Continuous phase modulation (CPM) is a very attractive digital modulation scheme, with constant envelope feature and high efficiency in meeting the power and bandwidth requirements. CPM signals with pairs of input sequences that differ in an infinite number of positions and map into pairs of transmitted signals with finite Euclidean distance (ED) are called catastrophic. In the CPM scheme, data sequences that have the catastrophic property are called the catastrophic sequences; they are periodic difference data patterns. The catastrophic sequences are usually with shorter length of the merger. The corresponding minimum normalized squared ED (MNSED) is smaller and below the distance bound. Two important CPM schemes, viz., LREC and LRC schemes, are known to be catastrophic for most cases; they have poor overall power and bandwidth performance. In the literatures, it has been shown that the probability of generating such catastrophic sequences are negligible, therefore, the asymptotic error performance (AEP) of those well-known catastrophic CPM schemes evaluated with the corresponding MNSED, over AWGN channels, might be too negative or pessimistic. To deal with this problem in AWGN channel, this paper presents a new split-merged MNSED and provide criteria to explore which conventional catastrophic CPM scheme could increase the length of mergers with split-merged non-periodic events, effectively. For comparison, we investigate the exact power and bandwidth performance for LREC and LRC CPM for the same bandwidth occupancy. Computer simulation results verify that the AEP evaluating with the split-merged MNSED could achieve up to 3dB gain over the conventional approach.

A joint continuous phase frequency shift keying (CPFSK) modulation and physical-layer network coding (PNC), i.e., CPFSK-PNC, is proposed for two-way relay channels (TWRCs). This letter discusses the signal detection of the CPFSK-PNC scheme with emphasis on the maximum-likelihood sequence detection (MLSD) algorithm for the relay receiver. The end-to-end error performance of the proposed CPFSK-PNC scheme is evaluated through simulations.

The Noise Shaper of a full digital amplifier overflows randomly when the Modulation Index of PWM is higher than a certain value. The clipping from the overflow produces an abrupt increase of THD+N that limits MI or the maximum output power. In this paper, we discussed the reason of NS overflow and derived the critical value of MI. We proposed a compensation method for the clipping error and optimized compensation in the audio band. The measurement results show that the proposed method can increase the maximum output power by 6.4% at a 1% THD+N condition. The compensation is more important where the power supply voltage and speaker impedance are difficult to change as that in a car stereo or mobile.

The performance of a UHF-band passive RFID system in a dense multi-reader environment is limited by both the reader-to-reader interference and reader-to-tag interference. In this paper, first, we propose a combination of subcarrier modulation backscattering and reduced carrier frequency offset among readers to reduce both the reader-to-reader interference and the reader-to-tag interference. Then, we propose a new distributed modulation index control scheme using the readers' estimation of the tag's SINR in order to further reduce the reader-to-tag interference. By adaptively controlling each reader's transmission modulation index, the asymmetric reader-to-tag interference can be effectively controlled to satisfy the required SINR of tags. Computer simulations show that the proposed scheme can reduce the minimum required inter-reader distance or increase the number of concurrently operable readers in dense multi-reader environments, especially when there are large differences in the levels of reader-to-tag interference. We show some optimizations of the proposed scheme for practical RFID applications. We also propose a bandwidth efficient modulation scheme for reader transmission which is suitable for the proposed modulation index control scheme.

We propose optical wireless multiple-input multiple-output (OMIMO) communications to achieve high speed transmission with a compact transmitter and receiver. In OMIMO, by using zero forcing (ZF), minimum mean square error (MMSE) or other detection techniques, we can eliminate the interference from the other optical transmit antennas. In this paper, we employ ZF as the detection technique. We analyze the signal-to-interference-plus-noise ratio (SINR) and the bit error rate (BER) of the proposed OMIMO with a linear array and a square array of optical transmit and receive antennas, where we employ subcarrier multiplexing (SCM) for each optical transmit antenna. Note that the proposed OMIMO is applicable to other arrangements of optical transmit and receive antennas. We show that the proposed OMIMO system can realize MIMO multiplexing and achieve high speed transmission by correctly aligning the optical transmit and receive antennas and the transmitter semiangle.

A digital noncoherent demodulation scheme is presented for reception of Gaussian frequency shift keying (GFSK) signals with small modulation index. The proposed differential demodulator utilizes oversampled signals to estimate the symbol timing and to compensate the frequency offset. The performance of the proposed receiver is evaluated in terms of the bit-error rate (BER). Numerical results show that the proposed demodulator provides performance comparable to that of conventional baseband differential demodulator, while significantly reducing the implementation complexity suitable for single chip integration with direct conversion radio frequency module. Finally the performance of the proposed receiver is improved by adding a simple decision feedback module.