Evolved EDGE

- summary, overview or tutorial about the basics of Evolved EDGE, the upgrade to EDGE to provide further improvements.

Evolved EDGE or E-EDGE is an upgrade that has been developed to enable GSM EDGE networks to be upgraded to provide similar performance levels to those provided by the more traditional 3G technologies including UMTS and CDMA20001x EVDO.

In view of the performance of Evolved EDGE, it has been seen as a route for operators not wanting the additional investment needed for 3G, while still needing the higher levels of performance offered by new technology.

As far as the user is concerned, the vanilla form of EDGE provides a speed increase of around three times over GPRS and it is usually possible to achieve speeds of up to 220 kbps. Using Evolved EDGE, speeds of around 1 Mbps are anticipated.

Despite the advantages of deploying Evolved EDGE, the take-up has been small. Operators have sent he majority of the market moving to 3G and beyond and with factors such as availability of handsets, and roaming mobility, the operator enthusiasm has not reached sufficient critical mass to for it to take off.

Evolved EDGE, E-EDGE basics

There are a number of new elements that are incorporated onto the original form of EDGE. A number of ideas have been introduced to provide the upgrades required. These include the following:

  • Higher Order Modulation:   In order to be able to provide its increase in speed over GPRS, the vanilla version of EDGE uses 8PSK modulation to enable a speed increase. This works by enabling 3 bits to be encoded per symbol. Evolved EDGE, E-EDGE uses higher orders of Quadrature Amplitude Modulation in the forms of 16QAM, which encodes 4 bits per symbol and 32QAM which encodes 5 bits per symbol. That said, 32QAM is only able to be used under ideal conditions because there is a trade-off using higher modulation orders. While they are able to provide higher data rates, they require a greater signal to noise ratio to provide error-free reception.
  • Receiver diversity:   The Evolved EDGE system provides for a scheme known as receiver diversity where a second receiver is used to decode the incoming signal a way that can receive it with different characteristics, e.g. position or polarisation. In this way, if the signal on one receiver is poor, there is a chance the signal on the second one is better and can be received with fewer errors.
  • Simultaneous channels:   The Evolved EDGE standard allows for the use of two channels, thereby providing the possibility of doubling the throughput.
  • Simultaneous transmission and reception:   One key element within GSM, and then GPRS and EDGE, was that to save costs, the Time Division Multiplexing scheme would ensure that the transmitter and receiver in a mobile handset were never active at the same time. This was achieved by using one slot for transmission, and a different time slot for reception. Even when multiple slots are used, one either side of the reception slot(s) was kept clear to allow for transmit / receive settling.

    Evolved EDGE allows for simultaneous transmission and reception as the cost of more effective filtering between the transmitter and receiver. Most EDGE mobiles on the market are restricted to four timeslots per carrier due to this phenomenon, having independent transmission and reception chains could allow mobiles to use all eight timeslots of a carrier.

Evolved EDGE take-up

While Evolved EDGE seems to tick many of the boxes for operators and users alike, take-up has been very poor. While the scheme can offer data rates of around 1 Mbps, many of the more up to date technologies such as HSPA and further on LTE offer much higher data rates. Operators are unlikely to want to invest in Evolved EDGE if they will ultimately need to introduce the newer technologies that offer far greater levels of performance. In addition to this, another major factor affecting the deployment of Evolved EDGE is the availability of handsets. With a lack of handsets it is not possible for the system to gain any headway. Despite this, the orginal form of EDGE is still in widespread use.

By Ian Poole

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