Der-Feng Tseng

An Anti-Collision Algorithm in RFID Systems Based on Interference Cancellation and Tag Set Partitioning

It is well known that anti-collision protocol plays an essential role in overall tag read time in radio frequency identification (RFID) systems due to the obstruction caused by tag-collision. With an aim at speeding up tag identification process, we propose an anti-collision algorithm, spread partial-Q slot count (SPSQ) algorithm, based on a slotted ALOHA code division multiple access (CDMA) technique along with tag set partitioning. A new packet structure is introduced preceded by a description of the mechanism of partition-wise identification process. In fact, according to received power levels tags are partitioned into a certain number of groups. In the partition-wise identification process tags belonging to two subsets are regrouped as a partition with a guarantee of uniformly largest received power-level difference in a tag set so as to be interrogated by the reader simultaneously. The identification process for each partition is then operated sequentially. Indeed, tag set partitioning in conjunction with spread spectrum techniques could enable a simple multi-tag access detection scheme and improve system throughput as well. Simulations demonstrated that SPSC algorithm outperforms some existing anti-collision algorithms in terms of throughput.

Anti-collision algorithm with the aid of interference cancellation and tag set partitioning in radio-frequency identification systems

It is well known that an anti-collision protocol plays an essential role in the overall tag read time in radio-frequency identification systems because of the obstruction caused by tag collision. With an aim at speeding up the tag identification process, the authors propose an anti-collision algorithm, the spread partial-Q slot count (SPSC) algorithm, based on a slotted ALOHA code division multiple access technique along with tag set partitioning. A new packet structure is introduced preceded by a description of the mechanism of partition-wise identification process. In fact, according to received power levels, tags are partitioned into a certain number of groups. In the partition-wise identification process, tags belonging to two subsets are regrouped as a partition with a guarantee of having a uniformly largest received power level difference in a tag set so as to be interrogated by the reader simultaneously. The identification process for each partition is then operated sequentially. Indeed, tag set partitioning in conjunction with spread spectrum techniques could enable a simple multi-tag access detection scheme and improve system throughput as well. Simulations demonstrated that the SPSC algorithm outperforms some existing anti-collision algorithms in terms of throughput.

Distributed space-time block codes with embedded adaptive AAF/DAF elements and opportunistic listening for multihop power line communication networks

Summary We consider the multihop power line communication (PLC) networks of one source, two repeaters, and one destination. In the previous scheme, when the repeaters receive the retransmission data from the source, they use the traditional distributed space-time block code (DSTBC) with all decode-and-forward (DAF) elements to transmit the data, and they do not consider the incorrect decoding. The original contribution is that we propose a novel DSTBC scheme with embedded adaptive DAF/amplify-and-forward (AAF) elements for data retransmission in multihop PLC networks with existing opportunistic listening (OL) protocols. The new scheme has two types (instead of only one type as in the previous scheme), and, in the second type, the coding matrix for data retransmission can use either all DAF elements or hybrid AAF/DAF elements depending on the correctness of OL results. The advantage is to avoid a loss of diversity because of incorrectly received data at the relays. The effectiveness of the proposed scheme is shown in the simulation results. For the impulsive noise parameter δ = 0.8 and worst case background noise (narrowband interference and colored noise) at bit error rate 10−3, our proposed system has 1 dB gain over the previous scheme with the traditional DSTBC with all DAF elements. Copyright

A realization of diversity waveform sets for delay-Doppler imaging

A realization of transmitting multiple radar waveforms and coherently combining multiple ambiguity functions is proposed. We propose to use the concept of synchronous code-division multiple access (CDMA) to do so. The spreading sequences are chosen to be orthogonal such as Walsh-Hadamard sequences. Multiple radar waveforms are synchronously transmitted by using orthogonal spreading sequences. Since they are transmitted at the same time and the same frequency, the respective received signals are affected by the same time delay and Doppler frequency shift. Therefore, coherent combining of low-resolution multiple ambiguity functions to get a high-resolution composite ambiguity function is now feasible.

