlink traffic, paging and broadcast burst types;

·         specifies the modulation, forward error correction, interleaving and scrambling for various burst types;

·         describes the various logical channels (broadcast, paging, random access, configuration and traffic channels) and their roles in establishing communication over the radio link; and

·         specifies procedures for error recovery and retry.

The protocol also supports Layer 3 (L3) mechanisms for creating and controlling logical connections (sessions) between client device and base including registration, stream start, power control, handover, link adaptation, and stream closure, as well as L3 mechanisms for client device authentication and secure transmission on the data links.

Usage

Various options are already commercially available using:

·         Desktop modem with USB and Ethernet ports (with external power supply)
·         Portable USB modem (using USB power supply)
·         Laptop modem (PC card)
·         Wireless Residential Gateway
·         Mobile Broadband Router

Assisted GPS

Assisted GPS, generally abbreviated as A-GPS or aGPS, is a system that can under certain conditions improve the startup performance, or time-to-first-fix (TTFF), of a GPS satellite-based positioning system. It is used extensively with GPS-capable cellular phones to make the location of a cell phone available to emergency call dispatchers.

"Standalone" or "autonomous" GPS operation uses radio signals from satellites alone. In very poor signal conditions, for example in a city, these signals may suffer multipath propagation where signals bounce off buildings, or are weakened by passing through atmospheric conditions, walls, or tree cover. When first turned on in these conditions, some standalone GPS navigation devices may not be able to fix a position due to the fragmentary signal, rendering them unable to function until a clearer signal can be received continuously for a long enough period of time.

An assisted GPS system can address these problems by using data available from a network to locate and use the satellites in poor signal conditions. For billing purposes, network providers often count this as a data access, which can cost money depending on the plan.

Basic Concepts

Standalone GPS provides first position in approximately 30–40 seconds. A Standalone GPS system needs orbital information of the satellites to calculate the current position. The data rate of the satellite signal is only 50 bits/s, so downloading orbital information like ephemeris and almanac directly from satellites typically takes a long time, and if the satellite signals are lost during the acquisition of this information, it is discarded and the standalone system has to start from scratch. In AGPS, the Network Operator deploys an AGPS server. These AGPS servers download the orbital information from the satellite and store it in the database. An AGPS capable device can connect to these servers and download this information using Mobile Network radio bearers such as GSM, CDMA, WCDMA, LTE or even using other wireless radio bearers such as Wi-Fi. Usually the data rate of these bearers is high; hence downloading orbital information takes less time.

AGPS has two modes of operation:

Mobile Station Assisted (MSA)

In MSA mode A-GPS operation, the A-GPS capable device receives acquisition assistance, reference time and other optional assistance data from the A-GPS server. With the help of the above data, the A-GPS device receives signals from the visible satellites and sends the measurements to the A-GPS server. The A-GPS server calculates the position and sends it back to the A-GPS device.

Mobile Station Based (MSB)

In MSB mode A-GPS operation, the A-GPS device receives ephemeris, reference location, reference time and other optional assistance data from the A-GPS server. With the help of the above data, the A-GPS device receives signals from the visible satellites and calculates the position.

Many mobile phones combine A-GPS and other location services including Wi-Fi Positioning System and cell-site multilateration and sometimes a hybrid positioning system.

Remote Radio Head

A remote radio head is an operator radio control panel that connects to a remote radio transceiver via electrical or wireless interface. When used to describe aircraft radio cockpit radio systems, this control panel is often called the radio head.

Current and future generations of wireless cellular systems feature heavy use of Remote Radio Heads (RRHs) in the base stations. Instead of hosting a bulky base station controller close to the top of antenna towers, new wireless networks connect the base station controller and remote radio heads through lossless optical fibers. The interface protocol that enables such a distributed architecture is called Common Publish Radio Interface (CPRI). With this new architecture, RRHs offload intermediate frequency (IF) and radio frequency (RF) processing from the base station. Furthermore, the base station and RF antennas can be physically separated by a considerable distance, providing much needed system deployment flexibility.

