Non-Regenerative MIMO Relaying with Channel State Information

This paper addresses channel state information (CSI) estimation in a wireless relay network, which consists of a base station (BS), a relay station (RS), and a mobile station (MS). We propose a method for the BS to obtain the instantaneous CSIs of the three links (BS-RS, BS-MS, and RS-MS links) with minimized overhead. The CSI availability plays an important role for the BS to adapt its transmission strategies to the given channel conditions. Our proposed method exploits the fact that the link condition between fixed BS and fixed RS tends to be stable, and the frequent CSI update is not necessary for this link. In order for the BS to obtain the CSI of the distant link (i.e. RS-MS link), RS amplifies a pilot signal received from MS with a pre-defined amplification factor, and forwards it to BS. This enables the BS to obtain the CSI of the RS-MS link based on the received pilot signal and pre-knowledge on the CSI of BS-RS link. We show by computer simulation that our proposed method can reduce the required overhead for CSI estimation with little degradation on the accuracy of the obtained CSI.

In this paper, we study three cooperative transmission schemes by use of amplify-and-forward (AF) relaying strategies. It is assumed that there is one source, one destination and several AF-relays. First, a parallel-relay strategy is considered wherein the transmitted message from the source is received by each relay independently. Then, the relay retransmit the message by use of AF relaying to the destination. Next, we consider the case where the message is being sent through the whole relays sequentially to the destination. Finally, we consider a general case, where we have multi-branches such that on each branch, there exist several relays sequentially cooperating to transmit the message to the destination. For each cooperative transmission scheme, we are looking for minimizing the symbol-error rate (SER) subject to sum-relay power (SRP). Hence, for each cooperative transmission schemes, we analyze the optimization problem and analytically derive the optimal power allocation at the relays to minimize the SER. Finally, we numerically show that when the SRP is low, we can optimize the number of active relays. That is, at low SRP increasing number of relays does not monotonically decrease the SER. On the other hand, at high SRP, employing more number of relays is more beneficial than allocating more power to a limited number of relays.

In this paper, a comprehensive comparison analysis in terms of outage probability and average symbol error ratio (SER) is presented for cooperative cognitive multiple-input and multiple-output (CC-MIMO) multiuser systems with amplify-and-forward (AF) protocol. Specially, we consider two scenarios where the CC-MIMO multiuser systems have the perfect and imperfect channel state information (CSI). The CC-MIMO multiuser systems consist of one multi-antenna source, one single-antenna relay, and multiple multi-antenna destinations. At the secondary source and destinations, the maximal ratio transmission (MRT) and maximal ratio combining (MRC) are employed, respectively. For such CC-MIMO multiuser systems, we first obtain the exact closed-form expressions of outage probability under the two cases where the CC-MIMO multiuser systems have the perfect and imperfect CSI. Then, to reduce the implementation complexity, the tight lower bounds of outage probability and average SER are derived. Finally, to obtain insight, by using the high signal-to-noise ratio (SNR) approximation, the asymptotic estimations of outage probability are achieved. The numerical results show that the derivations are agreed with the simulations, which validate our derivations. At the same time, the results show that, for the systems without perfect CSI, the achievable diversity order reduces to one, regardless of the number of antennas at the cognitive source and destinations as well as the number of the cognitive destinations. Nevertheless, these key parameters affect the coding gain of the CC-MIMO multiuser systems. When the systems have the perfect CSI (or without feedback delay), the achievable diversity gain is determined by the minimum between the number of source’s antennas and the product of the number of destinations and the number of destination’s antennas. For the effect of PU’s parameters, our results indicate that primary systems only affect the coding gain but not the diversity gain.

