Design and Implementation of Bluetooth MAC core with RFCOMM on FPGA

Design and Implementation of Bluetooth MAC core
with RFCOMM on FPGA
Sreekumari.B1 & Jiju.K2

ANEESH R
ER & DCI-IT
CDAC, Thiruvananthapuram, India
aneeshr2020@gmail.com

Power Electronics Group
CDAC, Thiruvananthapuram, India
sreekumarib@cdac.in1
jijuk@cdac.in2
II.

Abstract- The System-on-Chip (SoC) design of digital
circuits makes the technology to be reusable. The current
paper describes an aspect of design and implementation of
IEEE 802.15.1 (Bluetooth) protocol on Field Programmable
Gate Array (FPGA) based SoC. The Bluetooth is a wireless
technology designed as a short-range connectivity solution
for personal, portable and handheld electronic devices.
This design aims on Bluetooth technology with serial
communication (RS-232) profile at the application layer.
The IP core consists of Bluetooth Medium Access Control
(MAC) and Universal Asynchronous Receiver/Transmitter
(UART). Each module of the design is described and
developed with hardware description language-Very High
Speed Integrated Circuit Hardware Description Language
(VHDL). The final version of SoC is implemented and
tested with ALTERA STRATIX II EP2S15672C3 FPGA.
Keywords - IEEE 802.15.1, Bluetooth, MAC, SoC, FPGA, Serial
Port Profile

I.

INTRODUCTION

The IEEE 802.15.1 protocol is called Bluetooth. It is a short
range (10-100m) radio technology, which is developed for
Personal Area Network (PAN). Bluetooth is a standard
developed by a group of electronic manufacturers that allows
any sort of electronic equipment—from computers and cell
phones to keyboard and headphones—to make its own
connections, without wires, cables or any direct action from a
user. It offers the possibility of ad hoc network and delivers the
ultimate synchronicity between all personal devices.
Figure 1 shows the Bluetooth module with a
microcontroller to establish a serial communication link. The
proposed design of Bluetooth IP core aims for transmitting and
receiving data serially. So the upper layer of Bluetooth IP core
uses a RS-232 standard to achieve a reliable serial
communication.

Figure 1: A serial communication link using Bluetooth

IEEE 802.15.1 PROTOCOL

The Bluetooth physical layer is operating at 2.4 GHz and
has very low power consumption. It uses a frequency hopping
spread spectrum. That is it changes its carrier frequency after
every 625 us. There are two types of Bluetooth devices:
Master and Slave. The unit is said to be master if it is an
originator and arbitrator in a given piconet. The frequency
hopping sequence is selected according to the master device.
The slaves in the piconet must to be synchronized with the
master’s clock.
The Bluetooth system provides a point-to-point connection
(one Master and one slave) and point to multipoint connection
(one master and more than one slave).The network Bluetooth
defines two types of network:-Piconet and Scatternet. In the
piconet topology one master and up to seven slaves participate
in the network. The scatternet consists of more than one
master and slaves. One master in a network can be a slave in
the other network. One or more piconet combines to form a
scatternet.
A channel in Bluetooth is represented by a pseudo random
hopping sequence. The hopping sequence is unique for each
Bluetooth units in a piconet and is derived from Bluetooth
device address (BD_ADDR). A Bluetooth device hops 1600
times per second, which means that each device changes its
modulating frequency 1600 times per second. The hopping
sequences change its value regularly after 625 us.
Bluetooth uses a form of Time Division Multiple Access
(TDMA) that is called Time Division Duplex TDMA (TDDTDMA). TDD-TDMA is a kind of half duplex communication
in which a Bluetooth device transmits and receives the data
not at the same time. The channel is divided into time slots,
each of 625 us in length. The master device may transmit in all
even numbered time slots and a slave device in odd
numbered time slots. Figure 2 shows the data transmission
between a master and a slave.

