Expecting the drive for an SoC solution optimized for both form factor, pin count, and routing complexity will push eFEM vendors in a new direction, Intel's John Oakley describes using the MIPI RFFE serial communication interface to control multiple RF components for Wi-Fi/Bluetooth-enabled products. Since the serial communication adds an overhead time for each configuration, the suggested Master-Slave mapping helps minimize the number of telegrams for SISO, MIMO and Concurrent Dual Band (CDB) cases, while complying with the MIPI RFFE Specification.

1. RFFE:
Challenging the
WiFi/Bluetooth
Status Quo by
Unifying eFEM
Control
John Oakley
Intel Corporation

2. Abstract
• Today’s high-end wireless marketplace, where users seek high data rates and increased Wi-
Fi performance, requires challenging the status quo: the control scheme dominated by
discrete control signaling used by eFEMs targeting the Wi-Fi/Bluetooth technology segment.
• Expecting that the drive for an SoC solution optimized for both form factor, pin count, and
routing complexity will push eFEM vendors in a new direction, this presentation describes
use of the MIPI RFFE serial communication interface to control multiple RF components for
Wi-Fi/Bluetooth-enabled products.
• Since the serial communication adds an overhead time for each configuration, the suggested
Master-Slave mapping helps minimize the number of telegrams for SISO, MIMO and
Concurrent Dual Band (CDB) cases, while complying with the MIPI RFFE Specification.
• MIPI RFFE is a well adopted specification, developed by the MIPI Alliance, to offer a
common, widespread method for controlling RF Front-End designs. The MIPI Alliance
determined that the majority of today’s RF communication standards are proprietary or de-
facto and are not utilized industry-wide, and developed the MIPI RFFE specification in order
to establish a single standard for eFEM communication, from the PHY level to the protocol
and software levels.
2

3. Introduction
• The pursuit of high data rates and increased performance for
WiFi forces strict requirements on both TX and RX in order to
compete in the high end market segment. Current trend is to
suggest proliferations that incorporates external Front End
(eFEM) components, in order to achieve those high-end
requirements.
• The eFEM controls use discrete logic GPIOs, and with the
increase in external units, multi-band support and functionality,
we result in an increase in package pinout as well as
complexity on the routing, affecting the cost and Form Factor
(FF).
• This presentation summarizes a method for using MIPI RFFE
serial communication interface to control external/peripheral
RF components for WiFi (up to 2x2 dual-band) and BT
products.
3

4. Example 2x2 WiFi/BT Front End
• For example, 2x2 WiFi/BT solutions implement 13 discrete control
pins and 4 analog pins, for supporting up to 4 eFEMs, two WiFi Low
Band (LB) and BT, and two for WiFi High Band (HB).
4

5. Improved Example 2x2 Front End
• An example front using MIPI RFFE connections,
reducing the connections to the SOC to 3 wires.
5

6. Today’s WiFi/BT front end
• Today the eFEMs are controlled by discrete signaling. eFEM vendors
have consolidated common configurations for different eFEM system
modes. The figure below illustrates example eFEM modules for LB
and HB. The table below details the control configuration commonly
used on LB and HB eFEMs, showing all system modes for LB and for
HB.
6

7. Suggested WiFi/BT System Modes
• To unify the control of the front end devices, it is helpful to identify the system
modes. The table below shows nine typical system modes for a 2x2 system.
• An example of how these system modes are configured via RFFE control
registers.
• The enable/disable can be done with a single broadcast RFFE write to Reg1.
• The mode switch can be done with a single broadcast RFFE write to Reg0.
7

8. Simplified Control Interface
• Using the Reg0 and Reg1, the control of the WiFi/BT front end can
be quickly and easily updated for the given use case.
8
• Keeping the control
simple minimizes
necessary the firmware
support.
• Adapting for front end
differences does not
change control
procedure.
• For example, a 2x2 front
end could expanded to a
3x3 front end minimal
firmware changes.

9. RFFE Implementation Advantages
• Using a standard like MIPI RFFE allows for a reduced pin count of
the Connectivity SOC device.
• Today’s products are growing in complexity in features and interconnect, RFFE
allows this interconnect complexity to be managed and controlled.
• Carefully specifying the various devices allows for broadcast writes
with minimal latency and firmware overhead.
• With a GPO based approach, each device is typically independently controlled.
• With a RFFE based approach, there is a common control interface and common
mechanisms. eFEMs can be controlled simultaneously.
• MIPI RFFE is normally pull-down to ground and uses control skew
rate transitions which helps isolate SOC noise from the eFEMs.
9

10. RFFE Implementation Advantages cont…
• MIPI RFFE allows for more control options without
changing the chip interconnect.
• Adding a new control feature/register to an eFEM does not change the
connection.
• MIPI RFFE allows for the possibility of reading eFEM
devices to determine failure cases (like overheating).
• Adding debug and reliability is a KPI for many products.
• Billions of devices in the world use MIPI RFFE already.
10

11. Continued Reading
• MIPI published a white paper with more details
on usage RFFE in WiFi/BT Front Ends.
• http://resources.mipi.org/rffe-whitepaper
11