Capacity evaluation for equal gain diversity schemes over Rayleigh fading channels

In this paper, closed-form expressions for the capacities per unit bandwidth for Rayleigh fading channels with equal gain combining (EGC) diversity case are derived for power and rate adaptation, constant transmit power, channel inversion with fixed rate, and truncated channel inversion adaptation policies. Channel inversion policies provide the highest capacity over the other adaptation policies with EGC diversity. The constant transmit power policy provides the lowest capacity as compared to the other policies.     

Spectral Efficiency Evaluation for MRC Diversity Schemes Over Generalized Rician Fading Channels

In this paper, closed-form expressions for the capacities per unit bandwidth for generalized Rician fading channels are derived for power and rate adaptation, constant transmit power, channel inversion with fixed rate, and truncated channel inversion adaptation policies. The closed-form solutions are derived for the single antenna reception (without diversity combining) and maximal-ratio combining (MRC) diversity cases. Truncated channel inversion adaptation policy is the best policy for the single antenna reception case, while the channel inversion with fixed rate policy is the best policy for the MRC diversity case. Constant transmit power policy provides the lowest spectral efficiency as compared to the other policies with and without diversity.     

Spectrum Efficiency Evaluation with Diversity Combining for Fading and Branch Correlation Impairments

In this paper, closed-form expressions for capacities per unit bandwidth for fading channels with impairments due to Branch Correlation are derived for optimal power and rate adaptation, constant transmit power, channel inversion with fixed rate, and truncated channel inversion policies for maximal ratio combining diversity reception case. Closed-form expressions for system spectrum efficiency when employing different adaptation policies are derived. Analytical results show accurately that optimal power and rate adaptation policy provides the highest capacity over other adaptation policies. In the case of errors due to branch correlation, optimal power and rate adaptation policy provides the best results. All adaptation policies suffer no improvement in channel capacity as the branch correlation is increased. This fact is verified using various plots for different policies. With increase in branch correlation, capacity gains are significantly larger for optimal power and rate adaptation policy as compared to the other policies. The outage probability for branch correlation is also derived and analyzed using plots for the same.     

Performance Analysis of MC-CDMA Systems Under Nakagami Hoyt Fading

Based on an alternative expression for Q-function, a simple bit error rate expression is derived in this paper for multicarrier code division multiple access systems with maximal ratio combining in correlated Nakagami-q channels. Furthermore, in this paper, we derive bounds on the probability of error and ergodic capacity of spatially multiplexed MC-CDM systems with zero forcing unified successive interference cancellation technique. Closed-form expressions for Capacities per unit bandwidth and Outage probability using optimal power and rate adaptation policy are derived and plotted. Asymptotic approximations and upper bounds on spectrum efficiency are also derived and plotted. Numerical results for Symbol Error Rate are also derived and plotted using MATLAB.     

Spectrum Efficiency Evaluation for MRC Diversity Schemes Under Different Adaptation Policies Over Generalized Rayleigh Fading Channels

In this paper, closed-form expressions for the capacities per unit bandwidth for Generalized Rayleigh fading channels are derived for optimal power adaptation, constant transmit power, channel inversion with fixed rate, and truncated channel inversion adaptation policies. The closed-form solutions are derived for the single antenna reception (without diversity combining) and MRC diversity reception cases. Optimal power adaptation policy provides the highest capacity over the other adaptation policies both with and without diversity combining. Truncated channel inversion policy suffers a large capacity penalty relative to the optimal power adaptation policy as the number of degrees of freedom is increased. However, with increase in diversity, the capacity penalty for the truncated channel inversion policy decreases. Capacity gains are more prominent for channel inversion with fixed rate policy as compared to the other adaptation policies.

Novel Closed-Form Expressions for Ergodic Capacity of MIMO-OSFBC-OFDM Systems Over Channel Adaptation Policies

In this work, closed-form expressions for capacities per unit bandwidth for MIMO-OFDM systems employing Orthogonal Space-Frequency Block Coding over multipath frequency-selective fading channels are derived for adaptation policies like optimal power and rate adaptation, optimal rate adaptation with constant transmit power, channel inversion with fixed rate, and truncated channel inversion polices. A Signal-to-Noise Ratio based user selection scheme is considered. Optimal power and rate adaptation policy provides the highest capacity over other adaptation policies. Capacity penalty is the highest for optimal rate adaptation with constant transmit power policy, while the performance of channel inversion with fixed rate policy and truncated channel inversion policy lie between that of OPRA and ORA policies.     

