Tuesday, February 24, 2009
GSM-(Global System for Mobile communication)
GSM (Global System for Mobile communication) is a digital mobile telephony system that is widely used in Europe and other parts of the world. GSM uses a variation of time division multiple access (TDMA) and is the most widely used of the three digital wireless telephony technologies (TDMA, GSM, and CDMA). GSM digitizes and compresses data, then sends it down a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1800 MHz frequency band.
Since many GSM network operators have roaming agreements with foreign operators, users can often continue to use their mobile phones when they travel to other countries. SIM cards (Subscriber Identity Module) holding home network access configurations may be switched to those will metered local access, significantly reducing roaming costs while experiencing no reductions in service.
GSM, together with other technologies, is part of the evolution of wireless mobile telemmunications that includes High-Speed Circuit-Switched Data (HCSD), General Packet Radio System (GPRS), Enhanced Data GSM Environment (EDGE), and Universal Mobile Telecommunications Service (UMTS).
Since many GSM network operators have roaming agreements with foreign operators, users can often continue to use their mobile phones when they travel to other countries. SIM cards (Subscriber Identity Module) holding home network access configurations may be switched to those will metered local access, significantly reducing roaming costs while experiencing no reductions in service.
GSM, together with other technologies, is part of the evolution of wireless mobile telemmunications that includes High-Speed Circuit-Switched Data (HCSD), General Packet Radio System (GPRS), Enhanced Data GSM Environment (EDGE), and Universal Mobile Telecommunications Service (UMTS).
Tuesday, February 17, 2009
Flash-OFDM
Flash-OFDM (Fast Low-latency Access with Seamless Handoff Orthogonal Frequency Division Multiplexing), which is also referred to as F-OFDM, is a system that is based on OFDM and specifies also higher protocol layers. It has been developed and is marketed by Flarion. Flash-OFDM has generated interest as a packet-switched cellular bearer, where it would compete with GSM and 3G networks. As an example, 450 MHz frequency bands previously used by NMT-450 and C-Net C450 (both 1G analogue networks, now mostly decommissioned) in Europe are being licensed to Flash-OFDM operators.
In Finland the license holder Digital has begun deployment of a nationwide "@450" wireless network, operational in parts of the country since April 2007 and planned coverage of all of Finland in 2009.
T-Mobile Slovakia offers Flash-OFDM connections with a maximum downstream speed of 5.3 Mbit/s, and a maximum upstream speed of 1.8 Mbit/s. Cover is nearly all of Slovakia by Flash-OFDM.
In Finland the license holder Digital has begun deployment of a nationwide "@450" wireless network, operational in parts of the country since April 2007 and planned coverage of all of Finland in 2009.
T-Mobile Slovakia offers Flash-OFDM connections with a maximum downstream speed of 5.3 Mbit/s, and a maximum upstream speed of 1.8 Mbit/s. Cover is nearly all of Slovakia by Flash-OFDM.
Tuesday, February 10, 2009
More wireless of 3G
iPhone 3G delivers UMTS, HSDPA, GSM, Wi-Fi, EDGE, GPS, and Bluetooth 2.0 + EDR in one compact device — using only two antennas. Clever iPhone engineering integrates those antennas into a few unexpected places: the metal ring around the camera, the audio jack, the metal screen bezel, and the iPhone circuitry itself. And intelligent iPhone power management technology gives you up to 5 hours of talk time over 3G networks. That’s some of the best in the business.
iPhone 3G meets worldwide standards for cellular communications, so you can make calls and surf the web from practically anywhere on the planet. And if you’re in an area without a 3G network, iPhone connects you via GSM for calls and EDGE for data.
iPhone 3G meets worldwide standards for cellular communications, so you can make calls and surf the web from practically anywhere on the planet. And if you’re in an area without a 3G network, iPhone connects you via GSM for calls and EDGE for data.
Tuesday, February 03, 2009
Orthogonal frequency-division multiplexing
Orthogonal frequency-division multiplexing (OFDM) — essentially identical to Coded OFDM (COFDM) and Discrete multi-tone modulation (DMT) — is a frequency-division multiplexing (FDM) scheme utilized as a digital multi-carrier modulation method. A large number of closely-spaced orthogonal sub-carriers are used to carry data. The data is divided into several parallel data streams or channels, one for each sub-carrier. Each sub-carrier is modulated with a conventional modulation scheme (such as quad rapture amplitude modulation or phase shift keying) at a low symbol rate, maintaining total data rates similar to conventional single-carrier modulation schemes in the same bandwidth.
OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio broadcasting, wireless networking and broadband internet access.
OFDM has developed into a popular scheme for wideband digital communication, whether wireless or over copper wires, used in applications such as digital television and audio broadcasting, wireless networking and broadband internet access.
