EV-DO: Evolution-Data Optimized, or Evolution-Data Only

Code Division Multiple Access 2000 (CDMA2000), consisting principally of 1xRTT and One Carrier-Evolved, Data-Optimized (1xEV-DO) versions, is the second most widely deployed cellular technology in the world with a global market share of 9.8 percent and 409 million mobile connections as of 1Q 2009. 1xRTT is the most widely deployed of the CDMA2000 family of technologies, commercial on 272 networks, and is a CDMA operator’s first step towards wireless data services. Often compared to GPRS or EDGE in the GSM family of technologies, 1xRTT has a further evolution to EV-DO.

CDMA2000 represents a family of standards and includes:

• CDMA2000 1X
• CDMA2000 1xEV-DO Technologies
  • CDMA2000 1xEV-DO Release 0 (Rel 0)
  • CDMA2000 1xEV-DO Revision A (Rev A)
  • CDMA2000 1xEV-DO Revision B (Rev B)

A number of operators have deployed or are deploying 1xEV-DO, where a radio carrier is dedicated to high-speed data functions. In May 2009, there were 106 EV-DO Rel 0 networks and 62 EV-DO Rev A networks deployed worldwide, according to the CDMA Development Group.

EV-DO uses many of the same techniques for optimizing spectral efficiency as HSPA, including higher order modulation, efficient scheduling, turbo-coding, adaptive modulation and coding, though the technology standards are not interoperable. For these reasons, it achieves spectral efficiency that is virtually the same as UMTS-HSPA. The 1x technologies operate in the 1.25 MHz radio channels, compared to the 5 MHz channels used by UMTS, resulting in lower theoretical peak rates, but similar average throughputs for high level of network loading. Under low- to medium-load conditions, because of the lower peak achievable data rates, EV-DO or EV-DO Rev A achieves a lower typical performance level than HSPA. CDMA operators have quoted 400 to 700 kbps typical throughput on the downlink for EV-DO Rel 0 and between 600 kbps and 1.4 Mbps for EV-DO Rev A.

Deployed network versions currently are based on either Rel 0 or Rev A radio-interface specifications. EV-DO Rev A incorporates a more efficient uplink, which has spectral efficiency similar to that of HSUPA. Operators started to make EV-DO Rev A commercially available in 2007. One challenge for EV-DO operators is that they cannot dynamically allocate their entire spectral resources between voice and high-speed data functions. The EV-DO channel is not available for circuit-switched voice, and the 1xRTT channels offer only medium-speed data. This will become an increasing problem for CDMA operators as data usage expands, and this limitation could cause suboptimal use of radio resources.

Another limitation of using a separate channel for EV-DO data services is that it currently prevents users from engaging in simultaneous voice and high-speed data services, whereas this is possible with UMTS- HSPA. Many users enjoy having a tethered data connection from their laptops – by using Bluetooth, for example – and having the ability to initiate and receive phone calls while maintaining their data sessions.

EV-DO will eventually provide service using Voice over Internet Protocols (VoIP) through EV-DO Rev A, which includes a higher speed uplink, Quality of Service (QoS) mechanisms in the network, protocol optimizations to reduce packet overhead, and will address problems such as jitter. Nonetheless, operators will face difficult choices: How many radio channels at each base station should be made available for 1xRTT to support legacy terminals versus how many radio channels should be allocated to EV-DO? In contrast, UMTS allows both circuit-switched and packet-switched traffic to occupy the same radio channel, where the amount of power each uses can be dynamically adjusted. This makes it simple for users to migrate over time from circuit-switched voice to packet-switched voice.

Beyond Rev A, Third Generation Partnership Project 2 (3GPP2) has defined EV-DO Rev B as allowing the combination of up to 15 1.25 MHz radio channels in 20 MHz – significantly boosting peak theoretical rates to 73.5 Mbps. An operator would more likely combine three radio channels in 5 MHz. Such an approach by itself does not necessarily increase overall capacity, but it does offer users higher peak data rates. As of May 2009, no operators have yet publicly committed to EV-DO Rev B.

Beyond Rev B, 3GPP2 developed Revision C standards, also known as Ultra Mobile Broadband (UMB). UMB was standardized based on an OFDMA approach like LTE and mobile WiMAX (802.16m). However, as of May 2009, no operators have committed to UMB and there are legitimate questions about the commercial viability of the technology. In fact, many mobile operators with the current EV-DO technology will likely deploy LTE because of the benefits offered by the GSM family of technologies. Leading CDMA operators worldwide including Verizon, KDDI, KTF and SKT are among those confirming that they will converge with the 3GPP world, selecting LTE over other radio access methods as they are nearing the end of their existing technology roadmap.

Though the migration from CDMA2000 to LTE is feasible, it will be more complex than migrating from UMTS-HSPA to LTE, especially in achieving interworking between LTE and legacy networks.

The CDMA2000 family of standards will continue to serve operators well into the next decade. Many CDMA2000 operators are supplementing or evolving existing networks with OFDMA technologies such as LTE to deliver advanced mobile applications that require greater network capacity and data speeds. It will be necessary to develop solutions to ensure that CDMA2000 devices, networks and roaming provide a seamless user experience across CDMA2000 to LTE wireless technology platforms.

CDMA2000 clearly is a viable and effective wireless technology and, to its credit, many of its innovations have been brought to market ahead of competing technologies. Today, however, the GSM family has in excess of 3.8 billion subscribers – more than nine times the total number of subscribers in the CDMA2000 family of technologies.