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This letter is to correct the incorrect optimal relay coefficient at the k-th relay derived in [1] for an amplify-and-forward (AF) wireless relay network under received power constraints. While the trends remain the same, with the correct optimal relay coefficient in this paper, nonnegligible improvement, e.g., about 0.8 dB at BER = 10^{-7}, can be achieved. © 2013 IEEE.

This paper proposes to encode pilot bits together with information bits by using a systematic encoder and applying them to an iterative receiver, where channel estimation and decoding are iteratively performed. This paper then shows why and how the encoded pilot bits can give a positive gain over a conventional uncoded pilot system. Specifically, this paper considers an orthogonal frequency-division multiplexing system that is encoded by a low-density parity-check code under a frequency-selective fading channel and shows theoretical analysis as well as simulation results. Index Terms--Channel estimation, encoded pilot (EP), iterative receiver, low-density parity-check (LDPC), orthogonal frequency-division multiplexing (OFDM).

We propose a technique that enhances the performance of Torrieri and Bakhru's maximin algorithm in the presence of frequency offsets and modulated interferences, a common scenario in multiple-access environments, where we observed that the Maximin algorithm suffers performance degradation in the aforesaid scenario. To combat modulated interferences and fading effects, we propose to update the step length during every smart antenna weight vector update. We found that our scheme improves the robustness of the maximin algorithm to a greater extent. Simulation results for a frequency-hopping system confirm the validity of the approach and demonstrate improvements in the performance of the maximin algorithm in the presence of frequency offsets and data modulated interferences in a fading channel environment. Index Terms--Frequency hopping, maximin, smart antenna, step length.

It is known that computational loads of the propagator method (PM) can be significantly smaller, e.g., one or two order, than those of MUSIC and ESPRIT because the PM does not require any eigenvalue decomposition (EVD) of the cross-correlation matrix and singular value decomposition (SVD) of the received data. However, the PM of the parallel shape array has nonnegligible drawbacks such as 1) requirement of pair matching between the 2-D azimuth and elevation angle estimation which is an exhaustive search and 2) estimation failure problems when elevation angles are between 70[degrees] and 90[degrees]. The purpose of this paper is to show a way to remove these problems in the PM without additional computational loads. This paper will employ one or two L-shape arrays because the parallel shape used in the PM may cause the aforesaid problems. Simulation results verify that the PM with one or two L-shape configurations can remove these problems and improve the performance of the PM significantly, e.g., almost 5 dB in signal to noise ratio for the parameters used in this paper. Index Terms--Antenna array, direction-of-arrival angle (DOA) estimation, propagator method (PM), Smart antenna.

In this paper, we present an algorithm to estimate the direction of the arrival angles (DOAs) from noncoherent one-dimensional (1-D) signal sources such as binary phase shift keying (BPSK) and M-ary amplitude shift keying (MASK). The proposed algorithm can provide a more precise DOA estimation and can detect more signals than well-known classical subspace-methods MUSIC and ESPRIT for the 1-D signals. The complexity is the same as that of ESPRIT since the proposed algorithm uses the same array geometry and subarray processing that ESPRIT does. The main differences between the proposed algorithm and the ESPRIT algorithm are as follows: 1) the number of overlapping array elements between two subarrays is equal to M in the proposed algorithm, while in ESPRIT the maximum number of overlapping elements is M--1, where M denotes the total number of array elements, and 2) the proposed algorithm employs the conjugate of rotation matrix (CRM) [PHI]* while ESPRIT uses [PHI] with no conjugate for the second subarray geometry. Index Terms--Antenna arrays, array signal processing, direction-of-arrival angle (DOA) estimation, ESPRIT, MUSIC.

Recently, the smart antenna (a blind adaptive antenna array) has brought much attention to its ability to improve the future code-division multiple-access (CDMA) wireless communications systems. However, Adachi et al. [1], [2] employed only one out of M elements that are in a smart antenna array during the pseudonoise (PN) code acquisition process due to the difficulty in obtaining the weight coefficients of the smart antenna and PN code acquisition jointly and adaptively. Yet, as the PN code is acquired, all M elements are used in [1] and [2] to improve the signal-to-noise ratio (SNR) at a reverse link. In this paper, we propose an efficient PN code acquisition scheme where all elements are employed during PN code acquisition. Also, we show that by using all elements, the PN code acquisition time can be shortened by at least 40% for a given signal-to-noise ratio and M = 5, compared to the single element case. Furthermore, the power of a random access user signal in the reverse link can be lowered at least 3 dB. The additional computational load and complexity to use the proposed PN code acquisition are insignificant. Index Terms--Code.division multiple access (CDMA), pseudonoise (PN) code acquisition, smart antennas.