Due to the great potential in extending propagation distance and enhancing the link reliability, amplify and forward (AF) cooperative communications have attracted much attention recently. However, the existing studies mainly focus on the energy consumption analysis and optimization, and also the channels used in communications are based on Rayleigh/Rician fading model, and/or it was usually supposed that the channel state information (CSI) is known or can be acquired by a training sequence. In this paper, blind signal detection for AF cooperative communication systems based on time division multiple access (TDMA) is studied, in which the channels are modeled as frequency selective fading and the CSI are unknown. A blind signal detection algorithm of partial amplify and forward (PAF) cooperative communication is proposed based on semidefinite relaxation (SDR). This method can recover the data without the training sequence and need not to implement blind equalization for the unknown channels. With the correlation between data of different links, the proposed method can obtain the optimal solution efficiently and achieve better performance of signal detection than the traditional algorithm. By simulations, the energy consumption efficiency as well as the overall system performance of the proposed strategy are verified.

Researches show that the MSK (Minimum-shift Keying) modulation has the variety characteristic of modulator structure; moreover its modulator structure has the certain waveform encryption function for the input messages. In this paper, referring to the idea of frequency hopping communication, we apply the variety of MSK modulator structure to enhance the physical layer security of the cooperative transmission with untrusted relay. A cooperative transmission scheme with MSK modulation is proposed for the three nodes AF (Amplify-andForward) cooperative system with untrusted relay, where the MSK modulator structure can be changed according to a secret between the source and the destination. Through theoretical analysis and experimental simulation, we show that the BER (bit error rate) as high as about 50% makes demodulating practically infeasible for the untrusted relay in the proposed cooperative scheme, thus securing the communication between the source and destination. Furthermore, this security transmission scheme is independent on the channel variations of the wireless environment, and is very suitable for the wireless networks where the channel remains static for most of the network lifetime.

The following paper investigates the secondary sum rate of MIMO two-way cognitive relay networks with multiple relays using amplify and forward (AF) strategy. The capacity of the system can be maximize by using optimum power allocation (OPA) algorithm in place of equal power allocation(EPA) among all nodes, while assuming that all node having fully channel state information (CSI). It has been considered that MIMO cognitive relay with spectrum sharing and cooperative strategy between node to maximize the secondary sum rate and enormous use of the spectrum. Our aim is to maximize the secondary sum rate and efficient spectrum use. MIMO relay is going to use amplify and forward relay technique means relay is not decode the signal received from the secondary user's. Result shows that this technique is increasing the secondary sum rate without using extra power and spectrum.

This paper proposes interference-based decode and forward scheme that utilizes relay stations (RSs). In Long-Term-Evolution (LTE-) Advanced, heterogeneous networks in which femto- and picocells are overlaid onto macrocells are extensively discussed. However, interference between macro- and pico(femto)cells arises due to their different transmit power levels. Unlike conventional cooperative transmission schemes, the RS decodes interference in the first transmit timing period and forwards it to the user equipment (UE) in the second period. Moreover, cooperative transmission can be achieved without stopping the transmission from the base station (BS) to UE when forwarding the interference from the RS to the UE by utilizing the fact that signal-to-noise power ratio (SNR) between the RS and UE is much greater than that between the BS and UE. The basic performance of the proposed method is shown based on computer simulation. Moreover, the interference temperature and shadowing effect are measured when considering the coexistence between macro- and femtocells, and the performance of the proposed method is verified using measured shadowing effect.

In this paper, we propose a new amplify-and-forward (AF) cooperative transmission scheme with adaptive modulation to maximize overall system spectral efficiency. We quantify the average spectral efficiency performance of the proposed scheme through statistical analysis based on an upper bound of the combiner output signal-to-noise ratio (SNR) and obtain the closed-form solutions for some practical scenarios of interest.

Underwater acoustic channels normally have low data rate, long propagation delay, severe multipath effect, and time varying fading. Cooperative transmission is a new wireless communication technique in which diversity gain is achieved by utilizing relay nodes as virtual antennae. In this paper, we investigate cooperative transmission techniques for underwater acoustic communications. First, we study the performance of several cooperative transmission schemes, originally designed for radio communications, in an underwater scenario. Second, by taking advantage of the low propagation speed of sound, we design a new wave cooperative transmission scheme. In this scheme, the relay nodes amplify the signal received from the source node, and then forward the signal immediately to the destination. The goal is to alter the multipath effect at the receiver. Third, we derive the performance upper bound for the proposed wave cooperative transmission scheme. The simulation results show that the proposed wave cooperative transmission has significant advantages over the traditional direct transmission and the existing cooperative transmission schemes originally designed for radio wireless networks.

