An Ad Hoc network is a collection of wireless mobile nodes dynamically forming a temporary network without the use of any existing network infrastructure or centralized administration. The choice of medium access is difficult in Ad Hoc networks due to the time-varying network topology and the lack of centralized control. In this paper, we propose a novel multichannel schedule-based Medium Access Control (MAC) protocol for Ad Hoc networks named Multichannel Reservation Protocol for TDMA-based networks (MRPT). MRPT ensures collision free in successfully reserved data links, even when hidden terminals exist. The reservation of MRPT is based a control channel and in order to improve throughput we propose Four-Phase-Two-Division (FPTD) as a media access scheme of the control channel for broadcasting control or reservation messages. In FPTD, the collision can be solved rapidly with an efficient backoff algorithm which results in that system block is avoided in case of high traffic. In this paper, we also present the throughput performance of MRPT, which shows a high value and no system block even in case of high traffic load.

The accuracy of channel estimation significantly affects the performance of coherent receiver in a DS-CDMA system. The receiver performance can be improved if an appropriate channel estimation filter is used according to the channel condition. In this paper, we consider the design of channel estimation filters for pilot channel based DS-CDMA systems. When a moving average (MA) FIR filter is used as the channel estimation filter (CEF), the tap size is optimized by minimizing the mean squared error of the estimated channel impulse response. Finally, the analytic design is verified by computer simulation. Numerical results show that the optimum MA FIR CEF provides near optimum performance, i.e., quite similar to that with the use of Wiener filter.

We show a geometric method to compute the Van der Waals factor 1/r7 between the assemblies of amino acid molecules of the subunits of acetyl choline (abbreviated by Ach: a kind of neuro chemical transmitter) sensitive channel on the post synaptic membrane of the neural system. We induced a analytical geometric formula for the distances between helically arranged ten assemblies of the point amino acid molecules on two interacting membrane perforating poly peptides, M2 helices during channel opening deformation. Detailed geometric parameters have been utilized from reported biophysical measurements. The computed Van der Waals factor decreased rapidly as the slope of the first M2 helix along the central axis of the channel pore has increased. The Van der Waals factor also decreased by an increase in rising angle of the helically arranged amino acids on the M2 helices. The Van der Waals factor increased significantly as the first M2 helix has rotated around the central axis of the channel pore to take an opening position. We discussed the time dependent molecular structural changes of the Ach sensitive channel opening in conjunction with the Allosteric properties of the bio molecules. The molecular mechanism of Ach sensitive channel opening in terms of the Allosteric property may derive from the characteristic helical constitutional nature of the membrane perforating part (M2 helix) of the subunits of the channel molecule.

Direct sequence code division multiple access (DS-CDMA) provides flexible data transmission in wide range of data rates by the use of orthogonal multicode multiplexing. In a multipath fading environment, the transmission performance of multicode DS-CDMA degrades as that of single code DS-CDMA does. Chip interleaving is known to improve the bit error rate (BER) performance of the single code transmission by altering the fading channel into severely time selective fading channel. However, this partially destroys orthogonality property among spreading codes and thus, significantly degrades the BER performance of multicode DS-CDMA. In this paper, we propose the joint use of chip interleaving and time-domain minimum mean square error combining (MMSEC) equalization to improve the multicode DS-CDMA transmission performance. It is confirmed by computer simulations that the joint use of chip interleaving and MMSEC equalization significantly improves the BER performance of multicode DS-CDMA and achieves better BER performance compared to the single code DS-CDMA using chip interleaving and maximal ratio combining (MRC).

In this letter, we address the performance evaluation of a space-time block coded (STBC) orthogonal frequency and code division multiplexing (OFCDM) system encountered with time-variant channels. For the performance evaluation, the average bit error rate (BER) impairment due to imperfect channel information is investigated taking into account the effect of time-varying channels. Derived results show that the loss of orthogonality due to the time variation of the channel incurs the channel estimation error, which causes performance degradation.

