Analysis of Interference Between LTE System and TETRA System in The 800 MHz Band

Wireless communication is used in many sectors to support the need of communication, the example of wireless communication is applied in mission critical network. Wireless communication system that used in mission critical are Terrestrial Trunked Radio (TETRA) and Long Term Evolution (LTE). TETRA systems supports voice services while LTE supports voice and data services. Co-exsitence between LTE and TETRA in same frequency band is one of the optimilazition quality for mission critical network. For this research analyses interference in co-exsitence between LTE and TETRA in frequency band 800 MHz. There are four scenarios using extended-hata model propagation in urban area. There are several parameters that reviewed, desired Received Signal Strength (dRSS), interfering Received Signal Strength (iRSS), Carrier to Interference ratio (C/I) and probability of interference. In all scenarios occur Co-Channel Interference (CCI) between LTE and TETRA in frequency band 800 MHz so the performance not optimal. The performance increased when add guard band variation. The variation that applied are 0,5 MHz, 0,75 MHz, 1 MHz. Based on the result of the simulation that have been done, proposed the used of guard band variation for elevate the performance.


Introduction
Nowadays application and choice of suitable wireless communication that can support optimization to elevate the quality that user need because of every time there is increasing in traffic but also frequency allocation is limited. Wireless communication offers many variant of technology for some sectors, one of the example is services for mission critical network.
One of the technology that used in mission critical communication is Teresstrial Trunked Radio (TETRA). TETRA has primacy that usual techonology don't have. TETRA designed to offer wide coverage and high rate availbality network that can operate pretty well in disaster area. [1]. Along with the primacy TETRA also has lack and that is low data rate and smaller capacity if compare with usual cellular network. The lack that TETRA has make operator in mission network do coexesistence between TETRA with one of cellular technology, Long Term Evolution (LTE). LTE is a broadband technology. LTE network offer better quality if compare with previous generation of cellular technology.
Coexistence two different technology with same operate frequency could occur interference. In this research LTE and TETRA operate in 800 MHz band. LTE used 814-849 for uplink and 859-894 for downlink and TETRA used 806-824 MHz for uplink and 851-869 for downlink. The probability of interference that standardized by ETSI is 10%.

Basic Theory of Interference
Coexsistence more thans one base station in same coverage could occur intereference between transmitter and receiver. In general interference divided into two category co-channel interference dan adjacent channel interference [3].
Co-channel interference is interference signal have same carrier frequency with information signal or interference signal entering receiver get close with the center of bandwidth so the filter could not muffle [3]. In other word co-channel interference is an interference between cell that use same channel or same frequency. The Co-channel interference is illustrated in figure 1. Figure 1. Co-channel Interference [4] Interference that produce by assigned frequency with original signal defined as Adjacent Channel Intereference (ACI) [5]. In other word ACI is an interference of assigned channel. The ACI is illustrated in figure 2.

The Parameters Used
Parameters that being used in analysis of interference between LTE and TETRA are desired Received Signal Strength (dRSS), interfering Received Signal Strength (iRSS), and Probability of interference/Carrier to Interference (C/I).
dRSS is strength of victim wanted signal, a calculation of link budget between Victim Link Receiver (VLR) and Victim Link Transmitter (VLT) [6].

ℎ
(1) where: desired Received Signal Sterngth dBm transmit power from transmitter dBm gain total of transmitter dBi gain total of transmitter dBi Pathloss loss of link budget dB iRSS is calculation that consider as a link budget between VLR and Interfering Link Transmitter (ILT) [6]. where: interfering Received Signal Sterngth dBm transmit powerfrom transmitter dBm total gain from transmitter dBi total gain of transmitter dBi ℎ loss of link budget dB Carrier to Interference (C/I) is measure that used to rate between signal quality and interference stated with C/I (dB). C/I should higher than C/I minimum that standardized by standardization [4].

