On the diversity gain region of the dynamic decode-and-forward relay-assisted Z-channel

In an interference-limited system, the interference forwarding by a relay enhances the interference level and thereby enables the cancellation of the interference. In this work, interference forwarding by a half-duplex dynamic decode-and-forward (HD DDF) relay in a two-user Z-channel is considered. In the two-user Z-channel, one user is interference-limited while the other user is interference-free. The diversity gain region (DGR), which characterizes the tradeoff between the achievable diversity orders between the two users, is an appropriate performance metric for the Z-channel. Closed-form expression for the achievable DGR with the interference forwarding by the HD DDF relay is presented. The multiplexing gain regions (MGRs) where the HD DDF protocol achieves better DGR over the direct transmission scheme, full-duplex decode-and-forward (FD DF) and FD partial DF relay assisted Z- channel are identified. The HD DDF protocol is shown to achieve better DGR than the FD DF and FD PDF relay for a large range of MGR. The achievable DGRs for the HD DDF, FD DF, and FD PDF relay-assisted Z-channel and direct transmission scheme are presented for various interference levels and multiplexing gain pairs.     

Maximum available power gain of active 2-ports

Without evaluating the port terminations, it is shown that the maximum power gain of an absolutely stable active 2-port is realisable with conjugate-matching source and load immittances. Expressions for these optimum terminations and associated gain are obtained from a simple application of the well known image-parameter theory.     

Exact analysis of maximum available gain and unilateral gain including phase angle of S21

Exact formulae are presented for both maximum available gain (G/sub ma/) and unilateral gain (U), which include both the magnitude and phase angle of the S/sub 21/ parameter. The result for G/sub ma/ is not unique since there are many possible solutions to simultaneously match S/sub 11/ and S/sub 22/ when k>1. For the phase angle of U, the result tends to become 180/spl deg/ when using the topology of a variable coupler, a line stretcher, and a feedback amplifier. From the verifications, an amplifier using the unilateralizing technique will achieve 4-6 dB higher gain than that of the G/sub ma/ amplifier.     

Direct measurement of the available voltage gain of bipolar and field-effect transistors

A new method for the direct measurement of the available voltage gain of bipolar and field-effect transistors is presented. The method is easily automated using existing semiconductor parameter analysis systems. An example of direct measurement of the mismatch in available gain is also presented.     

An empirical relationship for path diversity gain

Existing 15.3 and 16 GHz path diversity gain data for earth-space propagation paths are used to generate an empirical relationship for diversity gain as a function of terminal separation distance and single terminal fade depth. The agreement between the resulting closed form expression and the data is within 0.75 dB in all cases.     

The diversity gain of transmit diversity in wireless systems withRayleigh fading

In this paper, we study the ability of transmit diversity to provide diversity benefit to a receiver in a Rayleigh fading environment. With transmit diversity, multiple antennas transmit delayed versions of a signal to create frequency-selective fading at a single antenna at the receiver, which uses equalization to obtain diversity gain against fading. We use Monte Carlo simulation to study transmit diversity for the case of independent Rayleigh fading from each transmit antenna to the receive antenna and maximum likelihood sequence estimation for equalization at the receiver. Our results show that transmit diversity with M transmit antennas provides a diversity gain within 0.1 dB of that with M receive antennas for any number of antennas. Thus, we can obtain the same diversity benefit at the remotes and base stations using multiple base-station antennas only     

Signal correlations and diversity gain of two-beam microcellantenna

The motivation of the present study is to investigate the possibility of using two independently directed antenna beams in a mobile base station to provide diversity gain and reduce fading problems in a microcellular environment. The signal correlation of the individual antenna beams is studied, and it is shown that correlation depends on beamwidth, separation angle of the antenna beams, and the location of the base-station antenna array. Signal correlations have been computed using narrow- and wide-beam antennas in two separate base-station antenna locations. Diversity gains of both antenna types have been optimized by selecting the beam orientations which minimize the signal correlation. The numerical simulations show that a considerable diversity gain can be obtained using this approach     

On the realized gain of arrays

A theorem concerning the maximum realized gain of arbitrary arrays is proven. The theorem is applied to the specie case of uniformly spaced circular arrays. A gain equivalence between multiple planar and circular arrays is also derived.     

Channel coupling in orthogonal polarisation diversity systems and its influence on diversity gain

The effects of channel coupling (CC) in two-branch orthogonal polarisation antenna diversity systems both on the correlation and the mean power difference between received signals are reported. It is shown that the presence of CC increases the correlation but probably decreases the mean power difference and hence improves the diversity gain.     

Analysis of equal gain diversity on Nakagami fading channels

An infinite series for the complementary probability distribution function (CDF) of the signal-to-noise ratio (SNR) at the output of L -branch equal-gain (EG) diversity combiners in Nakagami (1960) fading channels is derived. The bit error rate for a matched filter receiver is analyzed for the L-branch EG combiner and different fading parameters. Both coherent phase shift keying (CPSK) and differential coherent phase shift keying (DCPSK) are considered. The effects of gain unbalance between branches on the probability distribution of the SNR and on the bit error rates are investigated. Bit error rate results are also obtained for coherent and noncoherent reception of frequency shift keying (FSK). The effects of gain unbalances on FSK modulations are also investigated. Bit error rates for EG combining on Rayleigh fading channels are obtained for L>2. These results are presented as a special case of the more generalized Nakagami fading model     

