The LTE link budget tool support the analysis for DL Traffic, UL Traffic, as well as signaling channel. Then the smallest radius is used as the final coverage radius based on the link balance principle. First of all I clear LTE Link budget tool just give you theoretical result practical result of LTE link budget is varied. Here I write important parameters of LTE link budget tool and one small example and its result from LTE link budget tool.
Radio planning engineers should pay particular attention to the following input parameters:
- Type of MIMO multi-antenna technology used (At this stage, default is 2T2R)
- Design target area coverage probability. (Operator dependent ranging from 90 to 95%)
- The antenna in a base station is mounted at a height of 30 meters. The terminal antenna is mounted at 1.5 meters high.
- The Cost231-Hata model that is amended based on planning experience is generally used as the propagation model.
List of Link Budget tool critical and “selectable” parameters
Duplex Mode: Option Frequency division duplex (FDD)/ Time division duplex (TDD).
TMA used: Yes/No
TMA Gain: 12dB/24dB
Morphology: Dense Urban/Urban/Suburban/Rural/Highway
Channel Model: EPA, ETU, EVA, High Speed Train (HST)
Frequency (MHz): Frequency used in this system (700, 800, 850, 900, 1500, AWS, 1800, 2100, 2300, 2600)
Bandwidth: 1.4M, 3M, 5M, 10M, 15M, 20M
MIMO Scheme: Separately settable for Downlink (1×2, 2×2 SFBC, 4×2 SFBC+FSTD) and Uplink (1×2, 1×4, 1×8). Please Note, In a AxB configuration, A is always refers to the transmit function of the device
DL/UL Cell Edge Rate (kbps): Setting in accordance to the actual customer requirements
DL/UL Edge MCS: Total of 29 coding selection that can be chosen separately for DL and UL. As UL normally is the weakest link due to limited UE power, Most of use UL MCS coding of QPSK 0.25 at the Edge as UE power is shared across only 8 RBs for best Maximum path loss results against other MCS.
DL/UL Target Load: Target customer loading should be provided here separately for Downlink and Uplink so the desired interference margin can be incorporated into the link budget. Common values are 30%, 50%, 70% and 100%
Propagation Model: Option includes Cost231-Hata (Classic), Okumura Hata (Classic), SPM, Cost231-Micro (Classic) and vendor specified.
Transmit Power: Customer configuration specific, referring to per TX path transmit power value. Typical value is either 43dBm (20W) or 46 dBm (40W).
eNodeB cable loss: Value is dependent on cable configuration at customer site (0.5dB for RRU) vs 3dB (standard cable length) or more (extended length) for RFU based configuration
UE Transmit Power: Typical value is 23dBm +/- 2dB for a Class 3 unit. The minimum transmit power by this UE is -40dBm according to 3GPP TS 36.101. Actual UE power can be reduced by the modulation used.
UE Antenna Gain: Typical value is 0dB in the absence of any external antenna
Example : Below listed is an example for LTE link budget.
The link budget is based on only theories, and can neither ensure the capacity nor coverage reliability of the actual network. The coverage target and requirements also vary with different network requirement and the respective assumptions. As a result, the link budget result varies greatly, depending on the different input parameters.
Therefore, to design the link budget that reflects the requirement of a particular network, the designer must discuss with the operator to determine the value of each input parameter in the link budget.
Link budget also assumes a uniform landform, simple terrain, ideal site locations, and even subscriber distribution. System simulation covers detailed landform distribution, actual site location, terrain type, and subscriber distribution. Hence, the link budget result serves ONLY as the theoretical calculation result. The calculated coverage radius is used for reference in simulated site distribution.
The detailed coverage planning must be completed through system simulation. For a given coverage area, the number of planned base stations will depend on the system simulation result.