The Single Instruction, Multiple Data (SIMD) architecture enables computation in parallel on a single processor. The SIMD operations are implemented on some processors such as Pentium 3/4, Athlon, SPARC, or even on smart cards. This paper proposes efficient algorithms for assembling an elliptic curve addition (ECADD), doubling (ECDBL), and k-iterated ECDBL (k-ECDBL) with SIMD operations. We optimize the number of auxiliary variables and the order of basic field operations used for these addition formulas. If an addition chain has k-bit zero run, we can replace k-time ECDBLs to the proposed faster k-ECDBL and the total efficiency of the scalar multiplication can be improved. Using the singed binary chain, we can compute a scalar multiplication about 10% faster than the previously fastest algorithm proposed by Aoki et al. Combined with the sliding window method or the width-w NAF window method, we also achieve about 10% faster parallelized scalar multiplication algorithms with SIMD operations. For the implementation on smart cards, we establish two fast parallelized scalar multiplication algorithms with SIMD resistant against side channel attacks.

We analytically investigate combinatorial effects of timer control and backoff algorithms on performance of bulk data transfer over two-state Markovian packet error channels. Numerical results for throughput, energy efficiency, and the probabilities of packet loss and loss of bulk data indicate that linear backoff algorithms outperform binary exponential ones as a whole when they are employed at the logical link sublayer with timer control.

The side channel attack (SCA) is a serious attack on wearable devices that have scarce computational resources. Cryptographic algorithms on them should be efficient using small memory--we have to make efforts to optimize the trade-off between efficiency and memory. In this paper we present efficient SCA-resistant scalar multiplications based on window method. Moller proposed an SPA-resistant window method based on 2w-ary window method, which replaces w-consecutive zeros to 1 plus w-consecutive and it requires 2w points of table (or 2w-1 + 1 points if the signed 2w-ary is used). The most efficient window method with small memory is the width-w NAF, which requires 2w-2 points of table. In this paper we convert the width-w NAF to an SPA-resistant addition chain. Indeed we generate a scalar sequence with the fixed pattern, e.g. |00x|00x||00x|, where x is positive odd points < 2w. Thus the size of the table is 2w-1, which is optimal in the construction of the SPA-resistant chain based on width-w NAF. The table sizes of the proposed scheme are 6% to 50% smaller than those of Moller's scheme for w = 2,3,4,5, which are relevant choices in the sense of efficiency for 160-bit ECC.

This paper investigates the performance of an integrated voice/data wireless mobile network where a finite buffer is provided for voice calls since they can endure a tolerable time, or the reneging time, for service. Based on a given humanistic reneging time, we analyze the voice traffic blocking probability. The probability distribution of receiving service within the reneging time is obtained for each buffered voice call and based on this result, an appropriate amount of voice buffer is obtained. To alleviate the impact on data blocking probability caused by the voice buffer and to enhance the efficiency of data service, a dynamic multi-channel allocation scheme with channel de-allocation and guard channels is proposed for data traffic. Compared with the conventional method where the system adopts a single-channel allocation scheme without guard channel for data users, the proposed scheme shows significant improvement in data blocking probability, throughput and the mean service time. Furthermore, a system with an appropriate size of buffer for voice traffic can receive good improvement in voice blocking probability.

For the channel estimation in the pilot channel aided CDMA systems which can support a multi-code scheme, we consider a linear prediction using both pilot and traffic channels. After deriving a new form of the optimal Wiener filter which requires less computational load, for its practical implementation, we propose the decision-directed adaptive linear prediction filter (DD-ALPF). To prevent from falling into the false lock, the proposed DD-ALPF uses the conventional channel estimate obtained only from pilot channel as a baseline for checking the reliability of the filter output. It will be shown through computer simulation that the proposed method can improve the receiver performance and performs better in the fast fading environments, compared with the existing ones.

This paper presents the approximate error rates of M-ary phase shift keying (MPSK) for optimum combining (OC) with multiple interferers in a flat Rayleigh fading channel. The approximations, which have been used to evaluate the performance of binary PSK for OC, are extended to the performance analysis of MPSK for OC in the presence of arbitrary numbers of antennas and interferers. The mean eigenvalues of interference-plus-noise covariance matrix are analyzed to compare the approximation techniques, i.e., first-order approximation and the orthongal approximation. Using the moment generating function (MGF)-based method, the approximate error rates of MPSK for OC are derived as the closed-form expressions in terms of the exact error rates of MPSK for MRC. The approximate analytical results show the simple and accurate way to assess the average symbol error rate of MPSK for OC with arbitrary numbers of antennas and interferers.

In this letter, a concise formula for the SNR degradation of OFDM caused by carrier frequency offset is derived by approximations over a shadowed two-path channel, which explicitly shows the sensitivity of SNR degradation to various parameters including the frequency offset. It is shown that, for small frequency offset, the SNR degradation is proportional to the square of the frequency offset and the square of the number of subcarriers. It is also shown that, if Es/N0 is reasonably large, the SNR degradation becomes insensitive to Es/N0, which is contrary to the case of the AWGN channel.