The Guard Band
Guard band is frequency range that separate two bigger frequencies. Guard band used by communication channel to prevent interference that could decreased performance of transmission system. Guard band located between frequency LTE and TETRA. LTE

Scenario Design for Simulation on SEAMCAT
Each simulation on software SEAMCAT iterated with 21.000 samples. There are four scenarios simulated with each scenario with four schemes, co-channel (no guard band) and with guard band addition (0,5 MHz, 0,75 MHz, and 1 MHz). There are one interfering link and one victim link in each scenario. In Interfering link there are Interfering Link Transmitter (ILT) and Interfering Link Receiver (ILR). In Victim Link there are Victim Link Transmitter (VLT) and Victim Link Receiver (VLR). Every scenario produces dRSS, iRSS, C/I and probability of interference. The scenario of simulation on SEAMCAT is illustrated in figure 4.   There are four variations in scenario 2, no guard band, 0,5 MHz guard band, 0,75 MHz guard band, and 1 MHz guard band. Guard band variation located on TETRA. Guard band located between LTE frequency and TETRA frequency that caused shifted in LTE operating frequency LTE (interfering link). LTE used channel bandwidth 10 MHz and TETRA used channel bandwidth 25 KHz. The scenario 2 is illustrated in figure 6.

Scenario 3 (Downlink LTE vs Uplink TETRA)
There are four variations in scenario 3, no guard band, 0,5 MHz guard band, 0,75 MHz guard band, and 1 MHz guard band. Guard band variation located on TETRA. Guard band located between LTE frequency and TETRA frequency that caused shifted in LTE operating frequency LTE (interfering link). LTE used channel bandwidth 10 MHz and TETRA used channel bandwidth 25 KHz. The scenario 3 is illustrated in figure 7.  There are four variations in scenario 4, no guard band, 0,5 MHz guard band, 0,75 MHz guard band, dan 1 MHz guard band. Guard band variation located on TETRA. Guard band located between LTE frequency and TETRA frequency that caused shifted in LTE operating frequency LTE (interfering link). LTE used channel bandwidth 10 MHz and TETRA used channel bandwidth 25 KHz). The scenario 4 is illustrated in figure 8.  Then, the flowchart of analysis of interference between LTE and TETRA can be shown in Figure 9.   With guard band variation produced different result of each parameter in scenario no guard band occur Co-Channel Interference it showed with probability of interference is above the threshold, with guard band variation guard band 0,5 MHz, 0,75 MHz, and 1 MHz the value of probability of interference below threshold. Guard band addition increase system performance if it compared to probability of interference no guard band is higher than used guard band. When interference will occur and that will decrease the optimization of the system and that is in harmony with the result in table above, when probability of interference will be above the threshold and when the probability of interference will be below the threshold.  With guard band variation produced different result of each parameter in scenario no guard band occur Co-Channel Interference it showed with probability of interference is above the threshold, with guard band variation guard band 0,5 MHz, 0,75 MHz, and 1 MHz the value of probability of interference below threshold. Guard band addition increase system performance if it compares to probability of interference no guard band is higher than used guard band. When interference will occur and that will decrease the optimization of the system and that is in harmony with the result in table above, when probability of interference will be above the threshold and when the probability of interference will be below the threshold.  With guard band variation produced different result of each parameter in scenario no guard band occur Co-Channel Interference it showed with probability of interference is above the threshold, with guard band variation guard band 0,5 MHz, 0,75 MHz, and 1 MHz the value of probability of interference below threshold. Guard band addition increase system performance if it compares to probability of interference no guard band is higher than used guard band. When interference will occur and that will decreases the optimization of the system and that is in harmony with the result in table above, when probability of interference will be above the threshold and when the probability of interference will be below the threshold.  With guard band addition, power reduction, and tilting antenna produced result of parameter. In scenario no guard band occur co-channel interference it showed with probability of interference above the threshold, with guard band 0,5 MHz, 0,75 MHz, and 1 MHz performance system increased with the probability of interference decreased. System will be in optimum state when added 1 MHz guard band, power reduction of BS TETRA, and tilting antenna. When will occur inreference that will decreased performance of the system and that is in harmony with the result in table above, when probability of interference will be above the threshold and when the probability of interference will be below the threshold.  With guard band variation produced different result of each parameter in scenario no guard band occur Co-Channel Interference it showed with probability of interference is above the threshold, with guard band variation guard band 0,5 MHz, 0,75 MHz, dan 1 MHz the value of probability of interference below threshold. Guard band addition increase system performance if it compares to probability of interference no guard band is higher than used guard band. When interference will occur and that will decrease the optimization of the system and that is in harmony with the result in table above, when probability of interference will be above the threshold and when the probability of interference will be below the threshold. There are three categories, first category co-channel interference occurs if probability of interference above 10%, and in the same operating frequency. Second category, adjacent channel interference will occur if after added guard band the probability of interference still above 10%. Third category, interference minimum will occur if probability of interference below 10%. Simulation with guard band addition will increase system performance. Beside guard band addition, power reduction and tilting antenna also could increase system performance.