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Introduction
RF optimization execution consists of drive tests, problem area identification, verification drives, and final drives to ensure completion of exit criteria. The core activity is to provide system tuning, as well as data collection and reporting. Design changes relating to cell site layout modifications or adding a new cell site may be considered if critical coverage holes are discovered during optimization.
Antennae corrective actions are more frequent for new deployments, such as Greenfield or Overlay scenarios. They are uncommon in existing systems, such as Network
Expansion or Additional Carrier System. Fine tuning of the transmit powers is the most effective procedure in already optimized networks.
Cluster size
Cluster optimization consists of procedures performed on geographical groupings of cell sites that are large enough to have meaningful multi-cell site optimization. Several factors make it worthwhile to optimize the system in manageable sized clusters. There is a better focus on the area optimized, as smaller sector numbers make it easier to track the parameter changes and the impact of their performance.
Another benefit to smaller cluster optimization is that multiple teams can optimize different clusters simultaneously. Each team is able to maintain focus on its cluster with minimal impact from other teams. In addition, smaller cluster optimization aids in speeding up the system tests for commercial operation. Optimization in equipped clusters can proceed simultaneously with installation of other clusters.
When to perform cluster optimization
Cluster optimization should be performed for network sections that are fully deployed. This avoids a re-testing of already optimized clusters in case cell sites are later
integrated. All cell sites in the network (or a network section) are switched on. Each cluster is tested under unloaded and loaded conditions. If live traffic exists, cells in the tested clusters must be barred for all users except for the test users (optimization team). It is recommended to finish the unloaded cluster tests for all clusters within the
network or network sections before continuing with the loaded cluster tests. After a small set of adjacent clusters pass the exit criteria, a border exit drive must be performed. The border exit drive is performed under loaded conditions in order to verify and confirm the exit criteria at the borders of the clusters.
Drive testing
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Multiple cluster testing
During multiple cluster testing the optimization teams working on neighbor clusters must coordinate activities especially regarding neighbor relations, loading conditions or possible overshooting sites. Also, the UMTS on GSM overlay must be scanned for scattered coverage or coverage holes.
Cluster optimization tools
The required data collection, processing and analysis tools for cluster optimization are a phone-based data collection tool kit including CAIT3G, a UMTS terminal, WINDS as well as the post-processing tool LDAT3G. In addition to the phone-based tool kit, the scanner-based tool Agilent can be used during cluster optimization. The Agilent scanner is an important tool due to its multiple pilot measurement capability, which is especially useful for more in depth coverage analysis (e.g. pilot pollution) in
challenging RF environments (e.g. large water-bodies, bridges, un-even terrain, etc.) 3 phases of cluster optimization
Cluster optimization consists of three phases: • Unloaded cluster optimization
• Loaded cluster optimization • Cluster performance verification
Unloaded cluster optimization
During the first cluster optimization phase, a measurement drive is performed under unloaded network conditions using the optimization route. Once the data from the first phase is collected, problem spots are identified and optimized. The unloaded drive test identifies coverage holes, handover regions and multiple pilot coverage areas. It also spots possible overshooting sites (where interference is minimal) from areas belonging to neighbor clusters.
The first pass might lead to correction of neighbor lists and adjustments of the fundamental RF parameters such as transmit powers and/or antenna azimuths and antenna tilts. The drive test information highlights fundamental flaws in the RF design under best-case conditions.
Loaded cluster optimization
The second cluster optimization phase is performed under loaded conditions. The drive routes for the loaded cluster optimization are exactly the same routes as those used for the unloaded measurement drives.
Drive testing Perform cluster optimization
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Loaded testing produces a rise in the noise floor, which has the effect of shrinking the coverage area (cell breathing). This causes an increase of negative Ec/Io values, identify potential coverage holes, results in higher BLER, results in lower mobility throughput, and more dropped calls.
The objective is to fix the problems observed by the field teams. This involves the fine-tuning of RF parameters such as the transmit power or handover parameters. Antenna re-adjustments (e.g. down-tilts, azimuths, patterns/types or heights) are also occasionally performed.
Problematic cluster
Problem areas may be re-driven after implementing changes. It is not recommended to drive a problem area more than three times. If the problem cannot be solved after three test drives, either a root cause analysis is performed or cluster optimization proceeds with the next cluster. It is generally not recommended to attempt resolution of complex, time-intensive performance issues, such as location-specific problems like cell site equipment failures. For such problems, it is advisable to report the behavior and proceed with the next cluster. The problem cluster can be verified at a later stage. Cluster performance verification
In the third phase, the cluster performance is measured against the cluster exit criteria. The exit drive’s purpose is to verify and to confirm specific exit criteria demanded by the customer.
The final statistics from the cluster exit drive are presented to the customer for
approval. These statistics contain plots as well as data in tabular form. The approval to exit the cluster is based on the terms of the contract. Approval with exceptions allows the cluster to be exited under the condition that any problems will be resolved during system wide optimization. If the cluster is not approved, loaded cluster optimization must be continued until the troubles are resolved. A report specifying the reasons why the exit drive did not pass the exit criteria is required.
Drive testing Perform cluster optimization
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