Two important lemmas on the determinant of random matrixes are deduced in this paper. Then based on these results, expression for the mean capacity of MIMO system over Rayleigh fading channels is obtained. This expression requires little calculation and is simple and efficient compared with conventional methods, and furthermore, it gives an explicit relation on the mean capacity of MIMO systems with antenna numbers and the relation of mean capacity with signal to noise ratio (SNR). Accuracy of this theoretic formula has been verified by computer simulation.

A novel reconfigurable architecture has been proposed for a mobile terminal receiver that can drastically reduce power dissipation dependant on adjacent channel interference. The proposed design can automatically scale the number of filter coefficients and word length respectively by monitoring the in-band and out-of-band powers. The new architecture performance was evaluated in a simulation UTRA-TDD environment because of the large near far problem caused by adjacent channel interference from adjacent mobiles and base stations. The UTRA-TDD downlink mode was examined statistically and results show that the reconfigurable architectures can save an average of up to 75% power dissipation respectively when compared to a fixed filter length of 57 and word length of 16 bits. This power saving only applies to the filter and ADC, not the whole receiver. This will prolong talk and standby time in a mobile terminal. The average number of taps and bits were calculated to be 14.98 and 10 respectively, for an outage of 97%.

The effects of hybrid concatenated space-time (HC-ST) codes applying iterative a posteriori probability (APP) decoding are investigated. The bit error rate (BER) and frame error rate (FER) performance of the iterative decoded hybrid Tarokh, Seshadri, Calderbank space-time (TSC ST) coded system under flat Rayleigh fading is analyzed. At the FER 10-2 level the results show that the serially concatenated space-time (SC-ST) codes provide a coding gain of 3 dB compared to the TSC ST codes, where an additional coding gain of 1 dB beyond the SC-ST code performance can be obtained applying the HC-ST coding topology.

The channel noise in OFDM systems affects the accuracy of channel estimation, deteriorating the performance of equalization. We present a novel algorithm with MMSE (Minimum Mean Square Error) channel estimation based on Hadamard Transform, to mitigate the effects of noise. The performance of the proposed algorithm is proved to be better than that with LS (Least Square) estimation, and very close to that with the MMSE estimation based on Fourier Transform, while the computation required is pretty small due to the use of Hadamard Transform.

A mathematical expression for the received signal power in a severe frequency-selective fading channel is derived. Using the derived expression, the signal power distributions are obtained by Monte-Carlo simulation and compared with the Nakagami m-power distribution. It is found that the power distribution matches well with the Nakagami m-power distribution when the multipath channel has a uniform power delay profile.

Combining a layered space-time receiver with the OFDM for high-rate transmissions requires the multi-channel estimation process. So, this letter proposes a time-domain approach for new preamble structure in OFDM-based multiple antenna systems, and investigates the channel estimation performance based on the semi-blind processing and its imperfectness by using time-domain windowing. The proposed preamble can estimate the multi-channel up to the 8 transmit antennas in the WLAN standards using two long preambles.

This letter presents a lower bound and approximation for the coverage probability of the pilot channel that can be used for a CDMA downlink design. The approximation of a compound truncated Poisson distribution is used to obtain a closed form equation for the coverage probability of the pilot channel. Computer simulations show that our lower bound curve is truly less than the empirical curve, and our proposed approximation agrees well with the empirical result.

The detection performance of coherent OFDM receivers significantly depends on the accuracy of channel estimation. The accuracy of channel estimation can be improved by properly post-processing the channel estimate using a so-called channel estimation filter (CEF). Minimum mean-squared error (MMSE) filter is known optimum as the CEF, but it may not be practical due to its implementation complexity. We consider the use of a reduced-complexity CEF whose tap coefficient is real-valued and symmetrically weighted (RSW). The optimum RSW CEF is analytically designed using the SNR and multi-path intensity profile of the channel. For further improvement, we also propose a method to adapt the coefficient of the RSW CEF to the channel condition. Numerical results show that the proposed RSW CEF can provide channel estimation performance comparable to that of linear MMSE filter, while significantly reducing the computational complexity. In addition, the proposed RSW CEF can provide performance robust to unknown timing offset with a fractional dB loss compared to the optimum one.