wiki:Manual/Algorithms/Basics/BlockingAttenuation

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How to set blocking attenuation mode and function of victim receiver

It is very important that the victim receiver blocking attenuation mode and the associated blocking function are set appropriately and in co-ordinated manner, since the interpretation of blocking function trial will depend on the chosen attenuation mode.

Please see the annex on the definition of receiver selectivity and blocking attenuation PDF file (137 KB) for detailed guidance. Note that the information contained in this annex was derived assuming a desensitisation of 3 dB. The SEAMCAT blocking calculation has been extended to accomodate any desensitisation value. More generic equations are presented below.

Calculation of blocking attenuation

Blocking attenuation (also might be referred to as selectivity feature) is a function of the frequency difference between interfering transmitter and victim receiver Δf = fit - fvr. It is introduced to enable the evaluation of ability of victim receiver's filtering/selectivity mechanisms to withstand the interference from the full power of an interfering transmitter that is transmitting in an adjacent channel/band.

When the victim is generic, three calculation modes are available, according to the way the Blocking function is defined in the scenario (see section below):

  • Blocking function set as User-defined attenuation function, representing the actual receiver filter mask (in dB). In this case the blocking attenuation value is simply derived from the user-defined function depending on the IT-VR frequency shift as an argument;
  • Blocking function is defined in Protection ratio mode, corresponding to the required protection ratio (in dB). In this case the blocking attenuation value is derived as follow:

AvrBlocking Ratio = Bmask + C/(N+I) + (N+I)/N –I/N

  • Blocking function is defined in Sensitivity mode, representing the absolute maximum interfering power tolerated by the victim receiver (in dBm). In this case the blocking attenuation value is derived as follow:

Avrsensitivity = Bmask + C/(N+I) – sensitivity_receiver - I/N

An illustration of the protection ratio and the sensitity is given in the slide show.

Note that the C/(N+I) value used in the above formulas is taken directly from the interference criteria settings of the Victim Receiver. Therefore users must carefully set this value in the scenario. See further guidance on application of the above formulas with the consistency check.

When the victim is CDMA or OFDMA, only mode is available which is equivalent to the "User-defined".

CDMA / OFDMA simulation: How to simulate multiple ACS due to multiple interferers with various bandwidths?

When simulating cellular environment like LTE, the 3GPP standard provides different ACS values depending on the bandwidth of the interferer. For instance, it is known that LTE can support flexible channel bandwidth, 1.4MHz, 3MHz, 5MHz, 10MHz, 15MHz and 20MHz. Therefore, in order to be able to deal with more LTE co-existence scenarios in the future, it is unavoidable to support scenarios with different bandwidth interferers.

SEAMCAT is able to handle such a case. The following provides information on how to do define the workspace in SEAMCAT.

Defining the ACS mask

Let’s assume the following example of two interferers with two distinct bandwidth (10MHz and 5 MHz) which results in 2 ACS values. For this you would need to introduce a ACS “mask” so that it is defined at the specific interference frequencies for various interfering bandwidth and not to a same bandwidth. You need to define the ACS to the left for 10 MHz using the approximation of 3GPP TR36.942 (p75) and you can define the ACS for 5 MHz in the right hand side.



In the case where two interferers are geographically separated but transmitting at the same frequency, you can trick SEAMCAT by slightly shifting one of the frequency (a few kHz is enough) so that the value for a specific frequency is used in the simulation (see below).



The only situation, where it would be difficult (but still feasible) is when the interfering frequency is distributed over a large bandwidth, then you would have to define the “other” ACS value elsewhere in the frequency domain and you may have 1‐2 dB difference due to the propagation models (exact value to be assessed of course).

Calculating the average ACS value

According to 3GPP TR36.942 p75, there are some example calculations of average ACS. For example the following equation:





Which means Average ACS or called equivalence ACS values is equal to the following.



Note: Using this method, each BWN should be the multiple of unit bandwidth in reception mask. For example, in the case of 3GPP TR36.942, ACS1, ACS2 and ACS3are defined in 5MHz band and 30 MHz are the multiples of 5.

Conclusions

  1. Calculate the ACS values for each of the interfering bandwidth that you want to simulate.
  2. Set the “mask” in SEAMCAT so that for a specific interfering frequencies you have the appropriate ACS values

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