"Delta encoding is a way of storing or transmitting data in the form of differences between sequential data rather than complete files; more generally this is known as data differencing. Delta encoding is sometimes called delta compression, particularly where archival histories of changes are required (e.g., in software projects)."

$18 • "Optimal Layout takes the hassle out of organizing your application windows and helps you get the most out of your screen space, making you more productive."

Owned by Libelium.

Press release: http://www.sensor-networks.org/index.php?page=0932832814

"There are two main ways of performing outdoor location when tracking sensor devices in a large area such as a city. The most extended is using a GPS module to get the information sent by the satellites on the 1575MHz band and extract all the information possible (latitude, longitude, speed, direction). However, this methodology is not effective when requiring mobile scenarios where the nodes can change from a clear environment to an indoor one, such as going inside buildings, garages and tunnels.
[...]
...we center on how to track mobile sensor nodes which are moving through a huge area.
[...]
Both GPS and GPRS technologies are complementaries as a system with both technologies allows to track the position inside buildings, garages, and even inside tunnels (eg. subway railway system) while maintaining an accurate precission in a clear environment where the information from the GPS satellites can reach the sensor device.
[...]
The GPS module uses the A1084 GPS demodulator by Vincotech:
[...]
Let's see now how extract the information from the GPRS module in order to use it to track the sensor device position according the Cell ID's location and strength of the signal received (RSSI). [...] The GPRS module integrated in Waspmote is the model HiLo by Sagem. As it is Quadband it can operate with any operator from any country: [...] All the needed parameters: Received Signal Strength Indicator (RSSI), Cell ID and Timing Advance (TA) of the Base Station are accessible directly from the Waspmote API. [...] ...we will obtain information about the 8 closest Base stations (BT's) surrounding to our node. [...] As we can see, we obtain the RSSI, Cell ID and TA from each BT's detected around the node. These three parameters which we will use in order to calculate the location of our node. The RSSI parameter returned specifies the received signal level of the BCCH carrier. It can be used to know the link quality and locate a node using triangulation. The Cell ID parameter may be used to identify each BT's and be able to triangulate the signal and locate a node. The TA parameter is very useful as the BTS sends this information to each node according to the perceived round trip propagation delay BTS-node-BTS. So, to know the distance between the node and the base station you have to use this equation : Distance = (TA/2)x 3.6µs x C"

"By increasing the number of states that the carrier signal can take, the number of bits encoded in each symbol can be greater than one. The bit rate can then be greater than the symbol rate. For example, a differential phase-shift keying system might allow four possible jumps in phase between symbols. Then two bits could be encoded at each symbol interval, achieving a data rate of double the symbol rate."

"Below you will find icons, docks, and desktop pictures I have created and released in my spare time available for download. Downloads are licensed for personal use on your own computer(s) only."

"Two of the previous designs of this site are available as themes for use with any WordPress."

"Η φράση κατ' αρχήν (που γράφεται πια και καταρχήν) αντιστοιχεί στο λατινικό in principio (αγγλ. in principle) και σημαίνει «ως θέμα αρχής, για λόγους αρχής» («κατ' αρχήν διαφωνώ με το σκεπτικό τής απόφασης») και «στα βασικά σημεία» («το νομοσχέδιο ψηφίστηκε κατ' αρχήν»). Επομένως, το «κατ' αρχήν» δεν σημαίνει κατ' αρχάς, στην αρχή, εν πρώτοις, όπως καταχρηστικά χρησιμοποιείται ενίοτε. Με τη σημασία «πρώτα-πρώτα, εν πρώτοις, αρχίζοντας» χρησιμοποιείται η φράση κατ' αρχάς (και καταρχάς) ή στην αρχή («κατ' αρχάς νόμιζε πως ήταν σωστό, μετά τη συζήτηση όμως άλλαξε γνώμη»). "

"As a form cultivating what I already know, I’ve been turning to YouTube videos specifically from Jared Polin who’s energy and enthusiasm for the craft truly does make any complex concept about photography uncomplicated and here’s a few of my personal favorites."

"On these pages you find listings commercial and open source products that can solve your cross-platform problems."

$14 • "Hibari is a powerful Mac Twitter app that blocks annoyances and reveals gems."

Also:
http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4099020
http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1640087

"FalconTrak is an ongoing research project initiated in 2002. A total of 23 transmitters have been placed on young peregrines, however only 6 falcons are currently being tracked."

Too funny.

$15 • "Move your windows to where you want them, then have Stay store them. Once stored, windows can be returned to their stored state at any time by having Stay restore them."