Capacity of Rayleigh fading channels under different adaptivetransmission and diversity-combining techniques

We study the Shannon capacity of adaptive transmission techniques in conjunction with diversity-combining. This capacity provides an upper bound on spectral efficiency using these techniques. We obtain closed-form solutions for the Rayleigh fading channel capacity under three adaptive policies: optimal power and rate adaptation, constant power with optimal rate adaptation, and channel inversion with fixed rate. Optimal power and rate adaptation yields a small increase in capacity over just rate adaptation, and this increase diminishes as the average received carrier-to-noise ratio (CNR) or the number of diversity branches increases. Channel inversion suffers the largest capacity penalty relative to the optimal technique, however, the penalty diminishes with increased diversity. Although diversity yields large capacity gains for all the techniques, the gain is most pronounced with channel inversion. For example, the capacity using channel inversion with two-branch diversity exceeds that of a single-branch system using optimal rate and power adaptation. Since channel inversion is the least complex scheme to implement, there is a tradeoff between complexity and capacity for the various adaptation methods and diversity-combining techniques     

Capacity of correlative nakagami-m fading channels under adaptive transmission and maximal-ratio combining diversity technique

The study of channel capacity evaluation in conjunction with maximal ratio diversity-combining (MRC) is presented in this paper. Analysis of the capacity in correlative Nakagami-m fading channels is observed. Using the proposed fading model, the power and rate adaptation, constant transmit power, channel inversion with fixed rate and truncated channel inversion adaptation policies are analyzed. Our results show that the power and rate adaptation policy, being only slightly higher than capacity of constant transmit power policy, provides the highest capacity over the other adaptation policies. The results also show that truncated channel inversion adaptation policy is better alternative compared to complete channel inversion policy for all values of fading severity, diversity order and correlation coefficient.     

基于次用户功率控制辅助的合作频谱感知

传统的合作频谱感知一般将感知环境建模为单级信道,且次用户一般都以相同的发射功率向数据融合中心报告感知数据,难以体现并利用不同次用户感知数据之间的空间分集差异。为解决此问题并有效地设置次用户在感知数据上报阶段的发射功率,该文提出了3种最优功率控制方案,以获得相应设计准则下参与合作感知的次用户最优发射功率。在融合中心理想具备感知信道和报告信道的统计特性时,通过理论推导获得了基于信道统计特性的功率控制闭式解方案;当信道统计特性难以现实具备时,分别获得了基于联合信道统计特性估计的最大特征功率矢量及盲加权多特征功率矢量方案。理论分析和仿真实验表明,在不同的先验信息条件下,3种方案的性能皆远优于缺少功率控制的合作感知方案。     

Transmit power adaptation for multiuser OFDM systems

In this paper, we develop a transmit power adaptation method that maximizes the total data rate of multiuser orthogonal frequency division multiplexing (OFDM) systems in a downlink transmission. We generally formulate the data rate maximization problem by allowing that a subcarrier could be shared by multiple users. The transmit power adaptation scheme is derived by solving the maximization problem via two steps: subcarrier assignment for users and power allocation for subcarriers. We have found that the data rate of a multiuser OFDM system is maximized when each subcarrier is assigned to only one user with the best channel gain for that subcarrier and the transmit power is distributed over the subcarriers by the water-filling policy. In order to reduce the computational complexity in calculating water-filling level in the proposed transmit power adaptation method, we also propose a simple method where users with the best channel gain for each subcarrier are selected and then the transmit power is equally distributed among the subcarriers. Results show that the total data rate for the proposed transmit power adaptation methods significantly increases with the number of users owing to the multiuser diversity effects and is greater than that for the conventional frequency-division multiple access (FDMA)-like transmit power adaptation schemes. Furthermore, we have found that the total data rate of the multiuser OFDM system with the proposed transmit power adaptation methods becomes even higher than the capacity of the AWGN channel when the number of users is large enough.     

