Fengkui Gong

SER Analysis of the Mobile-Relay-Based M2M Communication over Double Nakagami-m Fading Channels

It has been shown that mobile-to-mobile (M2M) communications, where scatters are both around the transmitter and the receiver, may experience more severe channel fading than the fixed-to-mobile (F2M) communications. Double Nakagami-m fading is adopted to provide a realistic description of the M2M channel. By using the moment generating function (MGF) based approach, the exact symbol error rate (SER) expression, which can be numerically evaluated, is derived for the considered mobile-relay-based M2M system. Moreover, the asymptotic SER bound is provided at a high SNR regime for the insight of our approach. According to our analysis, an asymptotic diversity order of 2 × min(m1, m2) can be achieved in case of independent identically distributed (i.i.d) channels. Numerical studies illustrate that analytic results exactly match the simulations.

Distributed Concatenated Alamouti Codes for Two-Way Relaying Networks

In this letter, we consider a half-duplex amplify-and-forward two-way relaying network consisting of two sources with each having a single antenna and one relay having two antennas. For such a system, a distributed orthogonal space-time block code (STBC) is proposed by making use of the Alamouti coding scheme and jointly processing the signals from the two antennas at the relay node. Such a code turns out to make the equivalent channel at each source node be a product of the two Alamouti channels and thus, is called distributed concatenated Alamouti STBC. In addition, the asymptotic formula of exact symbol error probability (SEP) for a quadrature amplitude modulation (QAM) constellation with the maximum likelihood (ML) detector is derived. This result shows that the full diversity gain function is achieved and proportional to ln SNR /SNR2.

Cooperative mobile-to-mobile communications over double Nakagami-m fading channels

Double Nakagami-m fading model can be used to provide a realistic description of the mobile-to-mobile (M2M) channel. The moment generating function (MGF)-based approach is used to derive the symbol error probability (SEP) expressions for the multiple-mobile-relay-based M2M system. Under the consideration of better performance and lower complexity, both decode-and-forward (DF) and amplify-and-forward (AF) protocols are addressed in this study. For adaptive DF (ADF) relaying, the asymptotic SEP at high signal-to-noise ratio regime in addition to the exact SEP formulations are derived. Furthermore, the impacts of channel estimation error for the insight of non-ideal channel estimation are analysed. For fixed-gain AF (FAF) relaying, the authors present approximate SEP and asymptotic SEP to indicate the cooperative gain. For L mobile relays and under the assumption of independent and identically distributed (i.i.d) source- relay channels and i.i.d relay-destination channels, it is shown in this paper that asymptotic diversity orders of L × min(mRD,1, mRD,2) + min(mSD,1, mSD,2) and L × min(mSR,1, mSR,2, mRD,1, mRD,2) + min(mSD,1, mSD,2) can be achieved for ADF-M2M and FAF-M2M schemes, respectively. Simulations are performed to verify the analytical results.

Energy Efficiency and Spectral Efficiency Tradeoff for Asymmetric Two-Way AF Relaying With Statistical CSI

Both energy efficiency (EE) and spectral efficiency (SE) are two important design criteria that can hardly be achieved simultaneously. In this paper, we investigate the EE-SE tradeoff for a two-way relaying system with amplify-and-forward (AF) strategy. Applying a unified EE-SE tradeoff metric, a power-allocation problem is formulated as the joint EE and SE maximization problem with a tradeoff factor. In particular, only statistical channel-state information (CSI) is required, and the asymmetric traffic requirements are taken into consideration in our design. Through the exploitation of the theorem of nonlinear fractional programming, a unique closed-form optimum solution is obtained, and some useful insights are also achieved. It has been proved that the provided optimal solution is Pareto optimal for EE-SE optimization. Utilizing these results, one can flexibly make the tradeoff between EE and SE by simply setting the tradeoff factor. Simulation results highlight the effect of the proposed power-allocation scheme.

Novel Distributed Quasi-Orthogonal Space-Time Block Codes for Two-Way Two-Antenna Relay Networks

A half-duplex amplify-and-forward two-way relay network consisting of two single-antenna sources and N relays with each having two antennas is considered in this paper. For such a system, a tight lower bound of pairwise error probability (PEP) of a maximum likelihood (ML) detector for any distributed linear dispersion code with a fixed average amplifier is derived, revealing that diversity gain function cannot decay faster than lnN SNR/SNR2N, where rm SNR is signal to noise ratio. Particularly for the network having two relays, a novel distributed quasi-orthogonal space-time block code (QO-STBC) is proposed with two significant advantages. One is that the equivalent channel matrices at both source nodes turn out to be the block-circulant matrices, with each block being a product of the two Alamouti channel matrices. The other is that the equivalent noises at the both source nodes are Gaussian and white. Therefore, like QO-STBC for a multi-antennas system, the proposed code for the relay system still maintains low-decoding complexity for the ML detector. Asymptotic PEP formula is attained to show that the proposed code enables the optimal diversity gain function, i.e., meeting the lower bound of diversity gain, and the optimal coding gain. In addition, a near optimal power allocation that maximizes the received SNR of the worse link is presented and examined through comprehensive computer simulations for various kinds of asymmetric relay channels.

