OVTDM Communication System Implementation And Related Issues

Overlapped Time Division Multiplexing(OVTDM)is a new type of waveform coding theory proposed by Li Daoben.Based on the long-term accumulation of theory and practice,Professor Li proposed that if the signal is transmitted at a rate greater than the Nyquist rate,the overlap between the waveforms can be regarded as an encoding constraint relationship in essence,which further stimulates the potential performance gain of the system.The overlapping multiplexing technology can achieve high spectral efficiency at low signal-to-noise ratio and effectively solve the problem of limited bandwidth resources.Based on the theoretical basis of OVTDM,this thesis completes the construction of OVTDM communication system and studies it from the perspective of minimum Euclidean distance and avoiding the error pattern.The main contents of the thesis are:Firstly,the OVTDM system was built based on the software platform Labview and the Universal Software Radio Peripheral(USRP).Encoding and decoding of overlapping time division multiplexing signal are implemented on the Labview software platform.Signals are transmitted through the interfaces of two USRP devices.The simulation results verify that the overlapped multiplexed signal has high spectral efficiency after passing through the actual channel.The spectral efficiency of the OVTDM signal simulated by the hardware platform reaches 6(bits/symbol)which requires signal-to-noise ratio Eb/N0=14.2dB,while the Eb/No?18dB is required for 64QAM.When the Eb/N0?12dB,the error rate of K=4 and K=8 is two orders of magnitude different.Secondly,minimum Euclidean distance is a maj or parameter affecting the bit error rate.The normalized minimum Euclidean distance,error pattern and number of OVTDM signals based on different pulse shaping functions are calculated.The results show that when the roll-off factor is constant,the spectral efficiency changes within a certain interval does not lead to a decrease in the normalized minimum Euclidean distance(dmin).As spectrum efficiency increases,the error pattern is first presented as a single long alternating sequence followed by multiple short alternating sequences.The research results show that when K>3,the error pattern no longer has the overall regularity,but contains the same short difference sequence.An increase in the number of overlaps results in a decrease in the normalized dmin.When K = 12,the normalized dmin value of the OVTDM signal based on the raised cosine function is close to 0.01,which is 60-80 times lower than the value of dmmin at K=2 under the same conditions.and the difference in dmin value of the roll-off coefficient is different.Thirdly,restricted coding is a way of encoding reliable data by limiting the sequence of transmitted information.The generation of error patterns is avoided by controlling the binary input bits.The gain of the minimum distance of the overlapping multiplexed signal is obtained by losing a part of the code rate.Based on this,run length limited coding and design specific finite state machine are proposed to avoid the error pattern,and the channel capacity is calculated according to the adj acency matrix of the finite state transition diagram.The results show that the run length limited coding(1 k)can avoid the generation of the error pattern(+--),and obtain the"gain"of the normalized minimum distance when the overlap weight K is in the interval[4,12].And the system capacity increases as the k in the(1,k)code increases.Designing a specific finite state machine based on a short error alternation sequence can effectively postpone the position where the minimum Euclidean distance begins to fall.When the raised cosine coefficient a?0,the initial falling position of the minimum Euclidean distance is delayed from RIW?2.4 to R/W?3.3.The problem of channel capacity calculation after circumventing a certain long error sequence can be transferred to calculate the matrix radius of the corresponding cascade graph,and selecting a reasonable cascade graph path can maximize the system capacity.The performance results obtained by different avoidance strategies are different.Choosing a reasonable cascade graph path can maximize the system capacity.The evasion is performed in the cascading graph[G{10},G{01},G{10},G{01}],so that the normalized minimum distance when K=3,a=0.4 is kept constant.At this time,the total capacity of the OVTDM system is 2.08 times that of the Nyquist system.