Behzad Momahed Heravi

Pedestrian Direction of Movement Determination Using Smartphone

These days smart phones have changed the concept of mobile platform. Due to rapid growth in affordability, increased sensory and computational power has opened the ways for some interesting applications like activity recognition, gaming, navigation/tracking, augmented reality etc. In all these applications orientation of mobile phone is very important, once we know the correct orientation of the device, it becomes easy to develop such applications. Orientation can be determined by sensor fusion of accelerometer and magnetometer but it provides good accuracy as long as device is stationary or not moving linearly and also it suffers from surrounding magnetic interference. Orientation estimation systems often use gyroscope to increase reliability and accuracy. Although gyroscopes provide a quick response to change in angles and do not have problems like interference, they suffer from bias and integration errors which introduce drift in signal. In this paper an efficient and less complicated approach is utilized which minimizes the drift and noise in output orientation. In most of smart phone navigation applications these days, it is assumed that mobile is at fixed position like holding in hand facing forward, in trouser/jacket pocket or attached to waist. But if we assume that mobile position is changing arbitrary then situation becomes complicated. The goal of this work is to find accurately the direction of movement of a pedestrian while holding mobile in any position. In this work an accelerometer based approach is presented for pedestrian direction of movement estimation.

Improving transmission reliability of low-power medium access control protocols using average diversity combining

Embedded computer systems equipped with wireless communication transceivers are nowadays used in a vast number of application scenarios. Energy consumption is important in many of these scenarios, as systems are battery operated and long maintenance-free operation is required. To achieve this goal, embedded systems employ low-power communication transceivers and protocols. However, currently used protocols cannot operate efficiently when communication channels are highly erroneous. In this study, we show how average diversity combining (ADC) can be used in state-of-the-art low-power communication protocols. This novel approach improves transmission reliability and in consequence energy consumption and transmission latency in the presence of erroneous channels. Using a testbed, we show that highly erroneous channels are indeed a common occurrence in situations, where low-power systems are used and we demonstrate that ADC improves low-power communication dramatically.

Design, implementation and applications of low-complexity LDPC codes

Structured LDPC codes enable low-complexity decoding as well as efficient implementation of encoder reducing the complexity down to the order of the number of parity-check bits. Construction of structured LDPC codes is based on combinatorial approaches such as balanced-incomplete block-design (BIBD) and finite fields to design quasi-cyclic LDPC (QC-LDPC) codes. Well designed QC-LDPC codes can perform as well as randomly constructed LDPC codes with iterative decoding based on belief propagation in terms of bit-error probability. It has been shown that QC-LDPC codes can achieve lower error floor than randomly constructed LDPC codes. Within this work, the design of quasi-cyclic LDPC codes for a range of practical applications is discussed which includes construction of variable-rate large-block-length LDPC codes for DVB-S2 and DVB-T2 applications and adaptive short-block-length LDPC codes for HF applications. Moreover, efficient implementation of QC-LDPC decoder/encoder for FPGA devices which reduces memory requirements is presented.

Reliability comparison of transmit/receive diversity and error control coding in low-power medium access control protocols

Low-power medium access control (MAC) protocols used for communication of energy constraint wireless embedded devices do not cope well with situations where transmission channels are highly erroneous. Existing MAC protocols discard corrupted messages which lead to costly retransmissions. To improve transmission performance, it is possible to include an error correction scheme and transmit/receive diversity. It is possible to add redundant information to transmitted packets in order to recover data from corrupted packets. It is also possible to make use of transmit/receive diversity via multiple antennas to improve error resiliency of transmissions. Both schemes may be used in conjunction to further improve the performance. In this study, the authors show how an error correction scheme and transmit/receive diversity can be integrated in low-power MAC protocols. Furthermore, the authors investigate the achievable performance gains of both methods. This is important as both methods have associated costs (processing requirements; additional antennas and power) and for a given communication situation it must be decided which methods should be employed. The authors’ results show that, in many practical situations, error control coding outperforms transmission diversity; however, if very high reliability is required, it is useful to employ both schemes together.

Switchable-rate quasi-cyclic low-density parity-check codes for internet protocol over high-frequency systems

A switchable-rate quasi-cyclic low-density parity-check (QC-LDPC) coding scheme has been proposed for integration within the legacy and next-generation high-frequency internet protocol (HF-IP) systems. The novelty in this work is based upon using a class of switchable-rate short-block-length ( lt;;1500 bits) QC-LDPC codes for the HF fading channel modelled by the ITU-R F.1487 for all latitudes and conditions. The QC-LDPC codes are constructed using a switchable-rate approach based on finite fields which provides the ability to switch among three rates to combat varying channel conditions using a single encoder/decoder structure. The proposed structure enables low-complexity implementation of the low-density parity-check encoder/decoder for use within the existing data link (DL) layer of the standardisation agreement (STANAG) 5066 profile. The performance of the proposed scheme has been evaluated comprehensively for all the HF channel conditions and latitudes. A comparison between the proposed and the current coding scheme in HF-IP systems (based on convolutional coding) shows an improvement in error-rate performance.