The analysis in this paper concerns the performance of smart antenna algorithms when used in code-division multiple access (CDMA) wireless communication systems. Complex pseudonoise (PN) spreading, despreading, and pilot-aided channel estimates in the cdma2000 reverse link are some of major characteristics that are different from those in the IS-95 CDMA systems. These different features are included in our analysis. Four computationally efficient smart antenna algorithms are introduced: 1) smart antenna based on maximum output power criteria without lagrange multiplier; 2) smart antenna based on maximum signal-to-interference-plus-noise output power ratio (SINR) criteria with eigenvector solution; 3) smart antenna based on maximum SINR output criteria without eigenvector solution; 4) more simplified smart antenna based on maximum SINR output criteria without eigenvector solution. Algorithms (1) and (4) require only 4M computational instruction cycles per snapshot where M is the number of antenna array elements. Algorithms (2) and (3) require [M.sup.2] and (4M + 2[M.sup.2]) operations per snapshot, respectively. These computational loads are significantly smaller than those of typical eigenvalue decomposition blind detection approaches. Bit error rates (BERs) resulting from these algorithms are evaluated through simulation. Double spike power delay profile with equal or unequal power is used. Also, a cluster of interfering users and scattered interference users are considered. For BER comparisons, antenna diversity using equal gain combining is also analyzed. The four smart antenna algorithms show significant capacity improvement compared to the antenna array diversity using equal gain combining under the double spike power delay profile with equal power and scattered interference environments. Index Terms--Adaptive array antenna, code division multiple access (CDMA), mobile fading environment, multiple access interference, smart antenna, wireless communications.

Recently, a digital communication receiver, called a third-generation receiver, has been developed. This receiver takes samples of the direct-sequence spread signal at a nonzero intermediate frequency (IF) instead of the zero IF (baseband), and quantizes the samples by employing a 1-b analog-to-digital (A/D) converter at the receiver front end. These 1-b samples are digitally processed for pseudonoise (PN) code, carrier, bit synchronization, and bit decision with the use of an application-specific integrated circuit. In this paper, the effects of the IF sampling and 1-b A/D conversion on PN code synchronization are analyzed for a PN spread-spectrum communication system with oversampling rate, e.g., 12 samples per chip. In addition, bit-error rate (BER) degradation due to the 1-b A/D conversion is studied by assuming perfect PN code, carrier, and bit synchronization. It is observed that BER degradation due to the 1-b A/D is significant, e.g., 2.4 dB, when decimation is made after IF sampling such that only one sample per chip is used for bit decision. These analyzed BER results agree well with the simulated results. However, if no decimation is made and oversampling is used for bit decision, BER degradation due to 1-b A/D conversion is insignificant, e.g., 0.6 dB. Index Terms - Digital receiver, 1-b A/D signal processing, PN code acquisition, PN spread spectrum, satellite communications.

Recently, a digital baseband receiver called zero-intermediate frequency zero-crossing demodulator (ZIFZCD) was developed for digital FM signal detection. ZIFZCD is applicable to many worldwide mobile and personal communications systems. In addition, ZIFZCD offers lower power consumption and simpler implementation, compared to the conventional analog implementation [e.g., a limiter-discriminator integrator and dump (LDI)] and the conventional digital implementation [e.g., the cross-differentiate-multiply demodulator (CDM)]. An objective of this paper is to introduce the ZIFZCD and report the bit-error rate (BER) of the ZIFZCD under both static and fading environments. The analyzed and simulated BER results show that the ZIFZCD is comparable to the conventional CDM for a narrowband digital FM with modulation index 0.5, and the ZIFZCD is significantly better than the CDM for a wideband digital FM with modulation index larger than 1.5.