I'll probably use TPSN instead.

"GSM localization is the use of multilateration to determine the location of GSM mobile phones, usually with the intent to locate the user. Localization-Based Systems can be broadly divided into:
- Network based
- Handset based
- Hybrid"

Haven't read this.

"This page provides an index into various Medium Access Control (MAC) protocols specifically designed for use in Wireless Sensor Networks, where energy consumption, latency, throughput, and fairness have a different trade off than in typical WLAN (802.11) networks."

"When looking at the way in which GPRS operates, it can be seen that there are three basic modes in which it operates. These are: initialisation / idle, standby, and ready."

"The BSC assigns PDCHs to particular time slots, and there will be times when the PDCH is inactive, allowing the mobile to check for other base stations and monitor their signal strengths to enable the network to judge when handover is required. The GPRS slot may also be used by the base station to judge the time delay using a logical channel known as the Packet Timing Advance Control Channel (PTCCT).
[...]
The MAC layer is central to this and there are three MAC modes that are used to control the transmissions. These are named fixed allocation, dynamic allocation, and extended dynamic allocation.
[...]
Although GPRS uses only one physical channel (PDCH) for the sending of data, it employs several logical channels that are mapped into this to enable the GPRS data and facilities to be managed."

"The overall slot structure for this channel is the same as that used within GSM, having the same power profile, and timing advance attributes to overcome the different signal travel times to the base station dependent upon the distance the mobile is from the base station. This enables the burst to fit in seamlessly with the existing GSM structure."

"Within GSM there are eight time slots that can be used to provide TDMA, allowing multiple mobiles onto a single RF signal carrier. Within GPRS it is possible to use more than one slot to enable much higher data rates to be achieved when these are available. The different speed classes of the mobiles are dependent upon the number of slots that can be used in either direction."

Example applications: "HeartCycle" and "SensaPill"

"The key element of GPRS technology is that it uses packet switched data rather than circuit switched data, and this technique makes much more efficient use of the available capacity. This is because most data transfer occurs in what is often termed a "bursty" fashion. The transfer occurs in short peaks, followed by breaks when there is little or no activity.
[...]
Channel Bandwidth: 200 kHz"

"GPRS uses a packet-mode technique to transfer data and signaling in a cost-efficient manner over GSM radio networks and also optimizes the use of radio and network resources.
[...]
The allocation of these timeslots is flexible, ranging from one to eight timeslots per TDMA frame, and they can be shared by active users. This allows GPRS to handle bitrates from 9 to even up to 150 kbit/s per user."

"The base station subsystem (BSS) is the section of a traditional cellular telephone network which is responsible for handling traffic and signaling between a mobile phone and the network switching subsystem.
[...]
A BTS is controlled by a parent BSC via the "base station control function" (BCF). The BCF is implemented as a discrete unit or even incorporated in a TRX in compact base stations."

"A base transceiver station (BTS) or cell site is a piece of equipment that facilitates wireless communication between user equipment (UE) and a network. UEs are devices like mobile phones (handsets)... [...] The network can be that of any of the wireless communication technologies like GSM, CDMA, WLL, WAN, WiFi, WiMAX etc.

BTS is also referred to as the radio base station (RBS), node B (in 3G Networks) or, simply, the base station (BS).
[...]
A GSM network is made up of three subsystems: [...]
- The Base Station subsystem (BSS) – comprising a BSC and several BTSes
[...]
In this regard, a BTS forms part of the base station subsystem (BSS) developments for system management.
[...]
Typically a BTS will have several transceivers (TRXs) which allow it to serve several different frequencies and different sectors of the cell (in the case of sectorised base stations).
[...]
A BTS is controlled by a parent base station controller via the base station control function (BCF).
[...]
Splitting: The flow of power within a particular area of the cell, known as sector. Every field can therefore be considered like one new cell. By using directional antennas, the co-channel interference is reduced. A typical structure is the trisector, also known as clover, in which there are three sectors, each one served by separate antennas. Every sector has a separate direction of tracking of 120° with respect to the adjacent ones. If not sectorised, the cell will be served by an omnidirectional antenna, which radiates in all directions. Bisectored cells are also implemented with the antennas serving sectors of 180° separation to one another."

"There are two kinds of sensor nodes used in the sensor network. One is the normal sensor node deployed to sense the phenomena and the other is gateway node that interfaces sensor network to the external world."

