Examples of physical layer optimization are shown together with method to pinpoint the cells which require physical layer modifications (antenna downtilts, antenna direction alignment and antenna location changes). KPIs from network statistics are analysed in details and typical optimization actions are demonstrated with corresponding, expected results on different KPIs. Higher order multiple input multiple output (MIMO) performance and ways to improve dual- stream usage are discussed and practical performance gains from higher order MIMO shown. Also high-speed train performance improvement methods are discussed in details. All examples shown are from frequency division (FD) LTE networks but as such the optimization actions are applicable also to time division (TD) LTE networks. Also all examples in this chapter are for 10 and 20 MHz FD LTE deployment (actual carrier frequency varies between 700, 800, 900, 1800, 2100 and 2600 MHz) with 2x2 MIMO in downlink and 2Rx in uplink unless otherwise mentioned. 12.2 Key Performance Indicators The most common KPIs which can be based on either network statistics or drive testing are listed below together with example calculation formula: Random access setup success rate: Number of received radio resource control (RRC) con- nection request messages (message number 3) sent by the UE (successfully acknowledged by eNodeB) divided by number of preambles received by eNodeB sent by UE. Call setup success rate (CSSR) can be split further as follows (see Figure 12.8): Radio resource control connection setup success rate: Number of RRC connection setup complete messages (message 5) sent by UE and successfully received by eNodeB divided by number of received RRC connection request messages sent by UE. Evolved radio access bearer (E-RAB) setup success rate from UE point of view: Number of sent RRC connection reconfiguration completions divided by number of sent service requests. E-RAB setup success rate from eNodeB point of view: Number of initial context setup response messages (S1 app