Motorola Horizon macro BTS

The Motorola Horizon macro BTS is a BTS model manufactured by Motorola in the late 1990ies.

It can support up to 6 TRX, typically in a configuration of 3 sectors.

There is currently no support for it in OpenBSC, but we are working on it.


frontal view of the Horizon macro cabinet with 3 CTU top view of the Horizon macro cabinet


The up to 6 CTU modules are the individual transceivers (TRX) of the BTS cabinet.

They plug into the SURF RF backplane and have a front-accessible
DB9 serial port, as well as a SMA connector for the TX PA output.

This TX PA output is normally wired using a ~10cm semi-rigid SMA cable to the TX input port of a combiner/duplexer.

The CTU is of course fully shielded. But if you remove the shielding cover, it looks like this:

CTU1800 PCB view

You can see
  • two diversity receivers in the top left part
  • digital section in the top right part
  • transmit section (exciter) in the center
  • RF power amplifier in the bottom right part

digital part

The CTU digital part has the following connections
  • backplane connector for
    • power supply (27V DC)
    • two redundand 2048 Mbps TDM links with MCUF, manchester-encoded, 32 timeslots
  • three coaxial backplane connectors with SURF
    • Rx side A (diversity)
    • Rx side B (diversity)
    • Rx loopback (for transmitting into Rx path, loopback testing)
      The CTU digital part consists of three main processors:
  • RSS (Radio Subsystem)
    • communicates with MCUF via dedicated 64kbps timeslots in TDM link
    • communicates via dual-ported ram with CCCP
    • Flash EEPROM for boot loader and 8 MByte DRAM
  • EQCP (Equalizer and Control Processor)
    • DSP for radio control and channel equalization
    • alarm management
    • downlink burst building and modulator control
    • tx power control
    • synthesizer channel control
    • rf frequency hopping
    • receiver front-end and remote tune combiner control
    • uplink synchronziation and equalization
    • diversity receiver control
    • automatic gain control
    • receiver signal sthrength calculation
  • CCCP (Channel Coder Control Processor)
    • DSP for channel coding, data routing and baseband hopping
    • uplink channel decoding
    • downlink channel encoding
    • A5 encryption
    • baseband frequency hopping
    • TRAU frame collection and synchronization

The CTU has a three serial consoles routed to the same DB-9 plug. We describe it in Motorola_Horizon_macroCTU_Console


The combiner / duplexer combines the TX signal of two CTU and duplexes it with the Rx path in order to be able to have two TRX attached to one antenna


The MCUF is a full-size digital board and contains the BTS controller

MCUF PCB, top view
MCUF front view (CF slot, fiber optic connectors, etc.)


The NIU is a E1 interface card for up to two E1 lines. Multiple NIU boards can be plugged into the rack
NIU pcb photograph


The BPSM is a small power supply for the NIU, MCUF and other digital boards

BPSM (power supply for digital modules)


The ALARMS board is monitoring FAN and other alarms in the cabinet.

ALARMS board PCB photo

A-bis interface

The A-bis interface is via classic E1 lines. The Horizon indoor cabinet supports up to 6 E1 ports.

Each NIU module serves 1 or 2 E1 ports.

The E1 ports are physically routed to the BIB (Balanced Interface Board) module on top of the cabinet.

The pinout of the 37pin D-Sub connector on top of the BIB board has been reversed as:
Pin Transformer Usage
1 T1.1 NIUA0 Port 0 (Tx)
2 T2.1 NIUA0 Port 0 (Rx)
4 T4.1
5 T5.1
7 T7.1
8 T8.1
10 T10.1
11 T11.1
12 GND
13 T13.1
14 T14.1
15 GND
16 T16.1
17 T17.1
18 GND
19 GND
20 T1.8 NIUA0 Port 0 (Tx)
21 T2.8 NIUA0 Port 0 (Rx)
23 T4.8
24 T5.8
27 T7.8
28 T8.8
29 T10.8
30 T11.8
32 T13.8
33 T14.8
35 T16.8
36 T17.8



There is a 20MByte Intel Series2 Flash PCMCIA card inside the MCUF. It contains software + configuration for the BTS.

Intel PCMCIA Series 2 Flash used in the MCUF

There once has been a mtd_iflash2.c driver for Linux 2.4.x, but apparently it has never been merged mainline before the
big CardServices API redesign happened in 2.6.x. So unfortunately it's not straight-forward to read them out :(

The MCUF is able to run without the PCMCIA card. In this case, it will download all software + config via E1 from the BSC.

The MCUF has a very extensive command line interface (MMI), for more information check Motorola_Horizon_macroMCUF_Console


It is assumed that the CTU only contains a boot loader to download the real software from the MCUF.

Further reading

Updated by laforge over 8 years ago · 16 revisions

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