Typical advanced processing algorithms on RRHs include digital up-conversion and digital down-conversion (DUC and DDC), crest factor reduction (CFR), and digital pre-distortion (DPD). DUC interpolates base band data to a much higher sample rate via a cascade of interpolation filters. It further mixes the complex data channels with IF carrier signals so that RF modulation can be simplified. CFR reduces the peak-to-average power ratio of the data so it does not enter the non-linear region of the RF power amplifier. DPD estimates the distortion caused by the non-linear effect of the power amplifier and pre-compensates the data.

More importantly, many wireless standards demand re-configurability in both the base station and the RRH. For example, the 3GPP Long Term Evolution (LTE) and WiMax systems both feature scalable bandwidth. The RRH should be able to adjust – at run time – the bandwidth selection, the number of channels, the incoming data rate, among many other things.

RRH system model

Typically, a base station connects to a RRH via optical cables. On the downlink direction, base band data is transported to the RRH via CPRI links. The data is then up-converted to IF sample rates, preprocessed by CFR or DPD to mitigate non-linear effects of broadband power amplifiers, and eventually sent for radio transmission. A typical system is shown in Figure 1.

Remote Radio Head

A remote radio head is an operator radio control panel that connects to a remote radio transceiver via electrical or wireless interface. When used to describe aircraft radio cockpit radio systems, this control panel is often called the radio head. 

Current and future generations of wireless cellular systems feature heavy use of Remote Radio Heads (RRHs) in the base stations. Instead of hosting a bulky base station controller close to the top of antenna towers, new wireless networks connect the base station controller and remote radio heads through lossless optical fibers. The interface protocol that enables such a distributed architecture is called Common Publish Radio Interface (CPRI). With this new architecture, RRHs offload intermediate frequency (IF) and radio frequency (RF) processing from the base station. Furthermore, the base station and RF antennas can be physically separated by a considerable distance, providing much needed system deployment flexibility.

Typical advanced processing algorithms on RRHs include digital up-conversion and digital down-conversion (DUC and DDC), crest factor reduction (CFR), and digital pre-distortion (DPD). DUC interpolates base band data to a much higher sample rate via a cascade of interpolation filters. It further mixes the complex data channels with IF carrier signals so that RF modulation can be simplified. CFR reduces the peak-to-average power ratio of the data so it does not enter the non-linear region of the RF power amplifier. DPD estimates the distortion caused by the non-linear effect of the power amplifier and pre-compensates the data.

More importantly, many wireless standards demand re-configurability in both the base station and the RRH. For example, the 3GPP Long Term Evolution (LTE) and WiMax systems both feature scalable bandwidth. The RRH should be able to adjust – at run time – the bandwidth selection, the number of channels, the incoming data rate, among many other things.

RRH system model

Typically, a base station connects to a RRH via optical cables. On the downlink direction, base band data is transported to the RRH via CPRI links. The data is then up-converted to IF sample rates, preprocessed by CFR or DPD to mitigate non-linear effects of broadband power amplifiers, and eventually sent for radio transmission.

Hotspot Wi - Fi

Wireless internet really made the technological life easy and convenient. There are different methods or technologies to use the wireless internet everywhere and continue our regular and important work related to internet technology. One of these technologies is the Wi-Fi hot spots.  

A hotspot is a site that offers Internet access over a wireless local area network through the use of a router connected to a link to an Internet service provider. Hotspots typically use Wi-Fi technology. With the help of our mobile devices we can access the wireless network through hot spots from coffee shops, malls etc.

To set up a hotspot, all we need is

1. a hotspot kit (hardware, software and remote monitoring device)

2. a high speed internet connection (DSL, T1 or DS3)

 
The type of hotspot kit depends on whether we need a Single Access Point or Multiple Access Point. If we are going for multiple access points, the area where we want to deploy the network has to be considered – whether it is a multi-storey building or a medium sized hotel.

Setting up a Hotspot

If we already have a network held together by Ethernet and now want to upgrade to a wireless hotspot, we need to purchase a Wireless Access Point and join it with the Ethernet network.

