Enabling UMTS and GSM to Co-exist at 900 MHz
The Situation
UMTS (Universal Mobile Telecommunications System) is the world's most widely deployed 3G cellular technology. Designed to succeed GSM, it delivers higher data transfer rates to support advanced services like video and internet access. This new generation of high speed data is very sensitive to interference which needs to be controlled to realize high data throughput. Operators and regulators worldwide are beginning to understand the benefit of deploying UMTS at 900MHz for cost-effective coverage, especially because UMTS can be deployed along with existing GSM networks.
Deployment of UMTS in the 900 MHz GSM band will be the route through which European operators will achieve near 100 percent population coverage for advanced 3G wireless services. As wireless operators deploy UMTS systems, the interference between the new 3G network and the incumbent GSM system must be carefully controlled. Traditional network planning techniques for controlling this interference are very costly, since they require that substantial portions of valuable RF spectrum remain unused. Two methods have typically been used: frequency planning and spatial transition zones. Both of these methods use up capacity that could otherwise carry revenue-generating calls.
The Resolution
Fortunately, the co-channel interference isolation provided by adaptive notch filtering offers a more economical way to achieve the isolation necessary to operate UMTS 900 and GSM 900 in adjoining areas, simplifying network planning for UMTS 900 deployments. Instead of clearing space to accommodate both types of spectrum, adaptive notch filtering provides selective isolation against just those narrow band GSM signals present at the UMTS Node B's antennas, while leaving the UMTS signal unaffected. It has been shown that interference from the GSM uplink onto the UMTS uplink is the dominant cause of capacity loss in co-deployment scenarios. Thus, the use of intelligent, adaptive filters on the UMTS Node B transceivers, with the ability to selectively reject interfering GSM uplink signals can substantially reduce the size of guard bands and transition zones required to hit target performance levels. ISCO International's Proteus® product with PurePass® RF Digital Signal Processing performs this function. Deployments in the field with a European wireless operator confirmed the ability to reduce guard bands and transition zones when deploying UMTS at 900 MHz with legacy GSM networks.
Infrastructure Details
ISCO's Proteus® is a digital RF signal processor that monitors transmission paths and recreates signals free of noise in CDMA and UMTS wireless networks. GSM can be automatically removed from a UMTS uplink allowing operators an option to deploy in the 900MHz band. Proteus® utilizes a completely digital adaptive RF filter architecture, which provides unprecedented speed and flexibility and allows the platform to address entirely new classes of interferers (e.g. frequency hopped GSM). This product has been demonstrated to decrease transition zone widths by up to 50% and reduce guard bands by 400kHz or more.
PurePass® RF Digital Signal Processing technology allows wireless carriers to significantly reduce the cost of deploying the expanded coverage of 3G while maintaining 2G network assets. The technology supports mixed UMTS/GSM network environments as well as the flexibility to support technologies including UMTS, HSUPA, HSPA+, WiMAX and LTE.