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EDGE evolution: the next 2G upgrade
From facilitating mobile internet access to enabling TV on the move, mobile networks are experiencing an inexorable rise in demand for data services. At a time when high-speed wireline broadband services now reach so many homes, it is only natural for consumers to expect wireless broadband to follow suit, and due to the Third Generation Partnership Project (3GPP) and other mobile standards bodies, the infrastructure and service mechanisms are being put in place to do just that.
The 3GPP roadmap provides network operators with three mechanisms by which to deploy and evolve their networks: the GSM (2G) system, W-CDMA (3G or UMTS) and in the future; LTE (long-term evolution). These technologies are designed to coexist harmoniously. Hence, alongside the evolution and spread of
Packet data capabilities were initially added to GSM by means of general packet radio services (GPRS). With the majority of GPRS terminals supporting download speeds of up to 24kbit/s, depending upon which multi-slot class is in use, GPRS (often referred to as 2.5G) can be used for all data services such as internet browsing, WAP access, SMS and MMS.
The next evolution
The following step for GSM was enhanced data rates for GSM Evolution (EDGE), which has increased GSM data rates to an optimal 236.8kbit/s for four timeslots, or around 200kbit/s in practice. GSM’s next evolution is in progress.
EDGE Evolution quadruples standard EDGE network speeds, promising downlink data rates of 1.2Mbit/s, though the standard has headroom for up to 1.9Mbit/s. Similarly, u plink data rates of 474kbit/s are expected, although the standard specifies 947kbit/s. 3GPP standardised EDGE Evolution in 2007 (3GPP Release 7).
As the name suggests, EDGE Evolution comprises a set of features that do not all need to be implemented at once. Network operators have the flexibility to adopt EGPRS2, downlink dual carrier (
EGPRS2 provides optional support for higher order modulation and coding schemes that enable more bits per symbol, resulting in higher data rates. For the downlink, there are 16 additional modulation and coding schemes and for the uplink, 13 are defined. EGPRS2 supports a legacy symbol rate (referred to as Level A) and an increased symbol rate (Level B). By distinguishing between the different levels, a phased introduction of a higher symbol rate into the EDGE network can be achieved.
EDGE Evolution boosts maximum user data rate, improves spectral efficiency, capacity and coverage, as well as minimising latency between the mobile station and the radio access network. However, with emerging high-speed wireless technologies such as LTE and Wimax potentially taking data rates beyond 150Mbit/s, why would operators be interested in deploying a lower data rate technology?
While network operators are keen to adopt the latest technologies, these can require fundamental changes to existing networks, impacting existing cell plans, or requiring new sites or spectrum. With billions of dollars already invested in 2G networks, optimising the capabilities of existing infrastructure and ensuring service continuity across different radio technologies through network evolution are equally high on their agenda.
Minimal infrastructure impact
An EDGE upgrade involves hardware and software changes to mobile terminals – to decode/encode new modulation and coding schemes and carry the higher data rates to implement new services. EDGE Evolution infrastructure upgrades are feature dependent and different manufacturers have different evolution strategies, so a transceiver upgrade may be all that is required from a network infrastructure point of view. Notably, GPRS only required a software upgrade in the base station and hence, has been deployed worldwide very swiftly. Like GPRS and EDGE, EDGE Evolution has been designed to minimise impact to the existing 2G infrastructure.
There are few challenges involved when implementing EGPRS2 that network operators would not have encountered when deploying EDGE. Higher order modulation schemes can be prone to interference issues and require good signal to noise conditions in the channel for the data to pass. As with other mobile standards, verification of new radio features to prove RF performance conformity and performance is necessary.
Currently, operators must ask themselves whether it is worth implementing 3G, or updating existing infrastructure. There are cost implications for doing either, but an existing GSM network makes EDGE Evolution cheaper to implement. EDGE Evolution also becomes an attractive proposition for operators that may not have any or only one 3G licence, as it gives them the opportunity to improve the user experience by investing in their existing network infrastructure.
Operators’ network investment decisions are typically based on the cost per megabit per user – in built-up areas the data services that higher-capacity technologies such as Wimax and LTE may pay for the increased infrastructure investment very quickly, but there may not be the same justification in rural areas. Hence EDGE Evolution does compete with faster; more advanced technologies, but could have a role to play on the edge of major data rate areas.
Darren Tipton is product specialist at Rohde & Schwarz. Meik Kottkamp works for Rohde & Schwarz in
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