Exploiting the abundant freedom of UWB signals can increase the Euclidean distance among codewords which will lead to an enhancement of the communication quality. In this paper, a coded modulation UWB system combining PPM, PAMand convolutional coding is proposed, which can significantly increase the power efficiency without degrading the data rate. The performance of this coded modulation system primarily depends on the free Euclidean distance and the number of corresponding error bits induced by the error paths. The code generator with maximal minimum free distance and minimum error bits is found to optimize the system. In order to avoid the difficulty of channel estimation and accurate time synchronization in rich multipath environments, a joint multiple symbol detector and decoder for the coded modulation system is presented which is able to approximate the performance of uncoded PPM system in AWGN channel under viable computational burden. Simulation results obtained from Nakagami multipath channel agree with our analysis.

Recently, several detectors based on auxiliary vector (AV) filters are presented to suppress multiaccess interference (MAI) in direct-sequence/code-division-multiple-access (DS-CDMA) systems. Knowing the signature waveform of the desired user, these AV-based detectors are a class of promising candidates for MAI suppression due to their superior performance and low computational complexity. However, it is hard to obtain the desired user's signature waveform, which is the convolution of the user's spreading sequence and the channel impulse response, unless the channel vector is known or unless training signals are sent. In this letter, based on both of the merits of AV detectors and RAKE receivers, an AV-based RAKE-like receiver is proposed for DS-CDMA communication systems in multipath channels. Simulation results indicate that the performance of the new receiver is very close to that of the AV detectors, which know the exact signature waveform of the desired user.

In this paper, a new MAC protocol supporting cooperative diversity named as CD-Maca is presented. By making use of the information carried by the handshaking frames of the Maca protocol, which has been employed in IEEE 802.11 standard, the CD-Maca protocol allows terminals in the network to transmit data frames cooperatively, resulting in more reliable retransmission and better performance. We model the CD-Maca protocol with Markov chain and derive the throughout of the protocols. It's shown by numerical results and simulations that the performance of the CD-Maca protocol depends on the packet error ratio (PER) of the handshaking frames, the PER of the cooperative transmission and the network topologies.