Bluetooth demodulation algorithms and their performance

In our Software Defined Radio SDR project we aim at combining two different types of standards, Bluetooth and HiperLAN/2 on one common hardware platform. Goal of our project is to generate knowledge about designing the front end of an SDR system (from the antenna signal to the channel bit stream) where especially an approach from both analog and digital perspective is essential. Bluetooth uses Gaussian Frequency Shift Keying (GFSK) as modulation technique. As QAM and GFSK signal can be demodulated by using the same type of algorithms, the outer receiver of HiperLAN/2 can be used as a Bluetooth demodulator. So, whereas most commercial Bluetooth chips are low cost and inflexible, in our project flexibility and re-use of hardware is important. It is for that reason that a part of the channel selection and demodulation will be done in the digital domain. The choice of the demodulation algorithm determines the channel selection requirements (better demodulation algorithms require less SNR). This work analyzes the performance of several Bluetooth (GFSK) demodulation and decision algorithms using single bit decision. A simulation model was built to measure the performance of these algorithms. In our simulation model, low-IF or zero-IF Bluetooth signals are sampled with 80 MHz to get a realistic setting. The synchronization word in the Bluetooth packet is used for bit synchronization. To obtain a BER (Bit Error Rate) of 0.1%, specified by the Bluetooth standard, the best combination of demodulation and decision algorithm requires an SNR of about 15 dB. Ongoing research focusses on several subjects: multibit decision, advanced demodulation algorithms (such as (adaptive) decision feedback equalizers) and bit-synchronization algorithms. keywords: software-defined radio (SDR), Bluetooth, GFSK, demodulator.