Figure 2: Master-Salve communication

978-1-4673-2272-0/12/$31.00 ©2012 IEEE

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Bluetooth supports two types of physical link: Synchronous
Connection Oriented (SCO) link and Asynchronous
Connection Less (ACL) link. The SCO link is symmetric and
point-to-point link between the master and a specific slave.
The SCO link typically supports time bound information like
voice. The ACL link is a point-to-multipoint link between the
master and slaves participating in the piconet.
III.

reception operation between MAC and PHY. TX, RX pins
represents the transmission and reception from PHY. The
UC_TX and UC_RX signals provide the transmission and
reception signals from the RFCOMM.

PROTOCOL ARCHITECTURE

Figure 3 represents the protocol architecture for an IEEE
802.15.1 system with RFCOMM at the application layer. The
proposed protocol aims on transmitting and receiving the data
from the Bluetooth device to upper layer or other devices by
using a serial communication profile.

Figure 3: Protocol stack with RFCOMM
The Physical (PHY) layer is the first layer of the Bluetooth
system. The basic functionality of the PHY layer is to receive
a bit stream from the Medium Access Control (MAC) sublayer and transmitting the bit stream via radio waves to an
associated station and vice versa through antenna. The
Baseband layer is the heart of the Bluetooth system. It
performs the link establishment and associated operations for
an efficient data transmission and reception. The Link
Manager layer controls and monitors the link between the two
devices and performs the security in Bluetooth. The Logical
Link Control and Adaptation (L2CAP) layer provides the
protocol multiplexing, Packet composing and de-composing.
The Radio Frequency Communication (RFCOMM) layer
emulates the serial communication architecture. The
Baseband, Link Manager and L2CAP layer are defined by
IEEE, and together called MAC layer of the Bluetooth system.
IV.

IP CORE DESIGN

A. Top Level Entity
Figure 4 shows the top level entity of a Bluetooth with
RFCOMM. In this, FH_SS is a pseudo random number given
to PHY to perform the Frequency hopping spread spectrum
technique. Also it provides a CLK_1MHz, a 1MHz clock
signal to PHY for synchronizing the transmission and

Figure 4: Top level entity-Bluetooth with RFCOMM
B. Link Establishment Procedure

Figure 5: Link Establishment in Bluetooth
Figure 5 represents the link establishment between a master
and slave Bluetooth device. There are two major states:
STANDBY and CONNECTION; in addition there are seven
sub-states, inquiry, inquiry scan, page, page scan, master
response, slave response and inquiry response. The sub-states
are used to add new slave to a piconet. To move from one
state to another a command from the link manager or internal
signals in the link controller are used.
The STANDBY state is the default state in the Bluetooth
system. The controller may leave the STANDBY state to scan
for page or inquiry message, or to a page or inquiry itself. In a
Bluetooth system, an inquiry procedure is used in applications
where the destination’s device address is unknown to the
source.
C. Link Establishment- TX Routine
Figure 6 shows the detailed link establishment procedure
used in transmission procedure. In the TX Routine, device acts
as a master. Initially all the Bluetooth devices will be in stand
by state. From this, it moves to inquiry state to find any
Bluetooth devices are available within range. If any bluetooth
device is within range it will respond to inquiry scan state with
its devices access code. After the successful completion of the
inquiry procedure it moves to page state to confirm the link
establishment.

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bluetooth is cut down into several blocks to achieve the
functionality.

Figure 6: Link Establishment-TX routine
In page state, it transmits the slave device access code and
waits for response in page scan state. After the successful
completion of the page procedure it enters into the master
response state to transmit the FHS packet and wait for the
salve device access code in page scan state. Once it is
completed, it enters into the connection state to transmit the
data.
D. Link Establishment- RX Routine
Figure 7 shows the detailed link establishment procedure
in RX routine. In RX routine device act as slave. Initially all
the Bluetooth devices will be in stand by state. From this it
moves to inquiry scan state, to search any Bluetooth devices
are within the range. If any device found then it moves to the
inquiry state to transmit the slave device access code. After the
successful completion of the inquiry procedure it moves to
page state to confirm the link establishment.

