When social behaviors are considered into ad hoc wireless networks, the users prefer to forward the traffic from their social contacts. In this way, the network capacity is highly related with the social characteristics. To this end, we apply a social contact based wireless network model and explore its throughput capacity. The wireless network capacity will get improved when the contacts are located nearby the source node. Directional antennas are applied to further enhance the capacity performance, which can reduce the interference brought by other simultaneous communications. Our results demonstrate that when the wireless communications are dominated by the short-distance social contact traffics, the throughput capacity can be greatly improved. Meanwhile, when the directional antenna beamwidth is at the order of Ω( 1 √log ), the throughput capacity is a constant. The wireless network with social contacts is scalable.

Wireless sensor networks (WSNs) always collect an enormous amount of rich diverse environmental information. When WSNs grow large in scale, it is difficult for the sink to gather data due to the increasing transmission overhead. In order to improve the fidelity of data recovery and save energy, we propose a novel data aggregation and space-time global recovery scheme. The scheme exploits block Compressed Sensing (CS) to achieve both recovery fidelity and energy efficiency. We employ diffusion wavelets to partition a large WSN into sub-networks, which are regarded as blocks. For each sub-networks, diffusion wavelets are applied to get the sparse basis for the data to be compressed. In addition, we introduce temporal and spatial correlation into the optimum target function of global recovery algorithm. Simulation results show that space-time global recovery scheme holds higher fidelity of data recovery and greatly reduces the energy consumption. Typically, the normalized mean absolute error of our recovery scheme is less than 5%. Furthermore, the energy consumption is reduced more than 50% against plain CS.

This paper considers a multi-pair two-way relaying network, where multiple pairs of full-duplex users are served via a full-duplex relay with large-scale antennas under the amplify-and-forward protocol. Based on maximum-ratio combining/maximum-ratio transmission (MRC/MRT) processing, an exact achievable rate expression is derived by utilizing the statistical distribution of the channels to detect the desired signals, with the case of a finite number of relay antennas. We show that the exact expression is a tight lower bound of the ergodic rate. Then we obtain its approximate closed-form, which keeps very close to the exact one, especially in large number of antennas. The proposed approximate expression indicates that increasing the relay antenna number can greatly improve the sum rate. In addition, the optimal transmit powers of the users and the relay are obtained in order to maximize the achievable rate. Moreover, we demonstrate that with very large antenna arrays, the two-way full-duplex relaying scheme outperforms both the one-way full-duplex relaying scheme and the two-way half-duplex relaying scheme. Finally, numerical results are presented to verify the accuracy of the analysis.

In this paper, we consider a multipair amplify-and-forward two-way relay channel, where multiple pairs of full-duplex users exchange information through a full-duplex relay with massive antennas. For improving the energy efficiency, four typical power-scaling schemes are proposed based on the maximum-ratio combining/maximum-ratio transmission (MRC/MRT) and zero-forcing reception/zero-forcing transmission (ZFR/ZFT) at the relay. When the number of relay antennas tends to infinity, we quantify the asymptotic spectral efficiencies and energy efficiencies for the proposed power-scaling schemes. We show that the loop interference can be reduced by decreasing the transmit power under massive relay antennas. Besides, the inter-pair interference and inter-user interference in such systems can also be eliminated in large number of antennas. Moreover, we analytically compare the performance between MRC/MRT and ZFR/ZFT, and describe the impact of the number of user pairs on the spectral efficiency. We also evaluate the energy efficiency performance based on the practical power consumption model, and depict the impact of the relay antenna number on the energy efficiencies for the proposed schemes. Furthermore, we provide the available regions where full-duplex systems can outperform half-duplex systems. Finally, we show that the proposed schemes achieve good performance tradeoffs between the spectral efficiency and the energy efficiency.

