The 5G network and the mid-band spectrum (CBRS and C band in the United States) has created tremendous interest in new RU form factors. In particular, mMIMO systems with up to 32 to 64 antennas promise to greatly enhance the BTS capacity and coverage in the mid bands. The deployment of these mMIMO panels in the United States will likely be co-located on the same radio towers with existing PCS band or 4G/5G n2 band radios, both at downlink (DL) frequencies from 1930 MHz to 1990 MHz and uplink (UL) frequencies from 1850 MHz to 1910 MHz. The PCS/n2 band is of interest in this example case study because the second order harmonic distortion (HD2) and second order intermodulation (IMD2) products created by signals in this band fall directly onto the new C-band (3700 MHz – 3980 MHz). Other co-locating bands such as UMTS/n1 (2100 MHz) and 700M/800M are easier to design for in general and the analysis method would be the same.
The following table summarizes the high-level design requirements for the C-band system.
| Parameter | Value |
|---|---|
| 5G BTS band | C-band, 3700 MHz to 3980 MHz |
| Occupied bandwidth/instantaneous BW | 200 MHz/280 MHz |
| Duplex mode | TDD |
| Antenna configuration | 32 TX/32 RX |
| 5G BTS type | Type 1-H, wide area |
| TX power per antenna connector (TAB) | 10W (40 dBm) |
| Total system TX power | 320W (55 dBm) |
| RX noise figure (NF) per antenna receiver | ≤ 2.5 dB |
| Co-location band | PCS/n2, UL: 1850 MHz – 1910 MHz, DL: 1930 MHz – 1990 MHz, FDD duplex |
The analysis in this white paper mainly focuses on the co-location requirements mentioned in the previous section. Other 3GPP BTS requirements, such as TX SEM, RX narrow-band blocking, etc., are not directly included in this discussion as there are no specific co-location considerations for these requirements.