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Comprehensive information about GPRS and Edge GPRS, General Packet Radio Services

GPRS (General Packet Radio Services) is a packet-based wireless communication service that, when available in late 2000, promises data rates from 56 up to 114 Kbps and continuous connection to the Internet for mobile phone and computer users. The reality will be around 33 Kbps (2+1 or 3+1 @ CS2, 4+1 for fixed modem). GPRS is based on “regular” GSM (with the same modulation) and will complement existing services such circuit-switched cellular phone connections such as SMS or cell broadcast. Voice over Ip over GPRS is also explored.

In theory, GPRS packet-based service should cost users less than circuit-switched services since communication channels are being used on a shared-use, as-packets-are-needed basis rather than dedicated only to one user at a time. It should also be easier to make applications available to mobile users and Wap or i-mode should far more attractive for the user. In addition to the Internet Protocol GPRS supports X.25, a packet-based protocol that is used mainly in Europe.

Operator should deploy GPRS very fast as most of the interoperability test between the network and the Handset are now finished (September’00) and because GPRS is mainly a software upgrade for the BTS, BSC and servers.

GPRS avec different coding schemes. We may just see CS2 in the market.

Table of rate per slot according to coding schemes

CS1 : 9,05 kbit/s
CS2 : 13,4 kbit/s
CS3 : 15,6 kbit/s
CS4 : 21,4 kbit/s

Net rate: – 10 %


Packet switching means that GPRS radio resources are used only when users are actually sending or receiving data. Rather than dedicating a radio channel to a mobile data user for a fixed period of time, the available radio resource can be concurrently shared between several users. This efficient use of scarce radio resources means that large numbers of GPRS users can potentially share the same bandwidth and be served from a single cell. The actual number of users supported depends on the application being used and how much data is being transferred. Because of the spectrum efficiency of GPRS, there is less need to build in idle capacity that is only used in peak hours. GPRS therefore lets network operators maximize the use of their network resources in a dynamic and flexible way, along with user access to resources and revenues.

GPRS should improve the peak time capacity of a GSM network since it simultaneously: allocates scarce radio resources more efficiently by supporting virtual connectivity
immigrates traffic that was previously sent using Circuit Switched Data to GPRS instead, and reduces SMS Center and signaling channel loading by migrating some traffic that previously was sent using SMS to GPRS instead using the GPRS/ SMS interconnect that is supported by the GPRS standards.

Relatively high mobile data speeds may not be available to individual mobile users until Enhanced Data rates for GSM Evolution (EDGE) or Universal Mobile Telephone System (UMTS) are introduced EDGE, Enhanced Data GSM Environment

Enhanced Data rates for Global Evolution (EDGE) is a radio based high-speed mobile data standard. It allows data transmission speeds of 384 kbps to be achieved when all eight timeslots are used. In fact, EDGE was formerly called GSM384. This means a maximum bit rate of 48 kbps per timeslot. Even higher speeds may be available in good radio conditions.

EDGE was initially developed for mobile network operators who fail to win Universal Mobile Telephone System (UMTS) spectrum. EDGE gives incumbent GSM operators the opportunity to offer data services at speeds that are near to those available on UMTS networks.

EDGE can also provide an evolutionary migration path from GPRS to UMTS by implementing now the changes in modulation that will be necessary for implementing UMTS later. The idea behind EDGE is to eke out even higher data rates on the current 200 kHz GSM radio carrier by changing the type of modulation used, whilst still working with current circuit (and packet) switches.

Implementation of EDGE by network operators has been designed to be simple. Only one EDGE transceiver unit will need to be added to each cell. With most vendors, it is envisaged that software upgrades to the BSCs and Base Stations can be carried out remotely. The new EDGE capable transceiver can also handle standard GSM traffic and will automatically switch to EDGE mode when needed.

EDGE capable terminals will also be needed- existing GSM terminals do not support the new modulation techniques and will need to be upgraded to use EDGE network functionality. Some EDGE capable terminals are expected to support high data rates in the downlink receiver only (i.e. high dates rates can be received but not sent), whilst others will access EDGE in both uplink and downlinks (i.e. high data rates can be received and sent). The later device types will therefore need greater terminal modifications to both the receiver and the transmitter parts.

In addition, the TDMA industry association, the Universal Wireless Communications Corporation, has introduced what it calls EDGE Compact. This a spectrum efficient version of EDGE that will support the 384 kbits mandated packet data rates but will require only minimum spectral clearing and therefore could work for network operators with limited spectrum allocations. In fact, as a result of this, EDGE has been renamed Enhanced Data Rates for GSM and TDMA Evolution. (See the TDMA section below for more details).

EDGE is planned to be commercially available end of year 2001 (FOA).
High Speed Circuit Switched Data (HSCSD)

GSM Circuit Switched Data supports one user per channel per time slot. High Speed Circuit Switched Data (HSCSD) gives a single user simultaneous access to multiple channels (up to four) at the same time. As such, there is a direct trade-off between greater speed and the associated cost from using more radio resources- it is expensive for end users to pay for multiple simultaneous calls.

Assuming a standard Circuit Switched Data transmission rate of 14.4 kilobits per second (kbps), using four timeslots with High Speed Circuit Switched Data (HSCSD) allows theoretical speeds of up to 57.6 kbps. This is broadly equivalent to providing the same transmission rate as that available over one ISDN B-Channel. Some Mobile Switching Centres (MSCs) are limited to 64 kbps maximum throughput- this restriction is removed with GPRS.

In networks where HSCSD is deployed, GPRS may only be assigned third priority, after voice as number one priority and HSCSD as number two. In theory, HSCSD can be preempted by voice calls- such that HSCSD calls can be reduced to one channel if voice calls are seeking to occupy these channels. HSCSD does not disrupt voice service availability, but it does affect GPRS. Even given preemption, it is difficult to see how HSCSD can be deployed in busy networks and still confer an agreeable user experience- i.e. continuously high data rate. HSCSD is therefore more likely to be deployed in start up networks or those with plenty of spare capacity- since it is relatively inexpensive to deploy and can turn some spare channels into revenue streams. High Speed Circuit Switched Data (HSCSD) is however easier to implement in mobile networks than General Packet Radio Service (GPRS) because some GSM vendor solutions require only a software upgrade of base stations and no new hardware. This is not the case with D-AMPS networks and some GSM vendor solutions.

There are a couple of reasons why HSCSD may be the preferred bearer for certain applications when compared to GPRS. The fact that associated packets can be sent in different directions to arrive at the same destination should in theory make the transmission more robust since there are many different ways of achieving the end result. However, this nature of packet transmission means that packets are subject to variable delay and some could be lost. Whilst packet retransmission is incorporated into the GPRS standards, naturally this process does take time and in the case of applications such as video transmission can cause poor quality images.

Another preferred application for HSCSD could be the fact that whilst GPRS is complementary for communicating with other packet-based networks such as the Internet, HSCSD could be the best way of communicating with other circuit switched communications media such as the PSTN and ISDN. HSCSD is mainly supported by Nokia with little success.


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