If we are starting from the scratch, what we need is a Wireless Access Point Router. This kit contains:

· a port to connect the modem

· a router

· an Ethernet hub

· a firewall

· a wireless access point

We can then connect the computers with Ethernet cables or with wireless cards. Whichever we choose, once we plug in the Wireless Access Point on, the Wi-Fi hotspot will be functional.

We will need the 802.11a standard if we are setting the network for business purposes. For home use, we can either choose the 802.11b which is the least expensive but also the slowest, or 802.11g which costs a little more but is much faster.

 

To Bill or not to Bill

This depends on the nature and size of your business. Many businesses want to set up hotspots as another value added service to attract more customers.

If you decide to charge your customers, make sure that you are choosing a Wi-Fi provider who has a built in package that helps in billing. The hotspot kit you purchase should enable you to take credit cards to your gateway. In this model, you are likely to share the revenues with the service provider, and the service provider assists in the day-to-day operations and maintenance of the hotspot.

The so-called "User-Fairness-Model" is a dynamic billing model, which allows a volume-based billing, charged only by the amount of payload (data, video, audio). Moreover, the tariff is classified by net traffic and user needs. If the net traffic increases, then the user has to pay the next higher tariff class. By the way the user is asked for if he still wishes the session also by a higher traffic class. Moreover, in time-critical applications (video, audio) a higher class fare is charged, than for non time-critical applications (such as reading Web pages, e-mail).

Hotspot 2.0

Also known as HS2 and Wi-Fi Certified Pass point, Hotspot 2.0 is a new approach to public access Wi-Fi by the Wi-Fi Alliance. The idea is for mobile devices to automatically join a Wi-Fi subscriber service whenever the user enters a Hotspot 2.0 area. The intention is to provide better bandwidth and services-on-demand to end-users, whilst also alleviating mobile carrier infrastructure of traffic overheads.

Hotspot 2.0 is based on the IEEE 802.11u standard, which is a new set of protocols to enable cellular-like roaming. If the device supports 802.11u and is subscribed to a Hotspot 2.0 service it will automatically connect and roam.

Policy Charging and Rules Function

With surging demand for broadband connectivity and bandwidth, operators are compelled to maintain a delicate equilibrium between competitively priced offers and managing network congestion and costs of the data traffic. Policy Management enables operators to address network congestion by enforcing subscriber and application usage policies. But more crucially, these policy controls also provide the means to innovate, personalize the customer experience, and to monetize data usage. Policy Charging and Rules Function (PCRF) plays an important in enforcing the Policy Management.

PCRF is the software node designated in real-time to determine policy rules in a multimedia network. As a policy tool, the PCRF plays a central role in next-generation networks. Unlike earlier policy engines that were added on to an existing network to enforce policy, the PCRF is a software component that operates at the network core and accesses subscriber databases and other specialized functions, such as a charging system, in a centralized manner. Because it operates in real time, the PCRF has an increased strategic significance and broader potential role than traditional policy engines. It is an important entity in the LTE core network domain.

The PCRF is the part of the network architecture that aggregates information to and from the network, operational support systems, and other sources (such as portals) in real time, supporting the creation of rules and then automatically making policy decisions for each subscriber active on the network. Such a network might offer multiple services, quality of service (QoS) levels, and charging rules. PCRF can provide a network agnostic solution (wire line and wireless) and can also provide multi-dimensional approach which helps in creating a lucrative and innovative platform for operators. PCRF can be integrated with different platforms like billing, rating, charging, and subscriber database or can also be deployed as a standalone operational entity.

MultiSeat Desktop Virtualization

MultiSeat Desktop Virtualization is a method by which a common desktop PC, with extra keyboards, mice, and video screens directly attached to it, can be used to install, load, and concurrently run multiple operating systems. These operating systems can be the same across all "seats" or they can be different. It is similar to server based computing only in the fact that one mainframe is supporting multiple users. On the other hand, it is different because the "terminals" are composed of nothing more than the regular keyboard, monitor and mouse, and these devices are plugged directly into the PC. USB hubs can be used for cable management of the keyboards and mice, and extra video cards (typically dual or quad output) may need to be installed to handle the multiple monitors.

