In this paper, we propose a simple but effective way of improving the performance of channel estimation (CE) for pilot cyclic prefixed single carrier (PCP-SC) system. The proposed method utilizes the property that the shifting signal of the PCP pilot signal can also be utilized to estimate the channel information. The receiver can continuously estimate the channel information by just shifting the received pilot signal. Regardless of the signal-to-noise ratio (SNR) and the pilot type, the proposed method can achieve about a 1.72 dB performance gain in terms of the mean squared error (MSE) of channel estimation with a slight increase in computational complexity. The BER performance with the proposed CE improvement are evaluated in a multipath fading channel using a zero-forcing (ZF) equalizer and an minmum mean squared error (MMSE) equalizer by computer simulation. It is shown that the proposed CE improvment method using an MMSE equalizer which has an unbiased vlaue of noise variance (NV) estimator gives a promising BER performance. The proposed method also benefits the estimation of the SNR for the single carrier system.

IP Datacast over DVB-H has been adopted as a core technology to build complete end-to-end mobile broadcast TV systems. In order for this technology to be successful in the market, provisioning of acceptable QoE (Quality of Experience) to the users, as well as a wide range of business models to the service providers, is essential. In this paper, we analyze the channel zapping time, which is an important metric to measure QoE for mobile broadcast TV services. In particular, we clarify primary components that determine the channel zapping time for protected services in IP Datacast over DVB-H. Our analysis is based on the data gathered during the trial service of the OMA-BCAST Smartcard profile in Singapore, Asia. Based on the analysis, we show that a significant reduction in channel zapping time can be achieved by optimizing the transmission parameters related to the key derivation time and the synchronization time between the content stream and the key stream.

Channel errors may exist in Radio Frequency IDentification (RFID) systems due to low power backscattering of tags. These errors prevent the rapid identification of tags, and reducing this deterioration is an important issue. This paper presents performance analysis of various tag anti-collision algorithms and shows that the performances of RFID systems can be improved by applying a proposed robust algorithm in error-prone environments.

In this paper, we develop linear-programming (LP) decoding for multiple-access channels with binary linear codes. For single-user channels, LP decoding has attracted much attention in recent years as a good approximation to maximum-likelihood (ML) decoding. We demonstrate how the ML decoding problem for multiple-access channels with binary linear codes can be formulated as an LP problem. This is not straightforward, because the objective function of the problem is generally a non-linear function of the codeword symbols. We introduce auxiliary variables such that the objective function is a linear function of these variables. The ML decoding problem then reduces to the LP problem. As in the case for single-user channels, we formulate the relaxed LP problem to reduce the complexity for practical implementation, and as a result propose a decoder that has the desirable property known as the ML certificate property (i.e., if the decoder outputs an integer solution, the solution is guaranteed to be the ML codeword). Although the computational complexity of the proposed algorithm is exponential in the number of users, we can reduce this complexity for Gaussian multiple-access channels. Furthermore, we compare the performance of the proposed decoder with a decoder based on the sum-product algorithm.

As the demand for spectrum for future wireless communication services increases, cognitive radio technology has been developed for dynamic and opportunistic spectrum access, which enables the secondary users to use the underutilized licensed spectrum of the primary users. In particular, the recent studies on the MAC protocol for dynamic and opportunistic access have focused on sensing and using the vacant spectrum efficiently. Under the ad-hoc network environment, how the secondary users use the unused channels by the primary users affects the efficient utilization of channels and a cognitive radio system is required to follow the rapid and frequent changes in channel status. In this paper, we propose a self-scheduling multi-channel cognitive MAC (SMC-MAC) protocol, which allows multiple secondary users to transmit data though the sensed idle channels by two cooperative channel sensing algorithms, i.e., fixed channel sensing (FCS) and adaptive channel sensing (ACS), and by slotted contention mechanism to exchange channel request information for self-scheduling. The performance of the proposed SMC-MAC protocol is investigated via analysis and simulations. According to the results, the proposed SMC-MAC protocol is effective in allowing multiple secondary users to transmit data frames effectively on multi-channels and adaptively in response to the primary users' traffic dynamics.

Wireless body area network for sensing and monitoring of vital signs is the one of most rapidly growing wireless communication system and Ultra Wide-Band (UWB) is a favorable technology for wearable medical sensors. The wireless body area networks promise to revolutionize health monitoring. However, designers of such systems face a number of challenging tasks. Efficient transceiver design requires in-depth understanding of the propagation media which in this case is the human body surface. The human body is not an ideal medium for RF wave transmission; it is partially conductive and consists of materials of different dielectric constants, thickness and characteristic impedance. The results of the few measurement experiments in recent publications point to varying conclusions in the derived parameters of the channel model. As obtaining large amount of data for many scenarios and use-cases is difficult for this channel, a detailed simulation platform can be extremely beneficial in highlighting the propagation behavior of the body surface and determining the best scenarios for limited physical measurements. In this paper, an immersive visualization environment is presented, which is used as a scientific instrument that gives us the ability to observe three-dimensional RF propagation from wearable medical sensors around a human body. We have used this virtual environment to further study UWB channels over the surface of a human body. Parameters of a simple statistical path-loss model and their sensitivity to frequency and the location of the sensors on the body are discussed.