Capacity of Dual Branch MRC System Over Correlated Nakagami-<Emphasis Type="Italic">m</Emphasis> Fading Channels-A Review

Various papers on the channel capacity using different diversity combining techniques and/or adaptive transmission schemes are available to enhance channel capacity under fading environment without the necessity of increasing bandwidth and transmit powers. This paper provides the review on the channel capacity of MRC (Maximal ratio combining) over uncorrelated and correlated Nakagami-m fading channels with m = 1 (Rayleigh fading channel) under ORA (Optimum rate adaptation with constant transmit power), CIFR (Channel inversion with fixed rate) and OPRA (Optimum power and rate adaptation) schemes. We also highlight the effect of fade correlation on channel capacity and discuss the improvement of the system performance under the different adaptive techniques.     

Trellis precoding for MIMO broadcast signaling

Channel Inversion, and its Minimum Mean Square Error (MMSE) variation, are low complexity methods for Space Division Multiple Access (SDMA) in Multiple Input Multiple Output Broadcast Channel (MIMO-BC). As the channel matrix deviates from orthogonal, these methods result in a waste of transmit power. This paper proposes a trellis precoding method (across time and space) to improve the power efficiency. Adopting a 4-state trellis shaping method from [1], the complexity of the proposed method, which is entirely at the transmitter side, is equivalent to the search in a trellis with 4N states where N is the number of transmit antennas. Numerical results are presented showing that the achievable gains, which depend on the channel realization, can be significantly higher than the traditional shaping gain which is limited to 1.53dB.     

Performance analysis of an opportunistic multi‐user cognitive network with multiple primary users

Consider a multi‐user underlay cognitive network where multiple cognitive users concurrently share the spectrum with a primary network with multiple users. The channel between the secondary network is assumed to have independent but not identical Nakagami‐m fading. The interference channel between the secondary users (SUs) and the primary users is assumed to have Rayleigh fading. A power allocation based on the instantaneous channel state information is derived when a peak interference power constraint is imposed on the secondary network in addition to the limited peak transmit power of each SU. The uplink scenario is considered where a single SU is selected for transmission. This opportunistic selection depends on the transmission channel power gain and the interference channel power gain as well as the power allocation policy adopted at the users. Exact closed form expressions for the moment‐generating function, outage performance, symbol error rate performance, and the ergodic capacity are derived. Numerical results corroborate the derived analytical results. The performance is also studied in the asymptotic regimes, and the generalized diversity gain of this scheduling scheme is derived. It is shown that when the interference channel is deeply faded and the peak transmit power constraint is relaxed, the scheduling scheme achieves full diversity and that increasing the number of primary users does not impact the diversity order. Copyright © 2014 John Wiley & Sons, Ltd.     

Optimizing the transmit power for slow fading channels

We consider the design of power-adaptive systems for minimizing the average bit-error rate over flat fading channels. Channel state information, obtained through estimation at the receiver, is sent to the transmitter over a feedback channel, where it is used to optimally adapt the transmit power. We consider finite-state optimal policies to reflect the limitations of the feedback channel. We develop an iterative algorithm that determines the optimal finite-state power control policy given the probability density function (PDF) of the fading. Next, we present a discretized formulation of the problem and obtain a suboptimal solution via standard dynamic programming techniques. The discretization of the problem enables us to obtain a suboptimal policy for arbitrary fading channels for which the analytic expression of the fading probability density function is not available. Simulation results are used to draw conclusions regarding the effects of limited feedback channel capacity, delay and number of states on the bit-error rate performance of the proposed policies under slow and moderate fading conditions     

Maximizing the data transmission rate of a cooperative relay system in an underwater acoustic channel

