The performance gains associated with 1X Advanced are realized through a combination of mobile device enhancements and new base station modems. Some of the enhancements are standards-based (e.g., CDMA2000 1X Release E), while others are not.
- Enhanced Variable Rate Codec– Version B (EVRC-B): An advanced codec that improves voice quality without compromising network capacity, or it can be used to increase voice capacity without sacrificing quality.
- Quasi-linear Interference Cancellation (QLIC): Reduces the interference in the forward link, or directional path between the serving base station and the mobile device. The interference is due to other users within the cell or in adjacent cells, as well as the interference that is created by the pilot channel. By reducing the amount of interference at the mobile device, the serving base station can transmit at a lower power and still maintain the voice call. In turn, the power savings can be used to support additional voice calls within its serving area.
- Quasi-orthogonal Functions (QOF): Increasing voice capacity requires additional Walsh codes, beyond the existing 128 orthogonal Walsh codes. Whenever the forward link is limited by Walsh codes, 1X Advanced makes use of Quasi-orthogonal functions (QOF) to provide additional codes. However, QOF creates additional interference among users.
- Advanced QLIC: An interference cancellation technique that builds upon the capabilities of QLIC to further reduce forward link interference by canceling the additional interference from QOF and the interference from adjacent base stations in the neighbor set.
- Reverse Link Interference Cancellation (RLIC): Also known as BTS Interference Cancellation, RLIC reduces the interference in the reverse link to increase network capacity. RLIC also improves network coverage since the effective range of a cell site is typically limited by the reverse link (e.g., the transmit power of the mobile device). With RLIC the improved signal that is received at the cell site means that the device can transmit from a greater distance or in a harder to reach location (e.g., indoors) and still maintain the connection.
- Mobile Receive Diversity (MRD): Leverages two mobile device antennas to boost the quality of the received signal for a given transmit level at the serving base station. As such, the base station can reduce the amount of power required to support the connection, thus freeing up power that can be used to support additional voice calls and data sessions. MRD can also help increase battery life since downloads can occur more quickly, enabling the transmitter to be disabled sooner.
- New Radio Configuration: Changes to the CDMA2000 1X radio configuration or Physical Layer were introduced in CDMA2000 1X Release E (September 2009) to include the following features.
- Smart Blanking to eliminate the transmission of background noise that typically consumes air interface resources, unless it changes. To the extent the background noise remains constant – a likely scenario in most voice calls – the amount of data that the voice call requires is reduced.
- Efficient Power Control to reduce the overhead associated with the power control information that is shared between the network and the mobile devices. By reducing how often and how this information is exchanged, additional resources are made available to support more voice calls.
- Frame Early Termination (FET) in both the forward and reverse link, enables the base station (or mobile device) to not have to transmit an entire frame if the mobile device (or base station) has already successfully decoded the information and sent an acknowledgement (ACK) receipt. Similar to the gains achieved by the H-ARQ feature in EV-DO, FET reduces the amount of transmit power over a duration of time, thus increasing overall system capacity.
While seemingly a “voice only” feature, 1X Advanced has meaningful implications for data traffic, coverage, 1X data network capacity and femtocells.
- More Data Channels: By taking advantage of the capacity gain in voice traffic, an operator can free up spectrum for new EV-DO mobile broadband data services.
- 70% More Coverage: 1X Advanced can trade off voice capacity to increase 1X coverage by up to 70%
- Triple 1X Data Network Capacity: If additional voice capacity is not necessary, it can be traded off for additional 1X data network capacity. In effect, the 1X channel is used to transfer packets of data instead of packets of voice traffic. Increasing the data capacity of a CDMA2000 1X network by up to a factor of three is beneficial for rural/low data demand areas in emerging markets, where broadband connectivity is not deployed or economical.
- Enhanced Femtocell Performance: 1X Advanced also contains certain interference cancellation features to improve the performance of femtocells in a 1X network.
Thus, 1X Advanced can substantially improve the competitiveness of an operator by enabling:
- More efficient use of limited spectrum
- Lower cost per call or more available minutes of use
- Frees up spectrum for broadband data
- Up to 70% greater 1X coverage (tradeoff)
- Up to a threefold increase in 1X data network capacity (tradeoff)
- Improved femtocell performance
Based on their needs, operators can choose to dimension their networks such that the network operates at a point which gives both coverage and capacity improvements.
Since 1X Advanced is fully backwards compatible with CDMA2000, an operator has the flexibility to only deploy some of the 1X Advanced features or to introduce the features over time, knowing that the full benefits of 1X Advanced will not be realized until all of the devices and base stations are fully upgraded to 1X Advanced.