"Armed with my newfound knowledge, I began with 20 houseplants, a collection of Spathiphyllum and Phalaenopsis — the common peace lily and white orchid. These plants work as a team — among the common household pollutants they both filter, the lilies work on benzene, formaldehyde, and trichloroethylene and the orchids take care of xylene and toluene. And they all, of course, convert CO2 to good old oxygen."

CPU is "MSP430 F 1612" and radio is "CC1100".

Its dimensions are 36mm x 41mm or so. It goes for ~120 EUR. (Numbers taken from the older model's page: http://www.scatterweb.com/content/products/research_line/msb430.en.html)

"Optional: GSM/GPRS"
——
This is the link between the sensor network (comprised of ScatterNodes: http://www.scatterweb.com/content/products/technology/scatternode.en.html) and the BSS.

This is the same product as the one found here: http://www.scatterweb.com/content/products/technology/scattergate.en.html

"A ScatterWeb powered wireless network is ideally suited to develop solutions in:
- Supply Chain Management / Asset Tracking / Logistics
- Container Tracking and Security
- Automated Meter Reading (AMR) / Industry Automation
- Geographical Information Systems (GIS)
- Facility Management
- ZigBee and RFID interoperability"

"SquidBee normal mode ==> 69 - 70 mA. Power saved 69 mA
SquidBee power save mode ==>     14 mA in sleep mode 69 mA (sending state aprox. 0.5 s every 5 min)
Power saved ((14 mA x 295 s) + (69 mA x 5 s)) / 300 = 14. 91 mA
As you can see, the power saved is (69 - 14.91) / 69 = 78%"

"In 2G systems, GPRS provides data rates of 56-114 kbit/second.
[...]
It provides moderate speed data transfer, by using unused time division multiple access (TDMA) channels in, for example, the GSM system.
[...]
The upload and download speeds that can be achieved in GPRS depend on a number of factors such as:
- the number of BTS TDMA time slots assigned by the operator
- the maximum capability of the mobile device expressed as a GPRS multislot class
- the channel encoding used summarised in the following table:
[...]
The multiple access methods used in GSM with GPRS are based on frequency division duplex (FDD) and TDMA. During a session, a user is assigned to one pair of up-link and down-link frequency channels. This is combined with time domain statistical multiplexing; i.e., packet mode communication, which makes it possible for several users to share the same frequency channel. The packets have constant length, corresponding to a GSM time slot. The down-link uses first-come first-served packet scheduling, while the up-link uses a scheme very similar to reservation ALOHA (R-ALOHA). This means that slotted ALOHA (S-ALOHA) is used for reservation inquiries during a contention phase, and then the actual data is transferred using dynamic TDMA with first-come first-served scheduling.
[...]
Latency is very high; round-trip time (RTT) is typically about 600-700 ms and often reaches 1 s. GPRS is typically prioritized lower than speech, and thus the quality of connection varies greatly."

For the "Example Applications" section.

"Table 1 shows the different data rates that can be achieved with the different coding techniques."

"Dynamic TDMA: In dynamic time division multiple access, a scheduling algorithm dynamically reserves a variable number of time slots in each frame to variable bit-rate data streams, based on the traffic demand of each data stream. Dynamic TDMA is used in [...] The Packet radio multiple access (PRMA) method for combined circuit switched voice communication and packet data."

"In comparison to TDM, the STDM method analyzes statistics related to the typical workload of each input device (printer, fax, computer) and determines on-the-fly how much time each device should be allocated for data transmission on the cable or line."

"... extension on top of standard GSM. EDGE is considered a 3G radio technology and is part of ITU's 3G definition. [...] ...it is an upgrade that provides more than three-fold increase in both the capacity and performance of GSM/GPRS networks.
[...]
EDGE/EGPRS is implemented as a bolt-on enhancement for 2G and 2.5G GSM and GPRS networks, making it easier for existing GSM carriers to upgrade to it. EDGE/EGPRS is a superset to GPRS and can function on any network with GPRS deployed on it, provided the carrier implements the necessary upgrade."

"Hybrid positioning systems are systems for finding the location of a mobile device using several different positioning technologies. Usually GPS (Global Positioning System) is one major component of such systems, combined with cell tower signals, wireless internet signals, Bluetooth sensors or other local Positioning Systems. These systems are specifically designed to overcome the limitations of GPS, which is very exact in open areas, but works poorly indoors or between tall buildings (the urban canyon effect). By comparison, cell tower signals are not hindered by buildings or bad weather, but usually provide less precise positioning."