Figure 7: Link Establishment-RX routine
In page scan state it receives its own device access code. Once
it is found, it enters to the slave response state to transmit its
own devices access code and again moves to page scan state to
receive the FHS packet. Once it is received the FHS packet, it
adjust the 28-bit counter from the FHS packet. Once it is
adjusted it moves to the page state to transmit the slave device
access code and enters into the connection state to receive the
data.
V.

IP CORE IMPLEMENTATION

Figure 8: IP core-Block Level Diagram
Figure 8 shows the block level representation of IEEE
802.15.1 IP core with serial port (RS-232) profile at the
application layer. The Medium Access Control layer of the

A. Clock Generation
Every Bluetooth unit has an internal system clock which
determines the timing and hopping of the transceiver. The
clock generation module in the MAC layer provides the
appropriate clock signals such as 1µs, 312.5 µs, 625µs.This
module contains a 28-bit register which increments on every
change in 312.5µs clock. Also it provides the appropriate baud
rates clock signal for the RFCOMM.
B. TX_DATA_BUFFER and RX_DATA_BUFFER
The TX_DATA_BUFFER of size 480 bit is used in the
master mode operation. The Bluetooth device takes the data
from the TX_DATA_BUFFER and transmits along with
device access code. The RX_DATA_BUFFER is used during
the salve mode operation. The MAC layer collects the received
data from the PHY and performs several operations and
collects the payload from the received packet and stores into
the RX_DATA_BUFFER.
C. Baseband Control
The baseband control is the heart of the Bluetooth system.
It co-ordinates the transmission and reception operations. This
module creates, maintains and monitors the link. Inside this
module a well designed link establishment state machine is
running and this controls the activities of the Bluetooth system.
D. Access Code Correlator and RX_BUFFER
The RX_BUFFER of size of size 480 bit is used to receive
the data bits from the physical layer. It receives the packet
according to the state that it resides. The RX_BUFFER
receives the packet according to the 1µs clock. The packet
from the RX_BUFFER is given to the access code correlator.
The access code correlator fist checks for the preamble
(1010 or 0101), Device Access Code (DAC) and trailer (0101
or 1010). Once it has successfully received the preamble and
DAC, it checks the header information. In header section it
checks 1/3 FEC on header information, and if that matches
then will decompose the header information. First it checks the
TYPE of packet and AM_ADDR. If the TYPE of the packet is
data, then payload section is decomposed to extract data from
the packet, otherwise appropriate operations are performed
based on the state that it resides.
The payload mainly contains the payload header, data and
Cyclic Redundancy Check (CRC). The payload is 2/3 FEC
encoded. If a data packet is received it checks the payload
header and finds the length of the data field. First it performs
2/3 FEC on received data, if it is success then checks the CRC.
If all the checking is done successfully, it extracts the data from
the data field according to the length in the payload header.
The extracted data is stored in the RX_DATA_BUFFER.

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E. Packet Composer and TX_BUFFER
TX_BUFFER is used to store the data bits, which are
transmitted to the physical layer. It transmits the packet
according to the state that it resides. The TX_BUFFER
transmits the packet according to the 1µs clock. The
TX_BUFFER if filled from the packet composer.
For a data transmission the packet composer first adds the
preamble (1010 or 0101), Device Access Code (DAC), Trailer
(0101 or 1010). Then it adds header and header error correction
to make a total header of 18-bits. Before the transmission the
header information is 1/3 FEC encoded. The payload mainly
consists of payload header, payload body and CRC bits. The
payload header contains the length of payload and Flow
control. The payload body contains the data to be transmitted.
The 16-bit CRC is calculated by using data payload. Total
payload is 2/3 FEC encoded before transmission. Once the
packet is formed then it is loaded into the TX_BUFFER, and
transmitted using 1 µs clock.
F. Link Manager Protocol
The link manager protocol is used for link setup and
control. The bluetooth system uses link manager protocol to
setup, manage, and end RF communication. Link control
involves monitoring the channel status, exchanging control
information and processing link control commands. The link
manager supports two kinds of communication:-Asynchronous
Connection Less (ACL) and Synchronous Connection Oriented
(SCO). The ACL transmission is used for data transmission
and SCO transmission is used for audio/video transmission.
The link manager protocol messages are having higher priority
than data.
G. Logical Link Control and Adaptation Protocol (L2CAP)
L2CAP protocol supports higher level protocol
multiplexing, packet segmentation and reassembly, and
conveys the Quality of Service (QoS) information. The
L2CAP protocol is used to multiplex multiple logical channels
on a single physical link. To identify which logical channel the
packet belongs to, a connection identifier (CID) is included
with each L2CAP packet. L2CAP reserves at least one logical
channel as a control channel to setup and manage the logical
connections.

