HC-MCM, PC/HC-MCM And The Algorithm For Collision Recovery

This dissertation will propose a novel multicarrier system and design a new multicarrier system by combining the parallel combinatory coding. On the other hand, based on the flexible multicarrier system, this dissertation also proposes an effective method of collision recovery for OFDM-based wireless networks to solve the problem of hidden terminals. The underlying philosophy in all problems that are considered in this dissertation is a synergy between the physical and the MAC layers.In this dissertation, firstly, we will give the results which show that there is much to be gained from adaptive modulation and variable frame length in terms of goodput, range, and energy consumption for wireless networks. Three rules of design for such a tradeoff are obtained for wireless nodes. We utilize one rule for saving the energy consumption. The simulated results show that flexible transmission including adaptive modulation and variable length of frame can improve the throughput of system, save the energy consumption, and obtain better transmission area.Since high order M-QAM (M>64) is seldom used for wireless networks. On the other hand, adaptive modulation using different value of M will improve the design's complexity and cost. Therefore, one novel flexible multicarrier system (HC-MCM: high compaction multicarrier modulation) which can attain higher bandwidth efficiency (BWE) than that of the OFDM system has been proposed and extended. The HC-MCM can flexibly control the transmission rate and the communication quality. More importantly, only utilizing BPSK or QPSK modulation, it can adaptively achieve the transmission rate of high order M-QAM OFDM and control the length of frame by transmitting variable length of partial time-domain OFDM signal. This dissertation introduces the basic mathematical model of HC-MCM, explains its demodulation's complexity, and proposes a novel demodulation algorithm based on sphere decoding. In addition, simulated results show that HC-MCM signal has better peak-to-average power ratio (PAPR) characteristics than that of OFDM signal.Based on the HC-MCM, this dissertation proposes a novel flexible multicarrier modulation combined with the parallel combinatory OFDM (PC-OFDM), that is, parallel combinatory / high compaction multicarrier modulation (PC/HC-MCM) in this dissertation. The PC/HC-MCM can achieve any transmission rate of M-QAM that corresponds to not only integer M but also real number M. The PC/HC-MCM can also realize the adaptive length of frame which can be utilized to physical layer adaptation with the adaptive length of packets. Two types of PC/HC-MCM systems, which are named as PC/HC-MCM system and pure PC/HC-MCM system, are designed by this modulation. The PC/HC-MCM system can achieve better BER performance than that of HC-MCM system with the equal BWE by employing appropriate parallel combinatory codes. The pure PC/HC-MCM system can obtain excellent PAPR characteristics by selecting the optimal constellations for its subcarriers, which can be applied in MC-CDMA system. On the other hand, we combine the pure PC/HC-MCM and frequency hopping multiple access (FHMA) to propose a new multiple access (MA) system. This MA system can synchronously transmit multiple users' data within one symbol duration of the pure PC-OFDM.Finally, in this dissertation, we will propose an effective method of collision recovery for OFDM-based ad-hoc networks based on the flexible multicarrier system. From the flexible multicarrier system, the modulated message data of OFDM signal can be demodulated using the partial time-domain OFDM signal. Therefore, the partial time-domain OFDM signal can be adopted to reconstruct the whole OFDM signal with estimated channel information. Utilizing this advantageous property, a practical method of collision recovery, which is somewhat similar to the scheme of successive interference cancellation, can be realized. We simulate the recovery performance using different modulation for two users with identical SNR and weak near-far effect, and show that the method gives promising results and can be developed to solve the problem of hidden or exposed terminals of wireless networks. On the other hand, in the near-far situation, our method can achieve better recovery performance in the weak near-far condition which is more realistic in the wireless LAN. This method will dramatically benefit the protocol design of wireless networks, including ad hoc and sensor networks.