A high-performance, efficient, and reliable receiver for bluetooth signals

Abstract

High-performance Receiver.

In order to choose a suitable receiver, we first consider the use of high-performance receiver algorithms such as the Viterbi and the matched filter bank (MFB) receiver, both of which exhibit several dB gain over alternative schemes. However, the MFB receiver is more favourable because of the stringent accuracy requirements of the Viterbi receiver on parameters such as carrier frequency and modulation index, both of which have considerable tolerances in Bluetooth systems.

Efficient Receiver

However, the MFB receiver requires several matched filters of considerable length, and is therefore prohibitive to most applications in terms of computational cost. Hence, through the formulation of a novel recursive realisation of the MFB, which employs a much smaller filter bank but processes.the results over several stages, we decrease its complexity by two orders of magnitude without any sacrifice in performance, and thereby make the MFB receiver a more practical option.

Reliable Receiver

Efforts were made to combat irregularities with the received signal such as multipath propagation, carrier frequency and modulation index offsets, which would otherwise undermine the effectiveness of the efficient MFB receiver, and which can be expected in Bluetooth networks.

To deal with dispersive channels we require an algorithm that is resilient to carrier frequency offsets that may exist, and would not yet have been corrected for. Additionally, because of the short bursty nature of Bluetooth transmissions, and the requirement for equalisation to take place before parameter synchronisation algorithms further along the signal processing chain can converge, it is desirable that the equalisation algorithm should converge relatively quickly. Hence, for this purpose we adopt the normalised sliding window constant modulus algorithm (NSWCMA). However, to cater for the correlation between samples of a Bluetooth signal that could make the procedure unstable, we apply and compare a new high-pass signal covariance matrix regularisation, with a diagonal loading scheme.

For parameter synchronisation, a new algorithm for carrier frequency offset correction that is based on stochastic gradient techniques, and appropriate for Bluetooth, is developed. We also show the intermediate filter outputs inherent in the efficient realisation of the MFB may be used to detect carrier frequency and modulation index offsets, which can then be corrected for by recomputing the coefficients of a relatively small intermediate filter bank.

The results of this work could make it possible to achieve the maximum bit error ratio specified for Bluetooth at a much lower signal to noise ratio than is typical, in harsh conditions, and at a much lower associated cost in complexity than would be expected. It would therefore make it possible to increase the range of a Bluetooth link, and reduce the number of requests for packets to be retransmitted, thus increasing throughput.

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