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RESEARCH WORK MATLAB and Simulink Project
APRIL
2018
Bluetooth Voice Transmission
Bright Tagar Oyinkuro Atani Kelvin Akinnagbe
Department of Electrical/Electronic EngineeringDepartment of Electrical/Electronic EngineeringDepartment of Electrical/Electronic Engineering
University of Port Harcourt, Nigeria University of Port Harcourt, Nigeria University of Port Harcourt, Nigeria
Abstract: This paper is based on Bluetooth Voice Transmission. Bluetooth is a method for data communication that uses short-range radio links to replace cables between computers and their connected units. It is a widely used technology for communication between two devices. It provides a way to connect and exchange information between devices such as mobile phones, laptops, PCs, printers, digital cameras, and video game consoles over a secure, globally unlicensed short-range radio frequency. Bluetooth technology can transmit not only data but also voice signals between wireless nodes. The aim of this work is to define the features of Bluetooth wireless communication technology and how it can be used for voice communication for a small region. There are many unlicensed Industrial, Scientific, and Medical (ISM) band radio inference source such as microwave oven, 802.11b and Home RF devices which would drastically influence and degrade the performance of the Bluetooth communication, especially voice communication. This paper simulates Bluetooth voice transmission system using Matlab/Simulink.

Keywords- Bluetooth, Transmission, Communication, Gaussian Frequency Shift Keying (GFSK), Additive White Gaussian Noise (AWGN), Bit Error Rate (BER), Matlab and Simulink, Radio Frequency (RF).

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Introduction
Bluetooth is an open standard for wireless connectivity with supporters mostly from the PC and cell phone industries. New technologies and devices have provided easier and fast communication way for exchanging ideas and thoughts. In recent years, we have seen that the Bluetooth technology 6 becomes usable in diverse applications, in addition to being a standard feature in cell-phone devices. Due to its low costs, it has been used in most of the short distance communication systems, and there is a significant reason for that: the Bluetooth technology has free wireless bandwidth for short distance connection within 2.4 GHz frequencies. The growth of wireless networks has changed our daily life into such a situation that we can’t think of a life without devices like computers, mobile phones like that. The wireless networks interconnecting these devices are adding up more and more nodes into it each minute. These devices communicate with each other using many popular standards developed by IEEE and such other groups. is a short-range wireless networking/radio technology designed to replace cables for interconnecting devices such as computers, mobile phones, printers, keyboards, and mice, its perceived potential has evolved into far more sophisticated usage models. Bluetooth devices can form piconets of up to seven slaves and one master, enabling discovery of services and subsequent implementation of many varied usage models. Bluetooth is a low cost, low power, short Range radio technology intended to transfer data between cell phones. Bluetooth is also used as a medium for voice communication between cell phones 5. Bluetooth standard gives specifications for voice and data communication over a radio channel with a maximum capacity of 1Mbps. It is designed to be low-cost and low form-factor, so much design work is required to optimize resource usage. Bluetooth, however, is a radio frequency (RF) technology utilizing the unlicensed 2.5 GHz industrial, scientific, and medical (ISM) band. It shares this channel with devices used for other applications including cordless phones, garage door openers, and outside broadcasting equipment.

As Bluetooth offers the ability to provide seamless voice and data connections to virtually all sorts of personal devices the human imagination is the only limit to application options. Bluetooth standard gives specifications for voice and data communication over a radio channel with a maximum capacity of 1Mbps. Beyond un-tethering devices by replacing the cables, this technology provides a universal bridge to existing data networks, allows users to form a small private adhoc wireless network outside of fixed network infrastructures, enables users to connect to a wide range of computing and telecommunications devices easily and simply, without the need to buy, carry, or connect cables. The Bluetooth technology allows users to think about what they are working on, rather than how to make their technology work.

Brief History
The history of Bluetooth Wireless Technology dates all the way back to the 14th Century, drops by the 1940s, and really gets going in the 1990s. The birth and commercialization of the ubiquitous short-range wireless technology was more protracted than you might think. The name ‘Bluetooth’ comes from the Middle Ages, and is named after a Danish king, King Harald Blatand, whose nickname was ‘Bluetooth’, supposedly because he liked blueberries so much they stained his teeth blue was known for uniting warring factions in what is now Denmark, Norway and Sweden. Uniting devices from different manufacturers and with different purposes, like computers from Apple and mice from Microsoft, is what Bluetooth technology is all about – all at a low cost, with low power consumption and a secure connection every time.

However, the frequency hopping spread spectrum (FHSS) technique upon which Bluetooth wireless technology bases its communication protocol is accredited to a patent issued in August 1942. Entitled “Secret Communication System,” the patent details a FHSS technique for a radio-controlled torpedo. Because the radio signals hopped across the radio spectrum, an enemy couldn’t jam the signal.

Today, Bluetooth wireless technology is incorporated into billions of chips in thousands of applications, and Bluetooth low energy extends its usefulness to a huge new sector of devices powered by coin cell batteries. After nearly two decades of development, cumulative Bluetooth product shipments have passed 2.5 billion, membership has reached 19,000 and the technology is maturing into a product that has a very bright future indeed.