Hop-timing detection is of extreme importance for the reception of frequency hopping (FH) signals. Any error in the hop-timing detection has a deleterious effect on the performance of the receiver in frequency hopping (FH) communication systems. However, it is not easy to detect the hop-timing under low signal to noise power ratio (SNR) environments. Adaptive array antennas (AAA) have been expected to improve the performance of FH communication systems by beamforming for the direction of arrival of the desired signal. Since the conventional AAA exploits at least the coarse synchronization for dehopping of FH signals before achieving the beamforming, any fault in the hop-timing detection causes the deterioration of the performance of AAA. Using AAA based on the constant modulus algorithm (CMA), this paper proposes a new method for blind beamforming and hop-timing detection for FH signals. The proposed method exploits both the spatial and temporal characteristics of the received signal to accomplish the beamforming and detect the hop-timing without knowing any a priori information such as fine/coarse time synchronization and training signal. The performance verifications of the proposed method based on pertinent simulations are presented.

In this paper, we propose a new interference alignment (IA) scheme that jointly designs the linear transmitter and receiver for the 2-user MIMO X channel system, using minimum total mean square error criterion, subject to each transmitter power constraint. We show that transmitters and receivers under such criteria could be realized through a joint iterative algorithm. Considering the imperfection of channel state information (CSI), we also extend the minimum mean square error interference alignment schemes for the MIMO X channel with CSI estimation error. A robust iterative algorithm which is insensitve to CSI estimation error is proposed. Simulation results are also provided to demonstrate the proposed algorithm.

The polarization degrees of freedom (DOF) of the hexapolarized multiple input multiple output (MIMO) system over the ground reflected channel is studied in this paper by the deterministic field solution. Using the simple two-ray model, we could get some basic understandings for the influence of a single reflecting surface on the polarization DOF of the multipolarized MIMO system. Computation results show that the number of parallel independent channels in a multipolarized MIMO system depends mainly on the communication range and the height of antennas. In free space transmission, with equal height of transmitter and receiver antennas, large polarization DOF value only occurs in the near field case and it drops sharply to 2 with the increase of transmission range. Whereas for the ground reflect channel, there will be a polarization DOF larger than 4 occurring at longer communication distance with an unequal transmitter and receiver antenna height.

In this paper, an optimal power control for minimizing bit error rate (BER) subject to a power constraint for space-time block coded MIMO systems with beamforming over Rayleigh fading channels under imperfect channel state information (CSI) is presented. The optimal power control procedure is developed. It is shown that the Lagrange multiplier for the constrained optimization does exist and is unique. To simplify the power control procedure, a closed-form suboptimal power control scheme is drived based on the asymptotic performance analysis of the optimal power control and Taylor's series expansion. The calculation of the suboptimal power control is straightforward with low computational complexity. Moreover, the suboptimal scheme can provide the BER performance close to that of the optimal power control and is lower than that of the existing suboptimal scheme. Simulation results show that the proposed two power control schemes can provide BER lower than that of the equal power allocation and the existing suboptimal scheme under imperfect CSI.

This letter introduces a blind minimum interference symbol synchronization for orthogonal frequency-division multiplexing (OFDM) systems based on the cyclic prefix (CP). The basic idea of our contribution is to obtain an estimate of the channel-tap powers from the correlation characteristics of the CP. Based on the estimate of the channel-tap powers, a minimum interference metric is proposed. The proposed algorithm has low complexity and can be used to cope with long inter-symbol-interference (ISI) channels with length up to twice the CP length.

In this letter, we propose an efficient on-the-fly algorithm for maximum-likelihood decoding of Raptor codes used over the binary erasure channel. It is shown that our proposed decoding algorithm can reduce the actual elapsed decoding time by more than two-thirds with respect to an optimized conventional maximum-likelihood decoding.

Efficient resource allocation for delay-sensitive traffic, such as telephony and video streaming, in Orthogonal Frequency Division Multiple Access (OFDMA) networks is needed to increase system performance. In our system, users try to achieve a low queuing delay and buffer space usage by competing for transmission over the subchannels. We formulate this problem as a bargaining game and use the Nash Bargaining Solution (NBS) to realize a fair and efficient subchannel allocation for the users. Simulation results show performance improvements, with regard to packet dropping and delay distribution, over other algorithms.

