21 June 2005

What is "EDGE"?

Much of the buzz about PDAs nowadays is that they come equipped with EDGE. This, of course, cannot be Googled since "edge" is not only a common word, you're likely to wind up with a lot of adverts saying this or that device has "an edge," or worse, "Her humor has a real edge...here's what she says about couples who insist on necking in public (or other PDAs)."

I've been using the term PDA (personal digital assistant) to refer to electronic devices that are designed chiefly for storing or retrieving printed information, which are also very small. The most common are the RIM Blackberry, the PalmOne Tungsten and (formerly Handspring, now PalmOne) Treo, and the PocketPC (all links are to image searches). Initially PDAs amounted to beefed up calculators (Sharp Wizard), but now your PDA is likely to come with cellular functionality. Likewise, 3G cell phones refer to cell phones with a lot of the features commonly encountered on PDAs. Hence, it's become routine to hear "GSM," a mobile phone standard, used in connection with a PDA (which, in the early 1990's, would have implied that the speaker was Dilbert's boss).

GSM is the most common mobile phone standard; 70% of PCS subscribers use it and it's mandatory in the EU. However, it has a ceiling of 14 kilo bits per second (kbps) , whereas its designated successor, W-CDMA/UMTS, has a theoretical maximum of 2.3 million bits per second. UMTS licenses have already been sold and companies like Hutchison-Whampoa and DoCoMo are already operating 3G UMTS networks in the EU.

In order to bridge the gap, EDGE was created. It stands for Enhanced Data for GSM Evolution, and is a workaround the technical limitations of GSM. Here's the Wikipedia definition. Basically, this involves converting the square 0-1 signals of a digital signal into a gaussian wave, then offsetting those waves so data can be transmitted at multiples of the notional limit.
In addition to GMSK (Gaussian minimum-shift keying) EDGE uses 8PSK (8 Phase Shift Keying) for its upper five of the nine modulation and coding schemes. EDGE is producing a 3bit word for every change in carrier phase. This effectively triples the gross data rate offered by GSM. EDGE, like GPRS, uses a rate adaptation algorithm that adapts the modulation and coding scheme (MCS) used to the quality of the radio channel, and thus the bit rate and robustness of data transmission. It introduces a new technology not found in GPRS, Incremental Redundancy, which, instead of retransmitting disturbed packets, sends more redundancy information to be combined in the receiver. This increases the probability of correct decoding.

It can carry data speeds up to 384 kbit/s in packet mode and will therefore meet the International Telecommunications Union's requirement for a 3G network
Pre-EDGE technologies included (as the entry says) the less-capable GPRS by increasing signal confirmation data. So now you know.

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