Objectives
To analyze how Continuous Variable Slope Decoding (CVSD) & 64kbps Logarithmic Pulse Code Modulation (log PCM) were used in speech coding.

To simulate the modulation-demodulation process of voice in a short-range wireless network using Gaussian Frequency Shift Keying (GFSK).

To show how voice transmission occurs via the Bluetooth technology.

To be able to design the circuitry using MATLAB/Simulink.

Relate Works
There has been a great deal of related works, which has focused on the performance of the Bluetooth receivers and transmitters and its use for Voice Transmission. They detail ways to improve it, various methods on how to go about the setup.
For example 4 Lars Wernli and Riccardo Semadeni outline steps in their research for developing a reduced version of the DSR protocol for Bluetooth. The work also shows considerable delays when pre-existing protocols are just sent to Bluetooth without regard to its special properties.
In 1 Frank Kragl, Stefan Ribhegge, Stefan Schlott and Michael Weber also feature and analyze problems that Bluetooth face when transmitting audio data in their work titled “Bluetooth based Ad-hoc Networks for Voice Transmission”. Their work summarizes that the success of Bluetooth based Voice Transmission is dependent on the purpose intended, the environment and the distance of transmission.
In 3 Ravikiran R. Deshmukh work on Bluetooth Voice Transmission innovates by suggesting a combination of LAN and Bluetooth facilities. A full duplex form of communication is available in his findings.
The paper in 8 presents an improvement on the GFSK modulation method by using maximum likelihood sequence estimation (MLSE), based on a linearized model of the modulation. Furthermore, the authors were dedicated to evolving a scheme that had MLSE-oriented detection using the Viterbi equalizer considering a GFSK inherent inter symbol interference (ISI), with the channel gain sensitivity of 0 – 7 dB. In 2 Manisha Dawra, Sheelu Sharma and Anita Chauhan in their publication titled “Voice over Bluetooth: An Overview” detail an algorithm that can be used by the Bluetooth for connectivity purpose.

Design Methodology
In this paper, the design of the system was done using MATLAB and Simulink Integrated Development Environment (IDE). The Simulink model of the simple Bluetooth data link consists of error correction, frequency hopping and the 100MHz channel.
Frequency hopping was included to avoid interference between two or more devices transmission in the band.
The pulse generator was at 1MHz data bit rate.
The modulation method employed for the digital communication (Bluetooth) is the Gaussian Frequency Shift Keying (GFSK).

 In this scheme, the sender divides transmission time into 625-microsecond slots and uses a new hop frequency for each slot. We will be looking at Bluetooth Voice Transmission at a much larger bandwidth of 79MHz. A simulation model, using Simulink, has been created to simulate the Bluetooth voice transmission system with the integrated filters.

Matlab/Simulink Model
The Bluetooth voice transmission system has been created on Matlab/Simulink environments 9; the demo version has been modified for the purpose of our optimization. The high-level Simulink model is shown in the Figure below simulates Bluetooth Voice Transmission system. For Bluetooth connection to be established between devices, one must be set as a master and the other as a slave. One of them should be set as master and the other as the slave. Other than two Bluetooth devices, we also have an 802.11b packet generating block as an interference source, error reading meters and instrumentation.

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Figure 1: Simulink Model for Voice Transmission System
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Transmitter Subsystem
The transmitter subsystem performs speech coding, buffering, framing, header error control (HEC), forward error correction (FEC), GFSK modulation, and frequency hopping. Channel effects modelled include thermal noise, path loss, and interference. The Free Space Path Loss block, from the RF Impairments library, models path loss. The IEEE 802.11b interferer is a masked subsystem that opens up a mask dialog for user input on double-clicks. Mean packet rate, packet length, power, and frequency location in the ISM band can be specified
Figure 2: Master Transmitter Schematics
in the dialog. The Slave Receiver recovers speech from the transmitted signal, performing all the complementary operations that the transmitter does, but in reverse order 9.

Results and Discussion
Using the above model, we performed a series of tests to evaluate the transmission of voice over Bluetooth. The error rate display shows three types of error rates:
Raw bit error rate
Residual bit error rate
Frame error rate (FER)
The raw bit error rate displays the inconsistencies between the bits in the transmitted signal and the received signal. Frame error rate refers to the ratio of frame failure to the total number of frames. Frame failure, caused by noise and interference, is determined if the HEC fails to match the header info or if less than 57 bits are correct in the access code. If the frame fails, this is captured by a zero-valued Frame OK signal, which is used in the FER calculation as well as to exclude bad frames from the residual BER calculation.

The Instrumentation brings up the spectrum of the transmitted Bluetooth signal (narrow-band) with IEEE 802.11b interference. The timing diagram for the Bluetooth and interferer slots is also available. A dynamic plot of packet frequency versus time is shown by the Spectrogram plot. The thin lines are the Bluetooth transmissions, while the larger, more colorful blocks are the interferer slots. Most of the time, due to frequency hopping, there is not much overlap of these slots. In a few cases, the signals do collide, as the Spectrogram plot clearly shows.

