In our previous paper, we presented a concept of “Baseband Radio” as an ideal of future wireless communication scheme. Furthermore, for enhancing the adaptability of baseband radio, the adaptive baseband radio was discussed as the ultimate communication system; it integrates the functions of cognitive radio and software-defined radio. In this paper, two transmission schemes that take advantage of adaptive baseband radio are introduced and the results of a performance evaluation are presented. The first one is a scheme based on DSFBC for realizing higher reliability; it allows the flexible use of frequency bands over a wide range of white space. The second one is a low-power-density communication scheme with spectrum-spreading by means of frequency-domain differential coding so that the secondary system does not seriously interfere with primary-user systems that have been assigned the same frequency band.

Software defined radio, which uses reconfigurable signal processing devices, requires the determination of multiple unknown parameters to realize the potential capabilities of adaptive communication. Evolutional algorithms are optimal multi dimensional search techniques, and are well known to be effective for parameter determination. This letter proposes an evolutional algorithm for learning the mobile time-varying channel parameters without any specific assumption of scattering distribution. The proposed method is very simple to realize, but can provide precise channel estimation results. Simulations of an OFDM system show that for an example of OFDM communication under the time-varying fading channel, the proposed learning method can achieve the better BER performance.

This paper describes the experimental performance of eigenbeam multi-input multi-output with orthogonal frequency division multiplexing (MIMO-OFDM) systems as measured in a testbed implemented with field programmable gate arrays (FPGAs). The FPGA-testbed, characterized by the software-defined radio (SDR) technique, offers 1/5-scale real time signal processing. Extensive experiments on the testbed confirm the basic operation and performance of eigenbeam MIMO-OFDM with quadrature phase-shift keying (QPSK) and 16 quadrature amplitude modulation (QAM). From the packet error rate (PER) performance, we confirm that the eigenbeam 16QAM/MIMO-OFDM scheme with permutation matrix and three transmit antennas (Mt=3) drastically improves the required carrier-to-noise power ratio (CNR) by approximately 5.6 dB over the scheme without eigenbeam with Mt=2. Furthermore, to determine the impact of Doppler frequency fd, we focus on the transmission interval between the MIMO channel estimation and data transmission. To suppress the required CNR degradation to within 1.5 dB, it is found that the eigenbeam 16QAM/MIMO-OFDM scheme with permutation matrix and Mt=3 permits a transmission interval of approximately 68.5 ms when fd=1 Hz for a 1/5-scale model.

Wireless communications technology continues to change and yield new standards for satisfying the user demands. As a result, multiple standards coexist and wireless communications systems supporting different air interfaces cannot interact with one another. Software-defined radio is regarded as the most promising solution to cope with this problem. In this paper, we discuss the design considerations of SDR systems from a base station point of view and propose new architecture which meets the inherent requirements of SDR platform. We then introduce hardware/software of SDR platform we accomplished on the basis of the new architecture. In addition, the results of basic transmission and receiving performance are presented to prove the feasibility of the proposed platform as a base station.

Software-Defined Radio (SDR) represents a major paradigm shift in the design of radios, allowing a large fraction of the functionality to be implemented through programmable signal processing devices, enabling the radio to change its operating parameters to accommodate new air interface, features and capabilities. However, the actual realization of innovative and software-reconfigurable receiver diversity at mobile handsets in intermediate frequency band to provide wide-ranging benefits, including more effective filtered result, less cost of the mixed channel access, improved capacity, better link reliability, and reduced power consumption, has been slowed down largely due to an absence of effective architecture reducing the complexity of adaptive combining algorithms. This paper proposes a novel reconfigurable architecture for adaptive space diversity at handsets in MC-CDMA (multicode code-division multiple-access) systems. The key to which is the development of a valid and effective alternative to the time-consuming multiplication operation and despreading acquisition. A software definable algorithm can become a multiplier-free architecture if it can restrict the weight factors to power-of-two values and repetitive gradient search procedure to contain shift operations and predicate functions. The results of numerical simulation and experimentation confirm the expectation that the constrained approach should perform comparably to, but not better than the traditional diversity algorithm. That is, the feasibility of SDR depends on its trading some performance for reduced computational complexity, improved area efficiency and less power consumption.

A coplanar type lumped-element 6-pole microwave Chebyshev bandpass filter (BPF) of center frequency (f0) 2.0 GHz and fractional bandwidth (FBW) 1.0 % was designed. For the design method, theory of direct coupled resonator filters using K-inverters was employed. Coplanar type lumped-element BPFs are composed of a meander-line L and interdigital C elements. The frequency response was simulated and analyzed using an electromagnetic field simulator (Sonnet-EM). Further, the changes in f0 and FBW of the BPF were also realized by the mechanical tuning method.

This letter describes an efficient architecture for a Software Defined Radio (SDR) Wideband Code Division Multiple Access (WCDMA) receiver using for high performance wireless communication systems. The architecture is composed of a Radio Frequency (RF) front-end, an Analog-to-Digital Converter (ADC), and a Quadrature Amplitude Modulation (QAM) demodulator. A coherent demodulator, with a complete digital synchronization scheme, achieves the bit-error rate (BER) of 10-6 with the implementation loss of 0.5 dB for a raw Quadrature Phase Shift King (QPSK) signal.

Software-Defined Radio (SDR) receiver has the ability of operating in a multi-mode environment and has wide applications. However, efficient recognition of the currently active modulation system in real-time is a major problem faced by many applications. In this paper, an efficient method for the recognition of modulation system in a SDR receiver is proposed. The method is a classical two-stage approach based on (i) decision feature extraction and (ii) modulation system classification. In the first stage, decision features are extracted by the use of digital quadrature polyphase filter. In the second stage, an efficient parallel decision algorithm is proposed to classify the active modulation type. This proposed algorithm is proof to be more efficient than the conventional type of decision-tree approach. The complete recognition system is implemented using MATLAB. Simulation result shows that the proposed method achieved good robustness even with the presence of band-limited Additive White Gaussian Noise (AWGN). The overall successful recognition rate of 98.5% can be achieved even at a low signal-to-noise ratio (SNR) of 8 dB.