Base Station (BS) cooperation has been considered as a promising technology to mitigate co-channel interference (CCI), yielding great capacity improvement in cellular systems. In this paper, by combining frequency domain cooperation and space domain cooperation together, we design a new CCI mitigation scheme to maximize the total utility for a multi-cell OFDMA network. The scheme formulates the CCI mitigation problem as a mixture integer programming problem, which involves a joint user-set-oriented subcarrier assignment and power allocation. A computationally feasible algorithm based on Lagrange dual decomposition is derived to evaluate the optimal value of the problem. Moreover, a low-complexity suboptimal algorithm is also presented. Simulation results show that our scheme outperforms the counterparts incorporating BS cooperation in a single domain considerably, and the proposed low-complexity algorithm achieves near optimal performance.

We present an orthogonal frequency division multiple access (OFDMA) based multichannel slotted ALOHA for cognitive radio networks (OMSA-CR). The performance of an infinite population based OMSA-CR system is analyzed in terms of channel capacity, throughput, delay, and packet capture effect. We investigate the channel capacity for OMSA-CR with perfect or imperfect spectrum sensing. We introduce the proposed CR MAC based on two channel selection schemes: non-agile channel selection (NCS) and agile channel selection (ACS). Comparing them, we show the tradeoff between complexity and system performance. We verify the proposed CR system model using numerical analysis. In particular, using simulation with a finite populated linear feedback model, we observe the OMSA-CR MAC tradeoff between throughput and minimum delay whose results matched those of the analytical framework. Numerical results for the proposed system throughput are also compared to conventional MACs, including pure ALOHA based CR MAC.

Variable-weight optical orthogonal code (OOC) was introduced by G-C Yang for multimedia optical CDMA systems with multiple quality of service (QoS) requirement. In this paper, a construction for optimal (υ, {3,4}, 1, {s/(s+1), 1/(s+1)})-OOCs is given. For s=2, it is proved that for each prime υ≡ 1(mod 24), there exists a (υ, {3,4}, 1, {2/3, 1/3})-OOC. A recursive construction for cyclic difference family is also presented. By using these constructions, a number of new infinite classes of optimal (υ, {3,4}, 1, Q)-OOCs for Q = {1/2, 1/2} and {2/3, 1/3} are constructed.

We propose that the model in experimental design be expressed in terms of an orthonormal system. Then, we can easily estimate the effects using Fourier transforms. We also provide the theorems with respect to the sum of squares needed in analysis of variance. Using these theorems, it is clear that we can execute the analysis of variance in this model.

Recently, broadcast services are introduced in cellular networks and macro diversity is an effective way to combat fading. In this paper, we propose a kind of distributed space-time block codes (STBCs) for macro diversity which is constructed from the total antennas of multiple cooperating base stations, and all the antennas form an equivalent multiple input multiple output (MIMO) system. This code is termed High-Dimension-Full-Rate-Quasi-Orthogonal STBC (HDFR-QOSTBC) which can be characterized as: (1) It can be applied with any number of transmit antennas especially when the number of transmit antennas is large; (2) The code is with full transmit rate of one; (3) The Maximum Likelihood (ML) decoding complexity of this code is controllable and limited to Nt/2-symbol-decodable for total Nt transmit antennas. Then, we completely analyze the structure of the equivalent channel for the kind of codes and reveal a property that the eigenvectors of the equivalent channel are constant and independent from the channel realization, and this characteristic can be exploited for a new transmission structure with single-symbol linear decoder. Furthermore, we analyze different macro diversity schemes and give a performance comparison. The simulation results show that the proposed scheme is practical for the broadcast systems with significant performance improvement comparing with soft-combination and cyclic delay diversity (CDD) methods.

The Millimeter-wave Mobile Camera (MiMoCam) developed by NHK STRL uses millimeter-wave band (42 GHz/55 GHz) to transmit Hi-Vision TV picture with high quality and low latency. Multiple-input multiple-output (MIMO) technology which uses a number of antennas at both the transmitter and receiver can be adapted to use to transmit higher quality Hi-Vision TV picture. The camera was intended to be used in a studio environment where there is a high degree of multi-path, however there are also many requests for the MiMoCam to be used outdoor. This will present a different channel statistics where the camera will be operating in a near line-of-sight (LOS) environment without much reflected waves. We have conducted an outdoor transmission test and measured the outdoors transmission performance of the proposed MIMO system to clarify the possibility of using the MiMoCam in outdoor environment. This paper introduces the features of the MiMoCam system and the MIMO transmission technique used in the MiMoCam and presents the findings of this outdoor test. It was also confirmed that channel correlation of the MIMO propagation channels were suppressed by using orthogonally polarized waves and bit error rate (BER) characteristics with respect to the average receiving carrier-to-noise ratio (CNR) was improved. Finally, we could find the feasibility of the MiMoCam outdoor operation from these results.