Repetitive synchronization sequences in the time domain can be used to estimate Carrier Frequency Offset (CFO). The Un-Guarded Maximum Likelihood (UGML) estimator and Guarded ML (GML) estimator of CFO in the frequency selective channel are proposed in this paper. The results of theoretical analysis show that the UGML estimator is hard to implement if the channel response is not known while the GML estimator can be easily implemented due to inserted guard sequences. The guard sequences can be easily implemented as Cyclic Prefix (CP) in OFDM system. Therefore, the UGML estimator is only suitable for the systems where the channel response can be predetermined. This paper also gives a comparison with the existing CFO estimator. Theoretical and simulation results show that both the proposed estimators outperform the existing estimator.

In this paper, we present a fault analysis of the original NTRU public key cryptosystem. The fault model in which we analyze the cipher is the one in which the attacker is assumed to be able to fault a small number of coefficients of the polynomial input to (or output from) the second step of the decryption process but cannot control the exact location of injected faults. For this specific original instantiation of the NTRU encryption system with parameters (N,p,q), our attack succeeds with probability≈ and when the number of faulted coefficients is upper bounded by t, it requires O((pN)t) polynomial inversions in Z/p Z[x]/(xN-1).

The Medium Access Control (MAC) protocol that uses non-overlapping multiple channels, called the multi-channel MAC protocol, was proposed in order to increase the capacity of ad hoc networks. Since the number of packet interfaces on each node is less than the number of channels in ad hoc networks in general, the node needs to select a suitable channel for data transmission. This means that the multi-channel MAC protocol must be provided with a good channel selection algorithm. In this paper, we design a channel selection algorithm called Conditionally Randomized Channel Selection (CRCS) based on Extended Receiver Directed Transmission (xRDT) protocol that only uses one packet interface. Briefly, CRCS uses the acitve channel for data transmission until the amount of data packets reaches a threshold, at which point it selects one of the available channels other than the active channel. Although CRCS is a very simple channel selection algorithm, by using network simulator we find that CRCS is effective to increase the capacity of ad hoc networks and to keep the load balance of all channels compared to the other channel selection algorithms.

To realize transmit diversity for the time domain synchronous OFDM (TDS-OFDM) system, this letter proposes the space-time-frequency orthogonal training sequence and the corresponding flexible channel estimation methods. Simulation results indicate that an significant performance improvement could be achieved for low-density parity-check code (LDPC) coded TDS-OFDM system over multi-path fading channels.

This letter introduces a closed form expression for the channel capacity increase achieved by adding a new pair of transmit and receive antennas. By analyzing this expression, an iterative transmit/receive antenna selection algorithm of low computational complexity is proposed. The new algorithm has higher computational complexity than some existing algorithms, but as the results show, the performance improvement of the proposed algorithm approaching more to the optimal algorithm.

This paper presents a novel dynamic subchannel allocation scheme that can improve the cell capacity by coordinating the intercell interference (ICI) in a cellular orthogonal frequency division multiple access (OFDMA) system. The proposed scheme mitigates the ICI by adopting the virtual cell concept and improves the frequency reuse factor through subchannel reuse among different virtual cells. In particular, each virtual cell is assigned a primary and a secondary subchannel group, and each sector base station (BSs) allocates the subchannel resulting in the least ICI in probability out of the candidate subchannels to the mobile stations, dynamically searching from its primary group and then secondary group. In addition, an optional use of pico-cell overlay at the intersection of the virtual cells is also proposed to enhance the fairness of the proposed scheme with the BS-MS distance. Through computer simulation, it is shown that the proposed scheme has the advantages of improved cell capacity and fairness compared to the conventional schemes.

This paper proposes a new Ad-Hoc network system which comprises the multiple relay access points (APs) with multi channels. Ad-Hoc network systems are recently proposed and incorporated for the communication infrastructure, which relays wireless transmission among access points (APs) in wireless LAN (WLAN) system. System throughput is decreased due to hidden terminal problem when only a single channel is used for the Ad-Hoc network. In order to solve this problem, a new system with multi channels is proposed. However, even if the multi channels are employed, the co- and/or adjacent-channel interference occurs due to hidden terminal problem and multiple APs in a limited space, when considering a simultaneous transmit and reception at the relay AP. In this paper, we develop an Ad-Hoc network testbed which can reduce and avoid co- and/or adjacent-channel interference by using vertically arranged antenna configuration and distributed channel allocation scheme. Moreover, the effectiveness of our testbed is clarified by applying actual WLAN signals.