The dynamic channel allocation (DCA) scheme in multi-cell systems causes serious inter-cell interference (ICI) problem to some existing calls when channels for new calls are allocated. Such a problem can be addressed by advanced centralized DCA design that is able to minimize ICI. Thus, in this paper, a centralized DCA is developed for the downlink of multi-cell orthogonal frequency division multiple access (OFDMA) systems with full spectral reuse. However, in practice, as the search space of channel assignment for centralized DCA scheme in multi-cell systems grows exponentially with the increase of the number of required calls, channels, and cells, it becomes an NP-hard problem and is currently too complicated to find an optimum channel allocation. In this paper, we propose an ant colony optimization (ACO) based DCA scheme using a low-complexity ACO algorithm which is a kind of heuristic algorithm in order to solve the aforementioned problem. Simulation results demonstrate significant performance improvements compared to the existing schemes in terms of the grade of service (GoS) performance and the forced termination probability of existing calls without degrading the system performance of the average throughput.

We propose a simplified model of real-time joint source-channel coding, which can be used to adaptively determine the quality-optimal code rate of forward error correction (FEC) coding. The objective is to obtain the maximum video quality in the receiver, while taking time-varying packet loss into consideration. To this end, we propose a simplified model of the threshold set of the residual video packet loss rate (RVPLR). The RVPLR is the rate of residual loss of video packets after channel decoding. The threshold set is defined as a set of discrete RVPLRs in which the FEC code rate must be changed in order to maintain minimum distortion during increases or decreases of channel packet loss. Because the closed form of the proposed model is very simple and has one scene-dependent model parameter, a video sender can be easily implemented with the model. To train the scene-dependent model parameters in real-time, we propose a test-run method. This method accelerates the test-run while remaining sufficiently accurate for training the scene-dependent model parameters. By using the proposed model and test-run, the video sender can always find the optimal code rate on the fly whenever there is a change in the packet loss status in the channel. An experiment shows that the proposed model and test-run can efficiently determine the near-optimal code rate in joint source-channel coding.

This paper presents a pilot-aided channel estimation method which is particularly suitable for mobile WiMAX 802.16e Downlink Partial Usage of Subchannel mode. Based on this mode, several commonly used channel estimation methods are studied and the method of least squares line fitting is proposed. As data of users are distributed onto permuted clusters of subcarriers in the transmitted OFDMA symbol, the proposed channel estimation method utilizes these advantages to provide better performance than conventional approaches while offering remarkably low complexity in practical implementation. Simulation results with different ITU-channels for mobile environments show that depending on situations, enhancement of 5 dB or more in term of SNR can be achieved.

Based on game theory, a distributed power control algorithm with sequential subchannel nulling is proposed for ad-hoc networks. It is shown that the proposed method, by sharing subchannels appropriately according to the interference profiles, can reduce the power consumption of the network while satisfying the target rate of each link.

This study focuses on system throughput by taking into account the channel interference in IEEE 802.15.3c WPAN, which is based on the hybrid multiple access of CSMA/CA and TDMA, namely CSMA/CA-TDMA. To study the system throughput, we construct a novel analytical model by taking into consideration the channel interference caused by the hidden networks in CSMA/CA-TDMA. The obtained results show that the system throughput achieved by TDMA is highly affected by frame transmission in CSMA/CA. Furthermore, we show that channel interference, which causes a degradation in the system throughput, is a very significant problem in the IEEE 802.15.3c WPAN.

In this letter, we present a multiple-input multiple-output (MIMO) optimal combining (OC) scheme based on alternate iteration. With the channel state information (CSI) of co-channel interferers (CCIs), this algorithm can be used in flat fading and frequency selective channels to suppress CCIs. Compared with the optimal transceiver of MIMO maximal ratio combining (MRC) systems, results of simulation show that this scheme improves the uplink transmission performance significantly.