"GPS operation uses radio signals from satellites. In very poor signal conditions, for example in a city, these signals may suffer multipath where signals bounce confusingly off buildings, or be weakened by passing through walls or tree cover. When first turned on in these conditions, some non-assisted GPS navigation devices may not be able to work out a position due to the fragmentary signal, rendering them unable to function until a clear signal can be received continuously for up to 40 seconds (the time needed to download the GPS ephemeris). An Assisted GPS system can address these problems by using data available from a network. [...] A typical A-GPS-enabled receiver will use a data connection (Internet or other) to contact the assistance server for A-GPS information. Some A-GPS devices cannot fall back to standard GPS, needing cell tower or internet signal as these A-GPS devices won't function with only GPS satellite signal."

"RTLS typically refers to systems that provide passive or active (automatic) collection of location information."
——
It's probably better to look at the "Real-time locating" entry: http://pinboard.in/u:kostas/b:78aa403cb604

"RCPI (Received Channel Power Indicator) is an 802.11 measure of the received RF power in a selected channel over the preamble and the entire received frame. RCPI is exclusively associated with 802.11...
[...]
A similar, but not identical, metric is the RSSI (received signal strength indication), which also aims to provide some level of classification of the received signal. Both have their respective merits and uses. Indeed, received signal power level assessment is a necessary step in establishing a link for communication between wireless nodes. However, a power level metric like RCPI generally can't comment on the quality of the link like other metrics such as travel time measurement (ToA)."

"...a measurement of the power present in a received radio signal.
[...]
RSSI can be used internally in a wireless networking card to determine when the amount of radio energy in the channel is below a certain threshold at which point the network card is clear to send (CTS). Once the card is clear to send, a packet of information can be sent.
[...]
RSSI measurements are unitless and in the range 0 to 255, expressible as a one-byte unsigned integer. The maximum value, RSSI_Max, is vendor dependent. For example, Cisco Systems cards have a RSSI_Max value of 100 and will report 101 different power levels, where the RSSI value is 0 to 100. Another popular Wi-Fi chipset is made by Atheros. An Atheros based card will return an RSSI value of 0 to 127 (0x7f) with 128 (0x80) indicating an invalid value. There is no specified relationship of any particular physical parameter to the RSSI reading. The 802.11 standard does not define any relationship between RSSI value and power level in mW or dBm. Vendors provide their own accuracy, granularity, and range for the actual power (measured as mW or dBm) and their range of RSSI values (from 0 to RSSI_Max)."

"RTLS as standardized explicitly excludes passive RFID indexing (radio frequent transponder indexers) and Cellnet base station segment locators (location based services) from the scope of the ISO/IEC approach to RTLS standardization as well as all beacon systems, that ping without request. "RTLS as standardized explicitly excludes passive RFID indexing (radio frequent transponder indexers) and Cellnet base station segment locators (location based services) from the scope of the ISO/IEC approach to RTLS standardization as well as all beacon systems, that ping without request. Oftentimes the term positioning is used instead of locating. Locating is differentiated from positioning in that a positioning device informs the user of their location, while a locating system provides the user with the location of tracked objects. As an example, a Global Positioning System GPS navigation tool is commonly used in a vehicle or aircraft to inform the driver or pilot, respectively, of their location so that they may be guided to a desired destination. A Real Time Locating System is used to allow commercial organizations to find, or effectively direct the movement of, assets and resources in order to more effectively operate their business.
[...]
Oftentimes the term positioning is used instead of locating. Locating is differentiated from positioning in that a positioning device informs the user of their location, while a locating system provides the user with the location of tracked objects. As an example, a Global Positioning System GPS navigation tool is commonly used in a vehicle or aircraft to inform the driver or pilot, respectively, of their location so that they may be guided to a desired destination. A Real Time Locating System is used to allow commercial organizations to find, or effectively direct the movement of, assets and resources in order to more effectively operate their business.
[...]
Example two (2) requires that distances between nodes in the sensory network be determined in order to precisely locate a node. In this instance, the determination of the location is called Localization. The location is calculated through Trilateration or Multilateration from the determined distance between the nodes or through Triangulation from the determined angles between nodes."

Introduces the "First Order Radio Model" to calculate energy consumption. I don't know whether it can be applied w/r/t to the radio channel being symmetric.

"Martin gave Luke one of his first big breaks when he enlisted the younger musician as a partner on "Since U Been Gone," the 2004 Clarkson smash; the two continue to collaborate."

