How to consider Interference Protection and Isolation Requirement in LTE Plan

Similar to any radio network, standard isolation would be required if equipment from different vendors are to be combined. Which including guard band, filtering as well as vertical/horizontal separation.

In addition, indoor DAS (distributed antenna system) may contribute to interference problem particularly on the uplink due to PIM related inter-modulation, over drive of input RF power as well as impedance mismatch between components.

Wideband repeaters operating in the same or even adjacent band to the LTE networks may generate unwelcomed interference. Due the close vicinity to traditional microwave frequencies, LTE networks at 2.3G to 2.6G may also be subjected to interference either from standard microwave, satellite transmission or MMDS/LMDS networks. Conversely, 700/800MHz digital dividend spectrum could be subjected to interference signals coming from big television broadcasting towers. These two factors could lead to extra guard band and worst case full retune requirement for protection purposes. At certain cell site sectors, antenna orientation and tilt may need to be adjusted to avoid interference from external sources and existing operator network configuration may give hints in this direction.

Although external interference sometimes could be unavoidable due to various reasons, ideally, radio engineers should choose a spectrum that is relatively clean in both the uplink and downlink for new LTE systems deployment. Finally, interference increase due to traffic loading is always an important consideration especially when subscriber number increases. Careful planning of location update border and coverage control remains two of the most important techniques in resolving this problem.

Radio Related Equipment Selection

With the introduction of new Remote radio head technology, it is important the benefit of applying such products is reflected in our design proposal and link budget estimation. For instance, there is a 2.5dB reduction in cable loss in using different equipment. Radio engineers also need to understand the current configuration of operator sites so the realistic cable and/or combiner loss are reflected in their coverage design. Normally, a cable length of 30m is assumed but this definitely needs to be reviewed during the design stage on a site by site basis based on operator information (e.g. site drawing)

Network and Spectrum Evolution Consideration

Different Operators may have different network evolution considerations. For instance, most FDD based Operators will likely to be focusing on existing spectrum (850/900/1800MHz) reframing while WiMAX Operators will have major concern on co-existence between WiMAX and LTE TDD.

All these considerations will affect the selection of network components involved (e.g. filter bandwidth, power amplifier and guard band/spectrum requirement). Depending on the chosen direction, the total path loss will also be different so radio engineers need to discuss with operator in detail on their plan and preference to ensure the discussion results are reflected in the detail network design plan.

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