It is commonly known that modern day PC's are extremely powerful and have substantial excess CPU processing power. Server based computing has been around for a long time specifically to take advantage of this excess CPU power and allow multiple users to share it. However, the typical problem with this type of system is that it is dependent upon one operating system and one set of applications and there are many software titles that are not allowed to be shared among multiple users.

Virtualization is a type of server based computing. It is a method by which the "guest" operating system runs on top of, while being separated from the hardware, and can solve some of these problems. This means that multiple "guest" operating systems can be run, solving the problem of single user applications not being able to be launched for multiple, concurrent users.

Multiseat desktop virtualization is an entirely new methodology which combines the cost saving benefits and ease of maintenance of server based computing, the time savings of hardware agnostic cloning, and the capabilities of desktop virtualization, with the performance capabilities of real PC functionality. It takes advantage of multiple cores in present day CPUs to enable ordinary users to install a multiseat PC giving 2 "seats" with a dual-core CPU or 4 "seats" with a quad-core CPU. The operating system of this PC is initially installed just like a regular PC. Regular PC users can install and use this type of product without having to install servers, or know how to manage complicated, server based computing or server based virtualization products.

Type	Standard server/TCP-IP based computing	Virtualized server/TCP-IP based computing	MultiSeat Desktop Virtualization
Can run all single user applications	No	Yes	Yes
Can run multimedia without buffering	No	No	Yes
Easy to install	No	No	Yes
Each "seat" has their own IP and MAC address	No	Yes	Yes
Each "seat" cloned image is hardware agnostic across different sets of hardware	No	Yes	Yes

Web Feed

A web feed (or news feed, or syndicated feed) is a data format used for providing users with frequently updated content. Content distributors syndicate a web feed, thereby allowing users to subscribe to it. Making a collection of web feeds accessible in one spot is known as aggregation, which is performed by client software called an aggregator (also called a feed reader or a news reader), which can be web-based, desktop-based, or mobile-device-based.

Technically, a web feed is a document (often XML-based) whose discrete content items include web links to the source of the content. News websites and blogs are common sources for web feeds, but feeds are also used to deliver structured information ranging from weather data to top-ten lists of hit tunes to search results. The two main web feed formats are RSS and Atom.

A typical scenario of web feed use is: a content provider publishes a feed link on their site which end users can register with an aggregator program running on their own machines. Aggregators can be scheduled to check for new content periodically. Web feeds are an example of pull technology, although they may appear to push content to the user.

Benefits

Web feeds have some advantages compared to receiving frequently published content via an email:

·         Users do not disclose their email address when subscribing to a feed and so are not increasing their exposure to threats associated with email: spam, viruses, phishing, and identity theft.

·         Users do not have to send an unsubscribe request to stop receiving news. They simply remove the feed from their aggregator.

·         The feed items are automatically sorted (unlike an email box where messages must be sorted by user-defined rules and pattern matching).

GPS

The Global Positioning System (GPS) is a space-based satellite navigation system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites. It is maintained by the United States government and is freely accessible to anyone with a GPS receiver.

The GPS program provides critical capabilities to military, civil and commercial users around the world. In addition, GPS is the backbone for modernizing the global air traffic system.

Basic Concepts:

A GPS receiver calculates its position by precisely timing the signals sent by GPS satellites high above the Earth. Each satellite continually transmits messages that include

·         the time the message was transmitted

·         satellite position at time of message transmission

The receiver uses the messages it receives to determine the transit time of each message and computes the distance to each satellite using the speed of light. Each of these distances and satellites' locations define a sphere. The receiver is on the surface of each of these spheres when the distances and the satellites' locations are correct. These distances and satellites' locations are used to compute the location of the receiver using the navigation equations. This location is then displayed, perhaps with a moving map display or latitude and longitude; elevation information may be included. Many GPS units show derived information such as direction and speed, calculated from position changes.

In typical GPS operation, four or more satellites must be visible to obtain an accurate result. Although four satellites are required for normal operation, fewer apply in special cases. If one variable is already known, a receiver can determine its position using only three satellites.

