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Bluetooth® Voice Transmission

This model shows part of a Bluetooth® v1.0 system. Bluetooth is a short-range radio link technology that operates in the 2.4 GHz Industrial, Scientific, and Medical (ISM) band. The example modulates the signal using Gaussian frequency shift keying (GFSK) over a radio channel with maximum capacity of 1 Mbps.

The example uses frequency hopping over a 79 MHz frequency range to avoid interference with other devices transmitting in the band. In this scheme, the sender divides transmission time into 625-microsecond slots, and uses a new hop frequency for each slot. Although the data rate is only 1 Mbps, a much larger bandwidth of 79 MHz is required to simulate the frequency hopping effects.

Structure of the Example

The example contains the following elements:

  • Master transmitter

  • Radio channel

  • IEEE® 802.11b interferer

  • Slave receiver

  • Bit error rate (BER) display

  • Scopes

The transmitter subsystem performs speech coding, buffering, framing, header error control (HEC), forward error correction (FEC), GFSK modulation, and frequency hopping. Channel effects modeled 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 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.

The example makes extensive use of frame-based processing, which can propagate large frames of samples at each execution step, allowing for much faster simulation of digital systems. The double connector lines between the blocks indicate frame-based signals.

The example also uses subsystems to organize groups of blocks, and it uses Goto/From block pairs and colored regions to make the block diagram visually neater.

Parameters in the Example

You can open the Model Parameters dialog box by double-clicking the block labeled "Model Parameters". In the dialog box, you can specify:

  • The high-quality voice (HV) packet type in the HV Packet type field.

  • The initial slot pair type in the Initial Slot Pair for HV3 field.

Results and Displays

To examine the performance of the example, double-click the icons to open error rate display and scopes.

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 Scopes icon opens a display of the spectrum of the transmitted Bluetooth signal (narrowband) 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.

Selected Bibliography

[1] http://www.bluetooth.com

[2] http://en.wikipedia.org/wiki/Bluetooth#Bluetooth_v1.0_and_v1.0B

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