This paper computes the probabilities of detection and false alarm for a pseudonoise (PN) sequence code lock detector when a strong radio frequency interference (RFI) hits the communications link. A soft-limiter, a hard-limiter, and no limiter at the front-end of the receiver are considered. Both continuous wave (CW) type RFI and pulse type RFI are analyzed. It is shown that a soft-limiter or a hard-limiter can protect the PN-code lock detector against a typical pulse RFI, but in a CW RFI environment, the PN-code lock detector performance with a soft-limiter or a hard-limiter will be worse than that with no limiter.

A known jamming state information (JSI) scheme for a coded frequency-hopped M-ary frequency-shift-keying (FH/MFSK) system under partial-band noise jamming, plus additive white Gaussian noise, utilizes the maximum a posteriori (MAP) rule based on the total energy received in the M-tone signaling bands. It is assumed that the knowledge of partial-band noise jamming fraction is available to the JSI generator. Because this scheme reduces the M-dimensional information into one dimension, i.e., the total energy, the generated JSI may not be the best. In this paper, a neural network approach to the JSI generation is presented. The efficiency of the new JSI generator with known partial-band noise jamming fraction is compared with the MAP generator. The neural network scheme is then generalized to increase its robustness by allowing for an unknown partial-band noise jamming fraction. The neural network JSI generator with or even without knowledge of jamming fraction offers significantly better performance for a coded FH/MFSK communication system than the MAP JSI generator for high code rate.

In a recently proposed optical orthogonal code division multiple-access (OOCDMA) system, one bit of user's data is transmitted per sequence-period, and a threshold is employed for the final bit decision. In this paper, a system that can transmit multibits per sequence-period is introduced, and avalanche photodiode (APD) noise, thermal noise, and interference, are included. This system, derived by exploiting orthogonal properties of the OOCDMA code sequence and using a maximum search (instead of a threshold) in the final decision, is [log.sub.2]F times higher in throughput, where F is sequence-period. For example, four orders of magnitude are better in bit error probability at -56 dBW received laser power, with F = 1000 chips, 10 'marks' in a sequence, and 10 users of 30 Mb/s data rate for one-bit/sequence-period and 270 Mb/s data rate for multibits/sequence-period system. Furthermore, an exact analysis is performed for the [log.sub.2]F bits/sequence-period system with a hard-limiter placed before the receiver, and its performance is compared to the performance without hard-limiter, for the chip-synchronous case. The improvement from using a hard-limiter is significant in the [log.sub.2]F bits/sequence-period OCCDMA system (while it is not in a one-bit/sequence-period OOCDMA system in [7]).

In an optical multiple-access system, overall system throughput efficiency and significant implementation cost-reduction would be achieved if many users could access a common optical channel at any time without control among users. Recently one such scheme, an optical orthogonal code division multiple-access system (OOCDMA), was introduced by Salehi et al. for the case of no noise. In this paper, some extensions of the work in [2] are presented, including the effects of avalanche photodiode (APD) noise and thermal noise as well as interference for the OOCDMA direct-detection receiver. Since it has been shown that an optical hard-limiter before the receiver correlator can reduce the interference effect for the OOCDMA system in the absence of noise, the hard-limiter role in the presence of thermal and APD noise is also examined.

This paper analyzes the probabilities of data packet loss for both an encrypted channel in self-synchronous cipher feedback mode and a nonencrypted channel, in the space data systems. Simulation results show reasonable agreement with analytical results. When channel bit error probability is 10 to the -5 and the total number of packets per frame is 3, the analytical model gives 0.39% packet loss while the simulation gives 0.22% packet loss due to encryption. Although the analysis is performed for the space data systems, the resulting derived equations with minor change will be useful in many packet communication applications.

The space shuttle orbiter (SSO) Ku-band single access return (KSAR) link and the space station freedom (SSF) KSAR link via the tracking and data relay satellite system (TDRSS) use the same carrier frequency. The interference between spacecraft is minimized by opposite antenna polarizations and by TDRSS antenna beam pointing, but if the SSF and SSO are in close proximity, it is expected that mutual interference will be significant. Recently, Tsang and Su (1), (2) simulated the mutual interference effects, using a practical nonlinear band-limited channel. The purpose of this paper is to demonstrate that a simplified (i.e., linear band-limited channel) analytical approach will yield adequate accuracy for the expected range of operating conditions. Relative degradation in bit energy-to-thermal noise power spectral density ratio to achieve a 10 to the negative fifth coded bit-error-probability is determined to be 4 dB for the Ku-band SSO-to-TDRS I-channel return link with a 4.5 dB effective signal-to-interference total power ratio (S/I) when the Ku-band SSF-to-TDRS return link interferes, whereas Su's simulation yields approximately 5 dB degradation. For the Ku-band SSF-to-TDRS return link, both analysis and simulation results yield a relative signal degradation of 0.4 dB at the effective S/I = 21.6 dB. In conclusion, interference on the Ku-band SSO-to-TDRS I-channel return link is significant, but on the Ku-band SSF-to-TDRS return link it is negligible.