"The Place Lab approach is to allow devices like notebooks, PDAs and cell phones to locate themselves by listening for radio beacons such as 802.11 access points, GSM cell phone towers, and fixed Bluetooth devices that already exist in large numbers around us in the environment. These beacons all have unique or semi-unique IDs, for example, a MAC address. Clients compute their own location by hearing one or more IDs, looking up the associated beacons' positions in a locally cached map, and estimating their own position referenced to the beacons' positions."

"A location-based service (LBS) is an information and entertainment service, accessible with mobile devices through the mobile network and utilizing the ability to make use of the geographical position of the mobile device."
——
Have a look at "Locating methods" (a. Control Plane Locating and b. GSM Localization) and "LBS applications".

"In today’s competitive business climate it is no longer a matter of your product competing against someone else’s. It is also your supply chain competing against someone else’s. If you ship high value products, you need to minimize your exposure to theft. If your product does not get delivered, your customer may buy your competitor’s. The same can be said about products that are vulnerable to environmental conditions, such as temperature and shock, or that can not be tilted beyond a certain degree.  If your shipment is compromised or damaged while in-transit the first notification you will receive is from an irate customer. Crossbow provides shipment tracking and visibility solutions that allow you to maintain close surveillance on the location and more importantly the condition of your shipment. In-transit alerts mean you have time to react and can manage by exception. So, if you are shipping product to meet your customer’s ad date, if you are shipping items to keep a manufacturing line running, if you are shipping an expensive, built-to-order piece of equipment, Crossbow provides you the most detailed status and condition of your shipment."

"Crossbow’s asset tracking solution is unique in providing customers with instant global monitoring capabilities while requiring very little initial investment. This is accomplished by combining a variety of established technologies with state of the art hardware and software development. The following list describes some of the key technologies used:
- GPS/AGPS worldwide location tracking with special provisions for orientation independent GPS reception
- GSM/GPRS worldwide cellular radio communication
- GSM based worldwide location tracking in GPS denied environments
- Environmental sensor suite to monitor acceleration, temperature, humidity, and other conditions
- Ultra low power system processor to enable long battery life"

Also have a look here (same copy): http://www.xbow.com/asset-tracking/technology/index.html

"However on the GPRS,the LLC (between MS-SGSN) and RLC/MAC (between MS-
BSS) layer that make up the data link between the MS and the network. The protocol is
mainly an adapted version of the LAPDm protocol used in GSM.The LLC Protocol
establishes a logical link between MS and SGSN. Its functionality includes sequence
control, in-order delivery, flow control,detection of transmission errors, and
retransmission (automatic repeat request (ARQ)). The data confidentiality is ensured by
ciphering functions. It operates either in an unacknowledged mode, not taking care of
packet losses, or in an acknowledged mode, which applies retransmissions and flow
control to ensure a correct delivery of data.

The RLC/MAC layerat the air interface includes two functions. The main purpose of the
radio link control (RLC) layer is to establish a reliable link between the MS and the BSS.
RLC is always operated in an acknowledged mode with a sliding window flow control
mechanism and a selective ARQ mode providing a reliable link between MS and BSS.
This includes the segmentation and reassembly of LLC frames into RLC data blocks and
ARQ of uncorrectable codewords.

This new medium access control (MAC) scheme was changed to meet the demands of the packet oriented data transmission. The RLC/MAC layer ensures the concurrent
access to radio resources in a more flexible way compared to the unmodified TDMA
structure of GSM. It controls the access attempts of an MS on the radio channel shared
by several MSs. It employs algorithms for contention resolution, multiuser multiplexing
on a PDTCH, and scheduling and prioritizing based on the negotiated QoS. The
flexibility is achieved by the introduction of a logical Packet Data Traffic Channel
(PDTCH) which is multiplexed onto a physical data channel, the Packet Data Channel
(PDCH), which corresponds to one timeslot (TS) in the GSM TDMA frame. Up to eight of
these PDTCHs share one PDCH."

Best comment ever in the Intertubes: "There are people in this community who will continue to lobby against legal downloads no matter what the terms or what technology is used. I swear, sometimes I think that if Linus himself started a company that sold no-DRM OGG Vorbis songs for a penny a piece and you got a free blowjob from Natalie Portman with every 10 purchased tracks that we'd still see posts on slashdot justifying P2P piracy because we didn't get to pick out Natalie's outfit when she showed up at our parent's basement to deliver."

"Like iTunes™ for research papers. Mendeley is a free research management tool for desktop & web."

"HTML5 Boilerplate is the professional badass's base HTML/CSS/JS template for a fast, robust and future-proof site."