T. I. Yuk

Design of perfect-reconstruction nonuniform recombination filter banks with flexible rational sampling factors

This paper studies the design of a class of perfect-reconstruction (PR) nonuniform filter banks (FBs) called recombination nonuniform FBs (RNFBs). They are constructed by merging subbands in a uniform FB with sets of transmultiplexers (TMUXs). It generalizes the RNFBs previously proposed by the authors to allow more general choice of the sampling factors. The spectral inversion and spurious response suppression problems of these new RNFBs using cosine modulation are analyzed, and a simple design method based on a matching condition is proposed. It is also found that the FB and the TMUX in the recombination structure can be designed separately to satisfy the matching condition. In addition, real-time adaptive merging of the channels to provide dynamic nonuniform frequency partitioning is feasible. Another advantage of the RNFBs is that the recombination and processing of the subband signal can be done at the decimated domain of the uniform FB, which greatly reduces its implementation complexity. Design examples show that high quality nonuniform PR FBs with low implementation complexity and variable time-frequency resolution can be obtained by the proposed method.

Design and Complexity Optimization of a New Digital IF for Software Radio Receivers With Prescribed Output Accuracy

This paper studies the design, signal round-off noise, and complexity optimization of a new digital intermediate frequency (IF) architecture for a software radio receiver (SRR). The IF under study consists of digital filters with fixed coefficients, except for a limited number of multipliers required in the Farrow-based sampling rate converter (SRC). The fixed-coefficient filters can be implemented efficiently using sum-of-power-of-two (SOPOT) coefficients and the multiplier-block technique, which gives minimum adder realization. Apart from the multipliers required in the SRC, the digital IF can be implemented without any multiplications. While most multiplier- less filter design and realization methods address only the coefficient round-off problem by minimizing the number of SOPOT terms used, the proposed design methodology aims to minimize more realistic hardware complexity measure, such as adder cells and registers, of the digital IF subject to a given spectral and accuracy specifications. The motivation is that the complexity is closely related to the target output accuracy, which is specified statistically by its total output noise power generated by rounding the intermediate data. Two novel algorithms for optimizing the internal wordlengths of linear time-invariant systems are proposed. The first one relaxes the solution to real valued and formulates the design problem as a constrained optimization. A closed-form solution can be determined by the Lagrange multiplier method. The second one is based on a discrete optimization method called the Marginal Analysis method, and it yields the desired wordlengths in integer values. Both approaches are found to be effective and suitable to large scale systems. A design example and the field programmable gate array (FPGA) realization of a multi-standard receiver are given to demonstrate the proposed method

Performance of multichannel CSMA networks

Channel sense multiple access with collision detection (CSMA/CD) is a very simple and efficient way of allowing many stations to transmit messages to a central server down a shared channel. In wireless networks, however, collision detection is difficult to implement, and in such cases CSMA alone may have to be used. It is shown that a multichannel CSMA network can be almost as efficient in utilizing the bandwidth available to the network as an equivalent single channel CSMA/CD network. Furthermore, multichannel CSMA networks provide better throughput and delay performance than equivalent single channel CSMA systems, even when the message generation probability and the number of stations in the network are varied.

A wideband 360° analog phase shifter design

This paper proposes a reflection-type wideband 360 ° analogue phase shifter. The phase shifter employs a branch-line coupler circuit to achieve a wideband operation and a varactor-diode circuit to achieve a wide phase-shift range. Analytical formulas are derived to optimize the parameters in the coupler circuit for wideband operation and reduced attenuation ripple, and in the varactor circuit to minimize the frequency dependency of the output phase. Simulation results using the Advanced Design Systems (ADS 2005A) show that the design has a wide bandwidth, wide phase shift range, and low attenuation ripple, and is highly linear across the operation bandwidth.