Applications:

Civilian

•        Cellular telephony: Clock synchronization enables time transfer, which is critical for synchronizing its spreading codes with other base stations to facilitate inter-cell handoff and support hybrid GPS/cellular position detection for mobile emergency calls and other applications. The first handsets with integrated GPS launched in the late 1990s. The U.S. 

Federal Communications Commission (FCC) mandated the feature in either the handset or in the towers (for use in triangulation) in 2002 so emergency services could locate 911 callers. Third-party software developers later gained access to GPS APIs from Nextel upon launch, followed by Sprint in 2006, and Verizon soon thereafter.

•        Clock synchronization: The accuracy of GPS time signals (±10 ns) is second only to the atomic clocks upon which they are based.

•        Navigation: Navigators value digitally precise velocity and orientation measurements.

•        Phasor measurements: GPS enables highly accurate timestamping of power system measurements, making it possible to compute phasors.

•        Robotics: Self-navigating, autonomous robots using a GPS sensor, which calculate latitude, longitude, time, speed, and heading.

•        Surveying: Surveyors use absolute locations to make maps and determine property boundaries.

•        Tectonics: GPS enables direct fault motion measurement in earthquakes.

Military

•        Navigation: GPS allows soldiers to find objectives, even in the dark or in unfamiliar territory, and to coordinate troop and supply movement. In the United States armed forces, commanders use the Commanders Digital Assistant and lower ranks use the Soldier Digital Assistant.

•        Target tracking: Various military weapons systems use GPS to track potential ground and air targets before flagging them as hostile.

•        Missile and projectile guidance: GPS allows accurate targeting of various military weapons including ICBMs, cruise missiles, precision-guided munitions and Artillery projectiles.

•        Search and Rescue: Downed pilots can be located faster if their position is known.

•        Reconnaissance: Patrol movement can be managed more closely.

•        GPS satellites carry a set of nuclear detonation detectors consisting of an optical sensor (Y-sensor), an X-ray sensor, a dosimeter, and an electromagnetic pulse (EMP) sensor (W-sensor), that form a major portion of the United States Nuclear Detonation Detection System.

Other Systems

Other satellite navigation systems in use or various states of development include:

•        GLONASS – Russia's global navigation system. Fully operational worldwide.

•        Galileo – a global system being developed by the European Union and other partner countries, planned to be operational by 2014 (and fully deployed by 2019)

•        Beidou – People's Republic of China's regional system, currently limited to Asia and the West Pacific

•        COMPASS – People's Republic of China's global system, planned to be operational by 2020

•        IRNSS – India's regional navigation system, planned to be operational by 2012, covering India and Northern Indian Ocean

•        QZSS – Japanese regional system covering Asia and Oceania

Vehicular Communication Systems

VCS are an emerging type of network systems in which vehicles and roadside units are the communicating nodes, providing each other with information, such as safety warnings and traffic information, thereby being more effective in avoiding accidents and traffic congestions due to the cooperative approach.

The two types of nodes in vehicular communication systems, vehicles and roadside stations, are both  Dedicated Short Range Communications (DSRC) devices which work in the 5.9 GHz band with a bandwidth of 75 MHz and approximate range of 1000m.

Technical specifications:

Two categories of draft standards provide outlines for vehicular networks. These standards constitute a category of IEEE standards for a special mode of operation of IEEE 802.11 for vehicular networks called Wireless Access in Vehicular Environments (WAVE). IEEE 1609 is a family of standards which deals with issues such as management and security of the network:

·         1609.1 -Resource Manager: This standard provides a resource manager for WAVE, allowing communication between remote applications and vehicles.
·         1609.2 -Security Services for Applications and Management Messages
·         1609.3 -Networking Services: This standard addresses network layer issues in WAVE.
·         1609.4 -Multi-channel Operation: This standard deals with communications through multiple channels. 

Applications

Following are the categories of the possible applications of vehicular communication system:

·         Safety
·         Traffic management
·         Driver assistance systems
·         Policing and enforcement
·         Pricing and payments
·         Direction and route optimization
·         Travel-related information
·         General information services
·         Automated highways

Vehicular communications are usually developed as a part of a bigger, Intelligent Transport Systems (ITS) network. ITS seeks to achieve safety and productivity through intelligent transportation which integrates communication between mobile and fixed nodes. To this end ITS heavily relies on wired and wireless communications.