In this paper, we consider a one-pair amplify-and-forward relay channel, where two full-duplex users exchange information through a full-duplex relay with a very large number of antennas, while each user only has two antennas. Several power-scaling schemes are proposed based on the maximum-ratio combining/maximum-ratio transmission (MRC/MRT) at the relay. When the number of the relay antennas tends to infinity, we derive and quantify the asymptotic spectral efficiency of the proposed power-scaling schemes. We show that the very large antenna array can significantly reduce the effect of loop interference because of the antenna array gain. Furthermore, the theoretical results indicate that the loop interference can also be reduced by cutting down the transmission power, which is verified by the numerical results. The analytical and numerical results show that the proposed power-scaling schemes can achieve good performance tradeoffs between the spectral efficiency and the energy efficiency.

In this paper, we consider a multi-pair two-way amplify-and-forward relay interference channel, where multiple pairs of full-duplex users exchange information through a full-duplex relay with very large number of antennas, while each user only has two antennas. In order to save the transmission power, four typical power scaling schemes are proposed based on the maximum-ratio combining/maximum-ratio transmission (MRC/MRT) at the relay without the degradation of the performance. When the number of the relay antennas tends to infinity, the asymptotic achievable sum rates based on the proposed power scaling schemes are derived. We show that the very large antenna array can significantly reduce the effect of loop interference because of the antenna array gain. Furthermore, the theoretical results indicate that the loop interference can be reduced by cutting down the transmission power. Besides, the inter-pair interference and the inter-user interference in such systems can also be eliminated in the regime of very large number of antennas. Moreover, we analytically compare the upper bounds of the sum rates for the proposed power scaling schemes and describe the impact of the number of user pairs on the upper bounds.

Bit-cooperative coded modulation (BCCM), known as an improved bit-interleaved coded modulation (BICM) scheme [1], introduces known bits to jointly design the channel coding and modulation. In this paper, we contribute to the theoretical analysis of the turbo-coded BCCM scheme, and specifically, the impact of the known bits on the turbo decoding process. The characteristic of the iteration process is also analyzed for BCCM by the EXIT chart. Furthermore, to describe the fundamental tradeoff between the communication reliability and the data rate, we derive the error exponent for BCCM. Numerical results show that BCCM has a larger exponent than BICM and achieves a considerable gain on AWGN channels.

In digital predistortion (DPD) implementation, the computational complexity of coefficients estimation of the DPDmodel is a key performance metric. Conventional coefficients estimation algorithms, such as least squares (LS), recursive least squares (RLS), and least mean squares (LMS) cannot achieve a fast convergence with little computation. In this paper, we propose an RLS algorithm with reduced complexity by introducing orthonormal polynomial basis functions. The proposed algorithmis as simple as LMS algorithmyet as efficient as RLS algorithm. Simulation results validate our analysis.

With superior error correction capability, low-density parity-check (LDPC) has initiated wide scale interests in wireless telecommunication fields. In the past, various structures of single code rate LDPC decoders have been implemented for different applications. However, in order to cover a wide range of service requirements and diverse interference conditions in wireless applications, LDPC decoders that can operate in both high and low code rates are desired. In this paper, a new multi-rate LDPC decoder architecture is presented and implemented in a Xilinx FPGA device. Through selection pins, three operating modes with the irregular 1/2 rate, regular 5/8 rate and regular 7/8 rate are supported. The measurement results show LDPC decoder can achieve BER below 10-5 at SNR of 1.4dB in the most critical case with the irregular 1/2 mode.

This letter provides a comparative study of joint channel estimation and low-density parity-check decoding algorithms for flat Rayleigh fading channels based on the receiver factor graphs. Two approaches for joint channel estimation and decoding are proposed. Intensive simulation studies are carried out to evaluate the receiver sensitivity to the choice of the factor graph. Results show that when channel statistical information is not available at the receiver, a low-pass filtering approach gives a more robust and simpler solution, and it is only 0.5 dB worse than the optimum Wiener filtering. All methods have about 2 dB improvements over the noniterative receivers.