This paper presents a novel cross-layer approach to explore selection diversity for distributed clustering based wireless sensor networks (WSNs) by selecting a proper cluster-head. We develop and analyze an instantaneous channel state information (CSI) based cluster-head selection algorithm for a distributed, dynamic and randomized clustering based WSN. The proposed cluster-head selection scheme is also random and capable to distribute the energy uses among the nodes in the network. We present an analytical approach to evaluate the energy efficiency and system lifetime of our proposal. Analysis shows that the proposed scheme outperforms the performance of additive white Gaussian noise (AWGN) channel under Rayleigh fading environment. This proposal also outperforms the existing cooperative diversity protocols in terms of system lifetime and implementation complexity.

In this letter, the outage performance of multi-hop multiple-input multiple-output (MIMO) relaying systems is analyzed for spatially correlated Rayleigh fading channels. We focus on nonregenerative MIMO decouple-and-forward (DCF) relaying in orthogonal space-time block code (OSTBC) transmission and provide its outage probability given the assumption of ideal relay gain. The outage obtained here is shown a lower bound for using practical gains, which gets tight at high SNR. We conduct numerical studies to assess the impact of the spatial correlation between antennas on the outage probability.

We define the term sensor node profile (SNP) in IEEE 802.15.4, which considers the transmitting data type as well as a variety of nodal characteristics which are able to manage the channels of each node by using the SNP. Through the use of the SNP the nodes are able to maximize the channel resource usage, which could form the basis of algorithms that can provide the required Quality of Service (QoS).

In this letter, the sparse recovery algorithm orthogonal matching pursuit (OMP) and subspace pursuit (SP) are applied for MIMO OFDM channel estimation. A new algorithm named SOMP is proposed, which combines the advantage of OMP and SP. Simulation results based on 3GPP spatial channel model (SCM) demonstrate that SOMP performs better than OMP and SP in terms of normalized mean square error (NMSE).

With the process scaling, the leakage current reduction has been the primary design concerns in a nanometer-era VLSI circuit. In this paper, we propose a new lithography process-aware edge effects correction method to reduce the leakage current in the shallow trench isolation (STI). We construct the various test structures to model Ileakage and Ileakage_fringe which represent the leakage currents at the center and edge of the transistor, respectively. The layout near the active edge is modified using the look-up table generated by the calibrated analytic model. On average, the proposed edge effects correction method reduces the leakage current by 18% with the negligible decrease of the drive current at sub-40nm DRAM device.

The multilevel dual-channel (MLDC) not-AND (NAND) flash memories cell structures with asymmetrically-doped channel regions between the source and the drain were proposed to enhance read and program verifying speeds. The channel structure of the MLDC flash memories consisted of two different doping channel regions. The technical computer aided design simulation results showed that the designed MLDC NAND flash cell with asymmetrically-doped channel regions provided the high-speed multilevel reading with a wider current sensing margin and the high-speed program verifying due to the sensing of the discrete current levels. The proposed unique MLDC NAND flash memory device can be used to increase read and program verifying speed.

ISO/IEC 18000-7 Active RFID standard, a single channel system operating at 433 MHz, faces technical difficulties in supporting some recently introduced application demands because of its low transmission rates and vulnerability to radio interference between the readers. We propose a new multi-channel active RFID system operating at the 2.4 GHz band. The special feature of the proposed system is that a reader makes use of multiple interfaces to improve its performance. However, if only a small part of the interfaces is actually used, the performance improvement would not meet expectations. To overcome this problem, a multi-channel multi-interface active RFID protocol that balances the loads among all available interfaces is necessary. Three protocols, "Aggregated," "LP-Combined" and "AP-Balanced" are proposed in this paper. We carry out simulations to compare them under various conditions by changing numbers of tags, numbers of interfaces and tag data size. The AP-Balanced shows the best and the most stable performance and its performance increases almost linearly in proportion to the number of interfaces, which meets our expectation.