Space Time Code

STC is a method employed to improve the reliability of data transmission in wireless communication systems using multiple transmit antennas. STCs rely on transmitting multiple, redundant copies of a data stream to the receiver in the hope that at least some of them may survive the physical path between transmission and reception in a good enough state to allow reliable decoding.

                                                                                         

Space time codes may be split into two main types:

Space–time trellis codes (STTCs) – Space–time trellis codes (STTCs) are a type of space–time code used in multiple-antenna wireless communications. This scheme transmits multiple, redundant copies of a trellis (or convolutional) code distributed over time and a number of antennas ('space'). These multiple, 'diverse' copies of the data are used by the receiver to attempt to reconstruct the actual transmitted data. For an STC to be used, there must necessarily be multiple transmit antennas, but only a single receive antennas is required; nevertheless multiple receive antennas are often used since the performance of the system is improved by so doing.

Space–time block code (STBCs) – Space–time block coding is a technique used in wireless communications to transmit multiple copies of a data stream across a number of antennas and to exploit the various received versions of the data to improve the reliability of data-transfer. The fact that the transmitted signal must traverse a potentially difficult environment with scattering, reflection, refraction and so on and may then be further corrupted by thermal noise in the receiver means that some of the received copies of the data will be 'better' than others. This redundancy results in a higher chance of being able to use one or more of the received copies to correctly decode the received signal. In fact, space–time coding combines all the copies of the received signal in an optimal way to extract as much information from each of them as possible.

In contrast to space–time block codes (STBCs), STTCs are able to provide both coding gain and diversity gain and have a better bit-error rate performance. However, being based on trellis codes, STTCs are more complex than STBCs to encode and decode; STTCs rely on a Viterbi decoder at the receiver where STBCs need only linear processing.

SODAR

 Sonic Detection And Ranging is a meteorological instrument used as a wind profiler to measure the scattering of sound waves by atmospheric turbulence. SODAR systems are used to measure wind speed at various heights above the ground, and the thermodynamic structure of the lower layer of the atmosphere.

Sodar systems are like radar (radio detection and ranging) systems except that sound waves rather than radio waves are used for detection. Other names used for sodar systems include sounder, echosounder and acoustic radar.

Commercial sodars operated for the purpose of collecting upper-air wind measurements consist of antennas that transmit and receive acoustic signals. A mono-static system uses the same antenna for transmitting and receiving, while a bi-static system uses separate antennas. The difference between the two antenna systems determines whether atmospheric scattering is by temperature fluctuations (in mono-static systems), or by both temperature and wind velocity fluctuations (in bi-static systems).

Phased-array antenna systems use a single array of speaker drivers and horns (transducers), and the beams are electronically steered by phasing the transducers appropriately. To set up a phased-array antenna, the pointing direction of the array is either level, or oriented as specified by the manufacturer. 

The vertical range of sodars is approximately 0.2 to 2 kilometers (km) and is a function of frequency, power output, atmospheric stability, turbulence, and, most importantly, the noise environment in which a sodar is operated. Operating frequencies range from less than 1000 Hz to over 4000 Hz, with power levels up to several hundred watts.

Applications

Traditionally used in atmospheric research, sodars are now being applied as an alternative to traditional wind monitoring for the development of wind power projects. Sodars used for wind power applications are typically focused on a measurement range from 50m to 200m above ground level, corresponding to the size of modern wind turbines.

Tetra

Terrestrial Trunked Radio (TETRA) (formerly known as Trans-European Trunked Radio) is a professional mobile radio and two-way transceiver (popularly known as a walkie talkie) specification. TETRA was specifically designed for use by government agencies, emergency services, (police forces, fire departments, ambulance) for public safety networks, rail transportation staff for train radios, transport services and the military.

TETRA is a European Telecommunications Standards Institute (ETSI) standard that was first published in 1995.

