Cognitive radios are intelligent communications, and are expected to more efficiently utilize the radio channel. Modulation identification is one of the key issues in the cognitive radios. Many works were devoted to the classification of symbol-by-symbol modulations, however, few papers on block modulations have been published. In this paper, an identification error analysis is presented for block orthogonal modulations using General Orthogonal Modulation~(GOM). A symbol error probability is derived for the identified block orthogonal modulation. Numerical results of 4-dimensional block orthogonal modulation are presented with simulation results.

A Generalized Symbol-rate-increased (GSRI) Pragmatic Adaptive Trellis Coded Modulation (ATCM) is applied to a Multi-carrier CDMA (MC-CDMA) system with bi-orthogonal keying is analyzed. The MC-CDMA considered in this paper is that the input sequence of a bi-orthogonal modulator has code selection bit sequence and sign bit sequence. In, an efficient error correction code using Reed-Solomon (RS) code for the code selection bit sequence has been proposed. However, since BPSK is employed for the sign bit modulation, no error correction code is applied to it. In order to realize a high speed wireless system, a multi-level modulation scheme (e.g. MPSK, MQAM, etc.) is desired. In this paper, we investigate the performance of the MC-CDMA with bi-orthogonal keying employing GSRI ATCM. GSRI TC-MPSK can arbitrarily set the bandwidth expansion ratio keeping higher coding gain than the conventional pragmatic TCM scheme. By changing the modulation scheme and the bandwidth expansion ratio (coding rate), this scheme can optimize the performance according to the channel conditions. The performance evaluations by simulations on an AWGN channel and multi-path fading channels are presented. It is shown that the proposed scheme has remarkable throughput performance than that of the conventional scheme.

In this paper, an error correction scheme suitable for MC-DS-CDMA system with bi-orthogonal modulation is proposed. The input sequence of a bi-orthogonal modulator consists of n - 1 bit code selection bit sequence and 1 bit sign bit sequence. In order to apply an efficient error correction code, the following points should be considered; (1) if the code selection bits can be protected sufficiently, the sign bit error can also be reduced sufficiently, (2) since a code selection bit sequence consists of n - 1 bits, employing a symbol error correcting code is more effective for encoding code selection bits, (3) the complexity of the error correction encoder and decoder implementations should be minimum. Based on these conditions, we propose to employ Reed-Solomon (RS) code for encoding the code selection bits and no error correction code for the sign bit. Additionally, detection algorithm at the bi-orthogonal demodulator is modified for compensating degradations of the sign bit error rate performance. The performance in an Additive White Gaussian Noise (AWGN) channel is evaluated by both theoretical analysis and computer simulations. The performance evaluations by simulations on multi-path fading channels are also shown. It is shown that the proposed scheme has remarkable improvement.

In this paper, a multiple-pulse signaling format for M-ary equicorrelated modulation (ECM) is proposed to enable the noncoherent detection on a multiple-symbol basis. Several time-limited and band-limited basis waveform sets are designed to embody the multiple-pulse ECM signals and explored to determine the spectral performance characteristics. Based on the maximum-likelihood decision principle, a block receiver is developed for noncoherently demodulating multiple-pulse ECM signals on additive white Gaussian noise channels. Tight upper and approximate bounds are derived and verified by simulation to evaluate the bit and symbol error probability characteristics of the developed ECM block receiver. It is analytically shown that the noncoherent M-ary ECM block receiver with a small-sized blocklength offers comparable performance to the ideal coherent M-ary simplex receiver when the pairwise signal correlation is appropriately chosen. In particular, the proposed noncoherent nonbinary simplex modulation is found to strongly outperform the conventional noncoherent nonbinary orthogonal modulation in terms of both power and spectral efficiencies.