We present an alternative approach to what we call the "standard optimization", which minimizes a cost function by searching a parameter space. Instead, our approach "projects" in the joint observation space onto the manifold defined by the "consistency constraint", which demands that any minimal subset of observations produce the same result. This approach avoids many difficulties encountered in the standard optimization. As typical examples, we apply it to line fitting and multiview triangulation. The latter produces a new algorithm far more efficient than existing methods. We also discuss the optimality of our approach.

This paper proposes cooperative coding using cyclic delay diversity (CDD) for OFDM systems. The cooperative diversity is combined with channel coding while CDD is applied to the cooperative transmission of the multiple relays to improve the beneficial effects of the cooperating relays. Analyses of frame error probability (FEP) and the average channel power of the proposed scheme are shown. Simulation results show the frame error rate (FER) of the proposed scheme. The proposed scheme provides not only a simple code design and low system complexity compared to conventional space-time processing, but better FER and diversity gain compared to direct transmission and conventional cooperative coding without CDD.

Multipath is one of the major error sources that deteriorates tracking performance in global navigation satellite system (GNSS). In this letter, the orthogonal matching pursuit (OMP) algorithm is used to estimate multipaths which are highly correlated with the line of signal (LoS) signal. The estimated multipaths are subtracted from the received signal such that the autocorrelation function of the received signal is restored to optimize the tracking performance. The performance of the proposed technique is verified via computer simulations under the multipath environment of GNSS.

A novel broad-band ring-slot array antenna for simultaneous use of orthogonal polarizations is presented in this paper. In this antenna, the broad-band performance is obtained by integrating a 22 ring-slot array antenna and a broad-band π/2 hybrid circuit. The simultaneous use of the right-hand circular polarization (RHCP) and the left-hand circular polarization (LHCP) is achieved using orthogonal feed circuits on three layers. The both-sided MIC technology is effectively employed in forming this type of slot array antenna. Experimental results show that the proposed antenna has good circular polarization characteristics for both the LHCP and the RHCP. The measured impedance-bandwidth of return loss better than -10 dB are about 47% both for the LHCP and the RHCP. The 3 dB axial ratio bandwidths are 25% (RHCP) and 29% (LHCP). The isolation between the two input ports is better than -35 dB at center frequency of 7.5 GHz.

Orthogonal frequency division multiplexing (OFDM) signals have high peak-to-average power ratio (PAPR) and cause large nonlinear distortions in power amplifiers (PAs). Memory effects in PAs also become no longer ignorable for the wide bandwidth of OFDM signals. Digital baseband predistorter is a highly efficient technique to compensate the nonlinear distortions. But it usually has many parameters and takes long time to converge. This paper presents a novel predistorter design using a set of orthogonal polynomials to increase the convergence speed and the compensation quality. Because OFDM signals are approximately complex Gaussian distributed, the complex Hermite polynomials which have a closed-form expression can be used as a set of orthogonal polynomials for OFDM signals. A differential envelope model is adopted in the predistorter design to compensate nonlinear PAs with memory effects. This model is superior to other predistorter models in parameter number to calculate. We inspect the proposed predistorter performance by using an OFDM signal referred to the IEEE 802.11a WLAN standard. Simulation results show that the proposed predistorter is efficient in compensating memory PAs. It is also demonstrated that the proposal acquires a faster convergence speed and a better compensation effect than conventional predistorters.

We propose 3-hop cooperative diversity using QOSTBC (Quasi-Orthogonal Space-Time Block Code), which offers 3-hop cooperative diversity without signal separation in relay nodes. The key of our proposed scheme is encoding signal sequence in different signal unit according to relay stage. This letter explains details of the proposed scheme and shows that it offers interference reduction among streams and space diversity gain by result of simulations.