On the operation of cascode gain stages

The gain-enhancing action of the cascode is explained on the basis of a gain developing at an intermediate node. In this sense, a cascode with a high-impedance load acts as the cascade of an inverting and a noninverting stage, with the total gain determined by the product of the intrinsic gains of each. The cascode nevertheless retains the advantage of a significantly smaller loading, which it presents at its input terminal, compared to a common-source stage. This analysis approach is extended to other circuits configured for intrinsic gain subject to constraints imposed by current sources, where gain enhancement is obtained     

On the gain of a reconfigurable-aperture antenna

A full-wave analysis based on the method of moments (MoM) is carried out for a reconfigurable-aperture antenna consisting of a two-dimensional (2-D) array of filamentary microstrip-dipoles interconnected by lossy microelectromechanical-system (MEMS) switches. Activation of specific MEMS switches allows the dipoles to be maintained near the halfwave-resonant length as the frequency is reduced in octave increments between 16 and 2 GHz. This keeps the real part of the dipole self-impedance much higher and the imaginary part much lower than in a dipole having a fixed length of λ/2 at 16 GHz. Hence, the array antenna gain and aperture efficiency remain much higher with frequency than in an array of fixed dipoles. Broad side aperture efficiencies of -3.9, -6.0, -9.5, and -10.6 dB are predicted for 16×16, 8×8, 4×4, and 2×2 recap dipole arrays at frequencies of 16, 8, 4, and 2 GHz, respectively, for MEMS switches having 0.5 dB insertion loss. In contrast, fixed-element λ/2-separated arrays operating at the same frequencies have predicted efficiencies of -3.9, -24.2, -45.0, and -63.0 dB, respectively     

Long-term rain attenuation probability and site diversity gain prediction formulas

Simple models for long-term induced rain attenuation on a slant path and site diversity gain are presented in this work. As verified by numerous tests against the ITU-R databank and other data from the literature, the proposed models exhibit a very good performance. The novel slant path rain attenuation prediction model compared to the ITU-R one exhibits a similar behavior at low time percentages and a better root-mean-square error performance for probability levels above 0.02%. Moreover, comparing the proposed site diversity gain model with other widely accepted models from the literature, an improved performance is observed for distances less than 15 km, while the model performs equally well for greater distances. Furthermore, a sensitivity test between the proposed and Hodge's formula with respect to the separation distance D is also carried out. While the lower limit of the proposed model is found to be D=1.7 km, its extension covering large-scale site diversity is successfully compared with experimental data coming from Japan. The set of presented models exhibits the advantage of easy implementation with little complexity and is considered useful for educational and back of the envelope computations.     

基于空间分集增益的分布式快速空频编码算法

针对多点协作(Co MP)无线通信系统的下行传输问题,提出一种分布式快速空频编码(DF-SFC)的方案。通过将小区边缘用户分组和分享相邻小区间的子载波获得空间分集增益,有效缓解了载波间干扰(ICI),基于此设计分布式解码器,将用户的解码复杂度降低到相同的非分布式空频编码最佳解码器的50%。通过将所提方案与Alamouti多点协作和非多点协作方案做比较,对用户与其基站之间相对距离对比研究了可实现的传输速率,并且推断出它的性能上限和下限,用于确立小区边缘用户的阈值,实现在提出的多点协作和非多点协作模式之间切换,以提高整体性能。仿真结果表明,在服务小区边缘用户方面提出的方案均优于Alamouti多点协作和非多点协作方案。     

Instantaneous diversity gain in 10-30 GHz satellite systems

As usually defined, diversity gain is a statistical measure which conveys little or no information about the instantaneous behavior of site-diversity reception in a satellite communications system. A new quantity called instantaneous diversity gain is introduced and some measurements of it from an 11.6 GHz low-angle two-site downlink are presented. It is shown how instantaneous diversity gain is related to system reliability and some results are presented which indicate that designs based on statistical diversity gain will achieve their intended reliability levels.     

On the combination of spatial diversity and multiuser diversity

The intention of this letter is to clarify various aspects related to the combined use of spatial diversity and multiuser diversity in a mobile network. We consider a system with one base station and K users, and study five different spatial diversity transmission modes. We show that in general, the multiuser diversity benefit is not reduced by the proper use of spatial diversity. Numerical examples are provided.     

Moments-based approach to the performance analysis of equal gain diversity in Nakagami-m fading

In this letter, an alternative moments-based approach for the performance analysis of an L-branch predetection equal gain combiner (EGC) over independent or correlated Nakagami-m fading channels is presented. Exact closed-form expressions are derived for the moments of the EGC output signal-to-noise ratio (SNR), while the corresponding moment-generating function (MGF) is accurately approximated with the aid of Pade/spl acute/ approximants theory. Important performance criteria are studied; the average output SNR, which is expressed in closed form both for independent and correlative fading and for arbitrary system parameters, the average symbol-error probability for several coherent, noncoherent, and multilevel modulation schemes, and the outage probability, which are both accurately approximated using the well-known MGF approach. The proposed mathematical analysis is illustrated by various numerical results, and computer simulations have been performed to verify the validity and the accuracy of the theoretical approach.     

Simple construction of OFDM signals with diversity gain and low PAPR

A simplified orthogonal frequency division multiplexing (OFDM) system with low peak-to-average power ratio (PAPR) and frequency diversity is proposed. The considered OFDM system exploits a frequency diversity by using a simple symbol repetition as is the case in previous work (i.e. Ko et al., MILCOM2002). From the presented results, it can be seen that a modified OFDM signal can be easily implemented with low PAPR, still maintaining the same diversity gain at the receiver as in Ko et al. However, a small increase of decoding delay may be expected.