A new adaptive algorithm is proposed by introducing some modifications to the recursive least squares (RLS) algorithm. Except for the noise variance, the proposed algorithm does not require any statistics or knowledge of the desired signal, thus, it is suitable for adaptive filtering for channel estimation in code division multiple access (CDMA) systems in cases where the standard RLS approach cannot be used. A theoretical analysis demonstrates the convergence of the proposed algorithm, and simulation results for CDMA channel estimation show that the proposed algorithm outperforms existing channel estimation schemes.

A novel turbo coded modulation scheme, called the turbo-APPM, for deep space optical communications is proposed. The proposed turbo-APPM is a serial concatenation of turbo codes, an accumulator and a pulse position modulation (PPM), where turbo codes act as an outer code while the accumulator and the PPM act together as an inner code. The generator polynomial and the puncturing rule for generating turbo codes are chosen to lower the bit error rate. At the receiver, the joint iterative decoding is performed between the inner decoder and the outer turbo decoder. In the outer decoder, local iterative decoding for turbo codes is conducted. Simulation results are presented showing that the proposed turbo-APPM outperforms all previously proposed schemes such as LDPC-APPM, RS-PPM and SCPPM reported in the literature.

We present a predictive closed-loop power control scheme for delay-prone burst transmission systems. The scheme has a sample-by-sample predictor compensating burst delay and a built-in channel encoder reducing power control command bit error.

Ultra wideband (UWB) on-body communication is attracting much attention in biomedical applications. In this paper, the performance of UWB on-body communication is investigated based on a statistically extracted on-body channel model, which provides detailed characteristics of the multi-path-affected channel with an emphasis on various body postures or body movement. The possible data rate, the possible communication distance, as well as the bit error rate (BER) performance are clarified via computer simulation. It is found that the conventional correlation receiver is incompetent in the multi-path-affected on-body channel, while the RAKE receiver outperforms the conventional correlation receiver at a cost of structure complexity. Different RAKE receiver structures are compared to show the improvement of the BER performance.

This paper proposes a joint source-channel coding technology to transmit periodic vital information such as an electrocardiogram. There is an urgent need for a ubiquitous medical treatment space in which personalized medical treatment is automatically provided based on measured vital information. To realize such treatment and reduce the constraints on the patient, wireless transmission of vital information from a sensor device to a data aggregator is essential. However, the vital information has to be correctly conveyed through wireless channels. In addition, sensor devices are constrained by their battery power. Thus, a coding technique that provides robustness to noise, channel efficiency and low power consumption at encoding is essential. This paper presents a coding method that uses correlation of periodic vital information in the time domain, and provides a decoding scheme that uses the correlation as side information in a maximum a posteriori probability algorithm. Our results show that the proposed method provides better performance in terms of mean squared error after decoding in comparison to differential pulse-code modulation, and the uncoded case.

Motivated by the recent research in crosslayer design of cooperative wireless network, we propose a distributed cooperative routing algorithm for a multihop multi-relay wireless network to achieve selection diversity. We propose two algorithms, rate optimal path selection and outage optimal path selection, to satisfy the different requirements of the systems. Both algorithms work on distributed processing without requiring any centralized controller. Simulations are conducted to evaluate the performance of the proposal. The results of the simulations show that the proposed routing algorithms significantly improve the end-to-end data rate and outage performance compared with noncooperative routing protocols.

OFDMA femtocells in the macrocellular network of which frequency reuse factor is 1 cause serious interference to macrocell users, while the femtocells improve the performance of indoor users. In this letter, a novel downlink resource allocation algorithm for OFDMA femtocell networks is proposed to reduce interference between the macrocells and the femtocells. This algorithm allocates femtocell subchannels to avoid interference to macrocell users in the femtocell coverage, and minimizes the total transmission power of the femtocell to reduce the negative effect on the performance of the macrocell. Simulation results are provided to present the performance of the proposed algorithm.