EVDO is a protocol for high speed wireless broadband. Also known as EV-DO, 1xEvDO and 1xEV-DO, it's one of several major Third Generation (3G) wireless data standards. Mobile devices that use EVDO technology can upload and download data quickly, and the technology is always "on" whenever there is a signal from the wireless tower. Unlike a WiFi® connection, a device with EVDO does not need to be near a wireless hotspot; instead, the cell phone can itself become a hotspot and share its Internet connection with other devices.
Officially, the name defined by the Telecommunication Industry Association for this technology is "CDMA2000, High Rate Packet Data Air Interface." The acronym EVDO is short for "Evolution, Data Only" or "Evolution, Data Optimized," a reflection of the fact that it is the next evolution of the earlier Code Division Multiple Access 2000 (CMDA2000) family of wireless products. The EVDO standard was developed in 1999, but the protocol has been upgraded since then to improve its speed.
3G and CDMA
3G is designed to transmit voice and high-speed mobile data to people on the go. Several competing technologies are involved in the development of 3G networks as technology companies work on the best way to handle the mounting demand for wireless services around the world. Many firms invested in the development of 3G networks and technology use the Code Division Multiple Access (CDMA) approach, which has proved highly effective with mobile phone networks.
The biggest obstacle to implementing high speed wireless networks is the lack of bandwidth, or range of usable frequencies. Just as only so many radio stations can be squeezed onto the FM dial, only so much data can be transmitted across the available bandwidth. As the user load increases, the available frequencies tighten, and users can experience delays, dropped data, and other problems. Thus, providers have been working to find ways to use bandwidth more efficiently without sacrificing clarity and quality for their users.
How CDMA Works
CDMA uses advanced mathematical techniques to allow multiple wireless devices to transmit simultaneously on the same radio frequency. Every device, such as a cell phone, is assigned a unique mathematical signature. Transmitters apply this signature to the original signal and send a modified version. A receiver applies the inverse of the mathematical operation to recover the original signal.
The term "CDMA" is used both to refer generally to a channel access method and to the specific technologies that use that method as a backbone for radio transmissions. The intended meaning is usually clear from the context. CDMA2000, for example, is a data handling standard that uses CDMA technology.
How EVDO Works
Traditional wireless networks create a direct path between receiving and sending devices, much like traditional telephone networks. EVDO instead breaks data into individual packets, the same technique for data handling used on the Internet. Each packet is sent independently of all the other packets. This saves bandwidth for use by other devices; when neither party on a phone call is speaking, for example, the connection consumes no bandwidth. When an Internet site is accessed, no bandwidth is used until the site starts sending the web page.
The original EVDO protocol, called Revision 0, has a theoretical throughput of 2.4 megabits per second (Mbps). This is as fast as many wired DSL and cable broadband connections currently available in the United States. The upgrade to Revision A increases speed to a theoretical 3.1 Mbps. A third upgrade, to Revision B, was released in January 2010, although it is not fully deployed; Qualcomm, the developer, predicts download speeds as fast as 14.7 Mbps in some situations.
Qualcomm has produced impressive demonstrations of EVDO's capabilities. In one, a video conference was conducted with a participant traveling in a car at 60 mph (96 kph). Transferring the large amounts of data required for video conferencing is a major challenge, especially at such speeds. In another demonstration, a phone call was placed from a bullet train moving in excess of 150 mph (240 kph).
UMTS and HSDPA
The biggest challenge to EVDO has been the Universal Mobile Telecommunications System (UMTS). UMTS — which is sometimes known by the name of its radio interface standard, Wideband-CDMA (WCDMA) — uses larger bands for data transmission. This approach can be less vulnerable to interception and jamming than some other wireless technologies. Data transfer speeds are slower than with EVDO, however, with speeds of up to 2 Mbps.
HSDPA, which stands for High-Speed Downlink Packet Access, was built on WCDMA technology, but with a number of significant changes in the way that data is handled. This protocol is considered 3.5G or enhanced 3G, a step above 3G but not quite fourth generation. HSDPA shares one transmission channel between multiple users, and schedules data transfer to take advantage of the best possible conditions; this means that data may be sent to multiple users at the same time. Different speed versions of HSDPA are typically available to consumers, with download speeds ranging from 1.8 Mbps to 21 Mbps or higher.
How Does This Affect Users?
An advantage of EVDO is that it uses the same broadcasting frequencies as existing CDMA networks. As purchasing spectrum from regulatory agencies is extremely expensive, this brings down the cost of building and using new networks. HSDPA, while offering faster download speeds with the higher levels of service, may also be more expensive for the consumer.
Mobile Internet users should remember that what standard is used for transmitting data is usually dependent on the network; a cell phone from Verizon in the US will have access to EVDO, for example, but not HSDPA. Users who will be traveling in foreign countries with wireless devices may want to check to see if they are supported on a given network. For frequent travelers, it may be advisable to consider investing in a device that will work reliably on international networks in order to avoid problems with dropped calls, inability to send data, and other issues.
As new wireless standards develop, the quality of wireless services tends to improve. Various options are not available in all areas, and may have differing rates of performance. Newer technologies can come with unexpected kinks and service plans may be more costly. Early adopters can also find it difficult to access technical support and assistance, as technicians may not be as familiar with the products they are using.