CDMA2000 1X Advanced
- overview and tutorial about the CDMA2000 1X Advanced, the system providing a fourfold increase in capacity over standard 1X.
CDMA2000 1X Advanced provides operators with a simple incremental upgrade that provides a fourfold increase in capacity increase over the standard CDMA 2000 1X networks.
The CDMA2000 1X Advanced is provided by a software/channel card upgrade. Techniques including interference cancellation and radio link enhancements are used to increase voice capacity on existing or new CDMA2000 1X networks.
The CDMA2000 1X advanced system has been adopted by a number of carriers to provide a cost effective method of increasing capacity and also prolonging the life of existing CDMA2000 1X networks.
In addition to this, a further upgrade known as SVDO has been introduced at the same time. Although standard independent, it provides additional flexibility for users of 1X / EV-DO capability.
CDMA2000 1X Advanced techniques
The CDMA2000 1X Advanced system utilizes some simple upgrades to enable a significant increase in capacity to be provided.
The full improvement is gained when both cellular base-station and the handset are compatible with the new standard, but significant improvements can still be made when only the base station has been upgraded. Even this upgrade is straightforward and does not entail significant cost to the operator.
The improvements for CDMA2000 1X Advanced are gained primarily by adopting some new techniques:
- Utilisation of a new codec
- New interference cancellation techniques
- Mobile receiver diversity
- More efficient power control
- Smart Blanking of 1/8th rate frames
- Early Termination
- Quasi Orthogonal Function
These techniques are detailed more fully below:
Interference cancellation for CDMA2000 1X Advanced
One of the key limiting factors in any cellular telecommunications system is the attainable signal to noise ratio. As interference levels rise, so power levels have to increase and modulation formats, change (if adaptive modulation is available). Also higher levels of error coding are required which puts a further load on the air interface for the network. Additionally an increased number of re-sends may be required. As a result the lower the signal to noise ratio, the lower the data throughput.
The methodology for the interference cancellation has been understood for many years, but it has not been able to implemented because of the high levels of processing and memory needed. Now developments in semiconductor technology have enabled it to be implemented.
The interference cancellation can be utilised in both the reverse link and the forward link of the CDMA2000 1X Advanced system. The interference cancellation is performed at the base-station, BTS for the reverse link where it is sometimes referred to as RLIC (Reverse Link Interference cancellation), and within the handset or user equipment for the forward link.
Mobile receive diversity
Mobile receiver diversity, MRD used within CDMA2000 1X Advanced provides increased capacity through the use of two receiver chains and two antennas.
Power control is an essential element of any cellular system these days. It is particularly needed for CDMA systems to reduce the near-far problem where mobiles close to the base station could mask mobiles further away because signal strength reduces the greater the distance from the base station.
In order to overcome this the base station controls the power of the mobile or handset. However this requires signalling over the link and can reduce the capacity. By improving the efficiency of the power control, data required for this control can be reduced thereby reducing the data being carried over the link.
Smart blanking of 1/8th rate frames provides advantages reduces resource utilization during quiet periods in speech .
The use early termination within CDMA2000 1X Advanced exploits the times when the device is in good RF conditions.
Quasi orthogonal function
The quasi-orthogonal function is used to increase the number of simultaneous calls supported.
SVDO, Simultaneous active 1X Voice and EV-DO data, is a new device feature, in addition to IX Advanced that significantly enhances the performance without affecting the infrastructure side. Current systems allow, a handset or mobile to be paged to receive 1X voice calls while in an EV-DO data session. However no data connectivity is possible while the mobile remains in the voice call because separate receivers and transmitters are needed, i.e. two receivers and transmitters would be needed within the mobile.
The new SVDO feature allows separate voice and data sessions to be established using separate transmit and receive chain
The SVDO feature provides greater flexibility for the user allowing scenarios such as sending emails or accessing the Internet while voice calls are onging.
The introduction of CDMA2000 1X Advanced provides significant advantages over the original CDMA2000 1X system. Operators who have deployed 1X systems, will see CDMA2000 1X Advanced as a cost effective means of improving performance and capacity as well as extending the life of their networks.
By Ian Poole
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