This standard is developed by the third generation partnership project 2 (3GPP2), the body responsible for CDMA and EVDO. 1xEVDO is an enhanced version of CDMA2000-1x. There are four versions that have been released, namely, Rev. 0, Rev. A, Rev. B, and Rev. C.
1xEVDO is a high-speed data only specification for 1.25 MHz frequency division duplex (FDD) channels with a peak downlink (DL) data rate of 2.4 Mbps.
Improvements to CDMA2000-1x in the 1xEVDO Rev. 0 specification include:
- DL channel is changed from code division multiplexing (CDM) to time division multiplexing (TDM) to allow full transmission power to a single user.
- DL power control is replaced by closed-loop DL rate adaptation.
- Adaptive modulation and coding (AMC).
- HARQ.
- Fast DL scheduling.
- Soft handoff is replaced by a more bandwidth efficient “virtual” soft handoff.
1xEVDO Rev. 0, however, was designed to support only packet data services and not conversational services. In 1xEVDO Rev. A and EVDO Rev. C (also dubbed DORC), additional enhancements were added to the 1xEVDO specification. They include the following:
- DL: Smaller packet sizes, higher DL peak data rate (up to 3.1 Mbps), and multiplexing packets from multiple users in the MAC layer.
- Uplink (UL): Support of HARQ, AMC, higher peak rates of 1.8 Mbps, and smaller frame size
These enhancements in both the UL and DL of 1xEVDO Rev. A allow it to support conversational services.
