In consideration of the overcrowded spectrum resource, it is of great importance to study the combination of the cognitive radio (CR) and ultra wideband impulse radio (UWB-IR). In the cognitive UWB scene, the UWB pulse is supposed to constantly change its spectrum according to the state of the primary users to mitigate the potential interference to these vulnerable wireless systems. Meanwhile, the frequency utilization of the UWB pulse still eagerly requires improvement to guarantee their transmission reliability. In this paper, we propose a novel UWB pulse based on the neural network, and its simple implementation has also been presented. The frequency utilization of our designed UWB pulse can surpass any other existing UWB signals when no primary user is working around. Based on spectrum sensing information, our designed UWB pulse can adaptively alter its output spectrum to effectively avoid interference to the primary users. We also demonstrate that the proposed UWB pulse is much more suitable for the FCC emission limit than the ECC emission limit.

In this letter, a new recursive structure of a decision-feedback (DF) phase-tracking receiver for continuous phase modulation (CPM) is derived. This receiver uses the previously detected symbols to continuously estimate the initial phase in the current symbol and thus makes optimum coherent detection. The theoretical and simulation analyses of the error performance are given. It is shown that the BER performance of binary continuous phase frequency-shift keying (2CPFSK) and raised cosine (2RC) with a small modulation index is very close to the ideal bound, and the BER performance of GMSK is better than any previously known noncoherent detection.

Frequency hopping spread-spectrum systems have been popular in multiple-access communication systems. In such frequency-hopping multiple-access systems, multilevel sequences are used to specify which frequency will be used for transmission at any given time. One-coincidence sequences with specified distance between adjacent symbols for frequency-hopping multiple access are described. In such sequences, the distances between any adjacent symbols in any sequence are more than some specified amount. A theoretical bound is derived for the sequences, and two theorems on the construction of the sequences are given.

A new decision feedback (DF) receiver for minimum shift keying (MSK) is derived, which uses the previously detected symbols to estimate the initial phase in the current symbol for optimum coherent detection. Some of theoretical and simulated bit error rate (BER) performance results are presented. The results show that the DF detection provides good bit error performance in the AWGN channel, and is also an efficient detection method for MSK in a fast Rayleigh fading mobile channel.

The noncoherent least squares phase difference sequence estimator (LSPDSE) is presented for continuous phase modulation in an additive white Gaussian noise (AWGN) channel. The applications to Gaussian minimum shift keying (GMSK) and binary continuous phase frequency shift keying (2CPFSK) are considered.>

The least squares double-phase-difference sequence estimation (LS-DPD-SE), as a robust way of demodulating continuous phase modulation (CPM) signal subject to frequency variation such as Doppler frequency shift, is presented. The applications to Gaussian minimum shift keying (GMSK) and continuous phase frequency shift keying (CPFSK) are considered.>