Subspace algorithm for blind channel identification and synchronization in single-carrier block transmission systems

A blind channel identification and synchronization method for single-carrier block transmission system over frequency-selective fading channel is proposed. We employ cyclic prefix (CP) insertion to introduce the redundancy at the transmitter side. As a result, the channel impulse response (CIR) could be estimated in a blind fashion by means of subspace algorithm based on second-order statistics through the exploitation of the redundancy. The condition for identifying CIR along with the proof of uniqueness of CIR estimate is provided regardless of CP length relative to channel order as well as data frame size. We further develop a sorting approach to avert timing offset issue in block synchronization. Numerical results presented performance comparison with orthogonal frequency-division multiplexing (OFDM) systems in terms of bit error rate (BER) and channel estimation error. We also compare with traditional zero-padding OFDM systems in terms of the failure rate of block synchronization.

Threshold-based cooperative communication of energy harvesting active networked tags

Using cooperative transmission allows energy-harvesting active networked tags (EnHANTs) to cooperate regarding information transmission and reception, achieving higher throughput compared with non-cooperative counterparts. In this paper, a battery-threshold-based optimal cooperative transmission strategy is proposed for EnHANTs, allowing EnHANT-equipped objects to communicate with the destination (i.e., the reader) either directly or by cooperating with neighbouring objects. A strategy adapted to request states and available energy resources is considered, and an optimal transmission policy for EnHANTs is developed to maximise the long-term average throughput by formulating a Markov decision process (MDP) model. The simulated results indicate that the proposed strategy yields superior performance compared with single-link transmission.

Robust turbo decoding in single-carrier systems over memoryless impulse noise channels

Communication systems subjected to strong impulse noise are prone to performance degradation when the impulse occurrence is neglected in the decoding process: turbo decoders are likely to exhibit error propagation because the decision-making is dictated by excessive samples corrupted by impulses when the conventional decision metric, which is based on the assumption of additive white Gaussian noise, is used. A sophisticated decoder is widely known to yield a substantial performance improvement by exploiting impulse statistics; however, impulse statistics are difficult to model accurately and are generally not time invariant, likely leading the receiver complexity to be prohibitive. Based on our previous work - which proved the robustness of a soft limiter despite a lack of impulse statistics, this study incorporated a clipping operation into a single-carrier turbo-coded system in memoryless impulse noise channels. Further, the performance of the proposed decoder was evaluated according to the bit error rate to demonstrate the performance gain derived from various clipping thresholds, each of which reflects a different degree of impulse information to which the proposed decoder can leverage.

Amplify-and-forward cooperative relaying for single-carrier block transmission

In this paper, we consider amplify-and-forward relaying scheme with a single-relay framework, where the involved links between transmit-receive pairs may experience different delay spread. Without channel state information assumed or estimated at the destination terminal, unitary spacetime modulation (USTM) derived from complex orthogonal spreading sequence set was adopted for the distributed single-carrier block transmission. Our pairwise error probability (PEP) analysis indicates that the multipath diversity can be exploited based on the USTM in couple with the noncoherent demodulation rule. Numerical results vindicate the merit of multipaths under certain circumstances such as the link quality from the source to relay as well as power control at relay node.

A PSP-Kalman Receiver for Space-Time Trellis Coded OFDM Systems over Time-Varying Block Fading Channels

Space-time trellis coding systems employing orthogonal frequency division multiplexing technique over frequency-selective channels is considered, where fading gains vary within a frame interval. The channel time-evolution of each sub-carrier is modeled by an autoregressive process, while the receiver utilizing a recursive technique combining Kalman filtering with per-survivor processing is studied.

Iterative Interference Suppression for High-Rate Single-Carrier Space-Time Block-Coded CDMA

In this paper, we employ time-reversal space-time block coding (TR-STBQ in single-carrier direct sequence code- division multiple access (DS-CDMA) block transmission in the presence of multiple access interference (MAI) as well as intersyrnbol interference (ISI), which is subject to fairly long delay spread. We introduce the transmission rate improvement by capitalizing on the assignment of additional spreading codes to each user so as to expand the cardinality of space-time code matrix. Given perfect channel state information at the receiver, a simple linear frequency-domain interference suppression scheme on a basis of symbol-by-symbol processing is developed under certain circumstances. A soft receiver is facilitated by exploiting the serially concatenated structure at the transmitter to further enhance system performance. Simulation results justify the efficacy of our proposed system and also present performance comparison with well-known OFDM systems in terms of bit error rate (BER).