UL/DL Considerations of BDA fed Active DAS Steve Blum Senior Solutions Engineer Jan, 2014

Donor Site Noise Rise Avoid Donor site de-sense from DAS/BDA Noise Signal and Noise Noise Power – Path Loss Donor Antenna DAS Remote DAS Antenna A 1 BDA DAS Interface

Generic DAS Remote converts and amplifies RF Transport medium Head end with RF interface to signal source and conversion for transport

DAS UL Noise Figure Noise Figure is the degradation in Signal to Noise from the input to output Passive DAS 16 dB Loss -90 signal -113 noise SNR = 23 -106 signal -113 noise SNR = 7 -90 signal -113 noise SNR 23 Active DAS with 16 dB NF -90 signal -97 noise SNR 7

Noise Power DAS UL Noise Power = -174 dBm (thermal noise floor, 50 ohms, 1kHz) + 10log(Bandwidth of RX) + NF + Gain For CDMA = -113 + NF + Gain Coax adds to NF but subtracts from gain, net 0 impact to noise power

Combined Noise Power Noise Figure = Base noise figure + 10log (number of remotes) NF = 10 + 10log(4) or 6 = 16 dB NF Gain = 10 Noise Power = -113 + 16 + 10 = -87 dBm

Mitigating DAS Noise UL Attenuation will reduce Noise Small Impact to NF/SNR -90 Signal -113 Noise S/N = 23 Stages NF Gain Cascade Calculations   DAS 16.0 10.0 16.32 10.00 UL Atten 15.0 -15.0 -5.00 Passive 0.0 BDA Coax Antenna Stage 8 Noise -101.68 -80/-87 S/N = 7 -95/-101.7 S/N = 6.7 -15 dB NF 16, Gain 10

Noise Power ERP Noise Power ERP = DAS Noise - Coax + BDA Noise - Coax + Antenna Gain Noise Power ERP -113 + 16 + 69 = -28 dBm BDA DAS Remote A 1 DAS Interface Antenna gain 2 Coax BDA Gain Cascaded Calculation Stages NF Gain Cascade Calculations   DAS 16.0 10.0 16.00 10.00 UL Atten 0.0 Passive 1.0 -1.0 16.03 9.00 BDA 5.0 60.0 69.00 Coax -5.0 64.00 Antenna 0.5 Stage 8 Noise -27.97 The Noise Figure is pretty much set by the DAS so the only way to reduce Noise Power is to reduce the gain. But where we do that is important and we can analysis this with the cascaded calculation 1 Coax Noise Power

Reducing UL Noise Cascaded Calculator to evaluated effects of UL attenuation Goal is to reduce attenuation with minimal impact to NF 15 dB UL attenuation on DAS 15 dB UL attenuation on BDA

Optimizing UL Attenuation Splitting Attenuation reduces UL overdrive concerns with minimal degradation to NF

DAS Remote Gain Adjust Adjusting Remote UL Gain impacts NF Normal, 10 dB Atten Adjusting Remote UL Gain impacts NF Low, 1 dB Gain, 13 dB NF Normal, 11 dB Gain, 10 dB NF High, 21 dB Gain, 7 dB NF +6 to NF for 4 remotes Low, no UL Atten High, 20 dB Atten Keep in mind that UL IMD can become a concern with higher UL gain at the remote

Balancing Remotes High Gain on 1 remote will dominate the noise floor

DL Gain Considerations BDA DAS Remote A 1 DAS Interface DAS Remote adds gain to distribute RF DAS Net Gain = DAS Remote Composite Pout – BDA Composite Pout DAS HE attenuates DL for transport

Balancing DL Gain DAS Remote gain stays the same BDA DAS Remote A 1 DAS Interface DAS Remote gain stays the same BDA DL gain reduced = lower Pout Net effect = No gain change With lower Pin, DAS HE reduces attenuation

Balancing DL Gain? Net DL Gain = BDA Gain + BDA Pout – DAS Remote Pout BDA = 60 dB Gain and 30 Pout Remote = 33 Net gain = 63 Net UL Gain Remove donor coax and antenna Lower power DAS BDA = 60 dB Gain and 30 Pout Remote = 20 Net gain = 50 Either adjust the UL gain/attenuation to match DL or reduce DAS remote Pout

BDA – DAS Oscillation When Gain is higher than isolation Donor Antenna Isolation Attenuate and/or isolate the specific antenna DAS Remote DAS Antenna A 1 BDA At -5 isolation, the system will oscillate activating AGC and causing alarms. At 15, generally everything will be fine but 20 allows for no problems DAS Interface

Mixed Power Remotes DAS common head end with a mix of remote options

Summary UL Noise from a BDA fed DAS may de-sense the donor base site Noise is determined by the cascaded NF + gain Find best place to adjust gain while minimizing NF increase Increasing the DAS remote gain can reduce NF but may create IMD concerns Adjusting BDA DL gain to match UL gain adjustment will not balance the gain Adjusting DL net gain requires reducing remote Pout Preventing oscillation will require attenuating/isolating the offending antenna (DL/UL) DAS with mixed remotes may require independent head end components