In this paper, a novel orthogonal frequency-division multiplexing (OFDM) modulator/demodulator based on real-valued discrete Hartley transform (DHT) is presented and implemented for the IEEE 802.11a/g wireless local area network (LAN). Instead of the conventional complex-valued fast Fourier transform (FFT) for OFDM systems, the proposed architecture employs two real-valued fast DHT (FHT) kernels and one post processing unit. By taking advantage of the real-valued operation of FHT, this approach reduces the number of multiplications compared with the radix-2 FFT. The proposed DHT-based modulator/demodulator was designed and fabricated in 0.18-µm CMOS technology with a core area of 928935 µm2. The average power consumption is about 20.16 mW at 20 MHz and 1.8 V supply voltage. Measurement results of the integrated circuit illustrate its superior chip area and power consumption.

In this letter, DFT-based channel estimation (CE) with a strong interference detector is proposed for OFDM systems. Computer simulations demonstrate that the proposed scheme achieves similar performance to an interference-free system and is a significant enhancement over conventional methods.

Nonlinear distortions in power amplifiers (PAs) generate spectral regrowth at the output, which causes interference to adjacent channels and errors in digitally modulated signals. This paper presents a novel method to evaluate adjacent channel leakage power ratio (ACPR) and error vector magnitude (EVM) from the amplitude-to-amplitude (AM/AM) and amplitude-to-phase (AM/PM) characteristics. The transmitted signal is considered to be complex Gaussian distributed in orthogonal frequency-division multiplexing (OFDM) systems. We use the Mehler formula to derive closed-form expressions of the PAs output power spectral density (PSD), ACPR and EVM for memoryless PA and memory PA respectively. We inspect the derived relationships using an OFDM signal in the IEEE 802.11a WLAN standard. Simulation results show that the proposed method is appropriate to predict the ACPR and EVM values of the nonlinear PA output in OFDM systems, when the AM/AM and AM/PM characteristics are known.

This letter investigates the space-time block codes from quasi-orthogonal design as a tradeoff between high transmission rate and low decoding complexity. By studying the role orthogonality plays in space-time block codes, upper bound of transmission rate and lower bound of decoding complexity for quasi-orthogonal design are claimed. From this point of view, novel algorithms are developed to construct specific quasi-orthogonal designs achieving these bounds.

A differential inter-symbol interference (ISI) cancellation method for time domain synchronous orthogonal frequency division multiplexing (TDS-OFDM) systems is proposed. The differential output of an OFDM system can greatly reduce the impact of ISI in the frequency domain and it constructs a convolutional structure, thus the Viterbi decoding algorithm can be used to recover the transmitted information from the output signal. Simulation results show the effectiveness of the proposed method.

A circuit technique to correct Vdd/PM distortion and improve efficiency as supply modulation of cascode class-E PAs has been proposed. The experimental result shows that the phase distortion can be improved from 20 degrees to 5 degrees. Moreover, a system co-simulation result demonstrated that the EVM can be improved from -17 dB to -19 dB.

Recently, a new multi-carrier CDMA (MC-CDMA) system with cyclic-shift orthogonal keying (CSOK) has been proposed and shown to be more spectral and power efficient than conventional MC-CDMA systems. In this paper, a novel extension called the multiplexed CSOK (MCSOK) MC-CDMA system is proposed to further increase the data rate while maintaining a low peak-to-average power ratio (PAPR). First, the data stream is divided into multiple parallel substreams that are mapped into QPSK-CSOK symbols in terms of cyclic shifted Chu sequences. Second, these sequences are repeated, modulated, summed, and placed on IFFT subcarriers, resulting in a constant-modulus multiplexed signal that preserves the desired orthogonality among substreams. The receiver performs frequency-domain equalization and uses efficient demultiplexing, despreading, and demapping schemes to detect the modulation symbols. Furthermore, an alternate MCSOK system configuration with high link quality is also presented. Simulations show that the proposed MCSOK system attains lower PAPR and BER, as compared to conventional MC-CDMA system using Walsh codes. Under a rich multipath environment, the high link quality configuration exhibits excellent performance with both diversity gain and MCSOK modulation gain.

Estimating a location of mobile phones or sound source is of considerable interest in wireless communications and signal processing. In this letter, we propose squared range weighted least squares (SRWLS) using the range estimate attained from the Taylor series-based maximum likelihood. The weight can be determined more accurately when using the proposed method, compared with the existing methods using the variance of noise. The simulation results show that the proposed method is superior to the existing methods in RMSE as the measurement noise amount of sensors increases.