Two types of wireless system imperfections, namely, frequency offset and in-phase/quadrature (I/Q) imbalance, are addressed in this paper. The I/Q imbalance in radio frequency (RF) direct-conversion not only introduces an unwanted in-band image interference but also degrades the accuracy of carrier estimation. Toward this end, we propose a pilot-based scheme for both frequency offset and I/Q imbalance compensation at the baseband. A low-cost nonlinear least squares (NLS) frequency estimator robust to the I/Q imbalance is developed. Also derived is an I/Q imbalance compensation structure that consists of two stages: a finite impulse response (FIR) filter that compensates the frequency dependent imbalance; and an asymmetric phase compensator that corrects the frequency independent error. The compensation coefficients are optimized by exploiting the phase rotation embedded in the pilot symbols. Both computer simulations and experiment results verify the effectiveness of the proposed scheme in various I/Q imbalance scenarios.

This paper studies uplink traffic channel design tradeoffs for broadband OFDMA systems. For fixed and portable users, where the propagation channels are semi-static, we show that the uplink capacity can be maximized when user traffic channels are configured with the maximum frequency selectivity. For mobile services on the other hand, we show that the optimality depends on the outage threshold associated with the "outage capacity." In the low outage probability region, the outage capacity is maximized when the traffic channels are configured with the maximum frequency diversity. The opposite is true for the high outage probability region. Using the results presented, designers of OFDMA system can determine the optimum traffic channel configuration based on the types of services supported by the network.

The paper describes a multicarrier terrestrial multimedia broadcasting (TMB) system that offers system performance and service versatility suitable for future digital broadcasting networks. The new system utilizes variable rate, variable size LDPC (low-density parity-check) codes to allow simultaneous transmission of different programs with diverse requirements. A prototype system is implemented based on the proposed protocol. Results from both lab tests and field trials demonstrate significant performance advantages of the new design over existing systems such as DVB-T.

Field-programmable gate arrays (FPGAs) have become an extremely popular implementation technology for custom hardware because they offer a combination of low cost and very fast turnaround. Because of their in-system reconfigurability, FPGAs have also been suggested as an efficient replacement for application-specific integrated circuits (ASICs) and digital signal processors (DSPs) for applications that require a combination of high performance, low cost, and flexibility. Unfortunately, the use of FPGAs in mobile embedded systems platforms is hampered by the very large overhead of FPGA-based architectures. Coarse-grained configurable architectures can reduce this overhead substantially by taking advantage of the application domain to specialize the reconfigurable architecture via coarse-grained components and interconnects. This paper presents the design and implementation of an OFDM receiver in the RaPiD reconfigurable architecture as a case study for comparing the relative cost and performance of ASIC, DSP, FPGA, and coarse-grained reconfigurable architectures. RaPiD is a coarse-grained reconfigurable architecture specialized to the domain of signal and image processing. The RaPiD architecture provides a reconfigurable pipelined datapath controlled by efficient reconfigurable control logic: We have implemented the computationally intensive parts of an OFDM receiver on the RaPiD architecture and have developed careful estimates of corresponding implementations in representative ASIC, DSP and FPGA technology. Our results show that, for this application, RaPiD fills the cost/performance gap between programmable DSP and ASIC architectures, achieving a factor of 6 better than a DSP implementation but a factor of 6 less than an ASIC implementation.

Two types of RF front-end imperfections in direct-conversion receivers, namely frequency offset and I/Q imbalance, are addressed. The I/Q imbalance not only introduces an unwanted image interference, but also degrades the accuracy of carrier estimation. We propose a pilot-based scheme for both frequency offset and I/Q imbalance compensation. A nonlinear least squares (NLS) frequency estimator, robust to the I/Q imbalance, is developed. Also derived is an I/Q compensation structure that consists of two stages: the frequency dependent imbalance is compensated with an FIR filter whereas the frequency independent part is corrected with an asymmetric phase compensator. The compensation coefficients are optimized by restoring the phase rotation embedded in the pilot symbols.