Suvit Nakpeerayuth

Applying the Tree Algorithm with Prioritization for Body Area Networks

Wireless Body Area Networks (WBANs) are allowed to be applied in medical and non-medical fields. In this paper we present a prioritization mechanism for emergency case in both medical and non-medical WBANs applications. The main idea of this mechanism is to allow highest priority nodes or nodes of emergency to get the channel immediately at the expense of low priority nodes. This mechanism postpones the reservation of low priority nodes until the all high priority nodes are resolved. We apply a collision resolution protocol, tree algorithm, to achieve our goal. It can be observed from the simulation results that tree algorithm allows high priority nodes to get the channel first without contending with the low priority ones.

APP demodulator for turbo coded multiple symbol differential detection under correlated Rayleigh fading channels

In this paper, multiple symbol differential detection (MSDD) with iterative decoding (turbo decoding) of code rate 1/2 is developed to work under correlated slow and fast Rayleigh fading channels by using an APP demodulator with two different approaches. The first approach is to increase the number of the trellis states of differential encoders. In the second approach, the VA is modified and used to find a QPSK symbol sequence associated with each state for the APP demodulator.

APP demodulator for turbo coded differential unitary space-time modulation

In this paper, an iterative multiple symbol differential detection (MSDD) for turbo coded differential unitary space-time modulation (DUSTM) is developed by using an a posteriori probability (APP) demodulator under correlated slow and fast Rayleigh flat fading channels. The metric function necessary for the detection operates based on linear prediction. Two approaches are presented to utilize the metric. In the first approach, the BCJR algorithm is modified to deal with the increased-state trellis of the differential modulation. In the second approach, the VA is modified to find the symbol sequences associated with the survivors for the BCJR algorithm.

Turbo coded multiple symbol differential detection for correlated Rayleigh fading channel

In this paper, the multiple symbol differential detection (MSDD) with iterative decoding (turbo decoding) of code rate 1/2 is modified to work under both correlated slow and correlated fast Rayleigh fading channels.

Iterative multiple symbol differential detection for turbo coded differential unitary space-time modulation

In this paper, an iterative multiple symbol differential detection for turbo coded differential unitary space-time modulation using a posteriori probability (APP) demodulator is investigated. Two approaches of different complexity based on linear prediction are presented to utilize the temporal correlation of fading for the APP demodulator. The first approach intends to take account of all possible previous symbols for linear prediction, thus requiring an increase of the number of trellis states of the APP demodulator. In contrast, the second approach applies Viterbi algorithm to assist the APP demodulator in estimating the previous symbols, hence allowing much reduced decoding complexity. These two approaches are found to provide a trade-off between performance and complexity. It is shown through simulation that both approaches can offer significant BER performance improvement over the conventional differential detection under both correlated slow and fast Rayleigh flat-fading channels. In addition, when comparing the first approach to a modified bit-interleaved turbo coded differential space-time modulation counterpart of comparable decoding complexity, the proposed decoding structure can offer performance gain over 3 dB at BER of 10−5.

A Greedy Search Based Method with Optimized Lower Bound for QC-LDPC Codes

Autonomous decentralized system is need of the dynamically varying society. Various autonomous decentralized systems architecture proposed and deployed, use of IEEE 802.11n/ac (Wi-Fi) and IEEE 802.16e (Wi-max) standards for surveillance purposes in different geographical region. These standards use LDPC codes as a channel code having better error correcting performance. This article deals with a construction of less computational complexity method for constructing exponent matrix (3, K) having girth 8, 10, and 12 of quasi-cyclic low-density parity-check (QC-LDPC) codes. In this method, we first generate a base matrix and then the same matrix is further used for expanding till desired size of the exponent matrix. The construction of code deals with the generation of base matrix by a simple algorithm for girth 8, 10, and 12. Our method is flexible for any block-column length K. Finally, a new method is given with less computational complexity with optimized CPM size.

Tree-based anti-collision algorithm with single error bit tracking for RFID systems

In this paper, we focus on the problem of collision in tags identification in RFID systems. We propose tree algorithm with single error bit tracking that utilizes Manchester coding to know the position of collision bit among the ID of the tags. The reader broadcasts the Query bit that is updated in every collision. The update is done according to the position of the collision bit that allows to reduce the idle slots. Based on the comparison results, the proposed algorithm provides improvements to the existing tree algorithms.

A Frame Size Adjustment with Sub-Frame Observation for Dynamic Framed Slotted Aloha

In this paper, a simple frame size adjustment of dynamic framed slotted Aloha for tag identification in RFID networks is proposed. In dynamic framed slotted Aloha, the reader is required to announce the frame size for every frame. To achieve maximum system efficiency, it is essential to set the frame size according to the number unidentified tags appropriately. The proposed approach utilizes the information from a portion of the frame to adjust the size of the next frame. Simulation results show that the smaller number of observed slots results in faster frame adjustment and higher throughput. Compared to the existing anti-collision algorithms, the proposed approach achieves higher throughput and higher identification rate.

Bayesian Method of Slotted Aloha Based Anti-Collision Protocol for RFID Systems

In multiple access systems, knowing the number of tags is crucial for the performance. The problem of multiple access in RFID system has one different assumption from general communication systems in that there is no new user (tag) entering during the conflict resolution interval. This can significantly reduce the uncertainty in number of tags estimation. This paper uses Bayesian method to update the posterior probability distribution of number of users after each slot in Aloha protocol for RFID system. The posterior probability distribution can adapt quickly to concentrate around the true value in few slots. The tag access probability for each slot can also be derived from this posterior distribution to maximize the success probability. The simulation result shows that the system can approach the theoretical limit of the Aloha system with known number of tags.

A study of contention resolution algorithms with different types of feedback

This paper presents a frame based contention resolution algorithm that can be systematically applied for random access protocols under different assumption of feedback types which include binary, ternary and known multiplicity feedbacks. We introduce two new algorithms that can effectively utilize feedback information to resolve packet collisions. Based on extensive simulation results, the achievable delay performance is shown to be highly dependent upon the amount of feedback information available to each user and how the feedback information is used in contention resolution. Multiplicity feedback in particular where the information about number of accessing packets is available, significant improvement in average delay can be achieved compared to binary and ternary feedbacks.