Figure 9: Internal diagram-Frequency hopping module
Figure 9 represents the Frequency hopping module for a 79
hop system. The primary function of the module is to generate
a pseudo random hopping sequence. The output from the
frequency hopping module is given to the physical layer.
I.

Radio Frequency COMMunication (RFCOMM)

RFCOMM is a simple transport protocol, which provides
emulation of RS232 serial ports over the L2CAP protocol. The
RFCOMM protocol supports up to 60 simultaneous
connections between two BT devices. Serial port transmits and
receives data lines are connected to a UART. The function of
UART is to convert serial data to parallel data and vice versa.
Figure 10 shows the internal diagram of UART. It mainly
consists of Transmitter, Receiver, Baud rate generator and a
Control mechanism. The Baud rate generator is used to
generate different clock signals according to the baud rate
register. The UART transmitter accepts the parallel data from
the DATA_IN pin and transmits serially through TXD pin.
The UART receiver receives the serial data through RXD pin
and converts to parallel data which is available in
DATA_OUT pin. A control mechanism is used for controlling
the transmission and reception. The module is enabled only
when a high pulse is applied to ENABLE pin.

H. Frequency Hopping Module
The Frequency hopping is a method of transmitting radio
signals by rapidly switching a carrier among many frequency
communication channels using a pseudo random number
known to both transmitter and receiver. The inputs to the
frequency hopping module are from based band control
module.
Figure 10: Internal diagram-UART

425

VI.

SIMULATION RESULTS

The Bluetooth MAC units with RFCOMM profile at the
upper layer are simulated using MODELSIM SE 6.4. Figure
11, 12, 13 shows the simulation result of Frequency hopping
module, TX routine and a RX routine.

Figure 15: Internal Hardware-Frequency Hopping Module

Figure 11: Simulation-Frequency Hopping

Figure 16: Internal Hardware –connection Establishment unit
VII. CONCLUSION
Figure 12: Simulation-TX Routine

The main objective of this work is to design and develop a
System-on-Chip module with a Bluetooth IP core customized
for Bio-Medical equipment, which is successfully
implemented. The SoC is ported in an ALTERA STRATIX II
EP2S15672C3 FPGA for testing and is functioning well. The
logic utilization is shown in Table1. The minimum data rate of
the system is 108.8 kbps. As a Bluetooth SPP device this IP
core can be also used for other embedded applications.

Figure 13: Simulation-RX Routine

Table 1: Device Utilization
REFERENCES
[1]
[2]

[3]

[4]
[5]

Figure 14: RTL View from Altera Quartus II

Bluetooth, “Specification of Bluetooth System”. November
2003, Version 1.2.
Shu Lin, Daniel J. Costello, “Error Control Coding:
Fundamentals Applications” ”, ISBN – 0-13-283796-X, 198 K.
Elissa,
Hall, T.S., Hamblen, J.O., "System-on-a-programmable-chip
development platforms in the classroom", Education, IEEE
Transactions on, On page(s): 502 - 507, Volume: 47 Issue: 4,
Nov. 2004.
S.AL-Ashari,” System Verification from the Ground Up”
Integrated Systems Design, 1999
Charles H. Roth, Jr. Digital System Design by using VHDL,
PWS Publishing Company, 1998.

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Design and Implementation of Bluetooth MAC core with RFCOMM on FPGA

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