A baseband digital narrow-band FM receiver, called zero-intermediate frequency zero-crossing demodulator (ZIFZCD), has been recently developed. This demodulator may offer low complexity and simple implementation. However, the bit error rate (BER) performance of the ZIFZCD is inferior to that of the limiter-discriminator-integrate-and-dump (LDI) demodulator. In this paper, a simple decision feedback postprocessor (DFP) is proposed to improve the performance of the ZIFZCD. Analysis and simulation BER results of the ZIFZCD with the DFP are presented for minimum-shift keying (MSK) and Gaussian MSK (GMSK) signals under additive white Gaussian noise (AWGN) and mobile fading environments. Index Terms--GMSK, narrow-band digital FM, wireless communications, zero-crossing demodulation, zero-IF.

This current paper addresses the noncooperative distributed wireless relay networks under a jamming environment. The amplify- and-forward single-input multiple-output (SIMO) and multiple-input single-output (MISO) schemes are considered with multiple N-relay nodes. The main contribution of this paper is to determine the optimal relay precoder vectors by minimizing the minimum mean square error (MSE) criterion. Using the derived optimal relay precoder vectors, the impacts on the jamming environment in the AF SIMO/MISO wireless relay systems are investigated using bit error rate (BER). Results show that the diversity order of a system decreases under a jamming environment. It is also seen that the system BER performance enhances as the number of relay nodes N increases. [ABSTRACT FROM AUTHOR]

We fabricated 0.029 λ miniaturized Co2Z hexaferrite terrestrial digital multimedia broadcasting (T-DMB) antenna. T-DMB antenna was fabricated by winding 12-turn Cu tape around the Co2Z rectangular block. Antenna was mounted on the ground substrate with connection of coaxial feeding line. Fabricated Co2Z antenna showed 196.2 MHz of center frequency, -6.55 dB of 3-D average gain and 22.13% of radiation efficiency at 195 MHz. Average gain of Co2Z antenna is found to be greater than -17.4 dB in the range of 174-216 MHz. [ABSTRACT FROM AUTHOR]

This paper proposes to encode pilot bits together with information bits by using a systematic encoder and applying them to an iterative receiver, where channel estimation and decoding are iteratively performed. This paper then shows why and how the encoded pilot bits can give a positive gain over a conventional uncoded pilot system. Specifically, this paper considers an orthogonal frequency-division multiplexing system that is encoded by a low-density parity-check code under a frequency-selective fading channel and shows theoretical analysis as well as simulation results. [ABSTRACT FROM AUTHOR]

In this paper, we present an algorithm to estimate the direction of the arrival angles (DOAs) from noncoherent one-dimensional (1-D) signal sources such as binary phase shift keying (BPSK) and M-ary amplitude shift keying (MASK) The proposed algorithm can provide a more precise DOA estimation and can detect more signals than we D-known classical subspace.methods MUSIC and ESPRIT for the 1-D signals. The complexity is the same as that of ESPRIT since the proposed algorithm uses the same array geometry and subarray processing that ESPRIT does. The main differences between the proposed algorithm and the ESPRIT algorithm are as follows: 1) the number of overlapping array elements between two subarrays is equal to M in the proposed algorithm, while in ESPRIT the maximum number of overlapping elements is M - 1, where M denotes the total number of array elements, and 2) the proposed algorithm employs the conjugate of rotation matrix (CRM) V while ESPRIT uses 1 with no conjugate for the second subarray geometry. [ABSTRACT FROM AUTHOR]

A response by Jean-Pierre Delmas to a letter to the editor about the article on Conjugate ESPRIT is presented.