Spectrum Plot
The figure below shows the dynamic plot of the frequency of the transmitted signal against time which is another indicator of the performance of the Bluetooth signal. Bluetooth utilizes frequency-hopping spread spectrum technology to avoid interference problems. The ISM 2.4 GHz band is 2400 to 2483.5 MHz, and Bluetooth uses 79 radio frequency channels in this band, starting at 2402 MHz and continuing every 1MHz. It is these frequency channels that Bluetooth technology is “hopping” over. The signal switches carrier channels rapidly, at a rate of 1600 hops per second, over a determined pattern of channels. There are six defined types of hopping sequences. Information is conveyed by modulating the carrier channel frequency, using one of several modulation schemes. Gaussian frequency-shift keying (GFSK) modulation was initially the only type available, but recently other varieties have been enabled. GFSK is simply a type of frequency-shift keying (FSK), which is a modulation scheme where the bits of the transferred information correspond to discrete frequency changes in the carrier signal. The carrier signal is whichever band the device happens to be using at that moment and the modified signal is broadcast out. 7
Figure 3: display of the spectrum of the transmitted Bluetooth signal (narrowband)
802.11b effect on voice quality
The timing diagram gives a plot of the amplitude of the three signals (the Bluetooth transmitted signal, the 802.11b interferer signal and the time slot) to time for the transmitted signal.

Figure 4: Timing Diagram of the Channel
Spectrogram of the Channel
When the simulation runs with the instrumentation block turned on, the timing diagram in Figure 4 shows when the Bluetooth transmitter is operational. The plot in Figure 3, displays the power spectrum of each channel slot, showing the current Bluetooth hop frequency. These two characteristics are viewed together on the spectrogram scope in Figure 5 to easily track hop frequency versus time.

Figure 5: Spectrogram of the Channel
Our observations from the graphs above: The model makes extensive use of frame-based processing in Simulink, which can propagate large frames of samples at each execution step allowing for much faster simulation of digital systems. For example, a 10 tap FIR filter can process a 1MHz signal in real-time on an 800MHz Pentium. In this particular model, a top sample rate of 100MHz is used. Frame based processing also allows for easy modelling of block-based operations like forward error correction and cyclic redundancy checks (CRC), which operate on finite length frames of data. The Bluetooth TX has better frequency of propagation as shown in the second graph. The amplitude of the band spectrum (-100) at 0MHZ in the first graph will be appreciated by varying the parameters in the master transmitter or model parameters. The frequency spectra -100 and +100MHz may be compared with the existing standard if it is within the range then your model can be related to it as good comparison. The thin lines are the Bluetooth transmissions, while the larger, more colourful blocks are the interferer slots. Most of the time, due to frequency hopping, there is not much overlap of these slots. In a few cases, the signals do collide, as the Spectrogram plot clearly shows.

Conclusion
In the future, Bluetooth is likely to be standard in tens of millions of mobile phones, PCs, laptops, and a whole range of other electronic devices. As a result, the market is going to demand new innovative applications, value-added services, end-to-end solutions, and much more. Our analysis shows that situation gets worse as more and more devices come into play. Such a situation calls for the urgency of congestion free network. Techniques such as SCORT are a big leap in the future for such networks. By using SCORT packets we can minimize the effect of interference. Hopefully in the future wireless industry will mature in such a way that smooth data and voice transmission will be achieved and finally a solution for Coexistence without compromise can be realized.

REFERENCES
1 Frank Kragl, Stefan Ribhegge, Stefan Schlott, Michael Weber, “Bluetooth based Ad-hoc Networks for Voice Transmission” Proceedings of the 36th Hawaii International Conference on system sciences. 2003
2 Manisha Dawra, Sheelu Sharma, Anita Chauhan, “Voice Over Bluetooth: An Overview” IJSCT Volume 3. 2012
3 Ravikiran R. Deshmukh, “Voice Transmission Through Bluetooth” INTERNATIONAL JOURNAL OF INNOVATIVE RESEARCH IN ELECTRICAL, ELECTRONICS, INSTRUMENTATION AND CONTROL ENGINEERING Vol. 2, Issue 5. 2014.
4 L. Wernli, R. Semadeni: Bluetooth Unleashed-Wireless Networked one Grenzen,
http://www.tik.ee.ethz.ch/beutel/projects/sada/sa Semadeni Wernli.pdf 2001
5 J.C. Haartesen, “The Bluetooth Radio System”, IEEE Journal, Year: 2012, Volume: 1 Page: 911 – 914.

6 B. S. I. Group (2014) Bluetooth SIG. Bluetooth SIG. https://www.bluetooth.org/en-us7 R. K. Morrow, Bluetooth Operation and Use, (McGraw-Hill, 2002).

8 Lampe, L., Schober, R. and Jain, M. (2005) Noncoherent Sequence Detection Receiver for Bluetooth Systems. Selected Areas in Communications, IEEE Journal, 23, 1718-1727.
http://dx.doi.org/10.1109/JSAC.2005.8537919 Mathworks, Inc. (2014) Bluetooth® Voice Transmission. http://www.mathworks.com/help/comm/examples/bluetooth-voice-transmission.html

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