The impact of unavailable relays is a serious issue in cooperative communication schemes, where the operation state of relays affects optimal relay selection. In addition, secure signal transmission is an interesting approach to prevent the wiretapping actions of eavesdropper nodes in a wireless environment. In this paper, we propose two cooperative secrecy transmission schemes: a secrecy decode-and-forward protocol and a hybrid of direct secrecy and cooperative secrecy transmission schemes to enhance the spectrum utilization efficiency. In the proposed schemes, a source transmits data signals to a destination with the assistance of relays. At the same time, these data signals are eavesdropped by another node. The best relays are successfully selected in a safe manner based on both decoding from a source to a destination and the available state of cooperative relays. The secrecy performance of each scheme is analyzed and evaluated by the exact outage probability over Rayleigh fading channels. Monte Carlo simulations were performed to verify the theoretical analysis. Finally, a discussion and comparison of the cooperative secrecy transmission schemes and the direct secrecy transmission approach are presented.

In this paper, we study the performance of nonregenerative and regenerative cooperation under peak power constraint. We compare the following relay function scenarios: fixed gain amplify and forward (AF) relay, variable gain AF relay, scaled gain AF relay, and decode and forward (DF) relay. We show that under this practical peak-power constraint, the knowledge of the channel state information (CSI) is essential for the AF cooperation in order to improve the power efficiency of the relay and efficiently obtain the diversity gain.

Since the existing full-rate cooperative transmission schemes have a serious defect in low Bit Error Rate (BER) performance while the existing high-rate cooperative transmission schemes have a serious defect in low spectral efficiency, a distributed high-rate cooperative relay transmission scheme based on full-rate cooperative communication model is proposed in this paper, in which Cyclic Delay Diversity (CDD) technology and Linear Constellation Precoding (LCP) technology are employed. Moreover, the proposed scheme addresses the issue of obtaining maximum spatial and multipath diversity with low decoding complexity and high transmission reliability. The BER performance of the proposed scheme is contrasted to that of the full-rate transmission scheme where better performance is achieved, and is improved when the number of the multipath or the relay nodes increases.

This letter proposes a robust joint linear precoding scheme based on the minimum mean squared error (MMSE) criterion for amplify-and-forward (AF) multiple-input multiple-output (MIMO) relay broadcast systems with limited feedback, where only the quantized channel direction information (CDI) of the forward channel is available for the base station (BS) and the relay station (RS). The proposed scheme employs an iterative algorithm which alternately optimizes the BS and RS precoders to jointly minimize the expected MSE conditioned on the quantized CDI.

The use of cooperative schemes in wireless networks has recently attracted much attention in scenarios where application of multiple-antenna systems is impractical. In such scenarios, the requirement of having full channel state information (CSI) at the receiver side can be relaxed by using differential distributed (DD) transmission schemes. However, in the DD schemes proposed so far, the decoding complexity as well as the delay requirements increase with the number of relays. In this paper, we propose a low-rate feedback-based DD approach (with one-bit feedback per relay) that enjoys full diversity, linear maximum likelihood (ML) decoding complexity, and unrestrictive delay requirements. In addition, the proposed feedback scheme does not require any CSI knowledge at the receiver, and its implementation is simple. Computer simulations demonstrate substantial performance improvements of the proposed techniques as compared to several popular cooperative transmission schemes.

In this paper, we investigate the outage performance of an amplify-and-forward (AF) multiple input multiple output (MIMO) opportunistic relay selection system under time-varying channels. A practical scenario is considered, where both the relay selection and the beamforming transmission are performed with outdated channel state information (CSI), due to channel fluctuations and delays involved in relay selection and CSI feedback. To provide efficient means of evaluating the outage performance, a closed-form expression for the outage probability is given. The effects of parameters, such as the correlation between the outdated and current CSI, the number of antennas are also analyzed. All the analytical results are validated by Monte Carlo simulations.