Union Bounds for BER Evaluation and Code Optimization of Space-Time codes in 2-by-2 MIMO systems

n this paper, an exact closed-form formula for the pair-wise error probability (PEP) is derived for two transmit and two receive antennas MIMO systems using the probability density function (PDF) of the modified Euclidean distance. An exact union bound formed by this formula, together with the asymptotic union bound, are studied for optimization and bit-error rate (BER) evaluation of space-time (S-T) codes. Numerical calculations and Monte Carlo computer simulation have been used to study these two union bounds on a 2-by-2 MIMO system using a rotation-based diagonal S-T code (D code) in a block fading channel. Results show that the exact union bound is a very tight bound for BER evaluation while the asymptotic union bound is very accurate for code optimization

Lattice-reduction-aided semidefinite relaxation detection algorithms for multiple-input multipleoutput systems

Multiple-input multiple-output (MIMO) system is considered to be one of the key technologies of long-term evolution, since it achieves requirements of high throughput and spectral efficiency. The semidefinite relaxation (SDR) detection for MIMO systems is an attractive alternative to the optimum maximum likelihood (ML) decoding because it is very computationally efficient. In the case of the binary phase shift keying and four quadrature amplitude modulation constellations, the block error rate (BLER) performance of SDR detection is fairly close to the optimum BLER performance. However, for high-order modulation systems, their BLER performance is still unsatisfactory compared with the ML decoding. Lattice reduction technology can transform a matrix into a new equivalent one with more orthogonal and shorter basis vectors. It has been combined with linear decoders to improve their BLER performance. Inspired by this, the authors proposed two lattice-reduction-aided MIMO detection algorithms based on SDR. Simulation results demonstrate that they can provide near-optimum BLER performance with polynomial time complexity.

An RF predistorter for base station HPAs of NADC system

This paper presents the design of an effective and low cost RF predistorter for use in the base-station high power amplifiers (HPAs) of the North American Digital Cellular (NADC) system. A complex polynomial is used to model the characteristic of the HPA and the predistorter generates the inband intermodulation (IM) products required for predistortion of the HPA. The design of the predistorter has a simple structure, using Schottky diodes as the nonlinear device to generate the inband IM products. Experimental results using a practical HPA show that the predistorter can reduce the adjacent-channel-power ratio (ACPR) of the pi/4-DQPSK signal used in the NADC system by 20 dB at an HPA output power level of 30 W. Moreover, the constellation and eye diagrams of the pi/4-DQPSK signal show that the predistorter can also reduce the signal distortion caused by the HPA.

A Simple and Optimum Geometric Decoding Algorithm for MIMO Systems

Geometric decoding (GD) is a newly proposed decoding technique for multiple-input multiple-output (MIMO) transmission over the fading channels. With a complete search on all symbol vectors in the lattice structure, GD requires about the same decoding complexity to achieve the same optimum block-error rates (BLERs) as that of ML decoding. In this paper, we propose a simple implementation of GD for optimum decoding of MIMO transmission. The GD decoder uses the channel matrix to construct a hyper paraboloid and the zero forcing solution to obtain a hyper ellipsoid projected from the hyper paraboloid. It then restricts the search among the symbol vectors within the hyper ellipsoid. Computer simulation studies on 2×2, 3×3 and 4×4 MIMO systems transmitting 8PAM and 16QAM show that the proposed GD algorithm can achieve the same BLERs as those of the ML decoders, yet having complexity reduction of more than 90%.

A new family of Linear Dispersion Code for fast Sphere Decoding

In this paper, a new family of Linear Dispersion Codes (LDCs) that can be decoded using a fast Sphere Decoding (SD) algorithm in MIMO systems is proposed. The basic principle of this structure is to make the LDC to have as many as possible the rows orthogonal in the dispersion matrices. Monte Carlo simulation results show that the optimum LDCs with this orthogonal structure have nearly identical bit-error-rate (BER) performances as other optimal LDCs. We develop a simplified Sphere Decoding (SD) algorithm that can significantly reduce the decoding complexity in decoding the new LDCs with proposed orthogonal structure. Simulation results show that the complexity reduction is more significant for MIMO system transmitting higher level modulation. For 2×4 MIMO systems transmitting 4 64QAM and 256QAM symbols in a block length of 4, the reductions are about 71–83% and 76–88%, respectively.

Combined semi-definite relaxation and sphere decoding method for multiple antennas systems

In this paper, a new detection method which combines the semi-definite programming relaxation (SDR) with the sphere decoding (SD) is proposed for 256-QAM multiple-input multiple-output (MIMO) system. In this method, the SDR algorithms are engaged to obtain a primary result. Then, a hyper-sphere is constructed which is centered at the received signal and has its radius equals to the Euclidean distance between the primary result and the received signal. Finally, the SD searching strategy is employed to determine the final result which satisfies the principle of maximum likelihood. Simulation results show that the proposed method can offer optimum BLER performance as well as lower computational complexity than the conventional SD detectors.