Overview

TETRA uses Time Division Multiple Access (TDMA) with four user channels on one radio carrier and 25 kHz spacing between carriers. Both point-to-point and point-to-multipoint transfer can be used. Digital data transmission is also included in the standard though at a low data rate.

TETRA Mobile Stations (MS) can communicate direct-mode operation (DMO) or using trunked-mode operation (TMO) using switching and management infrastructure (SwMI) made of TETRA base stations (TBS). As well as allowing direct communications in situations where network coverage is not available, DMO also includes the possibility of using a sequence of one or more TETRA terminals as relays. This functionality is called DMO gateway (from DMO to TMO) or DMO repeater (from DMO to DMO). In emergency situations this feature allows direct communications underground or in areas of bad coverage.

In addition to voice and dispatch services, the TETRA system supports several types of data communication. Status messages and short data services (SDS) are provided over the system's main control channel, while packet-switched data or circuit-switched data communication uses specifically assigned traffic channels.

TETRA provides for authentication of terminals towards infrastructure and vice versa. For protection against eavesdropping air interface encryption and end-to-end encryption are available.

The common mode of operation is in a group calling mode in which a single button push will connect the user to the users in a selected call group and/or a dispatcher. It is also possible for the terminal to act as a one-to-one walkie talkie but without the normal range limitation since the call still uses the network. TETRA terminals can act as mobile phones (cell phones), with a full-duplex direct connection to other TETRA Users or the PSTN. Emergency buttons, provided on the terminals, enable the users to transmit emergency signals, to the dispatcher, overriding any other activity taking place at the same time.

Advantages

The main advantages of TETRA over other technologies (such as GSM) are:

•  The much lower frequency used gives longer range, which in turn permits very high levels of geographic coverage with a smaller number of transmitters, thus cutting infrastructure costs.

• During a voice call, the communications are not interrupted when moving to another network site. This is a unique feature which dPMR and DMR do not offer.

• High spectral efficiency - 4 channels in 25 kHz and no guard bands, compared to GSM with 8 channels in 200 kHz and guard bands.

•  Very fast call set-up - a one to many group call is generally set-up within 0.5 seconds (typical less than 250 msec for a single node call) compared with the many seconds (typically 7 to 10s) that are required for a GSM network.

• Works at high relative speeds >400 km/h. TETRA was used during the French TGV train speed record on 3 April 2007 at 574.8 km/h.

• The system contains several mechanisms, designed into the protocols and radio parameters, to ensure communication success even during overload situations (e.g., during major public events or disaster situations), thus calls will always get through unlike in cellular systems. The system also supports a range of emergency calling modes.

•  TETRA infrastructure is usually separate from (but connected to) that of the public (mobile) phone networks, resulting in (normally) no call charges for the system owners, substantially more diverse and resilient communications and it is easy to customize and integrate with data applications (vehicle location, GIS databases, dispatch systems, etc.).

• Unlike most cellular technologies, TETRA networks typically provide a number of fall-back modes such as the ability for a base station to process local calls. So called 'mission critical' networks can be built with TETRA where all aspects are fail-safe/multiple-redundant.

•  In the absence of a network mobiles/portables can use 'direct mode' whereby they share channels directly (walkie-talkie mode).

• Gateway mode - where a single mobile with connection to the network can act as a relay for other nearby mobiles that are out of range of the infrastructure.

• TETRA also provides a point-to-point function that traditional analogue emergency services radio systems did not provide. This enables users to have a one-to-one trunked 'radio' link between sets without the need for the direct involvement of a control room operator/dispatcher.

•  Unlike cellular technologies, which connect one subscriber to one other subscriber (one-to-one), TETRA is built to do one-to-one, one-to-many and many-to-many. These operational modes are directly relevant to the public safety and professional users.

• TETRA supports both air-interface encryption and end-to-end encryption
•  Rapid deployment (transportable) network solutions are available for disaster relief and temporary capacity provision.

• Equipment is available from many suppliers around the world, thus providing the benefits of interoperable competition.

• Network solutions are available in both the older circuit-switched (telephone like) architectures and flat, IP architectures with soft (software) switches.