PAPR and PICR Reduction of OFDM Signals With Clipping Noise-Based Tone Injection Scheme

Orthogonal frequency-division multiplexing (OFDM) suffers from a high peak-to-average power ratio (PAPR). Tone injection (TI) extends the original constellation to several equivalent points so that these extra freedom degrees can be exploited for the PAPR reduction. However, optimal TI requires an exhaustive search over all possible constellations, which is a hard discrete optimization problem. To address this problem, a novel TI scheme that uses the clipping noise to find the optimal equivalent outer ring extended constellations (ECs) and hexagonal constellations (HCs) is proposed. By minimizing the mean rounding error of the clipping noise and possible equivalent constellations, the proposed scheme can easily determine the size and position of the optimal equivalent constellations. Second, a new TI scheme is also introduced to reduce the nonlinear distortion in the presence of a power amplifier (PA). This scheme takes the root-mean-square peak-interference-to-carrier-ratio (RMS-PICR) reduction as the target to obtain a better bit error rate (BER) performance. Simulation results show that, to achieve a considerable system performance, the proposed TI schemes only need 18 fast Fourier transforms (FFTs), whereas other TI and partial transmit sequence (PTS) schemes need hundreds of FFTs.

Energy-Efficient Collaborative Alamouti Codes

A novel energy-efficient collaborative Alamouti space-time block code (STBC) design is proposed for a wireless communication system having two transmitter antennas and a single receiver antenna. This new design allows us to have more options for variable-rate modulation for fading channels with enhanced performance for signal transmission than the conventional Alamouti coding scheme while having complex-symbol-decodable complexity for the maximum likelihood (ML) detector. Subject to the constraints on a fixed transmission bit rate and unity average energy per each transmitter antenna, the optimal linear constellation combinations with the optimal energy-scales as the coefficients are attained by maximizing the coding gain. It is shown that the optimal coding gain of the newly-designed code is larger than that of the conventional Alamouti code if the transmission bit rate is greater than two bits per channel use.

Tone Reservation Technique Based on Peak-Windowing Residual Noise for PAPR Reduction in OFDM Systems

Peak-to-average power ratio (PAPR) of orthogonal frequency-division multiplexing (OFDM) may be reduced by reserving several tones to generate a peak-canceling signal (PCS). However, this method suffers from high computational complexity. To address this problem, this paper proposes an algorithm based on peak-windowing residual noise, which is generated by windowing the signal samples that exceed the predetermined threshold. Filtering the residual noise to satisfy tone reservation (TR) constraints and scaling with a scaling factor determined to minimize the out-of-range power generates the PCS. Simulation results show that the proposed algorithm can achieve 6.9-dB PAPR reduction with much lower complexity than other schemes.

Random Access Based Blind Relay Selection in Large-Scale Relay Networks

A random access based blind relay selection (RAB RS) scheme is proposed. Due to the size and the blind characteristic of the large-scale relay service networks, collecting the real-time status of the relays is a very difficult task. To address this problem, the proposed scheme enables the user to randomly select a relay through slotted ALOHA, without requiring any relay information. In addition, the high collision probability of the selection phase can be reduced by introducing an available relay region to adaptively decrease the number of the available relays. This geographical region consists of all the relays that satisfy the required rate of the user at the target outage probability. Compared with the upper bound that requires the complete relay information, the proposed RABRS scheme is implemented in a blind manner while maintaining almost optimal performance.

Low-Complexity Opportunistic Transmission Schemes for Multi-User Multi-Relay Asymmetric Bidirectional Relaying Networks

Two opportunistic transmission schemes, i.e., joint user-relay selection with beamforming (JURS-BF) and joint user-relay selection with antenna selection (JURS-AS), are proposed and analyzed for multi-user multi-relay bidirectional relaying networks (BRNs) composed of one N-antenna base station (BS)/ access point (AP), M single-antenna users, and K single-antenna relays. In particular, by considering the rate asymmetry between the BS/AP and the users, joint user-relay selection is tackled with beamforming and antenna selection to combine the benefits of multi-antenna diversity, multi-relay diversity, and multi-user diversity. To characterize the performance of the proposed JURS-BF and JURS-AS schemes, lower and upper bounds on the system outage probability are derived in closed form under Nakagami-m fading environment, followed by the diversity, coding gain analysis, and some discussions on the relay deployment. Our analytical results are verified through simulations, and it is proved that the proposed suboptimal schemes perform closely to the traditional outage-optimal counterparts while with much lower implementation complexity, which provides valuable insights into practical BRNs.