Why I cannot detect LTE cell networks without a SIM card?

Question

I am trying to detect Cellular signals without an installed SIM card. The phone I'm using is a Motorola Nexus 6. And the code I am using is below -

tm  = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);
List<CellInfo> cInfoList = tm.getAllCellInfo();  

for (final CellInfo info : cInfoList) {
  if (info instanceof CellInfoGsm) 
     sR =  "GSM: " + gsm.toString() + "\n" + ((CellInfoGsm) info).getCellIdentity();
  else if (info instanceof CellInfoCdma) 
     sR =  "CDMA: " + cdma.toString() + "\n" + ((CellInfoCdma) info).getCellIdentity();
  else if (info instanceof CellInfoLte) 
     sR =  "LTE: " + lte.toString() + "\n" + ((CellInfoLte) info).getCellIdentity();
  else if (info instanceof CellInfoWcdma) 
     sR =  "WCDMA: " + wcdma.toString() + "\n" + ((CellInfoWcdma) info).getCellIdentity();

When the SIM slot is empty, cInfoList contains only objects of CellInfoGsm and CellInfoWcdma, which are 3G. If I insert a SIM card and let it connect, then cInfoList contains only instances of CellInfoLte, which is 4G.

Can you explain me why I cannot detect LTE cell networks without a SIM card and why I cannot detect 3G networks with a SIM card?

Comments

SIM card contains authentication information about GSM/GPRS/UMTS/LTE network (including LTE signal type). So, it seems that your device just doesn't have LTE without the SIM. Do you see the network type icon on the top status bar....