Orthogonal modulation provides low probability of bit error, however its bandwidth efficiency is very low. Biorthogonal code may double the bandwidth efficiency, but its required bandwidth grows exponentially with the number of input bits as in orthogonal modulation. In this paper, we propose a multi-code biorthogonal code keying (MBCK) scheme that significantly reduces the signal bandwidth with the benefit from orthogonal waveform coding maintained. The system consists of multiple waveform coding blocks, and the sum of output codewords is transmitted. A problem with MBCK is that output signal is multi-level, which requires amplifier with high linearity. So it may not be an appropriate scheme for portable unit where power efficiency is highly important. We also propose a modified MBCK scheme that guarantees constant amplitude output. The transmitter of the proposed scheme contains a redundant waveform coder whose input is generated by encoding the information bits. Adding the codewords from all constituent waveform coding blocks, the composite signal has constant amplitude. It is also shown that the redundant bits are not only used to make constant amplitude signal but also used to improve the BER performance at the receiver.

This paper proposes a new SSB-QPSK modulation/demodulation method. The present method multiplexes the USB (Upper Side Band) and LSB (Lower Side Band) of a QPSK-modulated SSB (Single Side Band) on the same SSB complex frequency band. The present method thus achieves 2 bit/s/Hz. This method is an orthogonal SSB-QPSK method, because the multiplex signals are orthogonal to each other. The demodulator consists of two SSB demodulators. A simulation result in AWGN conditions, shows that the proposed method has better BER (Bit Error Rate) performance than 16 QAM. The degradation of BER in comparison with QPSK is less than 0.2 dB on Eb/No (bit-energy-to-noise-power ratio). In a fading/Doppler environment, the BER performance of the orthogonal SSB-QPSK is the same as that of QPSK.

In this paper, we describe a frame synchronization method for bi-orthogonal modulation systems. In bi-orthogonal modulation systems, several bi-orthogonal sequences are used for data transmission. Frame synchronization in bi-orthogonal modulation systems is difficult because transmitted sequences can change every frame. In the proposed method, each bi-orthogonal sequence consists of two different inner sequences. Each bi-orthogonal sequence has the same arrangement of two different inner sequences. A receiver can track the frame timing by observing the arrangement of inner sequences. In this paper, we analyze the bit error rate performance that takes into account the tracking performance of a system we developed based on our method. The spectral efficiency of the proposed system in code division multiple access (CDMA) systems is also investigated. As a result, we found that the proposed system is effective in synchronous CDMA systems.

This paper presents a variable rate transmission scheme suitable for bandlimited meteor burst channel. Meteor Burst Communication (MBC) is a unique type of radio communication, which is primarily used for non-realtime remote data collection. In the paper, along with conventional BPSK and QPSK modulations, QAM and M-ary Bi-orthogonal modulations are analyzed for software modem implementation in an MBC system. Performance of the modulation methods is presented for both static AWGN channel and meteor burst channel. The proposed scheme for variable rate transmission dynamically estimates the MBC channel and varies the modulation type of a software modem, to control the transmission rate between bursts. The scheme dynamically selects a modulation type and packet length that will maximize the average throughput of the system. Performance of the scheme is analyzed and compared with conventional fixed rate modems. A practical implementation for software modem is suggested that uses a common core modulator/demodulator structure.

In [3], the decision feedback channel estimation (DFCE) for M-ary orthogonal modulation in direct sequence/code division multiple access (DS/CDMA) systems was proposed. However, the performance of the DFCE in the multiuser environment is severely degraded due to multiple access interference (MAI). In this letter, to overcome this problem, we modify the DFCE as multistage configurations using a multistage parallel interference cancellation (PIC) scheme. According to the results of our simulations, the performance of coherent demodulation using the proposed multistage DFCE is significantly improved in comparison with conventional demodulation in [3].

In this letter, we propose the channel estimation technique in the uplink of a DS/CDMA system with M-ary orthogonal signaling over multipath fading channels. The channel estimation is carried out using the maximum correlator output of RAKE receiver. With the estimated channel parameters, the RAKE receiver can coherently combines the received multipath signals, resulting in a significant performace improvement. The hardware complexity of the proposed detection technique is slightly increased when compared to that of noncoherent detection.