In this paper, we investigate the problem of maximizing the data transmission rate of a cooperative relay system in an underwater acoustic communication channel. With amplify‐and‐forward relaying and adaptive source transmission, we present optimal transmit signal power adaptation policies that maximize the data transmission rate, considering both frequency and time domains. The analysis takes into account a physical model of acoustic path loss and ambient noise power spectral density. Typical characteristics of underwater channel such as frequency‐dependent fading and time variations are also considered. Capacity bounds for channel state information (CSI) only at the receiver and CSI at both transmitter and receiver are presented. To maximize the data rate, we use the notion of an optimal bandwidth which corresponds to efficient allocation of signal power across the transmission bandwidth. Under the constraint of an average transmit power, the optimal transmit power adaptation policy is found to be ‘water‐pouring’ in frequency‐time domain, while the transmit power adaptation policy with a total power constraint is ‘water‐pouring’ in frequency domain. Results show that both frequency domain and frequency‐time domain power adaptation schemes provide much greater improvement in average data rate over that of the constant power case. Copyright © 2011 John Wiley & Sons, Ltd.     

Wimax (IEEE 802.16 m) system based on space time block code and discrete multiwavelet transform and implementation in FPGA

MIMO (Multiple Input Multiple Output) scheme uses transmit diversity technique which results in high throughput with increased channel capacity. The complexity of MIMO system increases the area and power requirements of the system. The proposed work is to achieve good spectral efficiency and reduction of interference by introducing multiwavelet with MIMO technology. The improvements directly results in reduction of BER (Bit Error Rate) for a given SNR (Signal to Noise Ratio). Implementation of the proposed scheme in FPGA (Field Programmable Gate Array)—virtex5 (xcvlx30t-1f665) shows a considerable improvement in speed and area when compared with the existing methods.     

Joint Optimization Of “Transmission Rate” and “Outer-Loop SNR Target” Adaptation Over Fading Channels

Joint optimization of signal-to-noise ratio (SNR) target and transmission rate adaptation is examined for multilevel quadrature amplitude modulation (MQAM) over flat-fading channels, to maximize the spectral efficiency subject to an average transmit power constraint. We propose an adaptive transmission scheme in which the outer-loop SNR target and data rate are adapted to bit-error rate (BER), where total or truncated channel-inversion strategies are exploited for the (fast) inner-loop power control. We obtain the optimal solutions for both continuous and discrete rate adaptation, and consider cases where diversity combining is performed in the receiver. We show that by using this BER-based adaptive scheme, spectral efficiency can be improved compared with optimal SNR-based variable-rate variable-power MQAM. We also show that for continuous rate adaptation, the optimal SNR target monotonically increases with BER, while it descends within a BER range with constant rate     

MIMO wireless communication channel phenomenology

Wireless communication using multiple-input multiple-output (MIMO) systems enables increased spectral efficiency and link reliability for a given total transmit power. Increased capacity is achieved by introducing additional spatial channels which are exploited using space-time coding. The spatial diversity improves the link reliability by reducing the adverse effects of link fading and shadowing. The choice of coding and the resulting performance improvement are dependent upon the channel phenomenology. In this paper, experimental channel-probing estimates are reported for outdoor environments near the personal communication services frequency allocation (1790 MHz). A simple channel parameterization is introduced. Channel distance metrics are introduced. Because the bandwidth of the channel-probing signal (1.3 MHz) is sufficient to resolve some delays in outdoor environments, frequency-selective fading is also investigated. Channel complexity and channel stationarity are investigated. Complexity is associated with channel-matrix singular value distributions. Stationarity is associated with the stability of channel singular value and singular vector structure over time.     

浅述一种应用于MIMO系统的自适应调制方案

探讨了时变信道里MIMO系统的自适应编码调制问题并且提出一个低复杂率量化方案，被称为增强型码率量化方案，也叫ERQ。不需要大量计算，ERQ可以通过最佳连续码率和功率适应提高频谱效率。除此之外，ERQ还满足误码率和平均传送能量限制条件。     

Diversity factor-based capacity asymptotic approximations of MRC reception in Rayleigh fading channels

Two approximations to the Shannon capacity of a maximal-ratio combining (MRC) diversity system are proposed in terms of the diversity factor (DF). Asymptotic analysis shows that the approximations are identical to the true capacity in the low-SNR regime and have the same slope but different power offsets in the high-SNR regime. For Rayleigh-fading environments, the power offset differences are derived and shown to be considerably small quantities. Thus, the DF can be considered as an effective measure of the asymptotic capacity improvement offered by MRC diversity reception in Rayleigh fading channels.